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Northwest Mining Association Applied Structural Geology in Exploration and Mining

November 2011

Applied Structural Geology in Exploration and Mining

James Siddorn, Ph.D., P.Geo., is a Practice Leader with SRK, based in the Toronto office. James is a specialist in combining the structural analysis of the ore deposits with applied 3D geological modelling and 2D GIS (geological interpretation of geophysics). He also specializes in comprehending the structural control on ore plunge and the distribution of mineralization in precious and base metal deposits at deposit scales. James has extensive underground and surface mapping experience, combined with a broad mining knowledge. He is an expert in computer based 3D geological modelling and its application to applied structural-economic geology, hydrogeology and geotechnical analysis, using 2D and 3D GIS programs. James has over 15 years of experience in the exploration for and 3D modeling of Au, Ag, Ni-Cu-PGE, tantalum, and diamond deposits, with deposits and terranes ranging from Archean to the Mesozoic in age and covering five continents. James also has extensive teaching experience, teaching over 1000 geologists in the applied use of structural geology at both mine and exploration sites and conferences. [email protected] Blair Hrabi, M.Sc., P.Geo., is a Senior Structural Geologist with SRK, based in the Toronto office. He is a structural geologist with 18 years of experience with the exploration industry, government geological surveys, and in academic settings mapping and modelling the lithology, structure and mineral deposits in deformed Archean and Proterozoic terranes. Blair has a broad experience with the regional geological setting of mineral deposits and specific experience evaluating the structural controls of Archean lode gold deposits and showings. He is experienced in the 3D computer modelling of gold, magmatic nickel and VMS deposits to aid in resource evaluation and drill targeting. Blair enjoys teaching applied structural geology including field mapping, controls on mineralization and the use of oriented drill core. Blair has a special interest in the compilation and integration of diverse data sets including lithogeochemistry, regional magnetic and gravity data, satellite imagery and mapping-based structural and lithologic data to understand the evolution and geometry of complex, mineralized terranes and to aid in GIS-based exploration targeting. [email protected]

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

WORKSHOP SCHEDULE

DAY ONE 0800-0815

Welcome and Introduction.

0815-0900

General Concepts of Structural Geology and their Application to Mineral Systems.

0900-1030

Structural Mapping Techniques for Exploration and Mining Geologists.

1030-1045

Coffee Break

1045-1200

3D Visualization and Interpretation of Geology and Mineralization.

1200-1300

Lunch Break

1300-1430

Analysis of Structure in Drillcore: A Practical Introduction.

1430-1445

Coffee Break

1445-1600

Structural Analysis of Faults and Fault Systems – Part 1

DAY TWO 0800-1015

Structural Analysis of Faults and Fault Systems – Part 2

1015-1030

Coffee Break

1030-1200

Structural Analysis of Folds and Fold Systems

1200-1300

Lunch Break

1300-1430

Structural Analysis of Veins and Vein Systems

1430-1445

Coffee Break

1445-1600

Tectonic Regimes and their Control on Structural Architecture

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM1: General Concepts of Structural Geology and Their Application to Mineral Systems

© SRK Consulting (Canada) Inc.

4

Applied Structural Geology in Exploration and Mining

Applied Structural Geology in Exploration and Mining Northwest Mining Association Annual Meeting Reno, Nevada November 28-29, 2011 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Aims of Course •

Demonstrate why so many ore deposits are strongly structurally controlled;

•

Define the simple principles of “structural control”;

•

Give you the tools you require to do structural geology in the mining and exploration environment; and

•

Give you the confidence to apply these tools, and therefore to make a real difference! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Workshop Presenters Dr. James Siddorn

Practice Leader SRK Toronto

•

Specializes in: • • •

Deciphering the structural control on ore plunge and the distribution of mineralization at deposit scales; 3D applied geological modelling; and Applied structural geological interpretation of aeromagnetic data, focused on the controls on the distribution of mineralization.

Mr. Blair Hrabi

Senior Consultant SRK Toronto

•

Specializes in: •

Compilation and integration of diverse data sets including lithogeochemistry, regional magnetic and gravity data, satellite imagery, and mapping-based structural and lithologic data to understand the evolution and geometry of complex, mineralized terranes and to aid in GIS-based exploration targeting.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Workshop Schedule: Day 1 0800-0815 0815-0900 0900-1030 1030-1045 1045-1200 1200-1300 1300-1430 1430-1445 1445-1600

Welcome and Introduction. General Concepts of Structural Geology and their application to mineral systems. Structural Mapping Techniques for Exploration and Mining Geologists. Coffee Break 3D Visualization and Interpretation of Geology and Mineralization. Lunch Break Analysis of Structure in Drillcore: A Practical Introduction. Coffee Break Structural Analysis of Faults and Fault Systems – Part 1

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Workshop Schedule: Day 2 0800-1015

Structural Analysis of Faults and Fault Systems – Part 2

1015-1030

Coffee Break

1030-1200

Structural Analysis of Folds and Fold Systems.

1200-1300

Lunch Break

1300-1430

Structural Analysis of Veins and Vein Systems

1430-1445

Coffee Break

1445-1630

Tectonic Regimes and their Control on Structural Architecture Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Geology in Exploration and Mining CM1 - General Concepts of Structural Geology and Their Application to Mineral Systems Structural mapping - Why Bother?

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Geologist and the Engineer A man floating along in a hot air balloon began to realise he was lost. He reduced his altitude and spotted a person below. He descended a little more and shouted: "Excuse me, can you help me? I promised a friend I would meet him an hour ago, but I don't know where I am". The stranger replied, "You are in a hot air balloon hovering approximately 100 feet above the Goldstrike mine, along the Carlin trend, in northeastern Nevada.”

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Geologist and the Engineer "You must be a geologist", said the balloonist. "I am" replied the stranger, "How did you know?" "Well", answered the balloonist, "everything you told me is technically correct, but I have no idea what to make of your information, and the fact is I am still lost. Frankly, you've not been much help so far". The stranger below responded, "You must be a engineer". "I am," replied the balloonist, "but how did you know?" Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Geologist and the Engineer “Well," said the geologist, “you don't know where you are or where you are going.” “You have risen to where you are through a large quantity of hot air.” “You made a promise to someone that you have no idea how to keep, and you expect me to solve your problem, but you really aren't interested in the information I'm providing.” “The fact is you are in exactly the same situation you were before we met, but now, somehow, it's my fault”. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Geology Input to the Mining Process

Most operations do not maximize the value of continued geological input.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Geology Input to the Mining Process

Geology underpins every aspect of the mining process

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Ore Reserve Estimation Process

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

“The Geologist’s Toolkit”

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Geology Input to the Mining Process

Geology input lowers RISK!!!!

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

How Does Structural Geology Make a Difference? •

Direct input on the limits, size and shape of ore bodies;

•

Elevates confidence in predictability of ore behavior: • Geometrical – grade control, dilution, targeting; • Geochemical – grade control, ore quality/metallurgy; and • Geotechnical – ground control, dilution.

•

Definition of hydrogeological pathways, geotechnical domains, etc.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Conceptual Basis of Structural Control in Mineral Deposits • All hydrothermal ore deposits require transport of large quantities of relatively insoluble metals in solution from some source region to the site of deposition; • Metal transport takes place principally by percolation of the fluid through the rock, and the low solubility of the metals means that very large fluid fluxes are required.

Hydrothermal and sulphide depositional model

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Metals Abundance in Various Rock Types Element

Ultramafic

Mafic

Felsic

Cu ppm Zn ppm Pb ppm Au ppm Ag ppm

10 50 1 0.0008 0.06

87 105 6 0.0017 0.11

30 60 15 0.002 0.051

Greywacke

Cont. Crust

0.002 0.08

75 80 8 0.003 0.08

Solubility of metals Cu, Zn = not constrained by solubility in saline solutions, therefore approximate abundance in rocks.

Au = not constrained by solubility in hydrothermal solutions, especially those containing S, therefore approximate abundance in rocks. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Exercise 1: Fluids and Plumbing

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Exercise on Fluids and Plumbing •

Assume solubility of Au = 0.03 ppm;

•

How much fluid required for a 5Moz Au deposit?

1oz = 31g 1litre = 1kg

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Exercise on Fluids and Plumbing

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Fluid Required Deposit Size

Au (Moz)

5

grams

Solubility (ppm)

fluid (tonnes)

155,000,000

0.03

5,166,666,667

fluid (L)

5,166,666,666,667

Remember, these calculations assume 100% efficiency in depositing the metal at the deposit site! 5E+12 litres = 5

km3

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Fluid Required Toronto Skydome (Rogers Centre): Volume roof closed:

1,600,000 m3 1.6 x 109 litres

1m3 = 1000 litres

5Moz Au deposit: 5.0 x 1012 litres

Minimum fluids:

3,125 Skydomes

Another way of looking at this problem is that 1oz of gold will saturate an Olympic swimming pool full of a typical hydrothermal fluid!

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Basis for Structural Control •

Getting the metal to the deposit is first and foremost a severe hydrodynamic problem;

•

A simple analysis of this hydrodynamic problem provides the foundation for the principles of structural control; and

•

It also leads to a set of simple, practical structural geological tools for aiding the discovery, delineation and efficient exploitation of mineral deposits. ‘Brothers’ Black Smoker

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Basic Hydrodynamic Problem •

So how does the earth manage to channel several millions of Olympic swimming pools of fluid through the relatively small rock volume that is to be the mineral deposit?

Betze-Post deposit 40 million ounces Meikle deposit 7 million ounces Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

A Simple Hydrodynamic Analysis •

The migration of fluid through a porous and permeable rock mass is described macroscopically by Darcy’s Law.

Fluid flux = Pressure head x Rock permeability Fluid viscosity • Pressure heads have a limited range in the earth - eg, Plith - Phyd • Hydrothermal aqueous fluids have approx constant viscosities at upper to mid-crustal conditions.

Old Faithful, Yellowstone

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Driving Forces for Fluid Flow •

Pressure gradients factor of ~3 (lithostatic versus hydrostatic) • • • • •

•

Topography Seismic pumping Metamorphic dehydration Magmas emplaced in fluid-saturated rocks Fluids expelled from crystallising magmas

Buoyancy • Temperature (thermal expansion) • Salinity

•

Viscosity - range of 1 order of magnitude • 40-400 µPa*s at T = 100-800ºC and 50-300 MPa Mt St Helens Phreatic Eruption

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Driving Forces for Fluid Flow •

Permeability • Porous sandstone (Ø>15%) • Crystalline granite

= 1 darcy (10-12 m2) = 10-10 darcies (10-22 m2)

• Fault at mid-crustal depth

= 1 darcy (10-12 m2)

•

10 orders of magnitude!

•

Therefore only permeability can vary sufficiently to permit the large fluid fluxes required to form ore deposits.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control •

Only abnormally permeable rocks will permit the fluid fluxes necessary to form ore deposits;

•

Fractured rocks (i.e. fault zones) are the most likely conduits for transport of large fluid volumes;

•

But there is a built-in negative feedback in the system which will reduce the effectiveness of the fault zone to pass the fluid (and metal) volumes required. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control •

The evidence for this is ubiquitous in paleo-fault zones fractures are vein-filled, wall rocks are often highly altered, gouge zones are tight and cemented - all of which dramatically reduce the hydrodynamic efficiency of the zone.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control •

Therefore, in order to transport the required metal volumes, the permeability of the fault zone must be continuously regenerated – (permeability of an active fault at mid crustal depth ~4 darcies, or 10-8 m2)

•

This leads to the important conclusion that hydrothermal ore deposits are localised on faults that were (repeatedly / continuously) active at the same time the hydrothermal system was active and metal-pregnant

•

Therefore, the concept of “structural preparation”, whereby the fault sits around waiting for the mineralising fluid to come by is flawed.

San Andreas Fault

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structure active during mineralization

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Importance of Getting Timing Right •

Application of structural control principles requires that the timing of mineralisation must be carefully matched with the history of activity on a fault system.

Regional cleavage cuts high-grade mineralization Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control • Most (all?) hydrothermal ore deposits form on or adjacent to active faults/shear zones; • Especially in gold deposits, economic grade is broadly correlated with vein/fracture concentration, which in turn is a measure of dilatancy in the controlling structure; and • A key component of mineral exploration is identifying and locating sites of dilation in structures that were active at the time of ore formation. Sulphide filled dilational jog, Sudbury, Ontario Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control • • •

Permeability is unlikely to be the same everywhere on an active fault zone. Permeability will generally be highest where damage within and around the fault zone is highest. This will depend to some extent on host rock type, but will principally be localised by irregularities (e.g. bends, branches, steps, jogs) along the fault.

Damage zones around irregularities along fault zone are zones of enhanced permeability Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control •

Fluid flow is therefore maximized, and ore deposits are generally localized on irregularities (i.e., bends, bumps, branches and jogs) in fault zones.

•

Irregularities commonly extend beyond or sit off the main fault strand, which explains why deposits commonly occur on second- or third-order structures rather than on the main fault.

•

Aside from fluid flow, this concept applies to magma as well. Therefore, intrusions and breccia pipes and associated mineral deposits also commonly occur along irregularities.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control •

•

Zones of local damage and permeability enhancement in active fault zones have another key influence on fluid flow and deposit localisation The damage zone undergoes (fracture) porosity enhancement during each episode of fault movement. This increase in local porosity causes a transient reduction in local pore fluid pressure, which will suck fluid towards the damaged zone.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control Dilation sucks!! •

There are two other important consequences of this local pressure drop: • It encourages mixing of fluids sucked from the surrounding wall rock and along the fault zone; • It can drastically alter the solubility of metals in the fluid.

•

Both of these processes can lead directly to metal precipitation in the zone of maximum fluid flux. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

The Principles of Structural Control In summary, irregularities on active fault zones: •

Provide the very high-permeability fluid pathways that have the capacity to transport large volumes of metal to a local site of deposition;

•

Are fluid pumps which suck fluids into the zones of enhanced permeability; and

•

Encourage mixing of locally derived and equilibrated fluids with (hotter and metalsaturated) fluids travelling along the fault zone. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Control Principles There are three basic steps to applying these principles at regional to local scales: 1. Determine the timing of mineralization relative to structural events, and identifying the event(s) that produced the mineralization; 2. Mapping/logging/interpreting in 3 dimensions, to determine the structural setting and pattern of active structures during mineralization; 3. Determine the likely shapes, orientations, and locations of dilational sites on the active structures. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Control Principles •

Determine the timing of mineralisation in the event history and match it to the history of movement on the fault / shear zones in the region.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Control Principles •

Carefully map in 3 dimensions those faults considered to have been active at the time of mineralisation, paying particular attention to even the subtlest variation in strike, dip or continuity. Brunswick No 12 Mine Peter et al., 2007

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Control Principles •

Determine the direction and sense of movement on the faults, in order to predict the location, shape and plunge of zones of maximum damage / dilation.

Zone of dilation associated with bend on sinistral fault Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Control Principles When you have located a mineralizing structure: • Determine the displacement direction and sense, so that you can relate changes in dip/strike of the fault/shear to the formation of dilational sites; and • Relate fault movement and shape to vein/breccia orientations and locations in detail; always make sure you work out how veins/stockworks/breccias relate to faults. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

How Does This Apply To Your Area?

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM2: Structural Mapping Techniques for Mine and Exploration Geologists

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Applied Structural Geology in Exploration and Mining CM2 – Structural Mapping Techniques for Mine and Exploration Geologists

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structural Mapping: Some Basic Principles •

• • • •

Structural mapping SHOULD be part of everyday geological mapping practice, but this is often not the case. Where do I start? What do I map? What tools do I have? Why should I bother?

Betze-Post Mine, Nevada

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Ore Body Plunge

So you can decipher ore body plunge! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Geological vs. Structural Mapping Geological mapping

Structural mapping

•

•

•

•

90% of effort goes to primary rock identification; Outcrop map produced at end of the mapping campaign; and Systematic data gathering for later interpretation.

• • •

Strong emphasis on structure, alteration etc; Faults, shear zones as rock bodies; Integrated geological map that works in 3D; and Data interpreted during mapping and used to produce working map during the mapping campaign.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Key to Successful Geological Mapping •

Collect the data you need, not data for data’s sake;  Maintain context of what you are trying to achieve;

• • • •

Work in plan and section at the same time; Work in 4D; Follow geometrical principles - geology is fractal in nature, pattern recognition is key; Start interpreting right from the start!  Mapping is iterative, and geological maps should constantly evolve

•

Stretch the data and make decisions about relationships.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structural Mapping Structural mapping includes: • Determining the geometry (i.e. orientation + shape) of rock units, fabrics, discontinuities; • Mapping contacts is the key •

Determining movement sense and displacement on structures using available kinematic indicators;

•

Determining the history of (structural) events • Mapping in 4D!

•

Then place mineralization within this context Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Traditional vs. Structural Mapping

…somewhere in Tanzania Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

What Tools Do We Have? •

Stratigraphy • was originally horizontal and laid down in a particular order • younging, or “way-up” indicators

•

Structural fabrics and deformation • know how to recognize them • know what processes they represent

•

Geochronology • Cross-cutting relationships, structural overprinting, radiometric dating

•

Geometrical principles • map making and pattern recognition • structural balancing

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Map Patterns

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Map Patterns and Relationships •

•

The relative size and importance of features should be reflected in your map; Don’t just map “data”, map and interpret relationships. EXAMPLE In the map opposite from an underground crosscut (Hillside gold deposit, Australia), mineralised veins are red and faults are blue. Which faults are likely to be the main controls on grade distribution? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Map Patterns and Relationships • Gold is dominantly vein-hosted and grade correlates closely with vein density; • Fault-bounded zones of different vein density are mapped in the cross-cut; • Domain boundaries can be identified as mappable faults along the boundary between high-grade and medium-grade ore; • Defining and mapping the domain boundaries enables geostatistics, resource estimation and mine planning to be carried out with greater confidence.

HG

MG

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Geometrical Principles • Rocks must occupy 100% of their “space” at all times during their deformation history = “structural balancing”; • Thus, reconstruction of non-deformed state of rock package should be possible by inverting movement along faults; • Most cross-sections on published 1:100,000 and 1:250,000 maps are markedly “unbalanced” and therefore are likely incorrect.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Exercise 2: Mary Kathleen Exercise

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Mary Kathleen Map Exercise

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structural Balancing Faults 1-4 are all shown as vertical on cross-section and at consistently low angle to steeply Edipping stratigraphy Interpretation can be checked by reconstruction

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structural Balancing

Total throw (vertical displacement) across this group of 4 closely spaced, parallel faults is approximately 20 km - about half of the thickness of a normal crust! Therefore, faults are probably not vertical (especially as formed) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Structural Balancing (continued) An interpretation involving listric faults would be preferred, as it avoids the excessively large fault offset.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Work in Plan and Section

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Think in 4D - Structural Control in the Yilgarn •

Four principal deformation events between 2700-2600Ma.

•

Gold mineralization associated with Event 1/2 (“early”) and with Event 4.

•

Event 3 is a major fold / thrust event which reorients earlier (incl. mineralized) structures.

•

Traditional maps show all faults / shear zones as black lines - no discrimination according to age.

•

It is necessary to interpret age and kinematics of structures in order to effectively use structure as a targeting tool.

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Applied Structural Geology in Exploration and Mining

Yilgarn Craton 4D Structural Framework Event #1 Continental Extension

“Early” Au and base metal mineralizing event Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Yilgarn Craton 4D Structural Framework Event #2 Thrusting & Inversion

“Early” Au mineralizing event Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Yilgarn Craton 4D Structural Framework Event #3 E-W Crustal shortening and thickening Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Yilgarn Craton 4D structural framework Event #4 Weak Transpression

“Late” Au mineralising event Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Our interpretations must capture the timing of structures

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Applied Structural Geology in Exploration and Mining

Work in 4D and Place the Known Mineralization in this 4D Context Extensional structural architecture influences geometry of subsequent compressional events

Intersection of thrusts and transfer faults control position of large gold camps

Red Lake

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Applied Structural Geology in Exploration and Mining

It's a fact! There is no such thing as a fact map!!

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Applied Structural Geology in Exploration and Mining

Exercise 3: Flatland 3D Exercise

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Applied Structural Geology in Exploration and Mining

Flatland 3D Exercise

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Applied Structural Geology in Exploration and Mining

Flatland 3D Exercise

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Level 2 Answer

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Applied Structural Geology in Exploration and Mining

Level 3 Answer

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Applied Structural Geology in Exploration and Mining

Level 4 Answer

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM3: 3D Visualization and Interpretation of Geology and Mineralization

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining CM3 – 3D Visualization and Interpretation of Geology and Mineralization

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Where Did Mapping and 3D Geology Begin?

William Smith’s 1815 Geological Map

Emile Argand’s 1922 Geology of the Alps Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Why Do Geologists Need 3D Visualisation and Modeling? •

Primarily because geology is a 3D science;

•

Its has been treated in a 2D manner until recently because of lack of tools to adequately deal with the 3rd dimension;

•

Many of the surficial deposits have now been found and the future of exploration lies in new discoveries beneath cover or buried at depth;

•

To make these discoveries it will be necessary to start considering targeting in 3D;

•

Most structural interpretations require a good understanding of what is happening in all 3D; and

•

New 3D techniques and software now make this task practical for most mining and exploration companies; Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Importance of 3rd Dimension to Exploration •

Geological interpretation is still the basic skill underlying the mining and exploration industries;

•

Historically exploration activities have tended to be dominated by geochemical prospecting methods;

•

Frequently it is becoming more commonplace that meaningful interpretation of geochemical results require a much broader geological understanding of the mineralisation process than geochemistry alone.

•

The key driver for the exploration industry is the discovery of mineral deposits under cover or at depth;

•

This cannot be achieved using traditional 2D methods alone; and

•

Therefore 3D techniques are becoming essential as an integrated part of sub surface exploration in greenfields, brownfields and mine situations. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Visualisation Techniques • Geological maps; • Cross-section construction & apparent dips; • Structure contour analysis; • Orthographic projection; • Stereographic projection; • Computer software; •

Gemcom, Vulcan, Surpac, Datamine, Gocad, Leapfrog etc.

• Automated interpretation techniques. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Visualisation Techniques – The Basics • Be able to visualize in 3D and accurately outline shapes in 2D! • Use all tools: Maps, Cross-sections, LongSections! • All maps are interpretations! • Understanding geology comes from the process of trying to interpret observations, not the gathering of facts alone. » SINK or SWIM? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Importance of Fundamental Geological Skills •

•

New 3D software and computing power enhance the ability to interpret geological data, however, they remain an extension of the visualization capabilities of the structural geologist, who must routinely make sensible conclusions about subsurface geology through extrapolation from incomplete data, using; Timing relationships; Geological constraints on geometry: • Lithology; • Structural geology; • Geochemistry; Traditional tools!

•

3D visualization:

• •

• •

Better visualization leads to better 3D computer based models; Feedback between “geologist’s interpretation” and the modeling software;

•

How to think in 3D: • • • • •

Create a mental image of an object; Rotate the object mentally until a comparison can be made; Make the comparison; Decide if the objects are the same or not; Report the decision. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Rotation - Visualization •

A

Shepard and Metzler (1971) mental rotation test:

B

C

D

E

Which two are the same?

Shepard, R and Metzler. J. "Mental rotation of three dimensional objects." Science 1971. 171(972):701-3 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Mental Rotation Test 1.

A

B

C

D

E

A

B

C

D

E

A

B

C

D

E

A

B

C

D

E

2.

3.

4.

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3D Visualization • Ability to visualize in 3D related to right side of the brain; • For interpretation of visualized data - Avoid visual representations that require large mental rotations; • “the more an object has been rotated from the original, the longer it takes an individual to determine if the 2 images are of the same object…” Shepard and Metzler (1971); • New advances in computing power allow on-screen representation of large datasets; • Allows user to rotate data into an orientation that enables easier 3D visualization; and • However, view data on a 2D screen, so user still relies upon mental visualization, interpretation, and depth perception skills. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Apparent Dips and Cross Sections • IMPORTANT!!!! For correct illustration of geological features in 3D, where strike is at oblique angle to the section line the dip of unit along line of section is an APPARENT DIP. tan (APPARENT DIP) = tan (TRUE DIP) * cos ε Plane 030/40E

• Where ε = angle between true dip direction and the apparent dip direction, i.e. angle between the line of section and the true dip direction; and • Apparent Dip should always be lower than the True Dip. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Apparent Dips and Cross-sections  Fault oriented: 110/56NE Section oriented: 090

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Applied Structural Geology in Exploration and Mining

Apparent Dips and Cross-sections • Fault oriented: 110/56NE • Section oriented: 090

27 degrees?

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Traditional Tools - Structure Contour Analysis • Concept of structure contours same as topographic contours; • Structure contours define the surface of a geological feature, for example: • • • •

fault, shear zone, surface of stratigraphic unit, contact of intrusion

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Structure Contour Analysis Structure contours are lines that connect points of equal height above a datum level that are contained within a structure (bedding, unconformity, fold, fault etc.)

Image courtesy of Fault Analysis Group, UCD, Ireland)

Structure contours of a planar dipping surface (blue) form straight, parallel, equally spaced lines Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Structure Contour Analysis

Image courtesy of Fault Analysis Group, UCD, Ireland)

Structure contours of a simply folded dipping surface (blue) form straight, parallel lines. Their spacing and their elevation changes with the shape and elevation of the surface. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Structure Contour Analysis • Widely spaced structure contours indicate shallow dip of unit or contact; (= shallow surface slope of topographic contours)

• Close structure contours indicate steep dip of unit or contact; • Curved contours indicate rounding in surface (e.g. complex folds, intrusions).

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Structure Contour Analysis - Exercise • EXAMPLE of an application of structure contour analysis Granny Smith Mineralization Exercise • Western Australia Gold Deposit • Laverton District • Associated with Granite-Greenstone contact

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Exercise 4: Granny Smith Exercise

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Granny Smith Exercise

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Granny Smith Grade Map N

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Granny Smith Structure Contours N

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Granny Smith Combined Data N

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Granny Smith Combined Data N

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Granny Smith Combined Data N

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New Age of Structure Contours - gOcad

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Orthographic Projection •

2D representation of a 3D object, e.g. map or cross-section;

•

Series of lines link equivalent points on 3D object with positions on the projection surface = PROJECTION LINES

•

Normally projection lines are oriented perpendicular to the projection plane = ORTHOGRAPHIC PROJECTION

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Orthographic Projection

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Fundamental Geometrical Projections • • • • • • •

Compass bearing (trend) of a line can only be measured in plan view; True length of the line can only be measured in a view parallel to the line; True slope (plunge) of a line can only be measured in a vertical view parallel to the line; The point of intersection of a line and a plane (piercing point) can only be determined in a view perpendicular to the plane; The angle between a line and a plane can only be measured in a view parallel to the line and perpendicular to the plane; The angle of pitch of a line on a plane can only be measured in a view parallel to the plane; and The angle between two planes can only be measured in a view perpendicular to the line of intersection between the two planes. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Stereographic Projection •

Stereographic projections are commonly used to present & analyze structural data;

•

It is especially useful for solving geological problems requiring the determination of angular relationships that would otherwise have to be solved by tedious orthographic construction;

•

It is important to remember that stereographic projection cannot be used to determine the spatial relationships of different structures, such as the amount of offset across a fault. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Stereographic Projection

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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New Age of Stereographic Analysis - gOcad

Vein orientations

Foliation orientations Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Modelling Historical Perspective In the recent past 3D modelling was rarely considered as a routine part of mineral or deposit evaluation because of: • • • • •

High costs associated with 3D software; Building such models was time consuming and expensive; Inability to rapidly update the models produced; Lack of suitably trained personnel to drive the software; Complexity of software made it beyond the use of the average geologist; • Software not designed to utilise structural data.

What has changed ? • Software costs have reduced dramatically; • More software now available to tackle different types of problem; • New mathematical approaches to 3D modelling are starting to appear and replace the older style CAD systems resulting in faster model making capabilities and models that can be rapidly updated; • New generation of younger geologists familiar with computer aided techniques; • Need to look deeper and under cover to find new deposits; and • New software that can utilise structural measurements directly to build 3D surfaces. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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New Computer Aided Exploration Techniques • As geologists we need to embrace these new approaches to exploration in order to better understand mineralising systems and ultimately make new mineral discoveries, however: • Good fundamental geological skills are still required; • The importance of good field geology is still important; • The new additional skills required by geologists now and in the near future will be: • Good 3D modeling skills using a variety of software platforms appropriate to the task; • Good data mining skills and the ability to integrate and interpret many different datasets from disparate sources. • Whilst 2D computer techniques will still play an important role for many years in exploration these will be surpassed by an emphasis on 3D techniques. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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What Do the Majors Use? •

Rio Tinto, Vale, BHP Billiton, XStrata, Barrick, AnglogoldAshanti, Newmont, Freeport-McMoran, De Beers, Gold Fields, Goldcorp, Kinross, Cameco, Areva. 6%

4% 2%2%

19%

9% 11%

19%

11%

17%

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APPLIED MODELLING!

Workflow – Part a

3D model is not just a pretty picture

ROCK MECHANICS

QUESTION?

HYDROGEOLOGY

RESOURCE DEFINITION

APPLICATION

ENVIRONMENT

SCALE EXPLORATION

METALLURGY

DATA

MAPPING

STRUCTURAL MEASUREMENTS

DRILLHOLE DATA

PRE-MODEL VALIDATION

IMPLICIT

GEOLOGICAL CONSTRAINTS

GEOPHYSICS

GEOCHEMISTRY

DATA MANAGEMENT

Understand your genetic model!

FUZZY

CONSTRUCTION

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CONSTRUCTION GMP

Use conventional 2D geological tools to help

NO GLOBAL PANACEA

Workflow – Part b

GOCAD

INTERPRETATION/ VISUALIZATION

SOFTWARE

LEAPFROG

GMP EXPLICIT MODELLING

GEOMODELLER FRACSIS

PHOTOGRAM. MODELLING

RESULTANT MODEL

Use flexible approach, no point in creating a 3D model if it cannot be easily updated.

IMPLICIT GEOLOGY MODELLING

METHOD

SYN-MODEL VALIDATION

Youngest first?

IMPLICIT GRADE MODELLING

GEOPHYSICAL INVERSION

DYNAMIC!

MODEL APPLICATION

EXPLORATION

RESOURCE DEFINITION

GEOTECHNICAL ENGINEERING

METALLURGY

HYDROGEOLOGY

ENVIRO/CIVIL

TARGET RANKING

GEOSTATS & VOLUMETRICS

GEOTECH DOMAINING

DELETERIOUS ELEMENTS

WATER BALANCE

PLANT/TAILINGS LOCATION

MINE DESIGN

RISK ANALYSIS

RECOVERY

MINE DESIGN

MINE DESIGN

MILL TESTING

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Implicit Modelling Revolution In the past 5 years there has been a radical change in the approach used in the construction of 3D geological models. Early 3D models of the earth relied on CAD based explicit modeling systems found in most of the general mining packages.

Grade iso-surface generated in Leapfrog

New and emerging software uses an implicit mathematical approach to the construction of geological models. This mathematical new approach has the advantage of: 1. 2. 3.

Speeding up the process of modeling by a significant degree; Giving the user the ability to rapidly update their models as new data becomes available; Enabling the geologist to use all the available geological data (including structural measurements) to make an interpretation in true 3D;

Three examples of this new mathematical implicit approach which represent a paradigm shift in 3D geological modeling are: Geomodeller, GOCAD and Leapfrog.

Geomodeller screenshot

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Explicit vs. Implicit Geological Modelling

vs.

Mathematical

Manual

* Slide courtesy of Mira Geoscience Applied Structural Geology in Exploration and Mining Courtesy of P. Gleeson, SRK Consulting, Perth, Australia Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Geomodeller Geomodeller is an implicit geological modelling software package. It’s unique abilities are: • The ability to accept primary geological observations (such as structural information) to build the 3D geological model; • Every model is geologically sensible, adhering to built-in geological rules; • As new data becomes available, it can be rapidly incorporated, thus revising the model; • Accurately models complex geological settings and elements (overturned fold limbs, complex faults / shear zones, intrusions and basement); and • Enable rapid development of complex geological models in a fraction of the time more traditional methods take. • View geophysical datasets in the context of the your geological model; • Forward modeling of geophysical responses using physical properties; and • Refine your model using inversion of gravity and magnetic survey data. * Price: ~$4500 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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In contrast to a CAD-style model 3D Tools - Geomodeller which uses shapes and surfaces to describe objects within a model - a 3D Geomodeller (geology) model is described in terms of: • A stratigraphic pile • Geological contact points • Geological orientation data • Erosion / on lap rules • Fault networks • Lithological properties

* Price: ~$4500 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Leapfrog Leapfrog is a 3D geological modelling software based on the world’s first practical rapid 3D contouring code, using a radial basis function. Leapfrog excels at rapidly defining grade shells based on numeric data with out the need to use CAD based construction techniques. In short Leapfrog capabilities are: • Non-gridded assay data from drill-holes can be rapidly visualised allowing quick assessment of mineralisation; • Prospect evaluation can be rapidly achieved as grade continuities can be analysed for the entire deposit in one processing step; • Allows immediate visual and co-ordinate identification of potential targets for exploration and evaluation teams; • Allows geological models to be dynamic, since Leapfrog-generated meshes can be regenerated when new drill-hole data becomes available; and • Leapfrog can process very small to very large datasets including imaging sparse exploration data to dense grade control data.

Leapfrog wireframe “it is like giving a machine gun to a monkey if they don’t know what they are doing” Anonymous quote from major gold company

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3D Tools - Leapfrog - Workflow 1. Data import and preparation a. Import collar, survey, assay and geology drill hole data in csv format. b. Leapfrog completes a thorough drill hole validation routine. c. A compositing routine prepares composites of any length; d. Import existing wireframes in a variety of formats e. Georef and import Maps, images and cross sections in jpg, png and tif; 2. Interpolation (modeling) of data a. Leapfrog interpolation uses a Radial Basis Function, which allows scattered 3D data points to be described by a single mathematical function. b. Models can be isotropic, meaning without any trends or directional bias, or anisotropic, based on planar, linear or more complex structural trends. c. Assays and any coded drill hole data, such as lithology and alteration, can be interpolated. 3. Viewing and interpretation of results a. Isosurfaces, or wireframes, can be built at any assay value and at any resolution. b. In addition to wireframes, interpolation results can be viewed (evaluated) on surfaces and within a grid of points, similar to a block model. 4. Exporting results a. Leapfrog wireframes can be exported in a variety of formats; b. Leapfrog Scenes can be saved and viewed in the Leapfrog Viewer, which is free to download from www.leapfrog3d.com.

* Price: ~$10000 (lease) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Gocad - Sparse The Sparse plug-in was developed at the Geological Survey of Canada in response to the need to quickly build structural surfaces from sparse data that represent complex regional-scale geological objects. Using Bezier and NURBS-based graphical editing tools. Sparse utilises: • Structural information • Mapped contacts • Sectional information

* Price: ~$4000 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Gocad - SKUA SKUA (Subsurface Knowledge Unified Approach) is a new implicit geological modelling module from GOCAD. Its is similar to Geomodeller in that it describes a model in terms of: • • • • • •

A stratigraphic pile Geological contact points Geological orientation data Erosion / on lap rules Fault networks Lithological properties

Like Geomodeller it allows for rapid modelling of geological formation and fault networks in a fraction of the time taken by manual CAD based methods. Also it makes it easy to rapidly update the model as new information becomes available. Though designed for the oil industry it appears to have a great deal of promise for application in the minerals sphere. * Price: ~$19000 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Gocad - SKUA • • • • • •

Subsurface Knowledge Unified Approach; Workflow-based modelling environment; Developed upon the 3D Paleo-geographic transform (UVT); Uses matrix-DSI as internal interpolator; Beyond domain boundaries with the Geologic Grid; Fully integrated with downstream applications • Grid-based models • Volume-based models

* Slide courtesy of Mira Geoscience

* Price: ~$19000 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Tools - Gocad - SKUA •

• • • •

•

Geological rule-based modelling environment • Stratigraphic column • Unit depositional relationships • Fault relationships Fault network Stratigraphic horizons Geologic Grid Dynamic editing • Fault relationships • Fault throws • Stratigraphic column relationships Requires geologic knowledge, not software mechanics

* Price: ~$19000 * Slide courtesy of Mira Geoscience Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Modelling & Visualization Tools As well as the new generation implicit modelling software there are many other 3D geological modeling software and visualisation tools available. Each software has unique features and no single package can truly cover all the aspects and requirements of earth scientists CAD based general mining software is still the predominant technique used by mining and exploration companies for building 3D geological models for use in exploration and mining (e.g.. Surpac, Datamine, Vulcan, Gemcom etc). It is popular and has widespread use.

Datamine

Surpac

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3D Modelling & Visualization Tools •

Siro vision / 3DM Analyst. Rapid analysis – photogammetric structural mapping tool for pit walls and other geological structures.

•

This software is used to accurately map structural features from outcrop or mine excavations.

•

Its ability to map accurately structures and surfaces on remote site locations in mines or rock faces makes it ideal for use in structural mapping exercises where access can be difficult (i.e. pit faces)

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3D Tools - FracSIS •

•

•

FracSIS 3D Database. This software is probably the only true 3D geological database (based on Object Store) and visualisation system; Has the capability to import and export diverse data sets in different formats. Has few capabilities for actually building geological models; and FracSIS gives the geologists a true 3D spatial database with the capability to store, view and manipulate diverse data sets.

* Price: ~$4000 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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3D Modeling & Visualization Tools •

3D Geophysical Inversion software. UBC and Intrepid- Geomodeller. 3D inversion software for magnetics, density and EM data to help constrain and define geometries of geological units in the subsurface.

•

Inversion software whether constrained or unconstrained can provide the geologist with large amounts of information at all scales to help constrain geology in the subsurface and also provide information on geometries.

•

As it can be applied to most gridded potential field data sets (magnetics, density or EM) it is a cheap, effective method for providing subsurface information which can be directly used to constrain 3D geological models in the subsurface.

Mapped Antiform

Unconstrained inversions from UBC software

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Gocad and 3DGIS – Do we still need Stereonets ? • The use of 3D GIS and 3D geological models to solve complex structural problems is a relatively new approach. • The question is “Do we still need traditional stereo nets to solve structural problems now we have 3D models and 3-D GIS”? • The advantage of the 3D approach along with 3D GIS is that unlike stereonets alone, this new approach can spatially show us where the structures (folds faults etc) are located in space.

N 20

15

10

• Example a stereo net can tell us the dip and dip direction of the intersection of a set of faults, but it cannot show us spatially where they exist in a pit or tell us where such an intersection may cause wedge failures because they occur facing out (dipping easterly) on say the west wall of the pit.

5

20

15

10

5

5

10

15

5

10

15

20

• 3D models of the faults in combination with 3D GIS can: • Give the location of the faults and their intersection directions; and • Show where all east dipping intersections occur on the west wall of the pit to potential predict failures. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Gocad and 3DGIS – Do we still need Stereonets ? Traditional Stereonet showing planes of faults and intersections

3D model + 3D GIS. Area of all west dipping – plunging intersections of major faults on west wall of pit Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Conclusions 1. Despite the expansion of tools, and the increased range of problems that can now be tackled realistically in computer models, the difficulty of generating high quality geological interpretations remains the main limitation to applying 3D geological modelling to the wide variety of geological problems at a range of scales. 2. Geological interpretation is still the fundamental skill needed in exploration and mining. Fostering this skill in conjunction with new technologies is essential if future geologists are to have the skill sets necessary to make new discoveries and effectively solve geological problems. 3. Using appropriate technology in an appropriate way will ensure industry will be able to continue to solve the complex problems earth science poses that extend beyond and below the surface. 4. New 3D modelling technologies now offer the ability to rapidly create and update complex 3D models and interrogate large, complex data sets in 3D. 5. The new implicit technologies can now utilise structural data in a way older CAD based technologies do not. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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The Software Maxwell: http://www.max-geoservices.com.au acQuire: http://www.acquire.com.au Voxler: http://www.goldensoftware.com Discover 3D: http://www.encom.com.au Geosoft Target: http://www.geosoft.com MOVE: http://www.mve.com GMP’s (Vulcan, Datamine, Gemcom, Surpac, Minesight); SiroVision: http://www.sirovision.com FracSIS: http://www.runge.com Geomodeller: http://www.intrepid-geophysics.com Leapfrog: http://www.leapfrogmining.com Gocad: http://www.mirageoscience.com Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM4: Analysis of Structures in Drillcore: A Practical Introduction

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining CM4 – Analysis of Structures in Drill Core: A Practical Introduction

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Introduction and Scope • Introduction to modern approaches and techniques to record and understand structures in drillcore. • Emphasis is on collection and interpretation of good geological data, rather than mechanical aspects of drillcore logging. • Focus on oriented core uses, because: • Oriented core is extremely useful; • Currently very much under-used.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Structural Core Logging •

Qualitative: • Core photography; • Logging system to encourage freehand comments, sketches and digital photos; • Scan logging of 10-20m lengths laid out in angle-iron frame; • More emphasis on knowledge rather than data; and • Core axis / structure angles should be regularly measured, but emphasis should be on mapping variations.

•

Quantitative: • Requires oriented drill core and / or down-hole optical or acoustic images; • Simplest method for retrieving structural data from oriented core is by measuring ,  and γ angles directly from core; • Alternative is to physically re-orient core in “rocket launcher”. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Aims of Structural Analysis • Determine orientation of mineralized vein sets, i.e. whether all veins of the set are mineralized or not; • Detect other structures that may be controlling structures or parallel to controlling structures, e.g. faults, folds and foliations; • Determine local strain axes; • Predict preferred orientations of veins and mineralization, based on geometry of products of deformation; and • THESE REQUIRE ORIENTED DRILL CORE.

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Unoriented Drillcore: ‘the Norm’

• Planes in unoriented core define cones in 3D; • Extraction of meaningful orientation data is very difficult; and • Of limited use for correlations in highly deformed areas. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Unoriented Drillcore Uses • Unoriented core is good for descriptive purposes (description of lithologies, fabrics, fracture conditions etc.) where orientation is not necessary; • If the orientation of a structure is well-constrained (e.g. major fault), with care, it is possible to extract some kinematic data; • Unoriented core can be oriented if it contains a planar element (foliation, bedding) whose orientation is known to be consistent over the region of interest: - Use this as a reference frame to extract other data. - Need to be certain it is of a consistent orientation.

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Using Only Alpha Angles • Low alpha angle means the structure / layering is nearly parallel to the drill hole; • High alpha angles means the structure / layering is nearly perpendicular to the drill hole; • In between angles eliminate the above two possibilities; • This can be very useful information during modelling!!! • Measure and take note of changes in the alpha angle of layering while logging and look out for fold axes! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Routinely Orient Core • We strongly recommend that acquisition of oriented core be the standard in any program, at least over critical intervals. A decision NOT to orient any core in a hole should be carefully justified, rather than the current situation in most companies / projects whereby oriented core is an exception and requires special justification; • The cost of orienting core is now less than 10% and as little as 5% of total drilling cost, and adds less than 10% to handling and logging costs; • In our opinion, the value of orienting core is generally many times the cost, and NOT orienting core can cost money in the long run. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Unoriented vs. Oriented Drillcore • Where structure is important(!), the acquisition of oriented core should be the standard in any program, at least over critical intervals. • A decision not to orient any core in a hole should be carefully justified. • Current situation: oriented core is the exception and requires special justification.

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Unoriented vs. Oriented Drillcore • Oriented core enables greater confidence in the: − Correlation of faults and veins − Definition of form-lines from foliations − Distinction between different structural elements

• Cost difference usually amounts to additional: − 5-20% drilling costs − 10% logging and handling costs

• Principal objections to oriented core are human factors, not financial: − Lack of experience in using orientation tools − Reluctance to change

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How Can Oriented Data Help Us?

Holes are inclined, but not oriented Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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How Can Oriented Data Help Us? Without oriented data, many possible geometries

If we know orientation and shear sense, we have a chance! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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How Can Oriented Data Help Us?

• We can determine form-lines of complex geometries and use geometrical relationships to assist with the interpretation; • Reduce many possibilities to few or even one; • Apply proper structural analysis.

North

n=1 n=1 n=1 n=1 n=1 Num to

Equal area projection, lower hemisph

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Core Orientation • Correctly oriented drill core enables determination of spatial relationships between geological structures, which are essential for exploration.

Ore Foliation Use of oriented drill core can help determine that this shear zone is extensional , which has important implications for exploration.

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Oriented Core = More for Less Oriented core allows: • Reduce 3 intersections to one; • Start using statistical distribution of orientations for geotechnical design; • Interpolation away from intersection; • Increase confidence.

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Data From Oriented Core? • Orientation of planar features (e.g. contacts, bedding, cleavage & veins). • Orientation of linear features (e.g. stretching lineations & striations). • Kinematic data (e.g. minor folds, asymmetric fabrics, shear sense criteria). • Timing relationships (e.g. cross-cutting veins and fabrics).

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Analysis of Veins in Drill Core • Following principles apply to collection of data for analysis of drill core: (1) Core data must relate to good quality geological map information; (2) Timing of foliations, lineations & veins, as well as determination of primary and secondary mineral assemblages, must be carefully evaluated. • All veins must be related to controlling structures; • Vein systems develop as a result of fluid flow through rocks with enhanced permeability, which is generated by deformation; and • Therefore: veins and mineralization form during rock deformation.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Drill Core Orientation Techniques • Most common technique: inclined diamond drilling with an orientation tool: − − − − −

Van Ruth device; Asymmetrically weighted spear; Ballmark ; EZYmark; and ACT.

• Involves marking the orientation of the sample prior to removal from the core barrel; and • Measuring structures relative to this reference frame.

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Ballmark System •

Ball-bearing pressed into core before core is removed, marking the bottom of the hole.

•

Dramatically reduces time, therefore cost savings are realised.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Ezy-Mark Orientation Tool

• Tool goes into the core barrel; • Takes the shape of bottom of the hole at the start of the run using pin impression and/or pencil zero-point; • Three different gravity and non-magnetic measurements taken to get down direction; • Remove the run when drilled and align the tool impression with core and draw orientation line; • Quality control system.

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Ace Core Orientation Tool (ACT) • 3 accelerometers measure the gravitational direction of the core tube at any time. • The user enters the time at which the core was broken. • The instrument guides the user to rotate the tube to the position it was in at the given time. • The base of the core can then be marked. • Easy to Use • No consumables • “Black Box”

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Orienting Core Before Splitting Initial orienting is the main source of error. Should be marked-up at drill rig by someone diligent and competent. Reference line should be checked against adjacent runs by laying core out in angled-iron and checking for major changes. Note: changes could be real however! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Drawing the Orientation Line • • • • • • • • •

Note the change in β angle from run to run; Decide which runs are most consistent; Get a feeling for the variance from run to run; Note runs that have varied in β value more than usual; Look at geology to decide whether it is a natural geological variation or a problem line; Correct a problem line if confident, or leave and tag measurements that are suspicious; Draw lines up the core from the next run when broken core prevents drawing the line down-core; Use geological layering to fit the core between runs or across broken core; Note and comment on the reasons for changes in the orientation line from run to run. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Convention and Consistency are Key! • Various conventions for core orientation exist. (e.g. whether reference line goes on top or bottom of core).

• On any one project we must: 1. Agree on a convention. 2. Document the convention (in long-hand and on logs). 3. Stick to convention!

BE CONSISTENT! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Measuring Orientation: α-β-γ Method α β

Lineation

Angle of planar feature relative to core axis measured along longest axis of ellipse. Circumferential angle between orientation reference line and the long axis of the ellipse. SRK Convention: • Looking downhole; • Upper surface of core; • Measured to bottom of ellipse; and • Measured clockwise

γ

Angle between a lineation on the plane and the long axis of the ellipse.

Reference line

Line through bottom of ellipse Core Axis

SRK Convention: • Measured clockwise; • From bottom of ellipse. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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α-β-γ Method Step 1

Beta angle is measured clockwise (in the downhole direction) around core from the orientation line

Orientation line (marked previously)

Alpha = 42°

Downhole direction

Downhole direction

Maximum dip (alpha) angle measured

Step 2

Beta = 134°

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Measuring Orientations A goniometer is a tool for measuring angles

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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α-β-γ Method • Data is recorded into a spreadsheet as α-β-γ.

• Calculate real world orientations using α-β-γ values and drillhole survey data (built into spreadsheet). • Advantage: quick and systematic (hence, used commonly in geotechnical programs). • Disadvantage: true values are often obtained after logging has finished or at the end of the day. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Measuring Orientation: ‘Rocket Launcher’ Adjustable Core Frame

Measuring

Nonmagnetic table

Support rods (graduated in degrees) Tightening screws Frame to hold core Hinge Moveable compass

Horizontally rotating arm Core

Protractor

Hinge

Reference line at base of core is aligned with ‘V’.

• Allows measurement of true orientations of structural features. • No post-measurement corrections to be made. • Allows recognition of structural changes (e.g. fabric deflections) in the core on the fly. • Important for core mapping.

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Core in Sand Box

• Ensure sand is non-magnetic • Cheap, but sand needs to be cleaned from core, compass etc. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Problems with Handling Drill Core Data • Problems can arise with: (1) collecting data; (2) interpretation of errors introduced by drilling techniques; and (3) bias due to sampling. • Errors and omissions in the data are the main causes of such serious mistakes as drilling in the wrong direction! • In addition, geological errors and omissions can cause problems with the interpretation of structures; • For example, if only one vein set is mineralized, and two are measured and not distinguished when measuring and logging, aggregation of the data on stereo nets, particularly if contoured, can lead to incorrect conclusions.

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Data Checks • Comparison with orientation data from surface.

• Warning signs are: − Large amount of scatter in core data relative to surface data; − Little similarity between orientations of features; and − Distribution of data on small circles around the drillhole orientation on stereographic plots. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Bias Due to Orientation • Features oriented at a low-angle to the drillhole are sampled less frequently than those cutting at high-angles. • Spatial bias must be taken into consideration when analysing the data, especially when trying to extract quantitative data (e.g. fracture spacing). • Can correct using Terzaghi Weighting:

w = 1/sin(α)

α

where α is the angle between the drillhole and the normal to the fracture.

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Splitting Core

DO NOT CUT ALONG ORIENTATION REFERENCE LINE Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Down Hole Geophysical Tools Acoustic Televiewer

Optical Televiewer

• • • •

Can generate very accurate orientations; Orientation is affected by changes in the magnetic field; Picking is complicated by strongly laminated rock; Powerful supplementary tool particularly when core orientation fails or is not done.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Recording Data from Oriented Core Two approaches: Structural Core Logging systematic and data-driven Vs Structural Core Mapping less systematic and interpretation-driven Both approaches are complimentary. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Structural Core Logging • Typically log into a database form as part of a holistic logging program (e.g. with lithology, alteration etc.); • Systematic description and measurement of structures over given intervals, usually a core box; • Structural core logging should systematically record the nature and orientations of: • Lithological contacts; • Alteration contacts (where possible); • Structural fabrics (foliations, lineations), including mineralogy; • Veins; • Cross-cutting relationships; • Logging emphasis really depends on the deposit and the requirement.

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Structural Core Logging A large amount of data is amassed, useful for: • Modelling geometry and structural correlations; • Analysing orientation of structural populations (e.g. veins); But, there are some downsides: • A lot of data adds background, but is not critical; • Box-by-box mentality, ‘big picture’ is obscured; • Mindless box-ticking exercise - devoid of thought.

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Structural Core Mapping • Philosophy is similar to field geological mapping; • Focus on areas of interest rather than systematically recording all structures, particularly significant changes or structural features (e.g., foliation deflections, faults contacts etc.); • Extract the data that is critical to the understanding of the system; • Interpretational, rather than just data collection; • Allows critical relationships to be identified and (hopefully) solved; • Particularly useful in exploration environment – ore controls; • Note cross-cutting evidence, bedding-cleavage relationships, kinematic indicators, lineations / striations, fold.

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Structural Core Mapping How to do it: • Lay-out several boxes of oriented core in angle irons (orientation mark should be aligned and checked); • Plot the fence which includes the drillhole of interest on paper; • Map and sketch directly on to paper noting any critical structural information: • Cross-cutting evidence; • Bedding-cleavage relationships; • Kinematic indicators etc.

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Structure Classification • SRK recommends that all identified structures in drill core should be classified. • Such classification helps the interpretation of structural features.

Class 5

Class 3 Class 2

Class 1

Example structure classification 1. (a) Strongly sheared and deformed or (b) brecciated. 2. Clearly faulted with displacement or striations. 3. The rock mass is weakened by (a) alteration or (b) strong fracturing, a nearby major structure is likely. 4. The core is completely broken because of poor core recovery. Possibly structure related. 5. Core is strongly or completely weathered to residual soil/ mud.

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New Age of Oriented Core Data Analysis - gOcad

Vein orientations

Foliation orientations Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Summary • Oriented core has a wide-range of uses in the structural analysis of mineral deposits. • Data value of acquiring oriented core outweigh the fiscal costs in many deposits – often priceless. • Although, relatively straightforward, acquisition of oriented core can be prone to errors. • Oriented core data should be checked internally and against field data as a quality control. • Data-driven core logging amasses a lot of useful data but discourages critical thought. • Interpretational core mapping helps to identify critical relationships and should be supplementary to core logging. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Exercise 5: Oriented Core Exercise

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Oriented Core Exercise

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM5: Structural Analysis of Faults and Fault Systems

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining CM5 – Structural Analysis of Faults and Fault Systems

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics; Movement sense and direction.

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Fault Patterns in 3-D • •

Faults form 3-D linked arrays that move co-operatively to accomplish “balanced” deformation of rock masses; Too many published interpretations show cross-cutting lineaments and faults without mutual offset.

Note operation of 4 faults

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Fault Patterns in Athabasca Basin

What is wrong with this interpretation?

From Jefferson et al. 2007 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fault Networks Linked arrays of faults: • Basin linkage in the North Sea, off Norway (top); • Main faults in the Pannonian Basin, Hungary (bottom).

200km

NORTH SEA HUNGARY

100km

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Fault Networks

On a global scale, linked networks of divergent, convergent and transform (strike-slip) plate boundaries form a first-order fracture system in Earth’s lithosphere.

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Fault Networks Also 2nd order fault system – transfer faults.

Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fault Networks

Strike-slip pull apart basin

Normal-detachment fault array

Imbricate thrust duplexes Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Conjugate Fault Relationships • Important Factors:

• Rock type; • Confining pressure; • Pre-existing anisotropy or surfaces; • Subsequent deformation/flattening.

© Marli Miller, University of Oregon

Brittle conjugate faults in sedimentary rocks

English River Subprovince, Superior Province

30° 30°

Brittle ductile conjugate faults in migmatitic metasedimentary rocks Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Riedel Fault Relationships

P

• R shears small angle to main shear, synthetic movement • P shears synthetic movement • R’ shears conjugate antithetic shears, high angles to main shear

Identification of different fault orientations and their kinematics can aid in understanding fault systems as a whole

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Sinistral Riedel Fault System

Cerro Bayo Epithermal Silver Deposit , Chile Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Sinistral Riedel Fault System

Cerro Bayo Epithermal Silver Deposit Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fault Classification

• •

Faults are classified by their sense of slip; Specific differences in the nature of the fault types reflect their orientation and sense of slip relative to geological layering and the Earth’s surface. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics; Movement sense and direction. San Andreas Fault 1300 km length Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fault Displacement

• • • •

Fault displacements vary over the fault surface; At a broad-scale, the variations are systematic; Tip-lines are rarely regularly-shaped; Usually faults are not isolated, but part of an array.

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Fault Growth •

Despite the geometrical differences between fault types, the growth of all faults are controlled by two basic processes: • Fault propagation and segmentation; • Fault segment linkage.

•

These processes account for nearly all aspects of fault geometry and fault rock content.

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Fault Propagation and Segmentation (a)

(b)

(c)

(d)

Courtesy of: Fault Analysis Group, University College Dublin.

Tip-line bifurcation: Localized retardation in propagation of the fracture front results in segmented fault array. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fault Linkage

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Fault Linkage: Examples Dilational jog along low-angle reverse fault

Dilational jog along low-angle normal fault Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Segmentation and Dilational Jogs

• Tendency to think in 2D but, in 3D, similar to other fault systems; • Kinematics are favourable for dilation and fluid flow. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Dilational Jogs

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Dilational Jogs

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics; Movement sense and direction.

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Fault Zone Heterogeneity • Fault segmentation and linkage processes result in highly-variable width and content (fault rock types) of fault zones; • Fault zone thickness can range over 3 orders of magnitude for a particular displacement; • Drillhole intersections of the same fault will not be the same; • Consequently, faults are horrible to correlate from drillhole information.

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Fault Zone Heterogeneity and Fluid Flow

Silvermines, Irish Zn-Pb Province (after Andrew, 1986) Normal fault system >200m displacement

• Feeder zones, shown by presence of epigenetic ore, are localised in areas of structural complexity associated with segment linkage points; • These zones are not necessarily dilational, but are zones of high fracture permeability. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Brittle Faults and Ductile Shear Zones

• Deformation regime depends upon: temperature, pressure, strain rate, composition and the presence of pore fluids; • Deformation regime commonly changes during progression of an orogeny. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Brittle vs. Ductile Faults Brittle • Discrete discontinuities accommodate displacement; • Commonly faults are segmented on a range of scales; and • Contain variety of fault rocks (e.g. breccia, gouge) which partially reflect the strain accommodated by the fault. Ductile • Deformation is continuous with wall rocks; • Strongly developed planar and linear preferred orientation fabrics; and • Strain is reflected in the intensity of the foliation.

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Rock Types in Faults Incohesive gouge and breccia ± pseudotachylite

Cohesive crush Breccias and cataclasites ± pseudotachylite

Cohesive foliated highstrain zones and mylonites

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Rock Types in Faults

Breccia and pseudotachylite

Gouge

Cohesive crush breccias and cataclasites

Cohesive foliated high-strain zones and mylonites Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Mineralization Types in Faults

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics; Movement sense and direction.

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The Importance of Getting Timing Right •

Application of structural control principles requires that the timing of mineralisation must be carefully matched with the history of activity on the fault system.

Folded gold, Rainy River Gold project, Ontario. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Control Principles •

Determine the timing of mineralisation in the event history and match it to the history of movement on the fault / shear zones in the region.

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Folded Faults Early faults are susceptible to later deformation.

Extensional or compressional faults at low angles to sub-horizontal bedding are particularly susceptible to later folding.

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Single Progressive Deformation Event SINGLE PROGRESSIVE DEFORMATION EVENT This cross-section is from a gold deposit in which folds, foliation, faults and veins formed during a single deformation event

Wattle Gully gold deposit, Victoria, Australia Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Single Progressive Deformation Event

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics; Movement sense and direction.

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Kinematic Analysis

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Kinematic Indicators

Courtesy: Fault Analysis Group, University College Dublin

• Only way to be sure of the movement on a fault is if we can observe a displaced marker and a fault lineation. • Together, these yield absolute displacement. • Normally we don’t have this information so have to rely on secondary information – kinematic indicators. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Shear Sense Ground Rules: • Shear sense can be reliably determined only on sections at high angle to fault / shear zone and parallel to transport / stretching direction (i.e. lineation); • If possible, determine direction of displacement before looking for shear sense indicators; and • You must say which way you are facing to be unambiguous.

To correctly observe sense of shear indicators, look at the plane: - Perpendicular to foliation; & - Parallel to lineation .

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Lineations • Lineations probably are the most useful of all structures; • 2 basic types of lineations occur in deformed rocks: •

Intersection lineations; and (See CM6: Analysis of Folds)

•

Stretching, extension or mineral lineations.

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Stretching, Extension & Mineral Lineations Lineations in fault rocks are the main indicators of displacement direction. The 3 most important lineations include: (1) Slickenlines (grooves, striations) on fracture surfaces (slickensides) subparallel to fault zone; (2) Fibre lineations in vein-fill on fault plane; usually quartz or calcite; (3) Stretching / mineral lineations in the foliation surface in ductile shear / fault zones.

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics – Brittle Faults.

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Lineations on Brittle Fault Surfaces Lineations are common on fault surfaces, either: (1)

Due to grooving parallel to the movement direction called “slickenlines” (on fault surface or “slickenside”);

(2)

Mineral fibres that grow on the fault surface parallel to the movement direction.

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Lineated Brittle Fault Rocks Striations (slickenlines) on fault surface (slickenside) dipping steeply.

Slickenlines on fault surface, Detour Gold project, Ontario.

Slickenlines on fault surface, Seabee Gold Mine, SK.

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Kinematic Indicators: Brittle Faults Slickenfibres

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Fibre Lineations on Fault Surface Local separation of fault surfaces filled with vein material, commonly thin fibres or films of quartz or calcite.

(Gap faces in direction of movement of opposite face) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Mineral Fibre Growth In quartz, galena and gold – kinematics during ore formation!

6191M stope sample, Con gold deposit, Yellowknife

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Steps on Fault Surfaces

b.

Steps perpendicular to slickenlines and mineral fibres are assumed to face in direction of movement of opposite side of fault.

lineation

STEP

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Steps on Fault Surfaces (cont.) Steps show that this block (back block) moved to left (sinistral movement).

Back block

As fault is vertical, this is a strike-slip fault.

Front block

West Bay Fault, Yellowknife, Canada Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Steps on Fault Surfaces (cont.)

Steps perpendicular to slickenlines & mineral fibres; Surface dips 70 degrees out of page; What is the sense and direction of shear? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Steps on Fault Surfaces (cont.) Steps perpendicular to slickenlines & mineral fibres; Surface dips 90 degrees; What is the sense and direction of shear?

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Exercise 6: Fault Problems – Part 1

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Exercise 6: Fault Problems

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Exercise 6: Fault Problems

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Exercise 6: Fault Problems

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Exercise 6: Fault Problems

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics – Ductile shear zones.

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Tectonite Fabric Elements Stretching Lineation Aligned and stretched clasts and/or minerals.

Schistosity Planar foliation defined by alignment of platy minerals.

• Depending upon the type of strain, the rock may contain planar, linear or both fabric elements. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Foliation Definitions

•

•

•

Foliation: a planar fabric that is usually associated with a deformational origin. Slaty Cleavage: typical of slates (e.g., weakly metamorphosed shales) — individual aligned mica flakes (too small to observe by eye). Schistosity (schistose foliation): typical of moderately to strongly metamorphosed schists —individual mica grains define foliation (large enough to observe in hand specimens). Gneissosity (gneissose foliation): typical of high-grade metamorphic rocks —coarser-grained, non-micaceous minerals predominate —folia tend to anastomose around pods of minerals more resistant to deformation.

Increasingly coarse

•

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Foliation - Examples

Strong planar (gneissose) foliation

Flattened conglomerate

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Stretching Lineations • Stretching, extension or mineral lineations form parallel to the elongation, stretching or tectonic transport direction in deformed rocks. They are useful as strain or movement indicators; • Foliations & stretching lineations are part of the 3-D rock fabric formed by deformation, i.e. not separate structures, and reflect the 3-D nature of the strain.

Stretching lineation. StarMorning Mine, Idaho.

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Stretching Lineations (continued) • Markers (e.g. pebbles, fossils, breccia fragments) provide clear and direct evidence of rock strain and define stretching / extension lineations; • Most metamorphic rocks do not contain markers. However they commonly exhibit elongation of metamorphic mineral grains that define the rock fabric (e.g. mica, amphibole). These can be visible with the eye, but are commonly microscopic and can be used as a mineral lineation that reflects 3-D strain; • Stretching lineations are very valuable indicators of movement or tectonic transport direction, especially in shear zones. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Stretching Lineation Strong stretching lineation in ductile fault zone

Campbell Shear Zone, Con gold deposit, Yellowknife, Canada

Stretching lineation in quartzite

Indicates vertical (dip-slip) movement Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Stretching Lineation Strong stretching lineation (quartz and amphibole) in vertical ductile fault zone

Porphyroblasts of staurolite not lineated!! What does this indicate about timing of ductile deformation vs. metamorphism? Obotan gold deposit, Ghana.

Indicates oblique movement Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Sense of Shear in Individual Zone Foliation in ductile shear zones oblique to zone boundaries Obliquity reflects sense of shear Plan View

Caledonian Orogeny, Doughruagh, Ireland Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Sense of Shear in Individual Zone Hornblendite dike (black) has been highly deformed & thinned in shear zone Cross-section View

Kamila shear zone, Kohistan, Pakistan Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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S / C Fabrics in Fault / Shear Zone In ductile shear zones, shear commonly occurs in “mini” shear zones — heterogeneous strain

Compare to a pack of cards, except that some deformation occurs between the slip surfaces

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S / C Fabrics (continued) The less deformed layers are equivalent to the margins of the shear zone proper, and may develop an oblique foliation related to the sense of shear C-surface

S-surface

Individual shear zones are C-surfaces (“cisaillement” is French for “shear”), and oblique folia between them are S-surfaces (“schistocité” is French for “foliation”) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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S / C Fabrics in Fault / Shear Zone Cross-section View Plan View

C S

Ox Mountains, Ireland Cape Ray Fault Zone Dube et al., 1996

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S / C fabrics in a Shear Zone

Green shear zone, Star-Morning Mine, Idaho.

Crean Hill shear zone, Denison

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Asymmetrical Rotated Objects Rotated porphyroclasts with asymmetric wings (delta-type porphyroclast). Cross-section View

What is the sense of shear?

Parry Sound shear zone, Grenville Province, Ontario

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Asymmetrical Rigid Objects Clasts of relatively rigid (competent) material like boudins or large crystals (porphyroclasts or porphyroblasts) Plan View

Pine Lake Volcanics, Seabee district, Saskatchewan

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Strain Markers This is a reverse fault because the sense of shear markers (tails on deformed quartz veins) indicate rightup sense of movement

Campbell shear zone, Con gold deposit, Yellowknife, Canada Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Strain Markers Cross-section View Cross-section View

6 Shaft Shear, Creighton Campbell shear zone, Con gold deposit, Yellowknife, Canada

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Asymmetrical Strain (Pressure) Shadows 3 possibilities: (1) Asymmetrical elongation of deformed, recrystallized “tails” of porphyroclasts; (2) Asymmetrical fibre overgrowths in “pressure shadows”; (3) Asymmetrical lenses of residual, less deformed matrix, protected by the porphyroclast. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Strain (Pressure) Shadows

What is the sense of shear? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Thayer Lindsay Deposit

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Thayer Lindsay Deposit

What is the sense of shear? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Shear Bands Shear bands may develop in homogeneous, strongly foliated rocks especially in the most intensely deformed parts of shear zones

Sense of shear in the band is the same as the overall sense of shear in shear zone Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Analysis of Faults  Geometry of faults in 3D;  Fault networks, patterns and classification;  Fault growth and dilational jogs;  Character; Brittle vs. ductile, alteration, veining;

 Timing;  Kinematics – Ductile shear zones;  Displacement calculation. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Amount of Displacement The 2 principal means of determining / estimating the amount of displacement on a fault / shear zone are: (1) from the measured offset of markers / rock units across the fault, i.e. fault reconstruction; (2) from the degree of deformation in the fault / shear zone and the width of the zone.

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Fault Reconstruction Best way to determine displacement

Restore to pre-fault configuration —> —>

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Fault Reconstruction (continued) Pre-fault reconstruction:

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Fault Reconstruction (continued)

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Piercing Point Solutions

Intersection of two planes to create a common point in the hanging wall and footwall of the fault

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Amount of Offset on Shear Zone Difficult to determine, but can be roughly estimated from intensity of foliation 1. If rocks moderately foliated and original structures and textures are preserved: displacement = 0.5 to 2 X width of zone 2. If rocks intensely foliated and mylonitic in entire zone: displacement = 5 to 10 X width of zone Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Exercise 6: Fault Problems – Part 2

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Exercise 6: Fault Problems

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM6: Structural Analysis of Folds and Fold Systems

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Applied Structural Geology in Exploration and Mining CM6 — Structural Analysis of Folds and Fold systems

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Folds and Faults

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Folds, boudins, and mullions Folds, boudins, and mullions form due to a competence contrast between the layer being deformed and the surrounding rock. Which structure forms is a function of the relative competence contrast and the orientation of the layer to the main compression direction.

Fold

Boudin

Mullion

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Folds, boudins, and mullions • Folds – Layer at low angle to compression direction. Strong layer surrounded by weak rock; EXT

• Boudin – Layer at high angle to compression direction. Strong layer surrounded by weak rock; and

COM

COM

EXT

• Mullion – Layer at low angle to compression direction. Weak layer surrounded by strong rock.

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Mapping Techniques •

Orientations of bedding & axial plane foliation;

•

Fold vergence;

•

Lineations as indicators of fold axes;

•

Younging and structural facing;

•

Form line mapping;

•

Fold sequencing and fold patterns;

•

Recognizing transposition. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Folds • • • • • •

Basic geometry Orientations of bedding and axial planar foliation Fold vergence Intersection lineations as indicators of fold axes Younging and structural facing Polyphase folding

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Fold Geometry Symmetrical Fold

Interlimb angle

Asymmetrical Fold

Fold axial plane

Fold axial plane

For each fold we can measure: • Limb orientations • Fold axis (hinge line) • Fold axial plane • Interlimb angle Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Type – Based on Interlimb Angle Isoclinal

Tight

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Fold Type – Based on Interlimb Angle Open Close

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Fold Geometry Cylindrical folds: • Rectilinear hinge line; • Constant limb orientations; • Planar axial surfaces.

Non-cylindrical folds: • Curvilinear hinge lines; • Variable, but usually systematic, limb orientations; • Planar or curviplanar axial surfaces.

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Fold Geometry Doubly-plunging Folds

Zagros Mountains, Iran (Google Earth)

• Folds are rarely cylindrical; • Like displacements on faults, fold amplitudes may vary along strike. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Why do we need to know about folds? •

• •

• •

Many ore deposits occur in orogenic belts and are geometrically related to the structural architecture. Pre-deformation mineralization: will be folded along with the host sequence; Syn-deformation mineralization: location and/or plunge or ore shoots commonly related to fold structure; and Post-deformation mineralization: along inherited structure e.g. faults along fold limbs. It is essential to understand the timing relationship between the deformation events and mineralization in order to interpret the structural controls correctly. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Folded Sulphide Ore Zone – Pre-Folding •

• •

Stratiform sulphide thickened in fold closure into an accumulation of sufficient size to form orebody; Plunge of ore is plunge of folds; and Structural analysis can predict location of fold hinges and thus aid exploration targeting. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Folding Makes Space for Fluid Flow Subhorizontal extension veins

Fault breaching fold hinge Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Geometry – Control on Veins

Tangier anticline, Meguma district, Nova Scotia Schematic model of vein formation

Caribou deposit, Nova Scotia

Goldenville district, Nova Scotia

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Fold Geometry – Control on Veins Flexural slip

Folded vein, Deborah deposit, Bendigo Schematic model of vein formation Flexural flow

Tangential longitudinal strain

Laminated and extensional veins, Swan decline, Bendigo

Vein variation, Sheepshead anticline, Bendigo from Cox (2005)

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Post-Folding Skarn Mineralization: Antamina, Peru

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Folds and Mineralization In folded terranes, hinge zones are good targets for a variety of mineralization styles. Ore plunge is commonly (but not always) parallel to fold plunge

Where are the fold hinge zones? What is their plunge? Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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How do we identify folds? • Bedding orientation changes across a fold hinge; • Younging direction changes across a fold hinge: • Gross stratigraphy; • Younging indicators.

• Older rocks in core = anticline; and • Younger rocks in core = syncline. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Foliations and Folds Folds are often intimately related to foliation (cleavage or schistosity).

Axial planar foliation generally parallels fold axial plane Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Axial Planar Foliations and Folds

Axial planar foliation is often constant, therefore a range in the intersection angle between bedding and foliation occurs. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Bedding and Axial Planar Cleavage Cleavage at highangle to bedding in hinge.

Cleavage at lowangle to bedding in limbs.

Bedding steeper than cleavage in overturned limb.

Bedding shallower than cleavage in upright limb.

Using bedding-cleavage relationships we can start to determine the geometry of a fold. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Which way is the antiformal hinge?

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Crenulation Cleavage Outcrop showing bedding crenulated by small folds Alignment of fold limbs forms a crenulation cleavage

Is this outcrop in the hinge or the limb of a larger fold?

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Foliation Development and Lithology • Development of a foliation (cleavage or schistosity) depends on presence of platy minerals (e.g. clays, micas, amphiboles etc.); and • Foliation can appear very different in rocks with more / less abundant platy minerals.

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Foliation Development and Lithology The muddy horizons have developed a cleavage, and the sandy horizons have not.

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Fold Vergence - Parasitic Folds • The two limbs of an ideal fold are mirror images; • This symmetry relationship is a powerful tool for determining the position of an outcrop-scale fold on a large structure; • Small folds on limbs of larger structure are generally asymmetrical; and • This sense of asymmetry is used to locate fold hinges.

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Fold Vergence - Parasitic Folds

• ‘S’ folds - limbs • ‘M’ or ‘W’ folds – hinge • ‘Z’ folds - limbs Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Parasitic Folds ‘S’ Folds in Sand/Silts Parasitic Folds in Psammites

Z S

M?

W

Fold axial planar cleavage Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Parasitic Folds (continued) Additional examples:

domainal development of parasitic folds Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Vergence in the Field

S folds Z folds

Parasitic folds are especially useful to locate the position of axial traces of major folds in areas of poorly exposed, tight isoclinal folding

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Vergence Reality Variable plunge causes apparent changes in vergence Compare outcrops A&B Always determine vergence when looking DOWNPLUNGE

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View Folds Down-Plunge This vertical section is upplunge (so vergence is opposite to map view) and fold profile is stretched

Down-plunge section gives true view of fold geometry and same sense of fold vergence as map

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Orientations of Major Folds • How do we determine the orientations of major folds? • The following data is available from most folds: • Axial planar foliation; • Bedding or earlier foliation that defines the fold; and • Parasitic folds. • The intersection of these planes yields an intersection lineation that is parallel to the fold axis.

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Intersection Lineation Because bedding and cleavage are at high angles in fold hinge, and both are planes of weakness, some rocks break into “pencils” in the hinge area forming PENCIL LINEATION

Cleavage surface

Observe structures on cleavage surface

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Intersection Lineation The intersection of bedding and cleavage form an intersection lineation, which is parallel to the fold axis. On fold limbs, the lineation is best observed on cleavage surfaces

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Intersection Lineation Intersection lineations can be used to estimate trend and plunge of axes of major folds

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Intersection Lineation

(from http://nvcc.edu/home/cbentley/geoblog/labels/virginia.html)

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Common Intersection Lineations Bedding/cleavage intersection.

Crenulations of an earlier foliation.

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Bedding-Cleavage Relationship (vergence) Bedding-cleavage relationships can be used to determine the position of an outcrop-scale fold in a larger structure. LEFT

RIGHT

Is the nearest antiform located to the left or right of this outcrop? (or: what is the vergence?) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Bedding-Cleavage Relationship (vergence) •

Using only bedding-cleavage relationship, the antiform is inferred to be to the right of the outcrop i.e. vergence is to the right Bedding and cleavage at smaller angle in fold limb

LEFT

RIGHT

Bedding & cleavage at high angle in fold hinge

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Structural Facing • Structural Facing is rather complexly defined as: the direction of younging resolved in the foliation at right angles to the fold axis; • Facing: the direction in which the axial plane of a fold passes through younger layers. This term applies to the whole fold. • Younging: the direction towards which a rock unit or layer decreases in age. This direction changes around a fold.

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Facing • Direction of younging in the cleavage plane is the structural facing (direction); • Facing provides information on structural history.

The following slides examine each of these outcrops Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Facing — Outcrop A Is the facing direction upwards or downwards?

Graded bedding

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Facing — Outcrop A

The graded bedding youngs upwards, but faces downwards on the cleavage surface.

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Facing — Outcrop B Is the facing direction upwards or downwards?

Cross-bedding

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Facing — Outcrop B

The cross-bedding youngs and faces downwards on the cleavage surface.

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Fold Geometry at Depth A

• • •

B

Change in younging direction suggests that outcrops are on opposite limbs of a fold; In outcrop A, bedding is steeper than cleavage; In outcrop B, bedding is shallower than cleavage. Fold is synformal but… Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Geometry at Depth .. the fold is also an anticline!

Fold is a synformal anticline. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Why facing is important?

Downward facing implies earlier inversion Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Exercise 7: Fold Problems – Part 1

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Exercise 7: Fold Problems

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Fold Sequencing

What features would you select as being potentially critical in this outcrop?

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Fold Sequencing (continued) Main features are:

S2

• Bedding (S0) • Foliation (S1) sub-parallel to bedding • Earlier folding of S0 and S1: axial surface (S2) shown in red

S0/S1

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Fold Sequencing (continued) So, the main feature in this outcrop is an earlier fold (axial surface shown in red) re-folded by a larger, later upright fold (F3) Earlier fold probably parasitic on the limb of a much larger F2 fold

S2

F3

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Polyphase Folding • Multiple foliations associated with several folding events; • Primary compositional layering (S0); • Early penetrative foliation parallel to layering (S1), shown by minor veins; • Folding of S0 and S1 around F2 and development of new axial planar foliation S2; • Folding of S0, S1 and S2 around F3. No axial planar foliation is observed.

F3

F2

S2 S0 + S1

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Multiple Fold-Foliation Events Complicate Life!

Several cleavages and cleavage reactivation. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Interference

Fold interference patterns are a function of the relative orientations of the different fold phases

Only 2 fold phases!

BUT ALSO: On the outcrop, the pattern will depend on the orientation of the exposed surface Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Overprinting Deformation Events: Fold Interference

After Ramsay, 1976

TYPE 1 or Dome-and-Basin Fold Pattern is produced where fold axial traces are at high angle and both fold generations are upright or inclined Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Overprinting Deformation Events: Fold Interference

After Ramsay, 1976

TYPE 2 or Arrowhead / Mushroom Pattern is produced where fold axial traces are at high angle, but one fold generation is upright to inclined and the other is recumbent or reclined Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Overprinting Deformation Events: Fold Interference TYPE 2 or Arrowhead / Mushroom Pattern

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Overprinting Deformation Events: Fold Interference

After Ramsay, 1976

TYPE 3 or Wavy Tail Pattern (coaxial) is produced where the fold axes are parallel or sub-parallel, and one generation of fold is upright to inclined and the other is recumbent or reclined Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Interference What type of interference pattern is defined here?

Refolded folds in gneiss, Ruby Mountains, Elko County, Nevada (From NBMG Photograph Archive) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Interference

Shallow-plunging F2 syncline

Contains re-folded F1 folds in the heart of the deposit

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Fold Interference

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Fold Geometry – Remobilization and Refolding

Thompson Ni Belt, Manitoba

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Fold Interference - Thompson • D1 Extension – time of ultramafic intrusion • D2 Folding/Thrusting – peak metamorphism • D3 Refolding, steep reverse faults

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Sulphide Localization in Fold Hinges - Thompson •

•

•

Characteristic ore body geometry in F2 fold hinge – especially where refolded by F3 folds; Note sulphides not folded – F2 hinges “popped open” during F3 folding – dilation zones form ore bodies; and Sulphide horizons connected along P2 schist – and have ‘tails’ of ore projecting into fold hinge.

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Fold Geometry: Mineralization and Refolding Meadowbank gold deposit, Nunavut

adapted from Sherlock et al., (2001, 2004) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Analysis of Multiply- Folded Areas

• Once you have an understanding of the geometry of the last fold phase, work backwards to ‘unfold’ previous deformation phases (e.g. by looking at bedding/cleavage asymmetry etc.)

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Analysis of Multiply- Folded Areas Even the most complex areas can be puzzled out with a bit of time and patience

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Foliation Generations • It may be possible to distinguish between different generations of foliation and relate these to different fold events; and • If so, it is possible to analyze structure using S2/S1 relations etc. as analogy to S1/S0 relations in regions with only one phase of folding.

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Foliation Generations • But remember that foliation is developed to different degrees in different rock types – some may show F2 folding with no new foliation, whereas others may have penetrative S2 foliation that obliterates earlier S1 cleavage.

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Foliation Generations • Also remember that some rocks develop an early bedding-parallel foliation - it is common to have one more phase of foliation than of folding! • The foliation may be related to extension rather than folding – look for other evidence e.g. boudinage.

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Transposition: Folding and High Strain •

When the %$#&*# really hits the fan…

layers locally appear to join up across stratigraphy rather than along it

Sub-parallel sand lenses in silty shale form depositional(?) texture with enigmatic origin… Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Transposition: Folding and High Strain Vancouver Art Gallery Georgia Street entrance

Transposed folds are often more easily defined by their ‘enveloping surface’

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Transposition: Folding and High Strain Transposition

Implications for exploration

Mapped distribution of high grade appears to join up across strike Enveloping surface defines folded layer

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Transposition in Thin Section

•

To illustrate the guiding principal that geological structures are repeated on all scales: transposition of a silty layer in a graphitic schist. (Long axis of section 5mm).

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Sheath Folds: Folding and High Strain • Sheath folds have curvilinear fold traces, and the fold axes reverse their plunges around a point; • Sheath folds initiate as cylindrical folds with axes perpendicular to the transport direction and stretching lineation; • With progressive shear, the axes rotate to become parallel to the stretching lineation.

(Twiss and Moores, 1992)

(Hanmer and Passchier, 1991)

Grenville Orogen, Ontario

(http://ic.ucsc.edu/~casey/eart150/Lectures/ShearZones/15shearZns.htm)

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Things to Remember •

Fold symmetry » Parasitic folds » Vergence (careful of plunge!)

•

Fold–fabric relationships » Axial planar foliation » Folded? » Mineralization?

•

Structural facing » Need ‘way-up’ indicators » Important for identifying overturned beds, especially where ‘wayup’, alone, doesn’t work

•

Fold sequencing » Don’t be intimidated by ‘crazy’ patterns » Be mindful of the orientation of the exposed surface

•

Folding and High Strain – Transposition and Sheath Folds » Enveloping surface » Competence contrasts » Rotation of fold axes

REMEMBER: Folds are fractal. Small scale mimics larger scales. Relationships identified on the outcrop scale can be applied to the deposit scale and larger. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Exercise 7: Fold Problems – Part 2

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Exercise 7: Fold Problem

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM7: Structural Analysis of Veins and Vein Systems

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining CM7 – Structural Analysis of Veins and Vein Systems

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Veins in fault / shear zones •

• •

Veins form in or adjacent to both brittle and ductile zones, and they are the most useful indicators of direction and sense of displacement. Mineralized veins are especially useful - WHY??? Veins generally form oblique to their related fault, and the sense of obliquity is related to fault movement direction / sense.

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Veins exploit pre-existing fabric

Folded bedding parallel quartz vein, Goldenville, Nova Scotia Bedding parallel vein, Hill End Mine, NSW, Australia Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Geometry – Control on Veins

Tangier anticline, Meguma district, Nova Scotia

Schematic model of vein formation

Goldenville district, Nova Scotia Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Fold Geometry – Control on Veins Flexural slip

Folded vein, Deborah deposit, Bendigo Schematic model of vein formation Flexural flow

Tangential longitudinal strain

Laminated and extensional veins, Swan decline, Bendigo

Vein variation, Sheepshead anticline, Bendigo from Cox (2005)

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Veins Form During Folding

bedding-parallel fault-fill vein

Vein variation, Sheepshead anticline, Bendigo from Cox (2005)

• Extensional veins are generated due to slip along bedding planes.

Laminated and extensional veins, Swan decline, Bendigo Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Veins Form During Folding

• Such slip can also generate dilation in hinge zones and form saddle reefs;

• Saddle reefs are fold axis-parallel linear shoots.

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Veins Form During Folding • Extensional veins also form in outer arcs of fold hinges; • Such extensional veins may form hinge lineparallel networks (i.e. fold axis-parallel shoots).

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Fold Geometry – Control on Veins

Goldenville district, Nova Scotia Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Veins are Preserved in Fold Hinges

From Kisters, 2005

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Applied Structural Geology in Exploration and Mining

Competence contrasts in ductile fault zones • Formation of a quartz-carbonate vein in a schistose fault zone (e.g. biotite, chlorite, sericite) creates a large competence contrast between the strong vein and the surrounding weak schist; • This creates a positive feedback mechanism where during subsequent deformation the vein will fold/boudinage/fracture creating low stress sites that will focus the deposition of subsequent hydrothermal fluids.

Quartz vein in graphitic schist, Obuasi, Ghana

Pyrrhotite infilling boudin necks in a quartz vein, Detour Lake, Ontario

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Veins exploit pre-existing veins

Quartz tourmaline vein xc boudinaged ankerite vein, Red Lake

Quartz vein xc quartz vein, Con deposit, Yellowknife

Quartz tourmaline vein xc boudinaged ankerite vein, Dome deposit, Timmins

Quartz vein xc quartz vein, Con deposit, Yellowknife

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Positive feedback Deform ductile shear zone

Deposit vein system (barren or auriferous) Deposit veins localized on 1st/2nd/3rd vein system

Deform vein system Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Timing and gold endowment • It is important to understand the timing relative to deformation of the vein generations, and the controlling kinematics of the deformation at that time. • It is also important to understand the relative gold endowment of the different vein generations; e.g. barren-auriferous, auriferous-auriferous.

Folded gold with axial planar cleavage, Rainy River gold deposit, Ontario

Gold in cross-cutting fracture, Rainy River gold deposit, Ontario Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Significant gold enrichment?

Con, Yellowknife • •

Related to orders of magnitude variation in gold grade (~10 g/t to 1500 g/t); and Often associated with chalcopyrite, sphalerite and galena.

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Controlling Geometry? – Red Lake

Conjugate quartz-amphibole veins within ankerite vein

Folded ankerite vein, CARZ zone, Phoenix Island, Red Lake (Rubicon Minerals Corp. exploration property)

Overall geometry of later vein system can be strongly controlled by geometry of earlier deformed (folded/boudinaged) vein system

Folded ankerite vein crosscut by quartztourmaline veins

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Vein styles Vein Type Fault-fill veins

Extensional veins

Internal Features laminated structure; foliated wallrock slivers; slip surfaces; fibres at low angles to vein walls; filli mineral fibres at high angle to vein walls

Structural Site shear zone or fault; fold limbs

outside shear zones; AC joints in folds

Geometry

Formation Mechanism

parallel to host structure

shear fracturing; extensional opening of existing fractures

planar veins at moderate angle to shear zone; perpendicular to fold hinge

extensional fracturing; extensional-shear fracturing

Extensional vein arrays

internal layering: multiple openings

within shear zones

Stockworks

2 or more oblique to orthogonal vein sets

non specific

tabular to cigar shaped zones

Jigsaw Puzzle

angular clasts, no rotation

along faults

parallel to host structure

Fault breccias

vein and wallrock clasts; rotation and abrasion

fault or shear zone

parallel to host structure

Breccia Veins

fault slip

Adapted from Robert et al. 1994 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Vein styles

From Robert and Poulsen, 2001 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Vein styles: laminated fault-fill veins

Schematic representation of lateral zoning in vein to wallrock ratio

Sketch of individual veinlets amalgamating to form larger laminated quartz lenses. Sigma deposit, Val d’Or

Robert et al. (1994) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Vein styles: laminated fault-fill veins

Fault-fill veins with carbonate alteration. Motherlode, California

Fault-fill veins with carbonate alteration. Pamour deposit, Timmins

Fault-fill vein. Hoyle Pond deposit, Timmins

Fault-fill veins with sericite alteration. Con deposit, Yellowknife

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Vein styles: extensional veins

Robert et al. (1994).

• Planar extensional vein x-cutting shear zone; • Arrays of sigmoidal extensional veins (tension gashes) in shear zone; • Planar extensional veins within shear zone. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Vein styles: extensional veins

Extensional quartz-tourmaline vein. Red Lake.

Quartz tourmaline vein, Buffalo deposit, Red Lake

Extensional vein array perp. to foln and lineation. Star-Morning Mine, Idaho.

Extensional quartz vein array, Black Fox deposit, Timmins

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Vein styles: stockwork and breccia veins Stockwork and breccia veins can be regarded as composite structures resulting from a combination of multiple sets of veins and fractures

Quartz-breccia vein, Kirkland Lake

Vein stockwork, Black Fox deposit, TImmins

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Veins as Kinematic Indicators • Where high pore fluid pressures dominate (many hydrothermal environments), vein orientations can help determine the kinematics. • Sub-horizontal veins: • Contractional • Sub-vertical veins: • Parallel to faults: extensional • Or • Oblique to faults: transcurrent

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Veins as Kinematic Indicators Cross-section View

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Bogosu Au Deposit, Ghana, West Africa

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Veins as Kinematic Indicators • The Bogoso Mine occurs 60km to the SW of Ashanti along the same regional strike-slip fault system; • Gold mineralization occurs at bends along the strike-slip system; • Note vein geometries associated with opposing bends! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Veins in fault / shear zones

Vein (tension gash)

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Tension Veins S-shaped en echelon tension veins indicate a sinistral movement

Z-shaped veins indicate dextral movement

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Tension Veins

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Tension Veins Plan View

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Tension Veins

compressive stress direction

Dextral movement Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Vein array in ‘back’ Plan View – Back of drift looking up

Obuasi gold deposit, Ghana

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Vein array Cross-section View

Black Fox gold deposit, Timmins

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Vein networks

a

Relationship between reverse (compressional) fault, dilation and veining.

a b a

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Vein networks

Relationship between normal (extensional) fault, dilation and veining.

fluid expands rapidly in dilating part of the fault allowing for phase separation and mineralisation

"choke" on tight section of fault

fluid pathway

magma/fluid source

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Vein networks N

Relationship between strike-slip (wrench) fault, dilation and veining.

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Vein networks

veins ve ns

NORMAL FAULT

veins vei ns

Normal Fau t

STRIKE-SLIP FAULT

veins vei ns

Patterns of faulting and associated veining Indicates two different episodes of faulting

Strike Slip Fault

REVERSE FAULT Reverse Fault

vei ns

Veins characteristic of dextral strike-slip movement overprinting horizontal veins typical of compressional or reverse faulting. This type of relationship indicates two episodes of faulting.

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Applied Structural Geology in Exploration and Mining

Dilational Jogs

Patterns of faulting and associated veining

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Dilational Jogs

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Applied Structural Geology in Exploration and Mining

Obuasi Au Deposit, Ghana, West Africa

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Applied Structural Geology in Exploration and Mining

Plunge of ore shoots - Obuasi

10 km

1.6 km

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Plunge of ore shoots - Obuasi

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Applied Structural Geology in Exploration and Mining

Exercise 8: Epithermal Vein Exercise

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Applied Structural Geology in Exploration and Mining

Epithermal Vein Exercise

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Applied Structural Geology in Exploration and Mining

Geometric relationships in shear zones Poulsen and Robert (1989)

In an undeformed shear zone and vein hosted deposit the ore plunge will be aligned with the intersection of the foliation with extensional veining, normal to the stretching lineation.

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Ore plunge in low strain setting – SigmaLamaque, Val D’Or, Quebec

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Applied Structural Geology in Exploration and Mining

Sigma-Lamaque, Val D’Or, Quebec

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Ore plunge in low strain setting – SigmaLamaque, Val D’Or, Quebec

From Robert and Poulsen, 2001 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Ore plunge in low strain setting – SigmaLamaque, Val D’Or, Quebec

From Robert and Poulsen, 2001 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Ore plunge in relation to overprinting high strain

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Vein plunge Example – Con Au deposit, Yellowknife

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Applied Structural Geology in Exploration and Mining

Yellowknife Greenstone Belt Con Au deposit is hosted in ductile deformation zones that crosscut the Kam Group 2.722.7 Ga mafic metavolcanics

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Applied Structural Geology in Exploration and Mining

Con deposit

• Produced 5.5 Moz Au. • Strike length: 10,000 ft. • Depth: 6500 ft. • Refractory gold ‘locked’ in arsenopyrite and free-milling ‘metallic’ gold.

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Con deposit Vein styles

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Applied Structural Geology in Exploration and Mining

Campbell Zone Ore Trends 51° south rake

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Structural geology • •

Con displays protracted history of deformation and mineralization; Structural characteristics are result of 3 deformation phases: • D1 Early extension; • D2 Reverse-dextral shearing; • D3 Late brittle faulting.

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Vein plunge

STEEP SOUTH PLUNGING BOUDIN

5797M AC21002-31-02

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Orientation of F2 Fold/ B2 Boudin axes 103

56

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING: CM8: Tectonic Regimes and their Control on Structural Architecture and Ore Deposition

© SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining CM8: Tectonic Regimes and their Control on Structural Architecture and Ore Deposition.

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Why Do I Need to Know? • Tectonic environments have a relatively limited range of characteristic structural patterns & styles; • Recognition & application of these structural patterns is the single most important factor in the interpretation of spatial geological data; • Appreciation of the regional tectonic environment in which an ore deposit occurs, aids in understanding the local structural controls, which in turn allow better drill targeting.

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Applied Structural Geology in Exploration and Mining

Plate Tectonics and Ore Deposits • Regional tectonic environments are almost invariably controlled by large-scale plate tectonic movements; • Three tectonic environments can be distinguished in which specific ore deposits form (and may be deformed).

Earthquake locations highlighting plate boundaries; from Schellart and Rawlinson, 2009 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Regional Tectonic Environments • Extensional Settings: o Fault Architecture; o Ore Deposits; • Compressional Settings: o Fault Architecture; o Ore Deposits; • Strike-slip Settings: o Fault Architecture; o Ore Deposits; • Fault Reactivation and Basin Inversion.

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Extensional Settings

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Applied Structural Geology in Exploration and Mining

Extensional Settings • Extensional settings occur where continental plates move away from each other: • Mid-ocean ridges; • Subduction zones (slab rollback).

Ocean floor age isochrons (USGS) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Extensional Settings: Fault Architecture • Crustal thinning results in complex fault architectures, commonly characterized by the presence of shallow-dipping normal faults linking into subhorizontal ductile detachment faults at depth.

Twiss & Moores, 1992.

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Applied Structural Geology in Exploration and Mining

Extensional Settings: Fault Architecture • Extension is commonly accommodated by interaction between 3 main types of faults: (1) Detachment faults; (2) Normal faults; and (3) Transfer faults. • They move in co-operation forming fault arrays that maintain structural balance.

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Applied Structural Geology in Exploration and Mining

Detachment Fault Characteristics • Accommodate large, up to tens of kilometres (horizontal) displacement; • Separate medium- to high-grade metamorphic rocks of the lower plate from low-grade metamorphic rocks of the upper plate resulting in sharp metamorphic break and / or metamorphic core complexes; • Commonly progressively intruded by magmas during extension.

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Applied Structural Geology in Exploration and Mining

Normal Fault Characteristics • Commonly listric faults linking into detachment fault; • Secondary, antithetic faults are common; • Cause block tilting and the formation of basins and ranges juxtaposing older (basement) rocks against younger basin sequences; and • Basin sequences commonly dip in opposite direction to fault. Basins and Ranges (half-graben)

Detachment fault

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Transfer Faults • Transfer faults are accommodation structures, not strike-slip faults; • Commonly steep to vertical geometries; • Separate and offset extensional blocks that can operate relatively independently. Africa

South America Google Earth view of Mid-Atlantic Spreading Ridge showing numerous transfer faults

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Extensional Settings: Basin Formation Extensional basins form in 2 stages: 1. Rift stage: active during extensional faulting associated with heating; 2. Post-rift ("sag") stage: after extension associated with thermal relaxation and contraction.

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Rift Stage Characteristics • • • • •

Active faulting; Half-graben depocentres; Wedges of coarse clastic sediments; Rapid lateral facies changes away from fault scarps; May have volcanism.

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Sag Stage Characteristics • Sedimentary sequences generally fine upwards as topography reduces and subsidence slows down; • Gradual sedimentary facies changes; • Continuous units with little thickness variation across the basin; • Crustal cooling; little or no volcanism.

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Extensional Structures in Map View • Parallel ridges and valleys bound by normal faults (perpendicular to extension direction); • Normal faults are commonly discontinuous or stepped along transfer faults (parallel to extension direction).

Normal faults in red dash, transfer faults in yellow dash. Also note development of alluvial fans into basins Google Earth (oblique) view of Basin and Range Province, Nevada, USA Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Extension in Archean terranes

Dramatic change in stratigraphy across Adelaide Fault

Hannan Lake Serpentinite missing between these faults

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Early Extension & Ore Deposits

Gold deposits in Slave Province, Yellowknife associated with reactivated normal faults. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Early Extension & Ore Deposits

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Applied Structural Geology in Exploration and Mining

Extensional Settings & Ore Deposits • Crustal thinning is associated with the formation of sedimentary basins, high heat flow and magmatism, LPHT metamorphism, and deformation (even mountain building); • High heat flow, magmatism and metamorphism may drive hydrothermal activity and the formation of ore deposits.

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Applied Structural Geology in Exploration and Mining

Extensional Settings & Ore Deposits • The location of ore deposits in extensional basins is controlled by normal faults that act as pathways for metalbearing fluids to favourable stratigraphic horizons; • Reactivation of normal faults during subsequent inversion commonly introduces another phase of hydrothermal activity.

Goodfellow and Lydon, Mineral Deposits of Canada, 2007 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Ore Deposit Types in Extensional Basins • VMS deposits: o Commonly developed during active rifting (e.g. mid-ocean ridges and back-arc basins); o Precipitate from hydrothermal fluids on or below the seafloor. • Spectrum of sediment-hosted base metal deposits: o Commonly developed during rifting and / or sag stage during circulation of hydrothermal fluids in sedimentary basin sequences.

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Ore Deposit Types in Extensional Basins

Distribution of various ore deposit types along Canada’s western Laurentian margin. Nelson & Colpron, Mineral Deposits of Canada, 2007 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Exploration Targeting in Extensional Settings In extensional settings: • Expect steeply-dipping vein systems plunging sub-horizontally associated with fault-fill veins along normal faults; • Expect strata-bound ore lenses spatially associated with normal faults in extensional basins. Lydon & Goodfellow, 2007 fluid expands rapidly in dilating part of the fault allowing for phase separation and mineralisation

"choke" on tight section of fault

fluid pathway

magma/fluid source

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Compressional Settings

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Compressional Settings • Occur where continental plates collide: • Subduction zones; • Associated with mountain building.

Gravity anomalies measured by GRACE satellite highlighting distribution of mountain ranges across the globe (Flamsteed, 2007) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Compressional Settings: Architecture The architecture of compressional tectonic regimes can be characterized by one (or a combination of) structural styles: 1) Fold Belts; 2) Fold / Thrust Belts.

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Applied Structural Geology in Exploration and Mining

Fold Belts • Upright to overturned fold trains, with or without moderately to steeply dipping reverse faults; • Commonly associated with thin-skinned deformation involving only upper crustal, lithologically uniform terranes at low metamorphic grades (e.g. foreland setting).

Chevron folding at Loughshinny, Ireland (www.geologyrocks.co.uk) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Relationship Between Folds and Thrusts • Folding is generally accompanied by faulting on the same and / or broader scale than the folding; • In fact, many folds result from movement along faults, therefore, continuity of bedding around folds should be questioned, rather than assumed.

Cross-section of West Nepal (DeCelles et al., 2001) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Fold and Thrust Belts • Dominated by recumbent folding and / or thrusting in areas with strongly layered rock sequences and / or at higher metamorphic grade; • Commonly associated with thick-skinned deformation involving basement rocks; • Fold nappe terranes are dominated by the presence of shallow-dipping recumbent folds.

Cross-section of the Canadian Rockies (Boyce et al., 2002) Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Compressional Settings: Fault Architecture • Thrust faults may be listric (curved) from subhorizontal to steep (commonly inverted normal faults); • Alternatively, thrusts can have a "staircase" geometry made up of alternating "ramps" and "flats".

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Listric Thrust Geometry • Broad anticlines paired with tight (overturned) synclines are typically associated with listric thrusts; • These folds develop as a result of drag in both the hanging wall and the footwall of the thrust fault and are termed hanging wall (or roll-over) antiform and footwall synform respectively.

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Applied Structural Geology in Exploration and Mining

Ramp-Flat Geometry • Most common in thin-skinned deformation propagating along zones of weakness (flats; e.g. bedding planes) within a rock package, whereby higher angle faults are called ramps.

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Ramp-Flat Geometry • Ramps which form perpendicular to the transport direction are called frontal ramps; • Ramps that form parallel to the transport direction are called lateral ramps; • Those ramps inclined at other angles are called oblique ramps. Van der Pluijm & Marshak, 1997

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Imbricate Thrust Stacks • Thrusts typically occur in groups called imbricate thrust stacks; • Each fault in the array undergoes movement until it "locks" and a new fault develops in footwall of older thrusts, producing stacking of older thrust sheets on younger sheets; • Older sheets are carried “piggyback” on the back of younger sheets. 1

2

3 4

5

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Thrust Duplex • Series of imbricate thrusts commonly bounded by a (lower) floor thrust and (upper) roof thrust forming a thrust duplex; • These accomplish shortening and thickening of competent units with little internal deformation (similar to ramp-flat geometry).

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Thrust Duplex

Cross-section of the Appalachians, van der Pluijm and Marshak, 1997

Note how the earlier formed thrusts are steeper than the younger thrusts, due to continued deformation as the duplex propagates towards the left. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Complex Thrust Geometries • Geometry of thrust faults is rarely simple; • Most are either folded or breached by new imbricate faults as shortening progresses.

Backthrusts associated with a ramp.

Wedge thrust over a ramp. Van der Pluijm & Marshak, 1997 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Blind Thrusts • Blind thrusts are thrust surfaces that terminate before they reach the earth’s surface; • Blind thrusts may host “blind” ore bodies.

Ductile rock layers fold

Blind Thrust Fault Image courtesy of Stephen Nelson, Tulane University Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Blind Thrusts • Blind thrusts are thrust surfaces that terminate before they reach the earth’s surface (e.g. under basin cover).

Representative cross-section of McArthur River deposit, Zone B geology (after Craven and Perkins, 2009). Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Compressional Structures in Map View Characteristic elements of fold and thrust belts include: • Parallel fold and thrust traces – commonly sub-parallel to stratigraphy; • Hanging wall anticlines (A); • (Overturned) footwall synclines (D); • Truncated thrusts (C); • Ramp-flat geometry; • Imbricate thrust stacks.

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Overprinting Compressional Events • Many multiply deformed terranes are characterized by a combination of early thrusting and / or recumbent folding, overprinted by upright folds, followed by strike-slip faulting / shearing; • Worldwide, there are many examples of economically mineralized terranes with this structural history, in particular most Archean terranes.

Rouyn-Noranda

Val d’Or

50 km Cadillac-Larder Lake Deformation Zone on total magnetic intensity (Ford et al., 2007)

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Compressional Settings & Ore Deposits • Crustal thickening is associated with high heat flow, magmatism, metamorphism, and deformation; • High heat flow, magmatism and metamorphism may drive hydrothermal activity and the formation of ore deposits.

From Lydon, 2007 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Compressional Settings & Ore Deposits

Topography image of the Eastern Pacific Ocean and South American Andes (after Rosenbaum et al., 2005)

Major porphyry Cu-Au deposits and regional structural architecture in the Andes of northern Chile (after Richards, 2003)

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Compressional Settings & Ore Deposits

Distribution of gold deposits in the Tintina Gold Province and Tombstone Gold Belt (magenta) across Yukon and Alaska. F=Fairbanks, D=Dawson, M=Mayo, W=Whitehorse (after Hart, 2007).

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Applied Structural Geology in Exploration and Mining

Compressional Settings & Ore Deposits • In multiply deformed Archean terranes, regional structures control location of gold camps; individual gold deposits occur along secondary faults.

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Applied Structural Geology in Exploration and Mining

Exploration Targeting in Compressional Settings In compressional settings: • Expect shallow-dipping vein systems plunging sub-horizontally associated with fault-fill veins along reverse faults; • Keep in mind that post-depositional deformation may have a affected the geometry and plunge of an ore deposit. a b a

Figure 4 : Schematic cross-section of a reverse fault with (a) flat veins branching from it, and (b) within fault vein or breccia on more shallowly dipping part of Long section of Flin Flon-Triple 7-Callinan Cu-Zn-Au deformed the fault. This isorebody: the type of structural control expected Paleoproterozoic VMS deposit (Ames on & Jonasson, the NW-SE2007). faults in the Julietta region. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Strike-Slip / Wrench Settings

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Applied Structural Geology in Exploration and Mining

Strike-Slip Settings • Strike-slip settings occur where continental plates slide past each other (oblique convergence).

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Applied Structural Geology in Exploration and Mining

Strike-Slip Settings: Fault Architecture Strike-slip faults have the following main features: • Long, straight segments with purestrike-slip movement (principal displacement zones - PDZ's); • Consistent sense and amount of horizontal offset on a variety of geological (and landscape) features; • Sub-vertical dip, but complex geometry; San Andreas Fault, California, USA

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Applied Structural Geology in Exploration and Mining

Strike-Slip Settings: Fault Architecture • Small departures from linearity lead to severe, localized structural complexity; • Can form areas of extreme local uplift, or of rapid deep subsidence; • Individual faults are relatively easy to map, as they generally have linear traces in plan.

Altyn Tagh Fault, Tibetan Plateau (India-Asia collision zone); Cowgill et al., 2004 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Strike-Slip Settings: Fault Characteristics • Strike-slip systems can have complex structural architecture; • Fault sections may be curved in plan and crosssection; • Expect restraining and releasing bends; and • Expect stratigraphic variations across faults.

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Applied Structural Geology in Exploration and Mining

Strike-Slip Faults: Geometry Dextral

Sinistral

• Anisotropies in the crust may give rise to jogs, bends, step-overs and splays along PDZ; • These areas are important areas for fluid focusing and are commonly associated with mineral deposition. Twiss & Moores, 1992.

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Applied Structural Geology in Exploration and Mining

Releasing Bends (Dilational Jogs) Releasing bends in strike-slip fault systems are characterized by a mixture of extensional, dilational & strike-slip structures.

Dilation results in addition of material, usually minerals precipitated in veins & breccia. Strong potential for formation of ore deposits! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Restraining Bends (Compressional Jogs) Reverse or thrust faults are common at restraining bends & compressional jogs. They accommodate the compression, generally also causing uplift.

Thrusts may sole out into a low-angle detachment that forms the floor of the jog. Potential for formation of ore deposits! Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Strike-Slip Fault: Flower Structures • Narrow, sub-vertical PDZ at depth splays upwards at shallower depth; • Especially at bends, steps and jogs fault “flower structures” or “duplexes” may form.

Positive flower structure

Negative flower structure Twiss & Moores, 1992 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Applied Structural Geology in Exploration and Mining

Strike-Slip Fault: Flower Structures Positive flower structures: • Occur at restraining bends; • Contain oblique, reverse faults; and • Give rise to uplift (mountain building). Negative flower structures: • Occur at releasing bends; • Contain oblique normal faults; and • Produce local subsidence (pull-apart basins) Twiss & Moores, 1992 Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Strike-Slip Structures in Map View Porgera

Grasberg Porgera

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Applied Structural Geology in Exploration and Mining

Strike-Slip Settings & Ore Deposits • The Bogoso Mine occurs 60km to the SW of Ashanti along the same regional strikeslip fault system; • Gold mineralization occurs at bends along the strike-slip system; • Note vein geometries associated with opposing bends!

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Applied Structural Geology in Exploration and Mining

Exploration Targeting in Strike-Slip Settings In strike-slip settings: • Expect steeply dipping vein systems plunging sub-vertically associated with bends along strike-slip faults; • Where opposing bends occur along a strike-slip fault system both compressional and extensional vein systems may occur; • Active plate margins are ideal locations for ore deposit formation in strike-slip settings.

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Applied Structural Geology in Exploration and Mining

Fault Reactivation and Basin Inversion

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Applied Structural Geology in Exploration and Mining

Fault Reactivation and Basin Inversion • Extensional faults formed during basin formation are commonly reactivated during subsequent compression in a process called basin inversion; • This is an important process in the modification of the geometry of existing ore deposits (e.g. VMS) as well as the genesis of new ore deposits.

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Fault Reactivation and Basin Inversion

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Applied Structural Geology in Exploration and Mining

Fault Reactivation and Basin Inversion • Listric rotational faults and detachment faults reactivate as thrusts; • Basin sediments are folded and pushed back up the fault; • Transfer faults reactivate as strike-slip faults, accommodating movement between individual thrust segments.

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Basin Inversion: Zambia Copper Belt ?Mwashia-age, normal reactivation of early Katangan normal faults SW

Flat lying normal faults in “ ore shale”

NE Reactivated normal faults localise coarser facies - + volcanics in Mwashia

Copper-bearing unit LEGEND

Upper Roan/Mwashia

Ore shales

Lower Roan Quartzite Formation Syn - rift (Muva?) Pre-Katanga basement

Fluid Flow

Early normal faults linking into permeable basin lithologies localize stratiform copper mineralization. Applied Structural Geology in Exploration and Mining Northwest Mining Association, November 28-29, 2011 © SRK Consulting (Canada) Inc.

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Basin Inversion: Zambia Copper Belt Copper-bearing unit

• Basin inversion and reactivation of normal faults produces an imbricate thrust stack; • Stratiform copper mineralization now occurs as stacked lenses.

(a) Schematic cross-section showing early extensional faulting with imbricate normal faults cutting through Brockman Formation at high angle and smoothing out in the Wittenoom Dolomite Fault

(b) Schematic cross-section showing asymmetric folding of this geometry (eg, Whaleback) showing how bedding may be folded into overturned to recumbent folds, but imbricate normal faults remain unfolded, and appear to "cut" and postdate folds.

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Applied Structural Geology in Exploration and Mining

Inversion in the Field

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Basin Inversion & Ore Deposits

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Applied Structural Geology in Exploration and Mining

Exploration Targeting Combine observations at all scales! • Interpret map patterns, relate these to field observations; • Understand the tectonic history of your area of interest and determine the tectonic setting at the time of ore deposition; • Know what ore deposit types and / or geometries to expect in the tectonic setting at the time of ore deposition; and • Use local structural observations to further constrain your targeting model.

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APPLIED STRUCTURAL GEOLOGY IN EXPLORATION AND MINING:

Exercises

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Exercise 1: Fluids and Plumbing Calculate how much hydrothermal fluid is required to form a 5 million ounce gold deposit. • Assume 100% efficiency in depositing the gold from the hydrothermal fluid at the deposit site; • Assume the solubility of gold in the hydrothermal solution is 0.03ppm; • Assume 1 ppm = 1 gram per tonne; • Assume 1 ounce is equal to 31 grams; • Assume 1 litre of hydrothermal fluid is equal to 1 kilogram; and • Assume 1000 kilograms is equal to 1 metric tonne. Method: 1. 2.

Convert 5 million ounces into grams; Calculate how many tonnes of hydrothermal fluid are required to form the gold deposit based on the solubility of 0.03 ppm (0.03 gpt); and 2. Calculate how many litres of hydrothermal fluid this is equal to.

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Exercise 2: Mary Kathleen 1:100,000 Map Exercise Fault Interpretation You have been provided with the Mary Kathleen 1:100,000 geological sheet (central Mt Isa Inlier). One simple fault interpretation exercise based on relations on this map sheet is designed to illustrate general principals of 3D fault interpretation, structural balancing, and the dynamic/rock movement approach to structural mapping. This exercise is based on relationships in the eastern half of the map sheet, and you should spend a few minutes familiarising yourself with the principal rock units and stratigraphic sequence there.

Exercise 1 - Balancing faults in cross-section On the cross-section A-B-C-D, all of the faults are interpreted to be vertical. Four of these faults have been labelled 1 to 4, and the following exercise relates to these faults. Identify faults 1 to 4 on the map. What is their strike relative to that of the adjacent stratigraphic units?

You have been provided with a sheet of tracing film. Centre the film over the cross-section at faults 1 to 4 and trace the ground surface, faults 1 to 4 and the boundary between the Ballara Quartzite and the Argylla Formation in each fault block onto the film.

Now extend the faults and the

Ballara/Argylla boundary upwards and downwards as far as necessary to measure the vertical component of displacement on each fault. Measure the vertical component of displacement on each of the faults, and sum the total displacement across the four faults.

Comment on your answer? Is it geologically reasonable? If not, can you suggest a simple modification to the cross-section interpretation to improve it?

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Exercise 3: Flatland Exercise In the area shown in the map and block diagram, carbonate-hosted base metal veins show a strong spatial correlation with anticlinal fold closures in the hanging wall of thrust faults. The genetic model for mineralization suggests that hydrothermal fluid flow occurred during thrusting, with focusing of fluids into permeable and reactive limestones within the anticlinal hinges beneath a sandstone aquiclude. Your brief is to prioritise areas for exploration drilling, and provide a guide to the likely plunge of orebearing veins in the target areas. To accomplish this, you should:    

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Construct a map of the geology at level 2 on the block diagram. The map should show faults (with dip), folds and bedding orientation, as well as the lithological units. Draw a cross section (parallel to the front face of the block diagram) through an area you consider a high priority target. On your plan and section, indicate the probable vein orientations that may be intersected during drilling. What suggestions can you make for planning the drill program?

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1 2 3 4

20

Colluvium

10 35

Conglomerate

A

Sandstone

5 50

Limestone

50

C

B

30

5

Granite

5

C

C

7

5

5

5

5 10

5

2 3

5

25 50

5

A = major emergent thrust B = hanging wall anticline C = irregular faulting and folding of incompetent colluvium

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1 2 3 4

20

Colluvium

10 35

Conglomerate

A

Sandstone

5 50

Limestone

50

C

B

30

5

Granite

5

C

C

7

5

5

5

5 10

5

2 3

5

25 50

5

A = hanging wall anticline B = dome-shaped part of hanging wall anticline C = truncated thrusts D = overturned footwall E = ramp anticline

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Exercise 4: Granny Smith Structure Contours You are provided with two maps of the Granny Smith Au-Cu deposit, Laverton District, Australia. One shows a grade map for the Granny Smith deposit. The other shows structure contours for the granitegreenstone contact at Granny Smith. Gold mineralization is associated with a major ductile shear zone that occurs at the granite-greenstone contact.

1. Construct a cross-section representing a key high grade gold location along the granitegreenstone contact, then use it to answer the following questions: a. Is gold mineralization preferentially located at shallower or steeper sections of the granite-greenstone contact? b. What could this tell you about the structural regime during gold mineralization?

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Exercise 5: Resource targeting and evaluation using oriented drill core Exercise 5.1

Draw a geological cross-section incorporating the data of Fig 5.1. Join the Zn 2% intersections in a horizon parallel to stratigraphic trends. The answer is given in Fig. 5.2, but please don’t look at it until you have seriously attempted to answer the question. Attempt to draw a more interpretative cross-section from your answer. After doing this, compare your answer with the cross section shown in Fig 5.3.

Figure 5.1: Drill core data for exercise. The intersections showing Zn 10% are in a shear zone.

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Figure 5.2: Joining drill core intersections. Note the Zn 10% intersections in shear zone.

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Figure 5.3: Interpreted cross-section.

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Exercise 5.2

Figure 5.4 shows a map of stratigraphic form lines drawn through drill core intersections. On Fig. 5.5 draw structure contours of the Zn-bearing shear zone. After doing this, compare your result with Figure 5.6.

Figure 5.4: Stratigraphic form-lines joined through the drill holes

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Figure 5.5: Map of drill holes, showing spot heights of the 10% Zn-bearing shear zone horizon.

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Figure 5.6: Structure contours of the Zn-bearing shear zone

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Exercise 5.3

On Figure 5.7, construct structural contours for the disseminated Zn 2% horizon, remembering that this horizon is stratiform. After doing this compare your result with Figure 5.8.

Figure 5.7: Map of drill holes, showing spot heights of the 2% Zn-bearing horizon.

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Figure 5.8: Structure contours of the 2% Zn disseminated horizon.

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Exercise 5.4 Plot the junction between stratiform ore (Fig. 5.8) and shear zone ore (Fig. 5.9). Compare your result with Figure 5.10.

Figure 5.9: Structure contours of the Zn-bearing shear zone

.

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Figure 5.10: Junction between shear zone and stratiform ore.

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Exercise 6: Fault Problems – Part 1 Fault Analysis Problem 1A: Exercise on mapping & interpreting faults

Examine the map shown in Fig. 6.1, paying particular attention to the faults. The map shows a number of apparently conflicting or geologically unreasonable relationships. In addition, some information about some of the faults is missing. Make a list of the conflicting relationships, and say what additional information you would have collected when mapping the faults.

N

30 85

30 30

0

1

2

km Figure 6.1: Sketch map of fault relationships

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Fault analysis problem 1B Is the rock sample sketched in Fig. 6.2 from: (a) a N-S striking strike-slip fault, (b) a N-S striking normal fault, (c) an E-W striking reverse fault, or (d) a N-S striking reverse fault?

quart z fibre lineat ion

010 50

Figure 6.2: Sketch of fault outcrop

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Fault analysis problem 1C

Is the fault sketched in Fig. 6.3 a normal, reverse or strike-slip fault? Why?

breccia wit h q uar t z - sulp hide m at r i x

Figure 6.3: Sketch of fault and drillholes

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Fault analysis problem 1D

(a) Does the fault shown in Fig. 6.4 have a prospective site on it? Why?

(b) What assumptions have you made in reaching this conclusion?

(c) What information would you seek in the field?

N

granit e

f au l t

2 00 m Figure 6.4: Does this fault have a prospective site?

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Exercise 6: Fault Problems – Part 2 The map sketched in Fig. 6.5 shows the locations of outcrops sketched in Figs 6.6, 6.7 and 6.8.

(a) What can you determine about the fault at outcrop 1? What else might you look for if you could visit the outcrop?

(b) What information about the fault can you get at outcrop 2? Is it consistent with the information obtained at outcrop 1?

(c) What information about the fault can you get at outcrop 3?

(d) Write a brief descriptive statement about the fault, and indicate how your understanding of the fault would influence how you might drill targets on it.

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N 50

1

slates & quartzites

20

45

2

30

0

volcanics & volcaniclastics

3 200

400

met res Figure 6.5: Sketch map with dips of bedding and locations of outcrops in Figs 6.6, 6.7 and 6.8.

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slate with cleavage

quartzite

weak cleavage in volcanics

intensely foliated zone

Figure 6.6: Sketch map of outcrop 1 (Fig. 6.5)

quartz - sulphide veins

moderately sheared volcanics

weakly deformed volcanics

Figure 6.7: Sketch map of outcrop 2 (Fig. 6.5)

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quartz rods & mineral lineation slate with cleavage shown

quartzite intensely foliated zone with sheared quartz - sulphide vein remnants

Figure 6.8: Sketch map of outcrop 3 (Fig. 6.5)

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Exercise 7: Fold Problems Exercise 1: Several folds are illustrated in Fig. 7.1. Sketch the form of bedding on each face of the block diagrams. Describe and classify these folds. Indicate also the structural facing direction on each block diagram, where appropriate. Exercise 2: Figure 7.2 includes field structural data for a sequence of folded bedded sedimentary rocks. The data include measurements of the orientation of bedding, a fold axis-parallel foliation and parasitic fold vergence. No data on younging directions are available, and major fold axial planes were not identified during mapping. (a): Analyze the field data plotted in Fig. 7.2 and indicate the likely position of fold hinges. (b): Construct form lines that portray the orientation of the foliation across the face of the map. Is the foliation orientation constant? Remember to keep the form lines an approximately equal distance apart. (c): Add a second set of form lines to the map and cross-section illustrating the form of bedding. Describe the geometry of the folds.

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a.

87 51

72

03

overturned bedding bedding with plunge

fold axial plane strike and dip bedding / fold axial plane intersection lineation vergence of parasitic fold

b. 84 73

Figure 7.1: Block diagrams (continued over page)

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Figure 7.1 (continued): Block diagrams

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Figure 7.2: Map with structural data

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Exercise 8: Drilling Out an Epithermal Vein / Fault System The drill section attached summarizes the results of the initial diamond drilling beneath a mineralized fault + vein which outcrops as shown.

Before planning additional drilling, it is

important to try to work out as much as you can about the structural (and other) controls on the localization of mineralization. Understanding the structural controls will enable you to plan the most effective and efficient drilling program to outline the mineralization and define the resource. It is also important to plan drilling to maximize the acquisition of useful information. After you have examined the drill section, answer the following questions. 1. What is your initial interpretation of the structural controls on mineralization? 2. What additional structural information would you try to acquire in the outcrop and / or drill core to test and / or refine this interpretation? 3. A visit to the discovery outcrop shows that quartz fibres lineations on the fault plane pitch very steeply on the fault surface. Narrow quartz veins in the outcrop are vertical and vein / core axis angles are consistently about 30 degrees. Construct a cross-section showing the likely structural controls. 4. Has the drilling thoroughly tested the potential on this section? Justify your answer.

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Discovery outcrop narrow silicified fault zone & veins. Fault dips 60 degrees East. 35 g/t Au vein sample. DDH 1 Narrow silicified fault zone – same as outcrop 4m @ 8 g/t Au. Fault dips 60 degrees East. 35 g/t Au vein sample.

DDH 2

DDH 3

DDH 4

Narrow quartz veins with various Au grades.

Dilational Qtz-vein breccia averaging 25 g/t Au over widths shown.

Narrow silicified fault zone – same as outcrop 2m @ 6 g/t Au

50m Narrow, crustiform quartz vein – Grading 4 g/t Au over 2m.

JPS

8_Epithermal_Vein_NWMining_jps_rev01.doc

© SRK Consulting (Canada) Inc.

November 2011

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