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• Perkas Gaunder

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Lecture Outline - Ore Reserves

A) Preliminaries 1) Delineation: Exploratory Drilling Development Drilling

2) Core Logging, Sampling and assaying

3) Physical Definition of the deposit: Collar information Downhole surveys Lithology, Structures Cross-sections, longitudinal sections, plans

4) Definition of ORE

B) Classification of Ore Reserves Proven, Probable, Possible Measured, Indicated, Inferred Tonnage and Grade Compositing

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Lecture 3 - Ore Reserves Introduction

Once a target has been established, either by geochemistry, geophysics, or geological deduction, the next step is delineation. 1)

• Delineation: - is the evaluation of a target - typically involves drilling ( diamond drilling, rotary or percussion) - exploratory drilling:

no specific guidelines on hole spacing, diameter or type of drilling because this depends on the nature of the target and of the host rocks.

goal: determine if a detailed drilling program is warranted. rule:

exploratory

drilling

stops

when

there

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reasonable assurance that an economic deposit exists.

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_ development drilling:

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goal: to provide a three dimensional picture of the mineralisation, so that tonnage, grade and minability can be assessed. how: Drill a fence line, ie, a series of regularly spaced holes along a line perpendicular to the long axis of the deposit, where the best results were obtained during exploratory drilling. Repeat the pattern two or three lines on either side until barren ground is encountered. If there is too much variation between sections, then drill between sections. Ie, if computations using intervening sections affect the grade, then they are necessary.

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-. Cut-off Grade (COG) The ore grade yielding an ore value equal to the operating cost on a unit basis. Costs included in operating cost: • stoping • transportation • milling • smelting • refining • selling • administrative (administration, head office, exploration, etc.) Mineralized material greater-than-or-equal-to this grade is ore; less than'this grade it's waste.

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METRIC

AZIMUTH

ID.D.H. No.

FALCONBRIDGE LIMITED

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Figure 3.-Vertical Section across the Orebody, showing Generalized Ore Limits.

2) • Sampling and Assaying:

When core is available from diamond drilling, it is first logged. This means that a careful record is made of: -rock type and lithologic description -texture, weathering -structure -alteration features -depth & length of core run -condition of core, recovery For more thorough geotechnical logging:

-joint orientation, frequency and spacing -relative strength of rock

After logging, mineralized zones are split along the axis of the core; one half remains in the core librairy, and the other half is split into sample lengths (about 1m) and sent for assay. There are several assay techniques: -wet or chemical assaying (leaching & titration) -fire assaying (roasted, get a button) atomic absorption (chemical treatment -puts minerals in solution and analysed by atomic absorption)

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5) • Classification of Ore Reserves

Ore reserves are classified in order to give the user (geologist, mining engineer, financial analyst...), an estimate of the confidence level in the results. Two classification schemes are in use at the moment: the original categories of 1)PROVEN, PROBABLE, POSSIBLE and INFERRED. 2)MEASURED, INDICATED and INFERRED.

1) PROVEN: historically, ore that is "blocked out", ie, measured, sampled, and assayed on four sides.

(Pamour definition: blocks outlined by drifts above and below, raises

through the blocks, and some drill holes). PROBABLE: blocked on three sides. (Pamour : only partly developed). POSSIBLE: blocked on two sides. (Pamour : only DDH, and a x-cut through the ore for example) INFERRED: ore grade material known only on on side.

2) MEASURED : " ore for which tonnage is computed from dimensions revealed in outcrops, trenches, workings, and drill holes, and for which the grade is computed from the results of detailed sampling. The sites for inspection, sampling and measurement are so closely spaced and the geologic character is so well-defined that the size, shape and mineral content are well established." (White Pine Michigan: sufficient drilling is about 1000ft spacing). INDICATED: " ore for which tonnage and grade are computed partly from specific measurements, samples, or production data and partly from projection for a reasonable distance on geologic evidence.

The sites available for inspection, sampling and

measurement are too widely or otherwise inappropriately spaced to outline the ore completely or to establish its grade throughout." (White Pine, Michigan: sufficient drilling is about 3000 ft spacing). INFERRED : "ore for which quantitative estimates are based largely on a broad knowledge of the geologic character of the deposit and for which there are few, if any, samples or measurements. " 4

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In Canada most mines still use the older system of proven, probable and possible, but in the USA where tabular, vein-type deposits are rare, people have mostly adopted the USBM classification of measured, indicated and inferred. People have however, felt the need for subdivision of these categories, to further reflect the level of knowledge and confidence in the reserves. One major company uses the sub-categories: developed, semi-developed and undeveloped, to further rank proven reserves.

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