24-MMP-A1 General Geology and Exploration · May 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A1 General Geology and Exploration, 2018-May. Closed book; only a Casio or Sharp approved calculator permitted. Questions 1–4 are compulsory; a candidate then completes ONE more question chosen from Questions 5, 6 or 7.
Reference texts: Guilbert & Park, The Geology of Ore Deposits (genetic classification, deposit-type descriptions throughout); Evans, Ore Geology and Industrial Minerals, 3rd ed. (deposit classification, structural controls on ore); Klein & Dutrow, Manual of Mineral Science, 23rd ed. (crystal systems, diagnostic physical properties, hand-specimen identification); Telford, Geldart & Sheriff, Applied Geophysics, 2nd ed. (gravity, magnetic, electrical, EM and seismic methods); Kearey, Brooks & Hill, An Introduction to Geophysical Exploration, 3rd ed. (survey design and method selection); Rose, Hawkes & Webb, Geochemistry in Mineral Exploration, 2nd ed. (sample-medium selection, dispersion patterns); Peters, Exploration and Mining Geology, 2nd ed. (drilling methods and sampling).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
Drilling is the most expensive tool per unit of ground tested in an exploration program, so it is normally deployed AFTER surface methods – geological mapping, geochemical sampling and geophysical surveying – have generated and prioritised a well-defined target. Scout or reconnaissance drilling may begin once a strong anomaly is defined, but the bulk of drilling occurs progressively later: first to test/confirm individual targets, then, once a discovery is made, in closely spaced systematic campaigns to delineate the deposit for a compliant mineral resource estimate, and finally as grade-control drilling immediately ahead of mining.
Three main reasons for drilling are:
| Drilling type | How it works | Sample recovered | Typical use |
|---|---|---|---|
| Diamond (core) drilling | A diamond-impregnated annular bit cuts a cylindrical plug of rock, which is captured intact in a core barrel and brought to surface. | Continuous, oriented cylindrical rock core – the highest-quality sample available. | Resource-definition drilling, structural/geotechnical studies, and any hole requiring reliable oriented structural measurements; slower and more expensive per metre. |
| Rotary / reverse-circulation (RC) drilling | A rotating tricone or down-hole hammer bit grinds the rock into chips, which are returned to surface as cuttings by reverse air (or fluid) circulation up the inside of the drill string. | Rock chips/cuttings only – no intact core, and some risk of sample mixing/contamination between intervals. | Rapid, low-cost reconnaissance and grade-control drilling over large areas; faster and cheaper per metre, but with lower geological/structural resolution. |
The major differences follow directly from what each method physically recovers: diamond core preserves the rock's original fabric, so it alone can deliver oriented structural data, detailed geological logging and high-quality samples for geotechnical or metallurgical testwork, at higher cost and lower drilling speed; RC drilling sacrifices structural detail and sample integrity in exchange for a much faster, cheaper metre, making it the tool of choice for covering large ground quickly in the earlier, more exploratory stages of a program.
Core or cuttings are first geologically logged (lithology, alteration, structure, visible mineralisation) and then systematically sampled at set intervals and submitted for assay. Assay results are combined with each hole's collar coordinates and downhole deviation survey (since a drill hole is rarely perfectly straight) in a drill-hole database. Lithological and mineralised intervals are then correlated between adjacent holes to build cross-sections, level plans and, ultimately, a three-dimensional geological and grade model (a wireframe or solid model of the mineralised zone). That model is used to interpolate grade between the widely spaced drill holes – typically by a geostatistical method such as inverse-distance weighting or kriging – in order to calculate contained tonnage and average grade for a resource estimate, and the resulting confidence level (and any gaps or ambiguities revealed in the model) is what guides the design of further infill or step-out drilling.
