24-MMP-A1 General Geology and Exploration · May 2015
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, 2015-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, concordant/stratiform vs stratabound terminology); 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. (stream-sediment dispersion, survey design parameters); 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.
| Method | Physical property measured | Brief description |
|---|---|---|
| Gravity | Bulk density (contrast in ρ) | Measures small local variations in the Earth's gravitational field caused by subsurface density contrasts, after correcting for latitude, elevation, terrain and tides |
| Magnetic | Magnetic susceptibility & remanent magnetization | Measures local perturbations of the Earth's magnetic field caused by magnetic minerals (chiefly magnetite/pyrrhotite) in the subsurface |
| Electrical (resistivity / IP) | Electrical resistivity and chargeability (polarizability) | Injects current into the ground and measures the resulting potential distribution (resistivity), and the decay of induced voltage after current is switched off (IP, sensitive to disseminated sulphides) |
| Electromagnetic (EM) | Electrical conductivity | A time-varying transmitter field induces eddy currents in conductive subsurface bodies; the resulting secondary field is measured, giving conductivity without ground electrode contact |
| Seismic (refraction / reflection) | Elastic-wave (P- and S-wave) velocity | Measures travel times of seismic waves generated by an artificial source, which depend on rock density and elastic moduli and hence on lithology, layering and fracturing |
| Target | Best method | Reason |
|---|---|---|
| (i) Mississippi-Valley-type deposit | Gravity | Massive sphalerite-galena has a strong positive density contrast against the carbonate host, and gravity can also outline the karst/breccia collapse structures that localize MVT ore |
| (ii) Banded iron formation | Magnetic | Magnetite-facies BIF has an extremely high magnetic susceptibility contrast with adjacent chert/shale, producing large, easily mapped magnetic anomalies – the classic magnetic exploration target |
| (iii) Disseminated Au in metasediments | Induced polarization (IP) | Even a low volume percentage of accessory sulphide (pyrite, arsenopyrite) associated with the gold produces a strong chargeability response, making IP effective where the gold itself is not directly detectable |
| (iv) Salt deposits in a sedimentary basin | Gravity | Salt is markedly less dense than the enclosing clastic/carbonate sediments, producing a distinctive negative gravity anomaly – historically the classic method for locating salt domes/diapirs |
| (v) Kimberlitic diamonds | Magnetic | Kimberlite pipes commonly carry enough magnetite to produce a distinct, roughly circular magnetic anomaly, making aeromagnetic surveying the standard reconnaissance tool for pipe discovery |
| Method | Complicating factor |
|---|---|
| Gravity | Rugged topography requires precise terrain corrections, and variable overburden thickness/water-table depth produces near-surface density noise that can mask the target anomaly |
| Magnetic | The diurnal variation of the Earth's field (and occasional magnetic storms) must be removed with a base-station correction, and strong remanent magnetization in the host rocks can distort or offset the anomaly from its true source position |
| Electrical (resistivity/IP) | Apparent resistivity is strongly dependent on near-surface moisture content and water-table depth, and poor electrode contact in dry, frozen (permafrost) or resistive outcrop terrain degrades data quality |
| Electromagnetic | Conductive overburden (saline groundwater, clay-rich weathered material, or the seasonally conductive active layer over permafrost) can mask a genuine bedrock conductor or itself be misread as a bedrock target |
| Seismic | A highly variable near-surface weathered/unconsolidated layer produces large, spatially variable static time shifts that must be corrected before deeper reflectors/refractors can be interpreted reliably |
