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.
| Method | Description | Physical property measured |
|---|---|---|
| Magnetic | Measures small spatial variations in the strength/direction of the Earth's total magnetic field caused by underlying rock. | Magnetic susceptibility and remanent magnetisation (chiefly controlled by magnetite/pyrrhotite content). |
| Gravity | Measures minute variations in the Earth's gravitational acceleration from point to point across a survey area. | Rock density (bulk density contrasts between adjacent rock units). |
| Electromagnetic (EM) | An alternating primary field induces eddy currents in conductive subsurface bodies; the resulting secondary field is measured at surface (or from the air). | Electrical conductivity of the subsurface. |
| Induced polarization (IP) / resistivity | A current is injected into the ground through electrodes; resistivity measures the bulk resistance to current flow, while IP measures the decaying "chargeability" response left by polarisable minerals after the current is switched off. | Electrical resistivity (resistivity survey) and chargeability (IP survey) – the latter is diagnostic of disseminated sulphides. |
| Radiometric (gamma-ray spectrometry) | Measures natural gamma radiation emitted from the top few tens of centimetres of rock or soil, usually flown airborne. | Concentration of the naturally radioactive elements potassium (K), uranium (U) and thorium (Th). |
| Target | Best method | Why |
|---|---|---|
| (i) Pyrrhotite massive sulphide in a layered mafic complex | Electromagnetic (EM) | Massive sulphide is an excellent electrical conductor, giving a strong, unambiguous EM anomaly; magnetics is a valuable companion method here because pyrrhotite (unlike most sulphides) is itself magnetic. |
| (ii) Buried stream channel containing placer gold | Resistivity | Saturated, unconsolidated channel gravel has a markedly different resistivity from the surrounding bedrock, allowing the buried channel's geometry (and hence the placer trap) to be mapped in cross-section. |
| (iii) Disseminated Pb and Zn in carbonate rocks | Induced polarization (IP) | The sulphides are too finely disseminated to form a continuous conductor for EM, but each grain still polarises and discharges under IP, which is specifically sensitive to disseminated (as opposed to massive) sulphide mineralisation. |
| (iv) Oil traps in a sedimentary basin | Gravity | Structural traps (anticlines, salt domes, basin-margin faults) and the low density of a hydrocarbon-saturated reservoir relative to surrounding strata both produce recognisable gravity anomalies, the classical tool for regional basin and trap reconnaissance (seismic reflection is the modern industry-standard follow-up for detailed trap definition). |
| (v) Uranium ore in a conglomerate | Radiometric | Uranium and its daughter isotopes are directly, uniquely detectable by their natural gamma emission, making radiometric surveying the fastest direct-detection tool for near-surface or subcropping uranium mineralisation. |
| Method | Complicating factor |
|---|---|
| Magnetic | Diurnal variation of the Earth's magnetic field during the survey, and magnetic minerals in surficial cover (e.g. magnetite-rich till) that mask or mimic bedrock anomalies. |
| Gravity | Rugged topography requires large, uncertainty-prone terrain corrections that can easily swamp the subtle density anomaly being sought. |
| Electromagnetic (EM) | Conductive overburden (saline, clay-rich or graphitic weathered material) produces a strong near-surface response that can mask or be mistaken for a genuine bedrock conductor. |
| Induced polarization (IP) / resistivity | Clay-rich or conductive overburden and poor galvanic electrode contact in dry, resistive ground both distort the chargeability/resistivity response. |
| Radiometric | Very shallow penetration depth (only the uppermost tens of centimetres) means vegetation cover, soil moisture and snow strongly attenuate the signal and can completely mask buried mineralisation. |
