24-MMP-A1 General Geology and Exploration · December 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-Dec. 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, ore-body morphology); 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 radiometric 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/soil survey design); Peters, Exploration and Mining Geology, 2nd ed. (sampling methods, drilling programs).
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.
A passive sensor carries no energy source of its own; it simply records natural electromagnetic energy that already exists – reflected sunlight (visible/near-infrared/short-wave-infrared imagers such as Landsat and ASTER) or naturally emitted thermal radiation (thermal-infrared imagers). An active sensor generates and transmits its own pulse of energy toward the ground and measures the strength, timing and/or phase of the energy that is reflected back – synthetic aperture radar (SAR) transmits microwave pulses and measures the backscattered return, while satellite/airborne LiDAR transmits laser pulses and measures round-trip travel time. Because active sensors supply their own illumination, they can acquire data through cloud cover and at night, which passive optical sensors cannot.
Satellite remote sensors sample the visible (≈0.4–0.7 µm), near-infrared (≈0.7–1.3 µm), short-wave infrared (≈1.3–3 µm), thermal infrared (≈8–14 µm) and microwave/radar (millimetre-to-centimetre wavelength) regions of the spectrum. Much of the remaining infrared spectrum, together with parts of the ultraviolet, cannot be sampled from a satellite because Earth's atmosphere is not transparent at those wavelengths: water vapour, carbon dioxide and ozone strongly absorb (or scatter) radiation outside a set of narrow "atmospheric window" bands, so radiation at those wavelengths never reaches a satellite sensor in usable strength – ozone alone essentially blocks all wavelengths shorter than about 0.3 µm. Satellite sensor bands are therefore deliberately placed to sit inside the available atmospheric windows rather than being spaced evenly across the spectrum.
| Target | Method 1 | Method 2 | Why |
|---|---|---|---|
| (i) Cu porphyry deposit | Induced polarization (IP) / chargeability | Magnetics | IP directly detects the low-grade DISSEMINATED sulphide (pyrite±chalcopyrite) stockwork that defines a porphyry system, even where grade is too low for a resistivity contrast alone; magnetics maps the magnetite-rich potassic alteration core and the surrounding magnetite-destructive phyllic halo, both diagnostic of porphyry alteration zoning. |
| (ii) Black-sand placer deposit | Magnetic susceptibility survey | Ground-penetrating radar (GPR) / resistivity | Black-sand placers are enriched in magnetite/ilmenite (and often gold), so a magnetic survey directly maps the heavy-mineral concentration; GPR/resistivity images the buried paleochannel geometry and gravel thickness/depth-to-bedrock that controls where the placer is trapped. |
| (iii) Laterite | Electromagnetics (EM conductivity mapping) | Magnetics | Laterite weathering profiles have a distinctive layered conductivity structure (clay-rich horizons are conductive, silica/iron-cemented duricrust is more resistive), so EM images profile thickness and depth to fresh bedrock; magnetics can distinguish an iron-rich laterite crust and locate the underlying ultramafic/mafic bedrock that is its parent rock. |
| (iv) Skarns | Magnetics | Gravity | Many skarns are magnetite-rich, producing a strong, sharply defined magnetic high against a non-magnetic carbonate host; gravity detects the density contrast of dense sulphide/magnetite skarn ore replacing lower-density limestone/marble. |
| (v) Gemstones in pegmatites | Radiometrics (gamma-ray spectrometry) | Magnetics | Gem-bearing (Li-Cs-Ta) pegmatites are commonly enriched in K, U and Th relative to the host rock, giving a radiometric anomaly that can be mapped from the air; because the quartz-feldspar-rich pegmatite itself is non-magnetic, a magnetic LOW against a more magnetic host rock helps outline the pegmatite body's extent even though it cannot detect the gemstones directly. |
