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.
Other parameters commonly cited (survey timing/season, sample-preparation and QA/QC protocol, avoidance of anthropogenic contamination) are refinements of the same underlying principle: every parameter exists to preserve the true geochemical signal of the target through to the analytical result.
| Station | River / catchment | Predicted Au content | Reason |
|---|---|---|---|
| 1 | Ootus (downstream) | Low | Same catchment as the source, but furthest downstream of the three Ootus stations – progressive dilution of the sediment dispersion train with distance and with dilution from tributary inflow between Y and Station 1 |
| 2 | Ootus (mid-reach) | Moderate | Same catchment, intermediate distance downstream of the Y tributary junction – less dilution than Station 1, more than Station 3 |
| 3 | Ootus (closest downstream) | High | The first sampled station downstream of where Y's dispersion train enters the Ootus channel – minimal dilution, so the strongest anomaly of the network |
| 4 | Boobalie | Zero | Different catchment from Y (Boobalie system), separated by the local drainage divide – stream-sediment gold cannot cross a topographic drainage divide, regardless of straight-line map distance to Y |
| 5 | Boobalie | Zero | Same reasoning as Station 4 – hydrologically isolated from Y despite being the closest Boobalie station to Y in plan view |
| 6 | Unnamed tributary (separate catchment) | Zero | Drains a small area on the far side of the divide from Y; no hydrologic connection to the Ootus channel that carries the dispersion train, so no anomaly reaches it however close it appears on the map |
The reasoning that matters for full marks is not the specific tier assigned to each station but the underlying principle: a stream-sediment anomaly can only appear at a station that is hydrologically DOWNSTREAM of the source within the SAME drainage basin. Physical proximity on the map is irrelevant if a drainage divide intervenes (Stations 4, 5 and 6 here), and within the correct catchment, anomaly strength decays with distance downstream from progressive dilution by uncontaminated sediment entering from tributaries and bank erosion between the source and the sampling point (the classic exponential-decay "dispersion train" of exploration geochemistry).
The optimum spacing for a reconnaissance geochemical stream survey is not a fixed distance but is set by the drainage network itself: a sample should be collected immediately below every significant tributary confluence, so that each sample represents (as nearly as possible) a single, non-overlapping increment of catchment area – commonly stated as targeting an average catchment area of a few km² per sample for a first-pass reconnaissance survey, refined with closer spacing as a follow-up survey narrows toward a specific anomalous sub-catchment. Sampling density should therefore scale with drainage order and target catchment area, not with a uniform grid distance.
The stations on this map are not at optimum spacing: Stations 1, 2 and 3 all lie on the same uninterrupted Ootus reach with no intervening significant tributary confluence between them, so – on the drainage-network design principle above – Stations 1 and 2 are largely redundant with Station 3 for reconnaissance purposes (they resample essentially the same catchment, just with progressively more dilution). A more efficient design would place one station just below the Y-tributary confluence (near the current Station 3 position) and reserve the budget spent on the redundant intervening stations for extending coverage into unsampled tributaries elsewhere in the basin.
