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.
| Rock type | Definition | Typical ore / ore deposit |
|---|---|---|
| (i) Shale | A fine-grained, fissile (splits into thin sheets) clastic sedimentary rock formed by compaction and lithification of clay- and silt-sized mud on a quiet-water sea floor or lake bed. | Sedimentary-exhalative (SEDEX) Pb–Zn deposits and black-shale-hosted stratiform Cu–U deposits, where the organic-rich, reducing shale both traps metal-bearing brines and precipitates sulphides. |
| (ii) Sandstone | A clastic sedimentary rock composed of cemented sand-sized (0.06–2 mm) grains, typically quartz-rich, deposited by fluvial, aeolian or shallow-marine processes and later cemented by silica, calcite or iron oxide. | Sandstone-hosted ("roll-front") uranium deposits, where oxidising, U-bearing groundwater moving through permeable sandstone precipitates uraninite at a redox front; sandstone-hosted red-bed copper is a second common example. |
| (iii) Kimberlite | A rare, volatile-rich ultramafic igneous rock that rises explosively from great mantle depth (>150 km) as narrow, carrot-shaped pipes (diatremes), carrying mantle xenoliths and xenocrysts. | Primary diamond deposits – kimberlite pipes are the principal primary source of natural diamond, which forms at the mantle depths from which the kimberlite magma is derived. |
| (iv) Pegmatite | An exceptionally coarse-grained (crystals often >2 cm) igneous rock, usually of granitic composition, crystallised from the volatile- and incompatible-element-enriched residual melt left after a granite magma has largely solidified. | Rare-element pegmatites hosting Li (spodumene, lepidolite), Ta–Nb (columbite–tantalite), Be (beryl) and Sn, plus industrial mica and gem minerals. |
| (v) Norite | A coarse-grained mafic intrusive (plutonic) rock composed dominantly of plagioclase feldspar and orthopyroxene, texturally and mineralogically similar to gabbro. | Magmatic Ni–Cu–PGE sulphide deposits – the norite of the Sudbury Igneous Complex, Ontario, hosts one of the world's largest Ni–Cu sulphide ore systems. |
The five rock types span sedimentary, volcanic/hypabyssal and plutonic settings deliberately: shale and sandstone illustrate how ordinary clastic sediments can become ore hosts through diagenetic or groundwater processes long after deposition, kimberlite shows a deposit whose ore (diamond) actually pre-dates and is merely transported by its host rock, and pegmatite and norite show two very different products of the same broad process (igneous crystallisation) – residual-melt enrichment versus early cumulate sulphide segregation.
A placer deposit is a surficial mechanical concentration of dense, chemically and mechanically resistant minerals that have been physically liberated from a primary (bedrock) source by weathering, transported by moving water (or occasionally wind or ice), and concentrated by gravity sorting because of their high density relative to the light silicate sand and gravel that forms the bulk of the sediment load. Formation begins with weathering and erosion of a mineralised source rock (a vein, a mineralised zone, or simply ordinary rock containing accessory heavy minerals); the liberated grains are carried downstream where hydraulic sorting during transport progressively concentrates the densest, most durable grains into traps such as point bars, bedrock riffles and potholes, the base of gravel bars, and paleochannels buried by later sediment, while lighter silicate minerals are winnowed away and carried further downstream. Because the process is purely mechanical, only minerals that are both dense and resistant to abrasion and chemical breakdown survive to form an economic placer.
Five ore minerals commonly found in placer settings are: native gold, cassiterite (placer/alluvial tin, "stream tin"), magnetite and ilmenite (heavy Fe–Ti "black sand" concentrates), platinum-group minerals (native platinum/osmiridium), and zircon, together with diamond and monazite (a rare-earth phosphate) as further examples of the same style of deposit.
