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.
| Mechanism | How it concentrates ore | Example deposit |
|---|---|---|
| Fractional crystallisation / crystal settling (cumulate formation) | Dense, early-crystallising minerals (chromite, magnetite, some sulphides) nucleate first and, being denser than the remaining melt, sink and accumulate as layered cumulates on the floor of a slowly cooling magma chamber. | Chromitite seams of the Bushveld Complex, South Africa (layered mafic intrusion). |
| Liquid immiscibility (sulphide-liquid segregation) | A silicate magma that becomes saturated in sulphur (often through assimilation of crustal sulphur-bearing rock) unmixes into two immiscible liquids – a silicate melt and a denser Fe–Ni–Cu–S sulphide melt – which segregates and settles to form massive to disseminated sulphide ore. | Ni–Cu–PGE sulphide ores of the Sudbury Igneous Complex, Ontario. |
| Residual (late-stage) magmatic concentration | As a magma progressively crystallises, incompatible elements and volatiles that cannot enter the common rock-forming minerals become increasingly concentrated in the shrinking volume of residual melt, which finally crystallises as a volatile-rich, coarse-grained, element-enriched rock. | Rare-element (Li–Cs–Ta) pegmatites such as the Tanco pegmatite, Manitoba. |
The three processes share the same underlying driver – progressive crystallisation removes material from a cooling magma and thereby concentrates whatever it does not readily accept – but they differ in what gets concentrated and where: cumulate settling concentrates dense crystals into layers, immiscibility concentrates chalcophile metals into a separate sulphide liquid, and residual enrichment concentrates incompatible trace elements into the last, most evolved melt fraction.
| Deposit type | Classification | Rationale |
|---|---|---|
| (i) Banded iron formation | Sedimentary-hosted | Chemically precipitated, thinly banded Precambrian marine sediment (alternating Fe-oxide and chert/silica layers). |
| (ii) Iron-oxide–copper–gold (IOCG) | Plutonic-related | Genetically tied to the heat and fluids of large felsic-to-alkalic intrusive complexes (e.g. Olympic Dam). |
| (iii) Kimberlites | Plutonic-related | Ultramafic, mantle-derived intrusive pipes (diatremes) – a deep-seated intrusive rather than a surface-erupted volcanic product. |
| (iv) Kuroko ore deposits | Volcanic-related | Classic volcanogenic massive sulphide (VMS) deposits formed on the sea floor above felsic submarine volcanic centres. |
| (v) Copper red beds | Sedimentary-hosted | Stratiform Cu mineralisation precipitated within continental red-bed sandstone/siltstone by reducing diagenetic fluids. |
| (vi) Lode gold deposits | Vein-hosted | Orogenic (mesothermal) gold deposited in quartz–sulphide veins occupying shear zones and fault/joint systems. |
| (vii) Porphyry copper deposits | Plutonic-related | Centred on, and genetically driven by, shallow porphyritic felsic-to-intermediate stocks. |
| (viii) Mississippi Valley Type (MVT) deposits | Sedimentary-hosted | Epigenetic Pb–Zn deposited by basinal brines within (and partly replacing) platform carbonate sedimentary rock. |
| (ix) Skarns | Metamorphic-hosted | Calc-silicate rock formed by contact metasomatism where an intrusion meets carbonate country rock – the ore-bearing rock itself is a metamorphic/metasomatic product. |
| (x) Layered mafic intrusions | Plutonic-related | Large, slowly cooled mafic–ultramafic plutons (Bushveld, Stillwater) that differentiate by cumulate settling, as in part (a). |
