24-MMP-A1 General Geology and Exploration · December 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-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: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (crystal systems, diagnostic physical properties, hand-specimen identification); 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); Telford, Geldart & Sheriff, Applied Geophysics, 2nd ed. (gravity, magnetic, electrical, EM and seismic methods); 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.
| Process | Definition | Most likely genetic deposit type |
|---|---|---|
| (i) Fractional crystallization | Progressive crystallization of a cooling magma removes minerals from the melt in a fixed order (Bowen's reaction series); if dense, early-formed minerals (e.g. chromite, magnetite) sink faster than the melt can carry them, they accumulate as layered cumulates on the chamber floor. | Magmatic (cumulate) deposits – e.g. chromitite seams of a layered mafic intrusion (Bushveld-type). |
| (ii) Liquid immiscibility | A silicate magma that becomes saturated in sulphur unmixes into two immiscible liquids – a silicate melt and a denser Fe–Ni–Cu–S sulphide melt – and the sulphide liquid segregates and settles under gravity. | Magmatic Ni–Cu–(PGE) sulphide deposits (Sudbury-type). |
| (iii) Hydrothermal fluid circulation | Hot aqueous fluids (of magmatic, metamorphic, meteoric or basinal origin) leach, transport and then precipitate metals in fractures, veins or by wall-rock replacement, triggered by cooling, boiling, or mixing with a second fluid. | Hydrothermal vein / porphyry-copper / volcanogenic massive sulphide deposits (depending on the fluid's ultimate source). |
| (iv) Sedimentary deposition | Ore constituents accumulate within a sedimentary basin syngenetically – either by direct chemical/biochemical precipitation from basin water, or by mechanical (gravity) sorting and concentration of dense detrital grains during transport. | Banded iron formation / SEDEX Pb–Zn (chemical) or placer gold (mechanical) – autochthonous or allochthonous sedimentary deposits. |
| (v) Weathering | Near-surface chemical breakdown under oxidizing conditions either residually concentrates immobile elements left behind as more-soluble constituents are leached away, or mobilizes and redeposits soluble metals at depth. | Lateritic/residual Ni or bauxite deposits (residual concentration), or a supergene-enriched chalcocite blanket over a porphyry copper deposit (mobilization and redeposition). |
These five processes overlap directly with the genetic categories of Question 2: (i) and (ii) are both magmatic processes, distinguished by whether the concentrating mineral is a solid crystal (fractional crystallization) or a second, immiscible liquid (liquid immiscibility); (iii) spans the magmatic-hydrothermal and diagenetic-hydrothermal categories depending on the fluid's ultimate heat/metal source; (iv) covers both the autochthonous and allochthonous sedimentary categories; and (v) is the weathering-driven process behind the supergene category. Recognizing that "process" and "genetic category" are two views of the same underlying framework is itself a useful exam strategy – the same worked example can often answer both kinds of question.
