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.
Each deposit type below records a distinct combination of energy source, transporting medium and trapping mechanism, ranging from purely mechanical surface processes to deep magmatic and hydrothermal systems.
Placer deposits form by the mechanical erosion of a primary (lode) source of dense, resistant ore minerals – gold, cassiterite, magnetite/ilmenite, diamonds – followed by fluvial (or beach/glacial) transport and gravity-driven hydraulic sorting, which concentrates the dense grains in low-energy traps within a stream or beach system (point bars, bedrock riffles, paleochannel gravels). The process is purely mechanical: no chemical precipitation is involved, only density-controlled sorting during transport. Example: the placer gold of the Klondike goldfields, Yukon, derived from eroded lode-gold source rocks and concentrated in Pleistocene-to-Recent stream gravels.
Pegmatite deposits crystallize from the final, most hydrous and volatile-rich residual melt fraction remaining after a granitic magma has undergone extensive fractional crystallization. This residual liquid concentrates incompatible elements (Li, Be, Cs, Ta, Nb, Sn, REE) that could not be accommodated in earlier-forming rock-forming minerals, and its high volatile content lowers the liquidus and promotes very rapid, coarse crystal growth as the melt intrudes the pluton margin or surrounding country rock. Example: the Tanco pegmatite, Manitoba (Li-Cs-Ta mineralization).
MVT deposits form when warm (typically 75–150°C), dense basinal brines – mobilized by tectonic loading, gravity-driven basin dewatering, or topographic head, not by magmatic heat – migrate long distances through permeable carbonate aquifers and precipitate Pb-Zn sulphides where the fluid encounters a chemical trap: mixing with a reduced (H₂S-bearing) fluid, reaction with a reactive dolomitic host, or a structural/stratigraphic seal. The process is entirely epigenetic, post-dating the host carbonate by a large time interval, and produces disseminated-to-replacement ore confined within a specific stratigraphic/structural trap. Example: Pine Point, Northwest Territories, hosted in Devonian carbonate of the Western Canada Sedimentary Basin.
Skarn deposits form by contact metasomatism at the margin of a felsic-to-intermediate intrusion emplaced into reactive carbonate wall rock. Heat drives contact metamorphism (recrystallizing the carbonate to marble/hornfels), while an exsolved magmatic-hydrothermal fluid, together with fluid derived from the country rock, drives metasomatic ion exchange, replacing the carbonate with calc-silicate minerals (garnet, pyroxene, wollastonite) and precipitating ore sulphides/oxides within that calc-silicate assemblage. Example: Craigmont, British Columbia (Cu skarn related to a quartz-diorite intrusion into limestone).
VMS deposits form on or just below the seafloor within an active submarine volcanic (commonly bimodal felsic-mafic) sequence, where seawater is drawn down through fractured, hot volcanic rock, leaches metals (Cu, Zn, Pb, Au, Ag) from that rock, and is discharged back onto the seafloor as a hot, metal-charged hydrothermal vent fluid (a "black smoker"-type system). Rapid cooling and mixing with cold seawater causes sulphides to precipitate, both as chimney/mound structures at the vent site and as a stratiform blanket of exhalite draped over the contemporaneous seafloor. Example: Kidd Creek, Ontario, one of the largest and deepest VMS deposits known, hosted in Archean bimodal volcanic rocks of the Abitibi greenstone belt.
