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.
A tabular ore body is sheet- or slab-like, with two dimensions (length and width, or length and depth) much greater than the third (thickness). Sedex Pb-Zn-Ag deposits, e.g. the Sullivan Mine, Kimberley, British Columbia, form laterally extensive, sheet-like sulphide layers conformable with the enclosing sediment. Epithermal vein deposits (e.g. many low-sulphidation Au-Ag veins of the Canadian and American Cordillera) fill planar fracture/fault systems, producing thin, sheet-like, steeply dipping tabular ore bodies that can be traced for hundreds of metres along strike.
A tubular (pipe-like) ore body is roughly cylindrical or elongate in a near-vertical or steeply plunging direction, with a comparatively small cross-section. Kimberlite pipes (diamond deposits), e.g. the pipes of the Ekati and Diavik mines, Northwest Territories, are classic carrot-shaped diatremes narrowing with depth. Breccia-pipe deposits, such as the IOCG-style breccia pipe at Olympic Dam, South Australia, form when hydrothermal brecciation and mineralization are focused along a steep, roughly circular structural conduit.
A disseminated ore body carries fine, widely scattered grains of ore mineral distributed throughout a large volume of host rock, rather than concentrated along discrete veins or layers, so it is defined by an average grade rather than a sharp ore/waste contact. Porphyry Cu-Mo deposits, e.g. Highland Valley Copper, British Columbia, carry chalcopyrite and molybdenite disseminated through a stockwork of micro-fractures across a large volume of altered intrusion. Komatiite-hosted disseminated Ni-sulphide deposits (e.g. the Thompson Nickel Belt, Manitoba, in its disseminated zones) carry fine pentlandite-pyrrhotite grains scattered through the ultramafic host rather than as a massive sulphide mass.
A replacement ore body forms where a hydrothermal fluid dissolves the original host-rock mineralogy (commonly a reactive carbonate) and substitutes ore minerals in its place, so the ore body's outer shape is controlled by the permeability/reactivity of the host rather than by a fracture or a bedding plane. Skarn deposits form where metasomatic fluids replace carbonate wall rock at an igneous contact, e.g. Craigmont, British Columbia (Cu skarn). Mississippi Valley type (MVT) Pb-Zn deposits, e.g. Pine Point, Northwest Territories, form where basinal brines dissolve and replace reactive carbonate along permeable stratigraphic and karst/breccia horizons.
A residual ore body forms in place by the in-situ weathering removal of soluble/less-resistant constituents from a parent rock, leaving behind a chemically and mechanically concentrated blanket of the ore constituent at or near the modern land surface. Lateritic nickel deposits, e.g. Goro, New Caledonia, form by deep tropical weathering of ultramafic bedrock that leaches silica and magnesium while residually enriching nickel in the weathering profile. Bauxite (aluminum) deposits, e.g. the lateritic bauxites of Jamaica and the Amazon Basin, form by intense tropical weathering of aluminosilicate parent rock that leaches nearly everything except aluminum hydroxide/oxyhydroxide minerals.
