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.
The five minerals are compared directly in the table below, since parts (a), (b) and (c) ask the same three questions of each specimen.
| Mineral | Common crystal form (hand specimen) | Major ore element | Diagnostic physical property |
|---|---|---|---|
| (i) Spodumene, LiAlSi₂O₆ | Monoclinic pyroxene – elongated, flattened prismatic crystals, sometimes to enormous size in pegmatites (giant crystals metres long) | Lithium (Li) | Two prismatic cleavages at ~87°/93° (pyroxene-type cleavage) with prominent striations parallel to the crystal length, vitreous lustre, hardness 6.5–7 |
| (ii) Pyrrhotite, Fe₁₋₉S | Hexagonal to monoclinic – tabular platy crystals, most commonly massive/granular in sulphide ore | Iron (Fe), typically as an associated Ni-Cu sulphide-ore mineral | Bronze-brown metallic colour (darker/more coppery than pyrite) that is variably but often strongly magnetic – the one common sulphide besides magnetite that deflects a hand magnet |
| (iii) Apatite, Ca₅(PO₄)₃(F,Cl,OH) | Hexagonal – slender to stubby prismatic crystals with a hexagonal cross-section, commonly terminated by pyramidal faces | Phosphorus (P) | Hardness of exactly 5 (it defines that point on the Mohs scale), vitreous to resinous lustre, and frequently a pale green/blue-green colour |
| (iv) Halite, NaCl | Isometric (cubic) – well-formed cubes, sometimes with hopper (stair-stepped) faces | Sodium/chlorine (Na, Cl) | Perfect cubic cleavage in three directions, very low hardness (2.5), and an unmistakable salty taste |
| (v) Pitchblende (massive uraninite), UO₂ | Colloform/botryoidal – the "pitchblende" habit is specifically the massive, reniform-botryoidal crust with no distinct crystal faces (crystalline uraninite is cubic/octahedral, but pitchblende by definition is the massive variety) | Uranium (U) | Very high density (≈6.5–10), dull pitch-like to submetallic lustre (the source of the name), black colour, and measurable radioactivity with a Geiger counter or scintillometer |
Pyrrhotite's variable magnetism is itself diagnostic: the monoclinic polytype (more Fe-deficient) is strongly ferromagnetic while the hexagonal polytype is only weakly so, so a magnet test alone does not exclude pyrrhotite the way it would exclude most other bronze sulphides – pyrite, by contrast, is never magnetic and has a paler brass-yellow colour with cubic/pyritohedral crystal faces. Pitchblende's radioactivity is the single unambiguous field test available for any ore mineral in this set; density and dull lustre alone can be mimicked by other heavy black minerals (e.g. some manganese oxides), but no other common ore mineral will register on a scintillometer.
Excluding spodumene, pyrrhotite, apatite, halite and pitchblende, one representative ore mineral for each of the five elements is:
| Element | Ore mineral | Formula |
|---|---|---|
| (i) Lead (Pb) | Galena | PbS |
| (ii) Mercury (Hg) | Cinnabar | HgS |
| (iii) Potassium (K) | Sylvite | KCl |
| (iv) Titanium (Ti) | Ilmenite | FeTiO₃ |
| (v) Copper (Cu) | Chalcopyrite | CuFeS₂ |
Galena's perfect cubic cleavage and very high density (≈7.6) make it as diagnostic as halite's cubic habit, but galena is distinguished immediately by its metallic lead-grey lustre and much higher density. Sylvite is isostructural with, and easily confused with, halite (both isometric, both water-soluble with perfect cubic cleavage); the reliable field distinction is taste – sylvite is distinctly bitter as well as salty – and sylvite is typically found interbedded with, rather than instead of, halite in evaporite sequences (e.g. the same Prairie Evaporite potash beds of Saskatchewan that host the halite of this question set).
