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.
The five minerals are compared directly in the table below, since parts (a), (b) and (c) each ask the same question of every specimen.
| Mineral | Typical hand-specimen colour | Major ore element | Diagnostic physical property |
|---|---|---|---|
| (i) Covellite, CuS | Indigo-blue to blue-black, often with an iridescent purple/bronze tarnish | Copper (Cu) | Distinctive deep indigo-blue colour combined with a sectile habit (can be cut with a knife) and one perfect basal cleavage |
| (ii) Sphalerite, ZnS | Yellow-brown to reddish-brown or black, darkening with increasing iron content ("ruby jack" to "black jack") | Zinc (Zn) | Resinous lustre with six directions of perfect dodecahedral cleavage; a pale streak much lighter than the mineral's body colour |
| (iii) Arsenopyrite, FeAsS | Silver-white to steel-grey, sometimes with a faint pinkish tinge on fresh surfaces | Arsenic (As) | A garlic-like odour when struck or heated (arsenic fumes), together with a hardness (≈5.5–6) distinctly higher than most sulphides |
| (iv) Pyrrhotite, Fe₁₃₃₃S | Bronze-yellow to brownish-bronze, darker and duller than pyrite | Iron (Fe) | Weakly to moderately magnetic – attracts a hand magnet, unlike the visually similar pyrite and chalcopyrite |
| (v) Pyrolusite, MnO₂ | Iron-black to dark steel-grey, often dull and sooty-looking | Manganese (Mn) | Very soft in its earthy habit and readily soils the fingers black; leaves a black to bluish-black streak |
Pyrrhotite's magnetism is the single most useful field discriminator in this set: it is one of only a handful of common sulphides attracted to a hand magnet, which immediately separates it from the brassier, non-magnetic pyrite it otherwise resembles. Arsenopyrite's garlic odour on striking is likewise diagnostic and unmistakable once smelled, while pyrolusite's softness and readiness to blacken the hand distinguish it from harder, shinier black oxides such as magnetite.
Excluding covellite, sphalerite, arsenopyrite, pyrrhotite and pyrolusite, one representative ore mineral for each element is:
| Element | Ore mineral | Formula |
|---|---|---|
| (i) Nickel (Ni) | Pentlandite | (Fe,Ni)₉S₈ |
| (ii) Chromium (Cr) | Chromite | FeCr₂O₄ |
| (iii) Copper (Cu) | Chalcopyrite | CuFeS₂ |
| (iv) Tin (Sn) | Cassiterite | SnO₂ |
| (v) Uranium (U) | Uraninite (pitchblende) | UO₂ |
Pentlandite almost never occurs alone – it is intergrown with pyrrhotite (and lesser chalcopyrite) in magmatic Ni–Cu sulphide ores, so exploration for nickel in this style of deposit is itself guided by first finding pyrrhotite. Chalcopyrite is by far the world's most important copper ore mineral even though secondary minerals such as bornite, malachite and chalcocite are frequently more visually striking in outcrop.
