24-MMP-A1 General Geology and Exploration · May 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-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, concordant/stratiform vs stratabound terminology); 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. (stream-sediment dispersion, survey design parameters); 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) ask the same three questions of each specimen.
| Mineral | Common crystal form (hand specimen) | Major ore element | Diagnostic physical property |
|---|---|---|---|
| (i) Galena, PbS | Cubic – well-formed cubes, sometimes with octahedral modifications | Lead (Pb) | Perfect cubic cleavage in three directions at 90°, combined with very high density (≈7.6 g/cm³) and a bright lead-grey metallic lustre |
| (ii) Cassiterite, SnO₂ | Tetragonal – short prismatic to dipyramidal crystals, commonly twinned ("visor" twins) | Tin (Sn) | Exceptionally high specific gravity (≈6.8–7.1) for a non-metallic-looking mineral, adamantine lustre and no cleavage (conchoidal fracture) |
| (iii) Scheelite, CaWO₄ | Tetragonal – dipyramidal (bipyramidal), pseudo-octahedral crystals | Tungsten (W) | Bright bluish-white fluorescence under short-wave ultraviolet light – the standard field test used with a UV lamp |
| (iv) Sphalerite, ZnS | Cubic – tetrahedral habit, often as dodecahedra or resinous granular masses | Zinc (Zn) | Resinous lustre with perfect dodecahedral cleavage in six directions, colour ranging light-yellow to black with increasing Fe content ("ruby jack" to "black jack") |
| (v) Ilmenite, FeTiO₃ | Trigonal (rhombohedral) – thin tabular to platy crystals | Titanium (Ti) | Only weakly to sub-magnetic (unlike magnetite, which is strongly magnetic), black submetallic lustre, brownish-black to black streak, no cleavage |
Ilmenite's weak magnetism is the key field discriminator against magnetite: both are black, opaque, iron-titanium oxides commonly found together in mafic rocks and beach-sand placers, but a hand magnet or magnetic-susceptibility pen deflects strongly to magnetite and only weakly (if at all) to ilmenite. Cassiterite is likewise routinely confused with hematite or garnet at a glance; its diagnostic density – nearly three times that of quartz – is what a prospector actually uses ("heft" in the hand, or panning behaviour, since cassiterite concentrates with gold in a pan owing to its high specific gravity).
Excluding galena, cassiterite, scheelite, sphalerite and ilmenite, one representative ore mineral for each of the five elements is:
| Element | Ore mineral | Formula |
|---|---|---|
| (i) Aluminum (Al) | Gibbsite (the dominant mineral of bauxite ore) | Al(OH)₃ |
| (ii) Barium (Ba) | Barite | BaSO₄ |
| (iii) Arsenic (As) | Arsenopyrite | FeAsS |
| (iv) Manganese (Mn) | Pyrolusite | MnO₂ |
| (v) Lithium (Li) | Spodumene | LiAlSi₂O₆ |
Bauxite itself is a lateritic rock rather than a single mineral species, so the answer above names gibbsite – commonly the most abundant of the three aluminum hydroxide/oxyhydroxide minerals (gibbsite, boehmite, diaspore) that together make up bauxite ore. Spodumene is the classic pegmatite-hosted lithium ore mineral (see Question 2(ii)); lepidolite (a lithium mica) is an acceptable alternative answer for the same element.
