18-Geol-A1 Mineralogy and Petrology · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A1 Mineralogy and Petrology, 2017-Dec. Closed book; no calculator permitted. Part 1 requires all five 10-mark short-answer questions (50 marks); Part 2's page-1 header says "5 of the 8" while the page-3 instructions say "5 of the 7" and list exactly 7 questions (a source discrepancy noted on the exam page itself).
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (silicate/sulfide/carbonate structural classification, mineral chemistry and formulas); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, metamorphic agents/facies, volcanic processes, layered intrusions and cumulates, partial melting, ophiolites); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (carbonate mineral diagnostics).
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 of these five base/transition metals is chalcophile — it bonds preferentially to sulfur over oxygen under the reducing conditions of a magmatic sulfide liquid or hydrothermal ore fluid — and each has one dominant, diagnostic sulfide mineral.
| Metal | Mineral | Formula | Notes |
|---|---|---|---|
| Zinc (Zn) | Sphalerite | $\text{ZnS}$ | The dominant zinc ore worldwide; commonly Fe-substituted, forms in Mississippi-Valley-type and volcanogenic massive sulfide (VMS) deposits. |
| Copper (Cu) | Chalcopyrite | $\text{CuFeS}_2$ | The single most important copper ore mineral (porphyry, VMS and skarn deposits). |
| Nickel (Ni) | Pentlandite | $(\text{Fe,Ni})_9\text{S}_8$ | Forms by immiscible sulfide-liquid segregation in mafic/ultramafic intrusions, intergrown with pyrrhotite and chalcopyrite. |
| Iron (Fe) | Pyrite | $\text{FeS}_2$ | The most widespread sulfide mineral of any kind (isometric, cubic/pyritohedral crystals, brassy "fool's gold" lustre); pyrrhotite ($\text{Fe}_{1-x}\text{S}$) is the common magmatic-sulfide-associated alternative. |
| Lead (Pb) | Galena | $\text{PbS}$ | The dominant lead ore; perfect cubic cleavage, very high density; commonly intergrown with sphalerite in the same MVT/VMS deposits. |
