18-Geol-A1 Mineralogy and Petrology · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A1 Mineralogy and Petrology, 2016-May. Closed book; no calculator permitted. Part 1 requires all six 10-mark short-answer questions (60 marks); Part 2 instructs "four of the seven ten-mark questions" (40 marks).
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (mineral/silicate structural classification, ore mineralogy); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, cumulates, metamorphic reactions and facies, AFM projections, volcanic processes, oceanic crust petrogenesis); Nesse, Introduction to Optical Mineralogy, 4th ed. (index-mineral optics); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (sedimentary/pyroclastic textural context).
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 base/critical metal listed has one dominant, economically-mined sulphide ore mineral; several also occur as minor sulphosalt phases, noted where relevant.
| Metal | Mineral | Formula | Notes |
|---|---|---|---|
| Tin (Sn) | Stannite | $\text{Cu}_2\text{FeSnS}_4$ | The principal sulphide tin ore (a Cu-Fe-Sn sulphosalt); most tin is actually mined from the oxide cassiterite ($\text{SnO}_2$), so stannite is the sulphide-specific answer. |
| Zinc (Zn) | Sphalerite | $\text{ZnS}$ | The dominant zinc ore worldwide; typically Fe-substituted (up to several mol % FeS), forms in Mississippi-Valley-type and volcanogenic massive sulphide (VMS) deposits. |
| Nickel (Ni) | Pentlandite | $(\text{Fe,Ni})_9\text{S}_8$ | The principal nickel sulphide ore, forms by immiscible sulphide-liquid segregation in mafic/ultramafic intrusions, intergrown with pyrrhotite and chalcopyrite. |
| Lead (Pb) | Galena | $\text{PbS}$ | The dominant lead ore; cubic cleavage, high density; commonly intergrown with sphalerite in the same MVT/VMS deposits. |
| Copper (Cu) | Chalcopyrite | $\text{CuFeS}_2$ | The single most important copper ore mineral (porphyry, VMS and skarn deposits); secondary/supergene copper sulphides chalcocite ($\text{Cu}_2\text{S}$) and covellite ($\text{CuS}$) also form important enrichment-blanket ore. |
