24-MMP-A4 Mine Valuation and Mineral Resource Estimation · May 2016
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Mining and Mineral Processing Engineering, 09-Mmp-A4 Mine Valuation and Mineral Resource Estimation, 2016-May. 3 hours duration; one handwritten 8.5×11 in reference sheet permitted (not an open-book exam); only approved Sharp or Casio calculators allowed. Question 1 is compulsory (40 marks, parts 1.1–1.6); candidates then select THREE of the six optional Questions 2–7 (20 marks each) to complete the paper.
Reference texts: Isaaks & Srivastava, An Introduction to Applied Geostatistics (variogram modelling, kriging estimators, volume–variance relations); Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design (mine valuation, NPV and cut-off grade methodology, mineable reserves); Gentry & O'Neil, Mine Investment Analysis (Canadian mining taxation, inflation and financing effects on DCF yield, smelter/refining contract terms, net smelter return); SME Mining Engineering Handbook, 3rd ed. (mineral exploration/evaluation stages, ore reserve classification, ore deposit models); CIM Best Practice Guidelines and NI 43-101 (Canadian Securities Administrators).
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.
1.4.a) Copper head grade. BC porphyry coppers sanctioned as bulk-tonnage open pits typically carry 0.25–0.5% Cu head grade (e.g. Highland Valley ≈0.35%, Gibraltar ≈0.25–0.3%, New Afton higher-grade at ≈0.9% Cu because it also carries strong Au credits) – the low grade is offset by enormous contained tonnage and large-scale, low-unit-cost mining.
1.4.b) By-product head grades. Molybdenum typically runs 0.01–0.03% Mo (roughly a tenth to a third of the Cu grade, consistent with the question's own hint that "lead" runs "slightly less than" Mo grade in Q4); gold, where the porphyry carries an Au credit, typically 0.05–0.3 g/t (higher, 0.2–0.5 g/t, in the Cu–Au sub-type); silver typically 1–5 g/t, broadly tracking the Cu grade since Ag substitutes into the same chalcopyrite/bornite sulphides.
1.4.c) Concentrate grade. A conventional crush–rod–ball mill – flotation circuit on unoxidized porphyry sulphide ore typically produces a copper concentrate grading 24–30% Cu (commonly cited ≈28%), the practical ceiling set by the intergrowth of chalcopyrite with pyrite/gangue that rougher-cleaner flotation alone cannot fully liberate.
1.4.d) Separate molybdenum concentrate. Yes – where Mo grade justifies it, a bulk Cu–Mo rougher concentrate is treated in a secondary Mo flotation circuit that depresses the copper sulphides (commonly with NaHS or similar) and floats molybdenite selectively, yielding a separate, high-value MoS2 concentrate (typically 50–58% MoS2) sold under its own contract, distinct from the Cu concentrate.
1.4.e) Payable Au/Ag location and accounting. Gold and silver in a porphyry ore report almost entirely into the copper concentrate (they associate with the same sulphides, not with the gangue or the Mo concentrate), and are NOT recovered as a separate doré or bullion product on site. They are accounted for at the smelter, under the copper smelter contract's payable-metal terms – typically paid at a high payable percentage (often 90–95%+ once above a minimum deduction/threshold) based on the concentrate assay, with the mine receiving by-product revenue credits rather than shipping a distinct precious-metal product.
