24-MMP-A4 Mine Valuation and Mineral Resource Estimation · May 2017
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, 2017-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 five optional Questions 2–6 (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, smelter/refining contract terms, net smelter return, transportation logistics); SME Mining Engineering Handbook, 3rd ed. (cost-estimating relationships, mineral exploration/evaluation stages, ore reserve classification); Evans, An Introduction to Ore Geology and Guilbert & Park, The Geology of Ore Deposits (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.
(a) Head grade of copper milled (1 mark). A typical low-grade BC porphyry (e.g. Highland Valley Copper, Gibraltar, Copper Mountain) mills ore at roughly 0.25–0.45% Cu – "low grade" for a porphyry means well under 1% Cu, since these bodies are economic purely on bulk-mineable tonnage and low unit mining/milling cost.
(b) By-product head grades (2 marks). Molybdenum typically runs 0.005–0.02% Mo (a few hundredths of a percent – roughly 1/20th to 1/40th of the copper grade), reflecting the Mo:Cu ratio typical of calc-alkaline porphyries; gold typically 0.05–0.15 g/t Au; silver typically 1–3 g/t Ag. All three are recovered as by-products, not primary targets – their presence improves project economics but does not drive the mine design.
(c) Copper grade in concentrate (2 marks). Flotation of a fresh (non-oxidized) chalcopyrite-bearing porphyry ore typically produces a concentrate grading 25–30% Cu, the practical upper bound for a bulk copper-sulphide flotation concentrate before penalty elements and concentrate handleability (moisture, oxidation risk in transport) become limiting.
(d) Separate molybdenum concentrate (1 mark). Yes – because molybdenite (MoS2) floats readily alongside chalcopyrite in the bulk rougher circuit but is chemically and metallurgically distinct, a standard porphyry flowsheet depresses copper (commonly with NaHS or similar sulphide depressants) in a SEPARATE Cu–Mo separation circuit downstream of bulk flotation, producing a distinct, higher-value molybdenum concentrate (typically >50% Mo) rather than shipping molybdenum inside the copper concentrate, where a smelter would both fail to pay for it fully and may apply penalty deductions.
(e) Location of payable gold and silver (1 mark). Gold and silver in a porphyry deposit occur mainly as trace inclusions within (or associated with) the copper sulphides (chalcopyrite, bornite), so they report almost entirely to the COPPER concentrate during flotation (not the tailings or the moly concentrate). They are accounted for financially through the smelter contract's precious-metal payment terms – typically a fixed deduction (e.g. 1 g/t Au, 30–50 g/t Ag) followed by a high payable percentage (~90–95%) of the remainder, credited against treatment/refining charges.
