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24-MMP-A4 Mine Valuation and Mineral Resource Estimation · December 2018

Question 11 of 29: Porphyry Deposit Model — Canadian Cordillera

Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)

Notes on this paper

EGBC National Exam — Mining and Mineral Processing Engineering, 09-MMP-A4 Mine Valuation and Mineral Resource Estimation, 2018-Dec. 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 1.1–1.8); 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, anisotropy); Hustrulid, Kuchta & Martin, Open Pit Mine Planning and Design (mine valuation, NPV/IRR and cut-off grade methodology); Gentry & O'Neil, Mine Investment Analysis (smelter/refining contract terms, net smelter return, taxation and risk); Guilbert & Park, The Geology of Ore Deposits, and Evans, Ore Geology and Industrial Minerals (VMS/SEDEX and porphyry deposit models); SME Mining Engineering Handbook, 3rd ed. (mineral exploration/evaluation stages, ore reserve classification); CIM Best Practice Guidelines and NI 43-101 (Canadian Securities Administrators).

Question 3.1: Porphyry Deposit Model — Canadian Cordillera (6 marks)

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.

PotassicPhyllicArgillicPropyliticCu-Mo stockwork veinlets: potassic/phyllic transitionIntrusive stock (diorite-granodiorite), calc-alkaline arc magma
Idealized porphyry alteration zonation in plan/section (Lowell-Guilbert model): concentric potassic → phyllic → argillic → propylitic zones around the causative intrusive stock, with Cu-Mo stockwork veinlets concentrated at the potassic/phyllic boundary.

3.1.1 Tectonic setting. Subduction-related continental-margin (Andean/Cordilleran-type) magmatic arc — in the Canadian Cordillera, calc-alkaline to alkaline stocks intruded during Mesozoic–Tertiary accretion and subduction beneath the western margin (e.g. Quesnellia/Stikinia terranes), generating the porphyry belts hosting deposits such as Highland Valley and Copper Mountain.

3.1.2 Host (and associated) rock types. A shallow, multi-phase calc-alkaline to alkaline intrusive stock (diorite–granodiorite–monzonite, often a swarm of porphyritic dikes/plugs) intruding and thermally/hydrothermally overprinting coeval volcanic and volcaniclastic wall rocks of the same arc sequence.

3.1.3 Alteration mineralogy. Classic concentric Lowell–Guilbert zonation outward from the intrusive core: potassic (K-feldspar ± biotite ± magnetite) → phyllic (quartz–sericite–pyrite) → argillic (clay minerals) → outer propylitic halo (chlorite–epidote–calcite), reflecting progressively cooler, more distal and more acidic fluid conditions away from the intrusive heat source.

3.1.4 Associated economic minerals. Chalcopyrite ± bornite (± molybdenite, ± minor gold) hosted in dense stockwork veinlets concentrated at the potassic–phyllic transition, with pyrite increasing outward through the phyllic zone; supergene enrichment (chalcocite blanket) can locally upgrade near-surface grades where deep weathering has occurred.