Porphyry deposits of the northwestern Cordillera: A retrospective

Special Volume, Vol. SV 46, No. 1995, 1995

By any measure - tonnage of reserves discovered, milling capacity installed, expenditures expressed in constant dollars, concentration of exploration effort- the 1960s and 1970s were decades of mineral exploration and mine development unprecedented in the Canadian Cordillera and possibly in the world. Eight of the fifteen porphyry deposits mined in British Columbia were discovered during the period 1962 to 1968. A decade of achievement culminated in 1972 when jour major mines were brought on stream within the year. This paper reviews events surrounding this decade of discovery, beginning with early exploration of the Granisle deposit, and drilling on the Snowstorm and Iona claims in the Highland Valley in 1919, the first documented porphyry copper exploration project in the province. The modern era of copper and molybdenum mining in British Columbia dawned in 1954 when Herman "Spud" Huestis and his partners incorporated Bethlehem Copper Corporation to explore these same claims. The first thrust of exploration for new deposits, spearheaded by the American porphyry copper companies, was gathering momentum before Bethlehem announced its production decision in 1961. After it demonstrated that deposits lacking a supergene enrichment blanket could support a profitable mining operation, the floodgates opened. Discoveries followed at a brisk pace, but by 1970 the window of economic opportunity that made development of British Columbia's low-grade porphyry deposits feasible, was already beginning to close. It would be another dozen years before the Valley Copper orebody, discovered in 1968, was brought to production. Later surges of exploration focused on molybdenum in the late 1970s and gold-bearing porphyry deposits in the 1980s, have yet to result in a new mine opening. Looking back, it is remarkable that only two of fifteen porphyry copper and molybdenum mines brought on stream were financed by the established porphyry copper companies. Although first on the scene, they were largely unable to crown initial exploration success with new mine development. Several factors cone tributed to this outcome, most notably: a broader spectrum of alternative investment opportunities, including the alternative of expanding existing operations; United States tax law and also the constraints the United States imposes on corporate mergers and acquisitions; and perhaps a too rigid application of both economic and geological models developed in the American Southwest. On the other hand, relative newcomers to porphyry exploration adopted more flexible approaches to both prospect evaluation and property acquisition, and so garnered most of the rewards. The rewards were sometimes illusory. As pointed out in another paper in this volume, only about half of the new porphyry mines developed can be rated as financial successes; a jew have been short-lived disasters.
Keywords: Milling, Porphyry deposits, Mineral exploration, Copper mining, Molybdenum mining