The exploration and development of porphyry deposits during the 1960s and 1970s had a profound effect on the mining community in British Columbia. Between 1965 and 1987, one out of every four deposits brought into production in the province was a porphyry, and subsequent exploration for these polymetallic (copper, molybdenum, gold and palladium) deposits has contributed to an impressive database.
Today, gold resources contained within porphyry deposits exceed production by roughly 15 times. Indeed, in some porphyries, at today’s metal prices, gold is more economically significant than copper. The gold content of porphyries is often seen as crucial to a project’s economic viability, and mills are optimized to recover precious metals as byproducts. Recent mine developments include Mt. Polley and Huckleberry in 1997, and Kemess South in 1998. In 2001, Kemess South yielded 272,800 oz. gold and 66 million lbs. copper at an operating cash cost of US$190 per oz. gold, net of copper credits.
Significant gold resources have been identified at several undeveloped porphyry deposits, including Prosperity (Fish Lake), Mt. Milligan, Galore Creek, Red-Chris, Schaft Creek, Sulphurets Gold, Kerr, Poison Mountain, and Morrison/Hearne Hill. In 2000, Northgate Exploration discovered the Kemess North deposit (440 million tonnes grading 0.4 gram per tonne gold and 0.23% copper), 6 km north of the Kemess South mine in the Toodoggone area.
Other projects of note include the Pine and Atty properties in Toodoggone; which will be drill-tested by Stealth Minerals and Finlay Minerals, respectively; in 2000, Sultan Minerals discovered significant gold at its intrusion-hosted Kena prospect, near Nelson; DRC Resources has been exploring and expanding the copper-gold-palladium resource in a zone southwest of the Afton pit; Abacus Mining & Exploration, in an option agreement with Teck Cominco, will be evaluating seven projects, including Rainbow, adjacent to the Afton site; Eastfield Resources continues to test and expand copper-gold mineralization on its Lorraine property; Pacific Booker Minerals will complete definition drilling of its Morrison copper-gold deposit; in the Nation Lakes area, west of the Mt. Milligan copper-gold deposit, several porphyries are being re-examined; Fjordland Minerals plans to drill the Woodjam copper-gold target in the Horsefly area; Eagle Plains Resources has optioned the Copper Canyon copper-gold deposit, northeast of the huge Galore Creek deposit; and First Au Strategies, under an option agreement with Rimfire Minerals, plans a modest drilling program to test the Thorn high-sulphidation, gold-silver-copper system.
Although much of the gold in porphyry deposits is recoverable as a byproduct, the major exception is Barrick Gold’s Eskay Creek, which is one of the highest-grade gold and silver mines in the world. In 2002, production is expected to reach 366,000 oz. gold and 16 million oz. silver at a total cash cost of $51 per gold-equivalent ounce. Reserves at Jan. 1, 2002, consisted of 705,200 tonnes grading 65.5 grams gold and 3,036 grams silver per tonne directly shipped, and 761,800 tonnes grading 25.8 grams gold and 1,092 grams silver milled. The total inventory is 7 million oz. gold-equivalent.
Historically, mesothermal and epithermal veins have been the single most important source of gold production in the province. Some 428 mesothermal mines have yielded 13.3 million oz. gold, including 4.16 million and 2.78 million oz. from the Bridge River and Rossland camps, respectively. Moreover, 19 epithermal mines have yielded 2.9 million oz., including greater than 2 million oz. from the Premier camp. Resources for mesothermal and epithermal veins stand at 11.3 million and 4 million oz. gold, respectively.
In the Barkerville-Wells area, International Wayside Gold Mines, Island Mountain Gold Mines and Golden Cariboo Resources have tied up a huge land package and are drilling several targets. The most advanced project is Cariboo Gold Quartz. Another, Snip, is an intrusion-related, shear-hosted vein deposit which yielded 1.02 million oz. gold between 1991 and 1999. Meanwhile, Wheaton River Minerals has optioned the Elk property from Almaden Minerals.
Many Tertiary epithermal deposits appear to be associated with extensional tectonism and graben-related volcanism. The Nechako Plateau region in central British Columbia hosts several such deposits, including the Tsacha, which Southern Rio Resources will be drilling to extend reserves. In the south, Ecstall has acquired the Dusty Mac property, which appears to lie along the northerly extension of the Republic graben.
More than 350 skarns are known in the province, about 125 of which are enriched in precious metals. The highest-grade gold deposits have associated arsenic, bismuth and tellurides. Five main districts have each produced in excess of 100,000 oz. gold. By far the largest producer, at 2.5 million oz., is the Hedley mine, 40 km west of Penticton. East of Hedley is Goldcliff Resource’s Panorama Ridge project, where drilling is planned for 2002.
— The author is a senior regional geologist with the British Columbia Ministry of Energy and Mines.
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