Cominco advances Yukon deposit

Major companies with metallurgical infrastructure in Canada are perhaps more motivated than most mining groups to maintain an active exploration presence in North America.

This is certainly true of Cominco (TSE), which, although busy with several foreign ventures, is continuing to explore domestic prospects that have the potential to supply feed for its smelter complex at Trail, B.C. Among the most advanced of these is the 100%-owned Kudz Ze Kayah (Kaska Dene for “caribou country”) massive sulphide project in southwestern Yukon. The property has moved quickly from exploration to the prefeasibility stage. The discovery hole into the ABM deposit, drilled in the spring of 1994, returned an impressive 22.5 metres grading 0.5% copper, 2.8% lead, 10% zinc, and 278 grams silver and 2.9 grams gold per tonne.

“The discovery hole was the best intersection we got,” recalls William Wolfe, general manager Canadian exploration. “It was exciting to see that kind of thickness and grade.”

By late August of 1994, sufficient drilling had been done to outline an inferred resource of 13 million tonnes of 5.5% zinc, 1% copper, 1.3% lead, 125 grams silver and 1.2 grams gold (with no provision for dilution). Wolfe says the high precious metals values make this deposit particularly attractive and provide some protection against low base metals prices. “But we think what really makes it (of economic interest) is the shallow dip,” he says, adding that a good portion of the deposit is amenable to open-pit mining.

Cominco has now applied for two licences and an environmental review to enable advanced exploration work on the property this year. This work (to include about 13,000 metres of drilling in 110 additional holes) is required to confirm the feasibility of a mining project and could lead to a production decision by year-end.

Positive results would lead to an open-pit operation, featuring a 1-million-tonne-per-year mill. Startup would occur in the fall of 1997. The Kudz Ze Kaya project is 110 air km southeast of Ross River and 20 km southwest of Finlayson Lake, on the Robert Campbell Hwy.

Cominco says the project’s roots go back to the careful prospecting follow-up (by geologist Chris Schultze) of reconnaissance drainage geochemistry done by the Geological Survey of Canada.

Work in the broad U-shaped valley led to the discovery, in 1993, of an “ore-grade” cobble about 15 cm long. This discovery was made by Bruce Mawer, a retired geologist after whose full initials the ABM deposit is named. Horizontal loop electro-magnetic, magnetic and soil geochemistry surveys, conducted 1 km up-ice from the cobble, defined a drill target just before snowfall of that year.

Drilling in 1994 included 8,300 metres in 50 holes, 40 in the gently north-plunging deposit, and 10 around its periphery. The current resource is based on the 40 holes that intersected the deposit and which generally are spaced 100 metres apart.

The ABM deposit is of the volcanic-hosted massive sulphide class, and is hosted by Mississippian (?) felsic pyroclastics, aphanitic massive rhyolites and metasiliclastic rocks of the Yukon-Tanana terrain. The host rocks and the deposit are ubiquitously schistose.

The deposit measures up to 700 metres long, is up to 400 metres downdip and averages 18 metres in total thickness. It generally consists of one layer (although in one restricted area there are two) and its subcrop is everywhere mantled by 2 to 10 metres of glacial drift.

Cominco has a large land package surrounding its discovery, and plans to carry out more early-stage exploration this summer. Part of this work will involve the testing of a number of geophysical anomalies. “We hope it is true that these things (massive sulphide deposits) occur in clusters,” Wolfe says. Cominco also intends to secure licences to build a camp for 35 people and a 20-km tote road from the Robert Campbell Hwy. to the site. The crew of 35 will carry out detailed drilling and metallurgical sampling, engineering of site facilities and environmental activities. The road will be used to transport equipment, supplies, fuel and personnel.

Cominco has applied for a Class B water licence, under the Yukon Territory Water Act, for a stream crossing. This will necessitate a review of the project under the federal Environmental Assessment and Review Process Guidelines Order (EARPGO).

The company also applied for a licence of occupation under the federal Real Property Act, as a legal mechanism to secure access control. This application will also require an EARPGO review.

Consultations have been held with officials of the Territorial and federal governments, as well as with local First Nations groups. Cominco expects to sign a socio-economic agreement with the First Nations that will address issues such as jobs, training programs and wildlife protection.