BASE METALS SPECIAL — Mazenod Lake highlights Canada’s potential for Olympic Dam copper-gold deposits

They’re big, and they’ve got plenty of byproduct credits. Any company attracted to copper as a commodity has to be attracted to Olympic Dam models of mineralization. The similarity between the Canadian and Australian Precambrian has many explorationists thinking about the possibility of similar deposits here.

The Mazenod Lake area, about 170 km northwest of Yellowknife, N.W.T., is the most prominent of the areas with possible Olympic Dam potential. A northwest-striking volcanic belt in the Bear structural province of the Canadian Shield has long been known for uranium mineralization and polymetallic vein deposits.

In 1974, Noranda (NOR-T) explored the Sue-Dianne prospect, a hydrothermal breccia with copper and subsidiary gold, silver and uranium, hosted in a rhyodacite welded tuff.

A 14-hole drill program at Sue-Dianne outlined an 8-million-tonne resource grading 0.8% copper, but it also gave the area credibility as an environment for these copper deposits. At the same time, the big Australian miner, WMC, had started poking holes in the Stuart Shelf region of South Australia.

There, the company outlined the Olympic Dam, Acropolis and Oak Dam deposits, all hydrothermal breccias with copper and uranium, plus a panoply of other metals. When WMC announced a 2-billion-tonne deposit at Olympic Dam, with 1.6% copper, the mining world took notice.

Another step along the road was the work of the Geological Survey of Canada (GSC) in the Bear province. Regional mapping work, notably by Paul Hoffman, had produced the interpretation that the Wopmay Orogen, which makes up the bulk of the structural province, was made up of two continental volcanic belts that developed on the margin of the older Slave structural province during the early Proterozoic, about 1.8 billion years ago. Continental volcanism also appeared to be the key to the Olympic Dam deposits.

The GSC saw the possibility that regional airborne geophysical surveys might be useful in picking out possible exploration targets with the Olympic Dam model in mind. The abundant iron oxides provide a magnetic anomaly, and uranium mineralization and potassic alteration minerals both offer a chance to detect radiometric anomalies.

Fortune Minerals (FORM-C) was first into the area after the surveys were published, staking the Nico showing and a large package of ground around, and southeast of, Noranda’s Sue-Dianne property. Showings in the area tended to be associated with northeast-striking “giant quartz veins,” which have sulphides and pitchblende that are common in the southern Bear province. The Rayrock uranium mine, which operated from 1957 to 1959, worked one of these veins, which had a grade of 0.24% U3O8.

Another possible lookalike is in the Labrador Trough northwest of Schefferville, Que., where Virginia Gold Mines (VIR-M) and Kennecott have been exploring the Sagar property. The interest in the area started with mineralized boulders containing around 1.3% uranium and 70 grams gold per tonne. Airborne geophysics has been the major prospecting tool at Sagar.

The Seven Inch deposit, in the southwestern part of the Sagar property, has a preliminary inferred resource of 18 million tonnes grading 0.5% copper, and other showings have combinations of gold, uranium, copper and cobalt.

Cominco (CLT-T) and Major General Resources (MGJ-V) have a program of geophysics, mapping and soil sampling under way at their Olympic property in the Ogilvie Range, north of Dawson, Y.T. Here, soil sampling is key; soils in the northwestern Yukon are residual and not glacially transported, and geochemical anomalies develop in place over mineralization. A large area with copper concentrations exceeding 100 parts per million is believed to have potential for the same type of deposit.