Metall launches exploration program to extend life of Winston

Aiming to extend the life of its Winston Lake mine in northwestern Ontario, Metall Mining (TSE) has begun underground exploration of the nearby Pick Lake deposit.

A 2.5-km.-long drift, costing $2 million, is being driven to provide access to the orebody, both for test-mining and delineation drilling. During a recent visit to the property, The Northern Miner learned that the 3-metre-wide-by 3.5-metre-high drift had advanced a distance of 700 metres. It is being driven into the Upper zone, on a slight incline from the 615-metre level of the Winston Lake mine.

The Pick Lake deposit, which lies 2 km southwest of the Winston Lake mine, was discovered by deep drilling in 1984. Although geologically and mineralogically similar to the Winston Lake deposit it occurs at a deeper depth and in a slightly different stratigraphic setting.

Massive sulphide mineralization occurs in a 2-to-7-metre-wide sheet that is subdivided into an Upper and a Lower zone (the core area is considered waste). The sulphide sheet strikes roughly north-south, dips 50 degrees to the east and plunges 70 degrees to the north. It has a strike length of 400 metres and extends from 320 to 1100 metres below surface.

The immediate footwall of the deposit consists of a mafic-to-intermediate volcanic ash. This unit becomes more felsic and ash-rich toward its top, where the sulphide zone occurs.

The mineralized zone has an average horizontal thickness of 2 to 2.5 metres and consists of sphalerite, chalcopyrite, pyrrhotite and pyrite. The immediate hangingwall is a metasedimentary unit that consists primarily of greywacke.

Reserves in the Upper and Lower zones, based on 14 surface drill hole intersections and assuming 20% dilution, are estimated at 1.25 million tonnes grading 1% copper and 17% zinc plus 44 grams silver and 0.5 grams gold per tonne. However, Mine Geologist Gerard Doiron cautioned that the accuracy of the reserve figure is only plus or minus 25%. The inaccuracy of the calculation is largely due to the limited number of intersections and uncertainty as to the exact location of the holes.

The exploration program calls for drill stations to be established on the sides of the main exploration drift. Infill drilling on the Lower zone is scheduled to begin in December. The $2-million cost of the drift will be repaid through the processing of ore from the Upper zone, which is expected to be reached by April of next year.

Doiron says that if the exploration drilling pans out, the Lower zone will probably be developed via an internal winze.

When asked how this program would affect the mine life of Winston Lake, Doiron said: “We’re optimistic, but until additional work is completed, the project can only be considered an advanced exploration play.” Brought into production in 1988 at $72 million, the Winston Lake deposit is now in the late stage of its productive life. When it opened, reserves stood at 3.1 million tonnes grading 1% copper and 15% zinc plus 31 grams silver and 1 gram gold per tonne (assuming 20% dilution).

At the beginning of this year, reserves stood at 1.1 million tonnes grading 0.9% copper, 12.98% zinc, 25.21 grams silver and 1.05 grams gold, which are sufficient to sustain mining until early 1997.

The mill annually processes 365,000 tonnes of ore, yielding 90,000 tonnes of zinc and 10,000 tonnes of copper concentrate, grading 53.56% and 25.67% respectively. The concentrates are shipped to Schreiber by truck where they are loaded onto rail cars. Copper concentrates are processed at Hudson Bay Mining & Smelting’s plant in Flin Flon, Man., while zinc concentrates are sent to various European locations and to Noranda’s (TSE) refinery in Valleyfield, Que.

Faced with lower zinc prices and higher treatment charges, the mine reduced its operating costs in 1993 by 12%. On a per-pound basis for zinc, costs declined to US39 cents from US44 cents in 1992.

In anticipation of declining head grades, more economical mining methods have been adopted, as well. A revised mine plan has led to the adoption of open-stoping and alimak mining in addition to the modified avoca method used to date.

On a scientific note, an important discovery has been made relating to the genesis of the Winston Lake deposit. Doiron showed The Northern Miner a sulphide chimney that had been found over a thick portion of the massive sulphide zone. This feature confirms that the deposit was formed in a “black smoker” environment.