Redfern firms up plans for Tulsequah

A positive feasibility study is enabling Redfern Resources (TSE) to formulate mining and milling plans for its Tulsequah Chief property in northwestern British Columbia.

Rescan Engineering of Vancouver conducted the study, which projects a capital payback period of 3.4 years and annual pretax operating profit of $48 million. The figures are based on an initial minable reserve of 7.9 million tons grading 1.24% copper, 1.18% lead and 6.32% zinc, plus 0.07 oz. gold and 2.9 oz. silver per ton.

At a production rate approaching 1 million tons per year, the mine is expected to last 8.3 years, during which time it would yield 57,000 oz. gold annually, along with 2.3 million oz. silver, 22 million lb. copper and 113 million lb. zinc.

Base-case numbers used in the study include recoveries and prices of: 91.7% and US$1 per lb. for copper; 90.5% and US60 cents per lb. for zinc; 79% and US$6 per oz. for silver; as well as 81.6% and US$395 per oz. for gold. The exchange rate was assumed to be US73.5 cents.

The net smelter return, based on given metal prices, is estimated at $105 per ton milled, compared with a projected operating cost of $54 per ton.

The smelter return estimate assumes concentrates will be trucked to Skagway, Alaska, via a proposed 100-mile-long access road to the existing road at Atlin, B.C. The total distance would be 280 miles.

The capital cost, including the access road, is estimated at $125 million. A further $35 million in capital expenditures will be required, most of which is needed to sink an internal shaft.

Mining would be carried out from the lowest adits, which were originally developed by Cominco in the 1950s to mine the upper portion of the Tulsequah deposit.

A production ramp will be driven from the lowest adit for mining at 200-ft. levels. An internal shaft will have access at the 600-ft. level, and ore will be hoisted from a crusher at the shaft bottom.

The current minable reserve extends to a depth of about 2,300 ft. below the adit level and remains open to depth. Roughly 500,000 tons of this reserve exist above the adit level, and this will serve as the initial millfeed.

Seventy-five per cent of the minable reserve will be extracted using longhole stoping, with mining widths of up to 100 ft. The remainder is contained in narrower zones, which will be mined using shrinkage stoping.

Owing to steep topography and limited space on surface, the grinding and gravity circuits will be placed underground at the adit level.

The gravity circuit is expected to recover about 35% of the gold, with most of the remainder (including silver) reporting to a bulk copper-lead concentrate. The zinc will report to a zinc concentrate.

The company is considering a conveyer system within the mine ramp to move crushed ore from the upper portion of the deposit. This would postpone, and possibly eliminate, the need for an internal shaft.

Meanwhile, the milling circuit is being fine-tuned. Bench-scale tests indicate lead values (currently a penalty) in the bulk concentrate can be reduced by gravity methods, thereby boosting the copper content of the bulk concentrate to 25% from 20%. The change would also yield a payable lead concentrate.

The deposit is close to the Tulsequah River, which flows into the Taku River. The Taku then crosses from British Columbia into Alaska where it supports a significant salmon fishery.

Redfern is mindful of the potential hazard of acid being generated by the deposit, and plans to conduct all major mine development in the non-acid generating rocks within the hangingwall of the steeply dipping deposit.

It also intends to use a delayed paste backfill system in an effort to maximize the amount of tailings returned to the mine. Redfern will also spend about $2 million per year removing iron sulphides from tailings to ensure that 30% of the tailings are permanently stored on surface and that they do not generate acid. If necessary, the company will quarry and mill locally available limestone to ensure the tailings are neutralized.

Environmental baseline surveys were initiated in May, 1994, in concert with other permit-related studies, and Redfern expects to apply for a mine development certificate by the fall of this year. Government approval is anticipated by April, 1996.