New Mascot underground mine to augment surface production

Production at Mascot Gold Mines’ Nickel Plate operation near Hedley, B.C., has traditionally been from underground workings, despite the fact there is a major open pit mine there today. But Mascot has never ruled out mining underground reserves in conjunction with its existing open pit operation which apparently will be the case in the future.

According to Paul F. Saxton, president and chief executive officer, a new gold zone has been discovered beyond the limits of the company’s existing south pit which he hopes will support a production rate of 400 tons per day. An 1,800-ft access drift will be driven into the zone which has been defined by several widely-spaced holes, he said. Work on the portal entrance is now under way and he would like to see the program completed by the end of February.

The existing pit could be extended to incorporate this new zone but he said the higher strip ratio would negate the economics of mining there. Saxton thinks that Mascot will “come up with a substantial tonnage” in this area but certainly not enough to meet existing mill throughput of 2,400 tons per day. But he pointed out this higher grade material would boost head grades.

He said the recent drill program yielded some “excellent intersections” and estimated the over-all grade for the zone at about 0.35 oz gold per ton, the historical mine average. But he cautioned it was difficult to accurately assess grade, given the limited amount of drilling. This particular zone has no underground workings and is independent of areas where Mascot is carrying underground reserves in inventory.

Saxton predicted that November gold production will be about 10,000 oz and he said mill throughput has reached in excess of the 2,700-ton-per-day design capacity; recoveries are now averaging about 86% but they have “reached 93% on certain days,” he added.

Oxide material has been playing havoc with recoveries which could be alleviated with a proposed heap leach operation that is in the permitting stage, he said. It’s difficult to forcast the mining rate for the leachable oxide material but he said recovery plant capacity will be about 400 gallons per minute and the leaching operation would be located above the existing tailings dam.

The company’s conventional milling operation can handle about 400-500 tons of oxide material per day or 10-15% of its existing capacity. September and October were problem months in the plant, he conceded, pointing out that it took around one and a half months to overcome these difficulties. Mill costs have been running over budget because extra mechanics have been required owing to these operation difficulties, he conceded.

The addition of a gyratory crusher is expected to reduce costs and allow for increased throughput from the underground mining operation, he said. Mineable reserves have increased by 20% to 9.9 million tons averaging 0.133 oz gold and potential exists for “other open pitable reserves to the north of the North pit and to the east of the property,” he concluded.

Oxidized reserves grading 0.14 oz have been defined in preparation for heap leach treatment next year. Pad construction will be completed by May, 1988, and gold recovery should be under way by June. This operation is expected to generate about 25,000-30,000 oz of gold in 1988 and 1989 production. Estimated production to Sept 30, 1988, should be between 135,000 and 150,000 oz at an operating cost of about $170(US) per oz, said Saxton. By Oct 31 the Nickel Plate mine had produced 31,380 oz which generated production revenues of $18.8 million.