Sphinx heap-leachs gold in Quebec

Mention heap leaching and a person immediately thinks of the southwestern United States, where large tonnage, low-grade deposits are being mined year-round to yield relatively inexpensive gold. North of this established mining community in northwestern Quebec, 10 miles from the town of Amos, a junior mining company is trying to prove heap leaching can be just as successful as it is south of the border, despite forced shutdowns for the winter months.

The junior, Societe Miniere Sphinx (ME), began leaching 40,000 tons from its Duvay deposit in the spring of this year, and in mid-August poured its first gold, a dore bar containing 300 oz. gold and 200 oz. silver. A second pour was near when The Northern Miner visited the project in early September.

“We thought it would be interesting,” President Michel David said of the property which he and an associate, Gilles Laverdiere, optioned from a private prospector in 1986. Stripping of the property’s relatively thin overburden revealed a mineralized area about one mile long and 700 ft. wide.

David said past exploration work at the property identified large, open gold zones within a 1,000-ft.-wide shear zone of altered basalts. “The alteration has been extensive with intense carbonization and the emplacement of horizontal and vertical gold-bearing quartz veins,” he said, explaining that a “nugget effect” presented certain sampling problems.

Between 1986 and 1989, the company undertook numerous exploration campaigns involving drilling and bulk sampling. Results to date indicate an average grade of 0.06-0.07 oz. gold per ton, with areas in the 0.1 oz. and 0.2 oz. range, David said. The deepest vertical hole reached 3,000 ft. where mineralization was indicated, he said.

In 1989, the company began construction of a 100,000-ton-capacity heap leach pad and a 400,000-ton- per-year Merrill-Crowe treatment plant. In October of that year, the company mined and crushed about 50,000 tons of material; it then loaded 40,000 tons of that total on to the pad for test leaching.

Although laboratory testing indicated a recovery rate of 70-75%, David said a 50% recovery is expected for the 40,000-ton test leaching this year.

“The idea this year was to prove that leaching works and get some cash flow out of it for next year,” David said of his 24-hour, 7-day-per-week leaching operation. The project’s estimated production cost is $10-$12 per ton.

Four zones have been uncovered on the property. The discovery zone, or zone 1, contains proven reserves of 900,000 tons to a depth of 100 ft., David said.

For 1991, Sphinx plans to load half of the known zone 1 reserves, 450,000 tons, on a new pad. Trucks will be used to load the material instead of a conveyor belt system. Drip tubes will replace the current sprinkler system of cyanide-solution distribution. Project workers learned this year of the need to agglomerate. And David is optimistic his crew has learned enough to overcome channelling difficulties.

In addition, the mill in 1991 will function with a carbon-in-pulp system, which will enable the company to double its milling capacity to 800,000 tons per year.

When the cold weather this autumn brings a close to the milling operation, the company’s attention will turn to open pit mining of the zone 1 reserves. The rock will be broken and placed on a pad in preparation for a spring, 1991, leaching start. David said the winter mining operation will cost an estimated $4 million, that money to be raised, he said, through gold loans.

“We’ve spent about four years doing exploration work, not making much noise. Now we’re pouring some gold. That’s the main thing,” he said.

David, a geologist, worked previously for Malartic Hygrade Gold Mines. Sphinx is one of a number of juniors which operate under the corporate umbrella of David’s Ariel group.