Newmont tests bioleaching for Carlin refractory ores

Already North America’s largest gold producer, Newmont Mining (TSE), has joined the race to be the first U.S. company to successfully use the gold recovery process known as bioleaching.

A number of North American companies, including U.S. Gold (NASDAQ) and Giant Bay Resources (TSE), have experimented with the process which uses a naturally occurring bacterium known as Thiobacillus ferroxidans to break down iron and sulphide compounds in refractory ores and to release the gold for eventual recovery by conventional cyanidation.

But none have been able to apply the technology successfully at a commercial mining operation in North America.

Although U.S. Gold has attempted to incorporate the technology into its Tonkin Springs gold project in Nevada, it ran into financial trouble after experiencing technical difficulties in a 1,500-ton-per-day mill. So far only South African companies have been bioleaching gold ores at a mine in the Transvaal.

With advice from South Africa, Newmont says it is patenting its own bioleaching process and expects to use it to treat low-carbon sulphuric refractory ores at its Carlin gold mines in Nevada within three years. By 1993, the Colorado company will be ready to start processing refractory ores at open pit operations that are currently producing 1.5 million oz. annually from oxide material alone.

On Dec. 31, 1990, Newmont had proven and probable reserves of 334.8 million tons grading 0.056 oz. gold per ton or 18.8 million contained oz. outlined at Carlin.

According to Newmont, bioleaching technology is being tested at its Salt Lake City research laboratory.

If the experiment is successful, it could be the most significant breakthrough in the field of gold recovery since the U.S. Bureau of Mines introduced cyanidation during the 1930s, according to the September edition of Update, a monthly publication issued by the Ontario Ministry of Northern Development and Mines.

Meanwhile, Newmont is also investigating bacteria from Flin Flon, Man., to recover copper and zinc in co-operation with UMA Engineering and Hudson Bay Mining and Smelting (TSE).