Giant Bay, Coastech test bacteria oxidation system

A couple of Vancouver-based companies are involved in a race to develop a low cost oxidation process which uses live bugs to recover gold from refractory ore deposits.

As a skeptical mining industry awaits the results of their efforts, Giant Bay Resources (TSE) and Coastech Research have committed themselves to the bacteria- enhanced gold recovery system called bioleaching.

While the technology is being used to treat gold concentrates at General Mining Union’s Fairview mine in South Africa, North America’s top gold companies have been reluctant, until recently, to use bacterial oxidation at their own operations.

“It’s the old catch 22 situation, people want to see the other guy doing it first,” said Robert Handfield, vice-president of Giant Bay.

To prove the doubters wrong, Giant Bay and partner Wright Engineers are planning to have a 250- ton-per-day bioleaching plant in operation early next year. The facility is being built at the Congress gold project near Gold Bridge, B.C. Refractory ore

Coastech is also working with a number of companies in the Nevada gold belt where many of North America’s refractory ore deposits are located.

The process they are testing utilizes sulphide oxidizing bacteria to break down the sulphides in refractory ore deposits and liberate the gold which is locked inside.

At a cost of about $200(US) per oz, experts believe the process could turn dozens of low tonnage, low grade ore deposits into profitable mines.

As in conventional mining operations, the ore is ground up and then mixed with the bacterium — the most common is Thiobacillus ferooxidans — in a large agitation tank. After a period of up to several days, the bacteria oxidize the sulphide minerals before conventional cyanidation techniques are used to recover the gold. “In a nutshell, its like removing seeds from a grape,” said Handfield. “The bacteria are used to destroy the sulphides and the gold is left behind.”

While its advocates admit bioleaching won’t necessarily change the mining industry overnight, they claim the technique can increase recovery rates achieved in conventional milling methods by as much as 70%. Goldbridge project

Giant Bay says it is getting better than 90% recoveries at its Goldbridge pilot plant where the technique is being tested on a gold property owned by equal partners Levon Resources (TSE) and Veronex Resources (VSE). With a capacity of 64,000 gallons, the facility will be required to handle a geological reserve inventory of 670,000 tons grading 0.24 oz at a rate of 250 tons per day.

“This isn’t the pipe dream that it was a few years ago,” said Richard Lawrence, Coastech’s director of research. “We can back up the theory with hard data.”

According to Lawrence, bioleaching is less expensive than the heavy handed pressure leaching method which uses high temperatures to break down the sulphides in refractory ore deposits.

He says it is also much cleaner than the roasting method which emits sulphur dioxide at the operations where it is used and only a lack of willpower on the part of the mining industry has prevented bioleaching from becoming more popular.

Introducing bioleaching technology at the 3.15-million-ton (grade 0.92 oz) Tonkin Springs orebody in Nevada will save operator U.S. Gold around $45 million, says President Bill Reid. The Denver-based gold producer is building four 50 ft x 40 ft bioleaching tanks to treat the sulphide portion of the Tonkin Springs ore. “We feel it’s the most cost effective way to go,” said Reid. Tonkin Springs

After achieving 94% recovery rates during preliminary testing at the U.S. Gold operation, Coastech claims to be further ahead in developing the technology than anyone else.

But regardless of who wins the race to build North America’s first successful bioleaching plant, the implications for the companies involved and mining in general could be enormous.

As holder of a 16% stake in U.S. Gold, Placer Dome Inc. (TSE) stands to benefit from a successful operation and Western Gold Exploration, a subsidiary of New York- based Inspiration Resources, has already demonstrated it’s confidence in the technology by agreeing to buy control of Coastech’s parent Shamrock Resources.

Bioleaching will have a significant effect on the mining industry because an estimated 30% of the world’s remaining gold deposits are locked up in sulphides, according to a report by The Economist magazine. “With bioleaching, we could start looking at properties with ore reserves as low as five million tons, and grades in the 0.08 to 0.1 oz gold per ton range,” said Lawrence. “There are a lot of gold deposits in Nevada that fit into that category.”

But others are taking a more cautious stance. “Technology doesn’t always work the way researchers say it will,” said Ed Thompson president of Westgold affiliate Mingold Resources. He tested the process, at British Columbia’s Research Foundation, 20 years ago. While Thompson believes it is possible to extract minute particles of gold from pyrite and arsenopyrites using live bacteria, he said North America’s traditionally cautious mining industry may be slow to warm up to the idea. “It could be several years before bioleaching is widely used,” he said.