Gold Mining Bugs To Get A Taste Of New Metals

For the last 10 years tiny rod-shaped bacteria have been munching their way through gold ore at South Africa's Fairview Mine, revolutionising gold mining in the process.

Now these genuine gold bugs are to be put to work recovering nickel in Australia and could soon be commercialised for copper production. The weird Thiobacillus bacteria thrive in an environment lethal to most life forms, deriving their energy from oxidising sulphide ores, thereby liberating minerals which would otherwise be extremely difficult to access.

They have proved a boon to mining companies grappling with refractory gold, which is locked into minerals such as pyrite, and have achieved gold extraction rates above 95 per cent. Alan Haines of Gencor the South African mining house which developed the gold bioleaching process, says the technique is attractive both for its low capital costs and its lack of pollution. And the same principles which have worked for gold should also apply to other metals trapped in pyritic minerals, such as nickel and copper.

Avoiding acid rain Traditionally, winning metal from these rocks has involved roasting the ore, a process which produces large amounts of sulphur dioxide causing acid rain and frequently arsenic. A modern alternative is pressure oxidation, which is non-polluting but expensive in terms of upfront costs.

For a small but growing band of mines around the world, bioleaching refractory ore in specially built reactors has proved the answer. Within the Gencor stable, the BIOX process is being used both at Fairview where it has solved a major pollution problem and at the Sao Bente Mineracao Santa Barbara mine in Brazil. Outside the group, the technology has been licensed to Wiluna Mines in Western Australia and to Ghana's Ashanti Goldfields which now boasts the world's largest bacterial oxidation plant.

BIOX is also due to be installed at Minera Lizandro Proano's Tamboraque in Peru later this year and Lonrho plans to use it at the Amantaitau Goldfields project in Uzbekistan which it is co-financing. Trevor Pearton, mining analyst at stockbroker Societe Generale Frankel Pollak, believes there is likely to be a continuing trend towards bacterial bleaching in the years ahead.