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Besides, mining does not always involve sulphides, either in the ore itself or in rock that has to be broken to get at it. For instance, ores formed by weathering and evaporation, such as bauxite and borate deposits, are typically sulphide free or very low in sulphide. Some ores are naturally alkaline because the sulphides are hosted by carbonate rich rocks. Often, it is the aim of the miners to separate out all the sulphide-rich rock for processing and consign only sulphide-poor materials to the waste dumps.

So why is ARD being treated as such a menace to today's mining industry? One reason is that it exposes the industry to huge financial liabilities. In the US alone, the liability for potential acid generation by mining waste could be as high as US$20bn, say some. The estimate for Canada is US$1-3bn, and for Australia US$530m. The worldwide liability is unknown but has to be a vast figure - far larger than the total market value of all the world's mining companies.

The liability at individual mines may be very long lasting. "In many cases," says Stuart Miller, managing director of Environmental Geochemistry International, "ARD treatment may need to continue for ten or more years after mine closure - and sometimes more than a hundred years. This results not only in continuing financial liabilities but, increasingly, in concerns about corporate reputation."

It has never been more important for mining companies to demonstrate environmental care and surefootedness in managing environmental risks. With ARD the industry has a mountain to climb, partly because of natural ARD and pollution from abandoned mines, but also because of widely publicized incidents like the catastrophic failure of a tailings dam at the Los Frailes base metal mine in southern Spain in 1998.



Besides, mining does not always involve sulphides, either in the ore itself or in rock that has to be broken to get at it. For instance, ores formed by weathering and evaporation, such as bauxite and borate deposits, are typically sulphide free or very low in sulphide. Some ores are naturally alkaline because the sulphides are hosted by carbonate rich rocks. Often, it is the aim of the miners to separate out all the sulphide-rich rock for processing and consign only sulphide-poor materials to the waste dumps. So why is ARD being treated as such a menace to today's mining industry? One reason is that it exposes the industry to huge financial liabilities. In the US alone, the liability for potential acid generation by mining waste could be as high as US$20bn, say some. The estimate for Canada is US$1-3bn, and for Australia US$530m. The worldwide liability is unknown but has to be a vast figure - far larger than the total market value of all the world's mining companies. The liability at individual mines may be very long lasting. "In many cases," says Stuart Miller, managing director of Environmental Geochemistry International, "ARD treatment may need to continue for ten or more years after mine closure - and sometimes more than a hundred years. This results not only in continuing financial liabilities but, increasingly, in concerns about corporate reputation." It has never been more important for mining companies to demonstrate environmental care and surefootedness in managing environmental risks. With ARD the industry has a mountain to climb, partly because of natural ARD and pollution from abandoned mines, but also because of widely publicized incidents like the catastrophic failure of a tailings dam at the Los Frailes base metal mine in southern Spain in 1998.
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