I hadn't heard of using starch instead of cyanide. Though this relates to copper, I wonder if it would work with silver and gold. Sure would please the environmentalists.

From a Scorpio news release:

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"As previously announced on Nov. 8, 2008, the addition of higher-grade ore from high-grade production stopes versus earlier development stockpile material has increased the overall copper content of the mill feed and justified activation of the copper circuit. The standard procedure to extract the copper is to use cyanide; however, the company has conducted laboratory tests using environmentally friendly starch. This is the same starch that is used in the food industry and is a fraction of the cost of cyanide. During the last two weeks alone, modifications to the process resulted in a 30-per-cent to 70-per-cent reduction in consumption of the various costly reagents. This in turn has reduced the cost of processing a tonne of concentrate. The combination of processing higher-grade material and modifications to the circuit has resulted in an increase in the silver payable in the lead concentrate, a new cash flow of copper concentrate that includes silver revenues, and an increase in the percentage of zinc in the zinc concentrate. The new addition of copper and silver payables from the copper concentrate will augment the company's income and cash on hand.