Any residual mercury would also be dissolved by the cyanide, and it blocks recovery of the gold. If the mercury-contaminated material is processed alongside enough clean ore, the contamination issue is manageable. In fact, that's how Crystallex will remediate the effects of the illegal miners' activities, by extracting the leftover mercury along with the gold. But that requires very careful monitoring of the total mercury in the system, and careful additions of small amounts of the contaminated material over time. It is not possible to do cyanide extraction of gold from "mercury tailings" alone.

Lar