Tuesday, March 29, 2011

Silver Causes Huge Increase in Mercury Use in Artisanal Gold Mining

Although gold is the primary target of most Artisanal and Small-scale Gold Miners (ASGM) that use mercury, the role of silver on mercury use can be astonishing. When mercury is applied to ores that contain both gold and native silver, in order to get all the gold, enough mercury must be used to amalgamate both the gold and the silver. Because silver is less rare than gold, some ores can contain ten times as much silver as gold or more - silver to gold ratios of 10:1 or 20:1. So more mercury must be added to these ores to capture all the gold. However, because silver forms a weaker amalgam than gold, the situation is even worse than these numbers imply. A typical mercury-gold amalgam formed by small scale miners contains roughly 50% mercury and 50% gold. Mercury-silver amalgam formed under similar conditions however is closer to 70% mercury and 30% silver. In the case of an ore that contains 10 times more silver than gold, about 20 times more mercury is added in order to capture the gold. The silver is also captured, and even though it is worth 40 times less than the gold, it is still profitable and sought after, but by using mercury much more intensely.

The effect silver on mercury use is profound. Processing ores that only contain gold may require 1 to 10 units of mercury per unit of gold with perhaps an average of 4. Processing ores that contain 1 unit gold and 10 units silver may require 20 to 30 units of mercury. When mercury is used so intensively, mercury pollution and contamination are also intense. Mercury emissions to air and releases to water and soils skyrocket around high silver operations.

MORE INFO: The Artisanal Gold Council and University of Victoria together with collaborators YTS and Blacksmith Institute have visited high silver, high intensity mercury use operations in Central Kalimantan on Indonesia's side of the island of Borneo - http://worstpolluted.org/projects_reports/display/73.