BacTech Environmental Corp. announced that it has launched a new initiative to reduce the amount of mercury used in artisanal/small mining operations in Bolivia.
There are areas of northern Peru and southern Ecuador where artisanal miners are mining complex sulphide (refractory) mineralized material as the near-surface oxidized material becomes depleted. In many instances, mercury is used by the miners, who obtain as little as 10% of the contained gold from this difficult-to-treat mineralized material. The remainder of the material is then sold for little value and/or trucked 1,100 km to the southern region for eventual smelting.
This, said the company, presents an opportunity to contribute to the reduction of mercury, arsenic and cyanide contamination in the environment while giving substantial increases in gold recovery. This is achievable through the use of relatively simple gravity and flotation circuits and BacTech’s bioleaching technology to process the mineralized material, without using mercury and reducing other chemical requirements.
Recently the government of Peru enacted legislation to encourage artisanal miners to apply for legal mining licenses, stating that artisanal miners have been contributing up to 1 million oz of gold production annually. The origin of much of this gold has been difficult for government authorities to ascertain. Peru has initiated a formalization process designed to register all small-scale and artisanal mining operations. The registration allows the government to monitor and regulate health, safety and environmental issues for miners, and will allow these operations to legally sell their mineralized material to toll-milling facilities approved by the government.
This has led to increasing interest, predominantly among Canadian companies, to set up processing facilities for conventional processing. All of these facilities have been designed to process oxide material and “easy” or non-refractory sulphide material. The resulting sulphide concentrates are then treated with cyanide to liberate the precious metal, but often results in poor gold recovery due to the presence of refractory gold that is not recovered by such processing.
The grades of the refractory arsenopyrite-rich material in this area are high. It has been reported that arsenopyrite gold concentrate grades of 150 g/t (5 oz) and higher are common, given the high-grade material that is processed. BacTech said there is a strong business case to establish a gravity/flotation plant and a bioleach processing facility in a strategic location to address these refractory issues. The plant would eliminate the need to deliver arsenic sulphides long distances on public highways for processing.
This problem is not limited to Peru and Ecuador as there are other countries, such as Colombia and Nicaragua, that have similar issues.
BacTech said “there is no doubt” that bioleaching can play a big part in alleviating the mercury issues related to artisanal mining, and it will be aggressively pursuing these opportunities as they are presented.