Abstract
In place of mercury, small-scale alluvial gold miners in Tadó, Dept. Chocó, Colombia produce “green gold” (oroverde) using locally available plant extracts. The leaves of Balso (Ochroma pyramidale) and Malva (Hibiscus furcellatus) are crushed by hand and are mixed with water to make a foamy liquid that is added to the gold pan (batea) instead of mercury. After the plant extract is added, the gold, magnetite, and other heavy minerals sink and the lighter minerals are floated out of the gold pan. For final clean-up, a combination of other methods may be used. However, ICP (Inductively Coupled Plasma) analyses indicate that even green gold contains 208 - 4530 ppm Hg—this mercury may have been released from dragas or other small-scale gold mining operations that continue to use mercury; coal burning; volcanism; or native mercury released from cinnabar occurrences. ICP also indicates 308 - 106,000 ppm Ag and 452 - 585 ppm Pt.
Highlights
Gold has been mined from alluvial sources since ancient time using gravity methods in combination with mercury to amalgamate the gold [1] [2]; since the 1880s cyanide has been used to leach gold from disseminated gold-silver-copper ores [3] and gold-bearing pyrite
Even though mercury and the mercury vapors that result from smelting the amalgam are toxic, mercury is widely used in Perú [4], Colombia [5], and elsewhere in South America for small scale gold mining
Despite the use of this sustainable, environmentally-friendly plant-based method, Inductively Coupled Plasma analyses (ICP) indicate that even green gold produced without any mercury may still contain 208 - 4530 ppm Hg (Table 2)
Summary
Gold has been mined from alluvial sources since ancient time using gravity methods in combination with mercury to amalgamate the gold [1] [2]; since the 1880s cyanide has been used to leach gold from disseminated gold-silver-copper ores [3] and gold-bearing pyrite. Colombia, the Seed Award for their exemplary production of green gold, their aggressive efforts to reduce the use of mercury in the region, attention to conservation, and the elimination of mining practices such as the use of backhoes and dredges that pollute and destroy the streams [7]
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