"The estimate is 330 tonnes of gold per year or 12% of official world production. The estimate considers a variety of types of data from 70 countries. Other higher numbers such as the 20-30% noted inThe Global Atmospheric Mercury Assessment: Sources, Emissions and Transport by UNEP in 2008 rely on less data and less types of data. These higher numbers are also more difficult to align with other factors such as financial constraints and the magnitude of mercury consumption needed to produce the gold -- a very large percentage of ASGM gold is produced using mercury." Artisanal Gold Council, World Artisanal Gold Production, June 29, 2011
Mercury is why the EPA and others are so interested in this type of gold mining. When they use mercury to amalgamate with the gold to separate more of it out, they burn this amalgamation in their gold shops, killing and maiming many local people, but also releasing some 400 metric tonnes of airborne mercury each year into the atmosphere, the biggest mercury polluter of any sector. Counting what gets released into streams and other contamination, they think about 1000 tonnes of this deadly metal is released yearly by the gold artisans.
Knowledge about the use of mercury is poor, as this study points out, but by indirect monitoring via things like rain forest damage in artisanal regions, its use seems to have begun in earnest in the 1990s. This is significant to our tailings gold resource estimate in that prior to mercury use, an artisanal model like that of Burkina Faso, West Africa was producing all the artisanal tailings, and they are estimated to be of 8 g/t to 12 g/t ore grade with only the use of hand tools to claim the gold. Mercury extraction leaves around 2 g/t.
The Artisanal Gold Council has done an estimate of all the gold ever produced by the artisans prior to 2000. They come up with a very conservative 7000 tonnes. They also state in the above referenced gold production article that the artisanal contribution to the global total may be climbing beyond 15%. These facts, along with a figure for waste ore production rate for the Burkina Faso model above stated as 17 tons of ore producing 420 grams of gold (1.3 tonnes of waste per oz), allow you to do a calculation similar to the one above to get the global artisanal mining component of tailings gold. The estimates vary from a low of 12% to the EPA's 20%, and there is no hard data on the growth of mercury use, but assuming an average 15% artisanal portion of world production since 2000, and the 7000 tonne figure prior to 2000, and an 8 g/t average tailings ore grade, the artisans have deposited and abandoned some 4000 tonnes of high grade gold on the ground. That's a meaningful contribution to the 73000 tonnes from the regular miners and gives a total estimate of 77000 tonnes.
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