How efficient are they really? A simple testing method of small-scale gold miners' gravity separation systems

This paper demonstrates a simple, minimally-invasive method of estimating the gold recovery rate of gravitational separation equipment used by artisanal and small-scale miners at alluvial gold sites in the Guianas, South America. A local ASM group mining an alluvial gold deposit agreed to allow the research team to collect eight samples of ore material immediately before it was to be processed by their sluice and eight samples taken immediately upon exit from their sluice. Each sample was sieved into three grain size portions (<75 μm, 75-500 μm and >500 μm) and each portion assayed for gold content. The results indicate that the sluice at this site is capturing approximately 91% of the gold that enters the sluicing system, and the grain size distribution of the gold particles suggests that mercury amalgamation methods employed by the miners post sluicing are likely to be very efficient as well. Although this study and sample size is extremely small, and should not be taken as a full replacement of more elaborate geologic sampling and metallurgical analysis, this method could provide a useful tool for practitioners who want to quickly evaluate ASM gold processing methods and consider the effectiveness of introducing alternative processing technologies, especially those that aim to reduce mercury emissions from ASM.