Neoarchean gold grain size and artisanal mining in Migori, Kenya: review of current recovery methods

Artisanal and small-scale gold mining (ASGM) in Archean greenstone provides a significant source of income for rural communities. Understanding of the particle size distribution of gold is an important parameter for its recovery as it determines the most appropriate and effective mineral processing methods. However, published information is scarce. This study set out to determine the particle size distribution of gold in the ASGM areas in Migori, SW Kenya. The Neoarchean Migori Greenstone Belt in SW Kenya hosts the ‘Migori Goldbelt’. Gold mainly occurs in coarsely crystalline quartz ‘reef’ veins associated with sulfide mineralization as well as in banded iron formations and more disseminated in tuffaceous rocks. Based on scanning electron microscope grain count data, the mean particle size of the gold grains was found to be 3.5 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> </mml:math> m, too fine-grained for effective recovery by sluice boxes. Taking the weight of the gold particles into consideration, 80% of the weight of the gold is coarser than 15 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi>μ</mml:mi> </mml:math> m and could be recovered using a shaking table. Adopting improved ASGM practices would increase the recovery of fine-grained gold and help to reduce the amount of hazardous substances used in the recovery process. Improved gold recovery would help to boost local economies, secure livelihoods and enhance the quality of life for ASGM communities.