MEDICAL GEOLOGY AND GEOCHEMISTRY INSIGHTS INTO THE GLOBAL POTENTIAL FOR LEAD POISONING LINKED TO ARTISANAL OR RECREATIONAL METAL MINING

Over the last decade, price increases in gold and other metals have caused artisanal mining to burgeon globally. Mercury contamination and its and associated environmental impacts have been widely recognized in artisanal gold mining areas around the globe, due to the use of mercury amalgamation to extract the gold. However, in 2010 Médecins Sans Frontières discovered a previously unrecognized result of artisanal gold mining and processing in northern Nigeria—an outbreak of lead poisoning that has killed ~400 young children and affected thousands more. The lead poisoning resulted from contamination of soils, living areas, water supplies, and foodstuffs by the processing of weathered, lead-rich gold ores with abundant, highly gastric-bioaccessible secondary lead carbonate minerals (Plumlee et al., 2013, Env. Health. Persp. http://ehp.niehs.nih.gov/1206051/). At Kabwe, Zambia, thousands of people were similarly affected by lead poisoning, which resulted from artisanal re-mining of and environmental exposures to wastes from historical lead-zinc mining and smelting (Branan, 2008, Geotimes). As with Nigeria, secondary lead carbonates are a significant component of the ores and wastes at Kabwe. Recreational mining is also a common practice in a number of developed countries, and although not carried out at the same scale or intensity as artisanal mining, may pose some similar health concerns. Economic geology analysis of artisanal or recreational mining areas around the world helps identify those where workers may be at higher risk for lead poisoning and needing medical surveillance. Of highest risk are lead-rich deposit types that have abundant carbonate gangue, occur in carbonate host rocks, are low in acid-generating iron sulfides, and/or are located in dry climates where surface waters and ground waters are alkaline—characteristics that promote weathering of minimally bioaccessible primary lead sulfides to form abundant, highly bioaccessible, secondary lead carbonates. Examples include polymetallic replacement deposits, some polymetallic vein deposits, and Mississippi-Valley Type lead-zinc deposits. Artisanal re-mining in historical mining camps with prior uncontrolled smelting of lead-rich ores will have high bioaccessible lead and high lead poisoning risk regardless of deposit type.