2004 Denver Annual Meeting (November 7–10, 2004)

Paper No. 13
Presentation Time: 1:30 PM-5:30 PM


WEAVER, Jean N., U.S. Geol Survey, 12201 Sunrise Valley Drive, Reston, VA 20192, LABSON, Victor F., U.S. Geol Survey, P.O. Box 25046, MS 964, Federal Center, Denver, CO 80225 and GRAY, John E., U.S. Geol Survey, P.O. Box 25046, MS 973, Denver, CO 80225, jweaver@usgs.gov

Total Hg and methyl-Hg concentrations were measured in mine wastes, stream sediments, and surface waters in the Brownsweg area, Suriname, to evaluate Hg contamination around active small-scale artisanal Au mines. Methyl-Hg is a water soluble Hg compound toxic to living organisms, which biomagnifies in food chains. Artisanal Au mining in Suriname is poorly regulated and monitored, but is estimated to produce about 10-20 t of Au per year from the activity of as many as 60,000 miners. Gold in Suriname is found primarily in highly-weathered quartz veins in rocks of the Guiana Precambrian Shield. As a result of the use of Hg-Au amalgamation practices during mining, there is significant loss of Hg into tropical ecosystems. Estimates suggest that about 1-3 kg of Hg is lost for every kg of Au recovered. There is also deforestation, soil degradation, and extensive river silting due to small-scale Au mining. Mine-waste and soil in areas surrounding small-scale Au mines is primarily composed of clay- and quartz-rich saprolite, which is typical of tropical climates. Mine waste and stream sediment within 100 m of active mining contain the highest total Hg concentrations (103-150 ng/g), which greatly exceed Hg in sediment from regional baseline sites (5.5-14 ng/g). Similarly, concentrations of methyl-Hg (0.19-1.4 ng/g) are significantly higher in sediment from active mining areas when compared to methyl-Hg in sediment from uncontaminated baseline sites (<0.02-0.032 ng/g). Unfiltered surface water runoff from active and abandoned Au mines contains as much as 930 ng Hg/L, which significantly exceeds the 12 ng Hg/L standard recommended by the U.S. EPA to protect against chronic effects to aquatic life. Stream water downstream from mines is weakly acidic (pH 5.2-6.7) and highly turbid (as much as 1,000 turbidity units). Downstream transport of Hg is most significant in areas with highly turbid water indicating that Hg is absorbed onto particulate clay. These Hg results are similar to those found near artisanal Au mines in the Amazon Basin where Hg contamination has led to adverse effects to tropical ecosystems. Our results suggest that artisanal Au mining throughout Suriname poses potential health threats to humans and aquatic wildlife, especially fish and shellfish.