Geochemistry of heavy metals derived from gold-bearing sulphide minerals in the Marmato District (Colombia)

Abstract

Heavy metals (Cu, Pb, Zn, Cd, Ag, As, Hg, Sb, and Bi) released from the mining and processing of gold-bearing sulphide minerals from the Marmato District in western Colombia, were studied to determine their geochemical behaviour and distribution in regional streams. Waters from Marmato carry appreciable dissolved metals (Zn, Cd, Cu, and As). The concentrations of these metals and of cyanide (0.13–3.8 mg l −1) make these waters unsuitable for drinking, agriculture, or industrial use. The concentrations of these metals in sediments and particulate matter are: 129–619 μg g −1 for Cu; 330 μg g −1–2.28% for Pb; 1365 μg g −1–1.8% for Zn; 7.6–200 μg g −1 for Ag; 218–1850 μg g −1 for As; 6.8–56 μg g −1 for Sb; 28–240 μg g −1 for Cd; 95–370 ng g −1 for Hg; and 4–306 μg g −1 for Bi. The highest values were found for the Marmato River, while the larger Cauca River shows the lowest values, and the concentration of the metals in its sediments reflects the contents of its tributaries. Chemical speciation shows that Cd, Zn, Pb and Bi have the highest bioavailability potential (exchangeable fraction) while Sb and Hg do not have mobile fractions.