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

Heavy metals (Cu, Pb, Zn, Cd, Ag, As, Hg, Sb, and Bi) released from the min ing and processing of gold-bearing sulphide minerals from the Marmato Distr ict in western Colombia, were studied to determine their geochemical behavi our and distribution in regional streams. Waters from Marmato carry appreci able dissolved metals (Zn, Cd, Cu, and As). The concentrations of these met als and of cyanide (0.13-3.8 mg l(-1)) make these waters unsuitable for dri nking, agriculture, or industrial use. The concentrations of these metals i n sediments and particulate matter are: 129-619 mu g g(-1) for Cu; 330 mu g g(-1)-2.28%, for Ph; 1365 mu g g(-1)-1.8% for Zn; 7.6-200 mu g g(-1) for A g; 218-1850 mu g g(-1) for As; 6.8-56 mu g g(-1) for Sb; 28-240 mu g g(-1) for Cd; 95-370 ng g(-1) for Hg; and 4-306 mu g g(-1) for Bi. The highest va lues were found for the Marrnato River, while the larger Cauca River shows the lowest values, and the concentration of the metals in its sediments ref lects the contents of its tributaries. Chemical speciation shows that Cd, Z n, Pb and Bi have the highest bioavailability potential (exchangeable fract ion) while Sb and Hg do not have mobile fractions. (C) 1998 Elsevier Scienc e B.V. All rights reserved.