THE ROLE OF SULFATE-REDUCING BACTERIA ON THE FORMATION OF SUPERGENE GOLD

The role of sulfate-reducing bacteria on the mobility of gold in natural systems was examined using column experiments. A bacterial consortium possessing sulfate-reducing bacteria was enriched from the Driefontein Consolidated Gold Mine, Witwatersrand Basin, Republic of South Africa. In bacterial experiments, the gold precipitated initially at bacterial surfaces in framboidal and irregular shapes. While the framboidal gold was only formed at Desulfovibrio spp. surfaces, the irregular-shaped gold was associated with other types of sulfate-reducing bacteria (rod and spherical shape). The TEM observation showed that the gold was deposited on the outer and inner surfaces of the cell envelope and also inside the cells for some dead bacteria. The irregular gold then grew outward from the cell surfaces and formed crystalline cubic and octahedral gold (3-10 micrometers). The formation of millimeter-scale of gold in the column experiments after 120 days demonstrates that a mixed of sulfate-reducing bacteria may be important to the formation of supergene gold deposits through bio-reduction of Au(I) from gold thiosulfate complexes to Au(0).