BIOALTERATION OF SULFIDE MINERALS AT THE SEAFLOOR

We present the results of incubation studies conducted at low temperatures (~4°C) in the vicinity of a seafloor hydrothermal vent system. We reacted the Fe-, S-, Cu-, and Zn-bearing sulfide minerals pyrite, marcasite, chalcopyrite, sphalerite, elemental sulfur, and a natural chimney sulfide material for a two-month period at the Main Endeavour Segment of the Juan de Fuca Ridge in the Pacific Ocean. Our study utilizes fluorescent, light, and electron microscopic studies. The surfaces of these minerals are solely colonized by Bacteria and not by Archaea. Colonization densities vary over an order of magnitude with the following sequence: elemental sulfur > chimney sulfide > marcasite > pyrite > sphalerite > chalcopyrite, and positively correlate with the abiotic oxidation kinetics of these materials, excepting elemental sulfur, which is both the least reactive to oxidizing species and most heavily colonized. Colonization densities correlate with apparent degree of reaction (dissolution pitting + accumulation of secondary alteration products). Heavy accumulations of secondary Fe oxides on Fe-bearing minerals, most notably on the chimney sulfide, appear to form in-situ as the result of mineral dissolution and the activity of neutrophilic Fe-oxidizing bacteria.