U.S. Geological Survey Toxic Substances Hydrology Program--Proceedings of the Technical Meeting, Colorado Springs, Colorado, September 20-24, 1993, Water-Resources Investigations Report 94-4015

Investigations of Microbial Weathering of Minerals

Abstract

Mineral weathering in an oil-contaminated aquifer near Bemidji, Minnesota, was investigated using in situ methods. Small microcosms containing clean, freshly fractured, mineral fragments were suspended for ~1 year in wells penetrating the aquifer, and the mineral surfaces were then examined for evidence of microbial colonization and mineral diagenesis. After reaction, feldspar and quartz surfaces were lightly colonized with a variety of microfauna. Feldspars were deeply etched in the vicinity of attached microbes, whereas an unidentified clay precipitate was found on uncolonized surfaces of the same fragment. Quartz was lightly etched, with a generally roughened surface and scattered triangular etch pits, whereas most of the calcite showed evidence of carbonate precipitation. These results, combined with 10 years of geochemical data collected at the site, illustrate a complex geochemical system where microbial processes drive multiple reactions that are reflected in the mineral-surface diagenetic textures.