Geomicrobiology of pyrite (FeS2) dissolution: Case study at Iron Mountain, California

Abstract

Geomicrobiology of pyrite weathering at Iron Mountain, CA, was investigated by molecular biological, surface chemical, surface structural, and solution chemical methods in both laboratory and field-based studies. Research focused at sites both within and peripheral to the ore-body. The acid-generating areas we have examined thus far at Iron Mountain (solution pH <1.0, temperature> 35 C) were populated by species other than Thiobacillus ferrooxidans . 16S rDNA bacterial sequence analysis and domain- and specieslevel oligonucleotide probe-based investigations confirmed the presence of planktonic Leptospirillum ferrooxidans and indicated the existence of other species apparently related to other newly described acidophilic chemolithotrophs. T. ferrooxidans was confined to relatively moderate environments (pH 2-3, 20-30 C) that were peripheral to the orebody. Dissolution rate measurements indicated that, per cell, attached and planktonic species contributed comparably in acid release. Surface colonization experiments in the laboratory and field indicated that attachment was specific to sulfides instead of to silicates, occurred in crystallographically preferred orientations, and, after cell division, resulted in a monolayer of cells at a maximum density of 8 X 106 cells cm2. In situ geochemical characterization throughout the year revealed that the microbial community that controlled acid generation varied and could be correlated with seasonal and spatial fluctuations in geochemical conditions.