Geochemistry and Microbiology of Atacamite-Paratacamite Biofilms Floating on Underground Brine and Petroleum Pools in the White Pine Copper Mine, Michigan (USA)

At depth in an abandoned tunnel of the White Pine Copper Mine, green films of the Cu-OH-Cl minerals atacamite and paratacamite were found on standing pools of brine. Some pools were also coated with a thin layer of petroleum. Green films of atacamite were composed of individual blebs that averaged 20 μm in diameter and enclosed mixed colonies of Gram-negative, short rod-shaped, and sheathed filamentous bacteria. Carbon δ13C values in the atacamite–paratacamite mixtures reflect the isotopic values of bacteria and minor amounts of petroleum mixed with the minerals. Heterotrophic bacteria are interpreted to be using petroleum as a carbon source and may be catalyzing the precipitation of the copper hydroxy chloride minerals or acting as a template.