Cave Ferromanganese Deposits (a.k.a corrosion residues)

Diana E. Northup
University of New Mexico
Penelope J. Boston
New Mexico Institute of Mining and Technology
Michael N. Spilde
University of New Mexico
Clifford N. Dahm
University of New Mexico
Laura J. Crossey
University of New Mexico
Armand Dichosa
Los Alamos National Laboratory

Caves offer accessible subterranean environments in which to study the diversity of microbial life. These ecosystems are exposed to extreme environmental stresses and may be based on inorganic energy sources rather than sunlight. An excellent example of subterranean microbial life is found in Lechuguilla Cave (New Mexico), the deepest cave in the continental United States. Lechuguilla Cave, an immense, ancient cave in near pristine condition, contains sulfur, iron, and manganese deposits and extremely low nutrient environments harboring diverse microbial life. The carbonate wall rock and overlying corroded limestone provide an excellent model for studying how life has survived, adapted, and altered this rock environment. Preliminary evidence suggests that the diverse community of microorganisms inhabiting corrosion residues includes fungi and bacteria that live by using manganese and iron. We are investigating the nature of the unusual microorganisms present, the means by which they adapt to their extreme environment, the energy sources that they use, and the overall level of biological activity of the communities. Because of the potential for subsurface life on other planets and possible chemical similarity to Lechuguilla Cave, our research will also explore the relevance of cave communities to those that may exist elsewhere.

We are currently using Scanning Electron Microscopy (SEM) and Electron Dispersive Spectroscopy (EDS) analysis to study sites in Lechuguilla Cave to search for evidence of bacteria and their potential energy sources.

Corrosion residues occur in many colors, including black, gun metal gray, red, brown, yellow, ocher, pink, and orange. EDS has shown us that black residues contain the highest concentration of manganese oxides, while reds and browns contain the highest amounts of iron oxides. Using SEM, we are scanning samples of corrosion residue from Lechuguilla Cave and Spider Cave, and punk rock. The combination of SEM/EDS has revealed different morphologies of calcite, dolomite, gypsum, quartz, clays, iron oxides in the shape of discs, balls, and stars on the order of less than a micron to a few microns in diameter, manganese oxides, svanbergite, barite, and rutile, zirconium, apatite. Some samples of corrosion residue and wall rock reveal the presence of rare earth elements.

The calcium carbonate associated with corrosion residues shows pitting of various types, including pits in the wall rock behind the corrosion residues that contain putative bacterial filaments. Other bacterial morphologies have been observed in corrosion residues and punk rock.

Corrosion residues are also found in Jewel Cave (Jewel Cave National Monument). These residues are mainly browns and blacks and EDS analysis shows high iron content.

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