Filamentous Hydrous Ferric Oxide Biosignatures in a Pipeline Carrying Acid Mine Drainage at Iron Mountain Mine, California

ABSTRACT

A pipeline carrying acidic mine effluent at Iron Mountain, CA, developed Fe(III)-rich precipitate caused by oxidation of Fe(II)_aq. The native microbial community in the pipe included filamentous microbes. The pipe scale consisted of microbial filaments, and schwertmannite (ferric oxyhydroxysulfate, FOHS) mineral spheres and filaments. FOHS filaments contained central lumina with diameters similar to those of microbial filaments. FOHS filament geometry, the geochemical environment, and the presence of filamentous microbes suggest that FOHS filaments are mineralized microbial filaments. This formation of textural biosignatures provides the basis for a conceptual model for the development and preservation of biosignatures in other environments.

KEYWORDS:

• Biosignature
• Iron Mountain
• geobiology
• schwertmannite

Acknowledgments

The authors thank Iron Mountain Operations; the late T. Arman and IMM, Inc.; B. Hofmann for filament morphology measurement assistance; R. Southard, F. Hayes and I. Delusina for laboratory assistance; and D.K. Nordstrom, K. Walton-Day, and two anonymous reviewers for review comments. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

Funding

This work was supported by NASA Headquarters under the NASA Earth and Space Science Fellowship Program—Grant NNX11AQ51H, by USEPA interagency agreement DW-14-95567601 with the USGS, by the USGS National Research Program, and by the UCD Earth and Planetary Sciences Department Durrell Funds.