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GEOBIOLOGY OF AN ACID MINE DRAINAGE ENVIRONMENT ALONG A STREAM GRADIENT, CENTRALIA, PA
Centralia, PA, was a robust coal mining town from the 1840’s to the 1960’s. The Centralia Mine Drainage Tunnel (CMDT) was opened to drain a portion of the underground mine pool and improve the economic feasibility of coal mining in the region. In 1962, a large coal mine fire caught in the underground coal seams, effectively ending coal mining in the immediate area and forcing the residents to leave Centralia for safety reasons. However, the CMDT remains, discharging daily 3.3 million gallons of acid mine drainage (AMD) into the Big Mine Run AMD outlet, which flows into Mahanoy Creek. The chemistry of Big Mine Run is fairly consistent along the stream length (pH=3.8 to 3.7 and conductivity = 1114 to 1160 uS/cm). Extremophile organisms (e.g. bacteria) are known to live in similar acidic waters, and may be preserved in mineral precipitate to form mineral biosignatures. Rock varnish and flocculent mineral precipitate were collected along Big Mine Run during the fall of 2016 for mineralogic and geobiological analyses. Mineralogic analyses were conducted on a Bruker D8 Discover X-Ray Diffractometer (XRD) and geobiologic analyses were conducted using a Phenom Pro-X Scanning Electron Microscope (SEM) ) with energy dispersive spectroscopy (EDS) to characterize microbes and mineral biosignatures in the AMD samples. Rock varnish samples were primarily composed of quartz, clinochlore, goethite, biotite, muscovite and kaolinite, while flocculent mineral precipitate was primarily composed of goethite, schwertmannite, ferrihydrite, muscovite, kaolinite, and quartz. SEM analyses demonstrate the presence of five species of acid-tolerant diatoms such as Caloneis bacillum and Pinnularia sp., and several varieties of filamentous microbial organisms. These samples are mineralogically similar to some iron-rich environments on Mars, and these data can be used to refine the optimal resolution and sample preparation required to detect similar microbial biosignatures with an SEM on a future Mars mission.