Subsurface Geomicrobiology of a Volcanically Hosted Massive Sulfide Deposit (VHMS), Near Rio Tinto, Spain

Details Subsurface Geomicrobiology of a Volcanically Hosted Massive Sulfide Deposit (VHMS), Near Rio Tinto, Spain Subsurface Geomicrobiology of a Volcanically Hosted Massive Sulfide Deposit (VHMS), Near Rio Tinto, Spain

Dec 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufm.p51d0960s&link_type=abstract

American Geophysical Union, Fall Meeting 2005, abstract #P51D-0960

Biology

0406 Astrobiology And Extraterrestrial Materials, 0448 Geomicrobiology, 0456 Life In Extreme Environments

Scientific paper

Background. We investigated a subsurface lithotrophic microbial ecosystem in a volcanically hosted massive sulfide deposit (VHMS) of the Iberian Pyrite Belt. These extremely reactive rocks persist only because they are sequestered from the atmosphere. The Rio Tinto, in SW Spain is a 100 km-long ARD stream with extreme pH (ca. 2.3) and metal loading (> 2.5 gm/l). Springs feeding the river are already metal-laden, yet their pH can range to 6 and many are anoxic. We hypothesized that subsurface biological activity contributes to the weathering of the VHMS, and that anaerobic metabolism, using in situ electron acceptors was a major component of this putative underground bioreactor. Methods. We aseptically sampled rocks and ground-waters up-gradient from the VHMS, within the VHMS, and down- gradient from the VHMS through springs and continuously-cored boreholes. Samples were analyzed for the presence of microorganisms, resources that might support microbial activity, and metabolites produced by microbial activity. Results. Organisms detected included aerobic Fe and S oxidizers, anaerobic denitrifying S2O32-oxidizers, and SO42--reducing and methanogenic H2 oxidizers. Ground water up- gradient from the VHMS was neutral, aerobic and low in solutes. Within the VHMS, H2 at concentrations up to 1000 ppm was produced by water-rock reactions. Anoxically leached ore produced pH 5-6 solutions containing Fe(II), Fe(III), SO42- and NO2-. Incoming O2 reacted to form NOx gases and pH 3.5 fluids. Low CH4 throughout the VHMS, indicated widespread anoxia. Down-gradient from the VHMS, ground waters were anoxic low-SO42- high- CH4 (5000 ppm) fluids or low- CH4 high- SO42- (800 ppm) fluids with abundant FeS precipitates. Generally, Fe(III) and H2 decreased along the flow path while Fe(II) and CH4 increased. NOx and SO42- concentrations remained relatively constant along the flow path. Conclusions. A subsurface ecosystem driven by weathering of sulfide minerals is present beneath the Rio Tinto region. An unexpected variety of resources are available to drive microbial metabolism, including electron donors and electron acceptors supplied from the rock matrix. Production of H2 from water-rock interactions within the ore body supported profuse activity of H2-oxidizing microorganisms including methane generation. The variety of fluids discharged from springs is apparently due to the various pathways groundwater may take through the fractured rock environment, and mixing with aerobic water. However, many of the activities observed appear to be independent of resources from the surface.

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