TY - JOUR
T1 - The origin and age of biogeochemical trends in deep fracture water of the Witwatersrand basin, South Africa
AU - Onstott, Tullis C.
AU - Lin, L. H.
AU - Davidson, M.
AU - Mislowack, B.
AU - Borcsik, M.
AU - Hall, J.
AU - Slater, G.
AU - Ward, J.
AU - Lollar, B. Sherwood
AU - Lippmann-Pipke, J.
AU - Boice, E.
AU - Pratt, L. M.
AU - Pfiffner, S.
AU - Moser, D.
AU - Gihring, T.
AU - Kieft, Thomas L.
AU - Phelps, Tommy J.
AU - Vanheerden, E.
AU - Litthaur, D.
AU - Deflaun, M.
AU - Rothmel, R.
AU - Wanger, G.
AU - Southam, G.
N1 - Funding Information:
This research was supported by grants from the National Science Foundation LE × En program (EAR-9714214 and EAR-9978267 with supplemental funds from the NASA Astrobiology Institute and the National Geographic Society (6339-98) to Princeton University (T.C. Onstott). We gratefully acknowledge the support of Gold Fields Ltd., Harmony Gold Mines and Anglogold and the management and staff of Driefontein, Kloof, Tau Tona, Mponeng, Evander, Beatrix, Merriespruit and Masimong gold mines and SASOL coal mine. We thank G. Southam, G. Wanger, S. McCuddy, A. Welty, S. Devlin, A. Bonin, S. Knoessen, E. Trimarco, B. Tipple, J. Hoek, B. Baker, T.J. Pray, B. Gilhooly, D. Opperman and K. Takai for assistance in the collection of, preservation of and analyses of fracture water samples. We are especially indebted to Rob Wilson and colleagues at Turgis Ltd., Arnand vanHeerden of Kloof Mine, Dawie Nel of Driefontein Gold Mine, Colin Ralston and Walter Seymore of Evander Gold Mine, Jane Larkin of Merriespruit Mine, George Gilchrest of Tau Tona, Dave Kershaw of Mponeng and Bob Bellamey of Beatrix Gold Mine. We are also indebted to George Rose of Princeton University who designed and constructed the sampling equipment. Address correspondence to T.C. Onstott, Dept. of Geosciences, Princeton University, Princeton, N.J. U.S.A. E-mail: [email protected]
PY - 2006/9
Y1 - 2006/9
N2 - Water residing within crustal fractures encountered during mining at depths greater than 500 meters in the Witwatersrand basin of South Africa represents a mixture of paleo-meteoric water and 2.0-2.3 Ga hydrothermal fluid. The hydrothermal fluid is highly saline, contains abiogenic CH4 and hydrocarbon, occasionally N2 originally formed at ∼250-300°C and during cooling isotopically exchanged O and H with minerals and accrued H2, 4He and other radiogenic gases. The paleo-meteoric water ranges in age from ∼10 Ka to >1.5 Ma, is of low salinity, falls along the global meteoric water line (GMWL) and is CO2 and atmospheric noble gas-rich. The hydrothermal fluid, which should be completely sterile, has probably been mixing with paleo-meteoric water for at least the past ∼100 Myr, a process which inoculates previously sterile environments at depths > 2.0 to 2.5 km. Free energy flux calculations suggest that sulfate reduction is the dominant electron acceptor microbial process for the high salinity fracture water and that it is 107 times that normally required for cell maintenance in lab cultures. Flux calculations also indicate that the potential bioavailable chemical energy increases with salinity, but because the fluence of bioavailable C, N and P also increase with salinity, the environment remains energy-limited. The 4He concentrations and theoretical calculations indicate that the H2 that is sustaining the subsurface microbial communities (e.g. H2 -utilizing SRB and methanogens) is produced by water radiolysis at a rate of ∼1 nM yr-1. Microbial CH4 mixes with abiogenic CH4 to produce the observed isotopic signatures and indicates that the rate of methanogenesis diminishes with depth from ∼100 at <1 kmbls, to <0.01 nM yr-1 at >3 kmbls. Microbial Fe(III) reduction is limited due to the elevated pH. The δ13C of dissolved inorganic carbon is consistent with heterotrophy rather than autotrophy dominating the deeper, more saline environments. One potential source of the organic carbon may be microfilms present on the mineral surfaces.
AB - Water residing within crustal fractures encountered during mining at depths greater than 500 meters in the Witwatersrand basin of South Africa represents a mixture of paleo-meteoric water and 2.0-2.3 Ga hydrothermal fluid. The hydrothermal fluid is highly saline, contains abiogenic CH4 and hydrocarbon, occasionally N2 originally formed at ∼250-300°C and during cooling isotopically exchanged O and H with minerals and accrued H2, 4He and other radiogenic gases. The paleo-meteoric water ranges in age from ∼10 Ka to >1.5 Ma, is of low salinity, falls along the global meteoric water line (GMWL) and is CO2 and atmospheric noble gas-rich. The hydrothermal fluid, which should be completely sterile, has probably been mixing with paleo-meteoric water for at least the past ∼100 Myr, a process which inoculates previously sterile environments at depths > 2.0 to 2.5 km. Free energy flux calculations suggest that sulfate reduction is the dominant electron acceptor microbial process for the high salinity fracture water and that it is 107 times that normally required for cell maintenance in lab cultures. Flux calculations also indicate that the potential bioavailable chemical energy increases with salinity, but because the fluence of bioavailable C, N and P also increase with salinity, the environment remains energy-limited. The 4He concentrations and theoretical calculations indicate that the H2 that is sustaining the subsurface microbial communities (e.g. H2 -utilizing SRB and methanogens) is produced by water radiolysis at a rate of ∼1 nM yr-1. Microbial CH4 mixes with abiogenic CH4 to produce the observed isotopic signatures and indicates that the rate of methanogenesis diminishes with depth from ∼100 at <1 kmbls, to <0.01 nM yr-1 at >3 kmbls. Microbial Fe(III) reduction is limited due to the elevated pH. The δ13C of dissolved inorganic carbon is consistent with heterotrophy rather than autotrophy dominating the deeper, more saline environments. One potential source of the organic carbon may be microfilms present on the mineral surfaces.
KW - Groundwater
KW - Isotope geochemistry
KW - Methanogenesis
KW - Sulfate reduction
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U2 - 10.1080/01490450600875688
DO - 10.1080/01490450600875688
M3 - Article
AN - SCOPUS:33947312626
SN - 1433-6863
VL - 23
SP - 369
EP - 414
JO - Handbook of Environmental Chemistry, Volume 5: Water Pollution
JF - Handbook of Environmental Chemistry, Volume 5: Water Pollution
IS - 6
ER -