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					  Papers underway from Toronto
• 1. Sherwood Lollar et al. Evidence for
  Pervasive Methanogenesis and H2-Based
  autotrophy in the deep subsurface (for
  subm. to PNAS)
• 2. Ward et al. Origin of Hydrocarbon Gases
  in the Witwatersrand Basin (in revision for
  GCA Special Volume)
• 3. Slater et al. Radiocarbon constraints on
  the timing of Methanogenesis in the
  Witwatersrand Basin
    Paper 1: Evidence for Pervasive
Methanogenesis and H2-based autotrophy
        in the deep subsurface
• 1. Based on samples from 4 new sites (1 in
  Canada and 3 in South Africa) – abiogenic
  hydrocarbons pervasive in PreC Shield
• 2. Compositional and isotopic variability
  controlled by abiogenic-microbial mixing
• 3. H2 concentrations and CH4 isotopic
  compositions consistent with coupled
  oxidation of H2 and reduction of CO2 to
  CH4 via autotrophic methanogens
           Figure 1 – Abiogenic end-members
           -50

          -100
                                                          C3     C4
                                             C1 C2
          -150                                                          739

          -200         Drie
                                                                   Kloof              C4
d2H (‰)


          -250

          -300                                                                        C3
                                                                        Aump
          -350                      Dr938-3                MP104                      C2
          -400         Dr548
                                                                   Mponeng
                                         Kidd Creek                                   C1
          -450
                                                                   CCS-3
          -500
                 -56   -52    -48      -44    -40   -36    -32    -28     -24   -20


                                       d13C (‰)
               Figure 2 – Abiogenic-Microbial mixing
               0

              -50

             -100
                                                      Thermogenic
             -150
d2HCH4 (‰)


             -200
                                                          441
             -250                                                Kloof
                            Dr938-1                                      739
             -300
                                                Dr938-3
             -350         Microbial
             -400
                                                                         Kidd Creek
             -450
                                        Dr548
                                                                         CCS-3
             -500
                    -65          -55            -45             -35       -25

                                       d13CCH4 (‰)
 Figure 3: Microbial-Abiogenic mixing
10000

           Microbial
1000
               Dr938-1

 100
                                          Kloof
                                  441
                                        443
                             Dr938-3          739
                                                Abiogenic
  10
                     Dr548                CCS-3 13C-enriched
                                                end-members
                         KC7792
   1
        -70 -65 -60 -55 -50 -45 -40 -35 -30 -25

                    d13CCH4 (‰)
Figure 4 – H2-rich 13CCH4-enriched
     abiogenic end-member
100.00



 10.00



  1.00



  0.10



  0.01
         -75   -65   -55   -45   -35   -25

                     d13CCH4 (‰)
       Figure 4: Methanogenesis and
           H2-based autotrophy
• high H2 associated with the most 13C-enriched
  abiogenic CH4 – we have a disagreement on the
  amount of mixing in end members
• when released due to tectonics/mining, deep subsurface
  microbes gain access to the abundant geologically old
  stored H2-we disagree with origin of H2-it is
  continuously produced by radiolysis
• CH4-H2 rich abiogenic gases support a redox-driven
  ecosystem where rapid depletion of H2 and
  methanogenic 13C-depleted CH4 overprints abiogenic
  signature-just the H2 supports autotrophy-not the CH4
             Samples fall in overlap between Microbial
              and Microbial Mixing-according to this
             diagram the microbial looks thermogenic
                0

               -50
                                                           Thermogenic
              -100

              -150
                                       Beatrix
d2HCH4 (‰)


              -200
              -250

              -300             MB                      Evander
              -350         Microbial
              -400
                                                               Kidd Creek
              -450

              -500
                     -65           -55           -45     -35       -25


                                         d13CCH4 (‰)
                                                                  30



                                       Pretoria Precipitation     20



                                                                  10


                    d2Ho/ooVMSOW
                                                                   0
-14     -12     -10         -8        -6         -4       -2            0                   2   4   6

                                    Mine Water
                                                                  -10
                                                               Mean Precipitation
                                                                  -20




                                                                            d18Oo/ooVMSOW
                                    Ev219
                            0.6              0.2                  -30
        Ev818         0.8                             Karoo
                            Ev522
                                                                  -40


      Mixing Line
                                                                  -50



                                                                  -60
                                                          Cl- (ppm)
                 0
                      0           1000   2000           3000          4000   5000   6000    7000




                 -2
                            Karoo
                                         Mine Water
                 -4
d18Oo/ooVMSOW




                 -6
                                          Ev522
                          Ev219                                 Ev820
                 -8




                -10                                                                 Ev818
                                                Mixing Line

                -12
Paper 2: Origin of Hydrocarbon Gases
       in Witwatersrand Basin
           (J. Ward thesis)
• 1. Predominantly microbial origin for
  hydrocarbons at Beatrix, Evander and
  Middlebult.
• 2. But some degree of mixing.
• 3. Geological controls on mixing: samples
  in Witwatersrand mainly microbial
• 4. Samples from Ventersdorp = greatest
  degree of mixing of microbial with more
  13C-enriched CH –not true-all samples from
                  4
  Witwatersrand quartzites at Evander
   Maximum mixing in Ventersdorp
10000
              Microbial
                                 Beatrix
1000
                                        Witwatersrand

 100                                        Ventersdorp

  10
                                        Evander

                                       Kidd Creek
   1
        -70       -60      -50   -40      -30
                        d13CCH4 (‰)
Paper 3: 14C in DIC and CH4 in South
  African gold mines – evidence for
  current methanogenesis? Slater et
            al. STATUS???
• This study examines the stable and
  radiocarbon relationship between DIC and
  methane in three gold mines where there is
  evidence of microbial methanogenesis
• Goal to determine whether this microbial
  contribution represents methanogenesis
  from current DIC pools, or is evidence of
  bacterial activity over geologic timescales

				
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