Table 3.

Comparison of mineralogical and geochemical data relevant for biosignatures between the Bijiki Fe-silicate BIF and the Akilia Qp rock

Amphibolite facies Bijiki Fe-silicate BIFGranulite facies Akilia Qp rock
Agec. 1.85 Ga1>3.83 Ga2
Metamorphic temperatureT = 567 ± 50°C3T > 635°C4
MineralogyGrunerite, magnetite, quartz, dolomite, stilpnomelane, chlorite, pyroxene, biotite, graphite, apatite, pyrrhotite, pyrite3Quartz, pyroxene (hedenbergite-ferrosilite), magnetite, grunerite-hornblende, calcite, apatite, graphite, pyrrhotite, chalcopyrite, pentlandite4
Specific mineral associations with graphitic carbonApatite, dolomite, magnetite, stilpnomelane, grunerite, chlorite, pyrrhotite, quartz3Apatite, calcite, magnetite, hornblende-grunerite, chalcopyrite, pyrrhotite, quartz4
Evidence for fluid remobilizationApatite grains occur in carbonate veins3Apatite occurs in coarse quartz with fields of fluid inclusions4,5
Petrography of apatiteConcentrated in some sedimentary layers6Concentrated in some layers of coarse quartz6
δ13Ccarb−14.9‰6−3.3. to −5.5‰6
δ13Cgra (in situ)−21.3 to −22.9‰3−4.1 to −49.0‰6,7
δ13Cgra (bulk)−21.7 to −24.3‰3,6−12.6 to −23.6‰6
Crystallinity of graphitic carbonD-bands between 1346 and 1353 cm−1 (FWHM between 41 and 51 cm−1 and between 82 and 85 cm−1) and G-bands between 1574 to 1581 cm−1 (FWHM between 41 and 77 cm−1)3,6D-bands between 1344 and 1358 cm−1 (FWHM between 22 and 29 cm−1) and G-bands between 1573 to 1581 cm−1 (FWHM between 10 and 46 cm−1); presence of curled graphite structures4
d-spacing of graphitic carbon3.55−3.72 Å33.41−3.64 Å4
Atomic N/C in graphitic carbon10−4 to 10−1 3,610−6 to 10−4 6
Heteroatoms in graphitic carbonH, N, O, S, P, Ca, Fe3,6H, N, O, S, P, Fe6
Petrography of heteroatoms in graphitic carbonForms sub-micrometer-size hot spots3,6Forms sub-micrometer-size hot spots6
Molecular functional groupsAliphatic and carboxyl (both minor)3None detected3
  • 1 Schulz & Cannon (2007).

  • 2 Manning et al. (2006).

  • 3 This work.

  • 4 Papineau et al. (2010a).

  • 5 Lepland et al. (2010).

  • 6 Papineau et al. (2010b).

  • 7 Mojzsis et al. (1996).