Figure 3: Stable isotope geochemistry of the biogenic rocks at Las Cruces.
From: Formation of recent Pb-Ag-Au mineralization by potential sub-surface microbial activity
(a) Carbon–oxygen isotope composition of carbonates (sid, siderite; cc, calcite; ank, ankerite), overlying Tertiary sandstone and marl, and calculated δ18O-δ13C isotope composition of calcite in equilibrium with the local groundwaters (25 °C). Isotopic composition of the calcite in equilibrium with the water has been calculated from the tabulated δ18O-δ13C values together with the fractionation factors of Kim and O’Neil45 for oxygen and those of Romanek et al.46 for DIC. For comparison, data are shown for the Variscan (primary-ore related) hydrothermal siderite–ankerite assemblage occurring in VMS deposits of the Iberian Pyrite Belt. (b) Sulphur isotope composition compared with the δ34Ssulphate values of the local groundwater and δ34S values of the primary sulphides at Las Cruces19.
