Methane-derived carbonates in a native sulfur deposit: Stable isotope and trace element discriminations related to the transformation of aragonite tocalcite

Stable isotope (C-13, O-18, S-34) and trace element (Sr2+, Mg2+, Mn2+, Ba2, Na+) investigations of elemental sulfur, primary calcites and mixtures of aragonite with secondary, post-aragonitic calcite from sulfur-bearing lime stones have provided new insights into the geochemistry of the mineral form ing environment of the native sulfur deposit at Machow (SE-Poland). The car bon isotopic composition of carbonates (delta(13)C = -41 to - 47 parts per thousand vs. PDB) associated with native sulfur (delta(34)S = + 10 to + 15 parts per thousand vs. V-CDT) relates their formation to the microbiologica l anaerobic oxidation of methane and the reduction of sulfate derived from Miocene gypsum. From a comparison with experimentally derived fractionation factors the element ratios of the aqueous fluids responsible for carbonate formation are estimated. In agreement with field and laboratory observatio ns, ratios near seawater composition are obtained for primary aragonite, wh ereas the fluids were relatively enriched in dissolved calcium during the f ormation of primary and secondary calcites. Based on the oxygen isotope com position of the carbonates (delta(18)O = -3.9 to - 5.9 parts per thousand v s. PDB) and a secondary SrSO4 (delta(18)O = + 20 parts per thousand vs. SMO W; delta(34)S = + 59 parts per thousand vs. V-CDT), maximum formation tempe ratures of 35 degrees C (carbonates) and 47 degrees C (celestite) are obtai ned, in agreement with estimates for West Ukraine sulfur ores. The sulfur i sotopic composition of elemental sulfur associated with carbonates points t o intense microbial reduction of sulfate derived from Miocene gypsum (delta (34)S approximate to + 23 parts per thousand) prior to the re-oxidation of dissolved reduced sulfur species.