Application of oxygen carbon isotope variations as evidence of water/rock interactions in Renison carbonates, Tasmania, Australia

摘要

The large stratabound, carbonate replacement fin deposit is situated at Renison Bell on the west coast of Tasmania, Australia. The Renison sequence generally consists of three main dolomite units and siliciclastic sediments of Neoproterozoic age. Most altered dolomites contain low concentrations of Ca, Mg and high concentrations of Sr, Mn, and Fe relative to the unaltered Proterozoic sedimentary dolomite. Dolomitefluids δ18O and δ13C fractionation curves that best fit the Renison isotopic carbonate data and fluid inclusion temperatures are foran early stage Devonian magmatic fluid (δ18O=+9‰ SMOW, δ13C=-5‰ PDB), followed by late-stage mixtures of temperate Devonian meteoric water and magmatic fluids (Adabi, 1996). Isotherms on a δ18O and δ13C covariance plot illustrate that the isotopic variation in Renison carbonates are the result of changing temperature and fluid/rock interaction. Fluid/rock ratios were predicted to be as high as ～6 (open system) close to the carbonate replacement ore bodies, and decreased with declining temperatures away from mineralization.XH2CO3 values in solution may have increased from 0.01 to 0.1 molal during dolomite dissolution.