Carbon and oxygen isotopic equilibria in hydrothermal calcites.

Calcite-carbon solute species-water theoretical and experimental isotope fractionation factors, plus salinity correction data, allow theoretical calcite equilibrium isotope values to be calculated as a function of the temperature of deposition when other variables are constant. In several ore deposits carbonate isotope values lie close to theoretical equilibrium curves as depositional temperatures decrease and a large reservoir of carbon in solution is implied. Models attributing isotopic variations in hydrothermal calcites as due to pH and fO2 changes assume such a reservoir, and hence can be valid. In addition, the carbon isotopic value of the carbon in solution can be calculated to determine the origin of the carbon.

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