Michael Naylor Hudgins, Todd K Knobbe, Julia Hubbard, Andrew Steele, Justin G Park, Morgan F Schaller

Carbonate minerals are globally distributed on the modern and ancient Earth and are abundant in terrestrial and marine depositional environments. Fluid inclusions hosted by calcite retain primary signatures of the source fluid geochemistry at the time of mineral formation (i.e., pCO2) and can be used to reconstruct paleoenvironments. Confocal laser Raman spectroscopy provides a quick, non-destructive approach to measuring the constituents of fluid inclusions in carbonates and is a reliable method for determining composition in both the aqueous and gas phases in fluid inclusions. Here, we demonstrate a method for making accurate quantifications of carbonate concentrations and pH from fluid inclusions using confocal Raman spectroscopy. Instrument calibrations for carbonate (CO32-) and bicarbonate (HCO3-) concentrations and pH were performed using stock solutions. The host mineral does not affect the carbonate species. Accurate quantification of carbonate solution concentrations and pH can be used to estimate the pCO2 of a solution when measuring fluid inclusions with Raman spectroscopy.