DETERMINATION OF SODIUM, CHLORIDE AND SULFATE IN DOLOMITES - A NEW TECHNIQUE TO CONSTRAIN THE COMPOSITION OF DOLOMITIZING FLUIDS

A new analytical procedure has been developed to determine sodium, chl oride and sulfate concentrations in dolomite. Non-dolomite phases are removed during sample preparation, and 10 mg of at least 99% pure dolo mite are dissolved in nitric acid. This solution is diluted, and sodiu m, chloride and sulfate are determined by standard DCP and IC methods. To evaluate the geochemical significance of sodium, chloride and sulf ate abundances in dolomite, 108 samples from various locations were an alyzed. Their depositional age and the composition of the dolomitizing fluid were previously determined on the basis of petrographic, geoche mical and stratigraphic evidence. Dolomites that were interpreted to h ave formed from seawater-derived evaporitic brines, seawater/fresh-wat er mixtures and deep formation waters exhibit significant differences in sodium, chloride and sulfate content, and molar Na/Cl ratios. This new technique provides a valuable geochemical tool to constrain the co mposition of dolomitizing solutions, complementing field observations, petrographic evidence, isotope- and fluid inclusion data.