ANALYSIS OF MAJOR IONS IN DENSE BRINES USING PORTABLE X-RAY FLUORESCENCE SPECTROMETRY

The use of portable X-ray fluorescence (pXRF) spectrometers for environmental, research, and industrial applications are due to the convenience of portability, the speed of analyses, and precision of sample analysis for elemental content and concentration. For these same reasons NASA has included a fluorescence instrument, the Planetary Instrument for X-Ray Lithochemistry (PIXL), on its Mars 2020 rover to study the microscale chemical concentrations of the Martian surface. Several lines of evidence suggest past and current brines and evaporite sediments on the surface of Mars and other planetary bodies. Robust calibration of pXRF analyses for dense brines from analog environments will help to aid interpretation of such data in extraterrestrial settings. In this study, we have compiled dense brine samples from hypersaline systems across five continents and various geologic settings for analysis of major ion chemistry (Na, Mg, S, K, Ca, Cl) using pXRF. We apply a calibration approach following Lucas-Tooth and Pyne to collected pXRF spectra and a subset of reference data was used for validation of this calibration. Results show reliable quantification of major ion concentrations in brine sample when compared to outside laboratory results. Further, comparison of pXRF spectra at various energy and filter settings indicate that published methods for optimized returns of rock samples are not consistent for the analysis of a dense liquid matrix. These methods can then be applied to search for and study of shallow, salty groundwater of other planetary bodies and terrestrial analogues.