Major ion geochemistry in Na-Ca-Mg-K-Cl-SO4 brines using portable X-ray fluorescence spectrometry

Abstract

Knowledge of the geochemistry of natural waters contributes to the understanding of Earth systems including crustal evolution, geochemical cycles, precipitation and dissolution of chemical sediments, and limits for extremophilic microorganism, as well as contributing hypotheses about other planets and moons that host chemical sediments. However, the traditional methods for quantification of saline waters presents analytical challenges that can lead to inaccurate or unrelatable results. Here, we demonstrate the accuracy and limits of portable X-ray fluorescence spectrometry (pXRF) for analysis of major ion geochemistry in brines from five continents. Results from a validation sample subset show R2 values >0.95 for K+, Ca2+, SO42−, >0.90 for Mg2+, Cl−, and 0.85 for Na+ when compared with sample concentrations reported from external laboratories. Dilution experiments demonstrate that the minimum sensitivity of pXRF photon response by major ion varies from >1 to >1000 mg/L. The application of this method for quantifying saline water chemistry presents opportunities for further study of brines on Earth and the exploration of saline systems on other planetary bodies. Plain language summaryThe use of portable X-ray fluorescence spectrometry presents an untapped opportunity for characterization of saline waters. Here, we demonstrate the precision and limits of this proposed method for salt water samples collected from saline lakes and salt playas across the Earth.