Abstract
Alkaline earth elements and alkali metals (Mg, Ca, Na and K) play an important role in the geochemical evolution of saline lakes as the final brine type is defined by the abundance of these elements. The role of major ions in brine evolution has been studied in great detail, but little has been done to investigate the behaviour of minor alkali elements in these systems despite their similar chemical affinities to the major cations. We have examined three major anionic brine types, chloride, sulphate, and bicarbonate-carbonate, in fifteen lakes in North America and Antarctica to determine the geochemical behaviour of lithium, rubidium, strontium, and barium. Lithium and rubidium are largely conservative in all water types, and their concentrations are the result of long-term solute input and concentration through evaporation and/or sublimation. Strontium and barium behaviours vary with anionic brine type. Strontium can be removed in sulphate and carbonate-rich lakes by the precipitation of carbonate minerals. Barium may be removed in chloride and sulphate brines by either the precipitation of barite and perhaps biological uptake.
Highlights
The ultimate chemistry of a saline, closed-basin lake is determined by the initial composition of precipitation, the weathering reactions between dilute inflow water and lithology, and evapoconcentration of the lake water [1]
It is clear from these models that the abundance of major alkali elements, Ca, Na, K, and Mg, is key in determining the geochemical pathways involved in brine formation, yet there has been little work to extend the modelling efforts to aid in the prediction of minor and trace metal behaviour
Because chloride is conservative in most saline lakes, normalizing solute concentration relative to chloride can be used to monitor the progression of evaporation and chemical evolution [2]
Summary
The ultimate chemistry of a saline, closed-basin lake is determined by the initial composition of precipitation, the weathering reactions between dilute inflow water and lithology, and evapoconcentration (or sublimation) of the lake water [1]. Modelling of closed-basin lakes has focused on the major elements of most natural waters: Ca, Na, K, Mg, Cl, SO4, and carbonate alkalinity (HCO3 + CO3) and the simple salts that these ions produced during evaporation [1,2,3]. It is clear from these models that the abundance of major alkali elements, Ca, Na, K, and Mg, is key in determining the geochemical pathways involved in brine formation, yet there has been little work to extend the modelling efforts to aid in the prediction of minor and trace metal behaviour
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