The Conditions for the Formation of Strontium in the Water of Ancient Silicate Deposits Near the Arctic Coast of Russia

Strontium is a toxic chemical element widely distributed in groundwater. First of all, its appearance in water is associated with the dissolution of sulfate and carbonate rocks. The aim of this study was to assess the characteristics of strontium concentration in ancient aluminosilicate deposits that were filled with sedimentogenic brines and seawater in different geological periods. Studies were conducted on 44 water samples, in which the chemical and isotopic composition was determined with the subsequent assessment of saturation indices in relation to the main rock-forming minerals and the residence time of groundwater in the aquifer. It was found that minimal strontium concentrations are characteristic of the least mineralized waters and arise mainly due to the dissolution of carbonates. After their saturation in relation to calcite, the process of carbonate dissolution was replaced by their precipitation and an increase in silicate dissolution with an increase in strontium concentration in more mineralized waters. The incongruent dissolution of aluminosilicates resulted in the appearance of new clay minerals in the aquifer, which together with iron hydroxides and newly formed calcium carbonates created opportunities for sorption and ion exchange processes. The contribution of seawater consisted of an increase in strontium concentrations by approximately 15–20%. The effect of the duration of the water–rock interaction on strontium concentrations in groundwater was expressed in the fact that over a thousand years they increased by 0.1 mg/L, which is 20–30 times less than in the waters of carbonate deposits located 100 km to the east. An assessment of the non-carcinogenic risk to human health of contact with the groundwater showed the safety of using the studied groundwater for drinking purposes.