Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water-rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), NaCa-HCO3 type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has delta O-18 of -8.3 parts per thousand, delta D of -48.2 parts per thousand, delta B-11 of 1.5 parts per thousand, and Sr-87/Sr-86 of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5-8.0, mean 7.3), Na-Ca-Mg-Cl-SO4 type waters with moderate TDS (8.2 g/l-17.2 g/l, mean 9.3 g/l, brackish) and have delta O-18 values in the - 5.8 parts per thousand to - 9.3 parts per thousand range (mean - 8.1 parts per thousand), delta D values in the - 20.8 parts per thousand to - 85.5 parts per thousand range (mean - 47.0 parts per thousand),delta B-11 values in the + 9.5 parts per thousand to + 39.1 parts per thousand range (mean + 17.1 parts per thousand), and Sr-87/Sr-86 values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH=7.4), Na-Ca-Mg-Cl-SO4 type water with the highest TDS (249.1 g/l, brine) and has 6180 of -2.8 parts per thousand, delta D of -45.8 parts per thousand,delta B-11 of 21.2 parts per thousand, and Sr-87/Sr-86 of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and delta B-11 values along the pathway of groundwater migration which can only be interpreted in terms of water-rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water-rock interaction and mixing of meteoric water with connate waters contained in sediments. (c) 2007 Elsevier B.V. All rights reserved.