Groundwater geochemistry and flow in the Spring Mountains, NV: Implications for the Death Valley Regional Flow System

Abstract

Groundwater geochemistry and 87Sr/86Sr from spring waters in the Spring Mountains, NV were used to understand how groundwater recharging in the Spring Mountains influences regional groundwater flow in the Death Valley Regional Flow System (DVRFS). Previous researchers hypothesized that groundwater from the Spring Mountains contributes to the DVRFS, an interbasin groundwater flow system (IGF). However, the Spring Mountains are geologically heterogeneous, therefore, a uniform contribution of groundwater flow across the range is unlikely. Here, we use spring water geochemistry, spring water and host rock 87Sr/86Sr, and observations of the surrounding geology to determine what regions of the Spring Mountains are likely to contribute more flow to the DVRFS. Based on geochemical and isotopic evidence, Spring Mountains groundwater can be divided into three flow regions with distinct geochemical signals reflecting silicate or carbonate water-rock interactions and location relative to major thrust faults. The Keystone Thrust flow region (KST) has a 87Sr/86Sr of 0.710–0.711, is recharged by both rain and snow, and weathers both Mesozoic sandstones and Permian and Cambrian carbonate. Central Spring Mountains (CSM) groundwater has a 87Sr/86Sr of ~0.708, is primarily recharged by snow, and weathers Permian and Cambrian limestones and dolostones. The Montgomery Hills (MH) flow region has a 87Sr/86Sr 0.711–0.733, is recharged by both rain and snow, and weathers both Permian and Cambrian carbonates and Precambrian siliciclastics. Groundwater mixing between flow groups occurs along major thrust faults in the study area, as evidenced by 87Sr/86Sr signatures that reflect one flow group and δ18O and δ2H and geochemical signatures that reflect another flow group. The combination of geochemical and isotopic results suggest CSM groundwater is the most likely to reach Death Valley because CSM groundwater composition reflects the geochemical and isotopic signatures of the highly permeable rocks that connect the Spring Mountains to Death Valley. Flow leaving the KST and MH also influences the DVRFS after mixing with CSM groundwater along major thrust faults.