The Effect of Calcite-Bearing Veins on Groundwater Geochemistry, Poster 27

   The effect of bedrock on groundwater geochemistry in fractured bedrock aquifers is well constrained, with a focus on how naturally occurring harmful trace elements like arsenic and uranium can be incorporated in drinking... [ view full abstract ]

   The effect of bedrock on groundwater geochemistry in fractured bedrock aquifers is well constrained, with a focus on how naturally occurring harmful trace elements like arsenic and uranium can be incorporated in drinking water resources. However, previous studies examining trace elements in groundwater in fractured bedrock aquifers have found anomalous concentrations of strontium in groundwater across thrust faults in the Champlain Valley, Vermont. The metamorphosed pelites in the hanging walls have lower concentrations of Sr (88 ppm) compared to the relatively unmetamorphosed carbonates in the footwalls (160 ppm), but hanging wall groundwater has very elevated levels of Sr (2363 ppb) compared to footwall groundwater (196 ppb). Calcite veins were theorized as the source of these anomalous Sr levels, as calcite veins have been shown to incorporate high Sr concentrations elevated above their host rock. For this study, calcite veins were sampled from the hanging walls of the Hinesburg Thrust and the Muddy Brook Thrust in western Vermont. ICP-MS analysis yielded elevated Sr concentrations significantly elevated above the host rock averaging 3,143 ppm with a range from 2,386 to 4,725 ppm. This indicates that the calcite-bearing veins are a likely source of the elevated Sr in the hanging wall groundwater, and suggests that calcite-bearing veins can affect the trace element geochemistry of fractured bedrock aquifers.