The geochemistry of boron and its isotopes in groundwaters from marine and non-marine sandstone aquifers

The geological evolution of B in two UK sandstone aquifers is followed from precipitation chemistry through to groundwaters in both the unconfined and confined zones. Measurements have been made of major element geochemistry, B concentrations and B isotopic ratios. The isotopic measurements were carried out using ICP/MS following a simple preconcentration step. Isotopic measurements of rainfall show a bimodal distribution and it is suggested that enriched signatures are characteristic of Atlantic air over Britain and depleted signatures representative of continental air. In the marine Lower Greensand aquifer dissolution of glauconite results in the mobilisation of B and a correlation with SO4 suggests that this dissolution is related to the oxidation of pyrite which appears to be the SO4-forming reaction in the aquifer. In the non-marine Hastings beds isotopic ratios and a correlation with HCO3 suggest that B is associated with the dissolution of ferroan carbonates. In both aquifers the geochemical evolution of B is complex and more information is needed on the behaviour of B isotopes during evapotranspiration and groundwater recharge.