Abstract

Low to zero precipitation in Northern Chile means that the dissolution of silicate rocks and the formation of secondary phases occurs largely in the deep subsurface. Although the Li concentration of water can be high, the very minimal variation in Li isotopes compared to other regionsreflects the limited formation of secondary phases which fractionate Li.There isgreater variability in B isotopesdue to its volatility in volcanic systems and its pH-dependent speciation which leads to strong fractionation which is apparent in the Western Cordillera groundwater systems but only in the Precordillera where volcanic rocks, marine limestoneand gypsumare weathered. Mo shows a range in isotope compositions which is similar to temperate areas. The differences between the variability in theseisotopesystems is related to the occurrence of recent and ongoing volcanism in the West Cordillera of the Andes. Inthe Western Cordillera,there can be large volcanic fluxes of CO2driving weathering reactions at depth, which are absent in the Precordillera. Water geochemistry in the Western Arc is more complex as acidity is quickly neutralised by volcanic glassand by storage of solutes in evaporitic systems.