Using groundwater chemical and isotopic composition in the search for base metal deposits: hydrogeochemical investigations in the Hinta and Kayar Pb–Zn districts, India

Abstract

ABSTRACT As part of mineral exploration campaigns carried out by Anglo American plc in India, groundwater samples were collected from over 200 wells in the Hinta and Kayar sedimentary exhalative base metal districts to evaluate the usefulness of hydrogeochemistry in mineral exploration. Mineralization occurs here mostly as Pb and Zn sulphides in metamorphic silicic–felsic and carbonate basement rocks. Groundwater chemical and isotopic data from 27 wells at Hinta and 181 wells at Kayar were interpreted using major element concentrations, their ratios to a conservative element (e.g. Cl − ), isotope systematics and thermodynamic modelling. The results indicate that the following processes take place: evaporation, evapotranspiration, water–regolith–rock interaction (e.g. weathering of carbonate, silicate, and sulphate or sulphide minerals) and water mixing. Certain gradients, rather than absolute values, may reflect proximity to mineralization; these include: (1) concentrations of ore and related elements normalized to a conservative element (e.g. Zn/Cl − molar ratios from 1 × 10 −7 up to 2 × 10 −2 ; SO 4 2 − /Cl − molar ratios from 1 × 10 −5 up to 3.3); (2) isotopic ratios (e.g. δ 34 S from +23 down to +5‰ V-CDT, with two samples at −5‰); (3) saturation indices for ore, alteration or secondary minerals (e.g. SI jarosite from −15 up to zero). Hydrogeochemistry may be a useful tool to help vector toward ore deposits in deep or covered settings.