Biogeochemical networks in the abandoned historical gold mines affecting mobilization and transport of arsenic in Kolar

Enormous water-logging in ancient abandoned mining shafts of Kolar Gold Fields (KGFs), has largely induced the leaching of sulfide-rich gold minerals contaminating the aquifer system with hazardous elements. Transport of these contaminant has posed threat to the health of the urban population of Kolar township. A detailed survey of borewells, covering radius of 10 km of the KGF was carried out during pre and post-monsoon seasons and various parameters were assessed. Almost 80% of the water samples exceeded the regulatory limits of potable water criteria with excess arsenic (As; 12-127 ??????g/L), fluoride (F; < 0.005 ??????g/L), dissolved salts ( > 500 mg/L). Water Quality Index (WQI) was used to understand the overall urban groundwater quality. At the centre of sam-pling circle core , mineral dissolution was found to be the function of pH, induced by acidophilic sulfur oxidizing bacteria . Modelling of predicted microbial metabolic pathways in metagenomics libraries using PICRUSt, indi-cated complex functional networks. High expression of siderophore proteins (> 2 cm halo in the chrome azurol test) caused Fe-sequestration, secondary Fe-mineral formation and subsequent release of As. Sulfide bearing Au-rich minerals (Arsenopyrite, Scorodite, Jarosite) were bio-weathered leading to release of H3AsO3+ at low pH, resulted in groundwater composition of Ca-HCO3 type and Ca-Na-HCO3 or Ca-Mg-Cl type.