LEACHABLE U AND AU IN AN INDIAN SCHISTOSE QUARTZITE

Uranium-gold mineralization occurring together has been reported in a Lower Proterozoic sequence of schistose quartzite and quartz-chlorite- sericite-talc schist. Samples contain 0.54-1.17% U3O8 and 0.1-17 mg/kg Au. Three pairs of duplicate samples (-100 mesh) taken from the bulk ore were leached with dilute sulphuric acid and manganese dioxide over 6 h, Leachability of uranium varies from 86% to 96%. The uranium leac h residues, using thiourea as leachant, and for the first time biogeni cally generated ferric sulphate (using T. ferrooxidans) as oxidant, re corded up to 88% gold solubility. The leachability of gold in samples containing < 0.5 mg/kg Au is very poor (33-44%), indicating the occurr ence of gold in a refractory matrix - as inclusions in sulphides. Howe ver, samples with higher content of gold (> 0.5 mg/kg) have shown a hi gher leachability of up to 88%, indicating the availability of free mi lling gold. Instead of batch addition, as in the present study, ferric sulphate can be formed in situ by microbial oxidation in the gold dis solution reactor. Alternatively, ferric sulphate can be generated in a separate bacterial ferrous iron oxidation (BACFOX) reactor and contin uously supplied to the gold dissolution system for maintaining optimal oxidation potential.