Remote geochemical alteration proxy for mineral exploration: A case study from Lawa gold mines, India

Geochemical alteration indexes viz. carbonate chlorite pyrite index, ishikawa alteration index, hashiguchi alteration index, chemical alteration index and silicification index are conventionally used to study the degree and type of alteration. Thin section microscopic and X-ray Fluorescence analysis got similar roles for alteration study. Due to sparse and expensive sampling, the regional depiction of alteration patterns and their quantitative analysis are usually unavailable for exploration geologists. Here, we provided an alternative remote proxy-based approach to map the degree and type of alteration on a large scale, using visible-near infrared and shortwave infrared bundles of WorldView-3 imagery. The chosen study area is sparsely vegetated Lawa gold deposit in the North Singhbhum Mobile Belt, India. Partial least squares regression (PLSR) modelling of geochemical alteration indexes with reflectance spectra was used to understand the spatial variation in the degree of alterations. The remotely derived alteration indexes can be linked with field and microscopic studies of Cu-Au mineralization. We found dominance of alteration processes in the following order: ferruginisation, silicification, sericitization and chloritization. Demarcated intensely hydrothermally altered zones are present near the exposed mineralized outcrop. In addition, we identified new alteration zones with ore phases as a plausible mineralized zone.

Automated summary

This study successfully mapped the degree and type of alteration on a large scale using remote sensing methods in a gold deposit in India. The dominant alteration processes were found to be ferruginisation, silicification, sericitization, and chloritization, with intense hydrothermal alteration zones near the exposed mineralized outcrop.