Remote Detection of Hydrothermal Alteration Zones Using WorldView-3 VNIR-SWIR Reflectance Data: A Study from Lawa Gold Mines, India

WorldView-3 sensor with higher spectral and spatial resolution provides greater opportunity to map the hydrothermal alteration zones. Advancement of remote sensing techniques have been manifold in the field of mineral and alteration mapping enabling subpixel level mineral identification. However, remote mapping of alteration zone in vegetated terrain still remains challenging. The present work is aimed at mapping of hydrothermal alteration zones in a sparsely vegetated terrain using high resolution WorldView-3 data. Minimum Noise Fraction (MNF), Spectral Information Divergence classification (SID) and Selective Principal Component Analysis (SPCA) techniques are used collectively for mapping different alteration zones. The alteration minerals mapping has been further supported by laboratory spectroscopy methods, field observation and petrographic microscopic study. A comprehensive analysis on the ability of different techniques to detect the alteration zone in a sparsely vegetated terrain named Lawa mines, North Singhbhum Mobile Belt has been documented in this paper. Image-derived reflectance spectra corresponding to field locations have been used for SID classification and an accuracy of 78% is obtained for the current study. The vegetation covered areas have been classified as vegetated using both MNF and SID techniques. Besides, the SPCA results have better highlighted all the alteration zones present in the area by suppressing the vegetation effects. While MNF provides a broad overview of the spectrally different litho-units, SID classification gives more detailed pixel wise classification of various rock types present and furthermore SPCA method highlights various alteration types present in the area. Therefore, combined MNF, SID and SPCA can provide a detailed alteration map of the sparsely vegetated region. Ferruginisation, silicification, sericitization, and chloritization types of alterations primarily observed in both mesoscopic and microscopic scale. Ferruginisation and silicification alteration are predominant types among all. These alterations are also evident in hosting mineralization of Au, Ag, Cu and Rare Earth Elements. Mineralization is primarily associated with various rocks, such as quartz vein, quartzite and talc chlorite sericite schist.

Automated summary

This study successfully mapped the distribution of hydrothermal alteration zones in sparsely vegetated terrain using high-resolution WorldView-3 data and a combination of remote sensing techniques. The presence of alteration zones was further confirmed through laboratory spectroscopy methods and field observations. The combined use of MNF, SID, and SPCA techniques provided a detailed alteration map.