Tracking Acid Generating Minerals and Trace Metal Spread from Mines using Hyperspectral Data: Case Studies from Northwest India

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Abstract
A flight campaign over sites in India using the National Aeronautics and Space Administration (NASA) Airborne Visible Infrared Imaging Spectrometer-Next Generation (AVIRIS-NG) was undertaken in 2016. Among the sites overflown were abandoned and active mining sites, Ambaji and Zawar, in northwestern India in the states of Gujarat and Rajasthan. AVIRIS-NG data was examined for signs of acid-generating minerals that could contribute to acid mine drainage and for distinct minerals or changes in spectral absorption features that could be signs of contamination by trace metals released by mining activities. Processing approaches used included an expert system/spectral feature fitting programme, MICA (Material Identification and Classification Algorithm), that matches absorption features in image spectra to those in user-defined library spectra. Also used were low abundance material detection approaches. Over the Ambaji site, the acid-generating mineral jarosite was mapped with the MICA approach and relative abundance was mapped with a low probability detection algorithm. The Zawar mine has a better-defined drainage which was mapped with MICA. A larger number of phyllosilicate minerals were mapped in the Tiri River drainage from the Zawar mine than were observed in similar sized rivers in other Ambaji and Zawar AVIRIS-NG flightlines. The 2.2 μm absorption feature associated with the minerals mapped in these drainages was examined to determine band parameters associated with the absorption. It was determined that minerals mapped, including montmorillonite, muscovite, and illite had a wider scatter in band parameters, principally asymmetry, but to a lesser extent bandwidth, than similar exposures of these mineral classes in the other riverbeds in the AVIRIS-NG scenes. Also mapped in the Tiri River, using a spectral matched filter, were gypsum precipitates. Field samples of this precipitate had high trace metal abundances. The combination of mapping the precipitates, such as gypsum, and an association with distorted absorption features (due to trace metal adsorption) holds the prospect for using imaging spectrometer data to assess the spread of trace metals from mining sites.
Funding Information
  • National Aeronautics and Space Administration (80NSSC17K0544)

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