MULTI-PLATFORM VIS/SWIR HYPERSPECTRAL APPROACH TO THE STUDY OF ACID MINE DRAINAGE FROM SMALL ABANDONED MINES

Multi-platform hyperspectral VIS/SWIR data was applied to the study of Acid Mine Drainage (AMD) in two relatively small abandoned mines, Newton and Spenceville copper mines, in the massive sulfide belt of the foothills of the Sierra Nevada, California. Data ranged from high-altitude satellite and airborne imaging reflectance spectroscopy to low-altitude helicopter-borne and ground based reflectance spectroscopy integrated into digital mapping systems. The focus of this approach was mapping of predominant surface mineralogy for detection of AMD and the study of the geochemical processes governing its generation and evolution. Interpretation of high altitude spectra in combination with GIS analysis focused on mapping of regional geological features and lithology, assessing acid producing and neutralization processes and the impact of AMD on adjacent land/water. Detailed analysis of high-altitude hyperspectral data by spectral band matching yielded district-wide maps of AMD-buffering and AMD-indicator materials, offering a first view of geochemical processes likely to take place at the sites. Detailed site mapping using low-altitude hyperspectral reflectance spectroscopy integrated into digital mapping followed the high-altitude study. This phase of the study focused on detailed mapping of secondary iron minerals with emphasis on local sources and neutralization of AMD by integrating spectroscopy and real-time digital mapping at on two platforms: helicopter and ground based. This was made possible by synchronous use of a portable reflectance spectrometer, a digital mapping system with DGPS/laser range finder support, and a fast spectral mineral identification algorithm written for this application. The fast identification algorithm (FSTSpecID) timely processes hyperspectral data and provides maps of AMD-generated secondary minerals based on the characterization of the broad absorption band caused by electronic transitions of in iron minerals. Low-altitude maps allowed for detailed analysis of small, heterogeneous, inaccessible waste piles. Linking of mineral patterns, local erosion, weathering, evaporation, and the presence of very low pH efflorescent sulfate salts allowed identification of previously undetected sources of AMD.