Mapping hydrothermally altered rocks by analyzing hyperspectral image (AVIRIS) data of forested areas in the Southeastern United States

• Published in: Journal of geochemical exploration 2000-04, Vol.68 (3), p.145-166
• Main Authors: Rowan, L.C, Crowley, J.K, Schmidt, R.G, Ager, C.M, Mars, J.C
• Format: Article
• Language: English
• Subjects: altered rocks; geologic mapping; hydrothermal; hyperspectral; North Carolina Slate Belt; remote sensing
• ISSN: 0375-6742; 1879-1689
• DOI: 10.1016/S0375-6742(99)00081-3

Analysis of Airborne Visible/Infrared Imaging Spectrometer (AVIRIS) data of the Carolina slate belt, a region in the Southeastern United States, has shown that certain types of hydrothermally altered rocks can be delineated based on the spectral reflectance characteristics of forest vegetation growing on them. These altered rocks are typically highly silicified and commonly associated with gold, silver, and pyrophyllite ores. Field evaluation of the resulting forest classification identified several previously unmapped areas of altered rocks, and no areas that were mapped erroneously. Distinction of the altered rocks from unaltered siliceous volcanic bedrock areas, also silica-rich, is especially significant as chestnut oak forests are characteristic of both. We conclude that the dominant chestnut oak canopy and the lack of other species that are usually present here on the unaltered rocks, result in lower apparent canopy density at the altered sites, which is expressed in the AVIRIS data by lower O–H absorption intensity. These differences in species composition and canopy architecture may be caused by one or several factors, including soil depth and physical properties, direction and steepness of slope, moisture availability, and the amount of nutrients present and their availability to the trees.