THERMAL INFRARED-SPECTRA AND IMAGES OF ALTERED VOLCANIC-ROCKS IN THE VIRGINIA RANGE, NEVADA

Airborne Thermal Infrared Multispectral Scanner (TIMS) data and laboratory thermal infrared reflectance spectra were collected from sites of hydrothermally altered andesitic volcanic rocks near Virginia City, Nevada. Alunitic, kaolinitic, illitic, and propylitic alteration types have distinct laboratory spectral curves, although the individual spectra are difficult to interpret mineralogically. TIMS emittance spectra show a general shift in the wavelength of the silicate emittance minima to shorter wavelengths with increasing intensity of alteration, owing to the increasing abundance of secondary framework and sheet silicate minerals. Strongly altered volcanic rocks are identifiable on TIMS radiance and emittance imagery.