MAPPING LITHOLOGICAL VARIATIONS WITH VISIBLE TO THERMAL INFRARED SPECTROSCOPY: A CASE STUDY FROM GOLD BUTTE, NV

In 1998 and 1999 Airborne Visible Infrared Imaging Spectrometer (AVIRIS) and MODIS/ASTER Airborne Simulator (MASTER) data were acquired over the Gold Butte Block, NV in order to evaluate the use of visible to thermal infrared data for geological mapping. Both AVIRIS and MASTER acquire data in the visible to shortwave infrared region of the electromagnetic spectrum (0.4-2.4 um) with AVIRIS providing more spectral detail. MASTER also acquires data in the mid infrared and thermal infrared parts of the electromagnetic spectrum (3-12 um). The Gold Butte block was selected since it contains a diverse range of igneous, metamorphic and sedimentary rocks ranging in age from early Proterozoic to Tertiary.

Both datasets were calibrated and atmospherically corrected and the relevant geophysical information extracted. Analysis of the reflectance data indicated that using either the AVIRIS or MASTER data rock and soil exposures containing clay minerals versus carbonate minerals were easily mapped. However, the AVIRIS data proved more effective at separating calcitic from dolomitic exposures and mapping Mg-OH minerals due to the greater spectral detail.

Using the emissivity data, only available from the MASTER data, it was possible to map the known rock units as well as several additional units. In particular, the emissivity data permitted further subdivision of the Proterozoic rocks and the identification of a large quartz syenite. The quartz syenite body was subsequently found to coincide with a strong aeromagnetic low anomaly. The emissivity data were then used to produce a weight percent silica map based on the known shift in the emissivitiy minimum of igneous rocks from felsic to mafic compositions. The map was field checked and agreed with field samples to a few percent.

The results indicate that by using the combined wavelength region it is possible to map a wide range of minerals and rocks as well as estimate weight percent silica from igneous rocks

Acknowledgements

The work described in this paper was carried out in part at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration.