MINERAL MAPPING OF THE UBEHEBE PEAK CONTACT AUREOLE USING SPATIALLY REFERENCED VISIBLE AND NEAR INFRARED FIELD SPECTROSCOPY

The use of visible and near infrared (Vis/NIR, 0.35-2.5 μm) field and laboratory reflectance spectroscopy is a relatively quick method to identify minerals that have absorption bands in these wavelengths. When spatially referenced field and laboratory spectra are used in conjunction with Geographic Information System (GIS), mineral distributions can be mapped in a study area. In this study over 500 georeferenced field and laboratory spectra were collected to characterize the metamorphosed siliceous dolomite of the Ubehebe Peak contact aureole in the Panamint Range, within Death Valley National Park, California.

Over four field seasons (1998 – 2001), laboratory and field spectra were collected and spatially referenced so that their locations and attributes were input into a GIS system. Analysis of the samples was based on visual interpretation with the USGS spectral library, multivariate analysis, and automated feature matching based on key Fe, CO₃, and OH absorption features. Selected samples were also thin sectioned and spectral results verified. The key minerals identified were calcite, dolomite, tremolite, serpentine, brucite, phlogopite, epidote, scapolite, and grossular. This data was then used to generate mineral distribution maps of the contact aureole for the first appearances of brucite (after periclase), serpentine (after forsterite), and tremolite. Comparison of these mineral distribution maps with previous mapping both traditional and remotely sensed, show an excellent correlation. A secondary aspect to the use of reflectance spectroscopy and GIS software is that more than one mineral can be distinguished that may not be identifiable in hand sample, thereby allowing multiple distribution maps of the identified minerals. This could allow for the identification of prograde and retrograde mineralization and possibly the patterns of fluid flow. This study shows that field spectroscopy is a useful and effective tool in conjunction with traditional mapping and petrologic methods.