DISTRIBUTION OF METAMORPHIC MINERALS IN SILICEOUS DOLOMITES ASSOCIATED WITH THE BIRCH CREEK PLUTON, WHITE MOUNTAINS, CALIFORNIA; ANALYSIS OF AVIRIS IMAGING SPECTROMETER DATA

The Birch Creek pluton, located in the White Mountains, eastern California, has an exposed area of ~15 km² and consists of two-mica granodiorite and granite with associated aplite and pegmatite that intruded Precambrian metacarbonate and metaclastic strata at ~80 Ma. Previous studies have documented high temperature metasomatism and lithophile element mineralization coeval with emplacement. In this study, hyperspectral imagery from NASA’s Airborne Visible and Near Infrared Imaging Spectrometer (AVIRIS) has been processed to map the distribution of metamorphic minerals in siliceous dolomite units of the Reed Dolomite and Deep Springs Formation near the pluton.

AVIRIS imagery was acquired on June 13, 2000 with a spatial resolution of 20 meters and a spectral range of 0.35 to 2.5 micrometers. The spectral data were atmospherically corrected and calibrated to apparent surface reflectance using field spectra. Spectrally pure pixels were identified in the imagery data and evaluated by comparison with field and laboratory spectra to derive spectral endmembers for dolomite, calcite, tremolite, serpentine, and epidote. Based on these endmembers, mineral distribution maps were generated using the Mixture Tuned Matched Filtering (MTMF) algorithm.

Serpentine is identified in the Reed Dolomite within 1500 m of the contact and may represent metasomatic infiltration or retrograde alteration of forsterite. Tremolite (locally with some serpentine) is identified as far as 3000 m from the contact and is concentrated in distinct horizons within the upper Reed Dolomite and in the Deep Springs Formation. The distances of these mineral occurrence  from the pluton are greater than previously published for the Birch Creek contact aureole and may be due in part to regional  metamorphism from the emplacement of the Jurassic (180 Ma) Beer Creek pluton. It is also possible that some pixels classified as tremolite may contain significant phlogopite or talc, which have similar spectra to tremolite.