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Science for Watershed Decisions on Abandoned Mine Lands: Review of Preliminary Results, Denver, Colorado, February 4-5, 1998

Mapping of Acid-Generating and Acid-Buffering Minerals in the Animas Watershed by AVIRIS Spectroscopy

By B. Dalton,¹ T. King,² D.J. Bove,³ R. Kokaly,⁴ R. Clark,⁵ S. Vance,⁶ and G.A. Swayze⁷

Visible-wavelength and near-infrared image cubes for the Animas River watershed from Hermosa, Colorado, to the headwaters at Animas Forks, Colorado, were acquired on June 18, 1996, by the Jet Propulsion Laboratory's AVIRIS (Airborne Visible and InfraRed Imaging Spectrometer) instrument in a 17-minute pass under cloud-free, late-morning conditions. These image cubes have been analyzed using the USGS Tricorder V3.4 implementation (R.N. Clark, U.S. Geological Survey, written commun., 1998), an expert system which utilizes a database of over 300 laboratory spectra of end-member minerals and mineral mixtures to generate maps of mineralogy, vegetation coverage, and other material distributions from image cubes using both the spectral and spatial information dimensions.

Major iron-bearing, phyllosilicate, clay, carbonate, alteration, and other minerals were identified along with several vegetation classes. Subtle spectral variations enabled discrimination between similar hydrothermal alteration products, resulting in highly detailed maps, which were generated and field-checked during the 1997 field season. The maps reveal widespread distributions of anthropogenic as well as large localized outcrops of natural acid-generating mineral assemblages such as pyrite, jarosites, alunites, and goethite. Additionally, distributions of alkaline minerals such as calcite and dolomite were determined with sufficient precision to indicate a relation between acid-buffering assemblages and stream geochemistry within the watershed. Preliminary maps of mineral distributions were used as aids to field work by several teams during the 1997 field season, and improved maps of minerals of interest will again be utilized in the 1998 field season. These maps will be on display at the poster session of this meeting.

¹U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225

²U.S. Geological Survey, MS 964, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (tking@usgs.gov)

³U.S. Geological Survey, MS 905, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (dbove@usgs.gov)

⁴U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (raymond@usgs.gov)

⁵U.S. Geological Survey, MS 964, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (rclark@usgs.gov)

⁶U.S. Geological Survey, MS 973, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (svance@usgs.gov)

⁷U.S. Geological Survey, MS 964, P.O. Box 25046, Denver Federal Center, Denver, CO 80225 (swayze@usgs.gov)

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