Abstract

An airborne multispectral scanner was flown over the Gold Acres mining district, Nevada, as part of a joint NASA-Jet Propulsion Laboratory (JPL) program to determine the proper spectral bands for detecting hydrothermal alteration zones associated with mineral deposits. The Superior Oil Company acquired the computer tapes of this mission to analyze the flight data independently. A spectral ratio technique was used to enhance the information available in different spectral bands. Selection of the ratios was based on published laboratory reflectance spectra of several appropriate alteration minerals and vegetation. Several areas were chosen for field checking based on previous geologic mapping in the area. Laboratory spectrometry of field samples indicated the multispectral scanner was not calibrated on this flight and so the bands were normalized prior to determining the ratios. A color ratio composite image was created and, upon interpretation of the ratio image in conjunction with analyses of field samples, it is concluded that this technique is useful for discriminating a suite of alteration minerals which include clay minerals, iron oxides, and combinations of these. Areas of hydrothermal and supergene alteration, such as those that occur at the Gold Acres and Tenabo districts, are characterized by a combination of clays and iron oxides. Both of these districts, and altered extensions of the districts, are recognizable on the ratio image because of the enhanced discrimination of clays and iron oxides.

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