The Goldfield Mining District, located in southern Nevada, has an arid climate with limited vegetation cover. It is a high sulfidation, quartz-alunite type epithermal gold deposit, hosted in silicified early Miocene intermediate volcanics, and has produced over 4,000,000 ounces of gold since coming on production in 1910.

Mineralized structures, known as ledges, lie in an arcuate zone of fractures with extensive hydrothermal alteration containing quartz, alunite, kaolinite, dickite, diaspore, pyrophyllite and illite. Some ledges are barren, whereas others are ore-bearing. It has been very difficult to differentiate the barren from the productive structures until now.

Three recent open pits lie within the Main District and expose the alteration zoning. Minerals in the central core of the structures include: dickite with silica + diaspore; alunite along the margins; and kaolinite in the argillic envelope ( which grades into illite and montmorillonite).   This study shows that gold is likely to be present whenever dickite occurs in a quartz-alunite ledge. Apparently alunite-kaolinite-quartz alone is not gold-bearing. Kaolinite is considered indicative of very low grade or unmineralized rock. The presence of dickite was determined using the PIMA™ infrared spectrometer.

Hyperspectral remote sensing techniques were used to map potential gold -bearing dickite zones at Goldfield.

The NASA/JPL 225 band AVIRIS sensor was used first. AVIRIS has 20m ground pixels and 12-15nm band widths and can therefore discriminate mineral species.

Landsat TM images show only the alteration anomalies for iron-silica and clay.