Using imaging spectroscopy to map acidic mine waste

The process of pyrite oxidation at the surface of mine waste may produce ac idic water that is gradually neutralized as it drains away from the waste, depositing different Fe-bearing secondary minerals in roughly concentric zo nes that emanate from mine-waste piles. These Fe-bearing minerals are indic ators of the geochemical conditions under which they form. Airborne and orb ital imaging spectrometers can be used to map these mineral zones because e ach of these Fe-bearing secondary minerals is spectrally unique. In this wa y, imaging spectroscopy can be used to rapidly screen entire mining distric ts for potential sources of surface acid drainage and to detect acid produc ing minerals in mine waste or unmined rock outcrops. Spectral data from the AVIRIS instrument were used to evaluate mine waste at the California Gulch Superfund Site near Leadville, CO. Laboratory leach tests of surface sampl es show that leachate pH is most acidic and metals most mobile in samples f rom the inner jarosite zone and that leachate pH is near-neutral and metals least mobile in samples from the outer goethite zone.