Discrimination of iron alteration minerals in visible and near‐infrared reflectance data

Field and laboratory studies were conducted to relate the mineralogy of rock and soil samples containing hematite (α-Fe2O3), goethite (α-FeOOH), and jarosite (KFe3(SO4)2(OH)6) to their reflectance properties in visible and near-infrared wavelengths. Field reflectance measurements of regolith containing one or more of these minerals were made in the Goldfield, Nevada, mining district with a four-channel radiometer. The mineralogy and reflectance properties of regolith samples collected from these field measurement sites were then determined by laboratory studies. Mossbauer spectroscopy was used to identify the iron minerals present and their relative proportions. The reflectance spectra of samples containing hematite and goethite were characterized by a reflectance minimum near 900 nm. The location of this minimum could be accounted for by the relative proportions of hematite and goethite present in the samples. Under certain conditions it may be feasible to estimate the relative proportions of hematite and goethite on the earth's surface by determining the location of this near-infrared reflectance minimum in high spectral resolution remote sensing data. In addition, the field measurements suggest that the ratio of band passes at 852 and 982 nm may be used to distinguish qualitatively among hematite, goethite, and jarosite. Thus maps of the distribution of these minerals may be derived from scanner images acquired in those band passes.