Improved Automated Identification and Mapping of Iron Sulfate Minerals, Other Mineral Groups, and Vegetation using Landsat 8 Operational Land Imager Data, San Juan Mountains, Colorado, and Four Corners Region

Abstract

Multispectral remote sensing data acquired by the Landsat 8 Operational Land Imager (OLI) sensor were analyzed using a new, automated technique to generate a map of exposed mineral and vegetation groups in the western San Juan Mountains, Colo., and the Four Corners Region of the United States. Band ratio results were combined into displayed mineral and vegetation groups using Boolean algebra. New analysis logic has been implemented to exploit the coastal aerosol band in Landsat 8 OLI data and identify concentrations of iron sulfate minerals. These may indicate the presence of near-surface pyrite, which can be a potential nonpoint source of acid rock drainage. Zoned occurrences of iron sulfate minerals in areas surrounding and down gradient of known sources of pyrite have been mapped using this technique. They show high correlation with occurrences of jarosite-bearing mineral assemblages, as mapped using airborne imaging spectrometer data and supporting field verification surveys. Mapping the occurrence of iron sulfate minerals produced by the weathering and oxidation of pyrite in exposed hydrothermally altered rocks can also provide an important indicator of the genetic environment of alteration and the associated mineral deposit type. The automated analysis methodology is being employed to rapidly and cost-effectively generate maps of large regions of the United States in support of U.S. Geological Survey mineral resource and mineral-environmental assessments. This map, which includes the ERDAS IMAGINE (.img) thematic raster format in the data release, has been attributed by pixel value with mineral and vegetation group classification data, which can be queried in most image processing and GIS software packages.

Remote Sensing Survey of Altiplano-Puna Volcanic Complex Rocks and Minerals for Planetary Analog Use

“…Landsat 8 OLI has only one band in the 2.0-2.5 µm range; thus, the distinction among clay, sulfate, and mica was not made; this was instead performed with the more appropriate hyperspectral EO-1 Hyperion. The iron-sulfate mineral index captured the strong absorption of light in Band 1 (0.43-0.45 µm) in comparison to Band 2 (0.45-0.51 µm), which is not a characteristic of other iron-bearing minerals (oxide and hydroxide minerals [36]). As with index 4, the green vegetation band ratio was subtracted from the 2/1 band ratio to further mitigate effects of vegetation.…”

“…First, we applied the decorrelation stretch (DCS [35]) technique to obtain a general idea of the variabilities within the scene (Figure A1c). Next, band ratios based on Rockwell et al [36] were computed to map iron-bearing and alteration mineral groups (Table 1). Ferric iron 1 index captures the stronger absorption of blue/green light with respect to orange/red light that arises from charge transfer, and it is widely used to map ferric iron minerals [37].…”

“…Remote Sens. 2022, 14, x FOR PEER REVIEW 4 of 26 et al [36] were computed to map iron-bearing and alteration mineral groups (Table 1).…”

“…Landsat 8 OLI band ratios from Rockwell et al[36] used to characterize iron-bearing and alteration minerals.…”