English

Abstract

The upper Arkansas River basin of central Colorado contains watersheds that are affected by acid rock drainage (ARD) from both natural and mining induced sources, including the Leadville mining district. Hyperspectral, high-resolution remote sensing technology is being used to characterize and map the source mineralogy of ARD, changes in downstream water quality, and the fluvial deposition of mine tailings downstream. Two case studies are presented. The Lake Creek watershed is affected by natural ARD, emanating from two sources which are sub-economic, sulfide-mineralized, porphyry systems in the headwaters of two tributaries. Extreme metal- and acid- loadings from source areas affect the watershed for 30 km downstream. The main channel of the Arkansas River, primarily downstream of the Leadville District, contains disseminated tailings distributed by fluvial processes. The tailings are a continuing source of metals loading to the river. The two watershed systems share common mineral coatings, such as jarosite and copiapite for the high-acid sections and goethite for the neutral to alkaline stream rock coatings. However, these are very different systems chemically. Lake Creek contains considerably less sulfur, and therefore, its waters tend to precipitate sulfate, oxide, and hydroxide minerals in a textbook model with changing pH zones with flow down-drainage and as neutral inflows are received. The effluents from the Leadville District wastes are sulfur-enriched, and carbonate-buffered, and consequently produce quite different sulfates such as aluminite (Al sulfate) and amarantite (Fe sulfate). Copiapite and jarosite are restricted to ephemeral backwaters and small tributaries of the main river. Hyperspectral and multispectral remote sensing data were acquired for these areas using airborne and satellite sensors. Specific iron sulfate, iron hydroxide, iron oxide, and aluminum hydroxide mineral species are only stable within certain pH ranges and are indicative of stream pH at time of deposition. Along the Arkansas River, tailings and Leadville wastes deposited within the floodplain are mapped. These techniques assist in baseline characterization, evaluation of impact of ARD on watersheds, and planning and prioritization of remedial activities.