A GIS and statistical approach to identify variables that control water quality in hydrothermally altered and mineralized watersheds, Silverton, Colorado, USA

Abstract

Hydrothermally altered bedrock in the Silverton mining area, southwest Colorado, USA, contains sulfide minerals that weather to produce acidic and metal-rich leachate that is toxic to aquatic life. This study utilized a geographic information system (GIS) and statistical approach to identify watershed-scale geologic variables in the Silverton area that influence water quality. GIS analysis of mineral maps produced using remote sensing datasets including Landsat Thematic Mapper, advanced spaceborne thermal emission and reflection radiometer, and a hybrid airborne visible infrared imaging spectrometer and fieldbased product enabled areas of alteration to be quantified. Correlations between water quality signatures determined at watershed outlets, and alteration types intersecting both total watershed areas and GIS-buffered areas along streams were tested using linear regression analysis. Despite remote sensing datasets having varying watershed area coverage due to vegetation cover and differing mineral mapping capabilities, each dataset was useful for delineating acidgenerating bedrock. Areas of quartz-sericite-pyrite mapped by AVIRIS have the highest correlations with acidic surface water and elevated iron and aluminum concentrations. Alkalinity was only correlated with area of acid neutralizing, propylitically altered bedrock containing calcite and chlorite mapped by AVIRIS. Total watershed area of acid-generating bedrock is more significantly correlated with acidic and metal-rich surface water when compared with acid-generating bedrock intersected by GIS-buffered areas along streams. This methodology could be useful in assessing the possible effects that alteration type area has in either generating or neutralizing acidity in unmined watersheds and in areas where new mining is planned.

Mapping Abandoned Uranium Mine Features Using Worldview-3 Imagery in Portions of Karnes, Atascosa and Live Oak Counties, Texas

“…Some of the earliest hyperspectral studies demonstrated the utility of aircraft-flown airborne visible/infrared imaging spectrometer (AVIRIS) data for characterizing the type, distribution and abundance of alteration (and some gangue) minerals in mine waste, as well as downstream ferruginous sediments and resulting acid-mine drainage and runoff (e.g., [13][14][15][16]). However, these and other multi-and hyperspectral studies reviewed by Werner et al [17] focused mainly on the land-use, water quality and human health impacts of individual mine sites, and did not necessarily focus on broader regional mapping such as across entire watersheds (e.g., [18]) or even inventorying multiple waste piles and/or mine features.…”

Metals and dissolved organic carbon (DOC) of surface waters in two adjacent watersheds in the eastern Amazon

“…Some authors have indicated that Cu, Zn, and Cd are associated with farmlands that traditionally use organic fertilizers, such as animal manure and sewage sludge (Gupta and Charles, 1999;Antonious et al, 2008). However, in the ICU headwaters, stream water can receive leached metals from riparian vegetation found on nearby slopes, where soils can be acidified by rainwater, thus contributing to metal loads by increasing the rates of bedrock dissolution (e.g., Yager et al, 2013). Overall, the influence of discharge on the metal loads was clear: decreased discharge during the dry season resulted in similar variation in water chemistry in the headwaters of ICU as in the lower reaches ( Figure 6).…”