Using Imaging Spectroscopy To Map Acidic Mine Waste

Abstract

The process of pyrite oxidation at the surface of mine waste may produce acidic water that is gradually neutralized as it drains away from the waste, depositing different Febearing secondary minerals in roughly concentric zones that emanate from mine-waste piles. These Fe-bearing minerals are indicators of the geochemical conditions under which they form. Airborne and orbital imaging spectrometers can be used to map these mineral zones because each of these Fe-bearing secondary minerals is spectrally unique. In this way, imaging spectroscopy can be used to rapidly screen entire mining districts for potential sources of surface acid drainage and to detect acid producing 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 samples show that leachate pH is most acidic and metals most mobile in samples from the inner jarosite zone and that leachate pH is near-neutral and metals least mobile in samples from the outer goethite zone.

Monitoring the Extent of Contamination from Acid Mine Drainage in the Iberian Pyrite Belt (SW Spain) Using Hyperspectral Imagery

“…In contrast, conventional methods require tedious sample collection and chemical analysis, followed by interpolation of results through spatial mapping methods [1]. Imaging spectroscopy also allows for mineralogical diagnoses of thin ephemeral crusts, with significant concentrations of heavy metals on surfaces which are inaccessible to direct observation [2], providing an invaluable tool for environmental assessment.…”

“…Most previous mine waste mapping studies using hyperspectral data have focused on the identification of environmental evidence for predicting the extent of heavy metal contamination and acid drainage in surface water and groundwater [1,3]. Maps produced from historic Hymap data of the area studied [4][5][6] suggest that the mineralogical pattern within the mine waste and sediments is dependent on fluctuations in humidity and evaporation intensity, and could be used as a record of seasonal and annual climate changes.…”

Mapping Changes in a Recovering Mine Site with Hyperspectral Airborne HyMap Imagery (Sotiel, SW Spain)

“…Hyperspectral airborne HyMap data are used in this work to map the extension and evolution of pyrite weathering products in a mine site during the recovery of the mine facilities. Imaging spectroscopy using spectral libraries has been developed as a reliable technique for quick mineralogical analysis of mine wastes, which saves both time and costs versus conventional sample collection [2][3][4][5][6]. Additionally, it permits the mineralogical diagnosis of ephemeral thin crusts concentrating heavy metals on inaccessible surfaces [1], providing an invaluable tool for environmental evaluation and information.…”

Identification of materials related to acid mine drainage using multi-source spectra at S. Domingos Mine, southeast Portugal

“…When in contact with water and oxygen the sulphides react to oxidize and generate an acidic leachate which contains dissolved trace elements and sulphate. This acidic leachate is partly neutralised by hydrolysis reactions with the surrounding materials as the solution flows away from the active oxidation points leading to the accumulation of iron sulphates, oxyhydroxides and oxides in a spatial and temporal sequence that represents the buffering of the acidic solution as it moves away from its source (Swayze et al, 2000;Montero et al, 2005). In the pathway of the solution, it is then possible to identify mineralogical sequences, e.g.…”

“…In the pathway of the solution, it is then possible to identify mineralogical sequences, e.g. copiapite-jarosite-goethitehematite, with an increasing pH ranging from <3 to >6 or equivalent mineral`s pH indicators depending of the chemical composition of leacheates (Bigham et al, 1996;Nordstrom and Alpers, 1999;Swayze et al, 2000;Montero et al, 2005;Smith et al, 2006). Using IS principles it is possible to identify the unique spectral absorption characteristics of such secondary iron minerals (Clark, 1999).…”