Spectral identification of pyrite mud weathering products: a field and laboratory evaluation

Abstract

Monitoring of mine waste on sulphide deposits through remote-sensing hyperspectral data contributes to the prediction of potential surface-water quality, quantitatively estimating acid drainage and metal contamination on a yearly basis. Based on previous Hymap mapping of salt efflorescence on mine wastes, various domains within the mine facilities (Iberian Pyrite Belt, Spain), selected because of their geomorphological setting, were sampled to conduct a laboratory experiment. Samples from mine-waste piles, pyrite mud tailings and river sediments were continuously exposed to the atmosphere during the summer, and spectral measurements were collected in the dark room on several days. The spectral response was monitored throughout the summer, when the pyrite oxidation process is active and the mineralogy on the surface changes continuously. The mineralogical identification capability of algorithms such as the Spectral Angle Mapper, Binary Encoding and Spectral Feature Fitting based on archive spectral libraries is discussed. Trends of mineral growth differ spectrally over time according to the geological setting. Subtle mineralogical changes are described using the spectral response and their meaning as indicators of pyrite oxidation intensity on minewaste piles, pyrite mud tailings and river sediments. Therefore, sulphide mine-waste weathering products may be used as small-scale targets for a short-term record of climate variability, providing a useful tool to assess environmental geological indicators in semi-arid areas.

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

“…The interpretation of both field and laboratory spectra, which were collected during the summer of 2009, are based on laboratory spectra obtained for samples collected in the field in 2006 [6] and 2007 [16].…”

“…The observed mineralogical changes associated with the underlying microgeomorphology suggest short-term climate variability, which follows seasonal and annual climate change trends [4,5]. Precipitates on crusts over fluvial sediments were also studied using Hymap data, coupled with detailed spectral laboratory work monitoring mineralogical changes through the dry season [6].…”

“…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. Later field and laboratory spectral investigations, which monitored mineralogical changes in mine waste from the end of the wet season through the dry season [7,8], were in agreement with these observations [6].…”

“…Around 1,700 geologically documented spectra were measured both in the field and in the laboratory from field samples collected between 2005 and 2010. Laboratory monitoring of the mine dumps and river sediments was conducted in 2007 on 30 samples, using an additional 80 geologically documented field spectra [6]. The entire flow path of the Odiel River was analyzed, including 200 field spectra, which were measured in 2005 using an ASD spectrometer, and ~500 geologically documented field spectral measurements, which were collected in September 2008 and from June 2009 to August 2009 with an ASD FieldSpec 3 Spectrometer (for thematic purposes) [15].…”

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

“…This device measures the ground reflectance spectra covering the wavelength range from 350 nm to 2500 nm. The details of the procedure for diagnosing spectra using spectral reference libraries [14,19,20] in the area have also been previously published [21]. Eighteen existing spectra from sulfide oxidation products in public domain spectral libraries [10,22] were used as references with the Spectral Analyst [7] to get a comparative score of similarity both for spectra measured in the field and HyMap data.…”