A. Riaza

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

Monitoring mine waste from sulfide deposits by hyperspectral remote sensing can be used to predict surface water quality by quantitatively estimating acid drainage and metal contamination on a yearly basis. In addition, analysis of the mineralogy of surface crusts rich in soluble salts can provide a record of annual humidity and temperature. In fact, temporal monitoring of salt efflorescence from mine wastes at a mine site in the Iberian Pyrite Belt (Huelva, Spain) has been achieved using hyperspectral airborne Hymap data. Furthermore, climate variability estimates are possible based on oxidation stages derived from well-known sequences of minerals, by tracing sulfide oxidation intensity using archive spectral libraries. Thus, airborne and spaceborne hyperspectral remote sensing data can be used to provide a short-term record of climate change, and represent a useful set of tools for assessing environmental geoindicators in semi-arid areas. Spectral and geomorphological indicators can be monitored on a regular basis through image processing, supported by field and laboratory spectral data. In fact, hyperspectral image analysis is one of the methods selected by the Joint Research Centre of the European Community (Ispra, Italy) to study abandoned mine sites, in order to assess the enforcement of the European Mine Waste Directive (2006/21/EC of the European Parliament and of the Council 15 March 2006) on the management of waste from extractive industries (Official Journal of the European Union, 11 April 2006). The pyrite belt in Andalucia has been selected as one of the core mission test sites for the PECOMINES II program (Cracow, November 2005), using imaging spectroscopy; and this technique is expected to be implemented as a monitoring tool by the Environmental Net of Andalucia (REDIAM, Junta de Andalucia, Spain).

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

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 mine-waste 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.

River acid mine drainage: sediment and water mapping through hyperspectral Hymap data

The Odiel River (Huelva, southwest Spain) carries acidic water originating from mine waste contamination, including massive sulphide ore deposits. As the river approaches the coastal estuary, tidal factors influence both sediment and water dynamics. As water velocity decreases, sediment load transport capacity also decreases, building river bars consisting of boulders upstream and sands downstream. Salt water near the estuary affects river water chemistry by neutralizing acidity derived from mine wastes. The occurrence of pyrite mud and hydrated iron sulphate efflorescence, precipitated from acidic waters, is plugged by marine water with chloride, which precipitates from the salt water. Hymap airborne hyperspectral data were used to evaluate tidal influence using spectral features. Grain size variations on river pebble bars, localized crusts of variably hydrated iron sulphate and oxides and cation exchange with chloride salts in the lower river segment as it enters the estuary were spectrally described and mapped. The presence of vegetation proved particularly problematic for the spectral identification of contamination products as well as the precise delineation of inundated areas along the river. The transition from dry to wet zones is the crucial challenge in using spectral imagery to identify and track contaminants in the river and along its flood plain. The use of a reference mineralogical spectral library, developed in the laboratory, requires a careful geological context evaluation to provide efficient environmental information on contamination parameters. Based on hyperspectral analyses of critical spectral features, river locations that may be a key for tracing significant, future contaminant fluctuations were identified.

Pyrite mine waste and water mapping using Hymap and Hyperion hyperspectral data

Hyperspectral low spatial resolution Hyperion data are used to map mine waste from massive sulphide ore deposits, mostly abandoned, on the Iberian Pyrite Belt. Hymap high spatial resolution data are used for crossed interpretation. Mine dams, mill tailings and mine dumps in a variable state of pyrite oxidation are recognizable. Ponds of acid water in the mine sites are spectrally outstanding and, with simple image processing procedures, mappable. In addition, acid water with different chemical composition is mappable with hyperspectral data, whether of high or low spatial resolution. A sequence of hyperspectral image processing algorithms used to produce the maps is suggested. Therefore, hyperspectral data are invaluable in giving quick hints on the quality of the rapidly changing state of the contamination generated by sulphide mine waste, enabling the authorities to activate mitigation procedures.

Spectral mapping of rock weathering degrees on granite using hyperspectral DAIS 7915 spectrometer data

Abstract Rocks are weathered by chemical and physical processes into a mixture of loose material that produces soil. Mineralogical and textural changes are involved, which can be detected by imagery through digital image processing based on rock spectral behaviour as recorded by ground and laboratory spectrometers. Different densities of vegetation cover can be mapped qualifying further evolution of the area in terms of erosion, transport and sedimentation. Hyperspectral imagery helps to map the weathering front and different degrees of weathering on granite rock through mineralogical and textural associations related to the geomorphological processes in the area on various granitic facies. Abundance of feldspar and porfidic texture on the fresh rock are the critical parameters conditioning intensity of weathering in the area. Maps spectrally elaborated gather information on lithologies, mineralogical changes produced by geomorphological processes associated to landforms, topography and climate. Such maps contribute to estimating the spatial controls of erosion, suggesting soil particle size distribution, soil aggregation, soil depth, and consequently, helping to elaborate soil loss and soil conservation maps.

Monitoring acidic water in a polluted river with hyperspectral remote sensing (HyMap)

Abstract Sulphide mine waste extensively contaminates the Odiel River (southwest Spain), releasing sulphuric acid into the water body. Acidic water in this river precipitates and dissolves variably hydrated iron sulphate in a complex geological pattern controlled by climate. Local abrupt changes in the water pH in the vicinity of highly contaminated tributaries can be mapped by means of imaging spectroscopy using hyperspectral remote sensing (HyMap) data. Also, increased pH through mixing of acidic river water with marine water can be detected when the river reaches the area influenced by sea tides. Mapping the quality of water with hyperspectral data is confounded by vegetation, either dry or wet, rooted or floating. The spectral features of acidic water measured with a field spectrometer revealed the spectral influence of green vegetation, similar to the influence of the depth and transparency of water. Careful mapping of such parameters with HyMap data must therefore precede any spectral evaluation of water related to acidity in a river course. The spectral features detectable by HyMap data and associated with pH changes caused by contamination in river water by iron sulphide mine waste, and their controls, are described and references established for routine monitoring through hyperspectral image processing.

Monitoring of superficial contamination produced by massive sulphide mine waste along the Odiel River (Andalusia, Spain) using hyperspectral data

We present preliminary results from laboratory, field and airborne hyperspectral HyMAP data acquired on a small but typical sector of the Odiel River, a river in southwest Spain which drains abandoned sulphide ore mines from the Iberian Pyrite Belt. Ochres and alluvial sediments present typical absorptions related to iron-bearing oxi-hydroxides and sulfates as well as muscovite and other minerals from the bedrock. ¿Clean¿ sediments from a nearby river were also measured as a reference for future comparisons. Image analysis shows that the spectral response is also strongly dependent on grain size and moisture content. Yearly flights are scheduled over the river to monitor changes and define standard procedures for contamination monitoring.

Climate-dependent iron-bearing morphological units around lake marshes (Tablas de Daimiel, Spain) using hyperspectral DAIS 7915 and ROSIS spectrometer data

Emerged areas around open-system lakes developing marshes are sensitive environments to climate changes. Under a semi-arid climate the sediments oxidize and dehydrate developing red colors due to iron bearing minerals. Mineral climate-dependent mixtures are spatially traced using hyperspectral imagery. Iron oxide mixtures have been mapped along differentially dehydrated units in the past 2000 years using DAIS spectrometer data. Spectral behavior interactions and masking from iron and carbonate mixtures suffering desiccation on the sands are described on the imagery and laboratory spectra. Four morphological sandy units can be distinguished, located at different height from the lake coast-line. These units are related to terraces, eolian deposits and desiccated areas, and appear as both continuous and remnant sparse encased surfaces showing different stages of landscape development. Mineralogical variations on iron oxides and hydroxides developed when sediments are exposed to the atmosphere are easily recorded in the visible and thermal infrared wavelength range in the imagery. Quantitative evaluation of soil color and related mineralogy is attempted.