Application of geostatistical methods to arsenic data from soil samples of the Cova dos Mouros mine (Vila Verde-Portugal)
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A total of 286 soil samples were collected in the Cova dos Mouros area. All samples were dry sieved into the <200 mesh size fraction and analysed for Fe, Cu, Zn, Pb, Co, Ni, Bi and Mn by atomic absorption spectrometry (AAS) and for As, Se, Sb and Te by atomic absorption spectrometry-hydrid generation (AAS-HG). Only the results of arsenic are discussed in this paper although the survey was extended to all analysed chemical elements. The purpose of this study was to make a risk probability mapping for arsenic that would allow better knowledge about the vulnerability of the soil to arsenic contamination. To achieve this purpose, the initial variable was transformed into an indicator variable using as thresholds the risk-based standards (intervention values) for soils, as proposed by [Swartjes 1999. Risk based assessment of soil and groundwater quality in the Netherlands: Standards and remediation. J. Geochem. Explor.73 1–10]. To account for spatial structure, sample variograms were computed for the main directions of the sampling grid and a spherical model was fitted to each sample variogram (arsenic variable and indicator variables). The parameters of the spherical model fitted to the arsenic variable were used to predict arsenic concentrations at unsampled locations. A risk probability mapping was also done to assess the vulnerability of the soil towards the mining works. The parameters of the spherical model fitted to each indicator variable were used to estimate probabilities of exceeding the corresponding threshold. The use of indicator kriging as an alternative to ordinary kriging for the soil data of Cova dos Mouros produced unbiased probability maps that allowed assessment of the quality of the soil.
Keywordsarsenic geostatistics mining area risk probability mapping soil samples uncertainty
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- Carvalho Cardoso, J, Teixeira Bessa, M, Branco Marado, M. 1971Carta dos solos de Portugal (1:1000000)Agronomia Lusitana33481602(in Portuguese)Google Scholar
- Garrett, RG. 1969The determination of sampling and analytical errors in exploration geochemistry.Eco Geol64568574Google Scholar
- Garrett, RG. 1973The determination of sampling and analytical errors in exploration geochemistry – a replyEcon Geol68282283Google Scholar
- Goovaerts, P. 1997Geostatistics for Natural Resources EvaluationUniversity PressOxford, New-YorkGoogle Scholar
- IGM1990Gold Exploration at Marrancos-Portela das Cabras. Vila Verde – BragaIGMPortugal (in Portuguese)Technical ReportGoogle Scholar
- Isaaks, EH, Srivastava, RM. 1989An Introduction to Applied GeostatisticsOxford University PressOxford561Google Scholar
- Medeiros AC, Teixeira C, Teixeira Lopes J. 1974 Carta geológica, escala 1/50000, n° 5-B e respectiva Notícia Explicativa. Serviços Geológicos de Portugal (in Portuguese).Google Scholar
- Noronha, F, Ramos, JMF. 1993Mineralizações auríferas no Norte de Portugal. Algumas reflexõesCuaderno, Lab. Xeolóxico de Laxe, Coruña18133146(in Portuguese)Google Scholar
- Varian, Techtron 1984VGA-76 Vapor Generation AccessoryVarian Techtron, VictoriaAustralia27Google Scholar