Geochemical mapping and estimation of background concentrations in soils of Carajas mineral province, eastern Amazonian Craton, Brazil

摘要

Companhia de Pesquisa de Recursos Minerais (CPRM, the Brazilian geological survey) has carried out geochemical surveys focused on the Carajas region, the largest mineral province in Brazil. One of these surveys covered the area of Canaa dos Carajas, where 257 soil samples, including 32 duplicate samples, were collected from the B-horizon of soils within an area of c. 3500 km(2). The <0.177 mm fraction of these samples was ground and digested with aqua regia and then analysed for 53 elements by inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The statistical treatment of the data allowed the development of multi-element geochemical maps based on interpolation techniques and the establishment of geochemical background values in soils. Different methods of obtaining the geochemical threshold values are presented and compared. The geochemical behaviour of 43 elements, including potentially toxic elements, is discussed. Geochemical background values were established using different statistical methods and the most significant results were obtained from the iterative 2 sigma technique. The influence of the geogenic contribution in the study area is largely dominant over anthropogenic effects. There is no conclusive evidence of contamination related to human activity at the time when the geochemical survey was carried out. This paper provides multi-element geochemical maps and background values in the most prominent Brazilian mining province.