Selenium and other trace element in phosphorites: A comparison between those of the Bayovar-Sechura and other provenances

摘要

Data of trace element composition of phosphorites are scarce and incomplete. Phosphorites of different origins can vary substantially in trace element contents. In this paper 20 trace element concentrations of 35 sample phosphorites are reported. The geographical provenance is: Bayovar-Sechura (Peru), Khouribga, Youssoufia and Boucraa (Morocco), Gafsa (Tunisia), Florida (USA), Idaho and Phosphoria Formation (USA), North Carolina (USA), Algeria, Israel, Senegal, Syria and Togo. Aqua regia extracts were used to estimate the "pseudototal" values, following standard procedures (ISO 11466, 2002) and measured by ICP-AES and ICP-MS. The ratio of medians of trace elements from Sechura versus other provenances, decreases in the following sequence: Co(9)>Mo (3.5)>Mn (2.75)>As (1.65)>Sn (1.21)>Sr (1.16)>Cr, Cu, Ni, Pb (1.02)>T1 (0.86)> Se (0.67)>U (0.53)>Cd, Th (0.5)>V (0.44)>Sb (0.38)>Zn (0.29)>Ag (0.25)>B (0.24). Using multivariate methods we have seen that there are three main clusters: a first group with Phosphoria Formation, Idaho, Youssoufia and Senegal samples; a second group with Sechura phosphorites, enriched in Co and Mo and the third consisting of the remaining samples. The highest trace element enrichment factors in decreasing order are: Cd, 386 (Idaho, USA)>Ag, 78.5 (Idaho, USA) > Se, 73.3 (Youssoufia, Morocco) >U, 46.5 (Israel) >Mo, 43 (Sechura II, Peru) >Cr, 41 (Tobene, Senegal) >B, 11.6 (Khouribga KIIC, Morocco)>Sr, 10.4 (Israel)>Zn, 10.2 (Idaho, USA). Mo enrichment is peculiar to Phosphorites of Sechura. The Permian phosphorites from Idaho and Phosphoria Formation, accumulate Cd, Ag, Se, Zn Sb, V, As, Tl and Cu. The depleted trace element assemblages of Sechura phosphorites are different from the other provenance phosphorites. Selenium and B normality is the main difference between Sechura phosphorites versus the other provenance. The whole of the normal, enriched and depleted trace element in phosphorites, both individually and in assemblages, can be a useful tool such as a discriminating fingerprint in the research of the origin of the phosphorites.