SUPER-ENRICHMENT OF Se IN THE BOTTOM BLACK SHALES LOWER CAMBRIAN AT ZUNYI,GUIZHOU PROVINCE,CHINA

Abstract

Spectral analysis is one of the traditional methods to analyze Se in rocks.However,ICP-MS can provide qualitative Se data in a quick way.Based on the contrast between the quantitative Se contents by spectral analysis and the qualitative Se data by ICP-MS from a batch of typical samples of Lower Cambrian black shales at Zunyi,Guizhou Province,the authors put forward two experiential formulae to compute real Se contents in terms of the ICP-MS data:(1) for high-Se samples(Se_(ICP-MS)50×10~(-6)): Se_(real) = Se_(spectral analysis)=2.3492 Se_(ICP-MS) + 134.06;(2) For low-Se samples(Se_(ICP-MS) 50×10~(-6)): Se_(real)=Se_(spectral analysis)=5.592 Se_(ICP-MS)+0.0554.Se contents have been calculated by these formulae for the profile samples from K-bentonite strata and Ni-Mo-rich strata of the Lower Cambrian Niutitang Formation at Songlin dome,Zunyi,Guizhou Province.The results suggested that the element Se has been super-enriched in these two strata,and the average Se contents in K-bentonite and Ni-Mo strata are 473.93×10~(-6) and 2080.68×10~(-6),respectively.The excellent correlation between Se and Cu contents in K-bentonites shows that Se occurs in Cu-sulfides,implying the initial magma of K-bentonites should be attributed to trachyte,trachyte andesite,phonolite bearing noselite and(or) cancrinite.The good correlations between Se and Cu,Se and Ni,Cu and Ni in the Ni-Mo-rich strata show that Se occurs in Ni-Cu-sulfides, implying the initial mineralization sources of Ni-Mo metals are related to immiscible separation of Cu-Ni-sulfides during ultra-mafic magmatism.In light of the spatial relationship and geochemical characters of the K-bentonite strata and Ni-Mo-rich strata in Songlin dome,the authors suggest that some kind of complex alkaline ultra-mafic magamatism had occurred during the Early Cambrian at Songlin dome.