Water quality,natural chemical weathering and ecological risk assessment of the contaminated area of vanadium ore in Yinhua River,China:Evidence from major ions and trace elements

There are abundant vanadium ores in the Cambrian strata in southern Shaanxi,China.Many years of mining activities and surface leaching have polluted the surface water to a certain extent,but the researches on the water quality characteristics and pollution degree are relatively weak.This contribution was organized to investigate the surface water quality by general parameters,including TDS,Eh,pH,DO,TOC,COD,and EC,in the vanadium ore belt(Yinhua River basin).Major ions were determined to detect the water type and natural chemical weathering,while trace elements were used to illustrate their geochemical characteristics and ecological risk assessment of heavy metals.The study found that the surface water was weakly alkaline and mainly dominated from normal to pool grade.The particle size with1000–10,000 nm of suspended particles was the main carrier of organic matter.The concentration of HCO_(3)^(-)and SO_(4)^(2-)in the anions and Ca^(2+)and Mg^(2+)ions in the cations were relatively high,and the water type was Ca-Mg-HCO_(3)-SO_(4) type.Rock weathering had a great influence on surface water,and the weathering products were mainly silicate and carbonate.Compared with the Type river,the contents of V elements showed an obvious positive anomaly,which may be affected by mining activities of vanadium ore and the annual leaching of the tailings pond.As and Cd in the surface water was polluted seriously.The integrated pollution index suggested that the surface water pollution was serious,and the main stream was more serious with the increasing tailings ponds.

Constraints of palaeoenvironment on organic matter of Benxi Formation shale and discussion on enrichment mechanism under different facies

As a hydrocarbon-rich sedimentary basin in China,the Ordos Basin has enormous potential for shale gas resources.The shale of the Upper Carboniferous Benxi Formation is rich in organic matter,however,its palaeoenvironment and organic matter enrichment mode are yet to be revealed.In this study,the geochemical characteristics of the shale of the Benxi Formation in the east-central part of the Ordos Basin were analyzed to investigate its palaeoenvironment.At the same time,the organic matter enrichment modes in different sedimentary facies were compared and analyzed.The results indicate that:1)the shale of the Benxi Formation was mainly deposited on the continental margin and strong terrestrial clastic input;2)the deposition period of the Benxi Formation shale had a hot and humid climate with high palaeoproductivity and local volcanic hydrothermal fluid,and a high sedimentation rate with the strong stagnant environment.The bottom water was in dysoxic conditions and a semi-saline deposition environment;3)multiple factors,such as palaeoproductivity,volcanic hydrothermal,redox conditions,and palaeosalinity interact to influence the enrichment of shale organic matter in Benxi Formation;4)the organic matter enrichment modes of continental,marine-continental transitional,and marine shales can be classified into three types:“production mode”,“hybrid mode of preservation and production”,and“preservation mode”,respectively.This study provides a reference for the organic matter enrichment mode,shale gas formation conditions,and core area evaluation in these marine-continental transitional shales,and also offers new guidance for exploration ideas for shale gas in different sedimentary facies.