Geochemical Reactions Taking Place During Weathering Of The Lower-Cambrian Black Shales In Western Hunan,China

This research is based on the Black shale weathering section of Lower Cambrian in western Hunan,China.X-ray diffraction(XRD),Plasma mass Spectrometer(ICP-MS)and X-ray fluorescence spectrometer(XRF)are used to measure the mineral compositions major elmentes and trace elements in weathered and unweathered black shales.On the basis of analyzing the law of element activity in the weathering process of black shale,the geochemical effect of black shale weathering is discussed.The findings are as follows.(1)There are different mineral compositions of weathered rock,soil and fresh rock in the weathered section of black shale in Xiangxi,and the content of the clay minerals such as kaolinite increases gradually with the increase of weathering strength and the content of sodium feldspar and calcite.(2)In the process of weathering of black shale,MG,Ca,Na,P,Ba,Si,LOI,V,Ni,Cu,U,GE and other elements with weathering and tend to leaching loss,for lively elements,Al,Mn,Fe,K,Co,Zn,Pb,Rb,Cr,Cs,Th,GA and other elements can be leaching loss migration,Also can produce secondary enrichment,and ZR,Hf,Nb,Ta,TI,etc.are not released from the leaching rate,nor produce secondary enrichment?(3)The ? value of most of the lithophile elements is negatively correlated with the WB value,which shows that the leaching trend of these elements increases with the increase of weathering degree.The linear relationship between the ? value of most heavy metals and the WB value is not obvious,which shows that the activity of heavy metals in the weathering process of black shale is less influenced by weathering degree,and may be related to many other factors.(4)The main geochemical processes of weathering of black shale are as follows.The initial weathering layer is mainly oxidized by sulfide and organic matter,the moderate weathering layer and the strength weathering layer are mainly composed of sulfide oxidation,biodegradable mineral decomposition and silicate mineral decomposition,and the complete weathering layer and the black shale soil layer include sulfide decomposition,easy decomposition of minerals and decomposition of silicate minerals and transformation of clay minerals.The chemical differentiation in weathering process is related to the process,and the chemical homogenization of the soil process is influenced by soil organic matter,iron oxide minerals,clay minerals,phosphorus minerals and iron oxides.