Isotopic Tracer of Material Origin for Hydrothermal Sedimentary Rocks and Significance in Xicheng Mineralization Area
SUN Xing-li 1,2 ZENG Yun-fu 1 1(Chengdu Institue of Technology, Chengdu 610059) 2(Lanzhou Institute of Geology, Chinese Academy of Sciences, Lanzhou 730000)
By means of silicon,strontium and carbon isotope, the material origin of hydrothermal sedimentary rocks associated closely with stratiform ore body is discussed in the paper. The value of silicon isotope δ 30 Si NBS-28 for silica rocks ranges from -0.6 ‰to -0.1‰, and it is consistent with the value of sedimentary rocks. The result of silicon isotope indicates that silicon of silica rocks comes mainly from sedimentary pile under Devonian. The value of 87 Sr/ 86 Sr for hydrothermal sedimentary rocks, such as silica rocks, chloritite, baritite and carbonate, changes from 0.709 38 to 0.728 12 and lie between ocean strontium and crust strontium. The composition of strontium of hydrothermal sedimentary rocks belongs to mixed strontium and origins from recycled strontium of underlying sedimentary pile. δ 13 C PDB and δ 18 O PDB of hydrothermal sedimentary carbonate ranges respectively from -2.7‰ to 4.3‰ ,-10.0 ‰to -2.0‰, and the value of δ 13 C PDB is close to natural carbonate, but δ 18 O PDB of hydrothermal sedimentary carbonate is depleted. The result of silicon and strontium indicates that the composition of hydrothermal sedimentary rocks comes mainly from sedimentary pile underlying Devonian, but its forming manner is exogenous, as well as we can say that the hydrothermal sedimentary rock is entia of endogenetic and exogenetic.