西成矿化集中区热水沉积岩物质来源的同位素示踪及其意义

利用硅同位素、锶同位素和碳氧同位素,对西成矿化集中区与矿体紧密伴生的热水沉积岩的物质来源进行了探讨。硅质岩的硅同位素δ3 0 SiNBS -2 8=- 0.6‰～ - 0.1‰,硅主要来源于下伏沉积岩;热水沉积岩的锶同位素比值87Sr/ 86Sr变化于 0.70 938～ 0.72 812之间,位于海洋锶和陆壳锶之间,为混合锶,其锶主要来源于下伏沉积地层柱;碳同位素组成略低于正常沉积碳酸盐岩,碳主要来源于下伏沉积地层柱在循环碳,同时又受其它来源碳的影响。同位素研究结果表明,热水沉积岩的组成物质主要来源于下伏沉积地层柱 (地壳内部 ),形成方式主要是外生沉积作用,即热水沉积岩是内生作用与外生作用共同作用的结果,是内外生矛盾的统一体。

Isotopic Tracer of Material Origin for Hydrothermal Sedimentary Rocks and Significance in Xicheng Mineralization Area

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.