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Abstract:The rich Ge-Ag-bearing Zn-Pb polymetallic deposit concentrated district in Northeastern Yunnan is in the south central part of the Pb Zn Ag polymetallic metallogenic domain in Sichuan and Guizhou of the western margin of the Yangtze block of Yunnan, is strictly controlled by fracture zone. The reserves of Zn and Pb and other metals are more than 5 million tons, ore grade is between 35%～25%. But, There are a lot of controversies about the character of the ore forming fluid and the source of ore forming material. In this paper, the sampling of the Yinchang Ag Pb Zn deposit in the ore concentration area is carried out, and the authors had some tests on the C-O-S isotope and fluid inclusion temperature measurement. Combining with previous information, the genesis of the deposit is discussed in detail in the paper. The uniform temperature of the fluid inclusions is about 175-275 ℃, which is consistent with the temperature of the mineral thermometer of the sulphide ore, and the combination of the previous research data indicates that the mineralization temperature of the Yinchang deposit is medium low temperature. The sulfur isotope range of sulfide ore in the metallogenic stage is narrow, 8.4 ‰1000-17.24‰, the barite is between 26.8‰-29.3‰, these are obviously different with mantle sulfur, these show that sulfur source mainly from the thermochemical reduction of marine sulfate. The C-O isotope data shows that theδ13C of the calcite in the metallogenic stages is between 3.6-2‰, 18O is 17-18.6‰, the 13C the surrounding rock of is 3.6-0.7‰, 18O is 19.1-23.1‰, they are closer to each other. Based on the comprehensive analysis of C-H-O-Pb-Sr and other isotopes in this metallogenic region, it is considered that the ore-forming fluid is mainly derived from the formation water of the ancient basement or the surrounding rock. When the ore source layer with the evolution of the earth's crust is located exactly at the reduction zone which is between the dive and groundwater stagnant zone, the activity of ore-forming elements is stimulated. The metal elements which is dispersed in the surrounding rock in reductive environment of alkaline dissolved into complex ion and began to move, when the external physical and chemical conditions change or the primitive fluid encounters the partial acidic atmospheric water, the sulfide deposits of industrial value are formed under the favorable lithologic spatial and structural conditions. The ore controlling space of the ore body is mainly the secondary fault or the interlayer fracture zone near the source layer. Pyritization, baritization are the main alteration minerals, the gossan is weathering products of ore surface.
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