The Development Characteristics Of Evaporate And Its Metallogenic Significance In Jinding Lead-zinc Deposit, Yunnan

Jinding super-large lead-zinc polymetallic deposit is located in Lanping MesozoicCenozoic continental sedimentary basin in western Yunnan. It is the largest lead-zinc deposits in China, and receives much concern of geologists as the aggregation of large numbers of metal and non-metallic mineral. Lanping basin salt formations nearly 2000 meters, it has confirmed the existence of three evaporite buildings and six salt layers. The salt ore bodies are widely developed in the Jinding deposit and closely associated with the lead-zinc and other metal ore. But the source of the halite and its role in the lead-zinc mineralization process are not clear. Through the investigation and research on the development characteristics of mining area evaporite, combined with the characteristics of REE and trace elements and isotope geochemistry tracing, the results showed that:(1)The output shape and scale of evaporate are closely related to the dome structure of mining area: these salt ore bodies can reach larger scale, and output as single ore bodies; they can also output as salt dome structures and strong compressional deformation in the tectonic movement, so that the partial structure formed through salt thorns with strong sulfate and metal sulfide mineralization.(2)The element abundances between evaporite and surrounding rock samples have a certain consistency, on the whole performancing that, U relative enrichment; Sr enrichment obviously, and reaching very high levels; Zr and Nb loss, Hf relative loss; the average content of copper, lead, zinc and barium is low, but above the seawater and below the regional strata, indicating that its multi-source; the enrichment of Sr in metal ore is connected with the evaporates such as gypsum.(3) The total amount of rare earth elements in the evaporite and surrounding rock samples is relatively low, the chondrite-normalized REE curve shows LREE enrichment and the curve tilted to the right, existing negative Eu anomaly and Ce slight negative anomalies, showed that the provenance is consistent and relatively stable; fractionation between light rare earth and heavy rare earth elements are not obvious. Compared with the REE characteristics in Jinding ore mining: the chondrite standardized distribution curve between the evaporite and ore has a certain similarity. So they maybe have a reflecting homologous.(4)The hydrogen and oxygen isotopic composition of the ore-forming fluid features reflect that the ore-forming fluid is relate to ancient meteoric water, organic water basins and construction of water-related, and the metamorphic water may be involved in mineralization. The carbon and oxygen isotopic composition characteristics reflect that the CO2 in ore-forming fluid is related to the deposition of organic matter and marine carbonate rocks. The Pb isotopic composition characteristics indicate that the mining area metallic minerals(lead) is mainly derived from the earth’s crust.(5)The δ34S of evaporites is characterized by sulfur-rich heavy(12.6 ‰ ~ 14.6 ‰), the sulfur source is from the Triassic ancient oceanic sulfate minerals. The Sr isotope composition(87Sr / 86 Sr = 0.707813) is similar to the average value of Triassic seawater(87Sr / 86 Sr = 0.7077), and it maybe come from the Triassic marine strata. Comprehensive analysis, the mining gypsum formation mainly belongs to Triassic.(6) The δ34S of celestite ore between 11.59 ‰ ~ 15.63 ‰, combining with the characteristics of celestite distribution round plaster and microscopically the phenomenon of celestite replacement gypsum speculated that the sulfur mainly from the dissolution of gypsum. But the characteristics of sulfur isotopes in Jinding mining ore are multiple sources and sulfur-rich light(δ34S from-21.2 ‰ to-0.5 ‰), showing that the formation of the sulfide ore is also closely related to the reduction of evaporite strata.The above phenomenon indicates that the metal mineralization and accumulation are closely associated with evaporate. From the perspective of evaporite system and metal mineralization, can provide a scientific basis for further study of the mineralization mechanism of the Jinding deposit.