| On the basis of the results of previous researching on the Jinding super-large Pb-Zn deposit in Lanping area, combinating the progresses and the research team achievements of "The Fine Structure and the Lithofacies Mapping of the Typical Metallic Ore-deposits in Lanping Basin" subject, and the regional geological background and geological features researching, using the methods of isotope geochemistry and fluid inclusion analysising, it is obtained comprehensively the features of isotopic composition and fluid inclusions, and the ore-forming fluid evolution in this paper. The conclusion is list as follow:The ore-forming processes of the lead-zinc deposits (orebodies) is controlled by the composite role of the nappe structure and the salt domes. It can be divided into three kinds of metallogenic types, including the disseminated type of sandstone, the breccia type of limestone, and the gypsum breccia (Structural metallogenesis and the ore-controlling by the salt dome is the first official presentation in this subject).Sulfur isotopic tracing shows that, it include three sources of the deposits based on the sulfur isotopic composition, that is the gypsum-salt mineral sulfur, the biological sulfur, and the mantle sulfur. After statistical analysising, the composition of the δ34S has the following characteristics:1) The changing characteristics of their vable among the three metallogenic types display the order of gypsum breccia-type ore> limestone breccia-type ore> sandstone infection type ore.2) The changing characteristics of their vable among the the minerals display the order of celestine> gypsum> galena> sphalerite> pyrite.3.) The changing characteristics of their vable among the four ore block display the order of Fengzishan ore block> Tuzishan ore block> Paomaping ore block> Beichang-Jiayashan ore block.With the spatial variation of δ34S value within this ore field, the limestone-type ore bodies is significantly greater than the sandstone-type orebodies.The largest value is celestite, and form two groups with pyrite, sphalerite and galena, and the fractionation of the reaction is imbalance. From the Fengzishan ore block to Tuzishan ore block,δ34S composition reflects increasing trend from the deep ore bodies to shallow ore bodies. It achieve fractionation balance under temperature and high pressure, but has the dispersion characteristics in shallow ore bodies. And it comply the same frequent changes in Beichang-Jiayashan ore block. It also reflect that the main mineralization has the superposition and multi-stage mineralization.Lead isotopic composition of the source area is span, and the main resources come from the crust, and display the mixing characteristics between the crust and mantle. It is characteristics by the lead isotopic composition of the orogenic belt.The change of δ18O vable show that ore-forming fluids is related closely to the precipitation, yet there may mixed with the deterioration water. The δ13Cco2(PDB) vable show that the CO2was from sedimentary organic matter of the oxidation and decarboxylation. Organic matter plays an important role in mineralization of the Jinding Pb-Zn deposits.Through the fluid inclusion characteristics studying, it is show that the inclusions are divided into middle-low temperature and low salinity fluid inclusions, middle-low temperature and high salinity fluid inclusions. The fluid flows through the basin to receive rich H2O-hydrocarbon fluid in the formation by the test of Laser Raman technique, and extract a large number of ore-forming elements, then converge to the Jinding ore field. In the main mineralization stage, there are complicated mixing processes between the hot brine, the CO2-rich mantle-derived fluid with different salinity and temperature. And it convergence to the favorable mineralization parts of the shallow area. The ore-forming fluid pressure values is about15×10Pa and the mineralization depth is from17to563m.The evolution of the ore-forming fluids can be described as follow:Since the period of65Ma, under the thrust-nappe locating the eastern magin of Lanping basin, justly like the "twist towel effection", extrusion the meteoric water, structural water and the ancient formation water, then constitute a mixed fluid,the initial temperature was80～200℃, neutral hot water of low-salt, low-salinity. It dissolved the NaCl、HS-from the formation, constitute a complex medium and the carrier of transport into the mineral, form the metal sulfides and sulfate anion when migration to the center of the basin. It leaching and extraction the mineralized elements of the strata continuously, with the deep source of hot water and mineral mixed together to form the ore-bearing hot brine. It’s temperature up to240～350℃, the salinity between12～18%. By long-distance migration of ore-forming fluids, its salinity,temperature, higher, richer with minerals, Reach the center of the basin clastic rocks of the Cenozoic rift basin basement nappe structure in the central belt and forward with strong deformation parts gathered, the role of organic matter, H2S and other reducing agents, and tectonic stress release, prompting metal mineral precipitation into mineral deposits. In this process, the fluid flows through the basin to receive rich H2O-hydrocarbon fluid in the formation, and extract a large number of ore-forming elements of convergence to the jinding. In the main mineralization stage, the hot brine from the depths of the CO2-rich fluid, and the different salinity fluid temperature mixed convergence to the favorable parts of the shallow mineralization. |
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