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Geological, Geochemical Characteristics And Genesis Of The Chahe Copper Deposit At Yunnan Yuanjiang

Posted on:2016-07-29Degree:MasterType:Thesis
Country:ChinaCandidate:Y WangFull Text:PDF
GTID:2180330461456151Subject:Institute of Geochemistry
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The southwestern of the Yangtze block is an important copper, iron polymetallic ore district in our country with the production of Dahongshan, Lala and other large, oversize copper iron polymetallic deposit, by the attention of scholars at home and abroad. Chahe copper deposit is a typical copper polymetallic deposit in the area, but there is a lack of research on this deposit, and the research degree is not high. Restricting the understanding of the metallogenic regularity of the deposit will affect the prospecting.In order to study the geochemical characteristics and the genesis of Chahe copper deposits, supported by the cooperative item from CNNC and CNG(12120113095500) and the key research projects of China nuclear industry geological survey(201148), after conclusing previous research,based on the field work and laboratory analysis, taking surrounding rock, ore, quartz, calcite as the research object, metallogenic material sources, ore-forming fluid sources and genesis of the deposit were discussed by the analysis of trace element geochemistry, isotope geochemistry, fluid geochemistry, petrology, et al. The results are as follows.(1) Recovery of protolith according to the characteristics of major elements and rare earth elements of surrounding rock shows that, protolith of schist and quartzite are sedimentary rocks in Chahe copper deposit, and the type of samples belongs to the continental margin greywacke, which is probably formed in passive continental margin.(2) The sulfur isotope composition δ34S of chalcopyrite and pyrite shows negative value, indicating the source of sulfur in ore relates to formation.The lead isotope composition changes greatly in chalcopyrite, which has the characteristics of radioactive anomalous lead(uranium lead and thorium lead). Lead isotope shows source of upper crust in tectonic evolution diagram because of the high content of uranium and thorium in formation.So the source of lead comes from formation. The research of the trace elements and the rare earth elements indicates that metallogenic material may come from the surrounding rock and ore-forming fluid has different sources.(3) The values of carbon isotope in two-stages calcite are between magmatic carbon(-5%~8%) and marine carbon(-1‰~+2‰), showing that carbon sources may be provided by magmatic carbon and marine carbonate carbon, indicating that ore-forming fluid is mixtured by magmatic water and shallow fluid. Oxygen isotope shows a negative drift affected by precipitation.(4) Reserch on fluid inclusion of quartz shows that the ore-forming fluid is featured by medium-low temperature, moderate salinity and low density. Combining the study of carbon and oxygen isotope, composition of the fluid inclusion in quartz and the analysis of Raman spectrum, it can be concluded that the ore-forming fluid is a mixture of magmatic water, metamorphic water and meteoric fluids.(5) Genesis of Chahe copper deposit:In early Proterozoic period, the region has a series of marginal rift geosyncline, and a middle-shallow metamorphic degree volcanic sedimentary rock series riched in sodic and metal mineral were deposited. The Green weir movement at the end of Mesoproterozoic make formation preform distortion,and rock intrusive events exist,providing large-scale thermal power, activating the water of different forms in formation, gathering to the metamorphic hydrothermal fluid with high dissolution ability, mixing with magmatic water and precipitation. The mixture fluid is extracting ore-forming elements in formation during the migration process, activating and migrating ore-forming elements.When the fluid transports to the suitable environment, ore forming elements in the fluid precipitated and mineralized due to the reduced pressure and the changes of the physical and chemical conditions.
Keywords/Search Tags:Chahe copper deposits, the source of metallogenic material, the nature of the ore-forming fluid, the origin of ore-forming fluid, fluid inclusions, the genesis of the deposit
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