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Geology, Geochemistry And Genesis Of Kafang Copper Deposit In Gejiu, Yunnan Province

Posted on:2010-05-18Degree:MasterType:Thesis
Country:ChinaCandidate:Z X YangFull Text:PDF
GTID:2120360272488162Subject:Mineralogy, petrology, ore deposits
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Gejiu is the largest tin polymetallic ore-field over the world. It has been known as the Yanshanian granite-related deposit for long time, but recently some researchers argued that it is a syngenetic deposit formed by marine exhalation or it is a basalt-related. The genesis of deposit is an imortant problem to resolve ugly. Based on detailed field study of Kafang copper deposit, using some feasible methods such as EMPA, fluid inclusion homotemperature measuring, stable isotope measuring and radioactive isotope measuring, this thesis recognizes its characteristics and source of ore-forming fluid, source of ore-forming materials, the age of the Kafang copper deposit, and then gives a reasonable explanation about its genesis. The main conclusions that we got are as follow:1) There are two kinds of ore-body in Kafang copper deposit. One is stratiform-like ore-body, and the other is contact ore-body. Its wall rock alteration contains skarnization, actinolitization and phlogopitization.2) The analytical results of electron microprobe show that the clinopyroxene is diopside-andradite series. The end member of garnet is dominated by andradite and grossular, with minor spessartine and almandine.3) Fluid inclusion analysis indicate that the temperature of ore-forming fluid decreased significantly(260~360℃to 160~280℃), the salinity of ore-forming fluid increased slightly( 0.56 ~0.97g/cm3 to 0.78 ~1.03g/cm3), and the salinity of ore-forming fluid keeps constant basically(1.74~12.51wt% to 1.74~11.93wt%) from quarz-sulfide stage to calcite-sulfide stage. Hydrogen isotope analysis and oxygen isotope analysis show that the ore-forming fluid dominated by magmatic water in the early stage, but in late stage, it could be produced by mixing magmatic and meteoric water.4) The compositons of sulfur isotope show that sulfur of stratiform-like ore-body was derived from Triassic basalt, yet Triassic basalt and Yanshanian granite provide sulfur for contact ore-body together. The compositions of lead isotope show that the source of ore-forming matierial of stratiform-like ore-body is Triassic basalt, yet the source of lead of contact ore-body is Yanshanian granite.5) Re-Os dating of five molybdenite separated from the Kafang copper deposit gives an isochron age of 83.4±2.1Ma. This age is in good agreement with Laoka granite zircon LA-ICP-MS U-Pb age(85±0.85Ma). These ages suggest that the mineralization in the Kafang copper deposit was genetically associated to the Laoka granite.6) Based on the geochronological data of Dulong Sn-Zn deposit, Bainiuchang Ag giant deposit, Dachang tin polymetallic ore field and Wangshe Cu-W deposit and analysis of tectonic evolution of Southeast of Yunnan Province, we propose that these deposits occurred at the same geodynamic framework as a result of large scale extension during late Mesozoic in South China.
Keywords/Search Tags:skarn, EMPA, fluid inclusion, isotope geochemistry, Kafang copper deposit in Gejiu
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