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Lancang Old Plants Buried Granite Porphyry Petrology, Geochronology And Genesis Research

Posted on:2011-05-23Degree:MasterType:Thesis
Country:ChinaCandidate:H ChenFull Text:PDF
GTID:2190330332477712Subject:Geological Engineering
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The granite porphyry veins and skarm had been exposed by drilling in the 80's of the last century in Laochang of Lancang, but the research progress for the granite-porphyry Petrology, geochemistry, geochronology and its relationship with mineralization were slow and relevant results were scarcity until 2008, because the projects of exposing concealed rock body were very little and the limited core was obtained. In the implementation of "the special projects of Superseding Resources Prospecting in Crisis Mines-the program of Superseding Resources exploration for Lancang lead ore of Yunnan Province" in 2007, three granite porphyry veins and the skarns belt, the molybdenum had been revealed in the ZK153101 and ZK14824 drillings hole respectively. In 2009, many granite porphyry veins and the final hole of main rock had been exposed in ZK14827, ZK14830 hole. In order to verify the Laochang concealed granite-porphyry characteristic, this article starts with granite-porphyry rock mass geology, petrology, geochemistry, chronology and zircon typomorphic characteristic, and comprehensive study on its genetic type and the formation of tectonic setting.The concealed granite-porphyry and the related molybdenite mineralization, skarn-based that had been revealed in this area mainly distributes between exploration line 145 to 9, east of the F3 break to west of the F4 break, and the overall distribution along the F1 fault, there are approximately elevation of 900-1530m, tendency of high east and low west.The petrology research indicated that this area granite porphyry show light gray, greyish white, the porphyritic texture, massive structure. The phenocrysts are mainly composed of the orthoclase, the quartz, the plagioclase feldspar and the biotite, the matrix are composed of the equiaxed particle-fine orthoclase, quartz. The rock geochemistry studies have shown that the Laochang concealed granite-porphyry body is the meta luminum high-K calc-alkaline granite, trace elements K, La, Hf, Tb is relatively enrichment, Nb, Ta, P, Ti depletion, they has reflected the characteristics of the orogenic granitoids and the continental crust. The total REE is low, with an average of 126.56×10-6, light REE enriched slightly with (La/Yb) N of 12.01 24.85,87Sr/86Sr of 0.70835~0.71544, with an average of 0.71. The SHRIMP zircon U-Pb dating results confirm that the crystallization age of the Laochang granite porphyry is 44.6±1.1 Ma, and equivalent with the main collision terminal stage(65~41Ma) of the Cenozoic intracontinental collision orogenics. The Re-Os age (43.78±0.78Ma) of molybdenites in the Laochang Mining Area is similar to the SHRIMP U-Pb zircon age (44.6±1.1 Ma) of granite porphyry, both are formed in the early Himalayan (late Eocene). The age of molybdenites is lightly new to the rock mass age, it is basically consistent with the Basic Law of porphyry hydrothermal metallogenic period later than diagenesis stages.The zircon crystal forms of the Laochang granite-porphyry are Simple, including four main types and twenty Subtypes. The zircon crystals were composed of cylinder{110},{100}and cone{101},{211}. With{100} cylinder and{101},{211} cone being very well developed, and{101} more developed than{211}. The zircon typomorphic characteristics suggest that the zircon in Laochang granite-porphyry were formed in a low-temperature and too alkaline environment, and the Laochang granite porphyry was formed mainly by crust source petrogenesis with the addition of mantle source composition.A comprehensive analysis of chemical composition, chronology and zircon typomorphic of Laochang granite-porphyry shows that the Laochang granite-porphyry should be formed mainly by crustal remelting with the addition of mantle-derived materials, with mixing genesis. This area granite-porphyry forms in the transition period of the main collision stage to the late collision of the Qinghai-Tibet Plain Cenozoic intracontinental collision orogenics, occurred in a late Paleozoic rift zone in the west of the Lancangjiang fault in Space, the regional dynamics environment was a collision orogeny environment.
Keywords/Search Tags:Concealed granite-porphyry, Zircon SHRIMP U-Pb age, Re-Os dating, Zircon typomorpy, Geochemistry, Laochang in Lancang
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