Spatial-temperal Evolution Of The Magmatism And Mineralization In The Gejiu Supergiant Sn Poly Metal Lie Distirct And Insights Into Several Key Problems

This study targets at the magmatic rocks and Sn polymetallic ores in the Gejiudistrict, Yunnan Province, aiming to resolve the problems correlate with geodynamicsetting, ore-forming process and ore deposit model of the mineralization in the studyarea.Systematic new SHRIMP/LAICP-MS U-Pb zircon dating results indicate that allthe intrusive rocks in the Gejiu district are coeval, ranging from 78 Ma to 85 Ma.Elemental- and isotopic geochemistry of these rocks revealed that the granites in theGejiu district experienced different degrees of fractionation, and they mainly sourcedfrom crust-derived materials with minor input of mantle-derived magma. The Jiashagabbro derived from the partial melting of the lithospheric mantle with somecontamination of crustal materials, and the mafic microgranular enclaves represent theresults of magma mingling and mixing between the crustal- and mantle-derivedmagmas. Both alkaline rocks and mafic dykes sourced from lithospheric mantle butexperienced different evolution process. Based all these ideas, we concluded that anextensive interaction between mantle and crust happened in Gejiu district during LateCretaceous.Metal zonation, both in horizontal and vertical direction are clearly developed inthe Gejiu Sn polymetallic ore district, commonly from W-Be-Bi±Mo±Sn zone, toCu-Sn zone and to Pb-Zn zone. New data indicates that the homogenizationtemperature and salinity of the ore-forming fluid display continuous varations indifferent mineralization stages, which is a typical characteristics of the granite-relatedhydrothermal deposit. Sulfur isotope of various sulfide, Hydrogen and Oxygenisotopic compositions of different stage's quartz exhibit obvious difference, whichsupport the above idea from another points. Moreover, by applying of differentanalytical methods on different minerals, which include mica Ar-Ar, molybdenumRe-Os and LA-ICP-MS cassiterite U-Pb dating, new data revealed that all the orestyles in the Gejiu district formed in a short time, and all the mineralization andmagmatism ages are very similar. This means all the mineralization formed in LateCaretaceous rather than Triassic. Above all, the large scale metallic accumulation andmineralization in Gejiu district are hydrothermal origin, not syngentic.