Petrogenesis And Metallogenesis Significance Of The Lianhuashan Alkaline-rich Porphyry In Western Yunnan Province

The Lianhuashan alkaline-rich porphyry,located in the eastern Lanping basin,is an important part of the alkaline-rich porphyry belt in western Yunnan Province.Based on the research of the petrology,mineralogy,elemental geochemistry,zircon U-Pb geochronology and ore-bearing features,we focus on the material source,tectonic environment and metallogenesis of alkaline intrusion.The intrution is mainly composed of the quartz monzonite porphyries and amphibole quartz monzonite porphyries.The research indicates that all samples belong to shoshonitic series rock,showing the charateristics of K-rick high alkaline and Al₂O₃,but lower TiO₂.The Lianhuashan intrusion composed of feldspars,quartzs,hornblendes,biotites and so on.Electron microprobe analysis?EMPA?shows that the feldspars belong to alkali feldspars and oligoclases.The biotites in the rock are Mg-biotites.The most of hornblendes in the rock belong to actinolites and magnesiohornblendes,other hornblendes in the rock belong to edenites and hastingsites.The LA-ICP-MS zircon U-Pb dating reveals that the Lianhuashan intrution was emplaced during?35.2±0.4?^35.7±0.5Ma,i.e.,Eocene.The zircon's Ti thermometry shows that all the magmatite zircon samples have low crystallization temperatures of 562⁷88°C,which are similar to the biotites crystallization temperatures of 550⁷50^oC.The temperature suggests that the magama origin of the Lianhuashan intrusion was related with the subduction and collision.All samples are enriched in large ion lithophile elements?Rb,Sr,Th,U,Pb?and LREEs with negative Eu anomalies,but relatively depleted in high field strength elements?Nb,Ta,Ti?and HREEs.Besides,there are some inherited zircons detected from the porphyry samples,with the U-Pb ages of 1177Ma⁶8Ma and the Nb/U ratios of 1.31⁴.73,which indicates that the magmas might sourced from a metasomatic enriched mantle affected by the oceanic crust subduction,and mixed with crustal materials during its upward intruding process.The MgO and FeO^T/?FeO^T+MgO?diagram of biotites also suggests that the magmas sourced from a metasomatic enriched mantle mixed with crustal materials.Analysing the ages feature and the discrimination diagrams for tectonic settings of biotites and the geochemical characteristics,we conclude that the Lianhuashan intrusion was formed under a transitional tectonic setting from the collisional compression to post-collisional extension between the Indian and the Eurasian plates.The obvious gold,copper and plumbum mineralizations exist in the Lianhuashan alkaline-rich porphyries and the contact belt of upper Triassic maichuqing formation gray siltstones and alkaline-rich porphyries.The altered porphyries of the inside contact belt has the potential of be a gold,copper or plumbum mineral deposit.