Cenozoic Post-collisional High Potassic Alkaline Intrusions And Cu-Mo-Au Mineralization In Tongchang Area, Jingping, Yunnan Province

In Cenozoic, along the west of Ailaoshan - Red River Shear Zone, formed alkali-rich （potassium） magmatic activity and large-scale Cu （Au） mineralization, under the setting of India - Eurasia post-collision extension. Jin Ping Tongchang region is the southern section of Ailaoshan with large Cenozoic high potassic alkaline intrusions and related deposits. On the basis of detailed studies of literature, we finished systematic geological survey and data analysis. Through the study of Petrology, geochemistry and stable isotopes, We believe that the intrusions in Tongchang area have the features with high potassium（K₂O>3.99%,K₂O/Na₂O=1.11%～2.64%） and alkali-rich （K₂O+Na₂O=4.61%～9.84%）,belongs to high-K alkaline rocks. Rock originated in the upper mantle, assimilation contamination by crustal (LREE enrichment, Eu anomaly is not obvious,²⁰⁶Pb/²⁰⁴Pb=18.43～18.99,²⁰⁷Pb/²⁰⁴Pb=15.48～15.73,²⁰⁸Pb/²⁰⁴Pb=38.50～39.49). The subduction of continental material metasomatic replacement lithospheric mantle, causing partial melting of mantle, that can explain the formation of magma. Compared with the high-K alkaline intrusions in Dali-Jianchuan area, we think that the high-K alkaline intrusions in Tongchang area also formed in the setting of the India-Eurasia post-collision extension.By analysising on Chang’an gold deposit and Tongchang Cu-Mo deposit, we found the relationship between alkali-rich magmatism and mineralization. On the base of detailed description of geological features, We use test means, include fluid inclusions and stable isotope, to study on the deposits. The results of fluid inclusions show that the Chang’an gold deposit formed in low temperature （200～280℃）、in - low salt （6～18%） and low fluid density （0.72～1.27g/cm3） conditions. Deposit was located on the shallow crust （0.9～2.74km）, with epithermal gold deposit characteristics. Theδ34S value of ore ranges from -13‰to 3.57‰, concentrated in -2.06‰to 3.57‰, The average of the main part is 1.55‰. The value of ²⁰⁶Pb/²⁰⁴Pb、²⁰⁷Pb/²⁰⁴Pb and ²⁰⁸Pb/²⁰⁴Pb are 18.9977～19.5748、15.7093～15.784、39.3814～40.2004. Sulfur and lead isotope values are directed into a material source with the characteristics of crust-mantle mixed source. Gold is a Comprehensive analysis of Chang’an gold deposits reveals that this is an epithermal deposits, formed under favorable structural position, in the extensional tectonic regime. The Chang’an gold deposit and Tongchang Cu-Mo deposit are closely related at distribution in time and space, the ore sources, metal elements and the physical and chemical conditions of mineralization. The two deposits together constitute epithermal - porphyry - skarn copper, molybdenum and gold mineralization system in Tongchang area, which is related with the Cenozoic high-K alkaline rock.