The Magmatism And Mineralization Of Typical Fe-Sn Deposits In The Tengchong Area, Southwest Sanjiang

Aiming to studying on the igneous rocks related with the multi-metal deposits inthe Tengchong tin belt based on the previous research work, the author in this paperconducted the rounded research on the field observation, microscopic studies,petrologic geochemistry, geochronology etc. and the successive Lower Cretaceous,Upper Cretaceous and Paleogene metallogenesis, and also the research ofpetrology, geochemistry, petrogenesis, and the geodynamic settings of thenon-metallogenetic granite. Besides, the author discussed the genesis of theTengchong tin belt based on the field geology of typical deposits, fluid inclusions andthe data of ore-forming geochronology.From the data of the whole-rock major and trace elements of the igneous rocksassociated with the tin belt, and the studies of tin multi-metal metallogenesis, REEand zircon dating and Hf isotope geochemistry, the author identified three crystallizedepochs of the igneous rocks related with the Tengchong tin belt, which iscorresponding with the regional granite dating periods.1) Lower Cretaceous granite,aging from123to122Ma.2) Upper Cretaceous granite, ranging from75to70Ma.3)Paleogene granite, spanning from62to50Ma, while exposed a younger age in theLailishan,45Ma. All the data are based on the zircon U-Pb dating measured byLA-ICP-MS technique.Based on the geochemical studies, the rock mass associatedwith the Thengchong tin multi-metals share similar petrologic chemicalcharacteristics, even though formed at different dates. While, there is a smalldiscrepancy between the Lower Cretaceous granite and the late two epochs of granites,and the latter two ones have a higher similarity.All of the three epochs of the granitesbelong to the I-type granite. It’s just that they experienced different degree offractional crystallization and fluid-melt interaction, and the younger of the granite, thedegree of mineralization, differentiation and water-rock interaction. The outcome ofSr-Nd-Hf isotopes indicate that three epochs of the granites origin from the partialmelting of the igneous crust, however, the adding amount of the mantle materialsbegin to increase with the decline of their ages. From all the evidences above, at Lower Cretaceous, Upper Cretaceous and Paleogene epoch the research areasexperienced similar diagenetic process, and formed the large scale distribution of theigneous rocks, while at different tectonic settings.In this paper, Diantan iron (Sn) deposit, Dasongpo tin deposits, Lailishan tindeposit are our research objects. Based on the geology feature, fluid geochemistry andgeochronology study, we carried out a certain result. Research shows that inTengchong tin polymetallic mineralization belt, the deposits share the samegenesis,which is typical granite-related magmatic hydrothermal deposits. In addition,cassiterite LA-ICP-MC-MS U-Pb dating methods show that the ore-formation age ofthose tin deposits consistent with magmatic rocks within the error range, namely therole of Tengchong tin with tin mineralization occurred at both Early Cretaceous, LateCretaceous and Paleogene, and for the tin into magmatic hydrothermal origin,evolution of hydrothermal activity is shorter.