Ore-forming Evolution And Geochemistry Character Of Typical Deposit Of The Yidun Arc In Sanjiang Region, Western Sichuan Province

As a composite orogenic belt of the Himalaya giant orogenic zone, Yidun arc, Sanjiang region (means three rivers region, i.e.: Jinsha River, Nujiang River and Lancang River), experienced a complex evolution history and characteristic magmatic activity which resulted in typical ore-distribution and mineralization. This article illustrates a tectonic evolution history including Indosinian subduction orogeny of oceanic crust, Yanshanian arc-continental collision orogeny and Himalayan intra-continental strike-sliding shearing by studying the petrology and sedimentary records in different settings. The mineralization evolution of northern Yidun arc is analyzing the space-time distribution, geological characters, fluid inclusion characters, and sulfur isotope characters, lead isotope characters,oxygen isotope of the typical ore-deposits of Yidun arc including Gacun sliver deposit, Gayiqiong lead-zinc deposit, Shengmolong lead-zinc deposit Xiasai sliver-lead-zinc deposit and Gala gold deposit. Corresponding to the tectonic evolution history, we comprehensively analyzed the tectonic-magma-fluid-mineralization, in order to explain the evolution rule of these deposits.The mineralization of northern Yidun includes three periods: The first period: intra-arc rift mineralization in late-Indosinian, the geological time is 238-210Ma.The ore deposit type mainly is of volcanic-hosted massive sulfide deposit, the ore type mainly includes dissemination ore, stratiform ore and banding ore located in the bed ore body. The typical example is Gacun silver deposit. The second period: The arc-continent collision mineralization developed during the late-Yanshanian, the geological time is 100-70Ma. eposit of this type has close relationship with the A-type granites. The typical one is Xiasai silver-lead-zinc deposit. The third period: The intra-continental strike-sliding mineralization developed during Himalayan, the geological time is after 65Ma. The strike-sliding movement in large scale, make the metallic mineral formed in early time activated, so the metallic mineral was is getting more concentrated. Gala gold deposit is a typical one.Finally, ore-forming systems including subduction orogeny ore-forming sub-system, extensive late post-orogenic ore-forming sub-system and intra-continental strike-sliding ore-forming sub-system are divided by analyzing the tectonic and ore-forming processes evolution history in Yidun.