Metallogenic Mechanism Of Yuhai Cu-(Mo) Deposit In Eastern Tianshan, Xinjiang Uygur Autonomous Region

The Yuhai copper-(molybdenum)deposit is located at the Dananhu-Tousuquan island arc belt in eastern Tianshan,so is the Tuwu-Yandong giant porphyry copper deposits.Therefore,it is rather meaningful to study the Yuhai copper-(molybdenum)deposit because it will help summarize the metallogenic rules of this island belt,as well as enhance the ore prospecting potential.Utilizing Petrology,Mineralogy and Geochemistry methods,this study conducts a detailed study on the Yuhai copper-(molybdenum)deposit.Then,this study compares the similarities and differences between the Yuhai copper-(molybdenum)deposit and the Tuwu-Yandong porphyry copper deposits.LA-MC-ICP-MS Zircon U-Pb dating indicate that Yuhai ore-bearing quartz diorite(porphyrite)formed at(427.8 ±0.98)Ma,i.e.the middle Silurian,while the monzonitic granite formed at(318.4±0.66)Ma,i.e.the late Carboniferous.Major,trace elements data and isotopic data show that Yuhai quartz diorite(porphyrite)was not typical adakite,but Adakite-like.It is characterized by Large Ion Lithophile Elements enrichment and High Field Strength Elements depletion,Mg#>40,Sr-Nd isotopes plotting in the Island Arc Basalt zone.Therefore,we infer that it formed at island arc environment and was the product of mantle wedge which was metasomatised by subduction fluids/sediments.Combining with the tectonic evolution history,we consider that Haerlike-Dananhu island arc belt was an immature island arc in the early Paleozoic era,which was formed by southern subduction of Juggar Ocean.The ore-forming fluids of the K-silicate stage is charcterized by high temperature(307?423 ?),middle-low salinity(4.18%?10.11%);The ore-forming fluids of the quartz-sericite stage is charcterized by middle temperature(172?336 ?),low salinity(3.23%?8.55%);The ore-forming fluids of the propylitic stage is charcterized by low temperature(155?296 ?)?,low salinity(3.71%?9.08%).From K-silicate stage to quartz-sericite stage to propylitic stage,the temperature of ore-forming fluids decreased gradually and the salinities of three ore-forming stages were lower than 11%.The ore-forming fluids of the quartz-sericite stage were mainly magmatic fluids which mixed with meteoric water,while the ore-forming fluids of the propylitic stage mainly meteoric water which mixed with magmatic fluids.34S of sulfides ranged from-3.5‰?2.8‰,indicating sulfur was originated from ore-forming quartz diorite(porphyrite).The Yuhai quartz diorite(porphyrite)formed at the middle Silurian,while the Tuwu-Yandong plagiogranite porphyry formed at the Carboniferous,indicating they were formed by two differnent magmatic activities.Their geochemistry and Sr-Nd-Hf isotopes shared the similarities;both were formed in island arc environment.The source regions of the Yuhai quartz diorite(porphyrite)and the Tuwu-Yandong plagiogranite porphyry were different,while the latter was originated from direct melting of oceanic slab.The Yuhai quartz diorite(porphyrite)formed in an immature island arc,whose oceanic crust was relatively thinner;while the Tuwu-Yandong plagiogranite porphyry formed in a mature island arc,whose oceanic crust was relatively thicker and was formed on the early Paleozoic arc basement.The ore-forming fluids of the Yuhai copper-(molybdenum)deposit and the Tuwu-Yandong giant porphyry copper deposits were mixed magmatic fluids and meteoric water,and sulfur was originated from deep seated magma.Industrial ore bodies were centred on the K-silicate belt and quartz-seritic belt and the low-graded mineralization was at propylitic belt.Yuhai copper-(molybdenum)deposit had potash feldspathization belt,while the latter was not reported.