Geology And Genesis Of Magmatic Rocks In The Yuhai Cu-Mo Deposit, Eastern Tianshan And Implications For Copper Mineralization

The Eastern Tianshan belt,which is the southern part of the Central Asian Orogenic Belt,has a great ore-forming potential and prospecting potential for porphyry Cu mineralization.Owing to their economic significance,numerous studies focus on the large-scale Tuwu and Yandong deposits located in the middle section of the Dananhu-Tousuquan Arc.However,the porphyry metallogenic system in the eastern section is poorly understood.Based on the detailed field geological investigation and microscopic analysis,the chronology,petrochemistry,Lu-Hf isotope,Sr-Nd-Pb isotope and EPMA composition of the magmatic rocks are analyzed in this paper.The Yuhai porphyry Cu-Mo mineralization generally occurs as disseminations and veins in potassic and phyllic alteration zones,and is predominantly hosted in the quartz diorite,granodiorite and minor syenogranite intrusions.LA-ICP-MS zircon U-Pb dating indicates that the acidic syenogranite was emplaced at 318³20 Ma,younger than the Silurian intermediate rocks.The Yuhai intrusions exhibit geochemical affinities with normal arc rocks?e.g.high Y and Yb contents,and low Sr/Y ratios?,in contrast with the subducted slab-derived adakites hosting large porphyry Cu deposits in the middle section of the Dananhu-Tousuquan Arc.The Yuhai acidic syenogranite rocks have high SiO₂??74.90 wt.%?,and K₂O??3.48 wt.%?,relatively low Mg^#and compatible element contents?e.g.Cr=0.65³.37 ppm;Ni=0.63¹.02 ppm?,and strong depletions in HFSE?e.g.Nb,Ta,and Ti?.These geochemical features,coupled with isotopic data such as low initial ⁸⁷Sr/⁸⁶Sr??0.7033?,positive?_Nd?t??4.0 to 5.9?and?_Hf?t???11?values,young Hf model ages,and variable ²⁰⁶Pb/²⁰⁴Pb ratios?18.549 to 19.465?,suggest that their parental magmas originated from the partial melting of a juvenile lower crust and mixed with some old crustal components beneath the Dananhu-Tousuquan Arc.In contrast,the Yuhai intermediate intrusions exhibit relatively low SiO₂ and K₂O contents,high Mg^#values?40⁵6?,and a wide range of?_Hf?t?values,suggesting a source of sub-continental lithospheric mantle metasomatized by slab-derived fluids and melts.Zircon trace element and plagioclase compositions further imply that the Silurian intermediate intrusion-related magma was moderately oxidized?mostly Eu_N/Eu_N*>0.6?and water-rich?⁹ wt.%?,favorable for the copper mineralization,whereas the Carboniferous syenogranite-related magma was weakly oxidized?mostly Eu_N/Eu_N*=0.3⁰.6?but also hydrous?⁶ wt.%?.Combined with the regional tectono-magmatic activities and metallogenic processes,we suggest that the Yuhai Cu-Mo deposit and associated granitoids were formed in an arc setting,and that the magma nature and its source components are the key factors constraining the distribution,scale and style of the porphyry copper mineralization in Eastern Tianshan.