Chronology and Geochemistry of the Ore-forming Porphyry at the Paltagexi Copper Deposit in Eastern Tianshan and Its Significance
The Paltagexi Cu deposit in Eastern Tianshan is located in the Xiaorequanzi Carboniferous island arc belt.This study conducted petrological,isotopic geochemical,and isotopic dating analyses of the Paltagexi Cu-bearing porphyry.The zircon U-Pb dating yielded an age of 338.5±1.6 Ma(MSWD=0.92,n=47),corresponding to the Late Carboniferous period.The Paltagexi granodiorite porphyry has high SiO2(69.16%-72.88%),Al2O3(13.84%-14.76%),Na2O(4.02%-4.28%),Sr(594-681 μg/g),high Sr/Y(77-84)ratios,and low Y(<9 μg/g).The rocks exhibited peraluminous to slightly peraluminous features(A/CNK=0.99-1.07),with Mg#values ranging from 37 to 43.The ore-bearing granodiorite porphyry is depleted in high-field-strength elements,such as Nb,Ta,P,and Ti,but is enriched in large-ion lithophile elements,especially light rare earth elements.These geochemical characteristics suggest that the granodiorite porphyry is an adakite.Furthermore,the(86Sr/87Sr)i ratio(0.704066-0.704178),εNd(t)(6.8-7.0)and εHf(t)(10.2-21.9)values indicate that the rocks originated from the partial melting of the juvenile lower crust.Based on the isotopic dating and geochemical results,combined with previous research,it is concluded that the granodiorite porphyry originated from the partial melting of the subducted slab under a tectonic setting related to the northward subduction of the Paleo-Asian Ocean.The resultant melt migrated upward,metasomatized the mantle wedge,and subsequently formed the granodiorite porphyry with adakite characteristics and associated porphyry mineralization.
zircon U-Pb ageadakiteisland arc volcanic rocksPaltagexi Cu depositEastern Tianshan
万方数据
维普
