The Research on Akeqiaoke Granite and Mineralization in West Junggar, Xinjiang

Abstract: West Junggar is an important metallogenic area in China, and domestic and foreign geologists have given much attention to it over the years. The article, guided by the plate tectoics and tectonic magmatism, made some new understanding about West Junggar through detailed field geological survey and indoor data analysis, which provided substantial scientific basis to the tectonic evolution of the West Junggar and porphyry copper mineralization in-depth studie. The results show that:(1) The former Akeqiaoke granite body was been breaking into three small rock bodies, including granodiorite, monzodiorite and monzogranite porphyry according to mineralogy, petrology, geochemistry data. The former two had the typical geochemical characteristics of O-type adakites, rich in Na and poor in K, high in Sr and low in Y, and the average of Mg# values were 0.44, and the average of Sr/Y was 61.57, enriched LREE, relative deleted HREE, the average of La/Yb was12.41, no Eu anomaly, high oxygen fugacity and other features. REE patterns showed a typical right-wing flat graph style, suggesting that Akeqiaoke adakites were the results of subducted slab of oceanic crust occurred through dehydration partial melting.(2) LA-ICP-MS U-Pb zircon age of granodiorite was 410.5±2.9Ma, represting the crystallization age of the rock, and it belonged to the early period of Early Devonian, which rectified the former view that the granite in Akeqiaoke formed in the late Variscan and directed subduction of the West Junggar start time of ancient oceans. At the sme time,some older ages were found in those of 25 single particle, such as Tw1-16 (502Ma), Tw1-21 (498Ma), which may be the zircon ages of ancient crust in Precambrian captured in the process of magma intrusion,suggesting that there may be ancient Cambrian crust beneath West Junggar plate.(3) Akeqiaoke monzogranite had the characteristics of A-type granite with rich K and poor Na, high silicon, low Mg and Al, and poor calcium, belonging to metaluminous series, and enrichment of high field strength elements (HFSE) strongly and depleted Sr, Ba strongly. REE distribution pattern diagram showed a typical right-wing "seagull-type". Monzogranite was in 10000×Ga/Al diagram falling into the A-type granites and belonged to A2-type granite, monzogranite formed in the context of post-collisional extension, and may arise from felsic material, but the crust during the formation was thin, and it formed in a low pressure and high temperature, and basaltic magma from asthenospheric mantle underplating promote partial melting of lower crust.(4) The genisis of Akeqiaoke porphyry copper deposits is closely related to the formation of adakites, slab melt with high-oxygen fugacity damaged mantle S-saturation, and then extract the mantle of the Cu-Au element; and slab of oceanic crust was rich in Cu-Au element, with Cl, as a strong agent, continuous activation, extract useful components from county rock, forming materials were precipitated from the fluid under appropriate conditions forming the porphyry copper deposit…
Key words: geochemistry; granite genesis; A2-type granite; adakites; tectonic setting; porphyry copper; Akeqiaoke; Xinjiang

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