Study On Kexiaxi Cluster Of Small Intrusions And Its Copper Mineralization In The Northern Tulasu Gold Mineralization District, Western Tianshan, Xinjiang, China

Tulasu area is a gold ore concentration area consisting of Axi, Jingxi-Yelmand,etc, which are epithermal gold deposits in Western Tianshan, Xinjiang, Because thisarea is similar to the Southwestern Pacific-type island-arc, it is natural to ask whetherthere are also geological conditions in this area for searching porphyry-type Cu-Audeposit at depth or areas adjacent to these epithermal gold deposits.To this end, in this thesis we studied the Qiarbahete rock mass which was namedafter the1:200,000regional geological survey, and its copper mineralization, by fieldgeological mapping, actual geological sections, petrography, ore microscopy, elementgeochemistry, radiometric dating and isotopic geochemistry, We found the Qiarbaheterock mass was a cluster of small intrusions of Kexiaxi, containing pyroxene diorite,diorite, quartz diorite, granodiorite, diorite porphyry in crowds, and porphyry copperdeposits had already been discovered in some of the small intrusion.Rock mass in a cluster of small intrusions varies from intermediate-acid to acid,and it has the following properties: high SiO2, low MgO,calc-alkline,metaluminouswith apparent arc magma character. Comparing with the contemporaneous volcanicrocks, we found that their trace elements and evolution curves are similar, and theybelong to the comagmatic unified eruption-intrusion magmatic sequence from the lateDevonian to early Carboniferous in the setting of southward subduction of northernTianshan Ocean to the Yili plate, magma source region has the features that the mantleis enriched heterogeneously by LILE elements and LREE of the oceanic sediment orcrust contamination.Kexiaxi rock group has multi-screen and multi-intrusion features, Zircon U-PbSHRIMP dating indicates that, from357Ma to348Ma, the intrusive processes hadoccurred four or five times, and pyroxene diorite, quartz diorite, granodiorite, dioriteporphyry were formed successively, the above process was contemporary witheruption of Dahalajunshan volcanics which are ore-hosted strata of epithermal golddeposits in Tulasu area.Ore-forming fluids in the late stage of mineralization of Kexiaxi copper belongto the NaCl-H2O system with low-to-moderate temperature, low-to-moderatesalinity and low density, and originate from magmatic water and are affected byatmospheric precipitation in the late stage of mineralization, the sulfur ore has the characteristics of sulfur from deep source of magma, and copper mineralization isrelated with magmatic-hydrothermal which was formed in partial melting of theupper mantle during the subduction of oceanic crust.The geological condition of the epithermal gold deposits at Tulasu area inwestern Tianshan is beneficial to form the porphyry-type Cu-Au deposit system, and itis possible to make a breakthrough of ore prospecting on porphyry copper deposits inthis area.