Volcanic Rocks Tectonic Environments And Metallogenesis Of Typical Mineral Deposits In Kungai Mountains, West Kunlun

The Western Kunlun Orogenic Belt is subdivided into North Kunlun terrane,South Kunlun terrane, Tianshuihai terrane and Karakoram terrane from north to south. There are lots of late Paleozoic volcanic rocks between North Kunlun terrane and the Tarim block. They expose from the north slope of Kungai mountains, to Gaizi, to Kudi and to Shangqihan, and stretch thousands of kilometers from west part to east part of the West Kunlun Mountain. The late Paleozoic volcanic rocks belt hosts a series of small and medium-sized VMS deposits. Aketashi Copper-gold deposit and Saluoyi copper deposit are two of the most representative VMS deposits.In this paper, based on systematic studies and summarizations of geological characteristics of deposit, author has taken Aketashi Copper-gold deposit and Saluoyi copper deposit as research object and done some researches on them.Combining with the researches of ore rock, metallogenic tectonic environment discussion, diagenetic and metallogenic epoch, and ore-forming material sources, the author analyzes deposit type and establishes metallogenic model. The results are listed as follows:1 Through systematic analyses of the zircon U-Pb ages of Aketashi volcanic rocks, Saluoyi basalts and Gaizi andesites, author thinks the age of volcanic rocks which had been considered to be the carboniferous should be early Permian- late Permian. The age of Aketashi basic volcanic rock is 284.6Ma, Saluoyi basalt age is263.0Ma, Gaizi andesite is 263.8Ma2 Aketashi volcanic rocks, which are bi-model spot volcanic island arcs volcanic rocks and calc-alkaline basalts, formed in the development of the early stages of the arc expansion. Gaizi andesites and Saluoyi basalts are arc basalt and island arc andesite of N-MORB properties respectively, they have the same age.Hence, we infer that, both Gai Zi andesites and Saluoyi basalts may be same sets of volcanic rock. The change of the rock geochemical characteristics from Aketashi Volcanic rocks to Saluoyi basalts to Gaizi andesites, reflects the tectonic environment of the Volcanic rock was in the transition stage from island arc to back-arc( inter-arc) basin.3 Through the studies of rock geochemical characteristics of ore rocks in Aketashi Copper-gold deposit, the lithology combination of ore rocks in AketashiCopper-gold deposit is similar to ore rocks of the western Pacific Okinawa island arc VMS deposit. Ore rocks of Saluoyi copper deposit are the pillow structure tholeiites,which is consistent with ore rocks of Cyprus type VMS.4 The exhaustive researches to Ore deposit geochemistry of Aketashi Copper-gold deposit and Saluoyi copper deposit include researches of the mineral geochemistry, ore rock geochemistry and Sulfur isotope geochemistry. All the evidences indicate source of Aketashi Copper-gold deposit ore-forming materials is volcanic rock under the cover and source of Saluoyi copper deposit ore-forming materials are mixture of volcanic rock and marine sediments.5 Based on studies of major and trace elements of sulfides, Aketashi Copper-gold deposit and Saluoyi copper deposit have obvious zoning regularity of ore bodies respectively. The ore-forming process of Aketashi Copper-gold deposit and Saluoyi copper deposit should be divided into three stages respectively. The ore-forming process of Aketashi Copper-gold deposit consists of volcanic jet“stage”、Volcanic hydrothermal deposit “stage”、Ore-bearing hot brine+ Volcanic hydrothermal deposit “stage”. The ore-forming process of Saluoyi copper deposit consists of rich ore-bearing hot brine deposit “stage”, hot brine+ volcanic hydrothermal deposit “stage”, Ore-bearing hot brine deposit “stage”.6 Sulfur of Aketashi Copper-gold deposit is from Magma jet and sulfur of Saluoyi copper deposit have many sources such as sea water sulfur, magma jet sulfur and sediment sulfur.7 Age of synsedimentary-origin VMS is consistent with ore volcanic rock. By the analysis of the volcanic rocks in zircon U-Pb age, the metallogenic age of Aketashi Copper-gold deposit is Early Permian, the metallogenic age of Saluoyi copper deposit is Late Permian.8 The Re-Os isotope age of pyrite in Aketashi Copper-gold deposit is different from the U-Pb Zircon of ore volcanic rock. Equilibrium of Re-Os isotope system in pyrite has probably been broken. Author still reserves discussion to Re-Os isotope age of pyrite, because that it maybe reveals the age of the Kudi-Aoyitake remaining Ophiolite suites.9 Compared with the typical massive sulfide deposit type, Aketashi Copper-gold deposit and Saluoyi copper deposit have obvious characteristics of volcanic massive sulfide deposits. Genetic type of Aketashi Copper-gold deposit is the Besshi type and Saluoyi copper deposit is the Cyprus type.10 Strong alteration strata between Bi-model volcanic rocks or basic volcanic rocks and Sedimentary rocks are important layers for exploring VMS in western Kunlun area, especially in Late Paleozoic layer. Mineralized formation forming iron cap and jarosite belt, is important prospecting layer.