Study On Geological Features And Ore Genesis Of Aktash And Saluoyi VMS Deposits, West Kunlun

Western Kunlun Orogenic Belt locates in the northwestern part of China.As a result of natural conditions in the West Kunlun, the relative lack of basic geological data, Also Aktash and Saluoyi (SLY) deposits are relative lack of research, and make the ore genesis of these two deposits there is a dispute,besides the unclear of deposits geological information, the key problems led to this situation is the lack of study of tecotonic elvolution of Kungaishan mountain area,.According to the main stratigraphy and regional structure of the West Kunlun, it is usually divided into three zone,namely the North Zone,the Middle Zone and the South Zone. There are a series of ophiolites locates in the North Zone, from west to east, distribute the Oytag, the Kudi and the Subasi ophiolite respectively. The Lower Carboniferous volcanic rocks of the Wuluate formation is mainly composed of tholeiites which associated with intermediate volcanic rocks are spilite - keratophyre series, The Keziliqima formation which host Akatsh VMS is composed of a group Upper Carboniferous volcanic rocks (spilite - keratophyre - quartz keratophyre) and marine sedimentary rocks.According to geochemisitry study of Lower Carboniferous basalt of this aera ,the mafic volcano of Saluoyi shown geochemistry of MORB+OIB, Chondrite-normalized rare earth-element patterns for the tholeiite associations from the SLY is similar to MORB's, and the distribution of trace elements show the characteristics of island arc basalt. Nb*2 vs. Zr vs.4-Y discrimination diagram show that it formed in the E-MORB or N-MORB background, TiO2 vs. Zr show that it formed in the MORB background, Hf/3 vs.Th vs.Ta discrimination diagram show it formed in MORB background too, however, crystallization differentiation of homologous basaltic andesite and andesite basalt is in the region of island-arc environment. Geochemical natures of those are similar to the tholeiite of the Oytag-Kudi-Subasi ophiolite. Therefore the Kungaishan volcanic rocks is likely to a part of ophiolite of the North Zone. The Upper Carboniferous volcanic rocks are characterized by its incompatible elements are depleted, It can be derived from a source region which is relative loss the incompatible elements, the geochemical characteristics of volcanic rocks indicate that this is the generation of oceanic-crust environment. Geochemistry of the basalt of SLY have complex geochemical features of mixed MORB and island arc basalt features , It is worth mentioning that the basalt of SLY show accordance with the performance of the E-MORB + IAT characteristic, Shichito modern back-arc basin that show the feature similar to that (Yasuo Ikeda and Makoto Yuasa, 1989), suggesting that the Lower Carboniferous and Upper Carboniferous volcanic rocks of the Kungaishan mountain is likely to be the product of back-arc basin in different stages.SLY VMS hosted in the Lower Carboniferous volcanic rocks of Wuluate formation, mineralization often associated with the fractionated surrounding rock,ore types of No.ⅠandⅡore boby are mainly briquette-like type , disseminated type or stockwork type, Alteration of wall rocks associated with mineralization are chloritization, silicification, epidotization, carbonation. Ore-types of No.Ⅲore body of SLY is massive type, banded type . Ore body is composed of two parts, the upper exhalative rock, the thickness of about 3m; the lower ore body is composed of the massive, banded type ore, mainly by chalcopyrite and associated with a small amount of pyrite, sphalerite, magnetite etc., the thickness of about 2m. According to mineral assemblage, the combination of primary sulfide ores can be divided into three main types: pyrite ore, pyrite - chalcopyrite type and pyrite-chalcopyrite-sphalerite ore. According to structure of ore, it can be divided into three main types: massive, banded ore and disseminated- stockwork type.Aktash VMS hosted in the acidic end-member of the Upper Carboniferous volcanic rocks, which is depleted LILS and HFSE. Ore body is layered or plate-like between the tuff and the rhyolite which Metamorphosed to quartz schist or quartz-mica schist already. Ore body is composed of two parts, the upper massive, banded ore, and the lower disseminated- stockwork ore.Metal minerals mainly pyrite, a small amount of chalcopyrite, sphalerite and trace tennantite, such as the composition of the main gangue mineral is quartz, a small amount of sericite, muscovite and calcite, etc..The fluid in the fluid inclusions of epidote-quartz rock of SLY can be divided into two groups: a group of about 4% salinity, the other group without salinity (salinity may too low to detect), two types of packages with the similar gas-liquid ratio, and estimated the ore-forming temperature range of 167.4℃-217℃by limit the pressure of fluid.Comparison of modern seaftoor polymetallic massive sulfides hydrothermal system, combined with the ore-forming geological characteristics and the tectonic setting of SLY and Aktash VMS deposits, SLY is the Cyprus-type VMS; Aktash is similar to the product of the modern LAU back-arc basin "chimneys" ,and its geological features are similar to the Noranda-type VMS except ore-forming age. The geological features of Aktshi and SLY VMS show that the Pb, Zn are most likely to come from the surrounding rock.Some indirect evidence suggesting that Cu may also be derived from igneous rock by magmatic fluid and added into the hydrothermal system eventually .