Study On Geological Characteristics And Genesis Of Qieliekeqi Iron Deposit, West Kunlun, Xinjiang Province

West Kunlun orogenic belt is bounded on north by a thrust fault adjacent with Tarim basin, on the south by Kongka fault adjacent with Kalakunlun-Qiangtang block, on the west by Taxkorgan faulted basin adjacent with Pamirs and on the east by Alton strike-slip fault. The orogenic belt is generally S-shaped, about 1000km long and 300km wide. Some researchers had devided West Kunlun belt into different units according to large-scale faults and sutures(Jiang Chunfa, 1992, Pan Yusheng, etc., 2000, Sun Haitian, 2003, Li Xingzhen, etc., 2002, XIAO Wenjiao, etc., 2000, Jin Xiaochi,etc,1999, Ding Daogui, 1996). In this paper, we proposed a new division that West Kunlun orogenic belt should be divided into North, Middle and South belt by Aoyitage-Kudi-Qimanyute and Mazha-Kangxiwa-Subashi suture zones respectively.Strata in this area develop quite complete from Proterozoic to Quaternary. Precambrian strata, the basement of West kunlun, are exposed in Middle belt, as well as other areas like Tiekelike, Taxkorgan and Qogir Mountain. Early Palaeozoic strata are widely distributed in Kudi-Aoyitage area of North belt and Mazha-Ayilixi-Bulunkou area of South belt, defined by different components containing a set of pillow basalt siliceous rocks in North belt representing a geodynamic setting of the early Paleozoic oceanic basin and Silurian clastic carbonate formation with SEDEX siderite deposits in it. Late Paleozoic strata are marked by sedimentary sequence containing basic, medium-felsic volcanic rocks, volcano-clastic rocks, clastic rocks and carbonate, exposed in Akesayi-Gaizi-Kuerliang area of North belt. Mesozoic and Cenozoic especially Triassic strata are dominated by continental margin flysch formation, widely spread in Quanshuigou, Dahongliutan-Heweitan area in southeastern of South belt.West Kunlun orogenic belt has undergone several tectonic-magmatic evolution cycles since Palaeoproterozoic. Granite intrusions of Caledonian, Variscan, Indosinian and Yanshanian are generally parallel to suture zones, NW-SE trending. Caledonian granites on both sides of Aoyitage-Kudi-Qimanyute suture and Variscan intrusions in Middle belt are formed by subduction of North Ocean; Indosinian granites, parallel to Kangxiwa suture zone, are associated with the evolution of South Ocean, Yanshanian granites exposed at southern margin of South belt are closely related to the closure of Tethyan Ocean. These granites'ages are progressively changing younger from north to south with the development of the orogenic evolution.Qieliekeqi iron deposit is located in the South belt of West Kunlun, formed in an extensional tectonic setting in Silurian. The strata exposed in the mining area are mainly Proterozoic Bulukuole Group and Silurian Wenquangou formation. Huoshibieli fault passes through the northern mining area. Permian magmatic rocks constitute eastern part of Qiukutai rock mass. Three ore bodies occur as layer, layer-like and lentoid shape, in Wenquangou formation. Among them, ore body I with five Siderite layers are hosted in marble, whileore bodyⅡin schist and ore bodyⅢin schist granulite. Ore minerals are dominated by siderite, with minor amount of pyrite and chalcopyrite, gangue minerals are calcite, ankerite, quartz, muscovite and sericite. Ore textures are mainly euhedral coarse-grained texture, hypidiomorphic fine-grained texture and ore structures are block structure, banded structure, laminated structure, brecciate structure, fine vein structure, druse-like structure and disseminated structure.Researches on geochemistry and fluid inclusions are carried out accompanied with deposit geological characteristics and ore characteristics, in order to discuss the genetic type of Qieliekeqi deposit. Major element, trace element and REE date are obtained from four siderite samples and three carbonate samples. It suggests that all samples have characteristics of minor amount of Ti, Al, Al/(Al+Fe+Mn) ratio smaller than 0.35 and Fe/Ti ratio graeater than 20, indicating siderite and carbonate are formed by chemical sedimentation. Spider diagram of trace element normalized to normal carbonate of the world shows the enrichment of B,Fe,Co,Cu,As,Tb,Ba elements that associated with hydrothermal exhalative sedimentation. (Cu+Ni+Co)×10-Fe-Mn and Cr-Zr diagrams suggest a hydrothermal sedimentation genesis of siderite and carbonate.NASS normalized REE pattern of carbonate samples shows slightly positive Eu anomaly and enrichment of LREE, which is different from typical carbonate REE pattern, implying the participation of the hydrothermal. REE pattern of siderite is characterized by distinct Eu positive anomaly and HREE depletion, which is same to world's typical SEDEX siderite deposits, suggesting exhalative hydrothermal genesis.Homogenization temperature of fluid inclusions in siliceous bands ranges from 140℃to 160℃, the salinity is a little higher than seawater, the pressure is about 12MPa and the depth of seawater is 1.2km.Three types of fluid inclusions are recognized in quartz vein formed in post mineralization stage, which is liquid-rich type, vapor-rich type and halite-bearing multiphase type, representing the involvement of magmatic and meteoric water which transformed siderites from the earlier mineralization stages to vein ores.The genetic model of Qieliekeqi iron deposit is as follows: in Silurian, deep-cycling of seawater extracted iron from marine sediments, mixed with CO2-bearing fluid degassing from magma chamber, emitted out of seafloor, mixed with alkaline seawater above and lead to the precipitation of siderite and carbonates. In Devonian, siderite layers were transformed by high-T, high-salinity magmatic fluid during orogenic movement and cross-strata vein ores precipitated later by mixing of magmatic fluid and meteoric fluid.