Study On Regional Metallogenic Laws In Western Kunlun Orogenic Belt

Western Kunlun orogenic belt is located in the northwest margin of Qinghai-Tibet plateau, and it accompanies with abundant mineral deposits and becomes an important part in the metallogenic belt of the north margin of the plate. Based on regional geodynamic settings, metallogenic theory, metallogenesis, and combing metallogenic geodynamic settings, regional metallogenic analysis with typical deposits analysis, the author studies metallogenic geodynamic settings, metallogenesis and ore-controlling factors, then builds genetic types and metallogenic models for different mineral deposits, finally synthesizes metallogenic laws and delineates prospective areas.According to regional metallogenic settings, it was shown that tectonic evolution of the study area underwent long and complex crust evolution, including Archean continental core formation, subduction, collision and intracontinental tectonization. The predecessors considered the Kudi ophiolite and Qimanyute ophiolite are important evidences for breakup ocean and retroarc ocean basin. But the author thought they are product of paleo-ocean that developed to mature. The location of Kudi ophiolite is not the suture line of North Western Kunlun Ocean collision, but rather the obduction place by compressing later. By analysis of geochemical characteristics of Meso-Neo Proterozoic volcanic rocks, Changcheng system and Jixian system basic volcanic rock formed in mid-ocean ridge and ocean island environment. Determination of Aketashi and Saluoyi VMS deposits shows that there formed in mid-ocean ridge environment. It was proved that it was a paleo-ocean rather than a taphrogenic trough between western Kunlun and Tarim blocks in paleoproterozoic. The predecessors thought that the study area breakup began at proterozoic from Tarim plate, with same basement. Comparative study shows western Kunlun block is not a microplate from Tarim plate, but a unique Archean paleocontinent with unique geological structural evolutional history. It was separated by bilateral paleo-ocean, which was so-called"North Western Kunlun Ocean"and"South Western Kunlun Ocean".By researching geochemistry, geochronology and structural environment of granites of every era in the middle magmatic zone in westeren Kunlun belt, especially Caledonian and Hercynian granite, it was thought that east part of oceanic plate of North Western Kunlun Ocean subducted toward south and north continents scince 510-480Ma(Cambrian). These two continents collided during 440-430Ma(Early Silurian)and amalgamated completely until 410Ma(Early Devonian), while there is still an ocean in the west part of western Kunlun belt. The west plate of North Western Kunlun Ocean began to subduct bilaterally in early Hercynian, and bilateral continents collided until 270Ma (Permian)which means the history of North Western Kunlun Ocean is end. The evolution that there is a scissor-style .Based on above conclusion, it was considered that there are four stages for geodynamic evolution of western Kunlun orogenic belt, i.e.①Formation of western Kunlun paleocontinent;②Interior orogenesis----evolution and closure of North Western Kunlun Ocean;③Marginal orogenesis----evolution and closure of South Western Kunlun Ocean;④Uplifting----later evolution of western Kunlun orogenic belt.Making structural-magmatic activities and metallogenesis as mainline, the author studies petrology, geochemistry and geochronology for intrusive rocks of each era in western Kunlun belt. By LA-ICP-MS zircon U-Pb dating to biotite quartz monzonite and granite aplite in Busilajin Cu-Mo deposit in Datong town, diorite porphyrite in Bandier in Tashikuergan town, and alkaline granite in Siruuyidieer, and molybdenite Re-Os dating to Busilajin Cu-Mo deposit, the author gets lots of high precision ages, i.e. 449Ma, 446Ma, 239.8Ma, 13Ma. 446Ma and 449Ma represent post orogenic granites of Caledonian orogenic belt. Orogenesis began at east part in this era, which is a product extended environment during diapause of subduction. 239.8Ma represents early Indosinian magmatic thermal activity. 13Ma stands for results of Pamir tectonic knot. 439Ma of molybdenite Re-Os dating means there are metallogenic event in Caledonian in western Kunlun area.By studying to geological settings and metallogenic factors of some gold deposits in the study area, the author first proposes Huangyangling Sb(Au), Paximu Au, Yeerqianghe Au and Muji Au deposits belong to orogenic gold deposits. It was considered that mineralization of orogenic gold deposits may consecutively happen from low-mesothermal, epizonal (Huangyangling Sb(Au), Paximu Au, and Yeerqianghe Au deposits) to mesozonal (Muji Au deposit) with analysis of metallogenic temperature and depth from fluid inclusion researches. Then a crustal continuum model of orogenic gold deposit in the study area was proposed by the author.It was thought that Tamu and Kalangu Pb Zn deposits belong to not MVT type Pb-Zn deposits but rather low-mesothermal vein-type one related to basic diabase dyke, by studying on geological settings, mineralized and alterated characteristics and magmatic natures for Tamu and Kalangu Pb-Zn deposits in the north of western Kunlun orogenic belt, and analyzing the metallogenic physico-chemical conditions where the salinity of fluid is 3.45wt%NaCl and density is 0.90g/cm3.The exhalative sedimentary deposit was divided into VMS ones and poor-sulfide type ones by their characteristics. According to the exhalative sedimentary metallogenic characteristics on the Carboniferous seafloor in the north of western Kunlun belt, the author considers Aketashi and Saluoyi Cu deposits belong to VMS exhalative sedimentary deposit. Saluoyi Cu deposit belongs to Besshi type VMS deposit, and Aketashi Cu deposit may be Koroko-like type. By studying fluid inclusions in Heiqia and Qiliekeqi siderite deposits, it was shown that both two deposits are exhalative sedimentary-hydrothermal fluid reconstructed deposits, and affected by later magmatic hydrothermal fluid which enriched mineralization. While the author considers that sodic-feldspar siliceous rock and carbonate are all exhalative sedimentary rocks, which are evidences for exhalative sedimentary deposits.By studying geological characteristics, metallogenic fluid, geochronology of Busilajin Cu-Mo deposit, it was thought that this deposit belongs to low-temperature hydrothermal vein-type Cu-Mo deposit. It formed 435Ma according to molybdenite Re-Os dating first time i.e. middle Caledonian that is posterior to diagenetic age. The molybdenite may form in low-temperature condition because the homogenization temperature is 147～172℃based on fluid inclusion studying in ore-bearing quartz.The author builds a metallogenic model of western Kunlun orogenic belt and synthesizes metallogenic laws according to researches of typical deposits, isotopic geochronology, metallogenic geochemistry and metallogenesis based on metallogenic dynamic evolution. And on the basis of metallogenic model, ore prospecting symbols and conditions of large scale ore field, the author proposes 6 prospective areas, which may be scientific evidences for further ore prospecting and exploration in this study area.