Study On The Metallogenic Settings And Metallogenic Regularity Of Copper Deposits In Western Awulale Mountain, Xinjiang

Including huge thick strata of continental volcanic rocks of upper CarboniferousSeries-Permian, the Western Awulale Mountain have many copper deposits which are relatedto continental volcanism. Based on the petrology, geochemistry and geochronology researchof Permian volcanic rocks, subvolcanic rocks and intrusive rocks, this thesis completed fluidinclusion and stable isotope research for five typical copper deposits in this district. Accordingto these research works, the copper deposits types are reclassified, metallogenic mechanismand environment are analyzed. Moreover, this thesis summarizes the the metallogenicregularities of these copper deposits, and discusses the mineralization of this district. Themain innovation and new viewpoints are summarized as following:1. The typical bimodal volcanic rocks(basalts-rhyolite), subvolcanic and hypabyssalintrusive rocks of lower Permian in western Awulale Mountain are alkali and meta-alkaliseries which are generally characterized with higher Na2O and Al2O3contents, lower TiO2content and alkali-rich. Different rock types have different geochemical features which reflectthat they have diverse origin and magma sources. The basaltic magma is derived fromweak-depleted mantle. The subvolcanic rocks possess the characteristcs of S and A-typegranite which are production resulted from remelting of Precambrian basement rocks(oldcrust). Intermediate-acid intrusive rocks are I-type granite and related to the partial melting ofbasaltic lower crust, but many Carboniferous island-arc igneous rocks(new crust) are addedinto its magma.2. LA-ICP-MS U-Pb dating of magmatic zircons from the four granitic rocks in westernAwulale Mountain yield weighted average206Pb/238U ages from278.2±0.8Ma to312.9±1.3Ma, which reveal that the intrusion of magma in late Paleozoic occure from lateCarboniferous to early Permian. Some residual zircon cores have several groups ofCarboniferous age, indicating that the source of the granitic rocks likely containsCarboniferous island arc magmatic rocks.3. U-Pb dating of metamorphogenic zircons from the diabase yield207Pb/206Pb ages from1781.2±7.7Ma to1807.1±5.1Ma and weighted average age of1794.8±4.7Ma which is theoldest age of zircons in western Tianshan Mountain. Similarly, the age results of rhyolite in109ore district include two groups of ages from1739Ma to1961Ma and750Ma to1254Ma.These age results of metamorphogenic zircons are consistent with the Nd model ages,magmatic zircon ages and metamorphic ages of Precambrian metamorphic rocks in western Tianshan Mountain, which indicate that the crystalline basement has been formed in latePaleoproterozoic and the origin of subvolcanic rocks are related to these Precambrianbasement rocks.4. The copper deposits are reclassified to subvolcanic rock-type(SVR) and hydrothermalvein-type copper deposits(HTV). The SVR copper deposits occur in bottom and top strata oflower Permian Series; the orebodies are closely controlled by subvocanic rocks and faults;metal and vein minerals are less; the wall-rock alteration are generally weak; the metallogenicfluid are small size and single source which originate from a dry environment; theore-forming minerals are from deep magma. The HTV copper deposits occur near theinterface of top strata of lower Permian Series and bottom strata of intermediate PermianSeries; the metallogenic fluid are middle-lower temperature and salinity which is mixture ofvolcanic hydrothermal and circulated meteoric water; the ore-forming minerals source iscomplexity which include crustal and mantle source.5. The duration of the late Paleozoic rift evolution perhaps is short and the early Permianis its main stage in western Awulale Mountain. At the end stage of early Permian, sea basinhas been formed shortly in small scale. The rift evolution has ended because the tectonicsetting is changed from extension to compression after middle Permian. So, the rift is smallscale and immature. The regional mineralization is spatially consistent with the rift evolution.The continental volcanic generate numourous volcanic rocks and sedimentary strata whichconstitute the ore-source bed. The formation of different Cu deposit-types in different positonare controlled by the different mineral sources, structure and strength of continental volcanismcaused by the Permian rifting.6. The rift system has a small stretching extent in western Awulale Mountain whichcause the differentiation and evolution of magma activities are weak, accordingly, the igneousrocks are lack of multi-phase and hypabyssal or super-hypabyssal. In this environment, thesource and size of ore-forming fluids are finite, which makes against the formation of largercopper deposits. Comparatively, the hydrothermal vein-type copper deposits are moreimportant than subvolcanic rock-type copper deposits for exploration. Constrained bymetallogenic settings, the forming depth of copper deposits is shallow, thus, the prospect ofdeep exploration is generally not good. But, one or two deposits perhaps have relatively goodprospect for deep exploration, especially for Nulasai and Kezibulake copper deposits.