Superimposition Mineralization Of The Awulale Iron Deposit Belt In Western Tianshan, Xinjiang

Awulale iron metallogenic belt is a very important iron metallogenic belt foundin western Tianshan of Xinjiang province. A series of super large iron deposits aredistributed in this belt. These iron deposits occur mainly in the Carboniferousvolcanic rocks of the Dahalajunshan Formation, and display complex characteristicsresulted from superimposed metallogeny. Field investigation, microscopicobservation, and mineralogical and geochemical analysis have been carried out on theDahalajunshan Formation volcanic rocks (DFVR) and two typical iron deposits(Beizhan and Dunde iron deposits), with a focus on an analysis of ore depositcharacteristics and mineralization processes so as to set up a mode for regionalmetallogeny.The following are major achievements obtained in this dissertation.①The DFVR are dated at316.1±2.2Ma, showing its formation in the EarlyCarboniferous.②REEwith ME and Sr with Pb isotopic data show possible formation of theDFVR during the late period of the Early Carboniferous in the continental marginarc zone controlled by the subduction of Junggar plate to Middle Tianshan-Yili plate.The relevant magma might be produced by1%~5%partial melting of the mantlewedge spinel-lherzolite replaced by fluids from subduction zone, and undergo anAFC process during its ascending.③Pb, O and S isotopic data of the ores support derivation of ore-formingmaterials mainly from the deep magma system.④Ores, DFVR and granitic rocks from the Beizhan iron deposit have similarREE characteristics, indicating their close genetic relationship. Based on this resultcombined with relevant previous research data, It can be inferred that interruption offeeding of basaltic magma in the depth combined with more intensive crustalcontamination could result in liquation of the initial magma with composition of the volcanic rocks into an iron-rich magma and a silica-rich magma with composition ofthe granitic rocks. The REE simulation result shows that the weight proportion of theinitial magma, the iron-rich magma, and the silica-rich magma is14:1:13.⑤Analyses of major and Trace elements and S and O isotopes indicate adifferent formation process of the skarn in the Beizhan and Dunde iron deposits fromthat of traditional contact metasomatic skarn. This formation process might becontrolled by an ore magma-hydrothermal or magma-hydrothermal system withhigher temperature.⑥Both ofthe Beizhan and the Dunde iron deposits are superimposed deposits,which were formed by a complex processe of ore magma mineralization andhydrothermal mineralization. Ore magma mineralization played a key role in theformation of the Beizhan iron deposit, while magma hydrothermal mineralizationdid an important role in the formation of the Dunde iron deposit.