The Zhibo iron deposit is hosted in Carboniferous submarine volcanic rocks in Western Tianshan, NW China. A series of magnetite‐bearing intermediate‐mafic volcanic rocks are recognized in the periphery of the Zhibo ore district. Most of these volcanic rocks formed at 314 ± 2 Ma, possess tholeiitic–calc‐alkaline affinities, and display remarkable negative Nb, Ta, and Ti anomalies on primitive mantle‐normalized incompatible element diagrams. These features, together with those of their relatively complete rock assemblages and Th/Yb versus Nb/Yb diagrams, are indicative of their formation in an active continental margin arc setting. The wide compositional spectrum of SiO 2 values ranging from 47.11 to 62.75 wt.% and lower Mg # values (55–63) of basalts suggest that the Zhibo intermediate‐mafic volcanic rocks may have experienced magmatic differentiation. Their (Th/Ta) PM > 1, (La/Nb) PM > 1, Nb/Ta (11‐16), and Th/Ce (0.06‐0.23) values suggest that the source of these intermediate‐mafic volcanic rocks was significantly contaminated by crustal materials. The magnetites in the iron ore have lower contents of Al, Mn, Ti, and V, indicating that the mineralization of magnetite in the iron ore occurred under lower temperature and higher oxygen fugacity conditions than those in the intermediate‐mafic volcanic rocks. In addition, the magnetites in the Zhibo iron ores have lower contents of compatible elements (e.g., Ti, V, Mn, Co, Cr, and Zn) than those of the magnetite in the intermediate‐mafic volcanic rocks, suggesting that the Zhibo magnetites crystallized from late‐stage, residual iron‐rich magmatic melts/magmatic‐hydrothermal fluids. In addition, the textures of the volcanic rocks suggest that iron have ever enriched in the residual melt during the magmatic stage, and the iron‐rich fragments in andesitic volcaniclastic rocks indicate that the ore‐forming material was a high‐salinity fluid‐bearing iron‐rich melt. In combination of available information, including field observations and geochemical analyses, we interpret that the Zhibo iron deposit is magmatic‐hydrothermal in origin.
Only the small Qingbulake Ni—Cu sulfide deposit was discovered in western Tianshan, however, as part of the mafic—ultramafic intrusion belts in northern Xinjiang, there developed about tens of intrusions in the Qingbulake basic rock belt. Geochemical studies of the Qingbulake basic complex closely associated with the deposit show that it is characterized by low content of Ti, depletion of Nb and Ta, enrichment of large lithosphile elements and slight enrichment of LREE. The magma also displays some features of island arc magma. Combining with their isotope geochemistry, we propose that the formation of the complex may closely relate to the subduction of the southern Tianshan oceanic crust to the central Tianshan plate. The magma was derived from the MORB type depleted mantle, and was contaminated or slightly contaminated by the crust or wall-rock during the emplacement.
Abstract Zircons from granodiorite and biotite granite in the Yeniutan granitic intrusion in the western North Qilian Mountains yielded a weighted mean 206 Pb/ 238 U apparent age of 460±3 Ma, suggesting that the intrusion originated during the late stage of plate subduction. Its related Ta'ergou and Xiaoliugou deposits are two of the few large tungsten deposits formed in the plate subduction environment in the world. The U‐Pb dating of the zircons from the biotite granite gave a discordant lower intercept age of 183±4 Ma, which implies that the Yanshanian event was probably superimposed on the North Qilian region.
Abstract The west sector of the northern Qilian Mountains is well‐known for the Jingtieshan‐type iron deposits. A new breakthrough has been made in prospecting for gold and copper in recent years. In this paper, the distribution characteristics of ore deposits in the study area are discussed from the viewpoint of tectonic evolution. It is suggested that there are 9 stages of mineralization from the Palaeoproterozoic to Indosinian. Four minerogenetic series and two minerogenetic subseries of ore deposits are recognized. Iron mineralization occurred in several stages, while most of the metals were accumulated in large amounts in the Caledonian. The enrichment and mineralization of gold is related to large‐scale shear‐strike‐slip faults and the ascent and unloading of deep‐seated fluids.
Abstract Mesozoic epithermal gold deposits in eastern China are divided into calc‐alkaline and alkaline magma‐related gold deposits, and are also grouped as low‐sulfidation, intermediate‐sulfidation and high‐sulfidation types, of which the first two predominate. These gold deposits are distributed in the Tianshan–Yinshan–Great Xing’anling Variscan fold belt of North China craton, Qinling‐Dabie Indo‐Sinian fold belt of Yangtze craton, and South China fold belt or Cathaysian block, from north to south along the eastern China continent. Most of the epithermal gold orebodies are hosted either in volcanic rocks or their related granitoids, and volcanic breccia pipes. These orebodies are mainly associated with adularia–chalcedony–sericite, and alunite–kaolinite–quartz alteration. These orebodies formed in four mineralization pulses at 175, 145–135, 127–115, and 110–94 Ma. The first three pulses correspond to the post‐collision period between the North China and Yangtze cratons, an extension period during late‐stage rotation of the principal compressional stress from N‐S to E‐W, and a dramatic thinning period of the lithosphere, respectively. The last mineralizing pulse was the result of another extension in South China. Although the mineralizing pulses occurred at different times, they all occurred in extensional settings and were accompanied by crust and the mantle interaction.
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