The extension of the suture zone between the Siberian and Kazakhstan continents in China has been a matter of debate because few outcrops of ophiolitic m elange have been found so far. The recently found Tuerkubantao ophiolitic m elange, which is located east of the Kekesentao Mt. in the Buerjin County of the Chinese Altay, provides an important clue for this problem. This paper presents the results of field investigation, petrology, U-Pb isotope dating of zircons and bulk-rock geochemistry of the Tuerkubantao m elange rocks. The m elange consists of fault-contacted ultramafic rocks, gabbro, diabase, basalt, flysch and granitoids. The ultramafic-mafic rocks are Mg-rich ( # Mg Z 4.25e6.35) and w(SiO 2 ) spans 38.8%e46.8%. Basalt and gabbro are geochemically similar and are characterized by low w(FeO t ) (10.9%), total alkali w(Na 2 O þ K 2 O) Z 2.58%) and w(TiO 2 ) (1.17%) and affinity to the Mg-rich tholeiite series. The flat REE and trace-element patterns of the ultramafic-mafic rocks are indicative of their ophiolite origin, i.e., formation in a mid-oceanic ridge setting. The fragments of low-K gneissic granite formed in suprasubduction or syn-collisional setting. Zircons from gabbro and gneissic granite yielded U-Pb ages of 363 and 355 Ma, respectively, suggesting Late Devonian mid-oceanic GEOSCIENCE FRONTIERS journal homepage: www.elsevier.com/locate/gsf GEOSCIENCE FRONTIERS 3(5) (2012) 587e602 spreading and oceanic subduction accompanied by suprasubduction magmatism. The Tuerkubantao ophiolite together with the Qiaoxiahala and Buergen ophiolites of the Kekesentao belt define an ophiolitic m elange belt extending along the Erqis fault. This belt probably belongs to the UralZaisan-South Mongolian suture-shear zone formed during the subduction of the Paleo-Asian Ocean and subsequent collision of the Siberian and Kazakhstan continents. ª 2012, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. All rights reserved.
Platinum group element (PGE) mineralization is mostly related to maficeultramafic complexes of the dominant magmatic deposit type. Mineralization of this type mainly relies on two conditions: the abundance of PGE in magma, and the presence of mechanisms favorable to PGE enrichment and separation from sulfur-saturated magma during magmatic evolution. Maficeultramafic complexes are widely developed in North Xinjiang, including (1) the large-scale copper-nickel deposits of Kelatongke, Huangshan, Huangshan East, and Tulargen, (2) numerous small to medium-sized coppernickel deposits such as Xiangshan, Tudun, Hulu, Baishiquan, and (3) the Xiangshan West and Weiya medium-sized VeTi magnetite deposits. However, maficeultramafic complexes in North Xinjiang rarely form PGE deposits. Therefore, questions about PGE metallogenesis in North Xinjiang are discussed in this paper from the standpoint of the ore-forming mechanism of PGE deposits and the characteristics of the North Xinjiang magma sources. The rock types of the post-collisional maficeultramafic complexes in North Xinjiang are of a ferrous rock series formed by fractional crystallization, a rock type generally favorable for hosting PGE. For the Cu-Ni sulfide deposits of North Xingjiang, the assimilation of crustal material causes sulfide liquation during processes of magmatic evolution and mineralization. This can be
A large number of intermediate basic volcanic rocks and porphyry Cu-Mo deposits as well as volcanic-hosted magnetite deposit have been recently discovered in the Xilekuduk area. However, no reports concerning petrogenesis and age or their relationship with mineralization have been published to date. The purpose of this study was to make up for the absence of previous studies on Devonian volcanic activities in the area and to confirm the relationship between two stages of volcanic activities and mineralization so as to provide important theoretical basis for mineral exploration. Based on research results of zircon U-Pb geochronology and element geochemistry of volcanic rocks in the area, the ages of dacite, andesite, and stomatal andesite are considered as 375.2 ± 2.9 Ma, 386.5 ± 3.0 Ma, and 317.9 ± 2.9 Ma, respectively, corresponding to the Middle Devonian and Late Carboniferous Period. The Devonian volcanic rocks belong to the high-K calc-alkaline series and island arc volcanic rocks, which are enriched in LREE, strongly enriched in large ion lithophile elements Th, Rb, Ba, and K and relatively depleted in high-field strength elements (HFSEs) Nb, Ta, and Ti. The Carboniferous volcanic rocks are enriched in LREE, as well as the large ion lithophile elements Th, Rb, Ba, and K are strongly enriched, while depleted in the HFSEs Nb, Ta, and Ti; moreover, the contents of TiO2 and V are 0.94–0.97% and 178–183×10–6, which are higher than those of island arc basalts. According to mineralogical typomorphic characteristics and geochemical analysis, magnetite mineralization is divided into two phases. The early stratiform magnetite ore MT1 has magmatic characteristics, forming a volcanic rock type magnetite deposit related to Devonian volcanic eruption and sedimentation (375–386 Ma). The magnetite MT2 in the magnetite-quartz vein is considered as hydrothermal genesis, which is a metal mineral in the early metallogenic stage of Carboniferous (317.1 ± 2.9 Ma) volcanic eruption and subvolcanism, and may be related to porphyry molybdenum mineralization. Therefore, the volcanism and Fe-Cu-Mo mineralization in this area is characterized by multistage superimposed mineralization.
The black shale enriched in various precious metal elements and platinum group elements. And the PGE deposit in black shale series is a new promising mineral resource. Comprehensive research on the geology, geochemistry, petrology, mineralogy, fluid inclusion and geochronology of the PGE in black shale series has been carried out and made a series of achievements. This paper summarized the advances in PGE in black shale series and pointed out the controversial views about the source of the PGE.
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