Abstract
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 TiO2and 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.
Highlights
The Xilekuduk area in Fuyun County, Xinjiang, is located in the northern margin of the Junggar Basin, in the collision suture zone of the Siberian Plate and the Junggar Plate (Sengör et al, 1993; Windley et al, 2007)
In this study, LA-ICP-MS zircon U-Pb data show that the diagenetic age of dacite is 375.2 ± 2.9 Ma and that of andesite is 386.5 ± 3.0 Ma, indicating that the volcanic rock was formed in the Middle Devonian and the basaltic andesite is 317.9 ± 2.9 Ma, corresponding to the early Late Carboniferous
The strata in this area can be divided into two sets: the dacite-pyroclastic rocks in the southeast belong to the Beitashan Formation of Middle Devonian, and the clastic sedimentary rocks with stomatal andesite volcanic rocks in the northwest belong to the Lower Carboniferous Jiangbastao Formation
Summary
The Xilekuduk area in Fuyun County, Xinjiang, is located in the northern margin of the Junggar Basin, in the collision suture zone of the Siberian Plate and the Junggar Plate (Sengör et al, 1993; Windley et al, 2007). Some new scientific issues have been raised in this study: 1) The volcanic sedimentary assemblage of intermediate acid volcanic rocks–pyroclastic rocks–carbonate rocks distributed in the ore district obviously differs from that of the marine continental interactive facies clastic sedimentary rocks of the Lower Carboniferous Namingshui Formation (the Jiangbastao Formation). Are these volcanic rocks all formed in Carboniferous as previously speculated? Are these volcanic rocks all formed in Carboniferous as previously speculated? Are the two types of sedimentary assemblages the product of the same geological event? 2) In 2015, layered magnetite bodies that occurred at the interface between volcanic rocks and clastic rocks were successively discovered more than 100°m southwest of the porphyry copper–molybdenum deposit; their coupling relationship with volcanic rocks, remains unclear
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