Abstract The late P aleozoic W udaogou G roup, one of the oldest metamorphic units in the eastern Y anbian area, has important tectonic and metallogenic significance. Here, we provide new insights into their protoliths, tectonic setting of the metamorphic rocks and their relationships with the gold and tungsten mineralization, using new petrographic and whole‐rock geochemical data for various lithologies within the W udaogou G roup. The protolith of the metamorphic rocks of the W udaogou G roup was intermediate–basic volcanic rocks (e.g. basaltic andesite, trachyandesite, and basalt) and sedimentary rocks including argillaceous rocks, quartz sandstone, arkose and clayish greywacke, as well as pyroclastic sedimentary rock, covering tuffaceous sandstone. Before undergoing late P aleozoic epidote–amphibolite facies regional metamorphism, these protoliths were formed during the middle–late P ermian in an island arc setting within a continental margin collage zone. Combined with the regional tectonic evolution, it can be speculated that the formation and the subsequent metamorphism of the protoliths of the metamorphic rocks from the W udaogou G roup were influenced by the change from subduction to collision of the P aleo‐ A sian O cean. Similarities of the rare earth element ( REE ) patterns and parameters among the metamorphic rocks within the W udaogou G roup, auriferous ores from the X iaoxi'nancha gold (copper) deposit, and scheelites from the Y angjingou tungsten deposit, together with the favorable metallogenic element contents within the metamorphic rock series, imply that the W udaogou G roup could provide parts of metallic material for the gold and tungsten mineralization in the eastern Y anbian area, as exemplified by the Y angjingou deposit and X iaoxi'nancha deposit, respectively. Further, the metamorphic sedimentary rocks, especially the metamorphic sandstones, quartz schists and quartz mica schists within the W udaogou G roup, have closer genetic relationships with the Y angjingou tungsten mineralization. However, the specific lithologies within this group which control the gold mineralization are still uncertain, and need further research.
Abstract The Yangbishan iron–tungsten deposit in the Shuangyashan area of Heilongjiang Province is located in the center of the Jiamusi Massif in northeastern China. The rare earth element and trace element compositions of the scheelite show that it formed in a reducing environment and inherited the rare earth element features of the ore‐forming fluid. The geochemical characteristics of the gneissic granite associated with the tungsten mineralization show that the magma formed in this reducing environment and originated from the partial melting of metamorphosed shale that contained organic carbon and was enriched with tungsten. In addition, in situ Hf isotopic analysis of zircons from the gneissic granite indicates that they probably originated from the partial melting of a predominantly Paleo–Mesoproterozoic crustal source. According to LA‐ICP‐MS zircon dating, the Yangbishan ore‐related gneissic granite has an Early Paleozoic crystallization age of 520.6 ± 2.8 Ma. This study, together with previous data, indicates that the massifs of northeastern China, including Erguna, Xing'an, Songliao, Jiamusi, and Khanka massifs, belonged to an orogenic belt that existed along the southern margin of the Siberian Craton during the late Pan‐African period. The significant continental movements of this orogeny resulted in widespread magmatic activity in northeastern China from 530 Ma to 470 Ma under a tectonic setting that transitioned from compressional syn‐collision to extensional post‐collision.
ABSTRACT Tuffs are the significant medium to figure out volcanic activities, explore regional tectonic evolution and constrain the depositional ages in basins. Tuff intervals are found in the Early Cretaceous successions from the southwestern Ordos Basin, southwestern part of the North China Craton, which supplies new geochronological and geochemical evidence to understand the Early Cretaceous tectonic setting. In this work, whole‐rock and zircon geochemistry, zircon U–Pb dating and Hf isotopic analyses were conducted. Zircon U–Pb dating results yielded ages of 125.32, 121.71 and 118.20 Ma, which have recorded the erupting of rhyolites and constrained the depositional age precisely to belong to the Aptian. Two groups of zircons Hf isotopic data are ε Hf (t) of 8 with T DM2 of 693–570 Ma and ε Hf (t) of −11.7 with T DM2 of 1908 Ma. Westerlies or southwesterlies were prevailing in the Early Cretaceous and can bring cinerites from the western or southwestern part of China. Comparative analysis of geochemistry and zircon Hf isotopes exhibited that the volcanoes from the Qiangtang Block and the Qingling Orogen were the most potential sources for the tuffs. These Early Cretaceous volcanic eruptions were triggered by the subduction of the Bangong‐Nujiang Ocean and the Paleo‐Pacific Ocean with plate roll‐back and lithospheric destruction.
The hydrocarbon activity in Pengyang area, situated in the southwestern Ordos Basin, is notably prominent. Investigation on the migration laws of hydrocarbons is imperative for comprehending the involvement in uranium mineralization. Based on the analysis of spatial distribution of hydrocarbon containing fluid and hydrocarbon generation conditions of sandstone in the Luohe Formation, the organic geochemical characteristics including hydrocarbon components, carbon isotopes and biomarker compounds were analysed. The research results indicate that: (1) hydrocarbon fluid activities in the Luohe Formation are predominantly observed in layers exhibiting higher uranium mineralization. The mudstone of the Luohe Formation had low organic matter content and low thermal maturity, which was not conducive to hydrocarbon generation. (2) Hydrocarbon‐containing fluid in the sandstone of Luohe Formation not only contained reducing gases such as methane and hydrogen but also chloroform asphalt components. The carbon isotopes of hydrocarbon in sandstone inform Luohe Formation resemble oil and gas in the Mesozoic. The biomarker parameter inferred that the parent rock of hydrocarbons in the Luohe Formation was formed under reducing and freshwater conditions, and hydrocarbon generation occurred at the mature stage. As above mentioned, a comparison was carried out between the affinity of hydrocarbon‐containing fluid in the Luohe Formation and different layers of hydrocarbon source rocks. The migration behaviour of hydrocarbon‐containing fluid in the Pengyang area has been summarized, and the involvement of hydrocarbon‐containing fluid in uranium mineralization has been discussed. The main concepts are as follows: the sedimentary environment and thermal evolution conditions of hydrocarbons in the sandstone of Luohe Formation resemble those of the primary hydrocarbon source rocks in the Yanchang Formation. The main hydrocarbon charging events in the Luohe Formation occurred before the Late Cretaceous period, which is primarily related to two hydrocarbon generation events from 130 to 100 Ma in the Yanchang Formation and fault conduits connecting the Triassic to the Cretaceous Strata. The hydrocarbon‐containing fluid released from Yanchang Formation migrating to the Luohe Formation provides reducing conditions for the precipitation of uranium in oxygen‐bearing water bodies.
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