Geochemical characteristics, provenance, tectonic settings and their relationships with uranium mineralization of the rocks of the Yaojia Formation in the northeastern margin of the Songliao basin
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    Abstract:

    Characterising the provenance of uranium-enriched sand bodies is important for the prospecting and evaluation of sandstone-type uranium deposits. The Yaojia Formation is an important ore-forming horizon in the northeastern margin of the Songliao basin. In this paper, the major elements, trace elements, rare-earth elements and AFT tests of the 21 granite samples that were from the 〖JP2〗Yaojia Formation in the eroded provenance area of the northeastern margin of the northern Songliao were analyzed by ICP-MS. This study aimed to explore the impact of oxidation-reduction conditions, provenance, tectonic settings and paleo-climate evolution on uranium mineralization. The results revealed that: ① The sandstone of the Yaojia Formation is dominated by feldspar lithic sandstone. It has similar geochemical characteristics to the granites in eroded provenance area, with high silicon content (SiO2=66. 38%~77. 71%), rich in alkali (Na2O+K2O=6. 22%~9. 35%) and aluminum (Al2O3=12. 11%~17. 25%), but poor in magnesium and calcium (MgO=0. 13%~1. 15%,CaO=0. 21%~2. 41%). It shows the characteristics of crust-derived magma, with low total rare earth amount (∑REE=84. 29×10-6~239. 38×10-6), light rare earth fractionation coefficient (La/Sm)N of 2. 62~4. 69, heavy rare earth fractionation coefficient (Gd/Yb)N of 1. 48~3. 30 with obvious crustal source magma characteristics. ② The combination of element B, Sr/Ba, B/Ga and the combination of U/Th, V/V+Ni, V/Cr, Ni/Co indicated that the paleo-water medium was an oxygen-rich freshwater environment when the Yaojia Formation was deposited. Fe2+/Fe3+ indicated that the rocks of the Yaojia Formation underwent epigenetic reduction. ③ The ICV value ranged from 0. 65 to 0. 74, with an average of 0. 69. The revised average CIA value was 64. 01. It indicated that the rocks of the Yaojia Formation might have undergone recycling or moderate weathering during the first deposition. ④ The La/Th-Hf and Co/Th-La/Th discriminate diagrams showed that the sandstones of the Yaojia Formation were mainly sourced from the felsicprovenance area of the upper crust. The structure discriminate diagrams showed that almost all the sandstones of the Yaojia Formation and the granite samples of eroded provenance area fell in the range of active continental margin and volcanic arc granite, indicating the tectonic setting was an active continental margin environment. ⑤ According to the AFT tests, north of Songliao basin experienced a continuous cooling process from the Middle Jurassic,which can be divided into four stages. From Late Jurassic to Late Cretaceous (160~90 Ma), the whole northern basin underwent rapid cooling and uplift process;from Late Cretaceous to Paleogene Mesozoic (90~40 Ma), the northern basin underwent a slow cooling stage; from Paleogene Middle Epoch to Late Paleogene (40~25 Ma), the northern basin was at a relatively rapid warming stage; since Late Paleogene (25~0 Ma), there was weak tectonism. Therefore, the Songliao basin underwent a magmatic thermal event during the Late Cretaceous to Paleogene, which is the late large-scale uranium metallogenic material base, for uranium mineralization and hydrodynamic conditions to create the necessary structure, and the upper basic magmatic activity in the region was the same as the main uranium mineralization, indicating that may also be hydrothermal or thermodynamic assisted mineralization in the north of the Songliao basin. Based on the above comprehensive analyses, it is concluded that the paleo-climate, oxygen-rich paleo-water body, favorable sedimentary facies and thick sand bodies had important geological significance for the large-scaled mineralization of the sandstone-type uranium in the northeastern margin of the Songliao basin.

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Li Yan, Nie Fengjun, Yan Zhaobin.2021. Geochemical characteristics, provenance, tectonic settings and their relationships with uranium mineralization of the rocks of the Yaojia Formation in the northeastern margin of the Songliao basin[J]. Acta Geologica Sinica,95(11):3472-3491

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History
  • Received:April 26,2020
  • Revised:January 24,2021
  • Adopted:
  • Online: November 23,2021
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