Litho‐mineralogy, geochemistry, and chronology for the genesis of the Kamust sandstone‐hosted uranium deposit, Junggar Basin, NW China

Abstract

The Kamust sandstone‐hosted uranium deposit was recently discovered within the Middle Jurassic Toutunhe Formation of the eastern Junggar Basin. In this study, polarizing microscope and scanning electron microscope observation, electron microprobe analysis, and laser ablation inductively coupled plasma mass spectrometry measurement were carried out to define the petrology, mineralogy, and geochemistry of these sandstone‐hosted uranium ores. In addition, sulphur isotope signatures for the associated ore‐stage pyrites and the ore‐forming age were determined. The results show that the mineralized sandstones, which exhibit excellent reducibility with abundant organic matter and pyrites, are characterized by the secondary accumulation of uranium and are slightly enriched in rare earth elements (REE) and light REE (LREE). The uranium deposits are mainly composed of a large amount of uraninite, followed by some coffinites and uranium‐bearing titanium minerals and very few sorptive uranium‐bearing materials. Uranium minerals primarily exist within the interior and edge of clastic particles in colloidal, dispersed, and vein form, and some are closely interweaved with the colloidal and framboidal pyrites and carbonaceous detritus. Both uraninite and coffinite are strongly enriched in REE and LREE, as determined by in situ trace element measurements. Moreover, the δ34S values of the associated ore‐stage pyrites mostly range from −41.66 to −19.33‰, indicating biological origin, and light 32S demonstrates the relatively low‐temperature and open‐system mineralization processes related to the microbial anaerobic action on the organic matter. One of the δ34S values (6.88‰) is possibly caused by Rayleigh isotope fractionation due to the utilization of residual heavy 34S in the relatively later closed‐like mineralization system. The ore‐reforming ages of 27 ± 3.2 Ma, 22.4 ± 3.9 Ma, and 21.3 ± 2.3 Ma were obtained by U–Pb isotopic dating combined with U–Ra balance correction, corresponding to the rapid uplift event caused by the remote effect of the collision between the Indian and Eurasian plates at the end of the Palaeogene. In conjunction with the tectonic–sedimentary evolution of the study region, a four‐stage ore‐forming model for the Middle Jurassic Toutunhe Formation is preliminarily constructed: ① Development of ore‐bearing strata, ② initiation of the mineralization stage from the Late Jurassic to the Early Cretaceous, ③ deep burial by lacustrine and flood mudstone from the Cretaceous to the Palaeogene, and ④ the superimposed ore‐forming stage during the Neogene. These research results provide significant benefits for further uranium prospecting and in situ leach process mining in this basin.

Constraints on Sandstone-Type Uranium Deposits by the Tectonic Uplift and Denudation Process in the Eastern Junggar Basin, Northwest China: Evidence from Apatite Fission Track and Detrital Zircon U-Pb Ages

“…The Kamust U deposits occur in the Toutunhe Formation (J 2 t). The total length of the interlayer oxidation zone is approximately 110 km, with a width of 200-600 m, and the interlayer oxidation zone is approximately 5-30 km from the current provenance area [22]. Thus far, several industrial uranium and mineralized holes have been detected along the front of the interlayer oxidation zone, constituting a uranium mineralized zone approximately 100 km long.…”

“…Adsorption-state uranium is usually adsorbed by illite (Figure 4i) and organic matter. According to the electron probe microanalysis, the average composition of pitchblende is 80.18% UO 2 , 2.6% SiO 2 , 3.69% CaO, 2.17% TiO 2 , and 1.1% MnO, while the average composition of coffinite is 61.58% UO 2 , 17.04% SiO 2 , 3.46% CaO, 3.32% P 2 O 5 , 1.44% Al 2 O 3 , 0.46% Na 2 O, 0.23% Yb 2 O 3 , 2.23% Y 2 O 3 [22]. In situ rare trace element compositions from a single uranium mineral grain demonstrate that both pitchblende and coffinite are strongly enriched in REE.…”

“…022, 12, x FOR PEER REVIEW of intermediate-acid magmatic rocks, such as granite, granite porphyry, rhyolite, a desite. Uranium mineralization is rich in carbon detritus and pyrite, which contri uranium mineral precipitation [22]. The occurrences of uranium are mainly pitch followed by a small amount of coffinite, adsorption-state uranium, and other ur bearing minerals.…”

“…Pitchblende mostly fills the dissolution pores o ments, particularly the dissolution pores or edges of granite (Figure 4a) and feldsp ure 4b). Locally, pitchblende can replace granite fragments along the microfractur ure 4c-e) and are wrapped by anhedral pyrite (Figure 4f), indicating that pyrite Uranium mineralization is rich in carbon detritus and pyrite, which contribute to uranium mineral precipitation [22]. The occurrences of uranium are mainly pitchblende, followed by a small amount of coffinite, adsorption-state uranium, and other uraniumbearing minerals.…”

“…The discovery of the Kamust uranium deposit in the eastern Junggar Basin is a breakthrough in deep U-ore prospecting in the overlying mudstone area of Mesozoic-Cenozoic basins in China in recent years [8,[17][18][19]. The deposit is a typical sandstone-type uranium deposit formed by interlayer oxidation [20][21][22]. The interlayer oxidation extends approximately 10 km from Karameri Mountain to Junggar Basin, and the front line is approximately parallel to Karameri Mountain.…”