Uranium Mineralogical and Chemical Features of the Na-Metasomatic Type Uranium Deposit in the Longshoushan Metallogenic Belt, Northwestern China

Abstract

The Longshoushan Metallogenic Belt (northwestern China) is known for its word-class Jinchuan Ni-Cu sulfide (Pt) deposit and is also an important uranium metallogenic belt. The Jiling uranium deposit in this belt is a typical Na-metasomatic uranium deposit, which rarely occurs in China. Mineralization in the Jiling uranium deposit is hosted in granitoids that have suffered a Na-metasomatic alteration. There are three kinds of uranium minerals, including uraninite, pitchblende, and coffinite in the Jiling uranium deposit. Pitchblende is the predominant uranium mineral. Integrating the mineralogy and geochemistry of uranium minerals, and in situ electron microprobe analyzer (EMPA) U-Th-Pb chemical dating, we aimed to unravel the age and nature of the mineralization, to decipher the characteristics of the hydrothermal alteration and the U mineralization process. Based on the microtextural features and compositional variations, primary uraninite was altered to uraninite A and B, and fresh pitchblende was altered to pitchblende A and B. The best-preserved uraninite crystals displayed a euhedral-shape with high Pb and low SiO2, CaO, FeO, and Al2O3 contents, and was interpreted as primary uraninite. The EMPA U-Th-Pb chemical ages revealed that uraninite may have formed at 435.9 ± 3.3 Ma. High ThO2 + ΣREE2O3 + Y2O3 contents illustrated that the best preserved uraninite crystallized at a high temperature. Altered pitchblende A showed a relatively brighter gray color in backscattered electron (BSE) images and with a lower SiO2 content than B. Three analysis spots of the fresh pitchblende showed low contents of ΣSiO2 + CaO, indicating no obvious alteration. EMPA U-Th-Pb chemical dating gave a mean chemical age of 361 Ma. The low Th + ΣREE2O3 contents indicated that this pitchblende formed at a relatively low temperature. According to the different characteristics of occurrence and chemical composition, the coffinite in the Jiling uranium deposit can be divided into coffinite A and B, respectively. The compositional variation of the fresh and altered uraninite and pitchblende indicated that both uraninite and pitchblende underwent at least two discrete hydrothermal fluid alterations. The U mineralization was divided into two stages; uraninite was formed at a high temperature and possibly from a magmatic-hydrothermal fluid during ore stage I. Then, pitchblende was formed at a low temperature, during ore stage II. According to the petrographic observations and their chemical compositions, coffinite A and B resulted from the alterations of uraninite and pitchblende, respectively.

Alteration of Granitoids and Uranium Mineralization in the Blatná Suite of the Central Bohemian Plutonic Complex, Czech Republic

“…The Th-enriched uraninite, containing up to 7.3 wt % ThO 2 was described from uranium deposit Aricheng in Guyana, occurring in high-temperature albitites [38]. Similar, the Jiling uranium deposit in the NW-China contains Th-enriched uraninite with 6.5-12.6 wt % ThO 2 [37]. The Th-enriched uraninite from the Olympic Dam uranium deposit in Australia contains up to 7.4 wt % ThO 2 [33].…”

“…The Y-enriched uraninite occurring in the Olympic Dam uranium deposit, Australia contains up to 3.6 wt % Y 2 O 3 [33]. Recently the Y-bearing uraninite was described from the high-temperature Na-metasomatic uranium deposit Jiling, NW-China, containing 1.0-2.5 wt % Y 2 O 3 [37]. However, all these Y-enriched uraninites and coffinites occur in a high-temperature albitites, which originated by distinctly higher temperatures than the low-temperature aceites [11,33,35,37,38].…”

Exhumation and Preservation of the Jinchuan Ni‐Cu‐PGE Deposit under the East Longshou Mountain Thermal Evolution, Revealed by Apatite Fission Track Thermochronology

“…The Jinchuan world-class sulfide copper-nickel deposit is located in the Longshou Mountain uplift belt at the southwest margin of the Alxa Block, North China Craton, which is separated from the Qilian Fold Belt to the south by the South Margin Fault and liesadjacent to the Chaoshui Basin to the north at the North Margin Fault of the Longshou Mountain (Fig. 1a, b) (Chai and Naldrett, 1992;Naldrett, 1999;Gao Y L et al, 2009;Tang et al, 2014;Yu et al, 2020). The Paleoproterozoic Longshou Mountain Group dominates the basement of the Longshou Mountain Belt, the cover including Meso-and Neoproterozoic metamorphic sedimentary rocks.…”