Kaixing Wang

Chlorite is the dominant hydrothermal mineral in the Daliang deposit, a granite-related hydrothermal uranium deposit in South China. Despite the prevalence of chlorite, its characteristics and link to uranium mineralization have largely been neglected. Through comprehensive petrographic and geochemical analyses, we identified five distinct chlorite types (Chl-1 to Chl-5) and traced their formation mechanisms (dissolution−precipitation, layer-by-layer replacement, and dissolution−transport−precipitation) and crystallization temperatures (166−303 °C). Our analyses reveal that the chlorite compositions in the Daliang deposit effectively track the distinct evolutionary trends of the physicochemical properties of hydrothermal fluids across different paragenetic stages, including pH and oxygen fugacity. These observations suggest that the intragroup compositional variations in chlorite are primarily controlled by temperature. In contrast, the intergroup differences mainly reflect precursor mineralogy, fluid pH, and variations in oxygen fugacity. The formation of pre-ore chlorites (Chl-1 to Chl-3) provided favorable spatial conditions for uranium mineralization, whereas the evolution of mineralizing fluids from relatively oxidizing conditions (Chl-4) during the early ore stage to reducing conditions (Chl-5) during the main ore stage directly drove the pitchblende formation process. This research establishes new geochemical indicators for exploring uranium. Notably, elevated Cu/Li and Cu/Ga ratios—coupled with decreasing Li/U ratios and high U and Cu concentrations in ore-stage chlorite—emerge as effective proximal vectors for mineralization within the Daliang deposit. These results not only increase our understanding of granite-related hydrothermal uranium deposits but also provide practical tools for accelerating future exploration efforts.

The Nakexiuma area in the East Kunlun Orogen Belt hosts two spatially distinct mineralization systems: uranium-molybdenum (U-Mo) in schist and granitoid, and tungsten-molybdenum (W-Mo) in skarn and granitoid. To clarify their genetic relationship, we conducted U-Pb dating and trace element analyses on zircon, garnet, and uraninite. Zircon from granitoids yields a crystallization age of 250 ± 2.3 Ma, followed by W-Mo mineralization at 245 ± 2.1 Ma (garnet) and U-Mo mineralization at 235 ± 9 Ma (uraninite), indicating a prolonged magmatic-hydrothermal history spanning approximately 15 million years. Trace element data reveal a shift in fluid chemistry over time: Skarn garnets show high W contents, suggesting oxidizing, high-temperature fluids; uraninite displays REE depletion and negative Eu anomalies, precipitated from oxidizing fluids encountering a reducing environment. We propose that the W, U, and Mo mineralization in Nakexiuma is the result of this long-lived magmatic-hydrothermal system. The spatial separation of these mineralization systems is attributed to a multi-stage process involving host rock lithology and fluid redox evolution. Early oxidizing fluids from granitoids metasomatized carbonates to form W-Mo mineralization skarn. Later, meteoric water influx increased oxygen fugacity, generating U-rich, highly oxidizing fluids that precipitated uraninite and molybdenite upon interaction with the reducing meta-mafic rocks. These results highlight the roles of lithology and fluid chemistry in controlling spatially separated mineralization within the same system. Furthermore, they expand the Early Mesozoic metallogenic spectrum of the East Kunlun Belt, providing a refined model for polymetallic ore formation in a post-collisional extensional setting.

The Changjiang U ore field developed typical granite-related U mineralization in the Zhuguangshan complex, China. Pitchblende is the most important ore mineral in these mineralizations. In this study, the mineralogy and geochemistry of pitchblende were investigated by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) to identify the genesis of the Changjiang U ore field. Pitchblende exhibits colloidal, fragmented, spherulitic and fine-grained crystals in U ores. Its geochemical compositions are similar to those of other granite-related U deposits in South China, which have elevated contents of U, Sr, As and W; low contents of Pb, Th, Zr, Nb, Ta, Hf, Co, Ni and rare earth elements (REEs); and variable amounts of Ca, Si, Bi, Y, V and Zn. These geochemical signatures suggest that mineralization occurred through hydrothermal genesis and that the hosting Youdong and Changjiang granites acted as the dominant U sources. The uraninite in these granites might be the major U source mineral. Uranium mineralization occurred under the following conditions: low temperature (<250°C), low oxygen fugacity (log fO2=-29.5 - -25.5), weakly acidic (pH=5.3-5.9), high CO32- and F- contents and a silicon-saturated solution. Rapid changes in the physicochemical conditions of the ore-forming fluid are responsible for the precipitation of pitchblende. Combined with previous studies, we propose that U-rich granites, Cretaceous-Tertiary crustal extensions, regional faults and hydrothermal alterations were the critical factors for U formation in the Changjiang ore field.

The geochemical differences of magmatic rocks can be influenced by melt source and magmatic processes, including partial melting, fractional crystallization and magma mixing. New whole‐rock geochemical analyses, zircon U–Pb ages and Hf‐isotope data on granitoids from the Qingshanbao complex in the Longshoushan belt highlight a significant Late Ordovician–Early Silurian magmatic episode during the collision between the Alxa and Qilian‐Qaidam blocks, in which magma mixing was a fundamental process. The Qingshanbao complex comprises K‐feldspar granite, granodiorite and diorite emplaced coevally from 442 to 433 Ma. They exhibit peraluminous to metaluminous I‐type features, are enriched in large‐ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high‐field‐strength elements (HFSEs). Chondrite‐normalized REE patterns are fractionated (La_N/Yb_N = 10.2–34.9) with weakly negative Eu anomalies (Eu/Eu* = 0.66–0.94). The ¹⁷⁶Lu/¹⁷⁷Hf zircon two‐stage model ages (T_DM2) and the ε_Hf(t) on zircons extracted from the K‐feldspar granite (1613–2,316 Ma, ε_Hf(t) = −14.4 to −3.0) and granodiorite (1640–2015 Ma, ε_Hf(t) = −9.6 to −3.6) suggest they were formed by the mixing of melts produced by the melting of Mesoproterozoic crustal materials, most likely meta‐basic rocks from the Longshoushan Group, and to a lesser extent mantle materials. In contrast, zircons in the diorite yield T_DM2 ages ranging from 964 to 1767 Ma and ε_Hf(t) values of −5.5 to 7.1, implying melting of depleted mantle rocks with subordinate participation of lower crust materials. We suggest that the Qingshanbao complex was emplaced when the North Qilian area was in a transitional stage from a compressional to an extensional environment as early as approximately 442 Ma.

The Zhuguangshan complex hosts the main uranium production area in South China. We report (U-Th)/He and fission track thermochronological data from Triassic–Jurassic mineralized and non-mineralized granites and overlying Cambrian and Cretaceous sandstone units from the Lujing uranium ore field (LUOF) to constrain the upper crustal tectono-thermal evolution of the central Zhuguangshan complex. Two Cambrian sandstones yield reproducible zircon (U-Th)/He (ZHe) ages of 133–106 Ma and low effective uranium (eU) content (270–776 ppm). One Upper Cretaceous sandstone and seven Mesozoic granites are characterized by significant variability in ZHe ages (154–83 Ma and 167–36 Ma, respectively), which show a negative relationship with eU content (244–1098 ppm and 402–4615 ppm), suggesting that the observed age dispersion can be attributed to the effect of radiation damage accumulation on ⁴He diffusion. Correspondence between ZHe ages from sandstones and granites indicates that surrounding sedimentary rocks and igneous intrusions supplied sediment to the Cretaceous–Paleogene Fengzhou Basin lying adjacent to the LUOF. The concordance of apatite fission track (AFT) central ages (61–54 Ma) and unimodal distributions of confined track lengths of five samples from different rock units suggest that both sandstone and granite samples experienced a similar cooling history throughout the entire apatite partial annealing zone (~110–60 °C). Apatite (U-Th-Sm)/He (AHe) ages from six non-mineralized samples range from 67 to 19 Ma, with no apparent correlation to eU content (2–78 ppm). Thermal history modeling of data suggests that the LUOF experienced relatively rapid Early Cretaceous cooling. In most samples, this was followed by the latest Early Cretaceous–Late Cretaceous reheating and subsequent latest Late Cretaceous–Recent cooling to surface temperatures. This history is considered as a response to the transmission of far-field stresses, involving alternating periods of regional compression and extension, related to paleo-Pacific plate subduction and subsequent rollback followed by Late Paleogene–Recent India–Asia collision and associated uplift and eastward extrusion of the Tibetan Plateau. Thermal history models are consistent with the Fengzhou Basin having been significantly more extensive in the Late Cretaceous–Early Paleogene, covering much of the LUOF. Uranium ore bodies which may have formed prior to the Late Cretaceous may have been eroded by as much as ~1.2 to 4.8 km during the latest Late Cretaceous–Recent denudation.

Detrital zircon U–Pb–Hf isotopes and whole‐rock geochemical compositions of exposed Neoproterozoic sedimentary rocks in the Xiangshan area are determined to discuss provenances and the boundary between the Yangtze and Cathaysia blocks. Zircon dating results reveal that the exposed Precambrian sedimentary rocks in the Xiangshan area were deposited in the Late Neoproterozoic era. The age spectra and whole‐rock geochemistry show that the detrital materials of the Shenshan Formation originated from the Yangtze Block and that the detritus of the Kuli and Shangshi formations came mainly from the Yangtze Block and partly from the Cathaysia Block. The source for the Neoproterozoic sedimentary rocks in the Xiangshan area may been intermediate rocks, mainly from a mixture of felsic and mafic rocks in the Yangtze Block. In combination with previous studies, we suggest that the Xiangshan area belonged to the Cathaysia Block before the amalgamation between the Cathaysia and Yangtze blocks and that the real boundary between the two blocks is located in the northern part of the Xiangshan area.

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.

The Late Mesozoic Pucheng granitic complex in northern Fujian Province is composed of the Chengbu and Shipi peralkaline A‐type granitoids, the Pucheng A‐type granitoid, and the Yongxing I‐type granitoid. The Chengbu and Shipi peralkaline granitoids were dated at 160 and 130 Ma, respectively, and are explained by the melting of meta‐igneous rocks with T_DM² of 1.70 Ga and 2.01 to 2.05 Ga. The Pucheng A‐type granitoid was emplaced at 110 and 102 Ma and is divided into two groups. Group 1 comprises the extremely felsic A‐type granite (SiO₂ > 73 wt.%), high FeO^T/MgO (>16), and low Ga/Al ratios and Zr + Nb + Ce + Y content. Group 2 contains a less‐evolved A‐type granite with high Zr + Nb + Ce + Y content. Both groups can be explained by dehydration melting of meta‐igneous rocks at low pressure. The diversity between the two groups was caused by different physicochemical environments. The Yongxing I‐type granite, which is abundant in mafic microgranular enclaves, was emplaced at 106 ± 1 Ma. It can be explained by the mingling of mantle‐derived and crustal‐derived magmas. Our data along with previously published data demonstrate that the northern Fujian Province was under an extensional environment from 160 to 100 Ma. This was caused by the NW‐trending subduction of the palaeo‐Pacific Plate. The Jurassic peralkaline granitoids were probably generated in a rift environment as a result of the reactivation of pre‐existing faults caused by the initial subduction of the palaeo‐Pacific Plate. The Early Cretaceous peralkaline granitoids may represent a rift environment as a tectonic response from low‐angle subduction to an increasing subduction dip angle. The 100 Ma granitoids derive from an intraplate extensional environment caused by the roll‐back of the palaeo‐Pacific Plate.