The Huangsha uranium mining area is located in the Qingzhangshan uranium-bearing complex granite of the Middle Nanling Range, Southeast China. This uranium mining area contains three uranium deposits (Liangsanzhai, Egongtang, and Shangjiao) and multiple uranium occurrences, showing favorable mineralization conditions and prospecting potential for uranium mineral resources. Chloritization is one of the most important alteration types and prospecting indicators in this mining area. This study aims to unravel the formation environment of chlorites and the relationship between chloritization and uranium mineralization, based on detailed field work and petrographic studies of the wallrock and ore samples from the Huangsha uranium mining area. An electron probe microanalyzer (EPMA) was used in this study to analyze the paragenetic association, morphology, and chemical compositions of chlorite, to classify chemical types and to calculate formation temperatures and n(Al)/n(Al + Mg + Fe) values of chlorite. The formation mechanism and the relationship with uranium mineralization of the uranium mining area are presented. Some conclusions from this study are: (1) There are five types of chlorites, including the chlorite formed by the alteration of biotite (type-I), by the metasomatism of feldspar with Fe–Mg hydrothermal fluids (type-II), chlorite vein/veinlet filling in fissures (type-III), chlorite closely associated with uranium minerals (type-IV), and chlorite transformed from clay minerals by adsorbing Mg- and Fe-components (type-V). (2) The chlorite in the Huangsha uranium mining area belongs to iron-rich chlorite and is mainly composed of chamosite, partly clinochlore, which are the products of multiple stages of hydrothermal action. The original rocks are derived from argillite, and their formation temperatures vary from 195.7 °C to 283.0 °C, with an average of 233.2 °C, suggesting they formed under a medium to low temperature conditions. (3) The chlorites were formed under reducing conditions with low oxygen fugacity and relatively high sulfur fugacity through two formation mechanisms: dissolution–precipitation and dissolution–migration–precipitation; (4) The chloritization provided the required environment for uranium mineralization, and promoted the activation, migration, and deposition of uranium.

The Yuqia uranium deposit is a newly discovered sandstone-type uranium deposit in the northern margin of the Qaidam Basin. Concerning the sources of sediment in the basin, most scholars have focused on the study of Cenozoic sediment sources in the northern part of the basin, rather than on the study of Jurassic provenance and its implications for uranium mineralization. In this paper, the Jurassic sandstones in the area were selected for petrography, petrogeochemistry and electron microprobe analysis (EPMA), and the significance of sedimentary provenance and uranium metallogeny were further discussed, based on the previous data of detrital zircon chronology. It is reported here for the first time that coffinite and pitchblende are the main contributors. Independent uranium minerals in the region mainly occur in strawberry pyrite, xenotime, and margins or of quartz. The rocks in the source area, Jurassic sandstones, were mainly formed under the tectonic setting of the active continental margin; however, the sediments are mainly derived from the Indosinian and Paleozoic granitoids exposed in the northern margin of the Qaidam Basin. The uranium-rich granites in the source area led to the preconcentration of uranium in the sandstone of the target layer, and the uranium was brought into the ore-bearing target layer through uranium-bearing oxygenated water. The reduction reaction occurred under the action of reducing matter, and finally, the U⁶⁺ was reduced to U⁴⁺ in the formation of coffinite and pitchblende.

The Nanling region is located at the intersection of the Yangtze Block and Cathaysia Block and is characterized by complex geological and tectonic processes, as well as distinct W-Sn-REE mineralization. Despite extensive research on the mineralization of W-Sn and REE deposits in the Nanling region, the factors impacting the distribution pattern of eastern tungsten and western tin deposits, as well as the mechanism of REE enrichment in the parent rocks, remain uncertain. Deep structural and tectonic variability plays a crucial role in the formation of mineral deposits in the upper crust. Information on deep structural and tectonic variability is contained in the Moho depth, Curie depth, effective elastic thickness, lithospheric density, and thermal structure derived from the processing and inversion of satellite gravity and magnetic data. In this paper, we comprehensively analyse satellite gravity and magnetic data from the Nanling region, integrating the processing and inversion results with the tectonic evolution of this region and relevant geological information. It is hypothesized that the Chenzhou–Linwu fault serves as a channel for mineral and thermal transfer in the Sn ore aggregation zone, facilitating the material transport from the deep mantle to the surface and ultimately leading to the formation of Sn-enriched granite. The collection area of tungsten ore is more weakly associated with the Chenzhou–Linwu fault, and through deep heat transfer, tungsten components are primarily concentrated in the Earth’s crust to produce W-enriched granite. The primary source of REE enrichment in the parent rocks associated with REE mineralization is predominantly derived from the felsic crust, and the rapid intrusion of deep magma resulting from the subduction and retraction of the Palaeo-Pacific Plate is a contributing factor to the contrasting enrichment of light and heavy rare-earth elements. Mineral crystalline differentiation is relatively high, leading to the formation of ore-forming parent rocks with high heavy rare-earth element contents.

Middle Neoproterozoic sedimentary strata are widely distributed on the periphery of the Yangtze Block. In the western Jiangnan Orogen, they are divided into the Lengjiaxi and Banxi groups by the “Wuling unconformity,” and the Banxi Group is further divided into the Madiyi Formation and Wuqiangxi Formation by the “Xihuangshan unconformity.” However, the timing and tectonic significance of the Wuling and Xihuangshan unconformities remain unclear, which hampers our understanding of the Precambrian tectonic evolution of the Yangtze Block. Zircon U–Pb dating and Lu–Hf isotopic analysis were performed on the sedimentary rocks above and below the two unconformity boundaries in the western Jiangnan Orogen. These data were used to trace sedimentary provenance and provide new insights into the basin evolution and tectonic significance of the unconformities. Combined with previous studies, the Wuling unconformity is bracketed to have formed between ~830 and 813 Ma, and the provenance of the sediments above the unconformity remained unchanged. The detrital zircons from the upper parts of the Lengjiaxi Group and lower parts of the Banxi Group show the primary peak ages of 800–1000 Ma, 1.0–1.30 Ga, 1.40–1.90 Ga, and 2.30–2.60 Ga, and the provenance mainly derived from the southwestern margin of the Yangtze Block, Cathaysia Block, and Jiangnan Orogen. The provenance from the Cathaysia Block occurred in the upper part of the Lengjiaxi Group, indicating that the Yangtze Block and Cathaysia Block merged in the western Jiangnan Orogen earlier than the formation time of the Wuling unconformity (~830–813 Ma) and the collisional time in the eastern Jiangnan Orogen (~820–800 Ma). Thus, the collision between the Yangtze and Cathaysia blocks may have undergone a scissor-like closure process from west to east. The formation time of the Xihuangshan unconformity was at ~800–779 Ma. The field contact relationships changed from an angular unconformity to a disconformity and then to conformity, from north to south, indicating that the Xihuangshan unconformity was controlled by tectonic movement in the north. The provenance of the sedimentary strata changed above the Xihuangshan unconformity. The detrital zircon age peaks of the upper Banxi Group are 755–1000 Ma, 1.90–2.10 Ga, and 2.35–2.70 Ga, and the detritus were derived from the northern margin of the Yangtze Block and the Jiangnan Orogen. This unconformity is coeval with that of the ~800–780 Ma collisional orogeny at the northern and northwestern margins of the Yangtze Block. Thus, the Xihuangshan unconformity is likely a response to the collision orogeny in the northern and northwestern margins of the Yangtze Block and induces the transition of sedimentary provenance.

In recent decades, ion-adsorption-type rare earth element (iREE) deposits have been widely documented in the weathering crusts of granitic and volcanic rocks and their geological characteristics and genetic mechanisms extensively studied. Ion-adsorption-type REE mineralization was documented for the first time in the weathered crust overlying the epimetamorphic rocks in Ningdu County, China. In contrast to well-documented granite-derived weathering profiles, investigations of epimetamorphic rocks as protoliths for such REE deposits remain limited, particularly regarding the mineralogy of REE-bearing phases and the geochronology and geochemistry of their parent rocks. To address this gap, the present study combines comprehensive petrographic and mineralogical analyses of REE-mineralized Shenshan Formation phyllites with the U–Pb dating of zircon and apatite and trace element geochemical investigations. U–Pb zircon and apatite geochronology yields a protolith age of ca. 785 Ma for Shenshan Formation metamorphic rocks, consistent with mid-Neoproterozoic magmatism. REE-bearing minerals in the Shenshan Formation phyllites comprise allanite-(Ce), apatite, cerianite-(Ce), monazite-(Ce), rhabdophane-(La), rutile, Y-bearing thorianite and xenotime-(Y). Among these, apatite is the most abundant and likely the principal source of ionic REEs in the deposit. Ti-in-zircon thermometry indicates crystallization temperatures of 641–749 °C (mean ~704 °C), reflecting a prolonged magmatic–hydrothermal evolution. This extended history chiefly controlled the differentiation and redistribution of rare earth elements (REEs), thus governing their availability for subsequent supergene enrichment. Zircon-based oxygen fugacity (fO₂) estimates a range from −31.4 to −9.9 (mean −17.9), consistent with reduced magmatic conditions. Trace element correlation diagrams for zircon and apatite indicate that the intrusion underwent an extensive fractional crystallization of accessory phases (zircon, monazite, apatite, titanite, rutile) and plagioclase. The distribution patterns of trace elements further suggest that the Shenshan Formation protolith formed in a continental margin arc or arc-related orogenic belt setting, with geochemical signatures characteristic of an S-type granite. The Shenshan Formation phyllites in southern Jiangxi exhibit high REE abundances and host a labile assemblage of weatherable REE-bearing minerals, providing an optimal material framework for ion-adsorption-type REE deposits and indicating substantial mineralization potential.

Ion-adsorption rare earth element (REE) deposits represent strategic critical resources in China, which were traditionally considered to be predominantly hosted in granite weathering crusts. However, the recent discovery of new deposit types within the weathering crusts of shallow metamorphic rocks in South China has opened up novel exploration frontiers, while research on their metallogenic mechanisms remains insufficient. To elucidate the REE enrichment mechanisms in shallow metamorphic rock weathering crusts, this study focuses on the Getengzui ion-adsorption REE deposit in southern Jiangxi Province. Twenty-four samples were collected from the weathering crust profiles of the Qingbaikouan Shenshan and Kuli Formations. Multiple analytical approaches were employed, including major and trace element analysis, Chemical Index of Alteration (CIA), Base Leaching Index (BA), and quantitative evaluation of element mass transfer coefficients (τ). Trace element spider diagrams, REE distribution patterns, and A-CN-K diagram analysis were also utilized. The results reveal that the weathering crusts have progressed to the middle–late stage of chemical weathering. The average CIA value is 83 for the middle-upper part of the completely weathered horizon in the Kuli Formation. In contrast, for the completely weathered horizon in the Shenshan Formation, the value is 86. Intense chemical weathering has resulted in the near-complete decomposition of primary silicate minerals and extensive leaching of base cations. This progress has created an acidic pore water environment, which is critical for REE mobilization. REEs exhibit characteristics of in situ secondary enrichment, with significant enrichment of ΣREE in the middle-upper part of the completely weathered horizon. The peak τ(ΣREE) values reach 0.78 and 2.43 for the Kuli and Shenshan Formations, respectively. Apatite dissolution is identified as the primary source of REE ions. Differences exist in the geochemical mobility sequences of elements between the two formations. REE enrichment is controlled by multi-stage geochemical barriers, including an oxidation barrier and a clay adsorption barrier. The oxidation barrier preferentially fixes Ce⁴⁺, whereas the clay adsorption barrier serves as the dominant mechanism for large-scale REE enrichment. Parent rock lithology is the primary factor governing the efficiency, scale, and fractionation characteristics of REE enrichment. The Kuli Formation is favorable for forming the thick, large-scale orebodies enriched in light rare earth elements (LREEs). In the contrast, the Shenshan Formation tends to host higher-grade orebodies, characterized by a relatively balanced ratio of LREEs and heavy rare earth elements (HREEs). This study clarifies the main controlling factors for ion-adsorption REE mineralization in two shallow metamorphic rocks. It thereby provides a theoretical basis for future exploration. This framework is applicable to analogous REE resources within shallow metamorphic rock distributions across South China and nationwide.