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The Jiujiang region in northeastern Jiangxi Province is known for hosting many black shale-type vanadium deposits, which are mainly found in the Cambrian Hetang Formation and Sinian Piyuancun Formation. In this paper, based on stream sediment data, principal component analysis (PCA) and spectrum–area (S–A) fractal modelling are used to identify geochemical anomalies associated with vanadium (V) mineralization. First, a dataset containing 957 samples of stream sediments with 39 elements was processed using correlation analysis and cluster analysis to find the closest V-related elements, and Ag and Cd were obtained. Secondly, the raster maps of V, Ag and Cd were created using multifractal inverse distance-weighted interpolation. PCA was then employed to combine the concentration values of V, Ag and Cd into a single variable representing the internal relationships among the three elements. Finally, S–A analysis was used to decompose the first component pattern obtained through PCA and to extract anomalies from the complex background. The results show that the known V deposits are located within highly anomalous areas, which are well corelated with the distribution of black shales of the Hetang and Piyuancun Formations. It is suggested that the northeastern part of Jiangxi Province potentially hosts undiscovered V deposits, and the identified anomalies could be further used to guide mineral exploration. Thematic collection: This article is part of the Applications of Innovations in Geochemical Data Analysis collection available at: https://www.lyellcollection.org/cc/applications-of-innovations-in-geochemical-data-analysis [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of red beds on fluid flow in the Xiangshan Basin were examined. • The topographic variation of the red beds may act as driving force of fluid flow. • The fluids in the red beds can infiltrate into the deep volcanic rocks and the basement. The South China uranium metallogenic province is an important hydrothermal uranium metallogenic region in China, which is spatially and temporally associated with the Cretaceous-Neogene red beds. Previous studies suggest that the red beds might have played critical role in the ore-forming processes by providing oxidizing fluids. However, the effects of the red beds on fluid flow are poorly understood. In this study, numerical modeling was conducted to investigate the roles of red beds on ore-forming fluid flow in the Xiangshan basin in Jiangxi Province, hosting the largest volcanic hydrothermal uranium deposit in China. The modeling results show that the variation of the slope gradient of the red beds greatly affects the fluid flow patterns, whereas the change of thickness and permeability of the red beds has little influence on fluid flow pattern. The fluid can circulate into the volcanic and basement rocks driven by topographic relief of the red beds. Furthermore, for models with fault, although the fluid velocities in the fault were more than one order of magnitude larger than those in the surrounding strata, the overall fluid flow patterns in the strata did not show great variation. The modelling results suggest that the topographic relief of the red beds may have driven the oxidizing fluids into the underlying rocks which are necessary for uranium mineralization in the Xiangshan basin. [ABSTRACT FROM AUTHOR]

• Xiangshan volcanic-related uranium deposits are structurally controlled hydrothermal deposits. • Oxidizing fluids were developed in the redbed basins. • Uranium was mainly sourced from the host volcanic rocks. • Extensional brittle structures provided pathway for fluid flow and mineralization. • Heat provided by the deep-seated magmatic activities promoted uranium mineralization. The Xiangshan Basin hosts the largest volcanic-related uranium deposits in China. Despite several decades of extensive research, the key factors controlling volcanic-related uranium mineralization in the Xiangshan Basin remain unclear. In this paper, we present a review of previous studies and highlight the critical features that are closely related to the uranium mineralization in the Xiangshan Basin, with focus on the geological feathers, host rocks, ore-controlling structures, alterations, mineralization, fluid inclusions, and geochronological and geochemical data of the uranium deposits. Based on these reviews, a comprehensive genetic model is proposed to better explain the uranium mineralization mechanism. The uranium mineralization at Xiangshan is mainly hosted in felsic volcanic and sub-volcanic rocks, and spatially close to the Cretaceous–Tertiary redbeds. The mineralization mainly took place from ~125 to ~70 Ma, which is much younger than the ages of host volcanic rocks (~135 Ma) and broadly contemporaneous with the development of the redbed basins and mafic magmatism. The uranium mineralization occurs mainly as veins controlled by brittle structures such as fractures, faults and volcanic structures. The extensional reactivation of preexisting structures and development of new fractures created permeability for the circulation of the ore-forming fluids and provided spaces for uranium precipitation. The ore-forming fluids are characterized by basinal brines with a meteoric water origin, possibly mixed with mantle-derived fluids. The uranium was mostly contributed by the host volcanic and sub-volcanic rocks. The precipitation of uranium is related to redox reactions with reductants such as Fe2+, H 2 S and CH 4 as well as other mechanisms related to change of physical and chemical conditions due to fluid boiling. The comprehensive review of the geological characteristics related to uranium mineralization reveals that the key factors controlling the uranium mineralization in the Xiangshan volcanic basin are related to the coupling of shallow (development of oxidizing fluids in the redbeds and brittle structures in the volcanic rocks) and deep-seated (thermal activities related to mafic magmatism) geological processes. It is proposed that meteoric water infiltrated into the high-permeability redbed basins, and evolved to oxidizing basinal fluids. The oxidizing fluids further circulated into the volcanic basin along brittle structures and extracted uranium from the volcanic rocks. The heat provided by mafic magmatic activities accompanying upward-flowing deep-source hot fluids promoted the uranium extraction and transportation. [ABSTRACT FROM AUTHOR]

• Three main types of scheelite are recognized in the Zhuxi W deposit. • Different types of scheelite have distinct REE patterns and Mo contents. • Eu anomalies and Mo contents of scheelite are closed related to redox conditions. • REE patterns suggest most metals in the ores were derived from granitic magma. The Zhuxi W deposit in Jiangxi, South China, with a resource of 2.86 Mt W and an average grade of 0.54% WO 3 , is the largest W deposit in the world. The deposit occurs at the contact between a late Mesozoic granitic intrusion and Carboniferous – Permian carbonate rocks and Neoproterozoic metamorphic rocks. The ores are divided into three types: skarn ore (dominant), sulfide ore and greisen ore. Based on occurrences and petrographic relationships, scheelite (the dominant ore mineral) is classified into three types, i.e. type I (greisen), type II (skarn, specifically in the retrograde stage), and type III (hydrothermal sulfides). Type I and type II are time equivalent but spatially separated, whereas type III is later. The different types of scheelite have distinctly different REE and trace element compositions. Type I scheelite is characterized by an average ΣREE of 67.9 ppm, LREE/HREE ratio of 24.4, δEu of 8.5, Mo of 0.1 ppm and Sr of 1058 ppm, whereas type II scheelite features an average ΣREE of 48.1 ppm, LREE/HREE ratio of 10.6, δEu of 0.67, Mo of 1892 ppm and Sr of 90.1 ppm. Type III scheelite has an average ΣREE of 53.9 ppm, LREE/HREE ratio of 4.8, δEu of 17.5, Mo of 92.9 ppm and Sr of 37.1 ppm. The extremely high concentrations of Sr and highly positive Eu anomalies in type I scheelite are likely related to release of these elements from plagioclase in the granite during greisenization, whereas the extremely low concentrations of Mo may be related to the reducing and high-temperature nature of the magmatic fluid – Mo probably was mainly in the Mo4+ state and could not replace W6+ in the scheelite lattice. In contrast, the negative Eu anomalies and high Mo concentrations in type II scheelite suggest that the mineralizing environment in the retrograde alteration stage was relatively oxidizing, causing Eu to exist mainly as Eu3+, which is difficult to replace Ca2+ in scheelite, and Mo mainly as Mo6+, which is easy to replace W6+ in scheelite. In the sulfide mineralization stage, the fluid became relatively reducing again, and Eu2+ could easily replace Ca2+ in scheelite causing positive Eu anomalies, whereas Mo mainly exists as Mo4+ and precipitated as molybdenite, and so has limited substitution for W6+ in scheelite. The REE and trace element compositions of the dominant W mineral (type II scheelite), characterized by high concentrations of Mo, high LREE/HREE ratios and negative Eu anomalies, indicate that the ore-forming materials were mainly derived from the granitic intrusions. The variation of REE and trace elements in scheelite in time and space reflects a complex magmatic-hydrothermal mineralization process involving various fluid-rock reactions within the intrusion and in the country rocks. The formation of the Zhuxi W deposit is linked with a large fertile granitic intrusion, which delivered a large amount of W to the site of mineralization through convection within the magma chamber, and W precipitation in the skarn was largely caused by an abrupt drop in temperature and increase in pH of the ore-forming fluid. [ABSTRACT FROM AUTHOR]