Fusheng Guo

The Xiangshan Uranium Deposit located in Jiangxi Province represents the largest volcanic-hosted uranium deposit in Asia and serves as a critical uranium production base in China. Clay alteration serves as a key prospecting indicator for this deposit, and its quantitative characterization through high-resolution spectroscopy is crucial for elucidating the relationship between hydrothermal activity and uranium mineralization. Addressing the current shortcoming in hyperspectral alteration mapping—which primarily focuses on qualitative mineral identification while lacking systematic quantitative characterization of diagnostic absorption trough parameters—this study utilized ZY1-02E (Chinese Resource Satellite-1-02E) satellite hyperspectral imagery as the data source. Following preprocessing, key parameters of the diagnostic absorption trough at 2205 nm for clay-altered minerals—including depth, area, and symmetry—were quantitatively extracted to construct a spectral index reflecting the intensity of clay alteration. Subsequently, the spatial distribution characteristics of these parameters were systematically analyzed. It was found that, with the line connecting Yankeng, Youjiashan, Xiangshan, and Yunji serving as a boundary, clay alteration generally exhibits a distribution trend of being stronger in the northwest and weaker in the southeast, with morphological features characterized by a combination of strip-like, ring-shaped, and nodular patterns. Based on these findings, nine prospective exploration areas were delineated, including five Class-I and four Class-II prospective exploration areas. High-value anomalies in the absorption trough parameters show good spatial correlation with known uranium deposits and fault structures, effectively indicating the centers of hydrothermal alteration and fluid migration pathways. This study advances the remote sensing identification of clay alteration from qualitative mapping to the quantitative analysis stage, providing a scientific basis for further exploration in the Xiangshan mineralized area. The established method is highly applicable to similar volcanic-type uranium mineralized areas.

Hyperspectral remote sensing enables precise identification of alteration mineral through spectral–image integration and high-resolution capabilities. However, vegetation interference significantly hinders the extraction of alteration information in vegetated areas, thereby posing challenges to the reliable identification of alteration minerals. This study employs GF-5B satellite AHSI imagery acquired in the Huzhou region of Zhejiang Province, China, to address this challenge via a novel Zonal Adaptive Vegetation Suppression Technique (ZAVST). By constructing segmented statistical models that links reflectance characteristics across multiple spectral bands to NDVI values, ZAVST demonstrates an enhanced capability to mitigate vegetation obscuration effects on subsurface lithological features while substantially improving the identification of subtle spectral signatures characteristic of mineralization. Results reveal distinct spatial patterns: Fe-bearing alteration minerals (hematite, pyrite) align along NE-trending faults and volcanic basin margins; Al-OH alterations (montmorillonite, kaolinite) cluster near intrusive contacts; Mg-OH alterations (chlorite, epidote) occur at interfaces between carbonate sequences and concealed intrusions. Composite alteration anomalies exhibiting stacked mineral signatures (up to four distinct types) were identified across the region, demonstrating a strong spatial correlation with known mineralization centers. By integrating alteration zonation, structural lineaments, stratigraphy, geochemical anomalies, and orebody records, this study delineated four priority targets: Lijiaxiang Town, eastern Meixi Town, Miaoxi Town, and the central Moganshan Volcanic Basin.

The timing of uranium mineralization in the Xiangshan ore field has long been controversial. Although various geochronometers have been applied by previous researchers, including pyrite Rb-Sr, mica Ar-Ar, and fluorite Sm-Nd, the results remain inconsistent and inconclusive. In recent years, the discovery of abundant Pb-Zn veins in the deeper parts of the Xiangshan ore field has further complicated the interpretation of its metallogenic history. In this study, abundant vein-type hydrothermal apatites closely associated with U-Pb-Zn polymetallic mineralization were identified in both uranium and Pb-Zn ore veins. Combined major-element Electron Probe Microprobe Analysis (EPMA), Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) U-Pb dating, and trace-element analysis were conducted on these apatite grains. The results suggest a mineralization age of 130.9 ± 1.1 Ma for the Shannan uranium deposit, which is consistent with the previously reported apatite U-Pb age of 131.3 ± 7.2 Ma from the Zoujiashan uranium deposit and coincides with the main pulse of volcanic-intrusive activity in the Xiangshan ore field (133–137 Ma). The deep Niutoushan Pb-Zn deposit suggests a younger mineralization age of 124.5 ± 1.3 Ma, which is consistent with a thermal event age of 125.6 Ma determined by zircon fission-track dating and the zircon LA-ICP-MS U-Pb age of late-stage granite porphyry (125.4 ± 1.0 Ma). These ages may constrain the timing of U-Pb-Zn polymetallic mineralization in the Xiangshan ore field. Both magmatic and hydrothermal apatites are classified as fluorapatite and exhibit similar chondrite-normalized rare earth element (REE) patterns. Compared with magmatic apatites, hydrothermal apatites are characterized by elevated Th, U, Ca, and Sr contents, depletion in light rare earth elements (LREEs), Mn, and Na, and distinctly lower Th/U ratios. On major-element variation diagrams, magmatic and hydrothermal apatites define coherent trends but display clear compositional differences related to their formation stages. Apatites from uranium ore veins show strongly negative Eu anomalies and weakly positive Ce anomalies, similar to magmatic apatites. In contrast, apatites from Pb-Zn ore veins display positive Eu anomalies and weakly negative Ce anomalies, with lower Mn and Ga contents and higher SO₃ contents relative to both magmatic apatites and hydrothermal apatites from uranium ore veins. These features indicate that the ore-forming fluids during Pb-Zn mineralization were characterized by significantly higher oxygen fugacity than those during uranium mineralization and magmatism. Combined with published Sr isotopic data for the Xiangshan ore field, we propose that both uranium and Pb-Zn mineralization were genetically linked to the prolonged magmatic evolution of the deep volcanic-intrusive complex. The subsequent incursion of meteoric water modified the physicochemical conditions of the ore-forming system, particularly during the formation of the Pb-Zn mineralization.

Cavernous weathering is commonly found on sandstone slopes in different environments. Either a single dominant process or polygenetic agents require to be invoked in order to interpret the development. The Yongningshan hill of the central Loess Plateau is representative of cliff dwellings in Northwest China, which is characterized by well‐developed cavernous weathering features and provides a good opportunity for the better understanding of sandstone weathering in the Loess Plateau. Multiple methods, including field survey, in‐situ rock strength measurement, along with experiments on samples for microscopic observation, element composition and salt chemistry, were employed to investigate the controlling factors of cavernous weathering. The results show that cavern development is different on the four slopes with the western slope hosting massive honeycombs, tafoni and hardened surfaces. The porous and permeable aeolian sandstones are fundamental, because they provide space and pathways for the transportation of water and salt, honeycombs dominantly aligning within the lamination of cross‐beds. The environmental factors such as the seasonal wetting and drying cycle, aeolian salt, moisture and water vapor are key factors for the development of cavernous weathering forms. The northern and northwestern wind‐blown dust storms have brought abundant salts, the lengthier dry periods of the wetting and drying cycle being beneficial for salt accumulation within caverns, favoring salt weathering.