Sandstone-hosted Zn–Pb deposits constitute a globally important zinc and lead resource. However, the difficulty in constraining the time of mineralization poses substantial challenges for researchers attempting to decipher Zn–Pb mineralization processes through diverse geological phenomena. The Yanjiao deposit, where sulfides occur as vein-like structures within bleached Jurassic-Cretaceous red beds, is temporally associated with solid bitumen and multistage calcite veinlets. This geological assemblage provides an intriguing case for studying metallogenic processes in sandstone-hosted Zn–Pb systems. Solid bitumen developed parallel to bedding planes in calcareous sandstones indicates that hydrocarbon charging might have initiated as early as during the sedimentation. X-ray fluorescence element mapping of bleached zones reveals that high-permeability hydraulic activity dominated by sandstone liquefaction serves as the primary driver for element migration within sandstones. Symmetrical bleached bands along fractures margins were filled with solid bitumen + pyrite/marcasite (S2) + hydrothermal calcite. Fracture-hosted solid bitumen constitutes post-diagenetic thermal cracking or oxidation products derived from hydrocarbon fluid migration processes. The δ34SVCDT values of these S2 iron sulfides range from − 12.36‰ to + 36.12‰. Negative δ34SVCDT values indicate that H2S derived from organic compounds thermal cracking played a significant role in the initial stages of thermochemical sulfate reduction (TSR) within low-temperature open-system environments. Subsequent δ34SVCDT values ranging from moderately negative to positive values document mixing between thermal cracking-derived H2S and late-stage TSR-generated H2S characterized by progressive 34S enrichment. During Zn–Pb mineralization stage (S3), S3 sphalerite exhibits progressive enrichment in heavier sulfur isotopes from early to late sub-stages (S3-sp1: -25‰ to -14‰ and S3-sp3: -13.5‰ to -2.61‰), indicating that within the closed system, concurrent the reactions between hydrocarbons and sulfate facilitated the generation of increased quantities of H2S with elevated δ34SVCDT values. Rare earth element geochemistry of calcite reveals as shift from highly reducing (pre-ore: negative Eu anomaly) to moderately reducing (post-ore: positive Eu anomaly) hydrothermal conditions during hydrocarbon-aided reduction of sulfate. Uranium–lead dating of multi-stage fracture-filling calcites constraints mineralization to 39–28 Ma (Late Eocene–Oligocene), coinciding with late-stage Himalayan-Tibetan lateral collision orogeny-driven fluid pulsing. We develop a summary model for sandstone-hosted Zn–Pb deposits that provides a framework for future exploration in tectonically active orogenic belts.

An epigenetic model for the Yanjiao sandstone-hosted Zn–Pb deposit, China: constraints from petrology, geochemistry, and calcite U–Pb dating

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发表日期：

2026年1月15日

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Longlong Yue,
Yingchao Liu,
Linghao Zhao,
Shitou Wu,
Wang Ma,
Shiqiang Huang

摘要

Sandstone-hosted Zn–Pb deposits constitute a globally important zinc and lead resource. However, the difficulty in constraining the time of mineralization poses substantial challenges for researchers attempting to decipher Zn–Pb mineralization processes through diverse geological phenomena. The Yanjiao deposit, where sulfides occur as vein-like structures within bleached Jurassic-Cretaceous red beds, is temporally associated with solid bitumen and multistage calcite veinlets. This geological assemblage provides an intriguing case for studying metallogenic processes in sandstone-hosted Zn–Pb systems. Solid bitumen developed parallel to bedding planes in calcareous sandstones indicates that hydrocarbon charging might have initiated as early as during the sedimentation. X-ray fluorescence element mapping of bleached zones reveals that high-permeability hydraulic activity dominated by sandstone liquefaction serves as the primary driver for element migration within sandstones. Symmetrical bleached bands along fractures margins were filled with solid bitumen + pyrite/marcasite (S2) + hydrothermal calcite. Fracture-hosted solid bitumen constitutes post-diagenetic thermal cracking or oxidation products derived from hydrocarbon fluid migration processes. The δ³⁴S_VCDT values of these S2 iron sulfides range from − 12.36‰ to + 36.12‰. Negative δ³⁴S_VCDT values indicate that H₂S derived from organic compounds thermal cracking played a significant role in the initial stages of thermochemical sulfate reduction (TSR) within low-temperature open-system environments. Subsequent δ³⁴S_VCDT values ranging from moderately negative to positive values document mixing between thermal cracking-derived H₂S and late-stage TSR-generated H₂S characterized by progressive ³⁴S enrichment. During Zn–Pb mineralization stage (S3), S3 sphalerite exhibits progressive enrichment in heavier sulfur isotopes from early to late sub-stages (S3-sp1: -25‰ to -14‰ and S3-sp3: -13.5‰ to -2.61‰), indicating that within the closed system, concurrent the reactions between hydrocarbons and sulfate facilitated the generation of increased quantities of H₂S with elevated δ³⁴S_VCDT values. Rare earth element geochemistry of calcite reveals as shift from highly reducing (pre-ore: negative Eu anomaly) to moderately reducing (post-ore: positive Eu anomaly) hydrothermal conditions during hydrocarbon-aided reduction of sulfate. Uranium–lead dating of multi-stage fracture-filling calcites constraints mineralization to 39–28 Ma (Late Eocene–Oligocene), coinciding with late-stage Himalayan-Tibetan lateral collision orogeny-driven fluid pulsing. We develop a summary model for sandstone-hosted Zn–Pb deposits that provides a framework for future exploration in tectonically active orogenic belts.