Timing and genesis of the Longbohe Neoproterozoic VMS deposit: Constraints from apatite U-Pb geochronology and sulfur isotopes

• Longbohe deposit, located within the Ailaoshan-Red River shear zone of the South China Block, hosts significant copper mineralization within both volcanic and sedimentary formations. • Apatite U-Pb dating yields ages of 771 ± 20 Ma for the spilite-keratophyre sequence and 750 ± 17 Ma for copper ores, indicating contemporaneous volcanic-sedimentation and mineralization. • In situ sulfur isotope analyses suggest dual sources of ore-forming sulfur from magmatic sulfur and microbial reduction of sulfur in sedimentary country rocks. The Longbohe deposit, located within the Ailaoshan-Red River shear zone of the South China Block, hosts significant copper mineralization in both volcanic and sedimentary formations. Despite extensive geochronological studies on regional meta -volcanic and meta -sedimentary rocks, the timing and genesis of mineralization in the Longbohe deposit—especially in its understudied eastern ore belt—remain poorly constrained. This study presents new in situ U-Pb dating of apatite and sulfur isotope analyses of sulfides, focusing on the Longda ore block in the eastern ore belt of Longbohe deposit. Apatite U-Pb dating yields ages of 771 ± 20 Ma for the spilite-keratophyre sequence and 750 ± 17 Ma for copper ores, indicating contemporaneous volcanism and sedimentation with mineralization. In situ sulfur isotope analyses reveal that sulfides in volcanic rock formations have δ 34 S values ranging from −0.24 ‰ to 2.48 ‰ (mean 1.59 ‰), consistent with a magmatic sulfur source. In contrast, sulfides from sedimentary rock formations exhibit distinctly negative δ 34 S values (−10.09 ‰), likely driven by changes in physicochemical conditions (e.g., sulfate thermochemical reduction) in sedimentary environments. These results, combined with lithological, structural, and geochronological evidence, support that the Longbohe deposit is a volcanic-hosted massive sulfide (VMS) deposit formed during Neoproterozoic. This study provides critical guidance for future exploration of Neoproterozoic VMS deposits in the Ailaoshan-Red River shear zone, particularly targeting spilite-keratophyre sequences, the primary ore hosts in the eastern ore belt of the Longbohe deposit.