Genesis of the large Hebaoshan gold deposit, Southeast China: Constraints from in situ U-Pb dating of hydrothermal apatite and monazite and geochemistry of pyrite and carbonates

Abstract The Cathaysia Block in southeastern China hosts significant lode gold deposits. Similar to other metamorphic terrains, these deposits formed through prolonged infiltration of compositionally diverse hydrothermal fluids. However, the connections between gold mineralization and regional tectonics, magmatism, and metamorphism remain elusive due to insufficient constraints on mineralization ages. Here, we present new U-Pb age data on hydrothermal apatite and monazite, combined with trace element and isotope analyses of multiple pyrite and carbonate generations, from the large Hebaoshan gold deposit (41.5 t Au) in the Cathaysia Block. These new data refine the metallogenic model for this important ore deposit in South China. Two distinct mineralization events are recognized: (1) low-grade Mineralization Event I, characterized by quartz–carbonate–pyrite veins, and (2) the main Mineralization Event II, marked by quartz–carbonate–sulfide–hematite veins. Hydrothermal apatite texturally intergrown with pyrite from Event I yielded a U-Pb age of 395.3 ± 5.7 Ma, coinciding with host rock deformation, revealing a previously unrecognized late-stage hydrothermal event during the early Paleozoic orogeny. In contrast, hydrothermal monazite coexisting with auriferous sulfides in Event II veins yielded a significantly younger U-Pb age of 231.6 ± 2.6 Ma, representing the timing of the main gold mineralization. Pyrite from Event I (Py1) is enriched in Co and Ni, whereas Py2 and Py3 from Event II show elevated As concentrations. These chemical variations, attributed to distinct physicochemical conditions (primarily temperature) of the hydrothermal fluids, indicate higher formation temperatures for Event I than Event II. Carbonates from Event I exhibit insignificant Eu anomalies, suggesting precipitation under reduced conditions with dominant Eu2+. Conversely, Event II carbonates display positive Eu anomalies, indicative of crystallization from more oxidizing fluids. The main gold mineralization at Hebaoshan (ca. 232 Ma) predated granite emplacement in the region by >200 m.y., precluding their genetic link. Integrating our results with existing data, we propose that the Early Devonian and Late Triassic mineralization events at Hebaoshan correlate with regional metamorphism, deformation, and fluid circulation during the early Paleozoic and Indosinian orogenesis. Both events exhibit hallmark features of orogenic-type gold deposits. This study underscores the necessity of acquiring precise geochronological and geochemical data within robust geological and petrographic frameworks during early research stages. Such an approach ensures accurate determination of geological settings and the establishment of reliable metallogenic models for complex lode gold systems.