Zircon geochronology and geochemical characteristics of quartz veins in the Guangning area, Yunkai Massif: implications for tectonic evolution and mineralization

Abstract

The Guangning area, located in the northeastern margin of the Yunkai Massif, is an ideal site for investigating tectono-magmatic activities of the South China Block owing to the widespread exposure of quartz veins and ancient basement rocks. To unravel the Neoproterozoic basement evolution of the Yunkai Massif and its mineralization implications, this study conducts a systematic investigation of quartz veins from the Guangning area using LA-ICP-MS zircon U-Pb dating and in situ trace element geochemical analysis. The results show that most zircons in the study area develop typical magmatic oscillatory zoning with Th/U ratios all above 0.1. Their rare earth element (REE) patterns are characterized by light REE (LREE) depletion, heavy REE (HREE) enrichment, as well as pronounced positive Ce anomalies and negative Eu anomalies, indicating a dominantly magmatic origin. Zircon age spectra of the four samples are highly consistent, all featuring a prominent peak at ∼1.0 Ga, which corroborates the presence of material related to Grenville-aged tectono-magmatic events in the deep crust of the Yunkai Massif. Calculations yield zircon crystallization temperatures ranging from 640.2 °C to 943.8 °C, with an average of 790.1 °C. The mean relative oxygen fugacity (ΔFMQ) of the magma is −2.3, indicating that the deep-seated magma formed under a high-temperature and relatively reduced condition. The magma underwent significant fractional crystallization of plagioclase and apatite during its evolution. Tectonic discrimination based on zircon trace elements suggests a continental arc setting for zircon formation, recording a tectonic transition from arc-continent collision to post-collisional extension and collapse. This study confirms the existence of Grenville-aged tectono-magmatic activities in the deep crust of the Yunkai Massif. The ancient deep-seated materials may have supplied ore-forming components for regional gold mineralization; the high-temperature reduced system favors the activation and migration of gold; and the formation of tectonic faults provided migration pathways and precipitation spaces for ore-forming fluids. These findings provide theoretical support for regional gold exploration.