Formation of a granite-related Sn-Pb-Zn-(Ag) deposit from three discrete mineralization events around a common magmatic-hydrothermal center over a span of ~45 million years at Changpu, eastern Guangdong, South China
Authors: Yan Qing-He , Chi Guoxiang , Wang He , Liu Bingbing , Zhang Wei 
Published: November 2024

Abstract
Magmatic-hydrothermal Sn-(W) mineralization is commonly associated with Pb-Zn-Ag mineralization, forming Sn-polymetallic deposits that typically exhibit a zonation from proximal Sn-(W) to distal Pb-Zn-Ag, alongside a paragenetic sequence from early Sn-(W) to late Pb-Zn-Ag mineralization. Traditional models generally propose that these deposits formed from a single magmatic-hydrothermal event characterized by continuously decreasing temperatures. However, our study of the Changpu Sn-Pb-Zn-(Ag) deposit in eastern Guangdong, South China, reveals a more intricate mineralization history. There, metal zonation results from three distinct mineralization events occurring over a prolonged period. The Sn orebodies at Changpu occur as cassiterite–tourmaline–quartz–(muscovite) veins and breccia zones in the central part of the deposit, whereas the Pb-Zn-Ag orebodies occur mainly as sulfide-(cassiterite) veins peripheral to the Sn orebodies. The hydrothermal processes related to mineralization are divided into three periods, and each corresponds to a unique mineralization event. Period 1 is characterized by tourmalinization with minor Sn mineralization, period 2 represents the main Sn mineralization, and period 3 features predominant Pb-Zn-Ag mineralization. Different isotopic dating methods were used to obtain the ages of these mineralization periods: ca. 150 Ma for period 1 (U-Pb dating of cassiterite and Ar-Ar dating of fluid inclusions in quartz), ca. 130 Ma for period 2 (U-Pb dating of cassiterite), and ca. 105 Ma for period 3 (Ar-Ar dating of muscovite). These ages overlap with the reported zircon U-Pb ages for quartz porphyry dike (144.1 ± 1.2 Ma) and rhyolite (153.9 ± 1.3 Ma) in the deposit area. Fluid inclusions in cassiterite and quartz are of the H2O-CO2-CH4-NaCl compositional system in all of the periods and show a decrease in temperature and salinity from the early to late stages within each period. The H isotopes of fluid inclusions in cassiterite and quartz fall within the field of magmatic water, and the O isotopes of the ore-forming fluids calculated from the O isotopes of cassiterite and quartz are slightly shifted away from the field of magmatic water toward meteoric water. These geochronological and isotopic data, together with fluid pressures calculated from fluid inclusion data, suggest that three distinct magmatic-hydrothermal Sn-Pb-Zn mineralization events occurred at the same location over ~45 m.y., resulting in the observed metal zonation due to the evolution of the magmatic system and continuous surface erosion. The magmas responsible for the three mineralization events are linked via a deep fault to a crustal source region, where discrete partial melting processes are related to episodic slab-foundering or slab rollback of the paleo-Pacific plate during the Mesozoic in South China. This proposed model has significant implications for mineral exploration at depth within the study area and offers valuable insights for areas with similar geological contexts globally.