Apatite and garnet geochronological and geochemical constraints on the properties and evolution of the Tielukan Cu polymetallic deposit, Jiangxi Province

Abstract

During the forming process of magmatic rocks and related skarns, apatite and garnet typically accommodate various trace elements, whose variation could be utilized to monitor the ore-forming conditions within the magmatic-hydrothermal system. Situated in the Jiurui district, which lies along the Middle-Lower Yangtze River Metallogenic Belt (MLYRMB), the Tielukan copper polymetallic deposit represents a newly identified large-scale skarn deposit. Nevertheless, the age and the process of ore formation have not been well defined. In this study, analyses using Scanning Electron Microscope (SEM), Electron Probe X-ray Micro-Analyzer (EPMA), and Laser Ablation inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) were conducted to investigate the textures, geochemistry, and ages of apatite and garnet from the Tielukan deposit, aiming to illustrate its formation mechanism. Garnet in the Tielukan deposit is classified into two generations, including anhedral Grt-Ⅰ and euhedral Grt-Ⅱ. U-Pb isotope dating using LA-ICP-MS reveals that apatite, Grt-Ⅰ, and Grt-Ⅱ were formed at 145 Ma, 140 Ma, and 141 Ma, respectively. These ages are in alignment, suggesting a genetic link between the skarn formation and granodiorite. The geochemistry shows that granodiorite is adakitic and the primitive magma had high F content and elevated ƒO_2, sourced from the interaction between enriched lithospheric mantle and thickened lower crust. The normalized REE pattern of garnet indicates that the fluid system evolved from the closed state to an open state, resulting elevation of acidity and salinity, reduction of ƒO₂ and precipitation of ore-forming materials.