Geochronology and zircon geochemistry of auriferous intrusions in the Bumo deposit, Hainan Province, China

Intrusion-related gold deposits (IRGS) are a low-grade, large-tonnage exploration target. Recently, auriferous magmatic rocks were found in the Bumo deposit of the Gezhen shear zone in Hainan Province, China. However, the geochronology and geochemical characteristics of the intrusions, as well as the mineralization potential, are still unclear. Field and petrographic work show that the sulfide-bearing intrusions can be divided into diorite porphyrites, quartz monzodiorites and monzodiorites. Zircon LA–ICP–MS U–Pb dating demonstrates that diorite porphyrites, quartz monzodiorites and monzodiorites were formed at 104 ± 1, 114 ± 1, 114 ± 1 Ma, respectively. In addition, sulfides in Yanshanian intrusion-related gold mineralization have δ34S values of 0.2–4.4‰, lower than those in Hercynian-Indosinian (1.9–9.8‰) orogenic deposits (ca. 219–378 Ma) in the Gezhen shear zone. In addition, all these intrusions display close correlations between Eu/EuN* with Th/U, consistent with the differentiation of amphibole, apatite and titanite from a hydrous melt. Moreover, zircon Eu/EuN* in the intrusions are higher than 0.4, demonstrating that the magmatic rocks have high water contents and oxygen fugacity values, favorable for gold mineralization. Consequently, the Yanshanian magmatic rocks can be a new potential gold exploration target in the Gezhen shear zone.