Geochemistry and U–Pb geochronology of the granite porphyry in Bainiuchang, Southeastern Yunnan, China

The Bainiuchang Ag-polymetallic ore deposit, located in southeastern Yunnan, China, is one of the region’s largest deposits. However, the hypabyssal granite porphyry within this mining area has yet to be comprehensively investigated. In this study, we conducted geochemical, geochronological, whole-rock Sr–Nd isotope, and zircon Hf isotope analyses on granite porphyry samples collected from the Bainiuchang deposit. The results indicate that the granite porphyry formed between 87.5 and 87.4 Ma in the Late Yanshanian period. Geochemically, the granite is strongly peraluminous, with high silica and alkali contents consistent with S-type granite characteristics. The granite porphyry is enriched in large-ion lithophile elements (Rb, Th, U, and K) and is relatively depleted in Ba and Sr. The initial ⁸⁷Sr/⁸⁶Sr ratios are high (0.71392–0.71585), accompanied by low ε_Nd(t) values (− 8.9 to − 8.2). The zircons exhibited similarly low ε_Hf(t) values (− 9.31 to − 3.6). These data suggest that the porphyry-forming magma originated from a continental crustal source. The two-stage Hf and Nd model ages are estimated at 1534–1216 Ma and 1615–1561 Ma, respectively. Thus, the granite porphyry likely formed under a strike-slip extensional setting in the Late Yanshanian period and resulted from the re-melting of Proterozoic basement metagreywackes. This porphyry shares a similar magmatic origin with concealed granite bodies within the deposit and is associated with structural reactivation during the Yanshanian. The findings of this study provide valuable insights into the tectonomagmatic mineralization processes in the Bainiuchang area.