Mineralization Characteristics and Chronology of the Mafic Intrusions in the Tianbaoshan Pb–Zn Polymetallic Deposit ( SW China): Implications for the Mineralization Model

The Tianbaoshan deposit in the western Sichuan‐Yunnan‐Guizhou (SYG) metallogenic province contains a Pb–Zn–Cu–Ag assemblage and discrete Cu‐rich mineralization, distinguishing it from many Zn–Pb deposits in the region. However, the temporal relationship between mafic intrusion and mineralization remains controversial and directly affects the interpretation of the ore‐forming model. In this study, we combine underground and surface geological observations, ore petrography, TESCAN Integrated Mineral Analyzer (TIMA) mineral mapping, zircon cathodoluminescence (CL) and trace‐element data, zircon U–Pb geochronology by laser ablation inductively coupled plasma mass spectrometry (LA‐ICP‐MS), and whole‐rock geochemistry of the mafic rocks to constrain the origin and timing of the mafic intrusions and their relation to ore formation. Field, microscopic and TIMA observations show that ore veins fill fractures in mafic rocks and locally rework intrusive contacts between mafic dykes and dolostone, indicating that at least part of the sulfide mineralization postdated emplacement and brittle fracturing of the mafic rocks. The mafic samples contain inherited or xenocrystic zircons, whose age spectra is complex. The youngest grains yield ages of ca. 58 Ma and ca. 100 Ma, which provide maximum emplacement ages for the corresponding intrusions. Whole‐rock geochemical data indicate alkaline to weakly alkaline within‐plate affinities and are consistent with mantle‐derived magmatism modified by fractional crystallization and limited crustal contamination. These results support an epigenetic, structurally controlled hydrothermal model in which ore‐forming fluids were introduced after mafic emplacement. The available data permit a late post‐58 Ma mineralization stage for part of the system, but they do not justify assigning the entire Tianbaoshan deposit to a single Cenozoic mineralization event.