Late Triassic gold mineralization in the Buziwan breccia pipe (North China Craton): Integrated geochronology reveals magma-driven hydrothermal system and tectonic transition during cratonic reactivation

The Buziwan gold deposit, a breccia pipe-hosted deposit with proven reserves exceeding 10 tonnes Au, represents a distinct type of mineralization within the intracontinental North China Craton (NCC). Despite its economic significance, the precise timing of hydrothermal mineralization remains contentious, with proposed ages ranging from Late Triassic to Cretaceous. This critical uncertainty has hindered the development of definitive genetic models that link ore formation, breccia pipe evolution, and the regional tectonic setting. To resolve this geochronological dilemma, we present an integrated investigation combining field geological survey, ore microscopy, and advanced in-situ geochronology (sericite Rb-Sr and monazite U-Pb), complemented by Nd isotope systematics. Gold mineralization predominantly occurs as sulfide-quartz-sericite veinlets within the breccia pipe matrix, spatially constrained by an E-W striking main fault zone. Microscopic analysis reveals gold as native grains within sulfides, paragenetically associated with sericite, quartz, and monazite. Monazite exhibits weak negative Eu anomalies (Eu/Eu* = 0.49–0.81) and low Th concentrations (<0.38 wt%), confirming its hydrothermal genesis. High-precision U-Pb dating of monazite yields weighted mean ages of 227 ± 4 Ma and 227 ± 3 Ma, statistically consistent with the emplacement age of a concealed monzonite porphyry (229 Ma) within the breccia complex and the sericite Rb-Sr age (224 ± 13 Ma). This robust geochronological congruence establishes a genetic continuum between magma emplacement, breccia pipe formation, and gold mineralization during the Late Triassic. Hydrothermal monazite εNd(t) values are similar to those of the monzonite porphyry whole-rock samples, confirming ore-forming fluids exsolved from the crystallizing felsic magmas. These fluids migrated along breccia-conduit networks, precipitating sulfides via fracture-filling. Tectonically, this 228–224 Ma metallogenic event coincides with incipient lithospheric thinning and post-collisional relaxation of the NCC following the closure of the Paleo-Asian Ocean. We propose that gold mineralization was dynamically modulated by the Triassic tectonic transition from compressional orogeny to extensional collapse along Precambrian microcontinental margins – a regime characterized by high heat flow and a thinned lithosphere. This model not only reconciles the spatiotemporal association between auriferous breccia pipes and coeval igneous suites but also provides exploration vectors for concealed deposits in cratonic reactivation zones.