Abstract
The Puziwan gold deposit, located in north-western Shanxi province in North China, is a typical cryptoexplosive breccia-related gold deposit. Here we present new zircon U-Pb and pyrite Rb-Sr geochronology, and zircon Lu-Hf and pyrite S-Pb isotopic data to constrain the timing of ore formation and to gain insights into the source of the metal and genesis of the deposit. The clasts of the ore bodies of the deposit consist mainly of quartz porphyry and granulite. Pyrite and the oxidized limonite account for ∼70% of the total ore minerals associated with the entire ore-forming process. Gold is dominated by electrum and native gold which mainly occur in the interstices and fissures of pyrite. We identify six stages during the mineralization process: (1) gold-bearing quartz-pyrite, (2) quartz-pyrite-sericite, (3) quartz-sericite-Au-Ag polymetallic sulfides, (4) quartz-Ag polymetallic sulfides, (5) gold-bearing sulfide-quartz, and (6) carbonate-pyrite. The pyrite from the main mineralization stage yields Rb-Sr isochron age of 139.2 ± 1.1 Ma, suggesting that the Puziwan gold deposit formed during the Early Cretaceous, much later than the Triassic emplacement of the quartz porphyry (∼229 Ma). The S, Pb and Sr isotopic data suggest that the source of the ore is closely related to deep-seated magmatism derived through mixing of lower crust and mantle material. The geochronological and isotopic data preclude the associated Triassic quartz porphyry as the source, and suggest probable hidden deep-seated Cretaceous magmatism, forming an intrusion related auriferous system. The brecciation resulted from the cryptoexplosion and fluidization. Synchronously, or slightly after the brecciation, the ore fluids were channeled along the breccias and fractures or faults within the fracture zone. Occurrence of other gold deposits in the North China Craton which share similar geochronological and isotopic characteristics with Puziwan gold deposit indicates that these cryptoexplosive breccia-related gold deposits formed during lithospheric extension associated with craton destruction triggered by the subduction of Paleo-Pacific Plate during the Late Jurassic to Early Cretaceous.
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