Middle Devonian gold mineralization at the northern margin of the North China craton: Constraints from hydrothermal titanite, garnet, and zircon U-Pb geochronology of the Jinjiazhuang gold deposit

Abstract

The northern margin of the North China craton (NCC) is adjacent to the Central Asian orogenic belt. The region underwent arc-continental collision during the Middle Paleozoic, oceanic plate subduction and closure during the Late Paleozoic to Early Mesozoic, and tectonic reactivation during the Late Mesozoic. The Late Paleozoic–Early Mesozoic and Late Mesozoic tectonothermal events formed numerous gold deposits along the northern margin of the NCC. However, until now, it was unclear whether any gold mineralization formed during the Middle Paleozoic arc-continental collision. The Jinjiazhuang gold deposit is located in the Zhang–Xuan district at the center of the northern margin of the NCC. Gold mineralization is structurally controlled by NWW-SEE-striking faults cutting the Xiaozhangjiakou ultramafic intrusion and Da’nanshan alkaline complex, which exhibit zircon U-Pb ages of 400 ± 5 Ma (2σ, MSWD = 0.3) and 389 ± 3 Ma (2σ, MSWD = 0.8), respectively. Petrographic and geochemical data for titanite, garnet, and zircon grains from Jinjiazhuang gold ores indicate that these minerals have a hydrothermal origin and coprecipitated with the gold. Laser ablation inductively coupled plasma mass spectrometry analyses of the hydrothermal titanite, garnet, and zircon grains yielded reproducible U-Pb dates of 383 ± 12 Ma (2σ, MSWD = 1.4), 392 ± 2 Ma (2σ, MSWD = 0.79), and 391 ± 3 Ma (2σ, MSWD = 1.4), respectively. These new data suggest that the Jinjiazhuang gold deposit formed in the Middle Devonian and was coeval with the emplacement of the Da’nanshan alkaline complex, the genesis of which is related to post-collisional extension across the Bainaimiao island arc and NCC. The recognition of Middle Devonian gold mineralization related to alkaline complexes is of great significance for targeting similar gold deposits along the Fengning–Longhua fault, along which numerous Middle Devonian alkaline intrusions are located.