Nature, age, and tectonic setting of granitoid-hosted, orogenic gold deposits of the Jiaodong Peninsula, eastern North China craton, China

摘要

The Jiaodong gold province in the southeastern margin of the North China craton, along the northern side of the eastern part of the Qinling - Dabie - Sulu collisional belt, contains > 900 t Au mainly hosted in Mesozoic granitoids. This contrasts with typical Late Archean orogenic lode - gold deposits that occur dominantly in greenstones and other Phanerozoic oro-genic gold deposits of the Pacific Rim that are mainly hosted in metasedimentary rocks despite, in both examples, widespread syntectonic granitoids. The Jiaodong region is one of the largest granitoid - hosted orogenic gold provinces in the world. The Mesozoic granitoid host rocks were formed by extensive reworking of pre - existing crustal materials. The 250 - 200 - Ma age peak for zircons in the granitoids indicates that high - pressure metamorphic rocks of the Su - Lu terrane were involved in melting events beneath the entire Jiaodong Peninsula. Resulting granitoids intruded into Late Archean basement episodically at ca. 160-150 and 135 - 125 Ma. Gold deposits are ubiquitously controlled by faults that cut granitoids of both ages. Disseminated - and stockwork - style gold mineralization (Jiaojia - type) occurs in alteration zones along first - order faults and quartz vein - style mineralization (Linglong - type) is sited in subsidiary second - and third - order faults. Both styles of mineralization have an inner zone of silicification, sericitization, K - feldspar alteration, and sulfidation, and an outer zone of K - feldspar alteration and sericitization. Altered rocks are characterized by introduction of volatiles, Fe, Mg, K, Rb, As, Bi, Sb, Au, and Ag, and locally Cu, Pb, and Zn. Gold deposits from throughout the Jiaodong gold province have similar structural controls, alteration assemblages, ore fluid chemistry (CO_2 - rich), formation temperatures (250～350℃), and C-, H-, O-, and S- isotope signatures, indicating a broadly similar nature and origin of the deposits. The age of gold mineralization is constrained between ca. 126 and 120 Ma, by SHRIMP U - Pb zircon dating on host rocks and a post - gold dike in the Zhao - Ye gold belt, and Rb - Sr and K - Ar dating on hydrothermal alteration minerals and ores in the Zhao - Ye, Xixia, and Muping - Rushan gold belts. The lead isotope compositions of sulfide minerals from gold deposits in these belts reflect local host rock compositions. Gold mineralization in the Jiaodong Peninsula (126～120 Ma) is about 100 million years younger than the main part of the Qinling - Dabie - Sulu orogen (230～200 Ma). It does, however, overlap in time with subduction of the Pacific plate beneath the Eurasian continental crust during the Yanshanian orogeny. The 126 - 120～Ma age for gold mineralization is also characteristic of basement uplifts along the entire eastern half of the North China Craton. Available data favor a temporal link with the Pacific plate subduction.