Genesis of the gold deposits in the northeastern Jiaolai Basin, Jiaodong, China: Constraints from geochronology, geochemistry, and thermodynamic modeling

The northeastern Jiaolai Basin of China hosts significant gold resources (223 t contained Au) and has substantial exploration potential for the identification of new gold mineralization. However, the mineralization in this area differs from most deposits elsewhere in the Jiaodong gold province in terms of mineral assemblages and host rocks, meaning that the genetic processes that formed the Jiaolai Basin mineralization remain controversial. Here, we integrate field observations, petrography, in situ monazite U-Pb and sericite Rb-Sr dating, mineral chemistry, sulfur isotope analysis, and thermodynamic modeling of the Tudui, Longkou, and Houkuang deposits to develop a genetic model for the gold mineralization located within the Jiaolai Basin. The deposits in this area are hosted within Paleoproterozoic metamorphic rocks and granites and are dominated by disseminated sulfide-hosted Au mineralization controlled by NE-SW−striking faults. Monazite U-Pb and sericite Rb-Sr dating constrain the timing of mineralization to the Early Cretaceous (ca. 120 Ma), synchronous with regional gold mineralization elsewhere within the Jiaodong gold province. The mineralization contains two generations of pyrite: Pyrite-I is medium- to coarse-grained, euhedral to subhedral, and is present as large individual crystals that are commonly replaced by magnetite. Pyrite-II is anhedral to subhedral and coexists with pyrrhotite, chalcopyrite, magnetite, and gold. In situ sulfur isotope analysis indicates that δ34S values decrease from Py-I to Py-II (Longkou: 10.6‰ to 8.4‰; Houkuang: 9.5‰ to 6.3‰; Tudui: 7.4‰ to 6.3‰), indicating an increase in oxygen fugacity (fO2) of the ore-forming fluid. Thermodynamic modeling indicates that this increase in fO2, along with the formation of alteration minerals, reduced the solubility of Au(HS)2− complexes within the ore-forming hydrothermal fluid by ∼75%, leading to efficient gold precipitation. The overall heavy sulfur isotope values (6‰−12‰) combined with previously published lead isotope data that yielded values similar to those obtained for gold deposits elsewhere within the Jiaodong region suggest that the mineralization in the study area involved metals and sulfur derived from a subduction-modified region of the lithospheric mantle. These data demonstrate that gold mineralization in the northeastern Jiaolai Basin was contemporaneous with regional ore-forming events and that all of the deposits in this area derived metals and sulfur from similar sources and record identical metal precipitation processes. All of this indicates that the gold mineralization in the northeastern Jiaolai Basin is genetically linked to the regional-scale Early Cretaceous ore-forming system in the wider Jiaodong region.