Temporal coupling of fault valve and pattern switching model: New insights into the gold mineralization mechanism in the Jiaodong gold deposit

Many mesothermal gold-quartz vein systems are controlled by high-angle reverse faults. However, this observation presents a classic "structural paradox": in a regional compressional setting, such high-angle reverse faults not only contradict Anderson's fault theory, but also fail to serve as effective fluid conduits due to their friction-locking effect. Currently, there are two main explanatory mechanisms: the fault-valve model suggests that pre-existing high-angle fractures periodically reactivate during tectonic activity, driving the accumulation and release of fluid overpressure through seismic pumping, thereby promoting mineralization. The mode-switching model, based on the "capped" yield surface theory, proposes that high-angle reverse faults can spontaneously form under chem-mechanical feedback, accompanied by fluid pressure oscillations and rupture mode transitions, leading to mineralization through dissolution-precipitation processes. This paper compares the theoretical foundations and geological applicability of the two mechanisms and uses field and core observations from the Jiaodong gold deposits as an example for analysis. Two types of structural associations were identified in the cores: one is a high-angle reverse fault with ductile-brittle deformation prior to mineralization, which is consistent with the "cap-end" failure behavior under low fluid pressure and high differential stress conditions; the other is a near-horizontal tensional vein that cuts through early structures. The study indicates that during the formation of the Jiaodong gold deposits, the fault-valve and mode-switching models correspond to different evolutionary stages of the Jiaodong mineralization system: the early stage (> 135 Ma) was dominated by the mode-switching model in a compressional setting, forming high-angle reverse faults; the main mineralization stage (~120 Ma) showed a tectonic regime shift to extension, with the fault-valve model controlling the periodic reactivation of pre-existing fractures and large-scale gold precipitation; and the late stage (~115 Ma) during stress relaxation may have reverted to the mode-switching model. The transition and coupling of the two mechanisms are jointly controlled by regional stress state, pre-existing structures, and fluid pressure, shaping the unique mineralization structure and timing in the Jiaodong region. This study provides a new temporal framework and mechanistic explanation for understanding the coupling processes of tectonics-fluids-reactions in hydrothermal mineralization systems.