Multi-stage exhumation and preservation of the Mujicun porphyry Cu-Mo deposit, North China: A geo-thermochronological perspective

• The formation of the Mujicun deposit is related to the ca. 144 Ma rollback of the Palaeo-Pacific Plate. • Multi-stage different degree of cooling during ca. 110–15 Ma is revealed in the Mujicun deposit. • Subduction and collision dynamics along with East Asian monsoon drive exhumation and preservation. Porphyry deposits are critical global sources of Cu, Mo, and Au. However, the mechanisms of post-mineralisation modification, exhumation, and preservation across different tectonic regimes remain poorly understood. The Mujicun deposit, a rare intracontinental porphyry Cu-Mo deposit in the North China Block, formed during the Early Cretaceous lithospheric thinning induced by the Paleo-Pacific slab rollback. Early studies focused predominantly on its genesis, the lack of research on post-mineralisation evolution has hindered regional prospecting. This study employs multiple geo-thermochronology, including zircon-apatite U-Pb and (U-Th)/He dating, as well as apatite fission-track analysis, combined with associated thermal history modelling, to elucidate the deposit’s temporal evolution, exhumation history, and preservation potential. Geochronological data indicate that dioritic magma emplacement and related Cu-Mo mineralisation at Mujicun occurred at ca. 146–141 Ma and ca. 145–138 Ma, respectively, coinciding with regional extension driven by Paleo-Pacific subduction. Integrated geo-thermochronological data and thermal history modelling reveal four tectono-thermal phases: (1) Late Cretaceous rapid cooling (ca. 110–95 Ma) and slow cooling during ca. 95–66 Ma, linked to lithospheric thinning of the eastern North China Block and the early uplift of the Taihang Mountains, triggered by Paleo-Pacific subduction and Okhotomorsk-Eurasia collision; (2) Late Cretaceous to Paleogene weak reheating (ca. 85–35 Ma), attributed to coeval sedimentary burial in the North Taihang Mountain and the nearby Bohai Basin; (3) Paleogene slow cooling (ca. 66–35 Ma), correlated with Pacific slab rollback and far-field effects from the India-Eurasia collision, inducing extensional uplift and exhumation of the Taihang Mountains; and (4) Neogene enhanced cooling (ca. 35–15 Ma), driven by Pacific subduction, India-Eurasia convergence, Tibetan Plateau extrusion, and the intensified East Asian monsoon, resulting in differential exhumation and planation of the Taihang Mountains. The Mujicun deposit shows exceptional preservation, as its total exhumation depth since ∼110 Ma (∼3.56 km) closely aligns with its original ore-forming depth (∼3.2–3.9 km). This indicates minimal post-mineralisation exhumation and limited erosional modification. Whereas current exploration targets shallow mineralisation (<1.5 km), significantly deeper regional ore-forming depths (e.g., Dawan Mo deposit: 0.76–9.76 km) highlight the important potential for undiscovered Cu-Mo resources at depth within the North Taihang Mountain.