Multistage exhumation and preservation of Triassic porphyry deposits driven by Tethys tectonic evolution

Porphyry deposits emplaced at shallow crustal depths are vulnerable to overprinting during orogenic evolution, yet the balance between exhumation and preservation remains poorly constrained across variable structural settings. We integrate zircon U-Pb geochronology, zircon and apatite fission-track thermochronology, inverse time-temperature modelling, and quartz-hosted fluid-inclusion microthermometry for the Aikengdelesite Cu-Mo, Harizha Ag-Cu, and Halongxiuma Mo-W districts. Zircon U-Pb ages indicate emplacement of ore-related porphyries at 243-242 Ma, 235-223 Ma, and 236-235 Ma, respectively. Single-grain zircon fission-track ages define five post-emplacement cooling clusters at 212-203 Ma, 201-181 Ma, 177-157 Ma, 156-125 Ma, and 120-108 Ma, recording episodic Mesozoic cooling superimposed on long-term thermal relaxation after Triassic magmatism. Apatite fission-track ages, mean track lengths, and inverse t-T models indicate prolonged residence within the apatite partial annealing zone, followed by accelerated late Cenozoic cooling, most clearly expressed at ca. 20-15 Ma. Fluid inclusions yield trapping temperatures of 119-406 ℃, salinities of 0.18-21.87 wt.% NaCl eq., and pressures of 19-109 MPa, corresponding to average hydrothermal trapping depths of ca. 5-6 km. In contrast, preferred cumulative post-ore denudation is modest, at ca. 2.1 km for Aikengdelesite, ca. 1.5 km for Harizha, and ca. 2.3 km for Halongxiuma. Integration of thermochronology, fluid inclusion constraints, and alteration assemblages indicates that the three districts are moderately preserved porphyry systems, with deeper stockwork, potassic, and intrusion-proximal domains remaining prospective exploration targets.