Exhumation and preservation of the Tianyu Cu-Ni deposit constrained by low-temperature thermochronology: Insights into the thermo-tectonic history of the Chinese Eastern Tianshan

The Chinese Eastern Tianshan is an important metallogenic region where major Cu-Ni ores are mined. Previous research in the region primarily focused on the ore genesis. Precise thermochronological data to constrain the exhumation history and preservation of the ore deposits are limited at best. Tianyu is one of these Cu-Ni deposits in the area. Here we present new low-temperature thermochronological data to contribute to the understanding of its exhumation and preservation history. Zircon (U-Th)/He ages of -134-69 Ma, apatite fission track ages of -100-75 Ma, and apatite (U-Th)/He ages of -117-38 Ma from five granodiorite samples of the ore wall rock at different depths of a borehole in the Tianyu deposit were obtained. Our thermochronological data and inverse thermal history modeling reveal a moderate to rapid and final basement cooling phase during the Cretaceous (-115-85 Ma) with an averaged cooling rate of -3-4 degrees C/Ma. It is envisaged that this phase eventually exposed the ore deposits and that posterior erosion was limited, contributing to the preservation of the deposit. Combined with previously published geochronological and thermochronological data, a multi-stage cooling history of the ore bearing host rocks can be established. After its late Permian (-280-260 Ma) magmatic-hydrothermal for-mation, two phases of accelerated regional cooling (i.e., in the late Permian-Early Triassic,-260-240 Ma; and the mid-Cretaceous,-115-85 Ma) can be recognized. The more intense Cretaceous cooling is associated with the ore body finally being exhumed to the surface, and provides essential information for ore exploration in the region. Further, we propose that areas in the Eastern Tianshan with similar thermal histories to the Tianyu Cu-Ni deposit may be potential exploration targets.