Multistage gold mineralization linked to metamorphic core complex evolution: Constraints from geochronology and geochemistry of accessory minerals at the Fancha gold deposit (Xiaoqinling ore district, central China)

The Xiaoqinling district, hosted in Precambrian basement rocks of the Xiaoqinling metamorphic core complex (MCC) footwall, is one of China’s largest gold producers. However, the genetic link between gold mineralization and Xiaoqinling MCC evolution remains unresolved. This study uses in situ analysis of apatite, rutile, monazite, and scheelite from the Fancha deposit to constrain textural evolution, U-Pb ages, and geochemistry to directly link gold mineralization to Xiaoqinling MCC evolution. The Fancha deposit records four paragenetic stages: disseminated pyrite-apatite (stage I), quartz-pyrite (stage II), quartz-sulfide (stage III), and quartz-carbonate (stage IV). Metamorphic apatite from stage I yields a U-Pb age of 141.5 Ma, coincident with Xiaoqinling MCC initiation. Hydrothermal rutile and monazite from stages II−III yield tightly clustered U-Pb ages of 125−124 Ma, constraining main-stage gold mineralization to the time of Xiaoqinling MCC isostatic doming (ca. 127 Ma) and North China craton lithospheric thinning. Gold-related scheelite and apatite yield remarkably low εNd(125 Ma) values (−25.9 to −20.7), indistinguishable from those of the Taihua Group host rocks, whereas their 87Sr/86Sr ratios (0.7260−0.7737) span a wide range that may reflect variable contamination by heterogeneous Taihua Group lithologies. Sr-Nd isotopic mixing modeling indicates that the ore-forming fluids were derived from dehydration metamorphism at mid- to lower-crustal levels. Collectively, intensive gold mineralization in the Xiaoqinling district is interpreted as orogenic and genetically linked to Xiaoqinling MCC isostatic doming and synchronous lithospheric thinning at ca. 127 Ma, and this process was driven by Paleo-Pacific slab delamination and rollback during flat-slab subduction. Auriferous fluids generated during regional prograde greenschist- to amphibolite-facies metamorphism migrated along crustal-scale detachment faults and were focused into structurally favorable sites within ductile-to-brittle shear zones across the Xiaoqinling gold field.