In-situ monazite dating and mineral chemistry of Xiaonangou Au deposit, Qinling orogenic belt: Implications for Au mineralization

Abstract

This study investigates the Xiaonangou gold deposit, located in the Qinling orogenic belt, providing key insights into metallogenic processes linked to Mesozoic extensional tectonics. The main scientific questions focus on the timing of gold mineralization, the evolution of ore-forming fluids, and the mechanisms controlling gold deposition.

The geological background indicates that the Xiaonangou deposit formed during the Late Triassic post-collisional extensional tectonic regime, which is a critical period for the formation of orogenic gold deposits. The deposit is characterized by a multi-stage mineralization process, influenced by tectonic reactivation and magmatic-hydrothermal activity.

Mineral assemblages in the deposit, including pyrite, mica, and ankerite, display distinct geochemical signatures that reveal the evolution of ore-forming fluids. These fluids evolved from oxidized, Fe- and Sr-rich compositions in the early stages to reduced, Mg- and Al-enriched fluids in the later stages, reflecting significant changes in fluid chemistry and mineralization conditions.

Mineral chemistry data, including the trace element geochemistry of pyrite, mica, and ankerite, highlight the involvement of both magmatic and crustal sources, with notable concentrations of arsenic (As), tellurium (Te), and rare earth elements (REEs). The presence of these elements suggest significant fluid-rock interactions during the mineralization process, with arsenic and tellurium playing key roles in gold transport and deposition. Invisible gold was incorporated into pyrite and stabilized as gold-telluride complexes during fluid cooling and reduction.

Chronological data from U-Pb dating of monazite reveal a precise mineralization age of 213.7 ± 0.8 Ma, which corresponds to the Late Triassic, aligning with the period of tectonic reactivation and magmatic fluid emplacement.

The geological significance of the Xiaonangou deposit lies in its role as an orogenic gold system that formed during Late Triassic post-orogenic extension. The study highlights the genetic link between extensional tectonics, magmatic fluids, and hydrothermal fluid evolution, providing a comprehensive framework for understanding gold metallogenesis in the Qinling orogen and guiding future exploration for similar deposits in the region.