Revisiting the IOCG Sin Quyen Deposit, Lao Cai Province: A New Perspective on Fluid Evolution and Ore Genesis

Abstract

The Sin Quyen deposit in northern Vietnam is a representative Fe – Cu – REE (iron – copper – rare earth element) system genetically linked to prolonged magmatism and structurally controlled fluid flow. This study integrates fluid inclusion, isotopic, and mineral c hemical data to define a three - stage hydrothermal evolution: (1) an early high - temperature REE stage (~880 Ma), (2) a main - stage Fe – Cu stage (~840 Ma), and (3) a late Cu – Au overprint (~35 Ma). The early REE stage involved high - temperature, modera te - salinity fluids of crustal origin. The main Fe – Cu stage was driven by moderate - temperature fluids with a significant mantle component, as indicated by Nd – S isotopes. The late epithermal Cu – Au stage was facilitated by low - temperature meteoric fluids duri ng Paleogene tectonic reactivation. The entire system developed in an active continental margin, where episodic subduction - related magmatism and crust – mantle interaction were critical for metal endowment. This model underscores the importance of targeting areas with long - lived, composite magmatic - hydrothermal history for regional IOCG and REE exploration in Southeast Asia. Our findings provide a robust framework for identifying similar polyphase mineralization systems in analogous tectonic settings, particu larly along reactiated structures in ancient continental margins .