Research progress of fluid inclusions and its application in iron oxide copper-gold (IOCG) deposits

Abstract

Research on fluid inclusions in Iron Oxide Copper Gold hydrothermal systems has significantly progressed over the past few decades. This paper summarizes the major research advances including petrography, microthermometry, and the compositional of fluid inclusions, as well as the main theories regarding the origins and evolution of ore formation. Fluid inclusions are prevalent within hydrothermal minerals of IOCG systems, including aqueous biphasic (L-V), three-phase (L-V-S) and multiphase (L-V-nS), aqueous-carbonic (L_H2O-L_CO2) and aqueous-carbonic with solids (L_H2O-L_CO2-S), single phase (L_CO2) inclusions. The types and quantity of fluid inclusions are varied in different hydrothermal alteration and mineralization stages. Geochemical investigations have identified at least two distinct fluid contributors in IOCG systems: a hot, saline magmatic-hydrothermal fluid and an external, non-magmatic fluid (e.g., basin brine, meteoric water, formation water, or metamorphic fluids). It is generally believed that the early stages of the hydrothermal alteration are primarily controlled by magmatic fluids rich in metals and volatiles, with the Fe (-REE) mineralization. Non-magmatic fluids mixing at the last stage can effectively induce a temperature decrease or added reduced sulfur may be a significant factor contributing to Cu-Au precipitation.