Compositional data analysis of hydrothermal alteration in IOCG systems, Great Bear magmatic zone, Canada: to each alteration type its own geochemical signature

Abstract

Iron oxide copper-gold (IOCG) systems are characterized by a wide range of hydrothermal alteration types that can indiscriminately and intensively replace their host rocks over areas of > 100 km 2 . Element mobility and chemical changes associated with alteration can be of a magnitude beyond that of many other types of hydrothermal systems, and may also affect normally immobile elements. Principal component analysis of whole-rock geochemical data on hydrothermally altered samples coming from the Great Bear magmatic zone IOCG systems has enabled the characterization of sodic, calcic-iron, to high to low temperature potassic-iron and potassic alteration types of IOCG systems. Results show that potassic and potassic-iron alteration features are enriched in K, Al, Ba, Si, Rb, Zr, Ta, Nb, Th and U, with potassic-iron alteration being richer in Fe. In contrast, calcic-iron alteration is enriched in Ca, Fe, Mn, Mg, Zn, Ni and Co. These compositional variations can be portrayed by IOCG alteration index and discriminant diagrams. Combined with an IOCG alteration sequencing model, the lithogeochemical footprint of IOCG systems provides a useful tool to assess the potential fertility and maturity of IOCG systems and ultimately a vector towards ore zones during exploration