Metasomatic Mineral Systems with IOA, IOCG, and Affiliated Critical and Precious Metal Deposits: A Review from a Field Geology Perspective

Abstract

Worldwide, a growing list of critical (Bi, Co, Cu, F, Fe, Mo, Ni, P, PGE, REE, W, U, and Zn) and precious metal (Ag and Au) resources have been identified in mineral systems forming Fe-oxide-copper-gold (IOCG) deposits; Fe-oxide-apatite (IOA); Fe-sulfide Cu-Au (ISCG); and affiliated W skarn; Fe-rich Au-Co-Bi or Ni; albitite-hosted U or Au ± Co; and five-element (Ag, As, Co, Ni, and U) vein deposits. This paper frames the genesis of this metallogenic diversity by defining the Metasomatic Iron and Alkali-Calcic (MIAC) mineral system and classifying its spectrum of Fe-rich-to-Fe-poor and alkali-calcic deposits. The metasomatic footprint of MIAC systems consists of six main alteration facies, each recording a distinct stage of mineralization as systems have evolved. The fluid flow pathways and the thermal and chemical gradients inferred from the space–time distribution of the alteration facies within a system are best explained by the ascent and lateral propagation of a voluminous hypersaline fluid plume. The primary fluid plume evolves, chemically and physically, as metasomatism progresses and through periodic ingresses of secondary fluids into the plume. Exploration strategies can take advantage of the predictability and the expanded range of exploration targets that the MIAC system framework offers, the building blocks of which are the alteration facies as mappable prospectivity criteria for the facies-specific critical and precious metal deposits the systems generate. Global case studies demonstrate that these criteria are applicable to MIAC systems worldwide.