Australian intracratonic copper-gold and allied deposits: A clan of mineral systems

Abstract

A clan of intracratonic Cu-Au and allied deposits is proposed to define a diverse genetic group of hydrothermal mineral systems. Although there is far too much variation in both metal budgets and deposit style to be embraced within a single ore deposit class, a sensible clan, or spectrum, of deposit types is united by several common key features.

Deposits lie in the hanging wall of cratonic sutures that mark subduction-driven collision between two cratonic blocks at least some hundreds of millions of years before mineralization. They have a high-temperature combined geochemical signature that is distinctly magmatophile, with some combination of Cu, Au, Bi, W, Se, F, Mo, Sn, In, Pt, Pd, Ni, Co, U, and REEs. The deposits are broadly coeval with high-temperature, shallow-crustal, late- to post-orogenic felsic and minor basic magmatism with the size of that igneous footprint controlling the total endowment of the province. Broadly coeval felsic intrusions are generally not mineralized, nor do they have zoned alteration around the hot intrusions as they would have if there was a direct hydrothermal connection to mineralization. Rather they are interpreted to be a separate manifestation of the high heat flow environment that drives the intracratonic mineral systems. Rare, coeval, potassic mantle melts, for example, lamprophyres at Olympic Dam, are interpreted as directly derived from mantle lithosphere that was fertilized by fluids related to ancient subduction. Poorly constrained hydrothermal fluids are also interpreted to be derived from fertilized mantle lithosphere, with F and Se likely critical components. Fluorine is interpreted as an important silicate solvent and ligand and Se as a marker of a distinctly oxidized fluid source.