K.F. Cassidy

Crustal evolution constraints on the metallogeny of the Yilgarn Craton

Improved understanding of the evolution of the Archean Yilgarn Craton, Western Australia, indicates a collage of crustal fragments formed through both autochthonous and allochthonous processes. Komatiite-associated nickel sulfide (KANS), volcanichosted massive sulfide (VHMS) Zn-Cu and orogenic Au deposits are associated with specific crustal domains. KANS deposits are concentrated in terranes with evidence for pre-existing crust. In contrast, VHMS deposits are associated with rift-like zones of isotopically primitive crust. Gold mineralization predominates in domains with evidence for komatiite magmatism, melts sourced from subduction-modified mantle, and lithospheric-scale orogeny. Development of the mineral systems likely reflects interaction of specific geotectonic processes with the pre-existing crustal and mantle reservoirs.

Tectonic controls on the endowment of Archean cratons in VHMS deposits: Evidence from PB and Nd isotopes

Comparison of Pb and Nd isotopes of the well-endowed Abitibi-Wawa Subprovince with the poorly endowed Eastern Goldfields Province implies that volcanic-hosted massive sulfide (VHMS) endowment in Archean terrains is controlled by crustal character. The Abitibi-Wawa Subprovince contains mostly primitive crust formed in a wide extensional environment. The high heat flow, promoted by thin crust and high level intrusions, and the extensional structures that characterize such an environment encouraged the formation of extensive VHMS deposits. In contrast, extensional environments are limited to a relatively narrow zone in the Eastern Goldfields Province. Although this zone contains VHMS deposits, they are not abundant enough to create high endowment. Provinciality of Pb isotopes in lode Au deposits from near Leonora in the Eastern Goldfields Province supports the concept of a rift-like zone.