Hydrothermal alteration events controlling magnetite-rich iron ore at the Matthew Ridge prospect, Jack Hills greenstone belt, Yilgarn Craton

Archean Banded Iron Formation (BIF) hosts high-grade (>55% Fe) iron ore at the Matthew Ridge prospect, in the Jack Hills greenstone belt, of the Narryer terrane, Yilgarn Craton. The ca 3000 Ma (SHRIMP U-Pb on zircons) Algoma-type BIF contains magnetite-hematite ore zones that are a product of successive overprinting hydrothermal alteration events. Rock types in the prospect area include Archean gneiss, metasedimentary rocks and BIF that are interlayered with dolerite. All rocks record peak amphibolite metamorphic mineral assemblages that are variably replaced by greenschist facies metamorphic minerals. Hypogene iron ore formed owing to: (1) the replacement of primary silica-rich bands in the quartz-magnetite BIF by Stage 1 hypogene magnesite and magnetite alteration; and (2) subsequent removal of Stage 1 magnesite to concentrate residual Stage 1 magnetite. These magnetite-rich ore bodies define