Genesis of the Koolyanobbing iron ore deposits, Yilgarn Province, WA, Australia

The Koolyanobbing South Range in the Yilgarn Province, WA, Australia, hosts a variety of high-grade iron ore deposits illustrating processes of formation ranging from diagenetic loss of chert to hydrothermal replacement of chert bands by carbonate followed by supergene leaching of the carbonate. Quartz is leached from iron-rich superficial screes to form high-grade lump ore deposits, but there is no evidence of supergene or hypogene selective solution of quartz in the saprolite ore. Hydrothermal fluids have produced dramatic recrystallisation of the haematite in weathered ore and cherty banded iron formation (BIF), but have not affected the bulk chemistry of the rocks.