Synorogenic hydrothermal origin for giant Hamersley iron oxide ore bodies

Geologic mapping, basin analysis, and calculated fluid compositions indicate that giant orebodies of microplaty hematite, and possibly martite-goethite, in the Hamersley province of Western Australia, were formed by heated fluids driven by early Paleoproterozoic orogenesis, Detrital grains of microplaty hematite in the McGrath trough, a foreland basin in front of the northward-advancing Ophthalmian fold belt constrain the age of the earliest microplaty hematite ore formation to 200 degrees C and locally up to 400 degrees C were involved. Regional circulation of hydrothermal fluids, including heated surface water, through reduced banded iron formations occurred during or soon after the Ophthalmian orogeny. We speculate that martite-goethite orebodies, previously considered Mesozoic-Cenozoic, could also be related to heated Paleoproterozoic meteoric fluids migrating northward away from the Ophthalmian fold belt.