TOWARD A UNIFYING MODEL FOR GIANT MARTITE-MICROPLATY HEMATITE ORE DEPOSITS OF THE HAMERSLEY PROVINCE, WESTERN AUSTRALIA
Here we present the chemistry, mineralogy and petrography of hundreds of rocks from DGM, Mt. McRae Shale and Whaleback Shale across Hamersley Province, including at and beneath ore at Mt. Whaleback. Two crucial findings are: (1) silica within Mt. McRae Shale beneath Mt. Whaleback ore and along a major normal fault has been replaced by carbonate immediately after deformation, and (2) BIF surrounding Mt. Whaleback (and all across the southwest Hamersley Province) is comprised of hematite and chert without carbonate, indicating oxidation without silica removal. Combined with other recent results (Taylor et al., Econ. Geol., 2001), an internally consistent and testable basic model for martite-microplaty hematite orebodies of WA (and perhaps elsewhere) can be forwarded. Rocks of DGM were deposited during special ocean conditions, folded ca. 2.3 Ga, and subsequently intruded by carbonate-rich fluids along major normal faults. Pervasive oxidizing and acidic fluids converted magnetite to hematite and removed carbonate across large regions of the southern Hamersley Province. The orebodies lie precisely where sedimentary rocks of unusual chemical composition were locally altered and then overprinted by regional fluid flow.