Fortescue and Hamersley Basins

An integrated geochemical, isotopic and geochronological study of igneous and sedimentary rocks is being undertaken in the Fortescue and Hamersley Basins.

The 2775–2630 Ma volcano-sedimentary Fortescue Group and the conformably overlying 2630–2445 Ma Hamersley Group together with the 2445–2208 Ma Turee Creek Group constitute the Mount Bruce Supergroup, which unconformably overlies the granite–greenstones of the Pilbara Craton in Western Australia. Not only does this supergroup incorporate the world’s best preserved sequence of Archean ultramafic to felsic volcanic deposits, arguably the world’s most continuous transect across the Archean–Proterozoic boundary, and the Great Oxidation Event, it remains the most economically important stratigraphic unit on the Australian continent.

The Fortescue Group succession, Hamersley Ranges
The Fortescue Group succession, Hamersley Ranges
Pillow basalt unit in the Weeli Wolli Formation, Hamersley Group
Pillow basalt unit in the Weeli Wolli Formation, Hamersley Group

Project objectives

The project aims to use targeted field mapping and detailed, high-precision geochemical, isotopic and geochronological data, obtained from outcrop and diamond drillhole sampling for the following objectives:

  • a detailed, systematic, regional synthesis of the geochemical variation of magmatic units throughout the Mount Bruce Supergroup
    • to establish which of the mafic intrusive rocks of the region are related to the Fortescue and Hamersley Groups
    • to investigate the geochemical relationship between felsic igneous rocks of the Fortescue and Hamersley Groups and the associated mafic and ultramafic rocks
  • review the stratigraphy of the Mount Bruce Supergroup and revise where necessary
  • characterise associated sedimentary rocks (using lithogeochemistry) and determine the relative contribution of terrigenous vs volcanic sources
  • review the structural evolution of the region for compilation of a regional interpreted bedrock geology map
  • understand the relationships between the volcanic and sedimentary units and integrate this with petrogenetic constraints on magmatism to better constrain the tectonic setting and evolution of the Mount Bruce Supergroup.

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