Genesis of structurally-controlled, magnetite-rich hypogene ore zones in BIF at Madoonga, Weld Range, Western Australia

The Madoonga deposit in the Weld Range greenstone belt of the Murchison Domain, Western Australia is an example of an Archean BIF -hosted, high-grade (>55 wt.% Fe) iron ore deposit. Magnetite-rich ore zones are genetically associated with early-formed shear zones that are principally located along the margins of isoclinally-folded BIF. These shear zones most likely formed as a result of thrusting along the limbs of isoclinal folds during the first regional deformation event. During folding and thrusting, hypogene hydrothermal fluids were probably channelled within the shear zones, resulting in the precipitation of hypogene hydrothermal magnetite within the shear zones and adjacent BIF wallrock. Consequently, magnetite-rich ore zones are narrow (low-tonnage) and high-grade, with local areas displaying high-degrees of contamination by SiO2. A series of later, hypogene and supergene hydrothermal events were important for the replacement and Fe upgrade of early magnetite-rich ore zones in the Madoonga deposit.