Phanerozoic rocks in onshore Western Australia are primarily sedimentary. Volcanic and intrusive rocks are known from only a few areas and are mostly related to continental breakup along the northwest and western margins. The age and degree of faulting varies from basin to basin, depending on tectonic setting and period of principal activity as a depocentre, but most rocks are flat-lying to gently folded. The Southern Bonaparte, Southern Carnarvon, Canning, and Gunbarrel Basins are dominantly Palaeozoic depocentres. The Canning Basin was the dominant Ordovician depocentre, and the Southern Carnarvon Basin the dominant Permian depocentre. The Perth Basin is a polycyclic basin that was active from the upper Palaeozoic onwards, but is primarily Mesozoic. The Bremer and Eucla Basins were initiated in the Mesozoic in small local depocentres, but contain more extensive, thicker Cainozoic deposits. The age of initiation and the age of the thickest infill in each basin reflects the progressive separation of Western Australia from parts of Gondwana. In addition, transported and residual regolith blankets most of the Precambrian cratons, basins and orogenic belts. Mineralisation in Phanerozoic rocks is primarily strata-bound. Mississippi Valley-type base metals are present in Ordovician, Devonian, and Carboniferous rocks and are commonly associated with extensional faulting and evaporite-carbonate hosts. Coal swamps were important in the Permian immediately after the Gondwana glaciation and in Jurassic fluviodeltaic complexes. Mineral sands are associated with Cainozoic strandlines and associated coastal settings, but the concentration into potential economic accumulations is only partly assessed with respect to Mesozoic sediments. Significant thicknesses of evaporites (mainly halite with lesser anhydrite) are present in Ordovician and Silurian rocks, but are overshadowed by major gypsum and halite resources in Cainozoic barred marine embayments. Diamonds are associated with lamproitic intrusives of Miocene age in the Canning Basin, but have not been extracted from Phanerozoic rocks, except near Argyle, where Cainozoic gravel placers derived from the Argyle pipe are currently mined. Iron ore is mined from pisolitic channel iron deposits in Eocene palaeo drainages in the Pilbara. Various residual weathering, lateritisation and evaporation processes have concentrated significant accumulations of bauxite, uranium, and a number of industrial minerals within Cainozoic regolith.
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