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The Gawler Craton underlies the greater part of South Australia. It is defined as that region of Archaean to Mezoproterozoic crystalline basement that has undergone no substantial deformation, except for minor brittle faulting, since 1450 Ma. The margins of the predominantly polygonal shaped craton are well delineated by imaged aeromagnetic and gravity data. The northwest, northeast and western boundaries correspond to faulted margins of thick Neoproterozoic and Phanerozoic sedimentary basins. The Torrens Hinge Zone, the western limit of the Adelaide Fold Belt, defines the eastern and southeastern boundaries. Imaged gravity and aeromagnetic data clearly show that reworked Gawler Craton crystalline basement underlies the western margin of the Adelaide Geosyncline. The southern boundary is shown as the edge of the continental shelf.
The northwestern, central and southern western portions of the craton are underlain by Archaean to early Proterozoic amphibolite to granulite facies gneisses. Rock types include aluminous sediments, carbonates, calcsilicates, banded iron formations, cherty quartzites, pyritic and carbonaceous schists, komatiite, basalt and rhyodacite as well as peridotitic cumulus intrusives and late tectonic granites. Prograde metamorphism that affected these rock units throughout the craton occurred at 2450 Ma. U-Pb geochronology of lower grade amphiblolite facies acid volcanics and interlayered komatiite gives an extrusion age of 2520 Ma. These sediments and associated volcanics were deposited in an active tectonic environment involving mantle plumes, long-lived active plate margins and widespread contemporaneous arc volcanism. Archaean rocks are therefore prospective for greenstone hosted gold, nickel and PGEs as well as VHMS style copper-zinc. Gold is currently produced from high-grade felsic veinlets within aluminous sediments. Widespread gold anomalism in associated surficial carbonates indicates considerable further potential for discovery.
The Archaean core is overlain to the north and east by Proterozoic marine shelf sediments including pelitic sediments, carbonate, and banded iron formation. Sedimentary ages of the on lapping basins range from 2000 Ma to 1650 Ma reflecting changes in depocentres over time. High-grade silicate banded iron formations provide iron ore resources for the state's steel industry. Amphibolite facies metamorphism has affected these basinal sequences at 1740 - 1700 Ma.
In the volcanics and granites from 1600 - 1575 Ma the rocks are comagmatic and the source of the giant hematite rich Olympic Dam Cu-U-Au-Ag deposit. Large volumes of iron oxide both as hematite and magnetite were emplaced in the crust during this time. Aeromagnetic data allows delineation of these alteration zones that occupy thousands of square kilometres. Detailed gravity may indicate prospective hematite rich zones within or adjacent to these intense magnetic anomalies. Large areas remain to be explored.
In contrast the western Gawler Craton has had a different history. Large volumes of primitive as well as evolved gabbro, diorite and peridotite were intruded during 1740 -?1650 Ma. These rocks are prime targets for nickel, chromite and PGEs. Similarly primitive calcalkaline granite to gabbro intruded an adjacent eastern terrain at 1630 Ma possibly indicative of plate margin activity. Granulite facies deformation has overprinted the region at 1650 Ma and 1540 Ma. Geochronology indicates the craton cooled by 1450 Ma.
