Gawler Craton

TheGawler Cratoncovers approximately 440,000 square kilometres of central South Australia. ItsPrecambriancrystallinebasementcrustalblockwascratonisedca. 1550–1450 Ma. Prior to 1550 Ma the craton comprised a number of activeProterozoicorogenicbelts extending back in time to at least 2450 Ma.

The Craton can be subdivided into a number oftectonicsubdomains on the basis of structure and tectonostratigraphichistory.The south-centralEyre Peninsulastraddles the boundary between theArchaeanto earlyPalaeoproterozoicCoulta Subdomain and the Cleve Subdomain, a Palaeoproterozoic orogenic belt ( "mobile zone" ) probably representing a shelf or basinal depository for the Hutchison Group (ca. 1900–1845 Ma) prior to its deformation during theKimban orogeny(ca. 1845–1710 Ma). On northeastern Eyre Peninsula, the Cleve Subdomain is bounded by the slightly younger Moonta Subdomain which is characterised by less intensely deformedmetamorphosedacidvolcanicsandsedimentsranging from the Myola Volcanics and MoontaPorphyryto the Moonabie Formation and Wandearah Metasiltstone.

Subsequent deformation on the craton has been largelyepeirogenicforming shallow fault-bounded intracontinental depressions represented byCainozoicbasins, the southerncontinental marginandSpencer Gulf.

Physiography

The Gawler Craton, or Gawler Block, is a distinct physiographic province of the largerWest Australian Shielddivision. It includes the smallerStuart Range BasinandPimba Platformphysiographic sections.

Northwestern Fowler Domain

The Fowler Domain is a major tectonic zone on the north-western flank of the Gawler Craton comprising dense, magnetic, highly deformed, intermediate toultramaficintrusives overlain by thin Tertiary sands and recent sand dunes.Aeromagnetic surveysshow the presence of a high concentration of crustal scale fractures and faults in this area. These structures could have provided pathways for the intrusion ofmafic-ultramafic bodies with potential for nickel sulfides, chromite andplatinoids.

Eastern Olympic Copper-Gold Province

The Olympic Copper-Gold Province is a 650 km long corridor along the eastern boundary of the craton.

Eastern and Central, Gawler Ranges

Pink granite atHiltaba

Palaeoproterozoic rocks of the eastern and central Gawler Craton are overlain by relatively unmetamorphosedclasticsof the Corunna Conglomerate, theGawler Range Volcanics(GRV), the Pandurra Formation, and thin platformal late Proterozoic andCambriansediments of the Stuart and Spencer Shelves. In and around theGawler Ranges,the volcanics and older rocks were intruded byHiltaba Suitegranites (found in theHiltaba Nature Reserve) which are closely associated with formation of the giantOlympic Damore body of the Eastern Olympic Copper-Gold Province. Although relatively undeformed, the Gawler Range Volcanics, which extend from the centre of the craton to its eastern margin, represent a major period of crustal deformation ca. 1590 Ma which heralded the final consolidation and stabilisation of the craton as it is seen today.

Central Yarlbrinda Shear Zone

In the central Craton, the Yarlbrinda Shear Zone was likely formed by theKararan Orogenyand it is host to several major gold prospects including those in the Nuckulla Hill region (Sheoak, Myall and Bimba) and at Tunkillia.

Western Eyre Peninsula, Coulta Subdomain and Nuyts Subdomain

On western Eyre Peninsula, the Coulta Subdomain merges with the Nuyts Subdomain which is dominated by variably deformed ca. 1670–1610 Ma granitoids, mafics and felsic volcanics. Deformation is attributed to the Kalaran Orogeny which generated a major fold belt orshear zone,the Fowler Shear Zone, ca. 1600–1540 Ma.

Economic geology

Economically important deposits found in the craton includegold,diamonds,copper,nickel,granite,iron ore,lead-zinc,uranium,coal,industrial mineralsandarsenic.

The hugeOlympic Damcopper-gold operation is located in the Eastern Olympic Copper-Gold Province at the cratons eastern edge. TheProminent Hill copper-gold mineis northwest of Olympic Dam and theChallenger Gold Mineis to the west of Prominent Hill located in the centre of the craton. The 70 million tonneKalkaroo Mineis to the south and contains approximately 320,000 tonnes of copper, 1 million ounces of gold and 8.56 million kg of molybdenum in an optimised open pit designed to 230 metres depth.

The Wynbring area, a large part of the western Fowler Domain, covers approximately 2,000 square kilometres and consists of fractures that may include intrusion of mafic-ultramafic bodies with potential for nickel sulfides, chromite and platinoids. Exploration and regional drilling near the northern end of the Fowler Domain and within the Harris Greenstone Belt has identified numerous large mafic and ultramafic bodies which have the potential to host nickel sulfide mineralisation. Ultramafic intrusive rock hosting nickel bearing sulfides (pentlanditeandmackinawite) have returned values up to 0.49% nickel, 38 parts per billion (ppb) platinum and 58 ppb palladium. Previous explorations reported up to 0.74% nickel from samples obtained in shallow bedrock drilling.TheThompson Beltin Canada has similar features and is considered byPrimary Industries and Regions SA(PIRSA) as a possible analogue of the Fowler Domain. The Thompson Nickel Belt hosts major nickel deposits which have been mined by Inco since the early 1960s. Previous explorations in the Wynbring area consisted of wide-spaced reconnaissance bedrock drilling by PIRSA that indicated the presence of a 30 kilometre-long zone of intermediate to ultramafic rocks adjacent to a major fault and geochemically anomalous in gold, nickel, chromium, platinum and palladium.

Drilling has confirmed significant widespread uranium mineralisation at the "Warrior" palaeochannel in central Gawler just west of Prominent Hill and there is active uranium exploration over an extended portion of the Kingoonya Palaeochannel system within the southern Gawler Craton. "Warrior" is the most significant known uranium occurrence in the Gawler Craton.

See also

• Acraman crater
• Archaean
• Australian Shield
• Centralian Superbasin
• Geology of Australia
• Narryer Gneiss Terrane
• Ore genesis
• Perth Basin
• Pilbara craton
• Western Plateau
• Yilgarn Craton