The Gawler Craton is an extensive region of Archean to Mesoproterozoic crystalline basement underlying approximately 440,000 km² of central South Australia.

Age of major events

• Felsic magmatism of the Cooyerdoo Granite and associated tonalite-trondhjemite-granodiorite (TTG) basement (~3400–3150 Ma)
• Felsic magmatism of the Coolanie Gneiss (~2820 Ma)
• Bimodal magmatism and sedimentation of the Sleaford and Mulgathing complexes (~2560–2470 Ma)
• Sleaford Orogeny (~2470–2410 Ma)
• Felsic magmatism of the Miltalie Gneiss and equivalents (~2000 Ma)
• Craton-wide sedimentation and bimodal magmatism (~2000–1730 Ma)
• Cornian Orogeny (~1855–1845 Ma); metamorphism and bimodal magmatism of the Donington Suite (1850 Ma)
• Kimban Orogeny (1730–1690 Ma); metamorphism and bimodal magmatism of the Peter Pan Supersuite, synchronous with sedimentation of the Eba and Labyrinth Formations; deformation, shear zone formation and reactivation
• Sedimentation of the Tarcoola Formation and Corunna Conglomerate (1680–1640 Ma) and felsic magmatism of the Tunkillia Suite (~1690–1680 Ma)
• Bimodal magmatism (~1650–1610 Ma) comprising the Nuyts Volcanics, St Francis Granite and St Peter Suite
• Bimodal magmatism and local sedimentation (1594–1570 Ma) comprising the Gawler Range Volcanics and Hiltaba Suite, synchronous with metamorphism and shear zone formation
• Kararan Orogeny (1570–1540 Ma); shear zone formation and reactivation
• Coorabie Orogeny (1470–1450 Ma); shear zone formation and reactivation
• 1450 Ma magmatism in the northern Gawler Craton

Prospective commodities

Metals: Cu, Au, Fe, Ag, Pb, Zn, Co, Ni, Cr, Mn, Ti, V, platinum group elements (PGE), Mo, W, Sn, rare earth elements (REE)

Industrial minerals: graphite, kaolin, talc, magnesite, limestone, dolomite, barite, vein-silica, manganese oxide

Gem: jade, diamonds, chalcedony/agate

Construction materials: vast resources of road making material (limestone, dolomite, quartzite, sandstone, gneiss), dimension stone (granite) and regolith clay (brickmaking and refractory)

Energy minerals: U₃O₈, thorium

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Major exploration models

Demonstrated

• FeO-Cu-Au-Ag±U (hematite- and magnetite-dominated styles) (Olympic Cu-Au Province, e.g. Olympic Dam, Prominent Hill, Hillside, Moonta, Carapateena Prospect)
• Iron ore as massive hematite deposits by supergene enrichment (e.g. Iron Monarch, Iron Duke, Wilgerup)
• Iron ore as magnetite-bearing banded iron formation (e.g. Middleback Range, Bungalow Prospect, Hawks Nest, Skylark) to magnetite-rich metasediment (e.g. Warramboo)
• Iron ore as magnetite and hematite skarn/replacement styles (e.g. Peculiar Knob, Snaefell, Wilcherry Hill)
• Intrusion-related Au (Central Gawler Gold Province, e.g. Tarcoola, Tunkilla Prospect, Barns Prospect, Weednanna Prospect)
• Shear-hosted Cu, Au, U (e.g. Cairn Hill)
• Shear to unconformity-related U (e.g. Driver River in central Eyre Peninsula)
• Regolith deposits including kaolin (e.g. Poochera), supergene copper (e.g. Hillside, Alford West) and regolith manganese oxide (e.g. Hercules West, Jamieson Tank, Pier Dam)
• Orogenic Au (e.g. Challenger)
• Volcanogenic Pb-Zn-Ag (e.g. Menninnie Central and Telaphone Dam Prospect) and Cu-Fe (e.g. West Doora)
• Epithermal-style Ag-Pb-Zn (e.g. Paris) and Au-Ag-Pb-Zn (e.g. Parkinson Dam)
• Sedimentary-hosted Pb-Zn (Hutchison Group, e.g. Miltalie Mine, Mangalo Mine, Atkinson’s Find, Smithams)
• Graphite (e.g. Uley Graphite Mine, Kookaburra Gully, Koppio, Wilclo South)
• Metasomatic talc, magnesite and jade (Katunga Dolomite)

Possible

• VHMS deposits (Hall Bay Volcanics, Oakdale prospect southern Eyre Peninsula)
• Late Archean komatiitic and magmatic intrusive-hosted Ni-Cr-PGE (Lake Harris Greenstone Belt, Aristarchus)
• Magmatic Ni-Cr-Cu sulphides and PGE (Fowler and Christie Domains)
• Unconformity and Paleochannel U and Au (e.g. Corunna Conglomerate)
• Diamondiferous kimberlite
• Intrusion-related W and Sn (e.g. Moonbi W prospect, Zealous Sn prospect)
• Fe-Ti-V styles (e.g. Malbooma Anorthosite Complex, Wigetty prospect)

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Summary geology

The Gawler Craton is the oldest and largest geological province in South Australia, preserving a complex tectonic history spanning from ~3250 Ma to 1450 Ma. The craton comprises a Mesoarchean-Paleoproterozoic core that is intruded and overlain by Paleoproterozoic to Mesoproterozoic rocks. The Mesoarchean history of the Gawler Craton is dominated by felsic magmatism, the Neoarchean to Paleoproterozoic history by sedimentation and bimodal magmatism, and the Mesoproterozoic history by bimodal magmatism.

Solid geology map of the Gawler Craton

The southern boundary of the craton coincides with South Australia’s coastline, but the other craton boundaries are poorly constrained, being obscured by cover sequences. To the east, Neoproterozoic sequences of the Torrens Hinge Zone and Adelaide Superbasin separate the Gawler Craton from the Paleo- to Mesoproterozoic Curnamona Province. To the north and west, the Gawler Craton has a structural boundary with the Musgrave and Coompana provinces, which is overlain by the Neoproterozoic to Paleozoic Officer Basin.

The oldest stratigraphic unit in the Gawler Craton is the Cooyerdoo Granite (~3150 Ma), exposed in northeast Eyre Peninsula. It is the product of melting of pre-existing tonalite-trondhjemite-granodiorite (TTG) crust, and inherited zircons suggest that older crustal material up to ~3400 Ma may be present at depth. Gneisses with an older protolith up to ~3250 Ma are also known in this area but have not been stratigraphically defined. The Cooyerdoo Granite also contains a gneissic fabric. Metamorphic zircon ~2510–2500 Ma in the gneisses and Cooyerdoo Granite record the age of this fabric development, an event not known elsewhere in the Gawler Craton.

The next event recorded in the Gawler Craton is the intrusion of the protolith of the Coolanie Gneiss (~2820 Ma), a mylonitic augen gneiss with minor intercalated quartzite and metapelitic sediments. It occurs as a N-S-trending belt in the northeast Eyre Peninsula.

The late Archean to earliest Paleoproterozoic, (~2560–2470 Ma) was a period of basin development, represented by the Sleaford Complex in the southern Gawler Craton and Mulgathing Complex in the northern Gawler Craton. These two complexes contain a diverse range of metamorphosed and deformed rocks and were likely part of an adjoining basin now dismembered by Paleoproterozoic tectonism.

The volcano-sedimentary basin developed in a back-arc or arc-rift setting which accommodated the eruption of the Devils Playground Volcanics and Hall Bay Volcanics ~2560–2520 Ma, and plume-related mafic and ultramafic magmas, including the Lake Harris Komatiite ~2520 Ma. Synchronous deposition of sedimentary rocks occurred with the volcanism, including the protoliths of the Christie Gneiss, Carnot Gneiss and Wangary Gneiss, and continued until ~2480 Ma. Juvenile and evolved crustal melts also intruded the basin synchronous with volcanism and sedimentation at ~2520–2510 Ma, including the Coulta Granodiorite, Glenloth Granite, Minbrie Gneiss, Carpa Granite and Kiana Granite.

Maximum depositional ages of sediments in the Middleback Ranges (~2560 Ma) and Bungalow Prospect (~2555 Ma) directly south of the Middleback Ranges suggest sedimentation also occurred in the Neoarchean in the northeast Eyre Peninsula, but the relationship of these sedimentary rocks to the Sleaford and Mulgathing complexes remains uncertain.

Bimodal magmatism continued in the northern portion of the basin (Mulgathing Complex) from ~2490–2460 Ma, represented by poorly foliated tonalite-quartz monzonite (Mobella Tonalite), gabbroic gneiss (Burden Metagabbro), granitic gneiss and tabular feldspar granite (Aurora Tank Suite), amphibolite dykes (Aristarchus Metaperidotite), and garnet-bearing mafic gneiss, metagabbro, metapyroxenite, and metanorite (Skuse Hill Metapyroxenite).

Basin development was terminated by deformation and metamorphism of the Sleaford Orogeny (~2470–2410 Ma). Metamorphism reached amphibolite to granulite facies in the Mulgathing Complex, central Gawler Craton, and deformation was characterised by near horizontal fabrics folded into N to NE-trending open to tight folds.

The Sleaford Orogeny was followed by ~400 m.y. of tectonic quiescence. At ~2000 Ma felsic magmatism formed the protoliths of the Miltalie Gneiss and equivalents in the southern Gawler Craton, comprising a granodiorite containing high-grade migmatitic fabrics, and a quartzofeldspathic gneiss to the west at Bascombe Rocks. Synchronously in the southern Eyre Peninsula unnamed charnockitic granites intruded the Sleaford Complex. Extension is recorded in the northern Gawler Craton by an isotopically juvenile orthogneiss emplaced at ~1920 Ma, possibly marking an ocean-continent transition on the edge of the Gawler Craton. This magmatism is likely related to oceanic crust production between the Gawler Craton and the cratonic elements of Western Australia at ~1950–1900 Ma leading to the opening of the Mirning Ocean.

Late Paleoproterozoic extension led to widespread basin formation across the Gawler Craton, associated with sedimentation and bimodal magmatism over the period ~2000–1730 Ma. The <2000–1770 Ma Hutchison Group forms an extensive basement sequence in the eastern Gawler Craton, comprising quartzite, dolomite, iron formation, schist and amphibolite, deposited in a passive margin setting. The Hutchison Group may comprise two disconformable groups; an older Darke Peak Group (~1865 Ma) containing a sequence derived from highly evolved crustally reworked rocks older than ~2000 Ma, and a younger Cleve Group (~1790–1770 Ma) containing additional younger felsic material derived from less evolved ~1850 Ma and ~1790 Ma upper crustal sources.

Sedimentation was punctuated in the eastern Gawler Craton by the short-lived contractional deformation of the Cornian Orogeny at 1850 Ma on Yorke Peninsula. The Cornian Orogeny was accompanied by syn-tectonic felsic magmatism of the Donington Suite, which occurs along the entire eastern margin of the Gawler Craton. The Donington Suite includes pyroxene and hornblende-biotite bearing granitoids ranging from gabbro, gabbronorite, charnockite and granodiorite to gneissic and alkali granite. The Donington Suite is proposed to have formed inboard of a subduction zone setting. These melts underwent both crustal assimilation and fractional crystallisation as they ascended into the crust during the Cornian Orogeny. Granulite facies metamorphism was followed by decompression-dominated retrograde P-T evolution and S-directed extensional fabrics.

On southern Eyre Peninsula, Donington Suite is intruded by Tournefort Metadolerite, comprising deformed and partly metamorphosed norite, gabbronorite and dolerite dykes ~1810 Ma. Nd isotopic compositions of Tournefort Metadolerite reflect multiple mantle sources, including both ancient and juvenile lithospheric mantle source regions.

Following the Cornian Orogeny rifting, bimodal volcanism and felsic intrusive magmatism resumed along the eastern margin of the Gawler Craton, comprising the bimodal Myola Volcanics (~1790 Ma) and associated clastic sediments of the Broadview Schist, intruded by the Wertigo Granite (~1790–1770 Ma) and Tip Top Granite (~1775 Ma) on the northern Eyre Peninsula. Myola Volcanics and Wertigo Granite are derived from a mixed mantle and crustal source region, in an extensional setting, while the Tip Top Granite fractionated from a lower crustal source.

Widespread sedimentation occurred across the craton during 1790 to 1740 Ma rifting. This included deposition of the Cleve Group (~1790–1770 Ma) in the southern Gawler Craton, Peake Metamorphics (~1775 Ma) in the northern Gawler Craton, Price Metasediments (max. dep. age ~1765 Ma), McGregor Volcanics (~1755 Ma) and associated Moonabie Formation in the southern Gawler Craton, Wallaroo Group (~1770–1730 Ma) in the eastern Gawler Craton, and sedimentary rocks in the Mount Woods Inlier (max. dep. age 1770–1740 Ma), Nawa Domain (max. dep. age 1760–1740 Ma), and Fowler Domain (max. dep. age 1740–1720 Ma in the northern and western Gawler Craton, respectively.

Basin development was terminated by the Kimban Orogeny (1730–1690 Ma), comprising low- to high-grade metamorphism together with felsic and lesser mafic magmatism. Major crustal-scale shear zones formed during the Kimban Orogeny, including the Tallacootra and Coorabie shear zones in the west and the Kalinjala shear zone in the south. The Kalinjala Shear Zone is a dextrally transpressive subvertical high-grade high-strain zone 4–6 km wide along the eastern Eyre Peninsula, corresponding to a major magnetic discontinuity, and separates differing lithostratigraphic zones.

In southern Eyre Peninsula, Kimban-aged deformation and metamorphism resulted in non-cylindrical and chevron-style folding and up to granulite facies metamorphism, adjacent to the Kalinjala shear zone. In northern Eyre Peninsula, the metamorphic grade was lower and deformation resulted in E-verging fold-thrust systems. In the northern and western Gawler Craton, Kimban-aged metamorphism in the Fowler and Nawa domains reached upper amphibolite to granulite facies conditions with lower amphibolite facies conditions recorded in the Peake and Denison Inliers. In the central Gawler Craton sedimentation and volcanism continued coevally with the Kimban Orogeny, consisting of isolated fault-bound basins containing basal conglomerates, quartzite and shale with felsic and mafic volcanics of the Eba Formation (max. dep. age ~2538 Ma) and Labyrinth Formation (max. dep. age ~1715 Ma).

Pre-, syn- and post intrusive magmatism extended over most of the Gawler Craton during the Kimban Orogeny, comprising undeformed to migmatitic, metaluminous to peraluminous granites and minor mafic intrusions of the Peter Pan Supersuite (~1745–1700 Ma). The Moola Suite (~1745–1735 Ma) is exposed in northeastern Eyre Peninsula and occur in the subsurface in the Stuart Shelf, Peake and Denison Inliers and northern Gawler Craton, and comprises mica-poor, unfoliated to weakly foliated granite, diorite, dolerite and amphibolite. The Pinbong Suite (1735–1700 Ma) is widespread throughout the Gawler Craton, occurring on central and southern Eyre Peninsula, eastern Gawler Craton, northern Gawler Craton and central Gawler Craton, and includes foliated to migmatitic biotite-rich granite, dolerite and gabbro. The Moody Suite (1720–1700 Ma) is restricted to the Tumby Bay area on central-eastern Eyre Peninsula and includes unfoliated leucogranite, monzogranite and monzonite with metasedimentary xenoliths derived from Paleoproterozoic country rock. Moola Suite and Pinbong Suite granites were derived from lower-mid crustal sources in an orogenic setting. Mafic rocks in the Moola and Pinbong suites are indicative of extensional-related melting derived from a heterogenous mantle source region, including enriched lithospheric mantle and juvenile mantle. The Moody Suite represents post-orogenic granites derived from continental crust. Intrusions of the Tunkillia Suite (1690–1680 Ma) form an arcuate belt in the central Gawler Craton and discrete plutons in the western Gawler Craton, overlapping temporally with the youngest Kimban-aged intrusions. Geochemical attributes of Tunkillia Suite granites indicate this magmatism occurred in a post-orogenic setting.

The Kimban Orogeny was followed by a period of extension between 1680 and 1640 Ma, leading to localised sedimentation and magmatism. This includes fluvial conglomerate, sandstone and siltstone of the Corunna Conglomerate on Eyre Peninsula (max. dep. age ~1680 Ma); sandstone shale, dolomite and dacitic to andesitic volcanoclastic rocks of the Tarcoola Formation (max. dep. age ~1655 Ma) in the central Gawler Craton; sandstone, minor grit and pebble beds of the Blue Range beds (~1600 Ma) in the Eyre Peninsula; and unnamed psammitic to pelitic sediments (max. dep. age ~1640 Ma), in the western Gawler Craton, known only as metasedimentary xenoliths in Hiltaba-aged plutons.

In the southwest, a north-east trending zone of felsic magmatism is defined by the alkaline Nuyts Volcanics and associated St Francis Suite emplaced at ~1630 Ma. Nuyts Volcanics are regionally intruded by St Francis granite and juvenile felsic to mafic magmas of the St Peter Suite at ~1630–1610 Ma. Magmatism of the St Peter Suite was broadly in a continental magmatic arc setting.

St Peter Suite magmatism was followed by bimodal volcanism in the central craton, producing the voluminous (~90,000 km²) Gawler Range Volcanics. This magmatism has been linked to a mantle plume in a continental setting. The large volcanic province erupted over a geologically short time interval of ~8 million years, culminating in a widespread, voluminous flood rhyolite province. A hiatus of ~1–2 million years separates two distinct periods of volcanism. The lower Gawler Range Volcanics (~1595–1588.5 Ma) is a period of bimodal volcanism erupted from discrete volcanic centres tapping small magma chambers. Small, syn-volcanic fluvio-lacustrine basins developed locally at some of these volcanic centres. Basaltic to andesitic rocks were derived from a metasomatised lithospheric mantle source with some evidence for crustal contamination during ascent and emplacement. Dacitic to rhyolitic rocks were products of fractional crystallisation and crustal contamination of the basaltic magmas. The upper Gawler Range Volcanics (~ 1586.5 Ma) comprises voluminous (200–300 m thick), high-T (900–1100°C) rhyolitic and dacitic lavas derived from extensive crustal melting above a mantle plume. The volcanic rocks are comagmatic with felsic and minor mafic intrusions of the Hiltaba Suite (1595–1575 Ma). Mafic Hiltaba Suite intrusions were derived from heterogeneous metasomatised mantle and depleted mantle sources, consistent with a plume-lithosphere model. Felsic Hiltaba Suite rocks are products of crustal and lithospheric mantle melting, assimilation and fractional crystallisation. Crustal-derived magmatism represented by muscovite-biotite-garnet granites of the Munjeela Suite (~1580 Ma) occurs in the southwest Gawler Craton.

In the central Gawler Craton, Gawler Range Volcanics magmatism is coeval with NW-SE directed deformation partitioned into shear zones. These include the E-W-trending Yerda shear zone and N-S-trending Yarlbrinda shear zone in the central Gawler Craton, and the NE-SW-trending Bulgunnia shear zone along the southern margin of the Mount Woods Inlier. On the Eyre Peninsula retrograde shear zones with a dip-slip movement developed at this time. In the northern Gawler Craton, deformation resulted in S-verging nappe and fold-thrust structures and medium- to high-grade metamorphism in the Mount Woods Inlier, and granulite to ultra-high temperature metamorphism in the Coober Pedy Ridge and Mabel Creek Ridge. At the same time greenschist to lower amphibolite facies metamorphism and NE-SW-trending folding occurred on Yorke Peninsula in the eastern Gawler Craton.

The Kararan Orogeny (1570–1540 Ma) consists of high-grade metamorphism and shear zone development/reactivation affecting the western and central northern Gawler Craton. This event may represent the later stages of the deformation associated with the Gawler Range Volcanics and Hiltaba Suite. Granulite facies metamorphism is recorded in the Nundroo block of the Fowler Domain and may be linked with reactivation of the shear zones within the Fowler Domain. The Karari fault zone and associated shear zones in the central-northern Gawler Craton was also reworked at this time. High-thermal gradient metamorphism occurred between 1560 and 1500 on Yorke Peninsula, southeastern Gawler Craton. Temporally equivalent bimodal magmatism (~1565–1555 Ma) and felsic intrusive magmatism (~1515–1505 Ma) have been identified on southern Yorke Peninsula. The link between magmatism and metamorphism in this region is not yet fully understood. Minor localised magmatism occurred in the Peake and Denison inliers in the northern Gawler Craton (1555–1530 Ma).

The Coorabie Event is the youngest recorded in the Gawler Craton and consists of greenschist to amphibolite facies metamorphism and shear zones reactivation between ~1470 and 1450 Ma in the western Gawler Craton, and ~1450 Ma magmatism and granulite facies metamorphism in the northern Gawler Craton. The ~1450 Ma magmatic rocks are undeformed and unmetamorphosed, crustal-derived granites with A-type affinity (LREE enriched and high Ga/Al ratios).

Rifting coincident with metamorphism and magmatism led to the deposition of the Pandurra Formation siliciclastics in the Cariewerloo Basin in the northeastern Gawler Craton at this time. These depositional events are part of a widespread event ~1500–1450 Ma in the Northern and Southern Australian Cratons. Low T thermochronometers suggest that the reactivation of shear zones was associated with regional denudation of much of the Gawler Craton.

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