The Gawler Craton is an extensive region of Archaean to Mesoproterozoic crystalline basement underlying approximately 440,000 km2 of central South Australia.
Age of major events
- Felsic magmatism of the Cooyerdoo Granite and underlying 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 (~2480–2420 Ma)
- Felsic magmatism of the Miltalie Gneiss and equivalents (~2000 Ma)
- Sedimentation and bimodal magmatism (~2000–1730 Ma) including Hutchison Group, Broadview Schist and Myola Volcanics, Moonabie Formation and McGregor Volcanics, Wallaroo Group, Peake Metamorphics, Price Metasediments, and unnamed sediments in the Nawa and Fowler Domains and Mt Woods inlier
- Cornian Orogeny (~1855–1845 Ma); metamorphism and felsic magmatism of the Donington Suite
- Kimban Orogeny (1730–1690 Ma); metamorphism and felsic magmatism of the Middlecamp Granite and equivalents and Moody Suite, synchronous with sedimentation of the Eba and Labyrith Formations
- Sedimentation of the Tarcoola Formation and Corunna Conglomerate (1680–1640 Ma) and felsic magmatism of the Tunkillia Suite (~1690–1680 Ma)
- Felsic magmatism (1620–1570 Ma) comprising the Nuyts Volcanics, St Peter Suite and Gawler Range Volcanics and Hiltaba Suite, synchronous with metamorphism and shear zone formation
- Kararan Orogeny (1570–1540 Ma); shear zone formation
- Coorabie Orogeny (1470–1450 Ma); shear zone formation
Metals: Cu, Au Fe, Ag, Pb, Zn, Co, Ni, Cr, Mn Ti, V, PGE, Mo, W, Sn, 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 & refractory)
Energy minerals: U3O8, thorium
Major exploration models
- FeO-Cu-Au-Ag±U (haematite- 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)
- VHMS deposits (Hall Bay Volcanics, Oakdale prospect southern Eyre Peninsula)
- Late Archaean 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 Palaeochannel 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)
The Gawler Craton is the oldest and largest geological province in South Australia, preserving a complex tectonic history spanning from c. 3200 Ma to 1450 Ma. The craton comprises a Meso- to Neoarchaean core enclosed by Palaeoproterozoic to Mesoproterozoic rocks. The Mesoarchaean history of the Gawler Craton is dominated by felsic magmatism, the Neoarchaean to Palaeoproterozoic history by sedimentation and bimodal volcanism, and the Mesoproterozoic history by felsic volcanism.
The southern boundary of the craton coincides with the continental margin, but the other boundaries are poorly constrained, being obscured by cover sequences; the Neoproterozoic Torrens Hinge Zone and Adelaide Geosynine to the east separating the Gawler Craton from the Palaeo- to Mesoproterozoic Curnamona Province and the Neoproterozoic to Palaeozoic Officer Basin to the north and west separates the Gawler Craton from the Musgrave Province and Albany Fraser Belt and Yilgarn Craton in WA.
The oldest rock in the Gawler Craton is the Cooyerdoo Granite (~3150 Ma), exposed in NE Eyre Peninsula. It is the product of melting of preexisting tonalite-trondhjemite-granodiorite (TTG) crust, and inherited zircons and evolved Sm-Nd ages suggest that older crustal material up to ~3400 Ma may be present at depth. The Cooyerdoo Granite contains a gneissic fabric, and metamorphic zircons at 2500–2510 Ma, not known elsewhere in the Gawler Craton, may record the age of this fabric development.
The next event recorded in the Gawler Craton is the intrusion of the protolith of the Coolanie Gneiss (~2820 Ma), an S-type granite with minor intercalated quartzite and metapelitic sediments which occurs as a N-S-trending belt in the NE Eyre Peninsula.
The late Archaean to earliest Palaeoproterozoic, (~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 probably represent a single late Archaean belt. Arenaceous and aluminous metasediments, banded iron formation and carbonates (Carnot Gneiss, Wangary Gneiss, Christie Gneiss and Kenella Gneiss) were deposited coeval with calc-alkaline arc-like felsic magmatism (Devil’s Playground and Hall Bay Volcanics) and plume related mafic-ultramafic magmas, including the Lake Harris Komatiite. These volcano sedimentary rocks were intruded by felsic to intermediate magmas (Glenloth Granite and Dutton Suite) derived from contaminated mantle melts in a magmatic arc environment. 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 Neoarchaean in the NE Eyre Peninsula, but the relationship of these sediments to the Sleaford and Mulgathing complexes is uncertain.
Basin development was terminated by the deformation and metamorphism of the Sleaford Orogeny (~2465–2410 Ma). In the central late Archaean belt metamorphism reached granulite facies, and deformation was characterised by near horizontal fabrics folded into N to NE-trending open to tight folds. The metamorphic grade on the flanks of the late Archaean belt is generally lower grade.
The Sleaford Orogeny was followed by ~400 m.y. of tectonic quiescence. At ~2000 Ma felsic magmatism in central Eyre Peninsula comprised the intrusion of the protoliths of the Miltalie Gniess, a granodiorite containing high-grade migmatitic fabrics and a quartzofeldspathic gneiss to the west at Bascombe Rocks. Synchronously in the southern Eyre Peninsula, the Red Banks Charnockite and other unknamed charnockitic granites intruded into the Sleaford Complex.
Intrusion of the Miltalie Gneiss was followed by sedimentation and volcanism over the period ~2000–1730 Ma. The Hutchison Group (max. dep. ages ~2000–1790 Ma) forms an extensive basement sequence in the eastern Gawler Craton, comprising quartzite, dolomite, iron formation, schist and amphibolite and was deposited in a passive margin setting. The Hutchison Group may comprise two disconformable groups; an older Darke Peak Group containing a sequence derived from highly evolved crustally reworked ~2500 Ma and ~2000 Ma rocks and a younger Cleve Group containing a sequence derived from less evolved ~1850 Ma and ~1790 Ma felsic 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. Granitic to charnokitic and mafic magmas of the Donington Suite intruded along the entire eastern margin of the Gawler Craton, derived from a mantle melt contaminated by late Archaean basement. Granulite facies metamorphism was followed by decompression-dominated retrograde P-T evolution and S-directed extensional fabrics.
Following the Cornian Orogeny rifting and bimodal volcanism resumed along the eastern margin of the Gawler Craton, comprising the bimodal Myola Volcanics and associated clastic sediments of the Broadview Schist (max. dep. age ~1790 Ma). Widespread sedimentation occurred over the craton during the period ~1770 to 1740 Ma, including the Peake Metamorphics (~1775 Ma) in the northern Gawler Craton, the Price Metasediments (max. dep. age ~1765 Ma), McGregor Volcanics and Moonabie Formation (max .dep. age ~1755 Ma) in the southern Gawler Craton, and the Wallaroo Group (max. dep. age 1770–1740 Ma) and sediments in the Mount Woods inlier in the eastern Gawler Craton. Deposition in the Fowler Domain (max. dep. age 1740–1720 Ma) and Nawa Domain (max. dep. age 1760–1740 Ma) in the western Gawler Craton were broadly coeval.
Basin development was terminated by the Kimban Orogeny (1730–1690 Ma), comprising low- to high-grade metamorphism together with felsic and lesser mafic magmatism. A number of major crustal-scale shear zones formed during the Kimban Orogeny, including the Tallacootra and Coorabie shear zones in the west and the Gallipoli and Kalinjala shear zones 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 which corresponds to a major magnetic discontinuity and separates differing lithostratigraphic zones.
In southern Eyre Peninsula metamorphism and deformation occur adjacent to the Kalinjala and Gallipoli shear zones, comprising up to granulite facies metamorphism and non-cylindrical and chevron-style folding. In northern Eyre Peninsula metamorphic grade was lower and deformation was accommodated by E-verging fold-thrust systems. 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 coeval with the Kimban Orogeny, consisting of isolated fault-bound basins containing basal conglomerates, quartzite and shale with felsic and mafic volcanics of the Eba and Labyrinth Formations (max. dep. age ~1715 Ma).
Magmatism during the Kimban Orogeny comprises I-type and S-type granites and minor mafic intrusions ranging from weakly deformed to migmatitic extending over most of the Gawler Craton, including the Middlecamp Granite (~1735 Ma) and the Moody Suite (~1690 Ma) on southern Eyre Peninsula, as well as equivalents in the Fowler Domain, Coober Pedy Ridge, Peake and Denison inliers and central Gawler Craton. I-type intrusives of the Tunkillia Suite (1690–1670 Ma) form an arcuate belt in the central Gawler Craton and discrete plutons in the western Gawler Craton, overlapping with the youngest Kimban-aged intrusives, and indicates magmatism continued in a post-orogenic setting.
The Kimban Orogeny was followed by a period of extension between 1680 and 1640 Ma, leading to local sedimentation and magmatism, including 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 and in the western Gawler Craton unnamed psammitic to pelitic sediments (max. dep. Age ~1640 Ma), known only as included blocks in Hiltaba-aged plutons.
In the southwestern part of the craton the alkaline felsic Nuyts Volcanics erupted at ~1630 Ma. They were intruded by felsic to mafic, juvenile, possibly arc-related magmas of the St Peter Suite at 1620–1615 Ma. This was followed by continued felsic volcanism in the central part of the craton, probably in a far-field continental back-arc setting, producing the voluminous (~90,000 km2) Gawler Range Volcanics (~1592 Ma). These volcanics comprise an initial phase of felsic and minor magmas derived from fractional crystallization and crustal contamination of mantle melts erupted from isolated volcanic centres, and a mature phase of large (200–300 m thick) high T (900–1100°C) felsic lavas derived from extensive crustal melting. The volcanics are comagmatic with high T fractionated felsic and minor mafic intrusives of the Hiltaba Suite (1595–1575 Ma) derived from a depleted mantle sources with a significant crustal component, and S-type Munjeela Suite (~1580 Ma).
Magmatism of the Gawler Range Volcanics in the central part of the craton is coeval with NW-SE directed deformation associated with 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 in the northern Gawler Craton. At the same time greenschist to lower amphibolite facies metamorphism and NE-SW-trending folding occurred on Yorke Peninsula in the eastern Gawler Craton. Deformation in the central Gawler Craton was partitioned into shear zones, including the E-W-trending Yerda shear zone and N-S-trending Yarlbrinda shear zone in the central Gawler Craton, and the N-S-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.
The Kararan Orogeny (1570–1540 Ma) consists of high-grade metamorphism and shear zone development/reactivation affecting the western and central northern Gawler Craton and 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.
Minor localised magmatism occurred following the Kararan Orogeny, including magmatism in the Peake and Denison inliers in the northern Gawler Craton (1555–1530 Ma) and the Spilsby Suite in the southern Gawler Craton (~1500 Ma).
The youngest event recorded in the Gawler Craton consists of the reactivation of shear zones between ~1470 and 1450 Ma at greenschist to amphibolite facies in the western Gawler Craton. 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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