DMITRE Minerals

Jump to content

Search

 

Navigation

 

Gawler Craton Geology

3D modelling provides a mechanism to validate existing geoscientific data.

3D_Models_Front_Page_-_Gawler_image_resizedGawler Province 3D Model

3D image of Cultana geomodel

Cultana Regional Model

Pandurra_MainImage

Pandurra Formation

The following discussion of Gawler Craton Geology is divided into the following time-slices:
  • Archaean
  • Paleoproterozoic
  • Mesoproterozoic

Archaean

Several major rock units were formed during the late Archaean, the Sleaford Complex, exposed in the southern Gawler Craton and the Mulgathing Complex, exposed in the western and northern Gawler Craton. Both consist of ortho- and paragneiss variably metamorphosed to granulite facies.

The Sleaford Complex, comprises the Carnot Gneisses, Wangary Gneiss and the Dutton Suite. The Carnot Gneisses are composed of garnet-quartz-feldspar ± cordierite paragneiss, banded iron formation, calcsilicate, quartz-feldsparorthogneiss, hypersthene gneiss and tholeiitic meta-basalt/meta-gabbro.

High crustal level granitoids of the Dutton Suite, including the Coulta Granodiorite, Kiana Granite and Whidbey Granite, were intruded into Wangary Gneiss, a lower grade equivalent of the Carnot Gneisses, during the Sleafordian Orogeny. The Mulgathing Complex contains banded iron formation, chert, carbonate, calcsilicate, quartzite and aluminous metasediments of the Christie Gneiss and meta-igneous units of the Kenella Gneiss. The Lake Harris Komatiite (>2500Ma), Hopeful Hill Basalt, South Lake Gabbro, Skuse Hill Pyroxenite and Aristarchus Peridotite also form part of the Mulgathing Complex.

Gold mineralisation occurs in cordierite bearing metasediments in the northern part of the Craton.

Paleoproterozoic

In the southern Gawler Craton the Miltalie Gneiss (2000 Ma) forms a migmatitic grey granitic gneiss which is intrusive into the Sleaford complex and overlain by the Hutchison Group (2000-1850 Ma). The Hutchison Group metasediments are composed of a mixed sequence of chemical and clastic sediments and extrusive basic and acid volcanics, including the Warrow Quartzite, Katunga Dolomite, Lower Middleback Jaspilite, Burrawing Amphibolite, Cook Gap Schist, Upper Middleback Jaspilite, Yadnarie Schist and Bosanquet Formation (1850 Ma).

The Myola Volcanics (1790 Ma) and Broadview Schist comprise deformed acid volcanics, fine grained gneisses, schists and quartzites metamorphosed to upper greenschist to lower amphibolite facies. They are slightly younger, outcropping east of the Middleback Range.

In the northeastern Eyre Peninsula the McGregor Volcanics (1740 Ma) and Moonabie Formation consist of subaerial rhyolite to dacite with minor andesite-basalt, volcaniclastic debris and lithic rich sediments. Metasediments and metavolcanics of the Wallaroo Group (1760-1740 Ma) occur on the northern Yorke Peninsula, these include the Doora Metasediments, Wandearah Metasediments, Moonta Porphyry, Wardang Volcanics and Willamulka Volcanics. Younger alteration and mineralisation associated with Hiltaba Suite granite is assigned to the Oorlano Metasomatite.

A striking north-south aeromagnetic anomaly on the Coffin Bay Peninsula corresponds to disseminated magnetite bearing schists of the Price Metasediments (<1770 Ma) which are of similar age to the Wallaroo Group.

In the Tarcoola-Kingoonya region the Wilgena Hill Jaspilite overlies ortho and paragneiss of the Archaean Mulgathing Complex. This iron formation is distinctively banded and contains subordinate amounts of interlayered carbonate, calc-silicate, quartzite. The jaspilite is overlain by a number of restricted, fault bounded, intracratonic basins.The Eba Formation contains pebbles of Wilgena Hill Jaspilite and forms a sequence of conglomerate, quartzite, siltstone, shale, sandstone and interbedded amygdaloidal basalt. This is unconformably overlain by the Labyrinth Formation a sequence of chert and pebbly sandstone to bouldery conglomerate with a thin interbedded rhyolite (1720 Ma).

The Tarcoola Formation is over 2km thick with a basal conglomerate, quartzite and overlying carbonaceous shale unit interbedded with andesitic to dacitic tuffs (1660 Ma) and basaltic sills. Gold and base metal mineralisation occurs within quartz veins associated with Hiltaba suite or Gawler Range Volcanics intrusives. A range of intrusives occur in the Paleoproterozoic.

In the southern Gawler Craton the Donington Suite (1850 Ma) intrudes the Hutchison Group during D1 of the Kimban Orogeny. Quartz gabbronorite, megacrystic granite gneiss, charnockite, granodiorite gneiss and granite gneiss are common lithologies within this suite. The mafic Jusseiu Dykes were contemporaneous with this intrusion. Components of the Minbrie Gneiss on the central-northern Eyre Peninsula are thought to be equivalents of the Donington Suite.

A variety of granitic intrusives including the Middlecamp (1730 Ma) and Carpa Granites, post date the Donington Suite and were intruded during D2 of the Kimban orogeny.

The Moody Suite (1700 Ma) is a series of syn D3 intrusions consisting of monzonite, adamellite, microgranite and leucogranite. Later intrusives include deformed multiphase plutons of the Ifould Complex (1650-1540 Ma) that occur in the western Gawler Craton and deformed comagmatic granitoids of the St Peter Suite (1630-1620 Ma)

Mesoproterozoic

The Gawler Range Volcanics (1590 Ma) form a huge felsic volcanic province, in the central Gawler Craton, with over 25 000 km2 of preserved outcrop. They are divided into two broad groups, an upper and lower unit. The lower unit is more varied, gently to steeply tilted and contains dacite-rhyodacite-rhyolite, ignimbrites and flows with thick, interlayered sequences of basaltic lavas whereas the upper unit contains thick, subhorizontal, porphyritic dacite sheets predominantely ignimbritic in origin.

The extensive Hiltaba Suite (1600-1585 Ma) is comagmatic with the Gawler Range Volcanics and is dominated by felsic granite plutons. Outcrop is most abundant in the central Gawler Craton particularly on the western and south-western margins of the Gawler Range Volcanics. This unit is characteristically pink due to hematite dusting of the feldspar crystals. The Hiltaba Suite and Gawler Range Volcanics were derived from partial digestion of the crust by mantle plumes and are the source for widespread Au-Cu-U mineralisation within the Gawler Craton.

The Corunna Conglomerate unconformably overlies the Moonabie Formation and McGregor Volcanics and is intruded by dykes of the Gawler Range Volcanics. The basal conglomerate contains abundant basement clasts fining upwards to thick carbonaceous siltstone and sandstone. In the Kingoonya area the Mentor Formation, consisting of chloritic and sericitic mudstone, altered and tuffaceous granite breccia and tuffaceous rhyolite, overlies the Labyrinth Formation. This unit is considered contemporaneous with extrusion of the Gawler Range Volcanics and prospective for Au-Cu-U mineralisation.

The last known magmatic event in the Gawler Craton is the intrusion of the Spilsby Suite granites (1510 Ma). Outcrop is restricted to islands of the Sir Joseph Banks Group in the Spencer Gulf between Eyre and Yorke Peninsulas.

Gawler Craton Orogeny

Sleafordian Orogeny

Prograde mineral assemblages in the Carnot Gneisses record granulite facies metamorphism. Equilibration temperatures attained 800-8600C at pressures of approximately 9kb. New zircon growth at this time has been dated at ca 2440 Ma and is interpreted as the peak of prograde metamorphism. Peak metamorphism is contemporaneous with the development of dominant regional structures during the Sleafordian D3 event. Similar conditions prevailed in the Mulgathing Complex in the western Gawler Craton with granulite facies hypersthene-garnet, magnetite-spinel and cordierite-garnet mineral assemblages in the Christie Gneiss although some areas record amphibolite prograde facies conditions.

Kimban Orogeny

The Kimban Orogeny is defined from the eastern Eyre Peninsula of the southern Gawler Craton and consists of three tectonic events. The earliest produced a layer parallel schistosity (1845-1795 Ma) and was synchronous with intrusion of the Donington Granitoid Suite. This event was overprinted by the second (1795-1745 Ma), producing tight to isoclinal folds and an axial planar schistosity. Metamorphic conditions for this event varied from amphibolite in central Eyre Peninsula to granulite facies in southern Eyre Peninsula. The Middlecamp and Carpa Granites are thought to be syntectonic with this event. The third phase (1745-1700 Ma) produced upright, open to tight regional folds with variable plunges and major mylonite zones. Peak metamorphic conditions in central Eyre Peninsula attained lower amphibolite facies contrasting with amphibolite to locally granulite facies in high strain zones in the southern Eyre Peninsula. This event resulted in the intrusion of the Moody Suite.

Kararan Orogeny

In the northwestern Gawler Craton there are several high grade granulite facies events, one at 1650 Ma and other at 1565-1540 Ma. The earliest granulite facies event produced very high grade hypersthene-sillimanite and sapphirine-quartz mineral assemblages indicating metamorphic conditions of 8-10 kb and 950-10000C.The term Kararan Orogeny is given to these events which include zones that record lower strain and U-Pb ages up to 1670 Ma.

A more detailed description is available in the Gawler Craton chapter of the South Australian Mineral Explorers Guide or through the Gawler Craton Information page.