Gawler craton
Encyclopedia
Precambrian
The Precambrian is the name which describes the large span of time in Earth's history before the current Phanerozoic Eon, and is a Supereon divided into several eons of the geologic time scale...
crystalline basement
Basement (geology)
In geology, the terms basement and crystalline basement are used to define the rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin...
crust
Crust
Crust may refer to:* Crust * The Crust, television seriesPhysical sciences:* Crust , at least continent-wide structure* Soil crust, local biology-sensitive structureFood:* Crust, dense surface layer of bread...
al block was craton
Craton
A craton is an old and stable part of the continental lithosphere. Having often survived cycles of merging and rifting of continents, cratons are generally found in the interiors of tectonic plates. They are characteristically composed of ancient crystalline basement rock, which may be covered by...
ised ca. 1550-1450 Ma. Prior to 1550 Ma the craton comprised a number of active Proterozoic
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
orogenic belts extending back in time to at least 2450 Ma.
The Craton can be subdivided into a number of tectonic subdomains on the basis of structure and tectonostratigraphic
Stratigraphy
Stratigraphy, a branch of geology, studies rock layers and layering . It is primarily used in the study of sedimentary and layered volcanic rocks....
history. The south-central Eyre Peninsula straddles the boundary between the Archaean to early Palaeoproterozoic Coulta 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 the Kimban 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 deformed metamorphosed
Metamorphic rock
Metamorphic rock is the transformation of an existing rock type, the protolith, in a process called metamorphism, which means "change in form". The protolith is subjected to heat and pressure causing profound physical and/or chemical change...
acid volcanics and sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....
s ranging from the Myola Volcanics and Moonta Porphyry
Porphyry (geology)
Porphyry is a variety of igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. The larger crystals are called phenocrysts...
to the Moonabie Formation and Wandearah Metasiltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
.
Subsequent deformation on the craton has been largely epeirogenic forming shallow fault-bounded intracontinental depressions represented by Cainozoic basins, the southern continental margin
Continental margin
The continental margin is the zone of the ocean floor that separates the thin oceanic crust from thick continental crust. Continental margins constitute about 28% of the oceanic area....
and Spencer Gulf.
Physiography
The Gawler Craton, or Gawler Block, is a distinct physiographic province of the larger West Australian ShieldAustralian Shield
The Australian Shield, also called the Western Australian Shield or Western Plateau, occupies more than half of the continent of Australia. It occupies the portion of Australia west of a line running north-south roughly from the eastern shore of Arnhem Land on the Bay or Gulf of Carpentaria to the...
division. It includes the smaller Stuart Range Basin and Pimba Platform physiographic sections.
Northwestern Fowler Domain
Fowler Domain is a major tectonic zone on the north-western flank of the Gawler craton comprising dense, magnetic, highly deformed, intermediate to ultramafic intrusives overlain by thin Tertiary sands and recent sand dunes. Aeromagnetic surveyAeromagnetic survey
An aeromagnetic survey is a common type of geophysical survey carried out using a magnetometer aboard or towed behind an aircraft. The principle is similar to a magnetic survey carried out with a hand-held magnetometer, but allows much larger areas of the Earth's surface to be covered quickly for...
s show the presence of a high concentration of crustal scale fractures and faults in this area. These structures could have provided pathways for the intrusion of mafic-ultramafic bodies with potential for nickel sulphides, chromite and platinoids.
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
Palaeoproterozoic rocks of the eastern and central Gawler craton are overlain by relatively unmetamorphosed clastics of the Corunna Conglomerate, the Gawler Range Volcanics, the Pandurra Formation, and thin platformal late Proterozoic and Cambrian sediments of the Stuart and Spencer Shelves. In and around the Gawler RangesGawler Ranges
The Gawler Ranges are a range of stoney hills in South Australia to the north of Eyre Peninsula. The Eyre Highway skirts the south of the ranges. The Gawler Ranges National Park and Gawler Ranges Conservation Reserve are in the ranges north of Wudinna...
, the volcanics and older rocks were intruded by Hiltaba Suite granites which are closely associated with formation of the giant Olympic Dam orebody 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 stabilization of the craton as it is seen today.
Central Yarlbrinda Shear Zone
In the central Craton, the Yarlbrinda Shear Zone was likely formed by the Kararan Orogeny and 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 or shear zone, the Fowler Shear Zone, ca. 1600-1540 Ma.Economic Geology
Minerals that have been found in the craton include goldGold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
, diamond
Diamond
In mineralogy, diamond is an allotrope of carbon, where the carbon atoms are arranged in a variation of the face-centered cubic crystal structure called a diamond lattice. Diamond is less stable than graphite, but the conversion rate from diamond to graphite is negligible at ambient conditions...
s, copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
, nickel
Nickel
Nickel is a chemical element with the chemical symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel belongs to the transition metals and is hard and ductile...
, granite
Granite
Granite is a common and widely occurring type of intrusive, felsic, igneous rock. Granite usually has a medium- to coarse-grained texture. Occasionally some individual crystals are larger than the groundmass, in which case the texture is known as porphyritic. A granitic rock with a porphyritic...
, iron ore, lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
-zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...
, uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...
, coal
Coal
Coal is a combustible black or brownish-black sedimentary rock usually occurring in rock strata in layers or veins called coal beds or coal seams. The harder forms, such as anthracite coal, can be regarded as metamorphic rock because of later exposure to elevated temperature and pressure...
, industrial minerals
Industrial minerals
Industrial minerals are geological materials which are mined for their commercial value, which are not fuel and are not sources of metals ....
and arsenic
Arsenic
Arsenic is a chemical element with the symbol As, atomic number 33 and relative atomic mass 74.92. Arsenic occurs in many minerals, usually in conjunction with sulfur and metals, and also as a pure elemental crystal. It was first documented by Albertus Magnus in 1250.Arsenic is a metalloid...
.
The huge Olympic Dam copper-gold operation is located in the Eastern Olympic Copper-Gold Province at the cratons eastern edge. The Prominent Hill copper-gold mine is northwest of Olympic Dam and the Challenger Gold Mine is to the west of Prominent Hill located in the center of the craton. The 70 million tonne Kalkaroo Mine is 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 optimized open pit designed to 230 metres depth (Havilah, 2006).
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 sulphides, 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 sulphide mineralization. Ultramafic intrusive rock hosting nickel bearing sulphides (pentlandite and mackinawite) has returned values up to 0.49% nickel, 38 parts per billion(ppb) platinum and 58ppb palladium. Previous explorations reported up to 0.74% nickel from samples obtained in shallow bedrock drilling (Mithrill Resources, 2005). The Thompson Belt
Thompson Belt
The Thompson Belt, also referred to as the Thompson Nickel Belt, is an Archean and early Proterozoic geologic feature in Manitoba, Canada. It contains gneiss related to deformation of the Trans-Hudson orogeny....
in Canada has similar features and is considered by the Department of Primary Industries and Resources South Australia (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. (PlatSearch, 2004).
Drilling has confirmed significant widespread uranium mineralisation at the "Warrior" paleochannel 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. (Stellar, 2006).
See also
- Geology of AustraliaGeology of AustraliaAustralia is a continent situated on the Indo-Australian Plate.The geology of Australia includes virtually all known rock types and from all geological time periods spanning over 3.8 billion years of the Earth's history.-Components:...
- Australian ShieldAustralian ShieldThe Australian Shield, also called the Western Australian Shield or Western Plateau, occupies more than half of the continent of Australia. It occupies the portion of Australia west of a line running north-south roughly from the eastern shore of Arnhem Land on the Bay or Gulf of Carpentaria to the...
- Western PlateauWestern PlateauThe Western Plateau is Australia's largest drainage division and is composed predominantly of the remains of the ancient rock shield of Gondwanaland. It incorporates two thirds of the continent; 2,700,000 square kilometres of arid land including large parts of Western Australia, South Australia,...
- Pilbara cratonPilbara cratonThe Pilbara craton , along with the Kaapvaal craton are the only remaining areas of pristine Archaean 3.6-2.7 Ga crust on Earth...
- Yilgarn cratonYilgarn cratonThe Yilgarn Craton is a large craton which constitutes the bulk of the Western Australian land mass. It is bounded by a mixture of sedimentary basins and Proterozoic fold and thrust belts...
- Ore genesisOre genesisThe various theories of ore genesis explain how the various types of mineral deposits form within the Earth's crust. Ore genesis theories are very dependent on the mineral or commodity....
External links
- Havilah Resources NL. (2006) Third Quarter Activities and Cash Flow Report
- Mithril Resources. (2005) Quarterly Report
- PlatSearch Inc. (2004) "Announcement of Joint venture with INCO Wynbring Nickel Project, SA."
- Stellar Resources Limited. (2006) RCR Uranium Sector Review Report