A coherent set of timing constraints is produced for Tasmania's Proterozoic and Cambrian geology when only mineral ages are considered and whole-rock ages excluded. The oldest recognised event is the formation of sedimentary deposits which contain detrital zircons that indirectly indicate a depositional age younger than 1180 Ma. Partial melts of these sedimentary rocks were incorporated in Neoproterozoic, Devonian and probably Cambrian felsic magmas. Neoproterozoic granite on King Island has an age of 760 ± 12 Ma and is part of a high-level intrusive episode that accompanied the Wickham Orogeny, an event with regionally varied strain that is represented in northwestern Tasmania by a low-angle unconformity, by altered granitoid with a magmatic age of 777 ± 7 Ma, and by the thick turbidite pile of the Burnie and Oonah Formations with its syndepositional intrusions of Cooee Dolerite. The late Neoproterozoic was relatively quiet tectonically but by early in the Middle Cambrian a crustal collision which marked the early phase of the Tyennan Orogeny brought about high-level emplacement of ultramafic-bearing allochthons and deep-seated metamorphism of quartzose sedimentary and basaltic rocks. The ultramafic allochthons carried tonalite that had crystallised only shortly before at 510 ± 6 Ma, while the deep-seated metamorphism produced eclogite at 502 ± 8 Ma. By middle Middle Cambrian times the metamorphic rocks had been uplifted and they experienced repeated uplift during the period of Mt Read volcanism and onward to the close of the Tyennan Orogeny in the Early Ordovician, an overall period of some 20 million years from the early Middle Cambrian. Regionally varied strain was again a feature during the Tyennan Orogeny, with the Smithton area in northwestern Tasmania and King Island occupying relatively undeformed cratonic positions. * Table 3 [indicated by an asterisk (*) in the text and listed at the end of the paper] is a Supplementary Paper lodged with the National Library of Australia (Manuscript Section); copies may be obtained from the Business Manager, Geological Society of Australia.

No abstract available

The Tasman Fold Belt System in New South Wales includes three out-cropping fold belts: the Neoproterozoic-Early Palaeozoic Kanmantoo Fold Belt, the Early Palaeozoic-Carboniferous Lachlan Fold Belt, and the Early Palaeozoic-Triassic New England Fold Belt. Substantial production of metal has come from mineral deposits in the Lachlan and New England Fold Belts and from alluvial deposits in their cover rocks. The Kanmantoo Fold Belt has a restricted range of mineralisation, which includes stratiform(?) iron-rich copper lodes in metamorphosed mafic volcanics, lead-silver veins and gold-quartz veins. Geological similarities with Victoria and Tasmania suggest potential for gold and base metals developed in Late Proterozoic-Cambrian mafic arc rocks. The Lachlan Fold Belt contains a wide range of deposits. The most important types are porphyry, epithermal and skarn-type copper, copper-gold, and gold deposits developed in Ordovician basaltic and andesitic volcanics (shoshonites) and associated intrusives; base-metal and gold deposits, with both volcanogenic (VMS) and thrust-related features, in Silurian felsic volcanic-sedimentary rock trough and basin sequences; tin, gold and smaller tungsten, molybdenum and base-metal deposits in Silurian and Early Devonian granites; large gold and base-metal deposits in Early Devonian turbiditic rocks in the Cobar region (Cobar-type deposits), probably formed during deformation and closure of the Cobar Basin; and gold vein deposits in folded sedimentary rocks, for example at Hill End. There is good potential for discovery of further deposits within the Lachlan Fold Belt and in extensions under cover rocks. The main targets are deposits related to Ordovician and Silurian volcanism, Cobar-type deposits and deposits associated with sutures and thrusts. Recent investigations suggest that a poorly understood, but possibly widespread, Late Carboniferous-Early Permian metallogenic epoch occurs in eastern Australia, covering parts of the Lachlan and New England Fold Belts. The New England Fold Belt in New South Wales can be characterised as a tin, gold, antimony province. Deposits formed in a variety of settings. The most important associations are: base-metal deposits in Early Permian felsic volcanics; gold-silver-base-metal deposits in Late Permian felsic to intermediate volcanics of the Drake area; tin, gold, molybdenum, bismuth and tungsten deposits associated with Late Permian-Early Triassic granites; and metahydrothermal gold, antimony and tungsten-bearing quartz veins occurring in faults, shears and joints commonly associated with regional dislocations (and thought to have formed from metamorphic dehydration of accreted sediments and volcanics). Recent exploration has located epithermal gold mineralisation in Early Permian intermediate and felsic volcanic centres, in previously unexplored areas of the Tamworth Zone in the west of the New England Fold Belt, which were probably related to rifting in the foreland (Meandarra Rift).

Victoria provides the only well-exposed section across the southern part of the Lachlan Fold Belt and the easternmost Delamerides. Although the plate tectonic setting of this region in the Palaeozoic is still uncertain, the exposure provides important insights into its depositional, magmatic and structural evolution from the Cambrian to the end of the Devonian. The oldest known rocks are Late Proterozoic or Cambrian and either calc-alkaline arc-type volcanics (mainly in the west) or MORB-types (mainly in central Victoria). The MORB-types host small copper-gold deposits and may be the source for the turbidite-hosted gold. The arc-type volcanics have potential for major VHMS deposits. The volcanics are overlain by an extensive turbidite sheet, which is Cambrian in the west and Early Ordovician in central and eastern Victoria; in east-central Victoria the turbidites may be absent. The Delamerian Deformation affected rocks in the far west; the Benambran Deformation affected the east and the Bendigo and Stawell Zones in west-central Victoria. In the Bendigo and Stawell Zones, late phases of the Benambran Deformation coincided with the formation of the world-famous turbidite-hosted gold deposits. There was no Benambran Deformation in the Melbourne Zone in central Victoria, where marine deposition continued without interruption from the Cambrian to the early Middle Devonian. In the Silurian, the partly fluvial, partly shoreline facies Grampians Group was laid down on cratonic crust in western Victoria, at what may have been the western shoreline of the Melbourne Trough in central Victoria. This was followed in the Late Silurian by eruption of the subaerial Rocklands Rhyolite. In eastern Victoria, there are two cycles of rifting in transtensional rift-like grabens into which voluminous silicic volcanics and marine sediments were deposited. The first, Silurian, cycle formed the Cowombat Rift, host to significant base-metal deposits. Away from this rift, there seems to have been a shallow sea during most of the Silurian in eastern Victoria, into which a very condensed limestone seems to have been deposited; however, the limestone is mainly known from olistoliths in the rift sequence. A second cycle of transtension in the Early Devonian formed the Buchan Rift and smaller basins, into which volcanics and/or marine sediments were deposited. In western Victoria, numerous I-type granites were intruded. In eastern Victoria, mixed I-, S- and A-type granites were intruded; several broke through to the surface and formed calderas. The Middle Devonian Tabberabberan Deformation affected most rocks in central and eastern Victoria. It was rapidly followed by intrusion of several granites and the Woods Point Dyke Swarm in central Victoria, which hosts the large Woods Point-Walhalla gold province in the Melbourne Zone. In the Late Devonian, a molasse-type sequence, mainly fluvial redbed sediments and silicic pyroclastics and lavas, was deposited in the Howitt Province in east-central Victoria, from where the rivers probably flowed to the east coast via Gippsland. The Howitt Province overlaps with the Central Victorian Magmatic Province, where many more granites were intruded with, again, some rising to the surface to form calderas into which thick sequences of silicic volcanics were erupted. The last significant Palaeozoic deformation was the Kanimblan, in the Carboniferous, during which the Upper Devonian and Lower Carboniferous redbeds were mildly to strongly folded and faulted.

The folded Proterozoic and Palaeozoic rocks of Tasmania are host to a wide variety of mineral deposits, some of which are of world-class significance. The Proterozoic sequences host known iron ore, gold, copper and non-metallic mineralisation, but have not been intensively explored and have considerable potential for further discoveries, of both the known deposit types and a number of other sediment-hosted mineralisation types. Early Cambrian ultramafic/mafic complexes, now thought to be allochthonous, have historically given platinum-group minerals, chromite and nickel. The Middle- Late Cambrian Mt Read Volcanics, host to known world-class VHMS- gold deposits and intensively explored, are still considered to represent a prime exploration target. Disseminated zinc-lead mineralisation of possible Irish style has recently been recognised in Ordovician platform carbonate sequences in western Tasmania. Widespread mineralisation related to the intrusion of Middle Devonian- early Carboniferous granitoids includes tin-tungsten, silver-lead and slate-belt gold, and there is considerable potential for the discovery of further similar deposits. Recent advances in the recognition of structural complications caused by major thrust faulting have in some cases increased the known and perceived possibilities for potential sites of mineralisation. The late Carboniferous and younger cover rocks have traditionally been a barrier to mineral exploration, but geophysical flagging of favourable host sequences in the basement below these rocks, together with the discovery of mineralisation in basement inliers, suggests considerable mineral potential in the basement.

The Early to Middle Cambrian Stansbury Basin preserves a palaeogeographic zonation, from shallow shelf carbonates in the west (Spencer and Ardrossan Shelves) through extensional siliciclastic rift facies (Kanmantoo Trough) and volcanogenically influenced back-arc basin environments (Murray Basin basement). Sedimentation occurred from about 540 Ma to at least 510 Ma, with a distinctive phase of thick rift sedimentation in the Kanmantoo Trough from 526 Ma. Sedimentation continued beyond the 510 Ma onset of compressional orogenesis, in back-arc basin environments east of the Padthaway Ridge and, possibly, in a foreland setting now occupied by Gulf St Vincent. Granitoid emplacement accompanied both the main compressive deformation (syntectonic 1- and S-type c.51 0- 500 Ma) and subsequent relaxation and extension (post-tectonic A-type granitoids and mantle-derived mafics c.480-490 Ma). Variably deformed, syn- to post-orogenic acid volcanics occur along the Padthaway Ridge. Listric faults associated with extensional rift development along the southeastern margin of the Gawler Craton were inverted during the Delamerian Orogeny as preferential zones of shearing and thrusting. The change from rift basin to platform sequence is now marked by a discrete shear zone on Kangaroo Island and a broader zone of imbricate thrusting on western Fleurieu Peninsula. There was little detachment between basement and cover, with most thrusts rooted in southeast-dipping shear zones within the basement. Cambrian carbonates of the Ardrossan and Spencer Shelves have potential for epigenetic, structurally modified Mississippi Valley-type (MVT) mineralisation associated with basin dewatering along major structures. Key areas for mineralisation are unconformities, karst and porous carbonates around the margins of the basin and near reactivated thrusts and fractures that acted as conduits for fluid movement. There is also potential for stratabound Cu mineralisation at redbed-to-marine stratigraphic transitions on the shelf. Many base-metal deposits with stratiform or structurally modified genetic characteristics have been discovered in outcrop in the Kanmantoo Trough. A syngenetic association with flooding surfaces (sequence boundaries) and manganiferous sea-floor exhalites has been recognised. Varying degrees of structural control or structural modification of originally stratiform and sedimentary exhalative mineralisation are evident. Recent sub-economic discoveries at the Angas and Mt Torrens prospects are significant and encouraging for undiscovered economic syn-sedimentary lead- zinc- silver- gold deposits. Beneath the Murray Basin, there is potential for volcanogenic massive sulphide mineralisation analogous to the Mt Read Volcanics. Recent drilling on the northern flank of the Padthaway Ridge encountered a number of anomalous Zn, Pb, Cu and Au intervals associated with post-collisional lavas, intrusives and pyroclastics. Extensive syn- and post-tectonic granitoids near the southern and eastern limits of Kanmantoo Group exposure are potential sources for porphyry Cu-Mo, epithermal Cu-Au and skarn deposits. Platinum-group element mineralisation is also evident in post-orogenic, mantle-derived mafic intrusives.

The evolution of the geology and mineral deposits of the Proterozoic in Western Australia can be described in terms of episodes of continental breakup, terrane accretion and plate aggregation. The Hamersley Basin represents breakup of an Archaean continent in the late Archaean to earliest Palaeoproterozoic (2800-2300 Ma). A period of plate aggregation occurred in the Palaeoproterozoic between 1900 and 1750 Ma with the formation of the North, South, and West Australian Cratons, probably as parts of larger continents. A period of intracratonic basin formation followed in the earliest Mesoproterozoic, around 1600 Ma. A second period of terrane accretion and plate aggregation took place in the late Mesoproterozoic between 1300 and 1000 Ma, during which the main crustal components of Proterozoic Australia were assembled as part of the Rodinian supercontinent. Proterozoic Australia remained essentially intact during Neoproterozoic continental breakup at ~750 Ma. Old Palaeoproterozoic and Mesoproterozoic sutures were reactivated as intracratonic orogenic belts between 560 and 540 Ma, during the late Neoproterozoic assembly of a new supercontinent. Two broad groups of mineral deposits, related to different tectonic regimes, can be recognised: volcanogenic massive sulphide deposits, stratiform sediment-hosted deposits, and hydrothermal vein systems related to rifting and basin formation; and mesothermal lode mineralisation, formed from magmatic, deformational, and metamorphic events linked to compressional tectonics. Although there are similarities, the geological evolution and mineralisation of individual orogenic belts and basins do not conform simply to models developed in the Proterozoic of northern and northeastern Australia. Given the low level of exploration activity and poor exposure in many areas, and recognising that mineralisation related to large-scale hydrothermal systems has occurred at various times throughout the Proterozoic, the potential exists for the further discovery of large-scale mineralisation.

There are two Archaean cratons in Western Australia, the Pilbara Craton and the Yilgarn Craton. Although tectonic models for each are controversial, there are clear differences between the two cratons in terms of age, relative abundance of rock types and structure. There are also contrasting ranges of mineral deposits. The Yilgarn Craton is the more prospective, especially for nickel, gold and tantalum. It contains world-class deposits of each of these commodities and many other small to medium-sized deposits of nickel and gold. A vigorous approach to exploration in the Yilgarn Craton over the past fifteen years has been rewarded with a steady stream of discoveries and conversion of prospects to mines. The Archaean rocks of the Yilgarn have also given rise to large deposits of bauxite and heavy-mineral sands, as a result of Tertiary weathering processes. The Pilbara Craton appears to be less well-endowed with mineral wealth, but contains some large sub-economic deposits of platinum-group elements, molybdenum and barite, as well as several clusters of volcanogenic base-metal sulphide deposits. Some of these deposits may become operating mines in the medium term and indicate the potential for more, possibly higher grade deposits in the Pilbara Craton.

Phanerozoic rocks in onshore Western Australia are primarily sedimentary. Volcanic and intrusive rocks are known from only a few areas and are mostly related to continental breakup along the northwest and western margins. The age and degree of faulting varies from basin to basin, depending on tectonic setting and period of principal activity as a depocentre, but most rocks are flat-lying to gently folded. The Southern Bonaparte, Southern Carnarvon, Canning, and Gunbarrel Basins are dominantly Palaeozoic depocentres. The Canning Basin was the dominant Ordovician depocentre, and the Southern Carnarvon Basin the dominant Permian depocentre. The Perth Basin is a polycyclic basin that was active from the upper Palaeozoic onwards, but is primarily Mesozoic. The Bremer and Eucla Basins were initiated in the Mesozoic in small local depocentres, but contain more extensive, thicker Cainozoic deposits. The age of initiation and the age of the thickest infill in each basin reflects the progressive separation of Western Australia from parts of Gondwana. In addition, transported and residual regolith blankets most of the Precambrian cratons, basins and orogenic belts. Mineralisation in Phanerozoic rocks is primarily strata-bound. Mississippi Valley-type base metals are present in Ordovician, Devonian, and Carboniferous rocks and are commonly associated with extensional faulting and evaporite-carbonate hosts. Coal swamps were important in the Permian immediately after the Gondwana glaciation and in Jurassic fluviodeltaic complexes. Mineral sands are associated with Cainozoic strandlines and associated coastal settings, but the concentration into potential economic accumulations is only partly assessed with respect to Mesozoic sediments. Significant thicknesses of evaporites (mainly halite with lesser anhydrite) are present in Ordovician and Silurian rocks, but are overshadowed by major gypsum and halite resources in Cainozoic barred marine embayments. Diamonds are associated with lamproitic intrusives of Miocene age in the Canning Basin, but have not been extracted from Phanerozoic rocks, except near Argyle, where Cainozoic gravel placers derived from the Argyle pipe are currently mined. Iron ore is mined from pisolitic channel iron deposits in Eocene palaeo drainages in the Pilbara. Various residual weathering, lateritisation and evaporation processes have concentrated significant accumulations of bauxite, uranium, and a number of industrial minerals within Cainozoic regolith.

Australias known resources of a wide range of mineral commodities are considerable in comparison with rates of production. Australia has the worlds largest economic demonstrated resources of bauxite, lead, zinc, silver, ilmenite, rutile, zircon, tantalum, and uranium. In addition, Australia is ranked in the top three countries in the world for economic demonstrated resources of brown coal, copper, cobalt, gold, iron ore, manganese ore, nickel , gem/near-gem and industrial diamond. Despite a high rate of discovery of significant new mineral deposits, particularly since the 1950s, there is considerable potential for discovery of further mineral deposits in Australia. This is indicated by the abundance of high-quality known resources and the ange of prospective geological settings. Increasingly, future discoveries are likely to be in regions where there has been little exploration to date because of their remoteness or the presence of concealing regolith or sedimentary cover. The few widely used mineral commodities for which Australia has low levels of demonstrated resources include chromium, platinum group metals, trona, and some components of fertilisers, such as potassium salts, and elemental sulphur. Given the acceptance of widespread multiple or sequential land use, which accommodates responsible exploration and mining, Australia is very well placed to maintain its position as one of the worlds major suppliers of a wide range of mineral commodities.