Journal
Type of resources
Keywords
Publication year
Topics
-
Altered basalt, dolerite and gabbro have been dredged from a previously unsampled portion of the Macquarie Ridge (47o-48° S), using the commercial fishing vessel Amaltal Explorer. These rocks are petrographically and geochemically similar to mafic-ultramafic volcanic and plutonic suites of MORB-like petrological affinity, collected along the ridge between 49° and 58° S by previous investigators. The northernmost part of the Macquarie Ridge (Puysegur Bank) is thus geologically related to the rest of the ridge, even though it is bathymetrically part of the New Zealand continental shelf. Sedimentary rocks dredged from 47o-48° S were derived from both oceanic Macquarie Ridge and continental New Zealand sources. There is no evidence of subduction-related magmatism along any part of the Macquarie Ridge.
-
An introduction to this special issue of the Journal.
-
During 1.3-1.0 Ga, multiple magmatic/tectonic events, causally linked to extensive mantle melting, markedly affected the Musgrave Block, the Albany-Fraser belt and parts of the east Antarctic shield. It is possible that southern parts of the central Australian Arunta Block were also affected by this event. Equivalent terranes can be juxtaposed in conventional Gondwana reconstructions of southwestern Australia and Antarctica. Effects of a ~1060 Ma Gondwana-wide magmatism include areally extensive dyke swarms and volcanics of the central Australian Bentley Supergroup. It is unclear to what extent the effects of a ~550 Ma convergent event that resulted in significant crustal overthickening and high-P recrystallisation in Musgrave Block rocks can be extrapolated to neighbouring terranes. Nonetheless, this event may be indicative of plate margin processes of latest Neoproterozoic age that controlled the assembly of central Australia.
-
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.
-
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.
-
Current models for metamorphic fluid flow provide a framework for understanding the setting and genesis of Australian Precambrian ore deposits thought to have formed during metamorphism. Ideal conditions for formation of large metamorphogenic ores are a) an initial phase of metals dissolution by penetrative flow of devolatilisation, surface or igneous fluids along pathways of constant or increasing temperature, because channelised fluid flow will not normally provide the required metal volumes or transport continuity to subsequently form large ore deposits, and b) a subsequent phase of channelised fluid flow, particularly during retrogression or fluid mixing where temperature or fluid chemical changes combine with rapid fluctuations in fluid pressure accompanying dilatancy pumping. Protracted thermal histories and the identification of multiple hydrothermal events in major mineralised blocks (Yilgarn, Mt Isa, Broken Hill) provide some weight for multi-stage ore enesis models, particularly for giant ore deposits. Despite continuing uncertainty about the tectonic setting of many major mineral provinces, intra-plate orogeny, particularly in the Palaeoproterozoic and Mesoproterozoic, appears to provide the necessary conditions for development of rich mineral provinces. Such orogenies have the right combinations of temperature- pressure history, fluid evolution and magma generation to provide optimum conditions for ore genesis. A common feature to intracratonic belts of this age is an early phase of crustal extension following or synchronous with mafic magma underplating, and this early underplating may be the ultimate reason for primary metals enrichment. However, the subsequent path history of metals culminating in ore deposition is still controversial and poorly understood for most Australia Precambrian terrains.
-
No abstract
-
Platinum-group element mineralisation in Australian Precambrian layered mafic- ultramafic intrusions
No abstract
-
No abstract
-
No abstract