The article describes geological constraints on the formation of sandstone-hosted uranium depoists in paleovalleyes and paleochannels

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The North Australian Craton (NAC; Myers et al. 1996) includes Palaeoproterozoic orogens and basins in northern Australia including the Halls Creek, Pine Creek, McArthur, Mount Isa, Tennant Creek, Tanami, and Aileron (northern Arunta) geological regions. Archean basement to the NAC crops out in the Pine Creek and Tanami regions, with ages in the range 2.67 Ga - 2.50 Ga. An early phase of basin development at 2.05-2.00 Ga is reflected in the basal units of the Pine Creek Orogen. The nature of the basement remains unclear across much of the NAC, although geophysical and isotopic evidence suggests widespread presence of thick Neoarchean to Palaeoproterozoic continental crust. Recent work by the Northern Territory Geological Survey and Geoscience Australia , particularly the Arunta and Tanami Regions, has provided important new constraints on the tectonic evolution of the North Australian Craton. Current evidence suggest that most of the NAC was a coherent entity by 1.86-1.83 Ga, when large areas of the craton was covered by thick sedimentary packages which now form regionally important hosts for gold mineralisation. In the Northern Territory, apparent correlations are now possible between packages at 1.865-1.860 Ga (Finniss River and South Alligator Groups, Waramunga Formation, Junalki Formation), 1.84-1.83 Ga (Lander Rock Formation, Killi Killi Formation, lower Ooradidgee Group), and 1.82-1.80 Ga (Ware Group, Hatches Creek Group, Strangways Metamorphic Complex). Tectonism throughout much of the Northern Territory in this period was dominated by intraplate tectonics, although these are likely to have been driven by events at the northern and western margins of the craton, such as the postulated collision between the Kimberley and North Australian Cratons at 1.83 Ga (Sheppard et al. 1999). <p>Related product:<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&amp;catno=64764">Evolution and metallogenesis of the North Australian Craton Conference Abstracts</p>

Existing age constraints for geological events in the Tanami Block come predominantly from U-Pb geochronology of i) detrital zircons in sediments, and ii) magmatic zircons in granitoids. These constraints have been used together with observed and inferred geological relationships to help constrain timing of stratigraphy, magmatism, deformation, metamorphism and Aumineralisation (e.g. Vandenburg et al., 2001). Ongoing GA/NTGS zircon geochronology is continuing to refine our understanding of the stratigraphy and magmatic history of the Tanami, with attendant implications for tectonic evolution. In this regard it is noteworthy that detrital zircon ages of ~1815 Ma from the Killi Killi formation require either (or both) a revision of existing stratigraphy, or that the so-called Tanami Orogenic Event significantly post-dates ~1815 Ma, in contrast to previous estimates of ~1845 - 1830 Ma. However, detrital and magmatic zircons can provide no direct constraints on timing of deformation, metamorphism and Au-mineralisation, and consequently our current understanding of these processes in the Tanami region is relatively poor, despite being critical to predictive exploration models.

In July 2000, Geoscience Australia (then the Australian Geological Survey Organisation) joined with the Northern Territory Geological Survey (NTGS) in the North Australia NGA (National Geoscience Agreement) Project (NAP), a three year program to assist NTGS in their regional mapping and metallogenic programs in the southern Northern Territory.

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. Strikingly similar geological histories and metal endowments support the view that the Broken Hill (Curnamona craton) and Mt Isa regions were once contiguous, or at least formed part of a single continuous Zn-Pb and/or IOCG mineral province, during the late Palaeoproterozoic-early Mesoproterozoic (Giles et al., 2004). Pb model ages for major Zn-Pb deposits like Broken Hill and Cannington (1675 Ma and 1665 Ma respectively) are comparable (Carr et al., 2004) and high grade metasedimentary rocks hosting these deposits are thought to have been deposited at about the same time (ca 1690-1670 Ma) in either an intra-continental rift or a back-arc extensional environment (e.g., Blake, 1987; Walters and Bailey 1998; Betts et al., 2003). High grade deformation and metamorphism at 1580-1600 Ma (e.g., Page and Sweet, 1998; Page et al. 2004) preclude unequivocal identification of the original ore-forming environment in both cases, although clues to the tectonic setting and kinematic framework are still preserved in less intensely metamorphosed rocks of equivalent age in the Mount Isa Western Succession. The Western Succession rocks developed over a 200-Myr period from 1.8 Ga to 1.6 Ga (Blake, 1987) and, thus, overlap in age with five major tectonothermal events (Claoué-Long, 2003; Scrimgeour, 2005) recognised in the Arunta-Tanami region of the NAC. Major events identified at 1810 Ma and 1770 Ma (Stafford and Yambah), 1730-1700 Ma (Strangways), ~ 1640 Ma (Leibig) and 1560-1590 Ma (Chewings) in the NAC also find expression in the Mount Isa and Broken Hill regions (Page et al., 2000; Neumann et al., 2006), inviting speculation that the crustal processes and geodynamic framework inferred for these two regions are equally pertinent to the mineral provinces in the southern and eastern NAC.

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The minerals industry presently provides 49% of Australia's export income. Although most of this income is derived from the bulk commodities, the earliest mining in Australia was of precious and base metals. The first major mining boom in Australia, the Victorian gold rush, and later rushes to silver-lead deposits at Broken Hill and gold deposits at Kalgoorlie, laid the foundations of Australia's wealth in the latter half of the 1800s. These mining booms had major consequences in the founding of provincial cities such as Bendigo, Ballarat and Kalgoolie and funding early growth of Melbourne and Perth. These and subsequent mineral discoveries were major drivers in opening up regional and inland Australia, not only for mining, but also for agriculture and tourism. Analysis of major Australian mineral provinces indicate that despite differences in metallogeny and geological setting, these provinces share many common features, including an association with margins of crustal blocks; an association with (inverted) extensional faults, many of which penetrate the crust; a common association with mantle-derived magmas or fluids; a temporal association with plate reconfigurations; localisation of ores by chemical or physical gradients; and an association with major fluid flow caused by either thermal or tectonic events. Major mineral provinces are products of the supercontinent cycle and developed preferentially along the margins of crustal blocks. Localisation of deposits is controlled by the basinal, structural and chemical architecture developed during these processes. Formation of major provinces may be the consequence of unusual processes or events that overprint the supercontinent cycle. The Eastern Goldfields gold province is related to amalgamation of the first supercontinent, Kenorland, and the Australian zinc belt Olympic Cu-Au-U province relates to the first break-up after to GOE. The Victorian goldfields appear to be associated with Au-enriched sources.

Zn-Pb-Ag mineral deposits, which are the products of specific types of hydrothermal "mineral systems", are restricted in time and space in Australia. These deposits formed during three main periods: ~2.95 Ga, 1.69-1.58 Ga, and 0.50-0.35 Ga. The 1.69-1.58 Ga event, which was triggered by accretionary and rifting events along the southern margin of Rodinia, is by far the most significant, accounting for over 65% of Australia's Zn. With the exception of the 0.50-0.35 Ga event, major Australian Zn-Pb-Ag events do not correspond to major events globally. Over 95% of Australia's Zn-Pb-Ag resources were produced by just four mineral system types: Mt Isa-type (MIT: 56% of Zn), Broken Hill-type (BHT: 19%), volcanic-hosted massive sulfide (VHMS:12%), and Mississippi Valley-type (MVT: 8%). Moreover, just 4% of Australia's land mass produced over 80% of its Zn. The four main types of mineral systems can be divided into two groups, based on fluid composition, temperature and redox state. BHT and VHMS deposits formed from higher temperature (>200?C), reduced fluids, whereas MIT and MVT deposits formed from low temperature (<200?C), oxidized (H2S-poor) fluids. These fluid compositions and, therefore, the mineralization style are determined by the tectonic setting and composition of the basins that host the mineral systems. Basins that produce higher temperature fluids form in active tectonic environments, generally rifts, where active magmatism (both mafic and felsic) produces high heat flow that drives convective fluid circulation. These basins are dominated by immature siliciclastic and volcanic rocks with a high overall abundance of Fe2+. The high temperature of the convective fluids combined with the abundance of Fe2+ in the basin allows sulfate reduction, producing reduced, H2S-rich fluids. In contrast, basins that produce low temperature fluids are tectonically less active, generally intracratonic, extensional basins dominated by carbonated and mature siliciclastics with a relatively low abundance of Fe2+. Volcanic units, if present, occur in the basal parts of the basins. Because these have relatively low heat flows, convective fluid flow is less important, and fluid migration is dominated by expulsion of basinal brines in response to local and/or out-of-area tectonic events. Low temperatures and the lack of Fe2+ prevent inorganic sulfate reduction during regional fluid flow, producing oxidized fluids that are H2S-poor. The contrasting fluid types require different depositional mechanisms and traps to accumulate metals. The higher temperature, reduced VHMS and BHT fluids deposit meatls as a consequence of mixing with cold sewater. Mineralization occurs at or near the seafloor, with trapping efficiencies enhanced by sub-surface replacement or deposition in a brine pool. In contrast, the low temperature, oxidized MIT and MVT fluids precipitate metals through thermochemical sulfate reduction facilitated by hydrocarbons or organic matter. This process can occur at depth in the rock pile, for instance in failed petroeum traps, or just below the seafloor in pyritic, organic-rich muds. Mass balance calculations indicate that the size of a metal accumulation, although controlled at the first order by the mineral system container size, also depends on the efficiencies at which metals are extracted from the source and retained at the trap site. The shear size of minerals systems required to form giant deposits may partly explain why these deposits commonly occur by themselves, without significant satellite deposits. In addition to the size of the mineral system container, metal retention efficiency appears to be the most important determinant of the size of metal accumulations.

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