Добірка наукової літератури з теми "Eastern Gawler Craton"

The Blackbush uranium prospect (~12,580 tonnes U at 85 ppm cut-off) is located on the Eyre Peninsula of South Australia. Blackbush was discovered in 2007 and is currently the single example of sediment-hosted uranium mineralisation investigated in any detail in the Gawler Craton. Uranium is hosted within Eocene sandstones of the Kanaka Beds and, subordinately, within a massive saprolite derived from the subjacent Hiltaba-aged (~1585 Ma) granites, affiliated with the Samphire Pluton. Uranium is mainly present as coffinite in different lithologies, mineralisation styles and mineral associations. In the sandstone and saprolite, coffinite occurs intergrown with framboidal Fe-sulphides and lignite, as well as coatings around, and filling fractures within, grains of quartz. Microprobe U–Pb dating of coffinite hosted in sedimentary units yielded a narrow age range, with a weighted average of 16.98 ± 0.16 Ma (343 individual analyses), strongly indicating a single coffinite-forming event at that time. Coffinite in subjacent saprolite generated a broader age range from 28 Ma to 20 Ma. Vein-hosted coffinite yielded similar ages (from 12 to 25 Ma), albeit with a greater range. Uraninite in the vein is distinctly older (42 to 38 Ma). The 17 ± 0.16 Ma age for sandstone-hosted mineralisation roughly coincides with tectonic movement as indicated by the presence of horst and graben structures in the Eocene sedimentary rocks hosting uranium mineralisation but not in stratigraphically younger sedimentary rocks. The new ages for hydrothermal minerals support a conceptual genetic model in which uranium was initially sourced from granite bedrock, then pre-concentrated into veins within that granite, and is subsequently dissolved and reprecipitated as coffinite in younger sediments as a result of low-temperature hydrothermal activity associated with tectonic events during the Tertiary. The ages obtained here for uranium minerals within the different lithologies in the Blackbush prospect support a conceptual genetic model in which tectonic movement along the reactivated Roopena Fault, which triggered the flow of U-rich fluids into the cover sequence. The timing of mineralisation provides information that can help optimise exploration programs for analogous uranium resources within shallow buried sediments across the region. The model presented here can be predicted to apply to sediment-hosted U-mineralisation in cratons elsewhere.

The Olympic Cu-Au Province is a metallogenic province in South Australia that contains one of the world’s most significant Cu-Au-U resources in the Olympic Dam deposit. The Olympic Cu-Au Province also hosts a range of other iron oxide-copper-gold (IOCG) deposits including Prominent Hill and Carrapateena. This paper reviews the geology of the Olympic Cu-Au Province by investigating the lithospheric architecture, geodynamic setting and alteration systematics. In addition, since the province is almost entirely buried by post-mineral cover, the sedimentary cover sequences are also reviewed. The Olympic Cu-Au Province formed during the early Mesoproterozoic, ca. 1.6 Ga and is co-located with a fundamental lithospheric boundary in the eastern Gawler Craton. This metallogenic event was driven in part by melting of a fertile, metasomatized sub-continental lithospheric mantle during a major regional tectonothermal event. Fluid evolution and multiple fluid mixing resulted in alteration assemblages that range from albite, magnetite and other higher temperature minerals to lower temperature assemblages such as hematite, sericite and chlorite. IOCG mineralisation is associated with both high and low temperature assemblages, however, hematite-rich IOCGs are the most economically significant. Burial by Mesoproterzoic and Neoproterozoic-Cambrian sedimentary successions preserved the Olympic Cu-Au Province from erosion, while also providing a challenge for mineral exploration in the region. Mineral potential modelling identifies regions within the Olympic Cu-Au Province and adjacent Curnamona Province that have high prospects for future IOCG discoveries. Exploration success will rely on improvements in existing potential field and geochemical data, and be bolstered by new 3D magnetotelluric surveys. However, drilling remains the final method for discovery of new mineral resources.

Precambrian basement rocks exposed within tectonic windows in the North American Cordillera help to define the Precambrian crustal structure of western North America and possible reconstructions of the Late Proterozoic supercontinent Rodinia. New geologic mapping and U-Pb dating in the infrastructure of the Priest River metamorphic complex, northern Idaho, documents the first Archean basement (2651 ± 20 Ma) north of the Snake River Plain in the North American Cordillera. The Archean rocks are exposed in the core of an antiform and mantled by a metaquartzite that may represent the nonconformity between basement and the overlying Hauser Lake gneiss, which is correlated with the Prichard Formation of the Belt Supergroup. A structurally higher sheet of augen gneiss interleaved with the Hauser Lake gneiss yields a U-Pb zircon crystallization age somewhat greater than 1577 Ma. The slivers of augen gneiss were tectonically interleaved with the surrounding Hauser Lake gneiss near the base of the Spokane dome mylonite zone, which arches across this part of the Priest River complex. We conclude that the Spokane dome mylonite zone lies above the Archean basement-cover contact and that it was, in part, equivalent to the basal décollement of the Rocky Mountain fold and thrust belt. New U-Pb dates on metamorphic monazite and xenotime reveal peak metamorphism at ca. 72 Ma, compatible with movement along the Spokane dome mylonite zone at that time. The Archean basement could be interpreted as the western extension of the Hearne province, or a new Archean basement terrane separated from the Hearne province by an Early Proterozoic suture. The unique assemblage of 2.65 Ga basement, ~1.58 Ga felsic intrusive rocks, and the Middle Proterozoic Belt Supergroup can be used as a piercing point for the identification of the conjugate margin to Laurentia. Our new dating supports previous correlations of Australia's Gawler craton (2.55-2.65 Ga) and its 1590 Ma plutons with the Priest River complex basement gneisses. The Priest River complex basement may be a piece of eastern Australia stranded during rifting of the supercontinent Rodina in the Late Proterozoic.

The petrography and geochemistry of zircon offers an exciting opportunity to better understand the genesis of, as well as identify pathfinders for, large magmatic–hydrothermal ore systems. Electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, and energy-dispersive X-ray spectrometry STEM mapping/spot analysis were combined to characterize Proterozoic granitic zircon in the eastern Gawler Craton, South Australia. Granites from the ~1.85 Ga Donington Suite and ~1.6 Ga Hiltaba Suite were selected from locations that are either mineralized or not, with the same style of iron-oxide copper gold (IOCG) mineralization. Although Donington Suite granites are host to mineralization in several prospects, only Hiltaba Suite granites are considered “fertile” in that their emplacement at ~1.6 Ga is associated with generation of one of the best metal-endowed IOCG provinces on Earth. Crystal oscillatory zoning with respect to non-formula elements, notably Fe and Cl, are textural and chemical features preserved in zircon, with no evidence for U or Pb accumulation relating to amorphization effects. Bands with Fe and Ca show mottling with respect to chloro–hydroxy–zircon nanoprecipitates. Lattice defects occur along fractures crosscutting such nanoprecipitates indicating fluid infiltration post-mottling. Lattice stretching and screw dislocations leading to expansion of the zircon structure are the only nanoscale structures attributable to self-induced irradiation damage. These features increase in abundance in zircons from granites hosting IOCG mineralization, including from the world-class Olympic Dam Cu–U–Au–Ag deposit. The nano- to micron-scale features documented reflect interaction between magmatic zircon and corrosive Fe–Cl-bearing fluids in an initial metasomatic event that follows magmatic crystallization and immediately precedes deposition of IOCG mineralization. Quantification of α-decay damage that could relate zircon alteration to the first percolation point in zircon gives ~100 Ma, a time interval that cannot be reconciled with the 2–4 Ma period between magmatic crystallization and onset of hydrothermal fluid flow. Crystal oscillatory zoning and nanoprecipitate mottling in zircon intensify with proximity to mineralization and represent a potential pathfinder to locate fertile granites associated with Cu–Au mineralization.

AbstractNew mineralogical, geochemical, and geochronological data are presented for the Island Dam prospect, Olympic Cu-Au Province, South Australia. Skarn assemblages comprising actinolite/phlogopite + K-feldspar + magnetite suggest the presence of calcareous protoliths at Island Dam and indicate high-temperature alkali-calcic alteration in the early stages of IOCG mineralization, as seen in other deposits in the region. Dating of lamellar hematite intergrown with Cu-Fe-sulfides allows the timing of the alteration-mineralization event to be constrained at 1594 ± 28 Ma, contemporaneous with the ~ 1.59 Ga IOCG mineralization event recorded across the eastern Gawler Craton. The host metasedimentary sequence can be correlated to the Wallaroo Group based on lithology and fabrics, and stratigraphically by an underlying ~ 1850 Ma Donington Suite granite and the new U–Pb ages for superimposed mineralization. Oscillatory zoned silician magnetite in skarn displays a trace element signature comparable to that observed in the outer shell of the Olympic Dam deposit and the nearby Wirrda Well prospect and is consistent with early stages of IOCG mineralization. The geochemical signatures of hematite from skarn and banded Fe-rich metasedimentary rocks share a common enrichment in W, Sn, Mo, Th, and U seen in hematite from IOCG-style mineralization across the Gawler Craton. Relative enrichment in As, Sb, Ni, and Co is, however, specific to iron-oxides from banded Fe-rich metasedimentary rocks. These features can be attributed to pre-existing iron-rich lithologies.

The aim of this thesis is to map the distribution of alteration minerals and pathfinder elements from deposit to regional scale within the IOCG mi neral system of the eastern Gawler Craton , South Australia, and understand fluid rock interactions that control th at distribution. I present geochemistry petrology and mineral chemistry from a range of metasomatically altered rocks including four protolit h types; siliciclastic metasedimentary rock, calc silicate metasedimentary rock, g ranite and mafic magmatic rock. Techniques employed included; transmitted light microscopy, electron microprobe analyses ( EM), scanning electron microscopy (SEM) and laser ab lation inductively coupled plasma mass spectroscopy (LA ICPM). Thermodynamic modelling using the HCh software was then applied in order to further understand the temperature, pressure, fO2 and fluid-rock ratio conditions responsible for a range of alteration types Multiple, overprinting paragenetic relationships and unusual alteration textures in four contrasting protolith rocks from the central eastern Gawler Craton can be interpreted within the framework of five paragenetic stages (protolith; skarn; stage 1, K feldspar magnetite; stage 2, hematite chlorite muscovite, including the major Cu ore minerals; stage 3, post mineralization) corresponding to different mineral assemblages in the four protolith types. The paragenesis is consistent with successive per iods of Fe K metasomatism, with early higher temperature, more reduced (magnetite stable) alteration being consistently overprinted by lower temperature, more oxidized (hematite stable) alteration and with the bulk of Cu sulphide mineralization occurring a t close to the transition from magnetite to hematite. Minerals that pre-date the main sulphide phase (namely from the protolith, skarn and stage 1 assemblages) typically have major and trace element concentrations within expected ranges for comparable rock types outside the eastern Gawler Craton mineral province. Hematite associated with stage 2 assemblages has higher average concentrations of Ba, Cu, Mo, Nb, Pb, Th, Ta, U and SigmaREE compared to magnetite (between 1 and 2 orders of magnitude higher). In addition hydrothermal hematite contains elevated concentrations of Cu, U, Sb and Bi compared to the average crustal abundance. Hematite is the main host of Sb even when there are co-existing sulphide phases in the rock. Where sulphide minerals are present most chalcophile pathfinder elements (e.g. Ag, As, Bi, Cu, and Se) are dominantly deported in the sulphides, even at low concentrations, far from mineralisation. Pyrite is the most common sulphide, with chalcopyrite increasing in abundance closer to mineralisation. The pyrites are p-type, with S/Featom ratios of > 2 and Co/Ni ratios ranging between 0.4 and 10, but mostly above 1. This is consistent with a moderate-temperature hydrothermal origin for the pyrite. Concentrations of Co, As, Bi, Se, Te and Au in pyrite reach 2 to 3 orders of magnitude above crustal abundance. The chalcopyrite grains show variable enrichment in pathfinder elements and are most enriched in Bi, Se, Te and Ag, with values ranging between 1 and 4 orders of magnitude above crustal abundance. At elevated whole rock concentrations, within altered rocks, the REE are deported in hydrothermal apatite. This is consistent with the extreme capacity of the hydrothermal system to mobilise, and locally accumulate, even the most refractory elements. REE enrichment (up to 2604 ppm) is a good proximity indicator to ore, since it only occurs around the mineral system. Thermodynamic modelling was conducted using the HCh software to calculate equilibrium mineral assemblages predicted for model granite and calc-silicate protoliths mixed with a range of model hydrothermal fluids. Fluid compositions were consistent with fluid inclusion studies from the eastern Gawler Craton. Models were created in the C-H-O-Cl-S-Na-K-Mg-Fe-Si-Al-Cu-Ca-Mn chemical system at temperatures from 150(0) to 500(0)C, fO2 of -34 to -26 and fluid-rock ratios from 10-3 to 104. The modelling provides semi-quantitative constraints for mineral assemblages associated with IOCG mineral systems of the eastern Gawler Craton. The transition from protolith assemblages to magnetite-K-feldspar assemblages to chlorite-magnetite-K-feldspar assemblages to hematite-chlorite-muscovite assemblages with decreasing temperature, increasing fluid-rock ratio and increasing logfO2. This is consistent with the petrologic observations presented in this thesis, namely the consistent overprinting of stage 1, magnetite-K-feldspar alteration by stage 2, hematite-chlorite and muscovite alteration. Although Cu-sulphides are predicted to be stable over a range of temperature and fO2 conditions, they are predicted to be most abundant between temperatures of ~300(0) to 250(0)C, fO2 of -26 to -34 and at fluid-rock ratios >10. This corresponds to alteration assemblages at the magnetite and hematite boundary, with abundant chlorite and muscovite alteration. The distribution of pathfinder elements (measured in whole rock chemistry) within the central eastern Gawler Craton IOCG province can be predicted by combining petrological observations with mineral chemistry and thermodynamic modelling and are consistent with the observations of Fabris (2012, 2013). Elements associated with hematite alteration (notably Sb and W) are expected to have a wide geographic footprint. Elements enriched in pyrite (notably As, but also S and Se) are likely to have a broad geographic distribution in line with the presence of pyrite in both magnetite and hematite stable alteration assemblages. Elements most enriched in copper sulphides (Cu, Ag and Au) are largely restricted to within <5 km of known deposits.
Thesis (Ph.D.) -- University of Adelaide, School of Physical Sciences, 2018

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Multi-method thermochronology applied to the eastern Gawler Craton, beneath the Stuart Shelf cover (Olympic Dam Domain, South Australia), reveals multiple episodes of exhumation. Modelled data from Apatite Fission Track (AFT) analysis identifies four time periods where the eastern Gawler Craton basement experienced cooling into AFT closure temperatures (~60-120°C); at1050 ± 55 Ma (Mesoproterozoic), 439 ± 14 Ma (late Ordovician-Silurian), 304 ±36 Ma (mid-Carboniferous-mid Permian) and 245 ± 52 Ma (late Permian-early Jurassic). In addition, the Carboniferous and Jurassic peaks are supported by zircon (ZHe) and apatite (AHe) (U-Th-Sm)/ He results. The Ordovician peak is interpreted as resulting from the final pulses of the Delamerian Orogeny partially, mixed with the first pulses of the Alice Springs Orogeny. The Carboniferous-Permian event is linked with widespread exhumation likely due to the final pulses of the Alice Springs Orogeny (~300Ma). The preserved Mesoproterozoic event presents new AFT data in the area and coincides with some recent studies. However, it occurs only in samples obtained from the Gawler Range Volcanics and more prominent in core depth shallower than 500m. The late Permian-early Jurassic event is comparable to events believed have to stemmed from hydrothermal events. This event compliments AFT studies in the northern Flinders Ranges. The Late Ordovician-Silurian and Carboniferous-early Permian AFT pulses confirm events seen in studies of surrounding regions. Other geochronological studies around the Olympic Dam area indicate that this pulse either results from a localised hydrothermal event or distal effects of the Musgravian Orogeny. The Jurassic event suggests that the hydrothermal effect on AFT ages may be a more widespread event and not just localised to the northern Flinders Ranges as previously thought. The Ordovician event represents mixing between Delamerian and Alice Springs Orogenies. The Carboniferous-Permian event represents late distal effects of the Alice Springs Orogeny. These events match those of surrounding regions.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2015

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Detrital zircon ages obtained from the Corny Point Paragneiss and the Massena Bay Gneiss in the southeastern Gawler Craton, Australia, constrain their deposition to the interval ca. <1880 Ma. The presence of 2020 Ma, 2450 Ma and 2520 Ma detrital zircons within the Corny Point Paragneiss constrains the source region for the sedimentary protoliths to three possible domains within Australia; the Gawler Craton, the Glenburgh Orogen in the Western Australian Proterozoic, and the North Australian Craton, all of which contain rock systems with similar ages. Whole rock εNd (1850Ma) values from the Corny Point Paragneiss range from -1 to -5. These values potentially preclude the Late Archaean to mid Proterozoic crust of the Gawler Craton as a sole or major source region due to its highly evolved average εNd (1850Ma) of around -10. Preclusion of the Gawler Craton as a source is apparently confirmed by Hf isotopic compositions of 2020 Ma detrital zircons from the Corny Point Paragneiss, which have εHf (2020Ma) ranging between +3 to +7. This compares with εHf (2020Ma) of -1 to -4 for zircons from the 2020 Ma Miltalie Gneiss in the Gawler Craton. Available Nd isotopic data suggests that the Glenburgh Orogen is too crustally evolved to have provided the majority of sediment into the Corny Point Paragneiss protolith. The 2020 Ma detrital Hf isotopic compositions of the Corny Point Paragneiss are similar to the 2020 Ma Wildman Siltstone (εHf (2020Ma) +2 to +7) in the Pine Creek Orogen in the North Australian Craton. Two possible scenarios can be extrapolated from the detrital zircon and Nd isotopic data; (1) the Corny Point Paragneiss sediment was derived from a source region within the North Australian Craton and could share source regions with the Wildman Siltstone, or (2) the sediments were derived from a Gawler Craton source region that included a dominant juvenile component of the 2020 Ma Miltalie Gneiss in the adjacent Gawler Craton which has since been eroded. In the first scenario, the absence of connection to the Gawler Craton allows for the Betts and Giles (2006) plate reconstruction model, which proposes that the Corny Point Paragneiss formed part of the North Australia Craton, and was sutured to the Proto Gawler Craton at 1730-1700 Ma. The second scenario highlights a significant limitation in evaluating the significance of provenance data, particularly when considering old potential source terrains that have undergone significant levels of denudation. The proximity of the Corny Point Paragneiss to the rifted southern and eastern margins of the Australian Proterozoic means a thorough evaluation of the palaeogeographic significance of the Corny Point Paragneiss detrital signature requires corresponding datasets from regions such as Antarctica which were formerly contiguous with the Gawler Craton.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2006