No abstract available

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The Tanami seismic survey ran from May through July 2005 under the supervision of ANSIR (National Research Facility for Earth Sounding). The survey consisted of 720 line-km along four regional deep seismic traverses, 05GA-T1 through to 05GA-T4, aimed at providing orthogonal three-dimensional control on the regional fault geometry. Geoscience Australia processed the data in the 12 months following the survey, using the DISCO/FOCUS seismic processing package. Considerable effort was expended on the most critical aspects for improving the seismic reflection image, namely refraction statics correction, several passes of velocity analysis, and partial pre-stack followed by post stack migration of the data. Partial pre-stack migration (also known as dip moveout or DMO correction) was necessary for simultaneous imaging of horizontal and steeply dipping reflectors. <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>

Assessment of geological, geochemical and isotopic data indicate that a subgroup of volcanic-hosted massive sulphide (VHMS) deposits has a major magmatic-hydrothermal source of ore fluids and metals. This group, which is characterised by high Cu and Au grades, is distinguished by aluminous advanced argillic alteration assemblages or metamorphosed equivalents. These characteristics are interpreted as the consequence of disproportionation of magmatic SO2. Other than deposits associated with advanced argillic alteration assemblages, the only deposit for which we ascribe a major magmatic-hydrothermal contribution is the Devonian Neves Corvo deposit. This deposit differs from other deposits in the Iberian Pyrite Belt and around the world in being extremely Sn-rich, Comparison with 'normal' VHMS deposits suggest that these subgroups of VHMS deposits may form in specialised tectonic environments. The Cu-Au-rich deposits appear to form adjacent to magmatic arcs, an environment conducive to the generation of hydrous, oxidised melts by melting metasomatised mantle in the wedge above the subducting slab. This contrasts with the back-arc setting of 'normal' VHMS deposits in which relatively dry granites formed by decompression melting drive seawater-dominated hydrothermal circulation. The tectonic setting of highly Sn-rich VHMS deposits such as Neves Corvo is less clear, however thick continental crust below the ore-hosting basin may be critical as it is in other Sn deposits.

Presentations from 'THE ISHIHARA SYMPOSIUM' held at GEMOC, MACQUARIE UNIVERSITY, JULY 22-24 2003; on a variety of topics ranging from general granite processes to mineralisation associated with magmatism.

Orogenesis in Phanerozoic systems is rapid, diachronous, episodic, and involves the switching of tectonic modes (extension-compression). In contrast, many Archaean orogens have traditionally been viewed as having developed by relatively simple, long-lived, mono-mode deformational processes. New results, however, reveal that the late Archaean eastern Yilgarn Craton (EYC) evolved episodically and rapidly, with a diachronous series of approximately E?W coaxial switches in tectonic mode. Tectonic mode switching changed stress regimes and resulted in the development of `late basins?, the emplacement of granites, and early orogenic gold mineralisation diachronously from east to west (NE?SW). Fluids were driven from the lower crust (and below) via large-scale crustal imbricating thrust faults. These fluids promoted the passage of a compression-extension couplet along a basal detachment by successively `lubricating? faults (preparing the ground), and facilitating a propagating wave of foreland surge (D2a) and hinterland extension (D2E) followed by inversion, uplift and annealing (D2b). In this way, orogenic Au and westward orogenic surge with associated tectonic mode switches are linked. We predict that the compres-sion-extension couplets and early orogenic gold mineralisation propagated from the east to the west diachronously at a rate of ~3-5 m.y. between domains from ~2670 Ma to ~2650 Ma. Multiple mineralising episodes are also a predicted consequence of the orogenic surge model.

Presented at the Evolution and metallogenesis of the North Australian Craton Conference, 20-22 June 2006, Alice Springs. The Tennant Creek goldfield, the third largest goldfield in the Northern Territory, producing over 150 tonnes of gold (Wedekind et al., 1989), was only discovered in the mid-1930s due to the association of gold with ironstone rather than quartz veins. Over the last two decades ironstone-hosted gold deposits have been included in the group of deposits termed iron-oxide copper-gold (IOCG) deposits (Hitzman et al., 1992). Elsewhere in the Northern Territory, prospects with IOCG characteristics have been recognised in the southeastern Arunta (Hussey et al., 2005), and potential for these deposits has been recognised in the Mount Webb area of the Warumpi Province (Wyborn et al., 1998). <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>

The North Pilbara Terrane has the largest variety of mineral deposits of any Archaean province. It contains the oldest known examples of volcanic-hosted massive sulphide (VHMS), lode Au, porphyry Cu, orthomagmatic Ni-Cu-PGE-V, pegmatitic Ta-Sn and epithermal deposits, with a diversity more characteristic of Phanerozoic mobile belts. Despite this diversity the North Pilbara Terrane appears to lack any major mineral deposits, with the exception of the Wodgina Ta-Sn pegmatite field. Below, we present the metallogenic history of the North Pilbara Terrane in the context of its tectonic development and then compare it to other Archaean provinces to assess controls on metal endowment.

The paper reveiws metallogenic evolution of Australia. A comparison between Archaean, Proterozoic and Phanerozoic metallogeny reveals that in general there exist more similarities between the Archaean and the Phanerozoic that those between the Archaean and the Proterozoic and between the Proterozoic and the Phanerozoic metallogeny. The paper argues that the contribution of plate tectonic processes in the geological evoultion and metallogeny of Australian Proterozoic need revaluation for assessing mineral potetnial of deposit styles which are traditionally considered to be not important but large deposits of each are known to exist in the Proterozoic elsewhere.

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The late Archean Lake Harris Komatiite near the centre of the Gawler Craton is the only documented komatiite in South Australia, and the most eastern occurrence of such primitive ultramafic rocks in Australia. An integrated program of airborne magnetics, gravity, and core drilling was successful in 'seeing through' an extensive thin cover of Cainozoic alluvial sediments to define the distribution and volcanic architecture of the ca. 2520 Ma komatiitic flows. The greenstones form a series of sub-parallel east-northeast-trending sinuous magnetic high features flanked by large ovoid to elongate magnetic highs and lows that correlate with Archean-Proterozoic granitic bodies. The Lake Harris Komatiite is a steeply dipping greenstone sequence metamorphosed to middle amphibolite facies during the ca. 2440 Ma Sleafordian Orogeny and sheared during the ca. 1700 Ma Kimban Orogeny. The greenstones consist of cumulate komatiite (anhydrous 43-32% MgO), high to low Mg komatiite (32-18% MgO), komatiitic and tholeiitic basalt (<18% MgO), felsic volcanics, minor metasedimentary rocks, pyroclastics, and banded iron formation. They extend over 300 km in three subparallel east-northeast-trending belts that appear to be isoclinally folded around east-northeast axes and tectonically dismembered to the south by the Yerda Shear Zone. Komatiitic rocks have been confirmed by drilling in the three belts, but the absence of outcrop and structural complexities prevent detailed stratigraphic correlations within and between the belts. The komatiitic rocks display a range of textures that largely reflect the different habits of olivine and its alteration products. These include feather-quench and spinifex-textured chilled flow tops, fractured and jointed flow tops, with joints filled by metamorphic olivine or amphibole, massive aphyric variants, and various types of olivine-rich cumulates. Mesocumulates and orthocumulates are prominent with low porosity adcumulates comprising less than 10% of the more primitive cumulus zones. Lower to middle amphibolite facies assemblages are dominated by metamorphic olivine, with minor to trace amounts of igneous olivine, orthopyroxene, chromite, Cr-spinel, magnetite, ilmenite, and sulfide. Trace sulfides (pyrrhotite, chalcopyrite, pentlandite, pyrite, marcasite, polydymite violarite, heazelwoodite, millerite) form very small single-phase disseminated grains and coarser disaggregated grains. Their distribution largely reflects metamorphic and serpentinization alteration controls, with high Ni/S ratios and probable S loss from the more magnesian parts of the flows. The Lake Harris whole-rock data do not show any obvious Ni depletion during fractionation, but indicate a strong olivine control in dominantly S-undersaturated environments. Low S (100-600 ppm S) and high Pd+Pt (5-30 ppb) contents, and Ti/Pd ratios of 2 to 4 x 105 for the komatiitic rocks are similar to fertile S-undersaturated Archean komatiites hosting Ni-Cu-PGE deposits. The Lake Harris Komatiite has chemical (parent magma composition of 28% MgO, Al2O3/TiO2 = 16, depleted light REE) and initial Nd isotope (Nd = +2.8 to +3.0 at 2520 Ma) characteristics similar to 'typical' Al-depleted Archean komatiites, and there is no clear evidence of chemical modification by processes associated with contemporary subduction processes. Coherent patterns of trace elements (Th, Nb, REE, Ti, Y, Zr, and P) and typical initial Nd isotope signatures indicate a late Archean komatiitic system involving a depleted mantle source and no obvious crustal contamination. Its generation is consistent with mantle plume activity within a convective mantle system that probably exploited a lithosphere that was stretched and thinned by extension and/or thermal erosion in an intraplate environment.