No abstract available

Chemical alteration to certain end-member minerals, such as magnetite, pyrrhotite and pyrite, can produce density and magnetic susceptibility contrasts. These contrasts can be detected using gravity and magnetic surveys. Interpretation of alteration is made possibly by inverting the geophysical data (calculating subsurface properties from the survey results) and combining these inverse results with 3D geological mapping. An application of this method to

No abstract available

Hyperspectral airborne images from the Eastern Fold Belt of the Mount Isa Inlier, were validated as new tool for the detection of Iron oxide Cu-Au (IOCG) related alteration. High resolution mineral maps derived from hyperspectral imaging (4.5m/pixel) enables the recognition of various types of hydrothermal alteration patterns and the localisation of fluid pathways. Four different types of hydrothermal alteration patterns were identified with the hyperspectral mineral maps: (1) Metasomatic 1: White mica mineral maps were applied to map the spatial distribution of regional sodic-calcic alteration in metasedimentary successions of the Soldiers Cap Group in the Snake Creek Anticline. (2) Metasomatic 2: Alteration zoning is evident from albitised granites, assigned to the Williams-Naraku Suite, along the Cloncurry Fault show characteristic absorption features in the shortwave infrared range (SWIR) and can be detected with white mica mineral maps (white mica composition, white mica content, white mica crystallinity index).

The Broken Hill Exploration Initiative (BHEI) started in 1994 and is a joint effort between the New South Wales Department of Primary Industries - Mineral Resources, the South Australian Department of Primary Industry and Resources and the Commonwealth Government through Geoscience Australia. The aim of the BHEI is to provide a new generation of geoscientific data for the Curnamona Province, particularly the Broken Hill-Olary region, as a basis for more effective mineral exploration by industry. This initiative aims to provide the best possible knowledge and information-base for mineral and petroleum exploration investment in western New South Wales and eastern South Australia. The region will benefit from the application of new technologies and exploration methodologies to enhance knowledge of the geological controls of mineral deposit systems. BHEI conferences are held on a regular basis to highlight the geoscientific advances made during the life of the initiative. The contents of this Record are the extended abstracts of oral and poster papers presented at the BHEI conference that was held in Broken Hill on 26-28 September 2006.

Globally, iron-oxide Cu-Au deposits are a prime exploration target given the super-giant status of Olympic Dam, the type example. The most commonly identified primary ingredients for these deposit types are granites, mafic igneous rocks and oxidised host sequences (e.g., Hitzman 2000). The deposits are also characterised by sodic-potassic and potassic alteration which can be significant on a regional scale. Deposits in the Tennant Creek, Cloncurry and Olympic Dam regions are the three main examples of iron-oxide Cu-Au deposits in Australia: all are Proterozoic. A continent scale-spatial analysis of their regional setting reveals some common elements and suggests that these deposit types are unlikely to be found in the Archaean or the Phanerozoic of Australia. In all three cases, intrusive rocks occur in proximity, but whether the metals come direct from these or are leached from the country rock is unimportant to this analysis. The nearby granitic rocks are all fractionated, and show evidence of release of late stage magmatic fluids. Chemically these granites are a very specific type: all strongly oxidised, metaluminous, high temperature, high Ca granites that formed as a result of well above average geothermal gradients from crustal sources. These granites contain anomalously high concentrations of K, Th and U. Such granites are not found in the Archaean and rare equivalent Phanerozoic granitic types are of an order of magnitude smaller in size. This analysis shows that the known Australian deposits occur in regions of present-day anomalously high heat flow. Heat production is enhanced by high concentrations of K, Th and U in the nearby granites, particularly in the Olympic Dam and Cloncurry areas. Such elevated heat production may have resulted in anomalously long-lived hydrothermal cells and enhanced the metal leaching process. The large areal extent of the alteration zones in these two areas may also be a result of this fundamental crustal anomaly. Mafic igneous rocks are common in the vicinity of known Australia deposits, and might be another essential ingredient of an efficient Fe-Ox Cu-Au mineral system. They are regarded as an additional source of Cu for leaching. The regions with known deposits are dominated by oxidised rock packages containing hematite?magnetite. These oxidised packages are regarded as essential to maintaining the high redox state of the metal-bearing fluids. Elsewhere where similar granites intrude reduced packages, particularly those bearing graphite, Cu deposits are rare. Where oxidised host packages are not intruded by granites these deposit types do not occur. Equivalent oxidised host packages intruded by granites are not common in the Australian Archaean or Phanerozoic.

Economic geologists and remote sensing specialists have long been interested in hydrothermal systems for their valuable ore deposits. Alteration mineral assemblages caused by hydrothermal activity typically display certain spectral characteristics due to vibration of the hydroxyl (OH-) anion in the near infrared. This feature can be exploited by satellites using imaging infrared spectrometers. Hyperspectral equipment such as the Australian built HyMap airborne system and the PIMA II field spectrometer collect detailed spectral information, often in contiguous wavelengths, which can be analysed and interpreted to make highly detailed mineralogical and alteration pattern maps . Two Precambrian hydrothermal systems, well suited to testing remote sensing of hydrothermal systems are described here, the first in the northern Flinders Ranges in South Australia, comprising one of Earth?s largest hydrothermal deposits and, the second in the North Pole Dome in the Pilbara region of north western Australia, host to many famous stromatolitic horizons.

Comprehensive studies of the well preserved, Paleoarchean Panorama volcanic-hosted massive sulfide (VHMS) district provide for the first time definitive evidence that Zn, Pb, Cu, Mo and Ba were leached from the base of the volcanic pile and redeposited at the top in VHMS deposits. This leaching provided more than enough metal to form known deposits, implying that direct input of metal is not required. Sulfur is depleted from the base of the volcanic pile, in line with an increase in Fe2O3/FeO and hematite alteration. These data, combine with sulfur isotope data, indicate that seawater sulfate reduction was facilitated by the oxidation of rock FeO to hematite at high temperature in the H2S stability field. This is the first time such processes have been demonstrated regionally in ancient VHMS mineral systems. The data presented here require Paleoarchean seawater to be sulfate-bearing.

A metamorphic database covering the entire eastern Yilgarn Craton has been compiled from pre-existing mapping, 14,500 sites with qualitative metamorphic information, and 470 new key sites with detailed quantitative metamorphic data including P, T, temperature/depth ratio and P-T paths. The derived temporal and spatial patterns contrast with previous tectonic models and invariant crustal depth with the single prograde metamorphic event of the long-standing metamorphic paradigm. In particular, there are large variations in peak metamorphic crustal depths (12 to 31 km), and five metamorphic periods can now be recognised. &#149; Ma: Very localised, low-P granulite of high temperature/depth ratio (>50ºC/km). &#149; M1: High-P (8.7kb), low temperature/depth ratio (<20ºC/km) assemblages localised to major shear zones with clockwise isothermal decompression P-T paths. &#149; M2: Regional matrix parageneses with T ranging 300-550ºC across greenstone belts and elevated temperature/depth ratio of 30-40ºC/km throughout. Tight clockwise paths evolved through maximum prograde pressures of 6 kb and peak metamorphic pressures of 3.5-5.0 kb. &#149; M3a: An extension related thermal pulse localised on the Ockerburry Fault and post-volcanic late basins. Anticlockwise paths to peak conditions of 500-580ºC and 4.0 kb, define moderately high temperature/depth ratio of 40-50ºC/km. &#149; M3b: Multiple localised hydrothermal alteration events during a period of exhumation from 4 kb to 1 kb. Metamorphic patterns during each event have been temporally and spatially integrated with the new deformation framework (Blewett & Czarnota, 2007c) by a process of metamorphic domain analysis and using metamorphic field gradients. The continual evolution with time of fundamental metamorphic parameters throughout the entire history have been constructed as evolution curves and integrated with the deformation, magmatic, stratigraphic and mineralization history. <p>Related material<a href="https://www.ga.gov.au/products/servlet/controller?event=GEOCAT_DETAILS&catno=69771">East Yilgarn Craton Metamorphism and Strain</a> - Map.</p>

The physical properties of non-porous basement rocks are directly related to the mineralogy of those rocks. The MineralMapper3D software package originally developed by Nick Williams at the Predictive Mineral Discovery Cooperative Research Centre (pmd*CRC), Geoscience Australia, uses the physical properties of minerals to provide bounds on estimates of the abundance of specified minerals in non-porous basement rocks. This approach is applicable to both estimates of density and magnetic susceptibility derived from 3D inversions of gravity and magnetic data as well as physical measurements on specimens or down-hole derived physical properties.