Geoscience Australia, ACRES distribute Landsat Multispectral Scanner (MSS), Thematic Mapper (TM) and Enhanced Thematic Mapper Plus (ETM+) data for a series of epochs or time frames covering Australia. The first epoch is 1972. These data have been produced and provided by the Australian Greenhouse Office (AGO). AGO use the data in their National Carbon Accounting System for monitoring land clearing and revegetation. This data is only available through ACRES and ACRES Landsat Distributors, and not through the AGO. More information is available at <a href="http://www.ga.gov.au/acres/prod_ser/agosuite.jsp">http://www.ga.gov.au/acres/prod_ser/agosuite.jsp</a> This data is available in 1:1M tiles or as a full continental Mosaic. Tiles areas are available at: <a href="http://www.ga.gov.au/acres/prod_ser/agotilemap.jsp">http://www.ga.gov.au/acres/prod_ser/agotilemap.jsp</a>

Using the template based numerical modelling to understand the distribution of dialation in ramp-flat settings

Generic modelling approach to understanding the Kanowna Belle Au system

This dataset contains point, line and polygon data of the marine environment surrounding the Cocos (Keeling) Islands. It includes coastlines, bathymetric contours, coral outcrops and other features. Coverage extends to the whole of Cocos Keeling Isalnds. The themes have been grouped so as to increase the ease of use of the data. The individual themes have been grouped into the following shapefiles: Infralin.shp - Infrastructure lines Boundlin.shp - Boundary lines Marinelin.shp - Marine lines Surveylin.shp - Survey lines Islandlin.shp - Island outlines Marineply.shp - Marine polygon Islandply.shp - Island polygon Boundply.shp - Boundary polygon These shapefiles retain all spatial and non spatial data as supplied to GA. To view the sample of the marine environment with the legend click here. In December 2003 GA projected the data to UTM (WGS84) zone 47 using Arcview.

The absence of basement outcrop and the nearly complete lack of surface expression of mineralisation in the Olympic Cu-Au province is the major impediment to mineral exploration in the province. In such circumstances, analysis of potential field data is one of the usual ways of inferring hidden geology, as high-quality datasets, especially aeromagnetic data, are available for most of the actively explored areas of Australia. Quantitative interpretation of potential field data principally involve 2D forward modelling of profiles, or sections, by skilled interpreters but it can be difficult, and time-consuming, to correctly track structure and geology from one section to the next should one wish to create a 3D model of the geology. To alleviate this problem, we have used a modification of the methods of Li and Oldenburg (1996 & 1998), constrained by known geological information, to give geologically and geophysically consistent solutions to the possible distributions of sources giving the magnetic and gravitational fields observed in a region about Olympic Dam.

This report presents results of a reconnaissance-scale 40Ar/39Ar geochronological study of gold prospects in the central Gawler Craton. Prospects included in the study were: Tarcoola, Tunkillia, Barns, Weednanna and Nuckulla Hill. The aim of the study was to help constrain the age of mineralisation within individual prospects, and then to consider to what extent gold mineralisation throughout the central Gawler Craton was temporally linked. The age results are seen as a first step in testing the idea of a common origin for the prospects, and thereby testing the concept of a "Central Gawler Gold Province". Nineteen step heating experiments have been completed for samples from gold prospects in the central Gawler Craton. The majority of these samples are sericites from alteration zones spatially associated with gold mineralisation. Sixteen of the nineteen samples yield relatively well-behaved age spectra with the majority of the gas having apparent ages within uncertainty of the age bracket 1570 Ma to 1590 Ma, i.e., contemporaneous with Gawler Range Volcanics (GRV) and Hiltaba magmatism. In the case of the Tarcoola Goldfield, a hornblende age from a mafic dyke and geological relationships between this dyke and cross-cutting sericitic alteration tightly bracket the age of sericitic alteration at ~1580 Ma. Sericite 40Ar/39Ar ages from this deposit therefore appear to closely approximate the time of sericite crystallisation. Interpretation of age data from the other central Gawler Gold prospects is less clear at this stage. While the majority of the new 40Ar/39Ar data are consistent with gold mineralisation at ~1580 ± 10 Ma, the sericite 40Ar/39Ar data can also be interpreted as recording thermal resetting by Hiltaba and GRV magmatism. In the absence of independent evidence for maximum ages, the sericite 40Ar/39Ar ages should therefore be regarded only as minimum constraints on the timing of alteration. A simple first order conclusion is, therefore, that sericitic alteration occurred either contemporaneous with GRV and Hiltaba magmatism or earlier. It should be noted that even if the 40Ar/39Ar ages are interpreted as sericite alteration ages, the relationship between such alteration and gold mineralisation remains to be clearly established at most of these prospects. Addressing this question should be an important component of future studies. It is recommended that any future geochronology should be attempted only after more detailed petrologic studies on individual prospects have been undertaken. These studies are required to establish in more detail the nature and origin of alteration, the relationship between alteration and gold mineralisation, and evaluate the possibility of multiple alteration and/or mineralising events. Detailed studies at prospect-scale may identify critical relative-timing relationships that could be exploited in focussed geochronology studies to augment the reconnaissance-level results presented here. In particular, maximum age constraints for mineralisation are required at most of the prospects to complement the minimum age constraints reported here. As demonstrated at Tarcoola, maximum age constraints in some situations may be obtained from the age of dykes that are cross-cut by alteration and mineralisation. Such "second-phase" geochronology need not necessarily utilise the 40Ar/39Ar method, but may be more appropriately achieved via U-Pb or Re/Os analyses, depending on the particular questions being addressed.

New reconnaissance studies of Au mineralisation, alteration, geochronology, and palaeo-fluids in the central Gawler Craton support the existence of a major Au metallogenic province. The results show that Au mineralising systems were active along a >300 km belt at similar times (~1570 Ma to ~1590 Ma; Fraser et al., 2004, this volume) during the early Mesoproterozoic. The scale of this metallogenic belt is a positive indicator for Au prospectivity. Recent company results suggest that the potential for economic resources is high. The main similarities in the Tarcoola, Tunkillia, Nuckulla Hill, and Barns Au systems are: <ul><li>Gold occurs in both disseminated and veinlet-hosted styles. </li> <li>The main host rocks are ~1680-1720 Ma granitoids and, at Tarcoola, metasedimentary rocks (partly carbonaceous).</li> <li>Hydrothermal alteration is characteristically zoned around the Au mineralisation, with intense sericite-pyrite alteration and quartz veining proximal to Au mineralisation, and chlorite, epidote, hematite alteration distal (metres to 100s of metres) to mineralisation.</li> <li>Deformation was synchronous with the proximal sericitic hydrothermal alteration and mineralisation and was generally of brittle to brittle-ductile style including shearing.</li> <li>Au is associated with disseminated and vein-hosted pyrite and minor to trace galena, sphalerite, and chalcopyrite.</li> <li>Iron oxides have very low abundance in mineralised zones, where they are present mainly as haematite, manifest as de-magnetised zones in magnetic images.</li> <li>Hydrothermal white micas at Tarcoola, Tunkillia, Barns, and Weednanna all yield similar Ar-Ar ages of ~1570-1600 Ma. Sericitic alteration and Au mineralisation are interpreted to have formed within this period.</li> <li>Multiple fluids were present in some systems, but one fluid-type occurs in each of the Au prospects: a low-moderate salinity (up to 10 eq. wt.% NaCl; mostly 3-6 %) fluid with homogenisation temperatures mostly in the range of ~200 C to 300?C and trapping temperatures of ~300-400 C. This fluid is commonly associated with CO2-rich fluid inclusions.</li> <li>Galena yields broadly similar Pb isotope compositions at Tarcoola and Tunkillia. </li></ul> Differences between the Au mineralised systems at Tarcoola, Tunkillia, Nuckulla Hill, and Barns, such as the intensity of deformation, relative abundances of base metal sulfides, and sulfur isotope values, reflect differing local structural and lithostratigraphic settings. The Weednanna Au and nearby Mawson Au-Cu prospects bear some similarities to the other Au prospects of the central Gawler gold province, but we consider them to be possible hybrids of the early high-temperature alteration style of iron-oxide Cu-Au systems overprinted by Au hydrothermal systems. Late-stage epithermal-style quartz-carbonate-adularia veins in the Nuckulla Hill and Weednanna areas indicate potential for epithermal Au mineralisation in the region. Preliminary depth constraints suggest high-level crustal environments of mineralisation, possibly around 3-6 km deep, at temperatures up to 300-400 C. Spatial and genetic relationships with Hiltaba Suite magmatism remain cryptic, despite the broadly coeval timing of magmatism and Au mineralisation. The Au mineralisation style does not neatly fit deposit classes such as 'lode-gold', 'orogenic/mesothermal gold', 'intrusion-related gold', 'epithermal gold', or 'porphyry Au'.

A compilation of datasets gathered for the Central Gawler Gold subproject was released at the Gawler Craton: State of Play 2004 conference held in Adelaide on 4 - 6 August 2004. This presentation gives examples of some of the more recent datasets available in the data compilation, such as new AEM, Crystalline basement, Gravity, Magnetics, and worm layers.

Knowledge of the spatial and temporal relationships between fluid flow, the generation of structures, and crustal architecture is essential to understanding a mineral system. In regions dominated by cover, such knowledge strongly depends on interpretation of potential field data. Forward modelling and inversion of cross-sections, based on solid geology maps, provide valid approximations of 3D crustal geometries but reliability of interpolation decreases away from section planes. Models of crustal architecture are more rigorously produced by 3D inversion. Inversion programs derive physical property distributions that reproduce potential field observations consistent with a set of model parameters and geological constraints. The inversion techniques used in this study are based on the potential field inversion software, MAG3D and GRAV3D, developed at the University of British Columbia-Geophysical Inversion Facility (UBC-GIF). These programs have largely been used at the deposit-scale, but we modified the approach and settings for use at a regional-scale. The volume of crust chosen for study, centred on the Olympic Dam deposit, is 150 kmx 150 kmy 10 kmz. It comprises Archaean granulites, Palaeoproterozoic orthogneiss and metasediments (including BIFs), and early Mesoproterozoic felsic and mafic intrusives and extrusives. Zones of Fe oxide alteration are distributed throughout the upper parts of the crustal volume. Because a buffer is required to minimise edge effects, the volume for inversion is expanded to 198 kmx 198 kmy 18 kmz, discretised into 1 kmx 1 kmy 0.5 kmz cells. A series of trial inversions were run on a desktop PC with a 2.0 GHz processor and 2 GB of RAM. The initial trials were designed to investigate the feasibility of doing regional-scale inversions and to show where development of methods and support software were needed. For tractable computation, it is necessary to split each volume into a number of overlapping tiles that can be processed independently then rejoined. Even so, runs took up to 40 hours. The time elapsed can be substantially reduced if processing is performed as a distributed application across a network with each PC dedicated to a single tile. The inherent non-uniqueness of potential field inversion means that, even after some models have been rejected on 'geo-logical' grounds, a number of models consistent with the solid geology and 2D cross-section forward modelling, inter alia, will remain. Tests that prove or disprove the models may be devised, but actual physical testing may not be practical. However, we can make probabilistic determinations of the distribution of Fe oxide alteration, which may be used to map likely fluid pathways and guides to Fe oxide Cu-Au ore. Such predictions are amenable to testing through current exploration practice.

2004 Cassidy time space pdf presented at the December 2004 PDT meeting in Perth.