Globally supracrustal sedimentary rocks are known to preferentially precipitate gold between 2400 Ma and 1800 Ma (Goldfarb et al. 2001). The Palaeoproterozoic Tanami and Pine Creek regions of Northern Australia host one world-class gold deposit and many other gold deposits in anomalously iron-rich marine mudstones (Figure 1). New fluid-rock modelling at temperatures between 275 - 350C suggest a strong correlation between gold grade and these Palaeoproterozoic iron-rich, fine-grained sedimentary rocks.

The global distribution of mineral deposits in cratons, belts and districts shows that they are not equally and uniformly endowed with metal. Some cratons are highly fertile (e.g. Yilgarn Craton for Archaean greenstone gold and nickel) and there are those which are almost barren (e.g. Archaen greenstone belts in the Pilbara Craton). Within belts the distribution is equally non-uniform. For instance more than 80% of gold resources in the Yilgarn are concentrated in the Kalgoorlie Terrane of the Eastern Goldfields. At a first level the total endowment can be used to compare mineralised belts and districts, however the distribution of deposit sizes in them can provide a second level constraint on their fertility, in particular the nature and intensity of metal accumulation versus metal dispersion. More enigmatic from this point of view are belts and districts in which the total metal endowment is contained in one or two giant and/or super-giant deposits, such as the Broken Hill in New South Wales, Norilsk-Talnakh in Western Siberia, and Olympic Dam in South Australia. These mjaor deposits represent single "bull elephants" in an "elephant country". Cumulative frequency distribution curves of metals of major mineralized cratons, belts and districts are used to compare the nature of their metal endowment. The analysis shows that the curves of "elephant-bearing" belts and districts are remarkably different from those of "average" belts and districts, and that regional and/or district scale geological factors could have played a significant role in controlling metal endowment. A comparison of curves for belts and districts with similar endowment can be used to assess potential for yet to be discovered deposits and to assess their relative size.

The poster/panel summarises result of preliminary fluid flow and chemical modelling in the Frome Embayment

Controversy continues on the origin of gold deposits in metamorphic belts and the role of magmatism in these regions. We adopt a Minerals Systems approach to analyse and compare some chemical processes related to the formation of major Australian Au-dominated deposits that have been classified as either orogenic or intrusion-related. Fluid inclusion data was compiled from deposits in the Archaean Yilgarn Craton, the Proterozoic Tanami, Pine Creek and Paterson areas, and the Palaeozoic western Lachlan Fold Belt. On a regional scale, and a deposit scale, the dominant lithologies in each area are mafic and felsic igneous rocks, graphite-bearing clastic sediments and banded iron-formations. Significantly, evaporites are absent from all areas. A clear spatial association exists in the Tanami, Telfer and Pine Creek regions with reduced granites. The complied data show that the deposits form over a wide range of temperature-pressure conditions (<200 to >600ºC, <1.4 kbar) and that they involve fluids with broadly similar major chemical components (i.e. H2O+NaCl+CO2± CH4 ± N2). The main difference is that Telfer, Tanami and Pine Creek deposits have higher salinity fluids. Elsewhere, deposits classified as orogenic gold deposits have low salinity fluids (typically <10 wt.% NaCl eq.) with CO2 contents ranging from 10 to 25 mol.% (Ridley & Diamond, 2000), whilst intrusion-related gold deposits may show evidence of higher CO2 and/or high salinity fluid inclusions (Thompson & Newberry, 2000). Processes thought to cause gold precipitation in both types of deposits are fluid-rock interaction (e.g. desulphidation), phase separation, or fluid mixing. We have re-examined the impact of the H2O-NaCl-CO2 system on the nature of the dominant gold precipitation mechanisms at different crustal levels (Fig. 1). The latter infers different roles of chemical (fluid-rock interaction) vs rheological (phase separation and/or fluid mixing) host-rock controls on gold deposition. This also implies that at the site of deposition, similar precipitation mechanisms operate at similar crustal levels for both orogenic and intrusion-related gold deposits

Poorly exposed Paleoproterozoic sandstones and siltstones of the Killi Killi Formation record developement of a large turbidite complex. Killi Killi Formation sediments were eroded from the uplifted ~1860 Ma Nimbuwah and Hooper Orogens as indicated by detrital zircons with sediment deposition at ~1840 Ma. Facies analysis, isopach maps and detrital zircon populations, combined with Sm-Nd data from the Tanami region and Halls Creek Orogen, confirm the previously suggested correlation of the Paleoproterozoic successions in the Eastern zone of the Halls Creek Orogen and the Tanami region. Detrital zircons from the Aileron Province suggest the turbidite complex extends into the Arunta region, however, high metamorphic grade precludes direct facies comparisons in the Arunta region. Portions of the turbidite complex in the Tanami region are dominated by mudstones, consisting of low-density turbidites and associated hemipelagites, that potentially acted as a redox boundary to gold-bearing fluid. Gold prospectivity in turbiditic systems is increased within these mudstone sequences with the potential for further gold discoveries.

Geological investigation by the Bureau commenced late in July, 1948, and continued until the end of October of that year. The objects of the survey were to lay the foundation for future detailed studies of the mining field, to study the factors controlling ore localization, to assess the quantity and value of ore exposed to date, and to estimate the potential value of the field. In the search for orebodies, a knowledge of the geological factors can be of great assistance, and it is felt that the information given in this report and in the accompanying plans should be of considerable help in this respect. However, the prospector's methods - loaming, dollying, panning etc. are still quite fundamental to success in a prospecting field such as Tennant Creek and the suggestions made in this report are intended to supplement this type of work. The climate, topography, vegetation, gold production, general geology, and gold deposits of the area are described in this report. Detailed descriptions are given of the individual mines examined to date.

The authors were engaged in geological reconnaissance work in the Fitzroy Crossing - Halls Creek area, during the period 16th August to 23rd September, 1948. The principal object of the investigation was to examine the area covered by the Mt. Ramsay Sheet of the Army Series. Work was extended beyond the limits of this sheet however in order to obtain information with regard to the age relationship of some formations, and a visit was made to the Wolf Creek Meteorite Crater 63 miles south of Halls Creek. During the survey, work was concentrated chiefly in mapping the distribution of rocks and different geological periods, determining their relationships and economic possibilities, and recognising areas warranting more detailed investigations. Accompanying geological plans and aerial photographs are included.

The Kowan District occupies the north-eastern lobe of the A.C.T., to the north-east of Queanbeyan. The purpose of the survey was to determine the general geology and structure of the Kowen District as part of a planned mapping of the whole of the A.C.T. In addition a search was made for commercial occurrences of rock suitable for use as a building stone. Field work was extended over most of January and February, 1949. Igneous intrusions were plotted directly onto aerial photographs where possible. Strikes of beds and faults and other suitable information were measured by prismatic compass and dips and pitches were measured by Abney level or clinometer compass. Information was then plotted on a Federal Territory feature map. A full account of this survey work and its findings is given in this report. Descriptions of specimens and geological plans of the district are appended.

At the end of 1945 the area dredged by the Bulolo Gold Dredging Co. Ltd. was 831 hectares. At that time 307 hectares remained to be dredged and of this 227 hectares contained soil which has been shown by soil analysis to be reasonably good. Resoiling would not be practicable on about 70 hectares of this area, as the Company plans to dredge this section twice, first with shallow and then with deep-digging dredges. Similar soil exists on 3-400 hectares classified previously by the Company as marginal ground, but which, since the increase in the Australian price of gold, is now probably quite profitable. This makes the total area that might be suitable for resoiling about 500 hectares compared to 1,281 hectares that either has been dredged or to which for other reasons resoiling is not applicable. Revenue to the Administration from the gold produced at Bulolo is over £1,000 per hectare from royalty alone and as most of the area has now been worked it seems questionable whether resoiling is worth further consideration at this stage. No provision was made for resoiling in the terms of the original mining tenements, but the Company's officials have expressed willingness to co-operate in carrying out the wishes of the administration. It has been considered impracticable now to resoil the areas that have been dredged or to rebuild the existing dredges for mechanical resoiling, but if the Department of Internal Territories considers that the matter should be pursued further, the Company might be asked to consider removing soil from the dredge path by bulldozer or other mechanical means and replacing the soil on the flattened out tailings after the dredge has passed; also to provide details of the economics of carrying out a similar scheme on the areas in which values were previously considered to be marginal.

This report contains the results of brief geological investigations carried out in conjunction with the Land Research and Regional Survey Unit to provide information on land types and their distribution in the Burdekin River Valley. A geological map and sections at the horizontal scale of 4 miles to 1 inch have been compiled from air-photo interpretation controlled by widely spaced land traverses. An account of the stratigraphy is given, and palaeontological reports on the fossils collected appear as appendices.