These presentations from Geosciece Australia staff form part of the 2011 AGES (Annual Geoscience Exploration Seminar) meeting. Extended abstracts associated with these presentations can be found in the Northern Terriorty Geological Survey Record 2011-003.

Introduction Our understanding of the geological history and resource potential of Australia has been underpinned by over half a century of surface geological mapping. A synthesis of this effort is captured in the 1:1 000 000 surface geology map of Australia (Raymond et al., 2012), which shows that ~80% of the bedrock geology of Australia is covered by a veneer of sediments and regolith. Now, the challenge is to continue to unravel the geological history and resource potential of Australia beneath this cover. With this goal in mind, Geoscience Australia (GA), in collaboration with state/territory geological surveys, is embarking on compiling a series of national solid geology maps based on time slices. These maps will be compiled at an optimal scale of 1:1,000,000 exploiting potential field datasets, radiometric coverages, seismic profiles, borehole data and regional solid geology compilations. In the interest of efficiency, solid geology compilations at scales between 1:500 0001:2 500 000 will be incorporated with minimum modification. The end product will be a series of national geology maps in chronostratigraphic order, including the 1:1 000 000 surface geology of Australia, pre-Cenozoic solid geology, and ultimately older time slices (to be determined). Current work Pre-Cenozoic Geology of South Australia, New South Walse and Victoria in conjunction with a program to construct a chronostratigraphic isopach map of the Murray Basin. Work also started to produce a Pre-Cenozoic Geology map of Northern Territory.

The Browse Basin lies offshore from Western Australia's Kimberley region and hosts vast accumulations of natural gas, some of which are rich in condensate, making it Australia's next major liquefied natural gas (LNG) producing province on the North West Shelf. The Ichthys accumulation is estimated to host 12.8 trillion cubic feet (Tcf) of gas and 527 million barrels (mmbbl) of condensate (condensate:gas ratio (CGR) 60 bbl/MMscf) representing the largest hydrocarbon accumulation with recoverable liquids found in Australia since the discovery of the Gippsland Basin and Barrow Island oil fields in the 1960s. Similar amounts of gas, albeit drier (CGR 2030 bbl/MMscf) are hosted within the Brecknock, Calliance and Torosa accumulations (cumulative 15.9 Tcf gas, 436 mmbbl condensate). Despite the extensive ongoing exploration activity and prior research interest [1, 2 and 3], the basin's petroleum systems (PS) have not been publically updated for a decade. Collating the existing molecular and isotopic datasets for the wet gases and associated hydrocarbon liquids, along with the biomarker and 13C/12C and D/H ratios of the n-alkanes for the crude oils, has enabled the origin and extent of the petroleum systems to be redefined. In doing so, it is apparent that the filling of the gas accumulations within the Caswell Sub-basin and along the Scott Reef-Brecknock trend is complex, with the component gases originating from multiple organic and inorganic sources. Differing degrees of biodegradation are observed in the Cornea and Gwydion oil and gas accumulations. Four preliminary petroleum systems are defined for known accumulations by their 13C n-alkane isotopic profiles (Figure 1). The PloverPlover PS is a basin-wide gas-prone system where the gas is reservoired within the Middle Jurassic Plover Formation (e.g. Brecknock-Torosa, Ichthys) and sourced from mixed terrestrial and marine organic matter deposited in fluvio-deltaic sediments. The Plover/VulcanVulcan PS occurs within the central Caswell Sub-basin at Ichthys and Prelude/Concerto and is a wet gas-prone system reservoired within the Upper Jurassic Brewster Member, upper Vulcan Formation. This PS has a more marine source affinity with the additional hydrocarbons probably being sourced from the lower Vulcan Formation. The Plover/VulcanPlover/Vulcan/Nome PS is a gas-prone system within the Heywood Graben. The complex reservoir at Crux is sourced from mixed terrestrial and marine organic matter deposited that may be sourced from within Jurassic sediments. The Echuca ShoalsHeywood PS is an oil- and gas-prone system (e.g. Caswell, Cornea and Gwydion) sourced by marine algae and bacterial remains within Lower Cretaceous sediments [2]. The oils and gases on the Yampi Shelf vary in their degree of biodegradation. Further work is in progress to confirm these petroleum systems and redefine their extent by correlating the wet gases and oils with their source rocks.

Pesentation by Clinton Foster regarding Energy Security

The Arunta Region of central Australia is a geologically complex and tectonically longlived terrane which has been subjected to several periods of magmatism. SHRIMP U-Pb dating of zircons by Claoué-Long and Hoatson (2005) constrain the major mafic magmatic events to the dominantly tholeiitic ~1810-1800 Ma Stafford Event, the ~1790-1770 Ma Yambah Event, ~1690 Ma Strangways Event, ~1635 Ma Liebig Event, and a much younger event of probable early Palaeozoic age. A further event (Teapot) at ~1135 Ma has alkaline-ultramafic affinities. Field-relationships and mineralisation-features of the intrusions are described by Hoatson and Stewart (2001), and Hoatson et al. (2005). The intrusions form large homogeneous mafic granulite and gabbroic bodies, stacked sequences of high-level sills, small pods, laterally extensive amphibolite sheets, and relatively undeformed ultramafic plugs. The intrusions occur in proximity to major province-wide faults where differential movements have resulted in the exposure of the intrusions from crustal depths ranging from ~5 km to ~25 km. Metamorphic grades range from granulite to sub-amphibolite facies. Chilled and contaminated margins and net-vein complexes resulting from the commingling of mafic and felsic magmas indicate that most intrusions crystallised in situ and were not tectonically emplaced. <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>

This keynote address was presented at the Australian Nickel Conference held in Perth, 19-20 October 2005. Australia's nickel sulphide industry has had a fluctuating history since the discovery in 1966 of massive sulphides at Kambalda in the Eastern Goldfields of Western Australia. Periods of buoyant nickel prices and high demand, speculative exploration, and frenetic investment (the 'nickel boom' years) have been interspersed by protracted periods of relatively depressed metal prices, exploration inactivity, and low discovery rates. Despite this unpredictable evolution, Australia's nickel industry has had a significant impact on the world scene. This presentation reviews the characteristics and resources of Australia's nickel sulphide deposits, and highlights some of the more important challenges and new opportunities confronting the nickel industry today.

The tectonic evolution of the Gawler Craton is defined by two periods of tectonism both of which lead to apparent cratonisation. Megacycle 1 developed during the period 2550 Ma to 2400 Ma, and megacycle 2 tectonic events occurred from 1900 Ma to 1550 Ma. Recent research has lead to recognition of major basin(s) in the eastern and northern Gawler Craton, that formed around 1760-1720 Ma. Detritus in part was derived from a source region that has affinities with lower Willyama Supergroup sources. The role of plate margin processes in the evolution of the Gawler Craton is discussed. The St Peter Suite resembles an arc system, however sutures and even the polarity of possible subduction remain unclear. It is suggested that fertile mineralised regions are characterised by tectonic processes that lead to hydration of lower crust and upper mantle, and a tectonic regime that lead to large-scale deeply-derived fluid systems. We need to understand which structures were active during dehydration events and where major boundaries exist in terrains. We need to image those systems geophysically, and look for crust-mantle connections where rehydration processes are likely to have occurred

This talk outlines three key regional geological features considered to be essential for development of major iron oxide copper-gold systems in the Gawler Craton. They are as follows: 1. A plumbing system, comprising crustal-scale structures that developed during Palaeoproterozoic orogenesis along the margins of the Archaean core of the Gawler Craton. 2. Coeval timing of IOCG hydrothermal activity and Hiltaba-GRV magmatism at ~1575-1595 Ma. Anomalous high heat input to the crust, resulting in particular igneous rock compositions and high-temperature IOCG alteration at ~1575-1595 Ma

A PhD study into the Hiltaba Suite granites found that the stratigraphic term &#145;Suite&#146; is wrong for this Association and that they are divisible into at least four Supersuites. This includes two Supersuites with A-type affinities and two with I-type characteristics. A spatial variation of geothermal gradients plus source &#145;basement&#146; is indicated, and these may have bearing on resultant coeval mineralisation, with the eastern Olympic Cu-Au Province associated with the Roxby A-type Supersuite, and the Central Gawler Gold Province associated with the Malbooma I-type Supersuite.

Deep seismic reflection profiles and potential-field data show that the crustal architecture of the Olympic Cu-Au province in the vicinity of the giant Olympic Dam deposit is dominated by northwest-trending thrusts that acted as first-order fluid-pathways for its IOCG mineralising system. The thrusts were initiated sometime between the end of the Archaean and the late Palaeoproterozoic (~2.5 Ga to ~1.6 Ga), probably during the Kimban Orogeny (~1.73 Ga), and reactivated during a far-field response to convergence at ~1.6 Ga. Comparisons with the tectonics governing the mineralisation in the Andean margin demonstrate that extensional characteristics of the IOCG systems in that setting were also produced in response to convergence. Fe-oxide alteration in the Olympic Cu-Au province is readily detected in potential-field data and its distribution can be mapped, in 3-D, via inversion methods.