The role of lithospheric architecture and the mantle in the genesis of iron oxide copper-gold (IOCG) deposits is controversial. Using the example of the Precambrian Gawler Craton (South Australia), which hosts the giant Olympic Dam IOCG deposit, we integrate recently acquired geophysical data (passive seismic tomography, magnetotellurics) with geological and geochemical data to develop a new interpretation of the lithospheric setting of these deposits. Spatially, IOCG deposits are located above the margin of a mantle lithospheric zone with anomalously high electrical conductivities (resistivity <10 ohm.m, top at ~100-150 km depth), low seismic shear-wave velocities (horizontal component, Vsh <4.6 km/s), and unusually high ratios of compressional- to shear-wave velocities (Vp/Vsh>1.80). The high conductivity cannot be explained by water-bearing olivine-rich rock alone. Relatively fertile and metasomatised peridotitic mantle with additional high-Vp/Vs phases, e.g., clinohumite, hydrous garnet and/or phlogopite, could explain the anomalous velocity and conductivity. The top of this high-Vp/Vsh zone marks a mid-lithospheric discontinuity at ~100-130 km depth that is interpreted to reflect locally orthopyroxene-rich mantle. A sub-Moho zone with high Vp/Vsh at ~40-80 km depth correlates spatially with primitive Nd isotope signatures and arc-related ~1620-1610 Ma magmatism, and is interpreted as the eclogitic root of a magmatic arc. Mafic volcanics contemporaneous with ~1590 Ma IOCG mineralisation have geochemistry suggesting derivation from subduction-modified lithospheric mantle. We suggest that Olympic Dam formed inboard of a continental margin in a post-subduction setting, related to foundering and partial melting of previously refertilised and metasomatised lithospheric mantle. Deposits formed during the switch from compression to extension, following delamination-related uplift and exhumation.

This web service provides access to datasets produced by the mineral potential assement of iron oxide-copper-gold (IOCG) mineral systems in the Tennant Creek – Mt Isa region. The mineral potential assessment uses a 2D, GIS-based workflow to qualitatively map four key mineral system components: (1) Sources of metals, fluids and ligands, (2) Energy to drive fluid flow, (3) Fluid flow pathways and architecture, and (4) Deposition mechanisms, such as redox or chemical gradients. For each of these key mineral system components theoretical criteria, representing important ore-forming processes, were identified and translated into mappable proxies using a wide range of input datasets. Each of these criteria are weighted and combined using an established workflow to produce the final map of IOCG potential.

Mineral exploration in Australia faces the challenge of declining discovery rates despite continued exploration investment. The UNCOVER roadmap, developed by stakeholders from industry, government and academia, has highlighted the need for discovering mineral resources in areas of cover. In these areas, potentially prospective basement is covered by regolith, including transported sediment, challenging many traditional exploration methods designed to probe outcrop or shallow subcrop. Groundwater-mineral interaction in the subsurface has the potential to give the water geochemical and isotopic characteristics that may persist over time and space. Geoscience Australia’s hydrogeochemistry for mineral exploration project, part of the Exploring for the Future Programme, aims to use groundwater chemistry to better understand the bedrock-regolith system and develop new methods for recognising mineral system footprints within and below cover. During the 2017 dry season (May to September), ~150 groundwater samples (including QC samples) were collected from pastoral and water supply bores in the regions of Tennant Creek and McArthur River, Northern Territory. The Tennant Creek region has a demonstrated iron oxide-hosted copper-gold-iron(-bismuth) mineral potential in the Paleoproterozoic and Mesoproterozoic basement and vast areas of regolith cover. Among the critical elements of this mineral system, the presence/absence of redox contrasts, iron enrichment, presence of sulfide minerals, and carbonaceous intervals can potentially be diagnosed by the elemental and isotopic composition of groundwater. The McArthur River region, in contrast, has demonstrated sediment-hosted stratiform lead-zinc-silver mineral potential in the Paleoproterozoic to Neoproterozoic basement and also vast areas of regolith cover. Here, critical mineral system elements that have the potential to be identified using groundwater geochemistry include the presence of felsic rocks (lead source), carbonate rocks (zinc source), basinal brines, dolomitic black shales (traps), and evaporite-rich sequences. Preliminary results will be presented and interpreted in the context of these mineral systems.

Following the successful outcomes of the Tennant Creek-Mt Isa (TISA) mineral potential assessment (Murr et al., 2019; Skirrow et al., 2019), the methodology has been expanded to encompass the entire North Australian Craton (NAC). Like its predecessor, this assessment uses a knowledge-based, data-rich mineral systems approach to predict the potential for iron oxide-copper-gold (IOCG) mineralisation. With their high metal yield and large alteration footprint, IOCG mineral systems remain an attractive target in directing exploration efforts towards undercover regions. This mineral potential assessment uses a 2D GIS-based workflow to map four key mineral system components: (1) Sources of metals, fluids and ligands, (2) Energy to drive fluid flow, (3) Fluid flow pathways and architecture, and (4) Deposition mechanisms, such as redox or chemical gradients. For each of these key mineral system components, theoretical criteria representing important ore-forming processes were identified and translated into mappable proxies using a wide range of input datasets. Each of these criterion are weighted and combined using an established workflow to produce a models of IOCG potential. Metadata and selection rational are documented in the accompanying NAC IOCG Assessment Criteria Table. Two scenarios were modelled for this assessment. The first is a comprehensive assessment, targeting pre-Neoproterozoic mineral systems (>1500 Ma), using a combination of interpreted, geological and geophysical datasets. As geological interpretations are subjective to the geological knowledge of the interpreter, well-documented areas, such as shallow pre-Neoproterozoic basement, have a greater density of data. This increase in data density can create an inherent bias in the modelled result towards previously explored shallow terrains. The second assessment utilises only datasets which can be mapped consistently across the assessment area. As such, these are predominately based on geophysical data and are more consistent in assessing exposed and covered areas. However, far fewer criteria are included in this assessment, and observations are reflective of only the modern geological environment. Both assessments highlight existing mineral fields in WA, NT and QLD, and suggest that these regions extend under cover. Furthermore, regions not previously known for IOCG mineralisation display a high modelled potential, offering exploration prospects in previously unknown or discounted areas.

Mineral exploration ideally involves researching geological potential within the constraints of economic feasibility. Nevertheless, explicit consideration of economic factors is often delayed until late in the exploration cycle. This is not ideal. Like mineral prospectivity, projected economic feasibility can be used to refine the search space and thereby reduce the risks associated with mineral exploration undercover. Here, we outline an exploration strategy based on the notion of identifying economic fairways—that is, regions permissive to resource development from an economic perspective. The approach appraises the economics of Au, Cu, Ni, Pb, Zn, potash and phosphate deposits by modelling revenue against capital expenditure (such as the costs of employment, mining overburden and access to infrastructure). We demonstrate the economic fairways approach through regional assessment of a Tennant Creek–style iron oxide–copper–gold deposit across northern Australia. Our results indicate that such a mineral deposit is expected to be economically viable across much of northern Australia, including in areas with several hundreds of metres of overburden. Our analysis sheds light on the need for accurate cover thickness models, without which undercover economic fairways cannot be defined. Our online tool benefits mineral explorers, and also helps to inform investors about the relative strengths of potential mineral projects; policy makers could use it to plan regional infrastructure development in frontier mineral provinces. <b>Citation:</b> Haynes, M.W., Walsh, S.D.C., Czarnota, K., Northey, S.A. and Yellishetty, M., 2020. Economic fairways assessments across northern Australia. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

This web service provides access to datasets generated by the North Australian Craton (NAC) Iron Oxide Copper Gold (IOCG) Mineral Potential Assessment. Two outputs were created: a comprehensive assessment, using all available spatial data, limiting data where possible to capture mineral systems older than 1500 ma, and; a coverage assessment, which is constrained to data that have no reliance on outcrop or age of mineralisation.

This web service provides access to datasets generated by the North Australian Craton (NAC) Iron Oxide Copper Gold (IOCG) Mineral Potential Assessment. Two outputs were created: a comprehensive assessment, using all available spatial data, limiting data where possible to capture mineral systems older than 1500 ma, and; a coverage assessment, which is constrained to data that have no reliance on outcrop or age of mineralisation.

This web service provides access to datasets produced by the mineral potential assement of iron oxide-copper-gold (IOCG) mineral systems in the Tennant Creek – Mt Isa region. The mineral potential assessment uses a 2D, GIS-based workflow to qualitatively map four key mineral system components: (1) Sources of metals, fluids and ligands, (2) Energy to drive fluid flow, (3) Fluid flow pathways and architecture, and (4) Deposition mechanisms, such as redox or chemical gradients. For each of these key mineral system components theoretical criteria, representing important ore-forming processes, were identified and translated into mappable proxies using a wide range of input datasets. Each of these criteria are weighted and combined using an established workflow to produce the final map of IOCG potential.

One of the aims of the Exploring for the Future program is to promote the discovery of new mineral deposits in undercover frontiers. Iron oxide–copper–gold mineral systems are a desirable candidate for undercover exploration, because of their potential to generate large deposits with extensive alteration footprints. This mineral potential assessment uses the mineral systems concept: developing mappable proxies of required theoretical criteria, combined to demonstrate where conditions favourable for mineral deposit formation are spatially coincident. This assessment uses a 2D geographical information system workflow to map the favourability of the key mineral system components. Two outputs were created: a comprehensive assessment, using all available spatial data; and a coverage assessment, which is constrained to data that have no reliance on outcrop. The results of these assessment outputs were validated with spatial statistics, demonstrating how the assessment can predict the presence of known ore deposits. Both assessment outputs present new areas of interest with prospectivity in under-explored regions of undercover northern Australia. The intended aims are already being realised, as this tool has aided area selection for pre-competitive stratigraphic drilling as part of the MinEx CRC National Drilling Initiative. <b>Citation:</b> Murr, J., Skirrow, R.G., Schofield, A., Goodwin, J., Coghlan, R., Highet, L., Doublier, M.P., Duan, J. and Czarnota, K., 2020. Tennant Creek – Mount Isa IOCG mineral potential assessment. In: Czarnota, K., Roach, I., Abbott, S., Haynes, M., Kositcin, N., Ray, A. and Slatter, E. (eds.) Exploring for the Future: Extended Abstracts, Geoscience Australia, Canberra, 1–4.

This web service provides access to datasets generated by the North Australian Craton (NAC) Iron Oxide Copper Gold (IOCG) Mineral Potential Assessment. Two outputs were created: a comprehensive assessment, using all available spatial data, limiting data where possible to capture mineral systems older than 1500 ma, and; a coverage assessment, which is constrained to data that have no reliance on outcrop or age of mineralisation.