GEMOC ARC National Key Centre

Global Lithosphere Architecture Mapping II

Supported by ARC Linkage

Industry Collaborator: BHP-Billiton

Summary: Domains of different composition in the deep part of Earth’s rigid outer shell (the lithosphere) reflect processes of continent formation and breakup through Earth’s history. These boundaries focus the fluid flows from the deeper convecting mantle that may produce giant ore deposits. We will integrate mantle petrology, tectonic syntheses, and geophysics to image the 3-D architecture of the continental lithosphere, and provide a basis for realistic dynamic modelling of the behaviour of these deep continental roots and their response to geodynamic forces through time. This will provide a new approach to identifying predictive relationships between different types of lithosphere domains and structures, and large-scale mineralisation. The continents have been broken up and re-assembled along major zones of weakness many times through Earth’s history. Boundaries between such continental domains focus large-scale movements of fluids that can produce giant ore deposits. This study will provide new perspectives on the localisation of world-class economic deposits, the Earth resources on which society depends. Innovations in imaging the deep Earth beneath continents, and in numerical modelling, will maintain our high international profile in research relevant to National Priority 1.6 (Developing Deep Earth Resources). Unique geological maps of regions down to 250 km will make the composition of deep Earth regions newly accessible to geoscientists and all potential endusers.

Trace-element Analysis of Diamonds

Trace element analysis of diamond: new applications to diamond fingerprinting and genesis

Supported by ARC Linkage

Industry Collaborator: Rio Tinto

Summary: As diamond crystals grow deep in the Earth’s mantle, they trap minute inclusions of the fluids from which they crystallise. We will use recently developed laser-ablation microprobe techniques to analyse the trace-element patterns of diamond crystals from the Argyle, Diavik and Murowa mines (Australia, Canada and Zimbabwe). The results will define the nature and evolution of the parental fluids of the diamonds, and thus shed new light on the processes of diamond formation and the nature of fluids in the deep Earth. The data will be used to test the potential for fingerprinting diamonds by source; such fingerprinting can be used as a tool in controlling the flow of stolen and illegally mined diamonds. The project will provide new insights into the processes by which diamond crystallises in the Earth’s mantle. A better understanding of these processes can lead to improved models and techniques for diamond exploration, enhancing the prospect of finding new deposits in Australia and abroad. The project will test the potential of trace-element microanalysis to fingerprint diamonds by source. If successful, this technology will provide economic benefits by reducing theft and illegal mining, which represent significant losses to legitimate companies. Application of this Australian development could reduce the circulation of “conflict diamonds”, which would have real social benefits worldwide, especially in some developing countries.

Lithosphere Evolution Across a Craton Margin, Southern Africa

Supported by Industry and a matching Macquarie University Collaborative Grant

Industry Collaborator: De Beers

Summary:  The margins of cratonic blocks extend to 150-300 km depth, and exert a strong control on crustal tectonics.  Kimberlite magmas intruded across the southern margin of the Kaapvaal Craton (S. Africa) provide detailed sampling of the lithospheric mantle.  We will use these samples to map the composition and structure of the mantle in two time slices (120 Ma, 90 Ma), providing new information on how the craton margins channel fluids.  Linkages between crustal tectonics and mantle events will be constrained by comparing TerraneChron^® analysis of zircons from modern streams, and the kimberlites themselves, with existing Re-Os ages for mantle rocks.

Global Lithosphere Architecture Mapping

Supported by ARC Linkage

Industry Collaborator: BHP-Billiton

Summary:  Compositional domains in the subcontinental lithospheric mantle reflect the processes of continental assembly and breakup through Earth’s history.  Their boundaries may focus the fluid movements that produce giant ore deposits.  Mapping these boundaries will provide fundamental insights into Earth processes and a basis for the targeting of mineral exploration.  We will integrate mantle petrology, tectonic synthesis and geophysical analysis to produce the first maps of the architecture of the continental lithosphere, to depths of ca 250 km.  These maps will provide a unique perspective on global dynamics and continental evolution, and on the relationships between lithosphere domains and large-scale mineralisation.

Trace-element Analysis of Diamonds

Supported by Industry and a matching Macquarie University Collaborative Grant

Industry Collaborator: Rio Tinto

Summary:  Diamonds contain minute amounts of trapped fluids, representing the medium from which the diamonds grew; these fluids are a unique source of information on processes in Earth’s mantle.  New techniques for the trace-element analysis of these fluids, developed recently in GEMOC will be further developed, and applied to the analysis of selected populations of diamonds from the Argyle mine (WA).  The data will provide new insights into the genesis of diamond, with applications both to exploration models and to test the feasibility of "fingerprinting" of diamonds for exploration and forensic purposes (tracing illegal diamond sources).

Links between plume-mantle interaction, mantle sulfides and Ni-PGE endowment in Large Igneous Provinces

Supported by industry and a matching Macquarie University Collaborative grant

Industry Collaborator: BHP-Billiton

Summary: Most large Ni-PGE (Platinum Group Elements) deposits are associated with some, but not all, Large Igneous Provinces (LIP=plume-related flood basalts). Isotopic and trace-element data suggests that the magmas of “fertile” LIPs have interacted with the deep mantle roots of ancient continents. We will test the hypothesis that the Ni-PGE enrichment in some LIP magmas reflects the mobilisation of pre-existing Ni,PGE-rich sulfide phases as the magmas pass through these old, highly modified mantle roots. This model, if confirmed, will be a major advance on traditional models for Ni-PGE concentration, and will have a significant impact on exploration models.

Developing a geochronological framework for the Gawler Craton, South Australia

Supported by a matching Macquarie University Collaborative grant (2004-2005)

Industry Collaborator: PIRSA (Primary Industries and Resources, South Australia)

Summary: The aim of the project is to supply a geochronological framework for the evolution of the Gawler Craton of South Australia, by dating major Archean and Proterozoic magmatic and tectonic events across the Craton. At present, the geochronology of this large region is poorly known, and this is one main reason why the minerals industry is choosing better-known regions to explore. The development of a better geochronological base will support the industry partner’s goal of establishing an integrated tectonic model as an aid to mineral exploration, and provide new insights into crustal evolution.

Application of metal isotopes in exploration for magmatic nickel and volcanic-hosted copper deposits

Supported by a matching Macquarie University Collaborative grant (2004-2005)

Industry Collaborator: Anglo-American PLC

Summary: The major aim is to study, for the first time, the isotope geochemistry of Ni and Pd in a magmatic nickel deposit. Cu and Fe isotopic studies will also be carried out on a volcanic-hosted copper deposit.  The aims are to determine whether isotopic data for commodity metals can be used to discriminate between barren and fertile host rocks and whether these isotopic ratios can provide vectors to ore within a mineralised system.  The expected outcomes are development of new analytical methodologies and new isotopic exploration tools for blind ore deposits, which could be adopted by the Australian mineral exploration industry.

Improving Mineral Exploration Performance by Superior Management of Risk, Uncertainty and Value

Supported by Macquarie University Industry Collaborative Grant

Industry Sponsors: BHP Billiton, Codelco, Geoinformatics Exploration, Gold Fields, Jackaroo Drill Fund, Newmont, Placer Dome, Teck Cominco, WMC Resources.

Summary:  Mineral exploration performance has deteriorated significantly over the past 15-20 years, especially with respect to the rate and cost of the large, 'greenfields' discoveries that generate so much value for the industry and underpin its future resource base.  This research project is analysing past industry performance to identify opportunities for improvement, building probabilistic models of the mineral exploration business to provide a better decision framework, investigating the role of the high natural uncertainty and complexity on decision making, and developing a range of tools to improve risk and value management.  The project involves collaboration between geoscientists, statisticians, psychologists and business management across the university.

Mechanisms of PGE fractionation and concentration in mafic and ultramafic melts

Supported by: AMIRA and MERIWA

Industry Collaborators: BHP-Billiton, Independence, LionOreIn collaboration with Dr Marco Fiorentini from UWA with shared PhD student Marek Locmelis

Summary: A long-standing goal of research on nickel-sulfide (NiS) deposits has been the development of reliable lithogeochemical indicators that can act as guides for exploration. In order to better constrain how platinum-group element (PGE) signatures may be utilised as pathfinders for those NiS deposits, this project focuses on the processes that control the fractionation and concentration of PGE in mafic and ultramafic magma types. The study looks into a range of variables controlling the PGE geochemistry, including the role of sulfides (i.e. pentlandite, millerite), oxides (i.e. chromite), silicate phases (i.e. olivine, pyroxene) and platinum-group minerals (i.e. alloys, antimonides, arsenides, tellurides) in the concentration and fractionation of PGE in mineralised and barren sequences. Furthermore, the study investigates the spatial relationship between the PGE signature of mafic and ultramafic rocks and the occurrence of various types of NiS mineralisation, thus optimising the use of the PGEs as vectors towards mineralised environments.