GEMOC ARC National Key Centre

Basin development in Proterozoic South Australia: developing a time-integrated, compositional framework to assist mineral exploration

Supported by a matching Macquarie University External Collaborative grant
Industry Collaborator: PIRSA (Primary Industries and Resources, South Australia)

Summary: This project will generate significant new geochemical and age information to improve the existing geochronological framework for geologically ancient regions of South Australia. These chemical “fingerprints” and age data will be obtained for the mineral zircon (collected from river sands and rocks), that acts as a time capsule allowing us to determine the nature and sources of individual magmatic rocks and also sedimentary sequences. This will provide an integrated understanding of the geological history of the region to aid mineral exploration, and will also add to knowledge of the composition, metallogeny and assembly of this region of the Australian continent.

Global Lithosphere Architecture Mapping II

Summary: 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.

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.

Bill Griffin and Sue O’Reilly with Dave Ballantyne (L) and Claude Dalpé (R) during a visit to the Canadian Mounties lab in Ottawa.

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 are being constrained by comparing TerraneChron® analysis of zircons from modern streams, and the kimberlites themselves, with existing Re-Os ages for mantle rocks.

Bill Griffin and Alan Kobussen picking over a concentrate pile during a trip to South Africa.

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 were 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). This project led to the ARC Linkage Grant for 2007.

Rio Tinto came to GEMOC for a project review meeting L-R: John Takos, Esmé van Achterbergh (GEMOC PhD 2005), Paul Agnew, Sue O’Reilly, Bill Griffin, Phil Plaisted, John Chapman, Debora Araujo, Norm Pearson.

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 in this first-stage project is providing fundamental insights into Earth processes and a basis for the targeting of mineral exploration. We are integrating 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 (e.g. GEMOC Publication #423). These maps will provide a unique perspective on global dynamics and continental evolution, and on the relationships between lithosphere domains and large-scale mineralisation.

Seismic tomography (Vs) image of Africa at 100-175 km depth: cratons (high-Vs) stand out in “hot” colours while low-Vs East Africa Rift is in blue-black.

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 are testing 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. See GEMOC Publication #473.

Mechanisms of PGE fractionation and concentration in mafic and ultramafic melts

Supported by AMIRA and MERIWA and an international postgraduate scholarship from Macquarie University
Industry Collaborators: BHP Billiton, Independence, LionOre
In 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. See Research highlight p. 34.