Final Reports (Stage One Projects)
Architecture A1 Project -What are the fundamental characteristics of mineralised (trans-lithospheric) fault systems?
Introduction
The principal aim of the project has been to understand why some faults systems are mineralised and why others are barren, and whether a mantle component is essential to form major ore deposits. The objective of the study has been to determine, and rank, a set of critical parameters that could be applied to identify favourable conduits for ore-forming fluids and whether these fault systems are likely to be metallogenically well-endowed with respect to precious and base metal mineralisation.
High Impact Outcomes
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Integration of the approach applied in this study with deposit - to regional-scale computer-based methodologies - provides an effective tool in the construction of prospectivity maps applicable to predictive mineral exploration
- Roughness appears to be one important factor that determines mineral endowment of major faults in base metal provinces. An exciting implication of this conclusion is that fault roughness could be used as an exploration tool on a large scale in this and similar terrains where fault geometry can be mapped in detail.
Research Summary
The key outcomes of this work can be summarised as follows:
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The A1 Tectonics Targets data base provides a useful resource and interrogation serves to confirm the importance of parameters that are likely to influence the endowment of major faults, and spatially associated 2nd- and 3rd-order structures. But the information contained in the data base as is remains insufficient to clearly define or rank potentially critical parameters. A unified database protocol may eventually become available and enable full functionality of the Tectonics Target data base.
- Comprehensive data sets have been obtained, and integrated with existing data sets, for key faults and their surrounding regions. Investigations into the lithological and structural characteristics of some gold deposits has provided preliminary implications for mineralised in some regions and the absence of mineralisation in others. Interrogation of major fault and mineral deposit databases via multi-variant, phenetic and phylogenetic analysis largely confirms the relative importance of empirically-derived, critical and permissive parameters for mineralisation, such as proximity to crustal-scale faults, anticlinal hinge zones, dilational jogs, fault roughness, strong rheological contrasts and metamorphic grade.
- Prospectivity mapping of structural elements shows that elevated endowment can be correlated with the intersection of major faults and regional anticlines and fault jogs, particularly those of a dilatant nature. Presence and concurrence of these parameters determine the extent of metallogenic endowment of a given fault system and segments thereof.
- Mantle-driven processes are probably important in the formation of world-class ore deposits but the quantitative significance of mantle dynamics remains to be demonstrated. Where there is little direct evidence for a well-endowed fault to penetrate the lithospheric mantle, late-stage decoupling of the fault might have occurred along a more ductile lower crustal layer.
- Modelling of potential field (gravity, magnetics) gradients can successfully illustrate the spatial link between mineralisation and deep-seated, major faults and provides a reliable first-order area selection filter for exploration, especially in areas of poor exposure.
- On the basis of current data sets, the Mt Isa Fault can be interpreted as either an inverted extensional fault or a late-orogenic thrust. However, our data shows that the Mount Isa Fault is unlikely to have cut the entire crust, with spatially related, major shale-hosted massive sulphide Pb-Zn-Ag-Cu deposits probably formed in the absence of mantle plumbing systems.
- Roughness appears to be one important factor that determines mineral endowment of major faults in base metal provinces. An exciting implication of this conclusion is that fault roughness could be used as an exploration tool on a large scale in this and similar terrains where fault geometry can be mapped in detail.
- The Palmerville Fault is an inverted, first-order growth fault that controlled Early-Middle Palaeozoic basin development in the Hodgkinson Province. Orogenic gold endowment of the Palaeozoic Hodgkinson-Broken River Province is likely to be controlled and limited by the presence of Proterozoic, crustal-character Proterozoic basement underneath the basin.
- Multi-scale edge analysis ('worming') has proved to be useful in demonstrating that the effects of the 3D nature of faults and shear zones may result in overestimates of the amount of alteration and/or the anisotropy of phyllosilicate minerals caused by fluids moving along the faults and shear zones
- The implication of this is that the seismic method should be able to image the flow paths in gold mineral systems by mapping the physical property changes caused by alteration along the flow paths; fluid flux does not have to be extreme.
- Zones of high fluid flux at supralithostatic pressures would be an excellent locus for focussing the formation of detachment surfaces.
- Physical modelling suggests that fluids would break out of such regions into dipping high strain zones that project towards the surface; they should be reflective in seismic sections.
- Reflectors that might be interpreted as spill zones are seen beneath Kalgoorlie, Mount Pleasant, Sons of Gwalia and possibly Kanowna Belle in the Yilgarn Block and possibly also the Marimo fault in the Eastern Succession in Mount Isa.
- In regions where detachments did not form or are no longer recognised, spill zones have been interpreted for 9 km depth under Laverton, and at deep levels elsewhere along the Laverton/Leonora seismic line.
- The potential implications of theoretical considerations, as well as yet unanswered key questions can be addressed and tested effectively via the development of numerical modelling scenarios.
- Integration of the approach applied in this study with deposit - to regional-scale computer-based methodologies - provides an effective tool in the construction of prospectivity maps applicable to predictive mineral exploration.
List of Partners
- Monash University
- La Trobe University
- Geoscience Australia
* Please note that references, appendices etc are not published in this Final Report Summary. These can be found in the Final Report and available via the links below.
Full Report 
6.9Mb
Appendices
For Further Information Contact
Project Leader
Dr Frank Bierlein
School of Earth and Geographical Sciences
University of Western Australia
Tel: 08 6488 7846
Email: fbierlein@tsrc.uwa.edu.au
