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Geomechanical Modelling for mining and exploration

Dr John McLellanPrincipal Geoscientist

GMEX – Geological Modelling for ExplorationEmail: john@gmex.com.au

www.gmex.com.au

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BackgroundGMEX: Established in 2012Core business: Structural Geology and Geomechanical Modelling for explorationModelling: Finite Element and Discrete Element TechniquesWhy? To better understand deformation events, associated fluid flow and to enable predictive targeting based on geological ‘processes’

Dr John McLellan: Completed a PhD in Economic Geology 2004Specialities: Structural Geology and GeomechanicsCurrent Position: Principal Geoscientist, GMEXPrevious Positions: Senior Geoscience Consultant, A/Business Manager, Rockfield 2010-2012

Senior Research Fellow, James Cook University 2004-2010Experience: 12 years of geomechanical modelling and related prospectivity analysis, 7 years involvement with the Predictive Mineral Discovery CRC.Academic: Over 40 peer reviewed articles, current Adjunct Senior Research Fellow at James Cook University.Awards: Prospectors Suppliers Award 1997, AGSO Jubilee Prize 1998, Geological Society of Australia Gold Medal 1999, AUSIMM Bursary 1999, Australian post-graduate Award (APA) 2001, Pmd*CRC Scholarship 2003, Australian Post-Doctoral Fellowship 2009, Townsville Regional Resources Excellence Awards – Resources Professional of the Year 2011, Resources Project of the Year 2011.

www.gmex.com.au

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Why Geomechanical Modelling?Advantages:1. Provides insight into the formation of structurally controlled mineral deposits2. It explores the geological processes (i.e. deformation and associated fluid flow) rather than simply

collecting and presenting empirical data3. Provides a better understanding of the interactions between the mechanical response of the crust

to deformation events and fluid migration4. Can simulate the partitioning of both stress and strain during deformation and highlight the most

likely or favourable areas for fluid focussing5. Predictive capacity for targeting from within mine extensions to regional exploration6. Provides quantitative results which can be incorporated into prospectivity analysis in both two and

three dimensions

Methodology:7. A 2d or 3d conceptual model is derived from known data (e.g. lithology, structural data)8. Models are then built and meshed and an applied stress or deformation condition simulates the

deformational events9. After deformation has been simulated models are interrogated to highlight stress and strain

partitioning/anomalies, effects of competency contrasts, fault systems and fluid migration10. These anomalies are then used to highlight favourable predictive targets

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Predictive Capacity-To find mineral deposits we need to know the areas in the crust that will facilitate the fluids responsible for that mineralisation- We use ‘empirical data’ to test geological processes- The geomechanical response of the crust can indicate shear zones, faults and breccias, all of which can be important fluid conduits- We can identify target areas that have a higher likelihood of hosting mineralisation- Identifying not only favourable areas, but also areas of low favourability will reduce your exploration target area, reducing costs and increasing the chances of discovery

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TechniquesThere are two main modelling techniques employed:

1. Finite Element Analysis (FEA): a full 3-dimensional geological model is built and subjected to a simulated deformation event. We can then interrogate the model and examine the geomechanical and fluid flow response to the deformation.

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Conceptual Geological Model

Numerical Mesh with applied deformation

Volumetric strain outputs

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Techniques

2. Discrete Element Modelling (DEM): a 2-dimensional geological model is built and subjected to a simulated deformation event. We can then interrogate the model and examine the geomechanical and fault/fluid related response to the deformation.

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Conceptual Geological Model indicating fault architecture and lithological boundaries

Results can be integrated into most GIS environments and can be easily viewed in Google Earth for better clarity for the exploration team

Example of model results from applied stress conditions. We can clearly define areas of stress anomalies as a function of fault block movement

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Validation Case StudiesArchaean Granite-Greenstone Au Deposit (Sunrise Dam Gold Mine):- Structurally controlled mineralisation- Poor within mine targeting due to nugget effect, deformation styles and limited deep drilling- Aim was to highlight areas within the mine sequence that were most likely to contain both shear and fracture hosted gold mineralisation using a 3D FEA analysis

Outcome: Target areas defined based on geomechanical modelling predictions Target areas followed up by deep drilling Targeting successful, discovery of the new Vogue 12 million tonne orebody

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Example of SW plunging trend in numerical models

Mark Cutifani – CEO presentation June 2011This brownfield discovery is significant

And a potential game-changer for Sunrise Dam

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Validation Case StudiesVolcanogenic System, Ben Lomond U-Mo Deposit:- Structurally controlled mineralisation- Limited exploration within the tenement- Aim was to highlight areas within the tenement that had the highest likelihood of structurally controlled mineralisation, compare with known XRF data and generate priority geomechanical targets. This was done using both 3D FEA and 2D DEM analysis

Outcome: Target areas defined based on geomechanical modelling predictions of a combination of rock failure plots and stress variations Target areas have a good correlation with known XRF geochemical data Future targeting planned around the main geomechanical targets

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3D conceptual model and volumetric strain/flow outputs2D DEM outputs and comparison with known occurrences

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Validation Case StudiesFe-Oxide Cu-Au systems, Eastern Fold Belt, Mt Isa:- Structurally controlled mineralisation- Fault controlled system with competency contrasts- Aim was to highlight areas within the region that had the highest likelihood of structurally controlled mineralisation, using competency contrasts of metasediments/granites/mafics and regional deformation events. This was done using a 2D DEM analysis.

Outcome: Target areas defined based on geomechanical modelling predictions of a combination of rock failure plots and stress variations have a good correlation with known mineral occurrence data Fault architecture and competency contrasts have been the controlling structural components of mineralisation in the Eastern Fold Belt

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2D Conceptual model for the EFB 2D DEM outputs and comparison with known occurrences. Selwyn high strain zone very evident.

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Validation Case StudiesGeita Gold Mine, Tanzania:- Structurally controlled mineralisation- Fault controlled system with competency contrasts- Aim was to validate structural models and propose the most likely orientation of sigma1 responsible for mineralisation. Also, highlight areas within the region that had the highest likelihood of structurally controlled mineralisation in both plan and cross sectional view using a 2D DEM analysis.

Outcome: Structural model validated with the most likely orientation of sigma 1 responsible for mineralisation identified New targets defined as a result of stress anomaly combinations and fault aperture opening

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Fault movement and aperture opening Cross sectional differential stress outputs and joint displacement.

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Geomechanical Modelling of the Geological Process

-Both FEA and DEM are very powerful tools for mineral exploration- This type of analysis allows us to examine the mechanical geological process that has formed the mineralisation instead of simply relying on gathered empirical data and how we combine this to formulate the best targets- It can provide quick reliable data that can be used in a targeting prospectivity program in both two and three dimensions- Incorporating this data into a GIS platform can greatly enhance WOFE analysis as it provides an understanding of the mechanical process, which is the key to structurally controlled mineralisation

Understanding the process makes the ‘where’ easier to solve because you know the ‘why’

These techniques can be applied to most structurally controlled mineral deposits or regions. If you would like to discuss these techniques further contact Dr John McLellan at john@gmex.com.au

www.gmex.com.au