Geomechanical Modelling formining and explorationDr John McLellanPrincipal GeoscientistGMEX – Geological Modelling for ExplorationEmail: firstname.lastname@example.org
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 targetingbased 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 2010-2012Senior Research Fellow, James Cook University 2004-2010Experience: 12 years of geomechanical modelling and related prospectivity analysis, 7 years involvementwith the Predictive Mineral Discovery CRC.Academic: Over 40 peer reviewed articles, current Adjunct Senior Research Fellow at James CookUniversity.Awards: Prospectors Suppliers Award 1997, AGSO Jubilee Prize 1998, Geological Society of Australia GoldMedal 1999, AUSIMM Bursary 1999, Australian post-graduate Award (APA) 2001, Pmd*CRC Scholarship2003, Australian Post-Doctoral Fellowship 2009, Townsville Regional Resources Excellence Awards –Resources Professional of the Year 2011, Resources Project of the Year 2011.2www.gmex.com.au
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 simplycollecting and presenting empirical data3. Provides a better understanding of the interactions between the mechanical response of the crustto deformation events and fluid migration4. Can simulate the partitioning of both stress and strain during deformation and highlight the mostlikely 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 andthree dimensionsMethodology:1. A 2d or 3d conceptual model is derived from known data (e.g. lithology, structural data)2. Models are then built and meshed and an applied stress or deformation condition simulates thedeformational events3. After deformation has been simulated models are interrogated to highlight stress and strainpartitioning/anomalies, effects of competency contrasts, fault systems and fluid migration4. These anomalies are then used to highlight favourable predictive targets3www.gmex.com.au
Predictive Capacity-To find mineral deposits we need to know the areas in the crust that will facilitate the fluids responsiblefor 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 canbe 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 explorationtarget area, reducing costs and increasing the chances of discovery4www.gmex.com.au
TechniquesThere are two main modelling techniques employed:1. Finite Element Analysis (FEA): a full 3-dimensional geological model is built and subjected to asimulated deformation event. We can then interrogate the model and examine the geomechanical andfluid flow response to the deformation.5www.gmex.com.auConceptual Geological ModelNumerical Mesh withapplied deformationVolumetric strain outputs
Techniques2. Discrete Element Modelling (DEM): a 2-dimensional geological model is built and subjected to asimulated deformation event. We can then interrogate the model and examine the geomechanical andfault/fluid related response to the deformation.6www.gmex.com.auConceptual Geological Modelindicating fault architecture andlithological boundariesResults can be integrated into most GISenvironments and can be easily viewedin Google Earth for better clarity for theexploration teamExample of model results from appliedstress conditions. We can clearly defineareas of stress anomalies as a functionof fault block movement
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 andfracture hosted gold mineralisation using a 3D FEA analysisOutcome: Target areas defined based on geomechanical modelling predictionsTarget areas followed up by deep drillingTargeting successful, discovery of the new Vogue 12 million tonne orebody7www.gmex.com.auExample of SW plunging trend in numerical modelsMark Cutifani – CEO presentation June 2011This brownfield discovery is significantAnd a potential game-changer for Sunrise Dam
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 structurallycontrolled mineralisation, compare with known XRF data and generate priority geomechanical targets.This was done using both 3D FEA and 2D DEM analysisOutcome: Target areas defined based on geomechanical modelling predictions of a combination of rockfailure plots and stress variationsTarget areas have a good correlation with known XRF geochemical dataFuture targeting planned around the main geomechanical targets8www.gmex.com.au3D conceptual model and volumetric strain/flow outputs2D DEM outputs and comparison with known occurrences
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 controlledmineralisation, using competency contrasts of metasediments/granites/mafics and regionaldeformation events. This was done using a 2D DEM analysis.Outcome: Target areas defined based on geomechanical modelling predictions of a combination of rockfailure plots and stress variations have a good correlation with known mineral occurrence dataFault architecture and competency contrasts have been the controlling structural componentsof mineralisation in the Eastern Fold Belt9www.gmex.com.au2D Conceptual model for the EFB 2D DEM outputs and comparison with known occurrences. Selwyn high strain zone very evident.
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 formineralisation. Also, highlight areas within the region that had the highest likelihood of structurallycontrolled 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 formineralisation identifiedNew targets defined as a result of stress anomaly combinations and fault aperture opening10www.gmex.com.auFault movement and aperture opening Cross sectional differential stress outputs and jointdisplacement.
Geomechanical Modelling of theGeological 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 themineralisation instead of simply relying on gathered empirical data and how we combine this toformulate the best targets- It can provide quick reliable data that can be used in a targeting prospectivity program in both two andthree dimensions- Incorporating this data into a GIS platform can greatly enhance WOFE analysis as it provides anunderstanding of the mechanical process, which is the key to structurally controlled mineralisationUnderstanding 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 wouldlike to discuss these techniques further contact Dr John McLellan at email@example.com
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