4d modelling in the northern part of the fennoscandian shield
TRANSCRIPT
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4D modelling in the northern part of the Fennoscandian Shield
Case studies from the Skellefte and Vihanti-Pyhäsalmi districts
Tobias E. Bauer, PhD
Luleå University of Technology
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Why 3D- and 4D-modelling• Most European major mineral deposits
that outcrop have been discovered
• Estimation of the resource base belowsurface through geological modelling and estimation of geological conditions
• Realistic to anticipate that by buildingthe 4D geo-models of mature miningbelts we will be able to estimate an increased resource base by up to 50% in the individual belts
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Key ingredients
• Geology• Geochemistry and hydrothermal alteration• Metal zonation, isotope geochemistry, geochronology• Fluid migration, geohydrology• Tectonic evolution• Magnetic data interpretations• Gravity data interpretations• High resolution reflection seismic interpretations• Electromagnetic / electric / magnetotelluric interpretations
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The Fennocandian Shield
• Case study I:Vihanti – Pyhäsalmi belt
• Case study II:Skellefte district
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Case study I: Vihanti-Pyhäsalmi belt
The main volcanic units of the Vihanti-Pyhäsalmi ore district
Vihanti group(~1925 -1920 Ma)• felsic to mafic early arc volcanism• abundant volcaniclastics • calc silicate rocks• subvolcanic felsic intrusion
Pyhäsalmi group(~1930-1925 Ma)• bimodal felsic and mafic early arc volcanism• lavas, breccias and porphyries• subvolcanic felsic intrusion
Vihanti model
Pyhäsalmi model
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3D/4D Modeling methods for regional and semi-regional 3D models
Bedrock observations Geological analogies from the surrounding geology, theories and assumptions of the geological events and absolute age determinations
Magnetic maps
Geophysical surveys, drillholes and structural geological inference!
Bouguer maps
Drill hole dataGeological maps
Geophysical maps
Geological analogies from the surrounding geology, seismic sections and other geophysical surveys
Drill hole dataSurpac strings
Surpac solids
Semi-regional 3D model of Vihanti
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Methods used for Pyhäsalmi 3D/4D- models
• Lithogeochemistry• Deep penetrating geophysics
– Seismics– Magnetotellurics
• Sructural analysis• Modeling with goCad and Surpac- programs
??W E
Z=1000m
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Regional model of the Raahe-Ladoga zone
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Case study II: Skellefte district
Regional scaleSemi-regional scaleDeposit scale
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Structural and facies analysis in the Vargfors syncline
• Combination ofstructures and sedimentarystratigraphy
• Syn-extensionalsedimentation alonggrowth faults
• Inversion and formation of asymmetric synclines
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Regional scale structural analysis
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Regional scale structural analysis
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Regional scale structural analysisN: dominating coaxial deformation at shallower crustal level S: high metamorphic conditions and non-coaxial deformation at deeper crustal level
Strain partitioning during one SSE-NNW transpressional event OR two separate events with contrasting bulk shortening directions
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Regional scale structural analysis
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3D-modelling
• All– Data import into 3D-software– Application of conceptual model– Modelling of surfaces and bodies
• Deposit scale• Semi-regional scale (Nautanen shear zone)• Regional scale
– Uncertainty model– Prospectivity model
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Simplified 3D-models of VMS ore bodies illustratingvaryiations in shape and orientation
Deposit scale modelling in the Skellefte district
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3D-modelling in the Skellefte district
Semi-regional and regional scale
- Structural data from fieldmapping in 3D (sparse plugin for GoCAD)
- Interpolation along map traces- Cutting of surfaces
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Semi-regional scale 3D-model
Detailed, semi-regional scale Voxet model of the Vargfors syncline
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3D-modelling in the Skellefte district
Uncertainty modelling
Observed in field, mine or drillcore
Interpreted from geophysical data (reflection seismic-, IP-, resitivity-, MAG-, or MT-study)
Interpreted from structural data or extrapolated from geophysical data
Inferred / unknown
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3D-modelling
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4D-modelling in the Skellefte district
• Adding geological time to the 3D-model• Visualisation of the conceptual model• Validation of the 3D-model
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Multi-scale geologicalmodelling of the Gällivare area
Aitik
Malmberget
Svappavaara