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

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

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

The Fennocandian Shield

• Case study I:Vihanti – Pyhäsalmi belt

• Case study II:Skellefte district

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

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

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

Regional model of the Raahe-Ladoga zone

Case study II: Skellefte district

Regional scaleSemi-regional scaleDeposit scale

Structural and facies analysis in the Vargfors syncline

• Combination ofstructures and sedimentarystratigraphy

• Syn-extensionalsedimentation alonggrowth faults

• Inversion and formation of asymmetric synclines

Regional scale structural analysis

Regional scale structural analysis

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

Regional scale structural analysis

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

Simplified 3D-models of VMS ore bodies illustratingvaryiations in shape and orientation

Deposit scale modelling in the Skellefte district

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

Semi-regional scale 3D-model

Detailed, semi-regional scale Voxet model of the Vargfors syncline

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

3D-modelling

4D-modelling in the Skellefte district

• Adding geological time to the 3D-model• Visualisation of the conceptual model• Validation of the 3D-model

Multi-scale geologicalmodelling of the Gällivare area

Aitik

Malmberget

Svappavaara