4D modelling in the northern part of the Fennoscandian Shield

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
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Most European major mineral deposits
that outcrop have been discovered
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Estimation of the resource base below
surface through geological modelling
and estimation of geological conditions
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Realistic to anticipate that by building
the 4D geo-models of mature mining
belts we will be able to estimate an
increased resource base by up to 50%
in the individual belts
Key ingredients
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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 VihantiPyhäsalmi 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
Geophysical surveys,Geophysical maps
drillholes and structural geological inference!
Surpac
Geological analogies Bedrock observations solidsGeological analogies from the from the surrounding geology, surrounding geology, seismic sections and theories and other geophysical assumptions of the surveys
geological events and absolute age determinations Magnetic maps
Surpac strings
Bouguer maps
Semi-regional 3D model of Vihanti
Drill hole data
Drill hole data
Geological maps
Methods used for Pyhäsalmi 3D/4D- models
• Lithogeochemistry
W
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• Deep
penetrating
geophysics
– Seismics
– Magnetotellurics
Z=1000m
E
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• Sructural analysis
• Modeling with goCad and Surpac- programs
Regional model of the Raahe-Ladoga zone
Case study II: Skellefte district
Regional scale
Semi-regional
scale
Deposit scale
Structural and facies analysis in the Vargfors syncline
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Combination of
structures and
sedimentary
stratigraphy
Syn-extensional
sedimentation along
growth faults
Inversion and formation
of asymmetric synclines
Regional scale structural analysis
Regional scale structural analysis
Regional scale structural analysis
N: dominating coaxial deformation at
shallower crustal level
S: high metamorphic conditions and
non-coaxial deformation at deeper
crustal level
Strain partitioning during one SSENNW 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
Deposit scale modelling in the Skellefte district
Simplified 3D-models of VMS ore bodies illustrating
varyiations in shape and orientation
3D-modelling in the Skellefte district
Semi-regional and regional scale
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Structural data from field
mapping 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 MTstudy)
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 geological
modelling of the
Gällivare area
Svappavaara
Malmberget
Aitik