Pyhäsalmi – Vihanti
Transcript of Pyhäsalmi – Vihanti
4D modelling the Fennoscandian Shield Skellefte and Vihanti-Pyhäsalmi districts
ProMine final conference,
23-25 April 2013, Levi, Finland
Fennoscandian Shield
Pyhäsalmi-Vihanti ore district
The main volcanic units of the Pyhäsalmi-Vihanti 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 data Geological maps
Geophysical maps Geological analogies from the surrounding geology, seismic sections and other geophysical surveys
Drill hole data Surpac strings
Surpac solids
Semi-regional 3D model of Vihanti
Regional model of the RLZ
Semi-regional model of Pyhäsalmi
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
Inversion model of regional gravity data
Vihanni and Kuuhkamo models
The contact between Lampinsaari volcanites and granodiorite based on seismic data and geological maps
Vertical faults, NW dipping undefined discontinuity, the brown surface marks the possible lower boundary for the granodiorite underlied by volcanites and calc-silicate rocks, modeled using GeoModeller software Vihanti Zn and pyrite ore
1 km
N
Pyhäsalmi 3D- model
Regional structural evolution
4D-Pyhäsalmi
Deposition of voluminous felsic volcanics, intrusion of felsic&mafic synvolcanic intrusions, hydrothermal alteration, FORMATION OF MASSIVE VMS ORE
Deposition of overlying tholeiitic volcanic rocks and minor pyrrhotite rich mineralizations
Movement and deformation on thrust carries deposit over unaltered material, formation of sheath fold
Further folding & regional metamorphism at amphibolite facies
Refolding of the earlier structures into upright position, intense subvertical shearing +late pegmatites
Skellefte district Regional scale Semi-regional scale Deposit scale
Structural and facies analysis in the Vargfors syncline
• 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
• N: 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
Deposit scale 3D-model
Simplified 3D-models of VMS ore bodies illustrating varyiations in shape and orientation
Semi-regional and regional scale - Structural data from field mapping
in 3D (sparse plugin for GoCAD) - Interpolation along map traces - Cutting of surfaces
Uncertainty modelling
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-model of the Skellefte district
Prospectivity modelling
Correlation between distribution and shape of VMS deposits, and regional deformation patterns
Prospectivity modelling
4D modelling
- Schematic illustration of listric and related transfer faults, the formation of volcanic and sedimentary rocks and VMS deposits during crustal extension
- Subsequent deformation of rocks and transposition of ore bodies and the effect of different block-rotations, subsequent erosion and deformation between the neighboring fault-bound compartments and the tectonic transposition of the ore bodies