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GEOLOGICAL SURVEY OF FINLAND
Report of Investigation 195
2012
3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study
Edited by Eevaliisa Laine
GEOLOGIAN TUTKIMUSKESKUS GEOLOGICAL SURVEY OF FINLAND
Tutkimusraportti 195
Report of Investigation 195
Edited by
Eevaliisa Laine
3D MODELING OF POLYDEFORMED AND METAMORPHOSED ROCKS:
THE OLD OUTOKUMPU CU-CO-ZN MINE AREA AS A CASE STUDY
Front cover: Vuonos ore body and Ni contents.
3D visualization is done by Paradigm GOCAD software package.
Unless otherwise indicated, the figures have been prepared by the author of the publication.
Layout: Elvi Turtiainen Oy
Espoo 2012
Laine, E. (ed.) 2012. 3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study. Geological Survey of
Finland. Report of Investigation 195, 77 pages, 66 figures and 1 table.
The present work summarizes the results of the project “3D/4D modeling –
Outokumpu area as a case study” conducted during 2007–2009 and 3D modeling of the Outokumpu assemblage in the project “Development of geological
3D modeling using structural geology and geostatistics” in 2010 at the Geological Survey of Finland (GTK). The aims of these projects were to apply
and evaluate 3D/4D modeling software and formulate principles for visualizing
and analyzing complicated geological structures typical of Finnish bedrock.
The aim was to make recommendations for the use of 3D-modeling tools and
processes for 3D/4D modeling at GTK.
The 3D/4D modeling project resulted in suggestions for geological 3D modeling methods and processes presented by Eevaliisa Laine and Kerstin Saalmann and geological 3D models at different scales by Esko Koistinen, Kerstin
Saalmann, Timo Tervo, Tapio Ruotoistenmäki and Eevaliisa Laine from GTK
(Geological Survey of Finland), Gabriel Coirrioux from BRGM (France),
Rosa Diaz from the University of Huelva and Noora Salminen from Helsinki
University of Technology during 2007–2010, and the regional 3D model constructed by Tapio Ruotoistenmäki and Esko Koistinen using regional geophysical data. In addition, Noora Salminen completed her Masters thesis, entitled
Microstructures in 3D modelling, Outokumpu area as an example site, for the
Department of Civil and Environmental Engineering at Helsinki University of
Technology.
Keywords (GeoRef Thesaurus, AGI): bedrock, metamorphic rocks, structural
geology, metal ores, ore bodies, three-dimensional models, Proterozoic, Outokumpu, Finland
Eevaliisa Laine
Geological Survey of Finland
P.O. Box 96
FI-02151 Espoo
FINLAND
E-mail: [email protected]
ISBN 978-952-217-182-5 (PDF)
ISSN 0781-4240
Laine, E. (toim.) 2012. 3D modeling of polydeformed and metamorphosed
rocks: the old Outokumpu Cu-Co-Zn mine area as a case study. Geologian tutkimuskeskus, Tutkimusraportti 195, 77 sivua, 66 kuvaa ja 1 taulukko.
Raportti esittelee 3D/4D mallinnusmenetelmät – Outokummun alue esimerkkinä (2007–2009) ja sitä seuranneen geologisen mallinnuksen kehittäminen (2010) -hankkeiden tulokset. Hankkeiden tavoitteena oli soveltaa ja arvioida 3D/4D mallinnusohjelmistoja ja esittää Suomen kallioperälle tyypillisten
monimutkaisten rakenteiden mallinnuksen periaatteita. Lisäksi tavoitteena oli
antaa suosituksia 3D-mallinnuksen tekemisestä GTK:ssa.
Hankkeiden tuloksena syntyi suositus Suomen kallioperän muodostumien
3D- mallinnusprosessista, eri mittakaavaisia Outokummun alueen malmien
ja kivilajimuodostumien 3D-malleja sekä Noora Salmisen diplomityö mikrorakenteista.
Asiasanat (Geosanasto, GTK): kallioperä, metamorfiset kivet, rakennegeologia, metallimalmit, malmiot, kolmiulotteiset mallit, proterotsooinen, Outokumpu, Suomi
Eevaliisa Laine
Geologian tutkimuskeskus
PL 96
02151 Espoo
Sähköposti: [email protected]
CONTENTS
Editor’s Preface by Eevaliisa Laine..........................................................................................5
Problems and challenges of 3D modeling of the Precambrian of Finland
by Eevaliisa Laine and Kerstin Saalmann.................................................................................7
1 Introduction................................................................................................................. 8
2 3D geological models.................................................................................................. 10
3 Data used for 3D modeling......................................................................................... 12
4 Building a 3D geological model ................................................................................. 14
5 3D geological software packages................................................................................ 26
6 3D geological modeling process.................................................................................. 26
7 Practical considerations.............................................................................................. 28
8 Conclusions................................................................................................................ 29
Supplementary information on the web............................................................................ 29
References......................................................................................................................... 29
3D modeling of polydeformed and metamorphosed rocks at different scales
using geological and geophysical data from Outokumpu area
by Eevaliisa Laine, Esko Koistinen, Kerstin Saalmann, Gabriel Couirrioux, Rosa Diaz,
Noora Salminen and Timo Tervo............................................................................................ 31
1 Introduction............................................................................................................... 32
2 Geology of the Outokumpu region............................................................................. 33
3 Rock walls and microstructures in 3D........................................................................ 35
4 Ore models................................................................................................................. 43
5 3D modeling of the Outokumpu assemblage.............................................................. 52
6 3D modeling of the Sola serpentinites........................................................................ 60
7 3D model of the Vuonos area including detailed seismic FIRE-sections ................... 62
Supplementary information on the web ............................................................................ 66
References......................................................................................................................... 66
3D-pdf’s............................................................................................................................ 66
Three-dimensional modeling of the Outokumpu nappe area, SE Finland
by Tapio Ruotoistenmäki and Esko Koistinen......................................................................... 67
1 Introduction............................................................................................................... 68
2 General geology of the study area.............................................................................. 68
3 Major geophysical formations in the study area.......................................................... 69
4 Major structures of the Outokumpu nappe area........................................................ 70
5 Preparation of the three-dimensional model............................................................... 72
6 Conclusions................................................................................................................ 74
References......................................................................................................................... 74
Acknowledgements........................................................................................................... 75
4
3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study
Edited by Eevaliisa Laine
Geological Survey of Finland, Report of Investigation 195, 2012
EDITOR’S PREFACE
The present work summarizes the results of the project “3D/4D
modeling – Outokumpu area as a case study” conducted during 2007–2009 and 3D modeling of the Outokumpu assemblage
in the project “Development of geological 3D modeling using
structural geology and geostatistics” in 2010 at the Geological
Survey of Finland (GTK). The aims of these projects were to
apply and evaluate 3D/4D modeling software and formulate
principles for visualizing and analyzing complicated geological
structures typical of Finnish bedrock. The aim was to make recommendations for the use of 3D-modeling tools and processes
for 3D/4D modeling at GTK.
Geological 3D modeling combines 3D visualization with the
interpretation and interpolation of subsurface lithological and
tectonic structures and their relation to each other. It differs
from 2-dimensional mapping in the smaller amount of data that
are often unevenly distributed and often restricted to clustered
drill holes with large gaps between drilled areas. In cases of very
sparse data sets, a subsurface model is more or less a visualization of present ideas of the subsurface. 4D modeling means the
visualization of changes in rock formations as a function of time
in 3D. The important task is to restore the original rock structures before deformation. The present report concentrates on
geological 3D modeling, even though this is not possible without
understanding the geological processes as a function of time.
The tools and methods were tested by building geological
3D models of targets within the Outokumpu area by combining geological and geophysical data, applying geomathematical
methods (e.g. statistics) and by using different geological software packages (Fig. 1). The Outokumpu area was chosen because it includes several old ore deposits that have been studied
and mined since 1913. An important data source was the GEOMEX project from1998 to 2003 (http://vsa.gtk.fi/geomex/html/
source/start.html), which investigated the geological character,
evolution and metallogenic potential of the Outokumpu region
in Northern Karelia.
3D/4D project researchers came from GTK offices in Espoo,
Kuopio and Rovaniemi. Juhani Ojala and Nicole Patison from
Rovaniemi, Jouni Lerssi, Timo Tervo and Peter Sorjonen-Ward
from Kuopio and Esko Koistinen, Kerstin Saalmann, Tapio
Ruotoistenmäki and Eevaliisa Laine from Espoo worked in the
project workshops and 3D modeling. Gabriel Coirrioux from
BRGM (France) guided us in the use of GeoModeller software. Noora Salminen completed her Master’s Thesis on microstructures at the Horsmanaho and Sola open pits at Helsinki
University of Technology. Gyorgy Havas from the Hungarian
Geological Survey and Anneli Lindh from GTK Espoo office
constructed the elevation model of the Outokumpu area. Finally,
5
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine
Rosa Diaz from Huelva University (Spain) modeled the Sola serpentinite bodies using Surpac mining software. Nils Gustavsson
from the GTK Espoo office acted as a geomathematical expert
by providing many useful ideas for the project. The geological
modeling software included Gocad® by Paradigm, GeoModeller by Intrepid Geosciences and ISATIS from Geovariances, Surpac and Gems by Gemcom and Sirovision developed by CSIRO.
These represent the main types of geological 3D modeling software among several similar software packages for geological 3D
modeling. In addition general purpose softwares, such as Matlab
(MathWorks), were used in 3D modeling. The main emphasis
was on 3D modeling processes – not on the software.
The 3D/4D modeling project resulted in suggestions for geological 3D modeling methods and processes presented by Eevaliisa Laine and Kerstin Saalmann and geological 3D models at different scales by Esko Koistinen, Kerstin Saalmann, Timo Tervo,
Tapio Ruotoistenmäki and Eevaliisa Laine from GTK (Geological Survey of Finland), Gabriel Coirrioux from BRGM (France),
Rosa Diaz from the University of Huelva and Noora Salminen
from Helsinki University of Technology during 2007–2010, and
the regional 3D model constructed by Tapio Ruotoistenmäki
and Esko Koistinen using regional geophysical data. In addition,
Noora Salminen completed her Master’s thesis, entitled Microstructures in 3D modelling, Outokumpu area as an example site,
for the Department 3D
of Geological
Civil and Modeling
Environmental Engineering at
Helsinki University of Technology.
Outokumpu Cu-Ni-Co mining area as a case study
DATA
GEOMEX project
Other geological and geophysical data from the area
Geological theories and hypothesis for the origin of the
Outokumpu assemblage
METHODS
3D software
Geological inference
Geomathematical methods
3D modeling workshops
RESULTS
A suggestion for a work flow for 3D modeling of
Precambrian bedrock in Finland
Geological 3D models at different scales based on
geological and geophysical data from the Outokumpu
area
Discussion of problems and challenges in 3D geological
modeling
Fig. 1. 3D/4D modeling project, Outokumpu area as a case study.
6
3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study
Edited by Eevaliisa Laine
Geological Survey of Finland, Report of Investigation 195, 2012
Problems and chaLlenges of 3D
modeling of the Precambrian of
Finland
by
Eevaliisa Laine* and Kerstin Saalmann
Laine, E. & Saalmann, K. 2012. Problems and challenges of 3D modeling of
the Precambrian of Finland. Geological Survey of Finland. Report of Investigation 195, 17 figures.
Geological 3D modeling of complex geological structures has many challenges beginning with data organization. Because the structures and lithologies
have complex relationships with each other it is very difficult to predict the continuation of any structure to great depths, especially because there are practically no direct geological observations below 500 m. Large regional 3D models
should be based on geological expertise and indirect geophysical data. Interpretations are sometimes difficult, even at a smaller scale, because of the locally
high variability of lithologies. The use of different approaches and software
is needed in a comprehensive data capture and 3D visualization of complex
geology, such as present at the Outokumpu area. It is also evident that purely
technical visualization without involving geological ideas and interpretations
is impossible.
Keywords (GeoRef Thesaurus, AGI): bedrock, structural geology, topography,
three-dimensional models, data processing, Precambrian, Outokumpu, Finland
*Eevaliisa Laine
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
*E-mail: [email protected]
7
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
1 Introduction
A geological map displays geological features in a
plane. Rock units are shown by color or symbols
to indicate where they are exposed at the surface.
Actually, a map is a 2D illustration of a 3D geometry. Structural features such as faults, folds and
foliations are shown with strike and dip. These
tectonic symbols in addition to elevation lines
give the three-dimensional orientations of the
features. In general, geological maps also show
elevation lines, allowing the reconstruction of the
3D geometry. For this reason geological maps
have been considered as 2½ dimensional. Hence,
a geological map includes 3D information, and
an experienced geologist is able to see the third
dimension through a planar map.
Vertical cross sections are often drawn in order to visualize geology in the third dimension.
Because of recent developments in 3D modeling
software, it is nowadays possible to visualize geological subsurface structures and construct solid
models for further computation and modeling.
Geological 3D modeling combines 3D visualization with interpretation and interpolation of subsurface lithological and tectonic structures and
their relation to each other. It differs from 2D
mapping in terms of limited data that is often unevenly distributed and often restricted to clustered
drill holes with large gaps between drilled areas.
In cases of very sparse data sets, the subsurface
model is more or less a visualization of present
ideas concerning the subsurface. These models
may be improved by geophysical forward modeling and inversion. Despite these uncertainties,
these models are important in many applications
such as modeling of ore bodies, ore evaluation,
hydrocarbon exploration and engineering applications. The models can be used for the calculation and simulation of geological processes such
as fluid flow and thermal convection and conduction. It is also important to visualize 3D geology
to aid research and present interesting geological
sites to the public.
Geological 3D models have to take into account geological structures and their contact relations. In addition, an important task is to be able
to handle, measure and present the uncertainties
associated with geological 3D models. The uncertainties depend on the amount, distribution and
quality of data, bedrock heterogeneity and the
accuracy of local geological interpretations. The
uncertainty, especially related to geological data
from Finland, has been discussed in depth by Nils
Gustavsson (2010). The 3D visualization of uncertainties has recently been discussed, for exam-
8
ple, by Viard et al. (2011). Even though this is not
the topic of the present report, the uncertainty
will be touched on when different aspects of 3D
modeling are discussed.
During recent years there has been strong development of geological 3D modeling software.
In addition, many books and articles have been
written about the principles of geological 3D
modeling and new concepts have been defined or
suggested (e.g. Caumon et al. 2009; Kessler et al.
2009; Fernández et al. 2004; Gjøystdal et al. 1985;
Saksa 1995; Groshong, 2006; Mallet 1997, 2002;
Calcagno et al. 2008).
In his book Geomodeling, Mallet (2002) proposed in his book Geomodelling the notion of
geomodeling that emphasizes the specific nature
of 3D modeling:
“Geomodeling consists of the set of all the
mathematical methods allowing to model in
an unified way the topology, the geometry and
the physical properties of geological objects
while taking into account any type of data related to these objects.”
The first 3D geological models were drawings
and block models. In Finland,the most famous
block models have been done by Adolf Metzger
(e.g. Metzger, 1928). In addition, fence diagrams
and sometimes small sculptures of ore bodies (e.g.
a bronze model of the Keretti deposit shown in
Fig. 11 by Laine et al. 2012 in this volume) have
been used to visual subsurface structures before
computerized 3D modeling. The first Finnish
software for 3D geological modeling (Minenet)
was developed by Outokumpu Oy in the 1980s
(e.g. Brusila, 1983). In the 1990s it was replaced
by mining software packages such as Surpac and
Gems. The second Finnish software package is
RockCAD that was developed by consulting and
engineering company Pöyry in the 1990s for the
nuclear waste studies (Saksa, 1995). RockCAD
is a modelling system and 3D software tool for
geological and environmental subsurface studies. It runs in the AutoCAD environment, one of
most widely used CAD programs in the world.
RockCAD utilizes a project-based approach. The
sofware runs in standard Windows PC environment. RockCAD contains useful functions that
allow the construction of 3D earth models and
presentation of ground investigation data. Despite its good qualities, the software is not generally used in Finland. The AutoCAD software
has been also used directly in 3D modeling of
structural and metamorphic patterns by Timo
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Kilpeläinen (1998). In Finland, the main applications of the 3D modeling have been related to ore
deposit modeling (e.g. Parkkinen 2003), groundwater modeling (e.g. Luoma et al. 2010), nuclear
waste site studies (Mattila et al. 2007) and, in
general, geoenvironmental studies.
Worldwide, 3D modeling is widely used in hydrocarbon exploration in sedimentary basins with
a well known stratigraphy that is only weakly de-
A)
formed (mainly by faulting). Many 3D geological software packages have been developed for
this purpose. Modeling of highly metamorphosed
rocks is challenging because of the complex deformation and lack of established stratigraphic
relationships.
In the following we provide examples of Finnish bedrock modeling and discuss the challenges
and possible solutions. The examples are from the
Outokumpu region (Fig. 1). This region is located
in the North Karelia Schist Belt, which was thrust
on the late Archaean gneissic–granitoid basement
of the Karelian craton during the early stages of
the Svecofennian Orogeny between 1.92 and 1.87
Ga (Koistinen 1981).
B)
Fig. 1. A) Location of the Outokumpu area; B) Regional geology after Korsman et al. (1997).
9
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
2 3D geological models
3D geological models differ in scale, application,
use of geometry and applied interpolation methods. Regional 3D geological models cover areas
of tens of kilometers. In very large 3D models,
the vertical extent becomes small relative to horizontal dimensions, and in the visualization the
vertical dimension has to be exaggerated. Depending on the thickness of the investigated sections, ranging from less than one to 60 km, the
z-axis representing depth may become too small
as compared to the horizontal dimensions when
the horizontal scales are much larger. A value of
100 km may be kept as an upper limit for the horizontal extent, even for crustal-scale modeling, because the depth information otherwise becomes
lost. There is also very little direct geological observation below 500 meters. In the case of a regional model, the geological structures are based
on geological sections, potential fields and seismic
surveys. Here, geological ideas and theories concerning the regional geology play an important
role, for example in the case of the regional 3D
model of the Outokumpu area, with a size of 120
km x120 km x 40 km (Fig. 2A), prepared by Ruotoistenmäki & Koistinen (2012) in this volume.
In ore deposit and geoenvironmental studies,
such as nuclear waste site studies, abundant drillhole data or other data are available and the 3D
model may be data driven. Nevertheless, there is a
need for interpretation. The 3D model of the Outokumpu assemblage, including the surrounding
black schists (Fig. 2B), is based on vertical sections interpreted by Koistinen (Gaál et al. 1975)
and drill-hole data.
The smallest scale structures used in the project
are 3D visualizations of rock textures and microstructures. The 3D visualization in these cases depends on technical tools that are applied in photographing. 3D modeling of microstructures of
rock samples from the Horsmanaho open pit in
10
the Outokumpu area was performed by studying
oriented thin sections cut differently relative to
the tectonic directions under a polarizing microscope (Salminen 2009). The main difficulty was in
the relative positioning of oriented thin sections.
Geological 3D modeling simplifies the structures according to the scale. Lithological contacts are modeled by smooth surfaces, even if the
boundary between different rock types is often
gradational and usually very uneven because of
minor folding and primary irregularities of geological formations. Faults are also modeled as
surfaces of constant thickness, disregarding the
fact that their width can change from meters to
centimeters. A good example is the near vertical Kaasila fault cutting the Outokumpu ore
(Koistinen 1981), the width of which varies from
10 cm to a few meters (pers. comm. T. Koistinen).
Rock properties such as geochemical composition and petrophysical properties are usually presented as colored symbols in 3D and interpolated
into a 3D grid. The most common approach is to
use a rectangular grid and some mathematical interpolation such as the inverse distance method or
geostatistical kriging interpolation, which is based
on the stochastic model for spatial correlation
(e.g. Chilés & Delfiner 1999). The latter method
provides a possibility to study anisotropy structures and a kriging variance, which is a measure
of variability and thus, a type of measure of the
uncertainty (e.g. Rocha & Yamamoto 2000). The
rectangular grid is not adequate for undulating or
folded natural formations. A better approach is
to use a stratigraphic grid defined by undulating
layers. However, in Precambrian rocks the local
orientations are so variable that it is not always
possible to build a stratigraphic grid. The use of
local orientations selected from the geological
and geophysical data (Laine 1998) could be an
alternative in the interpolation of rock properties.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
A)
B)
Fig. 2. A) Regional model of the Outokumpu nappe based on geophysical data and interpretation of Tapio Ruotoistenmäki
(Ruotoistenmäki & Koistinen 2012, in this volume). The width of the nappe formation is about 40 km B) Geological model of
Outokumpu assemblage, including surrounding black schists, based on drill-hole data and several geological sections (Laine et
al. 2012, in this volume). Surrounded mica gneisses are not included. The width of the Outokumpu formation is about 1.5 km.
11
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
3 Data used for 3D modeling
Data for 3D geological modeling are derived from
various sources, including geological maps and
cross sections, geological outcrop observations,
drill-hole logs, geophysical maps and surveys. The
obvious problems related to data from several
sources are their different resolutions and scales.
Drill-hole data provide information on changes
in properties within a few centimeters, while large
kilometer-scale structures are mainly interpreted
from deep seismic sections.
Geological maps and sections are interpretations of outcrop observations and geophysical
maps. Thus, they do not present raw data, and
different interpretations lead to different kinds of
3D geological models. On the other hand, the 3D
modeling process may lead to new interpretations
of the stratigraphic relationships, which may in
turn change the geological map. This fact illustrates the difficulties when separating 2D and 3D
geological databases. A better approach would be
to construct two databases, one containing raw
data (1D, 2D, 3D) and the other storing geological models that result from the interpretation and
usage of raw data and which will be updated according to the availability of new data and geological theories. Outcrop data may be regarded as
geological raw data, even though every geological
observation includes interpretation. Geological
observations also reflect the time during which
they have been recorded.
Drill-hole logs contain detailed information on
rock types as well as geochemical and geophysical
properties. Naturally, the form of data collected
depends on the final purpose of the drilling. Lithologies are named in much more detail than
found on the corresponding geological maps.
Old drill-hole logs may also include rock types
based on quite different interpretation from present classifications. The process of unifying rock
names aiming to define rock units that can be
modeled at the desired scale may not be an easy
task. For example, the GEOMEX project (http://
vsa.gtk.fi/geomex/html/source/start.html) performed
significant work in unifying the lithologies in the
Outokumpu area according to the new interpretation of the alteration of the serpentinite body
(Peltonen et al. 2008).
The definition of rock units is accompanied by
the selection and drawing of the main discontinuity structures such as faults and shear zones interpreted from geophysical maps and sections, elevation data and outcrops. Understanding of the
12
kinematics of the fracture system and the relative
ages of fractures is needed in 3D modeling in order to properly draw lithologies between discontinuity surfaces.
Geophysical data are used in many stages of 3D
geological modeling, for example:
1.Geological maps are based on geophysical
data in areas covered by Quaternary deposits.
Lithologies observed from the outcrops are
connected by using geophysical maps. For example, the geological map of the Outokumpu
area (Fig. 3) has been drawn by using geophysical data especially magnetic low-altitude maps
(GTK).
2.Geological discontinuities such as faults and
shear zones are often interpreted from the geophysical data, and the nature of the discontinuity structure is determined by geological expertise.
3.Geological sections may be prepared by geophysical 2D inversion and used in 3D modeling
together with geological sections.
4.The 3D geological models obtained may be improved by using 3D inversion (e.g., Scales et al.
2001)
5.3D inversion may also be used in analyzing
the subsurface distribution of the petrophysical properties in order to build a 3D geological
model together with surface observations.
6.In addition, sophisticated geophysical map
processing has been used in order to understand bedrock structures in covered areas in
Finland. One example is the study of black
shales in Finnish bedrock by Airo et al. (2009).
The above is not a complete list of available data,
but it already gives an impression of the variety
of data sources, and the data list shows the need
to involve different experts in the 3D geological
modeling process. The visualization of all the
data in 3D may already help in understanding
the subsurface structures. However, it can very
often be confusing to consider too many different data sets at the same time. One of the major
future challenges is to find working practices for
handling and interpreting various 3D data sets. It
is important to make a difference between measured data such as geophysical and geochemical
data and interpretations such as geological maps
and sections.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Fig. 3. The magnetic low-altitude map of Outokumpu area processed by Timo Tervo (GTK) (red mark the highest values and
blue the lowest ones) and geologic map of the Outokumpu area compiled by T. Koistinen (Gáal et al. 1975).
13
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
4 Building a 3D geological model
Subsurface geology is often visualized or presented using cross sections. In the Outokumpu area
cross sections were drawn across the Outokumpu
assemblage rocks (Koistinen 1981, Fig. 3) . Data
available from the drill-holes, as in the case of
Outokumpu sections, help to contrain the subsurface geology in a cross section. Nevertheless,
there is room for interpretation, especially when
interpreting heterogenous and multiply deformed
midcrustal rocks. In addition, the bedrock of the
Outokumpu area is covered by Quaternary deposits, so there are very few direct observations
of the bedrock surface and the geological map is
strongly based on geophysical data. This is not an
uncommon situation in Finland because, in most
places, the bedrock is covered with the Quaternary deposits.
Because folding, shearing and faulting strongly
affect the midcrustal bedrock understanding of
tectono-magmatic and metamorphic evolution is
essential in drawing cross sections. In Figure 3 the
Outokumpu sections have been presented together with the geological map. This is one option to
visualize geology in 3D, and, is known as a fence
diagram.
Before computer applications, 3D visualizations were carried out using a block diagram that
illustrates the relationship between the surface
and subsurface structure by using an imaginary
block cut out of the earth’s crust. The top of the
block shows the areal geological map and the vertical sides represent geological sections. A block
diagram presents a three-dimensional picture that
helps to understand 3D structures. Figure 5 presents a block diagram of the Outokumpu assemblage from the Sola area. The applied projection
is isometric, in which all of the distances are equal
to the measurements along the corresponding directions in the maps and cross sections.
In addition to different kinds of geometrical
drawings and constructions (see eg. Groshong
2006), geologists like to make sketches in 3D. As
an example, a schematic diagram of the structural position of the Vuonos orebody by Koistinen
(1981) is presented in Figure 6. Diagrams of this
kind are still important in illustrating geological
ideas and theories. One of the challenges in computerized 3D geological modeling is to transfer
these ideas into the digital world.
Fig. 4. A Fence diagram of the Outokumpu assemblage after the geological map and cross sections by Koistinen (1981).
Reproduced by permission of the Royal Society of Edinburgh from Transactions of the Royal Society of Edinburgh: Earth
Sciences volume 72 (1981), 115–158.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Fig. 5. A block diagram of the Sola serpentinite massif and surroundings (Gaál et al. 1975). The Sola Cu-Co mineralization
is shown by red spots. (Kontinen et al. 2006.)
Fig. 6. A schematic diagram of the structural position of the Vuonos orebody (after Koistinen 1981). F1 and F2 are folding
generations and -2—marks the scistocity associated with the F2-folding. Reproduced by permission of the Royal Society of
Edinburgh from Transactions of the Royal Society of Edinburgh: Earth Sciences volume 72 (1981), 115–158.
15
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
Description of the geometries of the geological formations
3D modeling requires the description of the geologic formations and structures and their topological relationships. Some of the important features to
be included into the 3D models are listed below by
using examples from the Outokumpu Ore District,
a metallogenic province about 100 km long x 60
km wide that is defined by the occurrence of bodies of massive sulfide and minor disseminations.
• The topography gives the upper surface for the
3D model The topography of the Outokumpu area is rather flat, and an elevation model
has been constructed by the Land Survey of
Finland. In addition, elevation lines and water depths were used in order to build a more
detailed elevation model for the Outokumpu
area. This represents the upper surface of the
Quaternary deposits, which cover over 80% of
the land surface in Finland. In near future, the
whole of Finland will be measured using laser
scanning by the Land Survey of Finland in order to provide very detail elevation models.
• Bedrock topography gives the upper surface for
the bedrock, that is difficult to determine in
areas with thick post glacial layers, as is case
in large areas of Finland. In the Outokumpu
area, drill-hole data can be used in estimating
the thickness of the Quaternary deposits, and
it is therefore possible to reconstruct the bedrock surface. In areas where there is no drilling,
the bedrock surface may be defined by using
geophysical methods such as gravity, seismic
refraction and ground penetrating radar. This
surface is erosional and cuts all the older bedrock structures.
• Faulting and jointing is very common in the Precambrian bedrock in Finland. Locally it has a
pronounced effect on the bedrock structures,
and fault movements of several meters (e.g. the
Kaasila fault) affect the ore continuity and, in
turn ore exploration. Rock fracturing at different scales should be carefully modeled, preferably as the first step in 3D modeling. This may be
very difficult in areas with only a few outcrops.
Well-documented studies of rock fracturing exist from southern Finland (e.g. Pajunen et. al.
2008; Viola et al. 2011). The most difficult task
is to trace these often undulating and variably
thick structures to greater depths.
• Finally, the lithological units may be lineated. If
the lithological contacts are modeled by surfaces, the rock type classification need to be done
so that it is possible separate different rock
units by smooth surfaces representing lithological contacts. The Outokumpu assemblage that
hosts the ore is separated from the surrounding
mica schists and gneisses by black schist. On a
large scale it is possible to model the combination of the Outokumpu assemblage and black
schists as a single unit in the surrounding schists.
Simplification is necessary because a 3D model
using more detailed rock classification is almost
impossible to construct as both host rocks and
ores show the effects of polyphase deformation
and polymetamorphism (Koistinen 1981).
The above-described structural features and
lithological contacts are modeled by surfaces in
3D modeling software. 3D modeling in 3D geomodeling software usually begins with the digitizing of geological features from geological and
geophysical maps and cross sections (Fig. 7). 3D
models are then built using these digitized points
and lines, together with drill-hole data. Digitized
points and lines are connected into surfaces representing lithological contacts, faults and shear
zones using tectonic observations and taking into
account the relative ages of formations. Geological understanding of the structural geology is essential because lithologies may be connected in
many different ways based only on the drill-hole
data (Fig. 8). In this stage the main interpretation
is carried out. Every time a point is added outside
the known objects (points, drill holes), an interpretation is made.
There are several approaches to connecting the
lines and points into surfaces in 3D. The main approaches applied in 3D geological modeling are
described below in order to present the important
differences that affect the whole 3D geological
modeling process.
Triangulation
The most common method to build geological
boundaries is triangulation. Triangulation is the
division of a surface or plane polygon into a set
of triangles, usually with the restriction that each
triangle side is entirely shared by two adjacent
triangles. There are numerous algorithms for com16
puting triangulations in 2D and 3D. Delaunay
triangulation (Jones & Nelson 1992) is often used
because it ensures that the circumcircle associated
with each triangle contains no other point in its
interior.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
A)
B)
Fig. 7. A) Drill holes and B) the corresponding geological section interpretation (Kontinen et al. 2006) from Sola.
17
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
Fig. 8. Many different possibilities for section interpretation.
Triangulation honors the known data values.
Accordingly, the resulting model strongly depends on the amount of available data. Because
the data points are often irregularly sampled, direct triangulation seldom produces a good quality
mesh (Fig. 9). Geological interpretation of differently oriented cross sections provides more data
and results in a more realistic 3D model on the
assumption that the underlying geological model
is meaningful. Instead of using digitized points,
it is easier to model complicated structures by using digitized lines, as illustrated in Figure 8. Elongated ore bodies and faulted ore bodies such as
the Outokumpu ore have been modeled by connecting closed curves enclosing the ore in sections
using triangulation (Fig. 10).
Fig. 9. The bedrock surface was constructed from the elevation points extracted from drill-hole data by triangulation.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Fig. 10. The thin Outokumpu ore bodies modeled by traditional section-by-section interpretation using geological sections.
This seems to be the best way to delineate these thin and irregularly shaped orebodies. Modelling was performed by Esko
Koistinen using Gemcom GEMS software.
Interpolation of 3D surfaces using mathematical tools
Different interpolation techniques such as inverse
distance and kriging interpolation are often applied. These interpolation methods estimate the
elevation z as a function of geographic coordinates (x and y). The interpolation usually consists
of
1. the building of a regular grid according to the
study area;
2. in the case of kriging interpolation, variogram
modeling is needed in order to build a spatial
statistical model for spatial correlation; and
finally
3. calculation of the estimated values in a regular
grid.
This type of interpolation works with surfaces
without overturned folding or faulting. There can
be only one z-value for the same location. For example, the Outokumpu bedrock surface can be interpolated by using inverse distance (Fig. 11). The
SE–NW trends possibly reflect the fracturing in
the same orientation. Sometimes gridding shows
better features that are not obvious on the triangulated presentation.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
Fig. 11. The Outokumpu bedrock surface interpolated using inverse distance method and drill-hole data by ISATIS software.
Indirect surface construction
Caumon et al. (2009) have suggested one way to
avoid the limitations of direct triangulation methods using Paradigm GOCAD® software and the
following steps:
1. The surface boundary is first determined.
2. This boundary is then densified and filtered so
that all the edges of the polygon have roughly
the same length.
3. A surface is triangulated using this boundary.
4. This surface is fitted to the data points using
discrete smooth interpolation. DSI optimizes
all three spatial coordinates of mesh vertices
under a large set of constraints (Mallet 1992,
20
1997, 2002). Briefly, DSI solves the optimal
location of the surface nodes to minimize a
weighted sum of the surface roughness and the
constraint misfit.
One shear zone within the Outokumpu assemblage was modeled by using indirect surface construction in Paradigm GOCAD® software (Fig.
12). The shear zone was interpreted by Koistinen
(1981). These interpretations were digitized as
lines from cross sections and these lines were used
to build a surface representing the shear zone that
cuts the Outokumpu Assemblage.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Fig. 12. Indirect surface construction by using GOCAD®software. A) a median plane for the digitized lines; B) indirect surface construction of the shear zone; C) the obtained shear zone (in white) visualized together with Vuonos ore body (in red),
a boundary for the Outokumpu Assemblage (green) and a geological cross section reproduced by permission of the Royal
Society of Edinburgh from Transactions of the Royal Society of Edinburgh: Earth Sciences volume 72 (1981), 115-158.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
Implicit representations of surfaces
Explicit representation means the previously described triangulation and other interpolation
methods for estimating z=f(x,y) in building surfaces. The implicit representation is done by isosurfaces of a 3D scalar field (f(x,y,z)=constant).
Carr et al. 2001) proposed a method by computing the parameters of Radial Basis Function for
interpolating discrete data and reconstruct compex shapes. Ledez (2002) used Euclidean Distance Transforms computed on a Cartesian grid
for reconstructing complex geometries. Discrete
Smooth Interpolation (Mallet, 1992 and 2002)
has also been used in building the scalar field on a
discrete volumetric mesh (e.g. Frank et al. 2007).
As an example of the use of implicit representation, the application of co-kriging in computing
the scalar field (e.g. Calcagno et al. 2008) is presented. Calcagno et al. (2008) call the approach
a potential-field interpolation method. The Sola
sernetinite contact with the surrounded mica
schist was modeled by using GeoModeller software (Fig. 13).
In the case of sparse geological data, 3D models may be constructed by using lithological con-
tact points and orientation data using a potential-field interpolation method by Calgacno et al.
(2008) based on the earlier work of Lajaunie et
al. (1997). The method is based on the following
assumptions:
1. a geological interface limits two geological formations;
2. some orientation data sampled within geological formations are relevant to model the interfaces separating the formations;
3. the interfaces to be modeled may be regarded
as belonging to an infinite set of surfaces
aligned with the orientation field.
Calgagno et al. (2008) described this interpolation method as being close to classical geological
thinking in the sense that it attempts to reproduce
the natural drawing of a geologist simultaneously
guided by the knowledge of structural data.
Structural data are used in the interpolation
or building of the surfaces representing lithological contacts. This interpolation is performed by
cokriging (null) increment data (i.e. the change in
potential between any two points belonging to the
Fig. 13. Sola serpentinite and enveloping black schist by using Geomodeller software.
22
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
same geologic interface is null) and their derivatives (orientation data representing the gradient
or derivative of the field) according to Lajaunie
et al. (1997).
In the case where nearby layers share a geological history, combining the layers into a single series has the major advantage that data from one
horizon can influence the shape of other nearby
horizons, and vice versa. Measurements of strike
and dip recorded anywhere within the series will
all be taken into account at their point of measurement. In cases where the geological history is
more complex, and geological horizons are not
subparallel, separate potential interpolators must
be used – one for each series of strata. In this case
it is necessary to define the stratigraphic column,
which records the chronological order of the strata, and also the relationships (either ‘onlap’ or
‘erode’). Where two geological surfaces from different potential interpolators intersect, an ‘erode’
surface cuts across any stratigraphically older
horizons, whereas an ‘onlap’ surface would ‘stop’
against the older surface.
The use of lithological contacts and stratigraphic layering is challenging in the case of midcrustal rocks, because lithological boundaries are
not clear and often gradational. The use of any
stratigraphy is also difficult because of shearing
and faulting, which may be intense and difficult to
model in 3D. Partial or total melting also makes it
difficult to follow any particular horizon very far.
In the Outokumpu area, the clear erode surface is
the boundary between Quaternary deposits and
the bedrock. All the other surfaces are ‘onlap’.
It is not easy to decide when we can apply series
and when to separate them. As an example, Sola
serpentinite was modeled using this approach in
GeoModeller software (Fig. 12). The black schist
enveloping the serpentinite body could not be
modeled separately but was included into serpentinite. This interpretation differs from the the one
presented using the block model (Fig. 5).
Other methods for surface construction
There are several other methods for surface construction. For example, de Kemp & Sprague 2003
have presented a method to use sparse structural
data in surface construction. Presently this tool
is available as a SPARSE module in Paradigm
Gocad®.
The choice of particular surface construction
method depends on geometries of geological formations and on the data density. In addition to
lithological contacts, it is important to be able to
model discontinuities and folding.
3D modeling of discontinuity surfaces faults and shear zones
Faults and shear zones can be presented or visualized as surfaces, even though they are not necessarily continuous and their properties such as
thickness and structure vary. This makes it difficult
to connect them from drill hole to drill hole or between seismic sections (e.g. Markovaara-Koivisto
et al. 2009). The relative ages of faults and shear
zones are necessary but sometimes quite difficult
to determine because of the scarcity of outcrops.
Many of the 3D modeling software packages are
capable of handling faults and shear zones by:
1. presenting a fault or a shear zone in 3D and
cutting the lithological contacts with it;
2. using the information about which geological
formations are cut by the fault or shear zone;
3. using the relative ages of faults and shear
zones and showing these relationships in 3D
by stopping the structures on the older ones;
4. using the the fault dimensions in 3D modeling,
and
5. dividing the grid or voxet by a discontinuity
surface. This is important in interpolation, so
that the estimated values are not affected by
the values from the area across the fault or
shear.
3D modeling of folding
If fold structures have regular shapes they may be
modeled using automated tools in some of the 3D
geological software packages. For example, the
axial surface may be defined based on orientation
data and the axial surface may then be modeled.
The shape of the fold can be modeled using the
information whether it is anticline or syncline,
and additional parameters including the interlimb
angle.
In the case of the Outokumpu formation, the
23
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
interpreted folding is so intense and unregular
that it is not possible to make a simple mathematical model describing. However, locally using
structural geological expertice the simplified fold
patterns can be interpreted from the complicated
looking bedrock surfaces (Fig. 14).
Fig. 14. Horsmanaho open pit, the folded layers visible and the sample location x. Photo: Esko Koistinen, GTK and drawing:
Kerstin Saalmann.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Interpolation of rock properties
Geohemical compositions and
petrophysical properties are often
interpolated into a regular grid.
The volume for interpolation grid
should be divided using the obtained 3D model surfaces into
volumes within which it may be
assumed that geochemical and petrophysical properties are continuous, i.e. the applied mathematical
or statistical model is valid for
interpolation inside these subvolumes. Large changes in rock
properties occur across the lithological boundaries and tectonic
discontinuities. The rock properties change more across the layering than parallel to it. As the original or metamorphic layering is not
planar, rectilinear coordinates are
seldom an appropriate choice for
interpolation. The rock properties
should be investigated parallel to
lithological or structural features.
This can be carried out by using a
so-called stratigraphic grid or by
unfolding the data, i.e. transforming data into plane in order to be
able to use rectilinear coordinates.
The Figure 15 presents the stratigraphic grid along the slightly undulating Vuonos ore.
Fig. 15. Stratigraphic grid illustrating Nidistribution along the ore body colored
red.
25
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
5 3D geolOgical software packages
The present 3D geological software packages are
designed for different purposes, and accordingly
they use slightly different approaches. In the present study, different 3D software packages were
applied. There are several other software packages, and new ones will be developed along with
new computer technologies.
3D mining software packages aim to construct
ore solids. These software packages are able to analyze and composite drill-hole data. An essential
part is ore evaluation and often mine planning.
In addition to mining applications, these software
packages are also used in general geological 3D
modeling, such as Surpac in geological modeling
at the Olkiluoto nuclear waste site (e.g. Mattila et
al. 2007).
Many ‘general geological’ 3D software packages were originally planned for hydrocarbon exploration in sedimentary basins with a well-known
stratigraphy, which is then visualized using surfaces cut by discontinuities such as faults and unconformities. Presently, these are being applied in
modeling deformed rocks.
Geological software packages construct 3D
models using different approaches described in
the previous section. This is a critical property
that should be taken into account. Sometimes
it might be quite difficult to apply an approach
based on the known stratigraphy for strongly deformed rocks lacking any clear stratigraphic sequence.
These software packages also have individual
ways to save, import and export data. There might
be advantages in using software that directly uses
a general purpose database. In an ideal case, 3D
modeling software would work with a general
purpose database and be able to export 3D models in ASCII-format.
Most of 3D modeling software packages also
include numerical tools for statistical analysis,
and some contain modules for the simulation of
groundwater flow for the obtained model.
Based on our experience with the Outokumpu
case, a combination of different software packages is needed to construct a satisfactory model.
We have prepared the following list of wishes for
future 3D modeling tools in geology:
• Easier inclusion of drawings into the modeling
process. The best alternative could be a tool
for drawing directly into a model.
• Easier tools for changing and modifying parts
of models.
• It would also be good to be able to select modules that work independently in order to save
the computer capacity.
6 3D geological modeling process
The starting point of a 3D modeling process is
the interpretation or knowledge of the subsurface
geological structures. Before any further steps, the
major discontinuity structures, faults and shear
zones, should be known and their relative ages defined. These structures are key elements because
they divide the bedrock into separate units.
The collection and georeferencing of geological data is perhaps one of the most time-consuming parts of 3D modeling. Unifying the geological rock units from maps with those appearing in
drill holes may be difficult. The geological map of
the Outokumpu area (Gáal et al. 1975) contains
six rock types, whereas about 55 different rock
names were found for drill-hole lithologies. The
rock units used in our example are based on the
division of the GEOMEX project (Peltonen et al.
2008). Further simplification of the complex geology was achieved by defining the main structures
such as faults and folds.
26
The Outokumpu area has been affected by
a multiple-phase tectono-magmatic history
with polyphase folding and shearing of different orientations causing complex interference structures followed by polyphase fault
tectonics. The Outokumpu association was mod-
eled by using the geological model of Koistinen in
Gáal et al. (1975) (Fig. 2B). The modeling would
have been very difficult using solely drill-hole data
alone. Knowledge of the general trend and dip of
the structures and the geological map helps to
connect the lithologies in sections.
Areas built up of strongly metamorphosed
rocks, in particular in Precambrian terrains, often lack an established stratigraphy. Nevertheless,
rules can be determined for how the rock types
are distributed relative to each other, for example
cross-cutting relations and rock-type associations
related to certain tectonic, alteration or metamorphic events. Geometrical difficulties are caused
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
Fig. 16. Metamorphic rocks often show a layered structure due to intense deformation. The picture is from Hanko, illustrating
strongly deformed mafic and felsic layersin.
by overturned tight folds and lens-shaped bodies.
Relatively regular metamorphic layered structures
are found in Finnish bedrock, although these
rarely represent the primary layering (Fig. 16).
3D geological models are seldom fully realistic, and are not intended to be. This is because of
the lack of data. The correct idea for the form of
geological bodies helps in constructing a reliable
model. The way the software connects the points
to form a model also affects the results. Polygonal
shapes are caused by triangulation, while smooth
interpolated surfaces may leave out important
details. It should be kept in mind that all model
points outside the hard data points are a result of
interpretation.
In the case of Finnish bedrock and available
data, the following work flow could be recommended (Fig. 17):
1. Compilation of data and georeferencing.
2. Modeling of the surfaces of the youngest discontinuities that cut the geological formation
under study Digitizing of sections in the case
of abundant data and fairly linear bodies. In
the case of complicated bodies, a sophisticated
approach using tectonic orientations and contact points should be used. The latter approach
is also recommended if there is very little
knowledge of the subsurface and the model is
solely based on geological intuition or theory.
3. The use of geophysical data through forward
modeling in checking whether the obtained
model reproduces the measured potential
fields or signals. This is especially important in
the case of seismic surveys.
4. Improvement of the geological model using
geophysical inversion, i.e. optimization of the
model.
5. Saving the model together with hard data and
detailed documentation of the modeling process. A 3D model result should not be misunderstood to represent hard data. As we are
continuing a model outside the actual data
points, the model is uncertain. It is a result of
interpolation, extrapolation and interpretation, and also reflects the ideas and theories at
the time when it is constructed. Therefore, it
is more important to save the associated hard
data and to document the 3D modeling process together with underlying theories and a
discussion of uncertainties rather than saving
the geometric 3D objects alone.
In Figure 17 a workflow for a general 3D geological modeling process is presented. It shows also
possible applications of 3D geological models.
27
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Eevaliisa Laine and Kerstin Saalmann
7 Practical considerations
In 3D modeling it is important that geologists, 3D
modelers, and geophysicists work together. The
organization of the team work is not just a process of collecting people together, but demands
the learning of new methods of team work, communication, and dealing with ideas.
3D modeling demands a considerable amount
of time. Fast computers may create an illusion of
easy and rapid building of 3D geological models.
However, in order to build as reliable a 3D model
as possible, a considerable amount of data collection, georeferencing and digitizing work have to
be done, accompanied by many steps involving
cross-checking and continuous modification of
interpreted structures.
Fig. 17. A workflow diagram for a geological 3D modelling process.
28
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Problems and challenges of 3D modeling of the Precambrian of Finland
8 Conclusions
The biggest problem in the 3D modeling process
is the lack of data. The deepest data sources are
from depths above 1 km. Geophysical data can be
used to obtain some information on the spatial
distribution of petrophysical properties at depth.
However, geophysical fields and sections can be
interpreted in many ways. Several alternative explanations may exist for how the bedrock of the
certain area has been formed. Without extensive
drilling, the interpretation of the subsurface geology is more or less ‘informed guessing’, or simply
the visualization of someone’s geological ideas.
It would be also wise to use different geological ideas as starting points in 3D modeling when
searching for new ores or looking for possible nuclear waste sites. The few outcrop data may not
be sufficient to build a unique model of the subsurface geology. In the case of Outokumpu area a
lot of drill cores are available reaching a depth of
about 500 metres. Below that point structures are
continued using seismic sections. But the structures apparent on the seismic sections that do
not continue to the surface may not be correlated
with any of the surficial structures without deep
drilling. Still the modeling and 3D modeling is
the best way to get some idea about how the subsurface structures look like or what kind of structures are possible using all the available geological
and geophysical information.
Various software packages have certain
strengths, but also specific limitations. Complex
geology, the use of different data types and data
sets as well as different modeling approaches
makes it necessary to apply a number of software
packages.
We conclude that the use of different approaches is necessary for comprehensive data capture
and 3D visualization of complex geology, such as
present in the Outokumpu area. It is also evident
that purely technical visualization without involving geological ideas and interpretations is impossible.
It is important to understand that all models
contain a large degree of uncertainty, and very
different models may be constructed from the
same geological surface structures, geophysical
fields and reflections.
Supplementary information on the web
GEOMEX JV-project 1999–2003. Available at: http://vsa.
gtk.fi/geomex/html/source/start.html
Scales, John A., Smith, Martin L. & Sven Treitel 2001. Intro-
ductory Geophysical Inverse Theory. Available at: http://
samizdat.mines.edu
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3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study
Edited by Eevaliisa Laine
Geological Survey of Finland, Report of Investigation 195, 2012
3D MODELING OF POLYDEFORMED AND
METAMORPHOSED ROCKS AT DIFFERENT SCALES
USING GEOLOGICAL AND GEOPHYSICAL DATA
FROM OUTOKUMPU AREA
by
Eevaliisa Laine*, Esko Koistinen, Kerstin Saalmann,
Gabriel Coirrioux, Rosa Diaz, Noora Salminen and Timo Tervo
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. &
Tervo, T. 2012. 3d modeling of polydeformed and metamorphosed rocks at
different scales using geological and geophysical data from Outokumpu area.
Geological Survey of Finland. Report of Investigation 195, 41 figures.
3D models of the Outokumpu assemblage, the Keretti and Vuonos ore
bodies, and open pit rock walls at Horsmanaho have been constructed by using a variety of geological and geophysical data and by applying different approaches. Software packages used in the modeling process have different means
for interpolation and inference of geological structures such as lithological interfaces and faults. Different approaches are needed in order to model the complex contact relationships within Precambrian rocks. It is not always possible
to find geological cross sections for realistic 3D modeling of complicated fold
patterns. On the other hand, structural data in drill core loggings are usually
missing. The possibility of importing different data sets and models into the
same software platform facilitates the 3D interpretation of structures. However, the use of different approaches and data from several sources requires
detailed planning and documentation of the 3D modeling process.
Keywords (GeoRef Thesaurus, AGI): metal ores, ore bodies, metamorphic
rocks, three-dimensional models, structural geology, deep seismic sounding,
Paleoproterozoic, Keretti, Vuonos, Outokumpu, Finland
*Eevaliisa Laine
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
*E-mail: [email protected]
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
1 Introduction
The Outokumpu area was selected as a case study
for the 3D/4D project (at GTK 2007–2009) because of a long history of research, and hence the
availability of data from several sources. The mining history of this area extends from 1913 to 1988,
involving the exploitation of three major deposits: Outokumpu, Vuonos and Luikonlahti. Ou-
tokumpu and Vuonos deposits are considered in
more detail in this study. The use of different geological modeling techniques is presented through
examples according to the modeling scale (Fig. 1).
The smallest scale in this study was a few centimeters, i.e., 3D modeling of microstructures. Despite the problems with geocoding, pleochroism
A)
B)
Fig. 1. 3D modelling of the Outokumpu area at different scales. A) Regional geology Korsman et al. (1997) and the area for
the 3D geological model of Ruotoistenmäki & Koistinen (2011 in this volume). B) Geological map of the vicinity of Outokumpu by Tapio Koistinen in Gáal et al. (1975).
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
and interference colors, some planar structures
were modeled using thin section photographs in
the geological modeling software Paradigm Gocad® (http://www.earthdecision.com/index.html).
The results were presented by Salminen (2009) in
her Master’s thesis entitled ‘Microstructures in 3D
modeling, Outokumpu area as an example site.’
Rock walls in the open pit from Horsmanaho
and Sola represent the scale of tens of meters. 3D
models were constructed by transforming stereo
photographs with Sirovision software.
Keretti and Vuonos ores were modeled using
section drawings from the mines
and the traditional section-by-section interpretation method. This seems to be the best way to
delineate these thin and irregularly shaped ore
bodies, which were found to be rather continuous,
although locally truncated by vertical faults. The
triangulation into solid models was performed using Gems software in the case of Outokumpu ore
and Paradigm Gocad® in the case of Vuonos ore.
The ores are situated in the so-called Outo-
kumpu assemblage (Peltonen et al. 2008). This
assemblage and the associated black schists were
modeled by using geological sections and a geological map (Gáal et al. 1975) with GeoModeller
software (http://www.geomodeller.com). The resulting 3D models were combined and visualized
using Paradigm Gocad® (http://paraviewgeo.mirarco.org/index.php/Main_Page) and finally exported into 3DPDF formats.
The use of data from different sources was
demonstrated by visualizing the seismic sections
of the Outokumpu area together with together
with geological and geophysical maps using Paradigm Gocad®.
A regional 3D model of the area was inferred
from geophysical data by Ruotoistenmäki and
Koistinen (2010) and is presented in a chapter of
the present report.
The aim of this paper is to demonstrate the possibilities and limitations of 3D modeling with these
case studies.
2 Geology of the Outokumpu region
The Outokumpu mining district hosts a Palaeoproterozoic sulfide deposit characterized by
an unusual lithological association. It is located
in the North Karelia Schist Belt (Fig. 2), which
was thrust on the late Archaean gneissic–granitoid basement of the Karelian craton during the
early stages of the Svecofennian Orogeny between
1.92 and 1.87 Ga (Koistinen 1981). Two major
tectono-stratigraphic units can be distinguished,
(1) a lower, parautochthonous ‘Lower Kaleva’
unit and (2) an upper, allochthonous ‘upper Kaleva’ unit or ‘Outokumpu allochthon’. The latter
consists of tightly-folded deep marine turbiditic
mica schists and metagraywackes containing intercalations of black schist, and the Outo­kumpu
assemblage, which comprises ca. 1950 Ma old,
serpentinized peridotites surrounded by carbonate–calc-silicate (‘skarn’)–quartz rocks. The ore
body is enclosed in the Outokumpu assemblage,
which is thought to be part of a disrupted and
incomplete ophiolite complex (Vuollo & Piirainen
1989) that can be traced to the Kainuu schist belt
further north where the well-preserved Jormua
ophiolite is ex­posed (Kontinen 1987, Peltonen &
Kontinen 2004).
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
A)
B)
Fig. 2. A) Location of the Outokumpu area; B) Regional geology after Korsman et al. (1997).
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
3 Rock walls and microstructures in 3D
Rock walls were mapped and photographed in
the Horsmanaho quarries. Open pits are ideal for
understanding structures in 3D. For example, it is
easy to make observations of structures such as
faulting and schistosity from extensive rock walls
(Fig. 3).
3.1 Microstructures in 3D
Along with mapping of the quarry walls oriented
samples were taken. Thin sections are most commonly made from unoriented rock samples. In
this case, microstructures such as schistosity and
layering may be observed, as well as their mutual relationships. However, the orientation of
these is not related to any macroscopic features
in the rock. Oriented thin sections, in contrast,
allow these features to be related to macroscopic
structures such as schistosity or folds. The rock
slices chosen for the thin sections were oriented
parallel to the main planes of the strain ellipsoid; therefore, two section planes, XZ and YZ
were investigated for most rock samples; for 1 - 2
samples, the third plane, XY, was also included.
Microstructures alone generally do not provide
sufficient information without being linked with
field observations. A major aim was to visualize
the 3-dimensional microstructures coupled with
the 3D geometry on the outcrop scale in order to
illustrate how the microstructures reflect the outcrop patterns using 3D- modeling and 3D-visualization software.
The oriented sections from Horsmanaho are
presented as an example (Salminen 2009). The
rock type is black schist with a fairly high graphite content and strongly altered fracture surfaces.
Figure 4B illustrates the position of the sample
relative to the macroscopic folding at Horsmanaho. The photographs were taken using crossed
nicols in a polarizing microscope, and were georeferenced and imported into a Paradigm Gocad® project. The schistose structure was due to
the thin graphite layers (Fig. 4). It can be seen
that the shear zones and schistosity continue
from the vertical to the horizontal section, so
that the planes could be fitted and measured. The
obtained orientations are local because of the
scale of the study. In folded rocks the orientation
of layering is variable, so these orientations are
only meaningful when used in association with
outcrop observations. The study of oriented sections may provide an explanation for structures
observed macroscopically.
The whole process demands careful orientation
during sampling and thin section preparation.
Fig. 3. An example photograph from the Horsmanaho open pit. Photo: Esko Koistinen, GTK.
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Interference colors and phleochroism cannot be
observed in 3D view, and the interpretations of
structures could not therefor be carried out solely
using thin section photographs in 3D. However,
opaque minerals and microjoints look similar in
different orientations, and may be studied from
the thin section photographs in 3D.
In the future, it could be interesting to study
larger rock samples in 3D, for example by using
photographs of polished rock surfaces.
A)
B)
Fig. 4. A) Thin sections (the size of 2 cm x 3 cm) in 3D and the schistocity plane created from traces on two differently oriented sections (Photo: Noora Salminen); B) Horsmanaho open pit, the folded layers visible, and the thin sections were made
from the sample near the hinge of the fold. Photo: Esko Koistinen, GTK and drawing: Kerstin Saalmann.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
3.2 Rock walls using the Sirovision® 3D imaging system
The Sirovision® 3D imaging system creates 3D
images from digital pho­
tographs. These photographs were taken in Horsmanaho and Sola
pits, and the ex­act camera position and orientation as well as the position of marker points on
the photographed pit walls was surveyed by GPS
and using a ta­chymeter. With SiroJoint®, spatial
measurement of planes could be mapped from the
3D images and checked and combined with field
measurements of structural data.
Photogrammetry is essentially a process of triangulation using measurements of angle obtained
from images. The position of an object point ‘P’
in Figure 5 can be calculated from measurements
of the positions of the image(s) of the point in
the left and right images, that is the positions of
points ‘PL’ and ‘PR’. With these measurements
and using both the position and orientation of the
camera for each image, and the focal length of the
camera the position in space of point ‘P’ can be
determined. If the true positions of the camera(s)
are known the actual spatial position of the object
point ‘P’ is determined. If only the relative positions of the camera(s) are known the spatial position of the object point ‘P’ relative to the cameras
is determined. By repeating this process for a set
of objects, or points, a 3D map can be generated. The photogrammetry system developed by
CSIRO Exploration and Mining performs these
calculations automatically for a dense grid of
points in both images thus generating a detailed
3D map of the scene being analyzed.
Siro 3D: 8 steps to create a 3D image:
1. Plan The 3D Imaging Task
2. Acquire The Images
3. Correct The Images (Remove distortion)
4. Set up 3D Imaging Support Data (<=Acquire
Control Point & Image (Camera) Position
(Survey) Data and setup camera position and
orientation)
5. Set up The Imaging Task
6. Run The Matching
7. Create The 3D Image
8. Save The 3D Image
During a short field period in 2007, walls from
Horsmanaho and Sola open pits were photographed. Faulting and jointing of the obtained
3D models may be analyzed using SiroJoint®
software. SiroJoint® analyses 3D images of the
surface of a rock mass (topographic maps of the
surface of a rock mass integrated with visual images of the rock) to determine, for instance, the
dip, orientation and spacing of discontinuity sets.
It provides facilities for the visualization and analysis of rock slopes using accurate spatial data registered in a real world coordinate system.
Figure 6 illustrates the use of a digital camera
and control points on the rock wall. The Horsmanaho open pit consists of black schists, serpentinite and talc schist. The example Figure 7 presents a photograph and 3D image of the rock wall
consisting of black schist. Talc schist has been
mined away from the Sola serpentinite. The rem-
Fig. 5. Geometry for the determination of the position of a point in object space
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
nants were photographed over the water- filled
open pit. The obtained stereo photos were combined into 3D image (Fig. 8).
Discontinuities such as lithological contacts
were not easy to discern because of the uneven
and often dirty rock walls. In addition, lithologi-
cal contacts as well as fault surfaces are often
curved and may not be defined by one tectonic
measurement. Consequently, the main use of 3D
images of the rock walls is the analysis of jointing
and planar faults.
Fig. 6. Digital Camera and control points. Photo: Esko Koistinen, GTK.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 7. A SiroVision example from Horsmanaho. Photo: Esko Koistinen, GTK.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 8. Sola open pit as SiroVision 3D visualization. Photo: Esko Koistinen, GTK.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
As an example, the jointing of one rock wall was
analyzed using SiroJoint® software. In order to
measure all the joint orientations, the jointing of
rock walls was studied by examining the rock wall
from different directions (Fig. 9). The fracture
orientations were calculated by SiroJoint® and
presented in a stereographic projection (Fig. 10A)
and in a Rose diagram (Fig. 10B). SiroJoint® also
calculates the mean directions of the clusters, and
it is possible to show corresponding joint planes
in 3D (Fig. 10C). On the example rock wall at
Horsmanaho, the jointing is nearly vertical and
parallel and mainly perpendicular to the strike
of the Outokumpu assemblage rocks. The same
orientation of brittle structures is evident on the
geophysical maps, in the elevation model, and has
been confirmed by geological observations (See
Chapter 5). Geological observation is needed to
define of relative ages and movements of faults.
Furthermore, fracture properties such as fracture
fillings and openness should be observed directly
on the wall.
Fig. 9. Rock fractures studied on a 3D image from Horsmanaho pit from two different directions. Photo: Esko Koistinen,
GTK.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
A)
B)
C)
Fig. 10. A) Jointing on the stereographic projection; B) Presented with the rose diagram and C) Fracture plains visualized in
3D using SiroJoint®.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
4 Ore models
The Outokumpu (Keretti) and Vuonos Cu-CoZn-Ni sulfide ores in eastern Finland are hosted
by the distinctive Outokumpu assemblage, which
comprises serpentinized peridotite massifs that
have been altered and metamorphosed to quartz
rocks, Cr-silicate skarns and carbonate rocks. The
Outokumpu assemblage, and the enclosing metamorphosed black shales and turbidites belong to
an allochthonous nappe complex emplaced onto
the Karelian Craton margin during the early stages of the Svecofennian Orogeny. The Outokumpu
ore body, which was discovered in 1910, contained
28 Mt of ore, of which 23 Mt was mined before
closure in 1989. The Vuonos ore body, discovered
in 1965, some 10 km NE of Keretti, contained 6
Mt of ore, of which 4 Mt was extracted.
Recent geochemical models (Peltonen et al.
2008) ex­plain the close association of peridotites
with carbon­ate-quartz rocks as result of silicification and carbona­tion alteration of the ultramafic
rocks. Ni and Co have been derived from a different source, and a polygenetic development is
suggested, including the formation of a Cu-rich
proto-ore within the 1950 Ma seafloor followed
ca. 40 Ma later by mobilization of Ni and redeposition in disseminated Ni sulfides in response to
alteration during obduction of the upper Kaleva
unit. Later de­formation finally caused mixing of
the Cu and Ni ore components, leading to the uncommon metal associa­tion of Outokumpu.
4.1 Outokumpu ore model
In 1954 the 3D model of the Keretti (also called
Outokumpu) ore body was constructed using
bronze by Outokumpu Oy (Fig. 11). During the
project, Esko Koistinen carried out the modeling
of the Outokumpu ore using mine cross sections
and other maps stored at GTK’s archive in Outokumpu. The sections around Keretti area were
scanned in the GEOMEX project (http://vsa.gtk.
fi/geomex/html/source/start.html). The other sections around Mökkivaara and the Old Mine were
scanned in the ongoing 3D/4D project at GTK’s
Eastern Finland office.
The Outokumpu ore has been surveyed on a local co-ordinate system and vertical sections have
been drawn over a distance of forty meters in the
longitudinal SW-NE direction of the ore. In the
Keretti area, geological sections have a distance
of twenty meters. The sections are numbered 0 to
98 from NE to SW. The sections have been drawn
viewing towards NE. The coordinate system has
been changed twice during the production history
of the mine. Hence, the vertical sections are located in three different directions (Fig. 12).
The relation between the local mining coordinate system and the national coordinate systems
could not be found out in archives. The location
of the sections was derived by georeferencing the
mining area map of Figure 12 based on drill hole
locations on the map and their known national
KKJ coordinates. A maximum error in horizontal
locations is estimated to a couple of metres. The
oldest sections in the Kaasila area are numbered
from 0 to 12, the second system near the old shaft
is numbered from 13 to 31 and the third system
from the old mine through Mökkivaara to Keretti
is numbered from 32 to 98.
Geological drawings of the oldest sections,
numbered from 0 to 31, were prepared at a scale
of 1:800. An example of these drawings is given
in Figure 13. Section 23 is located at the old shaft
and section 24 is 40 m SW of the shaft. It can be
seen that the drawings do not describe the final
stage of ore caving. Sections 31 to 46 in the Mökkivaara area have been named “drill sections”
(syväkairausprofiili, Fig. 14). The scale is 1:800.
Sections 47 to 98 in the Keretti area have been
Fig. 11. A bronze-made 3D model of the Outokumpu ore body at a scale of 1:4000 1954. Photo: Jari Väätäinen.
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
A)
B)
Fig. 12. The mining area of Outokumpu. Vertical sections are situated in three different directions, A, B and C (Figs. A and
B). Mining started from the Kaasila ore body and finished in the Lietukka ore body. (GTK archives Outokumpu).
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 13. An example of the oldest section drawings numbered from 0 to 31. Section 23 is located at the old shaft and section
24 is 40 m SW of the shaft.
drawn at a scale of a 1:400 (Fig. 15). In the oldest sections 0 to 31 only the ore is shown, while in
the other sections the country rocks are also presented. All sections have been hand drawn. Some
occasional sections were lacking.
The sections were georeferenced using Gemcom GEMS software. KKJ coordinates were not
given in the section drawings, but sectional x coordinates (P100, P200 etc.) and the main working
levels of the mine (+200, +250, +280, +320) were
drawn. The sections were georeferenced according to these lines using certain construction lines
to assist work in the 3D space.
In GEMS software the ore body was digitized
to 3D rings using the georeferenced sections as
references. The 3D rings and the georeferenced
section 23 are shown in Figure 16. The 3D rings
were connected to produce a 3D solid model of
the ore deposit (Fig. 17).
Fig. 14. Section 44 as an example of the drill section drawings from 31 to 46 in the Mökkivaara area.
45
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 15. Section 71 as an example of the section drawings from 47 to 98 in the Keretti area
Fig. 16. Cross sections of the Outokumpu ore body digitized as 3D rings. Section 23 in the figure is located at the old mine
shaft.
46
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 17. The 3D rings are connected to a 3D solid model of the Outokumpu ore deposit.
Fig. 18. 3D model of the Outokumpu ore seen from SE. The vertical section 23 in the figure is located at the old mine shaft.
Kaasila on the right, Lietukka on the left.
Fig. 19. 3D model of the Outokumpu ore seen downwards from NW proves how thin the ore body is. The vertical section 23
in the figure is located at the old mine shaft. Kaasila on the left, Lietukka on the right.
47
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 20. A detail of the 3D model of the Outokumpu ore. A fault divides the Kaasila ore body (on the left) and the Kumpu
ore body from each other. Mining started as open pit mining at the outcrops of the Kaasila ore body. The vertical section 23
in the figure is located at the old mine shaft.
Fig. 21. A detail of the 3D model of the Outokumpu ore. A fault divides the Kumpu ore body (on the left) and the Lietukka
ore body from each other. Vertical section 71 in the figure is located at the Keretti head frame. The Poikanen ore body grows
out of the Lietukka body and is seen below the main body. Appendices 1 and 2 contain PDF3Ds files for this model.
The 3D model of the Outokumpu ore deposit
produced from the old mine sections is presented
in Figures 18 to 21. The model demonstrates well
the known main features of the ore. The length
of the deposit is 3686 m and the maximum width
406 m measured in 3D from the model. In the
conventional 2D presentations the Outokumpu
ore body gives the impression that the ore body
is much thicker than it in fact is (Fig.18). In 3D,
looking downwards from NW, the body appears
very thin (Fig. 19). The major, well-known faults,
which divide the body into the Kaasila, Kumpu
and Lietukka bodies, could also be modeled (details in Figs 19 and 20). The Poikanen ore body is
seen below the main ore body in the Keretti area
(Fig. 21). The model also demonstrates separated
small ore blocks and roughness of the ore surfaces, which are seldom present in illustrations of the
Outokumpu ore.
The volume of the 3D model is 8118 Mm3,
which gives an ore tonnage of 28 Mt with a density of 3.45.
4.2 Vuonos ore
The Vuonos ore was modeled using cross
sections scanned during the 3D/4D project at
GTK’s Eastern Finland office. The approach
was similar to the one applied in Outokumpu ore
modeling. In the Vuonos case, sections were imported into Paradigm Gocad® software. Gocad®
is an extensive software package for 3D geological
modelling. The ore was digitized along the vertical mining sections and then combined into a 3D
model of the Vuonos ore using triangulation. The
modeling process is illustrated in Figure 22.
Vuonos ore is gently folded, but not as strongly
48
as the surrounding serpentinite and its alteration
products (Fig. 23). It may be interpreted to be associated with a shear zone between two serpentinite bodies, because in many sections sheared
rocks have been found near the ore layer based
on the section drawings. This shear zone is also
present in the cross sections across Outokumpu
assemblage drawn by Koistinen (1981).
In addition to gentle folding of the ore body
along the strike, the flat ore body is a flexure together with the Outokumpu assemblage rocks on
the section drawings (Fig. 24). The ore body may
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
have folded together with the Outokumpu assemblage rocks, or simply filled the space conforming
to the roundish serpentinite bodies. These kinds
of features may not be modeled in detail by using
triangulation to connect vertical sections, because
the connection outlines between sections produce
a modeled thicker ore body instead of a curved
plane. Curving may be better modeled using potential fields (e.g. Lajaunie et al. 1997) if structur-
al measurements of the orientations of subsurface structures are available. This type of thin ore
layer is a challenge to any currently existing 3D
modeling software.
The Vuonos ore body gently dips to the northeast. The middle part of the Vuonos ore body is
more strongly deformed (Fig. 25) caused by faulting interpreted from geophysical data (Laine &
Saalmann 2008, Fig. 31).
A)
B)
C)
Fig. 22 A) Digitized ore outlines from
the section drawings; B) digitized outlines connected to form an ore body;
C) the whole Vuonos ore body.
49
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 23. An example of Vuonos mine sections. Green colors refer to serpentinite, red to ore, yellow to calc-silicate rocks, violet
to black schist, and blue to mica schist.
50
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 24. A mining section showing a detail of the Vuonos ore body (colored red).
51
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 25. Vuonos ore body colored red, three faults interpreted from seismic section (Laine & Saalmann, 2008). Seismic section
(to the depth of 2 700 m) is done by high resolution seismics (Heinonen et al. 2011) and further prosessed and interpreted by
Laine & Saalmann (2008).
5 3D modeling of the Outokumpu assemblage
The about 100-m-thick Outokumpu assemblage
enclosing the ore bodies was visualized from georeferenced maps and sections (Gaál et al. 1975),
based on structural geological in­terpretations. In
the 3D model, the Outokumpu assemblage and
enveloping black schists are grouped together.
The software used was GeoModeller, which enabled the use of constraints from structural observations, even though it was not possible to define
a reliable stratigraphy within these complexly de­
formed rocks. The present-day sequence of rock
layers was therefore used as an informal “pseudostratig­raphy”. Despite this problem, the resulting
model appears structurally realistic (Fig. 27).
GeoModeller software applies an interpolator
method (McInerney et al. 2005) that is based on
potential field theory. A set of smoothly curving,
sub-parallel geologic surfaces, such as lithological
contacts (Fig. 26), in 3D space are treated analogous to a set of iso-potential surfaces of a scalar
(potential) field. It is assumed that lithological
contact data lie on a potential field surface and
orientation vectors, e.g. schistosities parallel to
lithological layers, are orthogonal to a local tangential plane to the potential field. The field increment between any two points belonging to same
geologic interface is null. Orientation data rep-
52
resent the derivative of the field. The scalar field
is then interpolated by cokriging the increment
data and their derivatives (Lajaunie et al. 1997).
This method was applied on geological maps and
sections from the Outokumpu area, even though
very little tectonic orientation data exists of the
subsurface structures.
3D modeling of the Outokumpu assemblage
surrounding the Vuonos ore body began during
the Outokumpu workshop 2007. It was supervised by Gabriel Couirrioux from BRGM who
acted as a teacher and helped us in 3D modeling
of the Outokumpu assemblage surrounding the
Vuonos ore body.
Taking into account the complexity of the
zone, it was decided to model the boundary between the Outokumpu assemblage surrounded
by black schists and mica gneiss. Black schists envelope the Outokumpu assemblage according to
the interpretation on the geological map. Disharmonic folding makes modeling from cartographic data alone very improbable, and extrapolation
of the geometry at depth or even laterally is highly unpredictable without any information about
subsurface structures. In the Vuonos area, such
information was obtained from three geological
sections (Gáal et al. 1975).
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 26. Possible lithological contacts for iso-potential surfaces. The section was drawn by Koisinen in Gáal et al. (1975).
Fig. 27. Geological map, 3 sections, digitizing and the model. (1) On the left, digitalization of data in maps and sections relying on the georeferenced images. (2) On the right, the corresponding black-schists model.
53
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Figure 27 illustrates the digitalization of data
from georeferenced maps and cross section images as well as the obtained Outokumpu assemblage model. It was decided to model the envelope
of the Outokumpu assemblage rocks and black
schists by a single boundary. In this case, singularities such as fold hinges and sharp angles are
very difficult to link from one section to another.
This is due to the shape complexity, and the existence of narrow elongated zones that cannot be
resolved at the chosen scale. These zones can only
be retrieved by adding intermediate sections.
Another alternative is to consider the different
lithologies as an organization of formations with
Outokumpu assemblage rocks surrounded by
black schists and mica schist. It is then necessary
to correctly assign the drawing lines to the top of
formations. The pile presented here is an example of what is possible to do in that case. This is,
of course, not a unique solution. The only drawback is the creation of additional sub-formations.
However, the result is quite acceptable. Figure 28
shows the informal stratigraphy and data organi-
Fig. 28. An alternative way to organize the pile and data.
54
zation, while Figure 29 presents different views of
the model.
A further step during the 3D modeling process
was to add possible fracture zones into the model.
Faulting and jointing have already been described
by Väyrynen (1939). During the present project,
brittle structures were interpreted from an areal
elevation model interpolated from elevation lines
(Fig. 30) and geophysical maps (Fig. 31). Fracture
orientations are mainly oriented perpendicularly
to the strike of Outokumpu assemblage rocks.
They are assumed to be subvertical such as Kaasila fault (B) in Keretti area. The Outokumpu ore
is cut by this vertical fault (B) with a displacement
of 100 m in the vertical direction (e.g. Fig. 18).
A probable fracture zone (C) subdivide the Outokumpu assemblage into the Vuonos and Keretti
areas. In addition, structure A is a discontinuity
structure that borders the Outokumpu assemblage rocks to the southwest. The Vuonos area is
cut by a probable fracture zone D and bounded to
the North by the discontinuity structure E (Fig.
31).
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Step by step, more sections and drill hole data
were included in the model of the Outokumpu
assemblage. The applied stratigraphy consisted of
two rock types:
1.The Outokumpu assemblage, in which the enveloping black schists (i.e. metamorphic black
shales) were included in a model because they
are part of the alteration zone, and it is difficult
to exclude them geometrically.
2.Mica schist
The rock types along the drill holes were classified according to this classification. The geological map (Gáal et al. 1975) and geological sections
were digitized by using this classification (Fig. 32).
3D modeling was performed using GeoModeller softw are, and the 3D model presents the Outokumpu assemblage associated with the black
schists as an elongated body with an undulating
surface (Fig. 33) caused by folding, faulting and
the original structure of the serpentinite bodies.
Furthermore, the Outokumpu assemblage was
modeled using the present layering of the rock
formations from the southeast to north west:
1. Mica schist (above)
2. Black schist
3. Mica schist (middle)
4. Outokumpu assemblage
5. Mica schist (below)
The resulted 3D model is illustrated in Figure 34.
The probable fracture zones A, B, C, D and E are
also included in the model.
Fig. 29. Outokumpu assemblage rocks and mica schist.
55
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 30. An elevation model of the Outokumpu area overlaid by the geological map of the Outokumpu area (Gaál et al.
1975). Yellow lineaments were interpreted from geological and geophysical maps,and blue lineaments were interpreted from
the elevation model.
56
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 31. Low-altitude magnetic map (processed by Timo Tervo); lines A, B, C, D and E mark approximate locations of possible fault or fracture zones.
57
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Fig. 32. Lithologies, sections and faultsdigitized from the geological map (Gáal et al. 1975).
Fig. 33. Outokumpu assemblage (including black schists).
58
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 34. A model of the Outokumpu association and cross cutting fracture zones. The width of the formation is about 1.5 km.
59
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
6 3D modeling of the Sola serpentinites
At Sola and Horsmanaho (Fig. 1) the Outokumpu
assemblage rocks occur as roundish bodies slightly elongated in the SW-NE direction. The Sola
drill-hole data were analyzed in the Surpac mining software, which uses triangulation to build 3D
surfaces. The rock types were classified according
to the GEOMEX project (http://geomaps2.gtk.fi/
Geomex-tiedostot/kaytto/geomex_geology.html).
The rock types included in the 3D model were
black schist, serpentinite, mica schist, and quartz
veins (Table 1). The mafic dykes cutting the serpentinite body were not modeled separately, but
were included with the serpentinite.
The first stage in Surpac is to construct sections
Table 1. Rock types and corresponding rock codes and colors.Lisää alkuperäiset koodiselitykset
Code
BS
OUM
OBA
WA
QTZVE
Rock type
Black schist
Outokumpu Assemblage
OKU Metabasites
Mica schist
Quartz vein
Fig. 35. Digitizing serpentinite bodies on the sections.
60
Colors
Purple
Green
Green
Blue
Yellow
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
from drill-hole data. The outlines of serpentinite
bodies were digitized on each section (Fig. 35).
This is not a trivial task, and generally requires
previous knowledge of the form and orientation
of the ore bodies. Three serpentinite bodies were
modeled from sections and finally combined into
three serpentinite models (Fig. 36). Geological
sections and maps were used in improving the obtained model (Fig. 37):
Fig. 36. Surpac solid models of Sola serpentinites.
A)
B)
Fig. 37. Geological block model of the Sola serpentinites by Gáal et al. (1975); Kontinen (2008).
61
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
7 3D model of the Vuonos area including detailed seismic
FIRE-sections
Seismic reflection profiles from the Outokumpu
region measured in the FIRE project (Heinonen
et al. 2011) reach a depth of 2700 m. The migrated
sections were imported into Paradigm Gocad®
software. The amplitude values represent the seismic signal that obtains positive and negative values. In order to discern the reflectors the absolute
value was calculated. The reflectors were seen better (Fig. 36) when the indicator coding was applied:
I (|amplitude|) = 1, if |amplitude|>2.5,
0 otherwise.
The seismic sections were studied visually in 3D
using Paradigm GOCAD® software and compared with geological maps. The strength of the
GOCAD® software is its ability to combine data
from different sources.
The few examples of possible interpretations of
the OKUFIRE-sections are listed below:
• The first observation from the seismic sections
is that the Outokumpu bedrock can be divided
in two parts according to reflectivity (Fig. 38).
In the western side of this discontinuity surface
the reflectors are angular, in contrast to the
roundish forms on the other side. The boundary is marked with a green plane dipping to the
southeast (Fig. 39A). Reflectors in the southeast give a visual impression of movement that
has turned and thickened the layers.
• It can also be seen that the reflections in the
62
seismic section OKUFIRE3 do not continue
in the sections OKUFIRE1 and OKUFIRE2.
The reason may be inclined, folded and faulted
structures. The location of the actual reflecting
structures or layers may be at some distance
from the sections. The reflections on OKUFIRE3 are subhorizontal, indicating that the
section crosscuts the inclined reflectors (layering or shearing) (Fig. 38). In addition, faults
interpreted from seismic section OKUFIRE3
(Laine and Saalmann 2008; Fig. 25) cut the
Vuonos ore at the point where the ore body has
been faulted or sheared. These faults have also
been interpreted from the geological and geophysical maps (Fig. 31).
• The subsurface formations appear to be continuous and parallel to the Outokumpu assemblage (Fig. 40).
• It can be intepreted several possible orientations for discontinuity structures (Fig. 41).
Because seismic sections may be interpreted in
many ways. Deep drilling is needed to verify the
existence of shear zones or locations of the rocks
belonging to the Outokumpu assemblage. Drilling was first carried out near the OKUFIRE1,
and the petrology was described in the Deep
Drilling Project at GTK (Västi 2011). In general,
3D visualizations facilitate the interpretation of
seismic profiles, especially, when other geological
data sets can be visualized and compared with
seismic reflectors.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
A)
B)
C)
Fig. 38. A) FIRE-sections OKUFIRE1, OKUFIRE2 and OKUFIRE3 on the geological map (Gáal et al. 1975); B) The
original amplitude value presented in grey scale, and C) the indicator-transformed absolute value of the amplitude. The value
of 1 is marked with a white color.
63
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
A)
B)
Fig. 39. A) Seismic sections OKUFIRE 1 and 2 to the depth of 2 700 m and the surface, which divides the bedrock into
differently reflective parts. The continuity of the structures is also evident. B) Seismic sections OKUFIRE 2 and 3, geological
map (Gáal & Koistinen, 1973), Outokumpu ore body, Vuonos ore body and the dividing surface.
Fig. 40. OKUFIRE 1 and 2 to the depth of 2 700 m together with the Keretti and Vuonos ore bodies.
64
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
3d modeling of polydeformed and metamorphosed rocks at different scales using
geological and geophysical data from Outokumpu area
Fig. 41. OKUFIRE 2 section to the depth of 2 700 m and the Vuonos ore body (in red) surrounded by Outokumpu Assemblage (bounded surface in green) that is cut by a shear zone (in white); possible large discontinuity structures (in white, green
and yellow ) were interpreted from the seismic sections (Laine and Saalmann 2008). The corresponding 3DPDF is found in
Appendix 3.
8 Conclusions
The Outokumpu area has been studied since
1910, and the data source consists of old maps
and section drawings. Because the mining areas
are covered by thick layers of Quaternary deposits, very few outcrops are available. Hence, the section drawings and drill-hole data formed the main
geological data source in this study. The Keretti
and Vuonos mines are closed and inaccessible.
The complicated structures affected the 3D geological modeling in many ways:
1. It is difficult to correlate planar fabrics inferred
from microstructures with those observed macroscopically, because their orientations vary
over short distances.
2. The complex folding and shearing patterns
cause repetition of data in such a manner that
it is difficult to discern or model lithologies
separately. Simplification of rock type classification is usually needed for geometric 3D
modeling.
3. The oldest structures are complicated and their
continuation to greater depths is sometimes
very difficult to predict. Modeling of these
structures should be preceded by 3D modeling
of large faults or shear zones. Even though the
latter features are fairly planar or only gently
curved surfaces their subsurface orientation
and dimensions may be difficult to model. In
3D modeling of these subplanar features, geophysical data are essential and sometimes the
only data source.
4. Geophysical data, such as seismic sections,
may be interpreted in many different ways.
However, they are sometimes the only data
sources and provide some idea of subsurface
structures and their continuities, especially
when visualized and examined in 3D modeling
environments.
Because the Outokumpu area has a complex geology, a purely technical visualization using data
sets with­out involving geological ideas and interpretations and considering different view points is
impossible. It is also evident that the Outokumpu
3D model strongly depends on the interpretation
of the re­gional deformation and alteration history, so that a different interpretation of the geological history could lead to quite a different 3D
model.
However, structural features are more easily
interpreted by using modern 3D modeling software. The data and models from different sources
may be studied inside the same platform. Tectonic orientations may be used directly in 3D modeling. Nevertheless, data from different sources
at various scales and resolutions do not make the
modeling process easier, and demand a team of
researchers from different fields in geology and
geophysics rather than an individual specialist
working alone. The understanding and documentation of each step in the modeling process is essential.
65
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Laine,E., Koistinen, E., Saalmann, K., Coirrioux, G., Diaz, R., Salminen, N. & Tervo, T. 2012
Supplementary information on the web
GeoModeller, available at: http://www.geomodeller.com
GEOMEX-project, available at: http://vsa.gtk.fi/geomex/
html/source/start.html
Paradigm GOCAD®, available at: http://www.earthdecision.
com/index.html
ParaviewGeo, available at: http://paraviewgeo.mirarco.org/
index.php/Main_Page)
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Peltonen, P. & Kontinen, A. 2004. The Jormua Ophiolite: a
mafic-ultramafic complex from an ancient ocean-continent transition zone. In: Precambrian ophiolites and
related rocks. Developments in Precambrian geology 13.
Amsterdam: Elsevier, 35–71.
Peltonen, P., Kontinen, A., Huhma, H. & Kuronen, U. 2008.
Outokumpu revisited: New mineral deposit model for
the mantle peridotite-associated Cu–Co–Zn–Ni–Ag–Au
sulphide deposits. Ore Geol. Rev. 33, 559–617.
Salminen, N. 2009. Microstructures in 3D modelling, Outokumpu area as an example site. Master’s thesis, Department of Civil and Environmental Engineering, Geoenvironmental technology. 59 p. , 9 app.
Vuollo, T. & Piirainen, J. 1989. Primary minerals in the serpentinites of the Outokumpu Complex, North Karelia,
Finland: contributions to the origin. In: 28th International Geological Congress, Washington, D.C. USA,
9–19 July 1989. Abstracts, p. 313.
Västi, 2011. In: Kukkonen, I.T. (ed.). High resolution reflection seismics integrated with deep drill hole data in Outokumpu, Finland. Geological Survey of Finland, Special
Paper 51, 105–118.
Väyrynen, H. 1939. On the geology and tectonics of the
Outokumpu ore field and region. Bulletin de la Commission Géologique de Finlande. 124.
3D-pdf’s
Appendix 1: http://arkisto.gtk.fi/3d/outokumpu_geo_3d.pdf
Appendix 2: http://arkisto.gtk.fi/3d/outokumpu_topo_3d.pdf
66
Appendix 3: http://arkisto.gtk.fi/3d/vuonos_ore_body_
and_structures_interpreted_from_geological_and_seismic_sections.pdf
3D modeling of polydeformed and metamorphosed rocks:
the old Outokumpu Cu-Co-Zn mine area as a case study
Edited by Eevaliisa Laine
Geological Survey of Finland, Report of Investigation 195, 2012
THREE-DIMENSIONAL MODELING OF THE OUTOKUMPU
NAPPE AREA, SE FINLAND
by
Tapio Ruotoistenmäki and Esko Koistinen, GTK
Ruotoistenmäki, T. & Koistinen, E. 2012. Three-Dimensional Modeling Of The
Outokumpu Nappe Area, SE Finland. Geological Survey of Finland. Report of
Investigation 195, 8 figures.
The three dimensional geometry of the Outokumpu nappe area can be
evaluated using a combination of existing geophysical data and maps. The
trend of the outcropping trace of the buried nappe structure at depth can be
constrained from the long, continuous Haaralanniemi anomaly zone, discernible in both electromagnetic and magnetic maps. The deep cross section is determined from seismic and gravimetric interpretations. In the Juojärvi area
the magnetic anomalies define the interfering fold structure of nappe basement
dipping NE. In the Miihkali area the Haaralanniemi anomaly borders the local
Miihkali basin, representing the uppermost parts of the nappe. The base of
the nappe structure is interpreted to be cut and thrusted over itself below the
Kylylahti-Sola anomaly zone. The model used here provides a valuable qualitative tool for extrapolating the position of Outokumpu association rocks at
depth. However, the base of the nappe has been cut by Maarianvaara granitic
rocks. Moreover, the repeated stacking of thrust folds and faults is apparent in
the whole Outokumpu area in vertical sections. The model data were digitized
and prepared using Gemcom GEMS software and imported into Geosoft Oasis montaj system for further modeling.
Keywords (GeoRef Thesaurus, AGI): tectonics, nappes, three-dimensional
models, structural geology, geophysical methods, Precambrian, Outokumpu,
Finland
Tapio Ruotoistenmäki
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
Esko Koistinen
Geological Survey of Finland, P.O. Box 96, FI-02151 Espoo, Finland
E-mail: [email protected]
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Tapio Ruotoistenmäki and Esko Koistinen
1 Introduction
During 1998–2003, the geology, geophysics, evolution and metallogenic potential of the Outokumpu region in Northern Karelia, Finland, were
reassessed through the Geomex project, which
represented a joint venture between the Geological Survey of Finland and Outokumpu Mining
Oy. The purpose of the project was to collect, reprocess and archive existing geological and geophysical data and material and locate new target
areas for exploration. The geophysics subproject
of the Geomex project was reported in Ruotoistenmäki and Tervo (2006). The report also presented regional and local-scale tectonic models
based on geophysical and petrophysical data
from the study area. In this article, a ‘three-dimensional’ model is presented to demonstrate the
non-outcropping, deeper characteristics of the regional tectonic model for the Outokumpu nappe
area given in Ruotoistenmäki and Tervo (2006).
2 General geology of the study area
The general geological features of the Outokumpu
area are illustrated in Figure 1 by Sorjonen-Ward
and Luukkonen (2005). They classified the area
into roughly four major units: Proterozoic granitoids, allochthonous Paleoproterozoic supracrus-
tal rocks, parautochthonous Paleo-proterozoic
sedimentary-volcanic rocks and Archaean basement windows. For a more detailed geological
description of the area, see also Kontinen & Peltonen (2003).
Fig. 1. Simplified local-scale lithological map of the Outokumpu area studied in the Geomex project (outlined by yellow lines).
Semitransparent gray shades relate to the total magnetic intensity recorded by regional airborne surveys (high anomalies are
darker; reproduced from databases of the Geological Survey of Finland). Modified from the map by Sorjonen-Ward and
Luukkonen (2005).
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Three-Dimensional Modeling Of The Outokumpu Nappe Area, SE Finland
3 Major geophysical formations in the study area
Some major regional (= continuous) electromagnetic anomaly zones in the study area are illustrated in Figure 2. In the map, the NE-trending
Outokumpu anomaly zone (OZ) is the main
ore potential zone in the area, rising to the SW
against the NW-trending Juojärvi anomaly (JZ),
and together forming a T-shaped anomaly group.
Moreover, the Miihkali ‘basin’ (MB) and Kylylahti-Sola thrust zone (KS-T) form ore potential
structures on the northern part of the nappe. A
very important feature is the generally continuous Haaralanniemi anomaly zone (HA), which
represents the outcropping edges of the basin of
the whole Outokumpu nappe structure. In the
Fig. 2. Electromagnetic real (in-phase) component map of the study area. The map has been compiled from data recorded
by the Geological Survey of Finland. OZ = Outokumpu anomaly zone, JZ = Juojärvi anomaly, MB = Miihkali ‘basin’, HA
= Haaralanniemi anomaly, KS-T = Kylylahti-Sola thrust zone, SW-D = southwest ‘deep’, WNB = western nappe basin
(breakup of the Haaralanniemi anomaly). Map adopted and modified from Ruotoistenmäki and Tervo (2006).
69
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Tapio Ruotoistenmäki and Esko Koistinen
southwest ‘deep’ (SW-D), the base of the nappe
is not visible, but disappears below outcropping
sedimentary rock cover. On the west, at WNB,
however, the Haaralanniemi anomaly disappears,
exposing the uplifted base of the nappe cut by
younger, Proterozoic Maarianvaara granite.
4 Major structures of the Outokumpu nappe area
When interpreting the geometry of the regional
structures in the Geomex area, an important key
feature is the Juojärvi magnetic anomaly (JZ in
Fig. 3) in the SW part of the Outokumpu zone.
In the anomaly zone, a striking feature is its sinuous NW–SE trend. The geometry of the Juojärvi
anomaly zone can be best explained by the schematic fold model in the inset in the figure. In the
model, the geometry of the upper edge of the
folds emphasized by the blue line is analogous
to that of the Juojärvi magnetic anomaly. The
geometry suggests the presence of (at least) two
perpendicular regional fold groups in the Juojärvi
area, one with a SW–NE trend and another with
a SE–NW-trending fold axis, as shown in Figure
4. From the geometry of the magnetic anomaly
patterns, it can also be concluded that SW–NE
folds preceded the SE–NW folds.
In Figure 4, the geometry of the main Outo-
kumpu zone is largely defined by the SW–NEtrending folds, represented by blue lines for the
synformal fold axis and red lines for antiforms.
The SE–NW folds include the regional synform
NE from Juojärvi (JS) and the more deeply eroded
Juojärvi antiform (JA). The SE-trending magnetic anomaly zone southwest of antiform JA in the
figure represents the SW limb of the fold, which
could therefore contain Outokumpu assemblage
rocks. It must also be emphasized that the pattern
of the folds in the Juojärvi anomaly zone actually
reflects the geometry of the vertical cross-section
of the SW–NE-trending folds (i.e. the geometry
of the base of the nappe), as is evident from the
schematic model in Figure 3.
The intersecting SW–NE and SE–NW-trending antiforms southwest of the Juojärvi area also
explain the locations of the Archaean basement
windows SW of Juojärvi (Fig. 1). The antiforms
Fig. 3. Schematic model to explain the Juojärvi anomaly (JZ). The synform marked by red in the lowermost inset refers to the
Outokumpu anomaly zone (OZ).
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Three-Dimensional Modeling Of The Outokumpu Nappe Area, SE Finland
interfere at locations emphasized with red circles
in in Figure 4, thus generating antiformal domes
and exposing the Archaean basement, as depicted
in in Figure 1. Moreover, the geological dip obser-
vations agree with the inferred domal interference
patterns as shown in Ruotoistenmäki and Tervo
(2006).
Fig. 4. General tectonic features interpreted from geophysical maps of the study area. The base map is the magnetic low-altitude map (for abbreviations see text and Figure 2). The map is adopted and modified from Ruotoistenmäki and Tervo (2006).
71
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Tapio Ruotoistenmäki and Esko Koistinen
5 Preparation of the three-dimensional model
The preparation of the three-dimensional model
was based on the two-dimensional interpretation
shown in Figure 4. and seismic refraction and reflection profiles crossing the nappe area (Penttilä
1967 and Kukkonen et al. 2006). In the model,
the nappe area was divided in cross-sections
shown in in Figure 5 a and b. The model consists
of three basic sub-blocks: 1) the northernmost
block north of the Kylylahti-Sola thrust zone
(‘Oku-North’), 2) the main nappe zone (‘OkuSouth’) and 3) the Miihkali basin (MB). In Figure 5b, violet curves define the modeled basin of
Oku-North, blue curves refer to Oku-South and
red defines the course of Juojärvi antiformal interference domes.
The blocks were modelled in 3D by the LaPlace
Fig. 5. (a): Location of selected cross-sections used for constructing the three-dimensional model. Yellow curves define the
locations of the outcropping edges of the modeled structures. (b): The inferred variations of the geometry of the Outokumpu
nappe basin based on the model presented in Figure 4. (c): The three-dimensional model derived by the LaPlace gridding
method of Gemcom GEMS. The Outokumpu basin surface bordered by the Haaralanniemi anomaly is colored in magenta
and the Miihkali basin is in green. Antiforms are shown by blue curves, synforms by red and thrust zones by black curves.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Three-Dimensional Modeling Of The Outokumpu Nappe Area, SE Finland
gridding method of Gemcom GEMS. The model
data were further imported into the Geosoft Oasis montaj system, in which the data were compiled in the three-dimensional images presented in
Figures 6 to 8. In the figures, the magnetic map is
projected on the model consisting of three submodels built in succession from the lowermost
Oku-North ‘layer’ to the uppermost Miihkali ba-
sin. In the model, the yellow lines define the approximate outcropping of the sub-models.
It must be noted that the Oku-North and Okusouth layers do not necessarily imply primary
vertical succession. More probably, the nappe has
been ‘broken’ during the thrust processes along
the KS-T line and the southern part has been
thrust over the separated northern block.
Fig. 6. Three-dimensional model of the northern- and lowermost section (Oku-North) of the Outokumpu nappe (below
Miihkali basin in Figure 4)
Fig. 7. Three-dimensional model of the main SW block of the Outokumpu nappe (Oku-South) thrust over the NW section
in Figure 6.
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Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Tapio Ruotoistenmäki and Esko Koistinen
Fig. 8. Three-dimensional model of the Miihkali basin overlying the NW and SW sections in Figure 6 and Figure 7. The
approximate location of the Haaralanniemi anomaly (HA, Fig. 2), Kylylahti-Sola thrust zone (KS-T) and southwest ‘deep’
(SW-D) have also been marked in the figure.
6 Conclusions
The three-dimensional geometry of the Outokumpu nappe area can be derived by carefully
combining information from existing surface geophysics, geology and deep seismic studies. In the
Outokumpu area, a very important geophysical
key anomaly is the long continuous Haaralanniemi anomaly representing outcropping edges of the
base of the nappe, and thus defining the borders
of the nappe area. The Juojärvi anomaly defines
the SW geometry of the nappe and its interfering fold structure. Moreover, the Kylylahti-Sola
anomaly represents the NE thrust zone where the
Outokumpu nappe has been cut into two major
blocks, where the southern block is thrusted over
the NE block. The Miihkali basin represents the
uppermost part of a deep interference synform
on top of the Outokumpu nappe structure. These
anomalies of the Outokumpu nappe area are
good examples of two-dimensional features that
can provide valuable three-dimensional information when carefully studied.
References
Kontinen, A. & Peltonen P. 2003. Description and genetic
modelling of the Outokumpu type rock assemblage and
sulphide ores – a GEOMEX subproject. GEOMEX /
Preliminary Technical Report. Geological Survey of Finland.
Kukkonen, I.T., Heikkinen, P., Ekdahl, E.,Hjelt, S.- E., Korja,
A., Lahtinen, R., Yliniemi, J. & FIRE Working Group.
2006. FIRE reflection seismic transects: New images of
the crust in the Fennoscandian Shield. Abstract in: 27th
Nordic Geological Winter Meeting, Oulu, 9.–12.01.2006.
Bulletin of the Geological Society of Finland, Special Issue 1, 2006.
74
Penttilä, E. 1967. Outokumpu jakson räjäytysseismologisesta tutkimustyöstä. On the seismological study of the
Outokumpu zone. Report by Outokumpu Oy (in Finnish).
Ruotoistenmäki, T. & Tervo, T. 2006. Geophysical Characteristics of the Outokumpu Area, SE Finland. Geological
Survey of Finland, Report of Investigation 162, 37 p.
Sorjonen-Ward, P. & Luukkonen E. J. 2005. Archean rocks.
In: Lehtinen, M., Nurmi, P. A., Rämö, O. T. (eds.), 2005.
Precambrian Geology of Finland – Key to the Evolution
of the Fennoscandian Shield. Developments in Precambrian Geology 14. Amsterdam: Elsevier, 19–99.
Geologian tutkimuskeskus, Tutkimusraportti 195 – Geological Survey of Finland, Report of Investigation 195, 2012
Three-Dimensional Modeling Of The Outokumpu Nappe Area, SE Finland
Acknowledgements
Many thanks to referees for reading this report
and offering valuable comments and to Roy Siddall for English checking. I owe also thanks to my
daughter Carmela Lönnqvist for helping with illustrations.
Copyright owner
The Royal Society of Edinburgh/
RSE Scotland Foundation and Tapio Koistinen
Geological Survey of Finland
The publishers and authors listed below are
gratefully acknowledged for giving their permission to use original and redrawn figures based on
illustrations in journals they hold the copyright.
Journal
Transactions of the Royal Society
of Edinburgh: Earth Sciences
Figure number
Part I (Problems and challenges of
3D modeling of the Precambrian
of Finland): Figures 4, 6 and 12,
the cover page
Part I (Problems and challenges of
Geological Survey of Finland. Bulletin 3D modeling of the Precambrian
of Finland): Figures 3, 5, 7
Part II (3D modeling of polydeformed
and metamorphosed rocks at
different scales using geological
and geophysical data from Outokumpu area): Figures 1, 26, 27, 30,
31, 32, 37, 38, 39
75
www.gtk.fi
[email protected]
The present work summarizes the results of the project
“3D/4D modeling – Outokumpu area as a case study” conducted during 2007–2009 and 3D modeling of the Outokumpu assemblage in the project “Development of geological 3D
modeling using structural geology and geostatistics” in 2010
at the Geological Survey of Finland (GTK). The aims of these
projects were to apply and evaluate 3D/4D modeling software and formulate principles for visualizing and analyzing
complicated geological structures typical of Finnish bedrock.
The aim was to make recommendations for the use of 3Dmodeling tools and processes for 3D/4D modeling at GTK.
Several 3D geological models were constructed at different
scales using data from the Outokumpu mining area.
ISBN 978-952-217-182-5 (PDF)
ISSN 0781-4240