A state-of-the-art multi-component seismic survey

Progress report May-November 2015
StartGeoDelineation
State-of-the-art geophysical and geological methods for delineation of mineral
deposits and their associated structures – Sweden and Finland
Working group: Alireza Malehmir (1), Karin Högdahl (1), Michael Setter (2), Pasi Heino (3), Suvi Heinonen (4),
Bjarne Almqvist (1), Fredrik Karell (4), Christopher Juhlin (1) and Erik Jonsson (5)
Students: Georgiana Maries (PhD), Sara Eklöf (PhD), Andreas Bierk (MSc)
Short-term post-docs: Mahdieh (Azita) Dehghannejad and Joachim Place
Organizations: (1) Uppsala University (UU), (2) Nordic Iron Ore (NIO), (3) Yara, (4) Geological Survey of
Finland (GTK) and (5) Geological Survey of Sweden (SGU)
Progress report (May-November 2015): StartGeoDelineation
State-of-the-art geophysical and geological methods for delineation of
mineral deposits and their associated structures – Sweden and Finland
Working group: Alireza Malehmir*,1, Karin Högdahl1, Michael Setter2, Pasi Heino3, Suvi
Heinonen4, Bjarne Almqvist1, Fredrik Karell4, Christopher Juhlin1 and Erik Jonsson5
Students: Georgiana Maries (PhD), Sara Eklöf (PhD) and Andreas Bierk (MSc)
Short term post-docs: Mahdieh (Azita) Dehghannejad1 and Joachim Place1
Organizations: (1) Uppsala University (UU), (2) Nordic Iron Ore (NIO), (3) Yara, (4) Geological
Survey of Finland (GTK) and (5) Geological Survey of Sweden (SGU)
* Lead researcher and organization: Uppsala University, Dept. of Earth Sciences, Villavägen
16, SE 75236 Uppsala-Sweden (email: [email protected])
Summary
The StartGeoDelineation project has reached its one-year period. The project and preliminary results
were presented at the closing conference of ERA-MIN during October 2015 in Paris. Two PhD
students, both females and two short-term post-docs are partly employed to work in the project. Several
fieldworks were conducted during the summer and fall of 2015. A particular focus was given to physical
property measurements including 6 deep (> 450 m) downhole logging in Blötberget-Sweden and 3 in
Siilinjärvi-Finland. An extensive geological and geophysical survey was performed during fall 2015
that included seismic, gravity and magnetic, geoelectrical-based methods as well as detailed field
geological mapping. Nearly 25 students and researchers (Figure 1) took part in these surveys.
Grängesberg reflection seismic data was given a new attention with the reprocessed seismic section
suggesting the possibility of faulted mineralized zones at depth of about 600-700 m in the footwall of an
inferred fault at these depth ranges. The project will have a strong presence at the 32nd Nordic
Geological Winter Meeting-Helsinki (January 2016) with three presentations. The geological and
geophysical data acquired during fall 2015 will be presented. A progress meeting among the project
participants is planned in conjunction with this conference.
1. General planning of the project
A new PhD student (Sara Eklöf) with a focus on
the geological aspects of the project was
employed. Mining and associated business are
continuing to have their economic trouble
however, at this stage all the partners are
committed to the success of the project and to
their great extent contribute in the project. The
project had to support Michael Setter’s (NIO)
participation in the project to be able to obtain
crucial information required for the two-planned
PhD theses. It remains unclear how the current
mineral economy would influence the project
particularly in the Swedish side. We are hopeful
that the impact would not be significant at this
stage of our project.
Reporting after May 2015 where our first
progress report to Vinnova was provided, we
have conducted more downhole and laboratory
petrophysical measurements. Geological
mapping was continued during the
summer and fall 2015 with a focus on
major structural information from both
sites in Sweden and Finland. Seismic data
from Siilinjärvi is currently being
processed
using
new
processing
algorithms in order to improve their
quality and for a decision making on how
to proceed with its applicability in the site.
One week extensive geophysical field
campaign was conducted during October
2015 in Blötberget. The measurements
included an about 2.5-km long highresolution
reflection
seismic
line,
magnetic and gravity surveys as well as
geoelectrical-based methods only on the
southern site of the open pit.
Progress report (May-November 2015): StartGeoDelineation
Blötberget. A popular report about the
project was presented by Dalarna
newspaper (www.dt.se).
2. Physical property studies
Figure 1: A group photo from the students and researchers
taking parts in the acquisition of the geophysical data in the
Blötberget during October 2015.
The participants are working to evaluate these
data and planning for follow up measurements
and writing scientific articles already from these
investigations. GTK and SGU personnel are
currently involved providing PhD supervision
(Erik Jonsson) and technical supports to the
project. SGU also provided technical support and
personnel for blasting of explosive shots partly
used in the acquisition of seismic data in
During summer and fall 2015, several
samples from both sites and also
subsamples from existing drill cores were
obtained. The samples have been studied
for their magnetic properties including
their magnetic susceptibility but also their
dependency to external magnetic field and
temperature. Moreover several deep holes
(the deepest about 580 m) were logged for
natural gamma, magnetic susceptibility,
seismic velocity and conductivity at both
sites (locations shown in Figures 2 and 3).
These measurements should serve as a
basis for the interpretation of the surface
geophysical data but also providing
information about possible relationship(s)
between various types of mineralization
and lithologies encountered in the
boreholes. Preliminary results are
encouraging and allow clear identification
of mineralized zones (hematite or
Figure 2: (left) Ground total-field magnetic measurements projected onto airphoto from Blötberget
mining site showing the existing boreholes and some of those logged so far in the study area. The exposed
magnetite shows up to 95,000 nT which is quite remarkable. (right) Total-field magnetic map and the
location of the seismic profile acquired during fall 2015. The deepest hole in the area is about 1.2 km but
not accessible. The deepest hole logged so far is at about 590 m.
2(6)
Progress report (May-November 2015): StartGeoDelineation
Figure 3: 3D visualization of aerial photo with the 3D geometry of the Siilinjärvi open-pit mine and the
seismic profiles acquired to study the depth extent and geometry of various types of dykes including the
apatite-rich carbonatites in the southern parts of the pit. Three boreholes were logged during summer
2015 one clearly showing the southern extent of the complex interrupted by a major dioritic intrusion.
magnetite), weak zones in the
hanging-wall and also a way to
distinguish between hematiterich zones from magnetite-rich
zones (even their percentage
contributions) by studying their
temperature-magnetic property
relationships in the laboratory.
Figures 4 and 5 show example
downhole
property
measurements from one of the
six
boreholes
logged
in
Blötberget and one of the three
in the Siilinjärvi mine (Figures 2 and 3).
Figure 4: Example downhole logging results from Blötberget showing the clear presence of magnetite
mineralization in the susceptibility and conductivity-based measurements. A detailed study of these
measurements is currently on going.
Figure 5: Example downhole logging
results from Siilinjärvi mine showing the
complex nature of physical properties.
Some of the carbonatite dykes show strong
magnetic and natural gamma properties.
The Siilinjärvi complex appears to be cut
by a major dioritic intrusion as was
speculated before but confirmed by new
boreholes coordinated in this project.
3(6)
Progress report (May-November 2015): StartGeoDelineation
3. Geological mapping and studies
During summer and fall 2015, geological
fieldwork was conducted both in Siilinjärvi,
Finland, and in the Blötberget area in Sweden.
The
Neoarchean
carbonatite-glimmerite
complex in Siilinjärvi is transected by a large
number of Paleoproterozoic dolerite dykes. Field
relationships show that they belong to at least
two different generations. The majority of the
older dykes have a steep to moderate dip and are
occasionally sulphide-bearing. Thinner dykes
are amphibolitic whereas the wider dykes have
to a large part retained their magmatic
mineralogy. The sulphide-bearing and sulphidefree dykes may belong to different generations.
Both types of older dykes are often boudinaged
and shear strain has to a large part been localised
at the dyke boundaries, resulting in mica-rich
shear zones that vary in width from a few to
about 10 centimetres. These shear zones (Figure
6) typically show a top-to-east vertical
component. The younger generation is
represented by composite dykes that are
associated with a diorite with mixing and
mingling elements. They are less deformed than
the older dykes and have no or very narrow
boundary parallel shear zones. The dip for the
younger dyke generation varies from subhorizontal to nearly vertical and they appear to
be emplaced in a dynamic setting. They are
folded and faulted, but are not significantly
metamorphosed.
Figure 6. A steep shear zone developed at the
boundary of an older dolerite dyke generation
(Siilinjärvi main pit, Finland).
4(6)
A large number of dykes have been
sampled
for
geochemistry
and
petrography and a few for possible
geochronology, provided the host suitable
mineralogy. Some boundary parallel shear
zones
have
been
sampled
for
microstructures and textural setting of
minerals that can be used for
geochronology.
The Paleoproterozoic apatite iron oxide
(AIO) mineralisation at Blötberget is
hosted by intermediate metavolcanic rocks
and in the vicinity of the ore these are to a
large extent altered into phyllosilicate and
amphibole assemblages (sköl). Felsic
metavolcanic rocks are the predominating
lithology in the general area, together with
mafic and granitic intrusions that are
ubiquitous. Two generations of pegmatites
are also present. The older generation is
variably deformed whereas the younger
generation cut the penetrative, ductile
fabric. The structural pattern can be
divided into regions dominated by prolate
or oblate strain resulting in L>>S and
S>>L fabrics. In the latter two tectonic
foliations, S1 and S2, have been
recognised that are most pronounced in the
sköl-zones and in specularite-like hematite
(Figure 7), where S1 occurs as a
crenulated cleavage with a small angle to
S2. The intersection lineation coincides
with the constructed fold axis (with a
moderate plunge to the SE) given by all
foliation measurements. The intersection
lineation and the constructed fold axis also
coincide with the orientation of the
stretching lineation. Samples have been
collected for micro-structural studies and
geochronology.
The apatite iron oxide mineralisation
along the AIO-belt in western Bergslagen
is intimately associated with other iron
oxide mineralisation types. Magnetite
from all three AIOs (Grängesberg,
Progress report (May-November 2015): StartGeoDelineation
Blötberget and the small Kopslahyttan) and
associated skarn mineralisations in addition to
magnetite from veins and droplets in the
metavolcanic host rock have been sampled for
trace element LA-ICP-MS analysis.
jumps near the abandoned pit suggesting
the presence of significant magnetite
immediately south of it.
5. Presentations and publications
The project will have a strong presence at
the 32nd Nordic Geological Winter
Meeting but also at other occasions such
as the DDG-EAGE deep exploration
workshop planned for March 18 in
Münster-Germany and also the EAGENear Surface (Mineral exploration and
mining geophysics) conference planned in
Barcelona in the fall 2016. Students will
present their works at our internal project
meetings but also at institutional seminars.
Popular scientific presentations are also
planned and will have a focus next year.
Figure 7. Crenulated specularite-like hematite. The
crenulated fabric is related to S1, and developed on a
S2-surface. Blötberget.
4. Geophysical surveys and studies
The seismic data from Siilinjärvi is being
processed using more advanced processing
methods. At the same time we are inverting for
velocity models along the four profiles to extract
as much as possible information from the data
that can be used to better understand the near
surface properties of materials and help in
planning of new geophysical surveys. We have
obtained ground magnetic data but will aim at
obtaining airborne data from GTK and possibly
model them to further understand the internal
structures of the Siilinjärvi alkaline and
carbonatite complex.
In Blötberget, the new seismic data (about 2.5
km long) were acquired to first check the
possibility of imaging the known mineralized
bodies and if possible to provide information
about their depth extent beyond what is known
but also major structures in the hanging-wall that
are important for mine planning. Ground
magnetic and gravity data were also collected
but will be expanded next year to allow their 3D
modeling and a rough estimate of the shape and
potential tonnage of the mineralized bodies in
the study area. Ground magnetic and gravity
data collected during October 2015 show clear
5(6)
6. Work plans for 2016
NIO showed interest as part of a regional
development of their exploration and
mining plans to revisit an earlier reflection
seismic profile
acquired in
the
Grängesberg mining area (Place et al.,
2015) and study the deep mineral
potentials and possible presence of a
major fault in the region. This is currently
being done with the preliminary results
suggesting a strong and short reflection in
the footwall of an inferred fault in the
area. This combined with the physical
property measurements conducted on
similar kind mineralization (hematite and
magnetite) in Blötberget already suggest
that reflection seismic method can be used
in the area for deep exploration of ironoxide deposits. Further analysis of the
reflection data is required to better explain
the origin of the new reflection in the data.
Depending on the outcome of the 2015
geophysical
surveys
and
their
interpretations in conjunction with the
geological and petrophysical data, new
surveys will be planned. We are likely to
collect some manetotelluric (MT) data to
test their potentials for deep exploration at
the
site
given
the
encouraging
Progress report (May-November 2015): StartGeoDelineation
observations of their strong conductive nature.
The samples collected at Siilinjärvi will be
studied during the early parts of 2016. The
geochemical data and the mineralogy of the
older dykes will be analyzed in order to evaluate
if they are significantly genetically different.
Results from the petrography will also indicate if
the dykes host minerals suitable for
geochronology. Micro-structural studies on thin
sections from the shear zones will be conducted
for kinematic analyses and, if present, defining
the textural setting of monazite. Detailed
fieldwork is planned in and in the vicinity of the
mined in Siilinjärvi, with a focus on structural
features. Guided by the petrographic and
geochemical results, samples will be collected
for geochronology. Bulk samples from the shear
zones in the glimmerite will be collected in order
to conduct a mineralogical study on REEbearing phases.
In Sweden, more geological fieldworks will be
conducted both in the Blötberget area and around
Håksberg-Lekomberg also here with focus on
the structural features. Samples for microstructural studies will be collected together with
samples on key lithologies for geochemical
characterisation and geochronology. Samples for
geochronology will be prepared and analysed,
together with samples from Siilinjärvi, either
with SIMS or LA-ICP-MS techniques in 2017.
During spring 2016 the trace element
composition in magnetite from the AIOs and
associated iron oxide mineralisations in western
Bergslagen will be analysed by LA-ICP-MS at
Gothenburg University. This study will be part
of an MSc-project that will be presented later in
2016.
7. Appendixes

Abstracts submitted to the 32nd Nordic
Geological Winter Meeting (Helsinki,
2016)
6(6)

Report made by Dalarna tidning
(www.dt.se) during the fall 2015
field campaign in Blötberget.
Draft compiled by Alireza Malehmir
November 20-2015.
Delineating structures hosting
REE-bearing apatite iron-oxide
(Sweden) and apatite-rich
carbonatite-alkaline deposits
(Finland) through systematic
geophysical and geological
investigations
A. MALEHMIR1*, G. MARIES1, S. HEINONEN2, S. EKLÖF1,
K. HÖGDAHL1, B. ALMQVIST1, M. SETTER3, P. HEINO4,
F. KARELL2, C. JUHLIN1, AND M. SUIKKANEN4
Uppsala University, Uppsala, Sweden, (*correspondence:
[email protected])
2
Geological Survey of Finland, Helsinki, Finland
3
Nordic Iron Ore, Ludvika, Sweden
4
Yara, Siilinjärvi, Finland
1
The StartGeoDelineation project, initiated in 2015, aims
at studying two mining sites in Sweden and Finland. In
Blötberget-Sweden our goals are to delineate and better
understand structures hosting iron-apatite deposits and
provide information about their depth extent that are known
down to 800 m depth. Downhole geophysical logging in six
deep boreholes (> 450 m and intersecting the mineralization)
and laboratory measurements have been conducted. These
data provide constraints and valuable information for the
interpretation of surface geophysical data that were recently
acquired, including an approximately 3.5 km long seismic
profile complemented by high-resolution magnetic and
gravity surveys. The downhole logging data suggest potential
relationships between occurrences of pegmatite and hematite
(low-susceptibility) found under a distinct magnetite-rich
zone (high-susceptibility); they also show major weak zones
in the hanging-wall in the full-waveform sonic data. In
Siilinjärvi-Finland, one of our goals is to understand the
relationships between the carbonatite-apatite mineralization
and shear zones as well as different generations of basic
dykes. This will benefit the mine planning and reduce the risk
of unexpected failure in the open pit. Defining the contact
between the alkaline intrusion and country rocks is another
goal of the study. Three boreholes have been logged and four
short seismic profiles (2 km in total) acquired to constrain the
geophysical interpretations. Preliminary results are
encouraging and illustrate the significance of a systematic
approach combining physical properties, field geological
mapping and surface geophysical surveys for deep
exploration and multi-target tasks (e.g., exploration and mine
planning).
Towards a structural framework
for apatite-iron oxide deposits in
the Grängesberg-Blötberget area,
Bergslagen, Sweden
S. EKLÖF1*, K. HÖGDAHL1, E. JONSSON1,2, A.
MALEHMIR1, AND M. SETTER3
1
Department of Earth Sciences, Uppsala University,
SWEDEN (*correspondence: [email protected])
2
Geological Survey of Sweden (SGU), Uppsala, SWEDEN
3
Nordic Iron Ore (NIO), Ludvika, SWEDEN
The REE-bearing Kiruna-type apatite-iron oxide (AIO)
deposits at Grängesberg and Blötberget represent the largest
iron ore concentration in southern and central Sweden. Both
regarding immediate host rocks and actual mineralisation
type, this group of deposits stand out as a marked anomaly in
the Bergslagen ore province. The AIO deposits are situated in
the western part of this intensely mineralised Palaeoproterozoic province along a 40 km long NNE trending
winding line. This stretches from Grängesberg in the south,
via Blötberget to Idkerberget in the north and further east to
the small Kopslahyttan deposits. The Grängesberg deposit
consists of moderately to steeply dipping magnetitedominated lenses, which coincide with an inferred F1 fold
limb, suggesting a synmetamorphic structural control on the
ore. Around the lenses, prolate strain is focused at the lens
crests and oblate strain at the tapering edges, as a result of
competence contrast between competent bodies, including the
ore, and the phyllosilicate altered host-rocks during D2
shortening (Persson Nilsson et al. 2013). Preliminary results
from the Blötberget area suggest a similar location of prolate
and oblate strain around competent lenses. Two ductile planar
fabrics have been observed both in the host-rock and in the
ore. Platy hematite ore is in places crenulated, with a small
angle to S2, implying that this hematite type was formed prior
to D1. A similar fabric has been encountered in the
phyllosilicate altered rocks in Grängesberg. To better
understand the structures hosting the Bergslagen AIO
deposits, provide information about their extent at depth, and
their evolution and relations to other iron oxide mineralisation
types, a detailed structural study is currently being carried out
within the framework of the ‘StartGeoDelineation’ project
(ERA-MIN) supported by Vinnova, SGU, NIO, Tekes and
Yara.
Reference
Persson Nilsson, K. et al. 2013. The Grängesberg apatite-iron
oxide deposit. Research report. SGU. 45 pp.
Magnetic properties for
characterization and quantification
of magnetite and hematite in apatite
iron-oxide deposits at Blötberget,
central Sweden
1
A. BJÖRK1*, B.S.G. ALMQVIST1, M. SETTER2, K. HÖGDAHL1
1
AND A. MALEHMIR
1
Department of Earth Sciences, Uppsala University, Sweden
(*correspondence: [email protected])
2
Nordic Iron Ore, Ludvika, Sweden
Laboratory magnetic measurements can complement ore
geological and exploration geophysical studies. Analysis of
statistical relationships between magnetic properties and thin
section analysis can prove useful for this purpose. A methodology
is developed in the current study, with the aim to characterize the
Kiruna-type REE-bearing apatite iron-oxide deposits at Blötberget
in central Sweden. Twenty drill core samples, received from
Nordic Iron Ore, were used for this study containing up to 81
weight percent (wt%) magnetite and up to 83 wt% hematite.
Magnetic susceptibility measurements were carried out as a
function of temperature, using an MFK1-FA susceptibility bridge.
The measurements show that magnetite with strong susceptibility
contribution overshadows the hematite contribution in the
samples. Susceptibility drops are noticeable when crossing the
Curie temperatures; 580ºC and 680ºC for magnetite and hematite,
respectively. Although the bulk susceptibility of magnetite is
several orders of magnitudes larger than that of hematite, the
signals from the two phases are readily distinguishable from the
drop in susceptibility across their respective Curie temperatures.
The wt% magnetite, identified in thin sections, was compared with
drop in susceptibility across the 580ºC. A linear relationship is
identified between the magnitude drop in susceptibility and
magnetite content with R²=0.73. The same procedure was
performed for hematite in 6, out of the 20, measurements. Thus
another linear relationship with R²=0.81 for hematite. A lower
detection limit of 17 wt% hematite was identified when
characterizing susceptibilities associated with hematite using this
method, and the chosen sample size. This investigation illustrates
that magnetic laboratory methods are useful to accurately quantify
and characterize magnetite and hematite proportions in high grade
iron mineralized bodies.
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