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3D structural framework of the Leja Cu-Zn-Pb deposit and hosting Guldsmedshyttan syncline, Bergslagen, Sweden.

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3D structural framework of the Leja Cu-Zn-Pb deposit and
hosting Guldsmedshyttan syncline, Bergslagen, Sweden.
MSc Research Project Earth Sciences, Geology and Geochemistry
Author: Iris van der Werf
Student number: 2543997
AM_1187 27 EC
Submitted: 21-09-2020
Supervisors:
Dr. Fraukje Brouwer (VU Amsterdam)
Dr. Bernd Andeweg (VU Amsterdam)
Dr. Stefan Luth (SGU)
Cover photo shows mining equipment in an abandoned mine pit located within the Uksen Formation
limestones near Leja
Table of contents:
1 Abstract ............................................................................................................................................... 1
2 Introduction to the Bergslagen ore types and the study context .................................................... 2
2.1 Bergslagen’s importance and its ore types .................................................................................... 2
2.2 Study objectives, context and report build-up ............................................................................... 3
3 Geological setting ................................................................................................................................ 5
3.1 Regional lithology of Bergslagen .................................................................................................. 5
3.2 Regional polyphased deformation ................................................................................................. 6
3.3 Local geology ................................................................................................................................ 7
4 Methods ............................................................................................................................................... 8
4.1 Reasons and timing for fieldwork ................................................................................................. 8
4.2 Data processing ............................................................................................................................. 8
5 Results ................................................................................................................................................. 9
5.1 Field observations .......................................................................................................................... 9
5.2 Petrography of thin sections ........................................................................................................ 11
5.2.1 Petrography of metavolcanics .............................................................................................. 13
5.2.2 Petrography of limestones .................................................................................................... 13
5.2.3 Petrography of metasediments ............................................................................................. 13
5.2.4 Petrography of Skarns .......................................................................................................... 14
5.3 Ore mineral petrography ............................................................................................................. 14
5.4 Cross-sections .............................................................................................................................. 16
5.5 3D regional and deposit modelling.............................................................................................. 21
............................................................................................................................................................... 24
6 Discussion .......................................................................................................................................... 25
6.1 Summary of the tectonic evolution of Bergslagen ...................................................................... 25
6.2 Ore occurrence in the study area ................................................................................................. 25
6.3 Discussion of rock types, metamorphism and deformation history with petrography ................ 26
6.3.1 Discussion of the metavolcanics .......................................................................................... 26
6.3.2 Discussion of the Limestones ............................................................................................... 26
6.3.3 Discussion of the metasediments .......................................................................................... 26
6.3.4 Discussion of ore minerals ................................................................................................... 26
6.4 Discussion of cross sections and 3D models ............................................................................... 27
6.5 Interpretation of the relationship between ore bodies and geological structures ......................... 28
6.6 Recommendations ....................................................................................................................... 31
7 Conclusions ....................................................................................................................................... 32
8 Acknowledgements ........................................................................................................................... 33
9 References ......................................................................................................................................... 34
10 Apendices ........................................................................................................................................ 36
A.1 Drill logs ..................................................................................................................................... 36
A.2 SEM data .................................................................................................................................... 76
A.3 Coordinates of Studied outcrops and structural measurements. ................................................. 78
1
1 Abstract
The Guldsmedshyttan syncline in the Bergslagen mining district is an iron oxide and base metal sulphide
(Fe-Zn-Pb-Cu) hosting structure located in the Swedish part of the Fennoscandian shield. Between 1.9
Ga and 1.89 Ga paleoproterozoic rocks deposited in a highly volcanically active continental back-arc
setting, along an active convergent margin of the Svecofennian orogeny. The tectonic setting played an
important role in the deformation, metamorphism, metasomatism and ore (re)mobilisation of the
paleoproterozic rocks. Iron oxide ores in Bergslagen mainly occur in paleoproterozoic calc-silicate
rocks, whereas base metal sulphide ores generally occur in crystalline carbonate rocks. In Lovisa and
Håkansboda, both located in the northern part of the Guldsmedshyttan syncline, extensive surveys
constrain the genesis and geometry of ore bodies for renewed mining and scientific research. However,
the relationship between ore bodies and geological structures in the southern part of the
Guldsmedshyttan syncline is not yet established.
This study produced three cross sections in the southern part of the Guldsmedshyttan syncline and a 3D
structural framework visualizing layers of base metal (Cu, Zn, Pb) sulphide mineralization in
combination with structural and lithological data. We propose that the Guldsmedshyttan syncline is a
more complex structure than previously described by Lundström, (1983) and Carlon and Bleeker,
(1988). With sedimentation in halfgrabens during the initial extensional phase followed by polyphase
folding and (re)activation of faults in both the ductile and brittle regimes during multiple phases of
crustal shortening. The results demonstrate that the Leja deposit includes three distinctive ore layers
with variable contents of the metals Zn, Pb, Cu, and Au. The highest metal concentrations within each
ore layer occur in the vicinity of fault systems, suggesting a spatial relationship between faults and ore
bodies. As such, the faults acted as conduits for metal-bearing hydrothermal fluids, which reacted and
partly transformed the limestone into skarn and zones of Zn-Pb-Cu-Au mineralization during multiple
phases of deformation. Intersections between major faults, in particular occurring within limestone,
should therefore be considered important criteria for exploration in the search for similar ore deposits
within the study area and its direct surroundings.
2
2 Introduction to the Bergslagen ore types and the study context
2.1 Bergslagen’s importance and its ore types
Bergslagen was an important
region for metallic ore
exploration and mining in the
18th and 19th century and is still
important for hosting a
significant amount of base
metals, iron, REEs and
industrial minerals. Due to its
rich mining history and
potential Bergslagen is
significant for Europe and has
three currently operating base
metal sulphide mines in the
region, which are Garpenberg,
Lovisagruvan and Zinkgruvan
(Fig. 1; Stephens et al., 2009;
Beunk and Kuipers. 2012;
Jansson et al., 2018). The area is
not only famous for its mining
history but also because the
term ‘skarn’ originates from
this mining district and it hosts
several type localities of REEs
and minerals including minor
elements (Törnebohm, 1875
Jansson, 2011). In recent years,
mining interest in Bergslagen
developed strongly due to rising
metal prices worldwide. Since
most metallic ores in
Bergslagen occur in skarns and
crystalline limestones,
understanding their relationship to iron oxides and base metal sulphides is highly relevant for exploring
renewed ore exploration (Stephens et al., 2009). With that, the interest in skarn/limestone formations
and their genesis increased rapidly during the last decade. This interest is apparent for example in the
Bergslagen project from the Geological Survey of Sweden (SGU), which compiled information on the
entire Bergslagen mining districts geological and geophysical data while in addition presenting a new
bedrock geology synthesis (e.g., Stephens et al., 2009; Stephens and Jansson, 2020; Luth et al., 2019).
Previous studies for example Geijer and Magnusson, (1944), Carlon and Bjurstedt, (1990), Allen et al.,
(1996), Stephens et al., (2009), Jansson et al., (2011) identify two end member types of sulphide ore
bodies and several types of metallic ore deposits in the Bergslagen region. The first end member is
classified as Åmmeberg-type or stratiform ash-siltstone-hosted Zn-Pb-Ag sulphide deposits (SAS-type).
These Zn-Pb-Ag rich and Fe-Cu poor base sulphide deposits are found in e.g., Zinkgruvan and
Figure 2: Blown up Figure of the black square in Figure 1. This Figure
shows the location of thin sections (black dots), drill data (purple
dots), Leja mine and Siggeboda. The numbering in the thin section
locations corresponds with the numbering of outcrop data conducted
during the fieldwork. The two orange dots with red numbers are the
drill cores manually analysed during this study.
Figure 1: The Bergslagen ore district. The black square within the Figure outlines the exact
location of the fieldwork area which is shown in greater detail in Figure 4 (Modified after Luth et
al., 2019).
3
Lovisagruvan and characteristically occur in
sheet deposits hosted by 1.91-1.89 Ga ash-
siltstone metavolcanics (Allen et al., 1996;
Stephens et al., 2009; Jansson, 2018). The
second sulphide deposit type consists mainly of
Zn-Pb-Ag-Cu-Au and is known as the Falun-
type or stratabound volcanic-associated
limestone-skarn-type (SVALS-type). It forms
irregular lenses and podiform bodies hosted by
the same felsic metavolcanic sequence as the
first type and are generally strongly
interbedded with crystalline carbonate rocks
(Carlon and Bjurstedt, 1990; Allen et al., 1996;
Stephens et al., 2009). These deposits occur in
the Grapenberg and Falun areas, among others.
Carlon and Bjurstedt, (1990) suggest that both
ore types originated in hydrothermal vent
systems in which host rocks were altered due to
interaction with acidic hydrothermal fluids.
This study will consistently refer to SAS-type
and SVALS-type ore bodies to eliminate
confusion in terminology.
Skarnic supracrustal rocks occurring all over
Bergslagen are common iron oxide hosts
(Fig.1; Allen et al., 1996; Stephens et al.,
2009). Most iron oxide deposits consist of
magnetite and several calc-silicate minerals.
Two types of Mn-poor iron oxide occur in
Bergslagen. Primary’ Mn-poor iron deposits
are suspected to have a stratiform shape, generated by the interaction between crystalline rocks and
magnesium-rich volcanic sediments. In contrast, ‘reaction skarns’ indicate regional medium-grade
metamorphism related to intrusive volcanism (Geijer and Magnusson, 1944). Locally iron oxides are
manganese-rich, though this is not as common as manganese-poor iron oxide deposits (Geijer and
Magnusson, 1944; Stephens et al., 2009). Along with the iron oxide occurrences within skarns quartz-
rich BIFs are present in Bergslagen as well.
2.2 Study objectives, context and report build-up
Because of its economic importance Bergslagen is well studied in the past. However, most research and
mapping within Bergslagen is rather dated, incomplete, in an analogue format, and in need of
modernization. For example, the Guldsmedshyttan syncline hosts the currently active base metal
sulphide Lovisagruvan and closed Håkansboda mine. Because of the mining activity research in this
part of the syncline is current and ongoing. However, a few kilometres south of those mines lie the Leja
and Siggeboda mines with similar stratigraphy and Zn-Pb-Cu-Au mineral deposits but knowledge of
this part of the syncline is rather dated. Geological cross sections are present but the exact locations are
missing from the current data set, existing drill core data has not yet been digitized and combined with
structural or geophysical data and the genesis of a large number of deposits and their interaction with
local structures remains unknown till today. Remapping of the area contributes to more detailed
Figure 2: Blown up figure of the black square in Figure 1 and Figure 5. This
figure shows the location of thin sections and drill data used during the study.
The numbering in the thin section locations corresponds with the numbering
of outcrop data conducted during the fieldwork. The red outline is the study
area, black outline the regional geology 3D model (Fig.12) and the green
outline represents the 3D deposit models (Fig. 13, 14, 15 and 16).
4
knowledge of the complicated ore body distribution within the bedrock and therefore to the relationship
between geological structures and ore formation. These renewed insights of the area can be used for
scientific, as well as for exploration purposes. This study presents new data from outcrop studies and
thin sections within a study area around lake Uksen (Fig.2). These datasets form the basis for three
newly constructed 2D geological cross sections, which will be compared and complemented by existing
drill data and integrated in a 3D framework of the study area (Fig. 2). This framework includes and
correlates prominent ore deposits within the study area and ties them to geological structures and
deformation events.
This study was conducted as a collaboration research project between Vrije Universiteit Amsterdam
(VU) and Geological survey of Sweden (SGU) with 27 EC in the Geology and geochemistry track of
the VU Amsterdam Earth Science master. The SGU had this project available as part of their X-mine
project funded by the European Union’s Horizon 2020 research and innovation program under grant
agreement 730270. The author and a fellow student conducted fieldwork under supervision of SGU’s
structural geologist Stefan Luth. After a three day introduction to the area by Stefan Luth the author and
field partner split from him for fieldwork in the southern part of the Guldsmedshyttan syncline whilst
he operated in the northern part. During the fieldwork all three shared a residence provided by the SGU
so supervision whilst data processing was available. All equipment needed for fieldwork in Sweden was
provided by the SGU as well. All laboratory work such as producing thin sections, optical and reflected
light microscopy and EDS analysis was carried out at VU Amsterdam.
Chapter 3 of this report will elaborate on the regional geology, lithology and deformation history in
Berslagen before concentrating on the local geology of the Guldsmedshyttan syncline. Thereafter, in
chapter 4, the fieldwork and laboratory methods carried out during the study to construct the 3D
structural framework will be discussed. An overview of the field data including structural measurements
and cross sections, laboratory work such as petrology and SEM analysis and the constructed 3D
framework results will be described in chapter 5. In chapter 6 all results are combined to interpret and
discuss how ore deposits and geological structures in the southern part of the Guldsmedshyttan syncline
are related. In this chapter also findings of previous research on this subject will be incorporated and
compared to the findings of this study to constrain the best fitting theory. Last paragraph of this chapter
will be a paragraph of recommendations for further research which contributes to a more detailed
framework of the Guldsmedshyttan area. Afterwards, in chapter 7 the important conclusions from the
study will be presented. Chapter 8 is dedicated to acknowledgements and chapter 9 to references used
during the study. In the appendices drill logs with assays, SEM-EDS analysis and a complete overview
of structural field data can be found in this order.
5
3 Geological setting
3.1 Regional lithology of Bergslagen
The study area is situated in the southern part of the
Guldsmedshyttan syncline around lake Uksen, Bergslagen ore
district, south central Sweden. It includes the closed mines
Lejagruvan and Siggebodagruvan and was affected by bimodal
volcanism and metamorphism (Fig. 1, Fig. 2; Allen et al., 1996;
Stephens et al., 2009, 2020; Beunk and Kuipers, 2012). The
Bergslagen lithotectonic unit is part of the Fennoscandian
shield, which was affected by the Svecofennian orogeny (also
referred to as Svecokarelian orogeny; e.g., Stephens et al., 2009,
2020). During the Svecofennian orogeny several island arcs
accreted to the Archean craton in collisional setting which
increased the size of the landmass (Nironen, 1997; Korja et al.,
2006; Lathinen et al., 2009). During this orogeny, rock
formation occurred in a sedimentary basin between 1.9 Ga and
1.89 Ga. Deformation occurred simultaneously and after rock
deposition in a period between 1.9 and 1.79 Ga, with peak
metamorphism up to prograde amphibolite facies conditions
(Allen et al., 1996; Stephens et al., 2009). The oldest rocks in
the Bergslagen supracrustal sequence are turbiditic
metagreywackes, which shallow upwards into rhyolitic to
dacitic metavolcanics of medium-K composition known as the
Storsjön Formation of Lundström (Fig.3; Lundström, 1983;
Carlon and Bleeker, 1988; Stephens et al., 2009). Subfelsic
bimodal intrusives affected these metavolcanics during back arc
rifting (Oen et al., 1982; Stephens et al., 2009; Jansson, 2011).
Carbonate rocks and altered calc-silicates of the overlying
Uksen formation are host rocks of most metallic and sulphide
ore deposits and form the top of the volcanic sequence (Fig.3;
Lundström, 1983; Carlon and Bleeker, 1988; Allen et al., 1996;
Stephens et al., 2009). Carbonate layers in the area were
deposited in depression basins formed during the initial rifting
stage and immediately metamorphosed due to hydrothermal
seafloor interaction and interlayering with volcanic rocks (Oen
et al., 1982; Lundström, 1983; Carlon and Bleeker, 1988; Allen
et al., 1996; Cooke et al., 2000; Stephens et al., 2009).
Stratigraphically above this sequence metasediments consisting
muddy to sandy turbidites occur that deposited in a period of
waning volcanism (Fig, 3; Lundström, 1983; Stephens et al.,
2009). Because of the bimodal back-arc magmatism, during a
period spanning 100 Ma, several intrusive suites occur in the
Bergslagen deposits (Fig. 4). The oldest known intrusions are
Figure 3: Stratigraphic column of the Guldsmedshyttan syncline area based on the
work of Lundström (1983) and Carlon and Bleeker 1988 for the Storsjön and
Mårdshyttan formations and Jansson et al., 2018 for the Uksen formation.
Abbreviations: Fsp = feldspar, Hem = hematite, Mag = magnetite, Qz = quartz. Figure
is modified after Jansson et al. (2018).
6
felsic to sub-felsic granites, dolerites to gabbroids (GDG suite) and intruded between 1.90-1.87 Ga
(Nironen, 1997; Stephens et al., 2009; Beunk and Kuipers, 2012).
During the second event, mafic dykes and sills of the granite-syenitoid-dioritoid-grabbroid suite
(GSDG) intruded the Paleoproterozoic supracrustal rocks simultaneously with formation of the youngest
metasediment deposits (Stephens et al., 2009). This second intrusion phase , however, was not
continuous and consists of two episodes of 1.87-1.84 and 1.81-1.78 Ga, respectively. The final granite-
pegmatite suite (GP) and was active during 1.84-1.74 Ga. This is the youngest and also the highest in
uranium, thorium and potassium and could be easily mapped using airborne spectrometry (e.g., Stephens
et al., 2009).
3.2 Regional polyphased deformation
Vivallo and Rickard (1984) and Baker et al. (1988)
concluded that the felsic volcanics, as well as the
numerous sulphide deposits were generated in a
continental rift setting. Around 1.9-1.86 Ga back
arc spreading and accretion of microcontinents to
the Fenoscandian shield marked early Svecofennian
deformation (D1) (Fig. 4; Nironen, 1997; Korja et
al., 2006; Lathinen et al., 2009). Spreading caused
dextral slip motion and inclined mineral stretching
lineation within the whole Bergslagen.region
(Carlon and Bleeker, 1988 ; Stephens et al, 2009;
Beunk & Kuipers, 2012). Subsequent horizontal N-
S shortening in a transpressional regime (D2)
resulted in the formation of high strain belts with a
westward fold vergence (Nironen, 1997; Stephens
et al., 2009; Beunk and Kuipers, 2012). During this
compression phase peak metamorphism at
amphibolite facies was reached around 1.86 Ga
(Stephens et al., 2009). After shortening (D2) a
renewed phase of rifting took place (D3). During
rifting, granite dykes intruded the area and within the
forming rift basins conglomerates were deposited. In
a renewed horizontal shortening phase (D4)
secondary folding transformed the primary N-S oriented folds into eastward plunging folds with an E-
W axial plain. High strain belts formed during (D2) are affected by NW-SE shear zones during this
compression phase and the peak metamorphic grade reached during (D2) is partially overprinted
(Nironen, 1997; Beunk and Kuipers, 2012). West Bergslagen is tectonically affected by the Western
Bergslagen Boundary Zone (WBBZ) which runs through Garpenberg, Fagersta, Stråssa, Mårdshyttan
and ÄlvlångenVikern (Stephens et al., 2009; Beunk and Kuipers, 2012). The boundary zone consists
of many NE-SW conjugate retrogressive stepover shear zones originating from (D4). A significant part
of the WBBZ runs through carbonate horizons and causes the limestones to deform and recrystallise
into marbles with asymmetric folding indicating sinistral shear sense. Rock structures in the limestone
quarry near Mårdshyttan even indicate left-lateral oblique westward-down sense of movement (Stephens
et al., 2009; Beunk and Kuipers, 2012).
Figure 4: Diagram that shows the periods in which major geologic
events took place in the Bergslagen area. GDG = Granitoid-dioritoid-
gabbroid intrusive rock suite, GSDG = Granite-syenitoid-dioritoid-
gabbroid intrusive rock suite, GP = Granite-pegmatite intrusive rock
suite. The ages based on the findings of Oen et al., (1982); Korja et al.,
(2006); Stephens et al., (2009) and Beunk and Kuipers, (2012).
7
3.3 Local geology
In Leja the dominant structure is the NE-
SW trending overturned and broken
Guldsmedshyttan syncline with eastward
axial plain dipping (Fig. 5; Carlon and
Bleeker, 1988). Lundström (1983)
interpreted the syncline as a 1.9-1.8 Ga
F1 fold with an isoclinal nature and steep
westward slopes. Carlon and Bleeker
(1988) showed that a hook-like structure
in the northern part is the result of
secondary W-NW axial surface plane
folding (Fig.5). South of Siggeboda the
Western Bergslagen Boundary Zone
affects the syncline and truncates the fold
into NE shear zones. The
Guldsmedshyttan syncline is the host
structure for many mineral ore deposit in
the region such as BIFs, base metal
sulphides and Fe-oxides in skarn (Carlon
and Bleeker, 1988; Allen et al., 1996;
Stephens et al., 2009; Jansson et al.,
2018). Most ore deposits within the Leja
region manifest in skarns and marbles
which have had a complex
metamorphic history. The exact peak
metamorphic conditions within the
Guldsmedshyttan syncline are unclear
though estimated a amphibolite facies due to the occurrence of garnet, cordierite and sillimanite (Allen
et al., 1996; Nironen et al., 1997; Stephens et al., 2009).
The stratigraphy of the Guldsmedshyttan syncline comprises the Storsjön Formation, Uksen formation
and Mårdshyttan formation (Fig. 3). The oldest rocks in the area are rhyolites that occur on both sides
of the synclinal structure and are metamorphosed by 1.91-1.89 GDG intrusions (Stephens et al., 2009;
Jannson, 2018). These rhyolites are interbedded with alternating quartz and metallic ore mineral
banding. At the top of the sequence the rhyolites are finer-grained and classified as ash-siltstones, here
interbedded with Mn-and Fe-oxide rich layers. At the base of the overlying Uksen formation a limestone
layer of shallow marine origin was deposited during the initial rifting stage (Oen et al., 1982; Stephens
et al., 2009). The limestones are locally metamorphosed by the same GDG volcanic suite as the rhyolites
of the Storsjön formation but also affected by hydrothermal fluids and seafloor deformation on a regional
scale. No fossils can be recognized in the formation, not even in the undeformed rocks. Due to the alkali-
calcic nature of the GDG suite potassium and magnesium alteration induced base metal sulphide
precipitation in the limestones (Allen et al., 1996; Stephens et al., 2009). Stratigraphically above the
limestone member is another layer of fine-grained rhyolitic ash-siltstones with extensive Mn-and Fe-
oxide mineralisation, followed by the youngest lithology of the area, metasediments.
Figure 5: Geological map of the Guldsmedshyttan syncline which shows the doubly plunged
nature and the northernmost hook like structure of the syncline modified after Stephens et al.,
(2009) and Jansson et al., (2018). The black square is the outline of Figure 2.
8
4 Methods
4.1 Reasons and timing for fieldwork
Initially, the available structural data within the study area was limited to several strike/dip orientations
and a general lithological map provided by the SGU. This information proved to be insufficient to
complete the required coverage for the construction of the 3D models. Therefore, structural geological
fieldwork was conducted in the spring of 2018. During the fieldwork also oriented and non-oriented
rock samples were taken for thin section analysis at VU Amsterdam (See Fig. 2 for sample numbers and
locations).
4.2 Data processing
The thin sections were used for description of lithologies, ore-types and their abundance, stress/strain
relation within the study area and for shear sense indications. All thin sections with more than 1% opaque
minerals in a transmitted light microscope were also examined by reflected light microscopy and SEM-
EDS to determine the ore composition. The data is used to produce three geological cross sections spread
over the study area (Fig. 2). After manual logging of two selected drill cores from Leja and Siggeboda
to validate historical logs, drill cores provided by the SGU were used to reconstruct the horizons beneath
the surface the structure. Stress/strain relations, lithology and ore occurrences of the two cores selected
for logging are examined in thin sections as well. Since all available drill data was scanned and written
in Swedish they were first digitalized in excel and translated into English.
Finally, a 2-meter-resolution elevation model (Lidar) of the study area, general lithological map,
structural field data, the three geological cross sections and drill data from 45 drill holes are all
implemented in the 3D geological implicit modelling software Leapfrog to construct the 3D
geological framework. Based on this framework and information from the thin sections and field data
the correlation between zinc (Zn) enrichment horizons, lead (Pb) enrichment horizons and copper (Cu)
enrichment horizons, lithology and geologic structures was interpreted by gradually downscaling from
meso- to microscale.
9
5 Results
5.1 Field observations
During the structural fieldwork, geological structures were observed at 87 outcrops in the form of ductile
shear, brittle faults, lineation and foliation. Two thirds of the measured dip data consists of steeply SE-
dipping planes within the NE-SW trending Guldsmedshyttan syncline. Lithologies in the study area
comprise two types of metavolcanics rock, volcanic siltstone and rhyolites, marble, dolomite and
calcites, which all are referred to as limestones in this study, skarn, turbiditic metasediments and two
types of intrusives, pegmatites and granites of the GP suite. The Storsjön Formation metavolcanics
border both sides of the syncline whereas the Uksen Formation carbonates and Mårdshyttan
metasediments are mostly exposed in the centre of the structure (Fig.5). In the eastern flank of the
syncline 1.85 Ga granites of the GP suite intruded the Storsjön Formation metavolcanics. Skarns occur
in the Uksen Formation carbonates mainly between Leja and Siggeboda on the eastern limb of the
syncline. However, in the field more evidence of mining in the forms of residue boulder hills and mining
pit walls occur than actual skarn lenses which indicate former small scale mining. Within the residue
boulders sometimes patches or veins of magnetite or pyrite were found, suggesting Cu and Fe mining
in the pits (Fig. 6A). In the skarn outcrops it is particularly hard to determine bedding (S0) or foliation
(S1) structures due to heavy alteration. North of Leja the skarn lenses become discontinuous, decline in
size to a meter or less and eventually disappear. In the centre and western limb of the syncline the skarn
lenses are absent, but in the northwesternmost part of the study area near Uskaboda metallic ores occur
within the metavolcanics. There, lenses and veins occur with very high magnetite, pyrite and
chalcopyrite content (Fig.6B). However, in contrast to the continuous carbonate hosted skarn lenses in
the Eastern limb of the syncline, the lenses in the Western limb metavolcanics are discontinuous. Most
of the outcropping volcanic rocks have little or no indication of ore minerals with the naked eye.
However, in some of them pyrite, pyrrhotite, chalcopyrite and magnetite occur (Fig. 6B). Those mineral
occurrences are common features in skarns and skarnic carbonates on the eastern limb as well. Testing
magnetism with a small magnet in the field identified more rocks that are magnetic and therefore contain
at least small amounts of iron.
S0 and S1 within the study area are often found to be almost identical with only a few degrees difference
(Fig. 6C). Shear sense indicators observed in outcrops, such as rotated clasts and asymmetric folds,
reveal polyphase deformation of the study area. Dextral, sinistral, compressive and extensional
movements often occur within a single outcrops. Dextral displacement is accompanied by east dipping
listric faults indicative for an E-W extensional deformation phase (Fig.6D). In addition to this, western-
side-up shear indicators are commonly found throughout the entire area (Fig.6E). Figures 6F, 6G and
6H also show extensional features in the form of faulting and boudins. Figures 6G and 6H show boudins
that are stacked on top of each other, indicating extension before compression within the study area.
10
Figure 6: A) Pyrite patches in skarnic rocks on the edge of old mine pit. B) Block with very high magnetite, pyrite, chalcopyrite and
pyrrhotite content hosted by metavolcanics rocks. C) ) In the picture one can see that S0 and S1 is almost identical and hard to
observe in the field. D) Vertical dextral slip displacement accompanied by east oriented listric faults within a marble layer of the
Uksen formation. E) Western-side-up motion assumption based on microstructures. F) Normal fault 198/54 with epidote on the
facture plain, indicating fluid interaction during deformation. G) Mesostructure in quartz vein showing dextral shear that first broke
the veins into boudins and after that stacked them on top of each other during a shortening phase. D) First dextral motion and
afterwards sinistral motion boudins open in strike 335.
W
E
11
5.2 Petrography of thin sections
The thin sections were taken from outcrops during the fieldwork and of two selected drill cores, core
010.81 and 043.84, within the study area (location fig. 2). The thin sections were used to document
microstructures and overall mineralogy, with particular attention to ore occurrence within the rocks
(table 1). The stratigraphic rock types present can be divided into four main groups, metavolcanics,
limestones, metasediments and skarns (fig.7A,B,C,D) However, even within those groups sample
composition varies widely (table 1). In this study, skarn refers to altered calc-silicate ore hosting rock.
All of the rock types in this area host variable amounts of ore minerals. Most ore minerals occur within
the carbonate rocks and skarns and least in the metasediments.
Figure 7: A) Metavolcanic rock sample. B) Limestone rock sample. C) Magnetite hosted skarn sample. D) Metasediment rock sample.
12
Table 1: Mineral modes in percentages of all thin sections with their corresponding names and lithologies. The 1 to 8 series are thin sections of samples obtained during fieldwork and the 0.10()-043() are sections
sampled from drill cores.
Sample Lithology
Chalcopyrite (CuFeS2)
Pyrite(FeS2)
Pyrrhotite (FeS1+x)
Magnetite (Fe3O4)
Sphalerite (ZnS)
Galena (PbS)
Rutile (TiO2)
Quartz
Carbonate
Biotite Chlorite
White mica
Plagioclase
K-Feldspar Pyroxene Epidote
Amphibole
Zoïsite Garnet Actinolite spinel Silimanite Andalusitekyanite
1.1 Carbonate 90 10
1.3 Skarn 8 25 10 7 5 20 520
1.3B Skarn 10 35220 15 20 25
1.4 Skarn 7,5 2,5 10 30 520 15
2.1A Carbonate 10 510 25 20 520 10 5
2.2 Volcanite 2 8 3 30 35 5 5 10 2
2.5 Volcanite 10 230 25 25 7 1
3.2 Skarn 25 35 510 5 5 15
4.1 Skarn 5 10 30 35 10 10
4.4 Volcanite 1 55 30 9 5
5.1L Volcanite 10 530 25 15 10 5
5.1P Volcanite 5 5 30 35 10 10 5
5.6 Volcanite 5 75 510 5
5.10A Volcanite 15 525 15 15 510 10
5.10B Volcanite 5 30 40 5 2 3 15
6.1A Volcanite 40 40 5 4 4 7
6.1B Volcanite 40 45 5 5 5
6.2 Volcanite 5 20 10 20 10 525 5 5
6.3 Volcanite 15 45 5 5 15 15
6.5 Volcanite 60 5 8 25 2
6.6L Metasediment 35 30 20 15
6.6P Metasediment 5 30 40 20 5
6.7 Carbonate 15 70 5 5 5
6.9A Volcanite 5 70 10 15
6.9B Volcanite 5 50 10 25 5 5
6.11 Metasediment 35 30 15 10 10
7.7 Volcanite 40 10 5 5 40
7.11 Metasediment 50 15 530
8.1 Volcanite 5 20 30 20 55510
010.81A Skarn 10 5 5 20 520 10 10 10
010.81B Volcanite 5 3 2 50 30 10
010.81C Volcanite 5 15 40 30 10
010.81D Carbonate 5 7 8 50 10 10 5 5
010.81E Carbonate 30 30 10 20 10
010.81F Carbonate 2.5 2.5 85 10
010.81G
Carbonate
2.5 2.5 1 84 5 5
010.81H
Carbonate
1 1 5 5 63 10 10 10
010.81I Carbonate 7.5 2,5 60 20 5
043.84A Volcanite 2 8 20 20 40 10
043.84B Volcanite 2,5 2,5 25 10 10 50
043.84C Volcanite 5 5 40 15 65 5 5
043.84D
Carbonate
2 8 40 5 5
043.84E Skarn 15 10 25 35 510
043.84F Skarn 2,5 12,5 25 30 10 5555
12
13
5.2.1 Petrography of metavolcanics
The metavolcanics are mainly composed of quartz and biotite, furthermore they vary in the composition
of ores, chlorite, white mica’s, amphibole, epidote, clinopyroxene, sillimanite, kyanite, garnet, feldspars,
spinel, rutile and carbonates (table 1). The rocks are fine- to medium-grained, 30% contain garnet
phenocrysts and 45% contain quartz phenocrysts. In nine thin sections garnets cores are free of
inclusions, whereas the rims contain quartz, biotite and magnetite inclusions. In thin sections of drill
cores garnet to chlorite resorption is a common feature as well. The mineralogy of the metavolcanics
reflects amphibolite metamorphic conditions with sillimanite as the highest occurring index mineral.
Biotite grains show foliation and form around quartz grains (Fig. 8A). Quartz in most thin sections are
annealed (Fig. 8B). Biotite and quartz show schistose textures within 75% of the thin sections in the
remaining thin sections no apparent texture can be distinguished. In the case of quartz phenocrysts in a
biotite layer, the biotite tends to fold around the quartz minerals. Sericitisation of feldspar and epidotes
form veins through the metavolcanic rocks which disrupt the general structure of the rock. Both
sericitisation and epidote veins reflect fluid-rock interaction within the host rock. Magnetite is the most
common type of ore mineral in metavolcanics occurs as inclusions in chlorite and biotite, as well as in
schlieren, veins or in patches. Pyrrhotite and pyrite and chalcopyrite also occur in the metavolcanic rocks
as inclusions of biotite or as patches of grains. Very rarely quartz has inclusions of biotite and magnetite
but never of other minerals.
5.2.2 Petrography of limestones
The limestone rocks of this study show strong compositional variation. They range from relatively pure,
up to 90 percent carbonate minerals, to only 35 percent carbonate minerals. Additional minerals are
mainly amphiboles like actinolite or tremolite, clinopyroxene, garnet, epidote, zoisite, micas, spinel,
sphalerite, magnetite, pyrrhotite, chalcopyrite, pyrite and galena (table 1). Sphalerite in the study area is
strongly associated with carbonate and commonly occurs surrounded by carbonate grains or as carbonate
inclusion host (Fig.8C). Quartz, pyrite, pyrrhotite and galena occur as inclusions in carbonates and some
pyrrhotite, magnetite and pyrite are carbonate inclusion hosts (Fig. 8 D, E). Garnet in the carbonate
rocks is heavily altered and mostly replaced by chlorite. Also, garnet is a major host of inclusions such
as biotite, spinel, sphalerite, pyrrhotite and magnetite. Furthermore, galena, sphalerite and spinel also
form in veins. Galena and pyrrhotite occur as inclusions in spinel as well. Like garnet, amphibole shows
no inclusions at the centre but multiple inclusions at the rims. For amphibole these inclusions are
magnetite grains. Chlorite veins cut off quartz and carbonate veins indicating chlorite veins formed later
on in the time sequence.
5.2.3 Petrography of metasediments
Only few outcrops of metasediments occur in the study area. The metasediments are the youngest
stratigraphic lithology of the study (Fig. 3, table 1). They resemble the metavolcanics in composition
and structure since they also consists mainly of fine grained quartz and micas. However, the
metasediments are the only lithology that contains andalusite. Most, but not all andalusite grains show
rotational deformation patterns, indicating formation during waning tectonic activity (Fig. 8 F). The
andalusite grains contain quartz inclusions, which show that they formed later. Biotite grains tend to
form around rotated garnet and andalusite grains and define clear schistosity (Fig. 8G, 8H). Magnetite
and pyrrhotite occur in the metasediments as small anhedral minerals, less abundant than within the
metavolcanics and carbonates with a maximum of five percent (table 1). In thin section 7.11 a small
fracture with dextral movement is visible.
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5.2.4 Petrography of Skarns
Skarns are core hosting calc-silicate rocks in the study area and contain minerals like carbonate,
dolomite, micas, clinopyroxene, amphibole, garnet, quartz, epidote, feldspar and all sorts of oxide and
sulphide minerals (table 1). Amounts of oxide and sulphide minerals within these rocks vary between
outcrops (table 1). In some samples the entire matrix consists of pyrrhotite with magnetite and pyrite
inclusions, whereas in others ore minerals only occur as minor inclusions. In most skarn thin sections
recrystallisation is evident as reaction rims, annealed quartz, sericitisation and garnet to chlorite
resorption. Ore minerals manifest often in fractures and veins throughout the rocks (Fig.8I). Quartz,
biotite and ore inclusions in amphibole, garnet, chlorite and carbonate occur regularly. Ore minerals are
hosts of many inclusions as well (fig. 8E). In some samples magnentite and pyrrhotite grains show
similar to larger grain size than quartz and biotite. These large grains contain many quartz ore biotite
inclusions. In skarn samples magnetite and pyrrhotite grains commonly occur as small inclusions and
as large inclusion hosting grains (Fig. 8J). A lot of veins are filled with either epidote, carbonate or
chlorite and in lesser abundance, iron-bearing minerals like magnetite and pyrrhotite.
5.3 Ore mineral petrography
Most of the opaque minerals in thin sections are ore minerals and identified with the help of combining
reflected light microscopy with SEM-EDS data. Magnetite (Fe3O4), chalcopyrite (CuFeS2), pyrite
(FeS2), pyrrhotite (FeS), sphalerite (ZnS), galena (PbS) and rutile (TiO2) occur in the samples. Ore
minerals containing Fe are present in about 60% percent of the samples suggesting that it is the most
commonly occurring mineralisation element in the study area. In the thin sections all ore minerals occur
as inclusions and as matrix throughout the sample. Also, ore minerals commonly occur as inclusions or
veins in and around other ore minerals (Fig. 8J) . Table 2 show all types of occurrences in the study area
for each ore mineral plus quartz, biotite, carbonate, amphibole and feldspar since those occurs as
inclusions in ore minerals as well. Both magnetite and pyrrhotite form as inclusions and also have
inclusions within the same thin section. These size and occurrence differences in a single sample
suggests the possibility for two mineralisation events in the rock (Fig. 8J). In most thin sections the ores
tend to follow and fill fractures, form in patches and alter the neighbouring minerals.
Mineral
occurs in pyrrhotite chalco pyrite pyrite
magnetite sphalerite galena rutile biotite quartz
carbonate
amphibole Feldspar
matrix x x x x x x x x x x x x
veins x x x x x x
pyrrhotite x x x x
chalco pyrite x x x
pyrite x x x
magnetite x x x x x x x
sphalerite x x x x
galena
rutile
biotite x x x x
amphibole x x x x
chlorite x x x
Garnet x x x x
quartz x x x x
pyroxene x x x
carbonate x x x x x x x
feldspar x x x x
Table 1: This table shows the type of ore mineral occurrence in thin sections. Quartz, biotite, carbonate, amphibole and feldspar are added
since they are the only non-ore minerals that occur as inclusions in ore minerals. On the x-axis the minerals are presented and on the y-axis
where they occur in the thin sections.
15
16
5.4 Cross-sections
Using field data and additional structural data extracted from the SGU database, three geological cross
sections of the study area were constructed during this study (fig. 2). One in the north, one in the centre
comprising the Lejagruvan and one in the south comprising the Siggebodagruvan (Figs. 9.10, 11). These
three cross sections show a broken, overturned, tight, south-east dipping syncline as the major structure.
Listric faults occurring in all sections seem to be reactivated as reverse faults during a compression
phase. The northernmost cross section (A, fig. 9) is the only one containing a mappable portion of the
GP intrusive rock suite, which is the only intrusive rock suite in the area. The GP intrusion suite borders
the north-eastern part of the study area and its subsurface geometry is very uncertain. Cross-section A
also intersects the Fanhyttan marble quarry which is currently active and the inactive Vildgruvorna (Fig.
9). The youngest lithological member and centre of the syncline, the metasediments of the Mårdshyttan
formation, outcrops only within this cross section and disappears further south because of the south-
dipping nature of the syncline. Iron-bearing localities are present at the western limb near Uskaboda and
in rhyolitic-ash-siltstones of the Storsjön formation. Two east-dipping reactivated listric faults with
eastern-side-up motion occur in this part of the field area. The easternmost fault of cross section A is a
west-dipping back-thrust that is cut off by the GP intrusive suite. However, this back thrust is not
observed in the field. Evidence for this fault are west-block upward motion indicators manifested in this
part of the study area (Fig. 6G) and geophysical gravity charts provided by the SGU showing negative
gravity anomalies near the intrusive rock suite. The main structure of the study area is the
Guldsmedshyttan syncline but in the syncline also smaller scale parasitical anti- and synforms occur.
The middle cross section (B, fig. 10) crosses the closed Leja copper mine (Lejagruvan), which is
characterised by skarn alteration of the dolomite layers in the broken eastern part of the main synclinal
structure. The major syncline is accompanied by smaller folds broken-up by reactivated listric faults and
westward dipping back-thrusts. Between the easternmost listric fault and westernmost back-thrust a
skarn layer occurs in the Uksen limestones. In this cross-section the interlayering between dolomites
Figure 8: Microstructures in thin sections under plain polarized light (A, B, D, F, G, H, J)) and reflected light (C, E, I). The names of all thin sections
correspond with the names in figure 2 and table 1 A) Thin section 5.1L S-C structures in biotite. The biotite forms around a subhedral magnetite crystal
which has several small biotite inclusions. B) Thin section 5.1P. Anhedral magnetite harbours quartz and biotite inclusions, quartz grains are annealed.
C) Sphalerite occurrence near carbonate grains in sample 043.84D. D) Pyrrhotite inclusion in carbonate grains, sample 010.81F. E) Carbonate inclusion
in pyrite, sample 043.84A. F) Thin section 6.6L Deformed Andalusite surrounded by deformed biotite. Biotite foliation is also evident on sample scale
Black spots are graphite. G) Rotated garnet in sample 010.81B. Biotite folds around the rotated garnet H)Thin section 7.11. S-C fabric in biotite S2
microstructures are reworked by S4 dextral movement. I) Thin section 010.81. Broken and deformed pyrite vein crosses magnetite grain surrounded with
dolomite and biotite .J) Thin section 5.10B. Magnetite occurs in a variety of sizes within the thin sections. Smaller particles manifest in quartz layers while
larger grains form inclusions within biotite or loose grains. The bigger biotite grains are subhedral to euhedral whereas the smaller grains are anhedral.
17
and metavolcanic rocks is well defined. In the other cross-section localities precise mapping of dolomite-
metavolcanic interlayering is impossible due to the smaller scale and irregularities. The westernmost
part of the syncline consists completely of metavolcanics and only east of the westernmost listric fault
limestone rocks occur. Cross-section C is the southernmost of the study area and stratigraphically the
deepest of the three cross-sections. This cross-section comprises the closed but historically important
Siggeboda mine known for its high Fe-Cu-Zn-Pb content. Two major reversed listric faults and two
west-dipping back-thrusts appear in this cross section. Along-strike from the Leja mine and as well in
altered dolomite, skarn alteration occurs in between a listric fault and back-thrust fault-system in a
synclinal structure. Based on observed microscale parasitic folds in the metavolcanics parasitical folds
are added to all cross-sections. In the Stornsjön formation Fe-rich horizons and limestone beds appear
that are too small for precise mapping, therefore they are depicted as dashed lines within the cross section
to empathise their presence in the study area (Fig. 9, 10, 11).
18
Figure 9: Cross section A. Horizontal and vertical scale are identical. Location of the cross section in the field area corresponds with the cross section line in Figure 2.
18
19
Figure 10: Cross section B. Horizontal and vertical scale are identical. Location of the cross section in the field area corresponds with the cross section line in Figure 2.
19
20
Figure 11: Cross section C. Horizontal and vertical scale are identical. Location of the section in the field area corresponds with the cross section line in Figure 2.
20
21
5.5 3D regional and deposit modelling
The overall shape and structures of the study area were modelled in a 3D regional model which nicely
shows the regional stratigraphy and the Zn-Cu- Pb enrichment layers (Fig. 12, 13). This model is based
on the interpolation and the construction of surfaces using cross-sections in combination with existing
SGU maps, field data and drill core data. The regional geology model shows the simplified regional
geology of the field area which helps to comprehend surface and subsurface structures of the study area
(Fig. 12). In addition, the 3D deposit models show horizons that are rich in Zn, Cu and Pb (Fig. 13, 14,
15, 16). For the mineralisation elements different concentrations are determined in drill log assays of
the drill cores, which are implemented in the 3D models. Zn is the most abundant element with a
concentration of max. 2.8% followed by Cu with max. 0.39% and lastly Pb with max. 0.2%. However,
since the model is a simplified version of reality since interlayering of carbonates, differences in skarn
and metavolcanic types and their pinch outs were too precise and too complex to visualize with
leapfrog™. The 3D deposit models, using the drill core and assay data, reveal three metal-bearing
slightly asymmetrically horizontally folded ore horizons which are less than a meter to few meters thick
(Fig. 13). The middle of the three ore layers has the highest Zn and Pb content (up to 0.2% Pb and 2.8%
Zn) and was therefore labelled as the main ore layer (Fig. 14, 15). The other two layers have slightly
lower contents (up to 0.2% Pb and 0.6% Zn), labelled as the upper and lower ore layers. The upper and
lower intervals are both rich in Cu (up to 0.39%) whereas the amounts of Zn and Pb vary a lot (Fig. 14,
15, 16). Zinc is fairly abundant in the upper ore layer where there are minimal amounts of Pb. In contrast
the lower ore layer has higher Pb content where Zn is minimal (Fig. 14, 15). The ore layers are separated
by stratigraphic lithologies up to several meters thick ,which are barren and do not show ore occurrence
according to previous analysis of drill core data (Fig. 13). When visualized into the model the focal point
of the ore concentration is Siggeboda where Pb, Zn and Cu all occur in their highest amounts. In Leja
only Cu occurs greatly, Pb and Zn in slightly lesser but still present in small amounts (up to 0.39% Cu,
0.6% Zn and 0.03% Pb).
22
Figure 12: Regional geology visualized in a 3D model including the Lejagruvan in the east-flank in cross-section B and the Siggabodagruvan in
the east-flank in cross-section C. The model is constructed by combining field observations, SGU DEM’s, drill data and cross sections. The model
is simplified and therefore not all layers are visible, especially limestone interlayering was too precise and is not integrated in full detail which
causes cross section A to have a limestone layer which is not supported by the 3D regional model.
23
Figure 13: The 3D ore deposit model of the Leja-Siggeboda deposits showing 3 southeast-dipping ore layers extending to a depth of circa 400 meters
below the surface. In purplish pink the Lower ore layer, in wine red the Main ore layer and in turquois the Upper ore layer. The drill cores used to
construct the horizons are depicted as the coloured cylinders.
Figure 14: Lead mineralisation within the three ore horizons. Lead only occurs in the main ore horizon and the below main ore horizon. It is most prominent
in Siggeboda where the stratigraphy is bent but also occurs in Leja. Note that the modelled ore layers are gently folded. Blue= 0.01-0.03% Pb, green= 0.03-
0.14% Pb, yellow >0.14% Pb
24
Figure 16: Copper mineralisation within the three ore horizons, copper does not occur in the main mineralisation layer only in the above
and below mineralisation layers. Furthermore is it prominent in both Leja and Siggeboda both in bents in the stratigraphy. Note that
the modelled ore layers are gently folded. Transparent green < 0,07% Cu, green= 0.07-0.14% Cu, yellow= 0.14-0.39% Cu.
Figure 15: Zinc mineralisation visualized within the three ore horizons. Zinc occurs in all three horizons but is mostly in the main ore layer and the upper
ore layer. It is most prominent in Siggeboda where the stratigraphy is bent but also occurs in Leja. Note th at the modelled ore layers are gently folded.
Blue < 0,01% Zn, seablue 0.01-0.06% Zn, yellow= 0,06-2.8% Zn.
25
6 Discussion
6.1 Summary of the tectonic evolution of Bergslagen
The field observations and resulting structural interpretations presented in this study are largely
consisted with the multistage deformation history of the entire Bergslagen area as already proposed by
previous studies (e.g., Lundström, 1983; Carlon and Bleeker, 1988; Carlon and Bjurnstedt, 1990;
Jansson et al., 2018). The study area is located in the western part of the Bergslagen mining district and
is part of the Western Bergslagen Boundary Zone (WBBZ). In summary, the deformation history starts
with pre- and syn-tectonic deposition of bimodal extrusives interlayered with shallow marine carbonates
in a rift basin formed during D1 extensional deformation phase (Oen et al., 1982; Allen et al., 1997;
Stephens et al., 2009; Jansson and Allen, 2015). After E-W extension, horizontal N-S oriented folds
formed in a transpressional regime throughout the entire Bergslagen region including the fieldwork area
(Fig 6D, 6F, Lundström, 1983; Carlon and Bjurnstedt, 1990; Nironen, 1997; Jansson et al., 2018). Left
lateral shearing along the WBBZ occurred from this moment on during the deformation of Bergslagen.
After the formation of the primary faults, e.g., Stephens et al., (2009) suggested that secondary faults
formed in a later D2 phase as a result of strike-slip deformation in a transtensional regime. Beunk and
Kuipers, (2012) suggest that the secondary folds formed after a phase of renewed rifting (D3). During a
renewed rift phase (D3) sandy turbidites were deposited in the subsiding centre of the Guldsmedshyttan
syncline. After rifting, left lateral shearing and transpressional shortening became more prominent again
(D4), which caused buckling of steeply dipping bedding and overprinting of earlier foliation patterns
(Beunk and Kuipers, 2012). In this study schistose rock samples show strong crenulation suggesting
later overprinting of foliation patterns (Fig. 8H). Also, the study area contains mesoscale structures as
seen in Figures 6D and 6F where normal faults are reactivated as reverse faults with an dextral oblique
NW-SE shear component.
6.2 Ore occurrence in the study area
Iron oxides and base metal sulphides occur in all lithologies of the study area. However, the occurrence
of skarn and ore-bearing layers is restricted to two lithologies, the rhyolitic siltstones of the Storsjön
formation near Uskaboda and to the limestones of the Uksen formation in the eastern limb of the
syncline. The former of the two is discontinuous whilst the latter is continuous along the strike of the
syncline within the limestones (Fig. 12, 13). The skarn horizons or lenses are rich in magnetite similar
to most occurrences within the Bergslagen ore district (Stephens et al., 2009). In addition to the high
iron content, skarns in the study area are locally enriched in base metals hosted in sulphides (e.g., Leja
mine). It appears from this study that the skarns enriched in both iron and base metals are spatially
related to faults (Fig. 12). Despite an apparent structural control, the main character of the mineralization
appears stratabound. This is somewhat different from the Lovisa ore occurrence in the northern part of
the Guldsmedshyttan syncline, which has been interpreted as stratiform where ore minerals were
deposited in a brine pool (Cooke et al., 2000; Jansson et al., 2018). Therefore, we suggest a combination
of ore forming processes in which fault zones acted as conduits for metal-rich hydrothermal fluids and
lithologies rich in carbonate (skarn, limestone) were chemical traps in which metals from the
hydrothermal fluids precipitated. However, this may not apply to the skarn locality in the Storsjön
formation along which no significant faults were detected. We suggest that the host rock of this localized
iron-rich skarn lens might have been affected by seafloor alteration and contact metamorphism of acidic
intrusive rocks.
26
6.3 Discussion of rock types, metamorphism and deformation history with
petrography
Thin section petrography confirmed that the four main rock types in the study area are marbles,
metavolcanic rocks, skarns and metasediments (fig. 7; table 1). Microscopic examination combined with
SEM-EDS analysis show that in those types whole rock composition differs per sample, which might
be explained by differences in local metamorphism or local metasomatism in the study area (table 1).
6.3.1 Discussion of the metavolcanics
Metavolcanics are the oldest rock types in the study area and contain annealed quartz grains (Fig. 8B).
Previous work e.g., Stephens et al., 2009; Beunk and Kuipers, 2012 explains the annealing of quartz
grains as a product of contact metamorphism induced by volcanic intrusions. Some relict quartz
phenocrysts host zircons from the Archean basement (3.0-2.5 Ga) implying that original quartz-rich
Archean basement has been exposed to erosion near Bergslagen (Vivallo and Rickard, 1984; Carlon and
Bleeker et al., 1988; Allen et al., 1997; Stephens et al., 2009). Biotite-quartz schists in the western part
of the study area, closest to the WBBZ show foliation patterns in biotite (Fig. 8A). Carlon and Bjurstedt,
(1990), Stephens et al., (2009) and Beunk and Kuipers, 2012 suggested that left lateral shearing strongly
overprints older s-c structures near the WBBZ in the Guldsmedshyttan syncline. Therefore the
crenulation patterns in the biotite-quartz schists of this study is interpreted as D4.
6.3.2 Discussion of the Limestones
On top of the metavolcanics sequence limestones and skarns occur (Fig. 3). This interval shows e.g.,
carbonate replacement with sulphide minerals and garnet resorption, which indicates that the rocks are
affected by metamorphism and metasomatism. Hydrothermal fluids with high magnesium and
potassium contents extracted from felsic intrusive rocks that were present during and after rock
formation reached the limestone deposits via faults acting like conduits and caused local metasomatism
and precipitation of sulphide-bearing minerals in the host rock (Cooke et al., 2000; Jansson et al., 2018).
Metasomatism and precipitation of base metal sulphides are most evident in thin sections from sphalerite
infilling in voids of dissolved carbonate minerals and a mix of sphalerite inclusions in carbonate grains
as well as carbonate inclusion in sphalerite (Fig. 8C).
6.3.3 Discussion of the metasediments
Metasediments are the youngest rock types in the study area and contain deformed andalusite (Fig. 3,
fig. 8F). Andalusite forms during metamorphic processes that occurred after deposition, which suggests
the deformation phase that deformed the andalusite grains was younger than rock deposition. Since not
all andalusite grains are deformed metamorphism likely outlasted the deformation phase, which is also
suggested by Oen et al., (1982), Allen et al., (1997) and Stephens et al., (2009) in previous works. All
rock types in the study area are affected by metamorphism and deformation, which suggests they were
deposited during pre- to syn-tectionic times. Due to the abundance of quartz inclusions in other minerals
we suspect that quartz is likely the oldest mineral present in the region.
6.3.4 Discussion of ore minerals
The most abundant ore types in the study area are magnetite and hematite-bearing Mn-poor iron
minerals. This is consistent with reports from the entire Guldsmedshyttan syncline and throughout the
Bergslagen ore district (Geijer and Magnusson, 1944; Allen et al., 1997; Stephens et al., 2009, Jansson,
2011). Primary skarns occur stratiform at the contact of interlayered metavolcanics and limestones in
the Uksen formation where reaction skarns are observed within the Storsjön formation. This is in line
27
with previous work of e.g., Stephens et al., (2009), which stated the occurrence of both ‘primary skarns’
and ‘reaction skarns’ in the Guldsmedshyttan syncline based on previous papers. Rarer manganese-rich
iron oxide occurs in the limestones of the Guldsmedshyttan syncline as well (Stephens et al., 2009).
According to Stephens et al., 2009 manganese-rich deposits are mostly present high up in the
stratigraphic limestone member of the Uksen formation bordering the meta sediments. However,
manganese-rich levels were not identified in this study. Like the iron oxides, the base sulphide-bearing
minerals occurring in the study area form two main groups: iron-bearing sulphides like pyrrhotite, pyrite
and chalcopyrite and non-iron bearing minerals such as galena and sphalerite. Iron-bearing sulphide
minerals occur widely over all stratigraphic lithologies in the field area whereas galena and sphalerite
are more restricted to skarns in carbonate layers. Just like iron oxides, iron-bearing sulphides often occur
in veins as well and even overprint other minerals ( Fig. 6F). All sulphide minerals, mainly sphalerite
and galena, are inclusion hosts to carbonate (table 2). Sulphide minerals form as inclusions in carbonate
as well and occur as matrix to carbonate rocks. This suggests the sulphide deposits formed as carbonate
replacement during seafloor alteration and ongoing rock deposition (Allen et al., 1997; Jansson, 2011;
Jansson et al., 2018).
This study proposes that ore deposition occurred in at least two different phases based on the difference
in size and host-inclusion relationship of the ore minerals in the thin sections (Fig. 8I, 8J). Some ore
minerals, mainly magnetite, host inclusions of other ore minerals like pyrrhotite or pyrite (Fig. 8A, 8B,
8I, table 2). This is an indicator for multiple generations of ore deposition. Since there are several
intrusive events that all contributed to ore formation this seems probable as well (Allen et al., 1997;
Stephens et al., 2009). Oen et al., (1982) described three different ore formation events for the
Bergslagen region: 1) hydrothermal seafloor alteration and recrystallization with input of basic
intrusives in early rift phase. 2) compressional deformation causing underplating and regional
metamorphism during D2 and, 3) static recrystallization due to contact metamorphism and
metasomatism induced by reaction with post-rift felsic intrusions. These formation events may all apply
to ore formation within the study area. During and just before the early rift phase (D1) iron and sulphides
were deposited in the limestones of the Uksen formation due to interaction between the host rock and
supposedly acidic reducing thermal fluids (Cooke et al., 2000; Kampmann et al., 2017; Jansson et al.,
2018). When rifting was followed by (D2) compression amphibolite metamorphic conditions were
reached in the Guldsmedshyttan syncline, causing a shift in mineral assemblage and recrystallization.
(D4) Shearing provoked remobilisation of ore minerals mobile under brittle circumstances like
magnetite, pyrrhotite, pyrite and chalcopyrite. Galena and Sphalerite are more prone to ductile
deformation instead of brittle deformation and therefore did not remobilise much during this late
deformation stage (Kampmann et al., 2017).
6.4 Discussion of cross sections and 3D models
The cross sections show that the overall structure of the study area is a tight and overturned southeast
dipping syncline, which in detail is broken-up and more complicated than originally described by the
previous work of Lundström (1983). Skarn occurrences are depicted in the limestone and metavolcanic
members and not as individual mappable units because they are most likely a product of alteration and
metamorphism and often are too small to depict as individual layers in the cross sections. In addition to
the larger synclinal structure, parasitic SE-dipping antiform and synform structures reside in the syncline
(Fig. 9, 10, 11). Listric normal faults are reactivated during a compression phase causing western-side-
up movements, in line with (D4) deformation features (Fig. 6D, 6G, Korja et al., 2006; Stephens et al.,
2009; Beunk and Kuipers, 2012). Of the three cross sections only the northernmost (A) contains all
lithologies and displays the highest stratigraphic level (Fig. 9). Cross section B comprises the Leja mine
28
and two faults with westward dip direction are interpreted additionally to the east-dipping listric faults
(Fig. 10). Both westward faults are interpreted as back-thrusts hosting the Leja mineralisation in
between. Since the ore deposit formed close to the back-thrusts there might be a spatial relation between
faulting, the presence of limestone and the occurrence of ore minerals. The same fault-skarn relationship
occurs in cross section C in the Siggeboda area along strike of the Leja skarn occurrence (Fig. 11). The
continuous nature of the skarn alteration between Leja and Siggeboda suggests a connection between
both localities, probably related to the fault systems. Lithological layer thickness is inconsistent in the
field area, especially the limestone layers show thinning towards the listric faults. For this inconsistency
we propose that volcanic deposits are discontinuous and the carbonate rocks are deposited in ever
evolving rift basins (Lundström 1983; Allen et al., 1996; Stephens et al., 2009). In cross-section C a
limestone layer in the subsurface is added of which field observations were impossible. This layer is
added due to complications with reconstruction of the regional 3D model without adding the subsurface
limestone layer.
The 3D models for Cu, Zn and Pb indicate the presence of three mineralized horizons (Fig. 13). All
three horizons, which are a few meters to less than a meter thick, appear parallel and are steeply dipping
towards the southeast. Both Zn (up to 2.8%) and Pb (up to 0.14%) are mostly concentrated in the so
called “main ore layer” but Pb also shows to be abundant in the “lower ore layer” and not in the “upper
ore layer” whereas Zn is more abundant in the “upper ore layer” (Fig. 14, 15). Cu is not concentrated in
the “main ore layer” at all but typically in the upper and lower main ore layers (Fig, 16). Cu
remobilisation is more prone to brittle deformation and Zn and Pb are more prone to ductile deformation
(Cooke et al., 2000; Kampmann et al., 2017). The fact that Cu does not occur in the “main ore layer”
may indicate it was formed in a ductile regime. Since the upper and lower ore intervals are Cu-rich they
might have formed under different conditions. Therefore, we suggest at least two mineralisation events
due to the spatial diversity in mineralisation. This suggestion correlates with the highly volcanic past of
the area in which bimodal felsic volcanism caused multiple stages of fluid-rock interaction and seafloor
alteration multiple times in the past (Vivallo and Rickard, 1984; Baker et al., 1988; Stephens et al., 2007;
Jansson et al., 2018, Luth et al., 2019).
6.5 Interpretation of the relationship between ore bodies and geological
structures
To establish the relationship between ore bodies and geological structures the 3D models and input data
are compared to field data and thin section petrography to find clues on multiple scales that tectonic or
metamorphic events played a role in ore formation in the study area. This is shown in figure 17 for
copper. Ore mineralisation occurs in three horizons on the eastern flank of the Guldsmedshyttan syncline
and has a subvertical orientation just like the bordering stratigraphic lithologies. Sulphide-bearing
minerals mainly occur in the hanging wall of the interpreted fault at the eastern side of the syncline. The
main host rock of the sulphide deposits is the carbonate layer of the Uksen formation, which is unevenly
distributed in thickness along the synclinal structure. Previous research already suggested that
carbonates in Bergslagen to consist of shallow marine basin-filling stromatolites, which would also fit
the geometry we see here (Allen et al., 1996 et al., Jansson and Allen, 2015). Right next to the interpreted
faults in the cross-sections the carbonate layer is thickest and this study proposes that the genesis of this
feature is a half graben system in which the deepest part of the basin is right next to the fault and thus
filled the most with growing stromatolites interlayered with volcanic deposits. The fault likely acted as
a permeable conduit for hydrothermal fluids as well, in which sulphides and metals were transported.
Carbonates may then have acted as a chemical trap causing precipitation of the metals and alteration of
the carbonates (Jannson and Allen, 2015; Luth et al., 2019). After the D1 spreading phase and filling of
29
the supposed half graben, D2 compression tilted and folded the lithologies to a subvertical position
reorienting S0 in the process. Waning volcanic events and the regional high metamorphic grade during
this deformation phase caused ongoing skarn alteration and base metal precipitation. Renewed extension
(D3) has not been prominent in this part of the Bergslagen region but D4 compression and shearing
reactivated faults and caused western-side-up shearing. The shearing induced further remobilisation of
Cu and probably Fe mineralisation (Beunk and Kuipers, 2012; Kampmann et al., 2017). Since sphalerite
and galena are less prone to brittle deformation and more prone to ductile deformation those minerals
did not remobillise as much during this later deformation phase (Cooke et al., 2000; Kampmann et al.,
2017).
There are two end-members of ore mineralisation in Bergslagen, the stratiform-ash-siltstone type or
SAS-type mineralisation and the stratabound volcanic-associated limestone-skarn or SVALS-type.
Between the two main mineralisation types common for the Bergslagen mining district features
occurring in the study area would argue for SVALS-type mineralisation instead of SAS-type
mineralisation based on the stratabound nature of the deposits within the study area (Lundström et al.,
1983; Allen et al., 1996). SAS-type mineralisation is the mineralisation type suggested for the Lovisa
mine in the northern part of the Guldsmedshyttan syncline (Carlon and Bleeker, 1988; Jansson et al.,
2018). Because the area around the Leja mine has a stratabound nature with an apparent structural
control we show that SAS-type mineralisation is not the only type of mineralisation in the
Guldsmedshyttan syncline. Metasomatism might have occurred during D4 deformations since this
western part of the syncline has a particular schistose nature and in the thin sections D4 and Fe/Cu
overprinting is visible (Fig. 8H, Beunk and Kuipers et al. 2012). This particular part of the study area is
located in the WBBZ, which is a prominent left lateral shearing feature since (D2) compression
(Stephens et al., 2009; Beunk and Kuipers, 2012). The WBBZ might have acted as boundary fault along
which the half graben in this study area formed. It is possible that along these faults hydrothermal fluids
reached the limestone rocks as well, invoking the SVALS-type skarn formation in the Guldsmedshyttan
syncline. The localised ore occurrence near Uksaboda in the Storsjön formation likely formed during
seafloor alteration. During alteration, volcanic rocks reacted with seawater and precipitation of Cu-Fe
rich minerals occurred (Allen et al., 1996; Cooke et al., 2000). Thin sections in the area show Cu veins
overprinting magnetite grains which indicates remobilisation during a brittle deformation phase (Fig.
6F). At this locality small-scale mining activities in Vildgruvora are indicated by the presence of mining
pits. In light of the limited occurrence and absence of continuing mining history this type is most likely
isolated skarn as a result of localised metasomatism (Allen et al., 1997; Stephens et al., 2009).
No evidence contradicts the suggestion that iron-oxides formed stratigraphically during low -T seafloor
spreading alteration to form BIFs in quartz-rich layers. There is no reason to suspect that iron-oxide ores
have a different genesis than already stated in previous works from Geijer and Magnusson, 1944,
Stephens et al., 2009 and Jansson et al., 2018. Since Fe rich minerals are only examined in thin sections
and not visualized in the 3D model this study will not make any hard assumptions on the Fe-occurrence
and their interaction with sulphide minerals.
30
Figure 17: Overview of the different scales used during the study. Largest scale is the regional geology during fieldwork, visualized in
an 3D regional geology model. Zoomed in on the Cu horizons occurring in the study area constructed with help of examined drill cores
which in turn are examined with SEM and microscopy on thin section scale.
31
6.6 Recommendations
To extend our knowledge of ore occurrence in the southern part of the Guldsmedshyttan syncline it
would be useful to re-examine the drill cores from the area by using, for example, combined XRT
(tomography) and XRF drill core scanning. This technology has been recently developed with the EU-
project “X-mine” and is now tested on drill cores from the Lovisa mine (Luth et al., in prep.). That way,
the concentrations and spatial distribution of a large number of additional (critical) metals can be
included in the presented 3D deposit models. This technology has been recently developed with the EU-
project “X-min” and is now tested on drill cores from the Lovisa mine (Luth et al. in prep.). That way,
the concentration and spatial distribution of a large number of additional (critical) metals can be included
in the presented 3D deposit models. I would also recommend drilling cores in the northwest of the study
area in the Storsjön skarn occurrence to improve understanding of that particular area.
During this study the Leja and Siggeboda mines played an important role since they are rich in base
metal bearing sulphides, which were of key interest in the study. Providing proof of the connection
between Leja and Siggeboda would contribute tremendously to understand the behaviour of ores toward
faults and lithologies in the area, which then can be projected to other regions. New data obtained from
combined XRT-XRF scanning on a selection of drill cores could then provide more detailed 3D models
and knowledge of the ore body interaction with structural geology in the area. Despite the highest base
metal contents at Siggeboda, the modelled ore bodies are open and unsure at depth (400 meters) as well
as to the NE and SW, making this area a potential target for future mineral exploration. This study noted
stromatolites as possible basin infill, however this is purely based on the knowledge that stromatolites
formed in other parts of Bergslagen (Jansson and Allen, 2015). No hard evidence for the occurrence of
stromatolites in the study area is found nor has been a priority of the fieldwork. To confirm or reject this
assumption, suspicion a study on stromatolites in the Guldsmedshyttan syncline should be conducted.
32
7 Conclusions
The results and interpretations of this study advocate that the Guldsmedshyttan syncline is a more
complicated system that previously described by e.g., Lundström, (1983) and Carlon and Bleeker,
(1988). Three cross sections of the Guldsmedshyttan syncline were produced, which all show a typical
overturned synclinal structure, parasitical antiforms, reversed listric faults and back-thrusts (Fig. 9, 10,
11). The limestone layer of the Uksen formation is generally thickest on the eastern side of listric faults
but overall highly variable, suggesting a halfgraben setting during the D1 extensional phase. The shallow
marine setting is ideal for stromatolites which have grown on the subsiding basement to keep up with
the relative sea level whereas they stayed more steady and grown less rapidly near the edge of the basin
which causes the difference in thickness observed in the study area.
The 3D deposit models depict that base metal sulphides occur in three separate ore layers varying from
less than a meter to several meters thick. In these horizons Cu only forms in the lower and upper ore
layers. Thin sections show Cu overprinting other ore minerals and notable differences in size between
ore minerals in the same thin section. These findings indicate multi-stage ore precipitation in the study
area. Remobilisation of Cu likely occurred during D4 shearing since the element is most mobile in brittle
deformation environments, whereas both Zn and Pb are more mobile in ductile environments. Due to
the stratabound and even almost stratiform nature of the base metal sulphide minerals we agree with
Stephens et al., 2009 on the notion that the skarn horizons in the limestones classify as SVALS-type ore
formation.
From this multi-scale study, we conclude that base metals are spatially related to the occurrence of
limestone and major faults. We suggest that these fault zones acted as conduits for metal-rich acidic
hydrothermal fluids and limestones acted as chemical traps where metals precipitated. Furthermore, the
modelling results indicate that the ore bodies between Leja and Siggeboda are most likely connected
occurring within the same stratigraphic levels striking NE-SW.
33
8 Acknowledgements
I would like to thank Fraukje Brouwer for supervising this project, taking time to discuss findings and
providing me with the needed access to microscopes and the SEM. The Geological Survay of Sweden
(SGU) supported this study financially from their “X-mine” project funded by the European Union’s
Horizon 2020 research and innovation program under grant agreement 730270. Thanks for the fieldwork
and lending me the needed equipment for working in a heavily metamorphic altered, forest location. Of
the SGU I would like to thank Stefan Luth in particular, for supervising the fieldwork and always
answering my questions when I got stuck, he has also been of tremendous help by the construction of
the 3D models. Special thanks to Bernd Andeweg for helping out with licence problems and for being
the second supervisor, Linah Krigee for being my fieldwork partner and Frank Beunk for sharing his
knowledge of the area and reflected light microscopy with me. I would like to thank Bouke Laçet for
teaching me how to make my own thin sections and the availability of his lab and equipment. Finally,
thanks to Roel van Elsas for showing me how to work with SEM and interpret the obtained data.
34
9 References
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continental margin, back-arc, felsic caldera province with diverse Zn-Pb-Ag-(Cu-Au) sulfide and Fe
oxide deposits, Bergslagen region, Sweden. Economic Geology, 91(6), 979-1008.
Baker, J. H., Hellingwerf, R., & Oen, I. S. (1988). Structure, stratigraphy and ore-forming processes in
Bergslagen: implications for the development of the Svecofennian of the Baltic Shield. Geologie en
Mijnbouw, 67(2-4), 121-138.
Beunk, F. F., & Kuipers, G. (2012). The Bergslagen ore province, Sweden: Review and update of an
accreted orocline, 1.91.8 Ga BP. Precambrian Research, 216, 95-119.
Carlon, C. J., and Bjurstedt, S. (1990). Stratabound and stratiform sulphide mineralisation in the
evolution of the Guldsmedshyttan Syncline, Bergslagen, south-central Sweden. Geologiska Föreningen
i Stockholm Förhandlingar, 112(2), 176-177.
Carlon, C. J., and Bleeker, W. (1988). The geology and structural setting of the Håkansboda Cu-Co-As-
Sb-Bi-Au deposit and associated Pb-Zn-Cu-Ag-Sb mineralisation, Bergslagen, central
Sweden. Geologie en mijnbouw, 67(2-4), 279-292.
Cooke, D. R., Bull, S. W., Large, R. R., & McGoldrick, P. J. (2000). The importance of oxidized brines
for the formation of Australian Proterozoic stratiform sediment-hosted Pb-Zn (Sedex)
deposits. Economic Geology, 95(1), 1-18.
Geijer, P., and Magnusson, N.H., 1944, De mellansvenska jäirnmalmernas geologi: Swedish Geological
Survey, series Ca, v. 35, 654 p.
Jansson, N. (2011). The origin of iron ores in Bergslagen, Sweden, and their relationships with
polymetallic sulphide ores (Doctoral dissertation, Luleå tekniska universitet).
Jansson, N. F., & Allen, R. L. (2015). Multistage ore formation at the Ryllshyttan marble and skarn-
hosted ZnPbAg(Cu)+ magnetite deposit, Bergslagen, Sweden. Ore Geology Reviews, 69, 217-242.
Jansson, N. F., Sädbom, S., Allen, R. L., Billström, K., & Spry, P. G. (2018). The Lovisa stratiform Zn-
Pb deposit, Bergslagen, Sweden: structure, stratigraphy, and ore genesis. Economic Geology, 113(3),
699-739.
Kampmann, T. C., Jansson, N. F., Stephens, M. B., Majka, J., & Lasskogen, J. (2017). Systematics of
hydrothermal alteration at the Falun base metal sulfide deposit and implications for ore genesis and
exploration, Bergslagen ore district, Fennoscandian Shield, Sweden. Economic Geology, 112(5), 1111-
1152.
Korja, A., Lahtinen, R., & Nironen, M. (2006). The Svecofennian orogen: a collage of microcontinents
and island arcs. Geological Society, London, Memoirs, 32(1), 561-578.
Lundström, I., 1983, Beskrivning till Berggrundskartan. Lindesberg SV: Geological Survey of Sweden,
Af 126, 140 p.
Luth, S., Sahlström, F., Jansson, N., Jönberger, J., Sädbom, S., Landström, E., ... & Arvidsson, R. (2019).
Building 3D geomodels using XRF-XRT-generated drillcore data: The Lovisa-Håkansboda base metal-
and Stråssa-Blanka iron deposits in Bergslagen, Sweden. In 15th SGA Biennial Meeting 2019, Glasgow,
Scotland.
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Luth, S., and Bergman, S., (2020). Regional strukturanalys i Bergslagen från lineament till skjuvzon.
SGU-rapport 2020:13.
Nironen, M. (1997). The Svecofennian Orogen: a tectonic model. Precambrian Research, 86(1-2), 21-
44.
Oen, I. S., Helmers, H., Verschure, R. H., & Wiklander, U. (1982). Ore deposition in a Proterozoic
incipient rift zone environment: a tentative model for the Filipstad-Grythyttan-Hjulsjö region,
Bergslagen, Sweden. Geologische Rundschau, 71(1), 182-194.
Stephens, M. B. (2009). Synthesis of the bedrock geology in the Bergslagen region, Fennoscandian
Shield, south-central Sweden. Sveriges geologiska undersökning (SGU).
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Stephens, M. B., & Jansson, N. F. (2020). Paleoproterozoic (1.91.8 Ga) syn-orogenic magmatism,
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Society, London, Memoirs, 50(1), 155-206.
36
10 Apendices
A.1 Drill logs
(Coordinates in sweref99)
Bore Hole North East Azimuth Dip Total depth (m)
Leja 001/80 6610326.157 503106.5197 040 50,3
Bore Hole From (m) To (m)
Swedish description (original) English description Note
Leja 001/80 0,00 4,40
Jord Soil
4,40 44,95
Skarn, skiffrigt, klorit, biotit,
amfibol med granatporfyroblaster,
karbonathaltigt med magnetitsliror
4,90 - 6,10 kross
8,10 sprickfylln. svavelkris
13,45 - 14,40 sprickigt
17,70 - 17,75 spår Cu-kis, magnetkis
18,30 cm-band, magnetkis, svavelkis
18,60-70 svavelkis, spår Cu-kis
22,05 slip
25,70 - 25,80 FeS2 + ngt Fe
36,05 - 36,25 Fe-slira
37,40 - 37,55 spår av FeS2 och
CuFeS2
42,10 - 43,00 ZnS-impr + ngt Fe
42,90 polerprov
43,00-44,85 spår av ZnS + ngt Fe
44,30-44,60 kross (sköl)
44,95 ,,
Skarn, foliated, cholite, biotite,
amphibole with garnet
porfyroblasts, carbonate bearing,
some magnetite spots
4,90 - 6,10 broken
8,10 cracked pyrite
13,45-14,40 cracked
17,70-17,75 traced of chalcopyrite,
pyrrhotite
18,30 cm band of pyrrhotite and
pyrite
18,60-70 pyrite, traces of
chalcopyrite
22,05 thin sectio n
25,70-25,80 pyrite + some Fe
36,05-36,25 Fe-spots
37,40-37,55 traces of pyrite and
chalcopyrite
42,10-43,00 ZnS impregnations +
some Fe
42,90 polsih-proof
43,00-44,85 traces of ZnS + some Fe
44,30 - 44,60 broken fine grained
mica/chlorite/talc rich rock
44,95 ,,
42,10-43,00 ANALYS Zn, Pb, Au, Ag
43,00-44,85 ANALYS Zn, Pb, Au, Ag
44,95 50,30
Dolomit i början något skarnig.
Ställvis magnetitprickig
Dolomite, in the beginning
somewhat skarnic.
Some magnetite spots
SLUT
S Bjurstedt and H Persson
Bore Hole Sample From (m) To (m) Pb (%) Zn (%) Ag (ppm) Cu (%) Co (%) Au (ppm)
Leja 001/80 9412 42,10 43,00 0,07 1,8 24 0,03 X <0,1
Leja 001/80 9413 43,00 44,85 0,06 0,32 16 0,08 X <0,1
37
Bore Hole North East Azimuth Dip Total depth (m)
Leja 002/80 6610611.046 503389.7533 048 66,65
Bore Hole From (m) To (m)
Swedish description (original) English description Note
Leja 001/80 0,00 0,50
Jord Soil
0,50 57,25
Förskiffrat biot it, klorit-skarn.
Till 15 m med pyroxen, något kal kigt samt
med granater o ch magnetitsliror. Dm-
stora part ier av kalkrikt skarn med granat
15,95-16,15 FeS2-impr
17,00-17,07 ,, + något kross
20,20-20,45 FeS2-impr + något magnetit
20,60-20,65 FeS2 som sprickfylln.
21,25-21,35 FeS2 spår något magneti t
22,25-22,35 FeS2 + spår av CuFeS2 samt
magnetit
22,95-23,00 FeS2-slira. Något Fe
23,20-23,25 FeS2-slira + magnetit
24,40-24,50 ngt FeS2
25,40 FeS2
26,40 - 26,50 FeS2-impr
26,75-26,85 FeS2-sliror
31,10-31,15 FeS2+magn.
32,05-32,15 FeS2+magn.
32,60 FeS2 + magnetit
32,70 ,,
33,80-34,05 FeS2-impr + magnetit
34,40-34,55 FeS2-impr. + magnetit
35,00 FeS2 + ngt CuFeS2
35,10-35,20 FeS2-impr + CuFeS2-spår
35,50-35,85 god FeS2-CuFeS2-impr
Foliated b iotite, chlorite-skarn.
Untill 15 m containing pyroxene,
some chalk togeth er wih garnets
and magneti te spots. Dm-sized
portions of chalkrich skarn with
garnets
15,95-16,15 FeS2-impr
17,00-17,07 ,, + some fractures
20,20-20,45 FeS2-impr + some magnetite
20,60-20,65 FeS2 as crackfiller
21,25-21,35 traces of FeS2, some
magnetite
22,25-22,35 FeS2 + traces of CuFeS2 and
magnetite
22,95-23,00 FeS2-spots. Some Fe
23,20-23,25 FeS2-spots + magnetite
24,40-24,50 some FeS2
25,40 FeS2
26,40 - 26,50 FeS2-impr
26,75-26,85 FeS2-spots
31,10-31,15 FeS2+magn.
32,05-32,15 FeS2+magn.
32,60 FeS2 + magnetite
32,70 ,,
33,80-34,05 FeS2-impr + magnetite
34,40-34,55 FeS2-impr. + magnetite
35,00 FeS2 + some CuFeS2
35,10-35,20 FeS2-impr + CuFeS2-trace
35,50-35,85 FeS2-CuFeS2-impr
35,50-41,15 FeS2 and some CuFeS2 +
magn.
57,20-59,20 CuFeS2-impr and some ZnS
and PbS
35,50-41,15 Cu, Co, Au, A g (Zn, Pb)
57,25 57,55
Dolomit Dolomite 57,20-59,20 Cu, Co, Au, A g, Zn, Pb
57,55 58,10
Skarn, pyroxen med något granat
Skarn with pyro xene and some
garnet
58,10 66,65
Dolomit Dolomite
SLUT
Bore Hole Sample From (m) To (m) Pb (%) Zn (%) Ag (ppm) Cu (%) Co (%) Au (ppm)
Leja 002/80 9414 35,50 41,15 0,01 0,02 8 0,13 0,01 <0,1
Leja 002/80 9415 57,20 59,20 0,27 0,6 82 0,39 X 0,1
Leja 002/80 4091 59,20 61,20 0,01 <0,01 1 X X X
38
Bore Hole North East Azimuth Dip Total depth (m)
Leja 003/80 6610791.089 503548.5493 035 69,85
To (m)
Swedish description (original) English description Note
5,65
Jord Soil
12,10
Förskiffrat, biotit (klorit) skarn med
granat
Foliated, biotie (chlorite) skarn with
garnet
12,40
Kalkigt granatskarn Chalkish garnet skarn 12,10-12,40 FeS2-impr
21,00
Förskiffrat biotitskarn med granat.
Vid 12,60 0,10 m kf
12,40 FeS2 sprickf.
12,70-12,80 FeS2-slira
13,10 FeS2-impr
13,60 FeS2-fläck
14,50-14,60 FeS2-impr
14,95-15,05 FeS2-impr
15,80-16,00 ,,
16,70-16,90 ,,
17,65-17,75 FeS2-slira
18,20-18,55 FeS2-impr
Foliated biotite skarn with garnet
On 12,60 0,10 m k-spar
12,40 FeS2 in cracks
12,70-12,80 FeS2 spots
13,10 FeS2-impr
13,60 FeS2 spot
14,50-14,60 FeS2-impr
14,95-15,05 FeS2-impr
15,80-16,00 ,,
16,70-16,90 ,,
17,65-17,75 FeS2-spot
18,20-18,55 FeS2-impr
30,80
Granat-biotitskarn, med större granater
än föregående. Ej så starkt förskiffrad.
Vid 21,70-22,05 kross
Garnet-biotite skarn, with bigger
garnets than before. Not so
strongly foliated.
On 21,70-22,05 broken
31,10
Förskiffrat skarnig leptit Foliated skarnic leptite
31,30
Grönskarn med granater Green skarn with garnets
32,00
Förskiffrad skarnig leptit Foliated skarnic leptite
33,40
Grönskarn med granater Green skarn with garnets
34,20
Något förskiffrad skarnig leptit Sometimes foliated skarnic leptite
37,90
Granat biotit, kloritskarn Garnet biotite, chlorite skarn
45,15
Dolomit i början skarnig,
magnetitförande
Dolomite, in the beginning skarnic,
magnetite bearing
46,50
Dolomit med något ZnS, CuFeS2 samt
spår av PbS, magnetitförande
Dolomite with some ZnS, CuFeS2
and traces of PbS, magnetite
bearing
45,15-46,50 Analysis
Zn, Pb, Au, Cu, Co
47,40
Dolomit magnetitförande Dolomite magnetite bearing
50,10
Dolomit med något ZnS, CuFeS2, och PbS,
i början magnetit, sista 0,3 m
malakolitskarn
Dolomite with some ZnS, CuFeS2,
and PbS, in the beginning
magnetite, last 0,3 m skarn with
malakolith
55,05
Dolomit med inslag av malakolitskarn
Dolomite with elements of
malakolith skarn
69,85
Dolomit med aktinolit Dolomite with actinolite
SLUT
H Persson
Bore Hole Sample From (m) To (m) Pb (%) Zn (%) Ag (ppm) Cu (%) Co (%) Au (ppm)
Leja 003/80 9416 45,15 46,50 0,24 0,84 24 0,1 X <0,1
Leja 003/80 9417 47,40 50,10 0,24 1,3 100 0,17 X <0,1
Leja 003/81 4092 50,10 52,10 0,03 0,01 3 X X X
39
Bore Hole North East Azimuth Dip Total depth (m)
Leja 004/80 6610760.175 503460.0177 035 72,15
From (m) To (m)
Swedish description (original) En glish description Note Analysis
0,00 1,75
Jord Soil
1,75 29,90
Granatföra nde biotit, kl oritskarn, något
förskiffrad
Garnet bea ring biotite chlo rite
skarn, someti mes foliated
29,90 33,60
Finkornigare n ågot granatförande biotit-
kloritskarn, med några dm-breda
leptitband
Some finegrained garnet bearing
biotite chlorite skarn, with a few
dm-wide lept ite bands
33,60 39,30
Skarn som föreg., men utan lepti t
Skarn as d escribed before, but
without l eptite
39,30 40,10
Granatföra nde biotit-klori tskarn
Garnet bea ring biotite chlo rite
skarn
40,10 41,20
Kalkigt skarn med magnetit och nå got ZnS
Chalkish skarn with magnetit e and
some ZnS
Zn, Pb, Ag, Au
41,20 41,70
Granatföra nde grönskarn Garnet bearing green skarn
41,70 42,85
Granatföra nde kalkight grönskarn med
god ZnS-impr
Garnet bea ring chalkish green ska rn
with ZnS imp regnations
Zn, Pb, Ag, Au
42,85 43,80
Något skarni g dolomit med god ZnS-impr
Sometimes skarn ic dolomite with
ZnS impregnatio ns
Zn, Pb, Ag, Au
43,80 44,80
Skarnig dolo mit med god ZnS-impr
Skarnic dolo mite with ZnS
impregnation s
Zn, Pb, Ag, Au
44,80 45,60
Något skarni g dolomit med stä llvis god
ZnS-impr
Sometimes skarn ic dolomite with
local ZnS imp regnations
Zn, Pb, Ag, Au
45,60 47,65
Dolomit med magnetit-impr och n ågot
ZnS
Dolomite with magnetite
impregnation s and some ZnS
Zn, Pb, Ag, Au
47,65 48,65
Svagt skarnig do lomit med ställ vis god
ZnS-impr samt n ågot PbS
Weakly skarni c dolomite with l ocal
ZnS-impr and some PbS
Zn, Pb, Ag, Au
48,65 50,45
Något skarni g dolomit med god ZnS-impr
samt spår av PbS
Sometimes skarn ic dolomite with
ZnS impregnatio ns and traces o f
PbS
Zn, Pb, Ag, Au
50,45 52,10
Något skarni g dolomit med god ZnS-impr
samt spär av PbS
Sometimes skarn ic dolomite with
ZnS impregnatio ns and traces o f
PbS
Zn, Pb, Ag, Au
52,10 54,25
Något skarni g dolomit med magnet it-
impr samt spår av ZnS
Sometimes skarn ic dolomite with
magnetite imp regnations and
traces of ZnS
Zn, Pb, Ag, Au
54,25 56,00
Skarnig dolo mit med ställvis god ZnS, PbS-
impr
Skarnic dolo mite with local ZnS, PbS
impregnation s
Zn, Pb, Ag, Au
56,00 57,70
Kalkigt skarn med impr av ZnS och PbS
Chalkish skarn with impregnat ions
of ZnS and PbS
Zn, Pb, Ag, Au
57,70 59,25
Kalkigt skarn med impr av ZnS samt något
PbS
Chalkish skarn with impregnat ions
of ZnS and some PbS
Zn, Pb, Ag, Au
59,25 60,45
Mörk strökorns förande leptit Dark-min eral-phyric-leptite
60,45 61,45
Skarnig lepti t med ZnS i sprickor Ska rnic leptite with ZnS in cracks Zn, Pb, Ag, Au
61,45 62,00
Grå lepti t Grey leptit e
62,00 63,40
Skarnig dolo mit Skarnic d olomite
63,40 64,45
Skarnig lepti t och skarnig dolo mit med
ZnS som sprickfyll n
Skarnic lepti t and skarnic do lomite
with ZnS as crackfilling
Zn, Pb, Ag, Au
64,45 66,90
Starkt förskarna d dolomit Strongly skarned do lomite
66,90 72,15
Dolomit med skarninslag Dolomi te with skarn elemen ts
70,10 FeS, FeS2, slira
71,90-72,00 FeS-impr
68,45-68,55 FeS, Cu, Co, Ag, A u
71,90-72,00 Cu, Co, Ag, Au
SLUT
H Persson
Bore Hole Sample From (m) To (m) P b (%) Zn (%) Ag (ppm) Cu (%) Co (%) Au (ppm) Se (%) Te (%)
Leja 004/80 9500 40,10 41,20 0,04 1,4 4 X X X X X
9501 41,70 42,85 0,09 4,4 4 X X X X X
9502 42,85 43,80 0,02 4,4 4 X X X X X
9503 43,80 44,80 0,05 4,4 4 X X X X X
9504 44,80 45,60 0,02 4,4 2 X X X X X
9505 45,60 47,65 0,03 0,05 2 X X X X X
9506 47,65 48,65 1,1 1,5 48 X X X X X
9507 48,65 50,45 0,01 5,6 2 X X X X X
9508 50,45 52,10 0,44 4 14 X X X X X
9509 52,10 54,25 0,22 0,91 4 X X X X X
9510 54,25 56,00 0,14 3,2 6 X X X X X
9511 56,00 57,70 0,37 1,3 14 X X X X X
9512 57,70 59,25 0,13 2,9 8 X X X X X
9513 60,45 61,45 0,31 4,2 12 X X X X X
9514 63,40 64,45 0,08 0,89 4 X X X X X
9515 68,45 68,55 0,01 0,01 2 0,036 <0,001 0,1 <0,01 <0,01
9516 71,90 72,00 0,01 0,01 <1 0,009 <0,001 0,1 <0,01 <0,01
40
Bore Hole North East Azimuth Dip Total depth (m)
Leja 005/80 6611131.649 503763.6794 035 80,8
Bore Hole North East Azimuth Dip Total depth (m)
Leja 006/80 6611112.671 503786.8965 035 58
Bore Hole From (m) To (m)
Swedish description (original) English description Note
Leja 006/80 0,00 17,90
Jord Soil
17,90 20,60
Grå dol omit Grey dolo mite
20,60 20,75
Brun (skarni g?) dolomit Brown (skarnic?) dolomite
20,75 23,35
Kalkig dolomi t med skarnsliror Chalkis h dolomite with skarn spots
23,35 24,20
Malakolitskarn med i nslag av leptit och
kalkig dolo mit
Malakolith skarn wit h elements of
leptite a nd chalkish dolomite
24,20 25,85
Grå fink. l eptit Grey 'fink.(?)' leptite
25,85 25,95
Skarnslira Skarn spo ts
25,95 35,60
Kalkig dolomi t med skarsliror
Vid 27,95 uppsp rucket berg
Vid 29.15 Kross
Chalkish dolomite with s karn spots
On 27.95 fractured rock
On 29,15 Crushed
35,60 40,10
Grå tät leptit med ensta ka skarnin slag
Vid 36,45 kross
Grey (not visible b y eye) leptite
with single skarn spots
On 36,45 Crushed
40,10 43,00
Ställvis st arkt förskarnad grå tä t leptit Local ly strongly foliated grey leptite
43,00 45,55
Något förskarnad kalkig d olomit
Somewhat foli ated chalkish
dolomite
45,55 47,50
Starkt förskarna d grå tät leptit
Strongly foliated grey (not visible by
eye) leptite
47,50 48,70
Grå fläckig tät leptit
Vid 48,70 kross
Grey spotted lepti te
On 48,70 Crushed
48,70 58,00
Grå tät leptit med skarnsl iror här och var
Vid 53,80 kross
Vid 52,80 FeS2-impr
54,80-55,00 FeS, CuFeS2-impr
Grey (not visible b y eye) leptite
with skarn spot here and there
On 53,80 crushed
On 52,80 FeS2 impregnatio ns
54,80-55,00 FeS, CuFeS2 impregnation s
SLUT
H Persson
Bore Hole From (m) To (m)
Swedish description (original) English description Note Ana lysis
Leja 005/80 0,00 25,15
Jord Soil
25,15 31,05
Biotit-skarn förskiffrat med enstaka
granater
Kf vid 27,65 0,95 m
Kf vid 30,25 0,55 m
Kf vid 31,05 0,45 m
Foliated b iotite skarn with single
garnets
On 27,65 0,95 m K-spar
On 30,25 0,55 m K-spar
On 31,05 0,45 m K-spar
31,05 56,40
Dolomit; fram ti ll 33,70 magnetit-
mineraliserat. 35,00-36,20 trasigt berg.
(Kalcitspricka län gs kärnan)
54,80 sköl
54,80-55,40 skarn
Dolomite; unt il 33,70 magnetite
ores. 35,00-36,20 broken rock
(Calcitic cracks alon g core)
54,80 fine grained
mica/chlorite/ta lc rich rock
54,80-55,40 skarn
56,40 71,05
Grå tät l eptit, ställvis ska rninslag.
Vid 69,05 kf 0,35 m
Grey fine grained (not visible b y
eye) leptite, so metimes skarn
elements
On 69,05 0,35 m k-spar
71,05 72,20
Dolomit med skarninslag Dolomite with skarn elements
72,20 72,55
Grönskarn med något granat Green skarn with some garnet
72,55 80,80
Grå tät l eptit med skarnsli ror
Grey fine grained (not visible b y
eye) leptite wit h skarn spots
SLUT
H Persson
41
Bore Hole North East Azimuth Dip Total depth (m)
Leja 007/81 6610695.1 503413.277 035 102,65
From (m) To (m)
Swedish description (original) English description Note Analysis
0,00 1,40
Jord Soil
1,40 18,80
Granatföra nde biotitrikt skarn
Vid 5,50 FeS2, CuFeS2-slira
Vid 10,20-10,95 Svag sulfidi mpr.
Vid 10,60 CuFeS2, FeS-slira
Vid 13,20-13,80 svag FeS, FeS2-impr samt
något CuFeS2
Vid 14,25-14,90 svag FeS2, FeS-impr
Garnet bea ring biotite rich skarn
On 5,50 FeS2, CuFeS2 spo ts
On 10,20-10,95 weak sulphi de
impregnation s
On 10,60 FeS2, FeS spots
On 13,20-13,80 weak FeS, FeS
impregnation s and some Cu FeS2
On 14,25-14,90 weak FeS2, FeS
impregnation s
On 10,20-10,95 Cu, Zn, Pb, A g
18,80 19,80
Grönskarn med FeS-impr samt spår av
CuFeS2
Green skarn with FeS
impregnation s and traces of CuFeS2
18,80-19,80 Cu, Zn, Pb, Ag
19,80 21,10
Kalkigt skarn med FeS och CuFeS2-impr
Chalkish skarn with FeS and CuFeS2
impregnation s
19,80-21,10 Cu, Zn, Pb, Ag
21,10 41,15
Granatföra nde biotitrikt skarn
Vid 22,15 FeS-slira
Vid 27,80 FeS-slira
Vid 28,05-28,30 kalkigt part i med FeS
samt något CuFeS2
28,90 CuFeS2, FeS-slira
31,35-33,00 något kalkigt ska rnparti med
FeS, FeS+Fe samt något CuFeS2
Garnet bea ring biotite rich skarn
On 22,15 FeS spots
On 27,80 FeS spots
On 28,05-25,30 chalkish p art wih
FeS and some CuFeS2
On 28,90 CuFeS2, FeS spo ts
31,35-33,00 some chalkish s karn
part with FeS, FeS+Fe and some
CuFeS2
31,35-33,00 Cu, Zn, Pb, Ag
41,15 43,80
Grönskarn med något granat Green skarn with some garnet
43,80 45,70
Något kalkigt b iotitförande s karn Some chalkish biotite bearin g skarn
45,70 47,65
Granatföra nde biotitskarn Garnet bea ring biotite ska rn
47,65 58,35
Kalkig dolomi t
Vid 51,00-51,85 CuFeS2-impr
Vid 51,60 CuFeS2-slira
Chalkish dolomite
On 51,00-51,85 CuFeS2
impregnation s
On 51,60 CuFeS2 spot s
51,00-51,85 Cu, Ag (Zn, Pb)
58,35 61,65
Malakolits karn här och var ka lkigt
Vid 59,55-60,40 CuFeS2-impr
Malakolith skarn, here and there
chalkish
On 59,55-60,40 CuFeS2
impregnation s
Cu, Ag (Zn, Pb)
61,65 69,20
Kalkig dolomi t med aktinoli tnålar här och
var, ställvi s något skarnig
Chalkish dolomite with actinolite
needles her e and there, local ly
somewhat skarn ic
69,20 78,70
Dolomit (nå got kalkig) med aktino litnålar
här och va r
Dolomite (so mewhat chalkish) with
actinolite needles here and there
78,70 102,65
Dolomit med aktinolitnål ar
Vid 97,70-97,95 kalkslamm
Dolomite with actinolite need les
On 97,70-97,95 Chalk waste
42
Bore Hole North East Azimuth Dip Total depth (m)
Leja 008/81