1551912 B855.Pdf

UNIVERSITY OF GOTHENBURG Department of Earth Sciences Geovetarcentrum/Earth Science Centre

Mineralogical generations

and orientation of fractures,

based on drill cores from the

West-Link Project, Gothenburg

Vladimir Medan

ISSN 1400-3821 B855 Master of Science (120 credits) thesis Göteborg 2015

Mailing address Address Telephone Telefax Geovetarcentrum Geovetarcentrum Geovetarcentrum 031-786 19 56 031-786 19 86 Göteborg University S 405 30 Göteborg Guldhedsgatan 5A S-405 30 Göteborg SWEDEN Mineralogical generations and orientation of fractures, based on drill cores from the West-Link Project, Gothenburg.

Vladimir Medan, Göteborg University, Department of Earth sciences; Geoscience, Box 460, SE-405 30 Göteborg

Abstract

Core-drilled boreholes have been drilled in Proterozoic bedrock in the central parts of Gothenburg, SW Sweden, during the preliminary investigation for tunneling a railway in the West-Link Project. The Swedish transport administration is responsible for the planning of the project and to guarantee the safety, therefore significant information about the bedrock is obtained through preliminary investigations before excavating the tunnel. The aim of this study was to investigate the fracture mineralogy and the fracture orientations and if possible use as a predictive tool for future tunnel projects. Five generations of fracture minerals were identified that were precipitated during at least three major episodes of fluid migration in fractured Proterozoic bedrock, western Sweden. Data were used from the preliminary investigations of the West-Link Project and samples were taken from drill cores. The minerals identified were grouped into generations based on cross-cutting relationships for their relative age. Three major events of fluid migration have been identified in the West-Link. The first event is thought to have occurred during the Sweconorwegian Orogeny and formed generation (1) cataclasite fracture filling NW and NE striking fractures. During the later stages of the Sweconorwegian orogeny hydrothermal alteration of primary rock minerals such as biotite and plagioclase occurred and formed generation (2) mineralogy with E-W striking fractures and reusing previous fractures. During generation (3) and (4) the mineral assemblage indicates lower temperatures being precipitated somewhere between the Caledonian Orogeny and the Paleozoic producing low temperature minerals such as quartz, adularia and calcite in reused fracture groups. Subsequent to the Caledonian Orogeny shallow marine sediments were deposited in the foreland basin producing an environment suitable for generation (5) mineralogy comprising clay minerals in reused fracture groups. Analysis of the fracture orientations show that later generations typically reactivate the fractures of the previous generations, indicating that there is no easy and direct correlation between mineralogy and fracture orientation on which to prognose rock mass stability.

Keywords: West-Link, fracture minerals, hydrothermal alteration, fracture orientation

ISSN 1400-3821 B855 2015

Mineralogiska generationer och riktningar av sprickor, baserat på borr- kärnor från Västlänken, Göteborg.

Vladimir Medan, Göteborgs Universitet, Institutionen för geovetenskaper; Geologi, Box 460, SE-405 30 Göteborg

Sammanfattning

Kärnborrhål har borrats i Proterozoisk berggrund i den centrala delen av Göteborg, sydvästra Sverige, i samband med preliminära undersökningar till den planerade järnvägsförbindelsen Västlänken. Tra- fikverket ansvarar för planeringen av projektet samt säkerheten, därför är det viktigt att skaffa information om bergets egenskaper under de preliminära undersökningarna innan man börjar byggnationen av tunneln. Målet med denna studie är att undersöka sprickornas mineralogi samt sprickorienteringar och om möjligt använda informationen som en prognosmodell för framtida tunnelbyggen. Fem olika sprickgenerationer har identifierats som utfälldes under minst tre större episoder av hydrotermal cirku- lation i spricksystemen i den Proterozoiska bergarten. Data som användes i rapporten är från de preli- minära undersökningarna från projekt Västlänken samt att prover hämtades från borrkärnorna. Minera- lerna som identifierades grupperades i generationer baserat på korsande relationer mellan mineral för att ta reda på deras relativa ålder. Tre olika händelser av utfällning har identifierats i Västlänken. Första händelsen tros ha skett under Svekonorvegiska Orogenesen vilket fällde ut generation (1) ka- taklasit sprickfyllnad med NV och NÖ strykande orientering. Under den senare fasen av Svekonorve- giska Orogenesen skedde det en hydrotermal omvandling av de primära mineralen i sidoberget som biotit och plagioklas vilket producerade generation (2) mineral som har en Ö-V strykning samt återan- vänder äldre sprickgrupper. Under generation (3) och (4) indikerar mineralen längre temperaturer som utfälldes mellan Kaledoniska Orogenesen och Paleozoikum som producerade lågtemperatur mineral som kvarts, adularia och kalcit i reaktiverade sprickgrupper. Efter den Kaledoniska orogenesen avsat- tes grundhavssediment i förlandsbassängen som bildade en miljö som gjorde det möjligt att bilda generation (5) mineral som består av lermineral i reaktiverade sprickgrupper. Analyser av sprickor visar att senare generationer använder sig av spricksystem bildade i tidigare generationer, detta antyder att det inte finns något enkelt och direkt samband mellan mineralogi och sprickorientering som man kan använda för att göra en prognos för bergets hållfasthet.

Nyckelord: Västlänken, sprickmineral, hydrotermal omvandling, sprickorientering

ISSN 1400-3821 B855 2015

Contents 1. Introduction ...... 1 1.1 General background ...... 1 1.2 Aims and objectives ...... 5 2. Background ...... 5 2.1 Geological setting ...... 5 2.1.1 Proterozoic to Mesozoic geological evolution of the SW Sweden ...... 5 2.2 Earlier studies ...... 9 3. Methods ...... 10 3.1 Sampling and preparation for microscopy ...... 10 3.2 Petrography and mineralogy...... 10 3.2.1 Macroscopically ...... 10 3.2.2 Microscopy and scanning ...... 10 3.2.3 SEM-EDS ...... 10 4. Results ...... 11 4.1 Relative sequence of fracture mineralisations ...... 11 4.2 Fracture filling types ...... 11 4.3 Identified fracture fillings ...... 12 4.4 Fracture generations ...... 28 4.4.1 Generation 1 ...... 28 4.4.2 Generation 2 ...... 30 4.4.3 Generation 3 ...... 34 4.4.4 Generation 4 ...... 36 4.4.5 Generation 5 ...... 41 4.5 Local derivation of hydrothermal mineralization ...... 41 4.6 Observed alteration processes in the West-Link ...... 43 5. Discussion ...... 44 5.1 Generation 1 ...... 44 5.2 Generation 2 ...... 44 5.3 Generation 3 ...... 45 5.4 Generation 4 ...... 46 5.5 Generation 5 ...... 47 5.6 Timing of the hydrothermal mineralisations ...... 48 5.7 Redox conditions ...... 48

5.8 Fracture orientations ...... 49 5.9 Fracture filling generation model ...... 51 5.10 How can this information be used ...... 53 6. Conclusions ...... 54 7. Acknowledgments ...... 54 8. References ...... 55

1. Introduction 1.1 General background With an economic and population growth there is an important prerequisite that the population can reach their working place within a feasible amount of time. Ever since the late 20th century the problems have been more obvious where the limits have been reached and the current Gothenburg central station cannot manage more rail transport. With plans on increasing the freight traffic, the demands for a better shuttle traffic increase. The solution for this is an 8 km shuttle junction where 6 km is through tunnel under the central part of Gothenburg.

The West-Link is a part of the so-called West-Swedish Package, financed in part by the Swedish State, Gothenburg and surrounding communities and by road traffic taxes and this is an effort to improve the public transport with trains and roads included. Now the project is in projection phase where different alternatives are being considered. Four kilometers of the tunnel is going through bedrock and the excavation technique will be blasting. Two kilometers of the tunnel will be built in glacial clay where cut and cover technique will be used and the tunnel will be cast in concrete. The Swedish Transport Ad- ministration is responsible for planning the building of the tunnel.

When the West-Link Project is planned to be finished the year 2026 the connection in the city will be better with higher capacity and less congestion (Trafikverket 2015).

When a tunnel is finished it is important to guarantee the safety of the passengers using the railway as well as reducing the maintenance costs. This can be done by preventing problems before they occur. The most common method to prevent water from leaking in to the tunnel and increase stability is to use cement injection to reduce the seepage of water via fractures into the tunnel. Information about the bedrock and what controls the fractures and its fracture mineralization helps the engineer to decide how much cement injection to use and where.

The traverse of the West-Link subsurface tunnel is displayed in Figure 1.

Before building a tunnel it is important to understand the mineralogy of the fractures to understand the processes which could lead to increased seepage into the tunnels, during excavation and after comple- tion. This data are obtained through preliminary investigations to prognose what to expect from the bedrock from a geotechnical perspective. A large amount of data is available in the form of drill cores from the West-Link. Selected data from these form the basis of this study. Data are available from drill cores seen in Figure 2 and 3.

Figure 1: Map showing the planned traverse of the subsurface tunnel in Gothenburg (Modified from Trafikverket,2015).

Figure 2: Modified orthophoto with drill cores in the area near Haga, copyright Lantmäteriet (I2014/00696)

Figure 3: Modified orthophoto with drill cores in the area near Korsvägen, copyright Lantmäteriet (I2014/00696)

1.2 Aims and objectives The aim of this study is, based on data from drill core data to describe the bedrock fractures regarding orientation, mineralogy and origin of the fracture fillings found in the drill cores from the West-Link Project and to explain their relative mineralization sequence from a regional geological perspective. By combining specific mineralizations with their respective fracture orientations, a possible relation between orientation and type of mineralization will be investigated. Since many fracture directions have experienced multiple events of fracturing and mineralisation, detailed investigation of mineralisation sequences in thin-section are needed. If a correlation between certain types of mineralisations and fracture orientations are found, this could potentially be used as a predictive tool for rock quality as- sessments, in the West Link and other future subsurface excavations in the Gothenburg area. This study aims to discuss and answer the following questions:

 What is the fracture filling mineralogy in the West-Link?  What is the fracture filling sequence?  Which geological processes have influenced the precipitation of fracture filling minerals?  Do some fracture orientations host certain mineralogy?

2. Background

2.1 Geological setting

2.1.1 Proterozoic to Mesozoic geological evolution of the SW Sweden The Precambrian bedrock in Sweden belongs to the Fennoscandian Shield which has been reworked several times by different orogenies. The oldest deformation event that formed and deformed the granitoids and the Stora Le- Marstrand supracrustals in west Sweden is the Gothian Orogeny approximately 1750-1.550 Ma. The Gothian Orogeny metamorphosed the rocks, changing their mineralogy as well as overprinting a penetrative foliation and early veining. Between the Gothian and Sweconorwegian Orogeny there was magmatism which caused metamorphism during 1500-1.200 Ma and is called the Hallandian Orogeny. During the late Mesoproterozoic 1250-900 Ma the bedrock of the continent Bal- tica was metamorphosed and reworked by an orogenic activity caused by the collision between Baltica and another continent. This event is called the Sweconorwegian Orogeny which created tectonic units and major mylonitic shear zones 1.15-0.90 Ga (Andersson et al 1999). Along the planned West-Link tunnel the rocks exhibit varying degrees of veining and mylonitization, the latter often in an inhomo- geneous way not restricted to specific shear zones (Lundqvist et al 2000).

Most of the rocks which were affected by the Sweconorwegian Orogeny were formed 1750-1550 Ma and therefore were also deformed by the Gothian Orogeny. Slightly after the Sweconorwegian Oroge- ny there was magmatism which formed the Bohus granite 920 Ma and associated pegmatites. This magmatism added heat to the southwest part of Sweden. Also, dolerite intrusions in the area of Gothenburg and Tuve were associated to this ca 900 Ma period. By ca 500 to 400 Ma Laurentia and Baltica were joined during the Caledonian Orogeny which was a process that took 150 million years during which the Iapetus Ocean was subducted. The Caledonian Orogeny overthrusted Caledonian rocks on top of the Sweconorwegian and formed an over 300 km wide mountain chain and forming a foreland basin. The mountain chain was eroded down and the sediments formed by the erosion were deposited on the east side of the mountain chain. These sediments were deposited in shallow marine environment which formed shallow marine sediments later eroded resulting into isostatic rapid uplift. During the Cambrian to Silurian time marine sediments were deposited on the sub-Cambrian peneplain, the sediment layer was several hundred meters in the south Sweden (Sandström et al. 2009).

During Permian time there was high magmatic activity, which centered in the Oslo Graben 300 Ma. Co-temporaneous mafic sills intruded Paleozoic sediments east of Gothenburg (Lundqvist, 2000). This western magmatism and tectonism likely provided heat for mineralisation of fractures in the Gothen- burg area

Gothenburg lies within the Western Segment in the Southwestern Orogenic Province which consists of two segments that are the Western and the East segment. The orogenic province is located in the southwest part of Sweden and the eastern border of the province is the Protogine Zone where the Sweconorwegian deformation ends. The rocks in the area have been deformed, metamorphosed or formed during the Sweconorwegian orogeny that occurred ca 1.15-0.90 Ga (Figure 4).

The western segment consists mostly of gneisses and relatively to the eastern segment have more su- pracrustal rocks. The oldest rocks in the western segment are granitoid rocks which are approximately 1.6 Ga. These segments are separated by the extensive Mylonite zone (Figure 4) from the east by a tectonic zone towards the east which is called the zone of mylonites, which is a zone of deformation caused by the Sweconorwegian orogeny (Lundqvist et al 2000).

Figure 4: Map displaying the geological setting of the West-Link site with tectonic domains and deformation zones (Figure modified from SGU).

Four different types of rocks were identified in the area based on mapping and core logging (Traf- ikverket, 2013). The rock types are two types of gneissic granitoids, pegmatite and metabasite. The gneisses are the most common rock types and their compositions vary between granite, granodiorite to tonalite. These are generally penetratively foliated but there are parts which are less foliated as well (Trafikverket, 2013). Of the granitoids, granites have the highest alkali feldspar to plagioclase propor- tion, while granodiorites have less and tonalites are dominated by plagioclase with only minor alkali feldspar (Figure 5).

Figure 5: QAP classification triangle for igneous rocks (modified from the IUGS systematics of igneous rocks).

Based on the data collected in the West-Link Project the gneissic foliation is changing from northeast- southwest in the north to northwest-southeast in the south. The foliation has a strike between 130-225 degrees and the dip is 20-70 degrees towards west. The measured data can be seen in Figure 6 that display the contour plot with all the strike and dip data from the West-Link (Trafikverket, 2013).

Figure 7 shows a map of the bedrock 1:50 000 which shows the large-scale rocks and structures.

Figure 6: Contour plot which shows strike and dip data of all fractures measured in the West-Link (Trafikverket, 2013).

Figure 7: Map of the bedrock from SGU modified by Trafikverket, shows the most important information about the geology in Gothenburg (Map modified from Trafikverket, 2013).

2.2 Earlier studies Earlier studies of red stained granites in SW Sweden have been done by Eliasson (1993) where mineralogy, geochemistry and petrophysics of red stained granite adjacent to fractures have been studied in three different granites. These studies contributed to the understanding of red staining in granite rocks.

Fracture mineralogical studies were done in Oskarshamn SE Sweden on the core borehole KSH01 A+B by Drake and Tullborg (2004). The investigation was done on fractures, fracture minerals related to final storage of nuclear waste underground in bedrock. The studies of the fracture mineralogy in Oskarshamn provided knowledge about fracture filling minerals and their paragenesis.

Fracture mineralogical studies and wall rock alteration studies on drill cores KAS04, KA1755 and KLX02 were done by Drake and Tullborg (2005) in Oskarshamn SW Sweden. This investigation is similar to the one done in 2004 but with more core boreholes and data it gives more detailed information about fracture mineralogy and associated processes.

Studies of mineralogy, chemistry and redox potential of the red-stained rocks in Simpevarp were done by Drake and Tullborg (2006). These studies of red-staining adjacent to fractures, related to bedrock used as final storage of nuclear waste. These studies described hydrothermal alteration in combination with oxidation, which is the process that causes red-staining in the wall rock.

Fracture mineralogical studies in Laxemar SW Sweden were done on drill cores KLX03, KLX04, KLX06, KLX07A, KLX08 and KLX10A by Drake and Tullborg (2007). These studies were done to get further information about fracture mineralogy. This study showed that the fracture mineralogy in Laxemar is similar to Simpevarp.

Fracture mineralogical studies were done in connection with the construction of the tunnels Götatun- neln and Nygårdstunneln in SW Sweden by Persson (2007). The tunnels are located on each side of the Göta Älv-zone which is interesting because the Göta Älv-zone is separating the Eastern and West- ern Segment. The study by Persson (2007) is interesting because the core boreholes are geographically close to the West-Link.

Studies of oxidizing and reducing conditions in surface- and near-surface groundwaters in Os- karshamn SW Sweden were done to detect the redox front in a crystalline rock by Drake and Tullborg (2008). This study contributes with knowledge about how groundwaters change from oxidizing to reducing with larger depths, due to biogenic and inorganic reactions.

Studies, of which events could have caused the fracture mineralisation and oxidation in SE Sweden, were done by Drake (2008) in his doctoral thesis. In this doctoral thesis all the mineralisation events are correlated with orogenic and tectonic events.

3. Methods 3.1 Sampling and preparation for microscopy Before collecting the samples at Bergab offices in Gothenburg BIPS pictures from over 20 drill cores were examined for potential sampling, e.g. mineralized fractures with cross-cutting relationships. After the BIPS pictures were examined, approximately 30-40 different sites of interest in the drill core were identified. After this pre-sampling investigation, selections of the most promising samples were made at Bergab’s core lab. Samples were taken exhibiting cross cutting relationships and hydrothermal related mineralization.

Host rocks collected were gneissic to mylonitic, granodiorite or tonalite. A total of 12 core samples were collected with core pieces from 0.1 to 0.4m long. The samples were put into plastic bags and named in order S1 to S12 where the core name, depth and sample name were written down on the plastic bag. Sampling featuring mineralizing relationships were cut at the Department of Earth Scienc- es in Gothenburg to a size of 40x20x10 mm. When the pieces had the correct size all thin-sections were extra finely ground with diamond grinding disc, for use in in-house SEM-EDS. 3.2 Petrography and mineralogy Mineralisation events were identified by studying cross-cutting relationships and coexisting minerals in optical microscope and further identification in SEM-EDS. Textural characteristics of minerals were also added as a distinguishing characteristic, using optical microscopy.

3.2.1 Macroscopically All samples were first examined macroscopically to identify geological features which were interesting for this study. Features such as cross cutting relationships, difference in color of minerals, red- staining etc. were noted to get a more clear understanding of what to examine in the microscope and what to analyze in the SEM-EDS.

3.2.2 Microscopy and scanning The thin-sections were first scanned in a document scanning machine which works fine for scanning thin-sections in very high resolution. All the thin-sections were scanned in both plane polarized light and cross polarized light. The scanned images made it easier to identify the textural difference between the samples and to navigate in the thin-sections during the microscopy. Digital photos were taken with the microscope connected to a PC of all features and sites of interests to be analyzed in the SEM-EDS.

3.2.3 SEM-EDS Further information of the fracture filling mineralogy and chemistry was obtained by the SEM-EDS. The scanning electron microscope is a Hitachi s3400-n. The current used was 6.0 nA and a working distance of 9.2 mm. The thin-sections were coated with carbon before being analyzed to improve the imaging of the samples. Chemical analyses and detail textural relations images were made of all identified fracture related minerals.

4. Results

4.1 Relative sequence of fracture mineralisations Based on cross cutting relationships between minerals three major episodes of hydrothermal circulation which resulted into fracture mineralisations have been distinguished in the drill cores from the projected West-Link tunnels. The mylonites were formed during the Sweconorwegian Orogeny under ductile conditions. Mylonitic foliation overprints the earlier generally coarser grained partly veined gneissic foliations during the late stage of the Sweconorwegian Orogeny. This ductile foliation occurs with gradual strength and generally without distinct boundaries. This foliation has no spatial relation to the fractures, the fractures cross-cutting the mylonitic foliation. The first detectable structures after the Sweconorwegian overprinting are fractures with angular fragments in a fine grained matrix of the wall rock also known as cataclasite, which are generation (1).Precipitation of minerals closely related to generation (1) cement the cataclasite and seals the fractures, these minerals which cement the cataclasite are generation (2). During generation (2) there are signs of alteration in the wall rock which can be seen as chloritization of biotite, saussuritization of plagioclase and red-staining of the wall rock adularia. During generation (3) further alteration of the wall rock is seen and assemblages of minerals with lower precipitation temperature. Generation (4) and (5) minerals are found in open fractures with high hydraulic conductivity. The mineral assemblage consists mostly of calcite and clay minerals and cross cut all other generations.

The fracture filling sequence found in the thin-sections from this study are presented in Table 1.

GENERATIONS Mylonite: Biotite, Epidote, Chlorite, Muscovite, Quartz, Titanite, K-feldspar Generation 1: Cataclasite Generation 2: Epidote , Adularia, Chlorite, Titanite > Prehnite> Quartz Generation 3: Adularia, Fe-Oxides > Calcite Generation 4: Adularia , Quartz > Calcite > Pumpellyite, Pyrite, Fluorite, Chalcopyrite, REE-carb Generation 5: Clay minerals Table 1: Table showing the fracture filling sequence of the West-Link. 4.2 Fracture filling types The granitoid rocks in the area of investigation in the West-link Project have been affected by metamorphism and have undergone polyphase deformation where the ductile polyphase folding history is seen as a sequence of new metamorphic foliations overprinting older ones. Therefore older structures and fractures from the time before the rock was metamorphosed are overprinted by the finer grained ductile mylonitic foliation (Figure 8 left). The minerals present in the granodiorite and tonalite rock are the typical rocks forming minerals such as quartz, plagioclase and K-feldspar but also minerals which are characterizing different metamorphic facies. The mineral paragenesis that comprises gneiss- ose foliation belongs to amphibolite facies, overprinted by greenschist facies partial mylonitization.

The fracture fillings studied in this thesis are subdivided into two groups based on the origin of the fracture filling minerals. The two groups are cataclastic minerals and hydrothermally precipitated minerals from a fluid. The cataclastic minerals have its origin from the wall rock and are not hydrothermally precipitated. The cataclastic mineral occurs as cataclasite and breccia. When the cataclastic mineral occurs as breccia the fragments are angular and are set in a fine-grained matrix of crushed wall-rock mineral. When the clastic mineral occurs as cataclasite the grain size of the mineral has been reduced. (Davis and Reynolds, 1996) The other fracture filling types are hydrothermally precipitated minerals which are precipitated from a fluid. The second type is the neoformation of minerals derived from a hydrothermal fluid (Figure 8 right).

Figure 8: Image of the mylonite banding (left) from drillcore HK630KBH and hydrothermally precipitated minerals (right) from drillcore KK626KBH.

The factors which controls what kind of minerals are precipitated from the fluids depends on the pressure-temperature conditions, oxidation-reduction environment, chemical composition of the fluids, the mineralogy of the host rock, pH and which path the fluid is circulating in the fracture system (Tull- borg, 2001). 4.3 Identified fracture fillings The fracture filling minerals from the West-Link Project are presented in a list as a result from optical microscopy (Figure 9), SEM-EDS, XRD and macroscopic examination of the thin-sections and drill cores. The minerals are listed with a comment of abundance and where they occur. The most common fracture filling minerals in descending order are calcite, epidote, adularia, quartz, chlorite, and clay minerals. Plots show the orientations of fractures where a certain mineral is dominant mineral, identified ocularly and reported by Bergab (Trafikverket, 2013). Note that the same fracture may also contain other minerals, thus plotted in other mineral stereo plots. The minerals are present in alphabetical order.

Figure 9: Microphotograph of a cross-cutting relationship between two calcite mineralization where older calcite (blue) is being cut by the younger (red), drill core CH604KBH.

Adularia KAlSi3O8: Low temperature pure potassium feldspar (adularia) is a common hydrothermal mineral and is characterized by that it is almost totally pure potassium feldspar. It is hard to distinguish adularia from K-feldspar in microscope and SEM. It can be distinguished by its crystal habits, bire- fringence and occurrence since adularia is associated to other low temperature minerals. Adularia occurs often together with calcite but appears to have been crystallized before the calcite since the calcite is cutting the adularia. Macroscopically the adularia has a reddish color but in the microscope it appears grey with small inclusions of small red oxide minerals.

In this study there are at least two different types of adularia. One is formed by replacement and alteration of plagioclase and has residues of Na and Ca in it, the other variant of the adularia has a pure chemistry with KAlSi3O8. The adularia (Figure 10) which was formed during oxidizing conditions is heavily red stained. The other variant of adularia lacks red staining. Adularia found in the wall-rock is often found with other alteration minerals of the plagioclase such as epidote and albite.

Figure 10: Microphotograph showing a fracture filled with calcite (red arrow) cross-cutting adularia (blue arrow), the calcite is younger than the adularia, drill core HH618KBH.

Allanite (Ce, Ca, and Y) (Al, Fe) 3(SiO4)3(OH): Allanite occurs as accessory mineral in the granite surviving the alteration therefore found as islands in minerals such as adularia. The allanite is enclosed by the potassium feldspar. The allanite is different from epidote since the Ca+Fe is being replaced into REE+Fe (Deer et al 1992).

Biotite K (Mg, Fe) 3(AlSi3O10) (F, OH) 2: Biotite is a mineral which is a characteristic amphibolite facies mineral (Deer et al 1992) and is present as cataclasite grains derived from wall rock biotite. The fracture orientations of the biotite (Figure 11) are similar to the observed foliation in the area, which are steep fractures striking ENE. The biotite in the fractures is alterated into chlorite by the alteration process chloritization. The chlorite which is formed by the breakdown of biotite is associated with minerals such as titanite and adularia. Chlorite does not contain K+, therefore the break down of biotite is the main source of K+.

Figure 11: Orientations of fractures with cataclastic biotite, derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Brecciated materials: Host rock with or without fracture filling, which has deformed by brittle deformation. Fracture orientations (Figure 12) with brittle deformed material are gently dipping towards NE, steeply dipping towards SW and less commonly steep NE and WNW striking fractures.

Figure 12: Orientations of fractures with brecciated material derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Calcite CaCO3: Calcite is one of the most common fracture filling minerals. The stability temperatures of calcite varies from room temperature to 300°C in fractures (Lagat, 2009) . There are many different types of calcites present in the area, everything from pure calcite CaCO3 to calcite incorporating Mn and minor amounts of Fe,Mg and rare earths in solution with Ca. There are calcites with different crystal structure from rhombohedral to scalenohedral (Figure 13).

Calcite occurs in different forms such as fibrous and with and without lamellaes. The grain size of the calcite varies from large crystals to small brecciated crystals. Brecciated calcite is cryptocrystalline which means not identifiable without a microscope or hand lens while the largest crystals are up to a centimeter. Adjecent to the calcite the wall rock is heavily altered (Figure 14) the plagioclase has been altered by both sericitzation and saussuritization.

As seen in the stereo net (Figure 15) the calcites have many fracture orientations. Two large groups of orientations are the steep fractures dipping towards SW and flat fractures dipping towards NE, there are less common orientations dipping E-W which are flat.

Figure 13: SEM-EDS backscatter image of scalenohedral calcite crystals, drill core HH603KBH.

Figure 14: Microphotograph of heavily altered host rock adjacent to Calcite mineralisation (red arrow), drill core HH621KBH.

Figure 15: Orientations of fractures with hydrothermal precipitated calcite derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Chalcopyrite CuFeS2: Sulphide minerals are precipitated on the calcite such chalcopyrite. Chalcopy- rite is a common sulfide mineral which has tetragonal crystal symmetry and is found on the calcite (Figure 16).

Figure 16: SEM-EDS image of chalcopyrite on scalenohedral calcite crystals, drillcore HH603KBH.

Clay minerals (Smectite-group): Clay samples were analyzed. These belong to the smectite-group including smectite, corrensite (Figure 17) and montmorillonites (Trafikverket, 2013). The fracture orientation of the clay minerals are dominated by the NW striking steeply NE dipping and moderate to gently SW dipping set. Also represented are steep E-W and NE striking fractures (Figure 18). The smecite group of minerals show a swelling character (Trafikverket, 2013).

Figure 17: Backscatter image of smectite mineral Corrensite (blue arrow), drill core HH618KBH.

Figure 18: Orientations of fractures with hydrothermally precipitated clay minerals derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

2+ Chlorite (Mg, Fe ) 5 Al2Si3O10 (OH) 8: The chlorite minerals (Figure 19) are classified as chamosite, which means that it is magnesium and iron rich. Chlorite was analyzed in the SEM-EDS (Figure 20 & Table 2). Chlorite occurs both as mylonitic, cataclastic and hydrothermally precipitated minerals.

Figure 19: Microphotograph of the blue mineral chlorite with calcite (left) and with epidote (right), drill core HH618KBH.

The fracture orientation of chlorite (Figure 21) are dominated by SW dipping fractures and less frequent sets dipping steeply towards S and NE.

Figure 20: Backscatter image of chlorite together with titanite, epidote and adularia, from thin-section S3, drill core HH618KBH.

Spectrum MgO AlO2O3 SiO CaO MnO FeO Total Chlorite 1 12.77 20.33 29.43 0.07 0.46 34.24 97.31 Chlorite 2 13.02 20.73 29.66 0.53 34.09 98.04 Chlorite 3 12.53 19.58 28.88 0.10 0.47 33.60 95.16 Table 2: SEM-EDS analysis of Chlorite seen in Figure 20.

Figure 21: Orientations of fractures with hydrothermally precipitated chlorite derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

3+ Epidote (Ca2Al2) (Fe , Al) (SiO4) (Si2O7) O (OH): The epidote (Figure 22) occurs in similar ways as the chlorite i.e. mylonitic, cataclastic and hydrothermally precipitated mineral. Adjacent to the epidote mineralization the wall rock is hydrothermally typically hydrothermally altered by the process adularization or saussuritization. The fracture orientations of epidote are NW striking, dipping W (Figure 23).

Figure 22: Microphotograph of hydrothermally precipitated epidote. Adjacent to the fracture filling the host rock is being hydrothermally altered by adularization and albitization, drill core HH618KBH.

Figure 23: Orientations of fractures with hydrothermally precipitated epidote minerals derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Fluorite CaF2: Fluorite is a halide mineral with isometric crystal symmetry. The fluorite occurs as a precipitation on the calcites in open fractures (Figure 24).

Figure 24: Backscatter image of fluorite mineralisation in a calcite vein, drill core KA611KBH.

Oxide minerals (Hematite Fe2O3 / Ilmenite FeTiO3): Oxide minerals (Figure 25) are precipitated as a decomposition of Fe-rich minerals and they also appear as inclusions in the adularia which is thought to cause the red staining (Eliasson, 1993). The red staining is diffuse and strongest closer to the fractures, fading irregularly away from fractures.

Figure 25: Microphotograph of red-stained plagioclase with inclusions of oxide minerals, drill core HH612KBH.

Muscovite KAl2 (AlSi3O10) (F, OH) 2: Phyllosilicate mineral with potassium and aluminum (Deer et al. 1992) which is present both as a fine grain hydrothermal alteration mineral sericite in the wall rock along fractures. Muscovite occurs as well as in the older mylonitic foliation. The fracture orientations (Figure 26) of muscovite are steep fractures towards SW and towards NE.

Figure 26: Orientations of fractures with cataclastic muscovite minerals derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Palygorskite (Mg, Al) 2Si4O10 (OH) ·4 (H2O): Palygorskite is a magnesium aluminum phyllosilicate which is a late stage fracture filling in magnesium rich environments. The fracture orientations (Figure 27) of palygorskite are dominated by a NW striking and steeply W dipping set, with less pronounced sets striking NE with various dips.

Figure 27: Orientations of fractures with hydrothermally precipitated palygorskite minerals derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Prehnite Ca2Al (AlSi3O10) (OH) 2: Prehnite (Figure 28 & Table 3) is not so common in the samples in the West-Link but one small mineralization was found. The prehnite mineralization cross-cutting an epidote and adularia fracture indicating that it is younger.

Figure 28: Backscattered electron (BSE) image of a prehnite fracture filling (Spectrum 1) that is cross-cutting an epidote, drill core HH618KBH.

Mineral Al2O SiO2 CaO FeO Total Prehnite 1 20.89 43.95 28.00 5.05 97.89 Prehnite 2 24.94 39.26 24.81 11.15 100.16 Table 3: SEM-EDS analysis of Prehnite seen in figure 28.

Pumpellyite Ca2MgAl2 (SiO4) (Si2O7) (OH) 2 (H2O): Monoclinic crystals of pumpellyite (Figure 29) were identified with the SEM-EDS in low temperature alteration zones together with calcite.

Figure 29: Backscatter image of Pumpellyite together with calcite precipitated in sample S7, drill core KA611KBH.

Pyrite FeS2: The pyrite occurs crystallised on surfaces of calcite (Figure 30) and quartz. The fracture orientation (Figure 31) with pyrite are dominated by NW striking fractures, where one set dips steeply NW and the other gently NE. A few fractures strikes NE with moderatre/steep dips to NW.

Figure 30: Backscatter images of pyrite crystallized on surfaces on pyrite. The left image has a perfectly cubic pyrite with minor pentagon dodecahedral beveling, drill core HH603KBH.

Figure 31: Orientations of fractures with hydrothermally precipitated pyrite minerals derived from Bergab core logging data. Left stereo net shows orientations as point poles and right plot as great circles.

Quartz SiO2: Quartz has a transparent character in plane polarization (Figure 32) in crossed polarization quartz has a white to white grey color with extinction. Some of the quartz fracture fillings have pyrite on the surface of the crystal.

Figure 32: Microphotograph of quartz fracture filling that is cross-cutting epidote and adularia, drill core HK630KBH.

REE-carbonates (REE, Y) CO3: REE-carbonates were found in sample S2 and S7 and they occur as small crystals on fracture surfaces of calcite (Figure 33).

Figure 33: Backscatter image of REE-carbonates on the fracture surface of calcite crystals (red arrow), drill core KA611KBH.

Titanite CaTiSiO5: Titanite is found together with chlorite associated to the breakdown of biotite. The chemistry of the titanite is showing high aluminum and iron which indicates that the high-alumina titanite is a grothite. The titanite is most abundant in samples where there is altered biotite (Figure 34).

Figure 34: Backscatter image of elongated titanite crystals in the cleavage plane of chlorite (blue arrow), drill core HH618KBH.

4.4 Fracture generations The fracture filling sequence has been based on cross-cutting relationships between minerals (Figure 35) but also based on textural and chemical properties. In cases where the cross-cutting relationships are not present, data about the stability temperature of minerals and previous studies has been used to suggest and interpret the fracture filling sequence. Some minerals can be used as geothermometers since they are only stable in a certain interval of temperature. Some minerals are stable in a wide range of temperatures and can be found in several generations.

Figure 35: Image of drill core HK630KBH, showing pervasive ductile mylonitic foliation. The mylonite banding is cross-cutting fractures with cataclasites and hydrothermally precipitated minerals, drill core HK630KBH.

4.4.1 Generation 1 This generation is defined as fractures filled with cataclasites (Figure 36) derived from the host rock. This fracture filling is the result of the transition from ductile or semi ductile to brittle crustal condi- tion. Cataclasite is defined as a rock formed by cataclasis involving brittle fragmentations and rotation of grains along with grain sliding (Sibson 1977). The mineralogy of the brittle fragmentations and grains is the same as in the wall-rock.

The most common host rock minerals are biotite, quartz, chlorite, K-feldspar, epidote, and titanite. These minerals are common minerals in a granodiorite rock that has been in metamorphic conditions of amphibolite facies.

Cataclasite in thin-section S3 has angular fragments of K-feldspar, quartz and in a matrix of fine grained biotite and brown precipitations of Fe-oxides sealed by a mineral assemblage of hydrothermally precipitated epidote, chlorite and corrensite. Cataclasite from thin-section S4 has chlorite, titanite along with brown precipitations of Fe-oxides and these fractures also have the same orientation as the foliation. Cataclasite from thin-section S5 consists of altered plagioclase and altered biotite. Thin- section S11 has angular clasts of quartz and K-feldspar in a fine grained matrix of quartz and K- feldspar. Thin-section S12A and S12B have a mix of K-feldspar and quartz which are sealed by hydrothermal epidote.

Figure 36: Microphotograph of cataclasites in plane polarization from drill cores HH618KBH (S3 and S4), HH621KBH (S5) and KK626KBH (S11).

Interpretation: The granodiorite rock has undergone metamorphic conditions and high strain that resulted in penetrative foliation that formed under ductile conditions. During the mylonitization the grain size was reduced of the host rock producing mylonite banding of greenschist facies, overprinting earlier amphibolite facies foliation. The deformation changed from ductile to brittle deformation which changed the structural and mineralogical properties of the rock and produced cataclasite along brittle fractures. The minerals in the cataclastic fracture filling are derived directly from the bedrock as a result of brittle deformation. This produces fracture fillings with angular clasts in a fine grained matrix.

4.4.2 Generation 2 This generation is defined as a hydrothermally precipitated fracture filling and is sealing the cataclasite fractures (Figure 37). During this generation the alteration of some of the primary magmatic minerals is initiated and the neoformation of hydrothermally precipitated minerals.

Chlorite (Figure 38 left) and titanite occur together and this mineral assemblage is being this is found in thin-sections S3, S11, S12A and S12B. The minerals are coarser and the crystals are euhedral and more developed compared to cataclasite, which are broken and angular. The saussuritization of plagioclase together with chloritization of biotite are the main alterations that occur during this generation. Saussuritization of calcium plagioclase produces epidote (Figure 38 right) with the calcium that is released. Titanite and chlorite are produced by the chloritization of biotite. During lower temperatures the saussuritization of plagioclase is forming prehnite and adularia. In the thin-sections the biotite is almost completely chloritized where elongated crystals of titanite are in the cleavage planes of the chloritized biotite. The epidote crystals are found as euhedral crystals and are filling the fractures in areas where there is altered plagioclase. Adularia is precipitated during the later stages of generation (2) and is sealing the fracture and the brecciated fragments. In samples S12A and S12B quartz is cross cutting epidote and adularia mineral assemblage which indicates that quartz is the youngest mineral found in generation (2). In thin-section S3 generation (2) minerals are sealing the cataclasite fracture. Based on cross-cutting relationships the epidote fracture filling is oldest together with chlorite and titanite in the cleavage plane being cross-cut by prehnite and adularia which is cross cut by quartz. Thick quartz fracture fillings belong to generation (2). Quartz is precipitated after adularia of generation (2) according to cross-cutting relationships (Figure 39). In thin-section S12A and S12B there is evidence of quartz which is cross-cutting itself indicating several quartz mineralisations. Prehnite crystallized after the epidote according to cross-cutting relationships.

A good illustration of how biotite breaks down into adularia, chlorite and titanite can be seen in figure 40 and the SEM-EDS analysis in table 4. The adularization and albitization of the wall-rock is initiated during generation (2) forming adularia and albite at the margin zone of the altered plagioclase and in fractures. Adularia and albite often occur at the margin of an altered plagioclase and are formed relatively close to each other however the albite probably crystalized slightly earlier due to higher stability temperature, this indicating that the albitization and adularization occurs during this generation. SEM-EDS backscatter images (Figure 41 and 42) illustrate that adularia and epidote seem to form concurrently. However epidote has higher stability temperature than adularia therefore being considered as earlier in this generation. The data from the analysis is presented in table 5 and 6.

Interpretation: The granodiorite host rock has fractured during the brittle conditions where metamorphic fluids were circulating. During this generation there is a fluid-rock interaction which results in break-down mineral reactions with the primary rock minerals due to hydrothermal alterations. The hydrothermal alterations produce a mineral assemblage with epidote, chlorite, titanite, albite, adularia, prehnite and quartz. The mineral assemblage is stable in temperatures around 200-400°C (Eliasson, 1993).

Figure 37: Microphotograph of thin-section S11 with epidote and adularia fracuture filling healing the cataclasite and cross-cutting a calcite-filled fracture in the uppermost part of the core, drill core KK626KBH.

Figure 38: Microphotograph with chlorite (left) epidote (right). Adjacent to the fractures the wall-rock is altered, drill core HH618KBH.

Figure 39: Microphotograph of quartz that is cross-cutting adularia which has healed brecciated epidote, drill core HK630KBH.

Figure 40: Backscatter image of minerals which are formed during the breakdown of biotite, drill core HH618KBH.

Mineral MgO Al2O3 SiO2 K2O CaO TiO2 FeO Total Titanite 1.32 5.60 32.44 26,98 30.96 4.02 101.32 Chlorite 14.93 16.92 27.85 0.08 27.55 87.33 Adularia 19.05 67.2 17.04 0.24 103.53 Table 4: Table with chemistry from the SEM-EDS analysis of sample S3 seen in figure 40.

Figure 41: Backscatter image of Epidote being cross-cut by corrensite and calcite in sample S3, drill core HH618KBH.

Spectrum Al2O3 SiO2 CaO FeO Total Epidote 1 21.75 38.47 24.53 14.77 99.52 Epidote 2 21.63 38.50 24.31 15.20 99.64 Epidote 3 21.91 38.23 23.74 14.41 98.29 Epidote 4 21.24 38.39 24.30 15.25 99.18 Table 5: Table with chemistry from the SEM-EDS analysis of sample S3 seen in figure 41.

Figure 42: Backscatter image of a fracture filling with epidote and adularia, drill core HH618KBH.

Spectrum Al2O3 SiO2 K2O Total Adularia 1 18.59 66.23 17.05 101.87 Adularia 2 18.66 66.46 17.08 102.21 Table 6: Table with chemistry from the SEM-EDS analysis of sample S3 seen in figure 42.

4.4.3 Generation 3 This generation is characterized by the crystallization of adularia and calcite which are produced by the process of alteration or precipitation from a hydrothermal fluid. When the calcium-bearing plagioclase is altered the plagioclase can be reconstituted into a sodium-rich albite or potassium-rich adularia (Figure 43 red arrow) variety and the residual calcium joins the fluid forming calcite. Calcite is a late stage mineral of generation (3) and is precipitated last according to cross-cutting relationships (Figure 43 blue arrow). If the temperature is high enough the saussuritization of plagioclase is initiated, this producing large amounts of calcite and adularia in granodiorite rocks. The adularia has microscopic inclusions of Fe-oxides (Figure 44) which are formed during oxidizing conditions. The calcite of generation (3) is pure CaCO3 and has no MnO concentrations in it.

Figure 43: A microphotograph in crossed polars which shows generation (3) adularia (red arrow) and calcite (blue arrow), drill core HH618KBH.

Figure 44: Microphotograph showing the red-staining of adularia in the wall rock formed by alteration of plagioclase, plane polarization (left) and cross polarization (right) in thin-section S5, drill core HH621KBH.

Interpretation: Generation (3) minerals are stable in the temperature interval 50-180°C (Worku, 2012). Adularia in this generation is found in the fractures rather than in the wall-rock together with calcite. Adularia with inclusions of Fe-oxides is formed during oxidizing conditions indicating that adularia with red-staining is formed in an environment similar to generation (2) which is oxidizing. The calcite that occurs with adularia at (Figure 45) is precipitated during the same generation but at a later stage. Cross-cutting relationships indicate that calcite is younger than adularia. Calcite is formed by the calcium which is released into the fluid during the alteration of the plagioclase. Red-staining of the wall- rock adjacent to the fractures is still occurring during this generation.

Figure 45: Image showing a fracture with calcite (central zone) and adularia (margin) in the drill core HK628KBH.

4.4.4 Generation 4 Generation (4) consists of calcite with secondary minerals such as pyrite, fluorite and chalcopyrite. Pyrite is found on the calcite indicating reducing environment. Calcite is the most abundant mineral in the thin-sections. In all the thin-sections that were examined by microscope the calcite is cutting all other minerals which indicate that calcite is one of the youngest hydrothermally precipitated minerals. The calcite has large euhedral crystals and has clear twinning. The chemistry of the calcite is that the calcite is MnO-rich compared to the calcite of generation (3). In thin-section where generation (3) and generation (4) calcite are present (Figure 46 and 47) (Table 7 and 8) the MnO-rich calcite which is generation (4) is cross-cutting the pure calcite based on cross-cutting relationships. The calcite is present together with secondary minerals such as sulphides (pyrite, chalcopyrite), fluorite, REE- carbonate, pumpellyite etc. The secondary minerals have a perfect crystal structure. The different calcite types are MnO-rich calcite, fibrous calcite and microcrystalline calcite (Figure 48). In generation (4) adularia without red-staining is present in small thin fractures this indicating that the environment is changing from oxidizing to reducing. The main alteration in the wall-rock during this generation is sericitization rather than adularization. Thin-sections S6 and S7 with generation (4) mineralogy had wall-rock minerals which were little or unaffected by hydrothermal alteration. A minor amount of quartz has also been found in the same fractures as adularia.

Figure 46: Backscatter image of pure calcite (dark crystal) and MnO-rich calcite (light crystal), drill core CH614KBH.

Spectrum CaO MnO FeO Total Calcite 1 57.95 0 0 57.95 Calcite 2 58.31 0 0 58.31 Calcite 3 57.67 0 0 57.67 Calcite 4 58.38 0 0 58.38 Calcite 5 57.13 0.62 0.33 58.08 Calcite 6 55.8 0.71 0.15 56.66 Calcite 7 57.05 0.75 0.24 58.04 Calcite 8 55.8 0.62 0.20 56.62 Table 7: Table with chemistry from the SEM-EDS analysis of calcite seen in figure 46.

Figure 47: Backscatter image of MnO rich calcite in the same fracture as pure CaCO3 calcite, drill core HH621KBH.

Spectrum MgO CaO MnO FeO Total Spectrum 1 0.26 54.67 0.35 0.47 55.75 Spectrum 2 0.25 53.96 0.46 0.68 55.35 Spectrum 3 0.31 54.12 0.74 0.38 55.55 Spectrum 4 55.98 0.13 56.11 Spectrum 5 57.03 57.03 Spectrum 6 0.16 55.10 0.26 55.52 Spectrum 7 56,88 56,88 Spectrum 8 55,94 0,12 56,06 Table 8: Table with chemistry from the SEM-EDS analysis of calcite seen in figure 47.

Figure 48: Images of cataclastic calcite with both MnO-rich and pure calcite (S1) from drill core CH604KBH, large calcite crystals with twinning (S7) from drill core KA611KBH, fibrous calcite cut by MnO calcite (S5) from drill core HH621KBH and MnO-rich scalenohedral calcite with sulphides (S2) from drill core HH603KBH.

Interpretation: Cross-cutting relationships between calcite and adularia show that the calcite of generation (4) is younger than adularia (Figure 49 & 50). The relative age between adularia and quartz is that they probably precipitated relatively close in time. Calcite is one of the most abundant minerals due to the supply of calcium from the calcium bearing plagioclase. The crystals are big and euhedral and are not competing for space. The MnO-rich and pure calcite are present in the same fracture but the MnO-rich calcite is cross-cutting the pure CaCO3 calcite. The wide temperature range of calcite does not exclude the possibility of coexistence with the next generation (5).The secondary minerals on the calcite such as pyrite indicate reducing environment.

Figure 49: Microphotograph of calcite fracture filling (red arrow) cross-cutting adularia fracture filling (blue arrow), drill core CH604KBH.

Figure 50: Backscatter image of calcite cross-cutting adularia in generation (4), drill core CH604KBH.

4.4.5 Generation 5 This generation also consists of clay minerals mostly smectite-group and chlorite group (Trafikverket, 2013). In the drill core report from Bergab chlorite and clay group minerals were logged. A few samples were analyzed showing that smectite-group minerals were present together with chlorite. The minerals identified have swelling characteristics (Trafikverket, 2013). The clay minerals are mostly found in open fractures but also in sealed which could be seen in the BIPS images of the drill core. Bergab also identified a clay mineral as Palygorskite (Figure 51). In the analyzed thin-sections from the drill cores only one clay mineral was identified. The clay mineral identified in the SEM-EDS is corrensite. Corrensite which was found in sample S3 is a clay mineral with interstratification of chlorite and smectite and is found in alteration zones (Deer et al. 1992) at temperatures 100-250C but can be found at temperatures below 100°C (Jiang,1994).

Figure 51: Image of palygorskite identified in drill core KK606KBH by SGU, on behalf of Trafikverket (Trafikverket, 2013).

Interpretation: The clay minerals indicate a change in environment because clay minerals are formed as very low temperature alteration products (Barrenechea et al 2000) of primary rock minerals at low temperatures below 120°C (Hillier, 1993).

4.5 Local derivation of hydrothermal mineralization Some of the minerals precipitated in the thin-sections are controlled more by the supply from the local host-rock mineralogy than the pressure, temperature or fluid composition. When the fluid is migrating through the fracture systems there is a fluid-rock interaction that is recrystallizing the local fractures with material from the host-rock. This phenomenon can be seen in thin-section S1 where calcite (Fig- ure 52 A) fracture suddenly changes to adularia (Figure 52 B) when the wall-rock mineralogy changes from quartz to plagioclase. In thin-section S3 a similar recrystallization occurs when adularia heals the altered plagioclase (Figure 53 A) and epidote heals the epidote (Figure 53 B).

Figure 52: Microphotograph of fracture filling which is controlled by the host-rock mineralogy. When the fluid passed through the quartz calcite was precipitated (A.) meanwhile when it passed through the plagioclase then adularia was precipitated, drill core CH604KBH.

Figure 53: Microphotograph of adularia and epidote which is recrystallized when interacting with the fluid, drill core HH618KBH.

4.6 Observed alteration processes in the West-Link Some of the new minerals in fractures are formed by the dissolving of one mineral which results into the deposition of other minerals without changing the volume. In some cases when a mineral is dissolved and replaced a pseudomorph can be seen of the dissolved mineral. Adjacent to the veins and fracture fillings there are alterations of the wall-rock present as colour changes and mineral transfor- mations such as recrystallization caused by a fluid-rock interaction. The minerals which are most affected by the alterations are the primary rock forming minerals (Figure 54 & Table 9). Plagioclase is being altered into several minerals by saussuritization, adularization, epidotization, albitization and sericitization. Chloritization of the biotite produces chlorite. Breakdown of Fe-rich minerals results into precipitation of Fe-oxides.

Figure 54: Microphotograph of the different alteration types in the West-Link.

Alteration S1 S3 S4 S5 S6 S7 S11 S12A S12B Argillic alteration x Chloritization x x x Epidotization x x x x Feldspathization x x x x x x x x Oxidation x x x Saussuritization x x x x x x x x x Sericitization x x Table 9: Table with the alterations found in samples S1-S12B, also seen in figure 57.

5. Discussion As seen in section 4 of this thesis there are 5 major generations of fracture fillings. Each generation is associated with a tectonic environment or temperature change in the SW Sweden that resulted into precipitation and alteration of minerals.

5.1 Generation 1 The granodiorite to granite rocks in the SW Sweden were formed during the Gothian orogeny however all penetrative ductile geological structures were overprinted by the Sweconorwegian orogeny (1.15- 0.90 Ga), the previous structures were replaced by mylonitic banding of greenschist facies. When the Sweconorwegian orogenic phase was over the pressure and temperature decreased which resulted into the deformation transition from ductile to brittle. Brittle crushing and shearing of the host rock is called cataclasis and this process produced cataclasites, which are generation (1) fracture fillings.

The minerals in generation (1) are primary granite rock forming minerals together with greenschist facies mineralogy. According to stereo net plot the fracture orientation of cataclasite minerals such as biotite are close to the foliation suggesting that the cataclasite fractures open up along the foliation plane, these fractures are striking NW.

The fractures with cataclasites are the first fracture systems to develop since the Sweconorwegian overprinting because they are cross-cutting the mylonitic foliation. The cataclasites occur as angular clasts in a fine grained matrix formed by crushing and shearing, tex- turally it is clear that these angular fragments are not hydrothermally precipitated. The ductile-brittle transition occurs around 300-350°C (Davis and Reynold, 1997). The most characteristic cataclasite minerals are biotite, chlorite, epidote, quartz, k-feldspar and titanite which are typical greenschist facies minerals.

5.2 Generation 2 During the later stages of the Sweconorwegian orogeny temperatures held at lower greenschist facies. Hydrothermal circulation occurred with stability temperatures in the interval of generation (2) hydrothermally precipitated minerals T > 150-300°C. This generation can be divided in minerals derived from the alteration of biotite and minerals derived from the alteration of plagioclase. The minerals which are derived from the alteration of plagioclase are epidote, adularia, albite and prehnite. The minerals which are derived from the alteration of biotite are chlorite, titanite, adularia and quartz.

Generation (2) mineralogy is sealing the cataclasite. This observation indicates that generation (2) minerals are the first hydrothermally precipitated minerals. In thin-section S3 the epidote and chlorite mineral assemblage has semi-ductile structures indicating that some of the generation (2) minerals could have precipitated closely to the ductile-brittle transition. During generation (2) the fractures formed are extensional fractures rather than the cataclastic shear fractures.

The minerals crystallize in a relative sequence due to different stability temperatures. Epidote, albite adularia and prehnite are the minerals which crystallize during the saussuritization process, for this reaction to occur Ca2+ is released from the antorthite and used to form epidote. The source of the K+ in the fluid is possibly from the breakdown of biotite or K+ contaminant in the antorthite.

During the breakdown of biotite the minerals chlorite, titanite and adularia are produced, for this reac- 2+ 2+ + 2+ tion to occur Fe , H20 and Ca is used from the fluid and K , Mg , SiO2 are released into the fluid (Sandström et al. 2008).

The chloritization of biotite begins at temperatures around 300-350°C and the saussuritization begins at temperatures around 400°C (Morad et al., 2009), this suggests that the main red-staining of the wall rock occurred during generation (2) because no tectonic event could have pushed up the temperatures in SW this high post Sweconorwegian. In this generation epidote is the oldest mineral based on cross- cutting relationships and the result corresponds with the stability temperature for epidote which is highest of the minerals around T > 300-350°C (Exley, 2012).

Chlorite which is often found together with elongated crystals of titanite in the cleavage plane is precipitated after the epidote but still early since chlorite is the earliest alteration product of biotite. The most intense biotite alteration occurs at temperatures between 160-275°C (Zhang et al, 2010) suggesting that chlorite with titanite are the next minerals to precipitate in generation (2).

Albite together with adularia is formed by the alteration of the plagioclase through a dissolution- reprecipitation rather than replacement. At temperatures above 250°C albite is stabilized meanwhile at temperatures below 250°C K-feldspar is stabilized rather than the albite (Morad et al. 2009). Adularia in this generation is red-stained and this is thought to be caused by sub-microscopic hematite grains in the K-feldspar. The hematite grains are an indication of oxidizing environment.

As seen in the stereo net in section 4.2 the fractures with chlorite fracture filling have analogous orientation as fractures with mylonitic biotite. This strengthens the interpretation that the chlorite is formed as an alteration product of biotite. Prehnite is precipitated just like the Ca-Al-silicate epidote as a result of the saussuritization. Prehnite is formed at temperature 150-190°C (Rusinov, 2009) which puts it after the K-feldspar in the paragenesis of generation (2). Quartz which is cross-cutting all other minerals in this generation except prehnite where cross-cutting relationships are absent is the last mineral in the paragenesis of generation (2). Quartz is formed by the result of cooling ascending silica saturated hydrothermal solutions and the mineral is precipitated at a temperature below 250°C (Jeffrey, 2000). 5.3 Generation 3 Generation (3) represents lower temperature mineralogy possibly precipitated in a period between the later stages of Sweconorwegian orogeny and the early phases of the Caledonian Orogeny. The temperature of this fluid is in the stability temperature of adularia and calcite suggesting temperatures around 90-200°C.

Calcite is precipitated as a result of the saussuritization of anorthite component of plagioclase or from calcium saturated hydrothermal solution. The calcite found in generation (3) is found in the majority of the samples together with adularia where the adularia probably precipitated at a higher temperature than the calcite. The adularia in this generation is also red-stained like the adularia from generation (2) indicating oxidizing environment during generation (3).

The adularia from this generation is not associated to albite which is indicating lower temperatures of the fluid. Calcite from generation (3) is not contaminated with minor amounts of MnO like the calcite from generation (4). The adularia from generation (3) is red-stained unlike the adularia from generation (4) which is not red-stained. The red-stained adularia and the calcite lack sulphides such as pyrite is indicating oxidizing environment therefore generation (3) mineralogy is thought to have precipitated before the Paleozoic sediments. The sediment was deposited on the sub-Cambrian peneplain analo- gously in SW and SE Sweden. The mineralogy and alterations in the adjacent wall-rock indicate lower temperatures than the generation (2) mineral assemblage therefore generation (3) is thought to have mineralized during a major episode ranging from end of Sweconorwegian orogeny to the Caledonian Orogeny.

5.4 Generation 4 This generation is characterized by lower temperatures, during a later tectonothermal event possibly during the Paleozoic, where sediment was deposited into the foreland basin which was formed as a result of the Caledonian Orogeny. Fluid circulation during the Paleozoic with temperatures below 150°C formed the minerals adularia, calcite and quartz.

The adularia of this generation lacks red-staining and the calcite has pyrite which is an indication of the change from oxidizing to reducing environment and is the main reason why this mineral assemblage is separated from generation (3). Adularia of generation (4) forms thin fracture fillings together with quartz which could suggest that during this generation the tectonothermal event was not so intense suggesting temperature elevation due to marine sediment cover rather than a magmatic event.

The adularia consists of pure KAlSi3O8 which is an indication of lower temperatures. In SE Sweden studies of minerals in fractures in similar environment as the West-Link has been done. The studies show that sulphur reducing bacteria is the source to the pyrites (Drake 2013).

The geological evolution of SE and SW Sweden was analogous. Reports from the SE Sweden suggest that the source of the pyrite in the calcite is sulphide reducing bacteria. With similar geological environment and sediment layer on the sub-Cambrian peneplain in SW Sweden the source of the pyrite is probably also the sulphide reducing bacteria.

The sulphide reducing bacteria and reducing environment could be an indication that the precipitation of the minerals occurred when there was shallow marine sediments deposited in SW Sweden possibly during the Paleozoic. Calcite of generation (4) has large euhedral crystals and has been found with scalenohedral crystals.

Studies from Äspö and Laxemar indicate that the scalenohedral variant of calcite is precipitated in saline water. The scalenohedral crystals support the interpretation that generation (4) was formed when there was shallow marine environment in SW Sweden. The alteration process that occurs adjacent to these mineralisations is sericitization, which is a low temperature alteration (Rogers, 1916), indicating lower temperature of the fluid.

The analogous geological development in SE Sweden and SW Sweden where Phanerozoic sediments were deposited on the peneplain could explain the source of the MnO-rich calcite. Reports by Drake (2013) from SE Sweden describe how fluids were circulating in sediments with microbial activity and sulphide reducing bacteria producing MnO-rich calcite by recrystallizing the pure calcite. Another mineral to precipitate during this generation is pumpellyite which is a low temperature alteration of plagioclase, indicating low temperatures.

5.5 Generation 5 Generation (5) is the last generation which is identified in the drill cores suggesting temperatures for the mineral assemblage below 70°C (Gunderson, 2000). The clay minerals which are generation (5) are found in open and hydraulically conductive fractures which enable clay forming processes. The clay minerals are formed during weathering in the granitic rocks when rock interacts with water and chemical weathering processes occurs such as hydrolysis and hydration (Gour, 2014).

The chemical weathering results into the formation of secondary minerals which are the clay minerals. In the XRD-analysis by Eliasson and Jonsson (2013) the clay minerals found are from the smectite- group, chlorite group and palygorskite. An example of a reaction which could have occurred forming a clay mineral will be presented in the equation below (Equation 1) where a mineral in this case albite or antorthite is reacting with water and H+ which results into a chemical weathering process called hydrolysis.

+ +  Albite + H2O + H = Sodium montmorillonite + H4SiO4 + Na + 2+  Anorthite +H2O + H = Calcium montmorillonite + H4SiO4 + Ca

Equation 1: Reaction where silicate minerals react with acids forming clay minerals and silicic acid (Lang, 2009)

For a reaction like Equation 1 to occur there must be presence of water in the fracture system. As seen in the stereo net for the clay minerals they are found in all types of fracture groups indicating the clay minerals are alteration products of older mineralogy. The dominant orientations of the clay minerals are NE and NW striking fractures and these fractures were under horizontal pressure when the North Atlantic Ocean opened up 60 Ma (McElhinny, 2000).

A possible source for the clay minerals other than the feldspars is epidote and chlorite reacting with water forming palygorskite, goethite, Ca2+ ion and smectite-group mineral (Equation 2), this process occurs at low temperatures similar to modern groundwaters (Kamineni, 1993).

 Epidote+ Chlorite + Water = Palygorskite + Goethite + Ca2+ + Smectite‐group mineral

Equation 2: Alteration reaction with epidote, chlorite and water forming clay minerals (Kamineni, 1993).

The process of formation of these clay minerals is slow and requires acid water flowing through the fracture systems. Compared to previous generations this generation does not require elevated temperature. The clay minerals are formed as diagenetic alteration products through a slow process. The scalenohedral which is generation (4) calcite and the MnO calcite has been found concurrent with the clay minerals, both found in open and hydraulically conductive fractures.

Previous studies by Drake (2008) have correlated the formation of scalenohedral calcite from saline water thus suggesting generation (4) being Paleozoic. The clay minerals are thought to be formed during the same period of fluid migration in hydraulically conductive fractures, therefore generation (4) and (5) both could have been precipitated during the Paleozoic to recent time, which is the last major episode of fluid migration.

When comparing the stereo net from generation (4) and (5) both generations are present in the same fracture systems however generation (4) are more common in NE striking fractures dipping towards SW while generation (5) minerals are more common in NE striking NW dipping fractures. The clay minerals are using fracture groups formed during previous generations. This means that even though the clay minerals are more dominating in some fracture orientations they cannot be excluded from any fracture group.

5.6 Timing of the hydrothermal mineralisations During the Sweconorwegian orogeny pressure was applied from WNW associated to the thrusting of Gothian rocks. The present surface was under higher depth, pressure and temperature forming mylonites during the Sweconorwegian orogeny (1.15-0.90 Ga). Cryogenian crustal extension caused the collapse of orogeny and opening of Iapetus Ocean (Corfu, 2014) causing uplift and could be the timing of the ductile-brittle transition period which forms the cataclasite of generation (1) approximately at 0.95 Ga.

Post tectonic magmatism and extension 0.92 Ga associated to the Sweconorwegian orogeny (Eliasson et al. 1991) could be the source to the elevated temperature causing generation (2) mineralogy and the red staining of the wall rock. The mineral assemblages of generation (2) indicate temperatures above T > 250-300°C and these temperatures have been reached associated to the Sweconorwegian orogeny.

Generation (3) minerals are either late Sweconorwegian orogeny or far field effects a later major tectonic event, possibly during the Caledonian orogeny. Generation (3) minerals are definitely precipitated before the Paleozoic because the calcite is not contaminated with MnO which it would have been if there was hydrothermal circulation in the sediments during the Paleozoic. During generation (3) the temperatures were not as high as generation (2) which can be seen by the adjacent alterations and mineralogy T > 100-190°C. Proterozoic rifting during the rifting of Rodinia (Greene, 2010) could also have had generated elevated temperatures and therefore generation (3) minerals have precipitated somewhere between Sweconorwegian orogeny and the early Paleozoic. The red staining of the adularia in generation (2) and generation (3) indicate oxidizing environment at least until generation (3).

During the Paleozoic to more recent time fluids circulated in the fracture system T < 100°C when there was an organic rich sediment layer which formed in the foreland basin. The foreland basin is an effect of the Caledonian Orogeny (Sandström, 2009). In the sediment basin there was microbial activity reduced the sulphate forming sulphides. The last two generations are associated with hydraulically conductive fractures and interaction with water. This suggests that generation (4) and (5) were precipitated during Paleozoic to recent time.

5.7 Redox conditions Due to lack of resources there is no way to demonstrate why the samples S4, S5, S6 and S7 had red staining, however previous studies have been done regarding the red-staining in the bedrock. This question can still be discussed and the question can be answered by comparing these samples with the ones used in the previous studies that are from similar rocks but at other locations (e.g. Eliasson, 1993, Drake, 2008).

Red-staining is most likely a result caused by the hydrothermal alteration of minerals combined with oxidation. The plagioclase becomes altered and loses its transparency in plane polarized light which has been seen in the microscope.

Plagioclase that forms adularia is more common near the fracture and the alteration of plagioclase decreases further away from the fracture indicating alteration (Eliasson, 1993). The Ca-plagioclase is altered into different minerals forming albite, epidote, calcite, sericite and K-feldspar. The red staining in the altered plagioclase occurs as inclusions of iron rich minerals. The inclusions are dispersed amorphous Fe-oxyhydroxides (Eliasson, 1992). The Fe-oxyhydroxides are so small that they are hard to detect with microscopy and SEM-EDS. Fe-oxyhydroxide inclusions appear in altered plagioclase, along grain boundaries and along micro fractures.

According to Eliasson (1992) the minerals which were formed by the alteration of plagioclase were formed in a temperature around 300-400°C while the Fe-oxyhydroxide formed in a temperature 150- 200°C which represents when the wall rock is being cooled. The minerals which are formed by altera-

48 tions are called pseudomorphs and often keep some of the textural features of the protolith and it is in these minerals the red-stain occurs (Eliasson, 1993).

The results from the previous studies describe the red-staining in the samples from the West-Link accurately and it is certainly inclusions of Fe-oxides in the altered plagioclase which cause the red- staining. The red-staining is an indicator of oxidizing environment which means that the redox conditions during generation (1) to (3) were oxidizing. The reducing environment is indicated by the mineral pyrite which is found in the younger calcites.

In similar studies in SE Sweden it was concluded that the pyrite and chalcopyrite in fractures was formed by microbial activity where sulphate reducing bacteria is forming pyrite (Drake et al 2013).

Based on the red staining which presumably are Fe-oxides such as hematite Fe3+ and the sulphides such as pyrite Fe2+ information is being provided about the redox conditions. The Fe3+ are formed during oxidizing conditions meanwhile pyrite Fe2+ is dissolved during oxidizing conditions. The first evidence of oxidation is the brown precipitation in the cataclasite and this is thought to be due to hem- atitization and the breakdown of Fe-rich minerals such as biotite, chlorite and epidote. This means that during generation (1) was formed during oxidizing environment. The oxidizing environment continues until generation (3), where adularia has red micro-grains that occur as inclusions and give the feldspars a red color. During generation (4) and (5) the sediment layer gives a pleasant environment for sulphate reducing bacteria which form pyrite and reducing environment.

5.8 Fracture orientations The earliest fractures which were formed along the foliation are NW and NE striking fractures. These fractures were probably formed during the transition from ductile to brittle deformation and were fractured along the foliation. The fractures were filled with mylonite mineralogy and minerals such as muscovite and biotite are characteristic minerals in these types of fractures. The minerals can be seen in section 4 of this thesis. Therefore a stereo net with the fracture orientations of minerals such as biotite and muscovite is representing generation (1) fractures because biotite and muscovite do not appear in any other generation.

Alteration of the primary rock minerals produced minerals in the same fracture e.g. biotite is altered into chlorite and this can be seen by that there is chlorite in the same fracture system as biotite. The NE fractures are steep are generation (1) due to that the oldest minerals only exist in these fractures.

Epidote which is a generation (2) mineral is found in NW fractures which are generation (1) but also in E-W striking N and south dipping fractures which were formed during generation (2).

Chlorite is found in NW striking SW dipping fractures with a less frequent amount found in NE striking NE and E-W striking fractures dipping towards N and S. The NW striking fractures are thought to be fractures that are reused generation (1) fractures meanwhile the E-W striking with S and N dipping fractures were formed during generation (2).

Generation (3) and (4) both have calcite and therefore the stereo net data does not specifically tell whether the fractures with calcite were formed during generation (3) or generation (4). Calcite is found in all previous fracture groups which are NW striking and E-W striking fractures but as well in new fractures such as NE striking fractures. Generation (4) calcite has pyrite in it and the pyrite stereo net shows that pyrite is found in NW and NE striking fractures suggesting that these were open with water circulating in them due to the paleostress during the Paleozoic.

By comparing the pyrite and calcite fractures orientations the minerals are found in the same fractures which can also be seen in the thin-sections where the pyrite is found on the calcite crystals. The pyrite

49 is formed by reduction in oxygen poor environment possibly marine environment with shallow marine sediment in low temperatures. The NE striking SW and NE dipping fractures were probably active during this reduction process.

Generation (5) fractures are the youngest and are formed during slow alteration processes with the presence of fluid-rock interaction. Clay minerals fractures are found in all previous generations similar to generation (4).Chlorite is formed hydrothermally precipitated during generation (2) but also through alteration as a clay mineral during generation (5) .The less steep dipping NE striking west fractures filled with chlorite are probably chlorite formed by clay minerals alteration processes in low temperatures rather than the generation (2) chlorites, this indicating two chlorite generations. The flat NE fractures are thought to be younger since they only are present from generation (3) to (5). The fracture orientations are summarized in a figure below (Figure 55). One interesting observation which is noticed when comparing the stereo net with time is that the steep fractures are older and the fractures which are less steep are younger and that fracture sets are being reactivated.

Figure 55: Orientations of fractures from all generations derived from Bergab core logging data. Some of the minerals in the West-Link are only present in certain fracture systems which can be seen in this figure.

5.9 Fracture filling generation model By comparing the relative sequence of mineralization which was identified by cross-cutting relationships with the stability temperature of the minerals it can be seen that each generation represents an interval of temperature (Figure 56). During generation (1) temperatures are around the brittle-ductile transition which formed cataclasites. Generation (2) could be close in time to generation (1) suggesting high temperatures when generation (2) mineralogy was precipitated. Generation (3) does not reach as high temperatures as the previous generations which can be seen by its mineralogy and adjacent alterations. During that generation (3) the temperature is high enough for feldspar alteration to occur. During generation (4) there is similar mineralogy as generation (3) but these minerals were precipitated during a lower temperatures which is indicated by chemistry, texture and adjacent alterations. The clay minerals of generation (5) can be precipitated in low temperature but require hydraully conductive fractures for the alteration processes to occur. The temperature diagram is correlating very well with the cross-cutting relationship model, this indicating that the temperature is decreasing from generation (1) to generation (5).

Figure 56: Stability temperatures interval for the minerals found in the West-Link (references for cited temperatures, see above).

The geological crustal evolution can be simplified in a plausible tectonic model of fracturing and mineralization (Figure 57). Due to limited amount of resources for this project the dating method used is restricted to relative cross-cutting relationships rather than an absolute dating method.

In the studies from SE Sweden done by Sandström (2009) a similar study was done but the geological history of SE Sweden is not identical to the SW, this makes it interesting to compare the results from SW Sweden with SE Sweden to see if there are any similarities/differences in the fracture mineralogy.

The Forsmark area in SE Sweden which was investigated by Sandström has rocks that belong to the Svecofennian domain. The rocks were affected by penetrative ductile deformation during the Sve- cokarelian orogeny. A foreland basin was formed in SE Sweden as a result of the Sweconorwegian orogeny in the SW Sweden. During the Cambrian-Silurian marine sediments were deposited on the sub-Cambrian peneplain. During the Caledonian orogeny in the western part of Scandinavia a foreland basin was formed in SE Sweden where sediments were eroded down in the basin during the Paleozoic.

Four major episodes of hydrothermal circulation were identified at Forsmark SE Sweden where in generation (1) epidote, chlorite and quartz were precipitated somewhere between 1.8 and 1.1 Ga. This generation can be correlated with generation (2) in SW Sweden which occurred during the Sweconorwegian orogeny sometime between 1.1 and 0.9 Ga. The second major episode of hydrothermal circulation generation (2) precipitated adularia, albite, prehnite, laumonite, calcite and chlorite is thought to be a result of far-field effects from the Sweconorwegian orogeny somewhere between 1.1 and 0.9 Ga. Generation (2) from SE Sweden is similar to generation (3) in SW Sweden but it is not

51 certain whether generation (3) in SW Sweden is late Sweconorwegian or far-field effects from the Caledonian orogeny.

The third episode of hydrothermal circulation in SE Sweden precipitated quartz, calcite, pyrite which is thought to have occurred during the Paleozoic, this generation correlates more with generation (4) rather than generation (3) in SE Sweden. The fourth and final episode of hydrothermal circulation precipitated clay minerals, calcite, pyrite and goethite. These minerals are thought to have precipitated during a long period from Paleozoic to recent time. This generation correlates well with generation (5) in SW Sweden. The fourth major episode in SE Sweden is represented by generation (4) and (5) minerals in SW Sweden.

When comparing the tectonic model of fracturing and mineralization for SW Sweden with the results from SE Sweden it can be seen that the minerals precipitated during the Svecokarelian in SE were precipitated during the Sweconorwegian in SW Sweden. With little resources and no absolute dating methods it is impossible to tell if generation (2) and generation (3) were precipitated during late Sweconorwegian and due to far-field effects from the Caledonian Orogeny. It is also impossible to tell whether generation (3) and (4) are separate generations or if it is the same episode of hydrothermal circulation or just different p/t and redox conditions. Generation (5) from SW Sweden correlates well with generation (4) from SE Sweden.

Figure 57: Plausible tectonic model of fracturing and mineralization that describes the episodes of hydrothermal circulation.

By comparing the mineral generations with the sequence of mineral alterations similarities can be seen. During the earlier generations the rock minerals are being altered under higher temperatures producing hydrothermal minerals which are stable in high temperature environment. E.g. the elements from a biotite K (Mg, Fe) 3 (AlSi3O10) (F, OH) 2 are used to produce chlorite (MgO, FeO, SiO2, Al2O3, titanite (TiO2, SiO), and adularia (K2O, Al2O3, SiO). Similar process occurs when a fluid reacts with plagioclase CaAl2 Si3 O8 where material is used to form epidote (CaO, Al2O3, and SiO), prehnite (CaO,

Al2O3, and SiO), and adularia (Al2O3 and SiO). In environments which are not affected at all by high temperature fluids low temperature mineralogy can be seen, this forming calcite or clay minerals depending on the mineral being altered and the properties of the fractures. As seen in the conceptual model below (Figure 58) the sequence in the tectonic model (Figure 57) is similar to the conceptual model, this suggesting that every episode with fluid migration in the fractures produced mineralogy dependent on the fluid temperature, composition and available minerals that can be hydrothermally altered.

Figure 58: Conceptual model showing how the primary rock minerals are being altered into other minerals. 5.10 How can this information be used The objective of this thesis was to identify which fracture groups were present in the West-Link and whether certain mineralogy would be hosted by specific fracture orientations and if possible to be used as a predictive tool for future tunnel projects. Studies of the fracture mineralogy identified that the fractures with least strength such as calcite and clay minerals were of later generations (4) and (5). Studies of fractures indicate that during generation (1) to (3) fracture groups were developed based on the regional tectonic stress at that time. Generation (4) and (5) are reusing the fractures which were developed by previous generations and form new fractures in the same group. This implies that since the latter generations are reusing the older fractures it is hard to find an easy correlation between the minerals and orientations to predict the orientation of the minerals that reduce the rock stability. Still, the complexity of successive mineralizations and re-openings of fractures must be recognized and need to be properly mapped to provide a statistical basis for rock mass stability calculations.

6. Conclusions The fracture minerals and orientations are controlled by several factors which are complex. Infor- mation about the fractures is important in tunneling projects to avoid unnecessary problems and cost during the building phase. When fluids are circulating in the fractures minerals are being precipitated. Depending on which minerals are precipitated a fracture can attain a high degree of stability, e.g. quartz or epidote. While, minerals such as clays, calcite usually result in low degree of stability.

The most important conclusions:

* The fracture mineralogy is directly controlled by several factors such as the fluid composition, P/T conditions and the type of bedrock being hydrothermally altered.

* There are five different generations of fracture mineralogy and they were precipitated during at least three major episodes of fluid migration, with generally falling temperatures.

* During generation (1) to (3) fracture sets are formed. These fractures are commonly reopened and remineralized by following generations (4) to (5), thus inheriting the orientations of the earlier generations.

* There is no easy way to avoid minerals which contribute to reducing the stability (clays, calcite) because there is no correlation between those minerals and a particular fracture orientation.

7. Acknowledgments First of all, I would like to thank my supervisor Lennart Björklund, for supporting and guiding throughout the whole process of this thesis. I would also like to thank Lars-Eric Lundgren from ÅF who supported me in the early phase of this study by assisting me with material which made this investigation possible.

I would also like to thank Thomas Eliasson, Eva-Lena Tullborg and Sven-Åke Larsson, for all the interesting discussions and ideas.

Other people that have been involved in one way or another in this thesis are David Cornell, Joakim Johansson, Maria Göthfors, Emma Wingård, Emily Zack, Eric Austin Hegardt and Henrik Drake.

Last but not least I would like to thank ÅF and Bergab which made this project possible.

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