Geological Mapping of Investigation Trench OL-TK7 at the Olkiluoto Study Site, Eurajoki, SW Finland

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1 Working Report Geological Mapping of Investigation Trench OL-TK7 at the Olkiluoto Study Site, Eurajoki, SW Finland Seppo Paulamäki March 2005 POSIVA OY FI OLKILUOTO, FINLAND Tel Fax

2 Working Report Geological Mapping of Investigation Trench OL-TK7 at the Olkiluoto Study Site, Eurajoki, SW Finland Seppo Paulamäki Geological Survey of Finland March 2005 Base maps: National Land Survey, permission 41/MYY/05 Working Reports contain information on work in progress or pending completion. The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva.

3 ABSTRACT Geological mapping of investigation trench OL-TK7 was carried out by the Geological Survey of Finland at the Olkiluoto study site, Eurajoki, southwestern Finland, as part of the site investigations of Posiva Oy for the final disposal of spent nuclear fuel. The trench, ca. 300 metres in length and 1 to 3 metres in width, is situated in the southeastern part of the of the study site. The rock types were determined macroscopically from the bedrock surface, which was first cleaned by pressurised air and then washed by pressure washer. For the mapping purposes the trench was divided to 30 sections. The migmatitic mica gneisses in the trench can be divided to two main types: 1) vein migmatites, in which the amount of granite leucosome veins vary from ca. 10% to over 40%. The mesosome is fine- to medium-grained, biotite-rich mica gneiss with a weak, mm-scale quartz-feldspar segregation banding. 2) Mica gneiss migmatites, which are mostly (>70%) composed of coarse-grained granite leucosome, occurring as cm wide, more or less linear veins. The melanocratic part of the migmatite usually occurs as narrow, several millimetres wide, biotite-rich schlieren (melanosome) between the leucosome veins. In places, fine- to medium-grained mica gneiss with no or less than 10% of granite leucosome veins occur. Grey, medium- to coarse-grained, gneiss with granitic composition occurs in the eastern part of the trench. At the eastern end of the trench, the unweathered mica gneiss is overlain by ca. 2 metres of intensely weathered migmatitic mica gneiss. The foliation and associated granite leucosome veins usually strike ca. NE-SW and dip gently to the southeast, the dip direction/dip maximum being 147/43. The degree of foliation usually varies from weak to medium, the degree of foliation being weakest in the homogeneous mica gneisses and grey gneisses. It is folded by three successive folding phases gently plunging to the NE- ENE/ SW-SSW, SSE and SE. During fracture mapping a total of 200 fractures, equal to or longer than one metre, were investigated. Strike and dip, rock type, trace length, type of fracture trace, form (straight or curved), type (tight, open or filled), width and infilling, where present, were recorded for each fracture. Most of the fractures strike ca. N-S, NNE-SSW and NE-SW. In determining the fracture density (fractures/m) fractures cutting the median line of the investigation trench were measured, the mean fracture density being 0.57 fractures/m. The mean fracture trace length of all recorded fractures is 1.9 m, 33% of the fractures being visible in their full length. Most of the measured fractures are either open or tight. The aperture of the open fractures is usually some millimetres, and only few exceed 1 cm. Fractures with mineral infilling are sparse. Key words: Investigation trenches, rock types, ductile deformation, fracturing, nuclear waste disposal, Olkiluoto

4 TIIVISTELMÄ Tutkimuskaivanto, jonka pituus on noin 300 m ja leveys 1-3 m, sijaitsee kairanreiän KR4 ja KR8 välisessä maastossa. Kartoitus tehtiin paineilmalla puhdistetulta ja painepesurilla pestyltä kalliopinnalta. Kartoitusta varten kaivanto jaettiin 30 suoraviivaiseen tutkimuslinjaan. Tutkimuslinjojen alku-ja päätepisteet on paikannettu Posiva Oy:n toimesta. Havaintojen paikat tutkimuslinjoilla on määritetty kullekin linjalle pingotetun linjalangan avulla mittaamalla sen horisontaalinen etäisyys linjan alkupäästä ja langan korkeus havaintopisteen yläpuolella. Linjalankojen päätepisteiden sijainnin perusteella voidaan sitten laskea havainnon paikka x-y-z-koordinaatistossa. Tutkimuskaivannon pääkivilajina on migmatiittinen kiillegneissi, joka jakaantuu kahteen eri tyyppiin. Suonimigmatiitissa vanhempi osa, paleosomi, on kiillegneissiä ja siinä esiintyy karkearakeista graniittia kiillegneissin liuskeisuuden suuntaisina suonina, joiden osuus kivestä on noin 10-40%. Kiillegneissimigmatiitissa graniittisuonien osuus vaihtelee 50%:sta yli 90%:iin ja paleosomi esiintyy yleensä vain kapeina biotiittirikkaina soiroina graniittisuonien välissä. Siellä täällä esiintyy kapeita osueita homogeenista tai vain alle 10% graniittisuonia sisältävää kiillegneissiä. Migmatiittisessa kiillegneississä on sulkeumina linssimäisiä, kehärakenteisia sulkeumia, jotka ovat todennäköisesti Ca-rikkaiden kerrosten jäänteitä. Graniittikoostumuksellista, keskikarkearakeista, suuntautumatonta tai heikosti suuntautunutta harmaata gneissiä esiintyy kaivannon itäpuolella. Tutkimuskaivannon migmatiittisen kiillegneissin hallitseva rakennepiirre on liuskeisuus niiden suuntaiset graniittisuonet. Liuskeisuuden/raitaisuuden suuntaus on noin koillinen-lounas kaateen ollessa kaakkoon (maksimikaadesuuntal/kaade 147/43 ). Poimuakselit kaatuvat loivasti koilliseen-itäkoilliseen/lounaaseen-etelälounaaseen, eteläkaakkoon ja kaakkoon. Rakokartoituksessa tehtiin havaintoja 200 raosta (rakopituus 1 m). Kustakin raosta havainnoitiin raon kaade ja kaateen suunta, kivilaji, pituus, jatkuvuus, muoto, laatu, leveys ja rakotäyte. Suurin osa mitatuita raoista on suunnassa n. N-S, NNE-SSW ja NE-SW. Rakotiheyksien mittauksessa laskettiin tutkimuskaivannon ylle pingotetun langan määrittämää keskilinjaa leikkaavat raot. Rakotiheys tutkimuskaivannon linjoilla vaihtelee välillä rakoa/m, keskimääräinen rakotiheys on 0.57 rakoa/m. Keskimääräinen rakopituus on 1,9 m, 33% raoista ollessa koko pituudeltaan näkyvissä. Raot ovat enimmäkseen joko avoimia tai tiiviitä. Avoimien rakojen avaumat ovat yleensä muutaman millimetrin luokkaa ja vain harvat raot ovat yli 1 cm leveitä. Avainsanat: Tutkimuskaivannot, kivilajit, duktiili deformaatio, rakoilu, ydinjätteiden loppusijoitus, Olkiluoto

5 1 CONTENTS ABSTRACT TIIVISTELMÄ 1 INTRODUCTION RESULTS OF INVESTIGATIONS Lithology Ductile deformation Fracturing Fracture orientations Fracture densities Fracture characteristics SUMMARY AND DISCUSSION - GENERAL CORRELATIONS WITH NEIGHBOURING TRENCHES, BOREHOLES AND CURRENT BEDROCK MODEL REFERENCES APPENDICES... 53

6 2

7 3 1 INTRODUCTION Investigation trench OL-TK7 is located in the southern part of the study site, between boreholes KR4 and KR8 (Fig. 1-1). The length of the trench is about 300 m and the width is 1 to 3 m. For the mapping purposes the trenches were divided to 30 sections. The X-, Y- and Z-coordinates of the starting and end points of each section were determined by Prismarit Co., under contract to Posiva Oy. The topography of the bedrock surface in the investigation trench is shown in Figures 1-2 and 1-3. The topography rises slowly from the beginning of the trench (z = 3.69 m above sea level) until section P7 (z = 9.34 m), after which it quite rapidly falls to z = 5.12 m in section P11. After that the topography again starts to rise, reaching the highest value of m in section P26. After section P26 the bedrock surface rapidly drops more than 6 m to z = 8.26 m in section P29, after which it slowly starts to rise again. The mapping was performed using the standard operating procedures and guidelines of the Geological Survey of Finland (GTK) for the bedrock mapping (KPK3-O1). The rock types were determined macroscopically from the bedrock surface, which was first cleaned by pressurised air and then washed by pressure washer (Fig. 1-3). Tectonic investigations included measurements of foliation, lineation, fold axis and axial planes. During the fracture mapping all the fractures appearing in the trenches were investigated. Dip direction and dip, rock type, length, form (straight or curved), type (tight, open or filled), width and infilling, where present, were recorded for each fracture. A total of 200 fractures were investigated from the trench. Orientations of structural elements are displayed using Schmidt equal-area, lower hemisphere stereographic projection. In addition, orientation data are also presented using rose diagrams. The stereograms and rose diagrams were drawn using the Norwegian STEREO -software. In all contoured stereograms presented in the present report, the contouring method is angle of hemisphere, where the angle of contouring station and the data points is measured. The unit for contour lines is percentage, where the result from the calculation (divides?) the percentage each value represents (100/N) and contour lines are made for each percentage. The resolution is 100, which will make 100 x 100 = points. All contoured lines are drawn. The 5 declination has not been added to the diagrams. The location of each observation was determined by using a straight thread, which was extended and tightened over each section, and measuring the horizontal distance from the starting point of the section to the observation point as well as the vertical distance from the thread to the observation point. Knowing the coordinates of the starting and end point of the section, the location of the observation point in the x-y-z coordinate system can be measured. The measured fractures and other tectonic features are listed in Excel-tables in Appendices 1 2. The files were delivered to the TUTKA database of Posiva and the original hand-written observations to Posiva's archive. The investigation trench was photographed (stereophotographs) by Juhani Ojala, GTK. The detailed photographs were taken by Seppo Paulamäki. The photographs were stored on CDs and delivered to Posiva's archive.

8 4 Figure 1-1. Location of the investigation trenches at Olkiluoto. OL-TK7 Z (m) P-5 P-4 P-3 P-2 P-1 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 P31 Coordinate points Figure 1-2. Topography of the bedrock surface along investigation trench OL-TK7 based on the measurements of the starting points of each mapping section.

9 5 Topography of OL-TK7 Z (m a.s.l.) P-1 P7 P11 P Trench length (m) P22 P26 P29 Figure 1-3. Topography of the bedrock surface in investigation trench OL-TK7 based on location of investigated fractures. The length of the trench is m. A B Figure 1-3. A) Washing of investigation trench OL-TK7. B) Photo mosaic showing the cleaned and washed bedrock surface in the central part of investigation trench OL-TK7. East is to the left in Figure B. The length of the trench section is ca. 62 m. Photographs by Seppo Paulamäki (A) and Juhani Ojala (B), Geological Survey of Finland.

10 6 Table 1-1. X-, Y- and Z-coordinates of the starting points of the mapping sections in OL-TK7. SECTION X -COORDINATE (M) Y-COORDINATE (M) Z -COORDINATE (M) P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P P

11 7 2 RESULTS OF INVESTIGATIONS 2.1 Lithology The main rock types in investigation trench TK7 are mica gneisses, migmatitic mica gneisses, granitic grey gneisses and coarse-grained to pegmatitic granites. The distribution of the rock types in the trench is described in Table 2-1 and presented on a map in Appendix 4. The rock determined as mica gneisses in the trench are homogeneous or contain less than 10 % migmatizing granite leucosome veins (Fig A). The mica gneisses are mica-rich, fine- or medium-grained, weakly foliated and sometimes contain garnet porphyroblasts, visible to the naked eye. In section P28, medium- to almost coarse-grained, unfoliated mica gneiss with mostly potassium feldspar porphyroblasts or aggregates of potassium feldspar (0.5-5 cm in diameter) occur in abundance. The largest individual potassium feldspar grain is 3 cm in diameter. Large, reddish potassium feldspar grains are unaltered. Instead, smaller (1.5 cm in diameter) feldspar grains are strongly altered to a white or very faintly greenish, soft mineral. The alteration does not occur throughout the rock but only as small patches. In places, a rim of the same white, soft mineral also surrounds the large reddish potassium feldspar grains. It can be seen in places, how one potassium feldspar grain is totally altered, while the adjacent grain is unaltered. In the mapping of the migmatitic gneisses the terminology introduced in the Olkiluoto baseline report (Posiva 2003) and in the most recent bedrock model (Vaittinen et al. 2003) has been used. On the basis of the migmatite structure of the drill core samples, the migmatitic mica gneisses at Olkiluoto have been divided to three groups: vein migmatites, dyke migmatites and mica gneiss migmatites. The leucosomes of the vein migmatites show vein-like, more or less linear traces with some features similar to large-scale augen structures. Planar, sheet-like leucosome dykes characterise the dyke migmatites, while the migmatite structure of mica gneiss migmatites is more asymmetric and irregular. The amount of leucosome varies from less than 10% to over 80%, with a mean of %. Because these three migmatite types represent the end members in an alteration series of migmatite structures, the naming of the different kinds of migmatites turned out to be often quite difficult. The migmatitic rocks named veined gneisses in the earlier trench reports TK1 and TK2 (Paulamäki 1995, 1996) are comparable to mica gneiss migmatites of the present nomenclature, while the migmatitic mica gneisses are vein migmatites. The descriptive terminology of the migmatites used here is adopted from Mengel et al. (2001). The leucosome is the leucocratic, lighter-coloured portion of the migmatite with plutonic appearance. The mesosome is the darker-coloured, mesocratic part of the migmatite, with metamorphic appearance (in this case mica gneiss), while the melanosome is the biotite-rich stripes (schlieren) or narrow bands in the migmatite (2.1-1). The migmatitic mica gneisses in the trench can be divided to two main types. In the beginning of the trench (sections P-4 P-1) and occasionally in sections between P12 and P16, vein migmatites occur, in which the amount of leucosome veins varies from ca. 10% to over 40% (Fig B). The mesosome is fine- to medium-grained, biotiterich mica gneiss with a weak, mm-scale quartz-feldspar segregation banding. In the foliation surfaces of the mica gneiss mesosome, pyrite, in places, occurs rather

12 8 abundantly. Very narrow kaolinite veins occur here and there in the beginning of the trench. The reddish or pale-coloured, coarse-grained granite leucosome occur as asymmetric and irregular veins parallel to the foliation of the mesosome. The main migmatite type, designated here as mica gneiss migmatite, is mostly (>70%) composed of coarse-grained granite leucosome, occurring as cm wide, more or less linear veins. The melanocratic part of the migmatite usually occurs as narrow, several millimetres wide, biotite-rich schlieren (melanosome) between the leucosome veins (Figs C and 2.1-1D). In places, narrow discontinuous bands of biotite-rich mica gneiss mesosome occur. The granite veins show a pinch-and-swell structure. In section P3, the migmatite is cut by cm wide porphyritic granite with potassium feldspar phenocrysts, cm in diameter. The contact between the granite and migmatite is diffuse and the leucosome veins of the mica gneiss migmatite are bending towards the contact (Fig. 2.1-E). Lensoid skarn inclusions occasionally occur within the migmatitic mica gneisses (Fig E). The skarn proper in the centre of the inclusion is greenish, probably amphibole bearing or brownish, in which case it is most likely pyroxene bearing. These are regularly surrounded by a few centimetres wide rim of grey, quartz-feldspar-rich, homogeneous mica gneiss. In Section P-2, there is a 50 x 25 cm skarn inclusion with four rims. The outer rim consists of homogeneous mica gneiss, which is followed by a greenish amphibole rim and a black biotite-rich rim. The centre of the inclusion consists of potassium feldspar, which had not been encountered in the skarn inclusions before. In sections P7 and P8, there is a quartz-feldspar-biotite rock, in which the feldspar grains occur as porphyroblasts, cm in diameter (in places 5 cm), surrounded by biotite+quartz+feldspar (grain size 1-3 mm; Fig A). In places, the rock is very weakly foliated, otherwise the rock is unfoliated. The amount of feldspar grains can, in places, be more than 70% of the total volume of the rock. Mica gneiss with abundant potassium feldspar grains further occurs in sections P9 and P10, where it has turned greenish in colour, probably due to alteration of the medium-grained feldspar grains to mixture of epidote, chlorite, saussurite and sericite (Fig B). These kinds of rocks are named 'mica gneisses with K-feldspar porphyroblasts' in Appendix 4. In sections P23-P27, medium- to coarse-grained, weakly oriented, homogeneous, granitic grey gneiss (formerly granite gneisses, cf. Posiva (2003) occurs, which encloses abundant migmatite fragments and a few small fragments of mica gneiss and skarn (Figs C and 2.1-2D). The grain size of the feldspars is cm and they occur as phenocrysts. Some of the grains are idiomorphic. In Section P27, reddish or reddish grey, coarse-grained granite veins cut the mediumgrained granite. In places the coarse-grained granite brecciates the medium-grained granite, giving rise to an agmatic structure (Fig E). Both the medium-grained and coarse-grained granites have, in places, abundant small cavities after some mineral, which is totally eroded away. In sections P-5 and P-4, cm wide pegmatite dykes striking cut the migmatitic mica gneisses. The dykes are very coarse-grained, the grain size of potassium feldspar, quartz and biotite being several centimetres (Fig F). In addition, pegmatite contains muscovite, calcite and greenish quartz. Also quartz grains with brownish in colour (smoky quartz) occur.

13 9 Leucosome Mesosome A B Melanosome Leucosome C D E F Figure A) Homogeneous, fine-grained mica gneiss. OL-TK7, section P-1. B) Vein migmatite with alternating mica gneiss mesosome and veins of granite leucosome. OL- TK7, section P-3. C) and D) Mica gneiss migmatite with abundant granite leucosome and narrow biotite-rich melanosome schlieren. OL-TK7, sections P3 and P20. E) Granite cutting the mica gneiss migmatite. OL-TK7, section P3, F) Lensoid skarn inclusion within the mica gneiss migmatite. OL-TK7, section P5. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

14 10 A B C D E F Figure A) Porphyroblastic (potassium feldspar) mica gneiss. OL-TK7, section P7. B) Mica gneiss with unaltered (red) and altered (greenish) porphyroblasts. OL- TK7, section P10. C) Granitic grey gneiss. OL-TK7, section P24. D) Granitic grey gneiss with skarn and mica gneiss inclusions. OL-TK7, section P24. E) Reddish grey medium-grained granite migmatized by coarse-grained granite. OL-TK7, section P27. F) Vein migmatite cut by a pegmatite dyke. OL-TK7, section P-4. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

15 11 Regolith In Sections P29 and P30, an about 2 m thick layer of strongly weathered vein migmatite occurs directly on the unweathered mica gneiss (Fig A). The degree of weathering is so high that the rock can easily be crushed with a hammer or even with bare hands. Those parts of the migmatite, which have fewer granite leucosome veins, are more intensely weathered (Fig B.). An almost completely weathered, ca. 1.5 m thick part of the weathered part (regolith), which overlies the strongly weathered migmatite has been excavated in the trench but it is still visible on the walls of the trench. The lower, ca. 80 cm thick part of the regolith is composed of intensely weathered greenish, clayey vein migmatite (Fig A). In spite of very strong weathering, the structure of the migmatite is still clearly observable. It is overlain by ca. 70 cm thick layer of reddish granite or migmatite with abundant granite leucosome (Fig A). The rock is almost totally weathered to a small-grained gravel. The two layers are separated by ca. 15 cm thick layer of fine-grained sand, the lower 10 cm part being brownish grey and the upper, slightly laminated, 5 cm part yellowish brown (Fig B). The lower part disappears towards the end of the trench, and the layer is mostly composed of yellowish brown sand. The regolith is overlain by a layer of sand, which, in turn, is overlain by a very dense clayey till, which contains rounded rock fragments, 5 cm in diameter, and small, angular rock chips (Fig C). A B B Figure A) Strongly weathered migmatite lying on the unweathered mica gneiss (on the right). OL-TK7, sections P29 and P30. B) Detail picture of the weathered migmatite in section P30. The length of the weathered section in A is ca. 8 m. The length of the plate in B is 12 cm. Photographs by Juhani Ojala (A) and Seppo Paulamäki (B), Geological Survey of Finland.

16 12 A B C Figure A) Layers of intensely weathered vein migmatite (lower) and granite (upper) on the wall of trench section P30. B) Fine-grained sand separating the two layers in A. C) Sand and fine-grained clayey till overlaying the weathered granite. OL- TK7, section P29. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

17 Table Description of rock types in investigation trench OL-TK7. MGN = mica gneiss, MGT = mica gneiss migmatite, VMGT = vein migmatite, GGN = granitic grey gneiss, GRPG = granite pegmatite, GRGN = granite gneiss. SECTION POSITION (m) ROCK TYPE DESCRIPTION P VMGT Vein migmatite with dark, fine- to medium-grained mica gneiss mesosome and reddish, coarse-grained or medium-grained, pale-coloured granite leucosome as veins parallel to the foliation of the mesosome. The amount of leucosome veins is ca. 50%. Until 2.2 m the migmatite is strongly but chaotically folded. From 2.2 m on, the leucosome veins occur rather linearly, although some tight to isoclinal, intrafolial folds occur. The mica gneiss mesosome has, in places, a weak quartz-feldspar segregation banding. In the beginning of the section there is a 40 cm wide pegmatite dyke in the direction of 330. P VMGT Fine- to medium-grained, biotite-rich mica gneiss mesosome with a weak foliation and, mm-scale quartz-feldspar segregation banding. The amount of coarse-grained, reddish granite leucosome, occurring parallel to the foliation, is less than 20% GRPG 35 cm wide pegmatite dyke cutting the foliation and the leucosome veins in the direction of 335. The dyke is very coarse-grained with the grain size of potassium feldspar, quartz and biotite being several centimetres. In addition, pegmatite contains muscovite and calcite. Some of the quartz grains are greenish in colour MGN Homogeneous mica gneiss containing cm wide pyrite veins and less than 0.1 cm wide calcite and kaolinite veins. P VMGT Medium-grained, biotite-rich mica gneiss mesosome with a weak, mm-scale quartzfeldspar segregation banding. Two types of leucosome veins occur parallel to the weak foliation of the mesosome: 1) coarse-grained, pale-coloured granite veins and 2) reddish, coarse-grained granite veins. Pale-coloured, 2 cm wide veins are far more common than the reddish veins. In spite of the colour difference, the veins seem to be coeval. The colour difference is probably due to alteration of the feldspars. In addition to these veins, 5-15 cm wide granite pegmatite veins occur sparsely. The granite veins are in places weakly boudined and isoclinally folded. In the foliation surfaces of the mica gneiss

18 mesosome, there is, in places, rather abundant pyrite. Here and there, throughout the whole section, there are <0.1 cm wide kaolinite-filled fractures. In the beginning of the section, calcite occurs in the foliation surface. In the NE part of the section, two skarn inclusions occur with dimensions 30 x 16 cm and 85 x 25 cm. Both of the inclusion have a greenish, most likely amphibole-bearing centre, surrounded by a grey, homogeneous mica gneiss MGN Homogeneous mica gneiss, no granite leucosome veins. Because of the narrowness of the trench, it cannot be said if it is an inclusion or not. P VMGT Medium-grained mica gneiss mesosome with two types of leucosome veins occurring parallel to the weak foliation of the mesosome: 1) coarse-grained, cm wide, palecoloured granite veins and 2) reddish, 5-15 cm granite pegmatite veins. The latter occur only in the first metre of the section. Pale-coloured granite veins in places have a greenish colour due to alteration of the feldspars. In spite of the colour difference, the veins seem to be coeval, since the pale-coloured veins also contain reddish parts without any contact. The colour difference is probably due to alteration of the feldspars. The amount of leucosome is ca. 50%. At 2.30 m and 3.45 m, there are homogeneous mica gneiss portions without any leucosome veins. At 1.70 m, abundant kaolinite occurs on the foliation and fracture surfaces. At 1.20 m there is a 50 x 25 cm skarn inclusion with four rims. The outer rim consists of homogeneous mica gneiss, which is followed by a greenish amphibole rim and a black biotite-rich rim. The centre of the inclusions consists of potassium feldspar. P VMGT Dark, fine- to medium-grained, biotite-rich mica gneiss mesosome with 1-4 cm wide, pale-coloured, coarse-grained granite leucosome veins, constituting 20-30% of the total volume of the rock. The leucosome veins are folded by a tight, chaotic folding MGN Fine- to medium-grained, biotite-rich, almost unfoliated, homogeneous mica gneiss, in which no granite veins occur. In places, the biotite of the mica gneiss has altered to chlorite.

19 MGN Chloritized mica gneiss with small amount (ca. 10%) narrow, coarse-grained granite leucosome veins parallel to the foliation GRPG, MGN Section dominated by a granite pegmatite. In the beginning (until 9.80 m) the occurrence of the granite pegmatite is rather chaotic, probably due to folding with a fold axis plunging to the NE. The mica gneiss mesosome occurs as inclusions within the granite pegmatite. After 9.80 m granite pegmatite leucosome occurs as 2-10 cm veins separated by a mica gneiss mesosome. The veins are parallel to the foliation of the mesosome MGN Fine-grained, slightly chloritized, clearly foliated, homogeneous mica gneiss VMGT Migmatite with biotite-rich, fine- to medium-grained mica gneiss mesosome and coarsegrained granite leucosome, occurring as 1-5 cm wide veins parallel to the foliation of the mica gneiss mesosome. The leucosome veins comprise ca. 40% of the total volume of the rock GRPG 5-20 cm wide, reddish granite pegmatite veins separated by narrow, biotite-rich schlieren (melanosome). The granite pegmatite veins are tightly folded, the fold axis gently plunging to the NNE. P MGT Migmatite, which is mostly (>90%) composed of coarse-grained granite leucosome. The melanosome occurs as narrow, biotite-rich schlieren between the leucosome veins. Clear veined structure with alternating bands of mica gneiss mesosome and granite leucosome veins only occurs at end of the section. Here the granite veins are boudined or deformed in to pinch-and swell structure. At 0.90 m cm wide fine- to medium-grained, homogeneous mica gneiss occur, which is isoclinally folded and re-folded by a more open fold gently plunging to the ESE. Large-scale, open folding /wavelength ca. 2 m and amplitude 0.5 m) occur at 7.80 m and 8.80 m, the fold axis gently plunging to the ENE and NE, respectively.

20 P MGT Migmatite, which is mostly (>90%) composed of coarse-grained granite leucosome. The melanosome occurs as narrow, biotite-rich schlieren between the leucosome veins. The granite veins show pinch-and-swell structure and isoclinal folding. At m the migmatite is slightly weathered and broken off along the melanosome schlierens. The amount of leucosome increases after 2 m and the veining becomes more indistinct. At the end of this section, there are two small inclusions of homogeneous mica gneiss in the NE-part of the trench P "GRGN" MGT "Granite gneiss", in which the feldspar usually occurs as porphyroblasts cm in diameter. In places grains with a diameter of 3-4 cm occur. The migmatitic veining can be seen only vaguely. In places, mica gneiss occurs as small inclusions. In the SW-part of the trench the "granite gneiss" seems to cut the mica gneiss migmatite. Migmatite, which is mostly (>80%) composed of coarse-grained granite leucosome, occurs as cm wide leucosome veins. Between the veins there are narrow, biotiterich schlieren (melanosome) or narrow layers of mica gneiss (mesosome). The leucosome veins are boudined or, more commonly, deformed to pinch-and swell structure. In the beginning and at the end of the section ( m and m), the amount of leucosome is >90% and the veining is rather unclear. After 5.50 m the granitic veining is clear, although the amount of granite continues to be high (>80%). The migmatite is slightly weathered. At 9.00 m in the NE-side of the trench there is a 1.5 x 1 m inclusion of grey, quartz-feldspar-rich, weakly segregated mica gneiss with several brownish skarn inclusions. The mica gneiss with skarn inclusions is tightly to isoclinally folded with possible weak axial plane foliation. These structural elements are most likely remains of the deformation phases preceding the migmatite formation GR The migmatite is cut by cm wide porphyritic granite with potassium feldspar phenocrysts, cm in diameter. The strike of the granite is 120. It may be associated with a dextral, ductile faulting, since the granite leucosome veins are bending in the diffuse contact of the granite. The granite does not continue through the trench but dies out in the NW side of the trench ca. 80 cm from the central line.

21 P MGT Migmatite, in which the amount of coarse-grained granite leucosome is ca. 90%. The melanosome occurs as narrow (2-5 mm), biotite-rich schlieren between the leucosome veins. At m the granite leucosome veins are 2-10 cm wide but after 3.50 the width of the veins is less than 1 cm. The granite veins show pinch-and-swell structure and are in places clearly boudined, the rotated budins indicating dextral shearing conformable to the foliation. At 3.20 m the migmatite is cut by 10 cm wide ductile, sinistral shear/fault zone with an orientation 105/ MGN 95 x 25 cm fine- to medium-grained, homogeneous mica gneiss inclusion P MGT 80 x 10 cm skarn inclusion, in which the 60 x 5 cm brownish (pyroxene-bearing?) skarn proper is surrounded by grey, homogeneous mica gneiss. Migmatite, in which the amount of coarse-grained granite leucosome is ca. 90%. The melanocratic part of the migmatite usually occurs as narrow (2-5 mm), biotite-rich schlieren (melanosome) between the leucosome veins. In places, however, narrow, discontinuous bands of true mica gneiss mesosome occur, in which the mica gneiss is grey-coloured, medium-grained and has a weak metamorphic quartz-feldspar banding. The granite veins are clearly boudined or deformed to pinch-and-swell structure. At 6.10 m homogeneous, medium-grained, 4-40 cm wide mica gneiss band is isoclinally folded. The mica gneiss has two garnet porphyroblasts 3-4 cm in diameter. Small portions of "granite gneiss" with cm feldspar phenocrysts occasionally occur, which clearly cuts the migmatite. Within the "granite gneiss" there are narrow streaks of biotite x 23 cm lensoid skarn inclusion, in which the probably amphibole-bearing centre is surrounded by 1 cm wide brownish biotite rim. These are surrounded by 2-4 cm wide rim of grey, quartz-feldspar-rich, homogeneous mica gneiss. 80 x 6-16 cm skarn inclusion, which is surrounded by 7-8 cm wide rim of grey, finegrained, quartz-feldspar-rich, homogeneous mica gneiss. P MGT Migmatite, in which the amount of coarse-grained granite leucosome is 90%. The

22 P GRPG, MGT leucosome occur as narrow veins, which show pinch-and-swell structure and are isoclinally folded. The melanocratic part of the migmatite usually occurs as narrow, biotite-rich schlieren (melanosome) between the leucosome veins. In places, narrow, discontinuous bands of mica gneiss mesosome occur, in which the mica gneiss is fine- to medium-grained, biotite-rich and has garnet porphyroblasts cm in diameter. Another type of mesosome is medium-grained and quartz-feldspar-rich. Exceptionally wide (30 cm) granite leucosome vein with pinch-and-swell structure occur at m. Mixture of granite pegmatite and mica gneiss migmatite, The amount of granite leucosome is >90%. Narrow, biotite-rich schlieren (melanosome) between the leucosome veins. Skarn inclusions at 2.30 m and 3.90 m (40 x 15 cm). Potassium feldspar grains or aggregates, 5 cm in diameter, around the mica gneiss inclusion at m. 20 cm wide fine-grained mica gneiss inclusion at 5.50 m "MGN" Coarse-grained quartz-feldspar-biotite rock, in which the feldspar grains occur as porphyroblasts, cm in diameter (in places 5 cm), surrounded by biotite+quartz+feldspar (grain size 1-3 mm) ("porphyroblastic mica gneiss"). In places very weakly foliated, otherwise the rock is unfoliated "MGN" As before but the grain size of feldspar becomes smaller (0.5-2 cm) and its amount increases (>70%). The rock is slightly oriented but not foliated P MGT "MGN" Portion of vein migmatite, most of which is located in the NNE-part of the trench. The amount of medium- to coarse-grained granite leucosome is ca. 90%. Biotite-rich, medium-grained mica gneiss with abundant potassium feldspar porphyroblasts, cm in diameter. In places, very vague granite leucosome veining. The obscurity of the migmatitic structure may be due to the fact that only one gently dipping foliation surface is visible MGN Weakly chloritized, fine- to medium-grained mica gneiss, which, in places, contains

23 P MGT portion or discontinuous, narrow veins of granite pegmatite, as well as occasional potassium feldspar grains. At the end of the section there is an 80 x 15 cm inclusion of fine-grained, homogeneous mica gneiss, which has a strong greenish colouring due to alteration of biotite in chlorite. Reddish mica gneiss migmatite, in which the amount of coarse-grained granite leucosome is >90%. The feldspar within the melanocratic bands of the migmatite has altered to a greenish substance (probably a mixture of epidote, chlorite, saussurite and sericite). At 0.90 m there is a strongly altered (chlorite, epidote, sericite), soft skarn inclusion, surrounded by unaltered, fine-grained mica gneiss P MGT MGN MGN The mesosome and part of the leucosome of the mica gneiss migmatite has turned greenish in colour, probably due to alteration of the medium-grained feldspar grains to a mixture of epidote, chlorite, saussurite and sericite. Most of the leucosome is unaltered. The rock is homogeneous, unfoliated and is almost lacking in fractures. Blackish or greenish, granoblastic, medium-grained, biotite-rich (70-80%) mica gneiss with potassium feldspar porphyroblasts and occasional granite leucosome veins. Compared to the previous section, the alteration decreases, smaller feldspar grains being more altered than the larger reddish grains. Homogeneous, no clear foliation occurs. Pale-coloured feldspar grains are more altered than the reddish feldspar grains. The same rock as in the previous section. The alteration of the rock decreases towards the end of the section MGN The same kind of mica gneiss continues but the amount of biotite increases to 90-95%, the rock being almost black in colour. Occasional (<10%) reddish, coarse-grained granite leucosome veins. Skarn inclusion, 40 cm in diameter, at 0.30 m, surrounded by 10 cm wide rim of mica gneiss GRPG Homogeneous, reddish granite pegmatite vein with the dip direction/dip of 130/30.

24 P11 NOT EXCAVATED DUE TO LARGE BLOCKS, WHICH COULD NOT BE REMOVED. P MGN Medium-grained, only weakly foliated, homogeneous mica gneiss with occasional 5-15 cm wide pale-coloured, coarse-grained granite leucosome veins, which in places contain separate green minerals, unidentifiable with the naked eye. In the beginning of the section a 15 cm wide granite vein is isoclinally folded and refolded by a tight folding with fold axis very gently plunging to the W P VMGT MGT Vein migmatite with a medium-grained mica gneiss mesosome with a weak foliation and, mm-scale quartz-feldspar segregation banding. The amount of coarse-grained, reddish granite leucosome, occurring parallel to the foliation, is ca. 40%. Mica gneiss migmatite, in which the coarse-grained granite leucosome occurs as cm wide veins parallel to the foliation of the mica gneiss mesosome. The mica gneiss mesosome is medium-grained and shows weak quartz-feldspar segregation banding. The granite leucosome comprises ca. 70% of the total volume of the migmatite MGN Medium-grained mica gneiss with a weak quartz-feldspar segregation banding. Only small amount (<10%) of coarse-grained granite leucosome veins parallel to the foliation. Younger, 1-2 cm wide granite leucosome vein cuts the foliation in the direction of VMGT Vein migmatite, in which the amount of coarse-grained granite leucosome veins varies 50-80%. The mesosome is medium-grained mica gneiss with a weak quartz-feldspar segregation banding. In places, the leucosome veins are boudined but more commonly they show a pinch-and-swell structure. The veins are strongly folded. In places, narrow (1 cm) shear zones occur conformably to the axial plane. Most of this vein migmatite section is located in the NNE-side of the trench, the width of the migmatite being only 30 cm in the SSW-part.

25 VMGT Medium-grained mica gneiss mesosome with a weak quartz-feldspar segregation banding. The coarse-grained granite leucosome veins occurring parallel to the foliation of the mica gneiss comprise 40% of the total volume of the migmatite. P VMGT The migmatite of P13 continues. Medium-grained mica gneiss mesosome with a weak quartz-feldspar segregation banding. The coarse-grained granite leucosome veins (0.5-6 cm wide) occur parallel to the foliation. The rock has been broken off along the foliation surfaces MGT 50 cm wide section of mica gneiss migmatite, in which the reddish, coarse-grained, cm wide granite leucosome veins comprise more than 50% of the total volume of the migmatite. The granite veins, in places, show a clear pinch-and-swell structure VMGT Vein migmatite with a fine- to medium-grained mica gneiss mesosome and reddish, coarse-grained granite leucosome comprising ca % of the total volume of the rock. The leucosome occurs as narrow veins parallel to the foliation of the mica gneiss. At 3.35 m there is a 20 cm wide, quite strongly weathered, intensely foliated zone in the migmatite, which runs through the trench. The orientation of the zone is 080/ MGT Migmatite with a fine- to medium-grained, biotite-rich mica gneiss mesosome and reddish, coarse-grained granite leucosome, occurring as a few millimetres to 5 cm wide veins parallel to the foliation of the mica gneiss. The veins comprise ca 70% of the total volume of the migmatite. The strike of the foliation and the granite veins is rather linear. The granite veins show a weak pinch-and-swell structure. The veins are in places isoclinally folded and re-folded by an open folding plunging to the NE. At the foliation is clearly seen due to weak weathering of the migmatite GRPG Reddish, coarse-grained to pegmatitic granite/granite pegmatite.

26 P P GRPG VMGT VMGT Reddish, coarse-grained to pegmatitic granite/granite pegmatite, which runs through the trench parallel to the foliation of the mica gneiss migmatite (090/38 ). Vein migmatite with medium-grained, weakly foliated, rather homogeneous mica gneiss mesosome (50-70%) and pale-coloured, coarse-grained granite leucosome (30-50%) occurring as narrow, irregular, discontinuous veins parallel to the foliation or as small patches. The veins, in places, have a weak pinch-and-swell structure. The veins show isoclinal, intrafolial folding, which is refolded by tight to open folding, gently plunging to the NE or ENE. Fine-to medium-grained, biotite rich mica gneiss mesosome with less than 20% of narrow (0.5-5 cm), discontinuous, reddish, coarse-grained granite veins, occurring parallel to the foliation of the mica gneiss mesosome MGT A complex mixture of coarse-grained granite leucosome and mica gneiss mesosome, the granite comprising >50% of the rock. Only in places does the granite leucosome occur as clear veins paralleling the foliation of the mica gneiss mesosome. In the SSW-part of the trench there is a 1.5 x 1.5 m portion of rather homogeneous mica gneiss with only a few granite veins. P MGT Migmatite, in which the amount of coarse-grained granite leucosome is >80%. The melanocratic part of the migmatite usually occurs as narrow (2-5 mm), biotite-rich schlieren (melanosome) between the leucosome veins. At m, however, narrow, discontinuous bands of true mica gneiss mesosome occur, in which the mica gneiss is grey, medium-grained and has a weak metamorphic quartz-feldspar segregation banding. From the beginning of the section until 7.50 m the veining is rather unclear, because only one gentle foliation surface is visible. The migmatite is rather intensely folded with three interpreted folding phases. 22

27 P MGT Migmatite, in which the amount of coarse-grained granite leucosome is > 80%. The melanocratic part of the migmatite usually occurs as narrow, several millimetres wide, biotite-rich schlieren (melanosome) between cm wide, coarse-grained granite leucosome veins. In places, discontinuous bands or relicts of biotite-rich mica gneiss occur. The migmatite is intensely folded. Only at the end of the section, the veins strike rather linearly and here the weak pinch-and swell structure of the veins is visible. The surface of migmatite in the whole section is weakly weathered. P MGT Migmatite, in which the amount of coarse-grained granite leucosome is > 80%. The melanocratic part of the migmatite usually occurs as narrow, a few millimetres wide, biotite-rich schlieren (melanosome) between a few centimetres wide, coarse-grained granite leucosome veins. In places, a couple of discontinuous bands of biotite-rich mica gneiss mesosome occur. The granite veins show a pinch-and-swell structure and smallscale rootless, isoclinal folds, which are refolded by tight folds gently plunging to the SW. Two small (20 x 35 cm) skarn inclusions occur in the SSW-part of the trench. At 2.20 m and 4.80 m, two wide (20-40 cm) leucosome veins occur, the grain size of which varies from medium-grained to pegmatitic. The surface of migmatite in the whole section is weakly weathered. P MGT The same kind of migmatite as in Section P19. Only one discontinuous, 5-20 cm wide band of mica gneiss mesosome with a thin quartz-feldspar segregation banding. At 3.60, 120 x 45 cm portion of "granite gneiss", which deflects the foliation and the granite veining. Ghost-like veining is visible within the "granite gneiss". Ca. 50 cm wide, discontinuous granite pegmatite vein at 4.33 m parallel to the foliation. Tight, sinistral folding, gently plunging to the NE, which, in one place, is accompanied by narrow (2 cm) shear zone. This tight folding is re-folded by more open folding, plunging to the SE. P MGT The same migmatite as in Section P20 continues. In the first metre of the section the strike of the foliation is almost perpendicular to the one in the previous section. The foliation and the leucosome veins are folded by tight, dextral folding, gently plunging to the NE and accompanied by shearing along the axial plane. 23

28 MGT The coarse-grained granite leucosome veins are wider than before and narrow, a few millimetres wide, biotite-rich schlieren (melanosome) occur between the leucosome veins. For instance, at 4.50 m a 50 cm wide coarse-grained to pegmatitic granite vein occurs parallel to the foliation defined by the melanosome schlierens. The granite veins show a clear pinch-and-swell structure. In places, portions of the same "granite gneiss" as in the previous section, which here seems to cut the leucosome veins. At m, narrow bands of biotite-rich mica gneiss melanosome with a quartzfeldspar segregation banding occur, which is folded by tight, chevron-type folding, gently plunging to the ENE. In places, narrow granite leucosome veins occur parallel to the axial plane. P MGT The melanocratic part of the migmatite usually occurs as narrow, a few millimetres wide, biotite-rich schlieren (melanosome) between coarse-grained granite leucosome veins. The veins are usually a few centimetres wide but in places wider, ca. 30 cm wide veins occur. In places, the veins show a pinch-and-swell structure. At 6.00 m, in the SSW-part of the trench, a few discontinuous bands of quartz-feldspar-rich mica gneiss mesosome occur, the width of which ranges from a couple of centimetres up to 20 cm GR Medium- to coarse-grained granite vein with brownish mineral aggregates (about 0.5 cm in diameter), which have eroded a little deeper than the surface of the rock Ductile shear zone parallel to the foliation. The structure of the migmatite with pinchand swell granite leucosome veins has been developed to narrow (about 1 cm) veins, which in places show rotated megacrysts or budins. The potassium feldspar porphyroclasts are common. In places, small fragments of the mica gneiss mesosome occur, giving the rock a schollen migmatitic structure. The rotated budins, potassium feldspar porphyroclasts and mica gneiss fragments indicate dextral sense of shearing. At m the shearing is cut by a 0.5 cm wide quartz-feldspar vein with an orientation 085/67.

29 GGN Grey gneiss with a granitic composition. The rock is coarse-grained and has narrow biotite streaks and both small and large potassium feldspar porphyroblasts (or porphyroclasts?). The contact between the above shear zone and the granitic grey gneiss is diffuse, and it seems that the grey gneiss is somehow related to the shearing. The grey gneiss, in places, contains fragments of vein migmatite, giving the rock a schollen migmatitic structure. The strike of foliation within the fragments is perpendicular to the one in the grey gneiss. At m the rock is cut by ca. 1 mm wide biotite seam, oriented 005/75. It is possibly accompanied by a weak dextral faulting P MGT MGT Strongly folded mica gneiss migmatite, which, on the basis of Section P23 and adjacent investigation trench TK6, is part of a larger vein migmatite fragment within the granitic grey gneiss. Migmatite, in which the amount of coarse-grained granite leucosome is 70-90%. The melanocratic part of the migmatite usually occurs as narrow, a few millimetres wide, biotite-rich schlieren (melanosome). Abundant "rusty" spots after some unknown mineral, which has eroded away. The migmatite is a large fragment within the granitic grey gneiss GGN Narrow portion of granitic grey gneiss within the vein migmatite, which comes from a larger grey gneiss unit in the adjacent investigation trench TK GGN Medium- to coarse-grained, weakly oriented, homogeneous, granitic grey gneiss, which encloses abundant vein migmatite fragments and a few small fragments of mica gneiss. The grain size of the feldspars is cm and they occur like phenocrysts. Some of the grains are idiomorphic. In places, a ghost-like folding can be seen in the grey gneiss, which, however, can be relict from a migmatite fragment. In the SSW-part of the trench, the grey gneiss encloses rounded, banded mica gneiss inclusions, which show signs of early foliation and folding. One of the inclusions has rotated in the shearing concordant to the main foliation. Pegmatitic leucosome has accumulated at the boundary of the inclusion (pressure shadows?).

30 MGT Fragment of mica gneiss migmatite MGT Fragment of mica gneiss migmatite P MGT MGT Mica gneiss migmatite section, which widens towards the NNE-part of the trench and continues outside the trench. Folded mica gneiss migmatite, in which the amount of coarse-grained granite leucosome is 80-90%. The melanocratic part of the migmatite usually occurs as narrow, a few millimetres wide, biotite-rich schlieren (melanosome). This vein migmatite is a narrow section within the grey gneiss. At 0.70 m a 15 x 20 cm skarn inclusion within the vein migmatite GGN Medium- to coarse-grained (feldspars cm in diameter), weakly oriented, homogeneous, granitic grey gneiss with a few inclusions of skarn and fine-grained mica gneiss. A large (65 x 30 cm) skarn inclusion with coarse-grained quartz veins is located at 6.80 m on the SSW-side of the trench. 26 P GGN, MGT Reddish grey, medium- to coarse-grained (feldspars cm in diameter), almost homogeneous granitic grey gneiss, which in the SSW-part of the trench is bounded by a folded vein migmatite. The mica gneiss migmatite occupies the SSW-part of the section and reaches the median line of the trench but does not continue through the trench. It gradually changes to the grey gneiss. P GGN Reddish grey, medium- to coarse-grained (feldspars cm in diameter), slightly oriented, almost homogeneous granitic grey gneiss, which in places has a weak veining (biotite schlieren). A few deeply eroded skarn inclusions (<20 cm in diameter) and a couple of mica gneiss inclusions MGT Reddish to grey, isoclinally folded mica gneiss migmatite, in which the amount of coarse-grained granite leucosome is 60-80%. The migmatite has small ( cm in

31 diameter) cavities after some mineral, which has totally eroded away. 70 x 20 cm mica gneiss inclusion in the SSW-part of the trench, showing early foliation and folding. P GGN, MGT GGN Grey, slightly reddish, medium- to coarse-grained (feldspars cm in diameter), almost homogeneous granitic grey gneiss. In the NNE-part of the section the grey gneiss changes to the mica gneiss migmatite. The foliation and the veining of the migmatite are deflected by a large (170 x 70 cm), grey, fine-grained mica gneiss inclusion, which shows early foliation and folding. The mica gneiss has garnet porphyroblasts. Reddish grey, medium- to coarse-grained granitic grey gneiss, with potassium feldspar phenocrysts, 1-3 cm in diameter cm wide medium-grained granite veins in the direction of 035 cut the grey gneiss. In the NNE part of the section 3-5 cm wide granite pegmatite veins cut the grey gneiss in the same direction. At 1.1 m in the NNE-side of the section, the grey gneiss encloses a medium-grained mica gneiss inclusion (30 x 10 cm) P GR GR Reddish or reddish grey, medium-grained granite is cut by coarse-grained granite veins. In places the coarse-grained granite brecciates the medium-grained granite, giving rise to an agmatic structure. At 1.50 m on the SSW-side of the trench, the coarse-grained granite veins are tightly folded, the fold axis plunging to the S. At m, both the medium-grained and coarse-grained granites have abundant small cavities after some mineral, which is totally eroded away. The NNE-side of the section is composed of a complex mixture of granitic grey gneiss, medium-grained granite cutting it and coarsegrained granite, which cuts both of them. The SSW-side of the section is composed of the vein migmatite, which, in places, is clearly cut by the medium-grained granite described above. Reddish or reddish grey, medium-grained granite is cut by coarse-grained granite veins (same as in the previous section) MGT Mica gneiss migmatite, in which the cm wide, coarse-grained granite leucosome veins amount to ca. 40% of the total volume of the rock. The migmatite is tightly folded

32 with narrow shear zones concordantly to the axial plane (125/85 ). The fold axis plunges gently to the SW. At 1.30 and 2.50 m (SSW-side), 60 x 30 cm portions of the same medium-grained granite as in the beginning of the section. The coarse-grained granite veins, cutting the granite, have the same folding as the migmatite MGN Medium- to almost coarse-grained, unfoliated mica gneiss with mostly potassium feldspar porphyroblasts or aggregates of potassium feldspar (0.5-5 cm in diameter) in abundance. The largest individual potassium feldspar grain is 3 cm in diameter. Large, reddish potassium feldspar grains are unaltered. Instead, smaller (1.5 cm in diameter) plagioclase and potassium feldspar grains are strongly altered to white or very faintly greenish, soft minerals (illite and kaolinite?). The alteration does not occur throughout the rock but only as small patches. In places, a rim of the same white, soft mineral surrounds the large reddish potassium feldspar grains also. It can be seen in places how one potassium feldspar grain is totally altered, while the adjacent grain is unaltered. Small patches of reddish granite pegmatite occur occasionally. In places, weak vein migmatite structure is visible but it is never continuous. These places give an impression that the visible mica gneiss is only a gentle foliation surface and that the rock in reality is an ordinary migmatite P MGN VMGT Medium-grained, unfoliated mica gneiss with some potassium feldspar porphyroblasts (0.5-5 cm in diameter) and, in places, narrow, discontinuous, coarse-grained granite leucosome veins. The rock is unaltered. At the end of the section, there are 2-8 cm wide, gently dipping (20 ESE), coarse-grained granite leucosome veins. Vein migmatite with mica gneiss mesosome alternating with cm wide coarsegrained granite leucosome veins, which comprise ca. 40% of the total volume of the rock MGN Medium-grained, unfoliated mica gneiss with some potassium feldspar porphyroblasts (0.5-5 cm in diameter).

33 VMGT Strongly weathered vein migmatite lying directly on the rather homogeneous unweathered mica gneiss. The leucosome veins constitute more than 50% of the total volume of the migmatite. The rock is still quite compact but it can easily be crushed with a hammer. P VMGT The same kind of strongly weathered vein migmatite as before. The rock is still quite compact but can easily be crushed with a hammer VMGT The migmatite is much more weathered than before and it can be crushed just by hand. The amount of the granite leucosome veins is only ca %, which explains the higher degree of weathering (biotite-rich mica gneiss mesosome weathers more easily than the granite veins). In spite of the very intense weathering, the structure of the rock is still clearly visible. Due to strong weathering, the rock is strongly cleaved along the foliation surfaces VMGT The weathering is still strong but weaker than previously due to higher amount of the leucosome veins, which comprise 40-50% of total volume of the migmatite. The rock is still quite compact but it can easily be crushed with a hammer. The width of the granite veins is usually a few centimetres but at 4.82 m there is a 35 cm wide granite pegmatite vein parallel to the foliation. Ca. 50 cm thick layer of fine sand overlies the weathered rock. This sand is overlain by a fine-grained, very compact clayey till, which contains rounded rock fragments and angular mineral grains. 29

34 Ductile deformation The observations of the ductile deformation are presented in Appendix 1. The rock types of the investigation trench show a polyphase ductile deformation. The earliest deformational features can be seen in some mica gneiss and skarn inclusions within the migmatite, which have a fine banding and biotite schistosity (S 1 ), and which are isoclinally folded (F 2A ) (Fig A). The new foliation, axial planar to the folding (S 2A ), can be separated from the S 1 in fold hinges, elsewhere they are subparallel. These early deformation events were followed by development of a foliation S 2B and intense production of granitic leucosome veins parallel to the foliation, which more or less destroyed the early structures. The foliation S 2B includes here schistosity, metamorphic quartz-feldspar segregation banding, as well as the orientation of the biotite-rich melanosome schlierens (Fig B). The foliation usually strikes to ca. NE-SW and dips gently to the southeast, the mean dip direction/dip angle being 147/43 (Fig ). In sections P12-P16, the foliation has a more northerly strike, the mean dip direction/dip angle being 103/36. In sections P23-P28, there are three foliation maxima: 100/23, 125/54 and 140/81. The last maximum comes from the measurements in the granitic grey gneiss. The degree of foliation, using the Finnish engineering geological classification (Korhonen et al. 1974, Gardemeister et al. 1976), usually varies from weak to medium, the degree of foliation being weakest in the homogeneous mica gneisses and grey gneisses. Only in narrow sections is the mica gneiss strongly foliated. During the later stages of the D 2 deformation, the migmatites were intensely extended, as indicated by the granite leucosome veins and more competent mica gneiss mesosome layers showing boudinage or pinch-and-swell structures (Fig B). The veins are occasionally isoclinally folded (F 2C ). 147/43 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % 10 % 11 % 12 % Lower hemisphere - OL-TK7: Foliation N=106 K= Sigma=1.060 Peak=11.68 N=106 Lower hemisphere - OL-TK7: Foliation A) B) Figure Distribution of poles to foliation S 2B in investigation trench OL-TK7 (Schmidt equal area, lower hemisphere projection). A) Contoured stereogram, B) pole strereogram.

35 31 S 1 S 2B F 2A A B Figure Skarn inclusions with S1 foliation folded by isoclinal F 2A fold. Ol-TK7, section P3 B). S 2B foliation defined by biotite melanosome. Granite veins showing a weak boudinage and pinch-and-swell structure are parallel to the foliation. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland. In the next deformation phase, D 3, the mica gneiss and the granite leucosome veins with isoclinal F 2 folds were refolded by F 3 folding (Fig A). In investigation trench TK7, the F 3 -folds occur as small-scale, tight, and in places chevron-type folds with the fold axis gently (15 45 ) plunging to the NE-ENE or SW-SSW (Figs and 2.2-4A-C). In places, narrow granite veins and a weak dextral shearing/faulting occur parallel to the axial planes, dipping to the SE (Fig D). In places, the F 3 -folds are refolded by more open folds, plunging to ca. SSE or SE (Fig E). On the basis of structural interpretation by Paulamäki & Koistinen (1991) these folds may correspond to the deformation phases D 4 and D 5, respectively. F % 4.3 % 6.5 % 8.7 % 10.9 % 13.0 % F 3 Lower hemisphere - OL-TK7: Fold axis N=46 K= Sigma=1.000 Peak=6.40 N=46 Lower hemisphere - OL-TK7: Fold axis A) B) Figure Distribution of fold axis in investigation trench OL-TK7. Schmidt equal area, lower hemisphere projection. A) contoured stereogram, B) plot stereogram. A plunge of 90 plots at the centre and 0 at the outer perimeter.

36 32 F 2 F 3 A B D 3 shear C D F 5? F 3 E Figure A) Isoclinal F 2 folding refolded by F 3. OL-TK7, section P17. B) Tight F 3 folds. OL-TK7, section P13. C) Tight, partly chevron-type F 3 folds. OL-TK7, section P21. D) D 3 shear cutting the S 2B foliation and leucosome veins. OL-TK7, section P21. E) F 3 folding refolded by F 5 plunging to the SE. OL-TK7, section P17. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

37 33 Shear zone (structure R24) About a 5 m wide ductile shear zone parallel to the foliation occurs in Section P22. The structure of the migmatite with boudinage and/or pinch-and swell granite leucosome veins has developed into narrow (about 1 cm) veins, which in places show rotated budins (fragments of boudined granite leucosome veins). The potassium feldspar porphyroclasts are common. In places, small fragments of the mica gneiss mesosome occur, giving the rock a schollen migmatitic structure. The rotated budins, potassium feldspar porphyroclasts and mica gneiss fragments indicate sinistral sense of shear. The shearing is similar to the shear zones in investigation trenches TK1 and TK5, which belong to the same shear zone (structure R24 in the bedrock model by Vaittinen et al. 2003). However, the shear zone in TK7 is not weathered or fractured as in TK1 and TK5 and it is located in a different place than expected on the basis of these trenches. To find out if these shear zones in three adjacent investigation trenches do indeed belong to the same shear zone, the area between the trenches and outcropping parts of the zone in the vicinity of trenches TK1 and TK7 were excavated and cleaned. The investigations showed that the same shear zone R24 occurs in all three trenches, and that the zone is folded, which explains its different position in TK7 (Fig and 2.2-6). Fig shows some detailed photos of the shear zone. The shearing is strongest in the southern part of the zone, where a clear mylonitic foliation occurs (Figs A and 2.2-7B). Within the foliation there are larger and potassium feldspar grains or porphyroclasts. The grain size within the shear zone is clearly reduced compared to the migmatite protholith. The sense of shear is sinistral. The shearing is less pronounced, but still evident, in the middle of the zone in investigation trenches TK1 and TK5 (Figs D and 2.2-7D). The characteristic feature to this part of the shear zone is the slight weathering and fracturing of part of the zone. The weathered and fractured zone within the shear zone is at its widest in investigation trench TK5, where it is ca 3.5 m wide. The zone dies out towards TK7 and does not occur in TK7 anymore. Also to the SW of TK1 the zone becomes narrower and narrower and probably dies out ca. 15 m from TK1. The shear zone is at least 15 m wide in the area northeast of trench TK7. Also in this part of the shear zone shearing is conspicuous, although the rock is not as mylonitic as in the southern part of the zone (Figs E and 2.2-7F). The granite neosome veins occur as strongly extended narrow streaks and the strong penetrative foliation deflects around potassium feldspar porphyroclasts or megacrysts representing survivors from destruction of less ductile granite leucosome veins. Asymmetric megacryst structures indicate sinistral sense of shear (Fig F) The shear zone is interpreted as being a D 2 shear zone, which is folded by a large scale F 3 fold with an almost E-W axial plane, which can be seen in the ground survey magnetic map. The shape of the shear zone also indicates younger folding plunging to the SE, which can be seen in the migmatites near the shear zone.

38 34 Fig C Not exposed Fig B OL-TK7 Fig A OL-TK5 OL-TK6 Not exposed OL-TK1 OL-KR8 Figure Shear zone R24 in the area of investigation trenches TK1 (Paulamäki 1995), TK5, TK6 (Paulamäki & Aaltonen 2004) and TK7. Deep blue = mica gneiss, blue = migmatitic mica gneiss, orange = grey gneiss, red = granite pegmatite. A B C Figure A) Shear zone to the SW of TK1 and TK5. The view is towards NE. B) Shear zone between TK5 and TK7. The view is towards ENE. C) Shear zone to the NE of TK7. The view is towards NE. Photographs by Seppo Paulamäki, Geological Survey of Finland.

39 35 A B C D E FEF Figure A) Sheared vein migmatite in the S part of the shear zone with a strong mylonitic foliation. B) Sheared vein migmatite in the S part of the shear zone showing sinistral sense of shear. C) and D) Weathered mica gneiss migmatite in the shear zone in TK5. E) Sheared vein migmatite in the NE part of the shear zone. F) Sheared vein migmatite in the NE part of the shear zone with a potassium feldspar megacrysts showing sinistral sense of shear. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

40 Fracturing The results of fracture investigations are shown in Appendix 2. The first five columns show the position of the fracture in relation to the central thread and the x-y-zcoordinates calculated on the basis of this data. They are followed by the dip direction and dip of the fracture, the rock type, fracture trace length, type of fracture trace (Are one or both ends visible?), fracture form (straight - curved - winding), character (open or tight, filled), aperture (if open), possible fracture filling mineral and other remarks Fracture orientations The distribution of all fracture orientations and distribution of fracture orientations by rock types in investigation trench OL-TK7 are shown in Figs and 2.3-2, respectively, as Schmidt equal area, lower hemisphere projection and rose diagram. The main sets of the fracture orientations are shown in Table The five fracture sets presented in the Table cover 67.5% of all measured fractures. The remaining fractures, which are not included in the Table but are shown in Fig , are mainly evenly distributed between dip directions 105 and 180, i.e., between and in the range of fracture sets I and II. However, from the fractures with dip direction , fracture sets I and II cover 71.9%. The most common fracture set (I) represents fractures, which strike parallel to the foliation and have the same dip angle as the foliation. Fig and Appendix 3 suggest that there may be some differences in the fracture orientations between the rock types and in different parts of the trench. However, no definitive conclusions can be made due to the rather small number of fractures. The mica gneisses seem to favour fracture set IV, migmatitic mica gneisses fracture set I and the grey gneisses fracture set V. Absence of set I in the mica gneisses is most likely due to weak foliation in these rock types. Appendix 3 shows the distribution of fracture orientations along the trench in four different trench sections, which are mainly compiled on the basis of the main rock types. The most striking difference in the fracture orientations is in trench sections P12-P16, which are mainly composed of the vein migmatite. In these trench sections, fractures dipping steeply to the NW or WNW are abundant but fracture sets II and IV, which are common in other parts of the trench, are poorly represented. The foliation has a more northerly strike in this part of the trench than elsewhere in the trench, which in the fracture orientations are reflected by fractures gently dipping to the ESE. The same strike of foliation and related fracturing can also be seen in sections P23-P28. Table Distribution of main fracture orientations in investigation trench OL-TK7. Fracture set Fracture strikes (maxima and orientation range) Dip direction/dip (maxima and orientation range) I 064 ( ) 154 /35 ( /25-50 ) 23.5% II 355 ( ) 085 /85 ( /65-90 ) 21.0% III / % IV 352 ( ) 262 /82 ( /75-90 ) 9.0% V / % Percentage from all measured fractures (N = 200)

41 37 1 % 2 % 3 % 4 % 5 % 6 % Lower hemisphere - OL-TK7: All fractures N=200 K= Sigma=2.000 Peak=6.22 N=200 Lower hemisphere - OL-TK7: All fractures A) B) N=200 Lower hemisphere - OL-TK7: All fractures C) Figure Distribution of poles to fractures in investigation trench OL-TK7, (N = 200). A) Contoured stereogram and B) pole stereogram (Schmidt equal area, lower hemisphere projection), C) rose diagram, where the strikes of the fractures are presented regardless of the dip of the fracture (scale of ring in the rose diagram is 5%). Approximate trench trend is marked with a dashed line.

42 38 2 % 4 % 6 % 8 % 10 % 12 % 14 % 16 % Lower hemisphere - OL-TK7: Fractures in the mica gneiss N=31 K= Sigma=0.310 Peak=16.62 Lower hemisphere - OL-TK7: Fractures in the mica gneiss N=31 Lower hemisphere - OL-TK7: Fractures in the mica gneiss N=31 A) 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % 9 % Lower hemisphere - OL-TK7: Fractures in the migmatitic mica gneisses N=111 K= Sigma=1.110 Peak=9.13 Lower hemisphere - OL-TK7: Fractures in the migmatitic mica gneisses N=111 Lower hemisphere - OL-TK7: Fractures in the migmatitic mica gneisses N=111 B) 1 % 2 % 3 % 4 % 5 % 6 % 7 % 8 % Lower hemisphere - OL-TK7: Fractures in the grey gneiss N=46 K= Sigma=0.460 Peak=7.92 Lower hemisphere - OL-TK7: Fractures in the grey gneiss N=46 Lower hemisphere - OL-TK7: Fractures in the grey gneiss N=46 C) Figure Distribution of poles to fracturing by rock types in investigation trench OL-TK7. A) Mica gneisses, B) migmatitic mica gneisses and C) granitic grey gneisses. Contoured stereograms, pole stereograms (Schmidt equal area, lower hemisphere projection) and rose diagrams, where the strikes of the fractures are presented regardless of the dip of the fracture (scale of ring in the rose diagram is 5%). Approximate trench trend is marked with a dashed line.

43 Fracture densities Table and Fig presents the fracture densities of investigation trench TK7 in each section. All the fractures equal to or longer than one metre cutting the median line of the trench were recorded. A total of 167 fractures were recorded at the length of m. Accordingly, the mean fracture density is 0.57 fractures/m. The fractures cutting the median line of the trench cover 83.5% of all measured fractures. In terms of Finnish engineering geological rock classification (Korhonen, et al. 1974, Gardemeister et al. 1976), no fracture zones (>10 fractures/m) occur in the trench. However, in sections P-1, P1, P8, P17, P24 and P28, narrow zones of abundant fracturing (i.e. more abundant than in the immediate surroundings) occur (Table 2.3-2, Figs and 2.3-5). In section P-1 the fracturing is restricted to a narrow mica gneiss unit within the mica gneiss migmatite (Fig A). The fractures dip steeply to the west. In Section P1 all the fractures (4 fractures/1.3 m) dip steely to the WSW. In section P8 (Fig B) the fractures also dip steeply but the dip is to the E. The fractures are partly filled with calcite. In section P17 there is a narrow (0.50 m) fractured zone with four tight fractures steeply dipping to the WSW. In the fractured zone in section P24 (Fig C), the fractures (6 fractures/1.6 m) dip steeply to the E or ESE. They are long and have apertures of several centimetres, indicating that they may have also vertical continuation. In the fractured zone in section P28 (Fig D), the fractures (6 fractures/1.7 m) are tight and steeply dipping to the E. One single fracture, which may have a vertical extent, occurs in section 17. This vertical, NNW striking fracture can be followed more than 20 m to adjacent investigation trenches TK1 and TK5. In TK7 the surface aperture of the fracture is 20 cm but deeper it can be seen that the aperture is not as wide but the fracture is in fact composed of four adjacent, closely spaced fractures with apertures of just a few millimetres. Another long and open fracture occurs ca. 10 m SW of investigation trench TK1. However, it was not found or recognised in nearby borehole KR26. Section P12 is ca. 0.5 m lower than adjacent section P13 as if it had dropped down. It is thereby possible that there is a (sub)horizontal fracture beneath P12 and possibly also P11, which was not excavated due to large blocks. The gently SE dipping rock surface in sections P9 and P10 with almost no fractures probably represents the surface of this fracture.

44 40 Table The mean fracture densities along the investigation trench TK7 in Olkiluoto. MGN = mica gneiss, MGT = mica gneiss migmatite, VMGT = vein migmatite, GGN = grey gneiss, GR = granite, FZ = fractured zone. Section Rock type Section length (m) Number of fractures Fracture density (pcs/m) Remarks P-5 VMGT No fractures in the section. P-4 VMGT P-3 VMGT No fractures in the section. P-2 VMGT No fractures in the section. P-1 VMGT, FZ in mica gneiss, 5 fractures/2.8 m. MGN P1 MGT FZ, 4 fractures /1.3 m. P2 MGT P3 MGT Section covered with ice. P4 MGT Fracturing parallel to the foliation. P5 MGT, MGN P6 MGT Section covered with ice. P7 MGT, MGN P8 MGN FZ, 5 fractures/1.63 m P9 MGN m covered with mud. P10 MGM m covered with mud. P11 P12 Not excavated! MGN, VMGT P13 VMGT, MGT P14 VMGT, MGT P15 VMGT P16 MGT P17 MGT, MGT FZ, 4 fractures/0.52 m. P18 MGT FZ, 4 fractures/0.3 m P19 MGT P20 MGT P21 MGT P22 MGT, GGN Incl. 5 m wide shear zone with no fractures. P23 GGN, MGT P24 GGN FZ, 6 fractures/1.6 m. P25 GGN P26 GGN, MGN P27 GR P28 MGN FZ, 6 fractures/1.7 m. P29 MGN, VMGT m strongly weathered (regolith). P30 VGMT The whole section is very strongly weathered (regolith). P-5 P

45 41 Fracture densities Fractures/m P-5 P-4 P-3 P-2 P-1 P1 P2 P3 P4 P5 P6 P7 P8 P9 P10 P11 P12 P13 P14 P15 P16 P17 P18 P19 P20 P21 P22 P23 P24 P25 P26 P27 P28 P29 P30 Section number Figure Distribution of fracture densities in investigation trench OL-TK7. The fracture density is smallest, where the bedrock surface is at lowest.

46 42 A B Figure N-S striking narrow fractured zones in the mica gneiss in sections P-1 (A) and in section P8 (B). Olkiluoto, investigation trench OL-TK7. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland. A B Figure Ca. N-S striking fractured zones in the grey gneiss in section P24 (A) and in the mica gneiss in section P28 (B). The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.

47 Fracture characteristics The distribution of the fracture trace lengths is shown in Fig All fractures with a trace length equal to or longer than 1 m were measured with an accuracy of 0.5 m. The mean fracture trace length of all recorded fractures is 1.9 m, 33% of the fractures being visible in their full length (mean fracture length 1.5 m). Fractures with one fracture end covered constitute 37.5% of all fractures, the mean length being 1.65 m. Fractures with both ends under soil cover (29.5%) have the mean length of 2.75 m, the longest fracture being more than 22 m long. There is no connection between the fracture trace length and the fracture orientation but both short and long fractures occur in the same main fracture set presented in Table In most cases the fracture trace length is not dependent on the rock type. However, in the mica gneiss and skarn inclusion there are often short fractures, which are solely restricted to the inclusion (Fig ). Distribution of fracture trace lengths Number of fractures >10 Fracture trace length (m) Figure The fracture trace lengths measured in investigation trench OL-TK7. The value of 1 m includes the range from m, 2 m etc.

48 44 A B Figure A) Long (>4 m), ca. N-S striking, open fractures in section P24 in investigation trench OL-TK7. B) Short, open fractures, restricted to mica gneiss inclusion, Section P5. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland Most of the measured fractures are either open (54.6%) or tight (37.2%). The aperture of the open fractures is usually some millimetres, and only few exceed 1 cm (Fig ). The fractures with widest aperture are most likely to have been opened by frost. Fractures with mineral infilling are sparse (3.1%). Fracture fillings include calcite, chlorite, pyrite and clay minerals (Fig ). The measured fractures are either undulating (48.2%) or linear (40.2%), some of the fractures being slightly curved (11.6%). Aperture of open fractures Number of fractures >1 Aperture (cm) Figure Aperture of open fractures.

49 45 calcite pyrite A B Figure Calcite and pyrite (B) on the surface of minor fractures. OL-TK7, section P-3. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland. No clear brittle faults, i.e., fractures, along which the markers (veins, dykes, other fractures etc.) have moved past each other, have been observed. However, some fractures show signs, which may indicate a faulting component (Fig ) but the interpretations are uncertain. B Figure N-S striking fracture with a possible sinistral brittle fault. OL-TK7, section P24. The length of the plate is 12 cm. Photographs by Seppo Paulamäki, Geological Survey of Finland.