FI0000012

POS1VA 99-31

Lithological and structural bedrock model of the Hastholmen study site, Loviisa, SE

Kai Front VTT Communities and Infrastructure

Seppo Paulamaki Geological Survey of Finland

Henry Ahokas Fintact Oy

Pekka Anttila Fortum Engineering Oy

October 1 999 Maps: ©Maanmittauslaitos permission 41/MYY/99

POSIVA OY Mikonkatu 15 A, FIN-OO100 , FINLAND Phone (O9) 2280 30 (nat.), ( + 358-9-) 2280 30 (int.) Fax (09) 2280 3719 (nat.), ( + 358-9-) 2280 3719 (int.) POSIVA 99-31

Lithological and structural bedrock model of the Hastholmen study site, Loviisa, SE Finland

Kai Front Seppo Paulamaki Henry Ahokas Pekka Anttila

October 1999

POSIVA OY Mikonkatu 15 A, FIN-00100 HELSINKI. FINLAND Phone (09) 228O 30 (nat.). ( + 358-9-) 2280 30 (int.) Fax (O9) 2280 3719 (nat.), ( + 358-9-) 2280 3719 (int.) T 4 / O "Z ISBN 951-652-086-3 ISSN 1239-3096

The conclusions and viewpoints presented in the report are those of author(s) and do not necessarily coincide with those of Posiva. i - POSiva Report Raportintunnus-Report code POSIVA 99-31 Posiva Oy Mikonkatu 15 A, FIN-00100 HELSINKI, FINLAND Julkaisuaika-Date Puh. (09) 2280 30 - Int. Tel. +358 9 2280 30 October 1999

Tekija(t) - Author(s) Toimeksiantaja(t) - Commissioned by Kai Front, VTT Communities and Infrastructure Seppo Paulamaki, Geological Survey of Finland Henry Ahokas, Fintact Oy Posiva Oy Pekka Anttila, Fortum Engineering Oy

Nimeke-Title

LITHOLOGICAL AND STRUCTURAL BEDROCK MODEL OF THE HASTHOLMEN STUDY SITE, LOVIISA, SE FINLAND

Tiivistelma - Abstract

The Hastholmen study site is located within the anorogenic Wiborg rapakivi , 1640 - 1630 Ma in age. The bedrock consists of various rapakivi , which can be divided into three groups or lithological units: 1) wiborgite and pyterlite, 2) porphyritic rapakivi granite, and 3) even- grained or weakly porphyritic rapakivi granite, pyterlite being the dominant rock type. The even- grained and weakly porphyritic rapakivi granite has been interpreted to form a younger intrusive unit with a thickness of ca. 500 m, dipping approx. 20° to the NNW-NNE.

Surface fractures form a distinct orthogonal system, with three perpendicular fracture directions: fractures dipping steeply (dip >75°) to the NE-SW and NW-SE plus subhorizontal (dip <30°) fractures. The fracturing in the outcrops is sparse, the average fracture frequency being 0.6 fractures/m. The majority of the fractures in the drill cores are horizontal or very gently dipping and there is no difference in fracture orientations in regard to rock type or depth. Core samples are usually slightly fractured (1-3 fractures/m), even-grained rapakivi granites being in places abundantly fractured (3 - 10 fractures/m. The broken sections in Hastholmen core samples represent about 4.6% of the total length of the samples. Calcite, dolomite, Fe-hydroxides and clay minerals (illite, montmorillonite and kaolinite) form the most typical fracture mineral phases throughout the drill cores. Core discing is locally seen as repeated fracture-like subparallel cracks in core with spacing of about some millimetres to tens of millimetres.

The structural model contains 27 structures (denoted by the term R+number), more than half of which have been verified by direct observations from boreholes or from the VLJ repository. The remaining structures are mainly based on the geophysical interpretation, and have been classified as probable or possible fracture zones. In addition, local structures with uncertain orientation and continuity occur in the rock mass. They are not classified as R-structures but may still have hydraulic significance.

The most significant features of the bedrock are the subhorizontal structures Rl, R3, R18 and R19 located in boreholes over the depth ranges of 50- 150 m, 150 - 350 m, 300 - 500 m and 700 - 950 m, respectively. Transmissivity values for the R-structures measured by the double packer system and the flowmeter lie in the range MO*3 m2/s to MO"7 m2/s, the average being MO"5 m2/s.

Avainsanat - Keywords Precambrian, rapakivi granite, fracturing, hydr. conductivity, bedrock model, structural model, final disposal, nuclear waste

ISBN ISSN ISBN 951-652-086-3 ISSN 1239-3096

Sivumaara - Number of pages Kieli - Language 100 English î _ PAC jug ReDOrt Raportin tunnus-Report code POSIVA 99-31 Posh/a Oy Mikonkatu 15 A, FIN-00100 HELSINKI, FINLAND Julkaisuaika - uate Puh. (09) 2280 30 - Int. Tel. +358 9 2280 30 Lokakuu 1999

Tekijâ(t) - Author(s) Toimeksiantaja(t) - Commissioned by Kai Front, VTT Yhdyskuntatekniikka Seppo Paulamäki, Geologian tutkimuskeskus Henry Ahokas, Fintact Oy Posiva Oy Pekka Anttila, Fortum Engineering Oy

Nimeke - Title

LOVIISAN HÄSTHOLMENIN LITOLOGINEN JA RAKENTEELLINEN KALLIOMALLI

Tiivistelmä - Abstract Hästholmenin tutkimusalue koostuu rapakivigraniiteista, jotka kalliomallissa on jaettu kolmeen ryhmään tai litologiseen yksikköön: 1) viborgiitit ja pyterliitit, 2) porfyyriset rapakivet ja 3) tasarakeiset ja vaaleat, heikosti porfyyriset rapakivet. Kairanreikien kattamalla alueella yleisin kivilaji on pyterliitti ja viborgiittia esiintyy yleensä vain kapeina leikkauksina kairanrei'issä. Tasarakeiset ja heikosti porfyyriset rapakivet muodostavat noin 500 m paksun muodostuman, joka on mallinnettu kaatuvaksi noin 20°:een kaateella pohjoiskoillisen ja pohjoisluoteen välille. Rapakiven pintarakoilu on kuutiollista rakoilua, jossa vaaka- tai loiva-asentoisen (<30°) rakoilun lisäksi on kaksi kohtisuoraa, jyrkkäasentoista (kaade >75°) rakosuuntaa suunnissa NE-SW ja NW-SE. Tutkimusalueen kallioperä on pääosin harvarakoista, keskimääräisen rakotiheyden ollessa 0,6 rakoa/m. Kairanreikien rakoilu on pääsääntöisesti vaaka- tai hyvin loiva-asentoista. Rakojen asennoilla ei näytä olevan kivilaji- tai syvyysriippuvuutta. Kairasydännäytteet ovat yleensä vähärakoisia (1-3 rakoa/m) ja jotkut näytteet ovat harvarakoisia (<1 rako/m) jopa lähellä maan pintaa. Tasarakeiset rapakivigraniitit ovat paikoin runsasrakoisia (3 - 10 rakoa/m). Rikkonaiset kairanreikäleikkaukset vastaavat noin 4,6 % kairausnäytteiden kokonaispituudesta. Kalsiitti, dolomiitti, Fe-hydroksidit ja savimineraalit (illiitti, montmorilloniitti ja kaoliniitti) ovat tyypillisimmät raontäytemineraalit kaikissa rei'issä ja syvyyksissä. Yksi kairausnäytteiden erityispiirteistä on ns. core discing -ilmiö, mikä havaitaan paikoin muutamasta metristä kymmenien metrien pituisina jaksoina kairanrei'issä. Core discing on kairausnäytteen rakomaista, yhdensuuntaista viipaloitumista, jossa yksittäisten viipaleiden väli vaihtelee muutamasta millimetristä kymmeniin millimetreihin. Ilmiö liittynee kallion korkeaan jännitystilaan suhteessa kiven vetolujuuteen. Hästholmenin tutkimusalueen rakennemalli sisältää 27 rako- ja rikkonaisuusvyöhykettä (R-rakenne), joista yli puolet on varmennettu suorin havainnoin joko kairanrei'istä tai matala- ja keskiasteisen voimalaitosjätteen kalliovarastosta. Kallioperän rakenteet, joista ei ole suoria havaintoja, on tulkittu erilaisten geofysikaalisten tutkimusten perusteella. Kairanrei'issä esiintyy lisäksi paikallisiksi rajattuja rikkonaisia jaksoja, joiden suunta tai jatkuvuus on nykytietämyksen perusteella epävarma. Ne voivat olla kuitenkin vedenjohtavuudeltaan merkittäviäkin. Merkittävimmät rakenteet alueella ovat loiva-asentoiset rakenteet Rl, R3, R18 ja R19, jotka sijaitsevat syvyysväleillä 50 - 150 m, 150 - 300 m, 300 - 500 m ja 700 - 950 m. Varmistettujen R-rakenteiden transmissiviteetit vaihtelevat välillä MO"3 m2/s - MO"7 mVs, keskimääräisen arvon ollessa MO*5 m2/s.

Avainsanat - Keywords prekambrinen, rapakivi, rikkonaisuusvyöhykk., rakoilu, rakennemalli, litologinen malli, vedenjohtavuus, ydinjätt.loppusij. SBN ISSN ISBN 951-652-086-3 ISSN 1239-3096 Sivumäärä - Number of pages Kieli - Language 100 Englanti TABLE OF CONTENTS

Abstract

Tiivistelma

1 INTRODUCTION 5

2 HASTHOLMEN AREA 9 2.1 Topography and terrain 9 2.2 Regional geology 11 2.3 Rapakivi granites 13

3 SITE GEOLOGY 19 3.1 Rock types 19 3.2 Magma tectonics 23 3.3 Fracturing 24 3.3.1 Rock mass classification and terminology 24 3.3.2 Surface fracture studies 28 3.3.3 Fracture studies in the VLJ repository 32 3.3.4 Core sample fracture studies 33 3.3.5 Core discing 37 3.4 Rock mass modelling 39 3.4.1 Fracture Zone Index 39

4 LITHOLOGICAL MODEL 43 4.1 General 43 4.2 Distribution and occurrence of rock types 43

5 STRUCTURAL MODEL 51 5.1 Regional scale 51 5.2 Site scale 53 5.3 Present state of the structural model 58 5.4 Hydraulic properties of the R-structures 77 5.5 Fractured or anomalous borehole sections without correlation to other boreholes 83

6 SUMMARY 87

REFERENCES 91

NEXT PAGE(S) left BLANK PREFACE

Posiva established a site evaluation project "PARVI" in 1997 for summarising, by the end of 2000, the research conducted at the four investigation sites for the deep disposal of the spent fuel. The project produced among other things site reports of the detailed site characterisations. The current report updates, complements and give more detailed information on the present state of the lithological and structural bedrock models of the Hastholmen study site. This study has been carried out on contract for Posiva Oy. On behalf of Posiva Oy the work has been supervised by Aimo Hautojarvi, whereas Kai Front at VTT Communities and Infrastructure, and Seppo Paulamaki at the Geological Survey of Finland have been the contact persons on behalf of the authors.

This report has been prepared by the experts who have participated in the modelling of the Hastholmen site. Kai Front is liable for processing of Sections 1, 3.3.1, 3.3.4, 3.3.5, 3.4, 5.2 and for contribution to Sections 4.1, 5.3 and 5.5. Seppo Paulamaki is responsible for Sections 2, 3.1, 3.2, 3.3.2, 3.3.3, 4, 5.1, 5.3 and 5.5. Henry Ahokas compiled Section 5.4 and Pekka Anttila contributed to the writing of Sections 1, 3.3.3 and 5.2. Mrs. Auli Rautakivi did careful editorial work and finished the figures, illustrations and tables.

The authors wish to thank Dr. Tim McEwen of QuantiSci, United Kingdom, for his valuable criticism and checking the English of the text.

NEXT PAGE(S) left BLANK 1 INTRODUCTION

In Finland, two companies utilise nuclear energy to generate electric power - Teollisuuden Voima Oy (TVO) and Fortum Power and Heat Oy (formerly Imatran Voima Oy). The companies are preparing for the final disposal of the spent nuclear fuel waste deep in the bedrock. In 1996, they established a joint company, Posiva, to run the programme of site investigations, and other research and development for spent fuel disposal. Posiva will ultimately construct and operate the future disposal facility.

In 1992, on the basis of the preliminary site investigations at five sites, TVO proposed to continue detailed site investigations at three sites: Romuvaara in Kuhmo, Kivetty in Aanekoski and Olkiluoto in Eurajoki (Teollisuuden Voima Oy 1992). In 1994, the Nuclear Energy Act was amended to permit the Loviisa Nuclear Power Plant to return the spent fuel to only until the end of 1996. Thereafter, the spent fuel would also have to be disposed of in Finland. A feasibility study performed in 1996 showed the island of Hastholmen, the location of the Loviisa Nuclear Power Plant, to be a potential site for the spent fuel repository (Posiva 1996).

The upper parts of the bedrock at Hastholmen had already been characterised during investigations and construction of the underground repository for low- and intermediate-level operating waste (VLJ repository) excavated at a depth of about 110 m. These studies on the geology and the hydrogeological conditions of the site were documented in detail (e.g. Anttila 1986, 1988, 1997). The location of the repository and the boreholes related to it (marked with Y-symbols) are presented in Figure 1-1. Evaluations of the mineralisation potential and the geological conditions of the island of Hastholmen and its near-field area within a radius of 5 km were conducted by Kuivamaki et al. (1997a, 1997b). Geological mapping offshore was also carried out and is presented in Rantataro (1996).

In 1997, the Hastholmen study site was incorporated into the detailed site investigation programme. The objective of the investigations has been to extend the structural and lithological model generated earlier during the studies for the VLJ repository to the greater depths required for the repository for the spent fuel, as well as to check the extent of the subhorizontal fracture zones north of the site on the mainland.

The detailed investigations at Hastholmen have involved several activities:

- drilling of eight deep boreholes 600 - 1000 m in length (Fig. 1-1) - borehole geophysics - groundwater studies - hydrogeological testing - surface and airborne geophysics

The same equipment and methods have been used as at the other sites. Some of the equipment was improved after the preliminary investigations at the three other sites and some new methods have been applied (Hinkkanen et al. 1996). The investigation methods used at Hastholmen since 1997 are reported in detail by Anttila et al. (1999). Modelling of the bedrock at Hastholmen has been carried out since the early 1980s (e.g. Anttila et al. 1982, Anttila 1986, Pirhonen 1986), based on the investigations for locating and construction of the repository for low- and intermediate-level operating wastes, as well as for the safety assessment of the final disposal. The first 3-D structural model, covering the whole repository site down to the depth of 200 m, was presented by Anttila (1988). This model consisted of three subhorizontal fracture zones, and formed the basis for the final locating of the repository (cf. Fig. 5.2-1). The repository was constructed between the two uppermost fracture zones in 1993 -1996. After the construction of the repository the structural model was revised and consisted of 8 fracture zones (Anttila & Viljanen 1994). Later the size of the model was increased for the needs of the groundwater flow modelling to be included in the final safety assessment. The model comprised the whole island of Hastholmen, consisting of 17 bedrock structures (mainly fracture zones) based on borehole data, observations in the repository and seismic surveys (Anttila & Viljanen 1995). This model, supplemented by some local topographic lineaments, created the basis for the detailed site investigations commenced in 1997 by Posiva. The 3-D structural model (version 1.0) was summarised by Lindh et al. (1997).

The model was subsequently revised on the basis of information from four deep boreholes (KR1 - KR4), interpretation of an aerogeophysical survey, and interpretation of geophysical borehole logging (Okko et al. 1998, Paananen & Paulamaki 1998). This model (version 2.0), is summarised in Lindh et al. (1998) and consists of 25 fracture zones. In Section 4.2 the distribution and occurrence of the rock types are represented as lithological bedrock model. In Section 5.3 the fracture zones are described and the Lindh et al. (1998) structural model is further updated on the basis of new data and interpretations available from four new boreholes (Okko et al. 1999a, Okko & Front 1999). Additional data from boreholes KR7 and KR8 are still under examination (Okko et al. 1999b).

The process for conceptualising the present fracture zones, i.e. structural bedrock model included their direct observation in boreholes and the use of indirect evidence, mainly from the interpretations of geophysical surveys, e.g. standard single-hole surveys, acoustic full wave form logging, scanner investigations, such as dipmeter and borehole- TV (Siddans et al. 1997, 1998, Strahle 1998), and three-dimensional vertical seismic profiling (3D-VSP) methods (Keskinen et al. 1998a). The methodology of identifying and locating fracture zones consisted of integrated interpretation of geological observations of core samples and geophysical single-hole surveys, together with principal component analysis (Okko et al. 1998,1999a).

The current report presents the previous repository studies and the updated lithological and structural bedrock models, which combine the results from the previous VLJ repository studies (e.g. Anttila 1997), outcrop mapping (Kuivamaki et al. 1997a), borehole investigations (Gehor et al. 1997a, 1997b, 1998, 1999, Okko et al. 1998, 1999a, 1999b, Okko & Front 1999) and an interpretation of the aerogeophysical survey (Paananen & Paulamaki 1998). The report will also form the basis for the model version 3.0 (the ROCK-CAD model) to be prepared later in 1999. Figure 1-1. The Hdstholmen study site with the location of the deep boreholes KRl - KR8 and the shallow boreholes Yl - Y25. The location of the VLJ repository is also shown.

NEXT PAGE(S) left BLANK 2 HASTHOLMEN AREA

2.1 Topography and terrain

The Hastholmen study site comprises the island of Hastholmen and its immediate area on the mainland, located about 10 km southeast of the centre of the town of Loviisa (Fig. 1-1). Two units of the Loviisa nuclear power plant are situated on the island, as well as the repository for low- and intermediate-level operating waste (VLJ).

Most of the coastal area around Hastholmen has an elevation of between 0 - 20 m, the greatest elevation of 42 m being at the hill of Kasaberget, southeast of Hastholmen. The rest of the rapakivi granite area (see Fig. 2.3-1) has an elevation of 20 - 40 m. In the area northwest of the rapakivi granite the relief is greater and more variable, the highest elevations being between 75 - 100 m. The low lying areas are mainly covered by clays, whereas in the more elevated parts the bedrock is exposed (Fig. 2.1-1). The most common soil types in the area are till and clay (Valovirta 1972, Tynni et al. 1976, Punakivi et al. 1977). Predominantly sandy till deposits are usually thin, and the accumulation forms of till have usually no clear orientation, however, small end moraines occur both within the rapakivi batholith and in the Svecofennian area. Glacial striae demonstrate that the older movement of the continental ice sheet was from the northwest (315 - 330°) and the younger one almost from the north (350 - 360°). Abundant clay deposits, in some places over 20 m thick, are present in river beds, hollows and valley bottoms, the most extensive deposits occurring in the northern part of the rapakivi area (Fig. 2.1-1). Deposits of sand and gravel include thin and small shore deposits and a few discontinuous eskers trending roughly NW-SE. Peat bogs cover 10 - 15% of the land area in the region.

The actual study site has a subdued, prominently NNW-SSE oriented topography, having in most places an elevation of less than 10 m, with the greatest elevation of approx. 16 m in the middle of the area. The highest parts of the island rose above the sea level about 4000 years ago, the current annual uplift rate being 2-3 mm a year (Miettinen et al. 1999). The sea bottom immediately offshore has a general elevation of between -5 m and -10 m. Offshore, to the east of Hastholmen there is a clay- and till- filled basin, where the rock surface descends to a depth of ca. -70 m (Anttila 1988, Rantataro 1996), and which probably represents a missing block of bedrock removed by the continental ice sheet (Fig. 2.1-2). The circular basin of Hudofjarden, west of Hastholmen, has been interpreted to indicate an intrusion structure of the rapakivi granite (Kuivama"ki et al. 1997a). Another basin, trending NW-SE and with a maximum depth of greater than -30 m, has been found southwest of the island. In general, however, the rock surface around Hastholmen is less than 20 m below sea level (Anttila 1988). The soil cover at Hastholmen consists mainly of silty sandy till, which typically contains abundant erratic boulders. The till cover is usually 2 - 3 m thick, but in places may be about 8 m, the thickest and most continuous layers being in the eastern and southern parts of the island (Anttila 1988). The area is rather well exposed, the outcrops comprising about 6% of the total area. The Quaternary deposits on the sea bottom consist mainly of till, gravel and sand, overlain by silt and clay in the sub-sea depressions (Anttila 1988). Quaternary geology of the Hastholmen area

GEOLOGICAL SURVEY OF FINLAND Regional office for South Finland Espool998

Quaternary deposits

Bedrock terrain •

End moraine ridges and hummocks

Gravel and sand glaeiofluvial deposils

| | Gravel and sand littoral deposits

I I Clay ^ | | Gynja and peat

| | Watercourse

Quaternary geological map @ Geological Survey of Finland Digital elevation modd and base map © National Survey of Finland

permit No 13/rnatf98 HHlsbading is from NW, angle is 45 degrees.

18 27 km

Figure 2.1-1. Elevation model of the Hastholmen area with Quaternary geology. 11

3462000 3464000 3466000 o o o> o CD GO CO O) o CD o CO o

o o> o a> o to o> «3 o O> o o ^Hasthi

o o o

: ;: ; l ; 1000 • • -•,-.. ?• ?::••-. '•#^v:- .' - v;' - - ^ o 3 • ••1* .••>1**1 ...;;,•.•• .:;.;•.. •; •,. ;^^'-- ' ''• o o

Digital elevation model of Hastholmen study site

Geological Survey of Finland (GTK)

Figure 2.1-2. Topographic relief model of the Hdstholmen study site and its immediate area (modified after Kuivamaki et al. 1997a).

2.2 Regional geology

The crystalline bedrock of Finland (Fig. 2.2-1) is a part of the extensive Precambrian Fennoscandian Shield. The oldest part of the Finnish bedrock is the Archaean basement complex (3100 - 2500 million years in age) of northeastern Finland which consists mainly of tonalitic and granodioritic gneisses (Gaal & Gorbatschev 1987). Within the basement complex are narrow Archaean greenstone belts, which are composed of metavolcanics and metasediments. The majority of the Finnish bedrock is comprised of Palaeoproterozoic metamorphic and igneous rocks. Its long history of volcanism, sedimentation and igneous activity culminated in the 1900 - 1800 Ma million years ago (Koistinen 1996). Later the thickened and stabilised crust 12

Bedrock of Finland

Caledonian tectonic units 1 HHB| Schists, gneisses or intrusions of variable origin

Palaozoic 2 HI K]ai rock P'P8 Oivaaia) and carbonei'rte (SokB, 3 t—--H Sandstone and shale, Cambrian 6B° NBoprotarozoic 4 119 Sandstone and shale, Vsndian

5 I^H Dolerita dykes, northern fintand 6 H Dolerita sib, 7 W Sandstone and shale, Jotnian 8HB Fapalcivigrenrta 9 H| Gabbro-anorthosita 10 hisl Dolerita dyke swarms, Subjotnian

PalBopraterozoic

11 \ . ::\ Qiiartzfte and conglomerate, molesse of Lapland 12 Hi Postorogenic granitoids c. 1.8 Ga 13 ^gj Late erogenic granites 1.85 • 1.8 Ga 14 r~~~) Granite and granodiorite 1.88-1.86 Ga 15 H| Pyroxene granite end monzonite 1.88S • 1.87 Ga 161 | Granodiorita 1.89 Ga 17 m Gsbbro-diorite 1.89 -1.87 Ga T) TonaJrto 1.92-1.91 Ga 2 Mica schist and migmatite 20 \:~^S\ Mica schist 21 Kj Matavolcanic rocks 1.92-1.88 Ga 22 HI Serpantinite and othar rocks of ophiclits c. 1.98 Ga ; 231 | Garnet gneiss and diortte; Lapland grenuite bolt 24 §Hj 25 HH ^bted gabbro and granodiorite 1.9S • 1.93 Ga 26 RBil Gneissic granite Bdd hornblende gneiss 27 | | CUiartnt) and conglomerete 28 HH Metevolcanic rock and mica schist, the KfttSa alochthon 29 H| Calc-siicate rock, black schist, basic volcanic intercalates 30 | | Quirtnte with intercalates c. 2.3 - 2.0 Ga 31 HI Layered iitruskns 2.44 Gs 32 fHIH Mafic, iitermadiata and felsic matavolcsnic rocks 2.G • 2.0 Ga

Archean S2° 33 wm Latest granitoids Matavolcanic rocks of tha greenstone association Metasediments of the greenstone association Biot'fte ± homblands gneisses and migmatites OlkilliOt 37CZ1Tonalite'trondhjemite gneisses and migmatites ^-\ Faults and major shear or thrust zone C.3 Kmbarlte province •k Impact she Hastholman 60°

100 200 tan

Figure 2.2-1. The bedrock of Finland (Geological Survey of Finland 1999). 13 was intruded by anorogenic rapakivi granites, 1650 - 1540 million years in age, which originated from partial melting of the lower crust. The youngest basement rocks are the Jotnian sandstones (1400 - 1300 Ma) which are cut by Postjotnian olivine diabase dykes (1270 - 1250 Ma), and the 1100 and 1000 million years old dykes of Salla and Laanila in northern Finland. The bedrock had been eroded almost to its present level before the beginning of the Cambrian (about 600 million years ago). Due to subsequent erosion and continuous continental conditions, it is almost totally lacking in sedimentary rocks younger than the Precambrian.

2.3 Rapakivi granites

The HSstholmen study site is situated within the southwestern part of the anorogenic Wiborg rapakivi batholith (Figs. 2.2-1 and 2.3-1). The age of the batholith is 1650 - 1620 Ma, the emplacement of the rapakivi granite having occurred after the main phase of the Svecofennian orogeny (1900 - 1800 Ma). The exposed parts of the batholith cover an area of about 18 800 km2 on both sides of the Finnish-Russian border and the batholith continues for about 20 km to the south of HSstholmen under the , where it is in contact with the Svecofennian rocks (see Koistinen 1994). The Precambrian basement dips very gently (at <0.5°) southwards towards Estonia and the St. Petersburg region of Russia, where it is overlain by hundreds of metres of Vendian and Phanerozoic sedimentary rocks (Puura et al. 1996).

Wiborgite, characterised by ovoidal potassium feldspar megacrysts mantled by , comprises over 80% of the Finnish part of the Wiborg rapakivi batholith (Simonen & Vorma 1969). Other rapakivi granite types include pyterlite (rapakivi with ovoidal potassium feldspar megacrysts not usually mantled by plagioclase), porphyritic rapakivi granite with angular potassium feldspar megacrysts, dark-coloured, equigranular, hornblende- and fayalite-bearing rapakivi granite, even-grained rapakivi granite and porphyry aplites (Vorma 1971). The dyke rocks are granite porphyry, porphyry aplite, aplite and quartz porphyry. The rapakivi granites are characterised by higher Si, K, Rb, Ga, Zr, Hf, Th, U, Zn, and REE (except Eu), and lower Ca, Mg, Al, P and Sr abundances than granitic rocks in general (Ramo & Haapala 1995). The rapakivi magmatism is bimodal in nature, the above rock types representing the silicic suite, whilst the gabbro, anorthosite and diabase, which are associated spatially and temporally with the granites, comprise the mafic suite (Ramo et al. 1994). Within the batholith the gabbro and anorthosite only occur as minor inclusions, however, they may be more abundant at depth (Elo & Korja 1993). The rapakivi-related mafic rocks are also present in the northern satellites of the Wiborg batholith, the Ahvenisto batholith and the Suomenniemi complex, as well as in the Jaala-Iitti complex on the northwestern flank of the batholith. Swarms of subparallel, Subjotnian diabase dykes, occurring outside the batholith, are tectonically related to the batholith, and represent extensional tectonics during the emplacement of the rapakivi granites (Laitakari 1987). The Lovasjarvi mafic intrusion between the Wiborg batholith and the Suomenniemi complex belong to the same age group as the diabase dykes (Siivola 1987). Regional geology of the Hastholmen area

GEOLOGICAL SURVEY OF FINLAND Regional office for South Finland Espool998

Palaeoproterozoic rocks

iJHit^l Mafic metavolcanics

| [ Intermediate metavolcanic!

| | Mica schist and gneiss I I Q

Gabbro

| | Gianodioriteortonalite

|^§] Granite

| | Pegmatite «P»; p.- .. •"• * Mesopioterozoic rocks

^^H Rapakivi granite

j ] Watercourse

Topographic lineaments

Map of Pre-Quatemary Rocks & Geological Survey of Finland Digital deration model and base map © National Survey of Finland, permit No 13/mar/98 Hillshading is bom NW, angle is 45 degrees. 18 27 km

Figure 2.3-1. Regional geology of the Hdstholmen area. 15

Geophysical data suggest that the batholith is a relatively thin sheet-like body, about 10 km in thickness (Luosto et al. 1990). Interpretation of seismic soundings suggest that a 6 km thick high-velocity, presumably gabbro-anorthosite body lies at a depth of 10 km. The local magnetic and gravity anomalies within the batholith provide evidence that the batholith consists of separate intrusions and intrusion phases (Fig. 2.3-2b) (Elo & Korja 1993). Positive magnetic anomalies in the western part of the batholith have been interpreted to be due to a magnetic body between 12 and 15 km, which connects the low-density upper crust to lower crust, and represent a feeder channel of the rapakivi and gabbroic magmas (Fig. 2.3-2a). Interpretation of seismic and gravity data indicates that the crust is 15 to 20 km thinner beneath the Wiborg batholith than in the surrounding areas, and there is an upwelling mantle structure beneath the batholith (Fig. 2.3-2a and b) (Elo & Korja 1993, Korja et al. 1993). The generation of rapakivi granites and associated mafic rocks is thought to be due to partial fusion and upwelling of mantle material, which caused partial melting of the lower to middle continental crust (Ramo & Haapala 1995).

CRUST

MANTLE UPWEU.ING MANTLE

(b)

SW NE

CRUST

MANTLE

RAPAKIVI GRANITE DIRECTION OF EXTENSION

GABBRO-ANORTHCSfTE

DIABASE

Figure 2.3-2. (a) A schematic geophysical model of the Wiborg rapakivi batholith area based on seismic, magnetic and gravity data, (b) The origin of rapakivi granites based on a geological interpretation of the geophysical model (Elo & Korja 1993).The boundaries ofMoho 1 and Moho 2 lie at depths of 40 and 50 km, respectively. 16

The batholith has sharp, outward dipping contacts against the country rocks. Vorma (1972) describes a contact metamorphic aureole around the batholith, which is defined by the inversion of orthoclase to microcline. The aureole is less than 5 km wide in the northeastern part of the batholith and has a similar width or is slightly narrower in the southwest. Intrusive breccias with angular and rotated fragments of the Svecofennian country rocks occur along the boundaries of the batholith (Simonen 1987). Roof pendants are common, composed of Svecofennian migmatite-forming granite in the western part and both Svecofennian rocks and diabase in the eastern part of the batholith (Vorma 1975, Simonen 1987). The roof pendant diabases are slightly older (Subjotnian) than the rapakivi granites and represent subvolcanic-volcanic formations, which are related to the early evolution of the batholith (Laitakari et al. 1996).

Due to their anorogenic nature the rapakivi granites are unmetamorphosed rocks without heterogeneity caused by plastic deformation. Instead, magmatic flow fractures are reported in the site studies (Kuivamaki et al. 1997a). Fracturing of rapakivi granites is typically orthogonal in pattern and to some extent predictable. The structural elements from regional fracture zones to a single fracture, seem to have similar orientations, both within the study site and in the surrounding rapakivi granite area (cf. Pirhonen 1990).

Compared to fracturing, features such as miarolitic cavities and greisen-type deposits are more difficult to predict because of their random occurrence. Miarolitic cavities can vary from some centimetres to one metre in diameter. Both are typically associated with shallow-level late-stage magmatic intrusions with separate fluid phase.

Uneconomic greisen- and vein-type Sn-polymetallic mineralizations have been found in connection with the late-stage topaz-bearing microcline-albite granites, which resemble the Phanerozoic tin-bearing granites (Haapala 1977, Eden 1991). These strongly evolved rapakivi granite types have not been found at Hastholmen nor in the immediate area (Kuivamaki et al. 1997a).

The Finnish word rapakivi (crumbling stone) refers to its special kind of weathering, the ultimate result of which is the granular disintegration of the rapakivi granite into a saprolite of grus type, locally known in Finnish as mow. Within the Wiborg batholith two types of weathering can be distinguished, the commonest of which results in the disintegration of the matrix around the potassium feldspar ovoids into a gravelly sand, the ovoids themselves remaining less weathered (Kejonen 1985). The other type of weathering causes what is known as microsheeting, which intersects all minerals randomly and develops subconformably to the rock surfaces and or primary jointing planes. Usually weathering occurs only occasionally and the weathering products are more common and thicker in the central part of the batholith, where they are 1 - 3 m thick, than on the margins, where they are <1 m thick (Kejonen 1985). The weathering has penetrated to as much as 10 m from the surface and, in places, occurs as horizontal sections between portions of intact rock.

The country rocks southwest from the rapakivi batholith are composed of Palaeoproterozoic Svecofennian metamorphic and plutonic rocks (Fig. 2.3-1). The metamorphic rocks are of sedimentary and volcanic origin, including quartz-feldspar 17 gneisses, mica gneisses, amphibolites, hornblende gneisses and uralite and plagioclase porphyrites (Laitakari & Simonen 1963, Laitala 1984). The plutonic rocks include peridotites, gabbros, diorites, granodiorites and abundant granites. The Onas granite pluton, 1630 Ma in age, occurs in the southwestern part of the Svecofennian area in Figure 2.3-1. It consists of medium- to coarse-grained red granites and has sharp contacts against the country rocks with associated intrusive breccias.

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3 SITE GEOLOGY

3.1 Rock types

The determination of rock types at Hastholmen is based on visual, microscopic and lithogeocherriical investigations of rocks in outcrops, in the VLJ repository and in core samples (Suominen 1983, Anttila 1988, 1997, Lindberg 1994, 1996, Kuivamaki et al. 1997a, Gehor et al. 1997a, 1997b, 1998, 1999), as well as on the results of geophysical borehole logging and core samples (Okko et al. 1998, 1999a, 1999b, Okko & Front 1999). The bedrock of the site consists solely of different varieties of rapakivi granite, the most common forms being pyterlite, wiborgite, porphyritic rapakivi granite and even-grained or weakly porphyritic rapakivi granite.

Wiborgites and pyterlites are rapakivi granites with ovoidal potassium feldspar megacrysts. Traditionally in the rapakivi literature the wiborgites have been described as rapakivi granites, where most of the ovoids are mantled with plagioclase rims (Fig. 3.1-1), whereas in the pyterlites the ovoids are usually lacking in the plagioclase mantle (Fig. 3.1-2). However, there are rapakivi granites at Hastholmen with large numbers of ovoids mantled by plagioclase, which are not exactly wiborgites nor pyterlites. In outcrop mapping and borehole logging, rapakivi granites are described as wiborgites if more than 50% of the ovoids have plagioclase mantles, the rest of the ovoidal granites being described as pyterlites. Distinguishing the two varieties is often difficult, and they have been combined in maps and cross-sections presented in this report. The most common type of rapakivi granite in outcrops, the VLJ repository and core samples at Hastholmen is, however, pyterlite (Suominen 1983, Lindberg 1994, 1996, Kuivamaki et al. 1997a, Gehor et al. 1997a, 1997b, 1998).

The wiborgites and pyterlites are usually ordinary granites in their modal mineral composition, containing on average ca. 30% quartz, 39% potassium feldspar, 21% plagioclase, 4% biotite and 5% hornblende (Gehor et al. 1997a, 1997b, 1998, 1999). Deviations of the individual samples from these average compositions are 10 - 15% in case of the felsic minerals and 2 - 4% in case of the mafic minerals (Gehor et al. 1998). Accessory minerals include chlorite, epidote, apatite, carbonate, fluorite, sericite, sphene, zircon and opaque minerals. The diameter of ovoidal potassium feldspar megacrysts with plagioclase mantle ranges from 1 cm to 6.5 cm and that of ovoids without a mantle from 4 cm up to 12 cm (Kuivamaki et al. 1997a, Gehor et al. 1997a, 1997b). The plagioclase mantle has a width of 1 - 5 mm and consists of 1 - 3 mm long, randomly oriented plagioclase grains or laths. The potassium feldspar contains quartz, plagioclase, biotite and hornblende inclusions and strings of albitic perthite intergrowths. The groundmass between the ovoids is medium-grained (0.2 - 4 mm), and consists of quartz, plagioclase, potassium feldspar, biotite and hornblende. Sometimes plagioclase and quartz also occur as , measuring 5-15 mm in diameter.

Dark-coloured pyterlite, which is characterised by a greater amount of groundmass and grey, euhedral, often twinned plagioclase porphyroblasts, in comparison with the ordinary, reddish pyterlite, is found southeast from Hastholmen, but not in the actual study site (Kuivamaki et al. 1997a). 20

Figure 3.1-1. Wiborgite. Photo by Aimo Kuivamdki, Geological Survey of Finland.

Figure 3.1-2. Pyterlite. Photo by Aimo Kuivamdki, Geological Survey of Finland. 21

Porphyritic rapakivi granites, characterised by angular potassium feldspar phenocrysts (5 - 25 mm in diameter) without plagioclase mantles (Fig. 3.1-3), are present in boreholes KR2, KR3 and KR4. They are not exposed within the study site, and is only present in some outcrops south of Hastholmen. Porphyritic rapakivi granites contain on average 31% quartz, 18% plagioclase, 45% potassium feldspar, 3% biotite and 1-2% hornblende (GehSr et al. 1997b, 1998). In addition to potassium feldspar, quartz and plagioclase may also occur as phenocrysts. The groundmass between the phenocrysts is medium-grained (0.2 - 2 mm), consisting of potassium feldspar, plagioclase and quartz.

Even-grained or weakly porphyritic rapakivi granites are present both in outcrops on the mainland northwest of Hastholmen and in boreholes KR2-KR8. Reddish or brownish even-grained rapakivi granites (Fig. 3.1-4) are fine- or medium-grained, being typical granites in their mineral composition and containing 30% quartz, 19% plagioclase, 44% potassium feldspar, 3% biotite and 1% hornblende (Gehor et al. 1997a, 1997b, 1998, 1999). Accessory minerals are the same as in the wiborgites and pyterlites. Leucocratic, weakly porphyritic rapakivi granites are even-grained and medium-grained, but they also contain occasional potassium feldspar and quartz phenocrysts, comprising not more than 20 - 30% of the total volume of the rock, and also small number of homogenous or concentric ovoids. On average they contain 35% quartz, 25% plagioclase, 36% potassium feldspar, 3% biotite and rarely very small amounts of hornblende.

Coarse-grained granite and pegmatite, cutting both wiborgite/pyterlite and even-grained rapakivi granite with sharp contacts, are present as veins a few centimetres in width, which sometimes have a quartz nucleus (Kuivamaki et al. 1997a, Strahle 1998). Narrow aplite veins cutting the rapakivi granites are medium-grained, reddish and composed of quartz, potassium feldspar and plagioclase (Gehor et al. 1997a), with the amount of mafic minerals less than 5%. Narrow (<5 cm) veins, consisting solely of quartz are common in a sheared rock, where they fill NW-SE trending fracture swarms. A few greisen veins, consisting primarily of quartz, mica and topaz, and recording the circulation of late stage magmatic (hydrothermal) fluids in the fracture system, have been found in the vicinity of Hastholmen, but not from the actual study site (Kuivamaki et al. 1997b). The greisen veins cut all the other veins mentioned above.

Miarolitic cavities, filled with quartz or into which small idiomorphic crystals of potassium feldspar, albitic plagioclase and quartz protrude, are present especially in the medium- to coarse-grained, even-grained rapakivi granites, being more frequent near their upper contacts (Suominen 1983, Lindqvist & Suominen 1987, Kuivamaki 1997a). They are usually 5 - 20 cm in diameter, but more than 100 cm long cavities have been observed. Miarolitic cavities are originally gas- or liquid-filled vesicles. Their occurrence provides evidence for the internal structure of the rapakivi granite, as the gas bubbles in the magma are confined to regions close to interfaces, e.g. boundaries between different rapakivi granite types (Suominen 1983).

Pegmatite is present as veins a few centimetres wide which, according to borehole-TV logging (Strahle 1998), dip steeply (70 - 80°) to the SSE. Xenoliths of country rocks, comprising mostly of mica gneisses and amphibolites and measuring 10 - 100 cm in diameter, are rare (Kuivamaki et al. 1997a). 22

Figure 3.1-3. Porphyritic rapakivi granite. Photo by Antero Lindberg, Geological Survey of Finland.

Figure 3.1-4. Even-grained rapakivi granite. Photo by Aimo Kuivamdki, Geological Survey of Finland. 23

All the rapakivi granites described above are chemically similar, being metaluminous or slightly peraluminous (Geho'r et al. 1997b). They are close to typical granites of rapakivi composition, which are characterised by high Fe/Mg and K/Na -ratios and high Rb, F and Zr contents (cf. Nurmi & Haapala 1986). The analyzed samples have been inter- preted to be members of a rather limited differentiation series, in which the wiborgites and pyterlites represent the most mafic differentiates, containing ca. 69% SiC>2 and the even-grained or weakly porphyritic rapakivi granites the most evolved differentiates, containing ca. 75% SiO2 (Gehor et al. 1997b). The porphyritic rapakivi granites often lie between these end members. However, there are varieties of porphyritic and even- grained rapakivi granites, which, on the one hand, resemble the wiborgites and pyterlites and on the other the weakly porphyritic rapakivi granites (Gehor et al. 1998). Consequently, the rapakivi granites at Hastholmen have been divided into two groups, in which the wiborgites and pyterlites with similar porphyritic and even-grained rapakivi granites form one group, and weakly porphyritic rapakivi granites with associated porphyritic and even-grained rapakivi granites another group (Gehor et al. 1998). The AI2O3 content in the most mafic members is about 15%, decreasing to about 11 % in the most evolved differentiates. The TiC>2 content decrease respectively from ca. 0.5% to 0.1%, Mn content from 500 ppm to 100 ppm, CaO content from 2.5% to 0.5%, Fe2C>3 content from 5% to 2% and MgO content from 0.5% to almost 0%. In parallel with these changes the K2O content increases from 5.5% to 6%.

The trace element compositions of the analyzed rapakivi varieties are rather similar, however, samples of the even-grained and porphyritic rapakivi granites contain markedly less Ba, Mn, P and Sr and more Rb, Cs and Nb than the wiborgites and pyterlites. The fluorine contents are highest in the leucocratic, weakly porphyritic rapakivi granites. Also their Th, U and Y contents often are higher than those of the wiborgites and pyterlites. The Cl content is higher in the most mafic rapakivi types than in the silicic rapakivi varieties. The trace element compositions (especially the much lower Y content) of some granite and porphyritic granite samples indicate that they are either of Svecofennian origin (xenoliths) or granitoid varieties heavily contaminated by Svecofennian rocks (Gehor et al. 1997b). Only a few greisen veins from the vicinity of Hastholmen show elevated Sn, Zn, Pb and Cu contents (Kuivamaki et al. 1997b).

The kind of granular weathering of the rock surface described in Section 2.3 ("moro") is not present at the Hastholmen site, except in some erratic boulders. However, a different form of weathering does occurs within the fracture zones at greater depths, the weathering products containing unaltered, mechanically broken main minerals of the rock as well as chemical alteration products (Anttila 1988). The fracturing of the rock has enabled an interaction to take place between the primary minerals of the rapakivi granite and the aqueous solutions circulating in the fractures.

3.2 Magma tectonics

In some outcrops the rapakivi granites show compositional variations, which can be interpreted as a magmatic flow structure ("schlieren") or a magmatic bedding, with the main strike of such structure or bedding being NE-SW (Kuivamaki et al. 1997a). The 24 subhorizontal patterns observed in the dipmeter survey, have been interpreted as being due to some sort of layering or banding (Siddans et al. 1997, 1998). Based on observations from shallow (< 200 m) boreholes, Suominen (1983) has suggested a lamellar internal structure for the rapakivi granite, in which lenses and layers of various rapakivi granite types dip gently eastwards.

Thin, 10 - 20 mm wide, subhorizontal mylonites have been observed by borehole-TV logging at three depth levels: shallow (100 m), intermediate (300 - 500 m) and deep (800 - 900 m) (Strahle 1998) and coincide with the most significant subhorizontal fracture zones observed, Rl, R18 and R19 respectively (see Section 5.3).

3.3 Fracturing

3.3.1 Rock mass classification and terminology

The terminology used in this report has been developed over the period of the site characterisation programmes in Finland and has been previously applied in several reports of the site investigation studies conducted by TVO and Posiva. The terms mainly concern the description of the geological and structural features of the bedrock, and those most frequently used in the reports are defined below. A separate report (Aikas et al. 1999) has been prepared relating to the engineering geological rock mass classification of the Hastholmen site, especially from the construction point of view of the repository.

The Finnish engineering geological classification has been applied in this report, in particular for the description of the fracturing of the rock mass, and for the structural modelling of the bedrock. The classification (Korhonen et al. 1974, Gardemeister et al. 1976), which is published only in Finnish, was developed with reference to the specific bedrock conditions found in Finland, and was designed to be applied to construction activities. The criteria used in this classification system are:

- the properties of the rock mass (consisting of its state of weathering, the orientation of any internal structure, its grain size and its major minerals) and - the fracture properties (geometry of fracturing, fracture frequency and type of fractures) which together determine the rock quality.

A simplified description of rock quality based on this classification system is given in Table 3.3-1.

The structural solidity of the rock mass is divided into three classes: intact, loose and broken rock mass. In this report only the classes intact and broken are applied, because rock in the loose rock mass class has not been found in the site studies. 25

Table 3.3-1. Rock quality description according to the Finnish engineering geological classification (Korhonen et al. 1974, Gardemeister et al. 1976).

Structural solidity of Structural types of Structural types and Hardness and toughness rock mass rock mass frequency of fractures of main rock types (described in terms of the most dense fracturing)* Mass-structured Sparsely fractured Slightly fractured Abundantly fractured Intact rock mass Schistose structured Sparsely fractured soft Slightly fractured brittle Abundantly fractured tough Mixed-structured Sparsely fractured hard Slightly fractured Abundantly fractured Loose-structured Sparsely fractured Slightly fractured Abundantly fractured Loose rock mass Weathered- Should be described as thoroughly as possible structured bearing in mind the degree of weathering (RpO-Rp3)2 Cleft-structured (Ril) Planar fractures divide the rock mass into two or more separate sections Block-structured Abundantly fractured No fracture filling (Rill) Broken rock mass Fracture-structured Densely fractured Little filling in fractures (Rilll) Crush-structured Abundantly or densely Fractures filled with clay (RilV) fractured minerals Clay-structured - Abundantly clay material (RiV) in rock mass

Sparsely fractured <1 fractures/m * RpO Unweathered Slightly fractured 1-3 fractures/m Rpl Slightly weathered Abundantly fractured 3-10 fractures/m Rp2 Strongly weathered Densely fractured > 10 fractures/m Rp3 Completely weathered

The key terms used in the structural modelling are defined as follows:

A structure in a rock is any geological feature defined geometrically (Keary et al. 1993). A tectonic structure is produced by deformation and is synonymous with the use of the term deformation structure. In this report the use of the term structure implies a tectonic structure, unless otherwise stated. Every structure (or R-structure) in the bedrock model has an unique object name (i.e. R(number)) and is accompanied by information which 26 describes the attributes of the structure, e.g. its fracture density, its transmissivity, etc. The term R-structure is used particularly in Section 5.4 for separating the modelled structures (fracture zones) from other hydraulically conductive features included in the rock mass.

A fracture zone is a general term describing varying types of fracture structures as shown in Table 3.3-1 or a structure in the bedrock model with block-structured or fracture-structured properties (Rill or RilH), as explained in Table 3.3-1.

A major fracture zone contains crush-structured (RilV) portions (Table 3.3-1). A crush zone contains clay-structured (RiV) portions. The classification of such zones can also be based on the quantitative interpretation of their properties or, where only indirect evidence is available, on expert judgement (Table 3.3-1).

In this report the term intact rock is synonymous with the term averagely fractured rock which has been used commonly in other radioactive waste disposal programmes (e.g. that in ). The intact rock contains all types of fractures and fracture zones, both known and unknown, but only those which are not defined as structures in the bedrock model for the site.

The term zone (e.g. fracture zone) refers to a geometry in which the dimensions along the strike and along the dip direction of the zone are considerably larger (>10) than its perpendicular thickness.

Engineering geological classification

The fracturing in core samples was determined by measuring the proportion of broken rock and the number of fractures outside the broken sections as a function of the depth and the rock types. According to the Finnish engineering geological bedrock classification (Table 3.3-1), a core sample is regarded as broken if the number of fractures is more than 10 fractures/m (pieces of core samples per metre), it is dominated by filled and/or open fractures, or it is mesoscopically weathered. On account of these features, such samples are often damaged during drilling, resulting in core loss and difficulties in observing the number and types of fractures.

The broken sections in Hastholmen core samples (boreholes KR1 - KR8) represent about 4.6% of the total length of the samples (6884 m) as compiled in Table 3.3-2. In most of them (>98%) the rock is densely fractured (> 10 fractures/m) representing 2.1 - 9.0% of the length in individual borehole core (Okko et al. 1998). The rest of the broken sections represent crush- or clay-structured and densely-fractured rock (> 10 fractures per metre with clay-filled fractures or abundant clay material in the rock mass). 27

Table 3.3-2. The amount and proportion of the broken sections in the Hdstholmen borehole cores. Broken sections Rilll and RHV refer to Table 3.3-1.

Borehole Core sample [m] Sum of broken sections [m] [%] Top Bottom Length RiHI RilV Total KRl 3.07 1002.13 999.06 23.09 23.09 2.3 KR2 40.44 1005.48 965.04 71.94 2.04 73.98 7.7 KR3 202.30 803.35 601.05 54.29 54.29 9.0 KR4 40.16 1000.99 960.83 48.62 1.35 49.97 5.2 KR5 40.13 1001.54 961.41 40.45 40.45 4.2 KR6 40.06 700.91 660.85 37.19 0.06 37.25 5.6 KR7 40.50 815.91 775.41 16.98 0.23 17.21 2.2 KR8 40.69 1001.31 960.62 18.05 1.87 19.92 2.1 KR1-KR8 Summary 6884.27 310.61 5.55 316.16 4.6

Broken sections occur in every drill core, and they are most often 1 - 5 m in length. There is a close association at Hastholmen between the presence of these broken sections and the even-grained granites, or to the contact of these granites with pyterlite and wiborgite. In these sections, borehole-TV studies found only isolated open fractures or cavities which, however, possess remarkable large apertures and have high hydraulic conductivities (Okko et al. 1998,1999a).

The total amount of all weathered core in boreholes KR1-KR8 represents approx. 13% of the total length of the drill cores. The majority of the drill core samples represent either unweathered (RpO) or slightly weathered (Rpl) rock (Table 3.3-3). The width of the class Rpl weathered zones usually ranges from a few tens of centimetres up to a few metres. However, a 100 m wide zone of slightly weathered rock occurs in borehole KRl and two nearly 50 m wide zones in borehole KR2. The proportions of strongly (Rp2) to completely weathered (Rp3) rock are insignificant.

ROD classification

The RQD (Rock Quality Designation) number (Deere 1964) indicates the percentage of a core sample, consisting of parts at least 10 cm in length. Only primary fractures are taken into account, and not fractures formed during the drilling.

The mean RQD numbers for the intact and broken (>10 fractures/m) rock in boreholes KR1-KR8 are shown in Table 3.3-4. For the intact rock the average RQD number is 97.5%, characteristic of a rock of very good quality. The corresponding figure for the broken sections of the drill cores is 50%, demonstrating poor rock quality. 28

Table 3.3-3. Proportions of different weathering classes from the total length of the borehole samples. RpO - unweathered, Rpl = slightly weathered, Rp2 = strongly weathered, Rp3 = completely weathered. Compiled from Niinimdki (1997a-c, 1998) and Rautio (1997, 1998a-b, 1999).

Borehole Weathering class RpO% RpO-1 % Rpl-2 % Rp2% Rp2-3 % Rp3% KR1 80.1 1.8 16.0 1.7 0.4 - - KR2 88.6 9.6 1.0 0.4 0.4 - - KR3 74.6 2.2 22.6 0.4 0.2 - - KR4 90.8 6.0 2.9 <0.1 - 0.3 - KR5 83.5 13.7 4.7 2.2 0.3 - - KR6 72.8 12.8 14.2 - 0.2 - <0.1 KR7 93.1 5.4 0.9 - 0.6 <0.1 - KR8 95.2 2.6 1.5 0.4 0.3 - -

Table 3.3-4. The mean RQD numbers for the intact and broken (> 10 fractures/m) rock in boreholes KR1-KR8. Compiled from Niinimdki (1997a-c, 1998), Rautio (1997, 1998a-b, 1999).

Borehole Depth level (m) Mean RQD number (%) Intact rock Fractured rock KR1 3-500 97.9 34.0 500 - 1002 96.8 46.8 KR2 41 - 500 97.4 53.5 500 -1004 96.8 40.8 KR3 203 - 500 95.0 39.7 500-803 97.1 61.6 KR4 41 - 500 97.2 45.1 500 - 1001 95.5 62.9 KR5 41-500 98.3 55.5 500-1001 97.4 57.3 KR6 41 - 500 96.6 52.0 500 - 700 97.4 KR7 41 - 500 98.9 53.6 500-815 99.1 50.5 KR8 41 - 500 98.6 54.8 500 -1001 99.4 42.0

3.3.2 Surface fracture studies

Geological surface mapping of the site and its immediate surroundings, within a distance of 3 - 5 km from the island of Hastholmen (and referred to below as the Hastholmen area) has involved making measurements on fractures from 237 outcrops 29

(Kuivamaki et al. 1997a). During the fracture mapping all the fractures, equal to or longer than one metre, were investigated. For each fracture dip direction and dip, rock type, length, form (straight or curved), type (tight, open or filled), width and infilling, where present, were recorded. A total of 4426 fractures were investigated. Fracture orientations were displayed using the Schmidt equal-area, lower hemisphere stereographic projection. In addition, orientation data were also presented using rose diagrams.

The distribution of all fracture orientations measured in outcrops is shown in Figures 3.3-1 and 3.3-2. The main sets of fracture directions are presented in Table 3.3-5 in order of decreasing frequency. Surface fractures form a distinct orthogonal system, with three perpendicular fracture directions: steeply dipping (>75° dip) fractures striking NE- SW and NW-SE plus horizontal or subhorizontal (<30° dip) fractures. Because of the flat surface of the outcrops, gently dipping and horizontal fractures are under-represented in the data. The majority of the open (aperture over 1 cm) and long, (length over 10 m) fractures have a NE-SW orientation (fracture set I), whilst the tight fractures are evenly distributed in both of the steeply dipping fracture sets.

To investigate the spatial distribution of the fracture orientations the area was divided into nine sub-areas (Kuivamaki et al. 1997a). The area was found to be very homoge- nous in terms of its fracture orientations. Only in two sub-areas in the northwestern and northern part of the area, can separate pole maxima be distinguished, in addition of fracture sets I and II. This demonstrates that there may be, within these sub-areas, two separate cubic fracture systems of different age (Kuivamaki et al. 1997a).

Table 3.3.-5. Distribution of fracture orientations measured in outcrops at the Hastholmen area {Kuivamaki et al. 1997a). More dominant dip direction in bold.

Main sets of fracture directions Dip direction (pole maxima) Dip (pole maxima) I 58° 328° and 148° >75° II 328° 238° and 58° >75° III variable variable Horizontal or <30°

The fracture frequencies at the Hastholmen area were measured across each outcrop in N-S and E-W traverses (a total of 15 km). When possible, the fracture frequency for the horizontal fracturing was also measured. The resulting very low average fracture frequencies are shown in Table 3.3-6. Within the actual study site on the island of Hastholmen the maximum fracture frequency is 2.0 fractures/m and the average fracture frequency 0.6 fractures/m, the frequencies being lowest in the western part of the island (Suominen 1980). No essential differences exist in fracture frequencies between the different rapakivi granite types, although fracturing in the even-grained rapakivi granite tends to be slightly more frequent than in the pyterlites and wiborgites (Kuivamaki et al. 1997a). No fracture zones (> 10 fractures/m) have been observed during the mapping, the outcrops therefore represent the intact, i.e. least fractured rock. However, seismic 30 refraction and ground radar surveys (Sutinen 1997, Paananen & Paulamaki 1998) demonstrate that such zones may occur in the till-covered areas in the southeastern part of the island.

Figure 3.3-1. Distribution of all fracture orientations (N = 4426) measured in outcrops at the Hdstholmen area (Kuivamdki et al. 1997a). Schmidt equal area, lower hemi- sphere projection and rose diagram (the scale of ring in the rose diagram is 7%).

Figure 3.3-2. Distribution of horizontal and gently dipping fractures (dip <45 ° N = 207) measured in outcrops at the Hastholmen area (Kuivamdki et al. 1997a). Schmidt equal area, lower hemisphere projection.

To investigate the possible changes in fracture frequencies outside the Hastholmen area, the fractures in outcrops along two investigation lines were measured in the same manner as in the actual study site (Kuivamaki et al. 1997a). One of the lines trends to the west from the Hastholmen area towards the contact of the rapakivi batholith, the other one to the north from Hastholmen. The resulting fracture frequencies show that there are no differences in the fracture frequencies within and outside the study site. The 31

average fracture frequency is 0.68 fractures/m for the line trending to the west and 0.42 fractures/m for the line trending to the north. The lower fracture frequency in the latter is most likely due to differences in the level of exposure (Kuivamaki et al. 1997a).

Table 3.3-6. The fracture frequencies of the outcrops at the Ha'stholmen area (Kuiva- maki et al. 1997a).

Traverse Number of outcrops Fracture frequency (fractures/m) Mean Minimum Maximum E-W 211 0.58 0.05 1.62 N-S 212 0.62 0.00 1.39 Vertical 18 0.59 0.25 1.60

The majority of the fractures at the Hastholmen area are either open (54.5%) or tight (38.7%) (Kuivamaki et al. 1997a). The mean trace length of the measured fractures is 8 m, the fractures in the pyterlite being slightly longer than those of the wiborgite, porphyritic rapakivi granite and even-grained rapakivi granite. Open and filled fractures are longer (mean length 10.2 m) than tight fractures (mean length 4.5 m). Good exposure has allowed the reliable measurements of the longest fractures. 5.9% of the fractures are over 20 m in length and the longest fracture is over 100 m. The distribution of the fracture trace lengths is shown in Fig. 3.3-3.

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

LENGTH(m)

Figure 3.3-3. Distribution of fracture trace lengths at the Hdstholmen area (Kuivamaki et al. 1997a). 32

3.3.3 Fracture studies in the VLJ repository

The main rock type in the VLJ repository is pyterlite, with wiborgite occurring only occasionally (Lindberg 1994, 1996). It is cut by even-grained rapakivi granite dykes, the number of which is, however, insignificant. All the fractures over 2 m in length (a total of 1823 fractures) were investigated in the 1170 m long access tunnel and in the waste caverns and shafts, which have a maximum depth of 120 m (Viljanen 1994, 1996). Steeply dipping fractures oriented ENE-WSW and NW-SE (Fig. 3.3-4) dominate over the (sub)horizontal fractures, almost 80% of the fractures having a dip of over 45°. However, the fracture zones, in which the fracture frequency exceeds 10 fractures/m, are characterised by dense (sub)horizontal fracturing with clayey material, composed of kaolinite and fragments of the main rapakivi granite minerals (Viljanen 1994, Lindberg 1994, 1996). The steeply dipping fractures typically have chlorite-coated slickenside surfaces and are commonly filled with carbonates (calcite and dolomite), and more rarely with fluorite and kaolinite.

The fracture frequency in the intact rock outside the densely fractured, (sub)horizontal zones is 0.8 fractures/m in the access tunnel and 1.04 fractures/m in the waste caverns and shafts (Viljanen 1994, 1996). The mean trace length of the fractures is 10.6 m in the access tunnel and 9.14 m in the repository, the longest fracture being a 86 m long vertical fracture observed in the lift shaft. This is about the same order of length as the maximum trace length of vertical fractures measured in the outcrops.

The fracture orientations, lengths and frequencies correlate well with those observed in the outcrops. However, the number of open fractures is smaller in the repository than in the outcrops and it decreases with increasing depth (Kuivamaki et al. 1997a). The apertures of the open fractures in the repository are usually less than 2 mm, whilst in the outcrops the mean aperture of the open fractures is 16.5 mm.

Figure 3.3-4. Distribution of fracture orientations measured in the VLJ repository {Kuivamaki et al. 1997a). Schmidt equal area, lower hemisphere projection and rose diagram (scale of ring in the rose diagram is 5%). 33

3.3.4 Core sample fracture studies

The fracturing in core samples was determined by measuring the proportion of broken rock and the number of fractures outside the broken sections as a function of depth and the rock types. Typically core samples are usually slightly fractured (1-3 fractures/m), and some cores are sparsely fractured (< 1 fracture/m), even close to the surface. Even-grained granites are in places abundantly fractured (3-10 fractures/m), especially near the contacts with pyterlite and wiborgite or when they occur as narrow dykes. Table 3.3-7 gives an example of the mean fracture frequencies by fracture types in the intact (averagely fractured) rock of borehole KR3.

Table 3.3-7. Mean fracture frequencies (fractures/m) for open (Op), filled (Fi) and tight (Ti) fractures in intact bedrock sections as a function of depth and rock type. Borehole KR3, core sample. Rock types: PYT-WIB = pyterlite-wiborgite, EGR = even-grained granite; (F) = fine-grained and (M) medium-grained variety, PORGR = porphyritic granite.

Rock type Depth [m] Fracture frequency [fractures/m] Op Fi Ti Tot PYT-WIB 202.30 - 220.85 - 0.27 0.54 0.82 EGR (M) - 222.40 - 0.65 0.65 1.29 PYT-WIB - 273.60 - 0.18 0.35 0.53 EGR(F) - 359.30 0.33 3.16 1.17 4.66 EGR (M) -444.00 0.12 1.69 0.93 2.75 PORGR - 456.00 - 1.00 0.42 1.42 EGR(M) - 470.90 - 0.27 0.87 1.14 EGR(F) - 473.80 - 5.86 1.03 6.90 EGR (M) - 545.60 0.01 0.42 0.71 1.15 EGR (F) - 558.80 - 2.20 2.42 4.62 EGR (M) - 659.00 - 0.26 0.70 0.97 PYT-WIB - 670.50 - - 1.74 1.74 PORGR - 679.90 - 0.32 0.64 0.96 EGR (M) - 734.20 - 0.66 0.98 1.64 PORGR - 803.35 0.03 0.13 2.59 2.75 Average 0.05 0.82 1.06 1.93

The contact zone between even-grained granites and pyterlite-wiborgite seems to control the subhorizontal set of the major fracture zones at Hastholmen. In general, the mean fracture frequency does not change much as a function of depth or between the different boreholes, but is clearly related to the proximity of the above-mentioned contact zone and particularly to the fine-grained variety of the even-grained granites (Okko et al. 1998, 1999a). In borehole KR3, more than 50% of the fine-grained variety of the even-grained granite unit between 273-360 m is densely fractured (> 10 fractures/m) and the mean fracture frequency is about 4.7 fractures/m even in the intact part of the fine-grained granite. 34

Studies on core samples have the disadvantages of drilling-induced fracturing, core loss and core splitting. New, advanced wireline techniques, in which the borehole wall is scanned, e.g. borehole-TV, dipmeter, acoustic televiewer have all been used to examine in situ fracturing. Borehole-TV logging was found to be a practical method of investigating rock types and mineralogical features. An advantage of wireline techniques over core samples is the continuous 360° image of the borehole wall with a length resolution of 1 mm and cross resolution 1 pixel/degree. Borehole-TV imagery can be processed to identify and characterise fractures and to provide accurate data on their locations and orientations (Strahle 1998).

Table 3.3-8 shows the statistical characteristics for potentially hydraulic fractures, documented as open or channelled in borehole-TV studies. The data have been divided into two depth units, upper and deeper part of the rock mass representing 0 - 500 m and 500 - 1000 m in boreholes, respectively. The statistics support the general idea that the fracture frequency is lower deep in the bedrock than closer to the surface. It also exhibits that open space and average aperture becomes smaller along the depth. An exception is provided by the even-grained granite of the upper part, which hosts one of the major fracture zones in its hanging wall (see Figures in Section 5.3).

Table 3.3-8. Aperture characteristics of open and partly open fractures based on borehole-TV studies at Ha'stholmen. Data are given for two main rock types in two depth zones.

TV-record Fracture statistics Aperture statistics KR1- KR6 Rock type Length Number Frequency Sum Per metre Mean [m] [pieces] [1/m] [mm] [mm/m] [mm] Upper part Pyterlite-wiborgite 1865 1056 0.57 5158 2.77 4.88 0 - 500 m Even-grained granite 628 603 0.96 2598 4.14 4.31 Deeper part Even-grained granite 1182 379 0.32 1274 1.08 3.36 500 - 1000 m Pyterlite-wiborgite 1436 389 0.27 1113 0.78 2.86 KR1-KR6 Summary 5111 2427 0.47 10143 1.98 4.18

Most of the fractures recorded from the core samples are filled or tight. Calcite, dolomite, Fe hydroxides and clay minerals (illite, montmorillonite and kaolinite) form the most typical fracture mineral phases throughout the drill cores. Calcite and/or dolomite are frequently found in every core from every borehole, and surfaces coated with chlorite and chloritic slickensides are also present at all depths (Gehor et al. 1997b, 1998, 1999). Open fractures in core are abundant only to depths of 100 - 150 m, but single open fractures can be found at all depths - an attribute typical of granitic formations and as sporadic clusters close to sections of broken rock. 35

- HH-KR2: Al Bwhota-TV Iracbi a) b) —1J%I PMfc-15.96 I

| S>«rch T—»1.0*| P—X-M.S2 I C) d)

U bw«hol—TV fr»dufw.. e)

Figure 3.3-5. Distribution of the fracture orientations in Hdstholmen boreholes detected by TV-loggings, a) KRl, b) KR2, c) KR3, d) KR4, e) KR5, andf) KR6. Schmidt equal-area lower hemisphere stereographic projection. 36

Oriented fracture data were gathered from the drill cores and by borehole-TV logging (Fig. 3.3-5) from borehole walls. The majority of the fractures in the drill cores are horizontal or very gently dipping (Okko et al. 1998). In boreholes KR1, KR2, KR3, KR5 and KR6 there are, below the near-surface fracturing, some sections with mainly steeply dipping fractures. These sections are 260 - 600 m (fracture orientation 295/90°) in borehole KR1, 295-350 m (075/90°), 390-435 m(125/90°) and 630-765 m (195/50°) in KR2, 385 - 790 m (345/90°) in borehole KR3, 790 - 1000 m (245/90°) in borehole KR5, and 590 - 690 m (280/75° and 050/80°) in KR6. There appear to be no differences in fracture orientations with regard to rock type or depth.

Boreholes KR7 and KR8 have been drilled recently and are situated ca. 1.5 to 3.0 km NNW from the actual Hastholmen study site (Rautio 1998b, 1999). One aim of these multipurpose boreholes was to check the continuity of lithology and subhorizontal fracturing in immediate surroundings of the island of Hastholmen. Both boreholes were located in the same rock types as the Hastholmen site. The main rock type is wiborgite- pyterlite with cross-cutting even-grained rapakivi granites. Only borehole KR7 exhibits one longer continuous section of even-grained granites between 300 - 410 m in borehole length.

Boreholes KR7 and KR8 have fewer broken zones and fractures than the six earlier deep boreholes KR1 - KR6. The average fracture frequency is 0.98 fractures/m and 1.11 fractures/m respectively for boreholes KR7 and KR8, (Rautio 1998b, 1999), and the rock mass intersected by boreholes KR7 and KR8 is considered as sparsely to slightly fractured and is of high quality in terms of its engineering geological rock mass classification (see Section 3.3.1, and Aikas et al. 1999).

• HH-KRB: Co<« M a) b)

Figure 3.3-6. Distribution of the fracture orientations in Hastholmen boreholes KR7 and KR8 detected on core samples, a) KR7 and b) KR8. Schmidt equal-area lower hemisphere stereographic projection. 37

Oriented fracture data are obtained from drill core samples. In parallel with the other Hastholmen boreholes, the majority of fractures in boreholes KR7 and KR8 are horizontal (Fig. 3.3.-6). Borehole KR7 also shows a weaker maximum of subvertical fractures with a SW-NE strike, which are found at all depths.

3.3.5 Core discing

One notable feature of the core samples of rapakivi granite at Hastholmen is the presence of core discing and ring discing (Fig. 3.3-7). Core discing is a phenomenon in which the core is cut by multiple subparallel fractures normal to the core axis and with spacings of a few millimetres to tens of millimetres and is due to stress release mechanism. Ring discing is a similar phenomenon which occurs when a pilot hole is overcored (Hakala 1999). Core discing has been noted in sections of core several metres or tens of metres in length (Table 3.3-9).

10 &m ,0-J

Figure 3.3-7, Core disc fractures in borehole KR7 at depth of 775.80 m.

The first observations of core discing fractures are usually seen at the depth of about 200 m at Hastholmen. Core from all the boreholes, except KR1, exhibits core discing and each borehole contains tens or hundreds of such fractures (Table 3.3-9). The morphology of these disc fractures varies and has been classified into six types: flat, cup, petal, ring, saddle and petal centreline (Hakala 1999). The majority of disc fractures at Hastholmen are of the saddle type (Sacklen 1999). Ring disc fractures are associated with overcoring rock stress measurements performed in borehole KR6 (Ljunggren 1998). 38

Table 3.3-9. Occurrence of core disc fractures at Hdstholmen, boreholes KR1 to KR8 (compiledfrom Niinimdki 1997a-c, 1998, Rautio 1997, 1998a-b, 1999, Sacklen 1999).

Borehole Core disc fractures Number of Depth ranges of Principal depths of fractures occurrence occurrence KR1 3 455 KR2 190 245-931 638 - 639 706-712 764-765 929-931 KR3 76 351-799 559 - 560 776 - 780 KR4 89 217-862 217 - 229 689 - 695 786 - 803 813-837 KR5 317 225 - 998 390-424 520 - 533 818-900 971 - 989 KR6 177 129 - 609 424-433 480 - 540 KR7 243 302-816 602 - 622 706-719 753 - 784 808-816 KR8 756 392-1001 494-531 777 - 1001

The formation of core discing is related to the state of in situ stress and to the tensile strength of the rock (Hakala 1999) and it is neither observed in borehole studies by TV- logging nor by geophysical acoustic logging, a technique which is very sensitive to the presence of fractures. No unambiguous correlation between disc fractures and rock types or bedrock structures has been found. The borehole sections with core disc fractures show generally low hydraulic conductivities typical of the intact or averagely fractured rock, but core discing may have more significance for construction.

The recent laboratory studies (Hakala 1999, Song & Haimson 1999) suggest that in principle the morphology and thickness of core discs can be utilized as an in situ stress indicator with respect to both directions and magnitudes. 39

3.4 Rock mass modelling

The basic intention to understand the rock volume of the study site and make different utilisation plans needs information on rock types, their physical properties and distribution in space. The geological and geophysical information obtained from airborne, outcrop and borehole investigations has been in the first phase aggregated into three dimensional model, which is called a lithological bedrock model in this report (Section 4). The lithological surface model covers remarkably larger area than the actual Hastholmen study site.

The crucial features of the bedrock in regard to the safety of the final disposal of nuclear waste are the presence of groundwater, its flow and geochemical properties. The interpretation and model development process has had a very central position in the site investigations, starting from the processing of data and the interpretations of each geological and geophysical survey and continuing to the integrated assessment of all the results. The final stage in every processing and interpretation effort aims to produce conceptual model for bedrock phenomena in question.

An important initial state in the modelling consists of creating a basis for classification and conceptualisation. Of particular interest with reference to the Hastholmen site is how fracture zones have been defined and what assumptions have been made regarding the properties, geometry and the mutual relationships of the fracture zones. Different classes of fracture zone have been used which have been based on the intensity of the fracturing and weathering or alteration and on the hydraulic properties, and also on expert judgement (Section 3.3.5). In addition, the properties of the fracture zones and the definition of their boundaries have been analysed by principal component analysis (Section 3.4.1).

The final phase in the fracture zone modelling is to build up a structural bedrock model in site scale (Section 5.2), where the fracture zones (or R-structures) have the continuity between boreholes or between borehole(s) and the surface (in details, e.g. Teollisuuden Voima Oy 1992, Saksa 1995, Anttila et al. 1999).

3.4.1 Fracture Zone Index

The site investigation programmes which have been carried out since 1987 have included systematic surface and borehole geophysical measurements, hydraulic testing and geological mapping. The results from these studies have been combined with expert judgement in order to determine the location and geometry of the most important structural zones and lithological units. The conceptual structural bedrock models developed from these data have been used as the basis for the development of groundwater flow models and repository lay-out design for all the sites. The basis for these structural bedrock models has been the identification of anomalies believed to be related to significant hydrogeological structures. In fractured crystalline bedrock, fracture zones dominate the hydraulic behaviour. 40

However, there is always some degree of subjectivity in the conceptualisation process. The distinction between fracture zones and the averagely fractured or intact rock is often problematic from the visual examination of borehole core. Drilling-induced phenomena, such as core loss and splitting of core sample, can develop which make the core data unsatisfactory for classification purposes. For example, the Hastholmen core samples contain a lot of core disc fractures, which are not detectable by wireline logging. The number and type of anomalies from single borehole geophysical measurements, which are associated with fracture zones, may vary considerably, making the mutual comparison of fracture zones in different boreholes difficult. The description of fracture zone properties is, therefore, qualitative, and the definition of the width of a fracture zone, based on data from borehole at the intersections is based on the subjective interpretation of the available complex data.

It was, therefore, necessary to create a more objective, systematic and quantitative way of calculating a single parameter, such as the width of a fracture zone, when considering hydrogeologically important features. The principal component analysis (PCA) approach was applied, in order to distinguish between fracture zones and averagely fractured or intact rock using single-hole data (Korkealaakso 1991, Korkealaakso et al. 1994). Applying statistical analytical techniques, each measured parameter is first standardised by subtracting its mean value and dividing by its standard deviation. Then new standardised variables have a mean of 0.0 and standard deviation 1.0, and are used in PCA calculations. The order of the principal components is determined by the order of their variances, so that the first principal component has the highest proportion of the total variance, and represents the best combination of the linear correlations in the observations (Korkealaakso et al. 1994).

For the Hastholmen site, the fracture zone index (FZI) was defined as the first principal component of data derived from borehole wireline logs, such as resistivity, P-wave velocity, gamma-gamma density and the combination of these with measurements of hydraulic conductivity. These parameters were selected because it was considered that they indicated the presence of hydrogeologically important features. Data were available from boreholes KR1 to KR6 (Okko et al. 1999a). The parameters were transformed to a 2 m sampling interval, which is also the shortest sampling interval for the systematic flowmeter measurements, and therefore, represents the resolution of the PCA calculations.

The results of PCA calculations show that the first principal component (FZI) explains 45% of the total variance in Hastholmen. The first eigenvectors exhibit almost similar weights, resistivity having the smallest and conductivity having the most significant weight. The frequency distribution for the first principal component of the Hastholmen boreholes show an approximately normal, but distinctly skewed distribution with a long tail of higher positive values (Fig. 3.4-1).

Based on this frequency distribution, the rock mass was divided into averagely fractured rock ("intact rock"), represented by the more or less normally distributed part, and fracture zones, represented by the anomalous tail of positive values (Fig. 3.4-1). There is, of course, no exact boundary between the normal distribution and the averagely 41

120

100

| o

-3 -2 -1 0 12 3 4 5 6 7 9 10 11 Principal component 1

Figure 3.4-1. Frequency distribution of the first principal component (FZI) for boreholes KRl - KR6 at Hdstholmen.

KR4 KR3KR6 KR2 KR1 KR5 N

Figure 3.4-2. Profiles of the first principal component (FZI) for the boreholes KRl - KR6. The red colour represents the strongly fractured rock, blue the intact rock and yellow represents the transitional zone. Profiles are projected onto north-south trending vertical section. 42 fractured rock mass, but rather a "fuzzy" zone, which will almost certainly contain borehole sections which could be classified either as averagely fractured rock or as less fractured parts of the rock mass within or close to the boundaries of major fracture zones. At Hastholmen a transitional zone of FZI values between 1.6 and 2.4 was considered to represent this fuzzy zone between the intact rock mass (FZI <1.6) and the fracture zones (FZI >2.4).

In order to demonstrate the size, variation and distribution of the fracture zones, the calculated values of the FZI are displayed as borehole profiles in Fig. 3.4-2. The red colour represents the strongly fractured rock and blue the intact rock; whereas yellow represents the transitional zone. Using the above limiting values, fracture zones comprise of 6.8% of the total borehole lengths and transitional zones 5.1% (Okko et al. 1999a). The definition of fracture zones determined using the FZI is in agreement with the zones determined on the basis of the geological, geophysical and hydrogeological information combined with expert judgement (see Section 5.3). 43

4 LITHOLOGICAL MODEL

4.1 General

The bedrock investigations at Hastholmen, associated with the final disposal of low- and intermediate-level reactor waste started in the late 1970s and the first lithologica! bedrock modelling was presented in 1983 by Suominen (1983). Having carried out a feasibility study (Posiva 1996) Hastholmen was selected, in 1997, to be one of the potential sites for the final disposal of spent nuclear fuel, and a detailed investigation programme was started. This programme included extensive geological field mapping, the drilling of four deep boreholes (KR1-KR4), a low-altitude airborne survey and single hole wireline geophysical logging. Its aim was to determine the occurrence, composition and continuity of the rock types both on their surface and at depth. A lithological model, based on these investigations, was published by Paananen & Paulamaki (1998).

After the first stage of the site investigations four new deep boreholes (KR5-KR8) have been drilled with associated core logging and sampling and geophysical logging. The present report presents the updated lithological model, which combines the results from outcrop mapping (Kuivamaki et al. 1997a), borehole investigations (Gehor et al. 1997a, 1997b, 1998, 1999, Okko et al. 1998, 1999a, 1999b) and interpretation of the aerogeophysical survey (Paananen & Paulamaki 1998). The distribution of rock types in boreholes is based on the work of according to Gehor et al. (1997b, 1998), Okko et al. (1998, 1999a, 1999b) (Fig. 4.1-1). Small scale variations (<2 m) of rock types in boreholes have been ignored in the figures shown in this report, since it would not be possible to distinguish such small-scale. The surface geological map of the study site is shown in Figure 4.2-1 and vertical cross-sections of the bedrock through various boreholes in Figure 4.2-2 and Figures 5.3-2 - 5.3-6 in Section 5.3.

4.2 Distribution and occurrence of rock types

In the area covered by the deep KR-boreholes and the shallow Y-boreholes (drilled for investigating the VLJ repository) the bedrock mainly consists of pyterlite (Fig. 4.2-1), which is also the host rock of the VLJ repository. Only in borehole KR1 and in shallow boreholes Y22 and Y23 the dominant rock type is wiborgite (Gehor et al. 1997a, 1997b). Wiborgite occurs in borehole KR2 from the surface to a depth of 130 m, but below that depth only thin sections exist. Thin sections of wiborgite are also present in boreholes KR4, Y2, Yll, Y12 and Y24. No wiborgite exists in borehole KR3. Although pyterlite and wiborgite have been separated in the core sample studies, in the bedrock model it is considered reasonable to combine these two varieties of rapakivi granite because of their magmatic and structural similarity (see Section 3.1). N

PYT-WIB COARSE-GR. EVEN-GR. FINE-GR. PORHYRITIC NO SAMPLE

Figure 4.1-1. Drill core profiles of boreholes KRl - KR8 with the main rock types, Hdstholmen study site. PYT-WIB = pyterlite-wiborgite, COARSE-GR = coarse-grained rapakivi granite, EVEN-GR = even-grained rapakivi granite, FINE- GR = fine-grained rapakivi granite, PORPHYRITIC = porphyritic rapakivi granite. Profiles are projected onto north- south vertical section. 45

Except for some short sections in boreholes KR7 and KR8 no dark-coloured pyterlite {see Section 3.1) is present in the existing boreholes, but it is the most magnetised rapakivi variety in the area, and the interpretation of airborne magnetic survey suggests that it may occur under Hastholmen at a depth of about 1 km (Paananen & Paulamaki 1998). Due to the lack of further evidence it has not, however, been included in the lithological model.

Porphyritic rapakivi granite is present in boreholes KR2 (at 756 - 767 m and 781 - 852 m), KR3 (at 546 - 559 m and 680 - 734 m) and KR4 (at 756 - 867 m). It is not exposed within the study site, and is only present in some outcrops south of Hastholmen. Its presence in boreholes KR2 and KR3 has been interpreted as due to there being two inclusions of the porphyritic rapakivi granite within the even-grained rapakivi granite dipping gently (ca. 30-40°) to the N-NE (Fig. 4.2-2). The porphyritic rapakivi granite in borehole KR4 is in contact with the even-grained rapakivi granite, and has been interpreted as dipping very gently to the NNW-NNE. The porphyritic rapakivi granites in borehole KR8 at 194 - 218 m and 239 - 247 m have been interpreted to be more or less horizontal, because of their dominantly horizontal fracturing (Fig. 5.2-6). There is also a 46 m section of porphyritic rapakivi granite in vertical borehole Y24 at 32 - 78 m and a 6 m section in borehole Y2 at 42 - 48 m. There is no evidence of such porphyritic rapakivi granite in any of the surrounding boreholes, and it has been concluded that they must represent quite small inclusions within the wiborgite/pyterlite.

Even-grained or weakly porphyritic rapakivi granites are present both in outcrops and in boreholes KR2-KR8 over the depth range of ca. 300 - 1000 m. The extent and the form of the even-grained/weakly porphyritic rapakivi granite at the surface (Fig. 4.1-1) is based on the interpretation of aerogeophysical data, combined with the outcrop and borehole observations. Even-grained or weakly porphyritic rapakivi granites can be separated from the wiborgites/pyterlites using geophysical data, because of their weaker average magnetisation (Paananen & Paulamaki 1998). The circular structure revealed by the sea bottom topography west of Hastholmen {see Fig. 5.1-1) has been interpreted as indicating an intrusion structure of the even-grained rapakivi granite (Kuivamaki et al. 1997a).

The southern contact of the even-grained rapakivi granite, which occurs on the mainland northwest of Hastholmen (Fig. 4.2-1), can be seen in borehole KR1 at approx. 30 m depth. Based on the interpretation of the airborne magnetic data, the contact dips 30 - 40° NNW to a depth of approx. 200 m and then becomes steeper at greater depths (Paananen & Paulamaki 1998) (Fig. 4.2-2). The northern contact of the granite has been interpreted as dipping 75° to the SSE. According to magnetic data, the pyterlite- wiborgite inclusion within the even-grained rapakivi granite is steeply dipping, as shown in Figure 5.3-5. Co

if LOVIISA HASTHOLMEN O Lithology of the study site Legend: Wiborgite/pyterlite f 1 Even-aramed/weakly —•" porphyritic rapakivi granite 4 Borehole, horizontal projection Observation point Topographic lineament (possible fracture zone)

Compiled by: Airno Kuivamaki Markku Paananen Seppo Paulamaki Geological Survey of Finland 1999

Base map 3 National Survey of Finland Llconee no. 13/MYW89 Scale: 1:20 000 0 0.3 47

Beneath the island of Hastholmen the even-grained and weakly porphyritic rapakivi granites present in boreholes KR1-KR4 and KR6 have been interpreted as forming a lithological unit within the pyterlite/wiborgite, with a thickness of ca. 500 m (Fig. 4.2.2) (Paananen & Paulamaki 1998). The upper part of the unit consists of fine-grained and densely fractured rapakivi granite, which is associated with one of the main subhorizontal fracture zones in the study site (Paananen & Paulamaki 1998, Okko et al. 1998). The fine- grained, even-grained granite is located in borehole KR3 at 273 - 371 m, in borehole KR2 at 377 - 386 m and 460 - 463 m, and in borehole KR6 at 315 - 344 m.

The majority of the unit consists of medium-grained to coarse-grained, equigranular or weakly porphyritic rapakivi granite. It occurs in borehole KR2 at 463 - 735 m and 852 - 963 m, in borehole KR3 at 371 - 680 m and from 734 m to the bottom of the borehole (803 m), in borehole KR4 at 240 - 412 m, 469 - 478 m, 507 - 624 m, 685 - 723 m and 735 - 756 m, and in borehole KR6 at 344 - 442 m, 470 - 476 m, 518 - 521 m and 566 - 596 m. Only a few short sections of even-grained/weakly porphyritic rapakivi granite exist in boreholes KR1 and KR5. In boreholes KR2 and KR3 the even-grained granite seems to form quite a uniform unit, but in the bedrock volume covered by boreholes KR4 and KR6 it is divided into several parallel, subhorizontal dykes (Fig. 4.2-2).

Calculated from the upper contacts in boreholes KR2, KR3, KR4 and KR6 the even- grained rapakivi granite unit dips approx. 20° to the NNE. However, the VSP-reflector, dipping 345/25°, at the upper contact of the granite in borehole KR2, suggests that the dip may be to the NNW. Two reflectors with a similar orientation have also been identified in an HSP (Horizontal Seismic Profiling) survey, and Keskinen et al. (1998b) connect these to the reflector in borehole KR2. This would mean that the possible surface expression of the granite lies offshore a few hundred meters southeast of Hastholmen. The contacts of the fine-grained rapakivi granites observed in borehole-TV logging (Strahle 1998) dip gently between NNW and NNE, the pole maximum of dip directions being towards N. Since no even-grained rapakivi granite is present in borehole KR1, the dip of the unit must become steeper (approx. 40°) at greater depths, as shown in Figure 4.2-2.

The overall structure of the even-grained rapakivi granite within the study site can be seen in Figures 4.2-1 and 4.2-2. The even-grained granite west of Hastholmen is a circular intrusion, which descends deep into crust. The even-grained granite north of Hastholmen is a direct continuation of that intrusion. It is interpreted to be a bowl-like intrusion with a depth of about 1 km, which, however, has a narrow feeding channel, descending to greater depths (see Paananen & Paulamaki 1998). The even-grained granite seen in boreholes KR2, KR3, KR4 and KR6 is a sheet-like intrusion, which is connected to the northern granite and is probably intruded into a subhorizontal zone of weakness. It is uncertain whether it is also connected to the even-grained rapakivi granite west of Hastholmen. The interpretation of the airborne magnetic data (Paananen & Paulamaki 1998), however, suggests that its eastern contact dips gently to the west towards the centre of the intrusion. 48

KR6 KR4 NW Y18 Y22 Y5 Y8 SE

A I; 1 A • I 3. El

FigureI 4.2-2,] Schematic cross-section of the bedrock through boreholes KR4 and KR6. 1. wiborgite/pyterlite, 2. porphyritic rapakivi granite, 3. even-grained rapakivi granite, 4. fine-grained rapakivi granite, 5. borehole, 6. borehole projected onto the plane.

Another subhorizontal slab of even-grained rapakivi granite a few metres in thickness occurs closer to the surface between 25 m and 50 m depth and can be seen in most of the shallow Y-boreholes (Suominen 1983, Paananen & Paulamaki 1998). It is closest to the surface in borehole Y4, Y5, Yll and Y12, where it is almost horizontal (Fig. 4.2-3). Northwest of those boreholes it dips very gently (ca. 15°) to the NW, whilst the dip is 20° SE southeast of the above boreholes.

In boreholes KR7 and KR8 10 sections of the even-grained rapakivi granite occur. Except for two sections in borehole KR7 at 300 - 409 m and 672 - 694 m, their lengths are less than 10 m. The 100 m long section in KR7 may be connected to the steeply dipping even-grained rapakivi granite located northwest of Hastholmen, but the other sections are most likely narrow, subhorizontal veins with limited continuity (Fig. 5.3-6).

In outcrops and boreholes the even-grained granite is also present as narrow veins, ranging from a few centimetres up to one metre in thickness. According to borehole-TV logging (Strahle 1998) these veins are either subhorizontal (in boreholes KRl and KR2) or dipping steeply (70°) to the south (in borehole KR3). In outcrops the even-grained rapakivi granite is also common as roundish autoliths in the wiborgites and pyterlites, ranging from a few centimetres to some metres in diameter (Kuivamaki et al. 1997a). 49

Figure 4.2-3. Block model of the upper part of the Hdstholmen rapakivi granite based on boreholes Yl — Yll (redrawn from Suominen 1983). 1. wiborgite/pyterlite, 2. even-grained rapakivi granite, 3. water, 4. borehole. Borehole locations shown in Figure 4.2-1.

NEXT PAGE(S) left BLANK 51

5 STRUCTURAL MODEL

5.1 Regional scale

The lineaments shown in Figures 2.3-1 and 5.1-1 are based on the interpretation of 1:400 000 satellite images, 1:100 000 hill-shaded topographic relief maps combined with bedrock maps and maps of Quaternary deposits and high-altitude aeromagnetic maps and seafloor maps, which show the depth to the bedrock surface obtained from the offshore sonar surveys (Kuivamaki et al. 1997a). The lineaments are assumed to be regional fracture zones and are reflected in the surface topography in the form of elongated depressions and lakes. The classification of lineaments/fracture zones is presented in Table 5.1-1.

Table 5.1-1. Classification of the lineaments according to Salmi et al. (1985).

Class Width Length Supposed depth I > 1 km From tens to hundreds of >10km kilometres II 100 -1000 m From 5 to tens of kilometres From several kilometres to 10 km ni 10 -100 m 2-5km > 1 km IV «10m 100 m - 2 km « 1000 m

The Hastholmen area is dominated by NW-SE and NE-SW trending (Figs. 5.1-1 and 5.1-2) fracture zones, which divide the bedrock into blocks of variable shape and size. The most prominent swarms of NW-SE trending fracture zones occur in Ruotsinpyhtaa, in the Bay of Loviisa and especially at the western contact between the rapakivi batholith and the Svecofennian country rocks in the Pernaja area. In the Svecofennian area mylonites and fault breccias are often associated with the fracture zones (Laitakari & Simonen 1963, Laitala 1984).

The most notable NE-SW trending fracture zones are present offshore south of Hastholmen. East of Lake Hopjarvi there is a large circular structure in the magnetic map, which, according to the interpretation of Elo & Korja (1993), represents a strongly magnetised body, the upper surface of which lies at a depth of 12 - 15 km and which extends to the base of the crust. Several smaller circular structures are revealed by topography and bedrock maps in the vicinity of this large structure, e.g. around Lake Sarkijarvi and offshore west of Hastholmen (Fig. 2.3-1 and 5.1-1). 52

HASTHOLMEN AREA LINEAMENT INTERPRETATION

LEGEND

II Class Lineament

III Class Lineament

III Class Lineament (possible)

IV Class Lineament

10 km

Figure 5.1-1. Lineament interpretation of the Hdstholmen area (modified after Kuivamdki et al. 1997a).

Ltrmi htrrHphttt • Mtn fc«cfaif xont* of a* HltPwInwn «r

Figure 5.1-2. Orientation of 11 and III class lineaments at the Hdstholmen area. Schmidt equal area, lower hemisphere projection (Kuivamdki et al. 1997a). 53

5.2 Site scale

Model development

Modelling of the bedrock at Hastholmen has been carried out since the early 1980s. After the first drillings in 1980 it seemed obvious that the structure of the bedrock is dominated by gently dipping fracture zones. However, in the first structural interpretation (Anttila et al. 1982), the interconnection of the fracture zones between boreholes was still quite uncertain. A significant improvement in the interpretation, and potential for 3-D modelling, was brought about the geophysical cross-hole and single- hole measurements (e.g. Cosma 1983, Poikonen & Hassinen 1982, 1983, Saksa 1984).

The first attempts on 3-D structural modelling were made in the middle of 1980s (Anttila 1986, Pirhonen 1986). The model presented by Anttila (1988) covered the proposed VLJ repository site in the western part of the island, down to the depth of 200 m. The model consisted of three subhorizontal fracture zones, named the upper, intermediate and lower fracture zones (Fig. 5.2-1). The repository was constructed at the level of -110 m, in the intact bedrock block between the two uppermost fracture zones, in 1993-1996.

Based on the findings during the construction work the model was revised and consisted of altogether 8 fracture zones (Anttila & Viljanen 1994). Finally, the model was supplemented to comprise the whole island of Hastholmen for the groundwater flow modelling relating to the final safety assessment. The model consisted of 17 bedrock structures (R1-R17), representing mainly fracture zones, and based on borehole investigations, observations in the repository and on seismic surveys on the island and offshore (Anttila & Viljanen 1995). Figure 5.2-2 shows the vertical fracture zones of the model. The model was supplemented by some local topographic lineaments (potential fracture zones) and presented as version 1.0 of the bedrock model of Hastholmen (Lindh et al. 1997). This model was taken as basis for programming the detailed site investigations commenced by Posiva in 1997.

In 1998 the model was revised on the basis of information from four deep boreholes (KR1-KR4), interpretation of an aerogeophysical survey and interpretation of geophysi- cal borehole logging (Okko et al. 1998, Paananen & Paulamaki 1998). This model (version 2.0) is summarised in Lindh et al. (1998), and consists of 25 fracture zones. In Section 5.3 the fracture zones are described and the Lindh et al. (1998) model is revised on the basis of data from four new boreholes (KR5-KR8). Version 3.0 of the 3-D bedrock model of Hastholmen (i.e. the ROCK-CAD model) will be prepared later in 1999, based on the current report, and, probably, one additional borehole.

The process for conceptualising the present fracture zones included their direct observation in boreholes and the use of indirect evidence, mainly from the interpre- tations of geophysical surveys, e.g. standard single-hole surveys, acoustic full wave form logging, scanner investigations, such as dipmeter and borehole-TV (Siddans et al. 1997, 1998, Strahle 1998), and three-dimensional vertical seismic profiling (3D-VSP) methods (Keskinen et al. 1998a, 1999). 54

The methodology of identifying and locating fracture zones consisted of an integrated interpretation of geological observations of core samples and geophysical single-hole surveys, together with principal component analysis (Section 3.4.1). The orientation and continuity of the fracture zones between boreholes were based on geological and geophysical similarities ("fingerprinting") together with oriented borehole and rock mass data (Okko et al. 1998, 1999a, 1999b, Okko & Front 1999).

Y12 Y4 Y6 Y11 Y24 Y23 Y19 Y1_ JT22_ Y5 Y10

Intermediate fracture zone

Lower fracture zone -200

Figure 5.2-1. Structural bedrock model of the VLJ repository site (Anttila 1988). See borehole locations in Fig. 1-1. 55

Figure 5.2-2. Vertical fracture zones of Hdstholmen (Anttila & Viljanen 1995). Location of the VLJ repository is also indicated.

An example on major gentle-sloping fracture zones

Initially the bedrock conditions of the planned underground VLJ repository at HSstholmen were investigated by exploratory boreholes to a depth of 200 m. Sixteen near-vertical boreholes were drilled and the fracturing of the rock mass was studied 56

(Anttila 1988). Both fracture mapping and geophysical logs, in particular the dipmeter studies (Rouhiainen 1989) indicated mainly subhorizontal fracturing. In addition, a few sets of subhorizontal fractures were located in the holes. The non-uniform continuity of these fracture zones was investigated using cross-hole methods (Rouhiainen 1989).

In the detailed site investigation phase, fracturing in the new deep boreholes was analysed by the interpretation of different types of acoustic, density, resistivity and temperature logs. Most of the fractures are tight and subhorizontal plane in accordance with the typical cubic fracturing system of rapakivi granites. In core samples the fracture number (column A in Figure 5.2-3) is in places overestimated due to drilling- induced phenomena such as core discing and splitting of the core. Geophysical logs, particularly resistivity and also acoustic velocity, show over 100 m long anomalies that indicate altered sections in the rapakivi granite. Within these sections the hydraulic anomalies in fluid logs, tube wave attenuation profiles and hydraulic tests are, however, only 1 - 5 m in length (Okko et al. 1998, 1999a, 1999b, Okko & Front 1999). In detail, the borehole-TV images indicate only isolated open fractures.

Three major "altered sections" were correlated between six of the deep boreholes by examining similarities in the full waveform acoustic logs (Fig. 5.2-3). The uppermost of these section is related to the well-defined shallow sub-horizontal fracturing at a depth of 100 m, and two main fracture zones (Structures Rl and R2) were defined in this location during the exploratory investigations. However, the acoustic "fingerprints" have similar 5-fold character in the six recently drilled boreholes. Moreover, the derived logs for porosity (column B in Figure 5.2-3), Young's modulus (column C) and tube wave attenuation (column D) indicate clearly that the internal variation within the individual anomalies in the anomalous zones is rather strong (Okko & Front 1999).

The second major "altered section" (Structure R18) is located at the dipping contact of the even-grained granite in the depth range of 200 - 400 m, and is intersected by four of the six boreholes. The main fracturing and alteration is seen in two boreholes above the contact in the overlying wiborgite/pyterlite and in two boreholes below the contact in the even-grained granite. The total length of the anomaly in the P-wave velocity log is 150 m, but there are only 4 or 5 individual anomalies within the anomalous section. The fractured sections obviously follow irregularly the rock type boundary.

The third altered zone (Structure R19) is associated with subhorizontal fracturing at a depth of 900 m in the deepest boreholes KR1 and KR2. In these boreholes, alteration occurs over a borehole length of 100 m. The tube wave logs as well as the hydraulic test data indicate, however, that only a small proportion of this altered section of the rock mass is associated either with higher hydraulic conductivities or with tube wave anomalies. In the TV-image only single and often rusty near-horizontal fractures can be seen. The similar character in the acoustic logs over these sections in boreholes KR1 and KR2 suggest that they are part of the same altered zone. In addition, the VSP data available support the correlation of this altered zone between boreholes KR1 and KR2. 57

BOREHOLE KR4 BOREHOLE KR3 BOREHOLE KR2 BOREHOLE KR5 90

BOREHOLE KR2 BOREHOLE KR1 FRACT. FREOJfm ACPOROSITY.S YOUNG'S MOD, GPa TUBEWAVE, dB FRACT. FREQ.Km AC-POROSITY. % YOUNG'S MOD. GPa TUBEWAVE, dB . 0 10 20 0.0 3.0 6.0 30 50 70 -60 -40 -20 0 0 10 20 0.0 3.0 6.0 30 50 70 -30 -20 -10 0

850

950

Figure 5.2-3. A scheme of gentle-sloping fracture zones with the logs derived from the full wave form sonic log indicating the main fractured sections in boreholes (modified after Okko & Front 1999). The Hdstholmen study site, boreholes KRl - KR6. 58

5.3 Present state of the structural model

The present structural model contains 27 fracture zones (denoted by the term R+number structures), which are described in detail. More than half of these structures have been verified by direct observations from boreholes or from their exposure at depth within the VLJ, and they are listed in Table 5.3-1 with their status directly observed. The remaining structures are based on the interpretation of horizontal seismic profiling (HSP) surveys, reflection seismic surveys, an airborne geophysical survey, a ground radar survey and topographic relief maps, and have been classified as probable or possible fracture zones.

The hydraulic properties of the R-structures are discussed in Section 5.4. In addition to R-structures, local structures with uncertain orientation and continuity occur in the rock mass. They are not classified as R-structures but may still be hydraulically significant. They are described briefly in Section 5.5. Figure 5.3-1 shows those R-structures, which extend up to the ground surface. The topographic lineaments are also included in the figure as possible fracture zones. The occurrence of the fracture zones within the bedrock volume is shown by vertical cross-sections in Figures 5.3-2 to 5.3-6. In the cross-sections, however, only those structures identified by direct observations are presented. The structures presented in the model figures are simplified representations of geological structures of variable geometry and properties. 59

Table 5.3-1. Intersections of the observed fracture zones (in metres along borehole from surface) in shallow Y-boreholes and deep boreholes KR1-KR8.

Bore- Occurrence of the fracture zones in boreholes holes R1 R2 R3 R4 R7 R9 R17 R18 R19 R20 R21 R22 R26 R27 Y1 82-94 174-184 126-127 Y2 73-94 143-149 188-191 Y4 67-83 149-152 164-187 147-148 107-108 Y5 107-119 153-163 Y7 92-100 127-132 Y8 113-141 153-157 225-238 200-201 Y10 133-145 Y11 51-61 149-186 145-146 94-95 Y12 56-65 104-105 Y19 84-98 134-141 78-79 Y20 77-92 145-151 91-92 Y21 Y22 97-107 Y23 89-100 Y24 84-93 117-121 Y25 103-109 KR1 76-86 115-119 521-532 858-861 236-258 600-608 98-100 881-883 887-890 903-908 941-951 967-971 KR2 106-114 136-139 375-380 437-445 808-812 241-250 122-127 459-478 816-820 484-491 850-855 879-884 908-910 KR3 91-101 127-132 276-284 348-352? 308-332 104-105 340-347 376-382 397-404

KR4 112-124 149-152 213-221 163-167 526-533 686-688 705-711 126-130 179-184 714-724 208-224 KR5 81-87 707-728 105-112 732-753 KR6 98-123 138-146 316-318 329-334? 235-246 6B9-691? 124-128 159-183 269-275 289-291 340-346 KR7 767-768? 784-801? KR8 762-777? 798-802? 3 3

1

V I •i M i li a- f • i l ' M -1l| r 11 'I '!,• 1 " 1 1 ••

f h . li it 11 i 11 1 J i| r 8 y

1*1. > ru 1 1 " t

F , • 1 if

l

O a"

3 61

\

\ to

Figure 5.3-2. Vertical cross-section of the bedrock through borehole KR1. 1. Wiborgite/pyterlite, 2, Even-grained rapakivi granite, 3. Fine-grained rapakivi granite, 4. Fracture zone, 5. Borehole, 6. Projection of borehole onto plane of cross-section. 62

Ui

,8& *******#* f * +**/**** * * *VQ*)& * V *J * ******' £ \L&- * * *** ****** fi

7 /,///:

Figure 5.3-3. Vertical cross-section of the bedrock through borehole KR3. 1. Wiborgite/pyterlite, 2. Porphyritic rapakivi granite, 3. Even-grained rapakivi granite, 4. Fine-grained rapakivi granite, 5. Fracture zone, 6. Borehole, 7. Projection of borehole onto plane of cross-section. 63

UJ

\ <£>

D

Figure 5.3-4. Vertical cross-section of the bedrock through boreholes KR4 and KR6. 1. Wiborgite/pyterlite, 2. Porphyritic rapakivi granite, 3. Even-grained rapakivi granite, 4. Fine-grained rapakivi granite, 5. Fracture zone, 6. Borehole, 7. Projection of borehole onto plane of cross-section. 64

ui

S*Wh? .,:,- "V«S

r

J'""TT^—Tsa; , ' 'i - * - -it " v »y - - 'I ' ,••' 'A * l**** f M *.* * f * * V * ** *** ** * *******

Figure 53-5. Vertical cross-section of the bedrock through borehole KR5. 1. Wiborgite/pyterlite, 2, Even-grained rapakivi granite, 3. Fine-grained rapakivi granite, 4. Fracture zone, 5. Borehole, 6. Projection of borehole onto plane of cross-section. 65

\

IA

Figure 5.3-6. NW-SE trending vertical cross-section of the bedrock with projected bore- holes KR1, KR7 and KR8. 1. Wiborgite/pyterlite, 2. Porphyritic rapakivi granite, 3. Even- grained rapakivi granite, 4. Fracture zone, 5. Projection of borehole onto plane of cross- section. 66

Structure Rl

Structure Rl is a subhorizontal fracture zone, which was identified in deep boreholes KR1-KR6 and in 15 shallow Y-boreholes over the depth range of 50 - 150 m, as well as in the access tunnel and the shafts of the VLJ repository. In the area covered by the boreholes the structure is quite planar and dips gently (10 - 15°) to the NE-ENE. This structure is the upper fracture zone in the first geological model of Anttila (1988) (see Fig. 5.2-1).

In boreholes the structure ranges from 6 to 45 m in thickness and consists of several densely fractured sections (on an average 4 sections/borehole) separated by intact, i.e. less fractured rock. The fracture frequency in the latter is on average 4 fractures/m, whilst that in the fractured sections varies from 10 to over 20 fractures/m, the rock being fracture-structured to crush-structured, according to the Finnish engineering geological classification (see Section 3.3.1). The degree of weathering in the zone ranges from unweathered to strongly weathered. In boreholes KR1 and KR2 the rock is slightly mylonitized. In borehole KR4 the structure consists of several breccias cemented by hematite and also the intact borehole core is hematised, in particular the mantles of the ovoids (Geh5r et al. 1998). The main fracture mineral assemblage found in borehole cores is Fe-hydroxide-carbonate-clay mineral or Fe-hydroxi de-carbonate (Gehor et al. 1997a, 1997b, 1998, 1999). In some of the shallow boreholes (Y4, Y5, Y7 and Y8) the structure is associated with old, sealed fracture zones, which have suffered from later fracturing (Suominen 1983).

Data from the oriented cores, the dipmeter survey and borehole-TV logging show that the fractures in structure Rl are horizontal or very gently dipping, e.g. the pole maxima of open fractures identified in borehole-TV logging in boreholes KR1, KR2 and KR3 are 311/06°, 196/10° and 055/12°, respectively (Fig. 5.3-7). In the access tunnel to the VLJ repository the dominating fracture orientation (dip direction/dip) of the fractures within structure Rl is 0 - 45/5 - 20°. In addition to these subhorizontal fractures, steep fractures, dipping 70 - 80° to the SW-SE, are also present, both in the repository and in boreholes, as can be seen in Figure 5.3-7d. Abundant slickensided fractures occur in all of the main fracture sets. The subhorizontal character of structure Rl is further supported by the VSP reflectors at 060/06°, 070/10°, 060/10°, 000/00° and 060/03° which have been interpreted from the upper parts of boreholes KR1-KR6 (Keskinen et al. 1998a, 1999). In addition, the electrical and seismic measurements (Poikonen & Hassinen 1982, Rouhiainen 1987) between the shallow Y-boreholes provide evidence of horizontal structural connections.

Structure R2

Structure R2, the intermediate fracture zone of Anttila (1988), has been directly observed in 10 Y-boreholes, in boreholes KR1-KR4 and KR6 (Table 5.3-1) and in the access tunnel of the VLJ repository. The width of the fracture zone ranges from 2 to 10 m, being 5 m on average. In this structure densely fractured sections (1-2 sections/borehole) alternate with intact sections. The mean fracture frequency in the intact rock is 6 fractures/m, whilst the fractured parts are fracture- or crush-structured, 67

the mean fracture frequency being 15 fractures/m. The degree of weathering in the zone ranges from unweathered to strongly weathered.

The structures Rl and R2 can be considered as being parts of one and the same bedrock structure with five separate "subsections" or five subparallel, more or less continuous, thin broken "sheets" separated by much thicker layers of intact rock. (Okko & Front 1999 and Section 5.2). Differences in the distances between these "subsections" varies across the study site, being large enough to provide sufficient space for the VLJ repository between structures Rl and R2.

LOWT h«mUph«r» - H«»tfo1m«n TV: Riot M-12* m a) b)

two Mmtophr* - Hutholnun TV: Riot P2-100 m

C) d)

Figure 5.3-7. Orientation of open fractures in structure Rl according to borehole-TV logging in boreholes KR1, KR2 and KR3. a) KR1 at 76 - 86 m, b) KR1 at 98 - 124 m, c) KR2 at 106 - 114 m, d) KR3 at 92 - 100 m. Schmidt equal-area lower hemisphere stereographic projection. 68

Structure R3

Structure R3 is the lower fracture zone of Anttila (1988), and has been identified by direct observations from five Y-boreholes and from boreholes KR2, KR3, KR4 and KR6 over the depth range of 150 - 300 m (Figs. 5.3-3 and 5.3-4). Based on the borehole sections presented in Table 5.3-1, the structure dips less than 30° to the NE or NNE. In all of the above boreholes the structure is located close to the contact zone between the wiborgite/pyterlite and the fine-grained variety of the even-grained rapakivi granite.

The width of structure R3 ranges from a few metres to 37 m, the average width being 19 m. It consists of several densely fractured sections (on an average 4 sections/borehole), which typically alternate with intact sections. The mean fracture frequency in the intact rock is 5 fractures/m, whilst the fractured parts vary from fracture- or crush-structured to clay-structured, the mean fracture frequency being 15 fractures/m. The degree of weathering in the zone ranges from unweathered to completely weathered.

The oriented cores, the dipmeter survey and the borehole-TV logging indicate dominantly subparallel fracturing within the structure (Fig. 5.3-8). The fracture-filling minerals are Fe-hydroxides and clay minerals (illite, montmorillonite and kaolinite), and in borehole KR2 almost all the fractures are coated with chlorite (Gehor et al. 1997b, 1999). In borehole KR3 and KR6 fluorite is also present as euhedral crystals.

Lwwr h*mliphT» - H«nhdm«n TV; R»ot 37B-MB i a) b)

Figure 5.3-8. Orientation of open fractures in structure R3 according to borehole-TV logging in boreholes KR2 and KR3. a) borehole KR2 at 376 - 389 m, b) borehole KR3 at 277-285 m. Schmidt equal-area lower hemisphere stereo graphic projection. 69

Structure R4

Structure R4 is a poorly developed fracture zone observed in vertical boreholes Y2, Y4, Y8 and in horizontal borehole YT3 drilled from the access tunnel of the VLJ repository (Anttila & Viljanen 1994). It is 1 - 3 m wide, and is formed by a few parallel fractures, which dip <10° to the NW.

Structure R5

Structure R5 is represented by a swarm of vertical, N-S trending fractures, which have been observed in the access tunnel of the VLJ repository, as well as in boreholes YT5- YT7, drilled from the tunnel (Anttila & Viljanen 1994). The width of the structure is 30 - 50 m, and it consists of parallel, often slickensided fractures, which occur at 3 m intervals. This structure most likely stops before reaching borehole KR3, since it has not been identified in that borehole, which it was expected to have intersected at about 200 m depth.

Structure R6

Structure R6 is a vertical, NE-SW trending poorly developed fracture zone, which have been observed in borehole Y21 and horizontal boreholes YT3, YT4 and YT7 drilled from the VLJ repository (Anttila & Viljanen 1994). It represents unweathered rock mass, and has a fracture density, which is just little grater than that of the intact rock. The width of the fracture zone is 30 m, the interval between individual, often slickensided fractures is 3 m on average.

Structure R7

Structure R7 has been observed in the access tunnel of the VLJ repository (Anttila & Viljanen 1994). It is about 4 m wide, contains fracture- or crush-structured rock, and dips 60°SW. The rock is strongly or completely weathered in the central portion of the structure, the fracture frequency being about 20 fractures /m.

The structure is possibly represented by two fracture-structured sections in boreholes KR3 and KR6 at 348 - 352 m and 329 - 334 m, respectively. However, around these borehole depths the rock is densely fractured over long distances, and it is very difficult, if not impossible, to distinguish the structure for certain from the fracturing associated with subhorizontal fracture zones R3 and R18 (see below), which intersect borehole KR3 at a similar depth (Fig. 5.3-3). Since the fractures in the above mentioned borehole sections are subhorizontal, it is more probable that they are related to the structures R3 and R18, and structure R7 stops before reaching boreholes KR3 and KR6 (Figs. 5.3-3 and 5.3-4).

Structure R8

Structure R8 has been observed in the access tunnel of the VLJ repository. It is a 5 m wide, fracture-structured, unweathered fracture zone, with fractures trending NE-SW 70 and NW-SE. The orientation of the structure shown in Figure 5.3-1 is assumed to be parallel to the first of these fracture sets but, as stated by Anttila & Viljanen (1995), the structure seen in the access tunnel is most likely an intersection of two steeply dipping fracture zones, and may be only local in nature and extent.

Structure R9

Structure R9 is a SW-NE trending fracture zone located offshore northwest of Hastholmen and intersected by borehole KR1 at 531 - 532 m (Figs. 5.3-1 and 5.3-2). The orientation and location of the fracture zone are determined by VSP reflector 130/77° at 530 m in borehole KR1 and by four HSP reflectors with similar orientation, located offshore northwest of borehole KR1. The structure in borehole KR1 is a fracture-structured, slightly weathered (hematised) fracture zone, the fracture frequency being 20 fractures/m. No infilling minerals occur in the fractures. According to the borehole-TV logging the fractures are subhorizontal or dipping steeply to the SE.

Structures RIO - R16

Structures RIO - R16 have mainly been determined on the basis of topography and from the results of seismic refraction and HSP surveys, and have been included in the bedrock model as possible fracture zones.

Structure RIO was originally a NW-SE trending, possible III class {see Table 5.1-1) lineament interpreted on basis of sea bottom topography (Kuivamaki et al. 1997a). Its occurrence as a possible fracture zone is supported by two HSP reflectors 223/71° in survey line 4 and one reflector 220/90° in survey line 5 (Keskinen et al. 1998b). In Figures 5.3-2 - 5.2-6 it has been modelled as a 15 - 20 m wide fracture zone, dipping 70°NW. It may be intersected by borehole KR1 at a depth of approx. 900 m, however, a large subhorizontal fracture zone R19 lies at the same depth and the presence of structure R10 at this depth cannot, therefore, be confirmed. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available.

Structure Rll and structure R12 have been determined on the basis of a seismic refraction survey, and are included in the model as 10 m wide, possible fracture zones. No data exist on the degree of fracturing, weathering or hydraulic conductivity.

Structure R13 is a NE-SW trending topographic lineament located southeast of Hastholmen. The dip of the structure is determined on the basis of HSP reflector with an orientation of 135/80° in survey line 7. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available.

Structure R14 can be seen as a very clear linear basin in the sea bottom topography west of Hastholmen {see Figure 2.1-2). Its occurrence as a fracture zone is further supported by three vertical, NW-SE trending HSP reflectors in survey lines 1 and 2 (Keskinen et al. 1998b). Its continuation on the mainland northwest of Hastholmen is uncertain. However, Okko et al. (1999a) have proposed that it is represented in borehole KR5 by a 71

fracture zone at 525 - 533 m. It consists of two fracture-structured sections, which are mylonitized, densely fractured and brecciated. The degree of weathering ranges from slightly to strongly weathered. The fracture zone has been interpreted as dipping steeply to the SW on the basis of fracture orientations from oriented cores, a dipmeter survey and from borehole-TV logging. This is in spite of the VSP survey, which indicates a reflector, dipping steeply to the E.

Structure R15 has been interpreted on the basis of seismic refraction survey, and modelled as a vertical fracture zone. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available.

Structure R16 has been interpreted from the seismic refraction and ground radar survey on the island of Hastholmen and from HSP survey offshore northeast of Hastholmen. The modelled orientation of the structure is based on two HSP reflectors oriented 150/70°. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available.

Structure R17

Structure R17 is a zone of parallel slickensided fractures, dipping less than 20°SE, observed on the roof of the cavern of solidified waste in the VLJ repository and in boreholes Yl, Y4, Yll, Y12 and Y20 (Anttila & Viljanen 1995). The width of the fracture zone is about 1 m, and it ranges from intact to crush-structured rock. The number of fractures in the zone is 5 - 12 fractures/m.

Structure R18

Structure R18 is a multiple fracture zone observed in boreholes KR2, KR3, KR4 and KR6 (Table 5.3-1). The structure appears to be connected with the contact between the even-grained rapakivi granite and the wiborgite/pyterlite, which explains why it is not present in borehole KR1 (see Section 4.2). In borehole KR3 and KR6 the fracture zone is entirely within the even-grained rapakivi granite, whilst in borehole KR2 the rock is densely fractured on both sides of the contact.

In borehole KR2 the structure is composed of three fracture zones, which consist of 10 fracture-structured (in places crush-structured) sections with a total width of 18.3 m. The fracture frequency within the fractured sections ranges from 11 to more than 40 fractures/m, the main fracture-filling minerals being Fe-hydroxide and clay minerals (mostly kaolinite). Over the interval from 318 - 325 in borehole KR2 the core sample is porous and strongly altered and contains sealed fractures, cavities and hematite breccias (Okko et al. 1998). Brecciated rock with hematite matrix occur also over the interval from 442 - 451 m, and from 460 - 463 m the mafic minerals of the granite are strongly hematised (Gehor et al. 1997b). From 470 - 478 m mylonitized zones occur within the even-grained rapakivi granite. Both the dipmeter survey and borehole-TV logging indicate dominantly subhorizontal fracturing in the fracture zones. The pole maximum of open fractures from borehole-TV logging is towards NNE (dip direction) (Fig. 5.3-3). The dipmeter survey also indicates fractures dipping gently to the E. 72

In borehole KR3 seven fracture-structured sections occur within three fracture zones, totalling 37.9 m in borehole length. The fracture frequency in the densely fractured sections ranges from 10 to over 30 fractures/m. The main fracture mineral assemblages are Fe hydroxide and clay mineral (Gehor et al. 1997b). 1 - 2 m of mylonitized rock occur at 323 m and 342 m. According to borehole-TV logging, the open fractures dip gently to the W (Fig. 5.3-9), whilst the dipmeter survey indicates fractures dipping gently to the S, SW, NW and NE.

In borehole KR4 the structure is characterised by thoroughly hematized breccia zones. The fracture zone at 179 - 183 m ranges from fracturte-structured to clay-structured and the rock is strongly to completely weathered.

In borehole KR6 the structure is composed of four to five fracture zones, in which nine fracture-structured (in places crush-structured) sections occur, with a total width of 10.7 m. The rock in the broken sections ranges from unweathered to strongly weathered, and at 290 m the rock is completely weathered. Narrow mylonitic zones occur in each of the fractured sections. The fracture frequency is 10 - 20 fractures/m. The main fracture mineral assemblages are composed variably of Fe-hydroxides, carbonates and clay minerals (Gehor et al. 1999).

a) b)

Figure 5.3-9. Orientation of open fractures in fracture zone R18 according to borehole- TV logging in boreholes KR2 and KR3. a) borehole KR2 at 438 - 491 m, b) borehole KR3 at 308 - 401 m. Schmidt equal-area lower hemisphere stereo graphic projection.

The structure is assumed to dip gently in a direction between NNW and NNE. The intersections in boreholes KR2, KR3, KR4 and KR6 result in orientation of 010/20°, whilst the VSP reflector in borehole KR2 at 450 m, interpreted as indicating structure R18, has an orientation of 345/25°. 73

Structure R19

Structure R19 consist of several fracture zones in boreholes KR1, KR2 and KR5 (Table 5.3-1). In borehole KR1 the structure is composed of six sections, with a total of 4 m of fracture-structured rock. The fracture frequency in the broken sections ranges from 10 to 20 fractures/m. Hematite breccia and mylonitic breccia occur at 903 - 908 m and 927 - 951 m, respectively (Okko et al. 1998). The main fracture mineral assemblages are carbonate and Fe hydroxide-carbonate and cavities, in places with euhedral crystals, are common (Gehor et al. 1997b, Rautio 1997).

In borehole KR2 the structure can be divided into four fracture zones, in which 14 sections of fracture-structured rock occur with a total length of 19 m. Broken and porous sections at 846 - 855 m and at 873 - 883 m are accompanied by narrow mylonitic zones (Niinimaki 1997a, Okko et al. 1998). The fracture frequency is from 10 to more than 20 fractures/m within the broken sections. The main fracture mineral assemblages are carbonate - clay mineral and Fe-hydroxide - carbonate - clay mineral, the carbonates being calcite and/or dolomite, and clay minerals kaolinite, montmoril- lonite and illite (Gehor et al. 1997b).

In borehole KR5 the structure consists of two parts, the rock being fracture-structured in seven sections, with a total width of 10 m. The rock is brecciated (hematite breccia) and, in places, porous and thoroughly weathered (Okko et al. 1999a). Narrow mylonitic zones with cavities are common within the broken sections. The main fracture mineral assemblage is carbonate, which is present alone or together with Fe-hydroxides. Some of the fractures are unfilled chloritic slickensides with porosity and cavities (Gehor et al. 1999).

Both oriented core samples, dipmeter survey and borehole-TV logging indicate subhori- zontal fracturing within the fracture zone (Fig. 5.3-10). The fracture zone has been interpreted as dipping gently (ca. 20°) to the WSW based on the VSP reflectors 240/20°, 240/22° and 236/24° interpreted from boreholes KR1, KR2, and KR5, respectively (Keskinen et al. 1998a, 1999). The structure is possibly not present in other boreholes at Hastholmen but, on the basis of the interpreted VSP reflectors from the interpolated extensions of boreholes KR3 and KR6 (250/23° and 240/25°, respectively), it is located close to the bottom of those boreholes.

In boreholes KR7 and KR8, a multi-component fracture zone is present at depths of 767 - 801 m and 762 - 802 m, respectively. In many respects, it resembles structure R19, especially those sections found in borehole KR5 at depths between 715 - 753 m. This structure comprises a strongly altered, hematised and porous section from 767 - 768 m in borehole KR7 followed by a short section of unaltered core with strong core discing between 771 - 778 m. At greater depths up to 801 m there are several short fracture- and crush-structured sections, even a short clay-structured section, in the core (Okko et al. 1999b). 74

Lowf htmfrpEw -Hutholmtn TV: Ff

Figure 5.3-10. Orientation of open fractures in fracture zone R19 according to borehole-TV logging in boreholes KR1 and KR2. a) borehole KR1 at 881 - 951 m, b) borehole KR2 at 811 - 885 m. Schmidt equal-area lower hemisphere stereographic projection.

In borehole KR8, this structure comprises a hematitised, highly porous section of fracture- and crush-structured rock at depths from 762 - 777 m and a section characterised by densely-spaced core disc fractures between 777 - 784 m (Okko et al. 1999b). It is possible that the broken and altered borehole sections in boreholes KR5, KR7 and KR8 are associated with a single near-horizontal structure consisting of several subparallel more or less discontinuous altered, porous and fractured sheets separated by thicker sections of intact rock mass. This may represent the continuation of structure R19 to the nortwest of borehole KR1 (Fig. 5.3-6).

Structure R20

Structure R20 is a fracture zone identified in boreholes KR1 and KR2 at 248 - 254 m and at 241 - 246 m depth, respectively. In borehole KR1 the fracture zone consists of two 0.5 - 1 m wide mylonitic, fracture- structured sections, with a fracture frequency of 15-20 fractures/m. They are separated by more intact rock, in which the fracture frequency is 5 - 8 fractures/m. Fracture-filling minerals are mainly Fe-hydroxide and clay minerals (illite and kaolinite). In borehole KR2 the whole section is mylonitic and fracture-structured, the fracture frequency being 10-30 fractures/m. The fracture- filling minerals are Fe-hydroxide, carbonates and clay minerals.

The oriented cores, dipmeter survey and borehole-TV logging indicate very gently dipping fractures within the structure (Fig. 5.3-11) and structure R20 has been modelled as being subhorizontal (Figs. 5.3-2 - 5.3-4). On the basis of orientation data, two orientations (dip/dip direction) for the structure are considered most probable, either 15 - 20°E or 15°SW. 75

Lowf htmi»ph«r« - Hutholmin TV; Rim 248-254 m a) b) Stgm«-0.250 | P«JWS.»6

Figure 5.3-11. Orientation of open fractures in fracture zone R20 according to borehole-TV logging in boreholes KR1 and KR2. a) borehole KR2 at 248 - 254 m, b) borehole KR2 at 241 - 246 m. Schmidt equal-area lower hemisphere stereographic projection.

Structure R21

Structure R21 is a fracture zone observed in borehole KR1 at 603 - 608 m depth. The zone is slightly mylonitised and consists of two densely fractured sections, the fracture frequency ranging from 11 to more than 25 fractures/m. No infillings are present in the fractures. The rock in the fracture zone is mostly slightly weathered. On the basis of oriented core, borehole-TV logging and a VSP survey, the structure dips gently (< 30°) to the ENE. The fracture zone is most likely local in nature, since it has not been identified in boreholes KR2 and KR3.

Structure R22

Structure R22 is a brecciated, thoroughly hematised fracture-structured zone in borehole KR4 at 526 - 533 m. The fracture frequency is approx. 20 fractures/m, the typical fracture-filling minerals being Fe-hydroxide, carbonates and clay minerals. On the basis of the average main fracture directions in oriented cores (248/22° and 280/25°), the structure is modelled as dipping gently to the SW or W, although the dipmeter survey also indicates fractures dipping 15°N and the VSP shows reflector oriented at 020/78°. The connection of the structure to the epidote-bearing alteration zone at the bottom of borehole KR6 is possible but still uncertain (Okko et al. 1999a). 76

Structures R23 - R25

Structures R23 - R25 have been determined on the basis of topography, seismic refraction and HSP survey, and included in the bedrock model as possible or probable fracture zones.

Structure R23 is a possible fracture zone interpreted on the basis of ground-penetrating radar and seismic refraction surveys. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available. The estimated dip is 70 - 80°SE.

Structure R24 is a probable fracture zone, which can be seen in the sea bed topography as a linear basin southeast of Hastholmen (see Fig. 2.1-2). The presence of the fracture zone is supported by a low velocity zone in the seismic refraction profile, running across the basin. The dip of the zone, 40°ENE, is determined on the basis of three parallel HSP reflectors in survey line 7, with the dip direction/dip of 060/41°, 060/40° and 060/37° (Keskinen et al. 1998b). No direct observations exist on the internal nature of the structure, but it is estimated to be significant in terms of fracturing, weathering or hydraulic conductivity.

Structure R25 is a probable fracture zone, which is interpreted on the basis of a linear basin in the sea bed topography, accompanied by a linear aeromagnetic minimum. On the basis of the HSP reflector 060/90° in survey line 6 (Keskinen et al. 1998b), the zone is estimated to be vertical. No data exist on the degree of fracturing or weathering in this structure and no hydraulic conductivity data are available.

Structure R26

Structure R26 has been observed in borehole KR4 at 679 - 695 m, and it consists of five slightly weathered, fracture-structured sections with a total width of 3.1 m. The fracture frequency is 10 - 14 fractures/m and the fracture-filling minerals are illite, kaolinite and fluorite (Gehor et al. 1998). Oriented core between the densely fractured sections show subhorizontal fractures and fractures dipping steeply to the N. Dipmeter survey demonstrate subhorizontal fractures within the fracture zone, the main dip direction/dip being 336/17°. In borehole KR4 the fracture zone is located within the even-grained rapakivi granite, in the contact between it and the wiborgite/pyterlite. It is interpreted in Figure 5.3-4 that the fracturing is connected to that contact, which is assumed as dipping gently to the direction between NNW and NNE (see Section 4-2).

Structure R27

Structure R27 consists of two fracture zones observed in borehole KR4 on both sides of the upper contact of the wiborgite/pyterlite enclosed in the even-grained rapakivi granite. The fracture zone at 705 - 711 m is a porous hematite breccia, with two densely fractured sections, the fractures being almost horizontal (015/10°) according to oriented core (Okko et al. 1998). In the fracture zone at 714 - 724 m the fractures are slightly weathered and filled with carbonates (calcite and dolomite) and clay minerals 77

(kaolinite) with or without fluorite (Gehor et al. 1998). According to the dipmeter survey the mean fracture direction (dip direction/dip) is 027/12° at 701 - 727 m. Based on the above fracture directions and the VSP reflector 350/40° at 720 m, the fracture zone is interpreted as dipping gently to the N-NNE, which is in accordance with the interpreted dip of the even-grained rapakivi granite.

5.4 Hydraulic properties of the R-structures

The transmissivity of these R-structures (fracture zones) has been measured by two single-hole methods, the constant head injection test using a double-packer system (HTU) and flow logging using the flowmeter (Hamalainen 1998a, 1998b, 1998c, Pollanen & Rouhiainen 1998a, 1998b). In total, 50 single-hole T values have been measured from boreholes KR1 - KR6. If multi-element R-structures (such as R18A, R18B, R18C, etc.) are treated as a single zone with one T value, which is taken as the sum of the T values of all those sub-structures, the number of measured values of T for structures is 36 (Figure 5.4-1). The T values measured as part of the investigations for the VLJ repository are presented in Fig. 5.4-1 as averages for each R-structure (IVO International Oy 1996). The maximum number of measured T values from deep boreholes for a single R-structure is six (for structure Rl) which is interpreted as intersecting all boreholes at a depth of about 100 m. If boreholes drilled for the VLJ repository are taken into account, the corresponding maximum number of T values is 20 for structure Rl and those values are presented in Figure 5.4-2 to show the variability of T within a single structure.

In some cases there are differences between T values determined using the flowmeter and the HTU. It is possible that the relatively short duration of the double-packer injection test measures properties of the rock only in the immediate vicinity of borehole, i.e. measured values of K are correct but they represent only the near-field around the borehole. In addition, there is the possibility of injected water from the narrow test section returning to the borehole (i.e. a short circuit by-pass), which would result in higher K values being calculated using the double-packer system than when using the flowmeter. Those higher T values are presented in Figure 5.4-1 by open circles which are connected to the lower values (measured using the flowmeter) with dotted lines. There, therefore, is a range of T value for some structures, where the lower value represents probably some kind of effective T for the structure and the higher value a local maximum value of T close to the borehole. 78

log (T, m2/s) -7 -6 -5 -4 -3 -2 I I I <> R6

R • -•• R17 ^^ R1 R1 100 -• -__P-82. ^ • R2 ^T • R18 O R3 R18/F 200 -- B 9. O • 320 • R20 • R3 R18 > 300 ITR3 • --O • R7 R18 • R18 • R3

f 400-- • R18 "au R9 .. -•O 0) • R22 500 • R21

600 •- R26 m - -O

R19'' 700 -- g R19

R19 800 • O

Figure 5.4-1. Measured transmissivities of R-structures. Values from VLJ investigations are marked with open diamonds. Open circles represent the highest value of T determined for some structures. 79

log (T, m2/s)

-6 -5 -4 -3 -2

i i 1

• Y-boreholes • KR-boreholes 50 -- D • D • D Q. n # O D D 13 •o D a 15 * ] u 100 -- "E [

150

Figure 5.4-2. Measured transmissivities of structure Rl in 20 different boreholes.

Details of the fractures and the distribution of hydraulic conductivities measured over 2 m borehole lengths for structure R18 in borehole KR2 are illustrated by Figure 5.4-3. There are three highly conductive and narrow sections in the uppermost part (437 - 451 m) of structure R18 at depths of 439.0 m, 442.1 m and 449.1 m. The accurate location of most conductive fractures is based on detailed flow and single point resistance logs (Pollanen & Rouhiainen 1998a), which can be related to core and borehole TV data (Karanko et al. 1999). The most conductive of these sections is located at a depth of 442.1 m, where 5-6 open fractures lie in close proximity. Detailed investigations demonstrate that the hydraulic conductivity of this section is almost totally determined by these fractures and possibly by only one of them, whose aperture on the TV-log is 27 mm. Similar situations exist at depths of 439 m and 449 m, where the hydraulic conductivity at both depths is most probably determined by one open and slickensided fracture, even though there are seven open and slickensided fractures in close proximity. Immediately below the uppermost transmissive section of structure R18 there is single open fracture at a depth of 453.5 m whose transmissivity (T = 6-10"6 m2/s) is even higher than the total transmissivity (T = 4-10"6 m2/s) of structure R18 over the depth range of 437 - 451 m.

In the middle part of structure R18 (459 - 478 m) there are four narrow sections or single fractures which determine its hydraulic conductivity at depths of 468.2 m (one or two open fractures), 470 m (one open and slickensided fracture), 476.2 m (one or two open fractures) and 477.4 m (one or three open fractures). In addition, a set of open and slickensided fractures at a depth of 475.5 m and single fractures (or a set of two or three open fractures in close proximity) at depths of 459.8 m, 464.2 m and 466.2 m are 80 clearly more conductive than the rest of the rock over the depth interval of 459 - 478 m, even though the fracture density in this part of structure R18 is high.

The lowermost part of structure R18 lies at a depth range of 484 - 491 m and its hydraulic conductivity is clearly determined by a group of open fractures at a depth of 488 m. In addition, one open fracture at a depth of 489.4 m is relatively highly conductive.

Similar features have also been found for this structure, which is one of the major fracture zones at Hastholmen, in boreholes KR3, KR4 and KR6 too. In conclusion, the most conductive sections contain several open or slickensided fractures and, in general, there is a good relationship between measured values of K and the presence of open fractures, particularly when they form a narrow section of several open fractures. In many cases high values of hydraulic conductivity are related to single open fractures.

Two examples of the relationship between fractures and hydraulic conductivity for local fracture zones are presented below. The first example is structure R26, which is intersected only in borehole KR4 over a depth interval of 679 - 695 m. On the basis of detailed flow logging (PQUanen & Rouhiainen 1998b) and fracture analysis (Karanko et al. 1999) one single open fracture at a depth of 686.6 m determines the transmissivity of this structure. The transmissivity of this single fracture is 3.7-10"7 m2/s, the total transmissivity of the structure being 4-10"7 m2/s.

The second example concerns the case of structure R27, which lies immediately below structure R26 over a depth range of 705 - 724 m. In this case single open fractures at depths of 723.7 m, 714.8 m, 718.7 m, 708.9 m, 717.3 m and 724.4 m determine the transmissivity of the structure (see figure 5.4-4). The total transmissivity of structure R27 is 4.2-10"6 m2/s. The combined transmissivity of the two most conductive fractures is 3. MO"6 m2/s and the four other fractures 1.0-10"6 m2/s. In addition, three single fractures at depths of 715.6 m, 721.0 m and 722.4 m are relative highly conductive. Their combined transmissivity is about MO"7 m2/s. In conclusion, one or a small number of single open fractures determine the hydraulic conductivity of this kind of local fracture zone. 81

0 oripntatinn 30 fl intprspnt annlpfln OR apfiT.tur.fi 600 -10 hydr. cond.

Columns from left to right: S = oriented sample, H = core loss, Z = fracture zone, orientation = orientation by fracture type: open = O, tight = •, filled- •, weathered = ®, unknown = D, open slickenside = A, tight slickenside = A, filled slickenside = A, weathered slickenside = A, the tail of the mark shows the orientation, intersect. Angle = intersection angle by fracture type, aperture = fracture aperture (mm) and hydr. cond.= hydraulic conductivity (log K (m/s)): Flowmeter = blue bar, HTU = line.

Figure 5.4-3. A detailed presentation of fractures and their properties in borehole KR2 for the depth interval 430 - 510 m (Karanko et al. 1999). Structure R18 lies in the depth ranges 437 - 451, 459 - 478 and 484 - 491 m. 82

700 : 700

701 : 701 =e j

L 702 '• _ 702

703 i 703 r _ _ _ 1a- 704 I 704

705 \ 70S

706: r 708

707 j 707

708: 708 i 708.5

709 \ -- f 709 1 710.0 710 '• 710 -4-- 711 '• 711

712i L J 1 712

e" 713 : 713 71 _ f *i 714.4 714

L i I 715.3 716 ° 715; „

716 i •~7 - 716 l 716.9 ) 717: t- - 717 - - • *£

71B 718.3 718 : : : 719: \ i : 719 : ; 720 : 720 720.75 - 721: 721 \ I 722.0 722 722 ; j ^r— - U J

I 723: 723 r 7 1 723.4 : " "I _3 ; • w^^ 1 724.1 >l 724 • t" 724

725 i 725 s« 726 \ .A_j_-_, 726

727 •• 727

728 i 1 J1 728 1.E+00 1.E-KI1 1.E+02 1.E+03 1.E+O4 1.E+O5 1.E+O6 1.E+O1 1.E+O2 1.E+O3 1.E-t«4 1.E+O5 Flow rat* (ml/h) Slngi* point retittanc* (ohm)

Figure 5.4-4. Results of detailed flow and single point resistance logs from borehole KR4. Values between logs represent interpreted depths of most conductive single fractures (Polldnen & Rouhiainen 1998b). Depths are uncorrected. Corrected depths are referred in the text. 83

5.5 Fractured or anomalous borehole sections without correlation to other boreholes

In addition to R-structures, fractured and/or geophysically anomalous zones with unknown or uncertain orientation and continuity occur in boreholes. They are not classed as R-structures but may still be hydraulically significant. In many cases they are associated with narrow, vein-like sections of even-grained rapakivi granite, and are most likely local in nature.

Borehole KR1:

52 - 55 m: Consists of 1.6 m of fracture-structured rock, in which the fractures are horizontal according to borehole-TV logging. The fracture zone is associated with a slightly mylonitized, fine-grained and even-grained rapakivi granite at 52.5 - 54.0 m.

779 - 784 m: Anomalous section in geophysical logs with 0.5 m of fracture-structured rock in the core sample. The pole maximum of open fractures in borehole-TV logs is 035/10°. The VSP reflector at 780 m has an orientation of 065/05°.

Borehole KR2:

225 - 228 m: Two sections of fracture-structured rock with a total length of 1.4 m. The mean fracture orientation is 190/17° according to the borehole-TV log.

345 - 348 m: Anomalous section in geophysical logs with 2.3 m of fracture-structured rock in borehole sample. However, according to borehole-TV logging, the rock in the borehole walls is intact, containing only two open fractures and a ca. 70 cm long, reddish alteration zone dipping 65°ENE.

735 - 739 m: Consists of 2.2 m of fracture-structured rock in borehole core. The fracturing in this zone is associated with two 0.5 - 1 m thick granite veins, which, according to borehole-TV logging, are oriented 043/32° and 024/20°.

Borehole Y7/KR3

155 - 162 m: Three old, partly cataclastic, sealed fracture zones, which have later fractured again (Suominen 1982). According to borehole-TV logging the fractures dip 5 - 20°NE.

169 - 171 m, 174 - 176 m, 180 - 183 m: Five old, sealed fracture zones, which have later fractured again (Suominen 1982). According to borehole-TV logging the fractures mainly dip towards the NE at 5 - 20°.

268 - 276 m: Anomalous section in geophysical logs, probably related to the fracture zone R3 at 277 - 286 m. 84

Borehole KR4:

358 - 376 m: Anomalous section in geophysical logs, but only 0.5 m of fracture- structured rock in core sample at 373 m. The fracturing of the core is mainly due to core discing.

472 - 479 m: Two 1 m long fracture-structured sections, which are associated with the even-grained rapakivi granite at 473.3 - 475.2 m and two pegmatite veins at 477.5 - 477.9 m. The VSP reflector 060/10° at 475 m is associated with subhorizontal veins.

500 - 517 m: Anomalous section in geophysical logs with two 1 m long, fracture- structured sections at 510 m and 512 m. The fracturing is connected to the even-grained rapakivi granite at 507 - 517 m. The II class VSP reflector at 520 m has an orientation of 020/78°.

871 - 889 m: Anomalous section in geophysical logs with two <1 m long fracture- structured sections in core at 871 m and 876 m, the former being associated with aim long even-grained rapakivi granite section.

Borehole KR5:

50 - 57 m: Two fracture-structured sections with a total length of 4.2 m, which are partly mylonitized and strongly weathered and hematised. The mean fracture direction, according to the dipmeter survey, is 217/08°.

82 - 87 m: 4.7 m of fracture-structured, mostly strongly weathered rock. The fracturing is probably related to the even-grained rapakivi granite at 80.7 - 83.9 m, especially to its lower contact with the wiborgite/pyterlite but it may also be part of the structure Rl. The oriented core, dipmeter survey and borehole-TV logging all show fractures dipping 15 - 25°SW.

210 - 216 m: Two fracture structured sections, which are probably associated with a fine-grained rapakivi granite at 211.6 - 212.2 m. Both oriented core and the dipmeter survey demonstrate almost horizontal fracturing, and a connection of this zone to structure R20 in boreholes KR1 and KR2 is possible.

436 - 453 m: Six fracture-structured sections with a total length of 3.8 m. The dipmeter survey and borehole-TV logging indicate fractures dipping 20° to the N or NW.

598 - 602 m: The fractured hematite breccia in borehole KR5 at 598 - 602 m is associated with two narrow veins of fine-grained rapakivi granite at 599.5 and 600.5 m. It is most likely local in nature, since the mean length of the veins observed in outcrops is 13 m, the longest vein being 115 m long (see Kuivamaki et al. 1997a).

655 - 658 m: The core over this interval has been broken by fractures almost parallel to the borehole. A II class VSP reflector 072/82° has been interpreted at 660 m. 85

Borehole KR6:

73 - 79 m: Weathered hematite breccia with 2.2 m of fracture-structured rock between 73 - 76 m, the mean fracture direction being 100/10° according to the dipmeter survey.

138 - 146 m: Anomalous section in geophysical logging with single horizontal, weathered fractures.

198 - 203 m: Two fracture-structured sections with a total length of 0.95 m. Both dipmeter survey and borehole-TV logging indicate horizontal fracturing.

235 - 246 m: Anomalous section in geophysical logs with 1.5 m of fracture-structured rock in core. The orientation data are inconsistent, the mean fracture direction being 320/20° in borehole-TV logging and 267/42° in the dipmeter survey, whilst the VSP reflector at 230 m has an orientation of 070/70°.

431 - 433 m: 0.82 m of fracture-structured rock with "rusty" fractures. The fractures in borehole-TV logs are horizontal, whilst in the dipmeter survey they dip 40 - 60°SW. The VSP reflector at 430 m has an orientation of 070/79°.

689 - 691 m: Anomalous section in geophysical logs with 1.4 m of fracture-structured rock in borehole sample. The fractured section occurs within a long altered (epidote) borehole section at 625 - 695 m. The VSP reflector at 690 m has an orientation of 240/25°.

Borehole KR7:

179 - 200 m: Two fracture-structured sections with a total length of 4.39 m. The fracturing is associated with the upper contact of the even-grained rapakivi granite at 190.12-198.73 m.

274-291 m: Three fracture-structured sections with a total length of 3.04 m.

672 - 675 m: One metre of fracture-structured core. The fracturing is associated with the upper contact of the even-grained rapakivi granite at 673.34 - 695.65 m.

Borehole KR8:

114 - 124 m: Two fracture-structured sections with a total length of 1.89 m. According to oriented cores the fractures are subhorizontal, being associated with the even-grained rapakivi granite at 116.36 - 117.65 m.

152 - 162 m: Two fracture-structured sections with a total length of 1.1 m. The fractures are almost horizontal (dip <15°) according to oriented core. 86

174 - 186 m: Three fracture-structured sections with a total length of 4.21 m. Oriented core shows almost horizontal fractures, which are most likely associated with the even- grained rapakivi granite at 173.0 - 180.8 m.

193 - 194 m: 0.8 m of fracture-structured core associated with the even-grained rapakivi granite at 189.65 - 193.86 m.

209 - 211 m: 1.25 m of fracture-structured core, which is associated with the upper contact of the even-grained rapakivi granite at 209.97 - 217.80 m. Oriented core shows that the fractures are almost horizontal.

231 - 238 m : Two fracture-structured sections with a total length of 3.06 m, the fractures being almost horizontal according to oriented core. The fracturing may be associated with the upper contact of the porphyritic rapakivi granite at 239.0 - 246.8 m.

531 -534 m: 1.2 m of fracture-structured rock. 87

6 SUMMARY

The volume of bedrock at Hastholmen, which has been investigated by deep boreholes, consists mainly of pyterlite, with wiborgite being present only as short sections in boreholes. Both rock types are rapakivi granites with ovoidal potassium feldspar megacrysts and, because it is often difficult to distinguish them, they are displayed as a single rock type in maps and cross-sections presented in this report. They actually comprise a distinct, coherent lithological unit and both rock types have undergone the same structural evolution.

Porphyritic rapakivi granite is present in boreholes KR2, KR3 and KR4. It is not exposed within the study site, and is only present in some outcrops south of Hastholmen. Its presence in boreholes KR2 and KR3 has been interpreted as due to there being two inclusions of porphyritic rapakivi granite within the even-grained rapakivi granite, which dips gently (ca. 30-40°) to the N-NE.

Even-grained or weakly porphyritic rapakivi granites are present both in outcrops and in boreholes KR2 - KR8 over the depth range of ca. 300 - 1000 m. Beneath the island of Hastholmen the even-grained and weakly porphyritic rapakivi granites present in boreholes KR1 - KR4 and KR6 have been interpreted as forming another younger intrusive unit within the pyterlite/wiborgite, with a thickness of ca. 500 m. The upper part of the unit consists of fine-grained and densely fractured rapakivi granite, with the majority of the unit consisting of medium-grained to coarse-grained, even-grained or weakly porphyritic rapakivi granite. The upper contact of the even-grained rapakivi granite in boreholes KR2, KR3, KR4 and KR6 dips approx. 20° to the NNE or NNW. Another subhorizontal slab of even-grained rapakivi granite a few metres in thickness occurs closer to the surface between 25 m and 50 m depth and can be seen in most of the shallow Y-boreholes.

The surface fractures at Hastholmen form a distinct orthogonal system, with three perpendicular fracture directions: steeply dipping (>75° dip) fractures striking NE-SW and NW-SE plus horizontal or subhorizontal (<30° dip) fractures. Because of the generally flat surface of the outcrops, gently dipping and horizontal fractures are under- represented in the data. The maximum fracture frequency is 2.0 fractures/m and the average fracture frequency 0.6 fractures/m, the frequencies being lowest in the western part of the island. No essential differences exist in fracture frequencies between the different rapakivi granite types, although fracturing in the even-grained rapakivi granite tends to be slightly more frequent than in the pyterlites and wiborgites. The majority of the fractures are either open (54.5%) or tight (38.7%). The mean length of the measured fracture traces is 8 m, the fractures of the pyterlite being slightly longer than those of the wiborgite, porphyritic rapakivi granite and even-grained rapakivi granite.

The fracture orientations, lengths and frequencies observed in the VLJ repository correlate well with those observed in the outcrops. However, the number of open fractures is smaller in the repository than in the outcrops and decreases with increasing depth. 88

The fracturing in core samples was determined by measuring the proportion of broken rock and the number of fractures outside the broken sections as a function of the depth and rock type. Typically core samples are usually slightly fractured (1-3 fractures/m), and some cores are sparsely fractured (< 1 fracture/m), even close to the surface. Even- grained granites are in places abundantly fractured (3-10 fractures/m), especially near the contacts with pyterlite and wiborgite or when they occur as narrow dykes. The broken sections in Hastholmen core samples (boreholes KR1 - KR8) represent about 4.6% of the total length of the samples (6884 m). In most of them (>98%) the rock is densely fractured (> 10 fractures/m) representing 2.1 - 9.0% of the length in individual borehole core. The rest of the broken sections represents crush- or clay-structured and densely-fractured rock (> 10 fractures per metre with clay-filled fractures or abundant clay material in rock mass). Broken sections occur in every drill core, and they are most often 1 - 5 m in length. There is a close association between the presence of these broken sections and the even-grained granites, or to the contact of these granites with pyterlite and wiborgite.

Most of the fractures recorded from the core samples are filled or tight. Calcite, dolomite, Fe hydroxides and clay minerals (illite, montmorillonite and kaolinite) form the most typical fracture mineral phases throughout the drill cores. Calcite and/or dolomite are frequently found in every core from every borehole, and surfaces coated with chlorite and chloritic slickensides are also present at all depths. Open fractures in core are abundant only to depths of 100 - 150 m, but single open fractures can be found at all depths - an attribute typical of granitic formations - and as sporadic clusters close to sections of broken rock. The average total width of all apertures visible in borehole- TV logs per 1 m of borehole is 2 mm. If fractures are considered as uniformly distributed infinite plates this would mean an average fracture porosity of 0.2% for all the core from the surface to ca. 1000 m.

The majority of the fractures in the drill cores are horizontal or very gently dipping. In boreholes KR1, KR2, KR3, KR5 and KR6 there are, below the near-surface fracturing, some sections with mainly steeply dipping fractures. There appear to be no differences in fracture orientations with regard to rock type or depth.

One notable feature of the core samples of rapakivi granite at the Hastholmen site is the presence of core discing and ring discing. Core discing is visible as the presence of multiple, parallel fractures in the core when it is released from a stressed host rock. Ring discing is a similar feature which takes place in cases of overcoring with a pilot hole. Core discing has been noted in sections of core several metres or tens of metres in length, and the first observations are usually seen at the depth of about 200 m or deeper.

The methodology for the identification and location of fracture zones consisted of the integrated interpretation of geological observations of the core samples and geophysical single-hole surveys. The geophysical data used was obtained from standard single-hole logs, acoustic full wave form logging, scanner investigations, such as dipmeter and borehole-TV, and three-dimensional vertical seismic profiling (3D-VSP), which were analysed using principal component analysis. The orientation and continuity of fracture zones between boreholes were based on geological and geophysical similarities 89

("fingerprinting") together with oriented borehole and rock mass data. Ultimately, the process of conceptualising the fracture zones included direct observations in boreholes and indirect evidence, derived mainly from the interpretations of geophysical surveys.

The present structural model contains 27 fracture zones (denoted by the term R+number structures). More than half of these structures can be verified by direct observations from boreholes or from their exposure at depth within the VLJ repository, and they are listed in Table 5.3-1 with the status directly observed. The remaining structures are based on the interpretation of horizontal seismic profiling (HSP) surveys, reflection/refraction seismic surveys, an airborne geophysical survey, a ground radar survey and topographic relief maps, and have been classified as probable or possible fracture zones. In addition, local structures with unknown orientation and continuity occur in the rock mass. They are not classed as R-structures but may still be hydraulically significant.

The assumed location and geometry of the fracture zones within the bedrock volume are shown by vertical cross-sections. The structures presented in the various figures are simplified representations of geological structures, which are known to posses complex geometries and variable properties. In resistivity and in acoustic velocity logs in particular, anomalies in excess of 100 m in length are present that indicate altered sections in the rapakivi granite. Within these sections the anomalies in hydraulic properties, which can be seen in fluid logs, tube wave attenuation profiles and in hydraulic tests, have lengths of only 1 - 5 m long. Isolated open fractures are normally located by borehole-TV imagery.

The transmissivity (T) of R-structures (fracture zones) has been measured by two single-hole methods, the constant head injection test using a double-packer system (HTU) and fluid logs using the flowmeter. If multi-element R-structures are treated as a single zone with one T value, which is taken as the sum of the T values of all those sub- structures, the number of measured values of T for structures is 36 and values vary from MO'3 m2/s to MO"7 m2/s, the average being MO"5 m2/s.

Most conductive sections of fracture zones contain several open or slickensided fractures and, in general, there is a good relationship between measured values of T and the presence of open fractures, particularly when they form a narrow section of several open fractures. In many cases high values of transmissivity are related to single open fractures, particularly in the case of local (minor) fracture zones.

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Salmi, M., Vuorela, P. & Kuivamaki, A. 1985. Site identification survey for final dispo- sal of spent nuclear fuel (in Finnish with an English abstract). Helsinki, Finland: Nuclear Waste Commission of Finnish Power Companies. 121 p. Report YJT-85-27.

Siddans, A., Wild, P. & Adams, B. 1997. Dipmeter survey, processing and interpretation, Hastholmen site, Finland 1997. Helsinki, Finland: Posiva Oy. 269 p. Working Report 97-60e.

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POSIVA REPORTS 1999, situation 10/99

POSIVA 99-01 Measurement of thermal conductivity and diffusivity in situ: Literature survey and theoretical modelling of measurements Ilmo Kukkonen, Ilkka Suppala Geological Survey of Finland January 1999 ISBN 951-652-056-1

POSIVA 99-02 An overview of a possible approach to calculate rock movements due to earthquakes at Finnish nuclear waste repository sites Paul R. LaPointe, Trenton T. Cladouhos Golder Associates Inc., Washington, USA February 1999 ISBN 951-652-057-X

POSIVA 99-03 Site scale groundwater flow in Olkiluoto Jari Lofrnan VTT Energy March 1999 ISBN 951-652-058-8

POSIVA 99-04 The psychosocial consequences of spent fuel disposal Jura Paavola, Liisa Erdnen University of Helsinki Department of Social Psychology March 1999 (in Finnish) ISBN 951-652-059-6

POSIVA 99-05 The effects of the final disposal facility for spent nuclear fuel on regional economy Seppo Laakso Seppo Laakso Urban Research March 1999 (in Finnish) ISBN951-652-060-X

POSIVA 99-06 Radwaste management as a social issue Ismo Kantola University of Turku Department of Sociology March 1999 (in Finnish) ISBN 951-652-061-8

POSIVA 99-07 Safety assessment of spent fuel disposal in Hastholmen, Kivetty, Olkiluoto and Romuvaara - TELA-99 Timo Vieno, Henrik Nordman VTT Energy March 1999 ISBN 951-652-062-6 LIST OF REPORTS 2(6)

POSIVA 99-08 Final disposal of spent nuclear fuel in Finnish bedrock - Hastholmen site report Pekka Anttila, Fortum Engineering Oy Henry Ahokas, Fintact Oy Kai Front, VTT Communities and Infrastructure Heikki Hinkkanen, Posiva Oy Erik Johansson, Saanio & Riekkola Oy Seppo Paulamdki, Geological Survey of Finland Reijo Riekkola, Saanio & Riekkola Oy Jouni Saari, Fortum Engineering Oy Pauli Saksa, Fintact Oy Margit Snellman, Posiva Oy Liisa Wikstrom, Posiva Oy Antti Ohberg, Saanio & Riekkola Oy June 1999 ISBN 951-652-063-4

POSIVA 99-09 Final disposal of spent nuclear fuel in Finnish bedrock - Kivetty site report Pekka Anttila, Fortum Engineering Oy Henry Ahokas, Fintact Oy Kai Front, VTT Communities and Infrastructure Eero Heikkinen, Fintact Oy Heikki Hinkkanen, Posiva Oy Erik Johansson, Saanio & Riekkola Oy Seppo Paulamdki, Geological Survey of Finland Reijo Riekkola, Saanio & Riekkola Oy Jouni Saari, Fortum Engineering Oy Pauli Saksa, Fintact Oy Margit Snellman, Posiva Oy Liisa Wikstrom, Posiva Oy Antti Ohberg, Saanio & Riekkola Oy June 1999 ISBN 951-652-064-2

POSIVA 99-10 Final disposal of spent nuclear fuel in Finnish bedrock - Olkiluoto site report Pekka Anttila, Fortum Engineering Oy Henry Ahokas, Fintact Oy Kai Front, VTT Communities and Infrastructure Heikki Hinkkanen, Posiva Oy Erik Johansson, Saanio & Riekkola Oy Seppo Paulamdki, Geological Survey of Finland Reijo Riekkola, Saanio & Riekkola Oy Jouni Saari, Fortum Engineering Oy Pauli Saksa, Fintact Oy Margit Snellman, Posiva Oy Liisa Wikstrom, Posiva Oy Antti Ohberg, Saanio & Riekkola Oy June 1999 ISBN 951-652-065-0 LIST OF REPORTS 3(6)

POSIVA 99-11 Final disposal of spent nuclear fuel in Finnish bedrock - Romuvaara site report Pekka Anttila, Forrum Engineering Oy Henry Ahokas, Fintact Oy Kai Front, VTT Communities and Infrastructure Heikki Hinkkanen, Posiva Oy Erik Johansson, Saanio & Riekkola Oy Seppo Paulamaki, Geological Survey of Finland Reijo Riekkola, Saanio & Riekkola Oy Jouni Saari, Fortum Engineering Oy Pauli Saksa, Fintact Oy Margit Snellman, Posiva Oy Liisa Wikstrom, Posiva Oy Antti Ohberg, Saanio & Riekkola Oy June 1999 ISBN 951-652-066-9

POSIVA 99-12 Site scale groundwater flow in Hastholmen Jari Lb'finan VTT Energy May 1999 ISBN 951-652-067-7

POSIVA 99-13 Regional-to-site scale groundwater flow in Kivetty Eero Kattilakoski VTT Energy Ferenc Meszdros The Relief Laboratory, Harskut, April 1999 ISBN 951-652-068-5

POSIVA 99-14 Regional-to-site scale groundwater flow in Romuvaara Eero Kattilakoski, Lasse Koskinen VTT Energy April 1999 ISBN 951-652-069-3

POSIVA 99-15 Site-to-canister scale flow and transport in Hastholmen, Kivetty, Olkiluoto and Romuvaara Antti Poteri, Mikko Laitinen VTT Energy May 1999 ISBN 951-652-070-7

POSIVA 99-16 Assessment of radiation doses due to normal operation, incidents and accidents of the final disposal facility Jukka Rossi, Heikki Raiko, Vesa Suolanen, Mikko Ilvonen VTT Energy March 1999 (in Finnish) ISBN 951-652-071-5 LIST OF REPORTS 4(6)

POSIVA 99-17 Assessment of health risks brought about by transportation of spent fuel Vesa Suolanen, Risto Lautkaski, Jukka Rossi VTT Energy March 1999 (in Finnish) ISBN 951-652-072-3

POSIVA 99-18 Design report of the disposal canister for twelve fuel assemblies Heikki Raiko VTT Energy Jukka-Pekka Salo Posiva Oy May 1999 ISBN 951-652-073-1

POSIVA 99-19 Estimation of block conductivities from hydrologically calibrated fracture networks - description of methodology and application to Romuvaara investigation area Auli Niemi1'2, Kimmo Kontio2, Auli Kuusela-Lahtinen2, Tiina Vaittinen2 *Royal Institute of Technology, Hydraulic Engineering, Stockholm 2VTT Communities and Infrastructure March 1999 ISBN951-652-074-X

POSIVA 99-20 Porewater chemistry in compacted bentonite Arto Muurinen, Jarmo Lehikoinen VTT Chemical Technology March 1999 ISBN 951-652-075-8

POSIVA 99-21 Ion diffusion in compacted bentonite Jarmo Lehikoinen VTT Chemical Technology March 1999 ISBN 951-652-076-6

POSIVA 99-22 Use of the 14C-PMMA and He-gas methods to characterise excavation disturbance in crystalline rock Jorma Autio, Timo Kirkkomdki Saanio & Riekkola Oy Marja Siitari-Kauppi University of Helsinki Laboratory of Radiochemistry Jussi Timonen, Mika Laajalahti, Tapani Aaltonen, Jani Maaranen University of Jyvaskyla Department of Physics April 1999 ISBN 951-652-077-4 LIST OF REPORTS 5(6)

POSIVA 99-23 New data on the Hyrkkola U-Cu mineralization: The behaviour of native copper in a natural environment Nuria Marcos Helsinki University of Technology Laboratory of Engineering Geology and Geophysics Lasse Ahonen Geological Survey of Finland May 1999 ISBN 951-652-078-2

POSIVA 99-24 Dissolution of unirradiated UO2 fuel in synthetic groundwater - Final report (1996 - 1998) Kaija Ollila VTT Chemical Technology May 1999 ISBN 951-652-079-0

POSIVA 99-25 Numerical study on core damage and interpretation of in situ state of stress MattiHakala Gridpoint Finland Oy June 1999 ISBN 951-652-080-4

POSIVA 99-26 Hydrogeochemical conditions at the Hastholmen site Ari Luukkonen, Petteri Pitkdnen VTT Communities and Infrastructure Paula Ruotsalainen Fintact Oy Hilkka Leino-Forsman VTT Chemical Technology Margit Snellman Posiva Oy June 1999 ISBN 951-652-081-2

POSIVA 99-27 Tests for manufacturing technology of disposal canisters for nuclear spent fuel Heikki Raiko VTTEnergia Timo Salonen Outokumpu Poricopper Oy Ismo Meuronen Suomen Teknohaus Oy Kimmo Lehto Valmet Oyj Rautpohja Foundry June 1999 (in Finnish) ISBN 951-652-082-0 LIST OF REPORTS 6(6)

POSIVA 99-28 Land uplift and relative sea-level changes in the Loviisa area, southeastern Finland, during the last 8000 years Arto Miettinen, Matti Eronen, Hannu Hyvdrinen Department of Geology University of Helsinki September 1999 ISBN 951-652-083-9

POSIVA-99-29 Evaluation of the quality of ground water sampling: experience derived from radioactive waste disposal programme in Sweden and Finland during 1980-1992 J.A.T. Smellie Con terra AB, Uppsala M. Laaksoharju Intera, Sollentuna M.V. Snellman Posiva Oy P.H. Ruotsalainen Fintact Oy September 1999 ISBN 951-652-084-7

POSIVA 99-30 Future glaciation in Fennoscandia Lars Forsstrom Department of Geosciences University of Oulu September 1999 ISBN 951-652-085-5

POSIVA 99-31 Lithological and structural bedrock model of the Hastholmen study site, Loviisa, SE Finland Kai Front VTT Communities and Infrastructure Seppo Paulamaki Geological Survey of Finland Henry Ahokas Fintact Oy PekkaAnttila Fortum Engineering Oy October 1999 ISBN 951-652-086-3