P O S I V A O Y

FI -27160 OLKILUOTO, F INLAND

Tel +358-2-8372 31

Fax +358-2-8372 3709

Seppo Gehör

Au l i s Kärk i

Markku Paananen

June 2007

Work ing Repor t 2007 -45

Petrology, Petrophysics and FractureMineralogy of the Drill Core Sample

OL-KR20 and OL-KR20B

June 2007

Base maps: ©National Land Survey, permission 41/MYY/07

Working Reports contain information on work in progress

or pending completion.

The conclusions and viewpoints presented in the report

are those of author(s) and do not necessarily

coincide with those of Posiva.

Seppo Gehör

Au l i s Kärk i

K iv i t i e to Oy

Markku Paananen

Geo log ica l Su rvey o f F in l and

Work ing Report 2007 -45

Petrology, Petrophysics and FractureMineralogy of the Drill Core Sample

OL-KR20 and OL-KR20B

ABSTRACT

This report represents the results of the studies dealing with the drill core samples OL-

KR20 and OL-KR20B, drilled in the north western part of the Olkiluoto study site.

Lithological properties, whole rock chemical compositions, mineral compositions,

textures, petrophysical properties and low temperature fracture infill minerals are

described.

The drill holes intersect down to length of 250 m a fluctuating sequence of pegmatitic

granites, quartz gneisses and various migmatites in which individual intersections of

each lithological types range from 5 m to 30 m. Down to the drilling length of 360 m,

below previous migmatite section, a rather homogeneous unit of medium-grained TGG

gneisses is located. The lowermost part of the bore hole intersection is composed of

veined gneisses with a small amount of pegmatitic dykes and the hole ends into a mica

gneiss unit with a number of mafic gneiss interbeds. Detailed Petrological properties

have been analysed from 15 samples. Chemical compositions of the T type migmatites

studies in detail are moderate and SiO2 concentrations fall between 60 and 68 %. Major

element concentrations are exactly in the anticipated values for the members of the T

series. The P series is represented by a collection of migmatites and gneisses which

represents extensively the whole series. SiO2 concentration in the mafic gneiss variant is

ca. 48% while it in the most silicic TGG gneiss is close to 78%. The concentration of

phosphorus follows typical trend of the P series. P2O5 concentration is close to 2% in

the mafic gneiss and decreases close to 0.3% in the acidic migmatites and TGG

gneisses.

Petrophysical properties were studied from 15 samples. The parameters measured were

density, magnetic susceptibility, natural remanet magnetization, electrical resistivity, P-

wave velocity and porosity.

Borehole contains 2.8 fractures/metre. The chief fracture minerals include illite,

kaolinite, unspecified mixed clay phases (mainly illite, chlorite, and smectite-group),

iron sulphides and calcite. A number of fracture plains are covered by cohesive chlorite.

The degree of fracture related sulphidization is elevated at the drill core length 1.4 – 100

m and in those sequences where the strength of hydrothermal activity has been elevated.

Pervasive illitization concerns 25 % of the total core length and in addition to that the

fracture related kaolinite and illite infillings form a number of filling sequences, which

have 30 metres in maximum. Calcitic fracture fillings and calcite stockworks occur all

along the drill core sample and they constitute sequences which have 7.5 m core length

in average. The percentage of carbonaceous fractures is as much as 34 % of the bore

hole length.

Kairanäytteen OL-KR20 ja OL-KR20B petrologia, petrofysiikka ja rakomineralogia

TIIVISTELMÄ

Tässä raportissa esitetään kairausnäytteitä OL-KR20 ja OL-KR20B koskevien

tutkimusten tulokset. Kyseiset kairanreiät on tehty Olkiluodon tutkimusalueen luoteis-

osaan. Raportissa esitetään kairausnäytteen litologiaa sekä valittujen näytteiden koko-

kiven kemiallista koostumusta, mineraalikoostumusta, tekstuuria ja petrofysikaalisia

ominaisuuksia käsittelevien tutkimusten tulokset. Samoin kuvataan matalan lämpötilan

raontäytemineraalit

Kairanreikä lävistää 250 m:n pituudelle saakka vaihtelevaa, pegmatiittisista graniiteista,

kvartsigneisseistä ja erilaisista migmatiiteista muodostuvaa kallioperäyksikköä, jossa

kunkin itsenäisen litologisen tyypin leikkauspituudet vaihtelevat 5:stä 30 m:iin. Tämän

alapuolella, aina 360 m:n kairauspituudelle sakka ulottuu varsin homogeeninen,

keskirakeisista TGG-gneisseistä koostuva yksikkö. Kairanreiän alin lävistys koostuu

suonigneisseistä, joissa on pieni määrä pegmatiittisia juonia ja kairanreikä päättyy

mafisia gneissivälikerroksia sisältävään kiillegneissiin.

Yksityiskohtaiset petrologiset ominaisuudet on analysoitu 15 näytteestä. Analysoidut T-

tyypin migmatiitit ovat kemiallislta koostumukseltaan keskimääräisiä ja niiden SiO2

pitoisuudet vaihtelevat välillä 60 ja 68 %. Pääalkuainepitoisuudet ovat tarkasti odo-

tetuissa ja T-sarjan kivilajeille tyypillisissä arvoissa. P-sarjaa edustaa joukko

migmatiittja ja gneissejä, jotka edustavat kattavasti koko sarjaa. SiO2–pitoisuus on

mafisessa gneissimuunnoksessa noin 48 % kun taas happamin TGG-gneissi sisältää sitä

lähes 78 %. Fosforipitoisuus seuraa P-sarjalle tyypillistä trendiä. P2O5–pitoisuus on

mafisessa gneississä lähes 2 % mutta putoaa lähelle 0,3 %:a happamissa migmatiiteissa

ja TGG-gneisseissä.

Petrofysikaaliset ominaisuudet on määritetty 15 näytteestä. Mitatut parametrit ovat

tiheys, magneettinen suskebtibiliteetti, luonnollinen remanentti magnetoituma, sähkö-

vastus, P-aallon nopeus ja huokoisuus.

Kairausnäytteen OL-KR20 rakotiheys on keskimäärin 2.8 rakoa/metri. Rakoilu on

keskittynyt hydrotermisiin muuttumisvyöhykkeisiin ja muihin rikkonaisuusvyöhyk-

keisiin, joissa rakojen täytteinä esiintyy illiittiä, kaoliniittia, erikseen määrittelemättömiä

useamman savispesieksen muodostamia savisseostäytteitä (pääasiassa illiitti, kloriitti ja

smektiitti-ryhmä), rautasulfideja ja kalsiittia. Kloriitti muodostaa tyypillisesti rakojen

pinnoille kiinteän katteen, joka on usein alustana muille rakotäytteille. Rakotäytteissä

ilmenevää sulfidisaatiota esiintyy erityisesti kairauspituusvälillä 1.4-100 metriä

Kairauslävistyksestä on 25 % läpikotaisesti illiittiytynyttä. Rakotäytteisiin liittyvän

iliitti-kaoliniittimuuttumisen kairausleikkauspituus on keskimäärin 7.5 metriä. Kalsiitti-

valtaisia täyteseurantoja esiintyy 34 %:ssa kairausnäytteen koko pituudesta.

1

TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

1 INTRODUCTION ................................................................................................ 2 1.1 Location and General Geology of Olkiluoto .................................................... 2 1.2 Boreholes and Drill Core Samples OL-KR20 and OL-KR20B......................... 5 1.3 The aim of this study and research methods .................................................. 5 1.4 Research Activities ......................................................................................... 6

2 PETROLOGY...................................................................................................... 8 2.1 Lithology.......................................................................................................... 8 2.2 Whole Rock Chemistry ................................................................................. 15 2.3 Petrography .................................................................................................. 19

3 PETROPHYSICS.............................................................................................. 22 3.1 Density and magnetic properties .................................................................. 23 3.2 Electrical properties and porosity.................................................................. 24 3.3 P-wave velocity ............................................................................................. 25

4 FRACTURE MINERALOGY ............................................................................. 26 4.1 Fracture fillings at the major pervasive alteration zones............................... 29 4.2 Fracture fillings outside the major hydrothermal fracture zones ................... 30 4.3 Water flow indication..................................................................................... 32

5 SUMMARY........................................................................................................ 34

REFERENCES ............................................................................................................. 37

APPENDICES............................................................................................................... 38

2

1 INTRODUCTION

According to the Nuclear Energy Act, all nuclear waste generated in Finland must be

handled, stored and permanently disposed of in Finland. The two nuclear power

companies, Teollisuuden Voima Oy and Fortum Power and Heat Oy, are responsible for

the safe management of the waste. The power companies have established a joint

company, Posiva Oy, to implement the disposal programme for spent fuel, whilst other

nuclear wastes are handled and disposed of by the power companies themselves.

The plans for the disposal of spent fuel are based on the KBS-3 concept, which was

originally developed by the Swedish SKB. The spent fuel elements will be encapsulated

in metal canisters and emplaced at a depth of several hundreds of meters.

At present Posiva has started the construction of an underground rock characterisation

facility at Olkiluoto. The plan is that, on the basis of underground investigations and

other work, Posiva will submit an application for a construction licence for the disposal

facility in the early 2010s, with the aim of starting disposal operations in 2020.

As a part of these investigations, Posiva Oy continues detailed bedrock studies to get a

more comprehensive conception of lithology and bedrock structure of the study site. As

a part of that work, this report summarises the results obtained from petrological and

petrophysical studies and fracture mineral loggings of drill cores OL-KR20 and OL-

KR20B.

1.1 Location and General Geology of Olkiluoto

The Olkiluoto site is located in the SW Finland, western part of the Eurajoki municipal

and belongs to the Paleoproterozoic Svecofennian domain ca. 1900 - 1800 million years

in age (Korsman et al. 1997, Suominen et al. 1997, Veräjämäki 1998, ). The bedrock is

composed for the most part of various, high grade metamorphic supracrustal rocks (Fig.

1-1), the source materials of which are various epi- and pyroclastic sediments. In

addition, leucocratic pegmatites have been met frequently and also some narrow mafic

dykes cut the bedrock of Olkiluoto. The practice of naming the rock types follows the

orders of Posiva Oy (Mattila 2006).

On the basis of the texture, migmatite structure and major mineral composition, the

rocks of Olkiluoto fall into four main classes: 1) gneisses, 2) migmatitic gneisses, 3)

TGG gneisses, and 4) pegmatitic granites (Kärki & Paulamäki 2006). In addition,

narrow diabase dykes have been met sporadically.

Subdivision of the gneissic rocks has to be based on modal mineral composition. Mica

gneisses, mica bearing quartz gneisses and hornblende or pyroxene bearing mafic

gneisses are often banded but rather homogeneous types have also been met. Quartz

gneisses are fine-grained, often homogeneous and typically poorly foliated rocks that

contain more than 60% quartz and feldspars but 20% micas at most. They may contain

some amphibole or pyroxene and garnet porphyroblasts are also typical for one

subgroup. Mica rich metapelites are in most cases intensively migmatitized but

3

sporadically also fine- and medium-grained, weakly migmatized gneisses with less than

10 % leucosome material occur. The content of micas or their retrograde derivatives

Veined gneiss

Diatexitic gneiss

Pegmatitic granite

TGG gneiss

Sea/lake area

Building

Road/street

OL-KR8

N

400 0 400 800 Meters

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z$Z$Z$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z

$Z$Z

$Z

$Z

$Z

$Z

$Z

KR1

KR2

KR3

KR4

KR5

KR6

KR7

KR8

KR9

SK9

KR10

KR11

KR12

KR13

KR14

KR21

KR24

KR26

KR30

KR31

KR32

KR33

KR15BKR16B

KR18B

KR19B

KR20B

KR22B

KR23B

KR25B

KR27B

OL-KR20

Figure 1-1. General geology and location of bore hole starting points at Olkiluoto.

4

exceeds 20% in these rocks. Cordierite or pinite porphyroblasts, typically 5 – 10 mm in

diameter, are common constituents for one subgroup of mica rich rocks. Mafic gneisses

and schists have been seen as different variants that have been called amphibolites,

hornblende gneisses and chlorite schists. Certain, exceptional gneiss variants may

contain in addition to dark mica and hornblende also some pyroxene or olivine.

Migmatitic gneisses have been defined as migmatites including more than 10%

neosome. Ideal veined gneisses contain elongated leucosome veins the thicknesses of

which vary typically from several millimetres to five – ten centimetres. The leucosome

veins show a distinct lineation and appear as swellings of dykes or roundish quartz-

feldspar aggregates that may compose augen-like structures the diameters of which vary

between 1 and 5 cm. Stromatic gneisses represent a rather rare migmatite variety in

Olkiluoto and the most characteristic feature of these migmatites is the existence of

plane-like, linear leucosome dykes or “layers”. Widths of these leucosome layers vary

from several millimetres up to 10 – 20 cm. The palaeosome is often well foliated and

shows a distinct metamorphic banding or schistosity. The name diatexitic gneiss is used

for other migmatite rocks that are more strongly migmatitized and show more wide

variation in the properties of migmatite structures, which are generally asymmetric and

disorganized. The borders of palaeosome fragments or relicts of them are often

ambiguous and they may be almost indistinguishable. This group includes migmatites

that may contain more than 70% neosome and the palaeosome particles of which are

coincidental in shape and variable in size.

TGG gneisses are medium-grained, relatively homogeneous rocks which can show a

weak metamorphic banding or blastomylonitic foliation but they can also resemble

plutonic, not foliated rocks. One type of these gneisses resembles moderately foliated,

red granites and one other grey, weakly foliated tonalites. In places, these rocks are well

foliated, banded gneisses that show features typical for high grade fault rocks.

Pegmatitic granites are often leucocratic and very coarse-grained rocks. Sometimes

large garnet and also tourmaline and cordierite grains of variable size occur in the

pegmatitic granites. Mica gneiss inclusions and xenoliths are also typical constituents

for wider pegmatite dykes.

On the basis of whole rock chemical composition these gneisses and migmatites can be

divided into four distinct series or groups: T-series, S-series, P-series and mafic gneisses

(Kärki & Paulamäki 2006). In addition to those, pegmatitic granites and diabases form

their own groups which can be identified both macroscopically and chemically.

The members the T-series build up a transition series the end members of which are

relatively dark and often cordierite bearing mica gneisses and migmatites which may

have less than 60% SiO2. Another end in this series is represented by quartz gneisses in

which the concentration of SiO2 exceeds 75%. These high grade metamorphic rocks

have been assumed to originate from turbidite-type sedimentary materials and the end

members of that series have been assumed to be developed from greywacke type,

impure sandstones in other end and from clay mineral rich pelitic materials in other end

of the series.

5

The members of the S-series have been assumed to originate from calcareous

sedimentary materials or affected by some other processes that produced the final,

skarn-type formations. The most essential difference between the members of the S-

series and other groups is in the high calcium (>2% CaO) concentration of the S-type

rocks. Relatively low concentrations of alkalis and high concentrations of manganese

are also typical for this series. Various quartz gneisses, mica gneisses and mafic

gneisses constitute the most typical members of the S series while migmatitic rocks are

infrequent.

The P-series deviates from the others due to high concentrations of phosphorus. P2O5

concentration that exceeds 0.3% is characteristic for the members of the P-series

whereas the other common supracrustal rock types in Olkiluoto contain typically less

than 0.2% P2O5. Another characteristic feature for the members of the P-series is the

comparatively high concentration of calcium which falls between the concentration

levels of the T- and S-series. Mafic gneisses, mica gneisses, various migmatites and

TGG gneisses are the most characteristic rock types of the P series. SiO2 concentration

of the mafic P-type gneisses varies between 42 and 52%, in the mica gneisses and

migmatites it is limited between 55 and 65% and in the P-type TGG gneisses the

variation is more wide the concentrations falling between 52 and 71%.

1.2 Boreholes and Drill Core Samples OL-KR20 and OL-KR20B

The starting point of the borehole OL-KR20 is situated in the NW part of the Olkiluoto

study site (Figure 1-1). The coordinates of the starting point are: X = 6792623.56, Y =

1525655.39 and Z = 7.30. Starting direction (azimuth angle) of the borehole is 290o and

its dip (inclination angle) is 50.4o. The same values for borehole OL-KR20B are: X =

6792619.86, Y = 1525654.04 and Z = 7.25. Starting direction (azimuth angle) of the

borehole is 290o and its dip (inclination angle) is 49.5

o. Technical data dealing with the

OL-KR20 and –KR20B drillings is represented by Rautio 2002.

1.3 The aim of this study and research methods

Hitherto, more than 40 deep bore holes have been drilled at the study site. The aim of

this report is to represent the results of studies dealing with petrology, petrophysics and

fracture minerals of the drill core sample OL-KR20 and OL-KR20B. A description of

lithological units and their properties is presented in this report. Petrological properties

such as whole rock chemical composition, mineral composition and microscopic texture

of selected samples are described as well as the results of petrophysical measurements

of the samples. Another aim was to map the locations and types of low temperature

fracture infill minerals and, when necessary, to analyse and identify those.

Lithological mapping has been done by naked ayes utilizing the results of geophysical

borehole measurements. Whole rock chemical analyses have been carried out in the

SGS Minerals Services laboratory, Canada by X-ray fluorescence analyser (XRF),

6

neutron activation analyser (NAA), inductively coupled plasma atomic emission

analyser (ICP), inductively coupled plasma mass spectrometer (ICPMS), sulphur and

carbon analyser (LECO) and by using ion specific electrodes (ISE). The elements,

methods of analysis and detection limits for individual elements have been represented

in the Table 1-1.

Mineral compositions and textures of the selected samples have been determined by

using Olympus BX60 polarization microscope equipped with reflecting and transmitting

light accessories and a point counter.

Petrophysical measurements were carried out in the Laboratory of Petrophysics at the

Geological Survey of Finland (GSF). Prior to the measurements, the samples were kept

in a bath for 2.5 days using ordinary tap water (resistivity 50 – 60 ohmm). The

parameters measured were density, magnetic susceptibility, natural remanet

magnetization, electrical resistivity with three frequencies (0.1, 10 and 500 Hz), P-wave

velocity and porosity.

Mapping of fracture infill minerals has been done by naked ayes utilizing

stereomicroscopy when necessary. More detailed identification of mineral species of

selected samples has been done by Siemens X-ray diffractometer at the department of

electron optics, University of Oulu under control of O. Taikina-aho, FM.

1.4 Research Activities

Lithological logging and mapping of fracture infill minerals has been done by S. Gehör,

PhD and A. Kärki, PhD during a mapping campaign on 30.6. – 4.7.2003 at the drill

core archive of Posiva in Olkiluoto. During these studies Henri Kaikkonen and Pekka

Kärki acted as research assistants and they also transcribed the data collected during the

studies. Engineer Tapio Lahdenperä is responsible for the checking and correcting the

data files.

Drill core was sampled for studies of modal mineral composition, texture and whole

rock chemical composition and in the latest stage also for measurements of

petrophysical properties. The samples were selected by A. Kärki. Materials for detailed

further studies have been selected on the basis of their frequency of appearance. Thus,

the most common and typical rock types are represented roughly in the same proportion

that they build up in the core sample. Polished thin sections have been prepared from

these samples at the thin section laboratory of Department of Geosciences, University of

Oulu for polarization microscope examinations.

The total number of prepared thin sections is 13 from the drill core OL-KR 20 and 2

from the drill core OL-KR20B. Modal mineral compositions were determined by using

a point counter and calculating 500 points per one sample. Aulis Kärki is responsible for

microscope studies and also for description of petrography and handling of the results of

the whole rock chemical analyses.

7

Petrophysical properties have been measured at the Geological Survey of Finland from

the same samples that have been selected for petrological studies. Markku Paananen,

Lic. Tech. from the GSF is responsible for handling and description of petrophysical

data.

S. Gehör carried out the handling of fracture mineral data and he is also responsible for

the selection of fracture mineral materials for further studies. S. Gehör also composed

the section dealing with the fracture minerals.

Table 1-1. Elements, methods and detection limits for whole rock chemical analysis.

Element Method

Detection

limit Element Method

Detection

limit

SiO2 XRF 0.01 % Lu ICPMS 0.05 ppm

Al2O3 XRF 0.01 % Nb ICPMS 1 ppm

CaO XRF 0.01 % Nd ICPMS 0.1 ppm

MgO XRF 0.01 % Ni ICPMS 5 ppm

Na2O XRF 0.01 % Pr ICPMS 0.05 ppm

K2O XRF 0.01 % Rb ICPMS 0.2 ppm

Fe2O3 XRF 0.01 % Sm ICPMS 0.1 ppm

MnO XRF 0.01 % Sn ICPMS 1 ppm

TiO2 XRF 0.01 % Sr ICPMS 0.1 ppm

P2O5 XRF 0.01 % Ta ICPMS 0.5 ppm

Cr2O3 XRF 0.01 % Tb ICPMS 0.05 ppm

LOI XRF 0.01 % Tm ICPMS 0.05 ppm

Mn ICP 2 ppm U ICPMS 0.05 ppm

Ba ICPMS 0.5 ppm W ICPMS 1 ppm

Ce ICPMS 0.1 ppm Y ICPMS 0.5 ppm

Co ICPMS 10 ppm Yb ICPMS 0.1 ppm

Cu ICPMS 10 ppm Zn ICPMS 5 ppm

Cr ICPMS 10 ppm Zr ICPMS 0.5 ppm

Cs ICPMS 0.1 ppm Cl ISE 50 ppm

Dy ICPMS 0.05 ppm F ISE 20 ppm

Er ICPMS 0.05 ppm C LECO 0.01 %

Eu ICPMS 0.05 ppm S LECO 0.01 %

Gd ICPMS 0.05 ppm Br NAA 0.5 ppm

Hf ICPMS 1 ppm Cs NAA 0.5 ppm

Ho ICPMS 0.05 ppm Th NAA 0.2 ppm

La ICPMS 0.1 ppm U NAA 0.2 ppm

8

2 PETROLOGY

The practice for naming (Mattila 2006) and lithological classification proposed by Kärki

and Paulamäki (2006) has been utilized in the description and grouping of lithological

units. More detailed classification has to be based on the evaluation of whole rock

chemical composition or modal mineral composition and that is not possible without

information based on the accurate results of instrumental analysis. Results of these

studies have been utilized as far as possible.

2.1 Lithology

The drill holes intersect down to length of 250 m a fluctuating sequence of pegmatitic

granites, quartz gneisses and migmatites in which individual intersections of each

lithological type range from 5 m to 30 m. Down to the drilling length of 360 m, below

previous migmatite section, a rather homogeneous unit of medium-grained TGG

gneisses is located. The lowermost part of the sample is composed of veined gneisses

with a small amount of pegmatitic dykes and the hole ends into a mica gneiss unit with

a number of mafic gneiss interbeds (Figure 2-1).

A more detailed description of lithological units is presented in the Tables 2-1 and 2-2.

Table 2-1. Lithology of the drill core sample OL-KR20.

Drilling

length (m) Lithology

40.78 - 42.05 PEGMATITIC GRANITE which is rather homogeneous and contains

ca. 5% gneiss inclusions and dark porphyroblasts.

42.05 - 43.93 DIATEXITIC GNEISS in which subsections of diatexitic gneiss,

veined gneiss looking and homogeneous, mica gneiss looking rocks

alternate. The proportion of leucosome varies between 5 and 40%.

43.93 - 51.35 QUARTZ GNEISS which, for the most part, is homogeneous and

medium- or fine-grained. The section contains sporadically biotite rich

subsections and, in places, the rock resembles veined gneisses. The

average amount of leucosome is 10% and the rock is intersected by

several, 10 – 80 cm wide pegmatite veins.

51.35 - 63.60 VEINED GNEISS in which 1 – 5 cm wide leucosome veins compose

30 – 40 % of the rock volume. The rock changes to diatexitic gneiss

which contains close to 50% leucosome at the drilling length of 59 m.

63.60 - 68.20 PEGMATITIC GRANITE which is reddish, coarse grained and

porphyritic for a part.

9

0

-50

-100

-150

-200

-250

-300

-350

-400

-450

OL.208

OL.209OL.210

OL.211

OL.212

OL.213

OL.214

OL.215

OL.216

OL.217

OL.218

OL.219OL.220

Drilling Lithology Sample Leucosome

0% 100%Length (m)

Figure 2-1. Lithology, leucosome + pegmatite material percentage (= leucosome) and

sample locations, drill core OL-KR20.

Granite/pegmatitic granite

TGG gneiss

Quartz gneiss

Mafic gneiss

Mica gneiss

Veined gneiss

Diatexitic gneiss

Stromatic gneiss

10

more that 50% paleosome. In the migmatites of the whole section the

proportion of leucosome varies between 10 and 60 %.

68.20 - 73.50 DIATEXITIC GNEISS in which the type of paleosome varies from

rather homogeneous, quartz gneisses and greenish mafic gneisses to

biotite rich variants which are strongly migmatitized and may contain

73.50 - 81.50 PEGMATITIC GRANITE the texture of which varies from coarse-

grained, porphyritic type to medium- and even-grained, leucocratic

type. At the end of the section, from the drilling length of 76.50 m

onward, the rock is strongly altered and contains a couple of percents

mica rich inclusions.

81.50 - 83.35 DIATEXITIC GNEISS the texture and migmatite structures of which

vary remarkable in different subsections. Leucosome dykes, typically 1

– 10 cm in width, compose ca. 40% of the rock volume.

83.35 - 87.60 PEGMATITIC GRANITE which is reddish or grayish in tone, coarse-

grained and leucocratic. The rock contains ca 10% dark, 10 – 20 cm

wide zones some of which are composed of almost pure biotite.

87.60 - 96.35 VEINED GNEISS in which the proportion of 1 – 5 cm wide leucosome

dykes is ca. 30%.

96.35 - 101.15 PEGMATITIC GRANITE which is coarse-grained, porphyritic for a

part and contains 2 – 3% narrow, randomly situated biotite schlieren

and mica gneiss inclusions.

101.15 - 102.10 DIATEXITIC GNEISS the migmatite structure of which is irregular

and which contains ca. 30% leucosome.

102.10 - 104.10 PEGMATITIC GRANITE which, for a part in the beginning of the

section, is porphyritic and contains 10 – 20% mica gneiss inclusions. In

the lower part the pegmatite is coarse-grained and leucocratic.

104.10 - 107.00 DIATEXITIC GNEISS in which the amount of leucosome and

pegmatite dykes exceed 50%.

107.00 - 110.00 QUARTZ GNEISS which is medium- to fine-grained, greenish mica

gneiss for a part and intruded by 10 – 20 cm wide pegmatite dykes in

addition to 1 – 2 cm wide leucosome veins which together compose ca.

10% of the rock volume.

110.00 - 129.50 VEINED GNEISS the paleosome of which is medium-grained and

contains ca. 25% leucosome dykes. In addition, the rock is intruded by

10 – 30 cm wide pegmatite dykes.

11

129.50 - 134.35 PEGMATITIC GRANITE which is coarse- to fine-grained and

leucocratic but includes rather large garnet grains and occasionally also

mica gneiss inclusions and biotite schlieren. The pegmatite is

pervasively rather strongly altered.

134.35 - 136.45 STROMATIC GNEISS in which the proportion of leucosome is ca.

10% and the paleosome of which shows a distinct metamorphic

banding.

136.45 - 144.15 QUARTZ GNEISS-MICA GNEISS- mixture in which quartz gneisses

are fine- to medium-grained and mica gneisses typically medium-

grained. The mixture contains a small amount of leucosome and is

intruded by pegmatite dykes which are 10 – 40 cm in width.

144.15 - 162.95 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

contains some garnet grains. Mica gneiss and quartz gneiss inclusions

compose ca. 5% of the rock volume.

162.95 - 171.20 DIATEXITIC GNEISS in which the leucosome builds up ca. 50% of

the rock volume. The migmatite structure varies and it is possible to

find all kinds of variants from homogeneous gneisses to veined gneisses

and diatexitic gneisses. The rock is intruded by a few, 10 – 50 cm wide

pegmatite dykes.

171.20 - 173.00 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

contains large garnet grains and mica gneiss inclusions and biotite

schlieren ca. 20% in total.

173.00 - 177.20 QUARTZ GNEISS which is homogeneous, fine-grained and contains

banded, medium-grained and cordierite bearing mica gneiss interbeds.

A small amount of leucosome (max. 10%) is typical for these gneisses.

177.20 - 179.55 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

pervasively altered, epidote bearing.

179.55 - 181.70 DIATEXITIC GNEISS with veined gneiss-like and stromatic gneiss-

like subsections. Pegmatite dykes and ca. 50% content of leucosome are

typical for this section.

181.70 - 195.70 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

contains ca. 5% mica gneiss inclusions and biotitic schlieren.

195.70 - 197.20 VEINED GNEISS in which the proportion of leucosome is ca. 50%.

197.20 - 199.05 PEGMATITIC GRANITE which is coarse-grained for a part and

medium-grained for a part. Average content of mica gneiss inclusions is

5%.

12

199.05 - 207.65 VEINED GNEISS the paleosome of which is medium-grained and

certain layers in it may contain a lot of cordierite. Leucosome dykes are

typically 1 – 5 cm wide and they compose ca. 20% of the rock volume.

207.65 - 212.35 PEGMATITIC GRANITE which is leucocratic, medium- or coarse-

grained but contains gneiss-like subzones and gneiss inclusions and

biotite schlieren ca. 10%.

212.35 - 212.90 VEINED GNEISS the paleosome of which is medium-grained and

certain layers in it may contain a lot of cordierite. Leucosome dykes are

typically 1 – 5 cm wide and they compose ca. 20% of the rock volume.

212.90 - 214.45 MAFIC GNEISS which is medium-grained and homogeneous but

intruded by a few pegmatitic granite dykes.

214.45 - 223.85 VEINED GNEISS the paleosome of which is medium-grained. The

leucosome is found as 0.5 – 3 cm wide veins and they build up ca. 15%

of the rock volume. In addition, the migmatite is intruded by 10 – 80

cm wide pegmatite dykes.

223.85 - 226.25 PEGMATITIC GRANITE which is coarse-grained and contains a

couple percent of biotite schlieren. The rock is pervasively altered and

contains at least a remarkable amount of epidote.

226.25 - 230.95 VEINED GNEISS the paleosome of which is medium- or fine-grained

and poor in biotite but homogeneous and, in places, richer in biotite.

The average proportion of leucosome is 10 – 15%.

230.95 - 236.10 STROMATIC GNEISS in which the leucosome dykes are narrow, less

than 1 cm in width and compose ca. 10% of the rock volume. The

paleosome is medium- or fine-grained, contains quite a small amount of

biotite and cordierite grains. Pegmatite dykes, 10 – 40 cm in width,

intersect the migmatite.

236.10 - 241.20 MICA GNEISS – STROMATIC GNEISS-mixture the paleosome of

which is light, homogeneous and medium- or fine-grained but has

narrow mafic gneiss interbeds in places. Leucosome composes ca. 10%

of the rock volume.

241.20 - 251.40 VEINED GNEISS the paleosome of which is amphibole bearing for a

part but mostly typical, mica rich, banded gneiss. The rock changes to

TGG gneiss-like rock at the end of the section. Leucosome dykes are

typically 1 – 5 cm wide and compose ca. 30% of the rock volume. In

addition, more wide pegmatite-like dykes have been met sporadically.

251.40 - 261.40 TGG GNEISS which is medium-grained, contains garnet

porphyroblasts and has a blastomylonitic texture. The rock contains

leucosome ca. 20% and is intruded by several pegmatite dykes.

13

261.40 - 265.20 PEGMATITIC GRANITE which is grayish, coarse-grained and

contains dark porphyroblasts in places. Biotite schlieren and mica

gneiss inclusions compose ca. 5% of the rock volume.

265.20 - 273.40 TGG GNEISS which is medium-grained, contains garnet

porphyroblasts and has a blastomylonitic texture. The rock contains

leucosome ca. 20% and is intruded by several pegmatite dykes.

273.40 - 275.50 PEGMATITIC GRANITE which is grey and contains some biotite.

275.50 - 279.00 TGG GNEISS which is medium-grained, contains garnet

porphyroblasts and has a blastomylonitic texture. The rock contains

leucosome ca. 20% and is intruded by several pegmatite dykes.

279.00 - 283.40 DIATEXITIC GNEISS in which the proportion of leucosome is large,

typically 60 – 80% and which is intruded by several pegmatite dykes.

283.40 - 286.70 MICA GNEISS which is medium-grained, homogeneous and

amphibole bearing for a part. Narrow leucosome dykes compose ca. 5%

of the rock volume.

286.70 - 317.40 TGG GNEISS which is medium-grained and blastomylonitic. Augen-

like feldspar aggregates, typically 5 – 10 mm in diameter, are typical

for a part of the section while the other part is composed of gneissic,

more homogeneous and even-grained rock. Pegmatite dykes, 2 - 10 cm

in width, have been met thoroughly the section.

317.40 - 319.90 PEGMATITIC GRANITE which is grey, coarse-grained and

leucocratic. The pegmatite contains ca. 2% mica gneiss inclusions and

biotite schlieren.

319.90 - 324.05 TGG GNEISS in which the proportion of leucosome is ca. 5% and

which is intruded by 10 – 50 cm wide pegmatite dykes.

324.05 - 325.95 PEGMATITIC GRANITE which is grey, coarse-grained and

leucocratic and contains ca. 5% mica gneiss inclusions.

325.95 - 359.20 TGG GNEISS which, for a part, is medium-grained and

blastomylonitic and, for a part, rather coarse-grained rock the fabric of

which resembles pegmatitic fabric. The other part resembles veined

gneisses that compose of fine- or medium-grained paleosome and

narrow leucosome veins the typical proportion of which not exceeds

10%.

359.20 - 374.30 VEINED GNEISS in which the proportion of leucosome is relatively

low, typically 10% at most. The paleosome is homogeneous, fine- to

medium-grained and poorly oriented. At the drilling length of 366.00 m

the rock changes to stromatic gneiss or banded gneiss in which 1 – 5

14

mm wide biotite bands exists at intervals of 1 - 5cm. At the end of the

section, the paleosome is rather homogeneous and the rock is gneiss

looking.

374.30 - 414.20 VEINED GNEISS the paleosome of which is homogeneous and shows

a distinct metamorphic banding. The leucosome veins are 1 – 5 cm

wide and compose 20 - 40% of the rock volume.

414.20 - 416.60 PEGMATITIC GRANITE which is coarse-grained, biotite bearing and,

for a part, greenish.

416.60 - 424.05 VEINED GNEISS the paleosome of which is homogeneous and shows

a distinct metamorphic banding. The leucosome veins are 1 – 5 cm

wide and compose 20 - 40% of the rock volume.

424.05 - 427.40 PEGMATITIC GRANITE which is greenish in color and pervasively

saussuritized.

427.40 - 428.60 VEINED GNEISS which is strongly crushed.

428.60 - 441.20 QUARTZ GNEISS which changes at the drilling length of 430 m to

mica gneiss and at the length of 431.50 m to veined gneiss the

paleosome of which is banded for a part but rather homogeneous for a

part. The proportion of leucosome is 50 - 20%.

441.20 - 449.35 PEGMATITIC GRANITE which is coarse-grained, contains some

biotite and also large garnet porphyroblasts. The uppermost part of the

section contains 40 – 50 cm wide gneiss inclusions.

449.35 - 454.40 VEINED GNEISS the paleosome of which is homogeneous, greenish

and hornblende bearing for a part but the major part of it is composed

of banded, garnet bearing mica gneiss. The average proportion of

leucosome is 15%.

454.40 - 457.90 PEGMATITIC GRANITE which is coarse- or medium-grained, rather

homogeneous but contains ca. 20% dark gneiss inclusions.

457.90 - 480.00 VEINED GNEISS the paleosome of which is typically banded and

proportion of leucosome ca. 30%. In addition, the migmatite is intruded

by 20 – 80 cm wide pegmatite dykes.

480.00 - 486.60 STROMATIC GNEISS in which the leucosome dykes are 0.5 – 3 cm

wide and rather linear and planar. They compose ca. 10% of the rock

volume.

486.60 - 494.72 MICA GNEISS- MAFIC GNEISS mixture in which the both

components are fine- to medium-grained, homogeneous. The mixture

15

contains up to 5 – 10% leucosome and it is also intruded by 5 – 20 cm

wide pegmatite dykes.

Table 2-2. Lithology of the drill core sample OL-KR20B.

Drilling

length (m) Lithology

13.70 – 17.20 DIATEXITIC GNEISS which, for a part, is composed of irregular,

diatexite type migmatite in which the paleosome is cordierite bearing

and the contacts between paleosome and leucosome are irregular and

diffuse. The proportion of leucosome is close to 40% in that rock.

Medium-grained, cordierite bearing mica gneisses have also been found

in the section, and in those the proportion of leucosome ranges typically

between 5 and 15%.

17.20 – 20.85 MICA GNEISS-QUARTZ GNEISS mixture which is fine-grained,

homogeneous and contains up to 10% leucosome veins. In addition, the

rock is intruded by 5 – 10 cm wide granite pegmatite dykes.

20.85 – 25.30 VEIN GNEISS – DIATEXITIC GNEISS mixture in which the

migmatite structure alternates randomly as well as the proportion of

leucosome which ranges from 0 to 80%.

25.30 – 28.20 QUARTZ GNEISS-MICA GNEISS mixture in which homogeneous,

fine-grained gneisses are intruded by 5 – 20 cm wide granite pegmatite

dykes. Narrow, 10 – 20 cm wide, mafic-looking interbeds have been

met sporadically. The proportion of leucosome is ca. 10 – 20%.

28.20 – 30.75 MICA GNEISS which is medium-grained and contains some cordierite

porphyroblasts. The proportion of leucosome and intruding pegmatite

material is 10 – 20%.

30.75 – 36.80 MICA GNEISS-QUARTZ GNEISS mixture in which the gneisses are

fine- or medium-grained and which contains some greenish, 1 – 10 cm

wide and probably mafic interbeds and up to 10% leucosome.

36.80 – 45.10 DIATEXITIC GNEISS in which gneiss blocks of variable size and

composition are surrounded by a mass composed of heterogeneous

pegmatitic granites and augen gneiss-like rocks.

2.2 Whole Rock Chemistry

Whole rock chemical composition is analysed from 15 samples from the drill core OL-

KR20. The T series is represented by six samples of which two are diatexitic gneisses

16

and four veined gneisses. The P series is represented by one mafic gneiss sample, two

veined gneiss samples, three mica gneiss samples and three TGG gneiss samples. The

numerical results of the whole rock analyses are represented in the Appendix 1.

Chemical compositions of the T type migmatites are moderate. SiO2 concentrations fall

between 60 and 68 % while those in the whole series range from ca. 50% close to 80%.

Major element concentrations are exactly in the anticipated values (Fig. 2.2). The

concentrations of magnesium are very low which is typical for this type of gneisses.

Alkalis are the only elements which seem to have been controlled by the type of

migmatite structure even if the influence is not drastic. Total alkali concentration

(Na2O+K2O) is close to 7% in the T type diatexitic gneisses while that in the veined

gneisses is ca. 6% (Appendix 1). In general, this deviation is not characteristic for these

migmatite types. Trace element concentrations are close to identical in all these samples

and in typical values for the T type migmatites. The only remarkable difference is

visible in the concentrations of Y and Yb (Fig. 2.3) since those are noticeably depleted

in these diatexitic gneiss variants when compared to typical T type migmatites. Similar

difference is visible in the REE diagrams (Fig. 2.3). Light REE concentrations are in

typical numbers for the T type migmatites but heavy REE´s from Dy to Lu are depleted

from normal concentrations.

The P series is represented by a group of migmatites and gneisses which represents

extensively the whole P series. SiO2 concentration in the mafic gneiss variant is ca. 48%

while it in the most silicic TGG gneiss is close to 78%. The concentration of

phosphorus follows the typical trend of the P series. P2O5 concentration is close to 2%

in the mafic gneiss and decreases close to 0.3% in the acidic migmatites and TGG

gneisses. In other respects the compositions are typical for the P series. TiO2

concentration decreases from 2.5 % to 0,5%, Fe2O3 from 12% close to 4%, MgO from

4.5 to 1.0%, and CaO from 7 to 2% as SiO2 increases from 48 to 68% (Fig. 2.2). Al2O3

concentration is constant, between 16 and 17% in every sample in spite of variation in

silicity.

The behaviour of elements mentioned above follows linear, decreasing trends controlled

directly by the silicity. Then concentration of sodium seems to have an increasing trend

from 1% in the most basic migmatite to 4% in the most silicic migmatites and TGG

gneisses. Opposite to that, the K2O concentrations in the mica gneisses and migmatites

seem to follow a natural, slightly decreasing trend from 3.5% in the darkest migmatite

to 2% in the most silicic one (Appendix 1). TGG gneisses deviate from that trend as

they contain K2O 3.5 – 4.5% which is ca. 2 percentage units higher number than in the

corresponding migmatites. This seems to be a systematic feature for the whole P series.

REE diagrams (Fig. 2.3) demonstrate evidently that the REE concentrations are higher

in the mafic gneisses and in less silicic migmatites than in silicic migmatites and TGG

gneisses. Essentially, this trend is quite linear for the most REE´s (Appendix 1). The

same difference is weakly distinguishable also in the HFSE concentrations (element

from Nb to Yb) while LILE concentrations are quite identical in all P-type gneisses

(Fig. 2.3).

17

40 50 60 70 800

10

20

SIO2

AL

2O

3

40 50 60 70 800

1

2

3

4

5

SIO2

TIO

2

40 50 60 70 800

10

20

SIO2

FE

2O

3

40 50 60 70 800

10

20

30

SIO2

MG

O

40 50 60 70 800

10

20

SIO2

CA

O

40 50 60 70 800

1

2

3

4

SIO2

P2

O5

Symbols: = mafic gneiss (S- or P-series), = veined gneiss, = diatexitic gneiss,

= mica gneiss, = quartz gneiss, = TGG gneiss, diabase, = mafic

metavolcanic rock and = pegmatitic granite from the drill core OL-KR20. =

sample from some other drill core.

Explanation for the colours: blue = T-series, orange = S-series, violet = P-series, red =

granite, green = mafic metavolcanic rock and black = diabase.

Figure 2-2. Chemical variation diagrams, Harker diagrams (weight percentage values)

for the rocks of the drill core sample OL-KR20.

18

0.1

1

10

100

1000

3000

Sr

U

K

Rb

Cs

Ba

Th

Ce

P

Ta

Nb

Sm

Zr

Hf

Ti

Y

Yb

Sa

mp

le/N

-Ty

pe

MO

RB

A.

1

10

100

700

La

Ce

Pr

Nd Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

Sa

mp

le/C

1 C

ho

nd

rit

e

B.

Figure 2-3 A. Multielement diagram and B. REE-diagram showing the enrichment

factors for the samples from the drill core OL-KR20. Symbols as in the Fig. 2-2.

19

2.3 Petrography

Modal mineral compositions and textures have been determined from the same 15

samples that have been selected for chemical analysis. The T series is represented by six

samples of which two are diatexitic gneisses and four are veined gneisses. One mafic

gneiss, two veined gneiss, three mica gneiss and three TGG gneiss samples belong to

the P series. Modal mineral compositions of these samples are given in the Appendix 2.

T series

Veined gneisses (samples 210, 211, 213 and 218) represent moderate compositional

variants among the whole sequence of the T-type veined gneisses. Quartz content

ranges from 21% to 33% but not strictly following the increase in silicity. Plagioclase

content is roughly 30% in every sample and K-feldspar varies from 2% to 7%. Biotite

composes 22% - 32% and cordierite with its retrograde derivatives less than 10% of the

rock volume. Sillimanite is a typical accessory phase for all these samples. Opaque

minerals compose 0.5 – 2% of the rock volume and most typical phases are pyrrhotite,

pyrite and hematite with minor chalcopyrite, zinc blende and arsenopyrite.

Textures of paleosome materials are of two kinds. The samples OL.210 and OL.213

have a medium-grained paleosome which shows a distinct metamorphic banding.

Lengths of mica scales vary from 1 to 1.5 mm and their orientation follows mostly the

strike of darks bands. Segregation of mafic and felsic minerals is not perfect and the

borders between the dark and light bands are not extremely sharp but still well

demonstrable. The dark bands are often 1 - 2 mm wide while the light ones are a little

wider. The light bands may contain some biotite and diameters of roundish quartz and

feldspar grains in those are 1 mm at most. No lattice or mineral shape preferred

orientation is possible to detect from the components of the light bands and which are

granoblastic, as a whole. The samples OL.211 and OL.218 are coarser-grained and not

so clearly banded. They contain leucocratic, lensoidal spots or patch the diameters of

which range from 5 to 10 mm at least and which are composed of granoblastic quartz

feldspar mass in which the diameters of individual grains vary from 1 to 3 mm. The

dark “groundmass” surrounding the light spots is composed almost purely of micas and

other mafic minerals. Mica scales are 1 – 2 long as well as the diameters of cordierite

grains or pinite aggregates. Sillimanite is systematically situated between mica scales in

the dark bands. All these gneisses show features of low degree of alteration as the

cordierite is mostly strongly pinitized but plagioclase is pigmented only for a small part

by saussurite and a few biotite scales are chloritized.

The T-type diatexitic gneiss samples (OL.212 and OL.222) have close to median

chemical composition in this subgroup. On the contrary, mineral compositions of their

paleosomes deviate evidently. The less silicic sample, OL.212 contains ca 30% quartz,

40% plagioclase, only a minor amount of K-feldspar and 22% biotite. For the other

sample the values are 40% quartz, 13% plagioclase, 17% K-feldspar and 4% biotite and

close to 10% muscovite. The sample OL.212 contains a small proportion of garnet but

no cordierite while the other includes a little fresh cordierite and 3% pinite. In addition,

20

they contain disseminated grains of pyrite, pyrrhotite and chalcopyrite and in the sample

OL.222 also pyrite veins.

Textural dissimilarity is also evident. The paleosome in the sample OL.212 is fine-

grained and shows a clear metamorphic banding. Segregation of mafic and felsic

minerals is not complete, but 1 – 2 mm wide dark bands include the most of biotite and

in the light parts only some traces of micas are visible. Sulphides and oxides are also

concentrated into the dark bands. Biotite scales are 0.5 – 1 mm long in average and the

diameters of roundish, felsic mineral grains are about the same. The sample OL.222 is

medium-grained. Quartz grains in it are roundish and their average diameters ca. 3 mm.

The feldspar grains show more features of hypidiomorphism and the grains are 3 – 5

mm in diameter. Biotite scale piles have roughly the same diameter but they are more

angular. As a whole, the sample is granoblastic, weakly if not at all orientated and

medium-grained.

The sample OL.212 is relatively fresh and only plagioclase is saussuritized for a part. In

the sample OL.222 the degree of retrogressive alteration is higher. Cordierite is almost

totally pinitized, more than half of biotite is chloritized and large proportion of

plagioclase is pervasively saussuritized or at least pigmented by fine-grained material.

P series

The Mafic P-type gneiss sample, OL.219 is a typical hornblende bearing gneiss in this

sequence. It contains ca. 7% hornblende, 34% biotite, 34% plagioclase and 18% quartz.

Sphene and apatite are the most typical accessories and pyrrhotite, pyrite and

chalcopyrite the most frequent opaques.

Mafic minerals compose a network of 1 – 3 mm wide dark bands which enclose 3 – 6

mm wide, lens-shaped leucocratic spots of the rock. These are composed merely of

plagioclase and quartz, the diameters of which vary typically between 0.5 and 1 mm.

Dark seams contain in addition to hornblende and biotite also some plagioclase. Mafic

minerals are fairly well orientated along the strike of the dark bands but not even the

shape orientation is perfect. The sample is rather fresh by containing only slightly

saussuritized plagioclase while the other species are not at all altered.

The Mica gneisses of the P series (OL.209, OL.220 and OL.221) are typical mica rich

rocks in which apatite and sphene are common accessories. Biotite composes 30 – 35%,

plagioclase 30 – 45% and quartz 25 – 30% of the rock volume. Opaques compose less

than 1% of the rock volume and the most typical phases are pyrrhotite, pyrite and

chalcopyrite with a small amount of ilmenite.

The gneisses are fine-grained and their texture will classify more likely as granoblastic

than schistose. Felsic grains are roundish and their diameter is 0.5 mm in average.

Biotite scales are about the same size and they are randomly located among the felsic

minerals. No features of development of metamorphic banding are visible and mica

orientation is more or less random. Thus, the rock is not very well cleavable in any

direction but it can be evaluated physically close to isotropic. The samples are rather

21

fresh since only a small proportion of plagioclase is pigmented by microcrystalline

saussurite.

The Veined gneiss samples OL208 and OL.214 are biotite rich rocks in which 2 – 3%

apatite has been detected. The content of plagioclase is close to 30% in every sample

but biotite content varies from 17 to 41% and quartz from 45 to 19%. The decrease of

quartz content follows directly the decrease in silicity. The samples contain some

cordierite which is not typical constituent for the P-type rocks. Opaque phases are

composed of pyrrhotite, ilmenite and chalcopyrite.

The paleosome in the lighter sample, OL.208 shows a distinct metamorphic banding.

Narrow, 1 – 2 mm wide biotite bands build up an anastomosing network into the

leucocratic, quartz feldspar mass. The rock contains leucocratic spots which are of

variable size and typically somehow lensoidal in shape. Biotite scales in the dark bands

follow roughly the strike of dark bands but cleavage along dark bands is not perfect due

to wavy strike of those bands. The darker sample, OL.214 shows features of minor scale

augen structure by containing 4 – 8 mm long, lens-shaped spots in mica rich matrix.

Leucocratic spots are composed of granoblastic quartz-plagioclase mass in which

individual grains are somehow roundish and have diameters varying from 0.5 to 1 mm.

Dark parts are composed of approximately 1 mm long biotite scales with smaller grains

of felsic minerals. Preferred orientation of micas is not perfect. Apatite is concentrated

into the dark bands as individual crystals and inclusions of biotite. Degree of secondary,

retrogressive alteration is low as only the few cordierite grains are pervasively altered

and plagioclase is only for a small part pigmented by saussurite and minor part of biotite

is chloritized.

The P-type TGG gneisses (OL.215, OL.216 and OL.217) have mineral assemblage

typical for this sequence. The contain 20 – 32% quartz, 32 – 43% plagioclase, 13 – 26%

biotite and less than 20% K-feldspar. Apatite is a typical accessory species and pyrite,

chalcopyrite and magnetite compose the major part of opaques.

Texturally all the samples are roughly similar. Metamorphic banding and asymmetric

structural elements typical for high-grade, blastomylonitic fault rocks can be identified

in those. Elongated, lens-shaped spots which are 3 – 8 mm wide and 5 – 20 mm long

can be seen in everyone. These light spots are composed of granoblastic quartz-feldspar

material in which the diameters of individual grains vary from 1 to 2 mm.

Approximately 1 mm long biotite scales are located into more dark part or groundmass

which border the leucocratic patches. The degree of secondary alteration is rather low as

only the plagioclase is partially replaced by microcrystalline saussurite.

22

3 PETROPHYSICS

For the petrophysical measurements, the samples were sawn flat, the length of the

samples being typically 5 – 6 cm. The measurements were carried out in the Laboratory

of Petrophysics at the Geological Survey of Finland. Prior to the measurements, the

samples were kept in a bath for 2.5 days using ordinary tap water (resistivity 50 – 60

ohmm). The parameters measured were density, magnetic susceptibility, natural

remanet magnetization and its orientation, electrical resistivity with three frequencies

(0.1, 10 and 500 Hz), P-wave velocity and porosity.

Densities were determined by weighing the samples in air and water and by calculating

the dry bulk density. The reading accuracy of the balance used is 0.01 g and the

repeatability for average-size (200 cm3) hand specimens is 2 kg/m

3.

Porosities were determined by the water saturation method: the water-saturated samples

were weighed before and after drying in an oven (three days in 105 C). The reading

accuracy of the balance used for porosity measurements is 0.01 g. The effective porosity

is calculated as follows:

P=100 · (Mwa - Mda)/ (Mwa - Mww) (1)

where Mda = weight of dry sample, weighing in air

Mwa = weight of water-saturated sample, weighing in air

Mww = weight of water-saturated sample, weighing in water

P = porosity.

The magnetic susceptibility was measured with low-frequency (1025 Hz) AC-bridges,

which are composed of two coils and two resistors. Standard error of the mean for

repeated measurements is c. 10·10-6

SI.

The remanent magnetization was measured with fluxgate magnetometers inside

magnetic shielding. For repeated measurements, the standard error of the mean is c.

10·10-3

A/m.

The specific resistivity was determined by a galvanic method using the MAFRIP

equipment, constructed at the Geological Survey of Finland. Used frequencies were 0.1,

10 and 500 Hz, allowing also the determination of induced polarization (IP). The

measuring error is less than 2 % within the resistivity range of 0.1 – 100000 ohmm.

To determine the P-wave velocity, the length of the sample and the propagation time

through the sample must be known. An electronic pulse was produced by a pulse-

generator, and the propagation time was measured using echo-sounding elements and an

oscilloscope.

The petrophysical parameters measured are presented in a table in the Appendix 3.

23

3.1 Density and magnetic properties

Variation in density and magnetic properties in crystalline rocks are dominated mainly

by their mineralogical composition, however porosity may have a slight effect in

density. The measured density values for these 15 samples range between 2697 and

2901 kg/m3. The highest values, exceeding 2800 kg/m

3are related to a P-series

hornblende-bearing gneiss and two P-series biotite-rich mica gneiss samples. The

lowest density value (2697 kg/m3) is measured from a T-series vein migmatite, having

also anomalous porosity, 0.79 %.

All the samples are paramagnetic or weakly ferrimagnetic with susceptibility values

ranging from 230·10-6

SI to 990·10-6

SI. In Fig. 3-1a, susceptibility vs. density of the

measured samples is shown. For comparison, the data previously measured from

boreholes OL-KR1 – OL-KR6 are shown in Fig. 3-1b. Most of the samples measured

correspond rather well with the paramagnetic mica gneiss population from OL-KR1 –

OL-KR6. There is one slightly ferrimagnetic veined gneiss sample (number 210),

indicating small amounts of ferrimagnetic minerals.

a) b)

Figure 3-1. Susceptibility vs. density, a) samples 208 – 222, boreholes OL-KR20 and

OL-KR20B, b) data from previously examined boreholes OL-KR1 – OL-KR6.

2400 2600 2800 3000 3200

DENSITY (kg/m3)

10

100

1000

10000

100000

SU

SC

EP

TIB

ILIT

Y (

*10

-6 S

I)

268 samples

OLKILUOTO PETROPHYSICS

GRANITE PEGMATITE

MICA GNEISS GREY GNEISS

AMPHIBOLITE/MAFIC ROCK

CALCULATED VALUES

0.1%

0.5%1%

5%

10%

20%

Data: Boreholes KR1 - KR6

2400 2600 2800 3000 3200

DENSITY (kg/m3)

10

100

1000

10000

100000

SU

SC

EP

TIB

ILIT

Y (

*10

-6 S

I)

15 samples

OLKILUOTO PETROPHYSICS

VEIN MIGMATITE MICA GNEISS

GREY GNEISS HORNBLENDE GNEISS

Data: Borehole KR20, KR20B

BLUE = P-SERIESRED = T-SERIES

24

Since the samples are mainly paramagnetic (susceptibility < 1000·10-6

SI), they usually

do not carry significant remanent magnetization. The measured remanence values are

typically 10 – 40 mA/m, being below the practical detection limit of the measuring

device. There are only two clearly higher remanence values, 120 mA/m, related to

sample 208 (P-series mica gneiss) and 480 mA/m, related to sample 210 (T-series vein

migmatite), indicating small amounts of ferrimagnetic minerals (most probably

pyrrhotite). According to microscopic inspection, the contents of opaque minerals in

these samples are 1.4 % and 1.8 %. The determined orientation of the remanent

magnetization for sample 210 is 304 /58.4 (declination/inclination).

3.2 Electrical properties and porosity

The samples are poor electric conductors with resistivity values ranging from thousands

to hundreds of thousands of ohmmeters. There is a reverse correlation between porosity

and resistivity as indicated in Fig. 3-2a. P-series mica gneisses are usually highly

resistive and less porous than other rock types. The only exception is sample 208, which

is most porous (0.67 %) from the mica gneiss population. Opaque minerals also have a

slight effect in resistivity, as indicated in Fig. 3-2b, however this relation is not as

significant.

a) b)

Figure 3-2. Effect of porosity and content of opaque minerals in electric resistivity, a)

porosity vs. resistivity, b) opaque minerals vs. resistivity, OL- KR20 and OL-KR20B.

0 0.5 1.0 1.5 2.0

POROSITY (%)

50

500

5000

50000

500000

RE

SIS

TIV

ITY

(o

hm

m)

10

Hz

15 samples

OLKILUOTO PETROPHYSICS

VEIN MIGMATITE MICA GNEISS

GREY GNEISS HORNBLENDE GNEISS

BLUE = P-SERIESRED = T-SERIES

0 0.5 1.0 1.5 2.0

OPAQUE MINERALS (%)

50

500

5000

50000

500000

RE

SIS

TIV

ITY

(o

hm

m)

10

Hz

15 samples

OLKILUOTO PETROPHYSICS

VEIN MIGMATITE MICA GNEISS

GREY GNEISS HORNBLENDE GNEISS

BLUE = P-SERIESRED = T-SERIES

25

3.3 P-wave velocity

P-wave velocity of rocks depends on their porosity and mineral composition.

Furthermore, the rocks in Olkiluoto, especially mica gneisses, vein gneisses and

migmatites are often anisotropic, resulting anisotropy also in P-wave velocity. Typically

the highest values are measured along the foliation and the lowest ones perpendicular to

it. Measured P-wave velocities are 4670 – 5910 m/s, indicating typically rather

unfractured and unaltered crystalline rocks. In porosity vs. P-wave velocity diagram

(Fig. 3-3), the samples appear to form more or less distinct populations according to

their chemical composition. The highest velocity values are related to P-series samples,

which are mainly mica gneisses. The lowest velocity values are associated to the

samples belonging to T-series veined gneisses.

Figure 3-3. Porosity vs. P-wave velocity, OL-KR20 and OL-KR20B.

0 0.5 1.0 1.5 2.0

POROSITY (%)

4000

4500

5000

5500

6000

P-W

AV

E V

EL

OC

ITY

(m

/s)

15 samples

OLKILUOTO PETROPHYSICS

VEIN MIGMATITE MICA GNEISS

GREY GNEISS HORNBLENDE GNEISS

BLUE = P-SERIESRED = T-SERIES

26

4 FRACTURE MINERALOGY

The account on fracture mineralogy of drill core OL-KR20 aims to following targets:

1. Determinate the position and character of all the open fractures in drill core

sample

2. Produce geological classification of the fracture types

3. Make macroscopic identification of fracture filling phases

4. Visually estimate of filling thicknesses of the open fractures

5. Approximation the percentage that the fracture mineral phase coats of the

fracture plain area.

6. Characterize the occurrence of cohesive/semi cohesive fracture mineral phases

on the fracture plains (cf. chlorite, sericite, graphite, quartz) and the corroded

surfaces

7. Make observations of obvious water flow on the fracture plain

Figure 4-1 summarizes the information of the fracture mineralogy, filling characteristics

and observations of lithology (logged by A. Kärki), hydrothermal alteration (K. Front

and M. Paananen, 2006), zone descriptions (S. Paulamäki et al, 2006) and water

conductivity measurements (Pöllänen et al, 2005).

The borehole OL-KR20 contains 1235 in total, which indicated moderate fracture

density; 2.8 fracture/metre. The chief fracture minerals include illite, kaolinite,

unspecified clay phases (mainly illite, chlorite, smectite-group) iron sulphides (mainly

pyrite, minor pyrrhotite) and calcite. The occurrence of main fracture fillings are given

in the Figure 4-1.

The fracture plains are abundantly covered by cohesive chlorite, which typically forms

the underside for the above-mentioned phases (Fig. 4-1). In addition to that graphite,

quartz and sericite are present in numerous fractures. Iron oxides and oxy-hydroxides

are detected from few fractures at the first three metres of the drilling.

Eight zone intersections are reported from bore hole OLKR20 (Fig. 4-1, column 10).

All these zones are connected either with pervasive illitization, kaolinisation or with

hydrothermally featured fracture filling sequences.

27

100

200

300

400

FILL DEPTHFILL AREA

KAOL-ILL FF

(%)

ILL FF

FILL AREA

(mm)0100

(%)

Sulphides

CALCITE FF

LogK0 0 3 mm Q

UA

RTZ

GR

AP

HIT

E

SE

RIC

ITE

CO

RR

OD

ED

CH

LOR

ITE

0030 3 3(mm)

3 mm 1000

CC

-mo

nom

ine

ral

filli

ng

Py-

mon

omin

eral

fillin

g

OLKR 20

1 2 3 4 5 6 7 8 9 10 11 12 13 16 17 18 17

Fra

ctur

e In

dica

tion

IL+KA+GREEN and

Acid alteration < > Alkaline alteration

(mm)1000

(%)

18

FILL AREA FILL DEPTHGREY CLAY FILLING

FLO

W IN

DIC

.

FILL DEPTH

Per

vasi

ve K

A a

ltera

tion

Per

vasi

ve IL

alte

ratio

n

14 15 19

Lith

olog

y

20

ZONE

1.5

0.5

0.2

0.4

0.3

0.2

0.2

0.4

0.1

0.1

0.2

0.1

0.3

0.2

0.1

0.2

0.3

0.2

0.1

0.5

0.3

0.3

0.3

0.1

0.5

0.1

0.1

0.1

0.6

0.7

1.0

0.2

0.3

0.4

0.6

0.1

0.2

0.3

0.2

0.2

0.7

0.8

Figure 4-1.

28

Table 4-1. Explanations of the columns in Fig. 4-1.

4.1 Fracture fillings at the major pervasive alteration zones

The fracture filling phases have a close relation with the hydrothermal flow system.

Pervasive illitic and kaolinite alteration, which occur either jointly or independently, are

found only in few drill core transverses (Tables 4-2 and 4-3) which range in length from

Column No. Explanation

1Water conductivity measurement with 2 m packer interval. data from Pöllänen, Pekkanen, Rouhiainen 2005, KR20

2 Sulphide as monomineralic fracture filling

3 Sulphide fracture filling (thickness of filling on scale 0 - 3 mm)

4All clay phases in fracture including hydrothermal and secondary phases (thickness scale 0 - 3 mm)

5Lithology of drill core, see legend for the lithology on the right. Data logged by A. Kärki.

6Pervasive illitic alteration of the rock Data from K. Front & M. Paananen 2006.

7Pervasive kaolinite alteration of rock . Data from K. Front & M. Paananen 2006.

8 Fracture density

9

Deformation zone intersection. Brittle fault zone intersection, brittle joint cluster intersection, semi-brittle fault intersection Data from Paulamäki et al 2006.

10Percentage

1of kaolinite illite of the fracture plain area in drill

core section (scale: 0 -100 %)

11Thickness

2 of kaolinite-illite filling in fracture plain area (scale:

0 -3 mm).

12Percentage

1 of illite of fracture plain in drill core section area

(scale: 0 -100 %).

13 Thickness2 of illite filling on fracture plain area (scale: 0 -3 mm).

14 Occurrence of calcite as monomineralic fracture filling

15Percentage

1 of calcite of the fracture plain in drill core section

area (scale: 0 -100 %).

16Thickness

2 of calcite on fracture plain in drill core section

(scale: 0 -3 mm)

17 occurrence of chlorite in fracture plain

18 occurrence of quartz in fracture plain

21 occurrence of graphite in fracture plain

22 occurrence of sericite in fracture plain

23 occurrence of corrosion on fracture plain

24 Indication of flow marks on fracture plain

29

less than metre to 56 metres. The core length of the pervasively altered rock in bore hole

OL-KR 20 is 125 m in total. That makes 25 % of it’s total core length.

Table 4-2. Zones of pervasive kaolinite-illite alteration in OL-KR20. Highlighted in

grey are the zones in which the water conductivity values are raised

Start (m) End (m)

Core length(m)

40.0 96.0 56.0219.0 236.0 17.0

411.0 430.0 19.0

As the drill log data shows (Fig. 4-1) the bedrock has suffered mainly of kaolinite-illite

alteration. These zones of also contain other hydrothermal derivatives; mainly, calcite

and sulphides and unidentified clay phases (see Fig. 4-1). The degree of fracture related

sulphidization is elevated at the drill core length 1.4 - 100 m as well as at the

hydrothermal alteration zones at 180 – 205 m, 410 - 430 m and 464 - 470 m. The

magnitude of hydrothermal illitic alteration is relatively small; only two zones have

been detected. Nevertheless both these zones are also kaolinised and carbonatised.

The water conductivity data reveals a number of peaks that locate inside zones of

alteration. Distinguished in that respect are the core lengths 60.1 and 101 - 110 m

(kaolinite alteration), 190 m (bulky kaolinite-illite-clay-calcite-sulphide fillings, 420 m

(pervasive kaolinite and illite alteration zone, thick clay –calcite and sulphides) and 469

m (pervasive illite alteration + thick calcite, clay and sulphides).

Table 4-3. Zones of pervasive illite alteration in OL-KR20. Highlighted in grey are the

zones in which the water conductivity values are raised

Start (m) End (m)

Core length(m)

411.0 430.0 19.0

464.0 470.0 6.0

4.2 Fracture fillings outside the major hydrothermal fracture zones

At the zones where bore hole cross cuts fracture zones of second-rate hydrothermal

activity, the hydrothermal overprint on lithology is typically meagre; only the fractures

contain the alteration derivatives. These types of fracture zones are described next

within three categories 1) kaolinite-illite fractures 2) illite fractures and 3) calcite

fracture sequences.

30

1. Kaolinite-illitic fracture filling sequences

Fracture sets in which kaolinite ± illite is present as major filling phase are typically

defined by occurrence of calcite and sulphides in same assemblages. Kaolinite-illite

fracture fillings, outside the above mentioned pervasive kaolinite-illite alteration zones

are indicated in the Table 4-4. Kaolinite-illite fracture fillings at 60.54 m and 103 m

(kaolinite-illite accompanied by calcite, sulphides and thick clay) seem to be linked with

water conduction peak values. The same concerns the core length 187.5 – 191 m.

Table 4-4. Kaolinite- illite fracture filling zone (pervasive zones excluded). Highlighted

in grey are the zones in which the water conductivity values are raised.

Illite is dominating in fractures single phase fillings but more typically the fractures

have also variable amounts of kaolinite sulphides and/or calcite. The drill core lengths

of illitic fracture zones are given in the Table 4-5.

Table 4-5. Illite fracture filling zones (pervasive zones excluded). Highlighted in grey is

the zone in which the water conductivity values are raised.

2. Calcitic fracture filling sequences

The calcitic fracture filling sequences are composed of hair dykes or stock works in

which the amount of calcite can reach tens of percents of the rock volume. A number of

Kaolinite-illitealterationStart (m) End (m)

Averagefillingthickness (mm)

Core length(m)

59.9 62.2 0.4 2.375.6 93.2 0.1 17.5

103.1 105.8 0.1 2.8113.3 149.0 0.2 35.7153.4 158.5 0.1 5.1177.2 208.0 0.3 30.8278.9 283.2 0.1 4.3388.1 397.0 0.2 9.0451.3 454.2 0.2 2.9459.0 465.0 0.2 5.9

Start (m) End (m)

Averagefillingthickness (mm)

Core length(m)

188.29 191.56 1.5375 3.3217.96 218.78 0.54 0.8278.69 284.48 0.18 5.8

31

carbonatised zones overlie the pervasive or fracture related kaolinite-illite zones.

Typically the calcitic fracture zones are characterized by higher fracture density than in

the zones in which the influence of hydrothermal activity is insignificant. Calcite is

typically present in the zone intersections (Fig. 4-1, column 10).

A number of the calcite fracture filling sets are less than metre in core section but

individual zone may have core length of 35 metre (see Table 4-6). The total core length

of the calcite fracture sets is 166 metres, thus 33.7 % of the bore hole has calcite as

major infiling phase. Especially the calcitic fracture sequences at 101.8 - 110.9 m, 187 –

192.7 m, 411 – 431 m and 465 – 476 m contain thick calcite fillings/calcite stockworks.

Table 4-6. Calcite fracture filling sequences. Highlighted in grey are the zones which

represent advanced carbonatization and/or coincides with water conductivity peak

value.

4.3 Water flow indication

In number of fractures the secondary (grey – green) clay fillings have textural indication

of having been acting as possible conduits for water flow. The core lengths 49-51 m and

Start (m) End (m)

Averagefillingthickness (mm)

Core length(m)

15.4 50.9 0.3 35.561.7 80.0 0.3 18.285.5 86.3 0.3 0.897.8 98.7 0.1 1.0

102.0 111.4 0.5 9.4

118.0 124.1 0.1 6.1129.6 136.1 0.1 6.5145.7 152.0 0.1 6.3161.7 168.2 0.6 6.5175.8 178.6 0.7 2.8187.0 193.9 1.0 7.0

197.2 198.9 0.2 1.7244.2 245.6 0.3 1.4260.8 262.1 0.4 1.3274.7 278.7 0.6 4.0282.2 286.9 0.1 4.6331.2 336.9 0.2 5.6341.1 352.9 0.3 11.8359.2 360.7 0.2 1.5389.4 393.9 0.2 4.4410.6 431.1 0.7 20.6

466.3 476.0 0.8 9.7

32

79 – 94 m (Table 4-7) sequences in which the flow indication is detected in a number of

fractures (see also Fig. 4-1, column 21).

Table 4-7. Location of open fractures (m), which on textural relations are apparent

conduits of .water flow.

49.26 91.3250.86 91.3750.91 93.6879.03 93.9579.74 94.4381.68 94.782.13 94.73

85 110.4385.49 141.385.54 419.3789.77 419.5890.88

91.09

Iron oxides and oxy-hydroxides occur in 11 fractures as red-brown coloured fillings at

surficial zone. (Table 4-8)

Table 4-8. Fractures (core length in metres) having Fe-oxide and oxy-hydroxide in

fracture fillings.

VGN 1.59VGN 1.66VGN 1.74VGN 1.76VGN 1.9VGN 2.09VGN 2.24VGN 2.55VGN 2.65VGN 3.25VGN 3.43

33

5 SUMMARY

The boreholes OL-KR20 and OL-KR20B start in the NW part of the Olkiluoto study

area which is dominated by various veined gneisses. The drill holes intersect mainly

veined gneisses and pegmatites. The drill hole OL-KR20 intersects down to the length

of 250 m a fluctuating sequence of pegmatitic granites, quartz gneisses and veined

gneisses in which individual intersections of each lithological type range from 5 m to 30

m in length. Down to the drilling length of 360 m, below previous migmatite section, a

rather homogeneous unit of TGG gneisses is located. The lowermost part of the sample

is composed of veined gneisses with a small amount of pegmatitic dykes and the hole

ends into a mica gneiss unit in which a number of mafic gneiss interbeds is detected.

The T series is represented by six samples of which two are diatexitic gneisses and four

veined gneisses. These migmatites are moderate according to their chemical

compositions and their SiO2 concentrations fall between 60 and 68 %. Major element

concentrations are exactly in the anticipated values. The concentrations of magnesium

are very low which is typical for this type of migmatites. Alkalis are the only elements

which seem to have been controlled by the type of migmatite structure even if the

influence is not drastic. Total alkali concentration is close to 7% in the diatexitic

gneisses while that in the veined gneisses is ca. 6%.

The P series is represented by one mafic gneiss sample, two veined gneiss samples,

three mica gneiss samples and three TGG gneiss samples. The assemblage represents

extensively the whole P series as the SiO2 concentration in the mafic gneiss is ca. 48%

and in the most silicic TGG gneiss close to 78%. The concentration of phosphorus

follows typical trend of the P series. P2O5 concentration is close to 2% in the mafic

gneiss and decreases close to 0.3% in the acidic migmatites and TGG gneisses. In other

respects the compositions are typical for the P series.

The Veined gneisses of the T series represent moderate compositional variants among

the whole sequence. Quartz concentration ranges from 21% to 33% but not strictly

following the increase in silicity. Plagioclase content is roughly 30% and K-feldspar

varies from 2% to 7%. Biotite composes 22% - 32% and cordierite with its retrograde

derivatives less than 10% of the rock volume. Sillimanite is a typical accessory phase

for all these samples. Textures of paleosome materials are of two kinds. Sometimes the

paleosome shows a distinct metamorphic banding. Dark bands are 1 - 2 mm wide while

the light ones are a little wider. Certain samples are coarser-grained and not so clearly

banded. These include leucocratic, lensoidal spots or patches the diameters of which

vary between 5 and 10 mm. The dark “groundmass” surrounding the light spots is

composed almost purely of micas and other mafic minerals. The T-type diatexitic

gneisses have close to median chemical composition in their subgroup. Mineral

compositions of their paleosomes are different. One type contains ca 30% quartz, 40%

plagioclase, only a minor amount of K-feldspar and 22% biotite with a small proportion

of garnet while the other includes 40% quartz, 13% plagioclase, 17% K-feldspar, 4%

biotite, close to 10% muscovite and a little fresh cordierite and 3% pinite. The

paleosome in the first sample is fine-grained and shows a distinct metamorphic banding

while the other is medium grained and quartz grains in it are roundish and their average

34

diameters ca. 3 mm. As a whole, the rock is granoblastic, weakly if not at all orientated

and medium-grained.

The mafic P-type gneiss sample analysed from this core is a typical hornblende bearing

gneiss in this sequence. It contains ca. 7% hornblende, 34% biotite, 34% plagioclase

and 18% quartz. Sphene and apatite are the most typical accessories and pyrrhotite,

pyrite and chalcopyrite the most frequent opaques. Mafic minerals compose a network

of 1 – 3 mm wide dark bands which enclose 3 – 6 mm wide, lens-shaped leucocratic

spots of the rock. These are composed merely of plagioclase and quartz. The dark seams

contain in addition to hornblende and biotite also some plagioclase. Mafic minerals are

fairly well oriented along the strike of the dark bands but not even the shape orientation

is perfect. The Mica gneisses of the P series are typical mica rich rocks in which apatite

and sphene are common accessories. Biotite composes 30 – 35%, plagioclase 30 – 45%

and quartz 25 – 30% of the rock volume. The gneisses are fine-grained and their texture

will classify more likely as granoblastic than schistose. The P-type veined gneisses are

biotite rich rocks in which 2 – 3% apatite has been detected. The content of plagioclase

is close to 30% in every sample, biotite content varies from 17 to 41% and quartz from

45 to 19%. The decrease of quartz content follows directly the decrease in silicity. The

samples contain some cordierite which is not typical constituent for the P-type rocks.

The paleosome shows a distinct metamorphic banding. Narrow, 1 – 2 mm wide biotite

bands build up an anastomosing network into the leucocratic, quartz feldspar mass. The

P-type TGG gneisses have typical mineral composition for this sequence and contain 20

– 32% quartz, 32 – 43% plagioclase, 13 – 26% biotite and less than 20% K-feldspar.

Apatite is a typical accessory species. Texturally all the samples are roughly similar.

Metamorphic banding and asymmetric structural elements typical for high-grade,

blastomylonitic fault rocks can be identified in those. Elongated, lens-shaped spots

which are 3 – 8 mm wide and 5 – 20 mm long can be seen in everyone. These light

spots are composed of granoblastic quartz-feldspar material in which the diameters of

individual grains vary from 1 to 2 mm.

Petrophysical properties were measured from 15 samples. Their measured density

values range between 2697 and 2901 kg/m3. The highest values, exceeding 2800 kg/m

3

are related to P-type hornblende-bearing gneiss and two P-type biotite-rich mica gneiss

samples. The lowest density value (2697 kg/m3) is measured from T-type veined gneiss,

having also anomalous porosity, 0.79 %. All the samples are paramagnetic or weakly

ferrimagnetic with susceptibility values ranging from 230·10-6

SI to 990·10-6

SI. The

measured remanence values are typically 10 – 40 mA/m, being below the practical

detection limit of the measuring device. There are only two clearly higher remanence

values, related to one P-type mica gneiss and one T-type veined gneiss sample,

indicating small amounts of ferrimagnetic minerals (most probably pyrrhotite).

The samples are poor electric conductors with resistivity values ranging from thousands

to hundreds of thousands of ohmmeters. There is a reverse correlation between porosity

and resistivity. P-type mica gneisses are usually highly resistive and less porous than

other rock types. Opaque minerals also have a slight effect in resistivity, but this relation

is not as significant.

35

The drill hole OL-KR20 has moderate density of fracturing; 2.8 fractures/metre. The

chief fracture minerals include illite, kaolinite, unspecified clay phases, iron sulphides

and calcite. The fracture plains are occasionally covered by cohesive chlorite, which

typically forms the underside for the other filling phases. Pervasive kaolinisation and/or

illitization concerns 25 % of the total OLKR 20 core length. Respectively, 34 % of the

bore hole has calcite in fracture fillings. The degree of fracture related sulphidization is

elevated at the drill core length 1.4 – 100 m as well as at the hydrothermal alteration

zones at 180 – 205 m, 410 – 430 m and 464-470 m.

The frequency of fracturing is clearly higher at the intervals which have elevated

amount of hydrothermal clay phases. Especially the core lengths 10 – 95 m, 180 – 235

m, 410 – 430 m and 464 – 470 m, where either the zones of fracture related or pervasive

alteration is developed, represent the peaks in fracture density and have elevated water

conductivity values. The zones at core length 49-51 m and 79 – 94 m have flow

indication in their incohesive calcite -clay fracture plains.

36

REFERENCES

Front, K. & Paananen, M. 2006. Hydrothermal alteration at Olkiluoto: mapping of drill

core samples. Working Report 2006-59. Posiva Oy, Olkiluoto.

Gehör, S., Kärki, A., Määttä, T., Suoperä, S. & Taikina-aho, O., 1996. Eurajoen

Olkiluodon kairausnäytteiden petrologia ja matalan lämpötilan rakomineraalit.

Työraportti PATU-96-42. Posiva Oy, Helsinki.

Korsman, K., Koistinen, T., Kohonen, J., Wennerström, M, Ekdahl, E., Honkamo, M,

Idman H. & Pekkala, Y. (editors) 1997. Suomen kallioperäkartta -Berggrundskarta över

Finland -Bedrock map of Finland 1: 1 000 000. Geologian tutkimuskeskus, Espoo,

Finland.

Kärki, A. & Paulamäki, S. 2006. Petrology of Olkiluoto. Posiva 2006-2. Posiva Oy,

Olkiluoto, 77 p.

Mattila, J. 2006. A System of Nomenclature for Rocks in Olkiluoto. Working report

2006-32. Posiva Oy, Olkiluoto. 16 p.

Paulamäki, S., Paananen, M., Gehör, S., Kärki, A., Front, K., Aaltonen, I., Ahokas, T.,

Kemppainen, K., Mattila, J. & Wikström, L. 2006. Geological model of the Olkiluoto

site, version 0. Working Report 2006-37. Posiva Oy, Olkiluoto.

Pöllänen, J., Pekkanen, J., Rouhiainen, P. 2005. Difference flow and electric

conductivity measurements at the Olkiluoto site in Eurajoki, boreholes KR19 – KR28,

KR19B, KR20B, KR22B, KR23B, KR27B and KR28B. Working report 2005-52.

Posiva Oy, Olkiluoto.

Rautio, T. 2002. Core drilling of deep borehole OL-KR20 at Olkiluoto in Eurajoki

2002. Working Report 2002-50. Posiva Oy, Olkiluoto.

Suominen, V. 1991. The chronostratigraphy of southwestern Finland with special

reference to Postjotnian and Subjotnian diabases. Geological Survey of Finland Bulletin

356, 100 p.

Suominen, V., Fagerström, P. & Torssonen, M. 1997. Pre-Quaternary rocks of the

Rauma map-sheet area (in Finnish with an English summary). Geological Survey of

Finland, Geological Map of Finland 1:100 000, Explanation to the maps of Pre-

Quaternary rocks, Sheet 1132, 54 p.

Veräjämäki, A. 1998. Pre-Quaternary rocks of the Kokemäki map-sheet area (in Finnish

with an English summary). Geological Survey of Finland, Geological Map of Finland

1:100 000, Explanation to the maps of Pre-Quaternary rocks, Sheet 1134, 51 p.

37

APPENDICES

Appendix 1.

File KR20_APP1 in the disk enclosed. The Appendix contains the results of whole rock

chemical analyses.

Appendix 2.

File KR20_APP2 in the disk enclosed. The Appendix contains the results of modal

mineral composition analyses.

Appendix 3. Petrophysical parameters, drill core OL-KR20.

RESISTIVITY VALUES ( m) IP-ESTIMATES

HOLE SAMPLE FROM TO D(kg/m3) K( SI) J(mA/m) P-wave (m/s) R0.1[ m] R10 [ m] R500[ m] PL (%) PT (%) Pe(%) KR20 OL.208 47.46 * 2721 500 120 5710 2050 1190 958 42 53 0.67

KR20 OL.209 107.21 107.31 2783 370 10 5790 resistivities > 334864 0.04

KR20 OL.210 114.35 114.45 2727 990 480 5110 6860 6110 5200 11 24 1.19

KR20 OL.211 139.22 139.32 2736 330 40 5550 14700 13700 12000 7 18 0.42

KR20 OL.212 180.45 * 2722 310 20 4670 5410 5230 4880 3 10 1.24

KR20 OL.213 216.40 216.50 2738 340 30 5220 6850 6580 6100 4 11 0.63

KR20 OL.214 247.40 247.50 2864 480 10 5420 resistivities > 334864 0.14

KR20 OL.215 258.90 * 2723 260 20 5500 12300 12000 11500 2 7 0.23

KR20 OL.216 310.35 310.41 2703 230 10 5800 15900 15500 14500 3 9 0.23

KR20 OL.217 350.50 350.58 2702 240 10 5910 20200 19500 17900 3 11 0.21

KR20 OL.218 459.62 459.72 2746 390 30 5540 10300 9510 8240 8 20 0.58

KR20 OL.219 490.61 * 2901 580 20 5400 18900 17000 15100 10 20 0.22

KR20 OL.220 492.36 * 2840 440 10 5370 26200 23400 19900 11 24 0.18

KR20B OL.221 34.64 34.75 2772 410 30 5750 94400 89300 72200 5 24 0.13

KR20B OL.222 44.62 44.72 2697 230 20 5640 2500 2080 1750 17 30 0.79

D = density

K = magnetic susceptibility * The depth value was not readable from the sample

J = remanent magnetization

P-wave = velocity of seismic P-wave

R0.1 = electric resistivity, 0.1 Hz frequency

R10 = electric resistivity, 10 Hz frequency

R500 = electric resistivity, 500 Hz frequency

PL = IP effect = 100*(R0.1-R10)/R0.1

PT = IP effect = 100*(R0.1-R500)/R0.1

Pe = effective porosity

38