Petrology, Petrophysics and Fracture Mineralogy of the

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 -46

Petrology, Petrophysics and FractureMineralogy of the Drill Core Sample OL-KR21

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 -46

Petrology, Petrophysics and FractureMineralogy of the Drill Core Sample OL-KR21

ABSTRACT

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

KR21, 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 hole starts in a pegmatitic granite unit which includes various migmatite

blocks and interbeds and which extends to the drilling length of 19 m. The pegmatite is

underlain by a veined gneiss unit which continues down to drilling length of 57 m. A

rather wide pegmatitic granite unit is intersected between drilling lengths of 57 m and

79 m. Medium-grained, weakly foliated TGG gneisses dominate the next intersection

down to the drilling length of 111 m. The lowermost part of the core sample is

composed of veined gneisses which are intruded by a few pegmatites and have several,

narrow gneiss interbeds.

Detailed Petrological properties have been analysed from 11 samples. Veined gneiss

samples studied in detail from the T series contain SiO2 between 55 and 70 % and thus

the most silicic and most basic types are not represented by the assemblage. However,

chemical compositions of the analysed samples are strictly in anticipated numbers and

typical for the T series. The S-series is represented by one single quartz gneiss sample

which belongs to the high-calcium subgroup by containing close to 8% CaO and more

than 70% SiO2. Four TGG gneiss samples analysed from the drill core will classify to

the P series due to their high content (5- 5% P2O5) of phosphorus. These gneiss varieties

belong to a more silicic half in the P group and contain 62 – 65% SiO2.

Petrophysical properties were studied from 10 samples. The parameters measured were

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

wave velocity and porosity.

Borehole represents a relatively dense fractured rock having 4.1 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. Iron oxides and oxy-hydroxides are present in

fractures at surficial zone, in core length 6.3 – 47 m., while major of graphite

occurrences are concentrated by few fractures inside the core length interval of 41 -53

m. Pervasive illitization concerns 11 % 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 70 metres in maximum. Calcitic fracture fillings and calcite stockworks

occur all along the drill core and the percentage of carbonaceous fractures is as much as

59 % of the bore hole length.

Kairanäytteen OL-KR21 petrologia, petrofysiikka ja rakomineralogia

TIIVISTELMÄ

Tässä raportissa esitetään kairausnäytteitä OL-KR21 koskevien tutkimusten tulokset.

Kyseiset kairanreiät on tehty Olkiluodon tutkimusalueen länsiosaan. Raportissa esite-

tään kairausnäytteen litologiaa sekä valittujen näytteiden kokokiven kemiallista koostu-

musta, mineraalikoostumusta, tekstuuria ja petrofysikaalisia ominaisuuksia käsittelevien

tutkimusten tulokset. Samoin kuvataan matalan lämpötilan raontäytemineraalit.

Kairanreikä alkaa pegmatiittisesta graniittiyksiköstä, johon sisältyy erilaisia migmatiitti-

sulkeumia ja joka ulottuu n. 19 m:n kairauspituudelle saakka. Pegmatiitin alapuolella on

suonigneissiyksikkö, joka jatkuu 57 m:n kairauspituudelle ja sen jälkeen on taas

lävistetty pegmatiitteja kairauspituudelle 79 m saakka. Keskirakeiset ja heikosti

folioituneet TGG-gneissit ovat hallitsevia seuraavassa, 111 m:n pituudelle jatkuvassa

jaksossa. Kairausnäytteen alin osa koostuu suonigneisseistä, joita muutamat pegma-

tiittiset juonet lävistävät ja joissa on runsaasti gneissivälikerroksia.

Petrologiset ominaisuudet on määritetty yksityiskohtaisesti 11 näytteestä. Analysoidut

T-sarjan suonigneissit sisältävät SiO2:ta 55 - 70 % eli vain happamimmat ja emäk-

sisimmät tyypit koko sarjasta puuttuvat. Analysoitujen näytteiden kemialliset koostu-

mukset ovat kuitenkin tyypillisiä ja tiukasti T-sarjalle luonteenomaisissa arvoissa. S-

sarjaa edustaa vain yksi ainut kvartsigneissinäyte, joka luokittuu korkean kalsium-

pitoisuuden alaryhmään sisällettyään lähes 8 % CaO:a ja yli 70 % SiO2:ta. Neljä

kairausnäytteestä analysoitua TGG-gneissinäytettä luokittuu P-sarjaan korkean fosfori-

pitoisuutensa (5- 5 % P2O5) ansiosta. Nämä gneissimuunnokset kuuluvat happa-

mampaan joukkoon P-sarjassa ja sisältävät 62 – 65 % SiO2:ta.

Petrofysikaaliset ominaisuudet on määritetty kymmenestä näytteestä. Mitatut parametrit

ovat tiheys, magneettinen suskeptibiliteetti, luonnollinen remanentti magnetoituma,

sähkövastus, P-aallon nopeus ja huokoisuus.

Kairausnäytteen OL-KR21 rakotiheys on suhteellisen korkea, keskimäärin 4,1

rakoa/metri. Rakoilu on painottunut hydrotermisiin muuttumisvyöhykkeisin ja muihin

rikkonaisuusvyöhykkeisiin, 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. Rautaoksideja ja –oksihydroksideja esiintyy useissa raoissa kairaus-

pituusvälillä 6,3-4,7 m ja grafiittia välillä 41-53 m. Kairauslävistyksestä on 11 %

läpikotaisesti illiittiytynyttä. Rakotäytteisiin liittyvän iliitti-kaoliniittimuuttumisen

kairausleikkauspituus on enimmillään 70 metriä. Kalsiittivaltaisia täyteseurantoja

esiintyy 59 %:ssa kairausnäytteen koko pituudesta.

1

TABLE OF CONTENTS

ABSTRACT

TIIVISTELMÄ

1 INTRODUCTION .................................................................................................... 2 1.1 Location and General Geology of Olkiluoto .................................................... 2 1.2 Borehole and Drill Core Sample OL-KR21 ..................................................... 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 ................................................................................. 12 2.3 Petrography .................................................................................................. 16

3 PETROPHYSICS.................................................................................................. 19 3.1 Density and magnetic properties .................................................................. 20 3.2 Electrical properties and porosity.................................................................. 21 3.3 P-wave velocity ............................................................................................. 22

4 FRACTURE MINERALOGY ................................................................................. 23 4.1 Fracture fillings at the major pervasive alteration zones............................... 25 4.2 Fracture fillings.............................................................................................. 26

5 SUMMARY ........................................................................................................... 29

REFERENCES ............................................................................................................. 32

APPENDICES............................................................................................................... 33

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 core OL-KR21.

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-KR21

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 paleosome 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 paleosome 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 paleosome 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 content 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 contents of alkalis and high contents 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 contents of phosphorus. P2O5 content

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 content 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 Borehole and Drill Core Sample OL-KR21

The starting point of the borehole OL-KR21 is situated in the NW part of the Olkiluoto

study site (Figure 1-1). The coordinates of the starting point are: X = 6792706.86, Y =

1525473.47 and Z = 7.79. Starting direction (azimuth angle) of the borehole is 40o and

its dip (inclination angle) is 29.6o. Technical data dealing with the OL-KR21 drilling is

represented by Niinimäki (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-KR21. 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),

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

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

6

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 28.7. – 1.8.2003 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 dates 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 11. 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.

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

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

7

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.

2.1 Lithology

The drill hole starts in a pegmatitic granite unit which includes various migmatite

blocks and interbeds and which extends to the drilling length of 19 m in the bore hole.

A veined gneiss unit below that is intersected down to drilling length of 57 m. A rather

wide pegmatitic granite unit is intersected between drilling lengths of 57 m and 82 m.

Medium-grained, weakly foliated TGG gneisses dominate the next intersection down to

the drilling length of 111 m. The lowermost part of the core sample is composed of

veined gneisses which are intruded by a few pegmatites and have several, narrow gneiss

interbeds (Figure 2-1). A more detailed description of lithological units is presented in

the Table 2-1.

Table 2-1. Lithology of the drill core sample OL-KR21.

Drilling

length (m) Lithology

2.95 - 5.00 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

contains roughly 10% gneiss inclusions with diameters ranging from

10 to 20 cm.

5.00 - 6.10 DIATEXITIC GNEISS the migmatite structure of which is variable

but always irregular and in which the proportion of leucosome ca.

40%.


contains ca. 5% gneiss inclusions.

8.80 - 11.35 DIATEXITIC GNEISS – MICA GNEISS mixture in which rather

homogeneous gneiss blocks are surrounded by irregular migmatite

material. The lower part of the section is composed of homogeneous

quartz gneiss in which the proportion of leucosome is ca. 10%.

11.35 - 19.30 PEGMATITIC GRANITE, which is coarse-grained, leucocratic and

contains ca. 10% gneiss inclusions. The pegmatite is greenish for the

most part.

19.30 - 29.00 VEINED GNEISS - DIATEXITIC GNEISS mixture which is intruded

by 10 – 70 cm wide pegmatite dykes and includes ca. 15% leucosome.

9

0

-50

-100

-150

-200

-250

-300

OL.223

OL.224

OL.225

OL.226

OL.227

OL.228

OL.229

OL.230

OL.231

OL.232

OL.233

Drilling Lithology Sample Leucosome

0% 100%Length (m)

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

sample locations, drill core OL-KR21.

Granite/pegmatitic granite

TGG gneiss

Quartz gneiss

Mafic gneiss

Mica gneiss

Veined gneiss

Diatexitic gneiss

Stromatic gneiss

10

In places, the paleosome is abnormal homogeneous and it may have

some ghost-like relicts of primary sedimentary structures.

29.00 - 57.20 VEINED GNEISS the paleosome of which ranges from dark,

cordierite rich type to diatexitic gneiss-like variant in which the

proportion of leucosome may exceed 30% and further to

homogeneous mica gneiss and quartz gneiss which are poor in

leucosome. All kinds of migmatite variants from diatexitic gneiss to

veined gneisses and stromatic gneisses have been found in the section.

The migmatite is intruded by 10 – 60 cm wide pegmatitic granite

veins.

57.20 – 78.60 PEGMATITIC GRANITE which is coarse-grained, leucocratic and

for a part epidotized. At the end of the section, the rock contains a lot

of biotite schlieren and gneiss inclusions.

78.60 – 80.20 QUARTZ GNEISS which is fine- or medium-grained and contains ca.

10% leucosome and several, 5 – 10 cm wide pegmatite veins.


rather pure of inclusions.

82.40 – 111.20 TGG GNEISS which is medium-grained, weakly orientated and

lineated and contains occasionally located, medium-grained mica

gneiss interbeds. The proportion of leucosome is 5% in average and

the rock is intruded by narrow, 1 – 5 cm wide pegmatite-like dykes.


ca. 30% biotite schlieren and gneiss inclusions.

113.20 – 120.45 MICA GNEISS - QUARTZ GNEISS mixture in which the gneisses

are medium-grained, homogeneous or show a weak metamorphic

banding. The rock is intruded by 10 – 40 cm wide pegmatitic granites

and the leucosome and pegmatite dykes altogether compose ca. 40%

of the rock volume.

120.45 – 160.70 VEINED GNEISS the paleosome of which is often medium-grained

and banded and contains ca. 30% leucosome as 2 – 5 cm wide veins.

The rock is intruded occasionally by 10 – 30 cm wide, leucocratic

pegmatitic granite dykes and the paleosome changes to more coarse-

grained, TGG gneiss-like rock at the end of the section.

160.70 – 162.55 TGG GNEISS - MICA GNEISS mixture in which the gneisses are

medium-grained, homogeneous and contain ca. 5% leucosome veins.

162.55 – 183.10 VEINED GNEISS which contains a lot of cordierite in places and in

which the paleosome is clearly banded, not very dark and contains

30% 1 – 4 cm wide leucosome veins.

11

183.10 – 184.10 PEGMATITIC GRANITE which is coarse-grained, leucocratic but

contains garnet phenocrysts and is strongly epidotized for a part.

184.10 – 187.70 DIATEXITIC GNEISS which, for a part, resembles the veined

gneisses but is in places rather typical diatexitic gneiss in which the

proportion of leucosome varies remarkably (average proportion of

leucosome is 30 – 40%).


strongly epidotized in places. The pegmatite contains ca. 10% gneiss

inclusions and biotite schlieren.

197.00 – 202.10 VEINED GNEISS in which the leucosome veins are 1 – 4 cm wide

and compose ca. 30% of the rock volume. Typical paleosome is

medium-grained and banded.

202.10 – 203.50 PEGMATITIC GRANITE which is coarse-grained, leucocratic, red

and contains a lot of epidote in places but not gneiss inclusions.

203.50 – 215.85 VEINED GNEISS in which the leucosome veins are 1 – 4 cm wide

and compose ca. 30% of the rock volume and the paleosome is

medium-grained and shows a distinct banding.


strongly epidotized in places. The rock includes 2% dark phenocrysts

and biotite schlieren.

217.90 – 222.30 VEINED GNEISS which changes at the drilling length of 220.20 m a

banded mica gneiss in which he proportion of leucosome not exceeds

5%. The proportion of leucosome is 20% in the veined gneiss.

222.30 – 223.70 PEGMATITIC GRANITE which contains 5% biotite schlieren.

223.70 – 224.95 MICA GNEISS which is medium-grained, rather homogeneous and

contains ca. 10% leucosome veins.


has ca. 5% gneiss inclusions and biotite schlieren.

227.45 – 237.45 VEINED GNEISS the paleosome in which is medium-grained and

shows a distinct metamorphic banding. The proportion of 0.5 – 5 cm

wide leucosome veins is ca. 40%.


contains 5 – 10% gneiss inclusions.

238.90 – 249.05 VEINED GNEISS in which the proportion of leucosome is ca. 30%.

12

249.05 – 251.40 PEGMATITIC GRANITE which is coarse-grained and leucocratic. At

the beginning of the section the rock is strongly epidotized and in the

deeper part it contains a lot, more than 10% of gneiss inclusions.

251.40 – 264.90 VEINED GNEISS the paleosome of which is banded for the most part

but has narrow, homogeneous quartz gneiss interbeds. 1 – 4 cm wide

leucosome veins compose ca. 40% of the rock volume and the

migmatite is intruded by randomly located, 10 – 60 cm wide

pegmatite dykes.

264.90 – 267.50 TGG GNEISS the foot wall contact of which is rather sharp but the

hanging wall contact is an irregular zone of alteration. The rock

contains ca. 10% leucosome in average.

267.50 – 271.70 VEINED GNEISS in which the proportion of leucosome is 30% in

average.

271.70 – 273.70 TGG GNEISS which, for the most part, is a distinct blastomylonite

but which contains homogeneous gneissic subzones. The rock

contains ca. 5% leucosome and, in addition to that, it is intruded by

narrow pegmatite dykes.

273.70 – 301.08 VEINED GNEISS the paleosome of which is typically banded and has

ca. 30% narrow leucosome veins. In addition, the rock is intruded by

10 – 60 cm wide, garnet bearing pegmatite dykes.

2.2 Whole Rock Chemistry

Whole rock chemical composition has been analysed from 11 samples. One of those is

quarts gneiss of the S series. Six veined gneiss samples will classify to the T series and

four TGG gneiss samples have distinct chemical characteristics of the P series.

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

Veined gneiss samples of the T series contain SiO2 between 55 and 70 % and thus the

most silicic and most basic types are not represented by the assemblage. However, the

chemical compositions of the analysed samples are strictly in anticipated numbers. The

concentration of TiO2 decreases from 0.9% to below 0.4% while when silica

concentration measures as SiO2 increases from 55% close to 70% (Fig. 2.2). Similarly

decrease the concentrations of Al2O3 from 20% to 16%, Fe2O3 from 9% to 4%, and

MgO from 3.5% to below 1.5% following the increase in silicity. The concentrations of

calcium and alkaline elements fluctuate randomly but still within typical limits. CaO

concentration is close to 1% in four samples and close to 2% in two samples. Na2O

concentrations behave similarly and the four, Ca poor samples contain ca. 2% Na2O

while the others have 3 – 4% Na2O. Behaviour of potassium is contrary to that of

sodium. CaO poor samples contain ca. 4% K2O while CaO rich samples have ca. 2.5%

K2O.

13

Trace element concentrations are in the typical ranges of the series. Slightly anomalous

values are still analysed from other calcium rich sample (OL.230) in which the

concentrations of Sm, Zr, Hf, Ti, Y and Yb are depleted from most typical values (Fig.

2.3). REE concentrations (Fig. 2.3) of that sample are also anomalous and

systematically lower than in the typical migmatites of the T series. Equally, positive Eu

anomaly is detected only in this single sample of the T series.

The S-series is represented by one single quartz gneiss sample which belongs to the

high-calcium subgroup. CaO concentration of the sample is close to 8% and SiO2

exceeds 70%. Thus the quartz gneiss is one of the most silicic variants in the high-

calcium subgroup of the S-series. Concentrations of other elements are in typical values

of this assemblage. The concentrations of titanium and magnesium are low and the

concentrations of iron and phosphorus moderate (Fig. 2.2). Al2O3 concentration of 13%

is equally low also in the subgroup of acidic gneisses of Olkiluoto. REE and other trace

element concentrations are typical for the gneisses of the S series (Fig. 2.3) and also

similar to the quartz gneisses of the T series.

The four TGG gneiss samples analysed from the drill core will classify to the P series

due to their high concentration (5- 5% P2O5) of phosphorus (Fig. 2.2). These gneiss

varieties belong to the more silicic half of the P series and contain 62 – 65% SiO2. In

other respects, the compositions of the samples are typical for their assemblage. Al2O3

concentration is permanently 16 - 17% despite of change in silicity (Fig. 2.2).

Concentrations of TiO2, Fe2O3, MgO and CaO decrease linearly while SiO2 increases.

REE concentrations and element ratios follow strictly the average trends of the P series

and the same feature is also distinct for the other trace element concentrations (Fig. 2.3).

14

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-KR21. =

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-KR21.

15

0.2

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.

6

10

100

500

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-KR21. Symbols as in the Fig. 2-2.

16

2.3 Petrography

The study of petrography deals with the same 11 samples that were analyzed

chemically. The T series is represented by six samples which all show diverse veined

migmatite structures and will classify as veined gneisses. One quartz gneiss sample has

chemical characteristics typical for the S-type rocks and four TGG gneiss samples have

chemical composition typical for the P Series.

T-series

The T-type veined gneiss samples (223, 227, 229, 230, 231 and 232) represent their

sequence comprehensively as the silicity varies between 55% and 70% (SiO2) which is

close to the whole range analysed from this sequence. Quartz concentration follows

strictly the increase in silicity and the less silicic sample contains quartz ca. 18% and the

most silicic one ca. 36% that (Appendix 2). The content of plagioclase and K-feldspar

varies between 5 and 30% but the total number of feldspars increases systematically

from 10% in the less silicic type to 50% in the most silicic one. Accordingly, the total

number of biotite and its retrograde derivative, chlorite decreases from over 40% in the

less silicic migmatite to below 10% in the most silicic one. Cordierite is strongly

pinitized but primary proportion of cordierite has been 10 – 15% in the less silicic types,

5 – 10% in the moderate types and a couple of percentages in the most silicic one.

Hematite, pyrite, chalcopyrite and pyrrhotite are the most common opaques.

Veined migmatite structure is typical for all these samples but certain variation between

individual samples is visible. Leucosome veins are in the sample OL.227 rather small,

in cross section 5 – 10 mm thick and 10 – 20 mm wide lenses while, in some others, the

diameters of veins may be several centimetres. The leucosomes compose in every case

of leucocratic material the texture of which is coarse-grained and allotriomorphic-

granular. Paleosomes are darker and in real migmatite terminology they are known as

mesosome due to not complete segregation. Average grain size of paleosome materials

varies from fine- to medium-grained. The paleosome of the samples 229, 231 and 232 is

fine grained and moderately banded. Mica scales are 0.5 mm long in average and

concentrated to the dark bands of which they compose more than a half. Dark band are

0.5 – 1 mm wide. The mica scales are not perfectly oriented along the planes of the

wavy, dark bands but the scale directions may deviate tens of degrees from planes of

dark bands. Felsic minerals are a little bigger and typically they are equidimensional and

often somehow roundish. As a whole, the texture of paleosome material is granoblastic

even if weakly banded. Medium-grained varieties of paleosome are also more clearly

banded and in those 1 – 3 mm wide dark band can be seen between a little wider felsic

bands. In these rocks dark band may contain up to 90% biotite and preferred orientation

of approximately 1 mm long mica scales is better than in the fine-grained types. Felsic

bands of the medium-grained gneisses are granoblastic and average diameter of quartz

and feldspar grains is ca. 1 mm. Felsic grain are somehow roundish or they may be

slightly elongated to the direction of dark bands.

The samples 223 and 227 are rather fresh as their biotite is only slightly altered to

chlorite and a mall part of plagioclase is pigmented by microcrystalline saussurite. Only

17

cordierite is strongly pinitized. The rest of samples demonstrate moderate degree of

alteration by containing partially saussuritic plagioclase and chloritized biotite.

S-series

Only one single quartz gneiss sample (224) of the S series has been selected to the

detailed studies. This gneiss is typical hornblende bearing “skarn quartzite”. It contains

close to 50% quartz, 36% plagioclase, 3.8% hornblende and some biotite (Appendix 2).

Sphene and apatite are typical accessories. The sample contains also a small amount of

pyrrhotite, pyrite and chalcopyrite.

The gneiss is fine-grained and granoblastic. All minerals are somehow roundish and no

evidence of mineral shape orientation or foliation development can be imagined. The

sample shows features of moderate alteration. The amphibole is mostly fresh but

plagioclase may be pervasively saussuritized or replaced by rather coarse-grained

epidote.

P-series

The TGG gneisses of the P series represent a rather constricted selection from the

whole sequence as the silicity given as SiO2 ranges only from 62.5% to 64.5%. The

modal mineral compositions are also close to similar. Quartz content varies mainly

between 20 and 25% and plagioclase between 30 and 45% (Appendix 2). K-feldspar

composes often 1 – 7% of the mode but in the sample 233 the content of K-feldspar

increases to 17%. Biotite concentration has been in not altered rocks ca. 25% excluding

the sample 266 which contains 21% biotite and 4% hornblende. Apatite and sphene are

the most typical accessories which count up to a couple percentage units of the mode.

Hematite and pyrite are the most typical opaques with minor amount of pyrrhotite and

other sulphide minerals.

Textures of the TGG gneiss samples are twofold as the others show distinct

metamorphic banding but others contain roundish, 5 – 10 wide quartz feldspar

aggregates or patches surrounded by mica bearing “groundmass”. The later texture can

be designated as mottled texture. The patches (in the samples 226 and 228) are

composed of granoblastic quartz-feldspar mass in which individual grains have average

diameter from 0.5 to 1 mm. Some of those patches are totally leucocratic but they may

contain also some biotite. The “groundmass” is fine-grained and granoblastic but,

diverging from leucocratic patches, it contains 20 – 40% biotite. Orientation of biotite

scales and amphibole grains, if present, is absolutely random. Metamorphic banding is

distinct in the hand specimens and thin sections of the samples 225 and 233. The sample

225 is fine-grained and average diameter of felsic minerals is approximately 0.3 mm.

Biotite scales are typically 0.5 mm long and mostly located in the dark bands which are

0.5 – 1 mm wide and enclosed by 2 – 3 mm wide leucocratic bands. Segregation of

mafic and felsic minerals is not perfect in this sample. The sample 233 is coarser-

grained and metamorphic banding is more advanced. Micas are concentrated into the

0.5 – 1.5 mm wide, dark bands while leucocratic bands are often 2 – 3 mm wide.

Orientation of 1 mm long mica scales follows strictly the wavy strike of the mafic bands

while leucocratic bands are granoblastic, fine- to medium-grained and not at all

18

oriented. All of these samples are rather fresh as only a small part of biotite is

chloritized and a part of plagioclase is pigmented by microcrystalline saussurite.

19

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.

20

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 10 samples range between 2686 and

2787 kg/m3. The highest value is measured from sample 224, which is specified as

skarn or quartzitic gneiss.

All the samples are paramagnetic or weakly ferrimagnetic with susceptibility values

ranging from 270·10-6

SI to 1190·10-6

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 223),

indicating small amounts of ferrimagnetic minerals.

a) b)

Figure 3-1. Susceptibility vs. density, a) samples 223 – 233, borehole OL-KR21, 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)

10 samples


VEIN MIGMATITE GREY GNEISS SKARN

Data: Borehole KR21

BLUE = P-SERIESRED = T-SERIES

GREEN = S-SERIES

21

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 below 50 mA/m, being below the practical detection limit of the measuring

device. However, there are three clearly higher remanence values, 120, 320 and 770

mA/m, related to samples 228 (P-series TGG gneiss), 224 (S-type quartz gneiss) and

223 (T-series veined gneiss), respectively, indicating small amounts of ferrimagnetic

minerals (most probably pyrrhotite). The determined orientations of the remanent

magnetization for samples 223 and 228 are 364.1 /-4.2 and 353.8 /45.4

(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. TGG gneisses and the single quartz gneiss

sample are least porous (< 0.3 %), having also high resistivity values. Migmatites of the

T-series are clearly more porous (0.82 – 2.46 %) with lower resistivity values (c. 1100 –

2600 ohmm). Opaque minerals may 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- KR21.

0 0.7 1.4 2.1 2.8

POROSITY (%)

50

500

5000

50000

500000

RE

SIS

TIV

ITY

(o

hm

m)

10

Hz

10 samples


VEIN MIGMATITE

GREY GNEISS SKARN


GREEN = S-SERIES

0 0.5 1 1.5 2

OPAQUE MINERALS (%)

50

500

5000

50000

500000

RE

SIS

TIV

ITY

(o

hm

m)

10

Hz

10 samples


VEIN MIGMATITE

GREY GNEISS SKARN


GREEN = S-SERIES

22

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, veined gneisses and other

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 4620 – 6190 m/s, indicating typically rather

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

(Fig. 3-3), the samples form distinct populations according to their rock type as well as

chemical composition. The highest velocity values are related to the single quartz gneiss

sample and P-series TGG gneisses. The lowest velocity values are associated to the

samples belonging to T-series veined gneisses. Compared to the other samples,

variation in velocity and porosity of the veined gneiss samples is rather high.

Figure 3-3. Porosity vs. P-wave velocity, OL-KR21.

0 0.7 1.4 2.1 2.8

POROSITY (%)

4500

5000

5500

6000

6500

P-W

AV

E V

EL

OC

ITY

(m

/s)

10 samples


VEIN MIGMATITE

GREY GNEISS SKARN


GREEN = S-SERIES

23

4 FRACTURE MINERALOGY

The account on fracture mineralogy of drill core OL-KR21 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 Bore hole OL-KR21 contains 1126 in total, indicating thus a relatively dense

fracturing; 4.1 fractures/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 figure 4-1. The fracture plains are occasionally covered by cohesive chlorite, which

typically forms the underside for the above-mentioned phases (Fig. 4-1). In addition to

that, idiomorphic quartz crystallites and sericite are present in few fractures. Graphite is

met only in one fracture.

Drill core OL-KR21 contain two zones of pervasive illitite alteration. Although the drill

core does not contain any pervasive kaolinite alteration zones, the fractures appear to be

widely kaolinitised and also illite zones are found in four zones.

Eight zone intersections have been reported form bore hole OLKR21 (Fig. 4-1, column

10). Nearly all of them are featured by some kind of hydrothermal outcome; kaolinite,

illite, sulphides or calcite. The last mentioned forms extensive sequences along the drill

core and overlies typically the zones made up by the other hydrothermal phases.

In some extent the water conductivity measurements of drill core sample OL-KR21

imply a the relationship of water conductivity and fracture filling sequences. The peaks

at core length 217 and 245 m coincide with the zone intersections, which, respectively

are in immediate vicinity of the two zones of pervasive illite alteration (Fig. 4-1). The

water conductivity peaks at the core length less than 200 metres are more or less related

with the zones of kaolinitisation or carbonatization.

24

100

200

300

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

-mon

om

ine

ral

filli

ng

Py-

mon

omin

eral

fillin

g

OLKR 21

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

0.2

0.3

0.3

0.4

0.2

0.3

0.3

0.2

0.2

0.3

0.3

0.3

0.1

0.2

0.1

0.3

0.2

0.4

0.2

0.2

0.4

0.2

0.5

Figure 4-1.

25

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

4.1 Fracture fillings at the major pervasive alteration zones

The core length of the pervasively altered rock in bore hole OL-KR 21 is only 31 m in

total. That makes 10 % of total core length. Pervasive illite alteration form two zones

(Table 4-2). The upper one locates at core length 197 – 212 m and contains thick clay

fillings at 205 – 209 m and abundant kaolinite, sulphides and calcitic stockworks.

Column No. Explanation

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

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

26

Similarly the deeper pervasive illite zone contains thick fracture fillings (sulphides, clay

and calcite) at the core length of 234 – 235 m.

Table 4-2. Pervasive illite alteration zones in bore hole OL-KR21.

4.2 Fracture fillings

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

fractures.

1. Kaolinite-illitic fracture filling sequences

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

typically defined by occurrence of calcite and sulphides in the same assemblages. The

drill core lengths where the predominating filling phase is kaolinite is given in the Table

4-3 and that for illite in the Table 4-4.

Kaolinite is present in a wide range of the drill core transverse (see Fig. 4-1). Major of

the kaolinitised fracture filling sequences are located at the drill core length starting at

135 m and continuing with two interruptions to the end of the drill core sample. The

four fracture illite sequences are situated at the core length 179 – 270 m which length

visibly has elevated fracture density and represents a hydrothermal fluid conduit.

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. Typically

those fracture zones, which have calcite as major phase, are characterized by higher

fracture density than in the zones in which the influence of hydrothermal activity is

insignificant.

Start(m)

End(m)

Core length(m)

197 212 15

229 245 16

27

Table 4.3. Kaolinite- illite fracture filling zones.

Start (m) End (m)

Averagefillingthickness (mm)

Core length(m)

13.2 25.2 0.2 12.045.4 58.1 0.3 12.866.5 75.5 0.3 9.1

135.8 159.1 0.2 23.3165.9 212 0.2 49.8

227.6 299.8 0.3 72.2

Table 4-4. Illite fracture filling zones (pervasive zones excluded from this table).

Start(m)

End(m)


Core length (m)

179.1 200.1 0.2 21.0204.3 210.7 0.3 6.4266.8 270.3 0.4 3.4

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

individual zone may have core length of 36 metre (Table 4-5). The total core length of

the calcite fracture sequences is 177 metres (= 59 % of whole core length). The thick

clay filled zones occur at core length 182 – 207 m and 258 – 271 m Both these contain

thick calcite fillings/calcite stockwork.

28

Table 4-5. Calcite fracture filling zones in bore hole OLKR21. Highlighted in grey are

the zones which represent advanced carbonatization.

Start(m)

End(m)


Core length (m)

15.1 51.6 0.3 36.5

58.1 70.4 0.3 12.3

80.3 83.5 0.2 3.3

105.3 118.5 0.2 13.2

125.1 127.8 0.1 2.7

130.1 140.7 0.3 10.6

146.0 175.6 0.2 29.7

182.3 207.0 0.4 24.7

212.0 220.9 0.2 8.9

224.1 235.0 0.2 10.9

259.0 270.8 0.4 11.8

278.0 288.5 0.2 10.5

298.8 301.0 0.5 2.2

29

5 SUMMARY

The borehole OL-KR21 starts in the north western part of the Olkiluoto study area from

a large pegmatite unit and intersects in the lower parts mainly veined gneisses typical

for this part of the study site. The exposed pegmatitic granite unit includes various

migmatite blocks and interbeds and extends to the drilling length of 19 m. A veined

gneiss unit below that is intersected down to the drilling length of 57 m. A rather wide

pegmatitic granite unit is intersected between drilling lengths of 57 m and 82 m and

medium-grained, weakly foliated TGG gneisses dominate the next intersection down to

the drilling length of 111 m. The lowermost part of the core sample is composed of

veined gneisses which are intruded by a few pegmatites and have several, narrow gneiss

inclusions.

More detailed petrological character has been determined from 11 samples. One of

those is quarts gneiss of the S series. Six veined gneiss samples will classify to the T

series and four TGG gneiss samples belong to the P series. Veined gneiss samples of the

T series contain SiO2 between 55 and 70 % and thus the most silicic and most basic

types are not represented by the assemblage. However, chemical compositions of the

analysed samples are still very typical for the migmatites of the T series. The quartz

gneiss sample studied in detail will classify to the high-calcium subgroup of the S

series. CaO concentration of the sample is close to 8% and SiO2 exceeds 70% and thus

the gneiss belongs to the subgroup of most silicic variants in this sequence. Four TGG

gneiss samples analysed from the drill core will classify to the P series due to their high

content of phosphorus. These gneiss varieties belong to a more silicic half in the P

group and contain 62 – 65% SiO2. In other respects, the compositions of the samples

are very typical for their assemblage.

The T-type veined gneiss samples represent their migmatite sequence comprehensively

as the silicity varies between 55% and 70% (SiO2) which is close to the whole range

analyzed from this migmatite group. Quartz content follows strictly the increase in

silicity and the less silicic sample contains quartz ca. 18% and the most silicic one ca.

36%. The content of plagioclase and K-feldspar varies between 5 and 30% but the total

number of feldspars increases systematically from 10% in the less silicic type to 50% in

the most silicic one. Accordingly, the total number of biotite and its retrograde

derivative, chlorite decreases from over 40% in the less silicic migmatite to below 10%

in the most silicic one. Cordierite is strongly pinitized but primary proportion of

cordierite has been 10 – 15% in the less silicic types, 5 – 10% in the moderate types and

a couple of percentages in the most silicic one. Veined migmatite structure is typical for

all these samples but certain variation between individual samples is visible. Leucosome

veins may be rather small, in cross section 5 – 10 mm thick and 10 – 20 mm wide lenses

but elsewhere the diameters of veins may be several centimetres. Average grain size of

paleosome material varies from fine- to medium-grained and often it is moderately

banded.

The quartz gneiss of the S series is a typical hornblende bearing “skarn quartzite”. It

contains close to 50% quartz, 36% plagioclase, 4% hornblende and some biotite.

Sphene and apatite are typical accessories. The gneiss is fine-grained and granoblastic.

30

All minerals are somehow roundish and no features of mineral shape orientation or

foliation development can be imagined.

The TGG gneisses of the P series represent a limited selection from the whole sequence

and their modal mineral compositions are close to identical. Quartz content varies

between 20 and 25% and plagioclase between 30 and 45%. K-feldspar composes often 1

– 7% of the mode and biotite content has been in not altered rocks ca. 25%.Apatite and

sphene are the most typical accessories. Textures of the TGG gneiss samples are

twofold as the others show distinct metamorphic banding but others contain roundish, 5

– 10 wide quartz feldspar aggregates or patches surrounded by mica bearing

“groundmass”. The later texture can be designated as mottled texture in which the

patches are composed of granoblastic quartz-feldspar mass. Some of those are totally

leucocratic but they may also contain some biotite. The “groundmass” is typically fine-

grained, granoblastic and contains 20 – 40% biotite.

Petrophysical properties were measured from 10 samples. Their measured density

values range between 2686 and 2787 kg/m3. The highest value is measured from a

quartz gneiss (or skarn) sample.

All the samples are paramagnetic or weakly ferrimagnetic with susceptibility values

ranging from 270·10-6

SI to 1190·10-6

SI. Most of the samples measured correspond

rather well with the paramagnetic gneiss population from OL-KR1 – OL-KR6. There is

one slightly ferrimagnetic veined gneiss sample, indicating small amounts of

ferrimagnetic minerals. The measured remanence values are typically below 50 mA/m,

being below the practical detection limit of the measuring device. However, there are

three clearly higher remanence values, 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. TGG gneisses and the single quartz gneiss sample are least porous (< 0.3

%), having also high resistivity values. T-type veined gneisses are clearly more porous

(0.82 – 2.46 %) with lower resistivity values (c. 1100 – 2600 ohmm). Opaque minerals

may also have a slight effect in resistivity.

Measured P-wave velocities are 4620 – 6190 m/s, indicating typically rather unfractured

and unaltered crystalline rocks. In porosity vs. P-wave velocity diagram, the samples

form distinct populations according to their rock type as well as chemical composition.

The highest velocity values are related to the single quartz gneiss sample and P-type

TGG gneisses. The lowest velocity values are associated to the samples belonging to T-

type veined gneisses. Compared to the other samples, variation in velocity and porosity

of the veined gneiss samples is rather high.

The drill hole OL-KR21 has relatively dense fracturing; 4.1 fractures/metre. Pervasive

illitization concerns 11 % of the total core length and as much as 59 % of the bore hole

length has calcite as major constituent in fracture fillings The chief fracture minerals

include illite, kaolinite, unspecified clay phases, iron sulphides and calcite. Iron-oxides

and oxy/hydro-oxides are met in few fractures at core length 9.53 – 18.95 m. The

31

fracture plains are occasionally covered by cohesive chlorite, which typically forms the

underside for the other filling phases.

The frequency of fracturing is clearly higher at the interval starting at 135 meters nad

continuing to the end of the drill core sample. This depth interval contains zone

intersections and pervasive illite alteration zones. Calcite is present almost all along the

drill core sample and seemingly it overlies all the other hydrothermal zones.

The clay filled zones that appear at core length 182 – 207 m and 258 – 271 m contain

thick fillings and have extensive calcite fillings/calcite stockworks.

32

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.

Niinimäki, R. 2002. Core drilling of deep borehole OL-KR21 at Olkiluoto in Eurajoki

2002. Working Report 2002-56. Posiva Oy, Olkiluoto. 131 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.

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.

33

APPENDICES

Appendix 1.

File KR21_APP1 in the disk enclosed. The Appendix contains the results of whole rock

chemical analyses.

Appendix 2.

File KR21_APP2 in the disk enclosed. The Appendix contains the results of modal

mineral composition analyses.

Appendix 3. Petrophysical parameters, drill core OL-KR21.

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(%) KR21 OL.223 31.04 31.14 2737 1190 770 5570 2220 1420 1160 36 48 0.86

KR21 OL.224 50.90 51.00 2787 570 320 6190 resistivities > 334864 0.21

KR21 OL.225 82.90 83.01 2756 330 40 5720 28900 27800 25100 4 13 0.22

KR21 OL.226 96.38 96.46 2763 360 10 5910 33600 32000 27100 5 19 0.22

KR21 OL.227 142.08 142.16 2728 360 50 4890 1670 1600 1450 4 13 1.44

KR21 OL.228 162.05 162.14 2752 390 120 5770 55000 52800 44100 4 20 0.15

KR21 OL.229 170.11 * 2686 360 20 5010 1830 1790 1660 2 9 2.46

KR21 OL.231 221.25 * 2767 460 10 4620 1290 1170 982 9 24 1.52

KR21 OL.232 245.16 245.29 2732 330 20 5390 2670 2610 2390 2 10 0.89

KR21 OL.233 273.15 * 2718 270 10 5820 31300 30200 27300 4 13 0.23

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

34

Documents

Petrology, Petrophysics and Fracture Mineralogy of the