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
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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