Working Report 2007-44
Petrology, Petrophysics and Fracture Mineralogy of the Drill Core Sample OL-KR19 and OL-KR19B
Seppo Gehör Aulis Kärki Markku Paananen
June 2007
POSIVA OY FI-27160 OLKILUOTO, FINLAND Tel +358-2-8372 31 Fax +358-2-8372 3709 Working Report 2007-44
Petrology, Petrophysics and Fracture Mineralogy of the Drill Core Sample OL-KR19 and OL-KR19B
Seppo Gehör
Aulis Kärki
Kivitieto Oy
Markku Paananen
Geological Survey of Finland
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. ABSTRACT
This report represents the results of the studies dealing with the drill core samples OL- KR19 and OL-KR19B, drilled in the northern 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.
Veined gneisses dominate the NW part of the focal study site of Olkiluoto and the bedrock intersected by the boreholes OL-KR19 and KR19B are composed for the most part of veined gneisses. Besides to those, several 5 - 10 m long pegmatitic granite intersections and one, close to 30 m long mica gneiss intersection have been detected in the core sample. TGG gneiss sections among various veined gneisses have been found in the core sample section extending from drilling length of 130 m to 210 m. Detailed Petrological properties have been analysed from 19 samples. The P series is represented by one acidic TGG gneiss sample which contains more than 66% SiO2 and in which the P2O5 concentration exceeds 0.3% and CaO 2%. Selected mica gneiss samples represent moderate chemical variant among the gneisses and migmatites of the P series by having slightly below 60% SiO2 and close to 0.7% P2O5. Mafic gneiss sample is also quite typical amphibole bearing and mica rich rock of the P series. Low concentration of SiO2 (48%) and high concentrations of phosphorus (1.4% P2O5) and titanium (2.6% TiO2) analysed from this sample are characteristic for the less silicic members of the series. Two mica gneiss and three quartz gneiss samples are chemically close to identical and they fall into the low-calcium group of the S-series due to their moderate (2 – 4% CaO) calcium contents. The T-type gneisses and migmatites cover extensively the range of the whole T-series.
Petrophysical properties were studied from 19 samples. The parameters measured were density, magnetic susceptibility, natural remanet magnetization, electrical resistivity, P- wave velocity and porosity.
Borehole has 2.6 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.
Pervasive illitization concerns as much as 44 % of the total core length and in addition to that the fracture related kaolinite and illite infillings form a number of filling sequences. They are disseminated all along the core sample and have 20 metres core length in maximum. Calcitic fracture fillings and calcite stockworks occur all along the drill core sample and they constitute sequences which have 16 m core length in average. The percentage of carbonaceous fractures is as much as 50 % of the bore hole length. 2
Kairanäytteen OL-KR19 ja OL-KR19B petrologia, petrofysiikka ja rakomineralogia
TIIVISTELMÄ
Tässä raportissa esitetään kairausnäytteitä OL-KR19 ja OL-KR19B koskevien tutkimus- ten tulokset. Kyseiset kairanreiät on tehty Olkiluodon tutkimusalueen pohjoisosaan. Raportissa esitetään kairausnäytteen litologiaa sekä valittujen näytteiden kokokiven ke- miallista koostumusta, mineraalikoostumusta, tekstuuria ja petrofysikaalisia ominai- suuksia käsittelevien tutkimusten tulokset. Samoin kuvataan matalan lämpötilan raon- täytemineraalit
Suonigneissit ovat hallitsevia Olkiluodon keskeisen tutkimusalueen luoteisosassa ja tarkasteltujen kairanreikien lävistämä kallioperä koostuu pääosin kyseisenkaltaisista migmatiiteista. Niiden lisäksi on lävistetty useita 5 – 10 m:n levyisiä pegmatiittisia gra- niitteja ja yksi lähes 30 m:n kiillegneissijakso. Poikkeava, TGG-gneisseistä ja erilaisista suonigneisseistä koostuva jakso on lävistetty kairauspituusvälillä 130 – 210 m.
Yksityiskohtaiset petrologiset ominaisuudet on analysoitu 19 näytteestä. P-sarjaa edustaa yksi hapan TGG-gneissinäyte, joka sisältää yli 66 % SiO2:ta ja jossa P2O5– pitoisuus ylittää 0,3 % ja CaO 2 %. Valitut kiillegneissinäytteet edustavat keskin- kertaisia muunnoksia P-sarjan gneissien ja migmatiittien joukossa sisältäen hieman alle 60 % SiO2:ta ja lähes 0,7 % P2O5:ta. Mafinen gneissinäyte on myös hyvin tyypillinen amfibolipitoinen ja kiillerikas P-sarjan kivi. Näytteen matala SiO2–pitoisuus (48 %) ja korkeat fosfori- (1,4 % P2O5) ja titaanipitoisuudet (2,6 % TiO2) ovat luonteenomaisia sarjan emäksisimmille kivilajeille. Kaksi kiillegneissi- ja kolme kvartsigneissinäytettä ovat keskenään kemiallisesti lähes identtisiä ja ne luokittuvat S-sarjan matalan kalsium- pitoisuuden alaryhmään verrattain alhaisen (2 – 4 % CaO) kalsiumpitoisuutensa takia. T-sarjan gneissit edustavat varsin kattavasti koko sarjaa ja koostumukseltaan ne ovat tavanomaisia.
Petrofysikaaliset ominaisuudet on määritetty 19 näytteestä. Mitatut parametrit ovat tiheys, magneettinen suskebtibiliteetti, luonnollinen remanentti magnetoituma, sähkö- vastus, P-aallon nopeus ja huokoisuus.
Kairausnäytteen OL-KR19 rakotiheys on keskimäärin 2,6 rakoa/metri. Rakoilu painot- tuu hydrotermisiin muuttumisvyöhykkeisiin ja muihin rikkonaisuusvyöhykkeisiin, joissa rakojen täytteinä esiintyy illiittiä, kaoliniittia, erikseen määrittelemättömiä useam- man 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. Kairauslävis- tyksestä on jopa 44 % läpikotaisesti illiittiytynyttä. Rakotäytteisiin liittyvän iliitti- kaoliniittimuuttumisen kairausleikkauspituus on keskimäärin 20 metriä. Kalsiittival- taisia täyteseurantoja esiintyy 50 %:ssa kairausnäytteen koko pituudesta.
1
TABLE OF CONTENTS
ABSTRACT
TIIVISTELMÄ
1 INTRODUCTION ...... 3 1.1 Location and General Geology of Olkiluoto ...... 3 1.2 Boreholes and Drill Core Samples OL-KR19 and OL-KR19B...... 6 1.3 The aim of this study and research methods ...... 6 1.4 Research Activities ...... 7
2 PETROLOGY ...... 9 2.1 Lithology...... 9 2.2 Whole Rock Chemistry ...... 17 2.3 Petrography ...... 21
3 PETROPHYSICS...... 27 3.1 Density and magnetic properties ...... 28 3.2 Electrical properties and porosity...... 29 3.3 P-wave velocity ...... 30
4 FRACTURE MINERALOGY ...... 31 4.1 Fracture fillings at the major pervasive alteration zones...... 35 4.2 Fracture fillings outside the major hydrothermal fracture zones ...... 37 4.3 Water flow indication...... 39 4.4 Relationship between fracture filling data and calvanic connection ...... measurements ...... 41
5 SUMMARY ...... 43
REFERENCES ...... 47
APPENDICES...... 49 2 3
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-KR19.
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 4
sporadically also fine- and medium-grained, weakly migmatized gneisses with less than 10 % leucosome material occur. The content of micas or their retro grade derivatives
N
KR6 $Z OL-KR19 KR19B $Z
KR33 KR5 $Z $Z KR21 $Z KR13 $Z KR20B KR11 $Z KR32 $Z SK9 $Z KR2KR12 $Z $Z $Z OL-KR8 KR15B KR16B $Z $Z $Z $Z KR14 KR1 KR18B KR3 $Z $Z $Z KR10 $Z KR30 $Z KR9 KR7 KR22B $Z $Z KR25B KR31 $Z $Z $Z KR4 $Z KR24 $Z KR26 $Z $Z KR8 KR23B KR27B $Z $Z $Z
400 0 400 800 Meters
TGG gneiss Road/street Pegmatitic granite Building Diatexitic gneiss Veined gneiss Sea/lake area
Figure 1-1. General geology and location of bore hole starting points at Olkiluoto. 5
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 linear 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 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. 6
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-KR19 and OL-KR19B
The starting point of the borehole OL-KR19 is situated in the northern part of the of the Olkiluoto study site (Figure 1-1). The coordinates of the starting point are: X = 6792883.35, Y = 1525760.08 and Z = 6.34. Starting direction (azimuth angle) of the borehole is 306o and its dip (inclination angle) is 76,4o. Starting point of the borehole OL-KR19B is located at the point: X = 6792886.96, Y = 1525762.53 and Z = 6.34. Azimuth angle of this borehole is 305o and inclination angle 76,7o
The boreholes are drilled in 2003. The core sample OK-KR19 received by that work extends from drilling length of 40.60 m to 544.34 m thus being 503.74 m in total length. The core sample OL-KR19B extends from drilling length of 0.00 m to 45.05 m.
Technical data dealing with the OL-KR19 and –KR19B drillings 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 samples OL-KR19 and –KR19B. 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. 7
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 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 19. 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. 8
Table 1-1. Elements, methods and detection limits for whole rock chemical analysis.
Detection Detection Element Method limit Element Method 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
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. 9
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.
On the basis of the present practice for naming (Mattila 2006) and lithological classification (Kärki and Paulamäki 2006), the most part of the drill core sample is composed of veined gneisses and weakly migmatized mica gneisses.
2.1 Lithology
Veined gneisses dominate the NW part of the focal study site of Olkiluoto (Fig. 1) and the bedrock intersected by the boreholes OL-KR19 and KR19B is composed for the most part of veined gneisses. Besides to those, several 5 - 10 pegmatitic granite intersections and one, close to 30 m long mica gneiss intersection have been detected in the core sample. TGG gneisses with various veined gneisses have been found in the core sample from 130 m to 210 m. 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-KR19.
Drilling length (m) Lithology
40.60 - 42.30 VEINED GNEISS which contains ca. 10% leucosome.
42.30 - 43.50 PEGMATITIC GRANITE which is coarse-grained and leucocratic.
43.50 - 48.30 VEINED GNEISS which contains ca. 10% leucosome.
48.30 - 48.60 MAFIC GNEISS which is fine-grained and homogeneous.
48.60 - 69.93 VEINED GNEISS which is dark and, in places, contains a lot of cordierite. Between drilling lengths of 58.90 – 60.15 m dominates fine- grained, homogeneous mica gneiss. Occasionally, the migmatite is intruded by 10 - 40 cm wide pegmatitic granite dykes and its average leucosome content is ca. 20%.
69.93 - 70.55 PEGMATITIC GRANITE which is grey and leucocratic. Sporadically it contains garnet porphyroblasts but gneiss inclusions have not been detected. 10
Drilling Lithology Leucosome Sample Granite/pegmatitic granite Length (m) 0% 100% 0 TGG gneiss
Quartz gneiss
Mafic gneiss -50 Mica gneiss OL.189 Veined gneiss OL.190 -100 Diatexitic gneiss
Stromatic gneiss OL.191 -150
-200 OL.192 OL.193
OL.194 -250 OL.195
OL.196
-300
OL.197 -350
OL.198
-400 OL.199
OL.200 OL.201 -450
OL.202
-500 OL.203 OL.205OL.204
Figure 2-1. Lithology, leucosome + pegmatite material percentage (= leucosome) and sample locations, drill core OL-KR19. 11
70.55 - 79.95 VEINED GNEISS the leucosomes of which are 0.5 - 5cm wide, typically veins but for a part also planar dykes. The migmatite is intersected occasionally by 5 – 30 cm wide PEGMATITIC GRANITE dykes. The paleosome is mostly fine-grained at the uppermost part of the section and typically medium-grained below that. The proportion of the leucosome is below 20% in the upper subsection and ca. 30% in the lower one.
79.95 - 87.40 PEGMATITIC GRANITE which is coarse-grained and the plagioclase of which is pervasively altered to saussurite. The pegmatite contains ca 1% gneiss inclusions.
87.40 - 90.40 MICA GNEISS which is medium-grained, homogeneous and, in places, contains cordierite porphyroblasts. In the middle part of the section, the rock changes to VEINED GNEISS in which the leucosome content is ca. 10% and which is intruded by one 40 cm wide PEGMATITIC GRANITE dyke.
90.40 - 93.15 PEGMATITIC GRANITE which contains sporadically small MICA GNEISS inclusions (25% in average) and garnet porphyroblasts.
93.15 - 129.67 VEINED GNEISS which is intruded by narrow (< 0.5 m wide) pegmatite dykes and contains homogeneous, medium-grained MICA GNEISS subsections. The proportion of granitoid component is 10 - 20%.
129.67 - 132.25 PEGMATITIC GRANITE which is reddish and occasionally contains garnet porphyroblasts. In places the pegmatite has gneiss inclusions the average proportion of which is 2 – 3%.
132.25 - 139.00 TGG GNEISS – MICA GNEISS mixture. The rock texture fluctuates from fine- and even-grained to medium-grained and blastomylonitic. The most fine-grained variants contain more mafic minerals and are greenish. The proportion of leucosome is small and does not exceed 5%.
139.00 - 146.00 VEINED GNEISS the paleosome of which is homogeneous and relatively fine-grained. Leucosome veins are abnormal wide, typically at least 5 - 10 cm in diameter. The rock contains also several 10 - 50 cm wide PEGMATITIC GRANITE dykes. The average proportion of granitoid material is ca. 30%.
146.00 - 149.50 TGG GNEISS the texture of which varies from fine-grained and homogeneous to medium-grained and evidently blastomylonitic. The cross cutting pegmatite-like dykes are typically 1 - 2cm wide and their amount is 15% in average. 12
149.50 - 157.40 VEINED GNEISS in which the proportion of leucosomes and garnet bearing pegmatite dykes varies between 10 and 80% in different subsections.
157.40 - 162.45 TGG GNEISS which contains ca 15% leucosome and rarely veined gneiss subsections. The texture varies from homogeneous, blastomylonitic to typical veined structure. The average proportion of leucosome is ca. 15% in the whole section.
162.45 - 175.30 VEINED GNEISS in which the amount of paleosome varies widely. The composition of paleosome varies and, in places, it composes of almost pure biotite. In places, the texture resembles medium-grained TGG GNEISSES and in places medium-grained MICA GNEISSES. From the drilling length of 168.40 m onward the paleosome resembles TGG GNEISSES which contains ca. 20% leucosome.
175.30 - 175.82 MAFIC GNEISS or amphibolite which is fine grained and shows some features of confused layer structure.
175.82 - 182.50 TGG GNEISS the paleosome of which is mostly medium-grained and blastomylonitic but in certain subsections the rock resembles the migmatites.
182.50 - 203.10 VEINED GNEISS the paleosome of which is, mostly rather homogeneous and cordierite bearing. At the beginning of the section the rock contains only a small amount of leucosome veins but in the lower part the proportion of leucosome increases to 10 - 30%. The section contains also 10 – 80 cm wide PEGMATITIC GRANITE dykes.
203.10 - 209.70 TGG GNEISS which contains ca. 10% 1 – 3 cm wide leucosome dykes and has a distinct blastomylonitic texture.
209.70 - 224.80 VEINED GNEISS in which homogeneous (non-migmatitic), fine- grained and rather wide mica gneiss inclusions are common. The proportion of leucosome is 10 – 15%.
224.80 - 226.30 PEGMATITIC GRANITE which contains dark phenocrysts and sporadically fine-grained MICA GNEISS blocks and biotite seams ca. 5% of volume.
226.30 - 228.75 MICA GNEISS which, for the most part, is fine-grained and homogeneous but somewhere also medium-grained and contains dark cordierite porphyroblasts. The rock is intruded by a few, 3 – 5 cm wide PEGMATITIC GRANITE dykes and contains ca. 5% leucosome.
228.75 - 233.04 PEGMATITIC GRANITE in which dark phenocrysts and fine-grained MICA GNEISS inclusions (~ 10%) occur sporadically. 13
233.04 - 259.00 MICA GNEISS – QUARTZ GNEISS mixture the components of which are fine-grained and homogeneous or medium-grained and cordierite bearing. The section includes several VEINED GNEISS subsections and narrow, 10 – 50 cm wide PEGMATITIC GRANITE dykes.
259.00 - 287.65 VEINED GNEISS in which the proportion of leucosome varies between 5 and 30%. One narrow TGG GNEISS subsection is located between drilling length 263.65 – 264.25 m and, in addition to that, several 10 – 50 cm wide PEGMATITIC GRANITE dykes intersect the migmatite. The proportion of granitoids may increase to 80% in the end of the section, from the drilling length of 275 m onward and there the rock will classify as DIATEXITIC GNEISS.
287.65 - 295.61 PEGMATITIC GRANITE which is leucocratic but contains some dark phenocrysts. The subsection from the drilling length of 289.20 m to the length of 293.10 m contains a lot, up to 30 – 40% MICA GNEISS inclusions.
295.61 - 303.38 VEINED GNEISS the paleosome of which is medium-grained for the most part and contains cordierite porphyroblasts. The subsection from the drilling length of 299.00 m to 299.90 m contains three, 10 – 20 cm wide, homogeneous and fine-grained gneiss layers which are more dark and rich in biotite than the paleosome in average. The migmatite contains ca. 25% leucosome.
303.38 - 305.10 PEGMATITIC GRANITE of which MICA GNEISS blocks and biotite seams compose ca. 10%.
305.10 - 306.93 VEINED GNEISS the paleosome of which is greyish and homogeneous at the beginning of the section but changes to more dark and rich in biotite in the end of the section. The average content of leucosome is ca. 15%.
306.93 - 310.41 PEGMATITIC GRANITE which contains garnet phenocrysts and MICA GNEISS inclusions ca. 20%.
310.41 - 330.21 VEINED GNEISS the paleosome of which is mostly medium-grained and grey but contains sporadically dark, almost pure biotite bands (Leucosome 25%).
330.21 - 331.65 PEGMATITIC GRANITE which is medium- to coarse-grained and contains 1 – 2% gneiss inclusions.
331.65 - 332.63 MICA GNEISS which is homogeneous, medium-grained and intruded by a few, narrow PEGMATITIC GRANITE dykes. 14
332.63 - 337.65 VEINED GNEISS which, at the beginning of the section, is rather homogeneous but transforms to more typical migmatite in the end of the section.
337.65 - 339.40 PEGMATITIC GRANITE which is leucocratic and contains greenish plagioclase all over the section.
339.40 - 363.20 VEINED GNEISS the paleosome of which is mostly medium-grained and seems to contain a moderate amount of biotite. The subsection between drilling lengths of 349.50 m and 352.00 m is more homogeneous and poor in leucosome.
363.20 - 364.05 PEGMATITIC GRANITE which is grey, not very coarse-grained and close to free of inclusions.
364.05 - 372.05 MAFIC GNEISS – MICA GNEISS mixture in which the mafic variant dominates. The gneisses are intruded by 10 – 30 cm wide pegmatite dykes that compose 5 - 10% of the volume.
372.05 - 393.75 VEINED GNEISS the paleosome of which is mostly medium-grained and contains a moderate amount of biotite. Several fine-grained, homogeneous gneiss intersections have been penetrated by the borehole, and average proportion of leucosome is 15%.
393.75 - 395.00 PEGMATITIC GRANITE which is reddish, medium-grained and the plagioclase of which is pervasively altered, often greenish.
395.00 - 406.80 VEINED GNEISS the leucosomes of which are 1 – 4 cm wide and compose ca. 20% of the volume. In addition, the rock contains 10 – 40 cm wide PEGMATITIC GRANITE dykes.
406.80 - 408.50 PEGMATITIC GRANITE like the one in the previous section.
408.50 - 461.58 VEINED GNEISS of which 1 – 5 cm wide leucosome veins build up ca. 30%. The rock is intruded by a few, 10 – 50 cm wide PEGMATITIC GRANITE dykes. Homogeneous, fine-grained gneiss located between drilling lengths of 426.55 – 428.75 m is intruded by a few PEGMATITIC GRANITE dykes but is free of leucosome. The subsection from 451.60 m to 461.58 m is composed of fine-grained and homogeneous mica gneiss in which the proportion of leucosome is small.
461.58 - 464.15 PEGMATITIC GRANITE, leucocratic, coarse-grained and pervasively altered.
464.15 - 466.07 MICA GNEISS which transforms gradually to VEINED GNEISS with ca. 15% leucosome 15
466.07 - 466.92 PEGMATITIC GRANITE which is leucocratic, coarse-grained and pervasively altered.
466.92 - 470.70 QUARTZ GNEIS - MICA GNEISS mixture which is intruded by 10 – 40 cm wide PEGMATITIC GRANITE dykes (ca. 10 – 20% of volume).
470.70 - 476.45 PEGMATITIC GRANITE in which small gneiss inclusions occur. In the beginning of the section the feldspar is strongly altered and the lowest part of the section is evidently deformed and resembles TGG gneisses of granitic composition.
476.45 - 478.55 DIATEXITIC GNEISS of which leucosome and irregular pegmatite dykes compose ca. 70%.
478.55 - 484.35 MICA GNEISS which is medium-grained, mostly homogeneous and intruded by several pegmatitic granite dykes.
484.35 - 486.85 MICA GNEISS – QUARTZ GNEISS mixture which is fine- or medium-grained , homogeneous or banded and contains a lot, ca. 50% intersecting 10 – 70 cm wide PEGMATITIC GRANITE dykes.
486.85 - 487.85 PEGMATITIC GRANITE which is coarse-grained and contains dark phenocrysts and 5 – 10% gneiss inclusions.
487.85 - 490.10 VEINED GNEISS in which the proportion of leucosome is ca. 30%.
490.10 - 500.40 MICA GNEISS-QUARTZ GNEISS mixture which is intruded sporadically by 10 – 70 cm wide PEGMATITIC GRANITE dykes that compose ca. 10% of the rock volume.
500.40 - 504.05 VEINED GNEISS in which the proportion of leucosome is 20 – 30%.
504.05 - 505.00 MAFIC GNEISS - QUARTZ GNEISS - MICA GNEISS mixture.
505.00 - 509.35 VEINED GNEISS-MICA GNEISS mixture in which 2 – 10 cm wide leucosome veins compose ca. 25%. The paleosome is strongly assimilated into the leucosome material.
509.35 - 510.70 MICA GNEISS.
510.70 - 513.25 DIATEXITIC GNEISS in which the paleosome seems to be strongly assimilated into the leucosome material. The leucosome composes ca 25% of the volume.
513.25 - 514.50 PEGMATITIC GRANITE which is coarse-grained and the plagioclase of which is partly altered. 16
514.50 - 528.50 VEINED GNEISS the paleosome of which is often medium-grained and banded. The subsection from 521.70 m to 525.60 m is build up of homogeneous, medium- to coarse-grained gneiss but elsewhere the rock contains leucosome ca. 40%.
528.50 - 529.00 MICA GNEISS, medium-grained and homogeneous.
529.00 - 533.60 VEINED GNEISS in which the proportion of 1 – 3 cm wide leucosomes is 10-15%. The paleosome is mostly rather coarse-grained and resembles the TGG gneisses, but fine-grained, non-migmatitic mica gneisses occur, too.
533.60 - 535.20 DIATEXITIC GNEISS which, for a part, resembles the veined gneisses but has mostly irregular migmatite structure and contains leucosome ca. 60%.
535.20 - 544.34 VEINED GNEISS the paleosome of which is distinctly banded and medium-grained. The proportion of leucosome is ca. 35%.
Table 2-2. Lithology of the drill core sample OL-KR19B.
Drilling length (m) Lithology
0.00 - 5.30 QUARTZ GNEISS which is homogeneous, fine- to medium-grained and contains ca. 5% leucosome.
5.30 - 14.10 PEGMATITIC GRANITE which is coarse-grained and contains various gneiss inclusions ca. 5%. From the drilling length of 11.05 m onward the rock is red in colour.
14.10 - 14.87 Dark, fine-grained and homogeneous dyke rock, diabase which does not contain intersecting granitic dykes.
14.87 - 15.65 Red PEGMATITIC GRANITE which is close to free of inclusions.
15.65 - 18.60 MICA GNEISS – DIATEXTIC GNEISS mixture which is heterogeneous and contains gneiss blocks of variable sizes and shapes “assimilated” into pegmatite-like material. The proportion of granitoid component is ca. 50%.
18.60 - 22.00 QUARTZ GNEISS which is fine-grained, homogeneous and has a lot of mica bearing interbeds. The gneiss includes ca. 5% leucosome-like veins. 17
22.00 – 30.38 PEGMATITIC GRANITE which is red for a part but, for a part, grey, medium-grained rock which is rich in various gneiss inclusions. The proportion of gneissic material is 30% in average.
30.38 – 32.80 MICA GNEISS which is rich in cordierite and has only a few leucosome veins (5%).
32.80 – 34.30 PEGMATITIC GRANITE which is reddish and rather coarse-grained
34.30 – 45.05 VEINED GNEISS the paleosome of which is mostly banded but in the section from length of 37.00 m to 38.40 m it is medium-grained and homogeneous. The leucosome veins are 1 – 5 cm wide and they compose ca. 30 – 40% of the volume. In addition to that, the rock is intruded by several, 10 – 30 cm wide pegmatite dykes
2.2 Whole Rock Chemistry
Whole rock chemical composition has been analysed from 19 samples of these drill cores. Chemical classification and grouping follows the rules represented by Kärki and Paulamäki (2006). P series is represented by four samples. Two of those are P-type mica gneisses; one is TGG gneiss and one mafic gneiss. Three quartz gneiss and two mica gneiss samples will classify into the S series. The rest 10 samples have the chemical characteristics of the T series. Two of those are quartz gneisses, three are mica gneisses and five are veined gneisses. The numerical results of the whole rock analyses are represented in the Appendix 1.
The P series is represented by one acidic TGG gneiss sample (193) which contains more than 66% SiO2. The sample is a typical member in the P series in which the P2O5 concentration exceeds 0.3% and CaO 2% (Fig. 2-2). Similarly, ca. 5% concentration of Fe2O3, 1% MgO and 4% both K2O and Na2O are typical values for this kind of silicic P- type TGG gneiss. LIL-element concentrations resemble those of the T-type gneisses but the TGG gneiss is in enriched HFS-elements in addition to the high content of phosphorus (Fig. 2-3). Similarly, it is enriched in light REE´s and shows only a slightly negative europium anomaly while the heavy REE concentrations resemble those of the T-type rocks (Fig. 2-3). The mica gneiss samples (191 and 202) represent moderate chemical variant among the gneisses and migmatites of the P series. SiO2 concentrations are slightly below 60% and most of the other major elements are closely in the typical values for this kind of moderate members of the series (Fig. 2-2). P2O5 concentration close to 0.7% is very characteristic but CaO concentration of ca. 2% in the sample OL.191 is slightly lower than in the most typical members of the series.
Mafic gneiss, OL.198 is also quite typical amphibole bearing and mica rich rock of the P series. Low content of SiO2 (48%) and high contents of phosphorus (1.4% P2O5) and titanium (2.6% TiO2) analysed from this sample are characteristic for the less silicic members of the series (Fig. 2-2). On the contrary, high concentration of alkalis (close to 4% Na2O and over 4% K2O) is not so typical feature of this category. High contents of 18
light REE´s and hardly distinguishable Eu anomaly are typical features for the mafic members of the P series.
The S-type mica gneiss (200) and quartz gneiss samples (190, 203 and 206) are chemically close to identical and they fall into the low-calcium group of the S-series due to their moderate calcium concentrations (2 – 4% CaO). All major elements concentrations in these samples are very close to the expected values (Fig. 2-2). Regardless of similarity in major element concentrations, the low heavy rare earth element concentrations and anomalous element ratios of the sample OL.206 (Fig. 2-3) 19
20 5
4
3 10 TIO2
AL2O3 2
1
0 0 40 50 60 70 80 40 50 60 70 80 SIO2 SIO2 20 30
20
10 MGO FE2O3 10
0 0 40 50 60 70 80 40 50 60 70 80 SIO2 SIO2
20 4
3
10 2 CAO P2O5
1
0 0 40 50 60 70 80 40 50 60 70 80 SIO2 SIO2
Symbols: = mafic gneiss (S- or P-series), = veined gneiss, = diatexitic gneiss, = mica gneiss, = quartz gneiss, = TGG gneiss, metadiabase, = mafic metavolcanic rock and = pegmatitic granite from the drill core OL-KR19. = 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-KR19. 20
3000 1000
100
10
1 Sample/N-Type MORB Sample/N-Type
0.080.1 Sr K Cs Th P Nb Zr Ti Yb U Rb Ba Ce Ta Sm Hf Y A. 700
100
Sample/C1 Chondrite Sample/C1 10
4 La Pr Eu Tb Ho Tm Lu Ce Nd Sm Gd Dy Er Yb B.
Figure 2-3 A. Multielement diagram and B. REE-diagram showing the enrichment factors for the samples from the drill core OL-KR19. Symbols as in the Fig. 2-2. 21
are exceptional among the members of the S series and deviates from all supracrustal rock types of Olkiluoto. Similarly, low concentrations of P, Y and Yb and high concentrations of Zr and Hf are atypical for the succession of quartz gneisses and the spider diagram for this sample deviates evidently from the others (Fig. 2-3). Other samples in the low-calcium group are close to identical and also typical for their assemblage.
The sample OL.205 is a strongly altered, sericite and garnet bearing mica schist and chemically it deviates from others. The sample OL.205 contains 15% CaO which is the highest value analysed from the S-type mica gneisses. The concentration of aluminium in it is lower than in typical members of the high-calcium group (Fig. 2-2). In the present form the sample is epidote rich mica gneiss strongly affected by retrogressive alteration which explains the exceptional major element composition. Concentrations of heavy REE´s are similar to those in the typical gneisses of the T series, but the europium anomaly is positive and the sample is enriched in light REE´s (Fig. 2-3) so that the concentrations of Yb and Lu are even higher than in typical mafic gneisses of the P series. Other trace element concentrations in this strongly altered gneiss are close to similar with those of the other members in the T and S series but the concentrations of Rb, Cs and Ba are lower than in typical gneiss variants of the S series.
The T series is represented by ten samples which are veined gneisses (189, 196, 197, 199 and 201), mica gneisses (192, 194 and 204) and quartz gneisses (195 and 207). In this sequence the less silicic sample (OL.199) contains 59% SiO2 and the most silicic quartz gneiss (OL.207) more than 77% SiO2. These samples represent fairly extensively the whole T series because 77% concentration of SiO2 is maximal in this category and only a few samples have less than 59% silicon dioxide. The major element concentrations in individual members of this sequence are directly controlled by the concentration of silica. The concentration of Al2O3 decreases linearly from 19% to 10% and similarly decreases the concentration of Fe2O3 from 9% to 3%. Concentrations of magnesium, calcium and phosphorus are low (Fig. 2-2) and those of alkalis vary between 2 and 4%. The REE concentrations and element ratios in the samples of this ensemble are close to identical (Fig. 2-3) and also the other trace element concentrations fall close to identical values (Fig. 2-3). The only exceptions can be seen in the REE diagram of the less silicic veined gneiss sample, OL.199 in which the europium anomaly is deeper and the other REE concentrations higher than in the more silicic members. In that sample also the concentration of Ba is lower and concentrations of U, Ta and Nb higher than in the other samples of the assembly. The other exceptional sample is the veined gneiss OL.197 which is enriched in Zr and Hf and in which the concentrations of heavy REE´s are higher than in the other, corresponding migmatites.
2.3 Petrography
Modal mineral compositions and textures have been determined from the same 19 samples that have been selected for chemical analysis. The T series is represented by ten samples which are veined gneisses, mica gneisses and quartz gneisses. S series is represented by one quartz gneiss and four mica gneiss samples. In addition to those, two samples (101 and 102) studied in detail are pegmatitic granites. One mafic gneiss 22
sample, one TGG gneiss sample and two mica gneiss samples belong to the P series. Modal mineral compositions are given in the Appendix 2.
T series
The mica gneisses (samples 192, 194 and 204) of the T series have been cordierite bearing gneisses but now cordierite is totally replaced by microcrystalline pinite in each of those. The less acidic sample OL.192 contains 13% pinite and the others 4 - 5% pinite. Biotite content has been ca. 20% in each of those but now a remarkable proportion of it is replaced by chlorite and in the sample OL.204 only minor relicts of biotite are left due to strong chloritization. Feldspars have composed 30 - 40% of the rock but currently plagioclase is pigmented in some extend by saussurite and in the sample OL.204 a third part of plagioclase is totally saussuritized. In addition to those, fibrolitic sillimanite has been detected in the samples OL.192 and OL.194. Hematite composes the most of opaque minerals and in the samples OL.194 and OL.204 also some pyrrhotite and chalcopyrite is present.
The mica gneisses show a moderate metamorphic banding but due to low amount of biotite the dark bands are not totally continuous biotite bands but contain also some felsic mineral grains. Typical dark bands are 0.5 - 1 mm wide and they compose of 0.2 - 0.5 mm long and moderately oriented biotite scales with roundish feldspar grains of the same size. Biotite scales cover less than a half of the area of these dark bands. Textures of leucocratic bands are granoblastic and the material is fine-grained with average grain size from 0.5 mm to 1 mm. Cordierite porphyroblasts have been larger and typical diameters of those poikilitic grains vary between 2 and 5 mm.
All the samples are altered so that no primary cordierite has been detected in those but the degree of secondary alterations varies. In the sample OL.204 all biotite is chloritized and a third part of plagioclase has been classified as saussurite and also the rest part of it is pervasively pigmented. In the other samples a small proportion of biotite is chloritized and plagioclase is pigmented by saussurite but still recognizable as feldspar.
The T-type Quartz gneisses (OL.195 and OL.207) have close to identical modal compositions but the first has been affected by stronger alteration. They have been composed of 45 - 50% quartz, 20% plagioclase, 6% K-feldspar and close to 15% of biotite. The biotite in the sample OL.195 is almost totally chloritized but in the other sample it is rather fresh. The sample OL.195 contains also ca. 3% pinitized cordierite. Hematite is the most common opaque mineral in both of these samples and contains also some grains of iron sulphides.
Quartz gneisses are granoblastic and not well foliated rock. They are even-grained and the sample OL.195 is medium-grained with mean grain size of 1 mm while the sample OL205 is fine-grained and has a average grain size of 0.5 mm.
The T-type veined gneisses are cordierite or pinite and often sillimanite bearing quartz- feldspar-biotite rocks (Appendix 1). Biotite proportion ranges from 44% in the less silicic sample to 20% in the most silicic one. The amount of quartz increases from 24% to ca. 35% and plagioclase from 18% to 32% while silicity increases. K-feldspar is 23
concentrated to the silicic members in which it composes 2 – 5%. Fresh cordierite has been found in the samples 196, 197 and 201 but, excluding the sample 201, cordierite is strongly altered to pinite. In the samples 189 and 199 no fresh cordierite has been detected. The total amount of pinite and cordierite varies between 4 and 7% while sillimanite composes often 1 - 4% of the rock volume. The sample 189 contains, in addition to primary minerals, also ca. 8% saussurite and 3% chlorite. Opaque minerals compose less than 2% in each sample. Pyrrhotite, chalcopyritre and pyrite are the most common sulphide minerals but hematite is the dominating phase among the opaque minerals.
Paleosome materials in the samples 189, 196 and 197 are fine-grained and average grain sizes of major minerals in those vary between 0.3 and 1 mm. Paleosome shows a distinct metamorphic banding. Dark bands are often less than 2 mm wide and segregation of mafic minerals is not perfect. In the samples 199 and 201 dark bands are 2 - 5 mm wide, continuous and they are composed exclusively of micas and other mafic minerals. Felsic mineral in these are also coarser grained with average grain size of 2 – 3 mm. Biotite scales are ca. 2 mm long in these samples. Dark bands of all these veined gneisses are somehow wavy and compose lensoidal structures. Leucocratic bands are granoblastic in texture. Quartz and feldspar grains are roundish and often slightly elongated to the plane of rock foliation.
The samples 197 and 201are rather fresh and cordierite, biotite and plagioclase are only slightly altered in them. The sample 196 is in other respects similar but cordierite is pinitized for the most part. The degree of alteration in the samples 189 and 199 is moderate since their plagioclase is replaced for a part by microcrystalline saussurite and some biotite is chloritized in addition to totally altered cordierite.
S series
The S-type mica gneiss sample, OL.200 is a pure mica gneiss in which, in addition to biotite, quartz and plagioclase, other mineral phases are rare. Biotite builds up ca. 20%, anorthitic plagioclase 25% and quartz 49% of the whole rock volume. Only some garnet and opaque mineral grains have been detected in addition to the major minerals. Opaque minerals compose 1% of the rock volume and pyrrhotite is the dominant phase with minor amounts of pyrrhotite, chalcopyrite and hematite which is found as a secondary phase rimming biotite scales. In general, the sample is rather fresh and only the plagioclase is for a small part saussuritized.
The gneiss is granoblastic and fine-grained. Quartz and feldspar grains are roundish with diameters ranging from 0.3 to 0.5 mm. Biotite scales are about the same size, mostly less than 0.5 mm in length. The scales are moderately orientated to the plane of penetrative foliation but the scales are randomly located into the granoblastic quartz- feldspar mass thus making the rock not well cleavable and it shows not very high grade on anisotropy in its physical properties.
Sample OL.205 is strongly altered and in the present form it should not be classified as actual mica gneiss. The sample contains ca. 30% quartz and epidote. In addition to those, it contains 13% garnet, 7% chlorite and close to 10% opaque minerals. Hematite 24
is the most important opaque phase while only very few grains of sulphides have been preserved in the rock. Despite of strong alteration and abnormal mineral composition, the sample is granoblastic and medium-grained and could also be called as a quartz- epidote gneiss.
The S-type quartz gneisses (OL.190, OL.203 and OL.206) resemble chemically each other and also the S-type mica gneisses. They are biotite bearing rocks in which the major minerals, in addition to biotite, are quartz and plagioclase. The proportion of micas and their retrograde equivalents does not exceed 20% which makes the rocks quartz gneisses. The content of plagioclase varies between 25 and 30% and the content of quartz is ca. 40% in every sample. Samples OL.190 and OL.203 are granoblastic, weakly oriented rocks and the difference between these and the S-type mica gneisses is not great. The samples contain ca. 2% opaque minerals of which pyrite is the dominant phase in the sample OL.190 and pyrrhotite in the sample OL.203. Both of these samples are rather fresh and only a small proportion of plagioclase is pigmented by microcrystalline saussurite.
The sample OL.206 has been similar, granoblastic quartz gneiss than the others, but now it is pervasively altered. A half of biotite is altered to chlorite and plagioclase everywhere saussuritized in some extend. A third part of it is totally replaced by secondary phases, microcrystalline saussurite or more coarse-grained epidote and sericite. In spite of alteration, the sample contains over 10% large garnet grains which are poikiloblastic and have inclusions of all other major minerals.
P series
The P-type mafic gneiss sample OL.198 is the only representative of this group. The sample is strongly altered and contains only some relicts (ca. 1.4%) of primary amphibole. Plagioclase and biotite are the most typical constituents and they both represent over 20% of the modal composition. The proportion of K-feldspar is abnormal high, close to 20% which most likely is an indication of migmatization processes. High content of titanite is typical for mafic members of the P series and also this sample contains 3.4% that. Chlorite composes 7% and rather coarse-grained saussurite close to 6% of the mode. Pyrite and pyrrhotite are the most important opaque minerals and, in addition to those, some grains of ilmenite and magnetite as well as chalcopyrite have been detected in the rock.
The gneiss is granoblastic and fine- to medium-grained. Quartz and feldspars exist as totally irregular shaped, roundish grains with diameter of 1 mm in average. Biotite scales and hornblende grains have been ca. 0.5 mm in diameter, but in many cases the amphiboles are totally replaced by chlorite which is found as irregular spots typically ca. 1 mm in diameter. Titanite composes small, 0.3 mm long subidiomorphic crystals but it is also found as irregular, roundish and randomly located grains.
As demonstrated by the modal composition, the rock is strongly and pervasively altered. Amphibole is replaced by chlorite for the most part and some biotite is altered to chlorite, too. Plagioclase is pigmented all over the rock by microcrystalline saussurite 25
and, in addition to that, it is possible to find rather coarse grained carbonate-saussurite spots in the rock.
The P-type mica gneisses are chemically close to identical but their mineral compositions are totally different. The sample OL.202 is typical mica gneiss in which quartz, plagioclase and biotite compose roughly one third of the rock volume. In addition to those, apatite composes ca. 2% and secondary mineral phases a couple of percentage units. The sample is fine-grained and roundish quartz and feldspar grains are ca. 0.5 mm in diameter. Small pyrite, pyrrhotite and chalcopyrite grains with diameters less than 0.3 mm have been found in the rock. Extremely thin hematite scales may also rim the biotite scales as the alteration product of dark micas. Biotite composes exactly one third of the rock volume and the rock is moderately foliated but individual biotite scales are 0.5 mm in length and randomly located and surrounded by homogeneous felsic mineral mass. Thus the rock is not easily cleavable and despite of rather large proportion of biotite it is physically close to isotropic.
The sample OL.191 is a chlorite-saussurite rock in which roundish quartz grains are surrounded by microcrystalline saussurite and chlorite. Quartz grains are typically 0.5 mm in diameter but randomly located in the saussurite matrix. Chlorite replaces original biotite scales and in the present form the chlorite scales may be 0.5 - 1.0 mm in length and they form randomly situated spots with diameters varying from 1 to 2 mm. Fine- grained hematite is a typical constituent within these chlorite accumulations in which individual hematite grains are situated between chlorite scales. The material is isotropic but this kind of pervasively altered rock is mechanically weaker than the fresh counterparts.
The P-type TGG gneiss sample OL.193 is a moderately oriented, clearly banded and medium grained TGG gneiss. Both quartz and plagioclase compose close to 30% and K-feldspar and biotite 15 - 20% of the rock volume. In addition to those, the rock contains some apatite and minor amount of opaque minerals. Pyrite is the most frequently detected opaque mineral and, in addition to that, some hematite has been found between biotite scales and in chlorite mass and pyrrhotite and chalcopyrite as individual grains.
The rock shows a distinct metamophic banding, it is medium-grained and average grain size of it is 1 mm. Biotite is concentrated to the dark bands which are 1 mm wide at most but they are not continuous mica chains making the rock not very easily cleavable. The dark bands are also somehow wavy and the texture is similar to high grade blastomylonitic texture in which dark bands build up an anastomosing system. Quartz- feldspar mass between and also inside to the dark bands is granoblastic and felsic minerals are typically roundish and do not show any features of elongation to the plane of foliation.
The TGG gneiss is rather fresh except to its plagioclase which is all over the sample weakly pigmented by microcrystalline saussurite. The feldspar is never totally saussuritized and thus no saussurite is mentioned in the mode of the sample. Biotite is not markedly altered and other minerals are also quite fresh. 26 27
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/m3.
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 qC). 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 the Appendix 3. 28
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 19 samples range between 2660 and 2871 kg/m3. The highest values, exceeding 2800 kg/m3 are related to three mica gneiss samples. From these, samples 202 and 205 are highly altered (chloritized and saussuritized). Sample 198 contains hornblende and biotite and also an anomalous amount of titanite. Furthermore, porosities of samples 198 and 202 are extraordinary low, 0.03 – 0.12 %. Two of the densest samples are P-series and one T-series in terms of their chemical composition.
All the samples are paramagnetic with susceptibility values ranging from 130·10-6 SI to 630·10-6 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. The two quartz gneiss samples are the lightest, having also low magnetic susceptibility values. From the whole measured population, S-series mica gneisses have slightly smaller susceptibility-density ratios than other samples. a)Data: Borehole KR19, KR19B b)Data: Boreholes KR1 - KR6
OLKILUOTO PETROPHYSICS OLKILUOTO PETROPHYSICS
19 samples 268 samples 100000 100000 20%
10% SI) SI) -6 10000 -6 10000 5%
1% 1000 1000 0.5%
0.1%
100 100 SUSCEPTIBILITY (*10 SUSCEPTIBILITY (*10 10 10 2400 2600 2800 3000 3200 2400 2600 2800 3000 3200 3 DENSITY (kg/m ) DENSITY (kg/m3)
MICA GNEISS AMPHIBOLITE/MAFIC ROCK VEIN GNEISS GRANITE PEGMATITE GREY GNEISS GREY GNEISS QUARTZITIC GNEISS MICA GNEISS RED = T-SERIES CALCULATED VALUES GREEN = S-SERIES BLUE = P-SERIES
Figure 3-1. Susceptibility vs. density, a) samples 189 – 207, boreholes OL-KR19 and OL-KR19B, b) data from previously examined boreholes OL-KR1 – OL-KR6. 29
Since the samples are paramagnetic (susceptibility < 1000·10-6 SI), they do not carry significant remanent magnetization. The measured remanence values are typically 10 – 20 mA/m, being below the practical detection limit of the measuring device. There is only one clearly higher remanence value, 160 mA/m, related to sample 204 (T-series mica gneiss), indicating a small amount of ferrimagnetic minerals (most probably pyrrhotite). According to microscopic inspection, there are 1.4 % opaque minerals in this sample. The determined orientation of the remanent magnetization for this weakly ferrimagnetic sample is 304q/58.4q (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. Opaque minerals also have a slight effect in resistivity, as indicated in Fig. 3-2b. The most porous and least resistive (< 10 000 ohmm) samples are two biotite-rich T-series vein gneisses (sample numbers 199 and 201) and one highly altered S-series mica gneiss (sample number 205). The latter sample includes also an anomalous amount of opaque minerals, 9.9 %. However, its resistivity is almost equal to the two highly porous vein gneisses (199 and 201), indicating the dominating effect of porosity. a) b) OLKILUOTO PETROPHYSICS OLKILUOTO PETROPHYSICS
19 samples 19 samples 500000 500000
50000 50000
5000 5000
500 500 RESISTIVITY (ohmm) 10 Hz RESISTIVITY (ohmm) 10 Hz 50 50 00.511.52 02.557.510
POROSITY (%) OPAQUE MINERALS (%)
MICA GNEISS MICA GNEISS VEIN GNEISS VEIN GNEISS GREY GNEISS GREY GNEISS QUARTZITIC GNEISS QUARTZITIC GNEISS RED = T-SERIES RED = T-SERIES GREEN = S-SERIES GREEN = S-SERIES BLUE = P-SERIES BLUE = P-SERIES
Figure 3-2. Effect of porosity and content of opaque minerals in electric resistivity, a) porosity vs. resistivity, b) opaque minerals vs. resistivity, OL- KR19 and OL-KR19B. 30
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 4570 – 5900 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 S-series samples, which are all mica gneisses. P-series samples have medium velocities ranging from c. 5400 to 5700. The lowest velocity values are associated to the samples belonging to T- series. From the rock types, the lowest values are detected from vein gneisses, especially from two biotite-rich and porous samples (numbers 199 and 201) and one highly altered sample (number 189) with relatively low (0.33 %) porosity.
OLKILUOTO PETROPHYSICS
19 samples 6000
5500
5000
4500 P-WAVE VELOCITY (m/s) VELOCITY P-WAVE 4000 00.511.52
POROSITY
MICA GNEISS VEIN GNEISS GREY GNEISS QUARTZITIC GNEISS RED = T-SERIES GREEN = S-SERIES BLUE = P-SERIES
Figure 3-3. Porosity vs. P-wave velocity, OL-KR19 and OL-KR19B. 31
4 FRACTURE MINERALOGY
The account on fracture mineralogy of drill core OLKR19 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-KR19 has 1365 filled fractures in total, which makes 2.6 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 demonstrated 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.
Numerous zone interactions are reported from borehole OLKR19 (Fig. 4-1, column 10). Without exception these zones are featured by hydrothermal fluid circulation. 32 33
OLKR 19 Acid alteration < > Alkaline alteration ZONE KAOL-ILL FF ILL FF CALCITE FF
Sulphides IL+KA+GREEN and FILL AREA FILL DEPTH FILL AREA FILL DEPTH FILL AREA FILL DEPTH GREY CLAY FILLING (%) (mm) (%) (mm) (%) (mm) QUARTZ Lithology
Fracture Indication 0 3 0 3 mm 03 mm 100 033 0 100 0 0 100 0 SERICITE Pervasive IL alteration IL Pervasive Pervasive KA alteration CHLORITE CC-monomineral filling GRAPHITE CORRODED
LogK Py-monomineral filling INDIC. FLOW
12 3 4 5 6 78 9 1011121314 15 1617181718 19 20 0 0.3
0.9 1.0 0.5
0.3 0.1
0.1 0.1 0.1 0.1 0.3
0.2 100
0.3 0.2 0.2 0.3
0.4
0.2 0.2 0.1 0.3
0.2 0.3 0.3 200 0.6 0.1
0.4 0.3
0.3 0.1
0.2 0.6 0.3 0.3
0.3 0.6
0.2 0.3 0.2 300 0.3
0.3
0.3 0.4
1.9 0.1 0.3
0.2 400 0.1 0.4 0.3 0.2 0.3
0.2
0.2 0.3 0.4 0.2 0.3
500
0.4
0.1 0.2
Figure 4-1. 34 35
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 in a number of drill core transverses. Pervasively altered core lengths range from 2 to 127 metres (Table 4-2).
The core length of the pervasively altered rock in bore hole OL-KR 19 is considerable; 238 m in total. That makes 44 % of total core length. Along with illite these zones are characterized by abundant occurrences of the other hydrothermal derivatives; mainly kaolinite, calcite and sulphides (see Fig. 4-1). 36
Table 4-1. Explanations of the columns in Fig. 4-1.
Column No. Explanation Water conductivity measurement with 2 m packer interval. data 1 from Pöllänen, Pekkanen, Rouhiainen 2005 2 Sulphide as monomineralic fracture filling
3 Sulphide fracture filling (thickness of filling on scale 0 - 3 mm) All clay phases in fracture including hydrothermal and 4 secondary phases (thickness scale 0 - 3 mm) Lithology of drill core, see legend for the lithology on the right. 5 Data logged by A. Kärki. Pervasive illitic alteration of the rock Data from K. Front & M. 6 Paananen 2006. Pervasive kaolinite alteration of rock . Data from K. Front & M. 7 Paananen 2006. 8 Fracture density Deformation zone intersection. Brittle fault zone intersection, brittle joint cluster intersection, semi-brittle fault intersection 9 Data from Paulamäki et al 2006. Percentage1 of kaolinite illite of the fracture plain area in drill 10 core section (scale: 0 -100 %) Thickness2 of kaolinite-illite filling in fracture plain area (scale: 11 0 -3 mm). Percentage1 of illite of fracture plain in drill core section area 12 (scale: 0 -100 %).
2 13 Thickness of illite filling on fracture plain area (scale: 0 -3 mm).
14 Occurrence of calcite as monomineralic fracture filling Percentage1 of calcite of the fracture plain in drill core section 15 area (scale: 0 -100 %). Thickness2 of calcite on fracture plain in drill core section 16 (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
The water conductivity data does reveal elevated values at 22 m (kaolinite-illite alteration), 39-40 m ((iilite alteration) and a set of elevated values at the core length from 369-407 (kaolinite-illite fractures). 37
Table 4-2. Pervasive illite and kaolinite alteration zones in bore hole OL-KR19.
drill core drill core length from length to (m) (m) Illite alteration 40 167 194 202 210 212 230 260 307 311 337 343 385 423 461 472 479 486 532 537
Kaolinite alteration 337 343
Table 4-3. Kaolinite- illite fracture filling zone (pervasive zones excluded).
Average filling Core thickness length Start (m) End (m) (mm) (m) 225.3 226.6 0.2 1.2 268.4 269.4 0.4 1 291.4 299.7 0.2 8.3 372.7 375.4 1.9 2.6 466.6 466.6 0.2 0 472.9 473 0.4 0.1
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 fractures.
. 38
1. Kaolinite-illitic fracture filling sets
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
Table 4-4. Illite fracture filling zones (pervasive zones excluded).
Average filling Core Zone Zone thickness length start (m) end (m) (mm) (m) 182.5 191.7 0.3 9.2 253.6 264.8 0.3 11.2 295.6 297.5 0.3 1.9 303.2 309.1 0.3 5.9 372.6 376.3 0.1 3.7 471.1 488.1 0.2 17 533.7 535.7 0.2 2 fracture fillings, outside the above mentioned pervasive kaolinite-illite alteration zones are indicated in the Table 4-3. Notable is the fracture zone 372 – 375 m, which has bulky kaolinite-illite fracture filling.
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 Table 4-4.
2. Calcitic fracture filling sets
The drill core has remarkable quantity of calcitic fracture filling sets. These 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, having calcite as major phase, are characterized by higher fracture density than in the zones in which the influence of hydrothermal activity is insignificant. A number of the calcite fracture filling sets are less than metre in core section but individual zone may have core length of 74 metre (see Table 4-5). The total core length of the calcite fracture sets is 321 metres, thus 50 % of the bore hole has calcite in fracture fillings.
Especially worth mentioning is the zone 73.1 – 147.3, a pervasive illite zone which encloses two sequences of calcitic fracture fillings. Similarly, the zones 234.3 – 263.8 and 268.4 – 279 m, both of which are linked with illitie-kaolinite alteration and zone intersection. Calcite filling thickness is 0.6 mm in average and in fractures 239.7 and 253.6 m their thickness is even10 mm. 39
Table 4-5. Calcite fracture filling zones. Highlighted in grey are the zones which represent advanced carbonatization.
Average filling Core thickness length Start (m) End (m) (mm) (m) 14.4 65.4 0.3 51.0 73.1 147.3 0.3 74.2 151.4 161.9 0.2 10.5 165.1 173.8 0.3 8.7 179.4 179.8 0.2 0.4 182.4 203.1 0.3 20.7 210.6 212.8 0.4 2.3 216.7 226.8 0.3 10.1 234.3 263.8 0.6 29.5 268.4 279.0 0.6 10.6 291.4 299.7 0.2 8.3 324.3 325.8 0.3 1.5 340.0 342.8 0.4 2.8 365.1 399.5 0.3 34.4 405.6 409.4 0.4 3.8 415.3 417.0 0.3 1.8 443.6 446.4 0.2 2.9 452.0 488.8 0.3 36.7 509.7 513.8 0.4 4.2 529.2 536.2 0.2 7.0
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. These core lengths are given in the Table 4-6 (see also Fig. 4-1, column 21). There are 5 zones, each ca. 20 m in core length and in which flow indications are seem to form sequences at core length 46.2 – 65.4 m, 109.4 – 123.4 m, 148.8 – 157.7 m, 237 – 259.7 m, 446 – 470.5 m. All these zones are surrounded by hydrothermal alteration zones (Fig. 4-1) and a number of the fractures at zones have corrosion. 40
Table 4-6. Open fracture (rock type and core lengths in m) that are interpreted to contain on textural basis traces of water flow.
VGN 46.23 VGN 155.51 MGN 247.93 MGN 257.01 VGN 46.93 VGN 155.52 MGN 247.95 VGN 259.01 VGN 47.77 VGN 155.63 MGN 247.97 VGN 259.2 VGN 49.86 VGN 155.71 MGN 248.07 VGN 259.41 VGN 53.09 VGN 155.74 MGN 248.2 VGN 296.14 VGN 53.79 VGN 155.84 MGN 248.33 VGN 296.27 VGN 54.55 VGN 156.17 MGN 248.43 VGN 296.31 VGN 55.66 VGN 156.21 MGN 248.57 VGN 296.33 VGN 55.69 VGN 156.36 MGN 252.98 VGN 296.45 VGN 55.72 VGN 156.53 MGN 253.36 VGN 296.55 VGN 56.49 VGN 156.58 MGN 253.41 VGN 296.61 VGN 58.47 VGN 156.66 MGN 253.51 VGN 296.64 VGN 61.78 VGN 156.86 MGN 253.64 VGN 296.65 VGN 61.8 VGN 156.92 MGN 254.03 VGN 296.7 VGN 62.45 VGN 156.97 MGN 254.18 VGN 296.73 VGN 63.6 VGN 202.51 MGN 254.35 VGN 296.76 PGR 64.54 VGN 212.17 MGN 254.61 VGN 296.88 VGN 110.42 VGN 212.2 MGN 254.72 VGN 297.02 VGN 111.49 MGN 238.73 MGN 254.88 VGN 297.29 VGN 111.52 MGN 239.1 MGN 255.02 VGN 315.76 VGN 117.98 MGN 239.17 MGN 255.08 VGN 325.78 VGN 118.91 MGN 239.28 MGN 255.08 VGN 376.67 VGN 119.3 MGN 239.4 MGN 255.22 VGN 376.68 VGN 119.71 MGN 239.65 MGN 255.46 VGN 446.19 VGN 121.32 MGN 239.66 MGN 255.53 VGN 450.15 VGN 122.64 MGN 239.68 MGN 255.58 VGN 452.26 VGN 149.75 MGN 239.71 MGN 256.33 VGN 457.82 VGN 155.27 MGN 239.75 MGN 256.5 VGN 458.32 VGN 155.32 MGN 239.9 MGN 256.58 VGN 461.11 VGN 155.35 MGN 247.07 MGN 256.6 VGN 461.46 VGN 155.39 MGN 247.11 MGN 256.68 QGN 470.06 VGN 155.42 MGN 247.47 MGN 256.91 QGN 470.62
Iron oxides and oxy-hydroxides are found in 21 fractures as red-brown coloured fillings at surficial zone, which locates at 2.52-28.23 m core length (Table 4-7). 41
Table 4-7. Occurrence of Fe-oxide and oxy-hydroxides in fracture fillings.
QGN 2.52 QGN 19.75 QGN 2.68 QGN 19.8 PGR 13.11 QGN 19.9 MFGN 14.6 QGN 20.1 MFGN 14.72 QGN 20.17 PGR 15.16 QGN 20.21 PGR 15.79 QGN 21.93 PGR 17.82 PGR 22.41 QGN 18.77 PGR 22.63 QGN 19.36 PGR 28.83 QGN 19.57
Graphite forms in 18 fractures slickensides or pulverized fillings. It occurs chiefly in single fracture plains but is present in a number of fractures at the core length interval 76.9 – 119 m.
Table 4-8. Fractures (core legth in metres) that have graphitic fracture fillings.
76.95 324.63 89.58 333.97 104 465.21 114.13 465.29 114.16 465.32 117.4 528.65 117.63 528.66 119.2 528.99 278.13 535.17
4.4 Relationship between fracture filling data and calvanic connection measurements
Electrical measurement data (Lehtonen 2006) on the galvanic connections concerning the boreholes in the Table 4-9. All the groundings from OL-KR19 represent weak or detectable connections, while the strong connection point have not been found. The comparison of electric measurements and fracture fillings/alteration reveal that at the three core lengths, localized by electrical methods, situate inside altered rock; specifically surrounded by pervasive illite at core lengths 75 m and 105 – 135 m, and calcite filling zone at core length 445 m. The last mentioned core depth contains also water flow indication. The geophysical measurements yield the grounding potency for all these core lengths categories weak (highlighted in yellow) in table and discernable. 42
Table 4-9. List of the bore holes in which the data of galvanic connections is available.
OL-KR1 OL-KR2 OL-KR4 OL-KR6 - 8 OL-KR10 OL-KR13 - OL-KR14 OL-KR19 OL-KR22 -25 OL-KR27 – 32
Table 4-10. Galvanic connections grounded form OL-KR19 (connecting grounding core lengths given in rows) to the drill holes OL-KR4 and 25. The detected charge potentials, are reported (Lehtonen 2006) to fall into category “weak” (highlighted in yellow) or “discernable” (white).
OL- OL- KR19 OL-KR4 KR25 Pervasive illite, sulphides 75 314 see above 75 368 Carbonatizated fractures, obvious flow 445 760 marks Pervasive illite 105-135 383 see above 105-136 518 43
5 SUMMARY
Veined gneisses dominate the NW part of the central of the Olkiluoto study site and the bedrock intersected by the boreholes OL-KR19 and KR19B is composed for the most part of veined gneisses. Besides to those, several 5 - 10 wide pegmatitic granite intersections and one, close to 30 m long mica gneiss intersection have been detected in the core sample. TGG gneisses with various, sometimes coarse-grained veined gneisses have been found in the core sample from drilling length of 130 m to 210 m.
The P series is represented by four samples studied in details. Two of those are P-type mica gneisses; one is TGG gneiss and one mafic gneiss. Three quartz gneiss and two mica gneiss samples will classify into the S series. The rest 10 samples belong to the T series. Two of those are quartz gneisses, three are mica gneisses and five are veined gneisses.
The P-type TGG gneiss contains more than 66% SiO2 and is a typical member in the P series in which the P2O5 concentration exceeds 0.3% and CaO 2%. The mafic gneiss studied in detail is similarly quite typical amphibole bearing and mica rich rock of the P series for which low concentration of SiO2 (48%) and high concentrations of phosphorus (1.4% P2O5) and titanium (2.6% TiO2) are characteristic. All major elements concentrations in these samples are very close to the expected values.
The S-type mica gneisses and quartz gneisses are chemically close to identical and they fall into the low-calcium group of the S-series due to their moderate calcium concentrations (2 – 4% CaO). All major elements concentrations in these samples are in expected values. One mica gneiss sample is a strongly altered, now epidote rich and sericite and garnet bearing rock which deviates chemically from others. The sample contains 15% CaO which is the highest value analysed from the S-type mica gneisses and the concentration of aluminium is lower than in typical members of the high- calcium group. Strong retrogressive alteration explains the exceptional major element composition and high content of epidote.
The T series is represented by ten samples which are veined gneisses, mica gneisses and quartz gneisses. In this sequence the less silicic sample contains 59% SiO2 and the most silicic quartz gneiss more than 77% SiO2. The major element concentrations in individual members of this sequence are directly controlled by the concentration of silica and the element concentrations are strictly in anticipated values.
The mica gneisses of the T series have been cordierite bearing gneisses but now cordierite is totally replaced by microcrystalline pinite which composes 4 - 13% of the rock volume. Biotite content has been ca. 20% in each of those but now a remarkable proportion of it is replaced by chlorite. Feldspars have composed 30 - 40% of the rock but currently plagioclase is pigmented in some extend by saussurite and in one of the samples a third part of plagioclase is totally saussuritized. In addition to those, fibrolithic sillimanite has been detected in the samples. The mica gneisses have metamorphic banding but due to low amount of biotite the dark bands are not totally continuous biotite seams but contain also some felsic mineral grains. 44
The T-type Quartz gneisses have close to identical modal compositions but one has been affected by stronger alteration. They have been composed of 45 - 50% quartz, 20% plagioclase, 6% K-feldspar and close to 15% biotite. The biotite in one sample is almost totally chloritized but in others it is rather fresh. Quartz gneisses are granoblastic and not well foliated rock. Typically they are even- and medium-grained or fine-grained with mean grain varying from 1 mm to 0.5 mm.
The T-type veined gneisses are cordierite or pinite and often sillimanite bearing quartz- feldspar-biotite rocks. Biotite proportion ranges from 44% in the less silicic sample to 20% in the most silicic one. The amount of quartz increases from 24% to ca. 35% and plagioclase from 18% to 32% as silicity increases. K-feldspar is concentrated to the silicic types in which it composes 2 – 5%. The total amount of pinite and cordierite varies between 4 and 7% while sillimanite composes often 1 - 4% of the rock volume. Paleosome materials are fine-grained and average grain sizes of major minerals in those vary between 0.3 and 1 mm. Paleosome shows a distinct metamorphic banding. Dark bands are somehow wavy and compose lensoidal structures. Leucocratic bands are granoblastic in texture. Quartz and feldspar grains are roundish and often slightly elongated to the plane of rock foliation.
The S-type mica gneisses contain in addition to biotite, quartz and plagioclase only a minor amount of other mineral phases. Biotite builds up ca. 20%, anorthitic plagioclase 25% and quartz 49% of the whole rock volume. Only some garnet and opaque mineral grains have been detected in addition to the major minerals. The mica gneiss is granoblastic and fine-grained. S-type quartz gneisses are also biotite bearing rocks in which the major minerals, in addition to biotite, are quartz and plagioclase. The proportion of micas and their retrograde derivatives does not exceed 20%. The content of plagioclase varies between 25 and 30% and the content of quartz is ca. 40%. The gneisses are granoblastic, weakly oriented rocks and the difference between these and the S-type mica gneisses is not great.
The P-type mafic gneiss sample studied from this core is strongly altered and contains only some relicts of primary amphibole. Plagioclase and biotite are the most typical constituents and they both represent over 20% of the modal composition. Proportion of K-feldspar is also abnormal high, close to 20% which most likely is an indication of migmatization processes. High content of titanite is also typical for these mafic gneisses. The texture of this gneiss is granoblastic and it is fine- to medium-grained. The P-type mica gneisses are mainly rocks in which quartz, plagioclase and biotite each compose roughly one third of the rock volume. In addition to those, apatite composes ca. 2% and secondary mineral phases a couple of percentage units. The sample is fine- grained and roundish quartz and feldspar grains are ca. 0.5 mm in diameter. One gneiss sample is altered to a chlorite-saussurite rock in which roundish quartz grains are surrounded by microcrystalline saussurite and chlorite. Quartz grains are typically 0.5 mm in diameter and they are randomly located in the saussurite matrix. Chlorite replaces original biotite scales and in the present form the chlorite scales may be 0.5 - 1.0 mm in length and they form randomly situated spots with diameters varying from 1 to 2 mm. Fine-grained hematite is a typical constituent within these chlorite accumulations and individual hematite grains are situated between chlorite scales. P- type TGG gneisses are moderately oriented, clearly banded and medium grained. Both 45
quartz and plagioclase compose close to 30% and K-feldspar and biotite 15 - 20% of the rock volume. In addition to those, the rock contains some apatite and minor amount of opaque minerals. The rock shows a distinct metamophic banding, it is medium-grained with average grain size of it is 1 mm. Biotite is concentrated to dark bands which are somehow wavy and the texture resembles high grade blastomylonitic texture in which dark bands build up an anastomosing system.
Petrophysical properties were measured from 19 samples. Their measured density values range between 2660 and 2871 kg/m3. The highest values, exceeding 2800 kg/m3 are related to three mica gneiss samples. All the samples are paramagnetic with susceptibility values ranging from 130·10-6 SI to 630·10-6 SI. The two quartz gneiss samples are the lightest, having also low magnetic susceptibility values. From the whole measured population, S-type mica gneisses have slightly smaller susceptibility-density ratios than other samples. The measured remanence values are typically 10 – 20 mA/m, being below the practical detection limit of the measuring device. There is only one clearly higher remanence value, 160 mA/m, related to a T-type mica gneiss.
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, but also opaque minerals appear to have a slight effect in resistivity.
Measured P-wave velocities are 4570 – 5900 m/s, indicating typically rather unfractured and unaltered crystalline rocks. In a porosity vs. P-wave velocity diagram, the samples appear to form more or less distinct populations according to their chemical composition. The highest velocity values are related to S-series samples, which are all mica gneisses. P-series samples have medium velocities ranging from c. 5400 to 5700. The lowest velocity values are associated to the samples belonging to T-series. From the rock types, the lowest values are detected from vein gneisses.
The drill hole OL-KR19 has moderate density of fracturing; 2.6 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 illitization concerns as much as 44 % of the total OLKR 19 core length and in addition to that the fracture related illite and kaolinite form a number of disseminated sequences, which typically have core lengths less than 20 metres. Even 50 % of the bore hole length has calcite as major constituent in fracture fillings. The degree of fracture related sulphidization follows the strength of illitization and kaolinisation at the alteration zones. Graphite is concentrated into a number of fractures especially at core length 76.9 – 119 m.
The frequency of fracturing correlates with the weight of hydrothermal activity. Especially the core lengths 40 – 147 m, 234 – 279 m and 370 – 412 m, 450 – 490 m are conspicuous in that respect. These core length intervals are related with calcitic illite- kaolinite alteration and they overlie the zone intersections. The open fractures at core lengths 46.2 – 65.4 m, 109.4 – 123.4 m, 148.8 – 157.7 m, 237 – 259.7 m and 446 – 470.5 m have incohesive clay material that hold textures, which could refer to water flow. 46 47
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.
Lehtonen, T. 2006. Visualization and Interpretation of the Year 2004 Mise-a-la-Masse Survey Data at Olkiluoto Site. Working Report 2006-08. Posiva Oy, Olkiluoto.
Mattila, J. 2006. A System of Nomenclature for Rocks in Olkiluoto. Working report 2006-32. Posiva Oy, Olkiluoto. 16 p.
Paulamäki, S., Paananen, M., Gehör, S., Kärki, A., Front, K., Aaltonen, I., Ahokas, T., Kemppainen, K., Mattila, J. & Wikström, L. 2006. Geological model of the Olkiluoto site, version 0. Working Report 2006-37. Posiva Oy, Olkiluoto.
Pöllänen, J., Pekkanen, J., Rouhiainen, P. 2005. Difference flow and electric conductivity measurements at the Olkiluoto site in Eurajoki, boreholes KR19 – KR28, KR19B, KR20B, KR22B, KR23B, KR27B and KR28B. Working report 2005-52. Posiva Oy, Olkiluoto.
Niinimäki, R. 2002. Core drilling of deep borehole OL-KR19 at Olkiluoto in Eurajoki 2002. Working Report 2002-49. Posiva Oy, Olkiluoto. 220 p.
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. 48 49
APPENDICES
Appendix 1.
File KR19_APP1 in the disk enclosed. The Appendix contains the results of whole rock chemical analyses.
Appendix 2.
File KR19_APP2 in the disk enclosed. The Appendix contains the results of modal mineral composition analyses. 50 Appendix 3. Petrophysical parameters, drill core OL-KR19.
RESISTIVITY VALUES (:m) IP-ESTIMATES HOLE SAMPLE FROM TO D(kg/m3) K(PSI) J(mA/m) P-wave (m/s) R0.1[:m] R10 [:m] R500[:m] PL (%) PT (%) Pe(%) KR19 OL.189 68.13 68.23 2766 380 20 4570 56000 48600 33700 13 40 0.33 KR19 OL.190 88.16 88.26 2744 260 20 5780 11100 8440 6850 24 38 0.14 KR19 OL.191 136.63 136.72 2744 350 10 5620 32500 30100 21700 7 33 0.36 KR19 OL.192 197.15 * 2754 400 40 5300 108000 92900 57100 14 47 0.15 KR19 OL.193 206.72 * 2702 220 10 5710 22900 22200 20800 3 9 0.21 KR19 OL.194 240.73 * 2711 240 10 5330 65200 56000 42200 14 35 0.27 KR19 OL.195 250 250.1 2686 190 20 5440 117000 105000 67600 10 42 0.23 KR19 OL.196 266.4 * 2731 280 10 5530 58700 54300 42100 7 28 0.24 KR19 OL.197 334.23 334.3 2730 270 10 5380 151000 134000 85000 11 44 0.3 KR19 OL.198 365.5 365.6 2862 620 50 5430 232000 200000 108000 14 53 0.12
KR19 OL.199 395.74 * 2741 380 20 4870 3200 3050 2660 5 17 1.32 51 KR19 OL.200 428.45 * 2724 220 20 5580 72000 65300 50800 9 29 0.09 KR19 OL.201 435.5 * 2734 380 10 4800 4580 4410 4010 4 12 1.2 KR19 OL.202 467.59 * 2805 370 10 5470 >334864 >334864 >334864 0.03 KR19 OL.203 504.08 504.18 2724 170 30 5670 41800 36500 28800 13 31 0.12 KR19 OL.204 509.46 * 2720 630 160 5390 28100 24700 19000 12 32 0.32 KR19 OL.205 509.83 * 2871 250 10 5890 5150 4200 3290 18 36 1.13 KR19B OL.206 18.9 18.99 2746 200 10 5900 58600 54800 44600 6 24 0.3 KR19B OL.207 21.38 21.47 2660 130 10 5470 124000 109000 85600 12 31 0.2
* The depth value was not readable from the sample
D = density R10 = electric resistivity, 10 Hz frequency K = magnetic susceptibility R500 = electric resistivity, 500 Hz frequency J = remanent magnetization PL = IP effect = 100*(R0.1-R10)/R0.1 P-wave = velocity of seismic P-wave PT = IP effect = 100*(R0.1-R500)/R0.1 R0.1 = electric resistivity, 0.1 Hz frequency Pe = effective porosity