Databank

Workreport 1997-9

Back

Name:

Eurajoen Olkiluodon kairausnäytteen OL-KR9 petrologia ja matalan lämpötilan rakomineraalit

Writer:

Seppo Gehör; Aulis Kärki; Seppo Suoperä; Olavi Taikina-aho

Language:

Finnish

Page count:

71

Summary:

Working report: EURAJOKI, OLKILUOTO: PETROLOGY AND LOW TEMPERATURE
FRACTURE MINERALS IN DRILL CORE SAMPLE OL-KR9.


ABSTRACT

The results of petrological studies and low temperature fracture mineral mappings of drill
core OL-KR9 from the Olkiluoto area are presented in this report.

The petrographic mapping was performed with the naked eye and the textures and modal
mineral compositions of the rock samples were determined by polarization microscopy. The
chemical compositions of the plagioclase, biotite and amphiboles existing as major
components, were determined by JEOL-733 superprobe at the Institute of Electron Optics,
University of Oulu. Whole rock analyses were carried out at the XRAL laboratory (Canada)
using an X-ray spectrometer, neutron activation analyzer, LECO sulphur analyzer and ion
selective electrodes (ISE). The fracture minerals were mapped and identified with the naked
eye and by stereo microscopy and X-ray diffractometry.

The five main rock types of the study area are in terms of petrographic features and whole
rock composition: 1) migmatitic and veined mica gneisses, 2) quartzitic gneisses, 3)
amphibolitic mafic schists, 4) gneissose tonalites or granodiorites and 5) medium-grained
granites and leucocratic pegmatites. All these rocks were found from the drill core Ol-KR9.

Calcite, Fe sulphides (pyrrhotite and pyrite) and clay minerals (illite, montmorillonite,
kaolinite and vermiculite) form the most typical fracture mineral phases throughout the drill
cores, with analcime, laumontite, palygorskite and quartz to be found less frequently. Pyrite
occurs in small idiomorphic grains and in thin covers and patches, and is encountered at all
depths along the whole core. Pyrrhotite is detected less often and usually occurs together with
graphite. Kaolinite fracture fillings are loose powdered masses or dense, white coverings,
while illite occurs in a green, transparent, soap-like mass or in a grey to green, loose clay
variety together with montmorillonite. Graphite slickensides are found in some depth zone,
and quartz is detected in a few fractures.

Water conductivity seems not to have exercised any distinct control over the fracture mineral
assemblages, since in most cases the zones having the best water conductivity include the
same fracture minerals as those of lower conductivity. Similarly, the composition of the
fracture mineral assemblages seems not to have been controlled by the surrounding bedrock
type with the exception of the fractures in graphitic rocks, which are frequently graphite-
bearing.

Keywords: Palaeoproterozoic, bedrock, mica gneiss, metapelite, migmatite, granitoid,
petrology, mineralogy, fracture mineral.
EURAJOKI, OLKILUOTO: PETROLOGY AND LOW TEMPERATURE
FRACTURE MINERALS IN DRILL CORE SAMPLE OL-KR9.


ABSTRACT

The results of petrological studies and low temperature fracture mineral mappings of drill
core OL-KR9 from the Olkiluoto area are presented in this report.

The petrographic mapping was performed with the naked eye and the textures and modal
mineral compositions of the rock samples were determined by polarization microscopy. The
chemical compositions of the plagioclase, biotite and amphiboles existing as major
components, were determined by JEOL-733 superprobe at the Institute of Electron Optics,
University of Oulu. Whole rock analyses were carried out at the XRAL laboratory (Canada)
using an X-ray spectrometer, neutron activation analyzer, LECO sulphur analyzer and ion
selective electrodes (ISE). The fracture minerals were mapped and identified with the naked
eye and by stereo microscopy and X-ray diffractometry.

The five main rock types of the study area are in terms of petrographic features and whole
rock composition: 1) migmatitic and veined mica gneisses, 2) quartzitic gneisses, 3)
amphibolitic mafic schists, 4) gneissose tonalites or granodiorites and 5) medium-grained
granites and leucocratic pegmatites. All these rocks were found from the drill core Ol-KR9.

Calcite, Fe sulphides (pyrrhotite and pyrite) and clay minerals (illite, montmorillonite,
kaolinite and vermiculite) form the most typical fracture mineral phases throughout the drill
cores, with analcime, laumontite, palygorskite and quartz to be found less frequently. Pyrite
occurs in small idiomorphic grains and in thin covers and patches, and is encountered at all
depths along the whole core. Pyrrhotite is detected less often and usually occurs together with
graphite. Kaolinite fracture fillings are loose powdered masses or dense, white coverings,
while illite occurs in a green, transparent, soap-like mass or in a grey to green, loose clay
variety together with montmorillonite. Graphite slickensides are found in some depth zone,
and quartz is detected in a few fractures.

Water conductivity seems not to have exercised any distinct control over the fracture mineral
assemblages, since in most cases the zones having the best water conductivity include the
same fracture minerals as those of lower conductivity. Similarly, the composition of the
fracture mineral assemblages seems not to have been controlled by the surrounding bedrock
type with the exception of the fractures in graphitic rocks, which are frequently graphite-
bearing.

Keywords: Palaeoproterozoic, bedrock, mica gneiss, metapelite, migmatite, granitoid,
petrology, mineralogy, fracture mineral.

Keywords:

Paleoproterotsoinen; kallio; kiillegneissi; metapeliitti; migmatiitti; granitoidi; petrologia; mineralogia; rakomineraali

File(s):

Eurajoen Olkiluodon kairausnäytteen OL-KR9 petrologia ja matalan lämpötilan rakomineraalit (pdf) (1.5 MB)


Back


Share article:
This website stores cookies on your computer. These cookies are used to improve our website and provide more personalised services to you.
Close

Cookies

To make this site work properly, we sometimes place small data files called cookies on your device. Most big websites do this too.

1. What are cookies?

A cookie is a small text file that a website saves on your computer or mobile device when you visit the site. It enables the website to remember your actions and preferences (such as login, language, font size and other display preferences) over a period of time, so you don’t have to keep re-entering them whenever you come back to the site or browse from one page to another.

2. How do we use cookies?

A number of our pages use cookies to remember your actions and preferences (such as login, language, font size and other display preferences.)

Also, some videos embedded in our pages use a cookie to anonymously gather statistics on how you got there and what videos you visited.

Enabling these cookies is not strictly necessary for the website to work but it will provide you with a better browsing experience. You can delete or block these cookies, but if you do that some features of this site may not work as intended.

The cookie-related information is not used to identify you personally and the pattern data is fully under our control. These cookies are not used for any purpose other than those described here.

3. How to control cookies

You can control and/or delete cookies as you wish – for details, see aboutcookies.org. You can delete all cookies that are already on your computer and you can set most browsers to prevent them from being placed. If you do this, however, you may have to manually adjust some preferences every time you visit a site and some services and functionalities may not work.

Close