Databank

Workreport 1997-40

Back

Name:

Loviisan Hästholmenin kairausnäytteiden HH-KR1, HH-KR2 ja HH-KR3 petrologia ja matalan lämpötilan rakomineraalit

Writer:

Seppo Gehör; Aulis Kärki; Olavi Taikina-aho

Language:

Finnish

Page count:

196

Summary:

Working report: LOVIISA, HÄSTHOLMEN, PETROLOGY ANG LOW TEMPERATURE
FRACTURE MINERALS IN DRILL CORE SAMPLES HH-KR1, HH-KR2
AND HH-KR3

ABSTRACT

The results of petrological studies and low temperature fracture mineral mappings of drill
cores HH-KR1, -KR2 and -KR3 from the Hästholmen 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 four main rock types of the drill cores area are: 1)wiborgites and pyterlites, 2) porphyritic
rapakivi granites, 3) even grained rapakivi granites and 4) weakly porphyritic, leucocratic
rapakivi granites and applites. In addition to these in the cores has been found also granitic
rocks, probably not directly associated with the rocks of the rapakivi association. Wiborgites
and pyterlites are porphyritic rapakivi granites the phenocrysts of which are roundish K-
feldspar grains or ovoids surrounded by medium grained ground mass. The ovoids in the
wiborgites are mantled by plagioklase whereas the ovoids in the pyterlites typically have no
plagioklase mantles. Even and medium grained rapakivi granites are typical granites in their
modal mineral composition. Porphyritic varieties include phenocrysts 1 - 2 cm in diameter.
Weakly porphyritic, leucocratic rapakivi granites contain a few, scarcely visible feldspar
phenocrysts and mafic minerals less than 5 %. Applites are reddish, medium and even grained
granites including less than 5 % mafic minerals.

Calcite, dolomite, Fe hydroxides and clay minerals (illite, montmorillonite and kaolinite)
form the most typical fracture mineral phases throughout the drill cores. Carbonate
crystallizations consist of calcite and/or dolomite which have been found frequently in every
core. Carbonate fillings are typically less than 1 mm thick and ca. 3 mm at most. The
crystallization of calcite took place in at least two phases the products of which are
distinguishable by naked eyes. Fe hydroxides may exist serially in every drilling depths and
no depth control is established. Fe hydroxides form typically thin filmy covers, 1 mm in
thickness at most. Fluorite and Fe sulphides (pyrrhotite and pyrite) have been found less freq-

uently. The zones of high metasomatic alteration in which the feldspars are replaced by
kaolinite, illite and sometimes also by hematite affect directly to fracture mineral phases.
Fracture minerals in these zones consist of kaolinite, illite and hematite controlled by the
character of alteration zone and intensity of alteration process. Fracture walls coated by
chlorite and chloritic slickensides occur in every bedrock environments and in every depths.





Keywords: Palaeoproterozoic, anorogenic, rapakivi, granite, petrology, whole rock
chemistry, mineral chemistry, low temperature, fracture mineral
LOVIISA, HÄSTHOLMEN, PETROLOGY ANG LOW TEMPERATURE
FRACTURE MINERALS IN DRILL CORE SAMPLES HH-KR1, HH-KR2
AND HH-KR3

ABSTRACT

The results of petrological studies and low temperature fracture mineral mappings of drill
cores HH-KR1, -KR2 and -KR3 from the Hästholmen 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 four main rock types of the drill cores area are: 1)wiborgites and pyterlites, 2) porphyritic
rapakivi granites, 3) even grained rapakivi granites and 4) weakly porphyritic, leucocratic
rapakivi granites and applites. In addition to these in the cores has been found also granitic
rocks, probably not directly associated with the rocks of the rapakivi association. Wiborgites
and pyterlites are porphyritic rapakivi granites the phenocrysts of which are roundish K-
feldspar grains or ovoids surrounded by medium grained ground mass. The ovoids in the
wiborgites are mantled by plagioklase whereas the ovoids in the pyterlites typically have no
plagioklase mantles. Even and medium grained rapakivi granites are typical granites in their
modal mineral composition. Porphyritic varieties include phenocrysts 1 - 2 cm in diameter.
Weakly porphyritic, leucocratic rapakivi granites contain a few, scarcely visible feldspar
phenocrysts and mafic minerals less than 5 %. Applites are reddish, medium and even grained
granites including less than 5 % mafic minerals.

Calcite, dolomite, Fe hydroxides and clay minerals (illite, montmorillonite and kaolinite)
form the most typical fracture mineral phases throughout the drill cores. Carbonate
crystallizations consist of calcite and/or dolomite which have been found frequently in every
core. Carbonate fillings are typically less than 1 mm thick and ca. 3 mm at most. The
crystallization of calcite took place in at least two phases the products of which are
distinguishable by naked eyes. Fe hydroxides may exist serially in every drilling depths and
no depth control is established. Fe hydroxides form typically thin filmy covers, 1 mm in
thickness at most. Fluorite and Fe sulphides (pyrrhotite and pyrite) have been found less freq-

uently. The zones of high metasomatic alteration in which the feldspars are replaced by
kaolinite, illite and sometimes also by hematite affect directly to fracture mineral phases.
Fracture minerals in these zones consist of kaolinite, illite and hematite controlled by the
character of alteration zone and intensity of alteration process. Fracture walls coated by
chlorite and chloritic slickensides occur in every bedrock environments and in every depths.





Keywords: Palaeoproterozoic, anorogenic, rapakivi, granite, petrology, whole rock
chemistry, mineral chemistry, low temperature, fracture mineral

Keywords:

Paleoproterotsoinen; anorogeeninen; rapakivi; graniitti; petrologia; kokokivikemia; mineraalikemia; matala lämpötila; rakomineraali

File(s):

Loviisan Hästholmenin kairausnäytteiden HH-KR1, HH-KR2 ja HH-KR3 petrologia ja matalan lämpötilan rakomineraalit (pdf) (4.1 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