Databank

Workreport 1997-19

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Name:

Kuhmon Romuvaaran kairausnäytteen RO-KR11 petrologia ja matalan lämpötilan rakomineraalit

Writer:

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

Language:

Finnish

Page count:

68

Summary:

Working report: ROMUVAARA, KUHMO: PETROLOGY AND LOW TEMPERATURE FRACTURE MINERALS
IN THE RO-KR11 DRILL CORE SAMPLES

ABSTRACT


The results of petrological studies and low temperature fracture mineral mappings of drill core RO-
KR11 from the Romuvaara research area are presented in this report (the order 9543/97/MVS).

The petrographic mapping was performed with the naked eye and the textures and modal mineral
compositions of the samples were determined by polarization microscopy. The whole rock analyses
were carried out at the XRAL laboratory (Canada) using an X-ray spectrometer, neutron activation
analyser, LECO sulphur analyser and ion selective electrodes (ISE). The fracture minerals were mapped
and identified with the naked eye and by stereo microscopy and X-ray diffractometry.

Three main rock types in terms of petrographic features and whole rock compositions were: 1)
palaeosomes of grey migmatitic gneisses, 2) palaeosomes of leucotonalite gneisses, and 3) cross-cutting
migmatizing leucocratic dykes. The grey gneisses are grey in colour and show distinct metamorphic
banding. They are medium-grained and even-grained in texture. Tonalitic and granodioritic modal
mineral compositions are most typical of this unit, but granitic varieties were also found. The
leucotonalite gneisses are medium-grained and weakly striped rocks. Again tonalitic and granodioritic
modal mineral compositions are the most characteristic. The plagioclases of the gneisses are typically
oligoclases.

The most common low temperature fracture minerals are calcite, Fe sulphides, Fe hydroxides and clay
minerals which form 12 mineral assemblages in totality. The most common 5 assemblages are: calcite-
Fe sulphide-clay minerals; calcite-Fe sulphide-Fe hydroxide-clay minerals; Fe sulphide-clay minerals;
Fe sulphide-Fe hydroxide-clay minerals and Fe hydroxide-clay minerals.

The Fe-hydroxides (goethite - limonite) are rare and they mostly are situated above drilling depths of
ca. 140 m but in this sample above depth of 100 m and in the depth interval from 390 to 300 m. Calcite
is one of the most common fracture minerals, and it can be found in the samples below drilling depth of
150 m. Fe-sulphides are common in the drilling core of all depths as well as clay minerals. Most
common clay minerals identified in the fractures are kaolinite, montmorillonite and smectites, which
can be found at all depths. Quartz-bearing fractures have been found infrequently in drilling depths
below 120 m. Zeolites apophyllite, prehnite and analcime have been detected in several fractures and
also in all depths of the drill core.


Keywords: Bedrock, Archaean, grey gneiss, tonalite, trondhjemite, petrology, mineral chemistry,
fracture mineral
ROMUVAARA, KUHMO: PETROLOGY AND LOW TEMPERATURE FRACTURE MINERALS
IN THE RO-KR11 DRILL CORE SAMPLES

ABSTRACT


The results of petrological studies and low temperature fracture mineral mappings of drill core RO-
KR11 from the Romuvaara research area are presented in this report (the order 9543/97/MVS).

The petrographic mapping was performed with the naked eye and the textures and modal mineral
compositions of the samples were determined by polarization microscopy. The whole rock analyses
were carried out at the XRAL laboratory (Canada) using an X-ray spectrometer, neutron activation
analyser, LECO sulphur analyser and ion selective electrodes (ISE). The fracture minerals were mapped
and identified with the naked eye and by stereo microscopy and X-ray diffractometry.

Three main rock types in terms of petrographic features and whole rock compositions were: 1)
palaeosomes of grey migmatitic gneisses, 2) palaeosomes of leucotonalite gneisses, and 3) cross-cutting
migmatizing leucocratic dykes. The grey gneisses are grey in colour and show distinct metamorphic
banding. They are medium-grained and even-grained in texture. Tonalitic and granodioritic modal
mineral compositions are most typical of this unit, but granitic varieties were also found. The
leucotonalite gneisses are medium-grained and weakly striped rocks. Again tonalitic and granodioritic
modal mineral compositions are the most characteristic. The plagioclases of the gneisses are typically
oligoclases.

The most common low temperature fracture minerals are calcite, Fe sulphides, Fe hydroxides and clay
minerals which form 12 mineral assemblages in totality. The most common 5 assemblages are: calcite-
Fe sulphide-clay minerals; calcite-Fe sulphide-Fe hydroxide-clay minerals; Fe sulphide-clay minerals;
Fe sulphide-Fe hydroxide-clay minerals and Fe hydroxide-clay minerals.

The Fe-hydroxides (goethite - limonite) are rare and they mostly are situated above drilling depths of
ca. 140 m but in this sample above depth of 100 m and in the depth interval from 390 to 300 m. Calcite
is one of the most common fracture minerals, and it can be found in the samples below drilling depth of
150 m. Fe-sulphides are common in the drilling core of all depths as well as clay minerals. Most
common clay minerals identified in the fractures are kaolinite, montmorillonite and smectites, which
can be found at all depths. Quartz-bearing fractures have been found infrequently in drilling depths
below 120 m. Zeolites apophyllite, prehnite and analcime have been detected in several fractures and
also in all depths of the drill core.


Keywords: Bedrock, Archaean, grey gneiss, tonalite, trondhjemite, petrology, mineral chemistry,
fracture mineral

Keywords:

Kallioperä; arkeeinen; harmaa gneissi; tonaliitti; trondhjemiitti; petrologia; mineraalikemia; rakomineraali

File(s):

Kuhmon Romuvaaran kairausnäytteen RO-KR11 petrologia ja matalan lämpötilan rakomineraalit (pdf) (1.5 MB)


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