COMMISSION GEOLOGIOUE - arkisto.gsf.fi

10 Bulletin de la Commission geologique de Finlande N : 0 194.
INTRODUCTION
Previously, chromite had been met with in Finland only as a sporadic
additional component of serpentine rocks. In the summer of 1959 the
Geological Survey received for examination a boulder found by an amateur
prospector on the shore of the channel situated on the northeastern side
of the town Kemi. The boulder was found to contain chromite in considerable
abundance. An exploration of the locality where it had been picked
up led to the discovery of several narrow chromite veins at the bottom of
the channel, where the bedrock had become exposed during the digging of
the channel. Since the bedrock in the vicinity of the discovery was everywhere
overlain by overburden and, accordingly, it was not possible to investigate
the matter further by means of direct geological observations,
geophysical investigations were undertaken in the area and aimed toward
tracing possible chromite occurrences of greater extent. The susceptibility
and density determinations made of sampies taken from the veins and the
country rock indicated that magnetic and gravimetric methods would be
feasible providedthe dimensions of the occurrences sought were great
enough. The results presented in the following are based on the explorations
carried out by the Geological Survey in the region during the fall
of 1959 and the late winter of 1960.
Systematic magnetic, gravimetric and electromagnetic measurements
were performed over an area of seven square kilometers, which, six kilometers
long and 1-1.5 km broad, covers an anorthosite-serpentine intrusion
and a granite contact. The number of observation points is about
5000, or 715 points per square kilometer.
Field operations were in charge of Messrs. O. Kinnari and N. Puranen,
research assistants, who were assisted by Messrs. J . Kankaanpää and A.
Salo, work foremen. Messrs. O. Kinnari and J. Kankaanpää also performed
the calculations involved in the magnetic and gravimetric work.
By means of the geophysical measurements, particularly the magnetic
and gravimetric ones, an extensive chromite occurrence was localized beyond
the narrow veins first discovered,. in an area where there was not a
single bedrock exposure.
LOCATION, GEOLOGY AND TOPOGRAPHY OF REGION
Kemi, the most important industrial town in the province of Lapland,
is situated on the northeastern shore of the Gulf of Bothnia at about 65°
45' north latitude and 24° 30' east of Greenwich.