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34 Bulletin de la Commission geologique de Finlande N: 0 194.
The differentiated peridotitic rock appearing in the present map at the
southeastern margin of the ultrabasic zone contains ingredients predominantly
olivine and pyroxene by origin.
Mention should be made of the older view, presented by Hausen and
Väyrynen (Härme, op. cit., p. 46), according to which the vertical position
of the supracrustal complex was due to a north-south overthrust against
the resistant gneiss granite, in conjunction with which also the ultrabasic
intrusive was intruded into place.
THE GEOLOGY OF THE MINERALIZED ZONE
The mineralized zone, comprising the chromium ore belt and the country
rock on both sides of it, which, in respect to its special geological features
is associated either primarily or secondarily with the ore, liest at the northeastern
end of the Kemi-Elijärvi anorthosite-serpentine series parallel to
its southeastern border. The length of the zone, which is here restricted to
include only the part explored by drillings, is 3.3 km, starting from a channel
ab out 7 kilometers northeast from Kemi and extending to the northeastern
end of Elijärvi lake. The breadth varies between 200 and 400 meters. The
trend of the zone follows quite faithfully that of the southeastern contact of
the ultrabasic rock sequence - even to the extent that at the northeastern
end of the sequence, where the contact referred to curves northward, the
same kind of change in direction is observable in the zone.
The drillings have given a fairly detailed geological picture of the zone,
though naturally limits have been imposed by the fact that the research
material consists exclusively of drillcores. Three series of drillholes, one
at the site of the channel and the other two in the vicinity of Elijärvi, illuminate
the geological conditions prevailing farther on at the northwestern side
of the ore belt.
The profiles made reveal that at the northwestern side of the zone, some
50 to 150 meters from the ore, there apparently exists a continuous olivineand/or
pyroxene-bearing rock wall. Depending on the relative amounts of
olivine and pyroxene, the rock belongs in the categories from dunite to
pyroxenite.
Some thirty to eighty meters away, on the opposite side of the ore, there
is a continuous wall of coarse-grained albite rock which runs parallel to the
ore belt. Albite rock has been reached with numerous drillholes, and its
contact can also be clearly interpreted from geophysical profiles (see the
paper by Siikarla in this volume), which reveal that this variety of rock
extends several hundreds of meters farther to the southeast.