Program, Abstracts, and Guidebooks - University of Minnesota Duluth

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exhibit both gradational and sharp contact relations
to an overlying "syenodiorite" phase of netavolcanic
cap rock. Because of the gradational relations the
syenites were included with the syenodiorites on the
revised map.
Thin sections show phenocrysts of alkali feldspar
(unexsolved) in a fine—grained groundmass of alkali
feldspar (highly exsolved) ophitically enclosed by
barkevikite. Relict clinopyroxene (variety augite —
sodic augite) has been observed. Hematite staining
of feldspars is generally extensive.
This mineral assemblage is not much different from
the 'darker' varieties of porphyritic laurvikite and
likewise this rock type appears to represent a 'high'
level variety.
8.6
STOP 5 NEPHELINE SYENITE (Pig. 1, 5 & 6).
16.8
This outcrop (Fig. 5) is typical of nepheline
syenites where in contact with 'diabasic' lava. The
gross zonation within the feldspathoidal body is
generally parallel to the contact with the 'diabase'.
The diabase is variably nephelinized.
One can conclude that,
STOP 6 LAURVIKITE (Fig. 1)
18.4
(1) there were at least two periods of
dilation and emplacement (Fig. 61);
(2) emplacement of feldspathoidal magma
was controlled by jointing within the
'diabase' (see Figs. 6a, 6b, 6c);
(3) emplacements along the more vertical
joints preceded those along flats
lying joints (Fig. 6c);
(4) where present,
the later feldspathoidal intrusions show
nepheline pseudomorphed by the zeolite
natrolite (with associated thomsonite)
which is orange in colour.
'Red' contact variety of laurvikite highly charged with
inclusions of nearby 'diabase'.
STOP 7 PEGMATITE (Fig. I & 7).
Traverse along a composite, nepheline (zeolitized)
pegmatite emplaced into gabbros (Fig. 7).