Alcan Tahtsa Lake-—Kemano Tunnel

end of the tunnel at Kemano River. Actual mining commenced in October of
1951 and was completed December 2, 1953. Concrete lining and guniting of
the tunnel, where required, and installation of machinery and equipment were
accomplished by July of 1954, and power was first generated in that month.

Prior to 1951 little was known of the geological conditions along the
line of the tunnel, except that some metamorphosed volcanic rocks were
intersected by granite at the east end. It was expected that the greater part of
the tunnel would be entirely within granitic rocks of the Coast Intrusions.
Early in the season of 1951, the writer made several traverses from the head
of Tahtsa Lake westward towards the mountains on either side of Horetzky
Creek. Those traverses indicated that the volcanic and sedimentary rocks at
the head of Tahtsa Lake extended much farther west than was previously
believed and that they were intruded by tongues and cupolas of granitic rocks.
The tunnel provided a 10-mile cross-section through the contact zone of the
main body of Coast Intrusions with the older volcanic and sedimentary rocks,
and afforded an excellent opportunity for detailed study and research on the
mode of emplacement of the batholithic rocks and their contact relations with
the older rocks.

During the early months of 1952, through the efforts of Dr. H. C.
Gunning of the University of British Columbia, the National Advisory Com-
mittee on Research in the Geological Sciences, the Geological Survey of
Canada, the British Columbia Department of Mines, and the Aluminum
Company of Canada, agreed that a program of study should be carried out on
the tunnel, and that for the season of 1952 Mr. Roy Stuart of the British
Columbia Department and the writer should examine the available excavations
to September of that year. The writer examined approximately 4,000 feet of
tunnel at the Tahtsa Lake end and Mr. Stuart, who spent the whole season
on the project, examined the excavations at Kemano and Horetzky and carried
out detail mapping on the surface on a scale of 4 mile to the inch. A start was
also made on temperature and heat flow measurements along the tunnel.
During 1953 and 1954 Stuart mapped 180 square miles in the vicinity of the
tunnel on a scale of 1 inch to 4 mile, and completed mapping of underground
excavations on a scale of 1 inch to 50 feet. During 1954 Dr. Smith completed
the studies of special structures in the granitic rocks and during the same year
thermal conductivity measurements were completed. Final reports on these
studies will be published in the near future.

The Aluminum Company of Canada was most cooperative and helpful
during the progress of these studies.

Detail mapping by Stuart (1955, p. 108) indicated that the volcanic-
sedimentary assemblage in the vicinity of the tunnel is divisible into two
groups, a lower greenstone complex composed of metamorphosed andesites

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