62

Similar but gently inclined lavas, 24 miles southeast of the above
locality, are traversed by a shear zone about 5 feet wide trending north 50
degrees west and dipping 75 degrees northeast. The zone is exposed for a
length of 50 feet and contains scattered knots of epidotized rock with a
little bornite, malachite, and azurite. A picked sample of the mineralized
materials assayed: gold, 0-01 ounce a ton; silver, 0-30 ounce a ton; and
copper 3:30 per cent. About 630 feet above this occurrence a vertical fault
strikes north 55 degrees west through the same lava assemblage. The fault
zone is about 20 feet wide, with a sharp, slick northeast wall, and contains
sheared and epidotized volcanic rock with a little bornite, malachite, and
azurite. It crosses the crest of a precipitous ridge, the sides of which were
not examined.

A little native copper is reported! from serpentine and red volcanic
rock 14 miles north and 24 miles northeast, respectively, of the east end
of Sustut Lake.

West of Bear Lake

Many small veinlets of chalcopyrite, pyrite, galena, sphalerite, specu-
larite, crustified quartz, and calcite were seen in talus fragments of red
andesitic tuffs and lavas on the ridge immediately west of Bear Lake.
Some of these occurrences are reported to contain appreciable amounts of
gold. The largest seen in place by the Geological Survey is 44 miles south-
west of Bear Lake village. It is 3 inches wide and exposed for a length of
10 feet; it contains up to 60 per cent chalcopyrite in addition to banded
comb quartz and a little specularite.

Motase Group (7)2

The Motase group of thirty-five claims lies astride a mountain about
3 miles northeast of the southeast corner of the map-area. It was staked
by M.S. Lougheed, during the summer of 1945, on behalf of Yukon North-
west Explorations, Limited, and prospected and geologically mapped by
that company during the same season.

The claims are underlain mainly by red, green, grey, and buff,
andesitic lavas, tuffs, and agglomerates of the Takla group. Near the
known mineral occurrences these dip about 15 degrees southwest and are
cut by steep, light grey feldspar porphyry and quartz porphyry dykes,
which may be phases of the Kastberg intrusions.

Two mineralized areas, one about 1,000 feet northwest of the other,
occupy parts of the precipitous northeast face of the mountain; and a
third lies 1,500 feet southwest on the relatively gentle southwest slope of
the hill. The principal minerals, bornite and chalcocite, are associated with®
a little galena, pyrite, chalcopyrite, and possibly tetrahedrite. These occur
mainly in the voleanic rocks. There they occupy minute fractures, or are
disseminated throughout an inch or so of rock on either side of fractures, or
are scattered through larger masses of rock apparently unrelated to fractures.
Less commonly they have partly replaced the borders of porphyry dykes.
The minerals are not equally concentrated or abundant in all rock layers.

. (i communication from the late R. M. Godfrey of Vancouver, who prospected parts of the map-area
in 1945.
_ _? Description based in part on data supplied by K. J. Springer, Yukon Northwest Explorations, Limited, and
in part on observations made by the writer in 1941.

3 Lougheed, M. 8.: Yukon Northwest Explorations, Limited.