86

by rhyolite, dacite, and andesite flow breccias. Light-coloured, fine-grained
rhyolite is the most common rock in the vicinity of the workings. It
exhibits well-developed flow structure, and some of the individual flows
are packed with spherulites. Thirty feet north of the McPherson portal,
an outcrop of spherulitic rhyolite is composed largely of spherulites ranging
from one-eighth to three-eighth inch in diameter, arranged in parallel
bands through flowage. A specimen of spherulitic rhyolite taken from the
dump of the Compressor level contains spherulites up to an inch in
diameter. The rhyolite tuffs are very fine-grained, light yellowish white
to grey rocks. Most of them are finely laminated and have been silicified
so that they are as hard and brittle as the rhyolite. A small mass of
rhyolite flow breccia is intercalated with the rhyolite flows 500 feet north
of the north portal of the Compressor level and another small mass occurs
on the surface 150 feet northeast of the Thompson portal.

The flow breccias, in which the Dome and the combined Henderson-
Ashman vein-lodes occur, are dominantly dacites, but some are andesites
and some are rhyolite. These lavas contain abundant angular fragments
ranging up to 3 inches in diameter with an average size of about one-half
inch. There are both chert-like fragments of the same composition as the
matrix and variegated white, purple, grey, and black fragments of tuff
and lava.

Near the McPherson portal, spherulitic rhyolite and tuff beds strike
northwest and dip 70 to 80 degrees northeast. Farther northeast the rocks
have a comparable strike and may be seen in many places dipping 60 to
85 degrees northeast. Two hundred and fifty feet southwest of the
McPherson portal the flows also strike northwest, but dip 65 degrees
southwest. Four hundred feet southwest of the McPherson portal the
structure is interrupted by a strong fault (No. 1 fault), which strikes
northwest and dips 80 degrees southwest. Tuff beds southwest of the
No. 1 fault on the 500 level strike from north to northwest and dip 30
degrees southwest to west, but commencing 300 feet northeast of the fault
the rocks on this level strike northwest and dip from 25 to 87 degrees
northeast. The major structure then is an anticlinal fold the axial plane of
which strikes northwest and appears to dip at a steep angle to the southwest.
On the surface the crest of the anticline lies about 150 feet southwest of
the McPherson portal and the No. 1 fault runs along its southwest limb.
This major fold is masked by smaller folds, which were seen on the surface
south of the No. 1 fault and also north of the north portal of the Compressor
level. The anticline plunges at a low angle to the southeast judging by
the presence of overlying flow breccias in that direction.

One diorite dyke, a quartz-albite porphyry dyke, and numerous dykes
of lamprophyre and albite porphyry intrude the voleanic rocks (See
Figure 9). Medium to coarsely crystalline, grey diorite forms a dyke,
50 to 60 feet wide, which trends northwesterly across the Henderson claim
and dips about 80 degrees northeast. This dyke is intersected by the
McPherson adit 775 feet from the portal, and is entered for 21 feet at the
face of the Mill level drift along the Henderson vein-lode. Where crossed
by the Henderson vein-lode on the McPherson level, it is fractured, altered,
and bleached, but the fissures do not carry vein minerals.