362 V. DOLMAGE.

The minerals produced in this period were epidote, hornblende,
actinolite, quartz and a small amount of magnetite and hematite.

Following this, came a period of mineralization at a much
lower temperature, which deposited the zinc blende, chalcopyrite,
bornite, galena and chalcocite and produced much chlorite in the
tufts.

Then came a period of igneous activity in which the late dikes
were intruded, followed by a second period of high temperature
mineralization which produced the hematite, magnetite and chal-
copyrite, which characterize this period of mineralization through-
out the district.

Much later than this, a slight amount of surface oxidation and
enrichment has taken place, developing the covellite, chalcocite
and calcite.

The Open Fissure Type.

This type of deposit is represented by five principal deposits:
the High Grade, the King and Rainbow, and the Hunter, Idaho
and Colorado.

The first two are the most valuable, and because they were
affected by both periods of mineralization are much more com-
plex than the others. They will be described separately. The
other three, which are less important and more simple, will not
be described in this paper.

The High Grade.—Vhis claim contains the highest grade ore
to be found in the district, and though rich in copper and silver,
unfortunately is not plentiful, and being remotely situated, is not,
under present conditions, worth the cost of its transportation.

The claim is located at the top of the high, steep wall of a
large glacial valley occupied by Sunset creek, and is slightly more
than one and one half miles southwest of the contact of the
granodiorite stock. The cliff is almost perpendicular and well
exposes the thin-bedded, bright red tuffs for a vertical distance
of 150 feet below the upland plain which intersects the valley
wall at an elevation of 6,000 feet.

Cutting the tuffs and striking in a southerly direction are two
dikes of diabase, one about 15 feet in width is situated 100 yards