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Bonanza group and acquired it in 1914. The mine began producing in 1929
and has now produced a total of 397,000 tons of ore yielding 1,560 ounces
of gold, 133,000 ounces of silver, and 15,500,000 pounds of copper.

The Bonanza copper deposit lies in a shear zone in amphibolite. The
amphibolite body is irregular in shape and much elongated in a southerly
direction. It invades argillites and is apparently a tongue from the main
amphibolite body outcropping a short distance to the west. The east and
west contacts are parallel to the strike of enclosing sediments. At the
north end the body plunges under sediments partly because of a large fault
and partly because of a northerly pitch. The south end of the amphibolite
body, as seen on the south side of Glacier creek, enters the sediments as
sills and transgressing wedges and fingers. On the north side of Glacier
creek the amphibolite truncates severely folded overlying sediments and
shows local pillow-like structures and is locally fragmental. A long
inclusion of sedimentary rock in the amphibolite on Glacier creek contains
many quartz veins and has been silicified. The amphibolite in places is
severely sheared and the shearing strikes west and dips 30 degrees or less
north. In some shear zones biotite is very plentiful. In one or two places
it was evident that this mineral could have developed by shearing of
inclusions of argillite, but in other places where biotite occurred no inclusion
was seen.

The ore-body outcrops in Bonanza creek and lies in a shear zone that
strikes east and dips about 20 degrees north. Along the strike the shear
zone is only 300 feet long but is known to extend down the dip for half a
mile. It is 40 to 70 feet thick and has the shape of a very much flattened
tube pitching north. At the west side the shearing turns northward rather
abruptly and on the east side it turns southward. Faults are in evidence
locally on the east and west sides. To the north, down the dip, the zone at
a depth of 200 feet below sea-level is cut off by a fault that strikes north-
west along Bonanza creek and dips 65 degrees northeast. This fault has let
down the northern extension of the zone a distance of 800 feet or more.
South of the outcrop in Bonanza creek the zone disappears in the south
side of the valley because the slope of the hillside is steeper than the dip
of the zone. The southern limits of the zone are unknown, but it has been
traced to where it is 700 feet beneath the surface.

The ore-body has a strike length of about 200 feet and locally was 30
or 40 feet thick. The dip length is known to exceed half a mile and ore was
continuous throughout this distance. Where the shear zone was thinner the
ore-body narrowed also, but filled the whole shear zone. Where the shear
zone widened the ore-body was somewhat thicker but did not fill the whole
zone. Above the creek level the ore-body along its west side ends in two
blunt wedges one above the other. On its east side the ore-body in most
places is bounded by a minor fault, but in a few places ore of a somewhat
different appearance has been mined east of the fault. Below the creek
level the west side of the ore-body is bounded by a fault whose relations
with the large fault at the north end of the ore-body are not known, but the
large fault is probably later.

The walls of the ore-body are chlorite, actinolite, and biotite schists.
Locally augite, labradorite, and enstatite can be recognized. All the
shearing was accomplished before the ore minerals were deposited. All the