The copper era. (Clifton, Graham County, Ariz.) 1899-1911, 1910-07-29


rem ground frequently occur in the
vein and these are left in as pillars,
to support the walls.
Occasionally, parts of the vein are
too soft to be mined safely by over
hand STOPPING and the made of at
tack is changed. From the two
raises between which the ore softer
than usual, a drift is made 20 to 30
feet above the back of the slope and
connecting the raises. Midway in
this drift, down holes are drilled in
the floor and sides. AS these holes
are blasted and break down the shell
of ore between the floor of the drift
and the stope, mining is continued
back to the raise until the whole OF
the shell has thus been broken by I'M
derhand stopping. In using this
connects the raises must be sufficient
ly high to allow the handling of the
long jumper drills needed in break
ing down the floor. When approach
ing an upper level, the ore is always
broken by underhand STOPPING.
When the top of the orebody IS
reached in STOPPING, the remainder of
the broken ore is drawn off through
the crosscuts. A certain adm:xture
of wall rock and ore is unavoidable
when the last portion of the ore is
drawn, but this is easily removed on
the sorting platform over which the
ore is passed. The switches at each
crosscut on the roadway allow the
Shovelers to load their cars without
interfering with the haulage. The
ore is sledged and loaded by con-
tract, and when a car is full, it is
pushed into side track, where the
mule train is made up. A few miners
are required to ''blockhole" the
larger pieces of ore as they appear
at the shoveling openings. The adj
vantages of this method are Obvious:
one worthy of special notice is the
security in which the shoveler does
the work.
The Coronado mine, one of the
most important holdings of the Ari-
IONA Copper company, lies on the
southern slope of the Coronado
mountain, granite massit, whose
precipitous sides form a conspicuous
landmark in the district. The great
Coronado fault is at the base of these
granite bluffs. 1t strikes east and
west and shows on surface strong evil
dence of extensive earth movement.
The fault can be traced for a length
of two miles, disappearing to the
west beneath the lava flow and losing
its identity to the east in a series of
lesser faults. The movement has
been downward and westerly at it's
eastern extremity, resulting in a
vertical displacement of 1900 feet
between the basal quartzite on the
south of the fault and of that rest
ing upon the granite on the north.
The fault is complicated by uumer-
GUS cross faults at its western end e,
but, as indicated by the limestone
resting against the granite wall, the
displacement is more than that above
mentioned.
The vein, which fills the fault fs-
sure, is strikiugly marked on the sur
face by numerous groupings of oxi-
died ore and stacks of iron-stained
quartzite. Following the vein on the
south side is an intrusion of fine
grained green diabase, varying in
width up to 10 feet and carrying
some barren pyrite.
CORONADO ORESHOOTS.
There are three known oreshoots
on the vein at intervals of 1000 and
1000 feet respectively. The two
most westerly shoots, though expos
ing large bodies of ore in their shall
low workings, have not reached the
developed state of the easterly or
Coronado oreshoot and will not be
considered in this article.
The Coronado oreshoot is approx
mately 20OO feet long and will average
b feet in width. 1t has been opened
by a three-compartmeut shaft to a
depth of 700 feet, but as the hill
apexes about the center Of the shoot,
vertical depth of 1000 feet from
the surface is reached at that point
The vein is practically vertical. The
north or foot-wall is of slightly alter
ed granite and the south or hanging
wall is of quartzite to depth of $50
feet, below which the vein enters the
granite assure. The zone of sulphide
ore is reached at a depth of $50 to
800 feet; dboye this level, small bodies
of oxidized ore have been found.
NATITRE OLE rHE ORE