The copper era. (Clifton, Graham County, Ariz.) 1899-1911, 1910-07-29
Copper Mining in Mstcalf District,
Arizona.
Bv Peter.B. Scotland.

BY Peter.B. Scotland.
Mines worked since 1873; $500 tons
low-grade ore handled daily; milling,
sliciug and square-set methods used
little timbering.
The copper deposits of Metcalf are
in the northern portion of the Mo
renci-Clifton district, Graham county
Arizona, twenty-five miles from the
New Mexico border. AS early as
1873, small amounts of rich surface
ore we're mined and smelted in primi-
tive adobe furnaces at Clifton, but it
was not until the advent of the Ari-
zona Copper company and the De-
troit Copper Mining company in 1852
that important exploratory work
commenced From that date the
production of copper rapidly in
creased, till in 1909 it amounted to
74,OOO,OOO pounds annually or one
quarter of the output of the terri
tory. In all, not less than 700. 100000
pounds of copper have been produced
from the Morenci- Metcalf district
since 1882, the value of which ex-
ceeds $4,000, 600.
Low-GRADE ORE SUCCESSFULLY
WORKED.
Though few districts have SO envi-
able a record of successful work, it is
doubtful if any other copper district
of equal Importance is so little
known or,heard of in mining circles.
The operating concerns overcame
their difficulties and gained their
difficulties and gained their success
without spectacular newspaper or
stock-market pyrotechn:cs- Rail
roads were built in the face of an
arid climate, fierce Apaches aud un-
favorable topography. Smelling
problems were solved and later,
when the supply of high-grade ore
failed, the concentration and leach
ing of the low-grade ores were profit
ably undertaken.
The district has been dependent on
the low-grade ores for the last fifteen
years. Three thousand five hundred
tons per day are passed through the
concentrating mills of the three
operating concerns, namely the Ari-
zona, the Detroit and the Shannon
copper companies. The reserves of
low-grade sulphide and oxide ores of
these companies insure the district a
long productive life. This period is
being constantly increased by the
discovery of other ore bodies.
OCCURRENCE OF THE ORE.
1t is not the intention of this arti-
Gle to do more than briefly state such
facts in connection with the occur
renee of the ore as are necessary for
a proper understanding of the min
ing methods employed. The copper
bearing area is a triangular noun
tain mass, the sides of which are APP
proximately six miles in length, ris-
ing abruptly from the surrounding
gravel plateau TO d maximum eleva-
tlon of 400 feet above sea level.
Within this area, an immense intru-
sion of porphyry has shattered and
displaced the limestones, shales and
quartzites formerly resting on Pre-
Cambrian granite.
Extensive and severe faulting oc-
CURED during-and subsequent o this
intrusion, producing such under
ground and surface conditions as
were favorable to the deposition and
concentration from mineral solutions.
Erosion followed, laying bare the
limestones aud shales in the southern
or Morenci part exposed the under
lying quartzites and granite.
ORE DEPOSITS CLASSIFIED.
The ores are found under variety
of conditions but these may be
briefly classed as follows:
% Contact deposits between por.
phyry and limestone, quartzite or
granite.
(2) Lode deposits in or close to
fault assures in porphyry. In this
class the fauIting is sometimes so
slight that the ore bodies may be con-
sidered as impregnation deposits.
(3) Lode deposits in fault assures
in granite often accompanied by a
diabase intrusion.
PORPHYRY INTRUSIONS.
According to Lindgren, the intru-
sive stock of the Metcalf district is a
granite porphyry, characterized by
large quaftz crystals, and that of
Morenci district, dioritic and mon
zouite porphyry. The occurrence OF
this hard and silicious porphyay at
Metcalf has a most important bear
ing on the method of gaining the ore
as the STOPPING ground stands better
than in the softer porphyry of Mo-
renci.
Ia some of the ore deposits, an in
trusion of medium grained diabase
can be observed. Its constituents,
however, are much altered to chlor-
ite and sericite and its identity so
masked thereby that it is usually as
an altered porphyry.