The copper era. (Clifton, Graham County, Ariz.) 1899-1911, 1902-05-15


Thus far all had been serene and neaeef,l-
nothing but slow erosion and sedimen,ation
, but now the internal heat of the earth took q
hand in the pfav. Igneous forces long latent
began in Tremendous activity.
After the Cretsceous period followed an uplifr
1 Of great magnitude The accumulated sedi-
ments were lifted far above the sea and masse,
Of molten material were forced into them break
ing their way through the underlying granite
and tearing apart and baking the adjoining
sediments. This took place far below tn. sur
face-in fact these molten masses probably new
er reached the surface but consolidated far be-
low. They consolidated to the rock We now call
porphyry and which is exposed on so great a
scale Copper mountain and in the upper
basin of Gold Gulch.
THE BREAKDowN
At this time this region. once buried beneath
the waves must have formed a high plateau
But as often happens after big uplifts have tax
en- place the forces reacted. The great urlifted
arch broke into hundreds of fragments which
settled down irregularly. just as the surface
sinks and breaks above great chambers mined
out and left without SUPP 'rt. And this break
ing down it is which co" plicates the difficulty
in interpreting the .,Sfcgy of this region-
Originally we had a regular succession Of gran
ite, sandstone limestone one resting on another;
now we nave fragments mere anu inclS III llS
greatest confusion. Sandstone rests on granite
on the top of the Coronado mountain. The
same sandstone rests on granite at the Coronado
mine thousand feet lower and only short
distance away. Opposite the LOngfellow In-
! cline You may see sandstone abutting squarely
against granite. This is not the original posi-
: ton. but the former has slid down slip or
/ fault plane TO a place far below the granite.
/ The same layer of lime, once deposited n
horizontal sheet we now find AT widely differ
ing elevations. and to make the destruction still
greater the ever present erosion at once attacked
this broken down plateau and cut gorges and
canyons in it, ever bent upon reducing AMI lev
cling the work of the uplifts.
THE GREAT LAVA FLOWS.
We have now traced the history up to the
middle of the Territory aGe-that is to Il COM
parativcly recent time eeolosically speaking
ard Immediately preceding what gcologists call
the present or Quarternary age At this time
the great lava flows began. The interior fires,
dormant for a while, again became active and
the whole region, in fact the whole western
part of North America, became flooded by
molten masses of lava, breaking out through
assures in the rocks or through explosive vents.
Lava flows followed each other in endless sue
cessiOn, black basalt, rich in iron, now
light-colored rhyOltes, rich i'll silica. Along
the striking bluffs which Eagle creek and the
San Francisco river have carved in the lava
these formations may be seen 10 excellent ad-
vantage. Both river basins became vast rcscr-
voirs filled by lava flows, and the Morcnci re-
gion stood like an island in fiery sea, doubt
less now and then covered by ashes thrown ont
from the surrounding volcanoes. Most of the
cones of the latter have been cut down by GRO
sion, and few remain. Most similar 10 a lava
iS hat StrEiuo nvromiJ rising
two thousand feet above the San Francisco
river n few miles cast of Clifton.
Finally the volcanic c-uptons ceased. last
reminder of the subterraueau fires are the hot
springs, many of which still issue on the lower
Eagle, San Francisco aIad 6iia rivers.
THE GRAVEL BEDS.
But the vast bulk of cruptcd masses had
greatly changed the topography OF the country
The lower river courses were damned and the
high ridges of older rocks fanked by immense
thicknesscs of lava. Rough and inhnSpitable
was their surface and THAI is why the Spaniards
have called them nal pals or bad lands. The
blocking of the river courses caused great
masses of gravel TO accumulate along the base
of the mountains, and these gravels we now see
resting against the older rocks, high above the
present drainage. They finely shown at
the mouth of Morenci canyon, and Chase creek
and San Francisco river have cut deep trenches
through them. For no sooner had the accumu-
lation ceased than the rivercourses again began
their role of croding and securing agencies.
PRESENT EROSION.
And this is the last phase of the geological
history of Morenci. New canyons were cut by
the rushing torrents in the gravels and the
lavas and the older rocks. This process cf de
stroying what sedimcntatiOn and volclnism
built mp is still proceeding. Slowly but surely
the loosened rocks travel downward until the
rivers pick them up and carry them as sand
and silt down to the great resting place where
the debris of nearly all of Arizona's mountains
is deposited TO the Gulf of California.
THE COPPER DEPOSITS.
Perhaps l have spoken of everything in re-
gard to the geology of Morenci, except what in
tcrests you must-the great copper deposits, |
whose presence is the very cause of existence
Of this picturesque town with its intense activ
ity. 1t is large subject and it is difficult to do
it justice in few words.
The copper deposits of Morcnci Metcaf and
vicinity unmistakably connected with the
intrusion of porphyry which took place after
the close of the Cretaceous period. Before. |
there were, so far we know, no mineral de |
posits has been formed much later than that |
date.
1t seems clear that the molten rock which |
consolidated TO a porphyry brought up from |
unknown depths metallic yapors. Chiefly of
iron. copper and sulphur. Wherever lime stone |
came in contact with the molten porphyry it |
baked by the heat and its calcite partly !
changed to garnet, maGne lite, pyrite and |
chacopyrite. Thus one class of copper deposits |
was formed-that of the irregular mas scs in |
limestones.
After the porphyry had cooled ii, as well as |
the adjoining masses of granite and lime, be- |
came shattered and broken. partly along regular |
lines, partly wholly irregularly; this took place
during the period of general faulting mentioned |
before Warm solutions-water heated b. con- !
tact with the lower masses of still hot porphyry
aud having taken up iron. sulphur and silica |
from the rock began to circulate in these assures
and soon cemented them with quartz pyrite |
and chalcopyrite. Thus another class OF copper /
deposits was formed-that Of the issure veins
All this, you should remember, took place far |
below the surface. The gradual wearing down
of the mountains finally exposed these deposits
to the air and TO the percolation of surface
water. And now began a series of complicated |
chemical reactions The chalcopyritc was
altered to copper sulphate near the surface in
fact the surface was impoverished by lesching
OF the soluble sulphate. and the groupings of
the deposits today at many places scarcely con-
tain any copper at all. But the solutions of the
sulphate were carried down Oh the veins and in
the deposits and reacted with the limestone
the chalcopyrite and the pyrite precipitating