The White Pine news. [volume] (Ely, Nev.) 1906-1910, 1907-03-12
HOW ELY ORES
WERE FORMED
Interesting Report By Professor
Lawson Of University of Cal.
fOrnia On This District
ASTOPRIMARY DEPOSITS
Scientist Gives His Ideas of the Manner
in Which Metals Wore De-
80 posted in Copper Belt

In a report on the copper deposits
in the district surrounding Ely, Prof.
Andrew c. Lawson gives some inter-
esting information concerning how
the ores formed in the Ely mines.
Certain portions of the porphyry
mass, notably at the Ruth mine and
at Copper Flat have been so mineral
lied as to constitute an ore of cop
per- says Prof. Lawson. 'In consid-
ering the characteristic of this ore
and its genesis, it will be first nee
essary to recognize the fact that the
porphyry, considered as an ore, is
like most metalliferous deposits, sep
arabic into two zones: The zone of
oxidation near the surface, ard the
unoxidized zone beneath this, extend
ing to depths at present unknown
The porphyry of both zones may con-
stitute copper ore, but each in a
different way. At the Ruth mine the
most wholly, if not quite, devoid of
sulphides. 1t has a prevailing yell
lowish color but is in many places of
deep red color due to the abund-
ance of iron oxide. 1t carries never
more than a small fraction of | per
cent copper, and frequently none can
he detected. The passage from the
oXidiZed zone to the unoXidized is
very abrupt and sharp and below the
dividing line the porphyry through
out the mine is blush white and is
usually well sprinkled with crystals
of pyrite and chalcocite. The i'm
mediate appearance of these two sui
phides at the dividing line between
the oxidized and the unoXidized rock
and their absence above that line
minerals formerly existed in the up
per zone, and have been oxidized
and leached out by meteoric waters
descending from the surface
while there is thus a very sharp
line between the two conditions of
the porphyry in tht mine, that line
is extremely irregular and has no ref
erence to the present level of the
ground water. The water level in
the mine stands at present at 334
feet below the shaft mouth and the
mean lower limit of oXidization is
somewhere between 100 and 150 feet
below the shaft mouth. But the va
rious levels and crosscuts of the mine
have shown that tongues or wedges
of oXidized rock extend irregularly
the 500 foot level, with occasionally
limonitic stains along seams to still
greater depths. 1t appears to be
clear from this state of affairs that
the level of the ground water has
been lowered probably not less than
250 feet and possibly much more in
quite late geological time at such
rate that the oxidation process fail
ed to keep pace with it, SO that about
a couple of hundred feet of the un-
oxidized zone has been left stranded,
so to speak, above the water plane.
The irregular tongues and seams of
oxidized rock that project down into
the sulphide zone, of course, merely
represent the loci of more efficient
oxidation by waters percolating down
from the surface, in the general ten
dency of that process TO overtake the
retreating ground water.
at appears certain that the unox-
idized copper ore of the Ruth mine
porphyry impregnated with chalco-
cite and pyrite i'll sporadic crystals
owes It's value in part 10 secondary
enrichment by downward teaching
from the zone of oXidiZa ton. The
fact that the oxidized zone might ca
silly be robbed of its copper ore by
the teaching action of sulphide of
iron was eXperimentally verified by
placing mixture of pulverized chal-
cocite and porphyry in burette and
causing 10 per cent solution of fer
rous sulphide to pass through it in
presence of the atmosphere. The
chalcocite was taken into solution
and passed from the burette as cop
per sulphate (CuSOD at fairly
rapid rate. While this secondary en-
richment of the porphyry below the
zone of oxidation is unquestionable,
two important and significant facts
remain to be noted. The first of
these is that the products of this en-
richment are not localized at any
particular horizon in the porphyry
so far as the development of the mine
has yet gone. The copper values are
by no means evenly distributed in
the ore bodies thus far blocked out.
But the richer ground is apparently
rather determined by freedom of the
flow of descending solutions, that is
by local structural conditions in the
porphyry, than by any horizontal