The Salt Lake tribune. [volume] (Salt Lake City, Utah) 1890-current, 1907-03-11
HOW ORES FORMED
WITHIN ELY MINES
Discussion Interesting to the
GeOlOgist INDUCED in by
an Expert.
PROFESSOR LAWSON
GIVES HIS IDEAS
Primary Deposits Appear Only
AS Chalcopyrite With
Garnet or Quartz.

a State University should be an ad-
n!inlstIatlve center for directing and
undertaken by the State. in case the
State supports other similar instltu-
TONS, such as school OF mines and
agricultural college, these may share in
should be largely increased by such CO.
operation. says Ores and Metals. Among
the publications In which are recorded
the results of State University research.
the Bulletins Of the Department OF Geo
logy, University of California, deserve
especial commendation, They contain
many valuable contributions both TO
economic geology and geological theory.
Evidently the directors of the work have
not found the field TOO cramped because
Of the expansion OF the United States
Geological Survey: and while the depart
ment is I'm some respects an heir 10 the
better traditions OF the old State geoloGi-
cal surveys, the character OF the reports
show a gratifying Improvement in scien-
tific method.
Under the head of Cupelations Ores
and ana Metals has already quoted on por-
phyry and quartz blout from Prof. An
drew c. Iawsons report on the Copper
Deposits of the Robinson District OF Ne
vsda. and below is given a longer quota
tion, from that portion of the report
nealinS With the origin OF Ely ore de-
posits. Professor Lawson writes,
certain portions OF the porphyry
mass, notably at the Ruth mine and at
copper Flat. have been so minerali2ed
as TO constitute an ore OF copper In
considering the characteristic OF this ore
and It's genesis, IL Will be first necessary
TO recognize the fact that the porphyry.
considered as an ore. is like most metal
llierous deposits, separable into two
zones. The zone OF oxidation near the
surface and the unoNidizcd zone beneath
this, extending to depths at present un-
known. The porphyry OF both zones may
constitute copper ore, but each in
different way AZ the Ruth mine the
pcrphyry OF the oXidzed zone is almost
wholly. If not quite devoid Of sulphdes.
il has prevailing yelowlsh color but is
IN many places Of a deep red color due
10 the abundance OF iron oxide. 1t car
res never more than a small fraction
OF per cent OF copper; and frequently
the oNidized zone To the unoXidized Is
very abrupt and sharp. and. below the
dividing line: the porphyry throughout
the mine is blush white. and is usually
well sprinkled with crystals of pyrite and
chalcocite, The imrS ediate appearance of
these two sulphides al the dividing line
between the oXidizcd and the unoYidiZed
rock and their absence above that line
leave no room for doubt but that these
minerals formerly existed in the upper
zone, and have heen oXIdlzed and leached
ont by meteoric waters descending from
the surface.
While there is thus n very sharp line
between the TWO conditions OF the por-
phyry In the mine. that line lis extreme
ly irregular and has ,io references to the
present level OF the ground water The
water level stands in the mine nj pres
the mean lower limit OF oXldiZation is
somewhere between 100 and $50 feet be-
low the shaft mouth. BUT the various
levels and cross-cuts OF the mine have
shown that tongues or wedges of oXidiZed
rock extend irregularly down into the
oMldized zone as FAR as the 500-foot level,
with occasional limonitic stains along
seams 70 stu greater depths il appears
10 be clear from this stale OF affairs that
the level of the ground water has been
lowered probably not less than $50 feet
and possibly much more In quite late
geological time at such a rate that the
oxidation process failed to keep pace with
IT, so that about a couple of hundred feet
OF the unoXldlzed zone has been left
stranded. to speak. above the water
plane The irregular tongues and seams
oil oxldiZcd rock that project down into
lhe sulphide zone. OF course merely rep
resent the loci OF more efficient oxida-
tlon by waters percolating down from the
surface, In the general tendency OF that
PROCESS to overtalSe the retreating ground
water
1T appears certain that the unoxidized