Tonopah bonanza. [volume] (Butler City [i.e. Butler], Nev.) 1901-1909, 1904-07-23
SECONDARY ENRICHMENT.
Caused by the Rising of solutions
from Great Depth.

deposits by the oxidation Of the ores
of the sulphide zone, and the repre-
cipitation of the minerals under con-
ditions which were favorable to their
redeposition, at lower levels, has
come to be accepted as a fact, but
there are instances wherein it is diff
cult to account for the extreme rich
ness of some of the ore found in the
zone of enrichment. The phenomena
have been chiefly studied with refer
ence the copper deposits at Butte,
Montana, which appears to offer the
most tangible evidence to support
this really rational theory. 1t was
recognized for many years, before
the secondary enrichment" theory
took definite shape, that the iron
gossan Of many copper-bearing de-
posits had been deprived, to a great
extent, of the copper contents, and
that in many instances, beneath the
''iron hat" was found a zone of rich
carbonate and oxide ores of copper,
beneath which again was an enriched
sulphide zone, in which the ores were
usually ''glance" and similar minerals
with high values in silver or gold, or
both. 1t was realized or believed
that these rich zones were the result
of the precipitation Of ORES from the
oxidized surface portions, but the
secondary enrichment theory, as now
generally understood, had not yet
been offered to account for these oc-
|currences. In most cases where the
secondary enrichment of copper ore
had occurred the amount Of superb.
cial ore which has been leached has
evidently been sufficient to furnish
all the copper found in the zone of
enrichment. There are, however,
other deposits, wherein the enrich
ment must have been produced by
the continued precipitation of solu-
tions from below within the zone of
and during the period Of oxidation,
for no other theory could account for
the unusual richness of the ores, and
their amount. Take as an example
the rich cloride silver.lead deposits
of Fryer Hill, at Leadville, Colorado.
The famous mines of that fat emin-
ence-the Robert E. Lee. Matchless,
Little Pittsburg, Annie, Little Chief,
Ch~rysolite and others-all within the
oxidized zone, and occurring rela,
lively within a few feet of the surface
and above the horizon of local drain
age, and consequently of possible
secondary enrichment produced
millions Of dollars. 1t is now a well
known fact, long since established
that the normal ore of the lead silveI
mines of that district are low-grad,
pyritous ores, containing an abund
ance OF zinc sulphide and some coppeI
sulphide, ana that the normal ore
with a few exceptions, is low in silver
On Fryer Hill there was not enough
ore available above the level of thes,
rich deposits to have supplied tn,
large amount Of silver chloride an,
sulphide found in those noted depos
its, within the zone of secondary en-
richment, consequently the larg
amount of silver, mostly as the sec
ondary products of the alteration G
silver sulphide, must have been de
rived from below, not necessaril
from the ore lying in the immediat
neighborhood of the rich superficia
deposits, but more probably fror
solutions which continue to rise fror
great depth, and which supplied th
ore found in the normal deposits
There is no evidence, in fact, tina
these solutions are not still rising
and by their slow and imperceptibl
action still forming ore bodies. Tn
evidence furnished by the exposur
of the rock strata in mine working
in Leadville district leads to the cor
clusion that the ores were formed i
nearly horizontal beds at greatdept
not less probably than TO-, 900 fee
and that the faulting, which is sue
"a marked feature of the district
geologically, geographically, ard ii
cidentally commercially, occurre
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