The Salt Lake herald. [volume] (Salt Lake City [Utah]) 1870-1909, 1907-02-18

sist of intrusive masses of monzonite9 q. OF
Plutonic origin occurring In laceoiius
form
shale and limestone bodies of garnet rock
are developed and carrying chaicopyrlte
a product of contact metamOrpnlsm-
Copper signs are malachlte ana azuriee
stains in rusty rock.
The Nevada limestone on the contact
of which is the garnet zone Is changed
into marble. the copper-bearin por-
phyry is a light yellowish feldSpar rock
Showing individualized crystals of field
spar. Sedimentary rocks once arched
completely over the porphyry with PROD
able vents in the arch TO the surface.
These everything rocks have been large
" removed exposing the igneous mass
below on which they rested.
Large masses of iron ore associated
with the contact garnet zone occur on
the lower side of the porphyry mass
These as we'll as the garnets are due
TO a reaction between the intrusive lg-
neous poTphyry and adjacent limestone
The lime of garnets was derived from
the limestone and their silica from the
pcrDhyry.
This reaction was by watery solutions
from the porphvry. Garnet making con-
tinued after the actual sol1dl1lcdtlOn OF
the intrusive mass. The iron ore was an
after product due to the precipitation OF
the iron oxide at the contact of the lime
stone from soluble salts due to the down.
ward teaching of the porphyry-
Quartz 6foWouts.
A remarkable feature of the porphyry
is the occurrence on its periphery or
large bodies of quartz called by the Ne
distinct from the vein quartz This term
has been shortened by Mr.. Lawson into
'blout quartz or "blout. This -blout
represents 8 contact development be-
tween the porphyry and its roof of lime
stone now removed by erosion. but once
forming a continuous envelope encasing
the poTphyry on its upper side and inter-
Vening between IL and the oVerarcnlng
roof of limestone. The removal of the
limestone roof left thick, hard portions
behind on the porphyry. This "blout'
may be solid and compact or cayernous,
brecciated or cellular 1t weathers in
smooth. rounded knobs and has a STRAIT
form appearance indica tive of its origin
as the result of silification of the lime
stone shell together with that OF the por-
Dhyry itself on its margin. Quartz
''blout'' is associated with the garnet
rock carrying the chalcOpyrite.
Certain portions of the porphyry have
been so mineralized as to constitute an
ore of copper. There is an oXldfzed ana
unoxidized copper zone and the transit
ton from one to the other is abrupt and
sharp: below the dividing line the por-
phyry is sprinkled with pyrite showing
that these minerals formerly existed IN
the upper zone and have been oxidized
and leached out bv meteOric waters de-
scending from the surface.
he level of the ground water mas Deeh
lowered at such rate that the oxidiZa-
ton process failed to keep pace with it.
so that a couple of hundred feet of the
unoxidiZed zone has been left stranded
as it were above the water plane.
Irregular tongues ~ oxiGized rock pro-
ieCt uoWn into the suiphides showing
where bodies of water descenued in their
tendency to overtake the retreating
ground water. AS this lowering of the
ground water appears to have been syn
erroneous with the deSsicatiOn of the an
cient Lake Bonneville ii shows depend-
ence OF certain important features of ore
deDosits upon climatic conditions.
ChaIcocite in the mines is secondary to
pVrite occurring a she'll around ny
rite. Copper values are unevenly distTi-
buted in the ore bodies thus far blocked
out.
Limited bodies of copper pyrite occur
associated with garnet rock. one at con-
tact OF intrusive rocks with the lime
stone due TO contact metamorphism and
the other is in the quartz 'blout' asso-
rfaf aA xz-ifh