The Goldfield news. [volume] (Goldfield, Nev.) 1904-1911, 1908-12-12
1GOLDFIELD TYPE OF ORE OCCURRENCES


ing the original p~orpbyritie structure to
the dense finty, fine grained quartz
Ransome states that: 1.-THE native
gold of the ores is usually in particles
fine and so closely crowded in the
gangue that the precious metal is usual
ly invisible to the naked eye, but when
resembles a streak of yellow ochre.
The gold itself is not easy to see, ever
in the richest ore, until the specimen is
wetted; then it is seen in dull yellow
bands formed by minute particles. The
gold is sufficiently free, however, to per
init the use of the pan in ascertaining
what is rich ore; only the material must
be ground exceedingly fine before pan
ming.
cit is utterly impossible, in many in
stances, to distinguish ore from country
rock, and the pan and assay must con-
stantly be resorted to in prospecting.
"The milling ore of the Combination
would be taken for country rock by any
one not knowing from tests that it is
ore. The exceedingly high grade is
often in the fine grained quartz; and in
some instances where the specimen is
from one-third to one-half of it's mass
in gold, it requires considerable con-
centration of vision to determine the
gold, it is so finely disseminated
Ore Occurrences
A popularity of the Goldfield type of
ore occurrence is that the outcrop and
superficial zones are poorer, and the
good ore bodies are not, as a rule, en-
countered until reaching the sulphide
zone. The bottom of the zone of oxida-
ton was between los and lis feet be-
low the surface at Goldfeld. In the
Mohawk ground the pay ore usually did
not extend upward into the oxidized
zone, but in the Sheet-Ish and the Com
bination it reached to the surface.
Ransome says: "The ores, it should
Dt HOtCu, uO HOt ttu III bNRiC1i fCiho,
but in masses of shattered, altered rock
of very irregular shape. In small part
onl ydo they appear to have filed visi-
bly, open cavities or assures
Like all replacement-mineral occur
rences in intensely altered rock the ore
does not have sharply-cut boundaries
and grades or fades into the adjacent
country rock. According to Collins,
Richard and other writer's: "There are
no true veins. The lode-channel has be-
come by silicification harder than the
surrounding country. The best ore is
found in the small stringers and vein
lets and traverse the main body of the
lode. In the oxidized portions of the
mine, above the 130-foot level, these are
largely filed with small fragments of
quartz mixed with a characteristic yell
low or reddish ochery material which
is mainly kaolin (lunite) formed by the
decomposition of the feldspar in the
original rock
The lodes are shattered and assured
hot solutions under pressure from be-
low, which, following the lines of least
resistance, the fracturelets and frac-
lures, admitted the feldspar and de-
posted the silica and the minerals in
the zone of fracturing. As stated by
the authors named:
"These silicifed zones may be re-
garded as veins, and ore may be looked
for either on the foot or hanging wall
side, or even throughout the whole OF
the silicifed mass. As a rule, how
ever, the ore shoots follow lines of shat
tering somewhat diagonal to the general
course of the siliciied zone itself.
"When the sulphide zone is reached
the rich stringers in the lode are easily
followed, as the shattered clayey ma
terial is heavily impregnated with sui
phides forming a well marked dark
seam. The richest ore in the mine IS
usually found on the faces forming
the sides of these points, where the
gold bearing solutions have had the
best opportunity to precipitate.'
The common gangue of the unoxo-
died ore, the altered andesite country
rock, is quartz, kaolin and a%lunite.
Again quoting Ransome: "The quartz
is usually compact, almost finty in tex
ture, although porous in mass, and in
most cases bears unmistakable evidence
of having resulted from the si~licification
of dacite, rhyolite or andesite. Large
vugs and c~onspicuously crystalline
quartz, such as are found in typical
veins the world over, are practically
absent from the Goldfield district,
where the free development of quartz
crystals in open spaces is represented
only by drusy films, lining pores left
by the solution of phenocrysts or In
crusting small interstitial cavities in
b~reeciated material.
"In general the heavy metals brought
in by the solutions remained within, or
very close to the multitude of small, If
assures that afforded Opportun-
ity for the depositional process This
acids, on the other hand, pene-
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