Tonopah bonanza. [volume] (Butler City [i.e. Butler], Nev.) 1901-1909, 1903-12-26

eminent press. 1t appears in pam
phiet form as Bulletin No. PIG of tht
Geological Survey. A small geologic
map in black and white accompanie.
the pamphlet as an inset One gen
eral geologic section is given, and q
half-page map of the vein group:
complete the pictorial features.
Mr.. Spur ascrihes all of the vol
canic products in and about Tonopat
to the Tertiary period. The under.
lying floor, principally Of limestones,
falls, he thinks, into either the cam.
brian or silurisn age. In the eject
menta he has found fragments and
blocks of these primary rocks, show.
ing that at some uncertain depth
we must pass from the lavas into the
earlier primaries.
In reviewing the general geological
history of the camp, he points out
the fact that the hornblende
site (early andesite) is the lode por-
phyry in which the metallic deposits
of economic values exist. The vein
systems in some instances penetrate
the newer eruptions and may and do
carry values, but not in merchantable
quantities. He correlates the profit
able ore bodies wholly with the early
andesite. 1t is in this formation that
the veins about Mixpsh hill outcrop.
Like the volcanic rocks of so manv
regions, alteration has been very in
tense, and unaltered specimens are
extremely hard to find. In Becker's
search for unaltered specimens in
the Comstock he found only three
out OF several thousand taken.
The alteration is ascribed to the
activity of the circulating and ascend.
ing hot waters and solutions travers-
ing the fractures of the volcanic
mass. The waters, he says, were
remarkable for intensity of action.
The rocks which they traversed have
been chemically transformed, the
chief process being silicihcatio so
that they are now found more or less
completely altered to quartz and
sericite-other alteration products
are found in small and unimportant
quantities, but, he believes, bear no
direct relation or at least are not
usually adjacent to important ore
bodies.
Passing in succession all of the
later periods OF eruption, each fol-
lowed by its period of erosion, he
strikes the keynote to the real eco
nomic and scientific feature of the
camp, viz, the chief faulting.
Aside from some minor eruptions
of rhyolite, intrusions of quartz ande-
site, which he terms dacite, and
some obsidian flows, the chief faulting
period terminates the succession of
great dynamic events in the history
of vulcanism. While much of the
dacite and rhyolite has come up in
the form OF intrusions, the faults all
terminate against the necks up
which much OF this material flowed. |
The general map illustrates this
feature. He says that the area of
observed complicated faulting is
prac tically coextensive with the la te
lacite region. "This region, which
occupies the south eastern portion
of the district, is downsunken in
comparison with the unfaulted or
little faulted region on the north
west" This faulting has been pro-
ound, and while it has probably not
xercised any material influence upon
he enrichment of the veins, its eco
omic interest attaches because it
as cut and displaced them.
Much Importance therefore attaches
the necessity of careful observa-
ons by competent engineers of these
ults, where they are encountered. I
has been found that some OF the inn I
'rtantfault planes have become more a
less silicified, others carry some \
irag" ore, and thus simulate the S
ne veins. One conspicuous instance d
recalled by the reviewer where I
CD fault plane was followed for e