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

potion OF the vein.
Mr.. Spur describes the general
physical characteristic OF the rocks
, composing the various flows in suffi-
Gent detail to make it possible for
the miner in good many instances
to distinguish between the various
compositions, but more particularly
between the so-called lode porphyry
and its superimposed flows. Speak
ing OF this porphyry, he says: $50
far as observed it outcrops only on
"Mizpah and Gold Hills; but it has
been discovered In a number of
mines under the younger rocks. I"
There are, however, many ins tances
already noted, and many no doubt
yet to be encoun tered, where it will
be extremely difficult for the layman
to distinguish the difference. This
is due, as he points out, to very
complete alterat ton, the quartz-serl
cite type, Mr.. Spur says: "It has
the appearance of rhyolite rather
than of anything else, and does not
"at all resemble andesite." Thus it
will be seen that there are conditions
under which the miner might think
himself greatly removed from his
lode-porphyry when as matter of
fact he was within the sought-for
formation. Conversely, there are
conditions in which he might imagine
himself to be in lode-porphyry when
perhaps he would be far removed
from it.
One of the most valuable, indeed,
perhaps the most valuable feature
of Mr.. Spurs report is that he
makes these distinc tions as clear and
well-detined as it is perhaps possible
under the circumstances.
In speaking Of the latGr-andesite
and its distribution he says it out
crops over considerable portion of
the northern part of the district.
The upper portions, and in some
leases the whole, of the following
'shafts are in it; Montana -Tonopah'
North Star, Midway, Golden An,
"chor, Little Tonopah, Boston Tono-
"pah, Halifax, etc. In its highly
ALTERED phases the later andesite
becomes with great difficulty dis
"tinguishable from the early.ande.
"site, and where it is fine grained
1.-THE resemblance may become almost
exact. Rocks which are
''highly siliceous from alteration are
''apt to belong to the early rather
Ethan the late andesite,"
The report reviews in detail the
distribution and characteristics of
the formations in their geological
order and in the order here named:
Early andesite Code porphyry), later.
andesite, the rhyolites, the dacites.
the dacite- braccias, and the later in.
trusion dacite.
Mr.. Spur finds that there were no
less than four distinct periods of hot
spring action each accompanied by
more or less vein formation and min
eralization. Each OF these periods
was consequent upon lava intru-
'sion." In general, be says: "the
values found in the veins of these
different periods increase with in.
"creasing age. The earliest and mos
important class of veins can be
found only in the earlier andesite."
The report in general and particu
larry with reference to the vein
groups OF the early andesite mineral
cation bespeaks much for Tonopah.
He says: 'Tbe only productive veins
"thus far discovered are
those of the early andesite period.
On account of the later volcanic
rocks which cover the early andesite
in most of the district, these pro-
"ductive veins outcrop in only a
Small area, outside of which little is
known as yet. 1t is probable, how
lever, as Indicated by the great
'amonnt of alteration in the early
'andesite, the vein formation
"has been extensive, and that the
veins at present known are only
small portion of those that will
eventually be developed. ii
In speaking of the character Of the
veins, he very happily terms them
linked VEINS by reason of the fact
that they very frequently branch .
and reunite in both a horizontal and
vertical direction. la each group {
there is generally a main vein (veta :
yrande, the Spaniard would say from :
which the smaller veins branch.
Thus the main vein with its branches I
re terms a vein group. There are I
hree such groups, viz, the Montana c
'onopah group, the Mizpah group t
nd the Valley View group. The q
iizpah group is so far the only che @
developed to allow Of I.
etailed study of the vein system :
he three groups have a decided ?
ast-west trend. Fl