The Lewiston teller. (Lewiston, Idaho) 1900-1905, 1902-11-07
THUNDER MOUNTAIN
| N
Report on Geological Conditions by 4 Practical
Engineer and GsoIosist- General Conditions
Of the Great Gold Field. p.

Of the Great Gold Field.
. Zenas N. Vaughn, the civil engineer.
after spending nearly four months in
the Thunder Mountain country, returned
to Boise few days ago and by request Of
the Boise Statesman. furnished the fol.
lowing instructive observations and de.
| scription Of that country:
First, will say word about the geol-
ogy. Were disposed to verify the adj
age that Fools rush in where angels fear
to tread" might enter into a lengthy,
scientific discussion of this phase Of the
subject. l shall be brief but / hope 10
dispel one illusion. Thunder Mountain
is not all porphyry, 1t has a gootliy
sprinkling of it, to be sure, but there is
room there for almost everything and
almost everything is there.
Ientered Thunder Mountain from the
Sea Foam side. Up TO certain point
everything had been granite The Sea
Foam country is granite, though il has
immense upheavals of eruptive rock.
short distance north of the middle fork
OF the Salmon the granite $ replaced by
porphyry formations Notwithstanding
this, within ten miles Of the Dewey mine
there are large areas ofgrani,e which car
ries huge ledges Of quartz This is pre-.
eminently true Of the rock along the
southwest fork Of the Monumental. In
some places the formations are very com.
plicated. There are areas Of granite.
bird's.eye porphyry, quartz porphyry.
quartzite. diorite, phonolite and serpen-
tine mixed up in the most hewil.ierinp
confusion. Perhaps the most common
rock in Thunder Mountain is sort OF
phtnolite that splits up into very char
acteristic slabs.
Close to Roosevelt the structures are
either porphyry, phonolite or some allieI
eruptive rock. Ten miles to the north-
ward the geology changes and the country
IS granite, quartzite, serpentine, or quartz
porphyry. To the southwark of Indian
creek the porphyry is replaced by very
beautiful white granite, or in some places
gneiss. which holds its own for many
miles To the eastward. as above ex-
planned, the eruptions extend we'll niYh
to the middle fork Of the Salmon.
Dangerous as it is TO do so, it is difficuIt
to refrain from theorizing on the above
conditions. There is reason to believe.
however. that Thunder Mountain and
contiguous mountains are an intrusion of
volcanic rocks into an area Of preexist-
ing granite. Reyund this it is not safe 10
draw conclusions.
The naturalization Of this district Is
peculiar. The ores. though 80 widely
different in appearance. may he grouped
under two general heads The first Is the
one most pazzling. and the one that has
awakened such widespread interest in the
district. 1t is generally called por-
phyry, and in some cases tale While
there is no doubt talcose deposits. these
ores do not generally seem to the writer
10 be either porphyry or tale, but : sort Of
pnlverized quartz. which has been CO.
mented into coherent mass by infiirta-
ton Of waters holding 10 solution oxide
Of iron and carbonates Of lime, magnesia.
etc. These ores vary in color from SNOW
white to yellowish, brownish and blush.
The second class is quartz. occurring in !
regular ledges. generally carrying abund. !
r. = r. =