The Virginia enterprise. [volume] (Virginia, St. Louis County, Minn.) 1893-19??, 1913-10-03

a. In
: t.. CT,
DISCOVERIES
OF OPAL1N NEVADA
Mention has been made Of. the !
opal deposits of Virgin Valley, Hum
boldt County, New. in the chapter on
precious stones in several of the an
nual reports on the mineral resour-
ces of the United States, published by
the United States Geological Survey.
The quality of the opals was thus de-
scribed in the report for 1912:
The best gem opal from this region
is unexcelled in variety and brilliance
of fire and color by that from other
localities. The cut gems exhibit won
derful flashes of green, blue, yellow,
and red of various shades. In some
the color is uniform over the whole
stone or over large areas, changing
as the gem is turned from green to red
or from red to blue, and so on. Some
of the gems show a rich ultramarine
blue in one position with green or red
in another. Many gems display var
ious bright colors arranged in patches,
and each patch changes color as the
stone is turned. The brilliant flashes
of peacock-feather colors obtained
from the opal of dark color yields a
gem which might be called black opal,
but most of it is not like the Austral-
ian gem of that name, since it occurs
in thick pieces and the colors are less
localized. The majority of the dark
colored gems, no matter how beauti-
full in reflected light, become rich
reddish-brown color in transmitted
light. Lighter-colored opal with good
color and fire is also found and cuts
into very beautiful gems.
The locality was visited by Douglas
B. Sterrett, for the Geological Survey,
August 10, 20, and Fl 1913, for The
purpose of procuring information for
the report on mineral resources for
1913 and for an enlarged report on
precious stones to be prepared during
the course of the next three years.
Opals Found in Thinly Settled Region
The locality is in Virgin Valley, in
northern Humboldt County The
nearest postofice or small town is
DEMO, Greg, situated on the New
ada line. The opal field is about IS
miles southwest of DEMO and may be
that town 81 rom oeeda tef cal:
DEMO may be reached by stage, auto,
or team from Jungo or Winnemucca,
New, distance of about IS miles and
10 miles, respectively.
All the opal claims that have been
located were not visited by Mr.. Ster-
rett, but several of those from which
valuable gem material has been OBJ
tanned were examined. The occur
renee of the opal is similar at the
different localities. The matrix con-
sists of beds Of greenish clay inclosing
pebbles and debris of rhyolite and
other rocks with varying quantities of
petrifed wood. The opal-bearing clay
beds are interbedded with other strata
of white, gray, and yellowish, more or
less consolidated mud, sands, or gra-
wells. These formations contain a
large proportion Of volcanic ash and
breccia and are overlain by basalic
lava. The formations lie nearly fiat
or with dips rarely exceeding 10.
Block faulting has disturbed the for
nations considerably 50 that the opal
bearing strata occur at diverse ele7a-
tions. The opal deposits examined
lie at elevations ranging from about
5000 to $500 feet above sea level.
Erosion has exposed the formations
in different positions, so that the opal
strata outcrop in places as bands in
cliffs or steep hillsides or form blan-
ket beds over small areas under mesas
and plateaus.
The opal-bearing clay is sticky and
gumbo-like when moist, but on dry
ing it swells and cracks apart to a
crumbling mass. Pick and shovel
with horse scrapers are required for
surface mining and the former will
probably answer all purposes for IN
derground mining
Gems Associated with Petriied Wood
The greater part of the precious
opal is associated with petrified wood,
generally forming cast Of twigs,
limbs, banks, parts Of tree trunks, or
roots or occurring as seams or le-
posits in or around petriied wood IN
which the original texture Of the
wood is beautifully preserved.
,>o:.%~l.o ho- I~oou NADIA -, ~,,<%iprp