680 MINERAL RESOURCES, 1913----PART II.
At
the suggestion of H. D. McCaskey, of the United States Geological
Survey, specimens of opal containing cinnabar were cut with a view to
determining their suitability for gem purposes. This material came from
a quicksilver mine operated by J. B. Kiernan, of Beatty Nev. Specimens
of the rough mineral were kindly supplied by Mr. Kiernan and general
information on the deposit was given by A. A. Turner, a mining engineer
of Boston, Mass.
The
mine is in Bare Mountain in southwestern Nevada, the nearest point
being about 10 miles from the California State line. The Amargosa
Desert lies west of the mountain and Crater Flat to the east, the
highest point being approximately 6,235 feet above sea level. or 3,300
feet above the surrounding plains. The formations around the cinnabar
deposit are limestone, quartzite, schist, and a volcanic rock, probably
dacite. The deposit lies between two dacite dikes and is apparently a
replacement deposit. Opal impregnated with cinnabar was found within a
few feet of the surface and extended to a depth of 61 feet, the depth
of the workings at the time last examined by Mr. Turner. The opal is an
associated mineral but much of it contains sufficient mercury to smelt
with the regular ore. The opal bodies are surrounded by a fine white
sand resulting from the decomposition of impure opal. The nature of
the deposits and the presence of small vent holes in the sand near the
ore bodies indicate that they have resulted from past hot spring
activity.
Most
of the material that can be cut as a semiprecious stone consists of
milk-white to slightly translucent gray opal impregnated with bright
vermilion-red cinnabar. The cinnabar occurs in minute particles
disseminated or grouped in irregular tufts, patches, and streaks
through the opal. Specimens were seen in which the cinnabar was in a
duller chalcedonic material, probably altered quartzite. The contrast
between the red and the white or gray, with the variations of markings
displayed by the cut stones, make this an attractive semiprecious stone
which could be readily used in the western tourist trade. The
possibility of the cinnabar losing some of the brightness of its color,
as in the "myrickite" described under agate, will have to be taken into
consideration.
OREGON.
Mr.
Don Maguire, of Ogden, Utah, reports the occurrence of semiprecious
opal along Deschutes River, Crook County, Oreg. This opal is reported
to be abundant and very pretty. A limited quantity was shipped to
Portland, Oreg., for gem purposes during 1913.
TEXAS.
Specimens
of opal found near Alpine, Tex., were received from Mr. A. D. Hudson,
of El Paso. They consisted of small patches of white and bluish opal in
a dark red rhyolite-like matrix. Some of the opal showed flashes of
rich green and bluish fire. The reddish matrix might be cut showing
patches of precious opal, if pure gem can not be obtained in larger
pieces.
