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PRECIOUS STONES.
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ARIZONA.
The
production of turquoise in Arizona was all from Mohave County, where
turquoise is found in the hills to the east and south of Mineral Park.
These hills are Ithaca Peak, 1 mile east of Mineral Park; Aztec
Mountain, 1-1/2 miles southeast of Mineral Park and 1 mile south of
Ithaca Peak; and on the end of the ridge one-third of a mile west of
south of Mineral Park. Turquoise is also reported to have been found on
a mountain four-fifths of a mile east of south of Mineral Park. There
are several mining companies and individuals interested in turquoise
claims in this district. Some of these operate intermittently; others
work their claims regularly. At the time of visit (September, 1908),
four companies were mining turquoise. The following is a list of the
companies and individuals owning or operating turquoise mines or claims
in the Mineral Park region: Aztec Turquoise Company, 13 claims; Arizona
Turquoise Company, a portion of William Tell claim; Los Angeles Gem
Company, a portion of William Tell claim; Southwest Turquoise Company,
four claims; James Uncapher, one claim; Mineral Park Turquoise Mining
Company, two claims; John Caswell, one claim; Mrs. John Kay, one full
claim and fractions of two claims.
The
turquoise deposits of Mineral Park are in certain of the hills and
peaks along the west side of the Cerbat Range of mountains, at
elevations ranging from 4,500 to 5,000 feet above sea level. According
to F. C. Schradera the greater part of these mountains are
composed of pre-Cambri an gneisses andschistscut by later granites and
porphyries. Prominent among the pre-Cambrian rocks are hornblende
gneisses and schists and granite gneiss, which outcrop in the country
around the hills in which the turquoise is found. The turquoise occurs
in certain of the later intrusive porphyries, whoseoutcrops form rugged
rocky hills and peaks. Two varieties of porphyry are recognized,
granite porphyry and quartz porphyry, evidently phases of the same rock
with variations in texture. The change from one to the other often
occurs in different parts of the same turquoise deposit, and may take
place within a few feet. The granite porphyry is typical of that rock,
being composed chiefly of phenocrysts of quartz and orthoclase in a
medium-grained groundmass of the same minerals. Remnants of altered
biotite crystals are observed in thin section. Large quantities of
muscovite, probably chiefly secondary sericite, occur in some of the
porphyry. Microcline, zircon, and secondary epidote are also sometimes
present. In the quartz porphyry the phenocrysts are the same as in the
granite porphyry and the groundmass is finer grained. In one thin
section examined the groundmass was very fine grained and exhibited a
partial spherulitic texture, as in rhyohte. The partly corroded, glassy
quartz phenocrysts are more prominent macroscop-icallyin the quartz
porphyry thanin the granite porphyry. Both types of porphyry have
undergone more or less alteration, especially around the turquoise
deposits. Besides the sericitization, the feldspars of the rock are
also partially kaolinized, and the biotite mica, when present, has been
altered or removed. Accompanying the decomposition of the porphyries
there was a silicification in which quartz was deposited in joints and
seams through the rock and even between the grains. In this way the
rock has been hardened so that it resists erosion
a Mineral deposits of Mohave Coupty, Ariz.: Bull, V, S. Geol. Survey No. 340,1908, pp. 55-59.
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