NEW MEXICO.
Turquoise
is known to occur at several places in the Burro Mountains of Grant
County, N. Mex. A description of one of these deposits—that of the
Azure Alining Company, about 15 miles southwest of Silver City—with
notes on the geology of the surrounding region, has been given by Mr.
Edward R. Zalinsky." The Azure mine, the American Gem and Turquoise
Company mine, one-half mile southeast, and the Porterfield Turquoise
Company mine, one-half mile south of the Azure mine, were briefly
visited by the writer during the fall of 1907. The following
description has been prepared from Mr. Zalinsky's article and the
writer's notes:
During
the last part of 1907 a small amount of work was done on the Azure
mine, opening up the lower levels and preparing to push developments
during 1908. The mine had not been-operated since 1905. The American
Gem and Turquoise Company mines also have been idle for the last few
years. The Porterfield turquoise mine was not worked during 1907,
though there was a large production from small excavations in 1906.
The
country rock of the turquoise region is granite which presents various
phases in texture, composition, and degree of alteration. The greater
part of the granite has a porphyritic texture, which varies from coarse
to very fine. Much of this granite has undergone such extensive
kaolinization that it is often difficult to determine the constituent
feldspathic minerals. The texture varies considerably and in some
places is finer grained and more porphyritic than in others. A common
variety of the granite has coarse pink feldspar phenocrysts. A thin
section cut from a specimen or this granite collected at the Copper
King mine, about one-third mile southwest of the head of the Azure
mine, contained orthoclase, a plagioclase, quartz, biotite altering to
chlorite, magnetite, and zircon. Another section cut from a specimen
from near the east wall of the Azure vein contained orthoclase, a
little plagioclase, probably albite, and quartz in grains and veinlets.
The feldspars were partially kaolinized and the kaolin much stained
with limonite. Another form of occurrence is a spotted porphyritic
granite with phenocrysts of orthoclase and plagioclase 2 or 3
millimeters square. A thin section from this variety of rock at the
Porterfield mine contained orthoclase and plagioclase in phenocrysts
and biotite shreds scattered through a groundmass of feldspar and
quartz. All of the feldspars were partially kaolinized.
Mr.
Zalinsky describes the occurrence of mica-andesite porphyry stocks and
andesite dikes of pre-Tertiary and Tertiary age. It was probably during
the intrusion of these bodies that the rock of the region was fractured
and mineralized. The turquoise deposits adjoin the copper deposits of
the Burro Mountains on the northwest, and copper staining is present
throughout their extent.
Azure turquoise mine.—The
Azure mine has been worked on an immense scale by an open cut that is
about 60 feet deep in its deepest portion, from 70 to 100 feet wide,
and about 200 yards long, with adits on two levels below the open work.
The vein is in a badly fractured zone and strikes about northeast with
a dip of 45° to the southeast; it is about 40 feet wide, though locally
over 60 feet wide. The joints produced during fracturing dip both
parallel
a Economic Geology, JuJy-August, 1907, pp. 464-492.
