Precious Gem stones production in 1907 Page 62



	828	MINERAL RESOURCES.

	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.