Tyndall Mining District, Santa Cruz County, Arizona, USAi

Regional Level Types
Tyndall Mining District	Mining District
Santa Cruz County	County
Arizona	State
USA	Country

A Pb-Ag-Zn-Cu-Au mining area located in T21-23S, R14-15E, G&SRM, on the western slope of the southern part of the Santa Rita Mountains, south of the high peaks of the range, and about 65 miles south from Tucson. This is the largest and one of the most highly mineralized districts of the area. It joins the Old Baldy District on the south and west and is almost wholly in Santa Cruz County. It extends from Madera Canyon, near White House, and the county line on the north, southward to Sonoita Creek, a distance of 18 miles, and from the crest of the range on the east to the foot of the mountains and Grosvenor Hills, 6 miles distant on the west. The district contains about 110 square miles. A small part of it south of the Salero Camp is still spoken of as the Aztec District and includes the old Aztec Mine and some of the surrounding country.

The topography is varied and generally rough. The surface in the northern part of the district rises to Mount Hopkins, 8,072 feet, and Old Baldy, 9,432 feet in elevation. On the west the northern part of the border declines to 3,500 feet and the southern part to 4,000 feet. In the southwestern part of the district the general regularity in the slopes is interrupted by an irregular benchlike mass of hills, the Grosvenor Hills, averaging about 5,000 feet in elevation.

The district is occupied principally by a north-south belt of quartz diorite and quartz monzonite several miles wide on the east, bordered by granite on the north and overlian and flanked by the tertiary volcanic rocks, chiefly andesite, rhyolite, and quartz latite porphyry, on the west. In the northwestern part of the district, in the Montosa-Caliente region, there is a relatively small belt of the underlying Paleozoic shales and limestones.

Mineral deposits were first discovered in the district in the later part of the seventeenth century by the Jesuit missionaries, who worked the Salero, Montosa, and other mines. American activities began in the middle and late 1850's.

The mining properties lie mostly on or near the main drainage courses, which deeply score the district traversely and issue westward into the Santa Cruz Valley. These courses, beginning on the north, are Chino, Agua Caliente, Cottonwood, and Josephine canyons and Squaw Gulch.

The deposits, broadly described, consist of two main classes - argentiferous lead ores, which occur principally in fissure veins with a siliceous quartz-barite gangue in igneous rocks, and copper-silver ores, which occur similarly in fissure veins in igneous rocks and also as contact-metamorphic and replacement deposits, principally in the limestone.

Mineralization is varied: (1) Irrgular and lensing quartz fissure veins containing spotty argentiferous lead, zinc, and copper minerals and some barite. Generally shallow oxidation with supergene enrichment. Wall rocks are Cretaceous rhyodacite volcanics with interbedded arkose or Jurassic granite.; and (2) Replacement deposits of argentiferous lead and zinc minerals with minor copper in strongly faulted blocks of Paleozoic limestone. Deep solution and oxidation produced supergene enrichment in silver, and lead and zinc carbonates.

Workings include numerous scattered mines and prospects, some worked from the time of the Jesuits to recent times. The total estimated and reported production would be some 56,000 tons of ore containing about 9,400 tons of Pb, 2,800 tons of Zn, 520 tons of Cu, 480,000 oz. of silver, and 1,260 oz. of Au.

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