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Arizona Gypsum Mine (National Gypsum Co. Mine), San Pedro Valley, Brandenburg Mountain area, Pinal Co., Arizona, USA

Latitude: 32°52'29"N
Longitude: 110°40'23"W
A former surface gypsum mine located in secs. 25 & 34-36, T6S, R16E, on the east side of San Pedro Valley, about 4½ miles NE of Lookout Mountain, about 4¾ miles just S of W of Brandenburg Mountain, and about 7½ miles S of Winkelman. Operated by the National Gypsum Co.

Mineralization is a lacustrine gypsum deposit hosted in the Gila Group (silt, shale) in a 2.44 meter thick bed. Ore is the bedded gypsum.

Assay data: Massive, white to grayish white, granular to microcrystalline gypsum beds; 90+% gypsum.

This deposit may be extensive in area. It is exposed near the surface where mined, but buried to the S and E and eroded away to the W and N, except in isolated resual hills. In this area, a zone at least 100 feet thick contains thick (1-8 feet), massive, wjite to grayish white, granular to microcrystalline, flat-lying gypsum beds. The gypsum beds are separated by thin layers of calcareous and gypsiferous shale and silt. Ground raw gypsum was sold to the Arizona Portland Cement Co. at Rillito, Pima County, and also sold for agriculture. Reserves and resources not estimated but probably in the multimillion-ton range.


Blake, W.P. (1904) Gypsum Deposits of Arizona USGS Bull. 223, 129 pp.

Stone, R.W. (1920) Gypsum Deposits of the United States, USGS Bull. 697, 326 pp.

Phillips, K.A. (1987), Arizona Industrial Minerals, 2nd. Edition, Arizona Department of Mines & Minerals Mineral Report 4, 185 pp.

Peirce, H. Wesley (1990), Arizona Geological Survey Industrial Minerals card file.

USGS, Arizona Bureau of Mines, and US Bureau of Reclamation 1969, Mineral and water resources of Arizona, AZ Bur. of Mines Bull. 180: 375.

MRDS database Dep. ID #10105104 MRDS ID #TC10143.

Mineral List


1 entry listed. 1 valid mineral.

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