Feldman and Winkelman Gypsum pits (Feldman Quarry; National Gypsum Co. Mine), Feldman, Dudleyville area, Pinal Co., Arizona, USA
A Gypsum occurrence located in secs. 26, 27 & 33, T6S, R16E, about 3¼ miles S of Dudleyville, on the East side of the San Pedro River, about 8½ miles South of Winkleman. Operated by the National Gypsum Co. and the Superior Companies.
Mineralization is thick beds of lacustrine gypsum deposits on both sides of the river. Gypsum is white to greyish white, granular to microcrystalline gypsum beds. The beds are 2.44 meters thick hosted in clay, mud, silt, diatomite and shale. They dip 3E.
This deposit may be extensive in area. It is exposed near the surface where it was mined, but, it is buried to the S and E and eroded away to the W and N except in isolated residual hills. Diatomite occurs as interbeds in the gypsum. In this area, a zone at least 100 feet thick contains thick (1-8 feet), massive, white 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.
The shale is calcareous to gypsiferous. The lacustrine basin occupies at least 18 square miles, principally along the east side of the San Pedro River, and dips about 3E. An exploration hole drilled to evaluate one of the deposits intersected a continuous 300 foot thick formation of interbedded clay and gypsum. Correlation with other drill holes suggests that the section of clay and gypsum may be more than 595 feet thick. Aravaipa Creek bisects the deposit. North of the creek, massive gypsum with clay partings (30-50 feet thick) is being mined.
The gypsum ore is drilled and blasted; then the broken gypsum is loaded and hauled to crushing plants where the minus 3/8 inch fraction is screened off. The final product contains 92% gypsum and less than 4% insolubles.
Assay data: Mostly 90% + gypsum. Reserves and resources are not estimated but are probably in the multimillion ton range.
References:
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: 55-56.
Galbraith, F.W. & D.J. Brennan (1959), Minerals of AZ: 60.
Keith, Stanton B. (1969), Gypsum, in USGS & Arizona Bureau of Mines, and U.S. Bureau of Reclamation 1969, Mineral and water resources of Arizona, Arizona Bureau of Mines Bull. 180
Eyde, Ted, Wilkinson, P.A.K., and Weiland, E.F. (1986) Field Trip to Selected Industrial Mineral Deposits of Arizona, in Beatty, Barbara, and Wilkinson, P.A.K., editors, Frontiers in Geology and Ore Deposits of Arizona and the Southwest. Arizona Geological Society Digest vol. XVI: 312-318.
Phillips, K.A. (1987), Arizona Industrial Minerals, 2nd. Edition, Arizona Department of Mines & Minerals Minerals Report 4, 185 pp.
Peirce, H. Wesley (1990), Arizona Geological Survey Industrial Minerals card file.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 242.
MRDS database Dep. ID #10060185, MRDS ID #TC10142; and Dep. ID #10210233, MAS ID #0040210049.
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Map Reference: 32°52'41"N , 110°41'31"W
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