Leader Mine, Leader Hill, Helvetia, Helvetia-Rosemont Mining District, Pima County, Arizona, USAi

Regional Level Types
Leader Mine	Mine
Leader Hill	Hill
Helvetia	Town (Former)
Helvetia-Rosemont Mining District	Mining District
Pima County	County
Arizona	State
USA	Country

‡Ref.: Guild, F.N. (1907) The composition of molybdite from Arizona: American Journal of Science, 4th series: 23: 455-456.

Schrader, F.C. & J.M. Hill (1909), Some occurrences of molybdenite in the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 430: 154-163.

Schrader, F.C. and J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 92, 106-108.

University of Arizona Bull. 41 (1916-17), Mineralogy of Useful Minerals in Arizona: 29, 46, 50.

Wilson, E.D. (1941), Tungsten Deposits of Arizona, Geological Series No. 14, Arizona Bureau of Mines Bull. 148: 35-36.

Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 24.

Creasey, S.C. & G.L. Quick (1955), Copper deposits of part of Helvetia mining district, Pima County, Arizona: 312, 315-318.

Warner, L.A., Holser, W.T., Wilmarth, V.R., and Cameron, E.N. (1959) Occurrence of nonpegmatitic beryllium in the United States: U.S. Geological Survey Professional Paper 318, 198 p., 5 sheets, scales 1:480, 1:960, 1:4,800, 1:500,000: 103.

Kirkemo, H., et al (1965), Investigations of Molybdenum Deposits in the Conterminous United States 1942-60, Contributions to Economic Geology, USGS Bull. 1182-E: E11.

Arizona Bureau of Mines Field Notes (1971): 1(2).

Drewes, H.D. (1971) Geologic map of the Sahuarita quadrangle, southeast of Tucson, Pima County, Arizona: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-613, 1 sheet, scale 1:48,000.

Keith, Stanton B. (1974), Arizona Bureau of Geology & Mineral Technology, Geological Survey Branch Bull. 189, Index of Mining Properties in Pima County, Arizona: 126 (Table 4).

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

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 166, 302, 402.

USGS Sahuarita Quadrangle topo map.

Arizona Bureau of Mines file data.

MRDS database Dep. ID file #10103734, MRDS ID #M050045; and, Dep. ID #10183973, MAS ID #0040190284.

A former small underground Cu-Ag-Zn-Au-Mo-W-Be-Wollastonite mine located in the NW ¼ sec. 24, T.18S., R.15E., on several patented claims (Copper Fend, Copper World, Owasko), southeast slope of Leader Hill, about 1.2 miles east of Helvetia and 1/8 mile west of the Copper World Mine, at about 4,700 feet of altitude. Discovered about 1880. First produced 1880. One of the early discoveries of the camp and one of its leading producers. Reopened in 1942. Owned at times, or in part, by O.C. Mitchell; the Helvetia Copper Co. (Mrs. Lon Blankenship, Tucson); the Michigan-Arizona Development Co.; Helvetia Copper Co. of Arizona; Molybdenum, Inc.; Burney; and the Helvetia Mining & Milling Co. The first sulfide ore mined in the early days came from the Leader Mine.

Mineralization is banded seams and irregular lenses of pyrometasomatic replacement ore containing copper carbonates and sulfides, with considerable cupriferous pyrite, in shattered, silicated, thrust-faulted Paleozoic limestone along the thrust fault. Local spotty molybdenite and disseminated scheelite and powellite. Some minor sphalerite. Ore control was silicated limestone in a thrust fault where the fault is gently dipping. Ore concentration was due to permeable fracture zones. Alteration includes intense silication, pyrite-chalcopyrite-gossan, skarn, and iron staining. An associated rock unit is the Continental Granodiorite and quartz latite.

The mine lies at the footwall side of a thrust fault that dips 40ºNE, as does the limestone, which is much disturbed, shattered, altered, iron-stained, somewhat pyritic, and in part wet and cavernous. The fault has moved granitic rocks over limestone and siliceous limestone of the Naco limestone (restricted). In general, the limestone strikes NW-ward and dips to the East. It is highly brecciated and locally intensely altered to a brownish or greenish silicated rock ranging in character from one composed principally of garnet to one containing mainly pyroxene or epidote. Much of it is banded with seams of copper carbonate. In places, however, it is merely crystalline or completely marmarized.

Molybdenite occurs in limestone and garnet rock in the footwall of a low-angle fault; the hanging wall is granitic rock. The molybdenite occurs separately from chalcopyrite, the dominant copper mineral in the mine. The molybdenite is disseminated, forming scattered bunches or pockets of molybdenite-bearing rock. It also occurs in thin seams that commonly swell to small pockets as much as a foot long and several inches wide at intersections with other seams.

Workings include a 60 foot deep vertical shaft and an adit or 'long tunnel' some 400 feet long. There are some 700 feet of drifts on the haulage level, 415 feet of crosscuts and 4 stopes plus 5 sub-levels 30, 34, 40, 48 & 56 feet below the haulage level; overall 2,000 feet or more of aggregate workings to 140 level (1909). The mine produced sporadically some 30,000 tons of ore averaging about 6% Cu, 1 oz. Ag/T and minor Au. About 13 tons of 50% MoS2 concentrate were shipped in 1934.

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Link to USGS MRDS:	10103734

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