Helvetia-Rosemont District, Santa Rita Mts, Pima Co., Arizona, USA

‡Ref.: The Resources of Arizona - A Manual of Reliable Information Concerning the Territory, compiled by Patrick Hamilton (1881), Scottsdale, AZ: 47.

Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 91-141.

Schrader, F.C. (1917), The geologic distribution and genesis of the metals in the Santa Rita-Patagonia Mountains, Arizona, Economic Geology: 12: 237-269.

Galbraith, F.W. (1947), Arizona Bureau of Mines Bull. 153, Minerals of Arizona: 20.

Creasy, S.C. & G.L. Quick (1955), Copper deposits of part of Helvetia mining district, Pima County, Arizona, USGS Bull. 1027-F: 301-323.

Galbraith, F.W. & D.J. Brennan (1959), Minerals of Arizona: 81, 90.

Drewes, H.D., and Finnell, T.L. (1968) Mesozoic stratigraphy and Laramide tectonics of part of the Santa Rita and Empire Mountains, southeast of Tucson, Arizona, Field Trip II, in Titley, S.R., ed., Southern Arizona Guidebook III: Arizona Geological Society, p. 315-324.

Drewes, H.D. (1969) The Laramide orogeny of Arizona southeast of Tucson [abs.], in Abstracts for 1968: Geological Society of America Special Paper 121, p. 501-502.

Drewes, Harald (1970) Structural control of geochemical anomalies in the Greaterville mining district, southeast of Tucson: U.S. Geological Survey Bulletin 1312-A, p. A1-A49, 1 sheet, scale 1:24,000.

Anthony, J.W. & R.B. Laughon (1970), Kinoite, a new hydrous copper calcium silicate mineral from Arizona, American Mineralogist: 55: 709-713.

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Drewes, H.D. (1971) Mesozoic stratigraphy of the Santa Rita Mountains, southeast of Tucson, Arizona: U.S. Geological Survey Professional Paper 658-C, 81 p.

Drewes, H.D. (1971) Geologic map of the Mount Wrightson quadrangle, southeast of Tucson, Santa Cruz and Pima Counties, Arizona: U.S. Geological Survey Miscellaneous Geologic Investigations Map I-614, 1 sheet, scale 1:48,000.

Finnell, T.L. (1971), Preliminary Geologic Map of the Empire Mts quadrangle, Pima County, Arizona, USGS Open-file Report.

Drewes, H.D. (1972) Cenozoic rocks of the Santa Rita Mountains, southeast of Tucson, Arizona: U.S. Geological Survey Professional Paper 746, 66 p.

Drewes, H.D. (1972) Structural geology of the Santa Rita Mountains, southeast of Tucson, Arizona: U.S. Geological Survey Professional Paper 748, 35 p., scale 1:12,000, 4 sheets.

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Keith, Stanton B. (1974), Arizona Bureau of Geology & Mineral Technology, Geological Survey Branch Bull. 189, Index of Mining Properties in Pima County, Arizona: 123 (Table 4).

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Anzalone, S.A. (1995) The Helvetia area porphyry systems, Pima County, Arizona, in Pierce, F.W., and Bolm, J.G., eds., Porphyry copper deposits of the American Cordillera: Arizona Geological Society Digest 20, p. 436-441.

A Cu-Pb-Zn-Ag-Au-W-Mo-limestone-marble mining area located in T.17-18S., R.15-16E., in the northern and central Santa Rita Mountains, north-central part of the Patagonia quadrangle, in the eastern part of Pima County, comprising a northeast-southwest area about 12 miles long and 7 miles wide, or about 90 square miles, between the Empire District to the East and the Greaterville District to the SW.

The Helvetia District contains the north end of the Santa Rita Mountains, which here rise to about 6,000 feet and in or near whose axis most of the mines are situated. It extends from Box Canyon on the south to and beyond the Cuprite Camp in the head of Pantano Wash on the north and from the west base of te Santa Rita Mountains to Davidson Canyon on the east.

The principal camp is Helvetia, located SW of the center of the district. The Rosemont Camp is 4 miles SE of Helvetia on the east slope of the range.

Mineralization is varied: (1) Irregular, partly oxidized, pyrometasomatic replacement copper deposits with subordinate and spotty lead, zinc, tungsten, and molybdenum mineralization in thrust-faulted, sheared and altered Paleozoic limestone and quartzite, and in Cretaceous limy beds. Controlled by structures or bedding planes in contact with, or close to, Laramide quartz latite porphyry stocks & dikes. Locally the intrusive contains disseminated copper mineralization; (2) Spotty and irregular, partly oxidized base metal sulfides with some scheelite along quartz-shear zones or breccia zones in Precambrian and Laramide granitic intrusives; and, (3) PAleozoic limestones, locally metamorphosed to marble.

The main structural feature is a thrust fault with gentle dip to the SW, whose contact with the sedimentary rocks runs in an irregular line. This fault has brought the basal granite against the altered overlying Paleozoic limestones. The beds of limestone dip in toward the center from the north, south and west, while the east side is cut off by a fault.

At some time after the faulting and folding took place both the sediments and the granite were freely intruded by dikes, chiefly of the very acidic magma that produced principally the alaskite aplite. Since the intrusion of the various igneous rocks differential movement has produced considerable gouge and material resembling fault breccia along the dikes and elsewhere, and the movement was probably also attended by ore deposition.

The granite occupying the western half of the area is probably Precambrian. It is coarse-textured and in places porphyritic, with large feldspar phenocrysts. It is composed of orthoclase (including microcline), quartz, albite-oligoclase. biotite, and hornblende, with magnetite and zircon as accessory minerals. It is cut by 2 sets of joints trending north and east and by a sheeting which inclines gently to the west but in places is nearly horizontal. Along the faults it is shattered and altered, manganese and iron oxides are developed in the jloints, and locally it is epidotized.

Next above the granite come the pink to red Cambrian (?) quartzites, which are mostly heavy bedded and massive and in places considerably altered. They occur in three areas. Tghis rock forms the so-called buttes or high dome-shaped bald knobs that stud the crest of the range.

The limestones contain most of the ores of the camp.

Workings include fifty or more small to medium-sized mines and prospects that have been opened and worked since the early 1880's. Total estimated and reported production through 1972 would be some 430,000 tons of ore containing about 17,500 tons of copper, 350,000 oz. of silver, 680 tons of zinc, 260 tons of lead and a minor amount of gold, molybdenum and tungsten. An indefinate amount of limestone and marble have been produced.