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Old Dick Mine (American Mine), Helvetia, Helvetia-Rosemont District, Santa Rita Mts, Pima Co., Arizona, USA

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Latitude & Longitude (WGS84): 31° 51' 27'' North , 110° 46' 42'' West
Latitude & Longitude (decimal): 31.85750,-110.77833
Köppen climate type:BSk : Cold semi-arid (steppe) climate
Other regions containing this locality:Sonoran Desert, North America

‡Ref.: Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 92, 113-114.

Creasey, S.C. & G.L. Quick (1955), Copper deposits of part of Helvetia mining district, Pima County, Arizona, USGS Bull. 1027-F: 320.

Arizona Bureau of Mines field notes (1971), vol. 1, no. 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: 127 (Table 4).

Niemuth, N.J. & K.A. Phillips (1992), Copper Oxide Resources, Arizona Department of Mines & Mineral Resources Open File Report 92-10: 13 (Table 1).

USGS Sahuarita Quadrangle topo map.

MRDS database Dep. ID file #10039417, MRDS ID #M050052; and, Dep. ID #10259004, MAS ID #0040190340.

A former small surface and underground Cu-Ag-Pb-Zn-Au mine located in North-central sec. 23, T.18S., R.15E. (Sahuarita 15 minute topo map), about ½ mile east of Helvetia and 28 miles SE of Tucson, in the northerly slope of a detached spur or foothill at an elevation of about 4,500 feet, on the Old Dick and American claims. Opened in 1899 and worked until 1902. Reopened 1905 and worked until August, 1907. Produced 1940-1952. Owned at times, or in part, by the Helvetia Copper Co.; Michigan-Arizona Development Co.; Helvetia Copper Co. of Arizona; Helvetia Oil Co.; and R.E. Chilson; Helvetia Mining and Milling Co.; and James R. Cray.

Mineralization is irregular pyrometasomatic replacement orebodies and pipes with copper carbonates, oxides and sulfides, minor lead and zinc minerals, and iron oxides in a broken and silicated Paleozoic limestone block, about ¼ mile diameter, intruded by quartz latite porphyry, in a thrust fault klippé. The ore body is 4.57 meters thick. Ore control was the intrusive contact and shear zone. Alteration was pyrite-chalcopyrite-gossan; and skarn. The limestone dips to the north and NE at medium angles. Towards the west it is mostly white or light, but toward the east it is dark. Host rock units include the Willow Canyon Formation Cretaceous conglomerate and siltstone; and, the Concha Limestone (cherty limestone). An associated rock unit is quartz latite at 56 ± 2 MY.

Practically all of the ore came from the oxidized zone near the surface, where it was almost entirely malachite and azurite, with some cuprite and considerable iron oxide.

There are two ore zones in general separated by a few feet of limestone, with which the orebodies in general are crudely conformable, trending WNW with northerly dip, but some orebodies are vertical or chimney-like and form good examples of the ore replacing limestone. Some bodies of good ore are reported to have been 10 to 15 feet wide. Non-commercial deposits of chalcopyrite occur at the bottom of the mine, including efflorescences of chalcanthite.

Local structures include thrust and normal faulting, fracture zones, homoclinal. Regional trends include tilting and broad open folds in the south and extensive faulting in the north.

Workings include several shaft and large, quarry-like open cuts. About 3,000 feet or more of work on the first level. One of the oldest mines, producing sporadically from the late 1870's to 1907 and 1938 to 1952. Produced a probable total of at least 20,000 tons of ore averaging about 5% Cu, 1 oz. Ag/T and minor Pb & Au.

Mineral List

6 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on

1400 - 1600 Ma

ID: 2830999
Middle Proterozoic granitic rocks

Age: Calymmian (1400 - 1600 Ma)

Stratigraphic Name: Oracle Granite; Ruin Granite

Description: Mostly porphyritic biotite granite with large microcline phenocrysts, with local fine-grained border phases and aplite. Associated pegmatite and quartz veins are rare. This unit forms large plutons, including the Oracle Granite, Ruin Granite, granite in the Pinnacle Peak - Carefree area northeast of Phoenix, and several bodies west of Prescott. (1400-1450 Ma)

Comments: ~ 1.4 Ga

Lithology: Major:{granite}, Minor:{aplite}, Incidental:{pegmatite}

Reference: Horton, J.D., C.A. San Juan, and D.B. Stoeser. The State Geologic Map Compilation (SGMC) geodatabase of the conterminous United States. doi: 10.3133/ds1052. U.S. Geological Survey Data Series 1052. [133]

Data and map coding provided by, used under Creative Commons Attribution 4.0 License

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