Helena Mine, Empire Ranch, Helvetia-Rosemont District, Santa Rita Mts, Pima Co., Arizona, USA
|Latitude & Longitude (WGS84):||31° 52' 22'' North , 110° 42' 31'' West|
|Latitude & Longitude (decimal):||31.87278,-110.70861|
|Other regions containing this locality:||Sonoran Desert, North America|
|Köppen climate type:||BSk : Cold semi-arid (steppe) climate|
‡Ref.: Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 92, 138-141.
Arizona Bureau of Mines file data.
MRDS database Dep. ID file #10039613, MRDS ID #M050493; and, Dep. ID #10162153, MAS ID #0040190490.
A former small underground Au mine located in sec. 16, T18S, R16E, in the eastern part of the Helvetia district, 5 miles ENE of Helvetia, 1½ miles SE of Mount Fagan, 2 miles west of Davidson Canyon, and a mile north of the Scholefield Ranch, at an elevation of 4,550 feet, in the toe of the long ridge extending southward from Mount Fagan. Discovered in 1894 and owned by the Rosemont Copper Mining & Milling Co. (circa 1915).
Mineralization is deposits which occur in the rhyolite near its contact with the sedimentary rocks. They are contained in 2 or more fissure veins or ledges which dip west. The main vein has a width of about 7 feet and occupies a fault fissure along which the rhyolite has been considerably fractured and crushed. It dips 40º to 60ºW., and the ore shoots pitch to the north. It has a known extent of about 150 feet vertically and about 500 feet horizontally and a reported extension of ½ mile or more to the north of the mine. It consists principally of iron-stained, reddish-brown, or lavender-colored, crushed and silicified rhyolite and quartz. The quartz is mostly dark gray and impure, and much of it has obviously replaced rhyolite. Some of the quartz is milky white or of a greasy luster and shows by its pseudomorphic structure that it has replaced calcite. Near surface the gangue contains white pyrite, seemingly marcasite. The ore is well oxidized.
Country rock is a close-grained reddish Tertiary rhyolite, intrusive into the dark green shale and sandstone, of which it contains inclusions. These rocks are cut by a NE vertical sheeting.
Workings include drifts, inclines, winzes, raises, stopes, and shafts aggregating an estimated 500 feet of workings, mostly comprised within a vertical range of 150 feet and in a north-south belt about 500 feet long. The main drift is about 250 feet long. A winze off this drift is inclined and 40 feet deep. Production unknown. Gold content was about 10 oz./t.
3 valid minerals.
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 Macrostrat.org
|Ypresian - Campanian|
47.8 - 83.6 Ma
|Early Tertiary to Late Cretaceous volcanic rocks|
Age: Phanerozoic (47.8 - 83.6 Ma)
Stratigraphic Name: Williamson Canyon Volcanics
Description: Rhyolite to andesite and closely associated sedimentary and near-surface intrusive rocks; commonly dark gray to dark greenish gray or greenish brown. In the ranges west of Tucson, this unit includes thick welded ash-flow tuffs. Volcanic rocks of this unit are inferred to be derived from vents and volcanoes above magma chambers that solidified to form the granitic rocks of map unit TKg. These rocks are restricted to southeastern Arizona except for a small outcrop near Bagdad. (50-82 Ma)
Comments: Related, broadly, to unit TKg
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.