Latitude: 31°36'41"N
Longitude: 110°51'39"W
‡Ref.: Schrader, F.C. & J.M. Hill (1915), Mineral deposits of the Santa Rita and Patagonia Mountains, Arizona, USGS Bull. 582: 200-203.
Tenney, J.B. (1927-1929) History of Mining in Arizona, Special Collection, University of Arizona Library & Arizona Bureau of Mines Library: 315-316.
U.S. Atomic Energy Commission Preliminary Reconnaissance Report A-P-360 & 11 (1955).
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.
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., 1973, Geochemical reconnaissance of the Santa Rita Mountains, southeast of Tucson, Arizona: U.S. Geological Survey Bulletin 1365, 67 p., 2 sheets, scale 1:24,000.
Keith, Stanton B. (1975) State of Arizona Bureau of Geology and Mineral Technology, Geological Survey Branch Bull. 191, Index of Mining Properties in Santa Cruz County, Arizona.
U.S. Bureau of Land Management Mining District Sheet 668.
U.S. Bureau of Mines - Arizona Bureau of Geology and Mineral Technology file data.
U.S. Bureau of Mines file data, Alto Mine Group file.
MRDS database Dep. ID file #10037106, MRDS ID #M030411.
A former small underground Pb-Ag-Zn-Au-Cu-Mo-Sb-Baryte-U mine located on 13 unpatented claims. in the S½ sec. 12 & the N½ sec. 13, T21S, R14E, 2.5 miles N of Salero, about 1/2 mile NW of the Lineboy Mine, 3/4 mile NW of the Boundary post 113 on the Mexican border, on private land. Discovered in 1687 by Jesuit priests of the Tumacacori missionaries. Relocated by Americans in 1873 as the Gold Tree Mine. Produced from 1687 to 1959. Owned by R. R Hansen and Associates (1965). Operated by the Fortuna Mining Co. (1956).
Mineralization is the Alto vein which lies in latite and granite porphyry and contains most of the development work of the mine as a whole. It extends through a length of two or more claims and is from 3 to 7 feet wide. The average dip of this vein for the first 300 feet in depth is about vertical.
An auxiliary, or blind, vein dipping steeply to the north or vertical comes in from the WSW about 400 feet into the tunnel. This blind vein contains principally galena, sphalerite and other sulfides. Between 600 and 800 feet from the portal another small vein dipping steeply to the north contains chalcopyrite ore. Between the 1,400 and 1,560 feet in a large body of kaolin or gouge occurs and the vein is 6 feet wide. From the 800 foot point to the face of the tunnel the vein carries a more or less continuous 18 inch (45 cm) oreshoot in which the ore occurs in lenses and stringers of galena, 6 inches (15 cm) or more in maximum width. At the face of the tunnel the vein is about 4 feet wide and contains an ore shoot nearly a foot wide in the north or hanging wall side, the rest of the width consisting mostly of altered rock carrying sulphide ore minerals all the way across. The middle part of the vein in this portion of the mine is said to carry generally considerable sphalerite.
Ore control was tension fractures; six E-W-trending quartz fissure veins, mainly in La Tite and granite porphyry. Ore concentration was supergene enrichement and oxidation near surface. Alteration is kaolinization in fault gouge. Associated rock units are the Salero Formation; the Jospehine Canyon Diorite and the Squaw Peak Granite.
Local structures include E-W and NE-trending quartz fissure veins along contacts and fault zones in diorite and granite porphyry. The veins are generally well-defined, carrying ore shoots. Tectonic elements include the Salero Fault Block.
The main vein is opened by the 1,632 foot long Alto tunnel with connecting shafts. The blind vein is opened by a back drift known as the west drift, for 130 feet to the west. Most shafts are flooded. Operations included a 300 foot vertical shaft, 2000 & 1400 foot adits, a 175 foot deep vertical shaft with 200 feet of raise, and a 90 foot inclined shaft. Workings total 3048 meters in length and 67.06 meters in depth.
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