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Silver Reef Mine (Reef Mine; Cholla Mine; Silver Nugget Mine), White Horse Pass area, Silver Reef Mountains area, Chuichu area, Tat Momoli Mts, Silver Reef District, Tohono O'odham Indian Reservation, Pinal Co., Arizona, USA

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Latitude & Longitude (WGS84): 32° 42' 43'' North , 111° 49' 3'' West
Latitude & Longitude (decimal): 32.71194,-111.81750
Other regions containing this locality:Sonoran Desert, North America
Köppen climate type:BWh : Hot deserts climate

A former underground Pb-Ag-Cu-Au-Mo-silica mine located in sec. 23, T8S, R5E, about 2½ miles SW of White Horse Pass and about 3¼ miles SSW of Chuichu, on Indian Reservation land (located on the N slope of the Silver Reef Mountains). Claims extend slightly into secs. 26 and 24. Discovered 1885, produced 1905-1955. Previous owners and operators include Wm. Forbach (1917); Silver Reef M + M (1926, 1930); Arizona Leasing and Development (1927-1928); Albert C. Forbach (1942); and S.B. Owens (1951). May also have been operated in 1905 by the Arizona Mercantile Transportation and Smelting Co. Additional names which apply to this locality: Santiago Mine; Lead Boulder Mine; Hornsilver Mine; Horn Silver Mine; Greenhorn Mine; Greenhorn Mining Co. property; Unpatented claims MS 3369; Santiago MS 3369 unpatented claim; Lead Boulder MS 3369 unpatented claim; Hornsilver claims MS 3369 unpatented claim; Cholla MS 3369 unpatented claim; Arizona Mercantile Transport and Smelting Co. claim. Claims include the Horn Silver, Horn Silver No. 1 and No. 2, Santiago, Nugget, Nugget Fraction, Nugget Extension, Sahuara, Cholla, Lead Boulder, and the Silver Nugget. These same claims are also called the Silver Reef No. 1 to No. 9, (UPP. 3369).

Mineralization is secondary enrichment by ground water percolation down a fault zone. The ore body is in lenses at 15.24 meters thick aND 1828.8 meters long. The deposit is comprised of 3 to 4 veins in fault zones; the major vein strikes N79E and is traceable for 6000 feet, Vein width is variable from a few feet in the west to 25-50 feet in the east. Siliceous silver ores with copper, gold and lead. Ore control was E-W fractures, minor NW-striking faults. The main E-W vein dips 75-77S. Associated rock unit is the Oracle Granite (of Peterson) and vesicular andesite.

Local structures include an E-W fracture zone with minor NW-striking faults, Mf-934 maps E-W, mineralized zone, mainly in Oracle Granite, with some adjacent Tertiary andesite. Regional structures include an E-W striking fault with minor NW-striking faults.

Workings include the largest and earliest workings, which are the Horn Silver shaft with levels at 96, 200, and 240 feet, opened by an inclined shaft and adit; other workings include the Silver Nugget and Lead Boulder as well as other smaller workings.

Mineral List

15 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: 2913185
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

This page contains all mineral locality references listed on This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Tenny, J.B. (1927-1929) History of Mining in Arizona, Special Cllection, University of Arizona Library & Arizona Bureau of Mines Library: 340.
Tenney, J.B. (1934) Economic Geological Reconnaissance of Casa Grande Mining District. Arizona Bureau of Mines: 23-24.
US Atomic Energy Commission Preliminary Reconnaissance Report 172-488 (1953): 12.
Dunning, Charles H. (1966) Silver: 121-122.
Phillips, K.A. (1987), Arizona Industrial Minerals, 2nd. Edition, Arizona Department of Mines & Minerals Min. Report 4.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 300.
Rocks & Minerals (1988): 63: 327.
Rocks and Minerals (1989): 64: 58.
U.S. Bureau of Mines Mining District Sheet 561.
Arizona Department of Mineral Resources U file.
Arizona Department of Mineral Resources file data.
USGS Silver Reef Mountains Quadrangle map.
MRDS database Dep. ID #10046277, MRDS ID #M241169; and Dep. D #10159000, MAS ID #0040210765.

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