79 Mine (79th Mine; Seventy-Nine Mine; Seventy-Nine property; McHur prospect), Chilito, Hayden area, Banner District, Dripping Spring Mts, Gila Co., Arizona, USA

A former underground Pb-Zn-Cu-Ag-Au-Mo-Sb-V-Fe mine located in the SE¼ sec. 21 and sec. 28, T4S, R15E (Hayden 7.5 minute topo map), about 1½ miles W of Chilito ghost town, 4.5 miles NNW of Hayden, 2 miles NW of Toronado Peak, on federal land. Discovered 1879 by Mike and Pat O'Brien. Purchased 1921 by Continental Commission Co.; purchased May, 1922 by the Seventy-Nine Mining Co. and reconveyed back to the Continental Commission Co. (1919-1922, 1923-1926) after litigation. Sold at public auction in 1926. Reopened 1928 by the Seventy-Nine Lead-Copper Co. Closed in January, 1938 due to declining metal prices. Reopened in 1940 by the Shattuck-Denn Mining Corp. until 1949. Acquired by Callahan Zinc-Lead Company, Inc. 1950. Previous owners also included Grisson Mines. Some production until 1951. Owned by the ACM Corp. (1967). Mined for specimens until the late 1990's by John Mediz, Copper City Rock Shop, and others, when mud slides from an El Niño episode intruded into the workings. Subsequently reopened for specimens. As of 1992, site is closed to collectors.

Mineralization is deposit with an ore zone 335.28 meters long, 12.19 meters wide, with a depth-to-top of 0 meters, a depth-to-bottom of 152.4 meters, and 15.24 meters thick, striking N75E and dipping 40S. The deposit is hosted in limestone and rhyolite. Associated rock units are diorite and rhyolite. The mineralization occurs in fractures or broken, thin calcareous shale. 6 bedded zones were mined. Galena, sphalerite, Ppyrite, and quartz in replacement bodies in shattered, alternating thin bedded shale and impure limestone members of the Naco formation and as small discontinuous vein replacements in fractured and brecciated parts of a prominent rhyolite porphyry dike.

The oldest rock exposed in the area is the Younger Precambrian Mescal formation of the Apache group. It rests upon intrusive diabase and consists of approximately 50 feet of limestone with 90 feet of overlying sandy beds. Above the Mescal are the Middle Cambrain Troy quartzite, approximately 400 feet thick, succeeded by 225 feet of undifferentiated shale and quartzite, probably Middle Cambrian; Upper Devonian Martin limestone, consisting of thin beds with some shale, 250 to 328 feet thick; Lower Mississippian Escabrosa limestone, a massive cliff-former, 440 to 581 feet thick; and Lower Pennsylvanian Naco limestone, thin-bedded and cherty, 385 to more than 1,000 feet thick. This entire section appears to be conformable, although separated by at least three disconformities.

Intruded into the Mescal and the lower portion of the Troy are bodies of diabase with a maximum thickness of some 400 feet in outcrops; the total thickness of the diabase is unknown, as its lower contact is not exposed. The age of the diabase at Superior was determined as post-Middle Cambrian and pre-Upper Devonian (Short & others).

An extensive development of basic igneous material occurs near this mine and is expressed in the 79 Mine area by local basalt-porphyry sills (?) and plugs and andesitic and dacitic porphyry sills.

Presumably during the Cretaceous-Tertiary (Laramide) interval, this region was subjected to deformation, accompanied in its later stages by intrusion of acidic dikes, sills, and plugs, probably apophyses of the Central Arizona batholith.

The linear northwestward trend of the Dripping Spring Mountains reflects systematic structural deformation. A cross section (Ransome's) indicates the mountain range to be a complexly faulted anticline.

Throughout the 79 area on the southwestern flank of the range, the pre-Tertiary strata dip about 15º southward, with local variations in tilted fault blocks. Compressional stresses are evidenced by bedding plane faults and by a thrust fault exposed north of Tam O'Shanter Peak, 1½ miles north.

The steeply-dipping faults of the 79 area may be classified as of pre-ore and post-ore ages. Those of the earlier group were important in localizing mineral deposition. Some of the post-ore faults displaced orebodies, and others influenced topography.

The known orebodies of the 79 Mine occur as replacements in thin-bedded Naco limestone and as small discontinuous vein-replacements in the North dike of rhyolite porphyry. Ore deposition closely followed the pre-mineral faulting and may have begun before it entirely ceased. The mineralization is regarded as of Laramide (late Cretaceous and early Tertiary) age.

The several orebodies are: The Discovery, marked by string gossan; the Massive Pyrite orebody; and, discontinuous vein-replacement orebodies associated with the North dike of rhyolite porphyry, collectively termed the dike orebodies.

Workings totalled 3048 meters in length and achieved a depth of 137.16 meters. Princiapal development is a shaft 450 feet deep on the massive pyrite ore body; there is also a short exploratory shaft and a winze of 155 feet depth. Total production was valued between $3-4 million (period values).

References:
Ross, Clyde P. (1925a) Ore deposits of the Saddle Mountain and Banner Mining Districts, Arizona. USGS Bull. 771: 66, 68.

Tenney, J.B. (1930), The Second Report on the Mineral Industries of Arizona, Arizona Bureau of Mines Bull. 129: 75.

Elsing and Heineman (1936) Arizona Metal Production. Arizona Bureau of Mines Bulletin 140.

Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 17, 18, 30.

Kiersch, G.A. (1947) Seventy Nine Mine, thesis, University of Arizona.

Kiersch, G.A. (1949), Structural control and mineralization at the Seventy-nine mine, Gila County, Arizona, Economic Geology: 44: 24-39.

Wilson, E.D. (1951), Arizona zinc and lead deposits, part II, Arizona Bureau of Mines Bull. 158: 67-81.

U.S. Atomic Energy Commission Report 172-480 (1953), Gila County Preliminary Reconnaissance Report: 163.

Lewis, D.V. (1955), Relationships of ore bodies to dikes and sills, Economic Geology: 50: 495-516.

Galbraith, F.W. & Brennan (1959), Minerals of Arizona: 27, 36, 48, 50, 58, 61, 73, 80.

Keith, S.B. (1972), Mineralogy and paragenesis of the 79 mine lead-zinc-copper deposit, Mineralogical Record: 3: 247-264.

Hicks, Clifford J. (1979) Molybdenum Occurrences in Arizona, Arizona Department of Mineral Resources: 16.

Lapidary Journal (1980) September, 1980: 1278.

Niemuth, N.J. (1987), Arizona Mineral Development 1984-1986, Arizona Department of Mines & Mineral Resources Directory 29.

Blair, Gerry (1992), The Rockhound's Guide to Arizona: Helena, MT, Falcon Press.

Sawyer, M.B., Gurmendi, A.C., Daley, M.R., and Howell, S.B. (1992) Principal Deposits of Strategic and Critical Minerals in Arizona, U.S. Bureau of Mines Special Publication, 334 pp.

Rocks & Minerals (1985): 60: 295; 65: 23.

Mineralogical Record (1990): 21: 98.

Niemuth, N.J. & K.A. Phillips (1992), Copper Oxide Resources, Arizona Department of Mines & Mineral Resources Open File Report 92-10: 7 (Table 1).

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 111, 115, 123, 125, 146, 152, 156, 157, 161, 163, 166, 173, 177, 185, 190, 196, 201, 204, 215, 225, 228, 243, 248, 249, 252, 270, 275, 276, 286, 288, 292, 299, 301, 307, 308, 316, 331, 332, 337, 341, 342, 343, 357, 361, 374, 377, 391, 392, 401, 410, 425, 432.

U.S. Bureau of Mines - Arizona Bureau of Geology and Mining Technology file data.

USGS Hayden Quadrangle map.

Arizona Department of Mineral Resources 79 Mine file.

MRDS database Dep. ID #10026845, MRDS ID #M000500; and Dep. ID #10161288, MRDS ID #D000093, MAS ID #0040070606.