79 Mine, Chilito, Hayden area, Banner Mining District, Gila County, Arizona, USAi

Regional Level Types
79 Mine	Mine (Care and Maintenance)
Chilito	Town (Historical)
Hayden area	Town
Banner Mining District	Mining District
Gila County	County
Arizona	State
USA	Country

A former underground Pb-Zn-Cu-Ag-Au-Mo-Sb-V-Fe occurrence/mine located in the SE¼ sec. 21 and sec. 28, T4S, R15E, G&SRM, about 1.5 miles (2.41 km) W of Chilito ghost town, 4.5 miles (7.24 km) NNW of Hayden, 2 miles (3.22 km) NW of Tornado 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 1990s by John Mediz, Copper City Rock Shop, and others, when mudslides from an El Niño episode intruded into the workings. Subsequently reopened for specimens.

As of 1992, the site is closed to collectors.

Historical Side Note: Minerals of Arizona, Third Edition, page 34, states that the 79 Mine was claimed in Pinal County. This is correct. When it was claimed in 1879, Gila County did not exist yet! Gila County was created in 1881 from parts of Maricopa and Pinal Counties, shifting the 79 Mine to its current location in Gila County.

Mineralisation is a deposit with an ore zone 335.28 metres long, 12.19 metres wide, with a depth-to-top of 0 metres, a depth-to-bottom of 152.4 metres, and 15.24 metres thick, striking N75E and dipping 40S. The deposit is hosted in limestone and rhyolite. Associated rock units are diorite and rhyolite. The mineralisation occurs in fractures or broken, thin calcareous shale. 6 bedded zones were mined. Galena, sphalerite, pyrite, 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 (ca. 15 m) of limestone with 90 feet (ca. 27 m) of overlying sandy beds. Above the Mescal are the Middle Cambrian Troy quartzite, approximately 400 feet (ca. 122 m) thick, succeeded by 225 feet (ca. 69 m) of undifferentiated shale and quartzite, probably Middle Cambrian; Upper Devonian Martin limestone, consisting of thin beds with some shale, 250 feet (ca. 76 m) to 328 feet (ca. 100 m) thick; Lower Mississippian Escabrosa limestone, a massive cliff-former, 440 feet (ca. 134 m) to 581 feet (ca. 177 m) thick; and Lower Pennsylvanian Naco limestone, thin-bedded and cherty, 385 feet (ca. 117 m) to more than 1,000 feet (ca. 305 m) 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 (ca. 122 m) 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 the intrusion of acidic dikes, sills, and plugs, probably apophyses of the Central Arizona batholith.

The linear north-westward 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, 1.5 miles (2.41 km) 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 localising 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 mineralisation 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 10,000 feet (ca. 3,048 m) in length and achieved a depth of 450 feet (ca. 137 m). The principal development is a shaft 450 feet (ca. 137 m) deep on the massive pyrite orebody; there is also a short exploratory shaft and a winze of 155 feet (ca. 47 m) depth. Total production was valued between $3-4 million (period values).

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Link to USGS MRDS:	10026845

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References