|Latitude & Longitude (WGS84):||33° 3' 52'' North , 110° 48' 48'' West|
|Latitude & Longitude (decimal):||33.06444,-110.81333|
|Other regions containing this locality:||Sonoran Desert, North America|
|Köppen climate type:||Csa : Hot-summer Mediterranean climate|
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.
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 (15 metres) of limestone with 90 feet (27 metres) of overlying sandy beds. Above the Mescal are the Middle Cambrian Troy quartzite, approximately 400 feet (122 metres) thick, succeeded by 225 feet (68.5 metres) of undifferentiated shale and quartzite, probably Middle Cambrian; Upper Devonian Martin limestone, consisting of thin beds with some shale, 250 to 328 feet (76 to 100 metres) thick; Lower Mississippian Escabrosa limestone, a massive cliff-former, 440 to 581 feet (144 to 177 metres) thick; and Lower Pennsylvanian Naco limestone, thin-bedded and cherty, 385 to more than 1,000 feet (117 to more than 304 metres) 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 (122 metres) 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 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 10000 feet (3048 metres) in length and achieved a depth of 450 feet (137 metres). Principal development is a shaft 450 feet (137 metres) deep on the massive pyrite ore body; there is also a short exploratory shaft and a winze of 155 feet (47 metres) depth. Total production was valued between $3-4 million (period values).
Mineral ListMineral list contains entries from the region specified including sub-localities
80 valid minerals.
Rock Types Recorded
Rock list contains entries from the region specified including sub-localities
Select Rock List TypeAlphabetical List Tree Diagram
Entries shown in red are rocks recorded for this region.
- Igneous rock
- Sedimentary rock and sediment
- Unclassifed rock
- Superficial deposit
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
|Quaternary - Miocene|
0 - 23.03 Ma
|Cenozoic sedimentary rocks|
Age: Cenozoic (0 - 23.03 Ma)
Lithology: Sedimentary rocks
Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. 
|Kungurian - Moscovian|
272.3 - 315.2 Ma
|Permian to Pennsylvanian sedimentary rocks|
Age: Paleozoic (272.3 - 315.2 Ma)
Stratigraphic Name: Hermit Formation; Supai Group; Schnebly Hill Formation; Naco Group
Description: Interbedded sandstone, shale, and limestone usually characterized by ledgy outcrops. Orange to reddish sandstone forms cliffs near Sedona. This unit includes Supai Group and Hermit Shale in northern Arizona and Naco Group in southern Arizona. It was deposited in coastal-plain to shallow-marine settings during time of variable and changing sea level. Rocks of this map unit in southern Arizona may be in part equivalent to Permian rocks of map unit P in central and northern Arizona. (280-310 Ma)
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. 
Localities in this RegionShow map
- Gila Co.
- Dripping Spring Mts
- Banner District
- Hayden area
- 79 Mine (79th Mine; Seventy-Nine Mine; Seventy-Nine property; McHur prospect)
- Hayden area
- Banner District
- Dripping Spring Mts
- Gila Co.