Latitude: 33°24'7"N
Longitude: 110°52'21"W
A former underground Cu-Ag-Fluorspar mine located on 80 claims (1963) in the NW¼ sec. 30, T1N, R15E (Globe 7.5 minute topo map), under the townsite of Miami, on private lands. The U.S.Bureau of Mines gives the location as 33-23-30N, 110-52-30W. Cleve Van Dyke acquired the property on Miami Flat, now the site of Miami, and organized the Miami Townsite Co. This company sold building lots to individuals but retained the mineral rights below a depth of 40 feet from surface. He then organized the Van Dyke Copper Co. and these mineral rights were transferred to it. In 1916 the Van Dyke Copper Co. started drilling exploration. Owned and operated by Arimetco International, Inc. (1992).
The deposit is in the depressed hanging wall block of the Miami fault, opposite the east end of the Miami-Inspiration orebody. The ore zone is 1143 meters long, 434.34 meters wide, and 76.2 meters thick. It strikes NW and dips 20E. The shaft was sunk in Gila conglomerate and entered the underlying Pinal schist at a depth of 760 feet. To a depth of 1,440 feet, the schist has the general characteristics of capping formed by supergene oxidation and leaching of a low-grade, disseminated sulfide deposit. It contains residual limonite and small amounts of oxidized copper minerals. The shaft passed through a low-grade chalcocite zone from 1,440 to 1,600 feet of depth; and below this passed through schist containing a little pyrite and chalcopyrite. The lower 60 feet of the shaft is in very heavy ground, possibly the Miami fault zone.
The shaft intersected a breccia zone from 1,183 to 1,218 feet below the collar. This zone was mineralized with copper carbonates and silicate. The footwall of this orebody is clearly defined by a layer of tough red gouge that strikes a little west of north and dips 20ºE. About 200 feet NE of the shaft, the orebody is terminated by the Van Dyke fault, which is coincident with the footwall of a granite porphyry dike. The fault and dike strike N70ºW and dip 70ºNE. The localization of the copper minerals appears to have been controlled by the intersection of the low-angle fault zone with the Van Dyke fault. The greatest amount of brecciation and the best ore occurred near the intersection, and the amount of brecciation and ore minerals decreases progressively southward. The Van Dyke fault clearly served as a barrier to the copper-bearing solutions that seeped into the low-angle fault zone.
The ore minerals in the ore consist entirely of azurite, malachite, chrysocolla, and tenorite. These oxidized copper minerals are not the result of oxidation in place of a primary sulphide ore body which contained copper but were first deposited as carbonates and silicates by laterally moving or descending solutions either in a particularly barren fault zone or at least a fault zone containing small amounts of pyrite and traces of chalcopyrite. This fact is clearly demonstrated by the oxidized copper minerals which are filling voids and act as a cementing material for irregular angular fragments of practically unaltered schist. The oxidized copper minerals in-filling these voids between the schist fragments appear as crustations and in many places assume botryoidal form. By the early 1990's, it was recognized that the Van Dyke ore body was a down-dropped continuation of the mineralization at Inspiration and that primary copper mineralization extended under part of the town of Miami.
Mineralization is along faults or fracture zones in hydrothermally altered and leached schist or granite, a result of direct deposition, filling fractures and the interstices between breccia fractures. Small amounts of sulfides are disseminated in the wallrocks. Alteration was oxidation, silicification and carbonatization. Ore concentration was hydrothermal with supergene enrichment.
The Van Dyke shaft was sunk in 1919 to a depth of 1,692 feet (515.72 meters) and intersected the mineralized zone located by the drilling exploration. Work ceased in 1921 due to low copper prices. In 1928 the shaft was unwatered and development resumed and continued until 1931. It was reopened in 1943 but closed in June, 1945. In all, it produced 11,851,700 pounds of Cu.
Drilling on this deposit began in 1925 and it is one of the deepest deposits in the district. Kocide Mining Corp. suspended in-situ leaching operations at this site in 1990 due to iron build up in the recycled leach solution. They had been producing cement copper (precipitated copper) since 1988. The 250 foot length of workings is for workings away from the shaft, not total working length. In 1989, the mine was an in-situ leach-solvent operation with a cement copper plant. Production was further refined at Casa Grande to produce CuSO4. In 1992, Arimetco was finalizing plans to leach the entire deposit using the old Van Dyke shaft as an extraction well.
References
U.S. Bureau of Mines War Minerals Report 378 (1945).
Galbraith, F.W. & Brennan (1959), Minerals of Arizona: 27, 110.
Peterson, N.P. (1962), Geology and ore deposits of the Globe-Miami district, Arizona, USGS PP 342: 72, 135, 137-138.
Niemuth, N.J. (1987), Arizona Mineral Development 1984-1986, Arizona Department of Mines & Mineral Resources Directory 29, 46pp.
USGS Minerals Yearbook (1988) - Mining & Quarrying Trends: 14.
Arizona Department of Mines & Mineral Resources (1989), Directory of Active Mines in Arizona, incorporating sand and gravel operations 1989-1990, Arizona Department of Mines & Mineral Resources Directory 36, 14 pp.
Niemuth, N.J. & K.A. Phillips (1992), Copper Oxide Resources, Arizona Department of Mines & Mineral Resources Open File Report 92-10: 7 (Table 1).
Phillips, K.A., Niemuth, N.J., and Bain, D.R. (1992) Active Mines in Arizona – 1993: Arizona Department of Mines and Mineral Resources Directory 40, 25 pp.
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.
Long, K.R. (1992) Descriptive model for detachment-fault-related polymetallic deposits, in Bliss, J.D., ed., Developments in mineral deposit modeling: U.S. Geological Survey Bulletin 2004, p. 57-58.
Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 105, 391.
MRDS database Dep. ID #10102492, MRDS ID #M003083; and Dep. ID #10282908, MAS ID #0040070128.
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