|Latitude & Longitude (WGS84):||32° 21' 20'' North , 112° 51' 54'' West|
|Latitude & Longitude (decimal):||32.35556,-112.86500|
|Other regions containing this locality:||Sonoran Desert, North America|
|Köppen climate type:||BWh : Hot deserts climate|
A former large-output surface Cu-Ag-Au-Mo-Zn-Ti-Nb-Rb-Gemstones mine located in the SE ¼ sec. 22, SW ¼ sec. 23, NW ¼ sec. 26 & the NE ¼ sec. 27, T. 12S., R.6W., about ½ mile (0.8 km) South of Ajo. Discovered by the Spaniards in 1750. First produced in modern times in 1917. Owned at times, or in part, by the Arizona Copper Mining & Trading Co.; St. Louis Copper Co.; the Rescue Copper Co.; Cornelia Copper Co.; New Cornelia Copper Co. (1912-1916); Calumet & Arizona Copper Co.; and the New Cornelia Division, Phelps Dodge Corp.
Mineralization is an elliptical ore body 2,011.63 meters long, 1,206.98 meters wide, 487.68 meters deep, and 304.8 meters thick, with veinlets and disseminations of chalcopyrite, bornite, and minor pyrite, oxidized in the upper part to carbonates, silicates, and minor chalcocite, deposited in fractured and faulted, altered Laramide quartz monzonite and bordering quartz diorite facies, and often in close association with irregular pegmatite zones in the intrusive. Mineralization extends into bordering intruded and altered Cretaceous volcanics. Minor spotty molybdenite and sphalerite. Ore control was the fracturing of the porphyry. Ore concentration was governed by the permeability of rocks to mineralizing fluids; some secondary copper on fractures. Alteration included sericitic, clay, chloritization, kaolinization, silicification with oxidation down to the water table. The host rock unit is the Chico Shuni (Cornelia). An associated rock unit is the Cornelia pluton.
Contact of oxidized and sulfide ore is sharp. There is no leached overburden. Gold is more closely associated with copper sulfides than with pyrite. Units present include quartz monzonite, quartz diorite, granodiorite, Equigranular quartz monzonite, porphyritic quartz monzonite, and porphyritic micro-quartz monzonite.
Local structures include NNW fracture zones and a number of major faults with large displacements.
The working is a huge open pit operation (about 3,000 feet long and nearly 2,000 feet wide) at 750 feet deep. Haulage was by internal railroad installed in the pit. Total production from 1917 through 1972 amounts to some 350,000,000 tons of ore averaging about 0.8% Cu, 0.05 oz. Ag/T and 0.004 oz. Au/T. Higher grade ore was mined in the early years and lower grade ore in more recent years.
85 valid minerals. 2 (TL) - type locality of valid minerals.
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. 
|Ypresian - Campanian|
47.8 - 83.6 Ma
|Early Tertiary to Late Cretaceous volcanic rocks|
Age: Phanerozoic (47.8 - 83.6 Ma)
Stratigraphic Name: Williamson Canyon Volcanics
Description: Rhyolite to andesite and closely associated sedimentary and near-surface intrusive rocks; commonly dark gray to dark greenish gray or greenish brown. In the ranges west of Tucson, this unit includes thick welded ash-flow tuffs. Volcanic rocks of this unit are inferred to be derived from vents and volcanoes above magma chambers that solidified to form the granitic rocks of map unit TKg. These rocks are restricted to southeastern Arizona except for a small outcrop near Bagdad. (50-82 Ma)
Comments: Related, broadly, to unit TKg
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.