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New Cornelia Mine (Ajo Mine), Ajo, Little Ajo Mts, Ajo District, Pima Co., Arizona, USA
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Latitude: 32°21'20"N
Longitude: 112°51'54"W
 
 
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.

Mineral List

Ajoite (TL)
Albite
'Albite-Anorthite Series'
'Allanite'
Allophane
Alunite
Anatase
Anhydrite
Ankerite
Atacamite
Augite
Aurichalcite
Azurite
Baryte
Beidellite
Bieberite
'Biotite'
'Bisbeeite'
Bornite
Brochantite
Brookite
Calcite
'Chabazite'
Chalcocite
Chalcopyrite
Chamosite
'Chlorite Group'
Chrysocolla
Clinochlore
var: Diabantite
Clinozoisite ?
Conichalcite
Connellite
Copper
Covellite
Cuprite
var: Chalcotrichite
Devilline
Diaspore
Dolomite
Enargite
Epidote
Epsomite
'Ferrierite'
Ferrierite-Na
Fluorapatite
Forsterite
Galena
Goethite
Gold
Gypsum
Halite
Hematite
var: Specularite
'Heulandite'
'Hornblende'
Ilmenite
Jarosite
Kaolinite
Laumontite
'Limonite'
Magnetite
Malachite
Melanterite
'Meta-alunogen'
Microcline
Molybdenite
'Monazite'
Mottramite
Muscovite
var: Sericite

Neotocite
Nontronite
Olivenite
Opal
Orthoclase
Palygorskite
Papagoite (TL)
Phlogopite
Plancheite
Planerite
Posnjakite
Pseudomalachite
'Psilomelane'
Pyrite
Pyrolusite
Quartz
'Roméite Group
var: Stibiconite'

Rutile
Shattuckite
Siderite
Silver
Sphalerite
'Stilbite'
Sulphur
Talc
Tennantite
Tenorite
Tetrahedrite
Titanite
Torbernite
Turquoise
Zircon


102 entries listed. 83 valid minerals. 2 type localities (valid minerals).

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References

Joralemon, I.B. (1914), The Ajo copper district, Arizona, Engineering and Mining Journal: 98: 663.

DeKalb (1918).

Greenway, J.C. (1920) Success after failures, the story of New Cornelia Copper Company as related informally by Col. John C. Greenway: Arizona Mining Journal, v. 3, no. 8, January, 1919 [1920], p. 17.

Allen, A.W. (1922) Ajo enterprise of the New Cornelia Copper Company [two parts]: Engineering and Mining Journal-Press, [Part 1] v. 113, no. 22, p. 952-956; [Part 2] v. 113, no. 23, p. 1003-1008.

Richard (1923).

Richard (1925).

Bell, G.A. (1930) Leaching practice and costs at the New Cornelia mines of the Calumet and Arizona Mining Company, Ajo, Arizona.: U.S. Bureau of Mines Information Circular I.C. 6303, 30 p.

Ingham, G.R., and Barr, A.T. (1932) Mining methods and costs at the New Cornelia Branch, Phelps Dodge Corporation, Ajo, Arizona, U.S. Bureau of Mines Information Circular I.C. 6666, 18 p.

Schwartz, G.M. (1934), Paragenesis of the oxidized ores of copper, Economic Geology: 29: 55-75.

Gilluly, J. (1937), Geology and ore deposits of the Ajo quadrangle, Arizona, Arizona Bureau of Mines Bull. 141: 68-75, 79-81.

Gilluly, James (1938) Ajo district, in Some Arizona ore deposits: Arizona Bureau of Mines Bulletin no. 145: 86-90.

Gilluly, J. (1942a), Mineralization of the Ajo copper district, Arizona, American Mineralogist: 27: 222-223.

Gilluly, J. (1942b), The mineralization of the Ajo copper district, Arizona, Economic Geology: 37: 297-309.

Gilluly, J. (1946), The Ajo mining district, Arizona, USGS PP 209.

Galbraith, F.W. (1947), Minerals of Arizona, Arizona Bureau of Mines Bull. 153: 16, 17, 19.

Schwartz, G.M. (1947), Hydrothermal alteration in the 'porphyry copper' deposits, Arizona, Economic Geology: 44: 253-277.

Gilluly, James (1952) Geology of the New Cornelia mine, Ajo, Arizona (abstracted from James Gilluly, in Shride, A.F., McKee, E.D., and Harshbarger, J.W., editors, Guidebook for field trip excursions in southern Arizona, Geological Society of America, Cordilleran Section Meeting, April 10-14, 1952, Tucson, Arizona: Arizona Geological Society, p. 58-61.

Schaller, W.T. & A.C. Vlisidis (1958), Ajoite, a new hydrous aluminum copper silicate, American Mineralogist: 43: 1107-1111.

Schwartz, G.M. (1958), Alteration of biotite under mesothermal conditions, Economic Geology: 53: 164-177.

Galbraith, F.W. & D.J. Brennan (1959), Minerals of Arizona: 70, 75, 111.

Hardwick, W.R. (1960) Open-pit copper mining methods at New Cornelia Branch, Phelps Dodge Corp., Pima County, Ariz.: U.S. Bureau of Mines Information Circular I.C. 7938, 83 p.

Hutton, C.O. & A.C. Vlisidis (1960), Papagoite, a new copper-bearing mineral from Ajo, Arizona, American Mineralogist: 45: 599-611.

Sun, M.S. (1961), Differential analysis of shattuckite, American Mineralogist: 46: 67-77.

Newberg, D.W. (1964), X-ray study of shattuckite, American Mineralogist: 49: 1234-1239.

Sinkankas, J. (1964), Mineralogy for Amateurs, D. Van Nostrand Co., Inc., Princeton, NJ.

Guillebert, C. & M.T. Le Bihan (1965), Contributions à l'étude structurale des silicates de cuivre: Structure atomique de la papagoite, Bull. Soc. Franc. Min. Crist: 88: 119-121.

Dixon, D.W. (1966) Geology of the New Cornelia Mine, Ajo, Arizona, in Titley, S.R., and Hicks, C.L., editors, Geology of the porphyry copper deposits, southwestern North America: Tucson, University of Arizona Press, p. 123-132.

Mrose, M.E. & A.C. Vlisidis (1966), Proof of the formula of shattuckite, Cu5(SiO3)4(OH)2 (abs.), American Mineralogist: 51: 266-267.

Vlisidis, A.C. & W.T. Schaller (1967), The formula of shattuckite, American Mineralogist: 52: 782-786.

May, B.T. (1968) Magnetic properties of rocks associated with the New Cornelia porphyry copper deposit, Pima County, Arizona: Tucson, University of Arizona, Ph.D. dissertation, 159 p.

Wadsworth, W.B. (1968) The Cornelia pluton, Ajo, Arizona: Economic Geology: 63(2): 101-115.

Keith, Stanton B. (1974), Arizona Bureau of Geology & Mineral Technology, Geological Survey Branch Bull. 189, Index of Mining Properties in Pima County, Arizona: 83 (Table 4).

Wadsworth, W.B. (1974) Cornelia pluton, Arizona; petrogenesis inferred from grain-transition probabilities [abs.]: Eos, Transactions, American Geophysical Union: 55(4): 485.

Cox, C.J. (1975) unpublished data.

Wadsworth, W.B. (1975) Petrogenetic significance of grain-transition probabilities, Cornelia Pluton, Ajo, Arizona, in Quantitative studies in the geological sciences: Geological Society of America Memoir 142, p. 257-282.

Evans, H.T. & M.E. Mrose (1977), The crystal chemistry of the hydrous copper silicates, shattuckite and plancheite, American Mineralogist: 62: 491-502.

Arizona Pay Dirt (1979) Phelps Dodge Announces Pit Expansion that will Carry Ajo Mine Through 1980's: August, 1979: 30.

Arizona Pay Dirt (1980) Phelps Dodge is Constructing Moly Plant at Ajo: April, 1980: 22.

Arizona Pay Dirt (1981) (Supplement) Ajo, in Phelps Dodge – A Copper Centennial, 1881-1981: Summer, 1981: 64-68, 70-71, 90-91, & 180-181.

World Mining (1981) 1977-1980 production: September, 1981: 50.

World Mining (1982) 1981 production: September, 1982: 70.

Arizona Pay Dirt (1983) Phelps Dodge Bringing Copper Mine, Mill at Ajo Back On Line: February, 1983: front cover & 5A.

Thomas, W.J. & R.B. Gibbs (1983), Famous mineral localities: The New Cornelia mine, Ajo, Arizona, Mineralogical Record: 14: 283-298.

Singer, D.A., Berger, V.I., and Moring, B.C. (2008): Porphyry copper deposits of the world: Database and grade and tonnage models, 2008. US Geological Survey Open-File Report 2008-1155.

Anthony, J.W., et al (1995), Mineralogy of Arizona, 3rd. ed.: 103, 113, 114, 132, 137, 142, 146, 163, 166, 174, 183, 185, 190, 196, 202, 216, 220, 233, 235, 246, 272, 286, 294, 298, 312, 316, 318, 319-320, 330, 334, 341, 347, 369, 383, 399.

Arizona Bureau of Mines file data.

MRDS database Dep. ID file #10027145, MRDS ID M002273; and, Dep. ID #10283204, MAS ID #0040190008.

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Copyright © Jolyon Ralph and Ida Chau 1993-2014. Site Map. Locality, mineral & photograph data are the copyright of the individuals who submitted them. Site hosted & developed by Jolyon Ralph. Mindat.org is an online information resource dedicated to providing free mineralogical information to all. Mindat relies on the contributions of thousands of members and supporters. Mindat does not offer minerals for sale. If you would like to add information to improve the quality of our database, then click here to register.
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