Like many people I am fighting pandemic fatigue as it seems I am pretty much confined to my home, and to my "office" in the basement. The Covid pandemic has seemed to take away many joys of our lives and the daily news and numbers are really discouraging. But then I tell myself--suck it up, you are well and safe and have food and shelter. And I am never too old to set a new goal in life, or dream about a new writing project, and as long as the earth continues revolving then tomorrow is another day. And when I awake in the morning I am reminded that yesterday ended last night, today is a new day, and the coffee will taste wonderful.
Public Domain. Autor/artist unknown but thanks.
The major copper ores in Arizona have been/are found in very low- grade ore called porphyry copper deposits where the disseminated copper makes up less than 1% of the total ore. Anthony and others (1995) noted that these ore deposits are generally found in the Basin and Range Physiographic Province, “are always associated with an intrusive calc-alkalic porphyritic rock [distinctive difference in grain sizes]…typically quartz monzonite [intrusive igneous rock with equal amounts of orthoclase and plagioclase and 5-20% quartz], tonalite [intrusive igneous rock with major plagioclase and less than 10% orthoclase with more than 20% quartz], or granodiorite [intrusive igneous rock with major plagioclase, some orthoclase and greater than 20% quartz]…ranging in age from late Mesozoic through middle Tertiary…The major primary [hypogene] ore minerals [are] chalcopyrite (CuFeS2), some bornite (Cu5FeS4) [while] pyrite is typically the most abundant sulfide.” In some porphyry deposits, weathering of the upper exposed surfaces allowed the formation of sulfuric acid and iron and copper sulfates [especially from the pyrite] and percolated downward where secondary ore sulfides were deposited, especially chalcocite (Cu2S), in the supergene [layer around the water table]. The collectable secondary minerals of porphyry copper deposits such as azurite, malachite, cuprite, chrysocolla and others were deposited in the uppermost oxidized zone [above the supergene] or in deposits peripheral to the major porphyry deposits.
Cuprite, copper oxide, from the oxide zone at Ajo. Cuprite is an ore of copper. Width FOV ~1.5 cm.
The New Cornelia Mine is near the town of Ajo in southwestern Arizona, and in fact, Ajo was a company town for the miners and is the name typically associated with the mining district. The New Cornelia is a large porphyry copper deposit and copper was mined in one of those huge open pit mines about 7600 feet across and over 1100 feet deep. I find it amazing that in the initial mining “boom” in the mid-1800s, the miners needed to ship the New Cornelia ore clear to Swansea, Wales, for processing! I have not been able to locate the exact route the ore took on its journeys—but perhaps it was hauled by horses/mules to the Sea of Cortez and then by ship to the United Kingdom. As one might suspect, the profit margin of this low-grade ore was nonexistent. In fact, it was not until around 1915 that a smelter was constructed nearby, and miners begin to excavate the copper carbonates, for example azurite and malachite, in the upper oxidized zone.
During this process of mining with steam shovels, the New Cornelia became the first, large open pit mine in Arizona. But like most porphyry copper deposits, the easily mined copper carbonates became exhausted and miners then began to attack the underlying hypogene ore (chalcopyrite and bornite) by the mid- 1920s. Unlike many porphyry copper deposits, the New Cornelia did not contain a copper enriched supergene layer. Mining continued until about 1983 when “union problems” and low commodity prices forced the closure. New Cornelia produced over 6.3 billion pounds of copper (and some gold and silver) during its life (Arizona Department of Mines and Mineral Resources, 2008).
MinDat lists 83 valid minerals known from the New Cornelia including two, ajoite (K,Na)Cu7AlSi9O24(OH)6-3H2O) and papagoite (CaCu[H3AlSi2O9]), where the mine is the Type Locality. Both of these rare minerals were/are collected from the upper oxidized zone and my specimen of ajoite was described in a previous posting. Recently I acquired a very small specimen of papagoite and wish to add it to my listing of minerals.
Anthony, J.W., S.A. Williams, R.A. Bideaux and R.W. Grant, 1995, Mineralogy of Arizona, 3rd Edition: The University of Arizona Press, Tucson.
Arizona Dept. of Mines and Mineral Resources, 2008: Arizona's Metallic Resources Trends and Opportunities - 2008