Tuesday, March 31, 2015


By perusing the Blog postings readers probably realize that I have a hankering for nice blue minerals, most of which are associated with copper.  My home states of Kansas, Colorado, Wisconsin, South Dakota and Utah have supplied a few blue minerals in my collection---well maybe not Kansas; however, Arizona is a state I visit quite often and it supplies a plethora of blue minerals.  Of course, Arizona has been, and is, a major producer of copper.  Locals like to brag about the five Arizona Cs that supported the economy during the early years of statehood; copper, cotton, citrus, climate and cattle.  Today copper is still important although many of the big open pit mines have closed down and environmental concerns and litigations plague prospective new mines.  Cattle operations house only a fraction of the animals as were present a century ago.  Numerous other states now produce more beef and/or milk than Arizona.  Cotton is still plentiful; however, it is a major user of water and I presume production will decline as available water continues to decline.  The demise of citrus crops, as far as I can tell, is due to a vastly increased population and urban sprawl---cut down the orchards and plant houses.  Arizona’s climate is what attracts current money to Arizona in the form of tourists, snowbirds and retirees.  However, with the onset of, and continuing, global warming, the climate simply may get too warm for the available resources.  The state is in a multi-year drought and climatologists are not looking for an early relief.  Water is becoming scarcer every year although the developers seem to have problems digesting that tidbit of information.  I believe Maricopa County (Phoenix) is the second fastest growing county in the US.  Water is at a premium and fast relief is not in site.  Both Lake Powell and Lake Mead, the large reservoirs on the Colorado River in the north are less than 50% capacity.  All of the western states in the Colorado River Compact, plus Mexico, want a piece of the water action; however, the fact remains that states are using the water faster than replenishment.    

Major planning must begin as soon as possible; however, in Arizona the politics dictate an emphasis on other items and omit the 900 pound gorilla lurking in the corner. 

Back to copper.  I continue to try and better understand ore genesis but rely on the great books, Mineralogy of Arizona 3rd edition (Anthony and others, 1995) and The Frugal Collector; Part 1 (Jones, 2011 and his numerous articles in Rocks and Gems) as my guides to the state’s mineral resources and their genesis.  It is my understanding that one of the 3rd edition authors, Ray Grant, is working on a 4th edition of the minerals book and that part two of Jones’ work is near the press. 

One thing that I have learned, well sort of tried to digest, is that the major copper deposits in Arizona have been/are found in very low grade ore called porphyry copper deposits. Here 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 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.  Wow, it is much more complicated than this paragraphs indicates; however, I would need an entire university course to really embed the information in my mind (assuming I could kick out several gigabytes of unneeded information).

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. 

The New Cornelia open pit mine (lower center) and associated tailings (left) and ponds (upper right).  The former company town of Ajo (3300 people in 2010) is directly above the mine and is the closet US city to Organ Pipe Cactus National Monument.
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.

Blue-green mat of ajoite sprays coving an unknown matrix---right side of specimen.  Width of specimen ~2.1 cm.
I have a small specimen of ajoite, another one of those blue-green copper silicates oxidized from the copper rich hypogene minerals.  Ajoite is a fairly rare mineral best known from a few Arizona localities and South Africa.  The Arizona specimens are usually sprays of bladed prismatic crystals (elongated along the C Axis and small ~3-5 mm) and flattened.  The crystals on my specimen are the flattened sprays that almost appear to be mats.  However, the most sought after ajoite specimens are from South Africa (Messina District) where mineral inclusions occur in quartz crystals.
Crystals have a vitreous luster, are transparent in individuals, a greenish-white streak, and a hardness of ~3.5 (Mohs).  Ajoite may alter to another copper silicate, shattuckite [(Cu5(SiO3)4(OH)2], and also may form from the alteration of shattuckite.

Photomicrographs of sprays of ajoite crystals.  FOV ~1 cm.

So, ajoite is one of those nice, blue, uncommon minerals that I love for my collection.  I have not seen the quartz with included ajoite but am looking forward to this observation.  According to a friend, there was a dealer at Tucson  selling flats from South Africa---I missed those.


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

Jones, Bob, 2011, The Frugal Collector, Part 1, 2011: Miller Media/Miller Magazines, Inc., Ventura.

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