silver

Silver: The Versatile Metal Powering American Innovation

Here is a new infographic from the National Mining Association.  It shows the many uses of silver.  Six states, Alaska, Texas, Colorado, Montana, Idaho, and Nevada mine most of US silver.  Below the graphic are links to other NMA infographics, all of which can be used as teaching resources in the classroom.

NMA_Silver_Infographic_FINAL2

 

Other NMA Inforgraphics:

Gold in modern life

Importance of Copper

Importance of domestic mining to manufacturing

Iron – critical to nearly every industry

Minerals vital to modern life – a short video

Platinum group metals fight pollution and cancer

Potash and Phosphate help feed the world

How we use rare earth elements

Zinc the building block of summer fun

Advertisements

Silver project may become only US source of manganese

Manganese is a strategic and critical  metal used in alloys, mainly stainless steel. Other uses of manganese include production of dry cell batteries, in plant fertilizers and animal feed, and as a brick colorant.  Currently, the U.S. imports 100% of the manganese we use, mostly from Gabon, Australia, and South Africa. There has been no manganese mining in the U.S. since 1970.  The USGS estimates the value of imported manganese ore and compounds to be $1.4 billion in 2012.

Wildcat-location-map

 That may change if Wildcat Silver’s Hermosa project comes on line.  The project is located 50 miles south of Tucson near the town of Patagonia.  The project, in final exploration stage, is being developed for silver, but it contains a considerable manganese resource also. Wildcat’s preliminary economic assessment estimates a measured and indicated resource of 236 million ounces of silver and an inferred silver resource of an additional 79 million ounces.  Wildcat estimates that annual production will be 4.1 million ounces of silver, 233,000 tons of manganese carbonate, 20,187 tons of zinc cathode, and 960 tons of copper. Project life is estimated at 16 years. The company is researching the most economical way to extract the manganese. You can see some nice cross-sections of the mineralized zones here.  The sections show intercepts of mineralization and average metal grades.

Wildcat-silver-section

The project is, of course, receiving heavy opposition from environmentalists who seem to want no mining of anything anywhere.

Numerous manganese deposits are scattered over a large region in western Arizona and extend into southeastern California.  These deposits are low grade (generally only a few percent Mn) and formed during the past 25 million years. Most historic production occurred between 1953 and 1955 when the US Government purchased manganese at above-market prices. Total historic production is ~100,000 metric tons of manganese (226 million lbs.) from 24 mining districts.

The Aguila manganese mineral district, with 42 million pounds of historic manganese production, is within the proposed Sonoran Desert Heritage National Conservation Area in the northern Big Horn Mountains west of Phoenix. The Black Dome district, with 344 thousand pounds of historic manganese production, is located north of the Hieroglyphic proposed Special Management Area. Manganese in these districts has not been in economic concentrations historically, but could become so if serious supply disruptions occur and/or prices increase sufficiently.  However, if the Sonoran Desert Heritage Area is formally established, these resources will be off limits unless the proposed areas are excluded.

The Arizona Geological Survey has a special report on the mineral potential of the proposed heritage area (download full report here, 25Mb).  The proposed heritage area encompasses almost one million acres.

Wildcat’s Hermosa project will have to navigate the byzantine bureaucratic maze of the  National Environmental Policy Act (see: How NEPA crushes productivity), but if it does so successfully, it will become the only manganese producer in the United States.

See also:

The value of mining in Arizona

Potential targets for shale-oil and shale-gas exploration in Arizona

Arizona CO2 production could enhance American oil supply

Helium potential of Arizona may help fill shortage

Petroleum and Natural Gas Potential of the Paradox Basin

Arizona may become a major producer of potash

Mining and the bureaucracy

How NEPA crushes productivity

Mineral potential of the proposed Sonoran Desert Heritage Area

The value of mining in Arizona

Without minerals, we would not have electricity, food, or shelter. Minerals make today’s technology-based life possible, but that’s something many of us take for granted. We want the benefits from those minerals, but some want mining of minerals to be in somebody else’s neighborhood.  The importance of mining has long been recognized:

If we remove metals from the service of man, all methods of protecting and sustaining health and more carefully preserving the course of life are done away with.  If there were no metals, men would pass a horrible and wretched existence in the midst of wild beasts…  -Georgius Agricola, in De Re Metallica, 1556.

For Arizona, it is not just metals.  Arizona produces sand and gravel, limestone for cement production, coal for electrical generation, and a variety of industrial minerals which contribute almost $2 billion to Arizona’s economy (see here).

Arizona has a long history of mining.  There is archeological evidence that cinnabar, coal, turquoise, clay, pigments, and other minerals were mined in Arizona beginning at least 3,000 years ago. (See A History of Mining in AZ by the Arizona Mining Association.)

According to the Arizona Mining Association, Arizona currently produces 68% of domestically mined copper.  With that copper production comes by-product molybdenum, gold, silver, platinum, and rhenium.  Incidentally, The Sierrita Mine south of Tucson is currently the onlydomestic producerof rhenium, a metal used in high-temperature, super-alloy turbine blades for jet aircraft and other land-based turbines.  The Sierrita plant processes output from other mines on a toll basis. It may soon be joined by a second rhenium plant at the Kennecott (Rio Tinto) mine in Utah.

The direct and indirect economic impact of copper mining on Arizona’s economy is about $4.6 billion annually.  That includes $3.2 billion in personal income,  $500 million in state and local government revenues, and 49,800 high-paying jobs for Arizonans. Average labor income of mining company employees (including benefits) is $108,000 per worker vs. $47,000 for all Arizona workers.  If we add in non-metallic, non-fuel, minerals, then Arizona produced about $8 billion worth of mineral products in 2012 according to the U.S. Geological Survey.  Arizona ranks second, after Nevada, in value of total mineral production.  The U.S. total value of mineral production was about $76 billion which supported more than 1.2 million jobs in 2012.

Arizona is endowed with great mineral resources as shown on the map below prepared by the Arizona Geological Survey.

mineralmap

Currently ASARCO and Freeport-McMoRan Copper & Gold are the two biggest copper producers in the state.  ASARCO operates three mines and a smelter. According to the Southern Arizona Business Coalition, in 2012 ASARCO paid wages and benefits of $215.8 million, property, severance, and sales taxes of $47.2 million, and employed 2,198 people in Arizona. Freeport operates mines in Safford, Morenci, Bagdad, Miami, and Sierrita.  They paid wages and operational spending of $860 million in 2012, taxes of $274 million while employing 7,600 people directly and indirectly employing an additional 30,000 people.

In addition to past and current mining, there are many projects on the horizon, some in the exploratory stage, others navigating the byzantine regulatory permitting process.  (See my posts: Mining and the bureaucracy and How NEPA crushes productivity)

Perhaps the largest project is that of Resolution Copper near the town of Superior just west of the famed Globe-Miami mining district and just north of ASARCO’s Ray mine.  This is a bold undertaking because the orebody is 7,000 feet below the surface.  Resolution says that at peak production, this mine will be the largest copper mine in North America, producing over one billion pounds of copper per year.  Resolution estimates that over the 64-year life of the mine, the project will generate $61.4 billion in economic value, provide $20 billion in tax revenues, and provide 3,700 permanent jobs.

The Rosemont copper mine south of Tucson is nearing the end of its long journey through the regulatory maze, and mine construction may begin early next year.  This mine will generate 2,900 Arizona jobs and inject $19 billion into Arizona’s economy and pay $404 million in local taxes over its 20-year projected life.  The mine expects to produce 243 million pounds of copper per year.

Curis Resources is developing an in-situ copper mine near Florence, Arizona.  In this project, instead of mining rock, Curis Resources “seeks to dissolve copper minerals from an underground deposit by introducing water with a lowered-pH (making it slightly acidic).This low-PH, water-based solution dissolves the copper and allows it to be pumped to the surface through a continuous loop water treatment system.”  This deposit, lying 400-to 1200 feet below the surface contains approximately 2.84 billion pounds of copper.

Curis estimates that over the projected 28-year life of the project, it will generate $2.2 billion in economic activity for the state of Arizona, $1.1 billion in economic activity for Pinal County, $325 million in taxes and royalties for Arizona government, and $1.46 billion in increased personal income in Arizona, 170 direct jobs at the project site in Florence, and 681 jobs in the state of Arizona.

TheI-10 copper deposit, located along Interstate 10 between Benson and Willcox, Arizona, is being investigated as another in-situ copper leaching project by  Excelsior Mining Corporation, a Canadian junior company. They estimate the deposit currently contains an indicated oxide copper resource of 3.21 billion pounds and an additional inferred oxide copper resource of 0.88 billion pounds.

Wildcat Silver Corporation is in the exploration stage of its Hermosa Project which is evaluating the silver-manganese potential in the historic Hardshell mining district near Patagonia in Southern Arizona. Their preliminary economic assessment estimates a measured and indicated resource of 236 million ounces of silver and an inferred silver resource of an additional 79 million ounces.  Project life is estimated at 16 years.  Wildcat estimates that annual production will be 4.1 million ounces of silver, 233,000 tons of manganese carbonate, 20,187 tons of zinc cathode, and 960 tons of copper.

Copper Creek is an old mining district located on the east bank of the San Pedro River and on the western slope of the Galiuro Mountains about 75 miles northeast of Tucson. The property has been acquired by Redhawk Resources, a Canadian junior mining company that plans to develop an underground mine for copper, molybdenum, and silver.  Redhawk estimates a resource of 7.75 billion pounds of copper, 150 million pounds of molybdenum, and 32 million ounces of silver.

The Oracle Ridge mine is a small, underground copper mine in the Santa Catalina Mountains just north of Tucson. The mine was operated intermittently, most recently from 1991-1996. The mine is being developed by a junior Canadian mining company, Oracle Ridge Copper (project website).  The company anticipates employing about 200 people to run the mine which has a projected life of 11 years. The mine will produce 140 tons of concentrate (about 30% copper) a day which will be trucked off the mountain and transported to a smelter.

In northern Arizona, near the Grand Canyon are over 1,300 known or suspected breccia pipes many of which contain uranium oxide as well as sulfides of copper, zinc, silver, and other metals. According to the Arizona Geological Survey, “Total breccia-pipe uranium production as of Dec. 31, 2010, has been more than 10,700 metric tons (23.5 million pounds) from nine underground mines, eight of which are north of Grand Canyon near Kanab Creek.”  This area is mired in fears of contamination of the Colorado River (see Uranium mining and its potential impact on Colorado River water) and a 20-year, million-acre mineral entry withdrawal by the Department of the Interior.

In northeastern Arizona there is potential for a major potash deposit. American West Potash has recently delineated, a considerable resource estimated at  158 million metric tons of sylvinite (a mixture of sodium and potassium chloride, not to be confused with sylvanite, a gold telluride), with about 16 million metric tonnes of K2O; and inferred resources of 560 million metric tonnes of sylvinite with just over 66 million metric tons of K2O in the Holbrook Basin, about 30 miles east of Holbrook, Arizona.

The Holbrook Basin area also holds potential for helium and shale oil resources.

Arizona currently has three producing gold mines and several other prospects being actively explored for gold (see here).

“In 2011, the state of Arizona led the United States in the production of gemstones. Arizona has long been famous as a producer of turquoise, peridot and petrified wood. Gemstones such as azurite, chrysocolla and malachite are associated with the Arizona’s many copper deposits and have a long history of being produced there. Agate, amethyst, garnet, jade, jasper, obsidian, onyx, and opal have all been found in Arizona and used to make gems.” – Geology.com

As you can see, besides currently producing mines, Arizona holds future potential that will add jobs and economic value to the local, state, and national economy – if they can get through the bureaucratic regulatory maze.

Remember, the value of mining is not just the money, it is in providing the products we need to keep our civilization going.  If it can’t be grown, it has to be mined.

Mineral potential of the proposed Sonoran Desert Heritage Area

The Arizona Geological Survey (AZGS) has just published its study of the mineral potential of the Sonoran Desert Heritage Area (see full study here, 25Mb). Establishment of the heritage area, which consists of several detached conservation areas and wilderness areas, would prevent mineral exploration and development on almost one million acres west of Phoenix. A general location map, with mineral potential is shown below:

SDH-mineral-potential-map

 The AZGS assessment was limited to the following types of deposits: (1) sand and gravel (aggregates), which are used for concrete and asphalt, (2) porphyry copper deposits, which may yield large amounts of byproduct molybdenum, silver, and gold, (3) gold deposits in veins, some of which contain substantial silver, and (4) manganese deposits.

Some highlights from the report:

Aggregates:

“Rapid population growth in the greater Phoenix metropolitan area over the past several decades required enormous amounts of aggregate for construction of new homes, buildings, roads, and other facilities and infrastructure. Once urban development occurs, however, underlying aggregate resources are no longer accessible, and nearby resources may become inaccessible because of concerns about noise, dust, and truck traffic associated with quarry operations. Transportation costs, a major factor in aggregate costs, increase greatly if aggregate must be imported from distant areas.”

AZGS has identified five areas within and adjacent to the Heritage Area that are especially favorable as a supply for much needed aggregates.

Precious metal deposits:

The Harquahala – Big Horn Mountains area, which is included in the Heritage plan, has geology favorable for gold vein deposits. The map below shows the northern part of the area. On the map, orange areas show existing wilderness areas, purple areas show Sonoran Desert Heritage proposed wilderness areas, and the light blue line shows the boundary of the proposed Sonoran Desert Heritage National Conservation Area.

Harquahala

Small mines and prospects within the proposed conservation area have produced 506,000 ounces of gold and 549,000 ounces of silver.

Copper Deposits:

Arizona is the center of one of the world’s three great clusters of porphyry copper deposits

(the other two are in northern and central Chile). At the current copper price, Arizona total copper production from 1874-2010, would be worth $472 billion.

The Big Horn Mountains contain rocks of the right type and age for large copper deposits. Historic mining in the Big Horn Mountains yielded millions of pounds of copper and lead as might be expected for mineralization peripheral to a porphyry copper deposit.

The Gila Bend Mountains to the south are largely covered by younger volcanic rocks. The uncertainty in evaluating the possibility of porphyry copper deposits is high because of this cover, but there are enough indications of mineral deposits, including minor production from the Webb district (27,000 lbs. historic copper production) and scattered evidence of historic prospecting and small mines, that this area is considered to have moderate potential for porphyry copper deposits.

Manganese:

Manganese is used in the production of steel. Currently, the U.S. imports 100% of its manganese. Numerous manganese deposits are scattered over a large region in western Arizona and extend into southeastern California. These deposits are low grade (generally only a few percent Mn) and formed during the past 25 million years. Most historic production occurred between 1953 and 1955 when the US Government purchased manganese at above-market prices. Total historic production is ~100,000 metric tons of manganese (226 million lbs.) from 24 mining districts.

The Aguila manganese mineral district, with 42 million pounds of historic manganese production, is within the proposed SDH National Conservation Area in the northern Big Horn

Mountains. The Black Dome district, with 344 thousand pounds of historic manganese production, is located north of the Hieroglyphic proposed Special Management Area.

Manganese in these districts has not been in economic concentrations historically, but could become so if serious supply disruptions occur and/or prices increase sufficiently, see map below.

Manganese

The study should be considered an overview assessment. Note that the Arizona Geological Survey is serving as a scientific advisor and is not advocating any position, but I will. The Sonoran Desert Heritage Area proposal, if passed at all, should be reduced to exclude areas with medium to high mineral potential as a matter of economic and national security. If established there should be no additional “buffer areas” adjacent to the heritage area.

See also:

The importance of minerals to our economy and national security

Gold mining in Arizona 2012 update

Arizona currently has three producing gold mines and several other prospects being actively explored (see map). A new article from the Arizona Geological Survey gives the details of each mine and exploration project. (link to article)

GoldActivity2012_1

The producing mines are the Gold Road mine near Oatman, the Copperstone mine located about 15 miles north of Quartzsite, and the Fancher deposit in the Little Horn Mountains of western Arizona. These are all underground mines.

Millions of dollars are being spent to explore eight other properties in Arizona: the Moss mine in the Oatman district, the Sugar Loaf Peak prospect located southwest of Quartzsite, the Little Butte mine in the Plomosa Mountains, the famous Vulture mine south of Wickenburg, the Newsboy project also near Wickenburg, the Margarita mine in western Santa Cruz County, the Commonwealth mine at Pearce in Cochise County (Commonwealth has also produced 21 million ounces of silver prior to 1942), and Mexican Hat, seven miles south of Pearce.

You can see historical production by county here. That page briefly describes gold districts within the counties.

You can read about mining scams here, a report from the now defunct State Department of Mines and Mineral Resources. The site is now maintained by AZGS.

For an introduction to other Arizona Geological Survey publications see:

Helium potential of Arizona may help fill shortage
Arizona may become a major producer of potash
Arizona Geological Survey Leads Geothermal Energy Study
Uranium mining and its potential impact on Colorado River water
Sedona’s Sinkholes
Origin of the Grand Canyon

Once upon a time in Crown King

Crown King is a small village, a “living ghost town,” in the Bradshaw Mountains about 85 miles north of Phoenix, Arizona. It can be reached via a steep, narrow, winding dirt road wending its way up a mountain in Prescott National Forest. Crown King has been in the news recently because of the Gladiator forest fire raging near the village.

Crown-King-late-1800s

The current population is about 130, but in its heyday, spanning the turn of the 20th Century, Crown King had about 800 buildings and a booming mining industry producing gold, copper, lead, zinc, and silver. It even had a railroad at one time. An interesting history of the village and mines can be found at http://www.crownking.com/history.html.

One of the stories is of lost treasure:

“During the fall rainy season of 1897, an incident occurred that was to create one of the many lost treasure stories that endure in Arizona history. George Harrington, on the first leg of a visit to the east, was being driven in a buckboard to Prescott by experienced freighter J.P. Bruce. The buckboard also contained $5,000 in bullion from the Crown King Mine. They had crossed the rain-swollen Wolf Creek, about six miles from Mayer, and were climbing the far bank when one of the horses balked. The buckboard slipped back into the water and overturned. Harrington managed to save himself by grabbing a tree branch, but Bruce and the horses were caught in the flood. Unable to find Bruce, Harrington walked to Mayer and phoned to Prescott for help. A search party was sent out and Bruce’s body was found about a half mile below the crossing at 1am the next morning. The bullion was never found, even though it was searched for extensively after.” By the way, that $5,000 in bullion is worth about $420,000 at current prices.

The following description of the mines is summarized from Arizona Lode Gold Mines and Gold Mining, by Eldred Wilson, 1934, revised, 1967, Arizona Bureau of Geology and Mineral Technology. Wilson gives dollar values for the ore and concentrates calculated at a gold price of $20.67 per ounce and a silver price of about $0.60 per ounce versus $1595 for gold and $28.00 for silver today. To get a rough estimate of the current value of the ore, multiply Wilson’s figures by 80. Wilson mentions “middlings” which are an intermediate product from a washer, concentration, or preparation plant consisting of fragments of mineral and waste rock. The material is often sent back for crushing and retreatment.

The Crown King group of claims, southeast of Towers Mountain, includes the Crown King vein which has yielded the most of any deposit in the district. During the early days, this deposit yielded rich gold ore from near the surface.

From 1890 to 1895, the property was operated by the Crown King Mining Company. Their 10-stamp mill caught $10 to $12 per ton on the plates and made a lead concentrate that contained $150 to $350 in gold and silver per ton, besides a middling that carried 15 per cent of zinc and $12 in gold per ton. The middlings were stock-piled, and the concentrates were packed to Prescott, some 40 miles distant, at a cost of about $21.50 per ton. In 1895, the property was bonded to H. B. Chamberlin and Company, of Denver. The mine was operated until 1901 when it was closed by court order. [This closing was due to litigation by squabbling factions of the mine owners. The mine was closed and reopened in 1893 for the same reason.]

During the 1890-1901 period, the ore shoot was followed to a depth of 650 feet, with an estimated production of $1,500,000 of which $200,000 was paid in dividends. Transportation costs were greatly reduced by the extension, in 1899, of the Prescott & Eastern Railway into Mayer and further by the completion, in 1904, of the Bradshaw Railway from Mayer to Crown King.

During 1906 and 1907, the Crown King Mines Company worked the middlings pile and shipped concentrates containing gold, silver, zinc, iron and copper. In 1909, the property was sold at receiver’s sale to the Yavapai Consolidated Gold-Silver-Copper Company controlled by the Murphy estate, for $75,000. In 1916, lessees organized the Bradshaw Reduction Company which installed flotation equipment and made a few tons of concentrates from old middlings. Some ore is reported to have been blocked out above the 480-foot level, but was not mined.

In 1923, the mine was taken over by the Crown King Consolidated Mines, Inc. During the winter of 1926-1927, a flood wrecked the mill. The railway tracks from Middleton to Crown King were torn up during 1926 and 1927, and the grade has been utilized for a road. In 1933-1934, a 300-ton flotation-concentration mill was built.

The production of the mine since 1890 is estimated at $1,840,000.

That’s the way it was, once upon a time in Crown King.

Crown King’s mining days have past. The village is now a tourist destination.

See also:

Gold of Cañada del Oro and rumors of treasure

Old mines of the Tucson Mountains

Oracle Ridge Mine on Mount Lemmon

The Pontatoc mine in a north Tucson neighborhood

Saginaw Hill, another old mine in a Tucson area neighborhood

Sierrita Mine is only U.S. source of Rhenium

Surprising Structure of the Copper Deposits near Green Valley, Arizona

The I-10 copper deposit

The Pontatoc mine in a north Tucson neighborhood

Sometimes mines just vanish.  Such seems to be the case with the Pontatoc mine located near the north end of Pontatoc Road in Tucson and just south of Pontatoc Ridge.  The map below shows the general location (at the balloon).

 Pontatoc general locationThe Pontatoc mine was discovered in 1906 and worked until 1917.  It produced about 5,000 tons of copper, silver, gold, and molybdenum ore.  Mindat.org reports that handpicked ore assayed at 4% copper, 0.5 oz./T silver, and a trace of gold.

Mineralization occurred  in a wide altered breccia zone along the Catalina foothill fault dividing Catalina Gneiss, a Laramide metamorphic, from Tertiary to Quaternary Pantano conglomerate beds. “Ore occurred in the fault zones wherever rock alteration is intense. Alteration included silicification, propylitization, spordic dolomitization and epidote. Sulfides precipitated with quartz,” according to Mindat.org.

Workings consisted of two shafts, one 105 feet deep, the other 125 feet deep, plus a pit and tunnel operations.  The following graphic from the Pusch Ridge wilderness study by George S. Ryan  shows again the general location and location of mine workings on Pontatoc Ridge to the north.

Pontatoc-USBM

According to Ryan, Pontatoc Ridge was intensely prospected shortly after the production from the Pontatoc mine itself.  There were several shows of oxide copper on the ridge, but apparently they didn’t amount to much.

So far I’ve shown rather vague locations for the Pontatoc mine and it may surprise you where it was.  The map below shows the mine location with current development.

The following graphics show where I think the mine was, just west of the intersection of E. La Paloma Dr. and E Coronado Dr.  There is no trace of the pit or shafts, presumably they have been filled in. The detailed picture does show what is presumably the scarp of the fault in which the mineralization developed.

Pontatoc-location

Some mines just disappear and houses are built along or near fault zones.  This particular fault is apparently inactive, homeowners shouldn’t worry.

By the way, Ryan reports that gypsum was mined from Tertiary lake beds in the same area and used  for plaster in the Tucson building industry prior to 1966.

pontatoc-built-location

Pontatoc-detail1

References:

Ryan, George S., 1982, Mineral Resources  Investigation  of the Pusch Ridge Wilderness

Pima  County,  Arizona, U.S.B.M. open file report MLA  118-82.

http://www.mindat.org/loc-35539.html (Note this reference erroneously lists the Township as 12S rather than 13S.)

See also:

Florence Copper another mining controversy

Gold in Arizona

Gold of Cañada del Oro and rumors of treasure

Old mines of the Tucson Mountains

Oracle Ridge Mine on Mount Lemmon

Sierrita Mine is only U.S. source of Rhenium

The I-10 copper deposit

Ancient Undersea Volcano in Arizona at Jerome

We recently were treated to videos of the eruption of an undersea volcano. (See Video ).

Similar volcanoes erupted during Precambrian time (about 1.7 billion years ago) in what is now Arizona. Some of them produced mineral deposits called volcanogenic massive sulfide deposits that contain copper, zinc, lead, silver, and gold. About a dozen such deposits occurring in northern Arizona have had some production, the largest known of which is the United Verde mine at Jerome.

blacksmoker1In such deposits, a shallow magmatic source under the sea bed provides heat which sets up a convection cell in the surrounding rocks. Sulfur and metals derived from the volcano and from leaching of the sea floor sediments are erupted into the sea and deposited as sulfide-rich sediments. The sulfides often form a chimney called a “black smoker”.

The sulfide-rich “clouds” are taken by ocean currents and eventually settle to the sea floor, around the vent, to form layers of sulfide material containing pyrite (FeS2), chalcopyrite (FeCuS2), sphalerite (ZnS), and galena (PbS), together with the sulfates anhydrite (CaSO4) and barite (BaSO4).

An idealized model of the volcanic edifice is shown in the cartoon below:

VMS2

The volcanogenic massive sulfide deposits at Jerome are zoned, with the copper-rich portion in the volcanic vent and on the ancient sea floor adjacent to the vent. Zinc and lead sulfides, with iron oxide occur as marginal banded sediments, and banded iron and silica deposits occur at the extremities.

The photo below is copper ore from the volcanic vent at Jerome. The brassy material is chalcopyrite. The darker material is chlorite, an alteration product.

OLYMPUS DIGITAL CAMERA

The next photo shows the banded zinc and iron mineralization. Notice that these bands are folded.

JeromeRocks05

The circular structures in the photo below are cross-sections of the black smoker chimneys formed during eruption and preserved by the erupted material.

JeromeRocks10

The deposit at Jerome is far from the idealized drawing above. In the approximately 1.7 billion years since the deposit was formed, it suffered several episodes of folding and faulting. The following cross-section by Paul Lindberg, shows the structure as currently understood. Lindberg hypothesizes that the volcanic vent was along the edge of a caldera (cauldron fracture zone). Besides the main United Verde body, shown on the left side, there are two smaller deposits which have been faulted off the main body, the Hermit orebody and the UVX orebody. The graphic below is a west to east section looking north. The town of Jerome sits just west of the fault above the Hermit orebody.

Jerome cross section

Production from the Jerome deposits totaled about 3.6 billion pounds of copper, 97 million pounds of zinc, 693,000 pounds of lead, 1.6 million ounces of gold, and 57.3 million ounces of silver. And there is much more remaining, just waiting for the right opportunity.

Reference:

Lindberg, P.A., 1989, Precambrian ore deposits of Arizona, in Geologic Evolution of Arizona, Jenney, J.P. and Reynolds, S.J. eds., Arizona Geological Society Digest 17.