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| Superstition Mountains, Arizona, site of the infamous Lost Dutchmen gold mine legend. |
The abundant and repeating basins and ranges are a result of a major, head-on, collision by tectonic plates that buckled the western US. In fact, geological evidence suggests the Pacific plate on the west collided with the North American plate to produce deep fractures that propagated into the lower crust to provide conduits for volcanic eruptions throughout the province. Many of the mountain ranges popped up between basins. Everywhere one looks, there is evidence of past volcanic eruptions dating from the Tertiary to Recent. Some are so young that they almost look as if they erupted just last weekend.
To the north, the Basin & Range gives way to the Transition Zone province: a mountainous highland separating the Basin & Range from the Colorado Plateau further north. This transition zone encloses the Mogollon Rim and White Mountains.Further north, the Colorado Plateau represents a geologically stable province. While the Basin and Range suffered considerable folding, faulting and vulcanism; the Colorado Plateau had only minor deformation over the past 600-million years. The Plateau extends further northward to the Rocky Mountain province and ultimately to the Wyoming Craton in Wyoming and Montana. Further north, the basement rocks form parts of the North American Craton, where many commercial diamond deposits have been found in the past few decades.
Gold deposits are typically found in terrains that have suffered considerable fracturing, deformation, and volcanism. Thus areas of greatest potential for gold in Arizona are within the Basin and Range and Transition zone provinces (Hausel, 2010).
But, Arizonians suffer hot summers and deserts that lack water needed for placer mining and mills, but it is still a wonderland for prospectors. If the heat isn't bad enough, there is the added concern of foreign drug runners, terrorists with automatic weapons entering the US along the Mexican border, and snowflakes from California and is emphasized by a memorial to people killed by illegal immigrants.
Phoenix became a kidnapping capital with activity related to illegal immigrants, Mexican cartels, and human smugglers. Only Mexico City had a higher kidnapping rate. One source reported 83% of all warrants issued for murder in Phoenix and 95% of warrants issued in Los Angeles were for illegal immigrants. In a 2008 book on the Sierra Madre, Mexico, author Richard Grant wrote that the largest part of Mexico’s economy is based on selling and distribution of illegal drugs - imagine that!
As incredible as it sounds, the US government closed 3,500 acres of the Buenos Aries National Wildlife Refuge to American citizens because of “… safety concerns fueled by drug and human smuggling along the Arizona-Mexican border…” according to FoxNews.com - US Parkland Bordering Mexico. It has been closed to US citizens since 2006 even though it has considerable mineral potential.
Mineral Production
Arizona produces $6 to $8 billion in mineral wealth, annually. Much of which is mined from giant porphyry copper deposits where gold and silver is recovered as by-product of primary copper, zinc, lead, etc., during mining. For those unfamiliar with copper porphyries, these are root zones of ancient volcanoes that have distinct rocks that include multiple ‘granitic’ stocks (i.e., granodiorite, diorite, quartz monzonite) some of which have porphyritic texture. This texture is a rock fabric in which large crystals (such as feldspar and quartz) are dispersed throughout a finer grained matrix in an igneous rock as a result of slow cooling in a magma chamber at relatively shallow depth.
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| Underground at the Resolution mine, Superior, AZ |
When mineralized; porphyries can intrude reactive rocks such as limestone. This results in rich replacement deposits and skarns. Other types of mineralization include high-grade veins, low-grade cupriferous stockworks and low-grade disseminated copper and/or gold mineralization. These veins provide excellent targets for gold and silver.
Arizona is an important source for copper (Cu), molybdenum (Mo), lead (Pb), zinc (Zn), gold (Au) and silver (Ag). In 2007-2008, miners extracted copper, molybdenum gold and silver at Morenci, Bagdad, Sierrita, Safford, Miami, Ray, Mission, Silver Bell, Pinto Valley, Mineral Park, Johnson Camp and Carlota. In addition, exploration continued at Resolution, Rosemont and elsewhere (Niemuth, 2008).
Gold deposits include eluvial placers, dry placers, stream placers, veins, faults and breccia pipes along with gold associated with porphyry copper, massive sulfides and replacement deposits. Total historical gold production from Arizona is about 16 million ounces since records were kept beginning in the late 19th century. The state might produce more by simply providing exploration and mining incentives, as we'll as free prospecting education to the public (Hausel, 2011a, b).
Primary gold lodes include the Vulture mine, which produced 370,000 ounces of gold in the Wickenburg district north of Phoenix, the Oatman and Katherine camps which produced more than 2 million ounces of gold in the San Francisco district (NW Arizona) (Koschman and Bergendahl, 1968). Gold is found at Lost Basin and Chloride in western Arizona. Many gold properties are south of Tucson at Arivaca and Oro Blanco west of Bisbee. Gold is also found at Rich Hill-Weaver Mountains near the center of the state, the Big Bug district to the northeast of Rich Hill. Gold is described in several districts by Wilson and others (1969) and Wilson (1981).
Gold Placers
Gold placers occur in many counties in Arizona. Most are in fanglomerates associated with alluvial fans and pediments due to the arid environment. Similar to Australia, active stream placers are rare because of the lack of perennial streams. But at least we don't have any crocodiles.
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Rich, mineralized copper, gold, silver breccia, Arizona! |
One of the few active stream placers is Lynx and related placers in the Bradshaw Mountains at the southern edge of Prescott. More than 108,000 ounces of gold were recovered from this placer since 1863. The placers are along the entire length of the creek. Gold occurs as fine flakes and nuggets up to 4 ounces (nuggets are gregarious and never occur alone). Portions of the placer were set aside for recreational gold panning by the city of Prescott and the US Forest Service. Nuggets up to 11 ounces were also found in the Copper Basin placers about 15 miles to the west. Another wet placer was found in 1853 near the confluence of the Gila with the Colorado Rivers in southwestern Arizona. The discovery attracted more than 1000 prospectors in 1861, but the gold reportedly played out. And placers were found in the Big Bug district including one that weighed more than 20 ounces.
Gold in dry placers in Arizona was supplied by erosion of lodes up-slope. Some productive dry placers include LaPaz, Dome, Gila City, LaCholla, Weaver, Rich Hill, Greaterville, Quijotoa, King Tut and White Hills (Wilson, 1981). Flash flooding in the past concentrated gold in pay streaks in these placers. Notable is Greaterville south of Tucson. These were rich, but water had to be transported up-slope to the dry placers over a distance of more than 4 miles.
At the LaPaz placer west of Quartzsite, gold was discovered in 1862 along the Dome Rock Mountains of western Arizona. Gold was recovered at Goodman Arroyo, LaPaz Arroyo, Ferrar Gulch, Garcia Gulch and Ravenna Gulch. The gold-bearing gravels ranged from a few feet to many feet thick and was distributed throughout the gravel and enriched on bedrock. The district became known for large nuggets that included 26, 27, 47 and 65 ounces. Such large nuggets indicate a nearby lode source.
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| The classical lode. This narrow auriferous gold vein at Mary Ellen mine at South Pass, is a distinct, milky quartz vein hosted by tonalite (photo by the author). |
Most primary lode gold deposits occur as auriferous quartz veins with limited strike length and width. However, others, such as the Commonwealth at Pearce, Arizona, include multiple quartz veins, groups of crosscutting veinlets known as stockworks, and then there is gold-silver mineralization associated with detachment faults. Other nearby lodes include disseminated gold in altered rock at Mexican Hat and Gold Coin!
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| Commonwealth silver-gold vein at Pearce, Arizona. This large vein stands out as a resistant outcrop because of the hard quartz with silicified host rock. As such, this vein can be followed on the surface for a minimum of 2,500+ feet (photo by the author). |
DISTRICTS & MINERALIZED AREAS
Driving from northwestern New Mexico along I-40 to Apache County Arizona cuts through the Fort Apache and the Navajo Indian Reservations, and passes through the Petrified Forest, Painted Desert and the Canyon de Chelly all part of the Colorado Plateau. Although this terrain produces extraordinary sandstone buttes and monuments of the Chinle and Navajo Formations, the geologically stable terrain is not conducive to gold. But has potential for sandstone-type reef and roll-front uranium deposits and breccia pipes. Wilson (1961) noted gold placers of economic importance are found in every county in Arizona except Apache, Coconico and Navajo Counties (the Colorado Plateau).
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Basalt with peridotite nodules, Arizona. The peridotite has considerable gem-quality peridot andrepresents pieces of the earth's upper mantle plucked from depth and brought to the surface in the basalt lava. |
In the four corners region near the Red Rock Highway from Shiprock, New Mexico to Arizona, are volcanic rocks that form Ship Rock and other volcanic breccias. Ship Rock is a volcanic neck with radiating dikes. These volcanic rocks originate deep the earth’s mantle (much deeper than basalts and rhyolites).
Gemstones include pyrope garnet and peridot eroded from the Navajo volcanic field. The volcanics include serpentinized ultramafic rocks and breccias that have similarities to kimberlite (Hausel, 1998). In the past, many researchers even described these as kimberlites, but they are now referred to as lamprophyres known as minette (Hausel, 1998; Erlich and Hausel, 2000). Even so, a few minettes around the world contain diamond. Whether or not these have any diamonds is unknown. Garnets are mined by local Indians for their gem characteristics, and also by ants for ballast to stabilize their anthills. The ants drag the gems to their hills.
In 1871 and 1872, two enterprising prospectors from San Francisco decided to ‘salt’ an area in northern Colorado with diamonds and other gems in what we now refer to as the Great Diamond Hoax. Other gems included ruby and garnet. The diamonds were from the South African diamond fields, which had just been discovered and the garnets were pyrope and pyrope-almandine garnets collected from Arizona anthills. These were placed over a flat sandstone outcrop along the northern base of what is now referred to as Diamond Peak in Colorado (Hausel and Stahl, 1995) (40o57’01”N; 108o52’41”W). What is amazing about this scam was that the perpetrators did not realize pyrope garnet was a pathfinder mineral for diamond deposits. All they understood was garnet was the color of ruby and they were under the impression they were salting the outcrop with rubies and diamonds. Even more amazing was that the area they chose in northern Colorado sits 50 miles south of the Leucite Hills lamproites, 60 miles east-southeast of the Butcherknife Draw anthill garnets and chromian diopside (which tends to look like emeralds), 60 miles east of the Cedar Mountain diamondiferous lamprophyres, and 175 miles west of the diamondiferous kimberlites in the Colorado-Wyoming State line district. There are even reports that the Bishop Conglomerate at the top of Diamond Peak has pyrope garnet and chromian diopside (both pathfinder minerals for diamond) (McCandless and others, 1995).
In the Painted Desert, a region embracing a large geographic area of the Chinle Group (Triassic) of rocks, microscopic particles of gold are reportedly disseminated in residual clays. There are reports of prospectors recovering some gold from this formation near Show Low.
Ajo District. Gold was recovered as a by-product of copper mining at Ajo, south of Gila Bend and 75 miles south of Phoenix. Copper was initially recovered on a small-scale in 1750 AD by Spaniards and later by open pit at the New Cornelia mine in northwestern Pima County. By 1917, New Cornelia was developed into Arizona’s first open pit mine. Total by-product gold mined through 1959 was 1 million ounces with the 6.3 billion pounds of copper. Operations ended in 1983. But like most mines, the deposit was never mined out.
The Ajo ore body is elliptical (6,400 feet long by 3,900 feet wide and 1,560 feet deep). It consists of veinlets and disseminated chalcopyrite, bornite and minor pyrite. The upper part of the porphyry was oxidized with copper carbonate and silicate and minor chalcocite in fractured and faulted Laramide-age quartz monzonite and quartz diorite. Mineralization extended into the intruded Cretaceous volcanics and was controlled by fracturing and rock permeability and associated with fractures, veins and breccia. Rock alteration includes sericitic, chloritization, kaolinization, silicification with oxidation down to water table (Joralemon, 1914). Gold is closely associated with copper sulfide rather than pyrite.
The ore body was mined to a depth of 750 feet and total production from 1917 through 1972 amounted to 350 million tons of ore averaging 0.8% Cu, 0.05 opt Ag and 0.004 opt Au with some zinc (Zn) and lead (Pb)(Singer and others, 2008). Some copper minerals were gem quality and used for jewelry (ajorite, shattuckite and turquoise).
Ash Peak District. Gold (Au) and silver (Ag) was discovered in the Ash Peak district in 1900 with production from 1905 to 1970. Mineralization is described as tabular and narrow brecciated siliceous silver-gold ore in a vein complex nearly 2 miles long and 20 feet wide. The structure strikes N60oW and dips 80oNE in host Tertiary diabase, rhyolite and basalt. At least three parallel veins were recognized in the district with Ag-Au-Cu-Pb-Mn-silica ore shoots of fairly consistent grade. One assay reported 10.97 opt Ag and 0.025 opt Au.
The mineralized veins are in the SE¼ sec. 3, the NW¼ sec. 11, and in sections 2 and 10, T8S, R30E about 0.75 miles northeast of Ash Peak, 0.5 miles south of Highway 70 and 8-miles W-NW of Duncan. The Shamrock shaft was the main shaft on the Ask Peak claims.
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| Chrysocolla with secondary quartz in breccia from the Bagdad district, Arizona |
Mines included the Commonwealth shaft; the Hardy shaft (700 feet deep); the Shamrock shaft (1000 feet deep) and the Commerce shaft (500 feet deep). An open pit extends southeast from the Commerce. Lateral cross-cuts were driven every 100 feet in the Shamrock along with 11,000 feet of drifting. Drilling occurred to depths of 1400 feet. Two mills were constructed and the mineralization became a source for siliceous fluxing ore for nearby copper smelters.
Bagdad District. The Bagdad district is 80 miles northwest of Phoenix. The mine is an important source for copper, silver, gold, lead, zinc, molybdenum, titanium and rhenium. Copper was discovered in 1882 and production began in 1906 from a shaft sunk to 465-feet deep. Operations were later converted to open pit. In 2007, the operation yielded 202-million-pounds of copper and 10-million-pounds of molybdenum. The mine is being upgraded to extract larger amounts of molybdenum along with rhenium, a rare metal used in jet engine construction because of extremely high melting point. The operation also produced >300,000 ounces of silver with minor gold.
Bagdad is classified as porphyry copper with a blanket ore-body in the Brindle Formation. The ore is controlled by intersecting and closely spaced faults which increased permeability. Ore concentration was both hypogene and supergene. Alteration included sericitization and argillization.
Big Bug District. Southeast of Prescott is one of many mining districts in the Bradshaw Mountains. The Big Bug district is a massive sulfide district with both base and precious metals. The district lies along the northeastern slope of the Bradshaw Mountains near Poland Junction adjacent to Highway 69. Rhyolitic host rocks are common in this district, along with pyritic, cellular and sinter rocks typical of submarine hot springs. Such rocks are well-preserved at the world-class United Verde mine in Jerome, Arizona. In addition to gold and silver, many Big Bug deposits have significant zinc, copper and lead. A few have significant amounts of gold, such as the Iron King and McCabe mines.
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| Remember, as you prospect in Arizona (California, New Mexico and Texas) you have a good chance of seeing many friends of Obama and Biden. For now, we can carry guns (until the democrats and Rinos take away Constitutional rights), even so, the opposition carries automatic weapons and explosives. The Federal Government's responsibility is to protect our country! One of many signs posted near the Buenos Aires National Wildlife Refuge in Arizona. |
From 1901 to 1931, Wilson and others (1967) report significant copper, gold, silver, lead and zinc were mined which included 200,000 ounces of gold of which 1,500 ounces were recovered from stream placers. Later, more gold was produced at the Iron King, where total production was 617,746 ounces of gold, 18,529,982 ounces of silver, 125,375 tons of lead, 367,569 tons of zinc, and 9,553 tons of copper, making this one of the more productive gold mines in Arizona.
Along the eastern edge of the district, is a mineralized horizon recognized by meta-rhyolites outcropping on the west, with metamorphosed mafic flows on the east. The Lone Pine, Boggs, Iron Queen, and Upshot mines are within this mineralized horizon. A facies change from proximal at the Lone Pine mine, to distal facies massive sulfide at the Upshot, in evident.
Proximal facies are interpreted to also occur at the Pentland and Hackberry mines. The Pentland shows both proximal and distal characteristics, and the Hackberry mine has rhyolite inbetween the Pentland and Upshot zones. This rhyolite may be the same unit mapped at Pentland, but occurs in the opposite limb of an antiform. The Butternut mine is found on a limb of a major synform opposite to the limb that hosts the Iron King mine. Both the Iron King and Butternut have distal characteristics.
Placer gold was discovered in the Big Bug district in the l860s, and considerable sluicing, rocking, and panning occurred during the 1880s in upper Big Bug Creek extending south to Mayer. Gold was also found in Chaparral and other gulches near the McCabe ghost town (34°29'23"N; 112°17’16"W). And some dry-washing was employed.
Placer gold is found in stream channels and intervening mesas in an area about 20 miles east and northeast of the head of Big Bug Creek. The gold is coarse: one of the larger nuggets weighed 24.2 ounces. However, gold on mesas between Dewey-Humboldt and Mayer, is finely divided and associated with clay in the gravel. This pediment also extends up local gulches (Wilson, 1981).
Total placer gold recovered in 1934 amounted to 428 ounces. In 1940, the Big Bug Dredging Company operated a dragline on the Hill property and recovered 1,100 ounces of placer gold. Small-scale placer operations were active during 1932-33, when prospectors worked gravel benches and side gulches of Big Bug Creek northwest of Mayer. Some operations dug tunnels in the gravel before processing the material, but others were challenged by a large number of coarse boulders.
Some production from the Big Bug placers included 1,488 ounces (1910-31) and 13,214 ounces (1934-39) (Wilson, 1981). Topographic maps show dredge tailings in a number of placers along Big Bug Creek at: (1) 34°26'38"N; 112°16’22”W, (2) 34°26'0"N; 112°16’7”W; (3) 34°26'3"N; 112°16’4”W; (4) 34°25'40"N; 112°15’50”W; and (5) 34°25'4"N; 112°15’14”W [If you are trying to figure out what to do with these numbers, just plot them on Google Earth and then examine maps at Topozone. This will take you right to the deposit.
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| Lavender open pit mine at Bisbee, Arizona |
Bisbee (Warren) district. Copper was discovered in 1877 at Bisbee in the Mule Mountains of southern Arizona containing associated gold, silver, lead and zinc in massive sulfide and replacement deposits. Open pit operations began at the Copper Queen and Lavender mines on Sacramento Hill, and shafts were sunk to access higher grade ore at depth. More than 8 billion pounds of copper, 2.9 million ounces of gold, 100-million ounces of silver, 305 million pounds of lead and 372 million pounds of zinc, with 35,000 tons of manganese ore and some turquoise were recovered prior to termination of operations in 1977. These metals were valued (pre-Biden) at more than $6.1 billion (1975 prices).
Mineralization occurs as high-grade copper carbonate with minor lead and zinc in irregular replacement deposits in the Martin Limestone (Devonian). Some ore was also found in the Escabrosa and Naco limestones. The ore is controlled by dikes, sills, faulting and associated brecciation. Much ore is found as bornite replacing pyrite. Some malachite and turquoise was mined for gems (Bryant and Metz, 1966).
The Campbell ore body sits adjacent to the Lavender pit. This ore was largely an oxidized copper deposit with minor lead and zinc occurring irregular replacement ore in the Abrigo (Cambrian), Martin (Devonian) and Escabrosa (Mississippian) limestones. These deposits are associated with porphyry dikes and sills that were mined underground. The ore body formed primarily of chalcopyrite with masses of bornite and chalcocite containing increasing amounts of sphalerite and galena near the margins.
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| Massive chalcopyrite, Wyoming (Photo by the author). |
The district is in the Mule Mountains. East of the mountains is a broad Tertiary valley floor (Sulphur Springs Valley) that extends across 20 miles of valley fill before rising to the Pedregosa Mountains. West of the Mule Mountains, the San Pedro Valley extends 15 miles to the Huachuca Mountains.
We often forget that lying under valley fill soil and rocks, are similar rocks to those found in the mountain ranges. Thus what lies beneath these valleys are likely hidden ore deposits. Even under the open pit at Bisbee, there is likely undiscovered mineralization. But for prospectors, the better places to search for gold and other minerals, is within known mining districts because of rock exposures, exposed veins, mines, and because miners often missed ore deposits.
Highway 80 cuts the Mule Mountains south of Tombstone. The Mule Mountains consist of northwesterly-trending Mesozoic rocks north of the highway. The terrain is rough and difficult to negotiate and some slopes descend into canyons. To the south, Paleozoic and older rocks are relatively resistant to erosion. Rock formations in the Warren district include crystalline Pinal schist of Precambrian age, unconformably overlain by Paleozoic rocks. The Paleozoics include the basal Bolsa Quartzite (Cambrian) overlain by more than 4,500 feet of limestone which includes the Abrigo Limestone (Cambrian), Martin and Mural Limestones (Devonian) and Escabrosa and Naco Limestones (Carboniferous). During the Mesozoic, these were deformed by faulting and folding and intruded by granite. The principle episode of mineralization occurred during the early Cretaceous.
According to Francaviglia (1982), the main ore body at Bisbee was found where rocks of the Sacramento stock intruded metamorphic rock and limestone. Lead-silver ores were also discovered in the vicinity Hendricks Gulch along the west flank of Queen Hill in 1877. The ore forms irregular lead-carbonate masses replacing limestone in a fault. The ore is hosted by Martin Limestone near siliceous ore, which cropped out as silica breccia stained by manganese. The siliceous ore was porous due to oxidation and leaching. Enriched deposits of gold were found in the siliceous ore where mechanically and chemically concentrated (Trischka, 1938). The presence of gold suggests possibilities for limited placer gold in Hendricks, Uncle Sam and Silver Bear Gulches, south of Bisbee near Queen Hill!
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| A beautiful example of cupriferous gossan. This material is oxidized from chalcopyrite. Through time, primary chalcopyrite ore oxidized and was replaced by azurite (blue) and limonite and goethite (yellow-brown rust). Chalcopyrite often has some gold in its crystal structure, and the gold typically remains in place (photo by the author). |
Metals were recovered near the surface and at depth from underground operations at the Denn, Campbell, Calumet and other shafts and from open pit operations at the Copper Queen and Lavender pits. Some rich ore averaged an incredible 23% copper. Ore minerals include native copper, chalcopyrite, sphalerite, cuprite, azurite, malachite, brochantite, tenorite, aurichalcite with minor turquoise.
Search for “Bisbee, AZ” on Google Earth for a Birdseye view of the open pit and notable rusty (red to yellow) gossan at the eastern edge of Bisbee at Red Hill. The gossan lies along the northern edge of the Queen and Lavender open pits. I wonder what lies beneath?
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| Red Hill, Bisbee, Arizona |
Small gold placers are found 4 miles southeast of Bisbee at Gold Gulch (31o23’54”N; 109o51’28”W). The gold was eroded from the Glance conglomerate (Cretaceous) and concentrated in sand in the arroyo. In 1933, a group of miners worked the gulch recovering gravel that averaged 0.008 ounces/cubic yard of gold. About 247 ounces of placer gold was recovered in 1934 and only 25 ounces from 1935-41. Placer mining is limited due to lack of perennial streams.
Lead ore was initially reported in Hendricks Gulch (SW section 9, T23S, R24E). This ore was smelted at a spring near the present main street of Bisbee. Some oxidized lead ore was used as flux at the Charleston smelter and lead was also mined in Uncle Sam Gulch in the NE corner of section 17 in 1908.
Zinc was mined in 1917, and the Calumet and Arizona Mining Company shipped lead-zinc ore to paint manufacturers in Kansas. Shipment of zinc to smelters began in 1922. In 1927 Phelps Dodge constructed a flotation plant to treat low-grade lead ore at their nearby Douglas smelter (20 miles east-southeast of Bisbee). The smelter closed in 1930. In 1939 zinc-lead ore was mined in the eastern part of the Warren district and some was processed at the Shattuck-Denn custom mill at Bisbee and some processed at the Eagle-Picher mill at Sahuarita south of Tucson, until 1945, when Phelps Dodge completed its zinc-lead concentrator. Lead and zinc are also found in the western portion of the district.
Black Rock District. The Black Rock district (34°3'5"N; 112°34'53"W) in the Wickenburg Mountains west of the Bradshaw Mountains and north of Peoria Arizona, lies in the southern part of Yavapai County of the Central Mountain Region province. The district produced 9,700 ounces of gold, 110,000 ounces of silver, 400,000 pounds of copper, and 444,000 pounds of lead between 1902 to 1967 (Keith and others, 1983). Some average ore grades were reported as 0.26 opt Au, 2.28 opt Ag, 0.61% Cu and 0.10 % Pb (Arizona Geological Survey, Open file report 85-12).
The district is underlain by granitic gneiss (1.73 Ga) intruded into northwest-trending belts of Yavapai schist. The Yavapai rocks are overlain by intermediate to mafic volcanics (Tertiary) with areas of unconsolidated silt, sand and gravel (Quaternary). Laramide (68.4 Ma) Wickenburg granodiorite batholith crops out to the southwest (Nichols, 1983).
According to the Arizona Bureau of Geology and Mineral Technology (1985), northwest-striking Miocene rhyolite porphyry and mafic dikes cross-cut the east-northeast-striking fabric of Precambrian rocks. The mafic dikes are locally altered and are cross-cut by epithermal quartz-pyrite-siderite-fluorite veins, some which also have chalcopyrite, galena, arsenopyrite and tetrahedrite. Secondary specularite and chrysocolla occur locally in northwest-striking quartz-sulfide veins.
The Monte Cristo mine (34°3'54"N; 112°34'59"W) is described as having some nickel-cobalt arsenates and sulfides along with gold and silver. In contrast, the Grijalva and Oro Grande (34°1'39"N; 112°43'22"W) mines are characterized by pyritic copper-gold ores in thick, high-angle, northeast-striking quartz veins.
The majority of the Black Rock district ore bodies have northwest trends and appear to be associated with mid-Tertiary, listric, normal faults that rotate Precambrian basement and the Tertiary volcanic cover in the Wickenberg area. The distinctly different trend and character of the Grijalva and Oro Grande mines suggests a Laramide age for these latter deposits.
Black Canyon district. The Black Canyon district forms an area of 18 miles long by 8 miles wide extending from the eastern foothills of the Bradshaw Mountains to the Agua Fria River. The area runs from the vicinity of Cordes to the north to the Maricopa County border to the south: both lode and placer gold are found.
The geology includes a north-trending belt of metasedimentary Yavapai schist (about 2 miles wide) that is intruded on the east and west by Bradshaw Granite, and on the east by northward-trending diorite. The Yavapai rocks floor a former valley and hilly pediment covered on the east by a mesa of volcanic rocks that has been deeply dissected by the southward-flowing, meandering Black Canyon River and Aqua Fria River. The district lies at elevations from 2,000 to 4,000 feet above sea level.
Gold-bearing veins include: (1) Precambrian quartz veins in the vicinity of Bumblebee and Bland Hill areas; and (2) quartz veins which dip at low angles and appear to be genetically connected with younger dikes of rhyolite-porphyry. According to figures compiled by the USGS, the Black Canyon district produced some gold, silver, lead, and copper. About 3,341 ounces of gold were recovered.
The Precambrian veins, according to Lindgren, are glassy quartz containing free gold and sulfides. As they erode, the supply gold to placers. Placers occur along Black Canyon, which upstream branches into Turkey, Poland, Bumblebee, and other creeks and drains southward into the Agua Fria River.
Chloride district. The Chloride camp was founded in the early 1870's. Ores rich in gold and silver were mined in the 1870's, but activity declined with the collapse of the silver price in 1882. Base-metal ores located below the oxidized zone were not mined extensively until the completion of a railroad from Kingman to Chloride in 1899. Thereafter, lead-silver ores were mined and subsequent improvement in milling led to exploitation of complex lead-zinc ores.
Zinc-lead mining reached a peak from 1915 through 1917 owing to high metal prices during World War I. Production declined abruptly after 1917, and mining was confined to veins with relatively high gold content. Gold production increased in 1935 and reached a peak in 1937-38. From 1950 through 1956 gold production averaged more than 100 ounces annually. From 1904 through 1956 the district produced 125,000 ounces of gold.
Christmas (Banner) district. The Banner district (a.k.a. Saddle Mountain district & Christmas district) lies within the Dripping Springs Mountains in southern Gila County of southeastern Arizona. The Dripping Springs Mountains form a northwest-trending Laramide uplift. The district extends south to northern Pinal County and for this discussion continues further south to the Saddle Mountain. Drive 85 miles southeast of Phoenix and 20 to 25 miles southeast of Superior, where it is accessed by Highway 177 southwest of Superior. Principal communities in the area include Winkelman, a town of 260, and Hayden, a town of 650. At Winkelman, route 177 intersects route 77 which continues further south and also continues northeast around the southern tip of the Dripping Springs Mountains.
Basement rocks are Pinal Schist (Proterozoic). These ancient rocks are overlain by a thick succession of Cambrian, Devonian and Carboniferous sedimentary beds, which are in turn, overlain by Cretaceous volcanic and sedimentary rocks intruded by rhyolite and diorite (Tertiary) dikes. The district includes more than 30 mines: mineralization is associated with quartz-mica diorite dikes (andesitic); (Tertiary). The include (1) lead-silver veins, (2) pyritic gold in shear zones, (3) disseminated pyrite, and (4) contact-metamorphic deposits. The latter contain copper, lead, zinc, gold, silver and vanadium (Ross, 1925).
Extensive jasperoid-barite reefs and cross-cutting manganese-oxide and -carbonate veins, with localized bedding-replacement deposits, are described near Kelly Springs in the vicinity of the NW section 19, T4S, R15E. These exhibit colloform banding, open vugs and mercury-antimony anomalies that favor a hot spring origin for jasper. About 0.25 mile northeast of Kelly Springs, some prospects include galena, sphalerite, smithsonite and minor copper-carbonate and silver concentrations as high as 1,100 ppm (about 33 opt Ag); (33°7'20"N; 110°49’37”W) (Banks and Krieger, 1977).
Many deposits had been worked intermittently since the 1870's, but little ore was shipped prior to 1900 (Ross, 1925, p. 29). The Christmas mine (33°3'28"N; 110°44’40"W), discovered in 1880, was operated intermittently through 1954 and was the principal mine in the district. Nearby, the 79-Mine has extensive workings dug in well-developed, primary ore, overlain by oxidized ore, all modified by supergene enrichment. The 79-Mine became a popular site for mineral collectors: at least 74 different minerals were described from the mine.
From 1905 through 1959, production included 26,000 ounces of gold for the district. In addition, 550,000 tons of copper ore, 6,500 tons of lead-silver ore and a minor amount of zinc was shipped.
South of the border in Pinal County, pyritic-gold veins were identified in lower Ash Creek, as well as in the Hoosier prospects, Two Queens, and the Pool mine. Similar veins were described at the Hogvall prospect and Mellor prospect near Christmas. These type of deposits occur in shear zones and have northeasterly strikes and steep dips. Veins are hosted by Cretaceous rocks as well as the Martin and Naco (Tornado) limestones. Mineralized zones are sheared and brecciated, and have secondary quartz, chlorite, sericite and calcite, and pyrite and chalcopyrite may be present. Where these rocks are oxidized, they can be crushed and panned for metallic gold. Some oxidized ore is reported to assay 0.14 opt to 0.43 opt Au.
In places, disseminated pyrite is found in basalt and dark-colored andesite such as at Gaull, Little Gold Gulch, and near the old Christmas workings. Some rock in Little Gold Gulch is reticulated with quartz veinlets. On the east side of the gulch are shear zones.
Contact metamorphic deposits are primarily replacements in limestone. Most of these have secondary garnet with other contact metamorphic minerals, and found at the Christmas, London-Arizona, Schneider group, Gold-Copper, 79, Apex and Columbia mines. These types of deposits are hosted by Naco, Abriosa and Martin limestones, Troy quartzite, and Mescal limestone, and diabase. They all lie near quartz-mica diorite dikes.
Lead-silver veins with quartz, barite and calcite gangue are found in the Saddle Mountain district north of Old Mill between Ash and Deer creeks. Many occur at the Adjust, Saddle Mountain and Little Treasure properties. The veins are primarily in andesite and may be a few inches to 2 feet thick. Some are outlined by slight vegetation anomalies (greater density of linear arrangement of brush).
Mineralogy of replacement deposits include quartz, andradite, vesuvianite, wollastonite, epidote, pargasite, chlorite, fluorite, chalcedony, magnetite, specularite, chalcopyrite, pyrite, sphalerite, galena and bornite. Where oxidized, these may have chrysocolla, azurite, native copper, gold, manganese, limonite, cerusite, anglesite, plumbojarosite, wulfenite, gypsum and alunite. Vanadinite is found associated with wulfenite and three locations. Supergene ore may include covellite and chalcocite (Banks and Krieger, 1977).
The Christmas mine was dug at the southeastern margin of Dripping Springs Mountains. The deposit was discovered in 1880. Mining began in 1905 and operations terminated in 1982. The Christmas was a surface and underground Cu-Au-Ag-Mo-Bi-Pb-Zn-Be-W and garnet abrasive mine. Workings terminated at the 908-foot level even though mineralization continues deeper. The ore body is in a series of gently-dipping limestones (Paleozoic) overlain by volcanics (Cretaceous) and intruded by quartz diorite.
Mineralization is classified as contact metamorphic and replacement and found over a surface area of 4,900 by 2,600 feet and extends to a depth of 2,100 feet. The ore is controlled by limestone-diorite contacts, favorable limestone beds and garnet-rich zones and fractures. Some garnet was mined for abrasives. Production focused on the Naco and Escabrosa limestones, where ore is confined to 11 distinct, consistently-mineralized beds that formed a 425-foot thick zone. More than 55 million pounds of copper, 300,000 ounces of silver, and 26,000 ounces of gold were recovered from 1905 to 1943. The ore averaged 0.005 opt Au, 0.23 opt Ag and 2.04% Cu. At least three new minerals were described at the mine: apachite (hydrated copper-silicate), junitoite (hydrated calcium-zinc silicate) and ruizite (hydrated calcium-manganese silicate).
Hydrothermal alteration included epidotization, silicification, propylitic, K-silicate, quartz-sericite-chlorite, oxidation and carbonatization. The deposit has a pyrite-chalcopyrite core, chalcopyrite-bornite intermediate zone, and pyrrhotite-sphalerite-chalcopyrite margin.
Copper Creek district. The Copper Creek district is east Mammoth and San Manuel, and 50 miles northeast of Tucson in southeastern Arizona. It is part of the Bunker Hill district that includes
mineralization at San Manuel, Sombrero Butte and Copper Creek. Much exploration activity has occurred north of Sombrero Butte. Along the western margin of the district, gold was recovered at the Mammoth-Tiger mine, and copper recovered from the San Manuel open pit from 1953 to 2003.
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| Mineralized breccia, Arizona |
mineralization at San Manuel, Sombrero Butte and Copper Creek. Much exploration activity has occurred north of Sombrero Butte. Along the western margin of the district, gold was recovered at the Mammoth-Tiger mine, and copper recovered from the San Manuel open pit from 1953 to 2003.
In 1995, mineralized breccia pipes and associated deposits were discovered in the Giluro Mountains with an estimated 3 billion pounds of copper. Other companies explored the district intersecting significant resources in breccia pipes and porphyries. The district is known to have more than 500 mineralized breccia pipes along with buried copper porphyry stockworks and distal lead-silver veins. The breccia pipes are confined to the Copper Creek granodiorite and Glory Hole volcanics. Redhawk reported the following (drilled) measured and inferred resources:
Deposit Millions Tons Cu (%) Mo (%) Au (opt) Ag (opt)
Mammoth breccia 3.5 1.47 0.003 0.002 0.2
Old Reliable 1.13 1.21 0.012 0.003 0.09
Keel porphyry 0.25 1.19 0.032 0.004 0.08
Inferred
Mammoth breccia 0.334 1.59 0.003 0.000 0.02
Childs-Aldwinkle 0.62 2.01 0.043 0.005 0.18
Old Reliable 0.327 1.33 0.013 0.001 0.03
Keel porphyry 2.29 1.22 0.041 0.009 0.08
Breccia pipes include high-grade cupriferous pipes or chimneys, thought to be associated with underlying copper porphyry systems. Such pipes are circular to oval-shape and have higher grade mineralization along the outer edges with highly fractured ring structures that surround the pipes. In the southern portion of the district, exploration for breccia pipes at Sombrero Butte identified more than a dozen pipes!
The district is underlain by Cretaceous sedimentary rocks that lie on Precambrian basement rocks. These are overlain by volcanic tuffs and flows and intruded by granitic to dioritic intrusives. The Copper Creek granodiorite intrudes Cretaceous rocks and is the main host for the breccia pipes and related porphyries. The Copper Creek, Childs-Aldwinkle, American Eagle and Sombrero Butte breccia pipes occur within three parallel belts that trend N30oW.
Copper Mountain (Clifton-Morenci) district. Located in southeastern Arizona west of the New Mexico border near the town of Clifton. The Copper Mountain district encloses a giant porphyry copper deposit with gold and silver. Total by-product gold mined from 1882 through 1959 was 228,000 ounces. A small amount of gold was also recovered from silver ore at Ash Peak to the south.
Copper was discovered at Morenci in 1872, but development was hampered by lack of transportation. The completion of the Southern Pacific Railroad in 1881 lowered transportation costs sufficiently to permit large-scale mining. The discovery in 1893 of large, low-grade, copper ore at Copper Mountain assured a certain degree of stability for the district. Ore from Morenci also yields molybdenum, silver, lead and zinc. The deposit has minor rare earths, uranium, gemstones and garnet. Mineralization was accompanied by hydrothermal alteration that produced zones of kaolinization, sericitization, calc-silicate hornfels and skarn.
The district is zoned with a chalcopyrite-rich core surrounded by a pyrite envelope which is surrounded by protore. Silver and gold are more abundant in less altered areas. The greatest molybdenum concentrations are in granite porphyry and turquoise was found in the oxidized portion of the deposit. Massive andradite garnet also occurs in skarn at the southwest corner of the open pit mine.
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| Detachment fault above mine adit. |
Copperstone. Copperstone is an open pit, gold-silver-barite mine in the NE/4 section 12, T6N, R20W of western Arizona. The ore zone is tabular with a N30oW-strike, and 30oNE-dip. Mineralization is controlled by brecciation and detachment faulting with sericitized and chloritized wallrock. Mineralization is associated with the detachment fault between underlying metamorphosed volcanic rocks (Jurassic) from overlying sedimentary breccias. The presence of quartz, hematite, and chrysocolla are indicators of gold mineralization (Hausel, 2020).
Gold occurs in breccia above a listric fault, in quartz latite, within the fault plane, and in basalt plugs (plugs are least mineralized). The listric fault lies in the upper plate of a detachment fault and extends horizontally for 3,000 feet, a minimum of 1,000 feet down-dip and is generally several tens of feet thick.
Proven and probable reserves drilled on the property include 911,367 tonnes of ore at average grades of 8.75 grams per tonne (256,430 ounces of gold) or about 0.3 opt Au. The reserves are based on a cutoff grade of 4.5 grams with the highest reported assay at 171 grams (6 ounces/tonne). Measured and indicated resources include 313,183 ounces of gold with an additional inferred resource of 144,892 ounces of gold (Northern Miner, March 8-14, 2010).
Although the property was deemed to have been mined out by Cyprus Minerals; exploration in 2002 to 2006 by American Bonanza discovered additional gold in high-grade zones associated with favorable structures and geophysical targets. The mine lies within the regional Walker Lane mineral belt that continues northwest into Nevada. Copperstone is surrounded by dozens and dozens of dry gold placers that extend south to the Dome Rock Mountains.
Dos Cabezas & Tevistone districts. The Dos Cabezas mountains near Wilcox in Cochise County of southeastern Arizona are known for placer gold and nuggets in the Dos Cabezas and Tevison districts. The area is accessed from unimproved roads leading east from Dos Cabezas along Highway 186, while. the Teviston district is on the northeastern flank of the range and is accessed from the Page Ranch road running 5-miles south of I-10 and 6.5 miles west of Bowie.
The district surrounds the highest peaks in the range, 10 miles west of Fort Bowie historic site. Maximum elevation of peaks is 8,357 feet. Dos Cabezas translates as ‘Two Heads” in reference to two, prominent, granite peaks near 32°13'20"N; 109°36’43”W.
Gold occurs in placers and lodes. Wilson and others (1967) reported gold was found in the vicinity of the Dos Cabezas peaks at the top of the range, in the Teviston district at the northern end of the range, and in the vicinity of Apache Pass at the southeastern edge of the range. Some was found prior to the Civil War.
The mountains are highly-fractured and -faulted Precambrian granite and metamorphic rock with Cretaceous volcanic agglomerates and thin slices of Paleozoic sediments, all intruded by Mesozoic to Tertiary intrusives (Wilson and others, 1967) and rhyolite porphyry and diabase dikes. A number of copper, lead and silver prospects found in the district have by-product gold. Some deposits are found along steeply dipping fault- and fissure-filling veins, and as replacement veins near porphyritic intrusive rocks (Calder, 1982).
Placers in the Dos Cabezas district lie along the southwestern flank of the range, and also found in the Teviston district on the northeastern flank of the range. Much of the placer gold originates from lodes in the vicinity of the highest peaks in the range. Dos Cabezas placers were initially prospected in 1901, when gold was found in arroyos, gulches, benches and terraces. The gold is flat, ragged, and as coarse-grained nuggets. Nuggets of 1 to 20 ounces are described (Johnson, 1982).
Many placers between Howard Canyon (32°11'24"N; 109°34’14”W) near the LeRoy Mine, and Walnut Canyon (32°11’36"N; 109°36’19”W) and Mascot Canyon (Johnson, 1972), and are found in parts of sections 27 to 34, T14S, R27E. The gravels are dry much of the year with gold found in gravel in all arroyos draining the mineralized area. The placers are thin near the heads of the arroyos, and thick near Dos Cabazes village.
Placers in the Teviston district likely originated from veins form the Dos Cebezas district. The placers are in gulches and pediments at the edge of the range. Most placer mining occurred between Gold Gulch (section 24, T13S, R26E) (32°15'48"N; 109°39’2"W) and Ash Gulch (section 22 and 27, T13N, R26E; 32°19'24"N; 109°39’01”W). The gravels contain sand, clay and many coarse semi-rounded boulders. Some gravels sampled to depths of 6 feet assayed as much as 0.11 oz/yd3.
Lodes in the district are associated with a thrust fault between Cretaceous strata and granite that is marked by a vein named the ‘Big Ledge’. The Ledge is as much as 100 feet wide and splits and pinches but can be followed on the surface and viewed on Google Earth (32o12’04”N; 109o35’53”W). It forms a distinct, E-W trending, milky-quartz vein cropping out for a mile along strike. The vein is reported to have gold, but the values are sporadic. One source suggests the vein contains less than 0.5 opt Au, and another suggests the vein has values of 0.1 opt Au.
Other mineralized veins in the district are described as coarse white to gray quartz with disseminated sulfides including galena, pyrite, sphalerite and chalcopyrite. The gold (as well as silver) occurs in the sulfides (primarily galena). Some mesothermal veins (formed at depth under moderate hydrothermal pressures and temperatures) are found in Cretaceous granite associated with diabase dikes. The wall rock adjacent to such veins show silicification.
Other mineralization in the range includes beryl in granitic rocks at Beryl Hill and Live Oak. Some fluorspar is described in the northern part of the range in Precambrian granite as well as along the southwestern flank associated with radioactivity. Scheelite is in veins in Mesozoic-Cenozoic granite at the Comstock Lode mine and some marble was also quarried along the southern portion of the range
Many lode mines are near the small settlement of Dos Cabezas. From Dos Cabezas, the district lies up Bean (32°10'53.60"N; 109°35’7”W), Mascot (32°11'24"N; 109°36’27”W) and Philadelphia (32°11'10.64"N; 109°35’25.59”W) Canyons. Other prospects are located in nearby Silver Canyon (32°13'43"N; 109°39’8.38"W). Since the Civil war, only sporadic production was reported. Production through 1959 was 15,000 ounces.
There appears to be a possibly propylitically altered zone along the west flank of the range centered at about 32°12'50"N; 109°38’41”W. Such zones consist of altered rocks with secondary chlorite mica, some epidote, and calcite with disseminated and possibly veinlet sulfides.
Florence district. Not far from the Phoenix valley, copper porphyry was discovered within the city limits of Florence, and is being developed for in-situ leaching. In-situ leaching has been around for decades and is a relatively safe process by which wells are injected with a solution that leaches copper while the pregnant solutions are recovered by pumping other wells. The project is expected to produce 55-million pounds per year for 25 years from a 308-tonne ore body averaging 0.358% Cu. Most porphyry deposits have associated low-, but the precious metals will likely remain in-situ for future technological advances. Gold prices will need to rise considerably for the resource to have much value due to the low-grade nature of the ore.
The Florence project is a short distance southeast of the Santan Valley along the Hunt Highway. The project will likely provide valuable revenue to the town of Florence even though the deposit is located on State and Private land.
Globe-Miami district. Small gold placers were found on Pinal Creek upstream from the town of Globe and others found at Lost Gulch, Pinto Creek, and in small gulches draining into Richmond Basin. Copper mines, such as, Miami-Inspiration, Castle Dome, Copper Cities, Cactus, and Pinto Valley, all produced by-product gold. Some gulches peripheral to mines at Castle Dome and Golden Eagle Mine, yielded placer gold.
Copper was discovered at Globe in 1874, but it wasn’t until 1904 that development began on the large, low-grade, disseminated copper porphyry deposit. This district includes a group of mines and deposits 50 miles east of Phoenix, within the foothills of the Pinal and Apache Mountains. The mines in the district yielded several $billion in copper, lead, silver, gold and zinc. By-product gold recovered through 1959, was 191,801 ounces.
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| Miami Inspiration, Arizona |
Freeport McMoRan produced 20 million pounds of copper from residual leaching at the Miami open pit. Asarco’s Ray, Mission and Silver Bell mines and smelting operations at Hayden continue to operate and the company reported 400-million pounds of copper were produced in 2007. Nearby, the Carlota mine commenced production in 2008.
The Pinto Valley mine is 3 miles west of the Miami-Inspiration mine. Pinto Valley produced 27.6 million pounds of copper in 2007. The Silver Bell mine, 22 miles south of Arizona City, produced 46 million pounds of copper in 2007.
Golden Rule Hill (Dragoon) district. West of Dos Cabezas is the Dragoon district (also Golden Rule Hill district) in Cochise county. The district is 6 miles from I-10 and 25 miles west-southwest of Dos Cabezas, 12 miles northeast of Pearce and 4 miles east of the village of Dragoon. It can be accessed by driving west on the Dragoon Road from Highway 191. Highway 191 runs south from I-10 to Pearce, or it can be accessed by exiting I-10 at the Dragoon exit and driving 3.5 miles east to the Dragoon village and continuing another 3.5 miles on the Dragoon road to Golden Rule Hill.
The district was discovered in 1849, and the Golden Rule and Old Terrible mines were developed later because of threats of Apache attacks and the Golden Rule mine was developed after a treaty was negotiated in 1872. Mineralization includes oxidized galena, cerussite, anglesite, linarite, plancheite, and uncommon free gold in coarsely-crystalline, iron-stained, quartz, calcite fissure veins in the Abrigo Limestone (Cambrian); (32°1'30"N; 109°58’28”W). The limestone is intruded by rhyolite porphyry (Tertiary); (32°1'46.25"N; 109°58’24”W). Cherty dolomitic limestone trends N65oW and dips 30oNE. The primary vein is 1- to 2-feet wide and conforms to the dip of bedding in limestone. One block of limestone was thrust into place along an E-W trending fault 500 feet southwest of the mine.
Placer gold was discovered in washes downslope from Golden Rule Hill, but little mining has occurred ob these placers because of a lack of water. Gravels in the area may provide productive outings for prospectors with metal detectors. Lodes in the district were the primary targets of miners. Mine development at the Golden Rule began and about 6,580 ounces of gold was recovered by 1883. By 1902, 8,000 tons of gold-lead ore was mined. A 10-stamp mill was initially constructed and later a 20-stamp mill was built about 0.3 miles north (32°1'55"N; 109°58’6"W) of the mine near a well that provided water for milling.
The Golden Rule (Old Terrible) mine (section 23, T16S, R23E (32°1’42”N; 109°58’9”W) was developed for gold and lead. The mine, purchased by the Golden Queen Consolidated Mining Company in 1897, was sold to Old Terrible mining company in 1902. The property was later operated from 1905 to 1908, by the Manzoro Gold Mining Company. In 1904, the 227-foot inclined Jackson shaft was constructed. An older 325-foot inclined shaft, was filled with sand and gravel from a cloud burst in 1910. Between 1883 to 1929, the mine produced 10,500 ounces of gold with some silver, lead and copper. Metal production amounted to 17,000 ounces of gold, 72,000 ounces of silver and 320,000 pounds of lead.
The mine is located on three veins about 25 to 40 feet apart that lie conformable to bedding in limestone. The veins were traced for a few hundred feet. Quartz is coarsely crystalline and locally banded and brecciated with vugs stained by hematite and limonite (Wilson and others, 1967).
Green Valley (Payson) district. The Green Valley district, in central Arizona, is south of Payson in the foothills of the Mazatzal Mountains. Geographically, the district is in the central highlands between the Colorado Plateau, and the Basin and Range further south. Payson is reached by driving northeast along Highway 87 (Beeline Highway) from the east valley of Phoenix. Green Valley is underlain by Payson Ophiolite (1.73 Ga), formed of metavolcanics, sheeted dike swarms, diorite, gabbro and tonalite. These lie on a 1.75 Ga basement complex of granitic rocks that include felsic volcanics and volcanic rocks. Ophiolites are chunks of the earth’s oceanic crust, and underlying upper mantle, that have been uplifted above sea level in the past and emplaced into continental rocks.
The discovery of rich, free-milling gold-quartz veins in 1875, resulted in an influx of miners and prospectors. But, the veins in the district were limited in size and easily recoverable gold in the oxidized veins, gave way to refractory, low-grade, sulfide-bearing quartz below the water table at depths less than 200 feet. Thus, no major mines developed and production records were not kept.
Geologically, rocks in the district are highly fractured and faulted with some fissures provided pathways for gold-quartz vein injections: many veins strike N15oW to N65oW and dip northeast. If you examine the area immediately southwest of Payson and west of the Oxbow Estates on Google Earth you will see dozens of linear, structurally-controlled drainages following fractures and faults: most trend N70oW to N35oE. Distinct polygonal fractures are seen throughout the district and most intersect at right to near right angles, while others exhibit rhombohedral fracture patterns. Examine an area around 34°11'15"N; 111°22’30”W
Visible gold was found in veins at Gowan, Oxbow, Golden Wonder and Zulu mines and detrital (placer) gold was found downslope from the Oxbow mine, four miles south of Payson, that included minute flakes and flat nuggets up to 0.25 inch long. Minor copper and silver mineralization was also found, but gold was the primary target. Some wire and horn-silver is present in oxidized veins at the Silver Butte mine. Silver is also associated with galena (lead-sulfide) and tetrahedrite (copper-iron antimony sulfide). Chalcopyrite (copper-pyrite) was also found at both Silver Butte and Bishops Knoll south of Payson. Minor tetrahedrite, bornite (copper-iron-sulfide), covellite (copper sulfide), chalcocite (copper sulfide), malachite (copper carbonate), azurite (copper carbonate), chrysocolla (hydrated copper poly-silicate) and dioptase (copper cyclo-silicate) were found. The Green Valley copper deposits included lenses of tetrahedrite and some disseminated chalcopyrite and bornite in greenstones, as well as disseminated pyrite, chalcopyrite and chalcocite in schist and gabbro and diorite dikes.
Many gold-bearing quartz veins in the district were found as fracture fillings in faults enclosed by crushed quartz zones. Since the host rocks were extensively weathered, portions of veins stood out as positive, resistant, outcrops. Gold-bearing veins range from a few inches wide to the vein at the Gowan mine, which swelled to 12-feet wide. Gold was also found associated with hematite and limonite in the oxidized portions of the veins. Below the water table, visible gold was absent, and gold appeared to be associated with pyrite and chalcopyrite. Above the water table, free milling gold occurred suggesting the precious metal was tied up in sulfides.
Tiny gold flakes are described in secondary hematite and limonite in quartz above water table. Additionally, limonite pseudomorphs after pyrite were identified at the Oxbow mine. It was noted by miners that higher gold values correlated with higher limonite and hematite content, supporting that some gold was hosted by pyrite. At the Golden Wonder, explorers suggested gold was associated with high bismuth and tellurium in the veins, possibly indicating some gold was hosted by unrecognized tellurium minerals and possibly with native bismuth.
Below the water table veins with pyrite and chalcopyrite typically assayed less than 1 opt Au. In the oxidized vein above the water table at the Oxbow mine, samples yielded 0.24 to 3.87 opt Au, and values at the Gowan vein above the water table were as high as 4.85 opt Au. Most host rocks are described as diorite altered to chlorite, sericite and secondary quartz over a width extending several feet on either side of the veins (Lausen and Wilson, 1925). Kusky (2004) indicated the area underlain by most of the mines and prospects was part of the Payson ophiolite complex.
Mine in the district include Bishop's Knoll, Callahan (34°12'21"N; 111°22’55”W), Crackerjack, Delaware (34°10'49"N; 111°22’20”W), Eighty-five, Excursion, Gowan, Gold Rock, Golden Wonder, Lincoln, Little Green (34°11'11"N; 111°23’48"W), Little Maude (34°10'41"N; 111°22’41”W), Maggie, Mankin, Midget (34°9'48"N; 111°21’32”W), Oxbow, Payrock (34°12'40"N; 111°22’5”W), Rocky Ford (34°12'1"N; 111°22’18”W), Silver Butte, Silver King (34°13'34"N; 111°21’45"W), Single Standard (34°11'48"N; 111°22’8”W), Summit, Thompson, Zulu (Lausen and Wilson, 1925) and White Mountain (34°16'3"N; 111°24’12"W). A few properties were prospected over relatively large areas within the past 30 to 50 years such as the Golden Wonder, Maggie, Oxbow, and Zulu. These, in particular, should be examined for large-tonnage, gold mineralization. Some slope debris could provide opportunities for nugget hunters.
Placers are uncommon due to a lack of active streams. Some placer gold was recovered in drainages below the Oxbow mine during the rainy season when surface water was available. The gold was found in surface gravel, but in 1939, placer gold was apparently recovered from deeper gravels in a old channel unrelated to the current stream channel (Johnson, 1972).
Some of ore was hauled to the nearby Verde River where it was recovered by amalgamation in arrastra and later in stamp mills. Attractive agates and chalcedony are reported in the area including attractive banded agate (34°12’45''N, 111°22’13’’W) and fire agate (34°12’40''N, 111°13’2’'W).
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| Hatford district, Huachuca Mountains, Cochise County |
Hatford district. Hatford lies along the southern edge of the Huachuca Mountains in Cochise County, although at least one mine (Manila) was dug at the northern end of the range, but operations terminated after it was discovered to be within the military reservation. The district contributed minor copper and silver, and is primarily known for Cu-Pb-Zn-Ag-Au-W(Cd) mineralization from the Reef mine.
Types of mineralization include: (1) Base-metal oxides, carbonates, and sulfides in quartz veins, irregular replacement bodies, and disseminated mineralization in complexly folded and faulted Paleozoic limestones, and Cretaceous sedimentary and volcanic rocks. Some mineralization was found in exotic Paleozoic limestone exotic blocks trapped in Triassic-Jurassic volcanics intruded by Jurassic quartz-monzonite stocks and dikes; and (2) tungsten mineralization in quartz veins along with irregular bunches and disseminations in metamorphosed Paleozoic limestones and Cretaceous Bisbee Group sedimentary and volcanic rock.
Mines and prospects are small and and production from the district was only 9,000 tons of base and precious metal ore that yielded 37 tons of copper; 294 tons of lead; 188 tons of zinc; 393 ounces of gold, 25,000 ounces of silver and 170 tons of tungsten ore grading 60 to 78% WO3. The tungsten was mined as a strategic metal for steel hardening during World War I (Keith, 1973).
A portion of the district lies is inaccessible in the Fort Huachuca military reservation and part of the State of Texas mine lies within the Coronado wilderness where collecting is prohibited ("let it rot in place doctrine"). Overall, the district is not well-mineralized at the surface.
Hayden-Banner district. The Hayden-Banner district is 8 miles north of Winkleman and 22 miles south of Globe.
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In the background is the town of Jerome. And further back behind the 'V' in the mountains, is the old Jerome mine (United Verde). You can read more about this mine at the Mining Journal |
Jerome (Verde) district. The Jerome (Verde) district lies along the eastern slope of the Black Hills in central Arizona, 80 miles north of Phoenix, and west of the Verde River. Gold and silver were recovered with zinc-, lead-, and copper-sulfides from two major mines: United Verde and United Verde Extension both of which are classified as volcanogenic massive sulfides (VMS) hosted by rocks of a Proterozoic greenstone belt.
Historically, copper was utilized by Indians in this area, for jewelry and dyes. But the deposit remained undeveloped until explored by U.S. Army in 1875. This led to an influx of prospectors who located oxidized ores at the surface that were rich in gold, silver and copper. By 1882, much of the minable land had been consolidated in the ownership of the newly formed United Verde Copper Company, which began extracting near-surface oxidized copper ore rich in gold and silver. Underground mining began in 1883 and open pit mining was introduced in 1920. The ore is found in a steeply-dipping, cylindrical mass approximately 700 to 800 feet in diameter, extending down to a depth of 2,400 feet.
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| An unbelievable gossan exposed at the United Verde open pit at Jerome. This rusty and copper- stained rock was deposited about 1.7 Ga. In other words, these mineralized rocks were deposited 1.7 billion years ago by submarine hydrothermal vents, similar to the black and white smokers seen at great depth by specialized research vessels exploring the ocean bottom. Not only do the rocks support this interpretation, but miners actually extracted the fumaroles fossilized hydrothermal vents. |
The UVX mine operated on a large scale until 1938 when much of the high-grade ore was mined out and operations ceased, while the nearby United Verde mine continued mining. After 1931, much activity focused on open-pit. But, the depletion of ‘high-grade’ reserves forced that mine to close in 1953. However, operations left behind a giant, low-grade, ore deposit and possibly other undiscovered ‘blind’ deposits (Hausel, 2012).
Today, mining at Jerome is quiet, but the Verde open pit still shows an impressive gossan. The rest of the mine lies underground with 81-miles of tunnels and shafts hidden beneath the open pit and adjacent valley. Remains of the smelter works are visible further east near the Verde River. And take the time to visit the Museums (Douglas Mansion and Audrey Headframe Museum) at the edge of town as they have excellent mining exhibits.
When examining aerial photographs on Google Earth, a continues gossan is visible and extends 7 miles north of the United Verde Mine and 7 miles south! Such an extensive gossan likely hides ‘blind ore deposits’. And like most mines reported to have been mined out, the United Verde and United Verde Extension, were never mined out. The US Geological Survey reports twice as much unmined ore remains in place as was mined! It is extremely rare for any mineral deposit to be mined out, and most productive mines terminate operations due to declining prices, or due to poor decisions by CEOs.
Massive sulfide is an unusually, rich deposit of sulfide minerals. The massive sulfide at Jerome is rich in copper, zinc, silver and anomalous gold. Sulfide minerals in such deposits often enclose significant amounts of gold and silver. So much silver was found with this deposit that the silver essentially paid for all mining operations. Banded chert (known as exhalites) is typically associated with VMS. The VMS at Jerome was so rich in massive sulfide that exposure to oxygen during mining resulted in oxidation of the sulfides, which yielded considerable energy as heat, causing the rock (massive sulfide) to catch on fire! It burned for years!
VMS refers to a type of mineralization that has zones of massive and disseminated sulfide minerals originally deposited on the ocean floor in hydrothermal vents referred to as 'white' and 'black' smokers. They often have associated volcaniclastics (breccia) that represent past submarine eruptive vents. Some are so distinct that one Canadian geologist dubbed such volcaniclastics as ‘mill rock’ because he noticed operating commercial mills sat adjacent to many.
You might be wondering what submarine VMS deposits are doing in the dry deserts of Arizona? In the past (before global warming was invented by Al Gore), these deposits accreted to continents and buried by tectonic forces related to continental drift. After millions of years of erosion following mountain uplift, some were exposed at the surface, while many remain hidden and undiscovered. Still others continue to form in oceans, particularly along active volcanic island chains (such as Japan) and along spreading centers such as the Mid-Atlantic Ridge.
According to the Arizona Department of Mines and Mineral Resources (2007), 48 of 70 known VMS deposits in Arizona have produced ore - all of which are Precambrian age (1.7 to 1.8 billion years old). Most are steeply plunging and deformed, such as the United Verde, which has been described as a rod-like ore body or pipe located within an axis of a major, steeply-plunging, fold.
In 1989, the US Geological Survey described records from Phelps Dodge that indicated production from the United Verde Mine from 1884 to 1975 amounted to more than 2,926,900,000 pounds ($10.1 billion at 2012 prices) of copper, 97,891,000 pounds ($82 million) of zinc, 459,000 pounds ($390 thousand) of lead, 49,603,000 troy ounces ($1.4 billion) of silver, and 1,571,000 ounces ($2.5 billion) over the lifetime of the district. Based on statistics (U.S. Geological Survey and Phelps Dodge), the United Verde produced $14.8 billion in metals at 2012 prices (few major diamond mines are as productive).
The Verde VMS sits at the top of a submarine rhyolite dome and flow breccia known as the Cleopatra Member of the Deception Rhyolite. The ore is zoned and capped by chert and siliceous massive sulfide that grades down into pyrite-rich massive sulfide, zinc-rich massive sulfide, copper-zinc-rich massive sulfide, chloritic stringer ore, and chloritized quartz porphyry ore. Gold is found throughout but is in greater concentrations at the stratigraphic top (siliceous massive sulfide and chert ore).
For instance, on the 4500-foot mine level, black schist yielded 0.002 opt Au and 0.71 opt Ag. In chert near the surface, the ore yielded values as high as 0.12 opt Au and 4 opt Ag (60 times more gold). On the 700-foot level, massive sulfide averaged 10 times more gold than black schist. A positive correlation of gold with higher zinc content is recognized. This is important as much zinc ore was not mined.
Sulfides are exposed at the surface to the 4,500-foot mine level, but in the geological past, the ore extended upwards to the base of the Cambrian Tapeats Sandstone indicating at least 350-feet of vertical column of massive sulfide was removed by erosion. This means drainages down-slope from the massive sulfide likely have detrital gold, but based on the mode of occurrence, the gold likely is fine grained.
Ore minerals in the massive sulfide in decreasing abundance include pyrite, sphalerite, chalcopyrite, bornite, arsenopyrite, galena, tennanite and gold (electrum). Much electrum is thought to be present as microscopic inclusions in sulfide minerals. Silver is present in electrum and in late-stage tennanite (Cu12As4S13) in quartz carbonate veins, and in carbonate rich massive sulfide ore.
The Verde was the largest known volcanogenic massive sulfide in the US with 33 million tons mined, and 50 to 70 million tons of low-grade ore left in place. The massive sulfide is steeply-dipping, irregular- to cylindrical-shaped ore body, approximately 700 to 800 feet in diameter extending to a depth of 2,400 feet. The United Verde mine reached a depth of 3,515 feet. According to the US Geological Survey, proximal ore recovered from the mine averaged 4.77% Cu, 0.046 opt Au, and 1.65 opt Ag. Zinc and lead were not recovered during much of the operations. Another blind ore body was found in the lower levels of the mine 500-feet northwest of the roots of the main deposit.
Anomalous gold was detected in the pyritic and sphalertic massive sulfides and the chert rich ore: chloritic host rocks were gold poor. The zinc ore contained as much gold as the copper ore. And because only the high-grade copper-rich portion of the massive sulfide was mined, a very large tonnage of low-grade ore remains in place and it estimated at least 75% of the mineralized deposit remains unmined because it was too low-grade to mine.
At the United Verde Extension Mine, mineralization occurred in an elliptical ore body hosted by the Deception Rhyolite and Grapevine Gulch Formation. The main chalcocite ore body was found on the 1,400-level and was 269-feet wide and 440-feet long on this level.
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Cabochon cut from the tenorite, malachite, chrysocolla ore at the UVX mine, Jerome, AZ |
The UVX mine produced 3,879,000 tons of ore at a grade of 10.23% Cu, 0.039 opt Au, and 1.71 opt Ag. Ore minerals include chalcocite, cuprite, native copper, malachite, chrysocolla and azurite hosted by felsic fragmental rocks, massive rhyolite and quartz porphyry – all units of the Deception Rhyolite.
Part of the UVX operation was developed by the Haynes Shaft located west the United Verde open pit. This deposit was another blind ore body found at 2,500 feet depth. The UVX decided to explore the ground under the Haynes shaft by driving a tunnel at the 3,000 level. A drift started in 1930 and reached the Haynes massive sulfide in 1931.
The Haynes proximal pipe was a steeply-plunging massive sulfide. It extended a short distance above the 2,700-level downward to an undetermined point between the 3,450 and 3,700 levels of the United Verde. The Haynes was sunk to 700 feet between 1907 and 1911; subsequently deepened to 1,200 feet, with 1,700 feet of drifts and crosscuts on the 700 level and 700 feet on the 1200 level.
LaPaz district. The district includes the town of LaPaz in the Colorado River basin, and dry placers in the Dome Rock Mountains east of La Paz and west of Quartzite, and in the Plomosa placers east of Quartzsite. These are for the most part dry placers in gravel eroded from porphyritic quartz-chlorite schist and granite in the Dome Rock Mountains. The placers are located on the western slope of the Dome Rock Mountains in 1862, when Captain Weaver of the US Army was presented nuggets by local Indians. The first visit to the site by soldiers recovered 400 ounces of gold nuggets. Within the first year of mining placers, it is estimated that 50,000 ounces were recovered from the dry placers.
Nuggets are described to range from tiny specimens to 20 ounces. One, known as the Chispa, weighed approximately 58 ounces. The richest arroyos included the Goodman and Arroyo La Paz. The gravels are a few feet thick on hill sides and extend to an unknown depth in La Paz Arroyo. The gold is rough and angular with much containing magnetite attached to the gold. Boulders and cobbles of magnetite are found on the surface. Gold-bearing veins were discovered about the same time as the placers. Two types of veins are recognized: (1) stratiform veins that follow schistosity, and (2) crosscutting veins. Both carry gold, but only the larger stratiform veins have been mined in the past.
At the Goodman lode, a vein was traced for 3 miles along an east-west trend. The vein ranges from a narrow veinlet to as much as 40-feet wide. The north dipping vein was explored by inclined shafts with connecting tunnels. Gold is found in pyrite in the vein. Only about 2,000 ounces were recovered from the mine prior to 1900.
Placers on the east slope of the Dome Rock Mountains include Middle Camp, LaCholla and Orofino west of Quartzsite. These gravels are cemented by calcium-carbonate that requires crushing to recover gold.
Dry placers located to the southeast of Quartzsite are found in arroyos along the base of the Plomosa Mountains. The gold is in conglomerate cemented by calcium carbonate.
Lone Star (Safford) district. The town of Safford is 16-miles southwest of Morenci in southeastern Arizona, and 120-miles east of the Phoenix valley. A group of mineralized porphyries occur along a northwest trend that parallels the Butte Fault. Construction of an open pit mine began in 2006 and Freeport-McMoRan built a giant leach pad at the Dos Pobres open pit. Mineralized intrusives include San Juan, Lone Star and Horse Shoe quartz monzonite stocks that intrude andesite. A distinct northeasterly-shear is recognized in the volcanics.
Mineralization consists of disseminated pyrite and chalcopyrite with veinlets with minor bornite, molybdenite, sphalerite, galena, magnetite, specularite, chrysocolla, brochanitite, cuprite, malachite, native copper and turquoise (Cook and Robinson, 1962). The deposit has by-product gold and silver. Geophysical exploration at Safford suggests possibilities for additional hidden copper-gold deposits at depth. The Dos Pobres and San Juan deposits are currently reported to have a combined resource of 538 million tons averaging 0.37% copper.
Lost Basin district. Lost Basin is in northwestern Arizona near Mead City in the Lost Basin Range in Proterozoic basement rock of Mohave County. This district likely hosts a major gold deposit! Gold was discovered in gravels and fanglomerates and described as visible, and associated with pyrite and chalcopyrite. Mineralization is associated with a 7-mile long trend in fault breccia, dry placers, veins, pipes, fanglomerates and alluvium. Past work suggests zonation of mineralization with a central cupriferous belt (with gold) surrounded by a silver-lead-zinc halo enclosed by gold-dominant zones.
Highly anomalous gold-bearing iron formation, quartz veins and quartz breccia veins with a possible hidden porphyry copper deposit surrounded by auriferous veins and breccia veins are found north at the Climax mine. Gold-bearing iron formation south of the Bluebird mine is a pyritiferous iron formation with visible gold found along an E-W trend. Gold is reported in the iron formation and continues to the east for nearly a mile.
Several prospects near Cu-blowout and Road Runner prospect are anomalous. At the Cu-blowout, samples recorded by the US Geological Survey were opalized with chalcopyrite-bearing schist and visible gold in quartz veins. A magnetic low surrounding the anomaly is suggested to reflect a buried porphyry at depth. In addition, visible gold was identified in hundreds of hand specimens at the Golden Gate, Harmon, Gold Hill, Road Runner and Climax prospects. This district very likely not only hosts a hidden porphyry Cu-Au deposit, but also vein and iron formation gold deposits.
Lost Dutchman. When prospectors and treasure hunters talk about gold in Arizona, the Lost Dutchman and Vulture mine are mentioned. The Lost Dutchman is just that, a myth chalked full of holes that has been embellished over time as any good legend should be. According to the legend, a rich-gold vein was discovered by Jacob Waltz, a German immigrant, while prospecting in the Superstition Mountains east of Phoenix Arizona. If you've been to Phoenix, the Superstition Mountains is the impressive volcanic dome at the eastern edge of the valley that rise along near vertical cliffs with a maximum elevation of more than 5,000 feet above sea level. From Apache Junction, the Superstitions rise as impressive and rugged precipices.
The volcanic dome can be viewed on Google Earth: search for ‘Superstition Mountains, Arizona’. These rugged mountains are part of a 25-million year old, resurgent, rhyolite dome and caldera. As you back out of Google Earth to an eye altitude of 30 to 35 miles, you should see evidence of an 8- to 10-mile diameter, circular structure: this is the dome. The dome is formed of rhyolite, a volcanic rock that is the fine-grained equivalent of granite that occurs in a variety of colors, most notable light-gray to white and reddish-brown to pink due volcanic rocks with abundant fine-grained pink feldspar.
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The rugged Superstition Mountains, home of the Lost Dutchman legend (photo by the author). |
According to historical documents, Jacob Waltz (the Dutchman) prospected for gold in the Bradshaw Mountains north of present day Phoenix in 1863 to 1867. When he later died at his home in the Salt River valley (Phoenix area) in 1891, legend claims a box was found under his death bed that contained 48 pounds of high-grade gold ore including milky quartz with considerable visible, fracture-filling, gold. An alleged sample of this ore was made into a match box and the woman who provided care to Waltz in his last days came into possession of a map of the gold site, which some sources report she sold copies for $7 each (a relatively high price in 1891).
Is there any truth to the Lost Dutchman legend? I’m no expert on the legend, but as myths go, they are often best left for treasure hunters, CNN, parapsychologists and dowsers. The Lost Dutchman’s mine has never been found, but a rich quartz vein was discovered at the other end of the Phoenix valley in low-lying hills known as the Vulture Mountains. Records suggest the Vulture was the largest gold producer in Arizona in the historical past, and some suggest there may have been a connection between this and the Dutchman. The Vulture mine became known for its high-grade gold ore. Various reports suggest thieves made a living high-grading ore from the mine (today, we call these people politicians). The problem was so rampant that some thieves were hanged at the mine site. So, will the Lost Dutchman mine ever be found. Personally, I don't know as I'm not a treasure hunter and I'm, much better at searching for gold in old mining districts. But for those of you who search for the old mine, I hope one day you find it!
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Considerable gold fills fractures in milky quartz on this ornate match box apparently found under the Lost Dutchman's bed. Some suggest the Lost Dutchman high-graded gold from the Vulture mine. However, this quartz appears quite different from the exposed vein at the Vulture suggesting that the two had different gold sources. So is this a legend, or real? |
Mineral Park. At Mineral Park, copper, molybdenum, gold, lead, zinc, silver, turquoise and chrysocolla were discovered in 1906. The mineralization is part of a porphyry copper deposit which encloses crenulated, tabular, and crescent-shaped ore-bodies hosted by the Escabrosa Limestone. Duval Copper commenced production at the mine in 1963 and Mercator minerals purchased the mine in 2003. As of 2014, the mine is reported to have another 20-years of minable resources.
Mission-Sierrita district. The Mission district in southeastern Arizona encloses a group of large, open-pit copper mines known as Mission, Sierrita and Twin Buttes. These are 35 miles north of the Mexican border and west of Green Valley, 15 miles south of Tucson. The Sierrita mine has state’s largest mill capacity and produces copper, molybdenum and rhenium from ore averaging 0.26% Cu. The operator of the mine, Freeport McMoran, purchased the adjacent Twin Buttes mine which has 700 million tons of ore at an average grade of 0.43% Cu.
The nearby Mission mine produces copper, silver, zinc, molybdenum, lead, gold, tin, tungsten, fluorspar and cadmium. The deposit was discovered in 1953 by drilling through 200 feet of valley gravel. By 1961, a major open-pit mine was opened. The ore is reduced at the adjacent Pima mill and concentrator. The Mission mine produced 121 million pounds of copper in 2007.
Mineralization is skarn and copper porphyry with seams and disseminations of copper carbonates and sulfides in altered, complexly-folded and faulted Paleozoic limestone and Triassic sediments and volcanics all invaded by Laramide intrusives. A 2-mile-wide alteration halo was associated with mineralization. The bulk of replacement ore occurs in garnet and pyroxene tactite. The Mission mine includes the merged Mission, Pima and Eisenhower Mines in a single, large open pit. The ore averages 0.7% Cu, 0.13 opt Ag with considerable by-product zinc, molybdenum and lead, but very little gold.
Near the Helvetica property, another company, Augusta, filed a plan for the Rosemont project to produce 230 million pounds of copper per year. The Rosemont porphyry-skarn contain 543 million tons of ore at an average copper grade of 0.75% Cu, although other sources suggest the deposit averages 0.47% Cu.
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Boulder of azurite, malachite, cuprite and tenorite |
Morenci district. Morenci is another of the many porphyry copper open pit mines in Arizona. At Morenci in Greenlee County along the New Mexico border, quartz monzonite intrudes limestone and shale which produced a very large ore deposit vein and disseminated chalcocite, pyrite, chalcopyrite, and sphalerite.
These ore minerals were supergene enriched during erosion and chemical weathering. Erosion removed an estimated 1-mile of rock overlying the deposit and shed detritus to the north. The deposit lies under 2,000 to 3,000 feet of volcanic rocks as a result of mid-Tertiary extension and volcanism. Much of the supergene copper at Morenci appears to have been formed as a result of Basin and Range deformation 13 to 4 million years ago.
Oro Blanco district. The Oro Blanco district is located along the Arizona-Mexico border adjacent to the Buenos Aires National Wildlife Refuge in Santa Cruz County; thus, making this area dangerous to prospect. Geologically, it is underlain by a series of sandstones, quartzites, conglomerates and shale with some intercalated volcanic rocks. These rocks (Cretaceous?) rest on an irregular surface of altered, coarse-grained, grayish diorite and are intruded by mafic and felsic dikes.
Mineralization includes: (1) irregular quartz veins and lenses with spotty auriferous and argentiferous base metal sulfides and pyrite in fracture fillings, or as replacements along faults and at fault intersections. These show supergene enrichment of gold and silver. The host rocks are altered conglomerates and sandy sediments and volcanic tuffs with local disseminated pyrite. Most are limited in extent and depth; (2) Flat to shallow-dipping zones of quartz veinlets and stringers locally containing gold and silver and minor base metal sulfides usually associated with strong pyritization. Host rocks are strongly fractured, sericitized volcanic tuffs; (3) Steeply-dipping, tabular masses to lenses with brecciated shear zones containing native gold and silver associated with finely-crystalline quartz and weak iron and manganese oxides in volcanic tuff; (4) Small gold placers in several dry stream beds; (5) minor manganese oxides; and, (6) uranium in fracture zones in volcanic tuffs. Gold in the Oro Blanco district includes three types: (1) sulfide-bearing quartz veins, (2) mineralized shear zones, and (3) mineralized bodies of country rock.
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The Yellow Jacket prospect lies 6 miles north of the Mexican border and adjacent to the Buenos Aires National Wildlife Refuge. The Yellow Jacket was discovered in 1874 and periodically operated until 1959 when it was re-timbered and sampled for resources and deemed uneconomic to mine at $35/ounce even though ore grades were reportedly high (Ring and Ring, undated).
More recent exploration by Transatlantic Resources identified a significant gold resource at the mine. The prospect occurs on a series of quartz veins in a 30- to 50-foot wide shear zone. The veins range from 2- to 30-feet thick and have disseminated gold-bearing sulfides and uncommon base metals. The shear strikes northwest and dips steeply northeasterly and wall rock consists of welded tuff (Jurassic) cut by rhyolite dikes. The Yellow Jacket (section 21, T22S, R10E) sits adjacent and southeast of the Phoenix mine, which has additional high-grade ore (reported to average 0.47 opt Au).
Gold resources calculated for the Yellow Jacket mine include 5.3 million tons. The resource includes 740,000 tons of measured resources at an average grade of 0.37 opt Au (274,000 contained ounces), 560,000 tons of indicated resources at 0.25 opt Au (140,000 ounces) and 4 million tons of inferred resources at 0.15 opt Au (774,000 ounces) for a total resource of 1,548,000 contained ounces of gold with 527,000 ounces of silver. The Yellow Jacket produced 126,500 ounces during its early history and the nearby Old Glory mine was estimated to have produced 26,000 ounces prior to 1914. Based on the number of prospects and the identified resources in this district, it should be considered a priority exploration project if the Arizona/Mexico border is ever secured.
Patagonia district. The Hermosa deposit was discovered in 1879. Some production occurred on neighboring properties including the Trench mine between 1939 and 1964. The Hermosa property within the Patagonia mountains in southeastern Arizona has drilled proven and probable reserves of 145 million ounces of silver and 7.2 billion pounds of manganese with inferred resources of 50 million ounces of silver and 1.2 billion pounds of manganese - essentially, a world-class deposit.
The deposit is located in a series of Cretaceous ash flow tuffs and breccias deposited on the Permian Concha Limestone and dolomites and sandstones of the Scherrer Formation. The ore is located within epiclastic sandstone at the apex of a doubly plunging anticline. Faulting likely supplies the mineralizing fluids which migrated to the anticline apex.
Ray district. The Ray mine, situated halfway between Hayden and Miami, began as underground mine prior to 1911 and yielded an estimated 4.5 million tons of copper. The operation converted to open pit in 1955. Published reserves (1992) included 1.1 billion tons of ore averaging 0.6% Cu. The geology is complicated by faulting, host rock variations, two episodes of tilting, complicated enrichment history and hypogene and supergene alteration. The mineralization is controlled by rock type, faulting and enrichment, and found in a variety of Precambrian rocks and Laramide intrusions.
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The author stands next to a monster truck in front of the Ray open pit mine. Every red neck would give his ... to have a monster truck with tires like these - including me! |
San Francisco (Oatman) district. In 1863, local Indians presented samples of gold-bearing quartz to John Moss, an army officer stationed at nearby Fort Mohave. The samples were from a vein in the northwestern part of the Black Mountains, which later became known as the Moss vein (Hausel, 2013). About 12,000 ounces of gold were mined from the vein in the following year (1864) during the Civil War. A camp named Silver City was established 1.5 miles south of the Moss vein on Silver Creek and a mill was built near a spring in an otherwise dry drainage. A second mill was later constructed at Hardyville (renamed Bullhead City) on the Colorado River seven miles to the northwest. In 1866, war broke out between gold prospectors and Hualapai Indians, resulting in termination of mining operations: little prospecting took place over the next few decades.
In 1900, another mineralized vein was discovered south of the Moss vein and named the Gold Road vein. In the following year (1901), gold was found in another vein further south at what became known as Tom Reed. Following this discovery, a town known as Vivian was established (1902).
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| The Road Gold vein (photo by the author) |
A sample from the Gold Road sparked a rush after a prospector collected vein material from an ore shoot that assayed 40 ounces of gold to the ton! In 1906, rich ore was also intersected in the Tip Top and Ben Harrison ore shoots on the Tom Reed vein; and in 1908, the town of Vivian changed its name to Oatman. Reports suggest Oatman grew to 10,000 prior to declining to a few hundred residents by the mid-1920s.
Lode deposits are classified as epithermal veins associated with hot hydrothermal fluids and hot springs rich in silica and carbonate. Precipitation of silica resulted in veins forming resistant hard outcrops that produced linear ridges following erosion. Elsewhere, permeable fractures were flooded by soft carbonate resulting in rapid erosion of these.
Veins were prospected for rich ore shoots. A group of shoots along the Tom Reed vein included the Big Jim, Aztec and United Eastern ore bodies. A hidden (blind) shoot (Tip Top) yielded 580,000 ounces of gold. This shoot was mined under the town of Oatman until exhausted in 1924. Gold prices prior to 1924 were under $21 per ounce which suggests any unmined, low-grade gold in this so-called ‘exhausted’ shoot should be recoverable at today’s prices. The reports of rich ‘blind deposits’ suggests similar hidden ore bodies are likely to occur.
Over the years, a group of mines periodically operated and closed until all gold mines were closed by the War Minerals Board in 1942. Many of these properties were making a profit at $35.5/ounce. Some mines reopened after the war, but most did not and may be profitable presently.
Some veins, such as the upper level of the Gold Road, are tabular bodies with sharp wall-rock contacts. But most consist of stringer gold-quartz-calcite ore cutting blocks of silicified latite. Other veins consist entirely of reticulating stringer veins that traverse the country rock. This latter type is typical of portions of the Gold Dust vein. When stringer veins are sufficiently abundant, the rock is minable if gold content of the stringers is sufficiently high. Compound veins with two or more veins of solid quartz and calcite separated by country rock are common.
Some ore shoots had good lengths and widths such as the Big Jim-Aztec shoot which had a maximum width of 35 feet. The principal ore body on the Tom Reed vein mined at the United Eastern shaft, had a width of 48 feet.
Gold and silver content decreased at depth. At the United Eastern, the grade dropped from more than 1 opt to less than 0.5 opt in gold (Au) at 800 feet. The Big Jim-Gray Eagle ore shoot averaged 0.95 opt Au above the 600-foot-level but decreased to less than 0.3 opt Au below this level. Similar abrupt changes were noted elsewhere. Ore at the United Eastern, Tip Top and Ben Harrison all ended at nearly the same depth. Ore shoots extended a thousand feet or more at depth in the eastern part of the district, but in the western part, ore shoots were shallow and only a few hundred feet deep. The Gold Road, Tom Reed and Moss veins all had distinct outcrops. These were distinct not only because of silicification, but also because of iron and manganese that produced reddish- to black-stained gossan.
Crushing and panning gypsum and quartz from some veins yielded tiny gold flakes. In the San Francisco and nearby Union Pass district, calcite stained by iron or manganese was sometimes mineralized. A sample of calcite from the Pioneer vein assayed 0.16 opt Au, while unstained calcite yielded no gold. Pyrite is uncommon, but where found sometimes carries gold. A sample of pyrite from the Moss vein assayed 10.8 opt Au and 30.16 opt Ag. Cavities in the sample had visible gold in limonite. Water was lacking in most mines with the exception of the Aztec, Gold Road, and the United Eastern, where water was pumped from the lower workings.
Gold placers are limited due to lack of active streams. Even so, placers were reported at various localities along Silver Creek and in tributaries draining the Times Porphyry near Mt Hardy in the vicinity of Times Gulch. In the drainage below the Pioneer mine flakes of detrital gold were recovered from panned concentrates. Nearly all of the gold was found within three feet of bedrock. Placer gold was found below the Moss mine where the vein had some coarse gold. Overall, placer gold was minor.
The San Francisco district lies along the western flank of the Black Mountains of Mohave County in extreme western Arizona. The Black Mountains also enclose the Virginia, Pilgrim and Union Pass (Katherine) districts. The Black Mountains are a low-lying desert range 100 miles long by 20 miles wide that parallels the Colorado River. The highest peaks in the range reach heights of 5,000 feet: temperature extremes at nearby Bullhead City and Needles to the west (600-feet elevation) include a record low of 23oF and record high of 126oF with average annual precipitation of 7 inches. Kingman (3,300 feet above sea level) to the northeast reports temperature extremes of 6oF and 111oF with annual precipitation of 10 inches. Oatman (2,000 feet elevation) lies in the center of the Black Mountains and has annual precipitation of 6.4 inches compared to a national average of 38.7 inches. In this hot, dry, desert; detrital gold may be found near lodes, but water is as difficult to find, as an honest Congressman.
Access Google Earth and search for ‘Oatman Arizona’, and bleached mine tailings will be visible north and south of Oatman. These are part of the United Eastern (north) and Ben Harrison (south) operations along the northwest-striking Tom Reed vein. While viewing aerial photography, many mines, prospects, gopher holes, veins, fractures, lineaments and faults along with some clay alteration is visible. Try to count all of the mines and prospects in the region before going cross-eyed. I counted 85 mines and prospects before I gave up, and this didn’t even include veins, trenches and countless gopher holes.
The majority of the lodes in the district are linear, fracture-filling veins hosted by faults traceable on the surface for hundreds to a few thousand feet. Each vein typically has several prospect pits, trenches and mines. The Pioneer vein for example, shows a distinct northwesterly-trending, 4,600-foot long vein (with vein splits) that was prospected by trenches and some mine shafts. The veins all have trace gold and silver along much of their length with periodic secondary enriched zones. It is the enriched zones (ore shoots) that are sought by prospectors presently, as well as in the past.
Some supergene enrichment occurred in veins. In this process, poorly mineralized veins were enriched by redistribution of metal content. This near-surface phenomenon, requires meteoric water and chemical weathering to oxidize primary (hypogene) ore. Descending meteoric waters may dissolve some gold and transport the fluid through vein fractures until gold re-precipitates at depth. Gold dissolution likely is a result by dissolved salts in meteoric water reacting with manganese oxides during weathering (manganese oxides are common in the district). Gold in solution, may precipitate at depth when meteoric water reacts with pyrite, carbonate, and/or groundwater. Supergene enrichment of veins is evident by dramatic changes in ore grades at depth, and by distinct differences of the gold-silver ratios of precious metal in secondary supergene enriched zones compared to the primary hypogene ore. Veins are described as sulfide-poor with bands of andularia (low-temperature variety of potassium feldspar), quartz and calcite. Some have crustiform chalcedonic quartz banded with calcite.
Gold Road mine (center of section 11, T19N, R 20 W) sits on a vein with a distinct mineralized zone of stringer ore and banded crustiform, quartz-calcite in silicified latite. The vein has widths up to 100 feet, locally and strikes N50ºW and dips 80º to 85º NE. The vein occupies a fault in latite. At shallow depth, the Oatman Andesite forms the footwall of the vein while latite forms the hanging wall. Examination of aerial photos in this area suggests the Gold Road structure could be as much as 9,300 feet long with buried segments.
Addwest Minerals reopened the mine in 1995 and outlined a 2.6 million ton gold resources at an average ore grade of 0.355 opt Au. In 1998, the mine closed due to depressed prices after producing 88,000 ounces of gold. The company reported it had 524,000 tons of reserves at an average grade of 0.23 opt Au. Addwest (Mohave Desert Minerals) reopened the mine in 2007 and poured its first gold bar in 2010.
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Spectacular volcanic necks are seen when entering the Oatman area. |
Two veins are described on the property known as the north and south veins separated by barren latite. Much past mining focused on northern vein, but stringers of both extend into the barren host rock that was considered too low grade to mine at $20/ounce. The mineralized zone is 6,435 feet long and continues to a depth of at least, 680 feet.
Three ore bodies are described: (1) Number 1 shaft ore body, (2) Sharp ore body, and (3) the Rice ore body. The largest ore shoot was found in the Number 1 shaft. This shoot is 900-feet-long extending from the surface to the 700-foot-level with a maximum width of 22 feet. About 600 feet to the southeast the Sharp ore body, forms a blind ore shoot discovered underground above the 300-foot-level to the 500-foot-level. An extension of this shoot was mined between the 700- to 800-foot levels, while the vein between ore shoots was purportedly too lean to mine at a profit. Less than 200 feet south of the #3 shaft, another blind ore deposit (Rice ore shoot) was discovered between the 300- and 500-foot-levels. This shoot had a strike length of about 400 feet.
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| The Gold Road mine in 2012. |
South of the number 3 shaft, vein outcrops are stained by iron and manganese oxides and small outcrops were mined along 1,500 feet of vein exposure, but in most cases, the ore did not extend below 100 feet. The vein narrows to less than 2.5 feet wide at its southernmost extent.
Moss mine (S/2 section 19 and N/2 section 30, T20N, R20W) is 6 miles northwest of Oatman: the vein has an N60oW-trend and 60o to 70oSW-dip and the mineralized structure is 45-feet-wide locally. The structure ranges from 20- to 100-feet-wide with a wide mineralized zone and extensive stockworks and silicification. The Moss vein extends over a strike length of nearly a mile. The vein is hosted by the Tertiary-age Moss Quartz Monzonite Porphyry. The structure is open along strike and at depth.
A calcite-quartz vein occupies the hanging wall of a high-angle fault and is overlain by as much as 100-feet of low-grade mineralized stockwork and siliceous breccias classified as low-sulfide, adularia-sericite, epithermal vein typical of many near surface, hydrothermal veins. Such deposits are often related to paleo-hot springs and shallow geothermal systems. The vein contains some fluorite. Along the southern portion of the vein, a group of conjugate veins occur in the hanging wall that have similar trend. Much of the historical gold and silver production from the vein was from conjugate veins.
In recent years, Patriot Gold identified auriferous veins unrelated to the primary vein known as Discovery and Ruth veins. One hole drilled in these intersected a 5-foot section averaging 0.5 opt Au.
Using a 0.01 opt cutoff grade, the Northern Miner reported that the Moss deposit has 22.6 million measured and indicated tonnes grading 0.023 opt Au and 0.26 opt Ag plus 3.9 million inferred tonnes averaging 0.017 opt Au and 0.2 opt Ag. In total, the resources for this deposit include 603,000 ounces of gold and 6.6 million ounces of silver within 650 feet of the surface.
Identified gold and silver resources at the mine are reported to include 780,000 ounces of gold and 8,840,000 ounces silver (measured and indicated) with 216,000 ounces of gold and 2,517,000 ounces of silver as inferred resources. Ore grades range from 0.015 to 0.088 opt Au with high grade ore running 0.85 opt Au and 9 opt Ag, for a total resource of 996,000 ounces of gold and 11,357,000 of silver.
Holes drilled in the western extension of the vein tested the extension of near surface quartz-carbonate stockwork to the south. Multiple zones of stockwork veining were encountered within 500 feet of the surface suggesting potential for widespread stockwork mineralization to continue south. Eight additional drill holes demonstrated strong development of quartz-carbonate veins, breccias and stockworks that continue from the surface to at least 650 feet deep.
Gold Basin district. The Gold Basin placers begin along he eastern edge of the White Hills and extend east to Hualapai Wash in Mohave County of northwestern Arizona (T28 and 29N, R17 and 18W). The area lies south of Lake Mead, the Lake Mead Recreation area, and the Colorado River. The nearest communities are Meadview (36o00’00”N; 114o04’00”) and Dolan Springs (35o35’25”N; 114o16’25”W). Dolan Springs is the nearest community with basic supplies for prospectors such as food and gas. Due to the large number of retirees and snowbirds settling in the region, each community is surrounded by extensive suburbs.
The placers are dry placers in the desert, and have detrital 1 to 5 feet thickness of detrital gravel that lies on hard, false, bedrock of caliche-cemented gravel. Overlying gold-bearing gravels are weakly mineralized, with considerable black sand and quartz with fragments of schist and gneiss eroded from the Precambrian terrain in the White Hills. The gold content is poor and may only be 0.03 to 0.04 ounce per cubic yard at best; while the underlying consolidated gravel remains unexplored. Gold nuggets are rare: some up to an ounce have been found with the largest known nugget being 4 to 5 ounces in weight (Nevada Outback Gems). Much area prospected in Gold Basin is part of the White Mountains alluvial fan that extends from the eastern flank of the uplifted White Hills to Haulapai Wash to the east. The fan covers a surface area of 6 miles by 5 miles. One can access the area by driving northward on the Pierce-Ferry highway (Road 25) through Dolan Springs.
Gold was discovered in quartz veins in Precambrian rock in the 1870s. Placer gold derived from the veins was not found until the Great Depression. In 1932, W. E. Dunlop found gold in the dry gravel which attracted others to the area. The amount of gold recovered by the prospectors was minor and experienced miners only made about $1 per day (1933 wages). The total amount of gold recovered from the Gold Basin placers is only 415 ounces mined during the period of 1934-49. It is likely more gold was recovered, but not reported. Even so, it also suggests placers are small and very low grade.
A short time after gold discovery, a large-scale dry-wash plant was installed in 1933 by S. C. Searles in section 29, T.29 N, R 18W (35°52'52"N; 114°13’54"W) along the Gold Basin Road in the White Elephant Wash southeast of Golden Rule Peak. The plant was equipped with grizzly, trommel, screens, and a battery of twelve dry-washers and had a capacity of 20 cubic yards of gravel per hour. The amount of gold produced from this operation is unknown.
Gravels occur in arroyos and gulches at elevations of 3,300 to 2,900 feet. The gravels have medium-grained, angular schist and gneiss fragments with minor finely divided quartz. A small number of boulders are encountered that are generally less than 2 feet in diameter. Gold occurs as flour and less commonly as angular nuggets with some attached to black schist particles. The White Hills, which are made up of granitic, schistose, and volcanic rocks, have many argentiferous and auriferous quartz veins that are the likely source for much of the Gold Basin gold (Wilson, 1981).
Superior district. Superior Arizona is surrounded by porphyry copper mines including the Magma mines sitting on the edge of town. A major, hidden copper-molybdenum deposit was recently discovered in this district known as Resolution. Resolution was drilled and results indicate that the deep deposit has a minimum resource of 1.34 billion tons of ore averaging 1.51% Cu and 0.04 % Mo with gold and silver. The deposit is scheduled for production by 2020 and is located 3 miles east of the town of Superior. The deposit was discovered by drilling which interested mineralization at more than 4000 feet deep. One has to wonder how many similar deposits to Resolution occur in the states porphyry districts - probably several! When developed, the mine with its huge size and high grades could become Arizona’s largest mine. The property is operated by a Rio Tinto-BHP joint venture.
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| Taxi service in Tombstone, Arizona (photo by the author) |
Tombstone district. The Tombstone district in southeastern Arizona is primarily a silver district. From 1879 to 1932, >30 million ounces of silver, 36 million pounds of lead and >250,000 ounces of gold were mined with copper, zinc and manganese. Mines include the Lucky Cuss, Bunker Hill, Herschell, Empire, Comet, Contention, Emerald, Girard, Grand Central, Ingersol, Luck Sure, Oregon, Old Guard, Prompter, Silver Plume, State of Maine, Toughtnut, Tribute and West Side. The ore was found as silver-lead ore and silver tellurides in (1) irregular replacements of the Naco Limestone along fissures and crests of anticlines, and (2) in altered porphyry dikes.
Rich bonanza ores were associated with tellurides, particularly the mineral hessite. Reported ore and gangue minerals included hematite, limonite, cerussite, cerargyite (AgCl) (known as horn silver), native gold, native silver, native copper, argentiferous galena, sphalerite, pyrite, alabandite (MnS), malachite, chrysocolla, psilomelane, tetrahedrite [(Cu,Fe)12Sb4S13], hessite (Ag2Te) and wulfenite (PbMoO4) (Wilson and others, 1969; Williams, 1980).
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Inside the Good Enough mine dug into limestones of the Bisbee Formation. Photo by the author. |
The main structure is folded Paleozoic strata intruded by a porphyry dike. Mineralization occurs in quartz and in vertical joints particularly along the edge of the dike, in limestone as replacement deposits and in breccia, and as bedded deposits and fissure veins (Kemp, 1893). Many mines are along the south end of Tombstone and northeast of Ajax Hill in Tombstone Hills.
The Emerald mine enclosed one of the largest ore bodies in the district. The nearby Silver Plume shaft was 1,000 feet southwest of the Emerald where mineralization was hosted by the Abrigo Limestone and Bolsa Quartzite and consists of partially oxidized base metal sulfides with some wulfenite and horn silver in fault breccia. Ore control is related to a steeply-dipping, north-south dike-fissure zone. The ore zone is 1,100 feet long and 10 feet wide. The Emerald shaft as sunk to a depth of 840 feet and the Silver Plume to 788 feet. Underground workings did not reach the limit of the ore. Work was discontinued because of flooding: the pumps were unable to handle the water influx below the water table.
Turquoise (Gleeson, Pearce) district. Copper was discovered 20 miles north of Bisbee and 15 miles east of Tombstone, and a mining camp known as Turquoise was established in 1890 with a nearby town of Courtland. Four years later, gold and silver was found on the Commonwealth property to the north and the town of was Pearce was established. In 1895, a prospector named John Gleeson, prospected south of Turquoise Ridge and found copper and opened the Copper Belle mine and the town of Gleeson was established. Mines in this district continued to operate until copper prices dropped resulting in mine closures in the 1930s. In the southeastern Dragoon Mountains, ridges rise 900 to 1,200 feet above adjacent plains (Hausel, 2013).
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| Stockwork breccia at Commonwealth (photo by the author) |
Geology suggests this area has good potential for discovery of hidden gold and base metal deposits. A variety of deposits have already been identified in a broad, north-south, regional trend. Some of the more significant deposits include the Commonwealth silver and gold deposit at the north end of the district. To the south, two gold deposits of interest include Mexican Hat and Gold Coin.
Notable deposits include gold, silver and or copper prospects at Pearce, Courtland, Gleeson, Commonwealth, Mexican Hat Mountain volcanic-hosted gold mineralization (Tertiary) and the Gold Coin sedimentary-hosted gold project (Tertiary). Turquoise Ridge to the north is separated from the Gleeson Ridge to the south by a narrow gulch, Mexican Hat Mountain lies a short distance north of Turquoise Ridge. The ridge rise 900 to 1,200 feet above the adjacent plains. Quartz monzonite intrudes Paleozoic and older rocks, and granite cuts quartz monzonite and invades Cretaceous rocks.
Mineralization includes: (1) Irregular cupriferous blanket and replacement deposits where quartzite and limestone (Cambrian Bolsa Quartzite and Abrigo Limestone) are thrust over Carboniferous limestone. (2) Irregular, tabular, pyritic lenses in Carboniferous limestone along a contact with quartz monzonite. (3) Manganese, lead, zinc, silver and minor copper and gold in irregular deposits associated with fault and fracture intersections in Pennsylvanian-Permian Naco Group limestones; (4) Near-surface turquoise in stringers in altered granite and quartzite; (5) Spotty base metals with gold and silver in veins in intrusive rocks; (6) Disseminated gold in Tertiary rhyolite and breccia; and (7) Structurally-controlled disseminated gold in faults and breccias in sedimentary rocks. At least 887,000 tons of base metal ore and 250 tons of manganese ore was produced in the past with some turquoise and considerable quartzite for smelter flux.
Two interesting deposits in the district are epithermal gold deposits. Epithermal gold is identified in a mineralized structure 15- to 50-feet wide and 2,000-feet long at Mexican Hat Hill in the central part of the district. The gold is described as free gold on fractures accompanied by hematite and limonite in Tertiary rhyolite and rhyolite breccia. In 1990, Placer Dome and Oneida Resources reported a geologic resource in six mineralized zones to include 10.3 million tons of ore at an average grade of 0.035 opt Au (362,000 ounces of contained gold).
In a press release on January 22nd, 2012 it stated that Auracle Resources Ltd drilled 5 holes at Mexican Hat. The gold is in extensively fractured volcanic rock with abundant limonite/hematite alteration, and in areas of pervasive limonite/hematite within the volcanic hosts. The rocks are highly fractured making drilling difficult.
Drill Hole Results – Mexican Hat
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Hole# From(ft.) To(ft.) Intercept(ft.) Grams/Tonne(Au) _______________________________________________________________________
MH11-001 267 305 38 1.75
337 381 44 2.16
MH11-002 154 182 28 2.49
273.2 349 66 4.19
397 406.8 9.8 2.53
MH11-003 200.8 215.5 14.7 138.30
MH11-004 53.15 125 71. 85 0.41
170.9 194 23.1 0.70
170.9 194 23.1 0.70
471 496 25 1.34
MH11-007 50 70 20 13.40
A similar deposit south of Mexican Hat is the Gold Coin. This is also an epithermal deposit, but hosted by sedimentary rock. Secova geologists collected composite chip samples from trenches that include 45 feet of 0.11 opt Au (with an enclosed 20-foot zone averaging of 0.16 opt Au): the samples began and ended in mineralization. In another trench a composite chip sample yielded 60 feet of 0.06 opt Au (with an enclosed zone of 15 feet of 0.2 opt) (Hausel, 2013b)
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| Visible gold in rhyolite at the Commonwealth mine. (Photo by the author). |
Soil geochemical anomalies show strong signatures of gold, silver, arsenic and antimony. Combined geochemical and geophysical anomalies outline a NNW-trending zone 3,000-feet long by 1,000-feet wide with two other anomalies of 1,000-feet by 1500-feet and 2,800-feet by 750-feet. The area is covered by a thin veneer of soil making outcrop sampling difficult. Brecciated limestone in the mineralized zone has variable clay alteration and moderate to locally strong silicate veining and hematite veinlets. It is assumed that Tertiary gold-enriched fluids were emplaced along northward-trending structures and along sub-vertical to high-angle normal faults. Some Carboniferous limestones have extensive jasperoid alteration and strong limestone decalcification (Moore, 2010).
The Gleeson placers are dry placers with fine gold to medium size nuggets. The gulch west of the Copper Belle Mine has some coarse gold.
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Vein exposed on surface east of the Commonwealth silver-gold mine. Photo by the author. |
The Johnson Camp mine is in the Little Dragoon Mountains about 65 miles east of Tucson. The Mountains consist of a core of Precambrian granite and schist unconformably overlain by Precambrian metasedimentary rocks and Phanerozoic sedimentary rocks. The mine began production in 2008 and Nord Resources planned to reach full production of 25 million pounds of copper/year by the end of 2009. Total proven and probable reserves are reported to be 73.4 million tons of ore at an average grade of 0.34% Cu (492 contained pounds of copper).
Weaver (Rich Hill) district. The Weaver district at the southwestern margin of the Weaver Mountains, is 10 to 12 miles north of Wickenburg and 6 miles east of Congress. Yarnell is 2 to 3 miles to the northwest.
Following discovery of gold, three towns sprang up to support mining and all three developed notorious personalities. According to the Prescott newspaper in 1892, the residents like to “drink blood, eat fried rattlesnake, and fight mountain lions”. The towns of Octave, Stanton and Weaver were established following discovery of gold on Rich Hill followed by discoveries in Antelope Creek and Weaver Creek in 1863. The discovery occurred when a group of men camped along Antelope creek and their guide abandoned them while one member took off chasing a runaway burro. The individual tripped over a pile of gold nuggets described “as big as potatoes” and thus became known as the Potato Patch. A short time later, gold was found on top of Antelope Hill. According to Pauline Weaver, the leader of the group, the gold was so common that he was able to pop out nuggets with his knife. That one acre of ground was later reported to yield a half million in gold (period prices)!
Using a 1863 gold price ($31.23), a half million dollars was equivalent to more than 16,000 ounces. A gold rush followed and Antelope Station grew to 3,500 people. The town, was later renamed Stanton (34°9'54"N; 112°43'48"W) and received its namesake from Chuck Stanton, a notorious prospector who was accused of murdering several people in his quest to control the town and gold properties. Stanton was later killed by a Mexican gunman. The town of Stanton became known as a lawless town. By 1905, Stanton was turned over to the ghosts, but later was partially restored with live people from the Lost Dutchman Mining Association, which set up a member’s trailer park at the townsite.
The nearby ghost town of Octave (34°8'31"N; 112°41’24”W) was built to the east. The town is also a ghost town with much of the former town removed after the second world war. A third town, Weaverville (34°9'18"N; 112°42’25”W) is now a ghost town originally named after Pauline Weaver. The location of the town is in the Weaver Creek drainage between Octave and Stanton. Weaverville was renamed Weaver. The town at one time was under the control of bandits led by Francisco Vega.
The surrounding Weaver Mountains are formed of granite, diorite, and schist, intruded by aplite, pegmatite and mafic dikes, locally covered by lava. Mesothermal gold-bearing quartz-pyrite-galena veins occur in gently north-northwestward dipping fault zones.
The three largest lodes in the region are the Congress-Niagara-Queen mine in the adjacent Date Creek district which produced 700,000 tonnes of ore averaging 0.62 opt Au, the Octave (800,000 tonnes at 0.26 opt Au), followed by the Alvardo mine within the Weaver district. Several other mines exposed similar veins including Beehive, Commodore, Jerome, Leviathon, Minica, Rincon, Yarnell and others. These have shallow 15- to 50oNW-dipping quartz veins in shears and thrusts in and along diorite and rhyolite dikes within Precambrian granite and granodiorite (locally gneissic). The veins are oxidized near the surface with minor pyrite and lessor galena, chalcopyrite and sphalerite with minor silver. The district was the second largest gold-silver vein producer in Arizona after Oatman.
The Weaver and Rich Hill placers cover an area of approximately 5 by 8 miles and gold placers are scattered all over the hill sides and valleys in the area around Antelope and Weaver gulches, 6 to 8 miles east of Congress Junction. The more productive placers are in the northern half of the area. On Rich Hill, gold is found on bedrock where boulders and thin layers of clay are found. In the drainages below Rich Hill, iron-stained gravel and sand is more than 10-feet thick with abundant subangular boulders 2 to 6-feet in diameter. The Weaver Mountains rise to more than 2,000 feet above the adjacent desert plain to the south. Rich Hill attains an elevation of 5,200 feet and sits between the deeply eroded canyons of Antelope Creek on the west and Weaver Creek on the east. Since the higher portions of the Weaver Mountains receive at least 18 inches of rainfall per year, the two south-flowing creeks often have some water in their upper courses and are subject to torrential floods during rainy seasons. The flash floods often dislodge gold from the nearby veins to recharge the gold placers. An estimated 110,000 ounces of gold were recovered from the area.
In the early 1860s, Indians trading at LaPaz on the Colorado River reported finding gold to the east. One was persuaded to guide a party to the area that included Capt. Pauline Weaver, Maj. A. H. Peeples, and others, camped at the base of Rich Hill, after their guide had deserted them on the desert north of Wickenburg. A Mexican in the group, while looking for their strayed animals, discovered loose gold nuggets on top of Rich Hill. This discovery led to placers along Weaver and Antelope creeks.
This entire area was subjected to a gold rush, and in five years, produced about $500,000. Gold found underneath boulders and in crevices of rocks on Rich Hill was easily gathered, but more effort was required for sluicing for gold. As much as $40,000 is said to have been taken from a certain acre, and the production of the whole area prior to 1883 was estimated at $1,000,000. The value of known output from the Weaver and Rich Hill placers since 1900 has been approximately $150,000, of which $83,975 was recorded for the years 1905-31, and $62,049 for 1934-49.
Approximately fifty men were carrying on sluicing and rocking in this field during the winter of 1932-33, but their number decreased to eighteen with the advent of summer. Minor amounts of dry-washing have occurred in the vicinity of Oro Fino Gulch, in the southern part of the area.
The placer ground covers an area of approximately 8 by 5 miles. The most productive portions were in the northern half of this area and included about 10 acres on top of Rich Hill; portions of the sides of Rich Hill; channels and benches of Weaver, Antelope, and other washes; and gravel benches that lie between these washes.
Rich Hill is underlain by intensely jointed granite. It is cut by thin, lentIcular, quartz veins which carry pyrite, galena, and gold. The top of this mountain is a hilly mesa about 8 miles long that represents an erosional remnant of the elevated Weaver pediment. It includes several acres of broad, shallow basins and drainage channels whose granite floors are mantled by granite boulders and very thin, rusty, sandy soil. A few angular pebbles of quartz and hematite are locally present. The once-abundant placer gold in the shallow basins and drainage channels is proclaimed by numerous old workings that scoured every square foot of their surface.
Along washes and benches below Rich Hill, placer material consists of iron-stained gravel and sand, up to 10 or more feet thick, together with abundant subangular boulders 2 to 6 feet in diameter. One nugget worth $450, and three worth a total of $1,008 were found. The largest nugget found on upper Weaver Creek was worth $396, and two chunks of quartz contained $450. In the spring of 1931, a large nugget (known as the Ehrhart nugget) was described with a general outline shape similar to a human molar approximately 53 mm across the widest portion of the roots, and 47 mm from the bottom of the 'root' to 'the crown and weighed 8.71 ounces.’ Several fragments of slightly iron-stained quartz remain in the center of the mass. The total weight is 270.90 grams: the nugget consists of 252.38 grams of metal, 18.52 grams of quartz and 22.71 grams of silver .
During the 1932-33 season, a few nuggets ranging up to more than 3 ounces each in weight were found along Weaver Creek. Two nuggets, each weighing more than 5 ounces, were found in upper Antelope Creek. Away from the mountains, the coarse gold becomes progressively rare.
Wickenburg district. According to historical accounts, a prospector by the name of Henry Wickenburg was searching for gold along the Hassayampa River (a dry river much of the year) when he spotted a dark, iron-stained, outcrop on a hill (Quartz Butte) to the west. On close examination, he found visible gold in outcrop and filed a claim for the vein in 1863.
Wickenburg’s initial samples assayed 6-opt Au. Instead of mining, he sold ore to local prospectors for $15 per ton. The miners hauled ore to the Hassayampa River where the rock was processed in arrastras wherever water could be found in the intermittent stream. In 1866, Wickenburg sold his interest to the Vulture Mining Company and the company constructed a 40-stamp mill near the present town site of Wickenburg and gold was recovered from high-grade ore that ran 1.2 to 4.5 ounces per ton.
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| Lode vein at the Vulture mine (photo by the author) |
Early mine development focused on the western portion of the vein. High-grade ore was hauled by wagon to the mill and high-grading occurred both in the mine, at the mill and on the haulage wagons. This apparently became a serious problem for the mine owners.
In 1868, the western extension of the vein was mined by a separate operation known as the Smith group, which built the Smith mill 10 miles east of the mine to process their ore: this mill had 20 stamps. At least three mills were initially constructed because of divided property ownership. The third mill was constructed 3 miles north of the Smith mill at Seymour. In 1870, it was reported 300 miners were employed by mine operations and Vulture City had about 500 residents.
When the mine reached the 240-foot level, a rich pocket of gold was intersected where the vein swelled to 47-feet wide. This shoot produced ore that contained 7 to 12.5 ounces per ton gold. In 1872, the vein appeared to pinch out in the eastern portion of the mine and operations refocused on the western portion. In 1879, the Arizona Central Mining Company purchased the property and constructed a 16-mile long waterline from Wickenburg to the mine site and expanded mill operations with an 80-stamp mill. Mining continued on the western vein extension until the eastern vein extension was rediscovered at depth.
Nine years later (1888), the vein was again lost. The vein was cut by a fault known as the Talmadge Fault that sliced the vein on the 300-foot level and the vein had been down-dropped to an unknown depth. At the time, mining operations were restricted to the western portion of the vein above the fault and it wasn’t until 20 years later (1908) that a comprehensive geological study was conducted that led to the discovery of the vein offset. The mine reopened and ore was again processed to recover gold on amalgamation plates while tailings were stored for cyanide treatment. A new mill was constructed in 1910 that had 20 stamps with a capacity of 100 to 120 tons per day. Water wells were drilled. One intersected groundwater in a gravel lens beneath a lava flow at 400 feet deep. Another well was drilled to 1,000 feet before hitting water.
The mine operated until 1917 when the vein was again lost. This time it had been offset along a second fault (Astor Fault) on the 950-foot-level in the eastern portion of the mine. The Astor fault cut the vein also displacing it somewhere down dip.
Exploration for the offset vein began with the sinking of a 500-foot winze sunk from the 1050-foot-level. The vein offset was discovered on the 1,550-foot mine level and operations continued until the mine was closed by the War Production Board in 1942. At this time in history, the War Production Board closed all non-essential mines in the US to ensure maximum energy was directed towards the war effort. Many mines that were closed by the order never reopened, suggesting that at today’s gold prices, many of these likely have commercial ore.
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Glory Hole at the Vulture mine with ghost town in background - photo by the author. |
The Vulture mine sits at the southern edge of the Vulture Mountains 50 miles west-northwest of Phoenix. The basement (oldest exposed crustal rock) in this area is Proterozoic (2.5 to 0.6 billion year old) metamorphic and igneous rock (schist and gneiss) intruded by Cretaceous (145 to 65 million year old) granite and granodiorite that is unconformably overlain by lower to middle Miocene (23 to 5 million year old) volcanic (rhyolite and andesite) and sedimentary rocks. All of these have been tilted by rotational (normal) faulting such that the original bedding is now near-vertical to overturned. The Vulture vein is associated and related to the granite pluton.
The mineralized zone at the Vulture mine is fault controlled with the vein trending east-west nearly parallel to foliation with a dip of 45oN. The vein was traced 1,000 feet on the surface and is 32 feet wide on the surface. It is a complex mix of quartz and schist, such that mineralized quartz (about 6 feet thick) lies adjacent to footwall schist. The vein is overlain by chlorite schist followed by a large 30 to 50 foot thick quartz vein that includes low-grade white quartz and quartz with brecciated schist. The hanging wall is composed of chlorite schist and granite porphyry while the footwall is sericite schist. The vein was quarried on the surface in two, small, gossan-stained small open pits.
Gold mineralization occurs within and adjacent to a north-dipping quartz vein and quartz porphyry dike that extends eastward from the granite pluton. Gold is concentrated in quartz veins and in silicified and altered rock within and adjacent to the dike. The precious metal occurs as native gold or electrum and is also associated with pyrite, galena and minor chalcopyrite and sphalerite. There is a positive correlation between gold and secondary silica and sulfides. Granitic breccia clasts become progressively more common to the west in the vein. Where the vein extends into the granite pluton, it splits into smaller veins prior to pinching out.
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| Assay lab at the Vulture mine. Photo by the author. |
The geology suggests ore shoots occur en echelon in the vein. Another undeveloped shoot was proposed to occur further east and at greater depth that those mined in the past. In the area overlying this proposed ore shoot; surface rock exposures include Miocene volcanic tuffs and lavas which cover the older Proterozoic schists and gneisses. The metamorphic rocks are again found 3,000 feet further east where they show some evidence of mineralization. The faults which offset the Vulture vein are not exposed at the surface and are buried under gravel and lava.
Pervasive wall rock alteration adjacent to the vein resulted in replacement of feldspar and mafic (dark) minerals by sericite, hematite and clay. The gold was reported to be 760 to 780 fine. Production figures are incomplete. Available reports indicate the mine produced at least 340,000 ounces of gold and 260,000 ounces of silver from ore that had an overall average grade of 0.35 opt gold and 0.25 opt silver.
In recent years, there was an effort by preservationists to push the State of Arizona into purchasing the Vulture mine and ghost town and withdraw the property from mining. Such activities tend to set a dangerous precedent in letting government nationalize private property and control private land and businesses. Such activities lead to corruption and mining companies avoiding some states and regions. For now, Arizona’s Vulture mine appears to have weathered the effort to have the State of Arizona purchase private property and more recently, the property was optioned by a Canadian company: Source Gold Corporation. Read more about this mine and district at the Mining Journal.
Union Pass district. Union Pass to the northwest produced 128,000 ounces of gold and 313,000 ounces of silver from 1865 to 1942. The Virginia district to the north yielded 17,800 ounces of gold and 17,700 ounces of silver, with some copper and lead from 1907 to 1955. The Pilgrim district to the north produced 48,000 ounces of gold and 72,000 ounces of silver from 1929 to 1945, while the San Francisco (Oatman) district itself, contributed 2.2 million ounces of gold and 800,000 ounces of silver.
The Katherine mine was developed on a vein in sheared granite near the Colorado River. This vein had a width of >60 feet at the surface and pinched at depth. It was traced for and 1,700 feet along strike. The mine was developed to a depth of 900 feet.
Many mineralized faults in the district are poorly exposed and some are hidden under gravel. The veins are simple, being tabular bodies of quartz and calcite with well-defined walls, while others consist of several vein stringers separated by barren rock. These consist of quartz, calcite, andularia, fluorite, gold and silver.
Wallapai district. The Wallapai is located near the center of the Cerbat Mountains, which extend north of Kingman in western Arizona and enclose the Chloride, Mineral Park, Cerbat and Stockton camps. The Cerbat Mountains are an eastward-tilted fault-block of Precambrian metamorphic and igneous rock intruded by Tertiary granite porphyry. Mineralization consists of copper in shattered granite porphyry and lead-zinc veins with associated by-product gold and silver. The veins are superimposed upon and grouped symmetrically around the porphyry copper mineralization. Turquoise deposits formed in the supergene enriched porphyry cap. A late fault cuts both bedrock and alluvium at the western base of the range. This fault and surrounding alluvial blanket contains chrysocolla at the Emerald Isle copper deposit.
Yarnell district. The Yarnell lies along the southern edge of the town of Yarnell in the Weaver Mountains north of Phoenix. The district lies within Precambrian granodiorite. Mineralization occurs as gold in veins in the Yarnell fault. The gold grades are the highest in the vein within the fault and values decrease away from the fault. The grades and width of mineralization appear to decrease long strike but are open down dip.
CONCLUSIONS
Eastern Arizona has several important mines and known mineral deposits with potential for discovery of additional gold and copper resources in essentially every district. Areas of notable interest for gold are the Gleeson, Oro Blanco and Copper Creek districts. Western Arizona has many more primary gold deposits than eastern Arizona and there are a number of lode, placer and dry placer deposits that suggest several deposits likely remain hidden and undiscovered. Some notable deposits in western Arizona include the Vulture mine and Rich Hill within the Wickenburg district, the Katherine and Oatman properties in the San Francisco district, prospects in the Wallapai district, gold in Lost Basin district, and gold in the La Paz district within the Dome Rock Mountains, Plomosa Mountains and La Posa plain between these two mountain ranges. These will be discussed in a follow-up article on Arizona.
So how much is the mineral wealth in Arizona? The Arizona Department of Mines and Mineral Resources reported $7.6 billion in minerals were mined in 2007 – much of this wealth was from copper and precious metals. So what does government obtain from this? The answer is taxes and the state of Arizona gets jobs? It is very likely that more jobs and a greater tax base could be created by stabilizing the border with Mexico, creating incentives for exploration companies and gold prospectors to explore, and most of all, significantly cut taxes and government bureaucracy. All too often in natural resources, permitting is duplicated at the county, state and federal levels. For instance, while drilling for diamonds in Colorado a couple of years ago, a company I was consulting for was required to obtain the same permit (with different requirements) from three different government agencies. Without mining, we would fall back into the stone age. Stop, think! Is there anything around you that was not mined?
