Tombstone Mining District, Southeastern, Arizona

Tombstone Uber

Doc Holiday, Wyatt Earp, the OK Corral, gunfights, silver mines, lead bullets - all come to mind when most think about Tombstone. But for me, I visualize ‘the middle of nowhere’.

In 1877, a prospector named Ed Schieffelin discovered silver in ‘the middle of nowhere’ and staked two claims: ‘Tumbstone' and ‘Graveyard’. Soon a town and mining district were organized and acquired the name ‘Tombstone’ after making a spelling correction. And after all of these years, the town still remains in ‘the middle of nowhere’. But if you are into mines and gun fights, you’ll want to journey east of Tucson to see Wyatt Earp and the Clantons rise from dead and again shoot it out in downtown Tombstone.

The Tombstone mining district was organized in the 19th century because of discovery of rich silver bonanzas. The town lies 65 miles southeast of Tucson at an elevation of 4,500 feet and can be accessed from I-10 by taking the Benson exit and driving 20 miles south along Highway-80. Essentially all of the historical silver, lead and manganese mines lie west and south of the town in a block of land west of Highway 80, south of Highway 82, north of Highway 90, and east of the San Pedro River. 

Location map, southeastern Arizona

After the first mines began producing in 1878, a lack of water forced the operators to build concentrating mills along the San Pedro River 7 to 10 miles west of Tombstone at Charleston (31°38'5"N; 110°10’35”W), Contention City (31°45’59"N; 110°12’1”W), Emery City, Fairbank (31°43'23"N; 110°11’20"W) and Millville. These mill towns grew to 600 to 800 habitants, and at the same time, Tombstone soared to a population of 1,500, making it the largest town in Arizona in 1881. The Tombstone district not only surrounded the town and associated mill sites, but also enclosed mines and mineral deposits in the Tombstone basin adjacent to the town, the Tombstone Hills further south and southwest of town, and in the Charleston Hills adjacent to the Pedro River valley (Hausel, 2019) 

History. The first claim in the area was staked in 1857, but the claimant was murdered by his Mexican employee and nothing became of the discovery. This was followed by the outbreak of Civil War in 1861. With nearly all US troops diverted from Arizona to assist in the war effort, the Arizona territory became a lawless land of roaming Apaches and Mexican bandits. 

Tombstone district with nearby Charlston and Fairbank ghost (mill) towns.

Twelve years after the Civil War ended, prospector Ed Schieffelin filed claims on weakly mineralized rock in 1877. While prospecting nearby, he later discovered rich silver ore at sites he named Lucky Cuss (31°42'5"N; 110°4’54”W) and Toughnut (31°42'37"N; 110°3’59”W) which started a silver rush. 

Rich silver ore at the surface was oxidized and easily mined and milled, but the ore had to be transported to mill sites on the San Pedro River at considerable cost. After mining for three years. groundwater was encountered in 1881 at a depth of 520 feet in the Sulphuret shaft (31°42'16"N; 110° 3'47"W). Nearby, groundwater in the West Side mine (31°42'25"N; 110°4'2"W) was pumped with Cornish pumps and used in the newly constructed Girard 20-stamp mill at Tombstone; thus eliminating the need to haul ore to the San Pedro River. In the same year, the Benson Smelting and Refining works was built to treat silver-lead ore. Both the Corbin and Girard mills at Tombstone were later modified by adding small water jacket smelting furnaces.

As mines were dug deeper, more operations encountered groundwater. In 1884, the Charleston and Boston mills closed leaving only the Grand Central mill operating on the San Pedro River. By 1886, many of the large ore bodies had been mined down to the water table but production began to fall due to inefficient pumps and difficulties with milling non-oxidized ore below the water table. The pumps at the Grand Central mine burned leaving the mine to flood. In 1906, the Boom Shaft was sunk to a depth of 1000 feet and water was pumped at a rate of 3,000 gallons per minute. In 1909, boilers in the mine caused the pumps to seize on the 1000 foot level flooding the mine: the overtaxed boilers ruptured. New pumps and boilers solved the problem but at a very high cost and falling silver prices made many mines uneconomic. 

In 1878, silver was worth about $1.10/ounce, but the value began to decline. By 1892 the price had dropped to $0.63. By 1894, many mines closed and over the next several years, silver prices fluctuated and dropped below $0.50 in both 1903 and in 1916. After the first world war (1914-1918), silver prices bounced back and in 1920 rose to nearly $1.50/ounce before taking a nose dive during the Great Depression. Low silver prices during the first world war had been attenuated by high manganese prices. Manganese found in the district was needed in the war effort and used for steel hardening, but low prices during the depression turned out to be too much for most mines.

From 1879 to 1932, the district produced 29,843,800 ounces of silver, 35,669,800 pounds of lead, 271,000 ounces of gold, with some copper, zinc and manganese valued at about $745 million at today’s prices. From 1970 to 1985, an additional 2 million ounces of silver and 10,000 ounces of gold were mined. But the decline in silver prices more than anything sealed the fate of the district. Some mining occurred as late as 1985, when Tombstone Exploration operated an open pit mine on the Contention vein (31°42'15"N; 110° 3'42"W) and mined 3,000 tons of low-grade ore per day that averaged 1.25 opt Ag and 0.02 opt Au recovered through cyanide leaching, but the district was just a skeleton of its boom days. 

Copper-silver replacement mineralization of limestone.

In total, more than 165 mine names and 97 different ore minerals were recorded in the district (Butler and others, 1938). The mines included the Black Eagle, Bonanza, Boom shaft, Bunker Hill, Comet, Contention, Dry Hill, Emerald, Empire, Engine, Flora Morrison, Free Coinage, Girard, Grand Central, Head Center, Hershell, Ingersol, Little Joe, Luck Sure, Lucky Cuss, Mamie, Merrimac, Montezuma, Northwest, Old Guard, Oregon, Prompter, Pump, Randolph, Sailor, San Pedro, Silver Thread, Skip, Solstice, State of Maine, Tombstone Extension, Toughnut, Tranquility, Tribute, Vizina, and West Side along with dozens and dozens of prospect pits and trenches. In recent years, mine tours were available at the Good Enough mine at the south end of town (31°42'40"N; 110°4’1”W) (Butler and others, 1938).

MINERALS. Minerals reported in the Tombstone mines include hematite, limonite, cerussite, horn silver, and gold with locally abundant argentiferous galena, sphalerite, pyrite, alabandite, malachite, chrysocolla, psilomelane and wulfenite. Other minerals identified in the district included fluorite, calcite, barite, brachantite, chlorargyite, chalcocite, clinozoisite, cuprite, hemimorphite, mimetite, quartz, smithsonite, tetrahedirte, tremolite and willemite.

GEOLOGY. Tombstone lies within the Basin and Range province with alternating northerly-trending Precambrian-cored ranges that are unconformably overlain by folded and faulted layered Phanerozoic (< 600 million years in age) sedimentary and volcanic rock separated by broad alluvial basins filled with thick layers of Phanerozoic sedimentary rock. The Tombstone Hills south of town form a group of low-lying hills that extend north from the Mule Mountains and continue south to the Bisbee mining district.

The basement rock of Tombstone is 1.7 billion year old Pinal Schist (Precambrian), which was intruded by porphyritic and gneissic granite. In parts of district, these old rocks are unconformably overlain by 4,000 to 5,000 feet of Paleozoic sediment that includes quartzite, limestone, and siltstone ranging from Cambrian (541 to 485 million years old) to Permian (about 299 to 252 million years old). Overlying Mesozoic rocks (252 to 66 million years old) contain limestone, conglomerate and shale. Mesozoic rocks are in turn overlain by thin layers of Cenozoic (66 million years old to present) sediment that include Gila conglomerate, caliche, gravel, sand and silt. 

Paleozoic rocks in this region include Balsa Quartzite and Abrigo Limestone (Cambrian), Martin Limestone (Devonian), Escabrosa Limestone (Mississippian) and Naco Limestone (Pennsylvanian to Permian) all potential hosts for mineralization. In particular, the Naco limestone and dolomitic beds are described as favorable hosts by Butler and others (1938) for ore at the Luck Sure (31°41'50"N; 110°4'32"W), Lucky Cuss (31°42'5"N; 110°4'54"W), Oregon (31°41'34"N; 110°4'46"W) and Prompter shaft (31°41'32"N; 110° 4’32”W). 

The Naco Formation is unconformably overlain by Mesozoic conglomerates, thick-bedded quartzites and shales with a few thin limestone beds including those of the Bisbee Group (Cretaceous age) which contained many silver-lead deposits including those mined at the Randolph, Mamie, and Bonanza mines. The Bisbee Group was intruded by granodiorite and andesite porphyry dikes and the entire succession was folded and faulted. Late Cretaceous igneous rocks are exposed in the western and southern portions of the district and granodiorite dikes are exposed throughout the central part of the district.

The western region of the Tombstone Hills is structurally simple with exposed intrusive rocks and associated contact metamorphic sedimentary rock; whereas, rocks in the Tombstone Basin are more structurally complex. Rocks in the Tombstone Basin were folded into (secondary) anticlines and synclines that have general trends of N40oW to N65oW. Third order folds expressed as corrugations on the anticlines and synclines were termed ‘rolls’ by the early miners. These rolls also provided favorable sites for mineralization.

Intrusion of granodiorite (an intrusive igneous rock simiar to granite) was accompanied by metamorphism prior to mineralization. The intrusion of the Schieffelin Granodiorite during the Laramide orogeny (85 to 43 million years ago) resulted in baking and metamorphism of Bisbee Group rocks in the Tombstone Basin. Silver mineralization and rock alteration are dated at 74.5 million years and 72 million years old, respectively, suggesting that mineralization was related to the emplacement of the Schieffelin granodiorite (76 million years old) and the Uncle Sam porphyry (73.5 million years old). Other igneous rocks in the area include quartz monzonite porphyry and rhyolite (63 million years old) in the Tombstone Hills. 

Contact metamorphism adjacent to the granodiorite is characterized by rocks with secondary wollastonite, garnet and epidote. In the western area, the Uncle Sam Porphyry represents the extrusive (volcanic) equivalent of the Schieffelin Granodiorite. The granodiorite cuts most NE-trending faults in Bisbee Group sediments, which are also cut by porphyry dikes that intrude the faults. Some mineralization in the western portion of the district follows the faults postdating the intruded dikes. Most sedimentary rocks in the area are metamorphosed to spotted hornfels and includes hornfelsic schist and quartzite recrystallized from Bisbee Formation shale and sandstone. Limestone in both Bisbee and Naco rocks recrystallized and jasperoid was deposited in the basal novaculite member of the Bisbee Formation. 

The Tombstone Basin forms a syncline enclosing a series of smaller NW-trending anticlinal and synclinal folds (‘rolls’). To the west, the basin is truncated by the Schieffelin Granodiorite. Granodiorite dikes intrude many pre-existing faults and many faults and fissures were mineralized during the intrusion of the granodiorite resulting in NE-trending fissure veins expressed by a NE-alignment of mine shafts and prospect pits. There is evidence for several episodes of faulting and brecciation, some are mineralized and others are not. 

Mines of the Tombstone district (after Hausel, 2018, 2019).

MINERALIZATION. Mineralization in the Tombstone district consisted of erratically distributed oxidized lead and silver ore and some locally enriched gold placers. Much past mining focused on secondary supergene enriched ore found in structural traps along roll crests similar to petroleum traps. Primary mineralization was found along structural conduits (faults and fractures) which provided plumbing for overlying and adjacent replacement deposits in the structural traps. 

According to Force (1994), the The Bisbee Group is the main host for silver and includes 1,400- to 2,100-feet of conglomerate, quartzite, sandstone, limestone and argillite, with favorable horizons such as: (1) novaculite, (2) Blue Limestone, and (3) stratigraphically higher thin limestones interbedded with argillite. In addition, brecciation of silicified rock units during deformation resulted in favorable structural sites for some mineralization. Favorable structural zones include: (1) Tranquility fault set, (2) fissures, porphyry dikes and decollements (basal detachment faults) and (5) anticlinal rolls. (of note are detachment faults, which form a belt of gold deposits running northwesterly to southeasterly through Arizona) (Hausel, 2019). Mineralization includes erratically-distributed, oxidized, lead and silver ore, and rare, locally-enriched gold placers. Past mining focused on secondary supergene enriched lodes associated with structural traps along ‘roll’ crests similar to petroleum traps. Some primary mineralization occurs in structural conduits (faults and fractures) which provided plumbing for replacement deposits in overlying structural traps (Force, 1994). 

Ore deposits in the district include: (1) irregular limestone replacements along fracture and breccia zones that follow anticlinal (rolls) high points; (2) fissure veins; and (3) replacements of altered porphyry dikes. Some limestone replacement deposits were large: the ‘Blue limestone’ and ‘novaculite’ of the Bisbee Group of rocks provided favorable host rocks for these deposits but much of the good ore was recovered at groundwater level in a zone of supergene enrichment at 550 to 700 feet deep (such supergene zones form where mineralization is oxidized near or at the surface and is mobilized in oxygen-rich meteoric water that works downward through fractures over eons of time and deposits near the water table where it loses oxygen causing precipitation, and enriching already existing ore). 

Primary ore deposition occurred where ascending, hot, mineral-rich fluids from granodioritic magma followed fractures and faults in brittle quartzite and hornfelsic shales to produce fissure veins. Where these ascending fluids came in contact with limestone, the rock was partially replaced by ore. In places where the limestones were capped by unshattered, competent shale, the cap provided an impermeable barrier to the fluids similar to a petroleum trap resulting in the mineralizing fluids spreading throughout the capped limestone to produce rich replacement deposits. 

Many fissure veins were found in Bisbee Group quartzites and hornfels and replacement deposits were found in the Blue Limestone and Novaculite of the Lower Bisbee Group and the uppermost beds of the Naco Group. The “10-foot” and “Blue Limestone” were folded into tight anticlinal flexures producing fracture permeability. Being capped by impermeable hornfelsic shales made these rocks favorable beds for mineralization. 

Silver was found in galena, tetrahedrite and in some pyrite. A sample of massive pyrite from the Sulphuret mine assayed 4.18 opt Ag. Psilomelane (manganese oxide) generally contained less silver and lead and more copper than the oxidized sulfide ores which often had silver contents less than 20 opt. Even so, some manganese ore from the Prompter mine averaged 35 opt Ag. Silver to gold ratios of the ore was 6:1 in value. Gold appears to be locally enriched in the district. For example, Wilson and others (1967), describe a sample from a 140-foot-drift dug 90-feet below the water level in the Contention mine assayed >5 opt Au. And two shipments of ore from the Lucky Cuss mine averaged 1.7 opt Au.

The Skip-Shaft fissure was mineralized 900 feet along strike and more than 600 feet below the surface. The fissure produced ore at depth from the Naco Group to about 400 feet above the Blue Limestone in the Bisbee Group and was most productive within the Blue Limestone.

In the western portion of the district, mineralization is mostly lensoidal quartz veins and thin selvages of sheared and altered wallrock along steep faults and as mineralized porphyry dikes. Mineralization in the Tombstone Basin occurs at several horizons in the Bisbee Group including: (1) the ‘novaculite’ or a silicified, bleached argillite with interbedded limestone and limestone pebble conglomerate, (2) the Blue Limestone, and in (3) stratigraphically higher thin limestones interbedded with argillite at the top of the lower unit, particularly along the Tranquility-Contention structural trend (fault).

It was reported that a 140-foot drift dug 90-feet below the water level at the Contention mine yielded an assay of more than 5 ounces of gold per ton. Two shipments of ore from the Lucky Cuss mine averaged 1.7 opt Au. So, gold values were locally high.

Often, people get the erroneous impression that there are no ore deposits remaining simply because of a lack of operating mines. However, there is considerable unprospected ground in-between many linear-trends that only have a few prospect pits. Unknown amounts of ore was left below the water table due to the refractory nature of the ore and we have no idea how much low grade ore was left underground by the miners. Thus, the possibility for additional discoveries in this district is considered very good.

MINING

I highly recommend some excellent videos of Tombstone mines by TVR Exploring and others. These will give you a good perspective of some challenges of modern exploration as well as past mining, and the beauty of the historical mines. As you watch, note miners left considerable unmined low-grade ore throughout the mines and district, and much of of the district remains unexplored by geophysical methods as well as drilling in search for deep and shallow missed deposits. Currently, there is some modern exploration in the district by Tombstone. Every metal mining district in the world contains considerable unmined resources and many also have large, unexplored areas that could lead to discovery of enormous resources! Be sure to watch the Girade mine videos to see some of the fascinating artifacts left in these old mines. And also be sure to visit the Abandoned and Forgotten Places youtube site - an abandoned mine explorer and friend!

REFERENCES

Butler, B.S., Wilson, E.D., and Rasor, C.A., 1938, Geology and Ore Deposits of the Tombstone District, Arizona: University of Arizona Bulletin143, 108 p.

Devere, Jr., B.J., 1978, The Tombstone mining district history, geology and ore deposits: NM Geological Society 29th Field Conference Guidebook, p. 315-320.

Force, E.R., 1996, The Bisbee Group of the Tombstone Hills, southeastern Arizona - stratigraphy, 

structure, metamorphism and mineralization: US Geological Survey Bulletin 2042-B, 22 p. 

Hausel, W.D., 2020, Gold in Arizona - A prosector's Guide: GemHunter Books, Amazon, Kindle.

Hausel, W.D., 2019, Gold in Arizona - A Prospector’s Guide: GemHunter Books, Amazon, 376 p.

Hausel, W.D, 2016, The Tombstone Silver-Lead District, Arizona: CMJ Prospecting and Mining Journal, v. 85, no. 8.

Hausel, W.D., 2011, Eastern Arizona Gold and Base Metal Deposits (Part 1): CMJ Prospecting & Mining Journal, v. 80, no. 6, p. 27-35.

Hausel, W.D., 2011, Eastern Arizona Gold and Base Metal Deposits (Part 2): CMJ Prospecting & Mining Journal, v. 80, no. 7, p. 13-65.

Hausel, W.D., 2010, Gold in Arizona: CMJ Prospecting and Mining Journal, v. 80, no. 4, p. 31-

59.

Rassmusen, J., 2012, Geology, Mines and Minerals of Tombstone: Minerals of Arizona, 12th Annual Symposium, p. 1-5.

Wilson, E.D., Cunningham, J.B., and Butler, G.M., 1934, Arizona Lode Gold mines and Gold Mining: Arizona Bureau of Mines Bulletin 137.

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