The Tombstone mining district-history, geology and ore deposits

New Mexico Geological Society

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Devere, B. J., Jr.

1978, pp. 315-320. https://doi.org/10.56577/FFC-29.315

in:

Land of Cochise (Southeastern Arizona), Callender, J. F.; Wilt, J.; Clemons, R. E.; James, H. L.; [eds.], New Mexico

Geological Society 29

Annual Fall Field Conference Guidebook, 348 p. https://doi.org/10.56577/FFC-29

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New Mexico Geol. Soc. Guidebook, 29th Field Conf., Land of Cochise, 1978 315

THE TOMBSTONE MINING DISTRICT

HISTORY, GEOLOGY AND ORE DEPOSITS

B. J. DEVERE, JR.

ASARCO, Incorporated

Tucson, Arizona

INTRODUCTION

The Tombstone mining district, located in a small group of

hills 6 mi north of the San Pedro River and 65 mi southeast of

Tucson, Arizona, was one of the rich "bonanza" silver districts

of the late 1800's. Mining commenced in 1878, escalated

rapidly until 1882, and then slowly declined until the last

mine closed in the late 1930's. The total production from

1878-1957 amounted to approximately one million tons of

ore worth about $39,000,000; of that total value, half was

derived from the production during the seven-year period

1879-1886 (Wilson, 1962).

The district has been described in the literature by Blake

(1882), Church (1903), Ransome (1920), Butler and others

(1938), Gilluly (1956) and Newell (1974). Of these works,

that by Butler and others was the most extensive and detailed.

The accompanying geologic map and section (figs. 4, 5) are

from their publication and have been reproduced without

modification.

HISTORY

Ed Schieffelin discovered silver chlorides and lead carbon-

ates in a quartz vein in the southwestern part of what became

the Tombstone mining district in the late summer of 1877. On

the third of September, 1877, he recorded his "Tumbstone

Mine" and "Graveyard" claims in Tucson, County of Pima,

Arizona Territory (Devere, 1960). After recording his claims,

it took Schieffelin almost a year before he could raise suffi-

cient money and convince his brother Al, and Richard Gird, a

mining engineer, to join him in developing his discovery. The

vein proved to be small and poorly mineralized, so while the

disgruntled Al Schieffelin and Richard Gird attempted to

mine, the ever-optimistic Ed Schieffelin prospected further to

the north and east, and in two successive days, discovered the

large, rich lodes of the Lucky Cuss and Toughnut silver de-

posits (Butler and others, 1938).

With the discovery of the Lucky Cuss and Toughnut lodes,

the Tombstone silver boom was born. In rapid succession, the

lodes of the Goodenough, Grand Central, Contention, Vizna,

Empire and Tranquility mines were discovered. A town,

named after Schieffelin's original claim, the Tombstone (fig.

1), was established and mills were built on the San Pedro River

at what became the towns of Charleston, Contention and Fair-

bank. The "Arizona Weekly Star" of November 2, 1879,

reported that Tombstones' petition for incorporation had been

granted by the Pima County Board of Supervisors. The town

boasted a population of 1000-1500, while Charleston, a mill

town on the San Pedro River claimed 600-800 inhabitants

(Devere, 1960).

The silver-lead ores were high grade, near surface and easily

extractable. The only problem was the lack of local water for

milling; therefore mills were built along the San Pedro River

and ore was transported the 9 mi at a cost of $3.50 per ton

(Blake, 1882). That problem was solved in 1881 when water

was encountered at a depth of 520 ft in the Sulphuret mine.

With water, the future for mining seemed bright, but the water

that was thought to be the mines' savior, turned into their

executioner. In 1886, the pumps at the Grand Central mine

burned, leaving only the Contention mine pumps to handle the

water. Those pumps were inadequate, forcing the suspension

of all mining below the water table. From 1886-1901, mining

was at a low ebb, being carried on largely by lessees.

In 1901, the Grand Central Company, the Tombstone Mill

and Mining Company and the Contention Company were

joined to form the Tombstone Consolidated Mines Company.

With the joining of the three companies, the majority of the

larger mines in the district were consolidated and the decision

was made to once again pump the water and develop the

deeper ores. The company sunk the four compartment Boom

shaft, constructed a new 125 ton per day cyanide mill and

reconditioned the old levels in the Grand Central, Contention,

Empire, Lucky Cuss, Silver Thread, Toughnut and West Side

mines. By 1906, the Boom shaft had reached the 1000-ft level

and water was being pumped at the rate of 3000 gpm (fig. 2).

The deeper ores were only partially oxidized, so in the same

year the cyanide mill was converted and expanded. Using

stamps, slime cones, Wilfley tables and cyanide tanks, the mill

operated at a capacity of 225 tons per day (Butler and others,

1938). Independent mines reopened and mining at Tombstone

regained some of its old vigor. Silver was selling for 67 cents

per ounce, lead at 5.6 cents per pound and gold at the fixed

price of $20.67 per ounce.

In June 1909 water again dealt Tombstone mining a serious

blow. Due to defective fuel for the boilers, the steam pumps

on the 1000-ft level (fig. 3) of the Boom shaft seized and

stopped. Eight large steam sinking-pumps were installed, but

they were incapable of handling the water and it rose to the

900-ft level. As the water rose the overtaxed boilers ruptured

almost simultaneously, stopping all pumping. In 1910, a 4,000

cubic-foot compressor was installed and the sinking pumps

were run by air. With the air pumps and the installation of new

boilers, the submerged pumps were finally recovered and

development on the 1,000-ft level was resumed by the end of

the year (Butler and others, 1938).

The cost of defeating the water, pumping 3,500 gpm, the

decreasing silver price and the lack of sufficiently large, high-

grade orebodies at depth, finally took their toll. On January

11, 1911, pumping stopped and the pumps on the 600, 700,

800 and 1,000-ft levels of the Boom shaft were allowed to

flood (Butler and others, 1938). With the flooding of the

lower levels, mining by the Tombstone Consolidated Mines

Company ceased, though lessees continued to work the dumps

and search for ore above the water table.

In 1914, Phelps Dodge Corporation, one of the principal

creditors of Tombstone Consolidated Mines Company,

acquired all the company's holdings and started mining under

the name of Bunker Hill Mines Company. That company made

no attempt to recover the lost pumps or reopen the lower

workings. Rather, they concentrated on mining the shallower,

lower grade manganese-silver ores in the southern and western

part of the district. They mined until 1918, when they turned

their operations over to lessees.

In 1933, the properties of Bunker Hill Mines Company were

taken over by the Tombstone Development Company, which

attempted to operate the mines via lessees; their operations

continued sporadically into the late 1930's.

The Tombstone Extension, a lead-carbonate vein mine

located in the eastern part of the district, opened in 1930.

During 1932-33, the mine was the largest lead producer in

Arizona (Asarco files). That mine was turned over to lessees in

the mid-1930's and closed in the late 1930's.

Since the Second World War, the Anaconda Company and

Newmont Mining Corporation have both examined the district

in some detail; however, neither company was successful in

discovering sufficient ore to justify reopening the mines.

Two mining operations are being conducted in the district

at present. The Escapule Brothers, Charles and Louis, are

leaching the dumps from the State of Maine mine and plan to

commence mining and leaching of low-grade underground ores

in the near future. The other operation is that of Sierra Min

erals, which has during the last few years, been reworking the

old mine dumps and recovering silver and gold via a cyanide

leach process. The large dump east of Tombstone is the site of

their current operation.

REGIONAL GEOLOGIC SETTING

The Tombstone mining district lies along the axis and just

west of the deepest part of the Sonoran geosyncline. It also

lies within a belt of north-northwest trending mountain ranges

that are separated by broad alluvial-filled valleys and extend

from the Colorado Plateau in central Arizona, to Sonora, Mex-

ico. The region is underlain by a relatively thick blanket of

Paleozoic and Mesozoic sediments.

GEOLOGY

Rocks of the Tombstone mining district consist of schist,

granite, limestone, dolomite, shale, sandstone and conglomer-

ate of Precambrian through Mesozoic age, and younger grano-

diorite, tuff, rhyolite sills, plugs and dikes, andesite dikes,

valley fill and a basalt plug.

Precambrian rocks, Pinal Schist and granite, are exposed in a

north-south elongate window in younger sediments and vol-

canic rocks in the south-central part of the district (fig. 4).

Overlying Precambrian rocks are 440 ft of Cambrian Bolsa

Quartzite (Ransome, 1916) and 844 ft of Cambrian Abrigo

Limestone (Gilluly, 1956). Devonian Martin Limestone, 230 ft

of alternating limestone and shale, unconformably overlies the

Abrigo Limestone (Gilluly, 1956). The Mississippian is repre-

sented by 786 ft of Escabrosa Limestone and dolomite

(Gilluly, 1956).

The Pennsylvanian-Permian Naco Group, first described by

Ransome during his early work in the Bisbee district, 20 mi to

the southeast (Ransome, 1904), is well exposed in the Tomb-

stone Hills. Due to the excellent exposures, Gilluly and his

co-workers (Gilluly, 1956) were able to subdivide the Naco

into 999 ft of Horquilla Limestone, 584 ft of limestone, sand-

stone and shale in the Earp Formation, 633 ft of Colina Lime-

stone and 783 ft of limestone and dolomite in the Epitaph

Dolomite.

Unconformably above the Naco Group is the Cretaceous

Bisbee Formation (Gilluly, 1956). The Bisbee Formation at

Tombstone is not to be confused with the Bisbee Group

318

(Ransome, 1904) in the Mule Mountains to the southeast, as

the Glance Conglomerate, Morita Formation, Mural Limestone

and Cintura Formation do not occur, but their stratigraphic

equivalents may be present. It has been suggested that Cre -

taceous beds at Tombstone are all younger than the Mural

Limestone and "possibly even post-Cintura Formation"

(Stoyanow, 1949, p. 30). However, Reeside has noted that

"although the fossils of the Blue limestone (in the Bisbee For-

mation) at Tombstone are not precisely identifiable, they

resemble those of the Mural closely" (Gilluly, 1956, p. 77).

While there is little doubt of the Cretaceous age of the Bisbee

Formation at Tombstone, direct correlation of stratigraphic

units of the Bisbee Group, as they occur in their type locality,

cannot be made. The formation exposed at Tombstone is a

much faulted and metamorphosed sequence of sandstone,

shale and limestone that is 3,079 ft thick (Gilluly, 1956). Of

considerable importance as far as mineral deposition is con-

cerned is the lower 128 ft of the formation, which consists of

the "Novaculite" unit which contains 60 ft of basal shale and

limey sandstone with localized limestone conglomerate, the

"Blue limestone" which is 34 ft thick, 24 ft of shale and a

10-ft thick bed of limestone (Gilluly, 1956).

Late Cretaceous igneous rocks, the Schieffelin Granodiorite

and the Uncle Sam quartz latite tuffs (Butler and others,

1938), are exposed in the western and southern part of the

district, and dikes of granodiorite are found throughout its

central part. The granodiorite is a holocrystalline rock with a

hypidiomorphic granular texture. It is light gray to grayish -

pink and medium-grained, consisting of 35-40% plagioclase,

15-20% orthoclase, 5-10% quartz, 5-10% green hornblende,

3-5% biotite and 1-5% augite with minor amounts of clino-

zoisite, zircon, magnetite, sphene and apatite (Newell, 1974).

Newell (1974) describes the Uncle Sam quartz latite tuff

as a hypocrystalline rock that is slightly welded and

contains ash-phenoclasts that are embayed and set in a

devitrified matrix. The light yellowish-brown to gray-brown

lithic tuff, with moderately well-defined flow structures, contains

40-50% plagioclase, 20-25% quartz, 15-20% orthoclase, and 1-

5% biotite with traces of magnetite and apatite.

The tuffs have been dated at 71.9±2.4 m.y. (Newell, 1974),

whereas the granodiorite is 72 m.y. old (Creasey and Kistler,

1962). The close relationship of the two rock types, both

spatially and temporally, and the tendency for the tuff to be

less mafic and more siliceous than the granodiorite, suggest

that they are differentiates from the same magma.

The granodiorite and tuffs are cut by dikes of hornblende

andesite that are bluish gray to light olive-gray in color. They

consist of medium to coarse-grained hornblende phenocrysts

and fine-grained plagioclase in a microcrystalline groundmass

(Newell, 1974).

Rhyolite porphyry, dated at 63 m.y. (Creasey and Kistler,

1962) occurs as sills, plugs and dikes south and east of the

main part of the district. The rock is pinkish gray and made

up of medium- to fine-grained phenocrysts in devitrified

ground- mass. The texture is hypocrystalline, being typically

porphyritic aphanitic.

To the north and east of the district, the pediment of the

Tombstone Hills is covered by Gila Conglomerate. The rock

unit, which is probably a fanglomerate, is several hundreds of

feet thick, contains boulders up to 3 ft in diameter, as well as

cobbles and pebbles, all of which are set in a fine sand matrix.

The unit is generally poorly sorted, becoming finer grained and

vaguely bedded in its upper part.

DEVERE, JR.

The youngest rock in the area is a basalt plug which intrudes

the Gila Conglomerate on the east side of Walnut Gulch, north

of the central part of the district. The elliptically shaped plug

is dark gray to greenish black in color, being made up of fine-

grained olivine, diopside and enstatite that occur in the inter-

stices between felted plagioclase laths (Newell, 1974).

STRUCTURE

The Tombstone mining district is structurally complex.

Several periods of faulting, with movement along the same

structure, sometimes in different directions, has complicated

the unravelling of the tectonic history.

Two structural features predominate: the Ajax Hill horst

and the Tombstone basin (Butler and others, 1938). The Ajax

Hill horse, located mostly south and east of Figure 4, is a 6

area that is bounded on the west by the north -south

trending Ajax Hill fault, on the north by the east-west trending

Prompter reverse fault, and on the south by the northeast-

southwest trending Horquilla Peak fault (Gilluly, 1956). To

the east, the boundary is concealed by alluvium. Displacement

along the boundary faults has been significant; the Ajax Hill

fault has brought rocks of the Bisbee Formation, on the west,

into contact with Bolsa Quartzite, on the east; the Prompter

fault separates the northern Naco Group limestones from

southern Pinal Schist; while the Horquilla Peak fault has

brought upper Naco Group limestones on the south to rest

against the Abrigo Limestone on the north.

North of the Ajax Hill horst is the Tombstone basin, which

is shown by the large area of Cretaceous sediments on Figure

4. The basin is a broad synclinal warp, the axis of which trends

east-west and plunges gently to the east. The syncline is com-

plicated by a series of smaller west-northwest trending, anti-

clinal and synclinal folds that were called "rolls" by the early

miners. To the west the broad syncline and its associated

tighter folds abut and are truncated by the Schieffelin Grano-

diorite which is clearly younger than the folding.

Prior to the intrusion of the Schieffelin Granodiorite the

Tombstone basin was subject to east-west and north-south

faulting. Following the intrusion of the granodiorite, dikes of

similar composition were emplaced along many of the pre-

existing faults. The basin was then faulted along north-north-

east trends, and there was renewed movement along the east-

west and north-south faults which brought about the develop-

ment of a series of northeast tension fractures. Thereafter, the

faults and the tension fractures were mineralized, with the

tension fractures becoming the northeast fissure veins. Follow-

ing mineralization, the basin was again disrupted by faulting

along west-northwest and north-northwest trends. Movement

along the newly created and pre-existing faults tilted the basin

to the north and northeast.

METAMORPHISM

The intrusion of the Schieffelin Granodiorite and its accom-

panying dikes metamorphosed the rocks in the Tombstone

mining district prior to mineralization. Shale and sandstone of

the Bisbee Formation were converted to hornfels and quartzite

which fractured well and helped develop the long continuous

tension fractures during the many periods of faulting. Lime -

stone of the Bisbee Formation and upper Naco Group were

recrystallized, while the "Novaculite," the basal member of

the Bisbee Formation, altered to a jasperoid.

TOMBSTONE MINING DISTRICT

ORE DEPOSITION

The hornfelsic shales played a dual role: they fractured well,

thus providing excellent, confined channel ways for ascending

mineralizing solutions; and, because they were unshattered and

competent except in the immediate vicinity of the fissure

veins, they formed impermeable caps under which the solu-

tions could spread and replace favorable limestone horizons.

Since the Bisbee Formation is mostly shale and sandstone that

altered to hornfels and quartzite, much of the ore was con-

fined to fissure veins and faults. However, the largest orebodies

occurred as limestone replacement deposits. Favorable hori-

zons for replacement deposits were the "10-foot limestone,"

the "Blue limestone" and the "Novaculite," of the lower Bis-

bee Formation and the uppermost beds of the Naco Group.

The most favorable loci for ore deposition were where a

northeast fissure vein, dike or premineral fault cut a favorable

horizon that had been folded by one of the west-northwest-

trending anticlinal flexures. In most cases, the "10-foot" and

"Blue" limestones were more tightly folded and fractured than

were the underlying Naco limestones. These features, together

with the fact that the "10-foot" and "Blue" limestones were

capped and bottomed by impermeable hornfelsic shales, made

them the most receptive hosts in the district. Fracturing and

permeability are the greatest where the bends are the sharpest.

The folds are not symmetrical, and the sharpest bends may or

may not be at the crest of a fold. In some folds, slip along beds

produced permeable zones on the limb of the fold, and

mineralization often extended for some distance down a limb.

The Silver Thread fold has a flat crest that bends sharply

into a nearly vertical northeast limb. The bend has intensely

fractured the "Novaculite," and it is continuously mineralized

for 600 ft between a dike and a northeast fissure vein. The

"Blue limestone" on the same roll was replaced by sulfides for

400 to 500 ft from the dike (Butler and others, 1938). The

"Blue limestone," where it is cut by a large fissure vein along

the Sulphuret fold, produced an orebody that was stoped for

300 ft; the stope varies in width from 25 to 100 ft and from 3

to 8 ft in height. The ore averaged $70 per ton when it was

mined in 1904-05 (Butler and others, 1938). Figure 5, taken

along the West Side fissure between the Boss and Sulphuret

dikes is a good example of the complexity of folding and

localization of replacement ores within the district.

Several ore shoots occur in the fisure veins. The Skip-Shaft

fissure was mineralized for about 900 ft along strike and for

319

more than 600 ft below the surface. Stratigraphically, the

fissure made ore from the Naco Group to about 400 ft above

the "Blue limestone" in the Bisbee Formation. The fissure was

most productive along its intersection with the "Blue lime-

stone," where the limestone was replaced for some distance

away from the fissure. Maps of the old workings indicate the

fissure was stoped over a width of several feet regardless of the

rock type. The Arizona Queen fissure on the surface is a shear

zone 4 to 5 ft wide. Like the Skip-Shaft fissure, the Arizona

Queen has been most productive where it crossed the "Blue

limestone." However, in the altered shales the fissure was well

mineralized over a width of 10 to 12 ft, reaching a maximum

width of 20 ft (Butler and others, 1938).

In addition to the replacement and fissure vein deposits,

several orebodies were formed within the larger faults. These

deposits generally occurred at the intersections of faults and

fissure veins, particularly where a fissure vein hooked into and

paralleled the fault for some distance before continuing in a

northeasterly direction. Orebodies so formed were usually

irregular, erratic and pipelike in shape. The Prompter fault

contained irregular pipelike and tabular orebodies from the

surface to the water level, where mining stopped. In one stope

on the third level of the Prompter mine, approximately 180 ft

below the surface, the entire fault zone, a width of 30 ft, was

ore (Buchard, 1884).

The bulk of the Tombstone ores have been silver chlorides

and lead, zinc and copper carbonates, with the majority occur-

ring above the water table that stands at 4,120 ft above sea

level, 450 to 600 ft below the surface. At some time in the

past, the water table must have been lower, as oxidized ores

have been mined from below the water table in the Grand

Central, Lucky Cuss, Bunker Hill and Emerald mines.

There appear to have been at least two phases of mineraliza-

tion: an earlier iron, lead, zinc, copper sulfide phase that was

rich in silver and contained significant gold and a later man-

ganese-silver phase. The ore related to the sulfide phase of

mineralization contains little manganese and occurred as

masses of pyrite, galena, tetrahedrite and sphalerite with minor

amounts of chalcopyrite. The galena is later than the other

sulfides as it replaces them, but it does not appear to be asso-

ciated with the later manganese-silver mineralization. Galena

and tetrahedrite are both argentiferous as is some of the

pyrite. A sample of massive pyrite from the Sulphuret mine

assayed 4.18 ounces per ton silver (Butler and others, 1938).

320

The sulfide ore oxidized to limonite and cerussite that con-

tained considerable bromyrite and cerargyrite with minor

amounts of smithsonite, malachite, native gold and silver. In a

few phases, chalcocite and argentite were found with the

oxides.

The later manganese-silver ores occur mostly in the southern

and western parts of the district principally in orebodies asso-

ciated with the Prompter and Lucky Cuss faults. Most of the

manganese occurs as psilomelane; however, a mass of ala-

bandite was mined from the 350-ft level of the Lucky Cuss

mine. The alabandite occurred in a replacement deposit in

crystalline Naco limestone adjacent to the Lucky Cuss fault

and was surrounded by pyrite, galena and sphalerite, which it

in part replaced (Butler and others, 1938). The manganese ore

generally contained less silver and lead and more copper than

the oxidized sulfide ores, with the silver content usually being

less than 20 ounces per ton. Typical manganese ore from the

Dry Hill mine assayed 17 ounces per ton silver, 0.04 ounces

per ton gold and 0.17% copper (Butler and others, 1938).

However, some of the manganese ores from the Prompter mine

averaged 35 ounces per ton silver from production in 1883

(Buchard, 1884). Ransome (1920) concluded that there was

little doubt that the manganese-silver deposits occurred, at

least in part, due to the reaction between the carbonate host

rocks and the oxidizing sulfide deposits. However, the much

lower silver and lead, and the higher copper content of the

manganese-rich ores compared to the low-manganese sulfide

ores suggests a separate, distinct phase of mineralization.

Silver was the most economically important metal pro-

duced, but gold and lead were also significant. The silver to

gold ratio for ores produced was 6:1 in dollar value. The dis-

DEVERE, JR.

trict has produced 45,000,000 pounds of lead (Keith, 1973, p.

13), an average of approximately 45 pounds of lead per ton of

ore mined.

REFERENCES

Blake, W. P., 1882, The geology and veins of Tombstone, Arizona: Am.

Inst. Min. Eng. Trans., v. 10, p. 334-345.

Buchard, H. C., 1884, Production of gold and silver in the United

States, 1883: U.S. Dep. of Treasury, Doc. 604, p. 38-50.

Butler, B. S., Wilson, E. D., and Rasor, C. A., 1938, Geology and ore

deposits of the Tombstone district, Arizona: Arizona Bur. of Mi nes

Bull. 143, 114 p.

Church, J. A., 1903. The Tombstone Arizona mining district: Am. Inst.

Min. Eng. Trans., v. 33, p. 3-37.

Creasey, S. C., and Kistler, R. W., 1962, Age of some copper-bearing

porphyries and other igneous rocks in southeastern Arizona: U.S.

Geol. Survey Prof. Paper 450-D, p. 1-5.

Devere, J. M., 1960, The Tombstone bonanza, 1878-1886: Arizona

Pioneers Hist. Quart., v. 1, p. 16-20.

Gilluly, James, 1956, General geology of central Cochise County,

Arizona: U.S. Geol. Survey Prof. Paper 281, 169 p.

Keith, S. B., 1973, Index of mining properties in Cochise County,

Arizona: Arizona Bur. of Mines Bull. 187, 98 p.

Newell, R. A., 1974, Exploration geology and geochemistry of the

Tombstone-Charleston area, Cochise County, Arizona [Ph.D. disser-

tation] : Stanford, Calif., Stanford Univ., 205 p.

Ransome, F. L., 1904, Geology and ore deposits of the Bisbee quad-

rangle, Arizona: U.S. Geol. Survey Prof. Paper 21, 167 p.

----, 1916, Some Paleozoic sections in Arizona and their correlation:

U.S. Geol. Survey Prof. Paper 98-K, p. 133-166.

----, 1920, Deposits of manganese ore in Arizona: U.S. Geol. Survey

Bull. 710, p. 96-103, p. 113-119.

Stoyanow, A. A., 1949, Lower Cretaceous stratigraphy in southeastern

Arizona: Geol. Soc. of America Memoir 38, 169 p.

Wilson, E. D., 1962, A resume of the geology of Arizona: Arizona Bur.

of Mines, Bull. 171, 109 p.