DEPARTMENT OF THE INTERIOR 

ALBERT B. FALL, Secretary

UNITED STATES GEOLOGICAL SURVEY

GEORGE OTIS SMITH, Director

Bulletin 743

GEOLOGY OF THE OATMAN GOLD DISTRICT

ARIZONA

BY

F. L. RANSOME

WASHINGTON

GOVERNMENT PRINTING OFFICE

1923
ADDITIONAL COPIES

OF THIS PUBLICATION MAT BE PROCURED FROM

THE SUPERINTENDENT OF DOCUMENTS

GOVERNMENT PRINTING OFFICE

WASHINGTON, D. C.

AT

10 CENTS PER COPY

PURCHASER AGREES" NOT TO RESELL OR DISTRIBUTE THIS 

COPY FOR PROFIT. FUBt BBS. 57, APPROVED MAY 11, 1922
CONTENTS.

Page.

Introduction _ 1

Situation__________ 2

History of mining- : - 3

Topography ______ 8-

 General geology________ It

Outline________________ _-__ _ - Hi

Distribution and character of the principal igneous formations IT

Alcyone trachyte 17

Esperanza trachyte 20

Oatman andesite 21

. Gold Road latite___________-___ ________ 23

Younger volcanic formations __ 27

Moss porphyry________ _ _ 27

Times porphyry 28

Dikes and small intrusive bodies 30

The gold-bearing veins_____ _ _____ 32

Distribution, strike, and dip _ _ _________ 32

Material and structure of the veins __ _____ 32

Alteration of the wall rock __ ______ 38

Notes on some of the more important veins ______________ 39

Tom Reed vein______ _ __ _________ 39

Gold Road vein __ __ _________ 45

Moss vein ___________ _ _________________ 46

Leland vein ___ _ _ ______i______ 48

Gold Dust vein_ _ _ _ __________ 49

 Pioneer vein __ _____ _ ____ _ __________ 50

Midnight vein_____ _ : _________ 50

Other veins _ _ _ __________ 51

Practical conclusions___________-__________________ 51

Index ______ ___________ _ __ _________ 5T

ILLUSTKATIONS.

Page..

PLATE I. Geologic map of tbe Oatman district, Ariz_____________ 8". 

II. Topography of the Black Mountains, near Oatman, Ariz.: 

A, Western front, looking northeast from a point near Oatman ; B, View northeast over the broad top of the mountains 

southeast of Oatman________________________ $

in
IV CONTENTS.

Page.

PLATE III. Topography of the Oatinan district: A, General view to the 

northwest over the central and northwestern part of the 

district, from Ute Mountain; B, Leland Hill from the southeast - 8

IV. Topography of the Oatman district: A, Mountains on the 

northwest side of Times Gulch; B, Ruth and Moss mines 

from the south_______ 8

V. Topography of the Oatman district: A., Hills capped by Esperanza trachyte, 1$ miles south of Oatmau, looking southwest; B, Boundary Cone from the northeast________ 9

VI. Laminated structure of the Alcyone trachyte: A, Two miles 

south-southwest of Oatman, looking northwest; B, Near the 

Treadwell shaft of the Pioneer mine_____________ 32 

VII. Vein structure: A, Near view of the Gold Dust vein in a surface -cut just north of the No. 2 shaft of the Gold Dust 

mine; B, More general view of the Gold Dust vein at the 

same locality, looking northwest _ ___________ 32 

VIII. Vein structure: A, Part of the Pioneer vein at the Treadwell 

shaft, looking north; B, Pioneer vein, looking south along 

the vein and over the top of an old stope near the Thirtyfifth Parallel shaft________________________ 32

IX. Vein structure: A, The Gold Road vein as exposed on the Oatman-Kiugmau road, looking southeast; B, The Moss vein at 

the Moss mine___________________________ 33

X. Plan of tlie principal underground workings on the Tom Reed 

vein and its branches, with a generalized longitudinal projection of the ore bodies_____________________ 40

XI. Mines of the Oatman district: A, View northwest, toward Oatman, along the Tom Reed vein from the vicinity of the 

Aztec shaft; B, View southeast along the Tom Reed veiu__ 40

XII. Mines of the Oatman district: A, View up Gold Road Gulch, 

showing the surface relations of the Gold Road mine; B, 

Leland Hill from the southeast, looking along the vein___ 41 

FIGURE 1. Index map showing the situation of the Oatman district, Ariz_ 2

2. Sketches showing the structure of the Big Jim vein on the

400 level___ -__-__________________^__ 34

3. Typical banded ore from the stope. above the 600 level of the

United Eastern mine____________________._^_ 35

4. Quartz and calcite from the dump of the Black Eagle shaft of

the Tom Reed workings______________________ '36

5. Lamellar aggregate of .quartz, calcite, and adularia from the

dump of the Black Eagle shaft of the Torn Reed workings-- 37

6. Cross sections of the Tom Reed-Big Jim vein and Mallery

fault______..___________________________' 40

7. Longitudinal elevation of the Gold Road mine____:_____ 47
GEOLOGY OF THE OATMAN GOLD DISTRICT, 

ARIZONA.

A PRELIMINARY REPORT.

By F. L. KANSOME.

INTRODUCTION.

/ The field work upon which the present report is based was begun 

December 18, 1920, and completed April 15, 1921. The district was 

geologically mapped in detail, and the workings of such mines as 

were in operation at that time were studied. In April, 1921, the 

only productive mines in the district were the Aztec mine of the 

Tom Reed Gold Mines Co. and the United Eastern mine, and both 

were believed by many supposedly well-informed people to be nearing the end of their principal known ore bodies. The Gold Road 

mine, formerly a close rival of the Tom Reed in productivity, was 

idle. A large body of ore was known to exist in the Big Jim mine 

of the United Eastern Mining Co., and some excellent ore had been 

found in the American mine. On the whole, the outlook for longcontinued mining on an extensive scale can not be said to have been 

'particularly bright at the time when the field work was finished. 

At the end of the year, however, two events led to greatly increased 

activity in the district. One was the finding of a small body of rich 

ore near the surface on the Stoney-Ferra lease block, on the Tom 

Reed vein; the other, still more significant, was the discovery of ore 

by means of the diamond drill on the 600 level of the Oatman United, 

mine, where prospecting had been carried on'with persistency long 

after most of the shafts sunk in the stirring days of 1915 had been 

abandoned.

The success of the Oatman United has led to renewed efforts to 

find additional ore bodies, particularly by diamond drilling, and 

consequently to demands for information concerning the geology of 

the district. It is to meet, if possible, this demand that the present 

preliminary report has been prepared. The reader should understand that whereas the statements contained within it are believed to 

be generally correct, nevertheless much of the material collected in

1
2 OATMAN GOLD DISTRICT, ARIZONA.

the course of the field work is still unstudied, and many problems 

are yet unsolved. The statements made and particularly such deductions or conclusions as are now presented are subject to revision in 

the final report. To that report will be deferred particular acknowledgments of courtesies extended and aid given, as well as full bibliographic references to previous publications on the Oatman district.

FIGURE 1. Index map showing the situation of the Oatman district, Ariz. (shaded area).

No attempt is made in the present report to describe individual mines

and prospects.

SITUATION.

The area described in this report as the Oatman district (fig. 1) 

lies in western Arizona, in Mohave County, mainly on the western 

slope of the Black Mountains, particularly that part of the mountains to which the names Black Mesa and Ute Mountains or Ute
HISTORY OF MINING. . O

Mesa have sometimes been applied. Oatman, the principal settlement, is 12 miles east of Colorado River and about 23 miles southwest of Kingman, the county seat, which is a thriving town on the 

main line of the Atchison, Topeka & Santa Fe Railway. An excellent road, 30 miles in length, connects Oatman with Kingman, crossing the Black Mountains through Sitgreaves Pass. In a straight 

line Oatman is 16 miles northeast of Needles, whicjh is on the California side of the Colorado. Direct road connection with Needles is 

made, however, by way of the bridge at Topock, 16 miles by road 

southeast of Needles, where the Santa Fe Railway also crosses the 

river. A road has recently been completed between Oatman and 

Topock. A narrow-gage railway formerly connected the Leland and 

Vivian mines, in the Oatman district, with the east bank of Colorado 

River opposite Needles, but this railway, although it still appears 

on some maps, has long been abandoned, and the rails have been 

removed. Roads that are comparatively little used connect Oatman 

ivith a ferry near Needles, the Indian school at Mohave City on the 

Fort Mohave Indian Reservation, the old settlement of Hardyville, 

and otjier places on Colorado River. A rather rough road, with 

steep grades, runs north to Katherine and other points in the Union 

Pass district.

As used in the present report the name Oatman district designates 

only the southern part of the area comprised in what for purposes 

of record in the General Land Office is technically known as the 

San Francisco mining district. It does not include a number of 

mines to the north, among them the Thumb Butte, Arabian, and 

Katherine, which are also within the indefinitely bounded San Francisco district. The names Union Pass, Gold Road, Vivian, and 

Boundary Cone are sometimes used in connection with the word 

 " district" to designate certain portions of the San Francisco district. 

They are merely local names that [have no legal standing.

HISTORY OF MINING.

When, in 1862, Gen. J. H. Carleton and the Fifth California Volunteers occupied Arizona to prevent it from falling into the hands 

of .Confederate irregulars, many of his men who were experienced 

miners varied the monotony of garrison duty by prospecting. At 

that time the main trail from Camp Mohave eastward ran up Silver Creek, and the first settlement in what soon became the San 

Francisco district was made on this stream at a point about 4 miles 

north of the site of the future town of Oatman. Here, where water 

can usually be obtained at the surface throughout tfre year, the walls 

of a dozen or more stone cabins, commonly reported to have been 

built by Carleton's men, are still standing.
4 OATMAN GOLD DISTEICT, ARIZONA.

About this time, in 1863 or 1864, John Moss found free gold in a 

large lode, now known as the Moss vein, which crops out prominently 

about a mile north of Silver Creek. Moss is commonly reported to 

have taken out rich ore to the value of $240,000 from a pocket close 

to the surface, but although considerable development work was 

afterward done on the vein, as a whole it proved to be of disappointingly low tenor. Some of the ore was worked in an arrastre 

on Silver Creek near the settlement. Afterward, it is said, a 10- 

stamp mill was built in the same locality, and still later a mill was 

erected on the Colorado near the mouth of Silver Creek, about 7 

miles west of the mine.

The discovery of the Hardy vein, on the east side of Hardy Mountain; the Gold Dust (Victor-Virgin), about a mile southwest of 

Oatman; the Leland, on Leland Hill; and some others of the more 

prominently outcropping veins followed closely that of the Moss. 

Other very conspicuous veins, such as the Tom Eeed and Gold Road, 

must have attracted the notice of the early prospectors and were 

probably located, although no ore was found in them until many 

years later.

For fully 30 years after the early work on the Moss and Hardy 

veins there is little record of activity in the Oatman district. It Was 

not until 1901, when the Gold Eoad Co. sank the Tom Reed and 

Ben Harrison shafts to a depth of 100 feet on what is now generally known as the Tom Reed vein, that there was any general 

revival of mining.

About 1902 gold was discovered in the Gold Road vein. The 

ground was worked in a small way for several years under various 

owners, and at the time of the visit by F. C. Schrader, of the United 

States Geological Survey, in 1906-7,1 it was owned by the G©ld Road 

Mining & Explorations Co., incorporated under the laws of Arizona, 

with headquarters at Paris and Los Angeles.

In 1903 the Leland mine was bought by the Mount Mohave 

Gold Mining Co., afterward the Mohave Gold Mining Co. Without 

waiting to determine whether the ore bodies in the mine were such 

as to justify the expenditure involved, the new company built 17 

miles of narrow-gage railway from the mine to a point on the 

Colorado opposite Needles and erected a mill at a place named 

Milltown, about 11 miles from the mine, on the sloping plain that 

intervenes between the Black Mountains and the river. Considerable 

ore was stoped from tunnels in Leland Hill and, according to 

Schrader, about 4,500 tons of ore was milled. The value of the 

total output from the mine is locally reported to have been about 

$40,000. About the end of 1904 the mine was closed, and at the time

1 Schrader, F. C., Mineral deposits of the Cerhat Range, Black Mountains, and Grand 

Wash Cliffs, Mohave County, Ariz.; U. S. Geol. Survey Bull. 397, 1909.
HISTORY OF MINING. 5

of Schrader's visit many miles of the railway had already been 

washed out by floods.

In January, 1904, were located the Grey Eagle and Bald Eagle 

claims, which, as part of the Tom Reed ground, were to figure later 

in a notable lawsuit. In the same year the Tom Reed mine was 

sold, but failure of the purchasers to make payment led to the acquisition of the ground by the Title Insurance & Trust Co., of Los 

Angeles, as representative of various creditors. Shortly thereafter 

the Blue Ridge Gold Mines Co. was formed, took over the mine, 

built a 10-stamp mill, and began production. This company, however, was not successful, and in 1906 it sold the mine to the Tom 

Reed Gold Mines Co., the present owner. Up to April 1, 1922, the 

Tom Reed mines had produced bullion to the value of $9,488,622.

In 1911 the Gold Road mine was bought by the United States 

Smelting & Refining Co. at a price, as reported in the mining journals at the time, of $1,600,000.

Between the years 1903 and 1915 the history of the Oatman district was comparatively uneventful. The Tom Reed and Gold 

Road mines continued fairly steady production, prospecting was 

carried on in various parts of the district in a rather quiet way, and 

from time to time some of the smaller mines, such as the Ruth, 

Vivian, Pioneer (formerly the German-American), Gold Dust (formerly the Victor-Virgin), Midnight, and Gold Ore, yielded some ore.

Oatman, originally a very small settlement dependent upon the 

Tom Reed mine, appeared first under its present name in the mining 

news of the year 1912, when there seems to have been some renewal 

of activity in prospecting. During that year the Telluride Mining. 

Milling & Development Co. put up a hoist and began extensive underground exploration.

In March, 1913, J. L. Mclver obtained an option on part of the 

ground now owned by the United Eastern Mining Co. No distinct 

vein was exposed at the surface, but the observant prospector noted 

that the rocks on the two sides of the suspected line of the vein were 

slightly different in character, and this suggested the existence of a 

fault fissure. In November, 1913, Mclver and his partner, George W. 

Long, incorporated the United Eastern Mining Co., and in March, 

1914, they began sinking a shaft at the north end of the town. After 

a depth of 40 feet had been attained work was stopped until additional money could be found. In June, 1914, W. K. Ridenour, noted 

locally for his enterprise and sagacity, came to the rescue of the 

new company by taking stock at 25 cents a share and recommending 

to his friends the purchase of additional shares. Up to December, 

1914, about $13,000 had been raised by the sale of stock in comparatively small amounts. More money was necessary, however, to take 

up the option and to continue development. The late Frank A. 

20535 23 2
6 OATMAN GOLD DISTRICT, ARIZONA.

Keith happened about this time to be in Oatman, and, being convinced that Mclver and Long had a reasonable chance of success, he 

brought the venture to the attention of Seeley W. Mudd and Philip 

Wiseman, well-known mining engineers of Los Angeles. Keith, 

Mudd, and Wiseman put up $5,000 each and were joined by R. I. 

Rogers and C. H. Palmer, jr. Altogether, $50,000 was paid for the 

present holdings of the United Eastern Mining Co., mainly in cash 

but partly in stock; the final payment was made June 15, 1916. In 

March, 1915, a crosscut on the 465 level went through 25 feet of ore 

that assayed $22.93. By the end of 1916, after an ore body estimated 

to contain gold to the value of about $6,000,000 had been blocked out, 

a 200-ton mill had been built and a new shaft in the hanging wall 

of the vein had been completed and equipped. The mill was afterward enlarged to a capacity of 300 tons. Up to the end of 1920 the 

United Eastern mine had yielded its fortunate owners 377,138 tons 

of ore of an average gross value of nearly $22 a ton, at an average 

operating cost of about $8.50. To the end of 1921 the company had 

paid dividends amounting to $3,952,700.

Such success in a district wherein practically no new ore bodies 

had been found for many years was naturally followed by a great 

revival of prospecting. Early in 1915 an exciting boom was in full 

swing at Oatman. The fact that the United Eastern ore body did 

not reach the surface that it was found, in fact, where there was 

no evident sign of a vein at the surface gave a color of reasonableness and an appearance of probability to ventures that ordinarily 

would have received no financial support. The commonly expressed 

belief that it was necessary to sink from 300 to 500 feet before an 

ore body could be looked for has been recorded in the scores of shafts 

' which were sunk all over the district and most of which, in 1921, 

were abandoned. Although most of the work done during the period 

of excitement that followed the success of the United Eastern was 

futile, a few efforts were rewarded.

 About 1914 the Tom Reed Co. had begun the development of its 

Black Eagle claim, at the extreme southeast end of its long strip of 

mining ground. Work on the 421-foot level of the Black Eagle 

shaft showed the existence of a vein which was considered sufficiently promising to invite further exploration, and in 1916 drifting was in progress on the vein at a depth of 565 feet, just above 

the level of underground water. About the same time what is now 

known to be the same vein was cut by the Big Jim Mining Co. in 

ground adjoining tjie Grey Eagle claim of the Tom Reed Co.

The Big Jim claim had been located on September 2, 1908, by 

S. S. Jones and others, not because it showed any indications of a 

vein but because it happened to^be unlocated ground near a producing mine and might consequently have some speculative value. It
HISTORY OF MINING. I

lay immediately northeast of the Grey Eagle and Black Eagle claims, 

which cover a part of the Tom Reed vein lying southeast of what 

at that time was known as the productive part of the lode. Along 

this undeveloped part of the vein conspicuous outcrops are lacking, 

and this fact might well have been considered as giving additional, 

chances of success to a claim located alongside of the Grey Eagle.

During the period of active prospecting that followed the discovery of the United Eastern ore body a shaft was sunk on the Big 

Jim close to the so-called discovery vein, an insignificant quartzcalcite stringer, of no economic importance. This vein was so obviously unpromising that no drifts were run on it. On the 400 

level, however, a crosscut was run to the southwest, toward the supposed line of the Tom Reed vein, and at a distance of about 180 

feet from the shaft this crosscut entered what has since been known 

as the Big Jim vein.

After the discovery of the Big Jim vein the Tom Reed Co. in 1916 

sank the Grey Eagle and Aztec shafts. The Grey Eagle was intended particularly to investigate the relation of the Big Jim vein 

to the Tom Reed vein, and the Aztec was projected to give convenient 

access to the ore discovered from the Black Eagle shaft. Underground work from the Grey Eagle shaft soon showed that from 400 

to 500 feet below the surface the vein is cut off by a fault that strikes 

nearly parallel with the vein. The vein dips northeast, and the 

fault fissure dips southwest. Ellis Mallery, then a young geologist 

employed by the Tom Reed Co., appears to have been the first to 

reach the conclusion, which development has since clearly shown to 

be true, that the vein in the Grey Eagle mine is the upper, downfaulted portion of the Big Jim vein. The principal displacement is 

along the fissure now appropriately known as the Mallery fault, but 

the present distribution of the ore bodies has been effected in part 

also by other faults, which will be described in another part of the 

report. The Grey Eagle work also resulted in the finding of profitable ore bodies in an intermediate segment of the vein between the 

Big Jim vein and what has been called the Grey Eagle or Tom Reed 

vein. (See fig. 6, p. 40.)

In April, 1917, the United Eastern Co. purchased the Big Jim 

mine. The able mining engineers who were directing the United 

Eastern Co. were well aware that the Big Jim and Grey Eagle veins 

were probably once continuous and owed their separation to faulting, 

but they were convinced that the amount of the throw, about 400 

feet, was too great to enable the Tom Reed Co. to make successful 

claim to the apex of their vein. It soon appeared, however, that the 

Tom Reed Gold Mines Co. held a different opinion, and after an 

attempt to agree upon terms of consolidation had failed, this com-
8 CAIMAN GOLD DISTRICT, ARIZONA.

pany, on February IT, 1919, filed suit against the United Eastern 

Mining Co.

. The case was tried at Kingman, in the superior court of Mohave 

County, and was decided in favor of the United Eastern Mining Co. 

on March 28,1921. Appeal was taken, and at the date of writing the 

case had not been finally decided.

In 1920 some excellent ore was found in the American mine, owned 

by the United American Mining Co., in the Tom Reed vein, southeast 

of the part worked in the Aztec mine. At the time of visit, early in 

1922, this mine was still in the development stage.

The outstanding events in the early part of the year 1922 were 

the discovery of ore by diamond drilling from the 600 level of the 

Oatman United mine, about a quarter of a mile east of the town of 

 Oatman, and the success of Stoney & Ferra, lessees, in finding rich 

ore near the surface in the Tom Reed vein, practically within the 

town. These successes have led to a renewal of prospecting on all 

sides, particularly by the use of diamond drills. The Tom Eeed 

Co. has continued to work its Aztec mine on a diminished scale and 

has opened its mill to the ores of other mines, especially the American and Telluride, enabling these to carry on development work 

with some returns from ore already in sight. The United Eastern 

Mining Co., early in the year, completed an aerial tramway from 

the Big Jim mine to its mill near the No. 2 or main shaft of the 

United Eastern mine and began milling Big Jim ore. It also continued energetic prospecting, both by drilling from the workings 

of the Eastern mine and by sinking a new shaft to the north of its 

No. 2 shaft, to determine whether any additional ore bodies could 

be found in its original territory. In May it was reported that the 

Gold Road mill was being overhauled preparatory to the reopening 

of the Gold Road mine.la

Recently an attempt has been made to work the gravels of Silver 

Creek for placer gold by sinking and drifting. Reports in the local 

press indicate that some gold has been found, but it is not yet certain 

that the metal is present in sufficient quantity to justify extensive

operations.

TOPOGRAPHY.

Lying mostly on the western slope of the Black Mountains, the 

Oatman district as a whole inclines westward, toward the Colorado. 

.The highest elevation attained within the area mapped in connection with this report is 4,955 feet above sea level, in the extreme 

northeast corner of the area, although Nutt Mountain, within the 

unmapped northeastern portion of the quadrangle covered by Plate 

I, reaches a height of 5,065 feet above sea level. The lowest ground

10 Since this report went to press high-grade ore has been mined from the Telluride 

vein by the Telluride and Tom Reed companies.
BULLETIN 743 PLATE 1

EXPLANATION

LIST OF MINES

1. Meals

2. Tango

3. Rattan

4. Ruth

5. New York

6. Midway

7. Record Lode

8. Neglected

9. Sun Dial

10. Oatman Amlg.

11. Hercules

12. Pittsburg

13. Ivanhoe

14. Ariz. Gold Star

15. Big Lode

16. Times

17. Oatman Belle

18. Gold Range

19. Miller

20. Surprise

21. Comstock

22. North Star

23. Gold Reed

24. Blue Bird

25. Arizona Rex

26. Bonanza

27. United Western

28. Arizona Central

29. Red Cloud

30. Fessenden

31. Little Jim

32. Olla Oatman

33. Mohawk Central

34. Oatman United

35. Kokomo

36. Big Jim

37. Grey Eagle

38. Bald Eagle

39. Lucky Boy

40. Aztec

41. Oatman Combination

42. Telluride No. 3

43. Telluride No. Z

44. Telluride No. 1

45. Argo

46. Casey Jones

47. Sunnyside

48. Pictured Rock

49. Last Chance

50. Hi Henry

51. Leader

52. White Chief

53. Tom R.eed,Jr.

54. Gold Dust

55. Liberty Bell

56. Oatman Queen

57. Swiss American

58. Golconda

59. Gilt Edge

60. Vivian

61. Winchester

62. Alcyone

63. United Oatman

64. Peerless

65. Iowa

66. Lazy Boy

67. Esperanza

68. Highland Chief

69. Crescent

70. Adams

71. Oatman Syndicate

72. Oatman Southern

73. Murdock

74. Lucky Sam

(Includes gravel, as a rule with very imperfectly

a, sand, and silt. So

cemented and has been dissected by the present

intermittent streams. Some is the unconsol-

(Lava flows associated with tuff and lay

conglomerate or breccia and cut by basalt dikes)

Mines whose names appear on the face of 

the map are not included in the above list (Plugs and small irregular masses,

Cottonwood rhyolite

(Glassy spheriUitic flows)

(Irregular intrusive mass

of micrographic granite porphyry}

(Cream-colored pumiceous tvfin thic

Very variable in thickness)

^rd-^vein^^-^'

Meadow Creek trachyte

(Fine-grained volcanic flow imth fairly larg

but Undefined phenocrysta ofsanidine)

Flag Spring trachyte

(Fine-grained red-brown volcanic Aaw)

(Composed of many flows of wide range in

character and appearance. Probably includes

ite. Basal flow generally

(Intrusive mass of quartz monzonite porphyry)

(Volcanic flows connected in places with

intrusive bodies of the same rock)

(Dense Klae-gray to brown volcanic flow

(A gray vitrophyre wliere moderately fresh,

h of the rock is altered and is mottled

greenish gray. Mainly flows, but probably

some green porphyritw varieties are intrusive. Many local variations in texture and

(Coarse bedded breccia of pre-Cambrmt and

volcanic material, ivitii layers of sandstone

Granite, gneiss, and schist

Structure section alon^ line A B

Scale -4s,ooo

o______________L

GEOLOGIC MAP OF THE OATMAN DISTRICT, ARIZONA
U. S. GEOLOOICAL SURVEY BULLETIN 743 PLATE II

A. WESTERN FRONT, LOOKING NORTHEAST FROM A POINT NEAR OATMAN.

The original or No. 1 shaft of the United Eastern mine appears in the right foreground, at the 

north end of the town. The present main or No. 2 shaft, in the left center, is in the hanging wall 

of the vein. The dump in the left foreground is that of the Olla Oatman shaft, on the southwest 

branch of the Tom Reed vein. The flows whose edges appear along the mountain side are 

part of the Gold Road latitc. The lighter-colored, irregular areas are intrusive rhyolite.

B. VIEW NORTHEAST OVER THE BROAD TOP OF THE MOUNTAINS 

SOUTHEAST OF OATMAN.

Part of the western slope of the range appears on the left. The light-colored crag on the 

extreme left is the rhyolite plug known as The Elephant's Tooth.

TOPOGRAPHY OF THE BLACK MOUNTAINS, NEAR OATMAN, ARIZ.
U. 8. GEOLOGICAL SURVEY BULLETIN 743 PLATE III

A. GENERAL VIEW 3 THE NORTHWEST OVER THE CENTRAL AND 

NORTHWESTERN PART OF THE DISTRICT, FROM UTE MOUNTAIN.

The town of Oatman is mostly to the right of the view. The rough peaks in the foreground are 

Esperanza trachyte. The distant mountains are beyond the Colorado.

B. LELAND HILL FROM THE SOUTHEAST.

The shaft and mill low down in front of the hill are those of the Vivian mine. Higher and a 

little to the left is the Mitchell shaft of the Leland workings. The Leland vein is marked 

by a line of tunnels and dumps on the right or east slope of the hill. The prevailing rock in 

the view is the Alcyone trachyte.

TOPOGRAPEIY OF THE OATMAN DISTRICT.
U. S. GEOLOGICAL Sl.'RVEY BI:LLETIX 743 I>LATE iv

A. MOUNTAIN,-. i»i\ lllh iNuii I HVV bhl SIDE OF TIMES GULCH. 

The prevailing rock is Times porphyry.

B. THE RUTH AND MOSS \11\ES l-'KOM SOU1 H.

The prevailing rock is the Moss porphyry, In the left center are the shaft and mill of Ihe 

Ruth mine. Above and a little to the left is the shaft of the Moss mine, vith the prominent outcrops of the Moss vein stretching away to the right.

TOPOGRAPHY OF THE OATMAN DISTRICT.
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE V

A. HILLS CAPPED BY ESPERANZA TRACHYTE, U MILES SOUTH OF OATMAN, 

LOOKING SOUTHWEST.

Shows characteristic topography of the Esperanza trachyte with talus slopes of hard, clinking 

rock (lakes. The White Chief shaft, in the left center, is in Alcyone trachyte. Directly behind 

it is an exposure of the sedimentary beds that, separate the two trachytes.

B. BOUNDARY CONE FROM THE NORTHEAST. 

A plug of nearly white rhyolite that has been thrust up through Alcyone trachyte.

TOPOGRAPHY OF THE OATMAN DISTRICT.
TOPOGRAPHY. 9

in the district is in the southwest corner, where the bottoms of some 

of the gullies are only about 1,450 feet above sea level. The range 

of relief within the area mapped on Plate I is accordingly close to 

3,500 feet.

The district shows considerable diversity in topographic form, 

some parts being only moderately hilly, with comparatively smooth 

slopes, and other parts being characterized by slopes so steep and 

rough as to be impassable. Occupying from one-third to one-half 

of the width of the area, along the eastern border, is the principal 

ridge of the Black Mountains, divided, about halfway between the 

north and south boundaries of the district, by the east-west Sitgreaves Pass, 3,600 feet above the sea, through which runs the malm, 

road between Oatman and Kingman. These mountains have very 

clearly been carved from gently clipping volcanic rocks, chiefly lava; 

flows, and have the general character of a dissected mesa. The de~ 

gree of dissection, however, is far from uniform. North of Sitgreaves 

Pass the mountains, as a rule, have fairly sharp summits, from which 

the descent to the neighboring canyons is made by a series of great 

steps, of which the treads are gently sloping platforms, corresponding approximately to the upper surface of some lava flow, and the 

risers are cliffs, in places 300 to 400 feet in height. Battleship Mountain, of which only the south end comes within the area mapped, 

north and west of Cottonwood Canyon, is a conspicuous example of 

this type of topography.

South of Sitgreaves Pass for 2 miles, to the pass at the head of 

Antelope Canyon, the mountain slopes are rough and steep, but the 

bench and cliff topography is much less prominently displayed than 

farther north. The steep western front of this part of the range, 

as viewed from a point near Oatman, appears in Plate II, A.

South of Antelope Canyon the part of the Black Mountains within 

the area mapped, locally known in part as Ute Mountain, is decidedly mesa-like in character, with broad stretches of rolling upland 

(PL II, B) trenched by Warm Springs Canyon and its branches.

From the crest of the Black Mountains the descent is generally 

abrupt for about 1.000 feet to the hilly country in the vicinity of 

Oatman. A belt of such hilly country of very irregular width intervenes between the main ridge of the Black Mountains and thebroad alluvial slope that stretches westward to the Colorado and is 

represented by a few square miles of country in the southwest corner 

of the area mapped on Plate I. Beyond the boundary of the mapped' 

area this slope extends about 9 miles west of the river.

The general character of the topography of the hilly country between the main ridge of the Black Mountains and the valley of theColorado is illustrated by Plate III, A. Within this belt the hills: 

show much variety in form and a wide range in height. There are
10 OATMAN GOLD DISTRICT, ARIZONA.

no long, even-crested ridges, such as result in many places where areas 

of folded or faulted sedimentary rocks are eroded, but the characteristic features of the topography are groups or clusters of pointed 

hills with no recognizable linear arrangement. Directly west of 

Oatman the hills, carved from andesitic and trachytic rocks, are 

comparatively low, rising for the most part less than 500 feet above 

the adjacent drainage channels or " washes." The summit of Leland Hill, the most conspicuous eminence in this part of the area, 

stands about 750 feet above the streamway shown in the foreground 

of Plate III, B.

Farther north, between Times Gulch and Silver Creek (PI. I), is 

a group of higher and decidedly rugged hills, of which Mount 

Hardy (3.231 feet) is the dominant peak, and Cathedral Rock one 

of the most picturesque members. A view of these hills, which are 

composed partly of pink granite porphyry (Times porphyry) and 

partly of gray lavas (Alcyone trachyte), is shown in Plate IV, A.

In the northwestern part of the district is an area, 5 or 6 square 

miles in extent, underlain by monzonite porphyry the rock of the 

Moss mine. Generally this rock gives rise to a comparatively low 

and open topography, with relatively small, sharp hills where the 

rock has been locally hardened by silicification or is traversed by 

dikes or veins. Northwest of the Moss mine, however, especially in 

the vicinity of the contact between the porphyry and the overlying 

volcanic rocks, some of the hills, as shown in Plate IV, 5, are fairly 

.high and steep.

In the southern part of the district, south of Oatman, a flow of 

compact, hard lava that rests on softer material has given rise to 

hills of the type shown in Plate V, A. The upper portions of these 

hills are as a rule extremely rugged, and the lower slopes are 

mantled with talus composed of clinking rock fragments.

This brief characterization of the hill forms of the Oatman district would be incomplete without mention of two peaks that command attention from every visitor on account of their light color 

and tower-like form. One of these is the well-known Boundary 

Cone, 3^ miles southwest of Oatman, shown in Plate V, B. Why 

this mountain should have been named Boundary Cone is not clear, 

for, so far as known, it has never defined any important line of 

demarcation. The second peak is the small mass known as The 

Elephant's Tooth, which is a prominent feature of the eastern landscape as seen from Oatman and is shown in Plate II, B. As seen 

from the town this jutting mass of white rock has some resemblance 

to the fang of a carnivore but no real resemblance to any portion of 

the dental equipment of an elephant. The Elephant's Tooth and 

Boundary Cone are both plugs of rhyolite that, after being in-
GENERAL GEOLOGY. 11

truded into the surrounding rocks, have been stripped partly bare 

by erosion.

As the preceding description indicates, the Oatman district drains 

in general westward to the Colorado, although the water from the 

relatively small areas tributary to Meadow Creek, east of Sitgreaves 

Pass, and Antelope Canyon flows eastward into Sacramento Valley.

The principal drainageway is the channel of Silver Creek, which 

heads under Sitgreaves Pass and runs in a general northwesterly 

direction. Throughout most of the year the greater part of this 

channel is dry, but a small stream of water may persist through the 

summer north of Mount Hardy, near the site of the abandoned stone 

cabins of the California Volunteers. Excellent perennial water is 

found also in the upper branches of Cottonwood Creek, which is a 

northerly affluent of Silver Creek. This water, which issues from 

springs, supplies the Tom Reed mine and the town of Oatman.

A broad, flaring drainage channel, with many tributary washes, 

such as Iowa and Esperanza canyons from the south and Leland 

and Rattlesnake gulches from the north, heads near Oatman and 

merges to the southwest with the alluvial slope of the Colorado. 

This channel and its tributaries are generally waterless.

Times Gulch, which drains the west-central part of the district, 

is also normally dry, although it evidently on occasions carries a 

large volume of flood water.

GENERAL GEOLOGY.

OUTLINE.

The rocks of the Oatman district comprise a closely related series 

of Tertiary volcanic flows, with associated tuffs and some subordinate beds, of conglomerate or breccia, sandstone, shale, and limestone. The volcanic flows rest as a whole on pre-Cambrian crystalline rocks, chiefly granitic, and have been invaded and displaced in 

part by masses of porphyry that are closely related in composition 

to some of the flows and probably came from the same bodies of 

molten rock material or magma. They are also cut by numerous 

dikes and small irregular intrusive bodies of rhyolite and other 

rocks.

The igneous rocks have a wide range in composition, from siliceous 

potassic rhyolite to olivine basalt, but the preponderant members of 

the series belong within the compositional range represented on 

the one hand by latitic andesite and, passing through latite, on the 

other hand by latitic trachyte. The discrimination and classification 

of rocks which are so closely akin and between which there are no 

very definite distinctions present considerable difficulty, particularly 

as lavas of practically identical composition were erupted at dif-
12 OATMAN GOLD DISTRICT, ARIZONA.

ferent times. Classification and nomenclature will be fully discussed in the final report and illustrated by chemical analyses of 

the principal rock types. It must suffice here to give merely the conclusions from chemical and petrographical studies, so far as these 

have at present gone.

The volcanic flows as a whole dip to the east. The average dip 

can not be determined satisfactorily, as some of the flows are thick 

and only here and there afford any indication of their attitude. 

Such observations as have been made, however, indicate that the 

general dip of the series is about 15°, although in places the inclination is much steeper. The flows of basalt, the latest lava to be 

erupted, are apparently more nearly horizontal than some of the 

older rocks. The prevailing easterly dip and the fact that the 

eastern part of the district (PI. I) contains the crest of the Black 

Mountains result in the exposure of north-south belts of successively younger formations from east to west across the district. The 

pre-Cambrian rocks are found along the comparatively low western 

border of the area, and the latest basalt flows1 cap the high, hills 

along the eastern border. In general, these hills show precipitous 

or steplike western fronts, with rough and approximately horizontal banding indicative of the accumulation of successive lava 

flows, but less1 abrupt eastern ^slopes, on which the edges of the flows 

are as a rule not visible.

The general structure of a simple earth block tilted gently to the 

east is modified to spme extent by faulting and by the displacement 

that accompanied the intrusion of two large masses of porphyry. 

The older mass, extending from Silver Creek northward past the 

Moss and Mossback mines and beyond the boundary of the area 

mapped in Plate I, is quartz monzonite porphyry. It is here 

named the Moss porphyry, as the Moss mine is wholly within this 

rock. The younger mass is exposed within the triangular-area 

bounded on the northeast by Silver Creek, on the southeast by 

Times Gulch, and on the west by the alluvial plain of the Colorado. This rock, a granite porphyry, forms the main mass of 

Hardy Mountain, the pinnacle known as Cathedral Rock, and the 

precipitous peaks with their characteristic faintly rosy hue that are 

so conspicuous on the north side of Times Gulch. It is here named 

the Times porphyry.

Much smaller but very conspicuous intrusive masses are the 

white rhyolite plugs of Boundary Cone and of The Elephant's 

Tooth, half a mile east of Oatman (Pis. II, #, and V, B).

The general sequence of events as recorded in the rocks of the 

district was as follows:

In Tertiary time, before volcanic activity began, the region in 

which the Oatman district lies was floored by deeply eroded pre-
GENERAL GEOLOGY. 13

Cambrian crystalline rocks. Prominent among these were dark 

medium-grained, more or less squeezed and foliated granitic rocks, 

probably to be classed as quartz-mica diorites, micaceous schists of 

various kinds, probably some true granite, and dike rocks of considerable diversity. At the present time these ancient rocks are exposed only in a few small areas along the western border of the district and where so visible are generally decomposed and crumbling. 

They may be seen around the abandoned Chicago Syndicate shaft, 

south of the mouth of Times Gulch, and near the Murdock shaft, 

southwest of Boundary Cone.

The erosion surface of early Tertiary time was probably more 

or less hilly, but no definite information as to its topographic character has been obtained.

At a time which can not be closely fixed but which from our 

general knowledge of the geology of Arizona may be considered as 

probably middle or late Tertiary, volcanic eruptions broke through 

the pre-Cambrian rocks. This event must have been accompanied 

and perhaps immediately preceded by changes in the surface con-, 

figuration of the country and consequently in erosion and in the 

transportation and deposition of detritus. At some places, particularly near the mouth of Times Gulch, there is a coarse breccia, consisting of blocks of pre-Cambrian rock in a greenish matrix that 

^ ppears to have been originally a mud of fine volcanic detritus. 

With the breccia are lenticular layers of greenish sandstone and a 

few thin and nonpersistent beds of shale. This deposit is interpreted as representing the rather rapid accumulation in local basins, 

at the beginning of the volcanic eruptions, of material that was 

partly the rock detritus of the old prevolcanic surface and partly 

fine volcanic particles blown from some of the newly opened vents 

and carried to their resting place by the disturbed and shifting 

streams of this period of transition. The maximum observed thickness of this deposit is estimated to be between 100 and 200 feet.

Overlying the breccia and in places resting directly upon the 

pre-Cambrian rocks is a series of flows with probably some intrusive 

masses, which in this report will be designated the Alcyone trachyte (al-sy'oh-nee), from tKe Alcyone mine. This formation includes" what Schrader called the " basal andesite " or, in some parts 

of his report, the " older andesite." 2 It also includes, north of Times 

Gulch and west of Meals Camp, what Schrader referred to as " gray 

andesite." 3 The thickness of this formation is riot known. It is 

roughly estimated, from the section across the district shown on 

Plate I, as about 2,800 feet, but this estimate, like other estimates

3 Op. cit, pp. 34, 181. 

 Op. cit., p. 174.

20535 23 3
14 CAIMAN GOLD DISTRICT, ARIZONA.

of the thickness of the principal volcanic formations, depends fundamentally upon the assumed dip of the formation as a whole. The 

figure given is based on a supposed easterly dip of about 15°. If 

the formation as a whole is more nearly horizontal, tjie maximum 

thickness may not be more than 1,000 feet. Schrader estimated its 

thickness as " at least several hundred feet." A part of the Alcyone 

trachyte, particularly in the extreme western part of the district, 

west of Oatman, may be intrusive into flows of essentially the 

same composition. If so, it is highly probable that at) more than 

one place in the district the trachyte, instead of merely resting on 

the pre-Cambrian rocks, may extend indefinitely downward to what 

was originally its magmatic source.

The eruption of the Alcyone trachyte wag followed by a brief 

interval of erosion, during which there was local accumulation of 

some sandy beds whose materials were apparently derived from 

the trachyte. These beds, with a thickness of about 115 feet, are 

exposed in a steep north slope about 1£ miles south of Oatman and 

a quarter of a mile south of the abandoned White Chief shaft. 

(See PI. V, A.) This exposure is visible from the Oatman-Topock 

road and rather conspicuous from the contrast between the red 

color of the upper layers and the dark shade of a lava cap above 

them. The same beds, here apparently thinner, are exposed in the 

saddle east of Boundary Cone and appear in the dump of the United 

Oatman tunnel, on the south side of Esperanza Canyon.

These sedimentary beds are overlain by a flow or flows of a very 

compact ringing lava which Schrader described as "a densp dark 

reddish-brown or purple andesite, locally known as ' phonolite ' from 

its metallic ring when struck." 4 Its local designation by those prospecting within it in 1921 was " latite," and such the rock might be 

called. As will be shown, however, in the final report, the rock 

is not a typical latite but rather a latitic trachyte, almost identical 

in composition with the Alcyone trachyte, although it is plainly 

younger than that rock and is very different in appearance. It 

will be named in this report the Esperanza trachyte, from the canyon of that name. The Esperanza trachyte at present occupies 

a comparatively small part of the district, extending from a pointabout 1^ miles south of Oatman southward beyond the boundary 

of the area mapped, with its widest part just east of Boundary Cone. 

It is the prevailing rock of Iowa and Esperanza canyons and is the 

country rock of the Highland Chief mine. The maximum thickness 

of the Esperanza trachyte is estimated to be about 1,000 feet.

The next rock to be erupted after the Esperanza trachyte was the 

Oatman andesite, so named from the town of Oatman. This is

4 Op. cit, p. 199.
GENERAL GEOLOGY. . ° 15

what Schrader called "green chloritic andesite," a good descriptive 

designation but one that is rather cumbrous and not in accord with 

the present practice of the United States Geological Survey in giving 

rock names. This is the rock that has contained all the large ore 

bodies hitherto worked in the district with the exception of those 

of the Gold Road vein. As is more fully shown elsewhere in this 

report (p. 21), it is mainly a series of flows but in a number of places 

is clearly intrusive in the Alcyone trachyte, which appears generally 

to underlie it, separated by a thin accumulation of tuffaceous shaly 

and calcareous beds. Where the Esperanza trachyte is present, that 

rock, of course, intervenes between the Oatman andesite above and 

the Alcyone tracjiyte below. Owing to the partly intrusive character 

of the Oatman andesite and the probability that at various places 

within the district masses of it extend indefinitely and irregularly

downward through the older rocks, the thickness of the formation 

at any particular place is wholly indeterminable. The general maximum thickness of the formation as a whole, without regard to such 

possible downward extensions, is roughly estimated to be about 

2,700 feet. This estimate, however, like that of the Alcyone trachyte, 

depends upon the dip assumed. If the formation as a whole is approximately horizontal, the maximum thickness may not be more 

than 700 or 800 feet. Schrader's estimate was 800 feet.5 On the 

other hand, since Schrader's examination the Tom Reed and United 

Eastern mines have attained a depth of approximately 1,500 feet 

without, so far as known, getting out of the Oatman andesite.

Directly overlying the Oatman andesite to the east and forming 

the greater part of the Black Mountains east of Oatman is an assemblage of rocks, chiefly volcanic flows but with some tuff and intrusive material, which is here provisionally named the Gold Road 

latite, after the settlement and mine of that name. This formation 

corresponds in a general way to Schrader's " undifferentiated volcanic 

rocks" 6 but probably includes also what he termed the "rhyolite 

series " and " younger andesite." It consists mainly of biotitic latite, 

but there have been mapped with it on Plate I some overlying glassy 

and lithophysal rocks wjhich should perhaps be classed as rhyolite 

and which will be separately mapped and named in the final report. 

Between some of the flows are layers of tuff. The maximum thickness of this formation, whicji as mapped in this preliminary report 

includes all the flows exposed along the precipitous mountain front 

east of the town of Oatman, is estimated to be from 3,000to 4,000 feet.

Overlying the Gold Road latite and well exposed in cliffs along 

Cottonwood Canyon, in the northeastern part of the area, is a flow 

of compact brown lava that closely resembles the Esperanza trachyte.

»Op. clt., p. 35. 

6 Op. cit, p. 37.
16 o OATMAN GOLD DISTRICT, AEIZONA.

It is here named the Flag Spring trachyte, from Flag Spring, in 

Cottonwood Canyon. It forms a well-defined reddish-brown cliff 

on the south and east sides of Battleship Mountain and also the cliff 

just north of the Gold Ore mine. It apparently was not an extensive 

flow and is not represented south' of Sitgreaves Pass. It attains a 

thickness of about 250 feet.

Succeeding the Flag Spring trachyte in age and overlapping it 

slightly in position is a flow of nearly identical rock, which, from its 

occurrence on the north side of Meadow Creek, is here named the 

Meadow Creek trachyte. This flow, like the Flag Spring trachyte, 

is not extensive and is not known south of Meadow Creek, up which 

runs the road from Kingman to Sitgreaves Pass.

Resting partly on the Gold Road latite, partly on the Flag Spring 

trachyte, and partly on the Meadow Creek trachyte is an accumulation of pumiceous cream-colored tuff which forms very conspicuous 

bluffs along Meadow Creek, on the north side of the Oatman-Kingman road. This is named the Sitgreaves tuff, from Sitgreaves Pass. 

Variable in thickness and resting in places against steep slopes, it 

was evidently deposited after the underlying lavas had been rather 

energetically cut into by erosion. It appears to have a maximum 

thickness of 200 to 300 feet.

Overlying the Sitgreaves tuff and forming the top of Battleship 

Mountain and of other peaks and ridges to the north and east is a 

flow of very glassy spherulitic lava, which in places is probably 

from 500 to 600 feet thick. It is found only in the northeastern part 

of the district, about the headwaters of Cottonwood Canyon, but 

extends for an unknown distance north and east of the area mapped. 

It is here named the Cottonwood rhyolite.

Finally, overlying all the rocks named and, south of Sitgreaves

Pass, resting on the Gold Road latite, are thin flows of black olivine 

basalt, with associated red or gray tuffs. Undoubtedly the basalt 

once covered most of the range, but it has been reduced in area by 

erosion and now occurs as a capping on the higher hills and mesas. 

The most extensive exposure is that in the southeast corner of the 

district, where TJte Mesa, for many miles south and east of the area 

mapped, is covered by this somber rock. A considerable area is preserved also in the northeastern part of the area, north of Meadow 

Creek and east of Cottonwood Creek. The maximum thickness of 

the basalt and associated tuffs preserved within the area of the district as mapped in Plate I is about 1,000 feet.

After the eruption of the basalt the rocks of the region were 

probably faulted and tilted, and active erosion set in and has continued to the present time. While the [higher slopes underwent continuous erosion during this period, erosion and deposition alternated 

in some of the lower portions of the area, as shown by the presence
PBINCIPAL IGNEOUS FORMATIONS. 17

of alluvial terraces and gravel-capped ridges and by the dissection 

of some well-bedded fluvial deposits along Silver Creek.

DISTRIBUTION AND CHARACTER OF THE PRINCIPAL IGNEOUS

FORMATIONS.

ALCYONE TRACHYTE.

As would be expected of the lowest member of a generally eastward-dipping series of lava flows, the Alcyone trachyte is found 

mainly in the western part of the- district, where it is generally 

exposed over an irregular north-south belt as much as 2 miles 

wide. The group of high hills in the northwest corner of the district, west of Meals Camp and the Moss mine, are carved almost 

wholly from this rock. Together with the Times porphyry, which 

is intrusive into it, the Alcyone trachyte occupies the triangular area 

northwest of Times Gulch and southwest of Silver Creek. It is 

the prevalent rock from the west base of Leland Hill westward to 

the edge of the sloping detrital plain of the Colorado. It is the 

country rock of the Alcyone mine and is exposed on both sides of 

Oatman Wash as far easti as the village of Old Trails. It is the 

rock through which protrudes the imposing rhyolite plug of 

Boundary Cone, and it extends southward beyond the limits of the 

mapped area. 0

From the northern boundary of the mapped area southward to 

Times Gulch the Alcyone trachyte.is generally of uniform character. It is a gray vitrophyre that is, a rock in which small distinct 

crystals, chiefly white feldspar, lie in a blotchy, streaky matrix 

or groundmass that is mainly volcanic glass crowded with microscopic crystals. This is a common texture in rather siliceous lavas 

that become viscous or pasty before they completely crystallize and 

continue to flow in such imperfectly liquid condition. The microscope shows the feldspar phenocrysts as sanidine, or potash feldspar, and andesine, or soda-lime feldspar. With these is usually 

a little biotite or black mica.

A chemical analysis of a typical specimen (0-142) of the Alcyone 

trachyte from the summit of a hill three-quarters of a mile westnorthwest of Cathedral Kock, made by E. C. Wells in the Survey 

laboratory;, is as follows:

Chemical analysis of Alcyone trachyte. 

Si02 ____________.___ 65. 26

FeCL. 

MgOCaCL 

Na=O. 

K=O_.

5 26

6 39

1.98

1.21

.83

2.16

4 93

6.30

HaO above 110° C_ __ __.

H2 0 below 110° C _ .. .

TiO* __ _________

MnO _ _ __ ___ __ .

C02 _ _ _ __ __ _.

. ___ 0.34

47

. _ _ . 55

. _ __ .14

. ____ . 05

. ____ .14

100.05
18 OATMAN GOLD DISTRICT, ARIZONA.

The rock contains more plagioclase and consequently more lime 

and .soda than a typical trachyte and is close to the indefinite line 

that separates trachytes from latites. It might equally well be 

called a trachytic latite or a latitic trachyte, but as there are other 

latites in the area there is a gain in convenience and distinction in 

calling it a trachyte.

The line of Times Gulch marks in general a change in the appearance of the Alcyone trachyte which appears to be a gradation. The 

rock south of Times Gulch shows more alteration, and its general 

color changes from brownish gray to greenish gray. The vitrophyric 

texture is less evident,' and much of the rock is a rather massive 

porphyry, which crumbles on weathering. There is evidence in 

places that this porphyry is intrusive into finer-textured varieties, 

but an attempt to map it separately had finally to be abandoned. In 

places, especially on some of the higher hills between Times Gulch 

and Oatman Wash, are flows that are darker and rather fresher than 

the formation as a whole but are not separable units. The formation 

in this area is apparently a volcanic complex in which flows were 

cut and invaded by intrusive bodies of the same magma, the whole 

belonging to one period of igneous activity.

Along its eastern border the Alcyone trachyte is generally overlain by the Oatman andesite, which in gome places was poured over 

the trachyte but in other places has clearly been forced up .in molten 

condition through it. Where the Oatman andesite- overlies the 

trachyte the two rocks are generally separated by a deposit of sedimentary material of variable thickness and of considerable diversity 

in appearance. One of the most characteristic varieties is a rather 

massive shale which is pale or greenish.gray as seen underground 

but whiqh in weathered exposures is pale buff or cream-colored and 

is more obviously fissile than the unweathered rock. This shale is 

well exposed on the south side of Times Gulch, opposite the mouth 

of the gulch in which is the Oatman Belle shaft, where it is from 

100 to 150 feet thick and might be mistaken for a compact rhyolite. 

It is also exposed at a number of places near the Midnight a'nd 

North Star mines. In some places, as about a third of a mile northAvest of Leland Hill, the creamy shale is overlain by gray calcareous 

shale with thin lenses of limestone. These shaly beds, although in 

many places too thin to map on the scale used for the geologic map 

of the Oatman district, appear to be fairly persistent and, if the 

mines near Oatman ever pass through the bottom of the Oatman 

andesite, should be carefully looked for as an indication that the 

Alcyone trachyte is not far below. The Gold Key shaft, about twothirds of a mile northwest of Old Trails and 338 feet deep, shows 

some of the shale in the duinp, and according to Mr. Charles T. Weid-
PRINCIPAL IGNEOUS FORMATIONS. 19

man the shaft passed out of the Oatman andesite into this material 

at 300 feet.

The shale has been described as resting on the Alcyone trachyte, 

but the exact boundary between the trachtye and the overlying sedimentary material is in many localities very obscure. The trachyte 

in its upper part contains many fragments, also of trachyte, and appears to be a flow breccia that is, a lava which, after partly solidifying, continued to flow, breaking up its congealed crust and mingling 

the fragments with the still liquid lava. Such a rock can not always 

be distinguished from a sedimentary rock composed mainly of fragments of a lava upon which it rests or from rocks composed of particles of lava blown explosively from some volcanic vent. The difficulty in drawing a boundary between the Alcyone trachyte and the 

overlying sedimentary beds is well exemplified in the vicinity of the 

North Star mine. In many places, as just west of the Pioneer mine 

or between the Alcyone mine and Old Trails, the weathered trachyte 

exhibits rather conspicuous lamination, as shown in Plate VI. This 

is probably due to an original flow structure in the trachyte, which 

has been accentuated by weathering.

Near Boundary Cone and south of it the Alcyone trachyte contains 

some masses of volcanic rock that are more calcic than the trachyte 

and should be classed as latite or andesite. These appear to be intrusive in the trachyte as dikes or small irregular masses. It was 

not practicable to map them separately.

At the head of Times Gulch, east of Hardy Mountain and extending northeastward to Silver Creek, is an area of generally decomposed 

or altered rock of doubtful affinities. It has been provisionally 

mapped as Alcyone trachyte but is more biotitic than the typical 

trachyte and closely resembles some of the flows in the formation 

named Gold Eoad latite. As it appears, however, to underlie the 

Oatman andesite, which is certainly overlain by the Gold Koad latite, 

this rock is mapped with the Alcyone trachyte.

In the northern part of the district, particularly north of Times 

Gulch, the Alcyone trachyte contains some lenticular inclusions of 

breccia, composed almost entirely of fragments of pre-Cambrian 

rock and practically identical with the breccia at the base of the 

volcanic series, exposed at the mouth of Times Gulch. Presumably, 

while the trachyte was. being erupted some of the pre-Cambrian rocks 

were not covered by lava and, shattered possibly by volcanic explosions, furnished abundant angular detritus to be washed into local 

and transient basins and buried under later flows. Some of the inclusions are composed entirely of fresh granitic detritus cemented into 

a hard rock that looks and weathers so much like granite as to be exceedingly deceptive.
20 OATMAN GOLD DISTRICT, ARIZONA. 

ESPERANZA TRACHYTE.

The Esperanza trachyte, a rock of distinctive character, is restricted to the southern part of the district and is typically exposed 

in Iowa and Esperanza canyons and in the vicinity of the Highland 

Chief mine.

The general color of the rock as seen in extensive exposures is 

reddish brown, but on freshly broken surfaces it is a rather light 

purplish gray. The texture is very compact, the only minerals recognizable to the unaided eye being black mica in minute sparkling 

foils and hornblende in equally small crystals. Occasionally a few 

small phenocrysts of feldspar, 4 millimeters or less in length, can be 

detected. The rock breaks with splintery fracture and is a decided 

cliff maker. Typical topography associated with it is shown in Plate 

V, A. Sweeping up to the faces of the cliffs are steep detrital slopes 

composed of hard ringing flakes of the trachyte. So sonorous are 

these fragments that the rock has sometimes been referred to as 

phonolite. It is not uncommon to find in the talus slabs from half to 

three-quarters of an inch thick and 18 inches across that ring when 

struck like a plate of steel and require a severe blow to break them. 

With the slabs are slender splinters, perhaps three-quarters of an 

inch thick, 2 inches wide, and 2 feet long.

Under the microscope the rock shows little of interest. It is 

mainly a very fine textured felt of tiny, obscure feldspar crystals 

(microlites) of low refractive index, with probably some glass. Although very different in its lithologic properties it is chemically 

nearly identical with the Alcyone trachyte. It contains, however, a 

little less potassium and a little more iron.

Most of the Esperanza trachyte is a massive lava flow, or possibly 

two or more such flows. Associated with the massive rock, however, 

are some irregular and rather indefinitely bounded masses of breccia, 

made up of fragments of the same rock. Whether these are flow 

breccias or the products of volcanic explosion could not be definitely 

determined. They are believed to be the products of local explosions 

and may mark approximately places where the- trachyte broke 

through from below. The breccia has been cut by the massive 

trachyte.

The Esperanza trachyte extends for an unknown distance south 

of the area mapped, has a width of 2 miles east of Boundary Cone, 

and thence narrows rather rapidly northward, presumably because 

the flow decreases in thickness in that direction. Just north of Sunnyside Wash the trachyte rather abruptly disappears. The thinning 

northern portion of the flow is probably faulted down here, on the 

north side of the Gold Dust-Boundary Cone fault zone, and is covered to the north by the Oatman andesite.
PRINCIPAL IGNEOUS FORMATIONS, 21 

OATMAN ANDESITE.

The Oatman andesite, the " green chloritic andesite " of Schrader 

and the rock in which the largest ore bodies in the district have been 

found, is exposed over a very irregular area. South of Sunnyside 

Wash it crops out as a comparatively narrow belt, from a quarter to 

half a mile wide, separated from the Esperanza trachyte below by 

some light-colored tuffaceous sandstone that has an estimated maximum thickness of 50 feet and overlain directly by the assemblage of 

lava flows that has been designated the Gold Road latite. North of 

Sunnyside Wash and, still more noticeably, north of Oatman Wash 

the area of Oatman andesite expands abruptly to a width of nearly 

3 miles in the latitude of Oatman. At many places along the western border of this area the Oatman andesite rests upon the Alcyone 

trachyte, generally with a thin layer of shale at its base. This relation can be well seen southwest of the Pioneer mine and west and 

south of Leland Hill. In other places, as about a mile northwest of 

Leland Hill, the andesite is clearly intrusive into the trachyte and 

associated shale.

North of Oatman, along Silver Creek, the broad belt of Oatman 

andesite terminates abruptly, its place northward being taken by 

the intrusive Times porphyry and the Gold Road latite. The ending appears to coincide with a zone of faulting, which is obscure 

near the Oatman Amalgamated and Sun Dial mines but is supposed 

to be continuous on the northwest with the Gaddis & Perry lode and 

on the southeast with the Gold Road vein. If, as is probable, the 

downthrow along this fault is on its north side, the effect would be 

to shift to the west the outcrop of the Oatman andesite north of the 

fault. It is quite possible that the area mapped as Moss porphyry 

between the two main branches of Silver Creek may include some 

Oatman andesite. The rock of this particular area has been greatly 

altered, much of it beyond identification, by the introduction of 

finely disseminated pyrite and the subsequent oxidation of the sulphide with the generation of sulphuric acid. The iron of the original 

ferromagnesian minerals has been deposited as hydrous oxide, and 

the aluminous minerals have also been decomposed with the production of alum and other less soluble sulphates. Farther north the 

Oatman andesite is recognizable again at the Mossback mine and beyond the northern limits of the area mapped.

The Oatman andesite, although it comprises a number of flows 

and some intrusive rock, is as a whole fairly uniform in character 

and not difficult to identify in the field. As a rule it is more decidedly 

porphyritic than the rocks previously described, the larger crystals 

or phenocrysts of feldspar being particularly conspicuous. These 

are of moderate size, generally less than a centimeter in length, and 

20535 23 i
22 OATMAN GOLD DISTRICT, ARIZONA.

contrast with the general dark color of the rest of the rock. The 

hue of the rock as a whole ranges from dark gray or nearly black 

in fres;h specimens to moderately dark greenish gray in weathered or 

altered varieties. Some tint of green is almost invariably noticeable. With the exception of the basalt which caps some of the 

higher hills, the Oatman andesite has generally a more "basic" appearance than the other volcanic formations in the district. Unlike 

the trachytes it is, in many places, amygdaloidal that is, it contains 

steam bubbles that have been filled with calcite, quartz, chlorite, or 

minerals belonging to the group known as zeolites. These filled 

bubbles, or amygdules, are particularly abundant in surface exposures south of Sunnyside Wash and near the Gold Dust mine. Some 

as large as 2 inches in diameter were noted. They were observed also 

underground in a number of mines. »

At a few places in the Oatman andesite are found lenticular 

layers of greenish-gray tuffaceous sandstone. As this rock is rather 

soft and crumbling it is not as a rule well exposed at the surface. 

Some of it may be seen in the area of Oatman andesite southeast 

of the American mine and southwest of the Argo mine, where it appears to be about 25 feet thick. Another lens of about 20 feet in 

maximum thickness is exposed alongside the old road three-quarters 

of a mile west of Gold Road, where the sandstone and the Oatman 

andesite are cut by a small dikelike body of rhyolite. Mr. Oscar 

H. Hershey, who is familiar with the old workings of the Tom Reed 

mine, most of which could not be seen in 1921, informed me that in 

the course of his underground work he noted lenses of tuffaceous 

sandstone at various places in the Oatman andesite. The sandstone 

undoubtedly occurs between successive flows, perhaps at more than 

one geologic horizon, and represents intervals of erosion and local 

deposition of sandy detritus derived from the rocks previously 

erupted.

As shown by the microscope, the Oatman andesite consists essentially of feldspar (which ranges in composition from andesine to 

^ labradorite), augite, biotite, apatite, and magnetite in a groundmass 

of glass crowded with small crystals of feldspar and one or more of 

the other minerals named. In the freshest dark specimens the feldspar is clear, but as a rule it is partly decomposed and consequently 

milk-white and turbid. The augite in all but the freshest varieties 

of the rock has been changed to calcite. The biotite is very rarely 

fresji but as a rule has lost its dark-brown color as seen in thin 

sections and become pale green. The alteration product is, in a few 

specimens, identifiable definitely as aggregates of the mineral chlorite, but more commonly it seems to be a homogeneous intermediate 

product that retains some of the optical properties of the biotite. 

It is this prevalent alteration of the biotite which gives the Oatman
PEINCIPAL IGNEOUS FOBMATIONS. 23

andesite its greenish tint. In contrast with some of the flows of the 

Gold Road latite, the biotite of the Oatman andesite is never conspicuous, and neither it nor its alteration product can as a rule be 

recognized with the unaided eye.

An analysis of a sample of Oatman andesite obtained near the 

No. 1 shaft of the United Eastern mine, made by R. C. Wells in 

the Survey laboratory, is as follows:

 Chenvical analysis of Oatman andesite.

SiOa ________________ 56. 37 

ALOa ________________ 15.99 

FeaOa ______________ 2.56 

FeO ________________ 3. 41 

MgO________________ 2.97 

CaO_ _____ _:_____ - 6.81 

Na2O ________________ 2.99 

K2 0 __________________ 2.89

ftO below 110° C________ 0.38

H20 above 110° C________ 1.66

TiOa________________ 1.16

P2O8 ________________ . 41

MnO________________ .07

C'02 __-______-___ ___ _-___ 2.18

99.85

This analysis shows that the Oatman andesite is less calcic and 

slightly richer in alkalies, especially in potash, than a typical andesite and approaches a latite in composition. Another sample analyzed, from Leland Hill, contains 2.68 per cent of soda and 4.13 per 

cent of potash. This particular variety might be classed as andesitic 

latite. Schrader 7 records that a sample collected by him from Leland Hill was even higher in potash, containing 2.60 per cent of 

Na2 0 and 5.19 per cent of K2 0. He classified this rock, naturally 

enough, as latite, although he recognized it as being a part of his 

" green chloritic andesite."

Considered by itself the Oatman andesite might perhaps properly 

be called the Oatman latite. But it is notably richer in lime and magnesia than the other rocks of the district classed as latite and is also 

lower in alkalies.. This difference has led to the choice of andesite 

rather than latite as a general petrographic designation of the formation.

GOLD ROAD LATITE.

The Gold Road latite is a volcanic complex of lava flows and tuffs, 

with a minor proportion of intrusive rock that appears to have been 

forced through some of the lower flows and to pass with no definite 

boundary into some of the upper flows. The flows present considerable variety in texture and composition, ranging upward from fairly 

typical almost wholly crystallized latites to black obsidian-like, pumiceous, or lithophysal flows that might be classed as glassy rhyolite 

and will be separately mapped and named in the final report.

In the southern part of the district the Gold Road latite is largely 

covered by basalt, only a narrow strip being exposed in the cliffs of

7 Op. cit, p. 87.
24 OATMAN GOLD DISTRICT, ARIZONA.

Ute Mesa, at the heads of Iowa and Esperanza canyons. From 

the town of Oatman eastward to the boundary of the area studied 

the rocks forming "the upper part of the main ridge of the Black 

Mountains belong, with few minor exceptions, to this formation. 

Northward, the Gold Koad latite continues as an irregular belt past 

the Mossback mine and passes beneath the younger volcanic formations of the northeast corner of the district.

The basal flow of the Gold Road latite, particularly from Sunnyside Wash northward beyond the Mossback mine, is characterized 

by rather abundant sparkling flakes of biotite and somewhat larger 

phenocrysts of feldspar than the Oatman andesite. As a rule the 

latite is lighter in color than the Oatman andesite and does not have 

the green tint of that rock. A large proportion of the specimens 

from various localities show fairly conspicuous crystals of feldspar 

and many flakes of brilliant black mica in a dense pasty-looking 

groundmass that is pale red-gray or lilac-gray.

The actual contact between the Oatman andesite and the Gold 

Road latite is seldom well exposed. There is apparently no continuous separating layer of sedimentary material between the Oatman andesite and the latite, but in some places the andesite near the 

contact appears to be soft and decomposed, and in others it is a 

breccia, such as might occur, on the upper surface of a lava flow. 

Apparently there was no time for much erosion between the eruption 

of the two lavas. The main criterion for mapping the contact is the 

difference in character of the upper and lower flows. After some 

local field experience the distinction between the latite with its abundant flashing mica flakes and the dark-green Oatman andesite, in 

which fresh crystals of biotite are rare and inconspicuous, can be 

made with certainty. This distinction was recognized by Hershey 

in his work for the Tom Reed Co. and was utilized in his preparation 

of the case for that company against the United Eastern Mining Co.

One locality where the distinction between the Oatman andesite 

and the Gold Road latite is fairly plain is about a mile south of 

Oatman, just west of the saddle through which passes the road to 

the American and Argo mines. The upper part of the hill west of 

this pass, like that of the similar precipitous hill above the American 

shaft, is composed of Gold Road latite. On the west side of this 

hill the contact between the Oatman andesite and the biotitic basal 

flow of the latite can be traced from the north edge of Sunnyside 

Wash, just north of the Pictured Rock shaft, northward through a 

saddle, and then down the northern slope of the hill to a point near 

the Telluride No. 3 shaft. West of this contact is a similar but lower 

hill also capped by the Gold Road latite, which rests on the Oatman 

andesite with a fairly well defined contact. The difference between 

the two rocks can also be well seen near the water tanks on the hill-
PRINCIPAL IGNEOUS FORMATIONS, 25

side above the Bed Cloud shaft, north of Oatman, and the general 

line of the contact can be traced deviously around the hillsides past 

the Arizona Rex shaft to the vicinity of Gold Road. Along the 

ravine halfway between the Arizona Rex shaft and Gold Road, up 

which a road runs to what is supposed to be the United Northern 

shaft, the contact is displaced by what is thought to be the Mallery 

fault or a fissure of tKe Mallery fault zone.

Some upper flows that are here temporarily grouped with the Gold 

Road latite form the general crest of the high ridge east of Oatman 

and are exposed over much of the slope east of that crest and south 

of Sitgreaves Pass. TJiey include some layers of light-colored tuff 

and glassy flows of considerable variety in color and texture. Brown 

ropy lavas of compact texture are associated with nearly black brittle 

vitrophyres that are almost as glassy as obsidian and some frothy 

lavas that are nearly as light and porous as pumice. Some of these 

upper flows contain rough bubble-like cavities of a peculiar kind 

known as lithophysae (Greek for stone bubbles). Most of these 

cavities, some of which are 18 inches long, have been filled with infiltrated silica in the form of chalcedony and opal. When the rock 

weathers and crumbles the opal and chalcedony in large part remain, 

scattered in profusion over the ground. These upper members will 

be excluded from the Gold Road latite and given a distinctive name 

in the final report.

As seen under the microscope the Gold Road latite is found to be 

composed generally of fresh clear feldspars, near andesine in composition and showing by absence of zonal structure a fairly uniform 

composition; biotite; monoclinic pyroxene, pale green or colorless 

in thin section; with apatite, zircon, magnetite, and, in some specimens, titanite. These crystals lie in a microlitic glassy groundmass. 

Some specimens show hypersthene, and in a few quartz is present as 

phenocrysts. Amphibole is very rare. The more glassy varieties 

show less abundant phenocrysts of the minerals mentioned, in a 

matrix of volcanic glass that may contain incipient hairlike crystals 

known as trichites. Many of the glassy rocks display beautifully 

under the microscope the curved lines of flowage characteristic of 

some of the more siliceous lavas that have been solidified before complete crystallization could take place.
26 OATMAN GOLD DISTRICT, ARIZONA.

Qhemical analyses of two samples of the Gold Eoad latite, both 

made by R. C. Wells in the Survey laboratory, are given below:

Chemical analyses of Gold Road latite.

SiOa ....... ....................

A1808 .. .......................

Fe80|.. .............. .........

FeO.................. .........

MgO..........................

CaO.... ............. ..........

NajO..........................

KS0........ ........... ........

1

62.96 

15.36 

2.57 

2.09 

2.50 

4.26 

3.84 

3.96

2

68.94 

13.36 

1.29 

1.04 

.79 

2.02 

2.20 

5.89

H2 0 below 110° C. ............

H2 0 above 110° C .............

TiO«. .........................

PsOs. .........................

MnO... .......................

1

0.23 

1.37 

.72 

.28 

.04

100.18

2

0.28 

3.43 

.47 

.12 

.03

99.86

1. Three-quarters of a mile southwest of Sunnyside mine, near base of cliff. 

2. Three-fifths of a mile south of Sitgreaves Pass, on top of ridge.

The rock represented by analysis 1, although not the conspicuously 

biotitic variety described as particularly characteristic of the basal 

flow of the Gold Road latite near Oatman, represents fully as abundant and characteristic a part of the formation. Although this rock 

may in some places extend down to the base of the formation and in 

others constitute its upper part, it appears on the whole to occupy 

a medial position between the biotitic variety and the glassy, ropy, 

and more siliceous lavas that are generally found near the top of 

the Gold Road latite as here defined. More specifically, it represents the. brownish or reddish-gray, somewhat porous rock that 

forms the greater part of the cliffs along the western face of Ute 

Mountain, extending past the heads of Esperanza and Iowa canyons 

to Sunnyside Wash; it is the rock exposed around the Casey Jones 

shaft in Antelope Canyon and along the Oatman-Kingman road 

from Gold Road over Sitgreaves Pass and down to a point within 

a mile of the pumping station on Meadow Creek; and it is also the 

principal rock exposed in the lower slopes above Cottonwood Creek 

up to about a quarter of a mile below Flag Springs. Its general 

weathering tint is reddish brown. Some of this rock is locally 

known as rhyolite, and it appears to correspond, in part at least, to 

Schrader's "rhyolite series." 8 It rarely, however, shows any free 

quartz, and the analysis is not that of a typical rhyolite. Most 

of the springs in the district issue from this rock.

Analysis 2 represents certain dark, brittle glassy flows that generally overlie the rock of analysis 1, south of Sitgreaves Pass. The 

rock is considerably more siliceous than that of analysis 1, with less 

iron oxide, magnesia, and lime but with more potash and higher 

total alkalies. It might be called a rhyolite vitrophyre, but, as previously explained, it has not been mapped separately from the other 

rock in the present preliminary report.

8 Op. cit, p. 40.
PRINCIPAL IGNEOUS FORMATIONS. 27

The only places in which ore has be'en found in the Gold Road 

latite are in the Gold Road and Gold Ore mines, near Gold Road. 

It is possible that some ore in the Gray Eagle workings of the Tom 

Reed mine may have been stoped from this rock, but the latite is 

generally regarded by those familiar with that mine as unfavorable 

to ore deposition.

YOUNGER VOLCANIC FORMATIONS.

The formations that overlie the Gold Road latite in the northeastern part of the district, namely, the Flag Spring trachyte, the Sitgreaves tuff, the Meadow Creek trachyte, and the Cottonwood rhyolite, contain no ore deposits, so far as known, and will not be here 

described. Full accounts of them will be given in the final report. 

Description of the olivine basalt and associated tuffs, the latest 

products of volcanism in the district, will also be deferred until the 

complete report is prepared.

MOSS PORPHYRY.

The Moss poryhyry, which is the country rock of the Moss mine, 

forms an intrusive mass, a little over 2 miles wide, which extends from 

the vicinity of Silver Creek north-northwestward beyond the limits 

of the area mapped. The typical rock of the area is a pinkish-gray 

medium-grained porphyry, in which the poryhyritic texture is not 

particularly conspicuous, and whose general appearance is suggestive of granite. The recognizable phenocrysts are chiefly plagioclase as much as 1 centimeter in length, and these lie in a crystalline groundmass of pink feldspar (apparently orthoclase), biotite, 

and amphibole. Under the microscope the larger phenocrysts of 

sodic plagioclase (oligoclase-andesine) are seen to lie in a fine granular, in part micropegmatitic groundmass of cloudy orthoclase, 

quartz, biotite, and pale-green amphibole, with magnetite, apatite, 

titanite, and zircon.

A chemical analysis of typical Moss porphyry from a point by the 

road to Meals Camp, three-quarters of a mile north of the Moss 

mine, made by R. C. Wells in the Survey laboratory, is as follows :

Analysis of Moss porphyry. 

SiO, ___ - ____________ 62. 54

Fe2Oa 

FeO 

MgO _ 

CaO

K2O

32. 54

4.42

3.51

2. 5-f

2.41

4 9ft

3.83 

3.98

H»O under 110° C ___ .

H2 0 above 110° C _ __.

TiO. __ _ __ _ __ .

MnO_ ___ - _ - .

. ___ 0. 29

. __ .84

1.05

__ _ .36

.07

100.13
28 OATMAN GOLD DISTRICT, ARIZONA.

The mineral and chemical3 compositions are those of a quartz monzonite porphyry. The chemical analysis is nearly identical with 

that of the Gold Eoad latite (No. 1, p. 26). The Moss porphyry 

is younger than the Alcyone trachyte and, although definite evidence 

on this point was not obtained, is believed to be younger than the 

Oatman andesite. It is possible that the rock, as suggested by its 

chemical composition, may be the intrusive equivalent of the Gold 

Eoad latite.

A number of variations from the typical rock are to be noted. 

Where the porphyry is intrusive into the Alcyone trachyte, as west 

of the Moss mine, the contact is in many places very inconspicuous, 

as the porphyry grades marginally into varieties that closely resemble 

the trachyte. A quarter of a mile south of the Mossback mine, in 

the normal Moss porphyry, are some irregular masses of a more 

coarsely crystalline rock with large pink orthoclase crystals. This 

rock, which is probably a local variation of the Moss porphyry, has 

not been separately mapped on Plate I. ;

The area mapped as Moss porphyry south of the north branch of 

Silver Creek is occupied, as previously noted, by a much bleached 

and altered rock that is only in small part identifiable. It probably 

includes some Gold Eoad latite and considerable porphyry that is 

different in character from that near the Moss mine but is considered 

as probably belonging to the same mass. Much of this material 

along Silver Creek, near the old stone cabins of the early settlers, 

is a coarse breccia that weathers to a rather bright coppery green. 

The origin of this breccia is not clear, but the most reasonably explanation found- is that the Moss porphyry, probably carrying in 

this vicinity some inclusions of the volcanic rocks, was shattered by 

the continued movement of the intrusive mass after it had in part

solidified. Breccia and massive porphyry appear to be mingled in 

inextricable confusion. .

TIMES PORPHYRY.

The exposures'of Times porphyry are confined to the triangular 

area between Silver Greek and Times Gulch, .where the rock forms 

a very irregular body intrusive into the Alcyone trachyte, into 

which it has sent many little dikes, and, on the north, into the Moss 

porphyry. Hardy Mountain, Cathedral Eock, and the bold pinnacles 

along the north side of Times Gulch (PI. IV, A) west of the Times 

mine are all composed of this rock, which in general is easily 

recognized from a distance by its pale-pinkish tint and massive 

weathering.

The Times porphyry is a faintly pinkish rock of rather fine texture 

and not conspicuously porphyritic. At first glance it appears to be 

composed almost wholly of feldspar with ill-defined phenocrysts, the
PRINCIPAL IGNEOUS FORMATIONS. 29

largest 1 centimeter in length, of the same mineral and a few small 

ragged flakes of biotite. A hand lens shows, however, that quartz is 

abundant in the groundmass, although absent as distinct crystals.

Under the microscope, in thin section, the Times porphyry is seen 

to be composed mainly of quartz and orthoclase. These minerals do 

not as a rule occur in distinct separate crystals or grains but are 

intimately intergrown in the manner usually described as micropegmatitic or micrographic. Such intergrowths as seen through the 

microscope in polarized light with nicols crossed are striking objects, 

and the texture is rarely more beautifully exemplified than in the 

Times porphyry. A few thin sections show considerable areas of 

quartz and orthoclase that are not intergrown, but these areas rarely 

show any crystal boundaries and generally grade irregularly at their 

margins into the characteristic micrographic intergrowth. The mineral composition of the Times porphyry is very simple. In addition 

to the quartz and orthoclase, most sections show a little sodic plagioclase, biotite, apatite, and magnetite.

A chemical analysis of the Times porphyry, on material collected 

on the north side of Times Gulch, If miles south 6f Cathedral Rock,

_ ' w

has been made by R. C. Wells in the Survey laboratory. The results 

are as follows :

Chemical analysis of Times porphyry.

AL03 _____ 

Fe303 _ -

FeO

MgO _____ _ .

CaO_ ______ .

Na20 _ ____ _.

K20 ___ ___ .

_ _ _ _ __ 13.45

___ __ __ 1.11

24

4 01

__ ___ _ 5.40

H2 0 above 110°C ______

Ti02 _ __________

MnO ___ ____ _____

C02 _ __________

_______ . 40

. ___ . 39

_ ___ . 04

_ _ __ .06

___ _ .27

99 77

The analysis, although the proportion of soda is a little high, cor- 

: responds to that of granite, and the rock is classed as granite porphyry. The visible plagioclase seems insufficient to account for all 

the soda, and presumably the orthoclase is sodic. Whether it is soda 

orthoclase or a microperthitic intergrowth of normal orthoclase and 

albite could not be definitely determined, as the orthoclase is generally too turbid for satisfactory optical examination.

The analysis of the porphyry is nearly identical with that of the 

glassy spherulitic flow which in this report is named the Cottonwood 

rhyolite, and probably the rock is a product of the same magma. As 

the rhyolite, next to the basalt, is the youngest of the flows, this would 

indicate that the Times porphyry is also one of the younger rocks of 

the district.
30 OATMAN GOLD DISTRICT, ARIZONA.

The Times porphyry could be quarried in blocks of sufficient size 

for building stone were there any local demand for such material, and 

it should be readily worked and durable.

DIKES AND SMALL INTRUSIVE BODIES.

Dikes of various kinds are abundant in the Oatman district and 

may be classified roughly, in advance of detailed study, into felsite 

porphyry 9 and basalt. Under felsite porphyry are included numerous light-colored dike rocks, most of which show phenocrysts of 

orthoclase and quartz and are generally termed rhyolite in the district. A few are darker, evidently less siliceous rocks and may be 

andesite porphyry or latite porphyry. Narrow buff or pale greenishgray dikes of various trends and many of them sharply curved and 

branching traverse the Moss porphyry. As a rule, the rock of these 

dikes is not particularly fresh, and determination of its exact lithologic character.is perhaps not possible.

One rather large dike, in places 50 feet wide, can be traced from 

the western boundary of the district, half a mile south of Silver 

Creek, across Silver Creek at the old stone cabins and thence in a 

general east-northeasterly direction to a point two-thirds of a mile 

south-southeast of the Mossback mine. This is generally a lightgray or greenish-gray rock with conspicuous phenocrysts of quartz 

and orthoclase. In surface exposures it is as a rule decomposed, and 

crumbling well-formed Carlsbad twins of orthoclase can be picked 

from the soft disintegrated dike rock.

A similar but generally harder and fresher rock forms a dike 

that can be followed from the western boundary of the district 1£ 

miles north of Times Gulch eastward past the Times and Ivanhoe 

mines to a point about a quarter of a mile north of the Blue Bird 

mine. West of the Times mine this dike follows the contact between the Times porphyry on the south and the Alcyone trachyte on 

the north. It is conspicuously porphyritic, and rounded phenocrysts are particularly abundant in it.

Many smaller, more irregular, and less persistent felsite dikes 

occur in the central part of the district. Most of them trend from 

west to west-northwest, and some of them split into many branches. 

In tracing one of these dikes it is rather common to find that the 

individual dike followed comes to an end but that another can be 

picked up a short distance on either side of the one first followed. 

This second dike can be followed for some distance to another offset, 

and so on. A typical example of one of these small felsite dikes is 

crossed by the Oatman-Kingman road between the United Western 

and Arizona Central shafts and can be followed westward past the

9 In accordance with L. V. Pirsson's suggestion (Rocks and rock minerals, p. 202, New 

York, 1908) for the classification of rocks without the aid of the microscope.
PRINCIPAL IGNEOUS FORMATION'S. 31

Blue Bird, North Star, and Midnight mines to a point about a quarter of a mile north-northwest of the Oatman Belle shaft and perhaps beyond.

The basalt dikes occur mainly in the northeastern part of the district and as a rule are narrow but remarkably regular and persistent. 

Their general trend is from north to north-northwest. Some of them 

plainly cut some of the basalt flows, but it is probable tjiat these 

flows themselves were fed through similar fissures and that the 

dikes which now traverse them were the feeders of higher flows 

that have been removed by erosion.

Small bunchy, irregular intrusive bodies of a nearly white rhyolite are rather abundant in certain parts of the Oatman district, 

particularly in the Gold Road latite east of Oatman, and have produced two of the most conspicuous topographic features of the 

region. One of these is the sharp white spine locally known as 

The Elephant's Tooth, or The White Elephant, which is visible in 

eastward views from nearly all points near the town~ of Oatman 

(PI. II, B) ; the other is the still more imposing Boundary Cone 

(PI. V, B). These peaks are plugs which were forced up in molten 

condition through the surrounding rocks and which, owing to the 

resistance of their material, have been left as towers after the once 

inclosing rock has been stripped away by erosion. The Elephant's 

Tooth plug, as exposed at the surface, is oval in plan and only 

about 600 feet long. Northwest of it are a number of other intrusive rhyolite masses, the largest of which, about a quarter of a mile 

northeast of Oatman, is about 2,500 feet long and 800 feet wide. 

Most of these masses are nearly white glassy rhyolite, showing flow 

structure. Closely associated with these rhyolite bodies are some 

small masses of rather peculiar breccia. Some of this breccia in 

addition to rhyolitic fragments contains angular pieces of the Gold 

Road latite. The occurrence of the breccia in relatively small masses 

within the latite suggests that it is, in part at least, an intrusion 

breccia. It may be supposed that some of the small rhyolitic masses 

were intruded under a rather thin cover of older rock and, being 

stiff and viscous, were partly brecciated by the movement of the 

lava. Probably also there were volcanic explosions which shattered 

the inclosing latite.

Southeast of Oatman, in the vicinity of the Kokomo shaft of the 

Oatman Mines Co., is a rock intermediate in character between the 

Gold Road latite and typical rhyolite. It is intrusive into the latite 

but is closely associated with breccia and with glassy lithophysal 

lavas that can not be satisfactorily separated from some of the flows 

of similar material that make up much of the upper part of the 

formation mapped as Gold R-pad. latite. The rhyolitic rock near the
32 OATMAN GOLD DISTRICT, AEIZONA.

Kokomo shaft has not been separated from the Gold Road latite on 

the preliminary geologic map (PI. I).

The Boundary Cone plug (PL V, B) is a fine example of this 

form of intrusive body. The tower rises about 1,500 feet above the 

general level of t)ie country west of it. A prominent dike of rhyolite 

extends westward from the central mass nearly to the OatmanTopock road,10 where it is covered by the Quaternary alluvial deposits. A nearly horizontal offshoot, or sill, also projects into the 

Alcyone trachyte on the south side of the cone. A smaller plug, surrounded by the Alcyone trachyte, occurs just northeast of the main 

mass.

THE GOLD-BEARING VEINS. 

DISTRIBUTION, STRIKE, AND DIP.

There is in the Oatman district no general distinction to be made 

between faults and veins. Practically all the veins occupy fissures 

along which faulting has taken place, as a rule before, during, and 

after the period of vein formation. On the other hand, some 

fissures, such as the Mallery fault, "are 37 ounger than the veins and 

contain no original ore.

Vein-filled fissures are particularly abundant in the southern and 

central parts of the district, especially in the Oatman andesite and 

Esperanza trachyte. The general strike is northwest, but the strike 

of individual fissures may range from nearly north to nearly west. 

The dip as a rule is high, over 60°, and to the northeast. Many of 

the fissures branch, but there appears to be no recognizable rule in 

respect to this; some, fissures diverge to the northwest, as near Old 

Trails, and others to the southeast, as on Leland Hill. The veins 

vary in width, but few of them are wider at any point than 50 feet. 

Some are of simple tabular form, with well-defined walls; others are 

complex lodes, the main mass of vein material being accompanied 

by many branching, irregular stringers; others are aggregations of 

stringers, or stringer lodes. Some crop out boldly and conspicuously ; others are most insignificant as surface features. As a rule 

the large ore bodies- of the district have been mined from veins or 

parts of veins that are not prominent at the surface.

MATERIAL AND STRUCTURE OF THE VEINS.

The Oatman veins are mineralogically of simple character, consisting mainly of quartz, calcite, and adularia, associated, in the ore 

shoots, with free gold. As a rule only quartz and calcite are recognizable with the naked eye. The adularia occurs generally in

10 The old road. The new road crosses the dike.
U. S. (JBOLOQICAL SURVEY BULLETIN 743 PLATE VI

r"By. tiff $ " >- -r 

mak?nritim-^-£F'>ft:-: 

A. TWO MILES SOUTH-SOUTHWEST OF OATMAN, LOOKING NORTHWEST.

B. NEAR THE TREADWELL SHAFT OF THE PIONEER MINE. 

LAMINATED STRUCTURE OF THE ALCYONE TRACHYTE.
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE \'II

A. NEAR VIEW OF-THE GOLD DUST VEIN IN A SURFACE CUT JUST NORTH OF 

THE NO. 2 SHAFT OF THE GOLD DUST MINE.

The principal mass of quartz and calcite is here about 5 feet wide, with many stringers on holh

sides.

B. MORE GENERAL VIEW OF THE GOLD DUST VEIlN AT THE SAME LOCALITY, 

LOOKING NORTHWEST.

The extraordinary complex of quartz-calcite stringers here displayed is on the hanging-wall side of 

the vein shown in A and forms a zone at least 100 feet wide. Calcile is more abundant than 

quartz.

-,... -,.. :..- VEIN STRUCTURE.
V. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE VIII

A. PART OF TIIK PIONKKH VK1IN AT I Hi: I If ! ; \ I )\\ K| .1, SHVKT. LOOKING NORTH. 

Shows a complex of banded quarlz-ealcite slringers.

B. PIONEER VEIN, LOOKING SOUTH ALONG THE VEIN AND OVER THE TOP 

OF AN OLD STOPE NEAR THE THIRTY-FIFTH PARALLEL SHAFT.

This vein shows the smooth, regular hanging wall of a strike fault that is younger than the vein 

and supposedly cuts off the ore bodies above the 400 level.

 VEIN STRUCTURE. ;
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE IX

A. Till-: GOLD ROAD VEIN AS EXPOSED ON THE OATMAN-KINGMAN HOAD, 

LOOKING SOUTHEAST.

Shows the relatively regular /OIK; of sheeling followed by this vein.

I,. THE MOSS VEIN AT THE MOSS MINE.

One of the most massive quartz outcrops in the district. Fluorite appears to be generally more 

abundant than calcite in this vein.
GOLD-BEARING VEINS. 33

microscopic crystals, and gold is visible only in unusually rich ore. 

Sulphides, even pyrite, that almost invariable constituent of the 

ores of other districts, are absent from the typical Oatman ores, 

although a little chalcopyrite and chalcocite have been found in the 

Gold Ore vein, near Gold Road, and Schrader " reports that pyrite 

was present in the small ore body of the Rattan mine. The country rock near the veins may contain finely disseminated pyrite in 

small crystals, but it is nowhere conspicuous or abundant. Fluorite 

occurs in some of the veins, particularity those in the Moss and 

.Times porphyries, but apparently is not particularly significant as 

to the presence or absence of gold. In the rich ore from the upper 

workings of the Moss mine some of the gold was found embedded 

in fluorite, and gold was associated with fluorite in a narrow but 

high-grade ore shoot stoped in the Buckeye vein, a spur from the 

Hardy A-ein. On the other hand, fluorite, although a little was seen 

in 1921 in a small isolated ore shoot in the Aztec mine, is very rare 

in the larger ore bodies of the district. In the northern part of 

the district the mineral is found abundantly in some veins, which 

so far as known .are practically barren.

The proportion of quartz and calcite in the veins varies widely. 

Some veins are chiefly quartz; others chiefly calcite. A wide range 

also may be found in different parts of the same vein. As a rule the 

ore is found where both minerals are present. Veins or parts of 

veins that consist entirely of quartz or calcite are, m the Oatman 

district, generally of very low grade or barren.

The larger veins in the Oatman district are essentially stringer 

lodes of very complex structure. Some idea of their complexity 

may be had from figure 2, drawn from sketches, made in March, 

1921, of the Big Jim vein as exposed in crosscuts on the 400 level. 

It will be noted that what is generally termed " the vein " is actually 

made up of two or more veins (the term being here used with its 

narrower meaning for the filling of a fissure), together with many 

irregular veinlets or stringers and a considerable proportion of more 

or less altered andesitic country rock.

The appearance of some typical veins in surface exposures is shown 

in Plates VII-IX.

The individual veins and stringers appear banded in cross section, 

showing that the vein minerals were deposited in successive layers 

from the walls to the middle of the fissure. «Such banding was particularly noticeable in the large ore body of the United Eastern mine 

from the 700 level up, and a typical specimen of the ore from this

11 Op Cit., p. 172.
34 OATMAN GOLD DISTRICT, ARIZONA.

vein is shown in figure 3. In many of the larger stringers or individual veins of the lode the banding is interrupted, and it is plain 

that earlier vein material has been shattered and then cemented by 

later vein material. In the United Eastern and Big Jim veins the' 

shattered vein material consists in large part of gold-bearing, banded 

quartz and calcite, and the later material of relatively barren calcite.

sw. NE.

NE.

c

20 FEET

FIQCRB 2. Sketches showing the structure of the Big Jim vein on, the 400 level, a, Oatman andesite; 6, quartz and calcite, in places showing a banded structure; o, gouge; 

d, andesite traversed by many irregular stringers of quartz and calcite.

In a broad way in the Oatman veins the deposition of fine-grained 

white quartz, which has, in part at least, replaced andesite and contains little or no gold, has been followed by the deposition of the 

gold-bearing quartz accompanied by some calcite and adularia, followed in turn by barren calcite. This general sequence, however, is 

certainly far from being the complete record. Much of the quartz 

that was deposited nearly or quite contemporaneously with the gold
GOLD-BEABING VEINS. 35

has clearly replaced older calcite. Some of it, moreover, appears to 

have crystallized simultaneously with calcite. This indicates at least 

three generations of calcite. A specimen collected from the Big Jim 

dump shows also three distinct generations of quartz, all of which 

are probably older than the characteristic gold-bearing quartz. The

FIGURE) 3. Typical banded ore from' the stope above the 600 level of the United Eastern 

mina a, Brown quartz in thin crusts; 6, rather finely crystalline white milky quartz; 

c, thin layer of honey-yellow oily-looking quartz and probably also microscopic adularia; dt clear quartz intimately associated with the honey-yellow variety and with 

calcite, probably also microscopic adularia; e, layer of dark calcite, quartz, and probably adularia; f, pale greenish-white fine-grained quartz; g, thin layer of honey-yellow, 

oily-looking quartz; h, like f; i, rather coarsely crystalline milk-white quartz; k, oilyyellow quartz; I, clear comb quartz.

conclusion reached is tjiat during the middle stage of vein formation 

quartz and calcite were repeatedly deposited alternately and that 

during this period also they were at times deposited simultaneously 

and some calcite was replaced by quartz. Deposition of calcite has 

probably continued up to the present time.
36 OATMAN GOLD DISTRICT, ARIZONA.

The quartz of the Oatman veins is generally fine grained, and 

some of it, particularly in the finely banded Gold Road vein, is 

chalcedonic or flinty in texture. Crustification is common and gives 

the veins and stringers a banded appearance as seen in cross section, due to the fact that successive crusts or layers of quartz differ in texture or hue. The quartz in which the gold is embedded is 

generally honey-yellow with a characteristic oily luster. The cause

FIODBB 4. Quartz and calclte from the dump of the Black Eagle shaft of the Tom Reed 

workings. Drawn with camera lucida from a thin section as seen under the microscope. 

The calcite (lined shading) in ragged areas is believed to be residual, an originally 

calcitic vein having been partly replaced by granular quartz. Magnified 15 times.

of this tint and luster has not yet been ascertained, as the microscope throws no definite light on this peculiarity.

Much of the quartz associated with the gold in the Oatman veins 

has a lamellar structure. In some varieties the quartz is compact 

and fine grained, but when seen in thin section under the microscope 

with the polarizing nicols crossed the structure becomes strikingly 

apparent. Each lamella or leaf of quartz consists of granules which 

terminate sharply against rectilinear boundaries that are invisible 

in ordinary light. The structure is such as might be expected had
GOLD-BEARING VEINS. 37

the quartz crystallized between closely spaced parallel or slightly 

divergent impervious plane partitions so thin as to be invisible. In 

other varieties the quartz forms fragile septa with open spaces between, so that the mass as a whole is cellular or porous. These 

structures have been recognized as characteristic of the replacement 

of calcite by quartz, and there is ample evidence that such is their

FIGURE 5.-<-Lamellar aggregate of quartz, calcite, and adularia from the dump of the 

Black Eagle shaft of the Tom Reed workings. Drawn with camera lucida from a thin 

section as seen under the microscope. The remarkably thin plates of calcite are 

fringed with, bristling quartz crystals and separated by granular quartz (clear) with 

some adularia (light-line shading). The, section shows one small vug or cavity lined 

with quartz crystals. Magnifled 1-3 times.

origin in the Oatman district. The relation of quartz and calcite 

in the Oatman veins, however, presents some problems that will be 

discussed in the complete report. Figures 4 and 5 illustrate two 

occurrences of quartz and calcite in the Tom Reed vein.

Adularia, a clear variety of the potash feldspar orthoclase, is commonly present with the gold-bearing quartz but can rarely be recognized with the naked eye. Under the microscope, in thin sections, what at first looks like a granular aggregate of clear quartz
38 OATMAN GOLD DISTRICT, ARIZONA.

grains is seen on close inspection to contain grains with a lower 

index of refraction and lower birefringence than quartz. Some of 

these grains are of irregular form, but many show more or less 

of the characteristic rhomboidal or lozenge-shaped outline of adularia and fine cleavage lines. (See fig. 5.)

The calcite of the veins is generally white and shows no unusual 

features. Whether it contains manganese or other constituents besides calcium carbonate has not yet been determined.

The gold of the large ore shoots is invariably in very small clustered particles, like yellow dust included in the quartz. It is visible 

to the naked eye only in exceptionally rich ore. Coarser gold has 

been found in some small rich pockets, such as were worked in 

>early days in the Moss mine. As a rule the gold is rather narrowly 

confined to certain portions of the vein, and assays taken across a 

wide ore body, such as that of the United Eastern mine above the 

700 level, show great variation. One or two thin layers of quartz, 

perhaps less than an inch wide, may contain by far the greater part 

of the gold. Samples that include material from these layers may 

assay from $100 to $200 a ton, while others yield less than $10 a 

ton and the whole vein from wall to wall averages about $25 a ton. 

In the Big Jim vein there are in general two such comparatively 

rich streaks in an ore shoot that as a whole averages about $16 

a ton.

The ore mined on a large scale in the Oatman district has ranged 

in tenor from $7 tp $35 a ton. The ore mined by the Tom Eeed 

Gold Mines Co. from the Aztec mine in 1921 averaged between $7 

and $8 a ton and was 'about as low in grade as has been successfully worked in the district. The ore of the Gold Road mine during 

the later years of operation appears to have averaged about $9 a 

ton. The United Eastern ore in 1921 had an average assay value 

of nearly $22 a ton.

The United Eastern ore, up to the end of 1921, has contained 

from one-half to two-thirds as much silver as gold, by weight. So 

far as known the silver occurs only as the usual natural alloy with 

gold.

ALTERATION OF THE WALL ROCK.

The changes effected in the wall rock by the solutions that deposited the veins have not yet been carefully studied and can not 

here be fully described. In general, the Oatman andesite near the 

veins is light greenish gray and is softer than the original fresh 

rock. The feldspar phenocrysts are dull and chalky, and the groundmass contains disseminated crystals of pyrite, generally 1 millimeter or less in diameter. Thin sections'of such rock, seen under 

the microscope, show that the biotite has become pale green or has
GOLD-BEARING VEINS. 39

been altered to aggregates of chlorite; the feldspars are now aggregates of calcite, quartz, and sericite. Augite has been replaced by 

calcite, and calcite and quartz are abundant throughout the rock 

in irregular aggregates. The iron originally present in the rock in 

biotite, augite, and magnetite is now combined in chlorite and pyrite. 

The only original mineral remaining is apatite.

NOTES ON SOME OF THE MORE IMPORTANT VEINS. 

TOM REED VEIN.

The Tom Eeed vein, which, broadly considered, includes the 

American, Aztec, Big Jim, original Tom Reed or Benjamin Harrison, and United Eastern veins, has been by far the most productive 

in the district, having yielded to the end of 1921 gold and silver 

to the value of nearly $20,000,000.

The general course of this vein and its relation to the geologic 

formations of the district are shown in Plate I. The principal mine 

workings upon it appear in Plate X, and a view over the surface, 

along the lode, is reproduced as Plate XI, A. Another view, in the 

opposite direction, is shown as Plate XI, B.

The general course of the vein, like that of most others in the 

district, is approximately northwest. On the southeast it appears 

as a zone of fissuring and faulting that crosses the crest of the main 

mountain ridge about 2 miles southeast of Oatman and, apparently 

as two nearly parallel fissures, about 250 feet apart, continues down 

the steep west slope of the ridge past the Argo mine. Thence it is 

generally though not continuously traceable on the surface past the 

shaft of the United American mine and can be similarly followed 

northwestward nearly to the Aztec shaft of the Tom Reed Gold 

Mines Co. From the Aztec mine the vein is continuous underground 

through the Big Jim workings (see PL X), but its relations at the 

surface are complicated by a dislocation along the Mallery fault. 

The vein in the Aztec and Big Jim workings dips 70°-75° NE., 

whereas the Mallery. fault, striking nearly parallel with the vein, 

dips 60°-70° SW. The fault is normal, with a throw of about 400 

feet. The effect of the fault is to throw the upper part of the Tom 

Reed vein down and to the southwest, as illustrated by the cross sections of figure 6. As shown by these sections, the part of the vein 

under the fault plane has no outcrop but is limited above by the 

fault plane, from 100 to 400 feet below the present surface. On the 

'other hand, the part of the vein above the fault plane does theoretically come to the surface, although in places it is obscure or covered by superficial detritus. It is this portion above the fault plane 

that was originally developed and stoped by the Tom Reed Gold 

Mines Co. through its Grey Eagle and Bald Eagle shafts. (See 

PI. X.) The discovery that the Grey Eagle and Bald Eagle ore
40 OATMAN GOLD DISTRICT, ARIZONA.

SW. NE.

- 1,700

SECTION Z9

FIGURE 6. Cross sections of the Tom Reed-Big Jim vein and Mallery fault. Taken, with 

omission of some details, from a series of sections prepared by 0. H. Hershey, consulting geologist, and Herman Zulch, engineer, for the Tom Reed Gold Mines Co. Section 

3 is about 400 feet southwest of the Grey Eagle shaft, section 19 is through that shaft, 

and section 29 is about 250 feet northwest of the Grey Eagle shaft and about 80 feet 

southeast of the Big Jim shaft.
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE X

FEET

3,000 -

2,500 -

1,500

CO *SOLIDATED \

MON AR OH MINE

/ RISING SUN

AZTEC CEN-T/ER 8 rf^\

STANDARD

TOMREED EXT.

BENJAMIN HARR1 SON

>r outlining ore I odies 

part of vein lacking

Generalized stopes and known 

stoping ground in Aztec and 

Big Jim mines

A*GO FEET

SHAFT ..

-3,000

- Z.500

-z,ooo

SECTION 

PLAN OF THE PRINCIPAL UNDERGROUND WORKINGS ON THE TOM REED VEIN AND ITS BRANCHES AND GENERALIZED LONGITUDINAL SECTION OF THE ORE BODIES

1,500
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE XI

A. VIEW NORTHWEST, TOWARD OATMAN, ALONG THE TOM HEED VEIN FROM 

THE VICINITY OF THE AZTEC SHAFT.

1, Azlec sliafl; 2, Bald Eagle shaft; 3, Grey Eagle shaft; 4, Red Lion shaft; 5, Big Jim shaft; 

6, Henjamin Harrison shaft; 7, Olla Oatman shaft; 8, United Eastern No. 1 shaft; 9, United 

Eastern No. 2 shaft.

B. VIEW SOUTHEAST ALONG THE TOM REED VEIN.

1, Grey Eagle shaft; 2, Hooper sliafl, on outcrop of the upper segment of the Tom Reed vein; 

3, Bald Eagle shaft, on same outcrop; 4, Aztec shaft; 5, Black Eagle dump; 6, American 

mine.

MINES OF THE OATMAN DISTRICT.
U. S. GEOLOGICAL SURVEY BULLETIN 743 PLATE XII

A. VIEW UP GOLD ROAD GULCH, SHOWING THE SURFACE RELATIONS OF THE

GOLD ROAD MINE.

1, Gold Road mill; 2, No. 1 shaft; 3, No. 3 shaft. All the rock included in the view is the Gold 

Road latite. The general easterly dip of the flows is distinctly shown.

B. LELAND HILL FROM THE SOUTHEAST, LOOKING ALONG THE VEIN. 

1, No. 1 tunnel; 2, No. 2 tunnel; 3, No. 3 tunnel; 4, Mitehell shaft.

MINES OF THE OATMAN DISTRICT. ,
GOLD-BEARING VEINS. 41

was cut off below by the fault and the opening up of the deeper part 

of the vein in the Big Jim ground led to the litigation between the 

Tom Keed Gold Mines Co., owner of the Bald Eagle and Grey Eagle 

claims, and the United Eastern Mining Co., owner of the Big Jim 

claim. There can be no real doubt that the Grey Eagle vein was 

once the direct upward extension of the Big Jim vein. The question at issue was whether such former continuity confers a legal right 

on the owner of the older Grey Eagle and Bald Eagle claims to exploit the part of the vein under the fault plane, within the Big Jim 

claim.

Within the boundaries of the Big Jim, Grey Eagle, and Bald 

Eagle claims the Mallery fault has been carefully studied by geologists engaged by the mining companies, particularly by Oscar H. 

Hershey, for the Tom Reed Co. Its position has been mapped, and 

its effects are generally well understood. It is accompanied by other 

generally subordinate faults, some of which, however, in certain 

cross sections nearly equal it in displacement. The effects of the 

Mallery fault and its subsidiary dislocations are illustrated generally 

in figure 6, which has been reduced and simplified from the series of 

elaborate cross sections prepared by Mr. Hershey in connection with 

the lawsuit. The Big Jim -fault, probably a branch from the Mallery, is found in sections north of the Grey Eagle shaft. Between it 

and the Mallery fault, as shown in section 29 of figure 6, is a portion 

of the vein which has been called by one party to the litigation the 

' sideline vein," and by the other the " intermediate segment." Considerable ore has been stoped from this segment, and as it lies generally under the side line between the Grey Eagle and Big Jim 

claims, ownership was claimed by both parties to the suit. The decision rendered in the Superior Court of Arizona at Kingman, on 

March 28, 1921, asserted the existence of three distinct veins the 

Tom Reed vein, the sideline vein, and the Big Jim vein although 

it was acknowledged that " at some time in the dim and distant 

past" they had been continuous. It gave the Tom Reed vein to 

the Tom Reed Gold Mines Co. and the Big Jim vein to the United 

Eastern Mining Co. That part of the " sideline vein " that has its 

apex wholly within the ground of the Tom Reed Co. was decided to 

belong to that company; all other parts to the United Eastern Co. 

The case has been appealed and was argued before the Supreme 

Court of Arizona at Phoenix in April, 1922. Decision had not been 

rendered at the date of writing.

South of the Grey Eagle shaft another subsidiary fault, known as 

the Hoffman fault, lies under the Mallery.- Between the two fissures 

some small bodies of ore have been found. A number of minor 

faults associated with the Mallery' are known from underground 

work but will not be described in this preliminary report.
42 OATMAN GOLD DISTRICT, ARIZONA.

Where exposed in the ^mines the Mallery fault is generally easily 

recognizable. As a rule it shows a seam of reddish clayey gouge, 

rarely over an inch thick, lying between smooth slip surfaces and 

accompanied by about a foot of soft, crushed andesite or latite. 

In places there are two or three seams of red gouge, and the neighboring rock may be fissured and decomposed for a width of 2 or 3 

feet. There has been no deposition of vein material in the fault 

fissure, although near the places where it cuts the Tom Reed vein 

it generally contains some dragged ore, As a whole the fault itself 

is a rather inconspicuous feature in view of its considerable throw 

of about 400 feet. Whether the displacement is a simple dip slip 

or involves also a considerable strike slip that is, has a notable 

horizontal component parallel with the strike is not known. The 

lack of definite information on this point was brought out in the 

hearings before the superior court in Kingman, and the judge held 

that it is by no means certain that the part of the vein in the 

Grey Eagle claim was ever a direct upward continuation of the part 

now within the Big Jim claim.

At the surface the Mallery fault is very obscure. It has been 

exposed definitely in a small shaft under the aerial tramway to 

the Aztec mine, about 230 feet east of the Grey Eagle shaft. Soft, 

decomposed zones that probably mark the outcrop of the fault have 

been opened also by a few shallow cuts and pits on the Big Jim 

and Aztec Center claims. It probably lies a short distance west of the 

Hartman tunnel, a disused opening just south of the Aztec shaft, 

and passes under a little saddle between the tunnel and the Black 

Eagle shaft. The position of the Mallery fault near the Black Eagle 

shaft is not definitely known. A trip down this shaft, which is no 

longer used, failed to reveal the fault. TJie saddle which lies just 

southwest of the American shaft and through which passes the road 

to the Argo shaft is certainly determined by erosion along a fault 

that has dropped the Gold Road latite on the west against the Oatman andesite on the east. This may be the Mallery fault, it is traceable, though not continuously, in a general south-southeasterly direction througih the Lodestone and Sunny Side claims and apparently 

passes just west of the Sunny Side shaft. Thence it turns to the 

southeast and can be followed with some measure of probability for 

about 1£ miles.

North of the Big Jim shaft the position of the Mallery fault is 

also in doubt. It is apparently cut and displaced by a generally 

west-northwest fissure, which is shown on Plate I as the Oatman 

fault. This fault apparently has a throw of some hundreds of feet, 

with the downthrow on its north side. To the east it can be traced 

over the main ridge and down the north side of Antelope Canyon.
GOLD-BEARING VEINS. 43

To the west it presumably meets the Tom Reed vein obliquely and 

may be represented by the post-ore gouge seams along the Tom 

Reed and United Eastern veins. The ground where the Oatman 

fault and tjie Tom Eeed vein supposedly meet, mainly under the 

Rising Star claim, is covered by superficial detritus and for the most 

part unexplored by mining operations. The present accessible 1 underground workings throw no light on the relation between the Mallery 

and Oatman faults.

What becomes of the Mallery fault north of the Big Jim workings ? 

This question has not been finally disposed of. Some have been inclined to believe that the Mallery fault becomes coincident with the 

Oatman fault and is represented by the gouge-filled fissures that 

accompany the Tom Reed and United Eastern veins. This, however, is not .probable, for the dip and throw of the Mallery fault are 

to the southwest, whereas the dip and throw of the Oatman fault are 

to the northeast. It is more likely that the Mallery fault is represented by a fissure, shown on Plate I, which has been opened by 

some cuts and tunnels north of the Big Jim shaft and is traceable 

over the surface on the North Aztec, Emma, and Merrill claims, past 

the Oatman United shaft. This fissure apparently was the incentive for sinking the Oatman United shaft at the spot chosen and 

was followed by a drift for about 600 feet on the 600 level. As 

exposed on that level, the fissure contains a red gouge and shows a 

rather close resemblance to the Mallery fault as exposed in the Aztec 

and Big Jim workings. It contains a little calcite, but, so far as 

known, no ore. The general dip appeared to be between 70° and 75°, 

to the southwest. North of the Oatman United shaft the fissure, although in places obscure on the surface, appears to continue across 

the Tonopah No. 1 claim into the mass of intrusive' rhyolite that 

occupies portions of the Yankee, Dollar Princess, Surprise, and other 

claims east of the United Eastern mine. It could not be traced 

north of the rhyolite, but the displacement appears to 'be taken up 

by another fissure that forms the eastern boundary of the rhyolite 

and continues north-northeastward, through the United Northern 

group of claims. Here, about half a mile southwest of Gold Road, 

this fissure dips southwest and drops the Gold Road latite on the 

southwest against the Oatman andesite on the northeast. The throw 

is roughly determinable as about 400 feet. This fault thus corresponds in dip and throw to the Mallery fault. The probability that 

it is identical or, at least, that it is a member of the same fault zone 

is increased by the fact that most of the fissures in this part of the 

district dip northeast and the downthrow is generally to the northeast, as along the Gold Road and United Eastern veins.

Under the town of Oatman the Tom Reed vein branches. The 

southwest branch, which to all appearances is the main vein, shows
44 OATMAN GOLD DISTRICT, ARIZONA.

along most of its course a prominent outcrop of quartz and calcite. 

It represents a zone of fissuring along which the fissures have been 

filled with quartz, accompanied by some silicification of the Oatman 

andesite. Subsequently this material was shattered and cemented 

with calcite, which also forms separate veinlets. In places north of 

the Olla Oatman shaft this outcrop is from 30 to 40 feet wide and 

consists chiefly of calcite. Where the vein is crossed by the south 

branch of Kattlesnake Gulch it shows a change of dip. South of this 

point the dip is northeast, but in Rattlesnake Gulch it is southwest, 

at 80°. The width in the gulch is from 6 to 8 feet. In the north 

branch of Rattlesnake Gulch the lode consists of a vein of calcite 

only 3 feet wide, which dips 75° SW. For at least 100 feet in the 

hanging wall the andesite is traversed by many stringers of calcite. 

From this locality northwestward the vein becomes less conspicuous and within a short distance ceases to be recognizable as a surface 

feature. This southwest branch of the Tom Reed vein has been 

explored from the Olla Oatman and Ben Harrison shafts on the 300 

and 500 levels for a distance of more than 2,200 feet, but no ore 

in economic quantity has been found.

The northeast branch of the Tom Reed vein, or the United Eastern vein, in contrast with the other branch, is marked by no outcrop 

of vein material and probably would not have been recognized as a 

vein had it not been discovered by mining operations.

In April, 1921, it was still possible to reach the Tom Reed 500 

level through the fast-closing, abandoned stopes of the United Eastern mine and to see the place where the two veins separate. There 

was no ore at this point, which is about 200 feet northwest of the 

most northwesterly stope of the Tom Reed (Ben Harrison) mine. 

The main vein, consisting here chiefly of many irregular 'stringers 

of calcite accompanied by a strong gouge-filled fissure, plainly divides into two branches, each similar to the main -vein and each accompanied by a gouge-filled fissure. Nothing was seen to indicate 

that one branch is older than the other. The angle of divergence is 

about 50°, and as this angle is nearly bisected by the strike of the 

vein south of the point of branching, one branch is as much to be regarded as theudirect continuation of the main vein as the other. As 

already mentioned, the Tom Reed Co. followed what was afterward 

known as the United Eastern vein for about 100 feet, carrying the 

drift a short distance beyond the Tom Reed ground. Had the operators continued a few feet farther they would have discovered the 

largest and richest ore body yet found in the district, but they evidently did not consider the calcitic stringer lode sufficiently promising to justify purchase of the Tom Reed Extension claim, now owned 

by the United Eastern Mining Co., or to warrant further exploration 

of ground beyond their own boundaries. Subsequent exploration
GOLD-BEARING VEINS. 45

was accordingly confined to the southwest branch) covered by the 

Thomas B. Eeed, Olla Oatman, and Bessel claims, which so far as 

now known is barren.

The United Eastern vein nowhere appears at the surface as a 

distinct vein, although for about 1,800 feet northwest of the point 

of departure from the Tom Reed vein the fissure zone which the 

United Eastern vein occupies coincides, as nearly as can be. determined from the unsatisfactory surface exposures, with the contact 

between the Oatman andesite on the southwest and the Gold Road 

latite on the northeast. The vein fissure is a fault along which the 

Gold Road latite has been dropped against the Oatman andesite. 

The maximum length of the/ United Eastern ore shoot is about 800 

feet, and practically all of it lies southeast of the United Eastern 

No. 2 shaft. Northwest of the shaft the vein decreases in size, and 

before the long north and west crosscuts shown in Plate X are reached 

all vein matter has disappeared and only a gouge-filled fissure continues. Where the two crosscuts leave the drift the andesite is cut 

by a complex of rather irregular and individually nonpersistent 

fissures with no vein matter. It looks at this point as if the United 

Eastern vein had practically come to an end. About 1,000 feet farther northwest, however, the Red Cloud workings of the Tom Reed 

Co. are on a vein which is in line with the United Eastern and is 

supposed to be the same vein. So far as known, no body of ore has 

yet been found in the Red Cloud.

GOLD ROAD VEIN.

The Gold Road vein lies about 1£ miles northeast of the 

Tom Reed vein and has approximately the same strike nearly 

northwest. Not only does the vein appear to have originally 

cropped out conspicuously at many places, but it |has been well exposed by a chain of cuts, shafts, and open stopes for nearly a mile 

southeast of Gold Road. One of the old surface stopes is shown 

in Plate IX, A, a view taken where the vein is crossed by the Oatman-Kingman road, near the No. 3 shaft of the Gold Road mine. 

The general dip of the vein is 80°-85° NE. It follows a fault fissure on which there has been a normal displacement, with, a throw 

of probably over 300 feet. This displacement appears to have occurred before and during the deposition1 of the vein.

A general view showing Gold Road Gulch and the two principal 

shafts of the Gold Road mine is given in Plate XII, A.

At the time of visit, in 1921, the Gold Road mine was idle, and the 

only part of the underground workings to which access could be 

gained was the Line Road tunnel, shown in the longitudinal eleva-
46 OATMAN GOLD DISTRICT, ARIZONA. ,

tion of figure 7. This elevation, which has been compiled from maps 

on various scales, is probably not complete, but it indicates the existence of two main ore shoots, one in the vicinity of the No. 1 shaft, 

near Gold Road, and the other in the vicinity of No. 2 and No. 3 

shafts, in Gold Road Gulch. The lode is a fairly regular sheeted, 

zone 100 feet or more in total width. It appears to consist throughout most of the workings of two main nearly parallel veins, known 

as the North vein and the South vein, accompanied by many smaller 

stringers. As seen in the Line Road tunnel there is a tendency for 

stringers to branch off to the south that is, into the footwall at a 

small angle with the general course of the vein. Some of these have 

been followed in the hope of finding ore, but they are said to die out 

gradually as they diverge from the main vein. The vein as a rule 

is unaccompanied by gouge, but it is cut obliquely by a few faults 

that have shattered the quartz.

The material of the Gold Road vein consists generally of many 

thin layers of fine-grained flinty or chalcedonic quartz, so that the 

vein in cross section is beautifully banded, the effect being enhanced 

by the variety of coloring of the different layers, which range from 

white, pale yellow, green, or buff to dark brown. In some parts of 

the vein the deposition of these layers has been undisturbed; in others 

banded quartz of one generation has been shattered and the fragments cemented by similar quartz of a later period. Calcite occurs 

in distinct veinlets younger than the quartz and, so far as knoAvn, is 

barren. Some adularia is associated with the quartz but is recognizable only under the microscope. Pyrite is apparently absent. 

Free gold was not seen in 1921 but is said to be visible occasionally 

in the ore, which, as noted on page 46, is of low average grade.

Northwest of the No. 1 shaft of the Gold Road mine the vein is 

traceable for only a short distance over the surface. It was explored in this direction from the West Gold Road shaft, but, so far 

as known, no ore was found. The geologic map (PL I) suggests that 

the Gold Road vein may represent part of a zone of fissuring that, 

extending northwestward diagonally across Silver Creek, coincides 

with the contact between the Gold Road latite and Oatman. andesite 

north of the Sun Dial sjiaft and is represented by the Gaddis & 

Perry or Black Wonder lode, north of Hardy Mountain. Proof of 

this possible continuity, however, is not at present available.

MOSS VEIN.

The Moss vein is one of the most conspicuous veins in the district and was probably the first to be worked. The Mossi mine in 

early days yielded about $250000 from a body of high-grade ore 

near the surface, but subsequent exploration of the vein has failed
NW. 

FIGURE 7. Longitudinal elevation of the Gold Roa
48 OATMAN GOLD DISTRICT, ARIZONA.

to discover any large bodies of material containing sufficient gold 

to be classed as ore under present conditions.

From the Mossi mine eastward the course of the vein, about 12° 

south of east, is marked by large outcrops of white quartz associated with colorless to pale-green fluorite. Calcite, although not 

conspicuous in the croppings, is a fairly abundant constituent 

underground in the Moss mine. The quartz isi generally cellular, 

the little vugs or cavities being lined with projecting crystals of 

quartz. The vein dips about 70° S. West of the Moss mine 

there are no large outcrops of quartz, but the continuation of the 

vein is indicated by a zone of fissuring and silicification in the Moss 

porphyry, which is traceable for more than a quarter of a mile over 

the high hill west of the mine. To the east also, beyond the line of 

prominent outcrops, the Moss vein is represented by a zone of fissuring and silicification, with isolated outcrops of quartz and fluorite, past the Midway Moss mine, to a junction with the Mossback 

vein. The total length of the entire zone of fissuring and veining 

is about 2£ miles. Except at its extreme western end, where the 

zone loses its identity in the Alcyone trachyte, the general country 

rock is the Moss porphyry.

The workings of the Moss mine are of small extent, comprising 

a level 220 feet in depth with a total length of drifts and crosscuts 

of about 750 feet; a tunnel level at 65 feet below the collar of the 

shaft and about 900 feet in total length; and some irregular surface 

openings. The vein on the 220 level appears to be fully 90 feet in 

width and as a whole probably carries from $3 to $4 a ton in gold.

A fissure known as the Blind Boy fault, striking northwest and 

dipping northeast, passes just west of the shaft on the surface and is 

followed by the southeast crosscut on the 220 level. This apparently 

has effected some displacement of the vein, which in 1921 had not 

been identified underground on the southwest side of the fault. 

Nearly all of the exploratory work has been done on the northeast 

side of the Blind Boy fault.

LELAND VEIN.

The Leland' is a prominent vein that crops out over the summit of 

Lelancl Hill (PI. XII, B) and extends southeastward through the 

Swiss-American and Golconda mines to a junction witji the Pioneer 

vein at the abandoned Treadwell shaft. The general strike of the 

vein is about 30° south of east, and the dip 70° SW. The vein is 

one of a group of many branching lodes, among which are the Pioneer, 

Lilah, Gold Dust, and Boundary Cone veins. On Leland Hill the 

members of this group converge westward and disappear at or near 

the contact between the Alcyone trachyte and the Oatman andesite,
GOLD-BEARING VEINS. 49

on the west slope of the hill. There is evidently some faulting and 

disturbance of the Oatman andesite where the vein disappears, but 

the exact manner in which the vein terminates is not clear. That 

there is nothing in the character of the Alcyone trachyte itself to 

prevent the continuation of the vein west of Leland Hill is indicated 

by the fact that the vein is strong in this rock between the Golconda 

shaft and the Pioneer vein, appearing in places as a broad stringer 

lode over 50 feet wide. 

The Leland vein yielded, according to Schrader, about 4,500 tons

 of ore in 1903 and 1904 from stopes worked through tunnels in Leland Hill. The vein as seen in these old workings is a stringer lode

 with no gouge and no definite walls. The stopes are 15 feet in maximum width. The vein material is the usual quartz-calcite aggregate 

of the Oatman veins.

About 500 feet south of the Leland vein on the surface is the 

Mitchell vein, which shows croppings of rather promising quartz and 

calcite. Its strike is nearly parallel with that of the Leland vein, 

but the dip is north.

The Mitchell shaft, the only deep working on the Leland group, was 

sunk on this vein to a depth of more than 700 feet. The two veins are 

supposed to come together a short distance above the 700 level. The 

exploratory work from this shaft, which appears to have been neither 

extensive nor well planned, developed no ore, and the 700 level is now 

under water.

GOLD DUST VEIN.

The Gold Dust or Victor-Virgin vein lies about a mile southwest 

of the Tom Reed vein, with which it is approximately parallel, and 

crops out strongly on both sides of Oatman Wash at Old Trails. It 

is a stringer lode with, as a rule, no well-defined walls and shows 

considerable variation from place to place. In some exposures it 

consists of a quartz-calcite vein as much as 12 feet wide accompanied 

by innumerable small stringers, particularly in the southwest wall, 

as shown in Plate VII. In other places it is a brecciated mass of 

andesite, the fragments partly silicified and cemented by quartz and 

calcite. The country rock is the Oatman andesite.

The vein has been explored for a length of about 500 feet by the 

workings of the Gold Dust mine. Two ore bodies have been stoped. 

The larger, southeast of the main or No. 1 shaft, was about 200 feet 

long and extended from the surface to a depth of about 160 feet. 

The pay shoot was narrow, the stopes being kept to the smallest 

practicable working width. A smaller body was stoped between the 

surface and the first level near the No. 2 shaft, about 450 feet northwest of the main shaft. At the northwest end of the 500 level, as 

seen in 1921, the vein splits into two or more branches, illustrat-
50 OATMAN GOLD DISTRICT, ARIZONA.

ing the same tendency toward a northwesterly divergence that is 

shown by the Gold Dust and Boundary Cone veins at the surface.

PIONEER VEIN.

The Pioneer vein, formerly known as the German-American vein, 

lies about halfway between the Gold Dust and Leland mines and 

athwart tjie general zone -of fissuring to which the Leland and 

Gold Dust veins belong. Its general strike is N. 13° W., and its dip 

80°-85° E. The vein is distinctly traceable over the surface for 

nearly a mile and for much of this distance follows the contact between the Alcyone trachyte on the west and the Oatman andesite 

on the east. This is clearly a fault contact, the andesite being 

dropped against the trachyte. How much of the displacement 

occurred at the original opening of the fissure and how much since 

the deposition of the vein could not be determined.

The German-American mine, as it was then called, was in operation in 1907, at the time of Schrader's study of the district, and he 

devotes three and one-half pages to its description. The workings 

were afterward carried deeper, but in 1921 all work had ceased and 

no examination of underground conditions was practicable. There 

are three shafts. The southernmost, the Thirty-fifth Parallel, 220 

feet deep, and the Treadwell, next to the north, 340 feet deep, had 

been dismantled and abandoned prior to 1921. The northernmost 

shaft, the Pioneer, 420 feet deep, caved while an attempt was being 

made to unwater it for examination early in 1921. A number of 

ore shoots were stoped, particularly near the Pioneer shaft. These 

were as much as 400 feet long and 6 feet wide, and the ore had a maximum tenor of $40 a tofl in gold. All the ore bodies were exhausted 

above the 400 level. According to Mr. George F. Moser, superintendent of the mine, the ore was cut off by a fault which, from his 

oral description, appeared to be a strike fault with a dip very nearly 

the same as the vein. A strong fissure filled with gouge, which may 

be the fault referred to, can be seen accompanying the vein near the 

collar of the Thirty-fifth Parallel shaft, as shown in Plate VIII, B.

MIDNIGHT VEIN.

The Midnight vein, which was worked in the Midnight mine, 

about 2£ miles northwest of Oatman, resembles the Pioneer in, having a more northerly strike than most of the Oatman veins. Like 

that vein also, it is accompanied by or fills a fault fissure. The 

Midnight vein, however, dips west, and the downthrow is in the 

same direction.

The Midnight mine, which was described by Schrader,12 has been 

idle for years, and the workings were not accessible in 1921. The

» Op. cit, p. 194.
PRACTICAL CONCLUSIONS. 51

rock on the Avest or hanging-wall side of the fissure at the mine is 

the Oatman andesite. On the footwall side, however, are some areas 

of the peculiar shale that in this part of the district separates the 

Oatman andesite from the Alcyone trachyte. The occurrence of this 

shale suggests that the lower workings of the Midnight may be in 

the Alcj^one tracl^te.

OTHER VEINS.

There are man}^ other prominent or well-defined veins in the district, such as the New York, Mossback, Gaddis & Perry, Hardy 

or Record Lode, Pasadena, Blue Bird, Telluride, Lazy Boy, Esperanza, Crown Point, and Highland Chief, which deserve description 

in a complete report on the district. That they and some others 

not named are omitted from this preliminary report does not mean 

that they are necessarily less important or less promising than some 

that are mentioned.

PRACTICAL CONCLUSIONS.

To men interested in the mining development of the Oatman district, answers to certain questions are of great importance. Some 

of these questions are as follows: Are the ore deposits confined to 

any particular rock or rocks? What are the chances of finding additional ore bodies below or at greater depth than those now known ? 

At what depth will the known productive veins be found in preCambrian granite, gneiss, or schist? At what depth will veins 

now worked in the Oatman andesite go out of that rock, and what 

will be found below it? Are the large ore bodies confined to any 

particular area, or may they be reasonably sought for in other parts 

of the district?

Unfortunately, none of these questions can be positively and definitely answered. The geologist can not see below the surface, and 

in spite of all the study given to ore deposits, the conditions that 

determine wjiy a certain vein should contain an ore shoot worth millions of dollars Avhile others are barren remain practically unknown. 

Ore deposition takes place under circumstances that can not be reproduced in the laboratory. No one knows with certainty where 

the gold comes from or what delicate balance of complex circumstances determines its deposition in a particular place. We know 

that there is a connection between the occurrence of most gold ores 

and igneous activity. It is generally supposed, with considerable 

evidence in favor of this view, that the solutions which deposited 

the gold came wholly or in part from solidifying igneous material 

or magma. But notwithstanding the vigor and ability with which 

this opinion has been maintained by many geologists, it is certainly
52 OATMAK GOLD DISTRICT, ARIZONA.

very far from being so completely demonstrated as is, for example, 

the general theory of organic evolution or the dependence of certain 

' diseases upon particular bacteria.

No one who visits Oatman can fail to be impressed with the large 

number of well-defined veins, consisting chiefly of quartz and calcite. 

:Some crop out boldly and conspicuously; others, although less prominent, can readily be followed over the surface; still others, such as 

the United Eastern and parts of the Tom Reed vein, although large 

and productive, give very slight surficial indications of their presence. A notable feature of these veins is the general absence of 

minerals with metallic luster. The veins, in comparison with those 

of most other districts, have a barren appearance, and it must be 

admitted that few of them, on closer investigation, have dispelled 

this unfavorable first impression. In two lodes only, the Tom Reed 

and its branches and the Gold Road, have ore bodies large enough 

to warrant fairly extensive mining operations been found. Good 

ore has been found in 10 or 12 veins, and some are credited with 

outputs amounting to a few thousand dollars, or even, as at the Moss 

mine, to a quarter of a million dollars. These ore bodies, however, 

have been small and have been exhausted within a disappointingly 

short distance from the surface.

On the whole, therefore, in spite of the rather extraordinary number of veins in the Oatman district, such evidence as is available 

indicates that comparatively few of them contain ore shoots that 

would justify mining and milling equipment to handle over 200 tons 

of ore a day.

It can not be said that the veins of the Oatman district are confined 

to any particular rock, although, as shown in Plate I, the more conspicuous ones, those recognizable in the course of geologic mapping, are especially abundant in certain formations and rather lacking in others. They are more numerous, for example, in the Esperanza trachyte, the Oatman andesite, and parts of the Gold Road 

latite than they appear to be in the Alcyone trachyte. This difference, however, may have no relation to the character of rock but may 

be simply a matter of areal distribution. For example, if the Esperanza trachyte were removed, the same veins that now show so conspicuously south of Iowa Canyon might appear with equal distinctness in the underlying Alcyone trachyte. Some evidence that this 

may be the case is furnished by the Leland vein, which between the 

Golconda and Pioneer mines crops out strongly in the Alcyone trachyte. On the other hand, Schrader's report in many places records 

the opinion that the Alcyone trachyte (his "older andesite") is 

decidedly unpromising as regards the possible occurrence of ore, and 

this view is rather generally held in the district. It is quite true 

that the strong Leland vein does not appear to continue into the
. ~" PBACTICAL CONCLUSIONS, 53

Alcyone trachyte west of Leland Hill, that this rock as exposed at 

the surface shows comparatively few veins, and that no ore bodies of 

any importance have yet been found in it. There is some cause, 

therefore, for regarding it with disfavor. Nevertheless the rock is 

not very different in character from the Oatman andesite, and there 

is no apparent reason why, under favorable conditions, it should not 

contain ore. That it is everywhere barren or is a rock of such 

character that ore can not be deposited in it is certainly far from 

having been proved.

The mines near Oatman, the United Eastern, Tom Eeed, Big Jim, 

and Aztec, are mainly in the Oatman andesite, and the question has 

naturally arisen, At what depth will the shafts go out of this rock? 

This can not be answered with precision, for two reasons: First, the 

attitude or dip of the Oatman andesite as a whole is not known. 

Second, as the Oatman andesite is known in some localities to break 

intrusively through the older formations, it can not be assumed that 

its under surface is approximately plane, like that of a bedded 

formation such as sandstone. The Mitchell shaft of the Leland 

mine, for example, is reported to have gone through the bottom of 

the Oatman andesite into the Alcyone trachyte but to have entered 

Oatman andesite again at greater depth.

Attention may now be called to Plate I, which shows a section 

across the district approximately at right angles to the general strike 

of the formations. It will be observed that the Oatman andesite,

"

where crossed by this section, is bounded on the west.by the Pioneer 

fault. Its actual base at this point is not known but is assumed to 

be about 400 feet below the surface. If so, and if, moreover, the dip 

is regular, if the apparent thickness of the andesite between the 

Pioneer fault and the town of Oatman is not increased or diminished 

by faulting, if the bottom of the flow is a plane surface, and if the 

average dip is zero, then the bottom of the Oatman andesite under 

the town of Oatman should lie at a depth of about 800 feet. The 

andesite has been ascertained, however, from shafts and diamonddrill holes to be at least 1,500 feet thick vertically at that point; 

this thickness corresponds to a dip of 5°. If the dip is 10° and the 

conditions are as assumed, the depth to the bottom of the flow under 

Oatman would be about 2,200 feet. If, as seems probable, the dip is 

at least 15°, the depth would be 2,800 feet. A dip of 20°, which is 

possible, would give a depth of 3,400 feet.

Probably none of the conditions assumed is in accord with fact, 

but it is impossible to take account of the possible departures from 

the assumptions made. As a working hypothesis, it may be concluded that it would be necessary to sink from 2,500 to 3,000 feet to 

penetrate the Oatman andesite under the town of Oatman. The
54 OATMAN GOLD DISTRICT, ARIZONA.

reader is. again reminded that this is not an accurate determination, 

but is merely the best estimate possible under the circumstances.

There has been some speculation among mining men as to what 

would be found beneath the Oatman andesite, and the possibility of 

the mines going into pre-Cambrian granitic rock has often been 

discussed. It is highly probable, however, that the Oatman andesite 

is underlain by the Alcyone trachyte, which, if it is anything like 

as thick as it appears to be west of Oatman, would give a vertically 

measured thickness of at least 2,600 feet of volcanic rock to be penetrated below the bottom of the Oatman andesite, on the supposition 

of a 15° dip. The granite is not likely to be reached in the mines 

near Oatman.

Should the shafts or drills near Oatman go through the Oatman 

andesite, that fact will probably be indicated by the occurrence of 

distinctly bedded shaly layers such as generally mark the top of the 

Alcyone trachyte.

The largest and richest ore body yet found in the district, that of 

the United Eastern mine, extended from a point 270 feet below the 

surface to a depth of about 1,070 feet, having thus a vertical range 

of about 800 feet. It was about 1,000 feet in total length and as 

much as 50 feet wide. It exemplifies what is rather rare a large 

ore body which was intact when found, having undergone no erosion, 

and of which the lower limit is fairly well determined. The more 

northwesterly of the two ore bodies worked from the Benjamin Harrison shaft of the Tom Reed mine was stoped from a point about 70 

feet below the surface to a depth of a little more than 1,300 feet (to 

the 1,400 level). Its maximum stope length was 650 feet on the 300 

level, and the length decreased downward to less than 150 feet on the 

1,400 level. The second ore body, which came practically to the 

surface at the Benjamin Harrison shaft, was stoped to a depth of 

nearly 900 feet. Its maximum stope length was about 600 feet, on 

the 500 level. The Aztec-Big Jim ore body, which is probably the 

longest continuous ore shoot known in the district, has its relations 

to the surface complicated by the Mallery fault and is not yet fully 

defined by stoping. It apparently has a stope length in the Aztec 

and Big Jim workings of fully 1,500 feet. It is doubtful whether any 

considerable part of this vein will be worth stoping below a depth 

of 600 feet.

Not much information could be obtained in 1921 concerning the 

Gold Road ore bodies. The maps seen indicate that the ore body 

stoped from the No. 1 shaft, near Gold Road, extended from the surface to a depth of 700 feet, with a maximum stope length of 800 feet. 

According to Schrader,18 the ore in this part of the mine was as much 

as 22 feet wide. Whether the Sharp, Rice, and other ore bodies

18 Op. cit., p. 158.
PRACTICAL CONCLUSIONS. 55

shown on the maps as occurring in the Line Road and Billy Bryan 

claims are isolated shoots or parts of one large ore shoot is not known. 

The maps show no stoping in this part of the ground below a depth 

of 900 feet, although exploration appears to have been carried considerably deeper.

In the United Eastern mine the best ore was found above the 600 

level and, as seen in cross section, showed conspicuous banding of 

the kind illustrated in figure 3. On the 700 level little or no vein 

material of this character was found. In the Big Jim mine only 

about 50 feet of the vein on the 600 level contains ore, and the bottom of the ore shoot is probably only a few feet below the level. 

The TOO level of the Aztec mine, which had merely crosscut the vein 

at the time of visit, in April, 1921, showed quartz and calcite but no 

ore. Subsequent development on this level is' understood to have 

been discouraging.

To sum up, certainly very little ore has been found in the Oatman 

district below a depth of 1,000 feet, and most of the known ore 

bodies have terminated at depths considerably less than 1,000 feet.

Although in the Oatman ores the gold was deposited in the later 

part of the period of vein formation, it appears to be of hypogene 

origin; there is no evidence, so far as could be determined, of downward enrichment.

The general geologic history of the district indicates that at the 

time the veins were formed the ore shoots could not have been 

more than about 3,000 feet below the surface. The deposits are 

distinctly of the Tertiary bonanza type, formed at comparatively 

shallow depths, as an aftermath of volcanic activity. In such 

veins the ore shoots are generally confined to a fairly definite 

zone of vertical range, the parts of the veins above and, more particularly, below this zone being barren. The larger productive 

mines near Oatman have yielded and are yielding their output from 

this productive zone, which corresponds to the conditions of temperature and pressure under which the gold was originally deposited 

by general ascending and probably thermal solutions. Were the 

veins of different type, such as the older, more deep-seated veins of 

the western slope of the Sierra Nevada, the search for additional 

ore shoots at considerably greater depth than those now explored 

at Oatman might hold out promise of success. A careful consideration of all the evidence indicates, however, that in the Oatman district there is little chance that additional ore bodies will be found 

at much greater depth than those now known. This does not mean 

that some ore may not be mined below what are now the deepest 

stopes, but the hope that some hundreds of feet below such an ore 

body as that of the United Eastern another comparable body may be 

found has little to support it..
56 OATMAN GOLD DISTRICT, ARIZONA.

The occurrence of the Katherine ore body in the pre-Cambrian 

rocks north of the Oatman district and the fact that this ore, in 

structure and mineralogy, rather closely resembles that of the United 

Eastern mine of course suggest the occurrence of similar ore in the 

pre-Cambrian rocks under the volcanic flows of the Oatman district. 

The significance of this piece of evidence, however, would be greater 

if it could be shown that when the Katherine vein was formed the inclosing granite was covered by 8,000 or 10,000 feet of rock that has 

since been removed by erosion. Although the former presence of 

such a covering is possible, it does not on the whole appear probable, 

and the vein itself does not have the character of one formed at 

great depth.

In conclusion, it may be said that the Oatman district does not 

hold out inducements for extensive exploration at depths greater 

than about 1,500 feet, and that the possibility of finding in granite 

under the lava flows at Oatman ore bodies comparable to those known 

is practically negligible. For a strong company or a combination 

of companies to put down a few drill holes below the ground that 

has given them such rich returns is probably a wise and prudent 

expenditure of money, but the chances are believed to be decidedly 

against a successful outcome.

That additional ore bodies remain to be discovered in the Oatman 

district at moderate depths is probable. The district, as has been 

shown, presents some rather unusual difficulties to prospecting of the 

ordinary kind, as some of the largest ore bodies thus, far discovered 

gave little or no indication of their presence at or near the surface.. 

Some of the most conspicuous vein outcrops apparently have nothing 

of value beneath them, and no criteria have yet been recognized that 

will enable a prospector to determine from superficial operations 

whether or not a vein is likely to be productive at a depth of a few 

hundred feet.
INDEX,

Page.

Adularia in the veins, nature of_ 37-38

Alcyone trachyte, analysis of__ 17

eruption of ___ 13-14

hills carved from______ 10

laminated structure of, platea

showing_ 32

nature and distribution, of 17-19

possible occurrence of ore in 52-53

Alteration of the wall rock . 38-39

American mine, development in 8

Basalt, black olivine, thickness and

distribution of_ _ 16

Big Jim fault, displacement caused

by_____________ 4J.

Big Jim vein, discovery of 6-7 

litigation over __________ 7-8, 41 

Black Eagle claim, work on____ 6 

Black Mountains, topographic features of _______ 9-10 

view of, southeast of Oatman,

plate showing ___ 8 

western front of, plate showing 8 

Blind Boy fault, description of___ 48 

Boundary Cone, description of___ 10-11,

12, 31, 32 

plate showing____ ______ 9

Carleton, Gen. J. H., prospecting by

soldiers of_-____- 3 

Cottonwood Creek, flow of______ 11 

Cottonwood rhyolite, nature and distribution of______- 16

Deposition of the materials of the

veins _________ 33-35 

Dikes, occurrence and rocks of __ 30-32 

Drainage of the district-- _ 11

Elephant's Tooth, description of _ 10-11,

12,31 

Esperanza trachyte, hills capped by,

plate showing- ____ 9 

nature and distribution of ___ 14, 20

Flag Spring trachyte, nature and

distribution of _____ 15-16

Geology of the district_________ 11-32

German-American mine, condition

of_ _ 50

Page.

Gold, occurrence of___ ______ 33, 38

Gold Dust vein, discovery of_____ 4

features of ____________ 49-50

plates showing 32

Gold Road latite, analyses of____ 26 

nature and distribution of-- 15, 23-27

Gold Road mine, surface relations

of, plate showing __ 41

Gold Road vein, description of - 45-46 

discovery of __ 4 

plate showing __ 33 

work on ___ 5, 8

Grey Eagle shaft, discoveries made

in____________ 7

Hardy vein, discovery of_____ 4 

Hills, capped by Esperanza trachyte,

plate showing_ __ 9

forms of and rocks composing 9-11

History of mining in the district- __ 3-8

Hoffman fault, situation of_______ 41

Leland Hill, height of_________ 10

plates showing- ___ __ 8, 41

Leland mine, early development at_ 4-5

Leland vein, description of ____ 48-49

discovery of _ _____ __ 4

Mallery fault, description of____ 42-43 

displacement caused by______ 39-41

Map, geologic, of the Oatman district- ________ 8 

Meadow Creek trachyte, nature and

distribution of____ 16 

Midnight vein and mine, features of __ 50-51 

Minerals of the veins _______ 32-33 

Mitchell vein, features of_______ 49

Monzonite porphyry, topographic

features of __ __ 10

Moss mine, plate showing______ 8

Moss porphyry, analysis of___ _ 27

intrusion! of _ _ 12

nature and distribution of__^27-28

Moss vein, description _____ 46-48

discovery of __ _:__ __ 4

plate showing__ _ __ __ 33

Oatman andesite, analysis of 23

"formation probably underlying- 54

nature and distribution of__ 14-15,

21-23

thickness of__________ 15,53-54 

Oatman United mine, discovery of

ore in__ _ _ 8

57
58 INDEX.

Page.

Ore, minerals and structure of_ .32-38 

occurrence of, in particular

rocks ___________ 52-53

tenor of______________ 38

theory of deposition of____ 51-52

Ore bodies, downward extent of 54-55

Pioneer vein, features of_______ 50 

plates showing 32 

Pre-Cambrian rocks, improbability

of ore deposits in 56 

Prospecting, difficulties of- 56

Quartz of the veins, nature of 86-37 

Ruth mine, plate showing 8

Sedimentary rocks, deposition of- 14,

16-17, 22

Silver, occurrence of_______ 38 

Silver Creek, course and flow of 11 

placer mining on_______ 8 

Sitgreaves tuff, nature and thickness of- _____ 16

Tellurlde vein, mining on_ ___ 5, 8 

Tenor of the ore. __________ 38

Times Gulch, flow in _______ 11 

mountains on northwest side of,

plate showing 8

Times porphyry, analysis of___ 29

hills composed in part of 10

intrusion of 12

nature and distribution of_ 28-30

Page.

Tom Reed vein, course of_-____ 39 

faulting on____ _ _ 39-41 

mining on____________ 4, 5, 7, 8 

northeast branch of -- - 44-45 

plan of workings on _ _ 40 

southwest branch of_______ 43-44 

veins grouped with 39 

view northwest along, plate

showing 40 

view southeast along, plate

showing 40 

Topography of the district _ 8-11 

Trachyte, hills carved from 10 

See also Alcyone trachyte and 

Esperanza trachyte.

United Eastern Mining Co., history

of ___________ 5-6, 7-8 

United Eastern vein, features of 44-45 

Ute Mountain, view northwest from,

plate showing 8

Veins, great number of 52 

proportion that have proved

barren 52 

gold-bearing, distribution, strike

and dip of- 32 

material and structure of_ 32-38 

Victor-Virgin vein. See Gold Dust

vein. 

Volcanic flows, nature and sequence

of____ _ __- 12-16

Wall rock, alteration of 38-39 

Wells, R. C., analyses by_ 17, 23, 26, 27,29

o