UNITED STATES DEPARTMENT OF THE INTERIOR 

Harold L. Ickes, Secretary

GEOLOGICAL SURVEY 

W. C. Mendenhall, Director

Bulletin 859

GEOLOGY OF THE

SANTA RITA MINING AREA

NEW MEXICO

BY

A. C. SPENCER AND SIDNEY PAIGE

UNITED STATES

GOVERNMENT PRINTING OFFICE 

WASHINGTON : 1935

For sole by the Superintendent of Documents, Washington, D. C. - Price 40 cents (Paper Cover)

Page

Abstract.___--___---_____-___-____-__-- ---____-___-_--__-_-____ 1

Introduction _ ___________________________________________________ 2

Field work and acknowledgments.______________________________ 2

Geographic position.__----________.-_-_-__.__-__________--._-_ 3

Topography-__-________-___-___-__----__-___________-__-___-_ 3

Climate and vegetation.______.,________________________________ 4

Historical data__--__-___-_--_-__-_--_---._--.___.__----__------_ 5

History of mining..___________________________________________ 5

Production. ._._-...-_. . --____. .. -._. 9

Literature. _ _--___-___-___-_______--_--__-_______-_____--_____ 10

Stratigraphy__ _.________________________________________________ 12

Paleozoic formations_______________________________^________ 12

Bliss sandstone (Cambrian)____.________'___________________ 12

Limestone formations of the Ordovician and Silurian._________ 14

Percha shale (Devonian)___________________________________ 18

Divisions of the Carboniferous system._________---_------___ 19

Lake Valley limestone (Mississippian)_______________________ 20

Magdalena group (Pennsylvanian)__________________________ 22

Oswaldo and Syrena formations..__-_----_-_--__-__--___ 22

Abo redbeds (Permian)____________________________________ 26

Mesozoic formations______-____-------_-______________--_____ 28

Beartooth quartzite (Cretaceous)____________________________ 28

Colorado shale (Cretaceous)_________--______-_--_-__-_-____ 30

Tertiary formations._______--__-______--_____-_________--.____ 31

Gravel, sand, and tuff_____________________________________ 31

Igneous rocks___-_---_---___-_______-___-_-_____--_________-_--_-. 32

Volcanic rocks of Upper Cretaceous age_.______________________ 32

Intrusive rocks of late Cretaceous or early Tertiary age______._____ 33

Quartz diorite porphyry_______________.____________________ 33.

Granodiorite and granodiorite porphyry____'________________ 35

Santa Rita stock._____________________________________ 35

Hanover-Fierro stock..________________________________ 36

Stocks at Copper Flat-__--_-__-________________-_--___ 38

Other granodiorite dikes.___-__-__-_______--_----______ 39

Tertiary lavas______-__-______--_--______-________________ 40

Tertiary stocks and dikes._________________________________ 41

Structure ________________________________________________________ 42

Broad features..___--__--_-_---___------_____-___________-____ 42

Folds___--_------_------_-----_-_---__-______________________ 43

Faults..---.-.------_.__-___-.--_...___;______.__ 46

Metamorphism. __-_-___-_--_____-____---.______,____ ____________ 56

Geologic history.__________________---__._____.____-_-___.____-_ 60

m
IV CONTENTS

Page

Ore deposits.__.__________-_._____-_-__-_-_-___-___._._.--.-______ 64

Contact-metamorphic deposits..-_--_-_________._____'___-__-____ 64

Iron ores____--_----_-_-----_-___-----__-__-_---------__-- 64

Zinc ores-__--------___-------------_----___---_----_-_-_- 66

Ores of disseminated chalcocite at Santa Rita---__--_------------- 69

Veins..---------------.--_------------- -----__...___... 72

Index_____-------_--_-----_---------------------_---------_--.- 77

ILLUSTRATIONS

Page 

PLATE 1. Geologic map of Santa Rita quadrangle, New Mexico. __ In pocket.

2. Structure sections of Santa Rita quadrangle..__-._----._ In pocket.

3. Columnar section of formations in and near the Santa Rita

area._________________________________________________ 12

4. A, Tertiary gravel, sand, and tuff beneath rhyolite lava, south 

side of basin southeast of Lucky Bill shaft; B, Tertiary 

rhyolite resting on gravel, sand, and tuff_____._______.. 36

5. A, Lava range near east edge of Santa Rita quadrangle; B, Tertiary bedded sand and gravel near Hanover Creek ______ 36

6. A, Brecciated granodiorite cut by network.of quartz veins along 

Barringer fault zone; B, Colloform masses of silicate minerals replacing white limestone of Lake Valley formation_. 36 

FIGURE 1. {0re body, stripping limits, pits, and waste dumps at Chino

mines__ _ _-_-___---_----_--_--_____.-__--_____-_____ 70
GEOLOGY OF THE SANTA RITA MINING AREA, 

NEW MEXICO

By A. C. SPENCER and SIDNEY PAIGE

ABSTRACT

The Santa Rita, mining area (pi. 1), covering 35 square miles of semiarid 

mountainous land, lies within the Silver City 30-minute quadrangle, Grant 

County, N. Mex., and includes the most productive part of the Central or 

Hanover mining district. Ore was produced in this district as early as 1804 and 

production continued intermittently for a century before the developments were 

undertaken that led to large-scale copper mining, which began in 1912. The 

output of zinc, lead, and iron increased markedly about the same time.

The sedimentary rocks of the district include the Bliss sandstone (Upper 

Cambrian), El Paso, and Montoya limestones (Ordoviciari), Fusselman limestone (Silurian), Percha shale (Devonian), Lake Valley limestone (Mississippian), Magdalena group (Oswaldo and Syrena formations, Pennsylvanian), 

Abo redbeds (Permian), and Beartooth quartzite and Colorado shale (Cretaceous). Intense metamorphism has profoundly changed the appearance of 

the formations, particularly the limestones and the Abo redbeds, throughout 

much of the district, and for this reason it has been impracticable to map the 

Montoya and Fusselman limestones separately. Unconformities are recognized 

at the tops of the El Paso, Fusselman, and Abo formations. The thicknesses, 

especially of the lower formations, have been considerably reduced by the 

squeezing that accompanied the granodiorite intrusion in the vicinity of 

Hanover.

Igneous activity took place in Cretaceous and Tertiary time. The igneous 

rocks of known Cretaceous age include volcanic breccia intercalated in the 

upper part of the Colorado shale; the late Cretaceous or early Tertiary rocks 

include later stocks, sills, dikes, one great laccolith of quartz diorite porphyry, 

and still later intrusive stocks of granodiorite. Two of these stocks, the Santa 

Rita and Hanover-Fierro, are accompanied by the principal ore deposits of the 

district. The Tertiary formations include basal tuffs, breccia, and gravel deposited on a maturely eroded surface, alternating flows of rhyolite and andesite, 

and dikes and small stocks of quartz latite.

The principal structural features include folds of Cretaceous age and faults 

that were formed in late Cretaceous, Tertiary, and Quaternary time. The 

principal fold, called the Fort Bayard arch, extends southwestward across the 

area and is modified by a few local transverse folds, some of which were clearly 

formed at the time of the granodiorite intrusions. Although some faulting 

may have preceded these intrusions, the earliest clearly recognized faults were 

formed a little later, and many of them served as conduits for ore-forming 

solutions. Tertiary faults displace the lavas that rest unconformably on the 

Cretaceous rocks, and a few faults in or near the area displace alluvial deposits
2 SANTA EITA MINING AEEA, NEW MEXICO

that are presumably of early Quaternary age. Renewed movement along the 

older faults took place during the later periods of faulting.

Metamorphism is pronounced in fractured ground within and adjacent to 

the marginal parts of the granodiorite stocks. The effects of metamophism are 

reflected in the recrystallization of limestones, the development of silicates in 

limestone and shale, the replacement of limestone by ores of iron and zinc, 

the sericitization and silicification of shale and sandstone, and the widespread 

sericitization of quartz diorite and granodiorite. Alteration that followed intrusion of the Tertiary stocks was mainly expressed by alunite.

Prolonged erosion followed rnetamorphism and ore deposition and was accompanied by some enrichment of the deposits before they were covered by 

Tertiary rocks. After erosion had removed these rocks from the mineralized 

areas enrichment was resumed.

The principal ore deposits include the contact-metamorphic depostis of magnetite; sulphide deposits, mainly of .zinc blende, that have replaced limestone 

mainly in the vicinity of Hanover and Fierro; and the great deposit of disseminated copper sulphide that has impregnated granodiorite, quartz diorite, 

and adjacent siliceous sedimentary rocks in the vicinity of Santa Rita. The 

value of the copper ore is due almost entirely to supergene enrichment. Besides these large ore bodies there are many veins closely related to the replacement sulphide bodies in origin. Few of these veins have been profitably worked, 

but the Groundhog vein is a notable exception.

INTRODUCTION

FIELD WORK AND ACKNOWLEDGMENTS

Investigation of the Santa Rita area was begun by A. C. Spencer 

late in September 1914 and continued through January 1915. During this time he was assisted for 3 weeks by J. Fred Hunter and for 

7 weeks by Sidney Paige, who had previously mapped the Silver 

City 30-minute quadrangle, which includes the Santa Rita area. 

Diversion of the Geological Survey's activities during the World 

War partly accounted for suspension of work on the report, and it 

was not resumed until 1927, when Mr. Spencer was in the district 

from April to November studying new developments and mapping 

parts of the area in greater detail. This work also called for some 

revision of the topographic base map. In the spring of 1932 Messrs. 

Spencer and Paige revisited the district shortly before completion 

of the report.

During 1927 Mr. M. J: Balmier, of the Chino Copper Co., was of 

great assistance in the field and in the preparation of maps and other 

data, and Mr. R. E. Landpn served as Mr. Spencer's assistant for a 

- few weeks. In 1932 Mr. S. G. Lasky, of the United States Geological 

Survey, who had been studying the adjoining part of the central 

district, supplied data on the southwest corner of the area.

It is a pleasure to acknowledge the receipt of many courtesies from 

the mining men of the district. To the late Mr. J. M. Sully, local 

general manager of the Chino Copper Co., the writers are especially 

indebted for cooperation in affording every facility for the study
INTRODUCTION 3

of the mines at Santa Kita and in making available all the records 

of the company relating to churn-drill explorations, as well as a 

report made for the company by E. H. Wells in 1923. Mr. Wells, 

present director of the New Mexico Bureau of Mines and Geology, 

lost no opportunity to aid the writers in many different ways.

GEOGRAPHIC POSITION

The Santa Eita area is in Grant County, N. Mex., between 

meridians 10S°3' and 108°8' west longitude and parallels 32°46' 

and 32°52' north latitude. (See pi. 1.) It measures about 4.8 by 6.8 

miles and has an area of slightly less than 33 square miles. It lies 

within the Silver City 30-minute quadrangle and in the territory 

known officially as the " central mining district."

The mines at Santa Kita are about 12 miles east of Silver City, 

the administrative seat of Grant County, and 50 miles northwest of 

Deming, in Luna County. The region is served by branch lines of 

the Atchison, Topeka & Santa Fe Railway, one reaching the iron and 

zinc mines at Fierro and Hanover and another the copper mines at 

Santa Rita.

TOPOGRAPHY

South of the great upland of Arizona and New Mexico, the. Colorado Plateau, there is a mountainous region, with ranges rising, in 

part, from broad desert valleys. It has certain topographic and 

geologic features that resemble those of the Basin Range province 

of Nevada and Arizona. One of these relatively low and extensive 

desert valleys extends west and northwest from Deming, envelops 

several minor groups of mountains, and penetrates the more consistently mountainous region that forms the Continental Divide 

southwest and northeast from Silver City. Between the east edge 

of this desert and the upper valley of the Mimbres River there is a 

belt 15 miles long of irregularly disposed mountains and hills, 

within which the Santa Rita area is situated.

Streams of the Santa Rita area drain almost entirely southward 

into this desert valley, partly by way of Cameron Creek through the 

Fort Bayard Military Reservation but mainly through Whitewater 

Creek. Tributaries that join Whitewater Creek within the quadrangle are Gold Gulch, Hanover Creek, and Santa Rita Creek; the 

basin of Gold Gulch lies wholly within the area, and those of Hanover and Santa Rita Creeks extend only a short distance beyond the 

boundaries. The area is not well watered by running streams, but 

each of the creeks named has at least a small discharge throughout 

the year. During the summer wet season the streams fluctuate 

greatly in volume and are subject to floods after occasional violent 

rains.
Altitudes range from 5,820 feet on Whitewater Creek near the 

southwest corner of the area to 7,700 feet near the southeast corner 

and to 8,060 feet at a point iy2 miles east of the northwest corner. 

Along the southern margin of the area a deeply incised but bold 

escarpment faces north, marking the eroded edges of nearly flat-lying 

lava beds 800 feet or more in thickness. Picturesque serrated ridges 

above an irregular and sinuous line of cliffs dominate the generally 

rolling country drained by the upper Whitewater Valley, Santa Rita 

Creek, the lower part of Hanover Creek, and the gulches in the 

western part of the area that drain to Camerpn Creek.

In the north-central part of the area a series of ridges and peaks, 

ranging in altitude from 6,800 to more than 7,500 feet, enclose an 

oval flaring valley that constitutes the upper basin of Hanover Creek. 

Within this wider valley is a more constricted basin walled by resistant metamorphosed sedimentary rocks and floored by the rock 

of the Hanover intrusive stock, which, because it crumbles readily 

under the action of the weather, has been deeply eroded. Hermosa 

and Hanover Mountains, situated on the basin rim, rise to altitudes 

exceeding 7,500 feet, or about 800 feet above Hanover Creek, and are 

the highest points in the area outside of the lava mountains. The 

north edge of the area includes part of the bold southward-facing 

front of forest-clad, rugged lava ranges that occupy an extensive 

region to the north, similar geologically to the mountains south of 

Santa Rita.

CLIMATE AND VEGETATION

The climate of Grant County is semiarid, though by reason of a 

considerable range in altitude there are great local differences in the 

mean annual temperature and rainfall and corresponding marked 

differences in the character and density of vegetation. A summary 

of meteorologic observations x taken at Fort Bayard, 5 miles west 

of Santa Rita, for the years 1895 to 1903, shows a mean annual temperature of 56° F., with an absolute range from 1° to 103° F., and a 

mean annual precipitation of 14 inches. At Santa Rita the annual 

temperature is probably about the same as at Fort Bayard, but 

records kept by the Chino Copper Co. since 1911 indicate a somewhat greater precipitation, that for the years 1911 to 1914 ranging 

from 16.77 to 24.65 inches. The hottest weather is usually experienced in June and July, and the greatest rainfall usually comes 

during the summer in the form of daily afternoon showers and 

occasional heavy downpours.

The mountainous country north of the Santa Rita area, with altitudes between 7,000 and 8,000 feet, supports a rather dense forest

1 Henry, A. J., Climatology of the United States: U.. S.^ Weather.. Bur. Bull. Q, .p. 897, 

1906.
HISTORY OP MINING 5

growth, including conifers valuable for timber, whereas in lower 

country like the Santa Rita area such trees as the white pine are 

rather unusual, and jumper and pinon predominate. Throughout 

the region tributary to the upper basin of Whitewater Creek, these 

trees, together with a variety of live oak, also predominate, though 

ash and black walnut occur along some of the streams. These trees 

all grow to considerable size but are very unevenly and in general 

sparsely distributed, so that the country has a parklike rather than 

a forested aspect.

Among the larger shrubs mountain mahogany is of common occurrence, and among the smaller woody plants the thorny cat's claw. 

Very striking to one unfamiliar with the southwestern region are 

several large varieties of cactus, the maguey or century plant, two 

or more varieties of yucca, and the soap plant or saponilla, of somewhat similar appearance. The herbaceous flora comprises many 

flowering plants and a considerable variety of grasses, the latter 

mainly low species such as characterize the grazing lands of the 

high plains in Colorado and western Texas.

HISTORICAL DATA

HISTORY OF MINING /

Data are not at hand for more than a meager sketch of the history 

of mining in the Santa Rita area. First interest naturally centers 

about the early history and development of the Santa Rita copper 

mines, of which accounts are given by Raymond,2 Jones,8 and Sully.4 

These accounts have furnished most of the following data.

The Central mining district, sometimes called the Hanover district, appears to have been organized about 1860, or at the same time 

as the Pinos Altos district. However, the Hanover mine, near the 

present town of Fierro, was producing copper as early as 1858, and 

the copper at Santa Rita had then been known for many years.

Perhaps no more than traditional value attaches to the statement, 

but it is related that about the year 1800 the croppings near which 

the Romero shaft was afterward opened were shown to Lt. Col. Jose 

Manuel Corrasco, an officer in charge of the Spanish military posts 

in this general district, by a friendly Apache chief. Colonel Corrasco 

interested Don Manuel Francisco Elguea,5 of Chihuahua, Mexico, and 

a concession under the law applicable to New Spain and its provinces 

was obtained. Elguea, who was a subdelegate to the Spanish court,

8 Raymond, R. W., Statistics of mines and mining in the States and Territories west 

of the Rocky Mountains for 1869, pp. 402-404, 1870.

8 Jones, P. A., New Mexico mines and minerals, pp. 34-43, 1904.

4 Sully, J. M., private report printed in 1909.

8 In Raymond's account the name is given as " De Alguea ", and another variant given 

by Jones is " Lagera."
6 SANTA RITA MINING AEEA, NEW MEXICO

made a contract with the Government to furnish the vice royalty of 

New Spain with copper for coinage, the Government agreeing to take 

the whole product of the mines, and in 1804 he purchased the concession and began production. Though the indicated position is not 

correct, the Santa Rita mines were doubtless referred to in the statement made by Pike 6 in reporting on his expedition of 1807: " There 

are no mines known in the province, except one of copper situated in 

a mountain on the west side of the Rio del Norte, in latitude 34°. 

It is worked and produces 20,000 mule loads of copper annually."

In charge of the mines during the first years of operation was 

Juan Onis (or Ori), who, after the death of Elguea in 1809, worked 

the property under arrangement with his widow. Rough metallurgical works are said to have been provided, and the metal produced was transported by pack trains under military convoy to 

Chihuahua and thence to Mexico City.

A triangular adobe fort with massive towers at the corners was 

.erected as a needed protection against hostile Apaches. The towers 

were round and had walls more than 3 feet thick. Two of them were 

standing as late as 1909, and one has been roofed over and preserved 

as an interesting historical monument.

According to Jones, Onis was succeeded as lessee by two brothers 

named Pattie, and about the year 1822 the property was sold by the 

widow of Elguea. From 1826 to 1834 it was held and worked by 

Robert McKnight. Next the mines passed into the possession of 

one Siqueiros, who operated until the later part of the decade 

1850-60, though under difficulties due to hostilities on the part of 

the Indians.

From 1860 to 1870 the property was held by Sweet & Coste and 

their associates and appears to have been worked, except for a period

after 1862, when the territory was invaded by Confederate forces 

under General Sibley, the mine works were destroyed and a large 

amount of copper was confiscated. In 1869 a small blast furnace was 

in operation, and production for 8 months of the year was reported 

at 12,600 pounds.

The Hanover mine had been opened prior to the Sibley invasion 

and is said to have produced between 1858 and 1861 nearly 1,000,000 

pounds of copper. The ore was treated in a blast furnace and 

refined in a reverberatory furnace at a stated cost of 10 cents a 

pound.7 The product was hauled by way of Mesilla to Port Lavaca, 

Tex., and transported thence by schooner to New York, making the 

total cost 16^4 cents a pound; the normal price for copper at that 

time was 23 cents.

8 Pike, Z. M., Account of expeditions to the sources of the Mississippi, and a tour 

through the interior parks of New Spain, appendix to pt. 3, p. 5; 1810. 

7 Raymond, R. W., op. cit, p. 402.
HISTORY OF MINING /

After the Civil War efforts were made by different persons to 

obtain title to the Santa Kita mines under the mining laws of the 

United States. All applications for patent were denied, however,, 

the final decision having been reached by the Secretary of the Interior 

in 1873, with the ruling that the claimants had no right to the mine, 

which had been known to the Department for more than half a 

century as belonging to the Elguea' estate.

In the same year that this decision was rendered, M. B. Hayes and 

associates succeeded in obtaining title from the heirs of Elguea, who 

were sought out in various parts of Mexico and Europe. Afterward 

the lands were located, and eventually patents were obtained from 

the United States Government.

In 1875 the Chino and Yosemite mines, at Santa Rita, and the San 

Jose mine, 2 miles west, were mentioned by Raymond. About 1881 

the Santa Rita mines Avere purchased by J. Parker Whitney, whose 

name is associated with copper mining in the Lake Superior district, 

and in 1882 the plant included a stamp mill equipped with jigs, a 

Avater-jacketed blast furnace, and a reverberatory refining furnace.8 

Under the OAvnership of Mr. Whitney the property was worked 

mainly by tributers. In 1897 a lease and bond was given to the 

Hearst estate,, and development Avork, under the management of 

B. B. Thayer, resulted in the discovery of a large deposit of sulphide 

ore in the soutliAvestern part of the Santa Rita Basin. In 1899 the 

property was sold to the Santa Rita Mining Co., organized by men 

who Avere or had been connected with the Amalgamated Copper Co 

The policy of leasing was continued, and ore carrying about 10 percent of copper was purchased from lessees by the company.9 Material 

from old dumps was-treated in-a 90-ton concentrator, and an experimental leaching plant was installed.

Exploration Avork carried on about 1906 by the Santa Rita Mining 

Co. did not lead to the discovery of hoped-for ore bodies of high 

grade, and in 1909 the property was sold to the Chino Copper Co.

The deposits of iron ore in the vicinity of Fierro had long been 

regarded as an important asset, the realization of Avhich began 

with the building of the Hanover branch of the Silver City & Northern Railroad in 1891. Shipments to the Pueblo furnaces of the 

Colorado Fuel & Iron Co. began in that year, and each year since 

more than 100,000 tons of iron ore has been mined.

BetAveen 1891 and 1899, when the Santa Rita branch railroad Avas 

built several copper properties in the Hanover section were explored, operations Avere carried on at Copper Flat, and the mining 

of oxidized zinc ores began. Essentially self-fluxing copper-iron ores 

were developed, and smelters were erected at the Anson S. mine and

8 Min. and Sei. Press, vol. 45, p. 273, 1882. 

 Mineral Industry, vol. 9, p. 195, 1901.
8 SANTA EITA MINING AKEA, NEW MEXICO

at Copper Flat. Shipments of ore carrying excess iron had been 

previously made from the Iron Head mine, and in 1898 and 1899 a 

considerable tonnage was shipped to smelters at Deming and Silver 

City. At about this time the Phelps Dodge Co. became interested in 

the area and took over several properties, including the Modoc, 

Hanover, and Emma. In the Modoc mine a reserve of fluxing ore 

was developed but not mined. The Hanover and Emma mines were 

for several years producers of copper ore suitable for direct smelting. The Emma mine was worked by lessees in 1908 and by the 

Copper Queen Consolidated Mining Co. in 1910.

In 1903 a discovery of rich gold ore was made on the Pactolus 

claim, in Gold Gulch, but the deposit first found was soon worked 

out and, as others were not discovered the resulting excitement was 

only short-lived. The Hermosa Copper Co., affiliated with the General Electric Co., was organized in 1905. This company purchased 

or took options on several slightly developed properties of apparent 

promise and began a campaign of exploration on scattered claims 

near Hanover and on a compact group of claims adjoining the lands 

of the Santa Rita Mining Co. on the west. A concentrator for 

testing purposes was built on Hanover Creek iy2 miles below Hanover, shafts were sunk at eight points, and within 2 years nearly 3 

miles of underground workings were opened. It is reported 10 that 

as a result of this work only 25,000 tons of 3 percent copper ore was 

blocked out. In 1918 the lands of this company were transferred to 

the Chino Copper Co.

In 1906 J. M. Sully, then engineer and assistant superintendent for the Hermosa Copper Co., was detailed to study the copper deposits of the Santa Rita Basin, with a view to determining the possibility of developing them by methods that were 

then coming into prominence through the operations of the 

Utah Copper Co. at Bingham, Utah. Systematic sampling of accessible workings and 110 dumps was begun, and during this first 

investigation 2,876 samples weighing from 300 to 500 pounds were 

taken and submitted to assay. It is understood that the report made 

by Mr. Sully to his company recommended negotiations for the 

purchase of the property, but any move that may have been made 

in this direction is not known to the public. In 1908 Mr. Sully 

carried out a still more extensive sampling of the mine workings 

and prepared a report for the owners indicating the practicability 

of developing the property on an extensive scale as a low-grade mine. 

Early in 1909 the Sully report was privately printed and circulated 

in connection with a plan devised by Thomas W. Lawson for financ10 Copper Handbook, yol. 8, p. 785, 1908.
PRODUCTION 9

ing the Santa Kita Mining Co. Instead "of pushing the Lawson plan, 

the owners sold the property to the Chino Copper Co., organized in 

May 1909.

Exploration by means of churn drills, which had been begun in 

1908, was vigorously pushed by the new company, and by December 

1912 the amount of copper ore developed was estimated at 90,000,000 

tons, having an average grade of 1.8 percent. Steam-shovel operations were begun in September 1910, and before the end of that year 

four shovels were engaged in stripping the ore bodies. The construction of the concentrating mill at Hurley was begun in October 

1910. A year later the first one of five sections was started, and by 

the middle of 1912 ore was being mined and milled at the rate of 

more than 1,000,000 tons a year. Developments since then are 

reflected in the table of production on page 10.

PRODUCTION

According to Thorne,11 " no recorded figures are available for the 

years previous to 1845, but from the various works in which the 

Santa Kita del Cobre grant is mentioned, it is estimated that previous to 1845 there were produced not less than 41,000,000 pounds of 

copper." Figures on smelter production in New Mexico as a whole 

from 1845 to 1910 were assembled from the annual volumes of 

Mineral Resources, by Butler,12 who stated that this production 

was principally from the districts in Grant County; but as Grant 

County then included the Burro Mountains and Lordsburg districts, whose combined production in some years exceeded that of 

the Central district, a close estimate of the Central district's copper production during that period appears impossible. Comparison of the figures of smelter production for New Mexico as a 

whole with those of mine production in the Central district during 

1904r-10 shows that the district contributed from about three-sevenths 

to about three-fifths of the total. Since 1904 figures on production 

of metals except iron in the Central district have been published in 

Mineral Resources, and those for 190-4-30 are quoted below.13 According to this table the Chino Copper Co. became a large producer 

of copper in 1912, and production of zinc and lead, mainly from 

mines around Hanover, also increased greatly. Production was interrupted during the short industrial depression of 1921 but resumed its advance, with some fluctuations, until the great depression.

11 Thorne, H. A., Mining practice at the Chino mines, Nevada Consolidated Copper 

Co., Santa Rita, N. Mex.: U. S. Bur. Mines Inf. Circ. 6412, p. 4, 1931.

"Butler, B. S., U. S. Geol. Survey Mineral Resources, 1910, pt. 1, p. 204, 1911.

13 Henderson, C. W., Gold, silver, copper, lend, and zinc in New Mexico : U. S. Bur. 

Mines Mineral Resources, 1929, pt. 1, p. 747, 1931; idem, 1930, pt. 1, p. 805, 1932.
10 SANTA EITA MINING AREA, NEW MEXICO

that began in the fall of 1929. In that year copper production 

reached its maximum, but production of lead and zinc made further 

increases in 1930.

Mme production of gold, silver, copper, lead, and sine in Central district, Grant 

County, N. Mex., 1904-32, in terms of recovered metals

Year

IQfU

1QAC

1906--- 

1907... 

1908--. 

1909. .. ------

1910-.. --------

1911.. 

1912... 

1913-. 

1914. ----------

1Q1 C

1916 

1917- .. ------

1918---. 

1919..- -----

1920 - 

1921.... 

1922.. __ . .

1099

lQ9d

109";

1Q9/i

1097

1928. .. --------

1Q9Q

IQOfl

1Q19

Ore

Short tons 

21,048

20, 252

39, 155

57, 079

41,852

41, 456

37, 008

45, 584 

1, 136, 290

1, 948, 471

1, 934, 020

2, 395, 795

3, 134, 791

3, 668, 289

3, 908, 816

1, 789, 083

1, 882, 172

362, 331

1, 426, 783

2, 885, 711

2, 859, 688

3, 159, 167

3, 633, 821

3, 087, 823

3, 723, 753

4, 135, 864

2, 667, 267

2, 714, 360

1, 231, 876

53, 989, 605

Gold

$5, 582

4

5,659

777

816

104 

998

9,697

102, 971

102, 379

133, 962

138, 873

128, 577

57,280

68, 962

10, 439

24, 537

68, 108

71, 121

97, 299

109, 335

98, 963

113, 507

131, 631

77, 110

72, 708

31, 108

1, 662, 507

Silver

Fine ounces 

282

8

2,524

36, 813

296

1,380

404

8,673 

29, 586

12,500

42, 971

73, 267

116, 953

121, 386

111, 175

34, 508

26, 190

9,688

11, 326

29,264

38, 200

76, 547

86, 963

85, 963

143, 993

374, 398

407, 608

435, 338

474, 479

2, 792, 683

Copper

Pounds 

3, 264, 208

3, 179, 206

3, 075, 001

4, 994, 575

3, 994, 502

3, 348, 808

2, 679, 630

1, 413, 189 

29, 512, 812

51, 695, 656

55, 222, 874

66, 581, 366

74, 228, 606

82, 200, 421

77, 547, 300

40, 358, 634

44, 400, 088

9, 138, 442

28, 408, 184

54, 374, 770

66, 824, 015

68, 812, 280

75, 219, 200

66, 971, 008

80, 238, 820

87, 445, 648

57, 243, 200

56, 317, 175

26, 512, 900

1, 225, 202, 518

Lead

Pounds 

11,977

235, 070

855, 358

29, 122

23, 256

155

605, 978 

2, 172, 676

331, 440

365, 079

1, 542, 234

2, 122, 797

2, 250, 337

2,857,887

1, 283, 642

925, 513

4,422

352, 640

1,311,141

1, 183, 626

2, 363, 260

2,611,100

1/907, 476

2, 359, 155

7, 532, 318

7, 872, 000

6, 840, 600

7,041,400

56, 991, 659

Zinc

Pounds

Qfi 494

99, 656

73,729

251, 070

203, 278

1, 285, 500

290, 122 

2, 205, 824

2, 187, 266

3, 669, 513

5, 628, 870

7, 278, 575

7, 398, 853

8, 826, 967

4, 299, 658

6, 134, 593

95, 000

1, 333, 440

13, 017, 000

16, 921, 000

15, 033, 000

14, 327, 000

10, 076, 000

15, 089, 000

22, 448, 000

30, 638, 000

14, 099, 000

10, 241, 000

213, 247, 338

Total value

$424, 080

501, 650

614, 673

1, 078, 555

541, 231

448, 856

409, 955

225, 156 

5, 138, 779

8, 167, 144

7, 672, 759

12, 561, 729

19, 592, 956

23, 627, 822

20, 400, 099

7, 984, 543

8, 838, 068

1, 203, 935

3, 966, 369

9, 062, 131

10, 045, 216

11, 269, 879

11, 977, 701

9, 685, 941

12, 809, 393

17, 677, 723

9, 539, 879

6, 112, 683

2, 353, 696

223, 932, 601

The production of iron ore, according to information supplied 

by the United States Bureau of Mines, includes 44,500 long tons 

mined by the Southwestern Coal & Iron Co. for the period 1891-96 

and 4,685,301 long tons, most of it mined by the Hanover Bessemer 

Iron Association and its successor, the Hanover Bessemer Iron & 

Copper Co., for the period 1896-1931.

LITERATURE

In spite of the long period of mining at Santa Kita and the present 

industrial importance of the district, there have been very few published articles dealing with its geology or describing its ore deposits. 

The following list is probably essentially complete as regards papers 

of permanent value, and certain titles have been included merely 

because of their historical interest.

Owen, R. E., and Cox, E. T., Report on the mines of New Mexico, Washington, 

published by John S. Watts, Territorial Delegate, 1865. Notes on the occurrence of iron ore near Hanover and on the copper mines at Hanover, Santa 

Rita, and San Jose.
LITERATURE 11

Taylor, J. W., Report on the mineral resources of the United States east of 

the Rocky Mountains, Washington, 1868. On page 6 the Hanover and Santa 

Rita mines are described.

Raymond, R. W., Statistics of mines and mining in the States and Territories 

west of the Rocky Mountains for 1869 to 1875. The reports for 1.869, 1873, 

and 187,5 contain historical and geologic data relating to the Santa Rita and 

neighboring mines.

Blake, W. P., Zinc-ore deposits of southwestern New Mexico: Am. Inst. 

Min. Eng. Trans., vol. 24, pp. 187-195, 1894. Notes on the occurrence and 

mineralogy of the zinc deposits near Hanover.

Birkinbine, John, The occurrence of iron ores in the Rocky Mountains region: 

U. S. Geol. Survey 18th Ann. Rept. pt. 5, pp. 45-^9, 1897. Includes a brief 

description of iron-ore deposits near Hanover.

Emmons, S. F., The secondary enrichment of ore deposits: Am. Inst. Min. 

Eng. Trans., vol. 30, pp. 43-109, 1901. Brief account of the occurrence of copper 

ores at Santa Rita.

Frost, Max, Mines and minerals of New Mexico, Santa Fe, N. Hex., 1901.

Notes relating to the Hanover and Santa Rita mines.

Jones, F. A., Mines and minerals of New Mexico (World's Fair edition), 

Santa Fe, N. Mex., 1904. Includes geologic notes and historical review of mining at Hanover and Santa Rita. ,

Paige, Sidney, The Hanover iron-ore deposits, New Mexico: U. S. Geol. 

Survey Bull. 380, pp. 199-214, 1909. Describes the general geology of the 

Hanover Basin, the principal features of metamorphism adjacent to the Hanover stock, and the occurrence of the iron ores.

Sully, J. M., Report on the property of the Santa Rita Mining Co., Boston, 

1909. Contains a brief history of mining and notes on the geology of the Santa 

Rita Basin. The ground developed or partly developed at the time is credited 

with 12,000,000 tons of ore averaging 2.4 per cent copper.

Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., The ore deposits 

of New Mexico: U. S. Geol. Survey Prof. Paper 68, 1910. Describes the general and economic geology of the mining districts of Grant County, N. Mex.

Dinsrnore, C. A., The Chino Copper property, New Mexico: Min. World, 

vol. 33, pp. 357-359, 1910. A general description of the property in the development stage.

Sully, J. M., Milling the ore of the Chino mine: Min. and Sci. Press, vol. 

104, pp. 112, 464-^66, 1912. Description of the concentrating plant at Hurley 

and its operation.

Paige, Sidney, The geologic and structural relations at Santa Rita, N. Mex.: 

Econ. Geology, vol. 7, pp. 547-559, 1912. Gives a geologic map of the district 

and discusses order of geologic events.

Paige, Sidney, U. S. Geol. Survey Geol. Atlas, Silver City folio (no. 119), 

1916. Contains topographic and geologic maps of the Silver City 30-minute 

quadrangle, with a general account of the geology and descriptions of the ore 

deposits of the region.

Rickard, T. A., The Chino enterprise, III, Geology of Santa Rita: Eng. and 

Min. Jour.-Press, vol. 116, pp. 981-985, 1923.

Lasky, S. G., Geology and ore deposits of the Groundhog mine, Central district, Grant County, N. Mex.: New Mexico Bur. Mines Circ. 2, 14 pp., 1930.

Schmitt, Harrison, The Central mining district, New Mexico: Am. Inst. Min. 

Met. Eng. Contr. 39, 22 pp., 8 figs., 1933.
12 ' SANTA BITA MINING AKBA, NEW MEXICO

STRATIGRAPHY

PALEOZOIC FORMATIONS

The distribution of the sedimentary formations in and around the 

Santa Rita area is shown on plate 1, and their succession and thickness, where not profoundly changed by deformation, are shown in 

plate 3.

BLISS SANDSTONE (CAMBRIAN)

Throughout southern New Mexico the oldest formation of the 

Paleozoic succession is the Upper Cambrian Bliss sandstone, the type 

locality of which is in the Franklin Mountains, about 100 miles 

southeast of Santa Rita. In the Silver City region characteristic 

exposures are to be found on the west slope of the Continental Divide, 

where the normal thickness is about 180 feet, and along the west side 

of Mimbres Valley, where observations show thicknesses ranging 

from 125 to 165 feet. Typical sections show ledges of gray, green, 

and red or brown sandstone and quartzite, from 4 to 20 feet thick, 

separated by thin beds of limestone or dolomite, some of which are 

either earthy or sandy. Some of the sandstone layers are highly 

glauconitic. The usual aspect of the formation is indicated by the 

section tabulated below, which is exposed along the highway about 

6 miles east of Santa Rita.

Section of Bliss sandstone along highway 6 miles east of Santa Rita 

[Recorded by R. E. Landon]

Limestone at base of El Paso formation. Feet

Sandstone, dolornitic, crystalline 12

Sandstone, glauconitic; weathers red____________ 6

Hidden___________________________ 19

Quartzite, calcareous, thick-bedded _ ___ _ 15 

Limy beds with some shale_ _ 5 

Quartzite in two beds separated by a thin layer of glauconite- 11 

Limestone, sandy, with lenses of coarse grit- 20 

Dolomite, brown, crystalline. ___ 5 

Concealed ____________ ____________ 30 

Sandstone and shale, glauconitic, with pebble bed at the

base_ _ _ , 10 

Sandstone, vitreous, red, with 1 foot of shale at base___ 4 

Sandstone, glauconitic, cross-bedded, dark gray or green,

layers 1% to 2 feet thick____________________ 8 

Conglomerate, thin-bedded, with thin intercalations of shale

in lower part . 12

Within the Santa Rita area the Bliss sandstone has been penetrated at the Seven Hundred well, near the east side of the area, 

and it appears at the surface along the northward-trending borders 

of the Hanover granodiorite stock. Because of prevailing intense
U. 8. GEOLOGICAL SURVEY BULLETIN 859 PLATE 3

Age

Quaternary.

Tertiary.

Upper Cretaceous.

Upper (?) Cret.

Permian.

Upper Devonian.

Silurian.

o 

** Lower °

Upper Cambrian.

Pre-Cambrian.

Formation and group

Gravel and sand with lava flows.

Unconformity 

Lava flows; gravel, sand, and 

tuff.

Unconformity 

Andesitic breccia.

Unconformity (?) 

Colorado shale.

Beartooth quartzite. 

^Unconformity j

Abo redbeds. 1

§* Syrena formation.

I

i

5 Oswaldo formation.

Percha shale. 

-Unconformity 7

Fusselman limestone. 5

p_

C

 Si JS

Bliss sandstone.

Granite, syenite, and allied porphyries.

Section

fi llmniQII l|| ||H|i nun unillTHrtlmiiii'iiilnMr

> » *-'':»''Xv^V/' *.'>»* *!'.'-'°A**:''. !P'' v1 * £?.* .VlvMV.K*'.*.'^'?'.^;'*^^.* .. .'*' *; '*.\«;.yi 7.'-

:i:V:i=y^::wxA%>^«:^

'i ' 'i ' i ' [ ' i 1 i 1 'i ' i '-f

 ±il±'< ' ' ^

1 1 1 1 1 1 

1 1 1

ah - i - l-csl \-'l «==>!> « '! <s

1 1 ' 1 ' V 'l ' 1 ' 1

1 1 , ,1 , 1, ,

I 1 1 1 II 

,!,..,! 1 1 1 r

1 ' ' ' , , 1, ,'.r

 - 

y «=» / / =>/ ' / ( ./ A*y / /_ _ / / / /

L i J.iJ-]LiL|I i 7 i i i

= ip,T *r*^L

i i i i

i i ii ii._

. . ' |;;;'.-.l.-.-/.v.'i.-.-.-.-l!'.-.-.-l.-.-.-; 1 ' ' "

^C'??s^^;).

Thickness 

(feet)

1,000+

2,0004

»

900+

60-125

0-20C

400

400

150-300

300-500

500±

200±

Character of rocks

Gravel and sand, in part consolidated, with interbedded flows of basalt.

Ehyolite, latite, and andesite, with interbedded partly consolidated gravel, 

sand, and volcanic tuff.

Andesitic breccia intruded by diorite and diorite porphyry.

Dull-green shale and sandy shale with sandstone lenses at several horizons.

Light-colored sandstone with thin beds of limestone.

Dark-gray and black carbonaceous shale.

Quartzite with thin beds of shale.

Chiefly red shale with thin beds of limestone and limestone conglomerate.

Chiefly limestone with thin partings of shale.

Gray and green shale.

Chiefly limestone with thin partings of shale.

Massive blue limestone overlain and underlain by gray to green shale.

Blue limestone with nodules of black chert.

Chiefly siliceous limestone with some limy shale.

Dark-gray to black fissile shale with thin limestone beds in upper part.

Dark-gray dolomite with some chert.

Light-gray dolomitic limestone with thin layers of pink chert.

Dark-gray dolomite, sandy at base.

Quartzose sandstone and glauconitic sandstone, calcareous in upper part.

Granite, syenite, and allied porphyries.

COLUMNAR SECTION OF FORMATIONS IN AND NEAR THE SANTA RITA AREA.
. STRATIGKAPHY - 13

metamorphism in the vicinity of the intrusive contacts, and especially because of poor and scattered outcrops, no little difficulty is 

encountered in determining the true distribution of the formation. 

The only place where the altered rocks are sufficiently well exposed 

to show the sequence of strata is along the bed of a minor watercourse northeast of the Honeycomb shaft and about 900 feet south 

of the Humboldt shaft.

Section of altered Bliss sandstone and overlying limestone beds northeast of 

Honeycomb shaft, on east side of Hanover Basin

Montoya and El Paso limestones:

Pink chert member of Montoya limestone ____ _ ___ 35 

Massive crystalline limestone and dolomite, assigned to 

Montoya and El Paso formations ____________ 250

Section above uppermost layer of lean ore, 285 feet. 

Magnetite rock, thin-layered, gray tone ; 2 feet of dolomite 

at base _______ _______ 19

Magnetite rock, green ; 3 feet of brown dolomite at base___ 12 

Magnetite rock, somewhat schistose; crumbles under 

weathering; 4 feet of dolomite at base, assigned to 

El Paso limestone ___ __ _ _______________ 35 

Interval not well exposed, includes layers of crumbly 

magnetite rock _______________________ 29 

Section showing lean ore, assigned to El Paso limestone, 95 feet. 

Bliss sandstone :

Quartzite, varicolored, no magnetite, a little pyrite; four

ill-defined layers _______________________ 9 

Layered material, sandy on weathered surfaces ; carries

considerable magnetite ___ _______________ 39 

Quartzite, black, much magnetite, 2 feet; hidden interval

7 feet ; quartzite, black, much magnetite, 7 feet ___ _ 16 

Quartzite, green, dense, vitreous; breaks into smaller 

angular fragments ____ ____ ___ _ ____ __ 11

Schistose quartzite to granodiorite contact ________ 95 

Thickness assigned to Bliss sandstone, 170 feet.

The schistose quartzite that occurs on the Humboldt claim west 

of and stratigraphically under the lowest recognizable sandstone is 

believed to have been derived from beds belonging to the lower part 

of the Bliss formation. The alternative suggestion that this body 

of highly metamorphosed material belongs to the pre-Cambrian 

crystalline complex seems improbable, in view of the structural relations of these and the overlying rocks. Near the edge of the granodiorite body the invaded rocks are uptilted so that the beds stand nearly 

upright, and the fact that pronounced layering in both sets of 

rocks is strictly conformable throughout is taken as evidence in 

favor of the relationship that has been suggested. . This part of 

the section appears at the surface only within a narrow strip that

92311 35 2
14 SANTA. EITA MINING AEEA, NEW MEXICO

extends the full length of the Humboldt claim and has a total 

length of about 2,000 feet.

The varicolored quartzite, which has been taken as the uppermost 

member of the Bliss formation, has not been identified at other 

localities, but in several places on both sides of the Hanover Basin 

proof that this quartzite is present is found in the soil or talus fragments, which are in every way like the angular fragments shed by 

the green quartzite beds that lie between the schistose quartzite and 

the black quartzite in the measured section.

Observations in the mine pits along both sides of the intrusive 

granodiorite have led to the conclusion that tabular bodies of rather 

low grade iron ore, which commonly occur next to or near the igneous 

contact, occupy a stratigraphic position corresponding in a general 

way with the group of magnetite-bearing strata shown by the Humboldt cross section and to the belief that although most of this lean 

ore belongs to the El Paso formation, some of it should be assigned 

to the Bliss.

LIMESTONE FORMATIONS OF THE ORDOVICIAN AND SILURIAN

Throughout southwestern New Mexico the Bliss sandstone is overlain by a thick succession of limestones and dolomites, which is commonly divisible upon the basis of distinct fossil assemblages into 

three formations corresponding to the El Paso, Montoya, and 

Fusselman limestones, named and described by Richardson.14

According to Darton,15 the Ordovician and Silurian succession in 

all parts of southern New Mexico shows uniform and marked characteristic features. The Lower Ordovician El Paso limestone, which 

is apparently conformable with the Bliss sandstone, is in most places 

of unmistakable character, its conspicuous features being thin bedding, a light color on weathering, and brownish-buff reticulations 

on the bedding planes, caused by irregular layers of an iron-silica 

deposit probably due to a sea weed. Limestone and dolomite are 

both present. The thickness of this formation ranges from 1,000 

feet in the Franklin Mountains, north of El Paso, Tex., to about 600 

feet in Cooks Range, northeast of Deming, and to less than 500 feet 

on the west side of Mimbres Valley, east of Santa Rita.

A bed of sandstone 10 to 20 feet thick, which is noted in some sections, is taken as the basal member of the Montoya formation. 

Above the sandstone or, where this bed is not present, resting on the 

El Paso limestone there are massive beds of dark-gray dolomite.

"Richardson, G. B., U. S. Geol. Survey Geol. Atlas, El Paso folio (no. 166), 1909. 

16 Darton, N. H., Comparison of Paleozoic sections in New Mexico : TJ. S. Geol. Survey 

Prof. Paper 108, p. 34, 1918.
STRATIGRAPHY " 15

In the Silver City area the gray dolomite member, which is from 

40 to 60 feet thick, is overlain by an 80-foot bed of dolomite which 

carries thin plates of pink or brown chert. Because this bed of 

cherty dolomite can be readily identified in separate localities it was 

used as a stratigraphic marker in mapping the geology of the Silver 

City quadrangle. The section between the Bliss sandstone and the 

Percha shale was divided at the base of the pink chert, so that one 

map unit takes in the El Paso, limestone and the gray dolomite 

member of the Montoya and another unit includes the greater part 

of the Montoya and all of the Fusselman limestone.

In the type locality in the Franklin Mountains the Silurian Fusselman limestone has an estimated thickness of about 1,000 feet, but in 

New Mexico localities a maximum development of 220 feet has been 

noted in the San Andres Range and a minimum of 30 feet in the 

neighborhood of Silver City.

Sections measured in the Silver City quadrangle 10 show 503 feet of 

El Paso beds in the vicinity of Lone Mountain, 8 miles southwest of 

Santa Rita, and 542 feet at a locality iy2 miles west of Silver City. 

In the latter place the lower gtay dolomite.member of the Montoya 

is 60 feet thick, and as this member was included with the El Paso 

on the geologic map, the strata included by this map unit have a 

combined thickness of 600 feet. Adding to this figure 300 feet 17 for 

the upper member of the Montoya, and 40 feet for the Fusselman 

formation gives a thickness of 940 feet for a composite section of the 

pre-Devonian limestone formations.

The Bliss and El Paso formations and a good part of the Montoya 

are favorably exposed at localities near the highway 6 miles east of 

Santa Rita. Here a section measured by Wells 18 shows 164 feet of 

Bliss sandstone, 478 feet 19 of limestone and dolomite, 10 feet of 

coarse-grained cross-bedded white sandstone, 10 feet of sandy dolomite, and 65 feet of gray dolomite, sandy in the lower part, followed 

by 110 feet of cherty limestone-or dolomite at the top of the steep 

scarp. If the base of the white sandstone is taken as the dividing 

horizon, the El Paso formation is 478 feet thick, and the lower 

member of the Montoya measures 85 feet. Thus at this place the 

beds included in the El Paso and Montoya map unit of the Silver 

City folio show an aggregate thickness of 563 feet, a figure only 

37 feet less than that measured by Paige in the Silver City Range.

At the Apache Tejo warm springs, 12 miles southwest of Santa 

Rita, the log of deep well 5 (made available through the interest of

"Paige, Sidney, U. S. Geol. Survey Geol. Atlas, Silver City folio (no. 119), p. 3, 1916. 

"Idem, pp. 3-4.

18 Wells, E. H., private report for Chino Copper Co., 1923.

19 R. E. Landon, who measured a section at this place, gives 430 feet for this Interval.
16 SANTA EITA MINING AKEA, NEW MEXICO

Mr. J. M. Sully) shows an interval of 1,150 feet between the bottom 

of the Devonian black shale and the top of the Bliss sandstone. 

Because there are no bedrock outcrops in this vicinity, the attitude 

of the formations has not been determined, but as it seems hardly 

probable that they lie in horizontal position the true stratigraphic 

distance between the horizons named is probably less than the measure 

given. The descriptions of materials given in the record of well 5 do 

not lead to a definite opinion regarding the top of the El Paso formation, but there is a suggestion that this horizon was reached at a 

depth of 1,685 feet, where the log shows siliceous brown limestone, 

and on this basis the apparent thickness of the El Paso would be 540 

feet. The notes show a 4-foot bed of brown sandstone separated 

from the Devonian black shale by 140 feet of limestone, probably 

representing the Fusselman formation, which is known to be about 

200 feet thick in the Cooks Kange localities, about 25 miles to the 

east-southeast. This tentative division of the pre-Devonian limestone section leaves for the Montoya formation an apparent thickness 

of 470 feet at the Apache Tejo locality.

In mapping, the line between the two divisions has been placed at 

the base of a cherty dolomite member which corresponds to the pink 

chert beds that Paige also used as a stratigraphic marker in his mapping of the Silver City quadrangle. On the east side of the Hanover Basin a section of the rocks exposed on the second ridge south 

of the Humboldt mine, recorded by Harrison Schmitt,20 places this 

horizon 400 feet below the bottom of the Percha shale, and the Humboldt section, given on page 13, shows 345 feet of limestone, dolomite, 

and iron ore between the topmost sandstone bed of the Bliss formation and the base of the cherty beds, so that a composite section 

gives 745 feet for the pre-Devonian limestone section. This is from

135 to 195 feet less than the thickness shown by other sections noted 

above and 210 feet less than the measure of the pre-Devonian limestone group at the Seven Hundred well, 2 miles to the southeast. 

Although the thickness of the El Paso and lower Montoya map unit 

is not satifactorily indicated by the record of this deep well, it is 

regarded as significant that in the section 6 miles east of Santa Rita 

this group of beds measures 563 feet. The corresponding figure in 

the Humboldt section is 345 feet, and other sections for example, 

one near the common end line of the Humboldt and Eighty-six 

mining claims show less than 200 feet of limestone and iron ore 

between the Bliss and the cherty dolomite.

In place of the suggestion that the general deficiency in respect 

to thickness and the differences in thickness at localities only a few

20 Private communication. .
STEATIGEAPHY 17

hundred feet apart are original, it is held that these differences are 

the result of shearing and plastic flow attending intrusion of the 

Hanover-Fierro stock. On the west side of the Hanover Basin the 

division has been drawn at a horizon which is believed to be the same 

as that fixed upon in studying the formations east of the granodiorite 

stock. Here the cherty dolomite correlated with the pink chert beds 

of the Silver City folio are represented by crystalline dolomite carrying thin plates of yellow serpentine, grading into serpentine-magnetite rock, the so-called " tiger " ore, which may be seen in several 

of the mine pits on Union Hill.

Along the zone of intense metamorphism bordering the monzonite 

stock the masses of iron ore are tabular bodies conformable with the 

stratification. On Union Hill some of the best ore layers lie just 

under the " tiger " bed, and, so far as can be learned from observations at the surface, there are no extensive bedwise ore masses in the 

rocks immediately overlying this stratigraphic marker, though there 

are a few veinlike occurrences of magnetite. The metamorphic 

rocks that represent the El Paso and the lower part of the Montoya 

show a maximum thickness of 200 feet, and throughout the greater 

part of a zone 400 feet long the measure is in the neighborhood of 

100 feet, less than one-fifth of the normal thickness exhibited in the 

surrounding region. Because the metamorphosed sedimentary rocks 

next to the northward-trending borders of the granodiorite now 

stand on edge and because the strike of the beds is essentially parallel with these borders, it is obvious that during the intrusion of 

the igneous mass the invaded formations were uptilted and subject 

to lateral thrust. The conditions were those of high temperature 

and deep burial, under which the plastic yielding of limestone and 

dolomite would be in order, and the disposition of forces and resistances was such as would have tended to the upward escape of 

plastic materials and concomitant thinning of the formations 

involved.

The El Paso and lower Montoya limestone unit is of particular 

interest because of the bodies of magnetic iron ore that occur in it 

along both sides of the Hanover monzonite stock. In general, very 

little in the way of metallic mineralization has occurred in the upper 

part of the Montoya and the Fusselman limestone, but in many places 

the uppermost beds, lying just under the Percha shale, have been 

strongly mineralized. The segregation of metal-bearing minerals 

in corresponding positions at the top of the Fusselman limestone is 

a noteworthy feature in other New Mexico mining districts, as at 

Hillsboro, Lake Valley, Georgetown, Lone Mountain, and localities 

near Silver City.
18 SANTA RITA MINING AREA, NEW MEXICO

Section of pre-Devonian formations on east side of Hanover Basin

Feet 

Limestone overlain by Percha shale, greatly metamorphosed;

tremolite developed around nodules of chert, presumably the

Fusselman limestone_______________________ 40 

Dolomite and limestone, white, yellow, and blue, coarsely

crystalline; carries some chert__________________ 320 

Dolomite, fine-grained, crystalline, thin layers of chert basal

member of the Fusselman and Montoya map unit)______ 40 

Dolomite, crystalline, massive_____.__________-__- 250 

Magnetite rock with 3 intercalated layers of dolomite 2 to 4

feet thick_____________________________ 95

Beds assigned to the limestone section___________ 745

Bliss sandstone to edge of monzonite_______________ 197

PERCHA SHALE (DEVONIAN)

Throughout the southwestern part of New Mexico the Fusselman 

limestone is overlain by the Percha shale, named from Percha Creek, 

a tributary of the Rio Grande which heads in the Black Range west 

of Hillsboro and Kingston. Good exposures of the formation are 

to be found in the eastern part of the Silver City quadrangle near 

Georgetown and along highway 84, 5 miles east of Santa Rita. At 

these localities the lower part of the section shows about 100 feet 

of black fissile shale, and above this about 80 feet of gray shale with 

.calcareous nodules, grading into limy shale and fossiliferous shaly 

limestone 20 feet thick, a total estimated thickness of about 200 

feet.

In the Santa Rita area the Percha shale is not exposed outside of 

the Hanover Basin, where all the formations exhibit the- effects of 

metamorphism. The ringwise distribution of the shale outcrops 

shown on the geologic map reflects'the existence of a marked structural dome roughly symmetrical with the oval Hanover Basin but 

somewhat shorter. Along the eastern outcrop thin porphyry sills 

occur at the top of the Percha shale toward the south end of the belt 

and about 40 feet above the base, in the vicinity of the Jim Fair iron 

mine. On the other side of the dome, west of Union Hill, a 

porphyry sill, which is locally 400 feet thick, follows a horizon about 

20 feet above the bottom of the formation for nearly 4,000 feet along 

the strike. Toward the north end of this prophyry area, on the 

Queen Lil and Engineer claims, poor exposures suggest that the intrusive mass may cut upward across the stratification.

In a patch of country south of the Continental shaft, on the Anson 

S. and Engineer claims, the Percha shale does not appear between 

outcrops of the older and younger formations. North of the Anson 

S. claim the lowermost member of the Ljake Valley formation is 

represented by garnet rock capping the hill east of the Continental
STKATIGEAPHY 19

shaft and overlying the Percha formation in normal succession. 

From the surface distribution of the garnet rock and the shale it is 

evident that the strata dip toward the Barringer fault, and this 

conclusion checks with the fact that the black shale appears in the 

tunnel-level workings northwest of the Continental shaft. A structure section through the shaft gives the Percha shale an estimated 

thickness of 100 feet, compared with a determined minimum of 230 

feet in the block of ground adjacent to the lower end of the monzonite 

stock south of Hanover. Toward the north the Percha shale probably 

occurs on the McCarthy claim, but in this neighborhood exposures 

are all but lacking, so that the distribution of formations shown upon 

the geologic map is subject to correction. North of Fierro, on the 

Hugo and nearby claims, the mapping can be accepted as essentially 

correct.

In the Santa Rita area the older formations of the Paleozoic succession are exposed on both sides of the elongated mass of granodiorite which has been called the Hanover-Fierro stock, but because 

all the beds that lie stratigraphically below the Percha shale have 

been greatly affected by metamorphism, the idea of dividing the 

limestone section into parts that might correspond with the El Paso, 

Montoya, and Fusselman formations has been abandoned in favor 

of a twofold division.

The thickness of the Percha formation ranges from perhaps 100 

feet in the Continental mine to 230 feet in drill holes in the neighborhood of the Republic shaft and 300 feet in the northern part of 

the eastern belt of outcrops. West of Union Hill and south of 

Badger no. 1 claim a measured section shows 220 feet of shale above 

the porphyry sill, to which there is to be added about 20 feet for 

baked shale below the sill, a total of 240 feet. In the middle part 

of the eastern belt of outcrops measured sections show a range in 

thickness from 140 to 175 feet, and around the south lobe of the Hanover stock several diamond-drill cores show about 230 feet. An 

inspection of samples of drill cuttings from the Seven Hundred well, 

northeast of Santa Rita, indicates a thickness of about 190 feet for 

the shale formation at this place.

DIVISIONS OF THE CARBONIFEROUS SYSTEM

The f Fierro limestone 21 was defined in the text of the Silver City 

folio as a local map unit covering the rocks belonging to the Mississippian and Pennsylvanian series of the Carboniferous system. On 

this basis the f Fierro included beds equivalent to the Lake Valley

al A dagger (t) preceding a geologic name indicates that the name has been abandoned 

or rejected for use in classification in publications of the U. S. Geological Survey. 

Quotation marks, formerly used to indicate abandoned or rejected names, are now used 

only in the ordinary sense.
20 SANTA BITA MINING AKEA, NEW MEXICO

limestone (Mississippian) also the Kelly limestone -and the Magdalena group (Pennsylvanian) of other districts in New Mexico. 

The distribution of the fFierro shown on the folio map published in 

1917, however, makes it include not only the formations named but 

also, in the eastern part of the quadrangle, redbeds not mentioned 

in the folio text, which are doubtless to be correlated with the Abo 

sandstone, the lowermost Permian formation in central and eastern 

New Mexico. In the Continental Divide near Silver City the Abo 

redbeds are missing, but they appear beneath the Beartooth quartzite 

in the Santa Rita area and are prominently developed farther to 

the east and southeast.

The geologic map accompanying the present report (pi. 1) shows 

four Carboniferous formations the Mississippian Lake Valley limestone, the Pennsylvanian Magdalena group, divided into an upper 

(Syrena) formation and a lower (Oswaldo) formation, and the 

Permian Abo redbeds. The fFierro limestone of earlier reports having now been differentiated into several units, the name is considered 

to be no longer useful and is discarded.

Measured sections of the Lake Valley limestone show a maximum 

thickness of 500 feet at a locality west of Silver City. In the Santa 

Eita area the Magdalena group is 800 feet thick, and 2 miles east 

of the copper mines the Abo redbeds measure nearly 200 feet.

LAKE VALLEY LIMESTONE (MISSISSIPPIAN)

The Lake Valley limestone, of lower Mississippian age, bears the 

name of the Lake Valley mining district, where an incomplete section shows 210 feet of limestone underlain by Percha shale. In the 

Cooks Peak region 22 the formation is about 500 feet thick. It comprises an upper member of gray, more or less cherty, massive to

slabby limestone with intercalated layers of limy shale and a 150-foot 

basal member of bluish gray limestone which carries some chert.

According to Paige's interpretation of the fFierro limestone section,23 the Lake Valley formation is about 500 feet thick in the 

vicinity of Silver City, and in a section along the highway 5 miles 

east of Santa Eita the thickness is 497 feet.

Section of Lake Valley limestone 5 miles east of Santa Rita 

[Recorded by R. E. Landon]

Shale, 10-foot bed at base of Magdalena group. Feet 

Limestone, light gray, coarse-grained except near base;

white chert in upper part; many crinoid stems______ 55 

Limestone, thin-bedded or shaly; 2 feet of coarse-grained

limestone at base. ____,________________ 17

33 Barton, N. H., U. S. Geol. Survey Geol. Atlas, Deming folio (no. 207), p. 5, 1917. 

Taige, Sidney, op. clt. (Silver City folio), p. 5.
STRATIGRAPHY 21

Section of Lake Valley limestone 5 miles east of Santa Rita Continued

Feet

Limestone, dark gray, slightly shaly, with nodules of limestone and chert 10

Limestone, white, crystalline, thick-bedded 50

Limestone with chert,. somewhat shaly; basal bed of the 

crinoidal limestone member 5

Limestone, gray with reddish cast in part, fine-grained,

somewhat shaly toward top; some chert_ 130

Limestone, fine-grained, medium- to thin-bedded, reddish 

where thin-bedded________ _ _ 50

Limestone, blue, fine-grained, with chert layers in upper 

part_______________________-___-___- 35

Limestone, blue-gray, thick-bedded in upper part, thinbedded below; basal bed of lower blue limestone member 20

Limestone, dark gray to blue, with nodules of limestone and 

black chert; abundant Bryozoa_____________ 60

Shale, gray, calcareous, with thin layers of limestone, especially in lower 10 feet_________.___________ 65 

Shale at top of Percha shale. . 

497

In the Santa Rita area the Lake Valley limestone does not appear 

at the surface outside of the area of marked structural disturbance 

adjacent to the Hanover stock of granodiorite. Besides minor outcrops near the Continental and Hanover mines, essentially complete 

sections are to be found along separate belts on opposite sides of 

the northern or Fierro lobe of the stock, and to the west and south 

of the Hanover lobe the uppermost member of the formation is 

exposed along the crest of a curving anticline that extends around 

three sides of this lobe of the intrusive mass. At three places on 

the east side of Hanover Valley thicknesses ranging from 335 to 450 

feet have been recorded by E. H. Wells, who gives the following 

section as applicable to this general locality:

Composite section of Lake Valley limestone east of Hanover Valley 2i

Feet

Limestone, white, grayish, or light blue, coarsely crystalline, 

massive; many crinoid stems _ ________ 175

Limestone, medium to dark blue, fine to medium grain; ellipsoidal and irregular black chert nodules__________ 190

Limestone, blue, slightly shaly, fine-grained, with thin layers 

of chert- _ ____________________ 40

Limestone, light grayish blue, massive, with irregular chert 

layers and nodules.___ _________________ 30

435

** Quoted with changed wording from Wells, E. H., The geology and ore deposits of the 

Cnlno property, Santa Rita, N. Mex., unpublished report, 1923.
22 SANTA EITA MINING AKEA, NEW MEXICO

The following sections measured by Harrison Schmitt are given 

through the courtesy of the Empire Zinc Co.:

Section of Lake Valley limestone on second ridge south of Humboldt shaft 

[Recorded by Harrison Schmitt]

Shale at base of Magdalena group. Feet 

Limestone, gray to pink ; many crinoid stems_________ 35 

Limestone, massive, coarse-grained, crystalline; few fossils- 40 

Limestone, white, coarse-grained, crystalline, to base of

crinoidal limestone member__________________ 40 

Limestone, blue, medium- to thin-bedded; carries black 

chert; where thin-bedded carries crinoid stems. A shaly 

bed 10 feet below top, and 10 feet of calcareous shale 

at base ______________________________ 182 

Limestone and siliceous limestone, irregularly interbedded 41 

Limestone, siliceous, with small lenses of blue limestone_- 30 

Limestone, siliceous, thin layers interbedded with softer

material_________________________ ___ 30 

Shale at top of Percha formation. . 

398

Generalized section of Lake Valley limestone west side of granodiorite stock

[Recorded by Harrison Schmitt]

Feet

Crinoidal or white crystalline limestone member_______ 120 

Blue limestone member____________^________ 190 

Siliceous limestone member. __ ___ __ 100

410

In the Empire Zinc Co.'s ground diamond-drill explorations have 

shown that the crinoidal limestone member is from 130 to 140 feet 

thick along the crest of the curving anticline which encircles the

Hanover lobe of the stock, but that nearby on the limbs of this fold 

these beds are usually much thinner and in places the thickness is 

not more than 80 feet. These observations afford acceptable evidence that the crinoidal limestone has been locally subject to plastic 

deformation, and this conclusion serves to corroborate the opinion 

that the abnormal thinness of the Lake Valley and older limestones 

in this area is to be explained as the result of deformation of the 

same type.

MAGDALENA GROUP (PENNSYLVANIA]*)

OSWALDO AND SYRENA FORMATIONS

The name " Magdalena ", from the Magdalena Mountains in Socorro County, was.proposed in 1907 25 to designate the lower part of

* Gordon, C. H., Notes on the Pennsylvanian formations in the Rio Grande Valley, 

N. Mex.: Jour. Geology, vol. 15, p. 806, 1907.
STRATIGRAPHY 23

a 5,000-foot succession of limestone, shale, and sandstone beds occurring in the Rio Grande Valley of New Mexico. At first the whole 

section was placed in the Pennsylvanian series, but as the result of 

later studies the upper part, with the Abo sandstone at its base, is 

now assigned to the Permian series. In the central part'of the State 

the Magdalena group 20 is represented by the Sandia formation, about 

650 feet thick, composed principally of shale with intercalated beds 

of limestone, sandstone, and conglomerate, and above this the Madera 

limestone, at least 600 feet thick, composed of compact blue limestone 

in massive beds separated by layers of shale.

In the Silver City region and in the Black Range, 20 miles to the 

east, the maximum thickness of the Magdalena group is probably 

less than 900 feet, and its stratigraphic constitution is so notably 

different that divisions corresponding with the Sandia and Madera

formations have not been recognized. However, in course of the 

present study of the Santa Rita area it has been found convenient 

to divide the section into two parts, which have been mapped as the 

Oswaldo formation below and the Syrena formation above, the names 

chosen being those of patented mining claims about 1 mile, south of 

Hanover post office. The Syrena claim includes the common corner 

of sees. 21, 22, 27, and 28, T. 17 S., R. 12 W., and the Oswaldo claim 

adjoins it on the northwest.

Although there is a considerable stratigraphic hiatus above the 

Lake Valley limestone throughout the Silver City region, the beds 

above and below the break appear to lie in parallel position, and the 

only physical evidence that can be cited as suggestive of unconformity is a bed of white chert which occurs in many localities at the top 

of the crinoidal limestone member of the Lake Valley formation. 

Locally, the strata that are here assigned to the Magdalena group 

'are succeeded by red sediments that evidently belong to the Abo for- 

 mation, but elsewhere these red strata are absent and the Upper (?) 

Cretaceous Beartooth quartzite lies upon beds of Magdalena age. 

Irt the southwestern part of the Santa Rita area the upper part of 

the Syrena formation, to a depth of about 100 feet, had been cut 

away by erosion before the Beartooth formation was deposited,' 

whereas only a short distance east of the Chino copper mines, fully 

200 feet of redbeds are present between the top of the Syrena section 

and the bottom of the Beartooth.

Except in the northeastern part of the area, where a bed of coarsegrained sandstone occurs, about 100 feet above the base of the section, 

the Oswaldo formation is made up entirely of limestone and shale.

26 Lindgren, Waldemar, Graton, L. C., and Gordon, C. H., The ore deposits of New 

Mexico ,:.U. .S.. Geol. Survey Prof. Paper 68, .p. 233, 1910.
24 SANTA EITA MINING AREA, -NEW MEXICO

A bed of shale from 20 to .30 feet thick occurring at the base of the 

formation is followed by 80 to 90 feet of massive blue limestone, 

above which comes 300 feet of limestone occurring in relatively thin 

layers, some of which are separated by beds of shale. Because these 

partings are rarely exposed, the proportions in which shale and 

limestone are present cannot be stated, but it seems that the shale 

may constitute something like 15 percent of the whole.

The Syrena formation is also composed of limestone and shale, the 

limestone predominating. Immediately overlying the Oswaldo 

formation is a body of shale from 100 to 130 feet thick, and at two 

or three horizons in the lower part of this member there are thin beds 

of limestone made up of nodules showing the concentric structure 

which is characteristic of certain forms of the lime-depositing algae. 

Above the shale member is a succession of limestone and shale that 

shows a maximum thickness of 260 feet in places where it is capped 

by the Permian redbeds.

The surface distribution of the two Pennsylvanian formations 

within and to the east and northeast of the Santa Rita area reveals 

the general structure of the area as that of a broad arch or anticline with its axis trending southwest. On both sides of the north 

lobe of the Hanover-Fierro stock the Oswaldo beds have been cut 

out by the Barringer fault, but aside from this gap the formation 

appears along the crown of the arch, and the overlying Syrena beds 

crop out along flanking bands which converge and come together 

around the gently plunging southwest end of the arch.

Division of the Pennsylvanian series into two formations affords 

a satisfactory basis for areal mapping, but in detailed work by the 

geologic staff of the Empire Zinc Co. the section between the Lake 

Valley limestone and the Abo redbeds has been represented as consisting of six divisions, which it will be convenient to speak of as 

members of the Oswaldo and Syrena formations, as indicated in the 

following table:

Subdivisions of the Magdalena group as differentiated by the geologic staff of

the Empire Zinc Co.

Syrena formation, 390 feet: Feet 

Don limestone_________________________ 260 

Mountain Home shale-________________:___ 130

Oswaldo formation, 405 feet:

Banded limestone______________________ 80 

Upper blue limestone_____________'. _ ______ 210

Marker sill [porphyry], 50 feet.

Middle blue limestone____________________ 85

Parting shale_____ ___.._ ________ ______ 30

795
STEATIGEAPHY 25

The thicknesses given in the table apply to the section between 

Buckhorn Gulch and Humboldt Mountain, where Abo redbeds occur 

between the Syrena formation and the Beartooth quartzite.

On the east side of Hanover Creek a section measured by E. H. 

Wells shows a stratigraphic thickness of 804 feet between the base 

of the Beartooth quartzite on Topknot Hill (south of Santa Rita) 

and the marker sill that occurs above the middle blue limestone 

members. The upper part of this section shows 116 feet of highly 

altered sediments which Wells regarded as part of the Pennsylvanian 

but which are now assigned to the Abo redbeds (Permian), so that 

the Pennsylvanian part of the section measures 688 feet. The two 

basal members of the Oswaldo formation cannot be satisfactorily 

measured in nearby localities, but from the log of the Seven Hundred well, on the Joy claim, it seems that their combined thickness 

may be about 110 feet, which gives an estimate of about 800 feet 

for the stratigraphic distance between the Lake Valley limestone 

and the Abo redbeds. Because the measures of this section and that 

of the Humboldt section correspond so closely, it may be assumed 

that here as there the thickness of the Oswaldo formation is in the 

neighborhood of 410 to 420 feet, and that of the Syrena formation 

perhaps 380 to 390 feet. On this basis the horizon of the marker 

sill would lie from 300 to 310 feet below the Oswaldo-Syrena 

parting, an estimate which checks fairly well with the fact that the 

record of a diamond-drill hole near the south side of the Kearney 

claim shows that a body of fine-grained porphyry, 35 feet thick, 

was entered at a depth of 315 feet. Observations in the vicinity of 

this locality shows that the beds dip about 20° south and that the 

altered rocks which appear at the surface belong near the top of the 

Oswaldo formation. With the stated inclination of the beds a vertical depth of 315 feet corresponds with a stratigraphic thickness of 

about 280 feet.

A third estimate of the' thickness of the Pennsylvanian section is 

based on the record of a diamond-drill boring near the north end of 

Nellie Patterson claim 5 and about 350 feet northwest of the Hobo 

fault, made available through the courtesy of the local agents of 

the American Smelting & Refining Co. The distances given in the 

section have been scaled from the graphic log showing the results 

of this exploration.

Section indicated ~by record, of diamond-drill exploration on Nellie Patterson

claim 5

Feet

Beartooth quartzite________________________ 60 

Interval. ___^______________.__________ 225 

Porphyry sill ________________________ 10
26 SANTA EITA MINING AREA, NEW MEXICO

Section indicated, by record of diamond-drill exploration on Nellie Patterson

claim 5 Continued

Feet

Interval_______________________________ 105

Porphyry sill _____ :_ 90

Interval_________________ _________ 440

Porphyry sill, " marker sill "___________-______ 20

Interval_________________________ _ 40

Barren quartz__ __ __ '._ 4

Crinoidal limestone __________________________ 80

Limestone below crinoidal member __ 430

1,504

If the sills of porphyry are omitted the figures given indicate for 

the Pennsylvanian series a thickness of 810 feet, but the possibility 

that the section may not be complete is suggested by the fact that 

the original drawing shows a fault at the place where the 4 feet 

of barren quartz occurs, which may signify that the quartz was 

regarded as vein filling by the observer who kept the log. An alternative possibility would be that the material noted as quartz may be 

white chert like that which may be noted at the top of the Lake 

Valley formation in several places and which occurs as a layer from 

4 to 8 feet thick in the Combination mine, about 4,400 feet northeast 

of the locality here under consideration. From a careful study of the 

core samples it should be possible to decide concerning the presence 

or absence of the chert bed and of the parting shale member that 

ordinarily occurs above it. If this shale bed is present the need for 

assuming a fault disappears.

It is believed that the two bodies of porphyry shown in the upper 

pact of the Nellie Patterson section correspond with sills that appear 

at the surface in the country west of the Mirror fault and on the

Blackhawk tract, to the northeast. The 90-foot sill of the section 

corresponds with a sill 65 feet thick occurring in the vicinity of 

the.Combination shaft at a horizon about 60 feet above the OswaldoSyrena parting.

ABO REDBEDS (PERMIAN)

Redbeds that are assignable to the Abo formation of the Permian 

series on the basis of lithology and stratigraphic position are locally 

present within and to the east of the Santa Rita area, although they 

escaped the attention of geologists until 1923, when E. H. Wells 

examined and measured a 200rfoot section of them about 5 miles 

southeast of Santa Rita, This section, which has been made available through the courtesy of Mr. J. M. Sully, is here given:
STKATIGKAPHY 27

Section of Abo redleds 5 miles southeast of Santa Rita

Feet

Shale, red, upper part sandy 40 

Limestone conglomerate, pebbles of limestone with some

chert, diameters three-eighths inch or less _ _ 3 

Shale, red_____________________ __ 20 

Limestone, mottled purple and gray, brown on weathered

surfaces_____________ __ __ 4

Shale, red_____________________________ 12 

Limestone, mottled gray and purple____ _ 12

Shale, red_____________________-_______ 60 

Limestone conglomerate _ _ _-- 4 

Shale, red____________________ - _______ 41

Limestone, dark gray, fine-grained___ _ _______ 5

Shale, red_____________________ _ __ 6

207

Somewhat thinner but otherwise similar sections may be seen 

south of highway 180 about 1% miles east of Santa Rita,1 and near 

the head of Shingle Canyon, about 2 miles northeast of Fierro. 

In both places the formation is made up largely of red fine-grained 

calcareous and earthy sandstone with intercalated layers of earthy 

limestone and thin beds of limestone conglomerate containing conspicuous colonies of algae. Similar beds containing algae in redbeds 

in the vicinity of Cooks Peak have been correlated with the Lobo 

formation of the Florida Mountains by N. H. Darton and tentatively 

regarded as of Triassic age. According to unpublished observations 

by Harrison Schmitt the redbeds at Cooks Peak and those of the 

Shingle Canyon locality show identical characteristics, and as there 

is hardly room for doubt that the redbeds in the region between 

Fort Bayard and the Mimbres Valley must be correlated with the 

Abo formation rather than with the Lobo beds, it seems consistent 

to correlate those at Cooks Peak with the Permian Abo sandstone.

Within the Santa Rita area essentially unaltered Abo redbeds 

have been noted only on the north side of the Beartooth Creek 

drainage basin, where the usual thickness does not exceed 50 feet. 

Remnants of the Abo can also be identified between the Syrena and 

Beartooth formations on the hills north of Santa Rita, but here 

they are so greatly metamorphosed that their identity is not apparent to the casual observer. It is probable that the formation 

is not greatly altered in the extreme eastern part of the area south 

of highway 180, where the section is hidden by a mantle of loose 

debris, but the only localities where redbeds in their normal character have been observed are in the Beartooth drainage basin and 

in the northeast corner of the area where they appear along the
28 SANTA RITA MINING AEEA, NEW MEXICO

northwest side of the regional anticline and between the two forks 

of the Barringer fault.

In the ore pits at Santa Kita a body of metamorphosed rock, 

made up principally of dark-green chlorite and magnetite, which 

lies just below the Beartooth quartzite and in contact with the main 

stock of granodiorite, is believed to represent the Abo redbeds, and 

material of the same sort and in like stratigraphic position within 

the zone of intense metamorphism on the west side of the HanoverFierro stock, near the Modoc mine, where the estimated thickness 

of the section is about 120 feet, has also been mapped as Abo. To 

the north of Sully School on Topknot Hill and also on Humboldt 

Mountain measured sections show about 120 feet of greatly altered 

strata which can be assigned to the Abo with confidence, in spite of 

the fact that their normal features have been almost entirely masked. 

In both localities the red sandstones and sandy shales have been 

converted into dark-purple or dark-green hornstone, and at many 

places noteworthy amounts of epidote have been developed. Where 

the Abo redbeds have been shown in localities not mentioned above, 

the mapping is based upon at least a few outcrops of metamorphic 

rocks resembling those to be seen on Topknot Hill and upon ascertained structural features in the neighborhood.

MESOZOIC FORMATIONS

Two Mesozoic formations are described in the Silver City folio, 

the Beartooth quartzite and the Colorado shale. The same formations are recognized and mapped in this report.

BEABTOOTH QUAKTZITE

The Beartooth quartzite was named from Beartooth Creek, in the 

Fort Bayard Military Reservation near the west boundary of the 

Santa Rita area. It lies unconformably either upon the Abo redbeds, of Permian age, or upon the Syrena formation, of Pennsylvania age, and is overlain conformably by the Colorado shale. It 

is made up of beds of fine-grained sandstones a few inches to 25 feet 

thick, separated by relatively thin partings of shale or sandy shale. 

Nearly everywhere the beds of sandstone, especially in the upper 

part of the formation, have been changed to quartzite by silicification.

The following section, exposed about 4% miles southeast of Santa; 

Rita, is given to show the character of this formation in the general 

region, the details of its stratigraphy not being observable within the 

Santa Rita area because of very poor exposures. The thickness of 

the formation at this locality is essentially the same as that given in 

the Silver City folio for a section exposed near Silver City.
STRATIGRAPHY 29

Section of Beartooth quartzite 4Vz miles southeast of Santa Rita*

[By E. H. Wells, 1923]

Feet

Sandstone, massive, vitreous, medium- and coarse-grained, 

containing also some conglomerate; gray and pink, 

weathering in part to reddish brown and black; probably corresponds to upper part of Beartooth quartzite 

at Santa Rita_________ i 25 

Sandstone and shale^ poorly exposed______ 18

Sandstone, massive, thick-bedded, gray and buff, weathering to red and black-_________ __ 25

Shale, black, carbonaceous, laminated_ 8 

Sandstone, massive, vitreous, medium-grained to fairly 

coarse-grained, gray to buff; prominent bedding planes 6 

inches to 3 feet apart_______________ 20

Shale, sandy, gray _ 2% 

Sandstone, massive, gray____________________ 2 

Shale, slightly carbonaceous__ 2% 

Sandstone, massive, gray_ _ 3% 

Shale, black, laminated, highly carbonaceous; prospected for

coal_________________________ 3 

Sandstone, massive, light gray_________________ 4% 

Shale, black and gray, laminated, highly carbonaceous in

part; prospected for coal_ _____ 4 

.Shale, laminated, red and gray__________________ 2 

Sandstone and shale, red and gray _____________ 6

Sandstone, shaly__________________________ 4 

Shale, gray_______________________________ 2 

Sandstone, medium-grained, brown, with some red-mottled 

areas; underlain by red shale of Abo redbeds_______ 10

132

Within the Santa Rita area the formation is about 60 feet thick, 

.and a thickness of about 125 feet is probably the maximum. A thin 

bed of chert conglomerate, noted at several places, occurs at the top 

or 4 to 8 feet below the top of the formation.

In the Santa Rita area the Beartooth quartzite is exposed along 

the flanks of the broad anticline or arch that plunges toward the 

southwest, but owing to widespread faulting and intricate invasion 

by a variety of stocks and dikes, the formation is greatly disturbed. 

A few isolated inliers, of which the top of Humboldt Mountain 

is a conspicuous example, mark the crest of the arch, which in most 

places is eroded well down into the lower part of the Pennsylvanian 

.series. The distribution of the formation is exhibited by the geologic map except in a few areas, mostly near Santa Rita, where it 

has been necessary to generalize Because all efforts to acquire^true 

understanding of the local features have failed.

92311 35 3
30 SANTA RITA MINING AKEA, NEW MEXICO

According to Paige,27

No fossils have been found in the formation. It is similar in many respects; 

to the Dakota sandstone, but Dartou has obtained fossils belonging to the,' 

Washita group of the Cornanche (Lower Cretaceous) in the Demiug quadrangle, immediately southwest of the Silver City area. For the present, therefore, the age of the Beartooth quartzite remains in doubt, but it is tentatively 

regarded as Upper Cretaceous.

A thin bed of chert conglomerate noted at several places near or 

at the top of the formation suggests the possibility of a boundary 

between the Upper and Lower Cretaceous series.

COLORADO SHALE

The Colorado shale bears the name of the State of Colorado,, 

where rocks of this age are characteristically developed. Throughout the general region of which the Santa Rita area forms a part 

the formation lies upon the Beartooth quartzite, and its upper limit 

is either the present land surface or an older land surface which is 

now buried beneath the volcanic rocks of the region, so that the full 

sequence is nowhere to be observed.

As exhibited at different localities in the Santa Rita area, theformation comprises three rather well denned divisions a lower 

carbonaceous shale member, a middle member characterized by 

prominent beds of light-colored calcareous sandstone, and an upper 

member made up of prevailing dull-green shale, sandy shale, and 

fine-grained sandstone. Several measurements of the lower member 

within the quadrangle indicate that it is everywhere about 200 feet; 

thick. At the base there is from 80 to 90 feet of well-laminated 

dark-colored clay shale; above this 25 to 35 feet of shale alternating 

with thin beds of sandstone and sandy limestone, some of which 

carries well-preserved fossil shells, followed by about 90 feet of clay 

shale nearly black in the lower part but sandy and gray toward 

the top.

Exposures of the middle member in the vicinity of Gold Creek 

show 130 feet of sandstone occurring in rather massive beds. The 

sandstones are characteristically calcareous, and layers of sandylimestone a foot or more in thickness occur 15, 45, 85, and 110 feet, 

above the base of the middle member. The limestone beds are in. 

places fossiliferous. No detailed measurement of the middle member of the formation was possible, but it has an estimated thickness 

of 520 feet at the edge of the mapped area, east of Santa Rita, wherestratigraphic details are obscured by lack of outcrops.

The upper member comprises dull-green shales, sandy shales, and 

sandstones. In the eastern part of the area these beds have an

27 Paige, Sidney, op. cit. (Silver City folio), pp. 5-6.
STEATIGEAPHY 31

estimated thickness of 220 feet. The Colorado shale as a whole, 

measured in the locality last mentioned, is 920 feet thick.

The Colorado shale lies stratigraphically above the Beartooth 

quartzite. In the northern part of the area there is a broad exposure 

of shale between lava ranges to the north and a prominent fault to 

the south. In the southern part of the area faulted and in places 

metamorphosed blocks of Colorado shale are variously disposed, as 

indicated on the map.

The fossils in the following list, identified by T. W. Stanton, 

have been found in the Silver City quadrangle. Those from locality 

4 were found near the west boundary of the Santa Eita area by A. C. 

Spencer, and those from localities 1, 2, and 3 were collected by 

Sidney Paige. The impure limestone that carries Gryphaea newben-yi has been noted at several places in the southern part of the 

Santa Rita area and was thus a very useful horizon marker.

Fossils from Colorado shale

Gryphaea newberryi Stanton... .

Tapes? sp .I...................

1

X

2

V

X

v

3

v

X

4

v Plicatulacf. P.hydrothecaWhite.

1 2

X

X

3

X

X

X

4

X

X

X

The horizons are from 85 to 115 feet above the Beartooth quartzite.

1. 4 miles north-northwest of Silver City, east fork of Silver Creek near road.

2. 4 miles northwest of Silver City, about 300 feet above Beartooth quartzite.

3. About 1 mile north of west summit of Lone Mountain, 100 feet above Beartooth quartzite.

4. Near quarter-section monument on west side of sec. 31, T. 17 S., R. 12 W.

The above-named fossils indicate a horizon near the base of the 

Colorado group as represented in the lower part of the Mancos shale 

of southwestern Colorado and adjacent parts of New Mexico, Utah, 

and Arizona.

TERTIARY FORMATIONS 

GRAVEL, SAND, AND TUFF

Accumulations of ill-sorted gravel, sand, and tuff, regarded as of 

Tertiary age, in places underlie and in places are interbedded with 

the rhyolite and andesite lavas. The beds beneath the lavas consist 

of thin to thick bedded friable sandstone and tuff in which the 

lowermost materials have been derived mainly from the underlying 

intrusive rocks or sediments. (See pi. 4.) Most of the beds are bghtcolorecl, some being nearly white and others drab or brown. In 

some layers fragments of chert occur, but except at the very base 

pebbles of other sedimentary rocks are not present. In most places 

the lowest beds are hidden by talus so that their nature cannot be
32 SANTA RITA MINING AREA, NEW MEXICO

observed, but at a few points there are exposures of loose gravelly 

material made up of rock fragments mainly of very local derivation. 

A prospect near the divide between the San Jose and Lucky Bill 

mines shows more than 30 feet of unconsolidated shingle or gravel 

made up of shale and porphyry pebbles derived from formations 

now exposed in the area just to the north of the locality. Outside 

the area mapped but near its southwest corner, at the same horizon, 

there are loose deposits consisting of pebbles and boulders of magnetic iron ore and of garnet and epidote rock which must have been 

derived from a source near Hanover or near Santa Rita and the 

occurrence of which indicates that before the volcanic epoch the 

principal drainage lines of the immediate district were much the 

same as at present.

The aggregate thickness of the tuffs and sandy beds varies greatly 

from place to place, mainly because of irregularities in the prevolcanic topography. Deposition of the formation obliterated, this 

earlier topography, filling hollows, overtopping minor ridges, and 

flanking higher hills, so as to form a fairly even floor over which 

the lavas were afterward extruded. South of the open pits at Santa 

Rita there is no tuff beneath the rhyolite, and the old erosion surface has a gentle westward slope. Farther west the fragmental 

deposits again appear, and the surface on which they lie slopes 400 

feet in a distance of less than half a mile.

In the northern part of the area the lavas rest as a rule directly 

upon the pre-Tertiary formations except in the vicinity of Avalanche 

Peak, where there is a thick deposit of coarse gravel containing a 

large amount of igneous material. The bedded sand and gravel 

are well exposed in the topographic basin south of Hanover, where 

down-faulting has preserved the beds from erosion. (See pi. 5, B.)

VOLCANIC BOCKS OF .UPPER CRETACEOUS AGE

Within the northwest corner of the Santa Rita area, in a tract 

covering less than a square mile, there occurs a complex of breccias 

and dikes of andesitic and dioritic composition between the Tertiary 

lavas on the north, by which they are overlapped, and Colorado 

shale on the south. This complex extends far to the west of the 

Santa Rita area and is exposed for many square miles.28 A part 

of it is tentatively regarded as a group of flow breccias of Upper 

Cretaceous age interbedded with Colorado shale. The dikes cut 

the flow breccias and the Colorado shale and are earlier than the 

Tertiary lava flows by which the complex is overlapped, but their 

age cannot be precisely determined. The inference that the flow

M Paige, Sidney, U. S. Geol. Survey Geol. Atlas, Silver City folio (no. 199), p. 7, 1916.
IGNEOUS BOCKS 33

breccias are local representatives of a period of active and widespread volcanism during Upper Cretaceous time is supported by 

the presence of a thick series of similar deposits in the Upper 

Cretaceous of the Aravaipa and Stanley mining districts of Graham County, Ariz. 29

INTRUSIVE BOCKS OF LATE CRETACEOUS OR EARLY TERTIARY

AGE

Accompanying the invasion of the andesitic and dioritic dikes 

mentioned in the preceding section or perhaps somewhat later, 

masses of quartz diorite porphyry invaded the sedimentary rocks 

as stocks and sills, and these in turn were cut by stocks and dikes 

of granodiorite porphyry. It is known from observations in the 

Santa Rita area and elsewhere in the Silver City quadrangle that

all these intrusions considerably antedated the flows of Tertiary lava.

Sills or intrusive sheets of medium-gray fine-grained to moderately coarse-grained porphyritic quartz diorite occur parallel or 

nearly parallel to strata of the Percha. Oswaldo, and Syrena formations and as sills or laccoliths in the Colorado shale. The 

porphyry contains relatively large grains or phenocrysts of plagioclase, hornblende, and quartz in a fine-grained groundmass composed essentially of the same minerals.

The sills occurring in the Paleozoic formations range in thickness from a few feet to not less than 400 feet. The thicker ones 

occur northeast of Fierro, west of Union Hill, south of Copper Flat, 

and in the southern part of the area. The thinner ones occur in 

Buckhorn Gulch, east of the Hanover Basin,.and north and northeast of Santa Rita. Although in places the sedimentary rocks in 

contact with the sills are strongly altered, in the main the metamorphism is related not to these intrusions themselves but to a later 

invasion of igneous material. The extensive mass that invades the 

Colorado shale has been called the Fort Bayard laccolith.

The geologic map of the Silver City folio shows that the outcrop 

of the laccolith extends in a belt 1 to 2 miles wide for about 8 miles 

from Central to a point east of the Kneeling Nun. To the south 

the mass is overlapped by Tertiary lava, and Quaternary gravel, 

but outcrops 4 miles southwest of Central, taken together with the 

belt just described, suggest that the laccolith was roughly oval in 

form and that it covered an area of at least 50 square miles. Such

m Ross, C. P., Geology and ore deposits of the Aravaipa and Stanley mining districts, 

Graham County, Ariz.: U. S. Geol. Survey Bull. 763, pp. 25, 26, 51, 1925.
34 SANTA RITA MINING AREA, NEW MEXICO

studies as have been made indicate that the mass was thickest at a 

point south of Santa Rita, now covered by Tertiary lava, and that 

the mass extended to the north of Santa Rita to an unknown but not 

great distance.

On the east side of Santa Rita Creek, on the Silver Dollar mining 

claim, its thickness is 160 feet. A diamond-drill exploration near the 

Bull Frog shaft 5, in Gold Gulch, reveals a thickness of 500 feet. 

In the Lucky Bill and Groundhog mines it has been penetrated 400 

feet without reaching the base, and a churn-drill hole in the country 

south of Santa Rita shows a depth of at least 900 feet below the 

present surface. On the ridge that extends north from the Kneeling 

Nun the mass breaks across the beds of Colorado shale for at least 

600 feet, and in the southeast section of the mine pits at Santa Rita 

the rock cuts across the Abo, Beartooth, and Colorado formations 

for a stratigraphic distance of at least 300 feet. This observation 

of crosscutting together with the great thickness south of the present 

exposed edge of the intrusive, suggests that one of the feeders of the 

laccolith may have been located in this general region.

The rock of the Fort Bayard laccolith is essentially typical of that 

forming the other sills. It is gray or greenish gray, fine-grained, 

and very slightly porphyritic, through the presence of small phenocrysts of feldspar. For the most part specimens of rock from different intrusions do not vary greatly in general appearance, though 

the rock of the sill west of Union Hill is finer and less even grained 

than that of the other sills. In many places the rocks of the sills 

contain much epidote and instead of having the usual grayish color 

are distinctly green. Thin sections examined under the microscope 

show that the rock of the sills is everywhere greatly altered. Originally it was composed essentially of oligoclase, hornblende, and 

quartz, with magnetite and apatite as accessory minerals. Now the 

hornblende is as a rule completely altered to chlorite or to chlorite, 

calcite, and epidote, and the oligoclase is in part changed to sericite. 

Phenocrysts of oligoclase, rarely more than 3 millimeters in diameter, 

are set in a groundmass composed of smaller well-formed crystals of 

oligoclase, quartz, and chlorite derived from hornblende.

Two stocks of porphyritic quartz diorite occur in the northwest 

quarter of the area, north of the Barringer fault. (See pi. 1.) 

They break across the beds of the Colorado formation, and locally 

lava flows rest upon them. The Hermosa stock, named from Hermosa Mountain, occupies an area 2 miles long and from half a mile 

to 1 mile wide. The rock is greenish-gray porphyry, usually containing phenocrysts of black hornblende in a fine-grained groundmass which is itself slightly porphyritic through the presence of
IGNEOUS BOOKS 35

small phenocrysts of feldspar. The hornblende crystals have the 

form of narrow prisms, some of which are as much as 20 millimeters 

long.. Where the hornblende phenocrysts are sparse or essentially 

absent the rock has nearly the same appearance as the porphyry of 

the sills that have been described but is of a slightly darker tone.

Thin sections of fairly fresh material examined under the microscope show oligoclase, primary hornblende partly altered to chlorite, 

colorless hornblende secondary after well-shaped crystals of pyroxene, a little quartz, rather abundant magnetite, and an occasional 

crystal of apatite. The texture is markedly porphyritic with respect to the altered pyroxene and with respect to abundant crystals 

of oligoclase, whose diameters range from 2 to 5 millimeters. The 

groundmass, which forms not more than one-fourth of the rock, is 

composed of minute crystals of oligoclase and irregular grains of 

quartz. In specimens containing chlorite this mineral has been derived mainly through the alteration of primary hornblende rather 

than from pyroxene or secondary hornblende. Alteration products 

include the hornblende and chlorite mentioned above and also 

epidote, most of which replaces pyroxene but some of which replaces 

hornblende and oligoclase.

The rock of the stocks that lie west and north of Hanover Mountain is a dark bluish-gray fine-grained porphyry, which on weathered 

surfaces shows phenocrysts of feldspar and small pits from which 

mica has weathered out. Thin sections examined under the microscope show that the rock is composed mainly of albite-oligoclase, 

other constituents being quartz, biotite, magnetite, and apatite. The 

feldspar occurs both as phenocrysts from 3 to 5 millimeters long and 

as small laths that form a trachytic groundmass. The biotite occurs as minute crystals and in the form of aggregates with oval cross 

sections. Quartz occurs only as a minor constituent of the 

groundmass.

GRANODIORITE AND GRANODIORITE PORPHYRY

Granodiorite in the Santa Rita area occurs as stocks and dikes. 

The largest mass is the Hanover-Fierro stock, in the north-central 

part of the area, and the next largest is the Santa Rita stock, in 

which parts of the large open-pit mines are developed. The rock 

occurring in the 2 small stocks at Copper Flat and the 2 northeastward-trending dikes, about 1 mile to the east, differs from the ordi- 

.nary granodiorite in that it carries very small amounts of ferromagnesian minerals.

Santa Rita stock. The intrusive mass here called the Santa Rita 

stock invades Paleozoic and Mesozoic sediments as well as the quartz
36 SANTA RITA MINING AREA, NEW MEXICO

diorite porphyry of the Fort Bayard laccolith. Its relation to the 

laccolith could not have been determined at the surface, but in the 

southern mine pits dikes of the Santa Rita rock cutting the quartz 

diorite porphyry have been exposed. In the pits and underground 

mines the walls of the intrusion are nearly vertical, so that its structural relations are here those of a typical stock. Nevertheless, in its 

passage upward it deformed the sedimentary rocks, a feature that is 

discussed under " Structure " on page 43.

The normal character of the granodiorite at Santa Rita is well exhibited by material collected from the open mine pits at a point about 

1,000 feet north from the office of the Chino Copper Co. Freshly 

broken surfaces show a porphyry comprising a dense gray groundmass, evenly distributed phenocrysts of a slightly greenish striated 

feldspar, and less regularly distributed prisms and flakes of darkbrown or nearly black mica. The feldspar and mica crystals show 

about the same range in size and have diameters of 2 to 6 millimeters. 

Thin sections examined under the microscope show a groundmass 

composed essentially of quartz and orthoclase in equidimensional interlocking grains. In different specimens the average size of grain 

ranges from 0.03 to 0.07 millimeter. The larger porphyritic crystals are andesine and biotite, besides which there are aggregates of 

secondary mica, representing altered phenocrysts of hornblende. 

There are occasional corroded crystals of quartz, apatite, and titanite, as much as 0.5 millimeter in diameter. Magnetite is rather 

abundant, and minute crystals of zircon and rutile are present. The 

groundmass contains about equal amounts of quartz and orthoclase. 

A careful estimate indicates that the proportions of andesine and 

orthoclase are respectively about 40 and 16 percent, so that the stock 

falls under the classification of granodiorite rather than quartz 

monzonite.

Hanover-Fierro stock. The intrusive mass here called the Hanover-Fierro stock, from its occurrence in the Hanover Basin, is the 

largest of the granodiorite bodies of the district. It has a length of 

2% miles from north to south, and is from half a mile to 1 mile wide. 

The development of the topographic basin extending from Fierro to 

Hanover has resulted from the manner in which the rather coarsegrained granodiorite disintegrates under atmospheric influences, rendering it more easily eroded than the formations by which it is 

surrounded.

The walls of the intrusive are almost everywhere nearly vertical, 

and its general relations are clearly cross-breaking with respect to 

the sedimentary formations now exposed; but certain structural 

features of the surrounding invaded rocks suggest that in depth the
V. S. GEOLOGICAL SURVEY BULLETIN 859 PLATE 4

A. TERTIARY GRAVEL, SAND, AND TUFF BENEATH RHYOLITE LAVA, SOUTH SIDE OF 

BASIN SOUTHEAST OF LUCKY BILL SHAFT.

Photograph hy Sidney Paige.

B. TERTIARY RHYOLITE RESTING ON GRAVEL, SAND, AND TUFF.

The tuff was deposited on porphyritic diorite. Edge of Chirio dump on left. View looking southeast 

from highway 180. Photograph by Sidney Paige.
U. S. GEOLOGICAL SURVEY BULLETIN 850 PLATE 5

A. LAVA RANGE NEAR EAST EDGE OF SANTA RITA QUADRANGLE.

View looking southwest from point half a mile east of Santa Rita. Summits are of rhyolite, which resls 

on eroded diorite. Low cliffs in foreground are along White water Creek. Photograph by Sidney 

Paige.

B. TERTIARY BEDDED SAND AND GRAVEL NEAR HANOVER CREEK.

Haifa mile south of Hanover post office. Photograph by Sidney Paige.
U. S. GEOLOGICAL SURVEY BULLETIN 859 PLATE 6

A. BRECCIATED GRANODIOHITK CUT BY .\KT\voHk OF QUARTZ VEINS ALONG 

JBARRINGKH FAULT ZONE.

Photograph by Sidney Paige.

R. COLLOFORM MASSES OF SILICATE MINERALS REPLACING WHITE LIMESTONE OF 

LAKE VALLEY FORMATION.

In bed of Hiickliorn (Julrh west of Hanover post office. Photograph by Sidney Paige.
IGNEOUS KOCKS 37

mass may have a laccolithic form. (See p. 45.) In different places 

the igneous rock may be seen in contact with all the Paleozoic 

formations, from the Bliss sandstone up to and including the Oswaldo formation, and on the north it invades the Colorado shale. 

Where erosion has exposed the Bliss and El Paso formations adjacent to its walls the strata usually show rather steep dips away from 

the stock, and on the east side these formations stand nearly on edge. 

The Paleozoic formations above the El Paso limestone are less 

steeply inclined, and their dips decrease with the distance from the 

stock, so that it is evident that the domal structure locally exhibited 

by the Paleozoic formations was produced as a result of the igneous 

intrusion.

The granodiorite of the Hanover stock is a light-gray, moderately 

coarse grained rock in which the principal minerals are white or 

greenish plagioclase, dark-green hornblende, and brown or nearly 

black biotite. Usually visible, though less readily recognized, are 

quartz, orthoclase, and magnetite. Most of the rock carries much 

less biotite than hornblende. In general the rock appears nearly 

even grained, but varieties that are markedly porphyritic occur, particularly toward the north end of the stock, and such material is 

very much like the rock of the Santa Rita stock.

Thin sections examined under the microscope show that the rock 

from the Hanover stock varies considerably in texture and composition, largely through differences in the proportions of groundmass 

and phenocrysts. Where the proportion of groundmass is small 

the texture is nearly granular, but with increasing proportions of 

groundmass the habit becomes distinctly porphyritic and the rock 

shows a rather close resemblance to that of the Santa Rita stock. 

The minerals occurring in well-formed crystals are plagioclase, hornblende, and biotite. The essential minerals of the groundmass are 

quartz and orthoclase, and accessory minerals comprise magnetite, 

apatite, titanite, and zircon. Plagioclase crystals measuring 6 by 10 

millimeters occur, but most of them have maximum diameters of 

less than 3 millimeters. In different specimens the composition of 

the plagioclase ranges from albite-oligoclase to oligoclase-andesine. 

The hornblende, a green, slightly pleochroic variety, occurs both as 

anhedral grains and as prismatic crystals 3 millimeters in maximum 

length, having characteristic lozenge-shaped cross sections but lacking crystallographic terminations. Many of the hornblende crystals 

contain small, irregular inclusions of orthoclase. Some of the thin 

sections examined lack biotite, but where present this mineral occurs 

in well-formed but thin tabular crystals as much as 2 millimeters in 

diameter.
38 SANTA EITA MINING ABEA, NEW MEXICO

In specimens from different localities the groundmass consists of 

quartz and orthoclase, commonly in about equal amounts. They 

occur in irregular interlocking grains of approximately the samesize. Thus the groundmass presents an even granular appearance,, 

and the greater its amount the finer grained it is. As quartz and 

orthoclase occur only in the groundmass, it is evident that with the 

stated variations in the proportion of the groundmass there are considerable differences of mineral composition and that some of the 

rock may appropriately be called quartz diorite rather than 

granodiorite.

Stocks at Copper Flat. Near the west side of the Santa Rita 

area, at Copper Flat, two small, closely spaced stocks of granodioriteporphyry break through the Oswaldo formation. The locality is 

about on the axis of the Fort Bayard anticline, and in the vicinity 

of the intrusions a slight domal structure has been imposed upon 

this broad fold. Excavations along the contacts show nearly vertical walls and therefore the stocklike form of the igneous bodies.. 

Both stocks have rudely oval outlines; the smaller one, to the north,, 

measures about 400 by 1,300 feet, and the larger one about 900 by 

1,850 feet.

The granodiorite of the larger stock at Copper Flat is a lightgray fine-grained porphyry in which small phenocrysts of biotite, 

quartz, and colorless glassy feldspar are the only visible minerals. 

Thin sections of this . rock examined under the microscope show 

numerous corroded quartz grains, a few well-formed quartz crystals, 

phenocrysts of albite-oligoclase (Ab80An2 o), small crystals of biotite,. 

and a little apatite. The largest of the albite-oligoclase crystals are 

about 2 millimeters in diameter, but most of them measure around 

1 millimeter. The corroded grains of quartz are mostly smaller

than the feldspar phenocrysts, but many of the well-formed quartz, 

crystals are of about the same size, and a few are larger than the 

feldspar crystals. The biotite, which is present in rather subordinateamounts, occurs as thin tabular crystals with maximum diameters 

of about 1 millimeter. The groundmass, constituting about onethird of the rock, is so fine-grained that the mineral components 

cannot be fully determined, but it contains both quartz and 

orthoclase.

Near the center of the larger stock, and probably constituting a 

later intrusion, there is a dikelike body of rock that differs from 

the porphyry of the main mass in that it contains large perfectly 

formed crystals of orthoclase and smaller ones of quartz. The 

orthoclase crystals are elongated parallel with the clino-axis so that 

their form is that of a nearly square prism. These prisms are 

commonly from 1.5 to 2 centimeters in diameter and from 3 to 4
IGNEOUS KOCKS 39

centimeters long. The quartz crystals are doubly terminated prisms 

with axial diameters ranging from 1 to 1.6 centimeters.

Unaltered rock exposed near the northwest end of the smaller or 

northerly stock at Copper Flat is much like the porphyry of the 

larger stock, but it lacks quartz phenocrysts and has a slightly 

coarser texture. Thin sections examined under the miscroscope 

show a marked porphyritic habit due to phenocrysts of plagioclase, 

a large proportion of which have diameters near 2 millimeters. 

Small phenocrysts of biotite are also present. The groundmass 

contains both biotite and plagioclase but consists principally of 

equi dimensional interlocking grains of quartz and orthoclase having 

average diameters of about 0.1 millimeter. The feldspar phenocrysts 

are essentially albite-oligoclase (Ab80An2 o), but through this mineral orthoclase occurs as irregularly distributed or reticulating inclusions that appear to be of later origin than the host.

The rock of the two dikes that cross the highway about a mile 

east of Copper Flat is a light-colored quartz-bearing porphyry that 

closely resembles the rock of the larger of the stocks described above. 

South of the road, where the western dike expands into a stocklike body, the limestones near the contact have been locally metamorphosed and charged with sulphide minerals. Copper ore has 

been mined at this locality, and about a quarter of a mile to the 

southwest a small deposit of galena occurs in limestone on the 

east side of the easterly dike.

Other granodiorite dikes. Igneous intrusion did not cease with 

the emplacement of the granodiorite stocks at Santa Rita and Hanover. The fracturing that followed the cooling of these masses was 

accompanied by widespread intrusion of dikes, many of which are 

shown on the geologic map. v

Of the dikes related to the granodiorite stocks, some may have 

been injected earlier than others, for in some places they cut mineralized veins, and in others they are cut by such veins; but these 

relations, on the other hand, may indicate a difference in age of 

the veins. In the zinc mines south of Hanover there are granodiorite dikes, the relations of which to the replacement deposits of 

sphalerite are somewhat in doubt. In the Groundhog mine, however, in the southern part of the area mapped, these dikes are earlier 

than the veins, as has been observed by Lasky. These dike intrusions may be regarded as episodes in a period of fracturing, hydrothermal metamorphism, and mineralization that followed the emplacement of the stocks.

Although it is recognized that some dikes may have been injected 

at the same time as the main stocks or in advance of them and may
40 SANTA RITA MINING AREA, NEW MEXICO

thus be regarded as offshoots of these masses, nowhere has such a 

relationship been proved. The two westernmost dikes in sees. 29 

and 20, T. 17 S., R. 12 W., may be contemporaneous with the granodiorite intrusion of Copper Flat, for in composition and texture they 

are all much alike, but their interrelationship in time cannot be 

confidently established.

TERTIARY LAVAS

Tertiary lavas that are but parts of more extensive bodies occur 

on the north and south borders of the Santa Rita area. There is 

abundant presumptive and some direct evidence that these lavas once 

completely covered the Santa Rita area, and there are excellent 

structural reasons (see pp. 46-56) to explain their removal by erosion. 

Along the north border these lavas are almost wholly andesite or 

basalt, only two small outcrops of rhyolite appearing at the very 

base of the series; along the south border rhyolite flows at the base, 

aggregating 500 to 600 feet in thickness, are succeeded by a thin 

andesite flow and by higher rhyolites. These lavas dip southeastward at a rate of about 120 feet in a mile. (See pi. 5, A.)

The rhyolite south of Santa Rita, at a point about 21/2 miles south 

of Cobre siding, is a light-bluish rough-surfaced rock with pheno-, 

crysts of glittering clear glassy feldspar, plainly visible quartz, and 

some biotite in an aphanitic groundmass. The rock contains abundant prthoclase, some unstriated oligoclase, and large crystals of 

ilmenite. The groundmass is a fine-grained aggregate of glass and 

feldspar. The rock may be classed as rhyolite, though it approaches 

quartz latite in composition.

In the tuff and gravel series near Hurley, southwest of the area 

mapped, is a thin flow, a light salmon-pink cellular rock of pumiceous aspect, that contains many fragmental inclusions as much as 

an inch long. In its glassy base are scattered unstriated feldspar 

phenocrysts of albite-oligoclase and a few flakes of biotite. Its 

groundmass contains numerous fibrous or spherulitic crystalline 

growths. Straight curved, and forking figures are present, made 

up of crystalline fibers set at right angles to parallel walls. These 

incipient growths are characteristic of western rhyolitic lavas.

The flow along the north border of the area is typically a dark 

rock of deep reddish hue, showing a great number of glittering 

feldspars of the same deep red color. The rock is distinctly porphyritic. Well-formed, relatively large, slender phenocrysts of 

labradorite and olivine, in well-developed crystals, and small grains 

of olivine are set in a microgranular groundmass. The groundmass, 

which forms more than half the body of the rock, contains rodlike 

crystals of feldspar and much finely granular pyroxene with abun-
IGNEOUS ROCKS 41

dant fine grains of magnetite. Flow structure is plainly indicated by 

the parallel arrangement of rodlike crystals.30

TEBTIABY STOCKS AND DIKES

Within the Silver City quadrangle there are numerous stocks and 

dikes of postlava Tertiary age. Some of these stocks lie near but 

just outside the borders of the Santa Rita area. Within this area 

there .are two igneous masses regarded as of Tertiary age and a 

great number of dikes that are placed in the same category. The 

two igneous masses are the small mass at Bull Hill, on the north 

side of the topographic basin that lies south of Hanover, and the 

irregular mass mapped near the southeast corner of the same basin.

The intrusive relations of the mass at Bull Hill are obscure. 

Faulting on both the north and south sides of the mass is a possibility, but the petrographic character of the rock is so similar to 

that of nearby dikes that cut the Tertiary sand and gravel of the 

basin that the Tertiary age of the stock may be affirmed with a high 

degree of confidence. The contacts of the mass are mapped as 

intrusive.

The irregular mass that invades the sedimentary rocks east and 

southeast of the basin is somewhat different in character from the 

Bull Hill rock, but the absence of metamorphic minerals within it, 

such as are characteristic of earlier dikes, and the fact that at one 

place it appears to invade sand and tuff of Tertiary age dates the 

mass with considerable assurance.

Dikes of Tertiary age are in most places readily distinguished 

by their petrographic aspect. Where such dikes cut the Tertiary 

sand and gravel of the Hanover Basin there can be no question of 

their late age. Dikes exactly similar petrographically ha,ve been 

mapped at many places. These dikes are characteristically later 

than the numerous granodiorite dikes, at some places cutting 

squarely across them; and they are characteristically free of the 

metamorphic effects, particularly the development of epidote, that 

everywhere characterize the earlier granodiorite dikes.

At most places the late dikes carry well-developed chilled .selvages, 

and Avhile earlier dikes are in a few places so marked the prevalence 

of this feature is far more characteristic of the Tertiary dikes. 

These later dikes are also prone to have tortuous intrusive contacts. 

They range in texture from rather fine grained porphyry to rocks 

which in a few places are comparatively coarse grained, particularly 

in the middle of the dike; but at such places the total absence of 

epidote serves to identify them.

60 For a detailed description of the Tertiary lavas see Paige, ;Sidney, op. tit. (.Silver 

City folio), pp. 9-10.
42 SANTA BITA MINING AREA, NEW MEXICO

STRUCTURE

BROAD FEATURES

The folding and faulting that accompanied the invasion of 

Paleozoic and Mesozoic rocks by successive intrusions of quartz diorite 

porphyry and granodiorite and the Tertiary faulting that later affected the entire Santa Rita area have combined to produce complicated structure. Inasmuch as the structure disclosed today is the 

result of several definite movements widely separated in time, it is 

consistent to describe the folds and faults in the order of their occurrence, but a preliminary view of the broad structural features irrespective of the order of structural events seems desirable.

From the geology of the surrounding region as portrayed in the 

Silver City folio it is known that the Santa Rita area lies on the 

northeast limb of a shallow southeastward-trending syncline, the 

axis of which is about 4 miles southwest of Copper Flat. The 

syncline has an observed width of about 16 miles, from the crest of 

the Continental Divide, on the southwest, to Georgetown, on the 

northeast. It is modified by an anticlinal arch (named the Fort 

Bayard arch), the axis of which passes from northeast to southwest 

across the Santa Rita area, and this arch in turn is modified by a 

sharp transverse domelike anticline symmetrical with the topographic basin between Hanover and Fierro, by a more gentle dome 

having its crest north-northeast of Copper Flat, and by several folds 

on both flanks of the Fort Bayard arch. (See pis. 1 and 2.)

The existence of the Fort Bayard arch and the fact that its axis 

plunges gently to the southwest, or toward the keel of the broad 

syncline, is clearly revealed by strata of Beartooth quartzite that 

wrap around the Paleozoic formations so as to enclose them on three 

sides. These relations may be seen on plate 1, where also it may be 

 observed that the simple upwarping of the arch is increased by 

strike or near-strike faults along both flanks. On the northwest 

side of the axis all the complementary displacement occurs along a 

single normal fault zone, which has been called the " Barringer fault 

zone ", whereas on the southeast side of the axis the total displacement by faulting is distributed stepwise along numerous breaks, most 

of which show downthrow in a direction that increases the effect 

of the anticlinal uplift. At the south end of the Hanover-Fierro 

stock, where a number of small faults trend north, this rule does not 

hold. (See pi. 2, cross section B-B' .) Although the broad structural features of the region may thus be simply stated, the structure 

in detail is more complex. Invasion by sills, laccoliths, stocks, and 

dikes at different periods, coupled with the faulting that accompanied them and the faulting that occurred later in postlava time,
STBUCTUEE 43

lias greatly disturbed the orderly sequence of both Paleozoic and 

Mesozoic strata. To understand these disturbances, the effects of the 

successive invasions will be described in order.

FOLDS

Quartz diorite porphyry apparently invaded essentially flat-lying 

Paleozoic and Mesozoic rocks, though earlier gentle warping or tilting, whose effects are no longer distinguishable, may have occurred. 

The porphyry now appears in the form of sills in the Percha, Oswaldo, and Syrena formations and as sills, laccolithic bodies, and 

.stocks in the Colorado shale. In the formations below the Beartooth 

quartzite the sills follow definite horizons with a marked degree of 

fidelity and are in marked contrast with the great laccolith in the 

Colorado shale, which shows strongly crosscutting relations at several 

localities and also encloses many large and small blocks of the shale. 

The observed difference with respect to regularity of form between 

the intrusive masses below and above the Beartooth quartzite is 

perhaps obviously related to the fact that the load to be lifted 

where the injections penetrated the Paleozoic formations was measurably greater than that above the Colorado shale.

The position of the feeders for the sills and laccoliths is not known, 

but it seems that there may be some beneath Hermosa Mountain 

and the igneous masses immediately to the north, and that another 

may be represented south of Santa Kita by the quartz diorite porphyry that clearly cuts across the Abo, Beartooth, and Colorado 

formations.

A substantial upwarp must have occurred above the Fort Bayard 

.laccolith south of Santa Rita, for here the mass is still at least 1,000 

feet thick in spite of erosion. In the southwestern part of the area 

also the violent effects of the invasion are to be seen. The base 

of the laccolith invaded the Colorado shale within a stratigraphic 

range of 280 feet. Three horizons appear to have been favorable 

namely, the top of the Beartooth quartzite, the base of a 25-foot

 .sandstone bed 80 feet above it, and the base of a second sandy series 

200 feet above it. In places the laccolith crosscuts between these 

horizons, and here and there it has split so that it includes the beds 

between two of them. During the emplacement of the laccolith the 

invaded sediments were broken and pulled apart. Apparently nu--

 merous blocks of shale and sandstone were eneulfed in the magma,

~ O 5

.although in many places it is difficult to distinguish between intrursive and fault contacts.

The Fort Bayard arch, although of simple structure in broad 

outline, is modified in detail by a number of minor anticlines and 

.synclines, the axes of which are more or less parallel to the trend of
44 SANTA RITA MINING AREA, NEW MEXICO

the arch. Such folds, which in places are disturbed by later intrusions, especially north of the Barringer fault, suggest that compressional forces may have played a part in initiating this prominent 

structural feature, although it is recognized that the invasions of 

granodioritic magma, about to be described, were of such amplitude 

that a part of the doming may be assigned to their upward movement. In fact, it is reasonable to infer that here we have an example 

of magmatic movement impelled by compressional forces but resulting in effects that suggest local distention of the crust.

How long an interval elapsed between the invasion of the quartz 

diorite sills and the initiation of the granodiorite intrusions just 

referred to is not known, but it is to the movements related to or 

directly following these later intrusions that some of the larger 

folds and some of the faults of the area are due. There are within 

the area three centers where large masses of granodiorite appear 

and are obviously in a measure related to folding between Hanover 

and Fierro, at Santa Rita, and at Copper Flat. Although it cannot 

be asserted that intrusion was contemporaneous at these centers, 

the weight of evidence favors the view that all three masses came 

to place at about the same time and that the subsurface volume of 

the magma is greater than would be suspected by casual inspection 

of surface outcrops.

The emplacement of the granodiorites was certainly accompanied 

by folding. Broad upwarping is conceived to have begun at an 

early stage of the invasion or before it that is, before the magma 

had penetrated the Cambrian Bliss sandstone. At this stage the 

anticlinal arch was outlined and parallel folds within the arch 

initiated. The crest of the arch trends N. 60° E. from a point near 

Central, bisects the Hanover-Fierro intrusive mass, and corresponds 

with the crest of a fold in the quartz diorite sill near the edge of 

the area mapped. The arch plunges to the southwest, and its nose 

is clearly displayed at the surface by outcrops of Beartooth quartzite that encircle the Paleozoic formations. (See pis. 1 and 2, section A-A'.) Superimposed upon the Fort Bayard arch are 

two transverse anticlinal folds, the more prominent of which is 

related to the Hanover-Fierro mass of granodiorite. The other, 

lying west and southwest of Humboldt Mountain, is presumed to 

be related to a buried mass that connects beneath the surface with 

the granodiorite of Copper Flat. Between these transverse anticlinal folds there is a synclinal depression, along which two synclines indent the opposite limbs of the major arch but fail to 

depress its crest appreciably.

The causal relation between intrusion and the transverse folding 

is clearly displayed by the structural features surrounding the Han-
STBUCTUEE 45

over-Fierro mass of granodiorite. This elongate intrusive mass 

broke through the pre-Cambrian basement and in the early stages 

of its advance assumed the form of a laccolith. An elongate symmetrical dome was formed, the position of which has been established 

by direct observation at the surface. The continued upward movement of the magma was not directed symmetrically with respe'ct to 

this dome. As it violently forced its way through each successive 

higher formation, dragging along the sheared Bliss sandstone, mov-' 

ing upward and southward, the axis of the intrusion shifted toward 

the southwest as the magma was progressively deflected away from 

the southern nose of the ancient dome. (See pi. 1.) At a stage in 

its progress which apparently preceded the penetration of the Percha 

shale, two folds developed within the beds lying in advance of its 

path one a synclinal downwarp adjacent to the magma, the other 

anticline immediately beyond it. The synclinal downwarp was initiated in response to a marked southwest dip on the flank of the ancient 

arch, a dip that must have been increased by the bulge that necessarily formed above the wedge, of magma as it forced it's way southwestward and upward. The anticline beyond the syncline was a typical pressure ridge. Because the invading mass was narrow these 

folds developed a sharply bow-shaped outline along its front. (See 

pi. 1.) As the intrusive mass continued its advance, it forced the 

inner limb of the syncline to a nearly vertical position, with local 

overturning, and finally broke through and nearly obliterated it. 

The contact of the granodiorite at the surface today suggests that 

the magma then rose at a steep angle upward and outward on the 

northern limb of the anticline or pressure ridge. The present cuplike form of the broken syncline is regarded as due in part to the 

merging of the bow-shaped folds with the dip slope of the ancient 

arch and in part to the circumstance that hydrostatic pressure within 

the magma was directed circumferentially. The roughly circular 

lobe that characterizes its south end supports this view. The entire 

history of the invasion as interpreted from field observations emphasizes the conclusion that local structural features were first formed 

in advance of the magma and later disrupted by its continued 

progress.

It is clear from a consideration of the eastward dips of the Beartooth quartzite and the Colorado shale on the southeastern border 

of the Santa Rita stock and the westward dip of the same formations 

west of the ore pits on Lee Hill (north of the railroad station), that 

the upward passage of the magma warped the overlying beds into a 

definite arch. This view is supported by the outward dip of the beds 

in the Colorado shale that border the intrusive mass at its southwest 

corner.

92311 35 4
46 SANTA KITA MINING AKEA, NEW MEXICO

Related to the domelike anticlines just described are a number of 

downwarps. A mile and a half west of Fierro on the south side of the 

Barringer fault, there is a cuplike depression involving Cretaceous 

strata. This depression appears to occur at the northwest end of a 

synclinal axis that is marked at its southeast end by a broad, shallow 

embayment of Cretaceous strata indenting the otherwise regular 

boundary of the Fort Bayard arch southeast of Humboldt Mountain. 

This embayment is now obscured by numerous faults, as will be 

shown below. A smaller syncline occurs east of the Santa Rita stock. 

An anticline is found west of Lover's Lane (the northward-trending 

road half a mile west of Santa Rita station). Part of a small syncline is nearly surrounded by granodiorite at the north end of the 

Hanover-Fierro stock.

FAULTS

Within the Santa Rita area normal faults are widespread, but 

they are particularly well developed in the southern part of the area. 

Their structural significance is clarified by considering the fault 

pattern of a much larger area the 1,000 square miles embraced in, 

the Silver City quadrangle. The fault pattern displayed here may 

be resolved into two systems faults that trend northwest and faults 

that trend northeast. There is abundant direct and considerable 

presumptive evidence to prove that these faults are of Tertiary (post« 

lava) age.

Many of the shorter, northeastward-trending faults, such as those 

so well displayed in the range near Silver City, the Little Burro 

Mountains, and Lone Mountain, may reasonably be regarded as subsidiary fractures related to master dislocations that trend northwest 

and are longitudinally disposed with respect to mountain axes. The 

rocks forming these mountains were dislocated along these master 

faults and tilted toward the east, and it is clear that this movement 

did not cease in Tertiary time but has continued, in places at least, 

well into the Quaternary, for faults of considerable throw displace 

Quaternary gravel, notably the master fault at Georgetown, near 

the east edge of the Silver City quadrangle, and the fault along the 

western border of the Little Burro Mountains, to the west.

Within the Santa Rita area, however, there are faults that do not displace the Tertiary lavas. They are older than the lava and in most 

places are more or less mineralized. It is therefore a matter of considerable structural importance to discriminate so far as possible between 

prelava and postlava faults and to recognize, where possible, postlava movement on ancient mineralized fault planes or along nearby 

parallel fractures.

Viewed broadly, the continuity of the Fort Bayard arch is modified on both flanks by faults that either roughly parallel its axis
STRUCTURE 47

or, as in places on the south, penetrate the arch. To the east, at 

Georgetown, the arch is sharply terminated by a strong fracture on 

which there has been notable movement during Quaternary time. 

The combined effect of these movements was to raise the central 

portion of the arch with respect to its flanks, as will appear in the 

description that follows.

In the northern part of the area mapped there is but one strong 

fault or fault zone the Barringer fault zone, which passes between 

Fierro and Hanover Mountain. This dislocation, as shown in the 

Silver City folio, has been traced for 5 miles from a point near 

Shingle Canyon, on the northeast, to a point iy2 miles north-northwest of Copper Flat. It is named for the late D. M. Barringer, 

M. E., in recognition of his sustained interest in geologic studies 

during many years of activity in the development of the properties 

of the Hanover-Bessemer Iron & Copper Co., some of which lie 

along its trace. The nearly straight or gently curving trace of 

this fault throughout much of its course indicates the relative steepness of its dip, 45° or more to the north. It is a normal fault with 

downthrow on the northwest side. It transects in striking fashion a 

number of preexisting folds and emphasizes the distinction both ia 

time and in character between those movements that were brought 

about or accompanied by intrusion and resulted in folding and those 

that resulted in simple block displacement. The transected folds 

referred to appear on both sides of the fault, which lies well within 

the borders of the Fort Bayard arch. The ultimate northern extension of the arch, however, is partly destroyed by intrusion and 

partly concealed by overlap of Tertiary lavas. At the southwest 

end of the fault, on Ansones Creek, the Beartooth quartzite, which 

curves northeastward on the nose of the arch, is sharply cut off on 

the opposite side of the fault by Cretaceous sandstone (higher stratigraphically than the Beartooth quartzite), which abuts against it. 

The northwestward dip and northeasterly strike of the sandstone 

beds display clearly the dropped northern extension of the arch. A 

short distance farther east a local shallow synclinal depression appears on the north side of the fault. It is reasonable to suppose that 

this depression is related structurally to the larger cuplike depression, 

involving Beartooth quartzite and Colorado shale, that appears 

south of the fault arid but a short distance farther east.

A second fold, an anticlinal nose north of the fault, borders the 

Hanover-Fierro stock and marks its northern limit. This fold 

plunges gently northwest. Beartooth quartzite is here exposed resting on the Abo redbeds, beneath which are beds of the Syrena formation faulted down against the Percha shale, which forms the south 

side of the fault. Almost adjoining this plunging anticline but
48 SANTA RITA MINING AREA, NEW MEXICO

south of the fault line is a sharp synclinal fold plunging toward the* 

fault. Here Colorado shale on the north is faulted down against; 

Percha shale and Lake Valley limestone invaded by the HanoverFierro stock on the south.

Another very minor synclinal downwarp appears on the south side 

of the fault opposite the mouth of the small stream immediatelynortheast of Hanover Mountain. Some structural significance may 

attach to this downwarp in view of the fact that Hanover Mountain 

is in general a synclinal feature with a northward plunge. Cretaceous beds northeast of Hanover Mountain, though much disturbed' 

by faulting and by the intrusion of dikes, have general northeast 

strikes and northwest dips and therefore support the view that theFort Bayard arch extended at least as far north as the present position of the Tertiary lavas.

The Barringer fault passes directly across the end of the HanoverFierro stock. Its path through the massive granodiorite is marked" 

by intense shearing along numberless fracture planes, which are 

filled with an intricate network of anastomosing quartz veinlets- 

(pl. 6, A) in places so abundant that only mere vestiges of the 

igneous texture of the granodiorite can be discerned. Abundant 

pyrite and appreciable quantities of gold were introduced with thequartz. The close relation of the fault to the Fort Bayard arch, 

which was formed before the intrusion of the granodiorite, suggests 

that the faulting also at least began before the intrusion, but, asshown on page 49, there is no direct evidence to support this suggestion; on the other hand, the displacement of the minor folds that 

were formed at essentially the same time as the intrusion shows that. 

a considerable movement along the fault occurred after the intrusion 

and produced the openings along which silicification of the granodiorite took place. The exact course of the fault through the granodiorite, however, is not clearly defined, and for this reason it is. 

generalized on the geologic map.

The fault emerges from the east side of the stock where Colorado 

shale on the north is faulted down against successive beds of LakeValley limestone, Percha shale, and rocks stratigraphically higher 

in the section. It also transects a sill-like mass of diorite porphyry 

farther east. Near the north edge of the area mapped the fault, 

divides, and Colorado shale is brought down against the Abo and 

Syrena formations, which in turn are faulted down against the 

Oswaldo formation. The Barringer fault transects massive magnetite ore bodies developed in the underground workings of the 

Hanover-Bessemer Iron & Copper- Co., immediately west of the 

granodiorite contact. These relations are displayed on the mine
STEUCTUBE 49

.maps of the company and were observed underground. The Barringer fault is here a fault zone rather than a single break, and 

steeply northward-dipping faults carrying considerable gouge' 

sharply limit ore against barren ground. The magnetite ore bodies 

in this zone are merely dislocated fragments of bedded replacement 

deposits related in origin to the early stages of granodiorite intrusion. In this general locality it has been impracticable to separate 

the formations, and those within the fault zone are mapped as 

iindifierentiated.

The gentle deflection of the Barringer fault plane reflected in its 

'curve around the south end of the Hermosa Mountain mass of diorite 

porphyry and in its equally gentle curve in the opposite direction 

as it approaches and finally transects the north end of the HanoverFierro stock is regarded as supporting the view that both igneous 

masses were rigid bodies before the initiation of faulting at this 

place.

In the features that have just been described there is evidence to 

support the view that horizontal as well as vertical movement has 

played a part in the displacement along the Barringer fault zone.

The relative horizontal movement indicated was from east to west 

on the north side of the fault and may have been as much as 1,500 

ieet, though this figure is offered more as a suggestion than as a 

determined fact. In view of the fact that both north and south of 

the fault the terrane was folded and invaded by igneous rocks prior 

to the faulting, it is difficult to estimate the vertical throw precisely, 

for the apparent throw under such conditions is no true measure of 

the actual displacement and will vary from place to place. The 

throw of the Barringer fault is probably not less than 350 feet but 

may be more.

To fix the time at which movement began on the Barringer fault 

 or the time after which movement ceased is not a simple problem. 

There is some direct evidence to support the view that movement 

began after the consolidation of the granodiorite stock, and no positive evidence to the contrary. And there is indirect evidence to 

support the view that post-lava movement may have occurred. 

This indirect evidence lies in part in the fact that the Barringer 

fault appears to be but one of a group of faults, many of which 

clearly cut the lavas, the only difference being that the nearby lavas 

may have been recently stripped from above the Barringer fault; 

and in part in the fact that the Barringer fault zone includes toward 

the northeast strong parallel fractures that are not mineralized. 

At a point 1% miles northeast of the area mapped the Barringer 

fault is cut off by a master fault on which there has been even very
50 SANTA KITA MINING AREA, NEW MEXICO

recent movement. It is reasonable to suppose that in such major 

adjustments of the crust sympathetic movement occurred along the 

Barringer zone.

Faulting along the southern flank of the Fort Bayard arch did 

not follow a single fault zone, as on the north. On the contrary the 

displacement of the arch was effected through a number of normal 

faults of northeasterly to northerly trend, and for this reason the 

folds that antedated the faulting' are not so clearly displayed. 

Nevertheless, the relics of these folds may be observed, and there 

are many facts of observation to support the belief that the same 

structural forces that molded the northern flank of the arch were 

effective here.

When ths fault pattern along the south flank of the arch is; 

studied on the geologic map (pi. 1) several striking relations appear.. 

Notable first is the prevalence of faults that dip toward the southeast, a direction opposite to that displayed along the Barringer 

fault, on the north flank. Also noteworthy is the dropped block 

of Tertiary sand and gravel south of Hanover. Notwithstanding; 

the fact that there are a number of faults that dip to the west 

or northwest, and few of these appear1 to be of large displacement, 

the general effect of the faulting has been to depress the south 

flank of the arch with respect to its axial portion. This relation 

is emphasized if account is taken of a strong fault which lies east 

of the Santa Rita area and can be traced for many miles, and 

which, as will be shown later, probably displaces rocks within the 

area.

The position of the down-faulted block of Tertiary sand and 

gravel south of Hanover deserves special consideration. It is doubtful if this remnant could have escaped erosion had post-lava faulting not occurred. Although there can be but little doubt that the 

lava series once extended over the entire region under discussion, it. 

is reasonable to suppose that on the Fort Bayard arch the series was 

somewhat thinner than at other places to the north and south; and 

that after the faulting the arch stood even higher than before, in 

relation to the terrane to the north and south. Normally, therefore, 

it would be expected that the series of lavas would be removed first 

from the higher terrane. And apparently this has occurred, for in. 

no other place in the central area are representatives of the lava, 

series to be found. Some explanation is due, therefore, for the preservation of these particular outcrops of the basal formation of the 

lava series, and a reasonable explanation appears in the fact that 

these beds (see pi. 1) are surrounded on four sides by normal postlava faults.
OF

STBUCTUBE w i « , ^

The general fault pattern under discussion includes faults within 

the bordering Tertiary lavas to the south and thus invites special 

attention, for here it is possible in places to distinguish definitely 

between post-lava and pre-lava movement. Faults that are clearly 

of post-lava age will be described first; those that may have a component of post-lava faulting and those that appear to be definitely 

pre-lava will be considered together.

Of the several faults that clearly displace the lava series, three 

are notable breaks. The largest post-lava fault is known as the 

Groundhog fault (from the Groundhog claim, which it traverses). 

This normal fault lies about half a mile southeast of Hanover 

Junction, trends in general N. 45° E., and dips about 55° E. Rhyolite on its east side is faulted down against the basal sand, gravel, 

and tuff of the lava series. The throw near the Groundhog shaft is 

about 180 feet, but there is some basis for the opinion that this' displacement diminishes gradually toward the north. Efforts to trace 

this fault northeastward from Whitewater Creek have not been 

successful, first, because both walls are here in quartz diorite porphyry, and, second, because late movement that reopens older mineralized fractures is difficult to recognize. In line with the projected trace of the fault, however, a definite shear zone certainly 

occurs, and it is along this zone that the effects of the fault probably 

extend within 1,000 feet of the Ivanhoe shaft, if not farther, to join 

what is known as the Copper Glance fault (pp. 54-55).

A second post-lava fault lies about 700 feet southeast of Hanover Junction, also trends northeast, and dips to the east. It brings 

Tertiary gravel and sand on the east down against quartz diorite 

porphyry on the west. This fault is directed toward an area of 

quartz diorite porphyry in which mineralized fractures of pre-lava 

age trend east-northeast, and it is reasonable to suppose that any 

post-lava movement was absorbed on these older openings. The 

fracture certainly cannot be traced across a group of such veins 

that lie about half a mile north of Whitewater Creek.

A third fault that cuts the Tertiary lavas crosses Whitewater 

Creek about a mile southwest of Hanover Junction. This normal 

fault trends north-northeast, dips to the east, and brings the Tertiary gravel, sand, and tuff series down on the east against quartz 

diorite porphyry. It might be expected to pass near the east side 

of a block of intricately faulted Cretaceous strata to the north, 

but it may or may not extend that far north.

Another fault on which post-lava movement can be recognized 

marks the western boundary of the down-faulted block of Tertiary 

sand and gravel south of Hanover and may be traced 2 miles to the
52 SANTA EITA MINING AREA, NEW MEXICO

southwest, where it appears to fork and die out within an intrusive sill of quartz diorite porphyry and within Cretaceous shale. 

This normal fault dips about 80° E. and is remarkable for the 

clean-cut break that it displays in fact, it is called the " Mirror 

fault" from the highly polished surfaces that may be observed in 

the Blackhawk or Combination mine workings, where metamorphosed S}7 rena limestone on the east side of the fault is brought 

down against the metamorphosed Oswaldo limestone on the west. 

It is estimated that at the Combination mine the throw of this fault 

is about 400 feet and that it diminishes gradually toward the 

southwest.

Three faults remain to be described that are clearly of post-lava 

age. These faults bound the dropped block of Tertiary sand and 

gravel south of Hanover on its north, south, and east sides. The 

eastern and southern faults can be traced without difficulty. The 

eastern fault for much of its course coincides with the west side 

of a dike that is regarded as younger than the fault. Near the fault 

the dips of bedded sand and gravel that strike N. 50° W. may be 

observed to steepen gradually from 45° to vertical as the fault is 

approached and reached. The southern fault is clearly marked by 

the sharp contact of sand, gravel, and breccia against Cretaceous 

shale or diorite porphyry. This fault curves northwestward and 

joins the Mirror fault on the west side of the basin. On the north 

side there are two faults with a general northeast trend connected by 

a northward trending fault lying west of the latite porphyry of 

Bull Hill.

At the road crossing of Hanover Creek a dike of latite porphyry 

is brecciated, but it is not apparent whether the brecciation is due 

to its mode of intrusion or to later movement.

On several faults that remain to be described it cannot be affirmed 

that there has been post-lava movement, though there may have been; 

and there are others on which there has almost certainly been little, 

if any, post-lava movement. These faults are so interrelated structurally that evidence as to their age will be presented as the faults 

are described. They do not fall into separate groups.

The block that lies southeast of the Mirror fault is limited on the 

southeast by a system of subparallel faults that have been named the 

Hobo fault zone, from the Hobo mining claim, which is about 3,000 

feet southeast of the Combination shaft. The general course of the 

fault system is somewhat more northerly than that of the Mirror 

fault, the average direction being about N. 30° E. Through the 

greater part of the zone there are two prominent faults from which 

spurs diverge at a narrow angle toward the west, as the observer 

travels northeast. Within the fault zone the displacement is step-
STRUCTURE 53

wise, the downthrow, with one minor exception, being on the southeast. From observations at the surface the dips of all these faults 

are steep toward the southeast. The combined displacement within 

the zone is probably about 500 feet. This estimate is fairly acceptable in the vicinity of the Combination mine but is subject to correction farther south, where' the fault zone is flanked by a wedgeshaped graben, or down-faulted block, limited on the southeast by a 

readily recognized fault that roughly parallels Hanover Creek for 

nearly 3,000 feet and dips steeply to the southwest. From relations 

observed to the east, south, and west, it is apparent that a sill of 

porphyry occurs within this down-faulted block, but because the 

thickness of the sill is not known it is impossible to make a definite 

estimate of the displacement along this fault: it may be as much as 

500 feet. The principal faulting along the Hobo zone is believed to 

have been initiated prior to granodiorite intrusion. This belief is 

based on a study of the complex system of mineralized fractures in 

the southwestern part of the area mapped, which indicates that 

this whole section was subjected to intricate deformation prior to 

the period of metamorphisni and mineralization that followed the 

emplacement of the granodiorite stocks at Hanover and Santa Rita.

Within areas occupied by the Fort Bayard porphyry laccolith it 

is impossible to determine whether there has been displacement along 

any particular fracture, but where the Colorado shale is present it is 

possible to determine that faulting has occurred at least along some 

of the fractures. Such faulting may be demonstrated in many 

localities between Gold Gulch and the southwest corner of the area 

mapped, where the belt of Colorado shale is intricately broken and 

where most of the fractures show the effects of strong mineralization. 

Along most of these faults the downthrown block is on the southeast. 

Most of the prominent breaks trend about N. 40° E., but a few have 

more easterly courses.

A marked zone of fracturing occurs along or near the southeast 

edge of the shale belt from the south edge of the area to Gold Gulch 

and beyond. Here the displacement is also downward on the southeast side, but, because the thickness of the porphyry sill is not known 

and because its position in the Colorado shale has not been determined, the amount of displacement cannot be estimated with confidence. The post-lava fault that enters the area where the Atchison, 

Topeka & Santa Fe Railway track crosses the southern boundary is 

indicated by the local displacement of the quartz diorite porphyry 

and the basal gravel of Tertiary age. Although it is obvious that 

this break must continue toward the north, its position has not been 

located. In fact, it is possible that such movement may have occurred 

along old faults far to the north and even along the Hobo fault zone.
54 SANTA .RITA MINING AREA, NEW MEXICO

The Copper Glance fault is named after the Copper Glance 

mining claim, which lies north of Highway 180, about 1 mile northeast of Hanover Junction. This fault has been traced for a distance of about 3,000 feet. In the vicinity of the Copper Glance 

shaft the course is about S. 70° "W. It follows about this course to 

a point 500 feet toward the southwest, where it assumes a nearly 

east-west course. Toward the east it can be traced for about 1,600 

feet, to a point where it meets a well-marked and strongly mineralized fracture that can be traced south-westward nearly to Hanover 

Creek, a distance of perhaps 1,800 feet. These two fractures mark 

the edge of a block that is downthrown south of the Copper Glance 

fault. In the vicinity of the Copper Glance shaft black shale that 

belongs near the base of the Colorado shale and lies under the Fort 

Bayard laccolith occurs on the north side of the break. Toward 

the west a body of shale which lies above the laccolith occurs on the 

downthrown side. This relation indicates that the displacement 

could be measured if the thickness of the laccolith were known. 

Evidence in regard to the age of the fault is seen first in the fact 

that it is strongly mineralized and second in the fact that it is 

crossed by several dikes of granodiorite porphyry that are regarded 

as contemporaneous with the premineral dikes in the Ivanhoe, 

Groundhog, and San Jose mines. To the east of the Copper Glance 

shaft the fault can be traced to a point north of the Ivanhoe no. 1 

shaft, where Beartooth quartzite appears on the north side and the 

porphyry of the laccolith on the south side. Beyond this point the 

break follows a dike of granodiorite about 150 feet wide, with exposures of metamorphosed Syrena limestone on the northwest side 

and of Colorado shale on the southeast side. The dike can be traced 

to the southwest across the Clara Barton and Ivanhoe claims, the

point of divergence being about 1,200 feet southwest of the Ninety 

shaft. The single dike that continues toward the northeast is about 

100 feet wide where exposed along the highway near the Ninety 

shaft. From this place it can be traced for a distance of about 300 

feet, beyond which it is not exposed. In a small ravine just north 

of the common corner of the Ninety and Star mining claims Syrena 

beds are exposed on the northwest side of the dike and sandstone of 

the Colorado shale on the southeast side. Northeast of this point 

the actual position of the fault cannot be determined for a distance 

of 2,400 feet, but Colorado beds are exposed along the west side of 

the valley and Syrena beds on the hill slope toward the northwest, 

and the existence of an important fault trending about N. 25° E. 

is obvious. (See pi. 2, section E-E' .) Observations on the Door Key 

claim suggest shearing along the north side of the dike and indicate 

the possibility of late faulting along this line that may be connected
STRUCTURE 55

with a northern extension of the Groundhog fault. The apparent 

'displacement is about 400 feet.

The Romero fault, named after the Romero mining claim, occurs 

northeast of the granodiorite stock at Santa Rita. This break is 

to be seen on the east wall of the open pit, where metamorphosed 

Abo limestone, Beartooth quartzite, and Colorado shale are exposed

 on one side and beds that belong to one of the Pennsylvanian formations on the other side. From the mine pit for a distance of about

 600 feet 'the course of the fault is about N. 20° E. Farther northeast the course is about N. 53° E. The dip in the neighborhood of 

the open pit is about 45° ESE. As may be seen from the geologic 

map the formations in the downthrown block have been considerably 

warped, and as a result it is obvious that the amount of displacement at different points would show a considerable range, but because 

it has been impossible to recognize definite horizons in the northwest 

upthrown block the amount of displacement cannot be estimated. 

On the south side of the north pit and on the south side of the south 

pit post-ore shear zones have been noted in the projected trace of 

this fault and may represent its continuation to the south. The 

weight of evidence thus favors movement of postgranodiorite age on 

this fracture, though the data are not decisive. Inasmuch as the 

.shear observed on the south wall of the north pit involves a late, 

(post-lava) dike, post-lava movement on this break is also suggested, 

but in view of the fact that outcrops are obscured by slide and mine 

waste a decision on this point is reserved.

The Joy fault, named after the Joy mining claim, follows the same 

general course as the upper valley of Santa Rita Creek and has been 

traced from the edge of the area mapped toward the southwest for 

3,000 feet. Northeast from the point of intersection with the Romero 

fault its general course is about N. 29° E., and south of this intersection it trends about S. 10° W. for 1,500 feet or so and then makes 

.a sharp change to about S. 30° W. In the neighborhood of 

the Seven Hundred well the dip is about 70° NW. and the estimated

 displacement is 360 to 400 feet. (See pi. 2, cross section B-B' .) 

The full extent of the fault toward the south is not known, but the 

.amount of displacement obviously decreases in that direction, because 

there is no evidence of any corresponding break across the Beartooth quartzite along the east side of the mine pits. Movement along 

this fault probably occurred before the period of metamorphism 

that followed the injection of the granodiorite stock at Santa Rita, 

but clear evidence to prove this suggestion has not been obtained. 

Northeast of the junction with the Romero fault the rocks on both 

sides of the Joy. fault are comparatively free from the effects of 

metamorphism, but south of this junction an increasing amount of
56 SANTA EITA MINING AREA, NEW MEXICO

rock alteration is observed toward the south, which suggests that the 

fracture may have offered a free course for the circulation of solutions during the period of ore deposition that followed the granodiorite injection.

A notable fault trending N. 80° E. lies just outside of the Santa 

Rita area, east of the southern mine pits at Santa Rita. This fault, 

which is normal and dips to the south, can be traced southwestward 

from the east edge of the Silver City quadrangle to a point about 

1,000 feet distant from the east edge of the Santa Rita area. From 

this point westward the prevalence of highly silicified and oxidized 

Cretaceous shale and porphyry obscures the surface relations, but 

on the east edge of the south mine pit three small normal faults 

(not mapped), downthrown to the south, can be seen to offset the 

base of the Cretaceous rocks. In view of the fact that in tracing the 

fault southwestward a splitting into three parts was noted, there is 

strong presumptive evidence that this fault breaks the granodiorite 

porphyry. Whether there has been post-lava movement along these 

fractures is undetermined.

The formations within the anticlinal fold that adjoins the Hanover stock on the south are broken by several faults, most of which 

have courses that do not depart 10° from north. (See pi. 2, cross 

section D-D''.) Some of these breaks are older than the ore deposits 

of this area, and others are younger. So far as noted, all the faults 

of this system dip steeply toward the west. Only one of these faults 

exhibits a displacement as much as 200 feet. Some of the faults of 

the system have offset the boundary between the granodiorite stock 

and the invaded sediments.

The rocks around the Santa Rita and Hanover stocks, as well as 

parts of these intrusives themselves, are notably altered in appearance and composition. After the solidification of the stocks marked 

fracturing occurred within them and around their borders, and 

heated mineral-bearing aqueous solutions, taking advantage of the 

paths thus afforded, arose from the lower portions of the cooling 

magma and circulated freely through the fractured rocks. In general, fracturing appears to have been a necessary forerunner of pronounced metamorphism, particularly in the igneous rocks, for where 

there are no fractures the invading rocks are not greatly altered, but 

where fractures are present there is notable rock alteration. The 

intrusion of quartz diorite porphyry represented by the Fort Bayard 

laccolith and related sills appears, on the other hand, not to have 

been accompanied or closely followed by any noteworthy amount of 

metamorphism.
METAMORPHISM 57

Metamorphic aureoles that surround the Santa Rita and Hanover stocks overlap and form an irregular zone of altered rocks 

a mile or more in width that extends from north to south nearly 

across the area mapped. A separate and smaller aureole surrounds 

the intrusive granodiorite at Copper Flat, and in the southwestern 

part of the area the results of rock alteration, though not general, 

are conspicuous along numerous northeastward-trending fractures. 

Within large masses of igneous rock, such as the Fort Bayard 

laccolith, channels of circulation were furnished by countless fractures, but where sedimentary formations have been altered it appears that differences in the composition of strata, together with 

the attitude of the beds and the position of fractures, dikes, or sills, 

played an equally important part in directing the course of the 

solutions.

With respect to the Santa Rita area as a whole metamorphism appears partly to reflect original differences in the composition and 

temperature of the active solutions from time to time and from place 

to place. The varied effects of metamorphism are seen in the recrystallization of limestones, the development of silicate minerals 

in limestone and shale, the conversion of limestone into ores of iron 

and zinc, the sericitization and silicification of shale and sandstone, 

and generally in the widespread serieitization of both quartz diorite 

and granodiorite.

Two distinct types of alteration have affected the sills and laccoliths of quartz diorite porphyry. Everywhere this rock shows the 

effects of a slight alteration by the presence of epidote and calcite 

replacing original hornblende, but in the southern part of the area, 

especially in the vicinity of Santa Rita, this alteration was masked 

by a later and far more intense alteration characterized by abundan,t 

sericite, and this sericite alteration likewise affected to a large degree the later granodiorite intrusions at Santa Rita and Hanover.

All the sedimentary formations of the Santa Rita area appear in 

contact with the Hanover-Fierro stock, at one place or another, although only the lowermost beds of the Colorado shale are involved. 

Within a border zone 800 to 2,000 feet wide that surrounds the 

stock the invaded formations exhibit the effects of hydrothermal 

metamorphism in greater or less degree, and in several outlying 

localities, some of which are more than 4,000 feet from the contact, 

marked alteration is also to be observed. In general, however, the 

most striking effects are close to the contact. Here a large amount 

of magnetite ore represents replacement of the Bliss sandstone and 

the El Paso and Montoya limestones. In these formations replacement appears to have been accompanied by plastic deformation, as 

the normal thickness of the formations has been in places greatly
58 SANTA KITA MINING AREA, NEW MEXICO

reduced. The magnetite ore bodies are tabular masses that generally conform' with the stratification of the rocks and alternate with 

layers of limestone within which serpentine and wollastonita havor 

formed abundantly and garnet and epidote to a minor degree.

In most places the iron ore replaced only part of the El Paso and! 

Montoya limestones, but along Union Hill, where the thickness o-± 

the group is very much reduced, the replacement extended up to and! 

included the topmost member. The limestone between the ore zoneand the base of the Percha shale has been changed to marble without the development of noteworthy amounts of silicate minerals.. 

Calcareous beds in the lower part of the Percha formation haverather generally been changed to a porcelainlike material, and locally 

similar alteration products occur in the upper part of the formation ; 

in places large amounts of epidote have been developed in these limy 

shales. ;

The hydrothermal alteration of the Oswaldo, Syrena, and Aboformations had no very definite relation to the proximity of the 

granodiorite masses. The metamorphosing solutions were guided in 

part by cross-breaking fractures, but to a large extent they followed 

strata underlying beds of impervious shale or sills of intrusive* 

porphyry.

The most thorough-going metamorphism of the Oswaldo formation 

is to be observed around the borders of the Hanover lobe of the 

Hanover-Fiierro stock. Here the shale at the base of the formation 

has very generally been converted into epidote rock and the limestone 

beds have been extensively silicified or converted into magnetite ore. 

All the altered materials carry sulphide minerals in more or less 

abundance.

The same sort of alteration continued toward the south as far as 

the Santa Rita stock and affected both the Oswaldo and Syrena 

formations. Immediately north of the Santa Rita stock, where the 

rocks dip gently toward the south, layers of limestone that belong 

in the upper part of the Oswaldo formation have been extensively 

replaced by magnetite. Near the Ironhead mine, where the Oswaldo 

formation appears on the south side of the Barringer fault, the rocks 

have been altered in the same manner as in the vicinity of Hanover, 

the basal shales being converted into epidote rock and the limestones 

being silicified and charged with magnetite and sulphide minerals.

Northeast of Fierro, in sec. 3, T. 16 S., R. 12 W., marbleization of 

limestone beds in the Oswaldo formation has occurred at several 

places. Alteration of the rocks to silicates is unusual, but limestone 

beds have been replaced by magnetite in the vicinity of strong northeast-southwest fractures; and in the SE1/^ sec. 3 considerable bodies
METAMORPHISM Otf

of magnetite have been formed by replacement of limestone beds 

in the lower part of the Oswaldo formation.

The rocks exposed in the immediate vicinity of the granodiorite 

of Copper Flat belong in the upper part of the Oswaldo formation. 

The metamorphic aureole surrounding the intrusive mass is from 

100 to 700 feet wide but not definitely limited on its outer borders. 

There is an inner zone of garnet rock charged with magnetite arid 

sulphides and an outer zone of marbleized limestone.

East of Santa Rita the black shales that occur as the basal member of the Colorado formation have been converted to a dense hornstone, but in the vicinity of the pits these beds have instead been 

greaty sericitized and charged with pyrite. The same sort of alteration has been imposed on the sandstone beds that lie stratigraphically 

above the black shale and on the Beartooth quartzite that lies 'below 

this shale, and it is also noted west of the Santa Rita mine pits on 

Lee Hill.

Within a zone about 800 feet wide and 3,000 feet long, extending 

in a northwesterly direction from the Treasure Vault shaft, there 

are areas where the Colorado formation and the quartz diorite 

porphyry are characterized by the presence of alunite, which represents a hydrothermal alteration probably superimposed upon an 

earlier sericite-pyrite alteration, evidently in Tertiary time, inasmuch as the latite porphyry stock at Bull Hill is affected by similar 

alteration.

The calcareous argillite of the Abo redbeds, overlain by the relatively impervious Beartooth quartzite, was particularly susceptible 

to alteration, as may be observed at Humboldt Mountain and on 

the high ridge north of Santa Rita. As a rule this formation is 

altered to dense hornstone, but in the ore pits at Santa Rita it has 

been converted to a mixture of pyrite, magnetite, and chlorite.

Hedenbergite and ilvaite, of somewhat sporadic occurrence, are 

usually found with zinc sulphide, characteristically in places somewhat more distant from the intrusive masses than garnet and epidote. 

Fine examples of "replacement by hedenbergite may be seen in Buckhorn Gulch west of the Hanover mass of granodiorite (pi. 6, B).

While the sedimentary rocks were being replaced by oxides, sulphides, and silicates, the igneous rocks underwent somewhat different changes in response to the action of solutions that \vere 

presumably very similar in chemical make-up. In the igneous rocks, 

sericitization, with the deposition of abundant quartz (in places 

astonishing amounts) and iron and copper sulphide, was the dominant process.

It is apparent that hydrothermal alteration operated during a 

considerable: period of time, beginning in the .early stages of the
60 SANTA RITA MINING AREA, NEW MEXICO

emplacement of the stocks and certainly proceeding on a grand scale 

after fracturing had occurred and even after granodiorite dikes 

had invaded the stocks and the surrounding sediments. The facts 

that in places apophyses of essentially unaltered granodiorite cut 

massive replacement bodies of magnetite and that these apophyses 

are in turn cut by aplite dikes (the earliest manifestations of dike 

intrusion that followed the solidification of the magmas) strongly 

suggest that replacement of limestone by magnetite occurred at a 

very early stage. The alteration of later granodiorite dikes, shown 

by the almost universal occurrence of epidote and sericite and the 

local occurrence of pyrite, proves that the processes of alteration 

were long drawn out. The fact that in places, notably in the 

Groundhog mine, sulphide ore bodies cut cleanly across these 

granodiorite dikes supports this view.

GEOLOGIC HISTORY

The Santa Rita area is so small (about 35 square miles) that many 

facts throwing light on its geologic history and geomorphology must 

be sought in the larger area that surrounds it. The quotations that 

follow, from the Silver City folio, are directly applicable to the 

Santa Rita area and will lead naturally to a discussion of its 

geomorphoJ ogy.

The long period that preceded Cambrian deposition doubtless comprised many 

intervals of sedimentation, erosion, ancl disturbance, representing in all a 

longer time than that represented by all succeeding geologic history. Only 

the merest fragments of this history can be read in this area. The preCambrian rocks are largely granites, in which are enmeshed the almost indistinguishable traces of a sedimentary record. A few small areas of quartzite and 

schist point to the existence of ancient seas. The metamorphosed and fragmentary character of these ancient sedimentary rocks snows that their history 

has been varied.

There is abundant reason to believe that old mountain ranges existed in this 

region and that forces of erosion in the past even as today carried on their 

work of denudation. The character of the surface upon which the earliest 

Cambrian strata [Upper Cambrian Bliss sandstone] rest in this area serves to 

verify what has been observed at many other localities namely, that a period 

of prolonged erosion and baseleveling preceded the subsidence of the preCambrian land beneath the sea, forming a floor of moderate relief on which 

the Cambrian sands were deposited.

 The nature of the basal Cambrian strata, which are composed of quartzose, 

limy, and glauconitic material, shows that at the time of their deposition the sea 

was gradually transgressing upon a land surface of moderate relief. It is 

probable that as the sea advanced, wave action reduced still further the Cambrian sediments, and the pre-Cambrian basement is in part a result of this 

action.

The subsidence whose beginning is marked by these Cambrian beds endured 

for a long period. As the seas gradually grew deeper or as the shore line 

slowly transgressed landward, limy sediments gradually became more prevalent,
GEOLOGIC HISTORY 61

and finally they formed the only record of deposition. Though these seas 

were not deep they were probably extensive. Whether the interval of time 

indicated by differences in the fauna of the Bliss sandstone and that of the 

El Paso limestone includes a period when Cambrian beds were raised above 

sea level and subjected to erosion cannot yet be determined. Apparently there 

was a rather abrupt transition from the sandy limestone layers of the older 

formation to the more limy beds of the younger formation, but if there is 

an unconformity it has not been detected. The incursion of sandy layers in 

the upper part of the El Paso limestone marks the unsettling of a delicate 

balance of depth rather than any great uplift. The quartz sands found in this 

 part of the Cambrian system may have been carried there by currents that 

swept across wide areas of shallow seas or may have been blown from neighboring beaches by violent winds, for limestone deposits may be formed close to 

the seashore provided great quantities of debris are not being contributed 

to the sea.

The record of Silurian time, with its fossiliferous and chert-bearing beds, 

shows that the conditions then were similar to those of the preceding period.

The abrupt change, however, from Silurian limestone to Devonian shale 

suggests a fundamental difference in conditions of sedimentation. Though the 

bedding of the Silurian limestone and the Devonian shale seems to be concordant, there is reason to believe that the beginning of Devonian deposition 

was preceded by marked erosion in this southwestern area. At Bisbee, for 

example, as stated by Ransome,a Devonian beds rest upon Cambrian limestone; 

at Clifton, as shown by Lindgren, Devonian overlie Ordovician beds; and in the 

Silver City region Devonian rest upon Silurian beds. These facts and the 

sudden change in sedimentation marked by the deposition of Devonian shale 

on Silurian limestone point to decided irregularities in the Paleozoic sequence 

in this southwestern province, probably indicating a period of uplift and 

erosion.

The gradual change from shale to limestone observed at the top of the 

Percha shale indicates an uninterrupted period of deposition between Devonian 

and Carboniferous time and a decided clearing of the seas. The faunal changes 

are likewise noteworthy. The muddy waters in which the top of the Percha 

shale was laid down seemed especially adapted to Devonian forms, but when 

the waters became clearer they were no longer a suitable habitat for the 

Devonian fauna which, therefore, disappeared and Carboniferous forms became 

prevalent.

The oldest Carboniferous fossils are found in the Mississippian 

. Lake Valley limestone and no indication of interruption by sedimentation is disclosed until the base of the Pennsylvanian beds is 

reached. Here the Oswaldo formation is introduced by 20 to 30 feet 

of shale, beneath which in many places is to be found a bed of 

white or pink chert from a few inches to 8 feet in thickness. These 

features are the only indications of a physical break in sedimentation, 

for throughout the Silver City region the beds above and below the 

break appear to lie in parallel position. These relations indicate 

that although emergence of the sea bottom may have taken place, 

no substantial warping occurred at this time in this region.

M Ransome, F. L., U. S. Geol. Survey Geol. Atlas, Bisbee folio (no. 112), p. 12, 1904. 

92311 35 5
62 SANTA RITA MINING ABE A, NEW MEXICO

A somewhat similar stratigraphic relation is found where the 

Permian Abo redbeds rest on the Pennsylvanian Syrena formation; 

here no notable disconformity was observed.

The point has now been reached where, instead of picturing quiet Paleozoic 

seas, the imagination must depict the gradual emergence of a Mesozoic continent. No evidence is at hand to prove that the uplift was accompanied by 

notable structural disturbance. No certain pre-Cretaceous faults are recognized, nor has any folding been observed which might not be assigned to later 

periods. It must be assumed, therefore, that though the emergence was widespread, it took place in this area without other deformation than that of gentle 

warping and tilting. That the tilting was appreciable is shown by certain 

relations between the basal Cretaceous beds and the underlying Paleozoic rock. 

For example, the Beartooth quartzite shows a remarkably clean-cut flat surface 

at its base, suggesting a decided leveling of the underlying floor, its contact 

on the summit of the Little Burro Mountains being a notably flat surface. 

Now, as the basal Cretaceous beds were deposited on [Permian], Pennsylvanian, Mississippian, Devonian, Silurian, and pre-Cambrian rocks, one may 

infer that these old rocks were tilted during their uplift and eroded nearly 

to baselevel across their dipping beds.

The absence of Triassic or Jurassic.strata beneath the Cretaceous sediments 

points either to the existence of a continent during those periods or to an 

even more prolonged period of denudation than has just been inferred.

The accumulation of Cretaceous sandstone, shale, and limy shale to a 

thickness of probably several thousand feet followed the subsidence of this 

eroded land surface. The quiet sedimentation, however, may have been interrupted by subaqueous outbursts of andesitic and allied volcanic rocks. The 

breccias of the andesite-diorite complex have here and there the appearance of 

sills, being both underlain and overlain by shale; but as the pyroclastic nature 

of the breccia precludes'an intrusive origin, it is suggested that near the close 

of Cretaceous sedimentation,' or after its close, volcanoes added their quota 

of material to the marine Cretaceous accumulations. The apparent sill-like 

relation observed may, however, be due to faulting.

There is abundant evidence of intense activity from this time on. Thousands of dikes cut both the Cretaceous shale and the breccias, indicating that 

the outbursts that furnished the pyroclastic accumulations were followed by 

 continued long-extended fracturing of the strata and concomitant filling with 

igneous material. The great preponderance of this complex in the Cretaceous 

rocks suggests that a center of volcanic activity existed somewhere near or^ 

north of Pinos Altos, though there may have been subsidiary centers near the 

Little Burro Mountains.

The history of the region now enters upon a period notably different from 

the preceding long record of sedimentation. There is no evidence that the 

land was ever again beneath the sea, but there is conclusive evidence that 

no less than five stages of intrusion succeeded the one already described, and 

further that they were associated with notable structural dislocations.

The first of these intrusions is represented by quartz diorite 

porphyry, which now appears in the form of numerous sills in the 

Percha, Oswaldo, and Syrena formations and as sills or laccolithic 

masses and stocks in the Colorado formation.. The position of the 

feeders for the sills and laccoliths is not known, but it seems possible
GEOLOGIC HISTORY 63

that the Hermosa Mountain stock and the thick mass south of Santa 

Rita may represent such feeders. Considerable warping of the 

strata must have occurred above the Fort Bayard laccolith and above 

the Hermosa Mountain stock, with gentler warping in the beds overlying the thinner sills, and it is clear that these invasions were accompanied by more or less disruption of the invaded strata.

It is known that some time intervened between the invasions just 

described and the emplacement of the granodiorite masses at Hanover, Santa Rita, and Copper Flat, for these masses invade the 

quartz diorite porphyry.

The broad anticlinal upwarp, here named the Fort Bayard arch, 

on which there are numerous minor folds, was developed during this 

interval, evidently by compressional forces, and was essentially completed before the invasion of the granodiorite masses. This invasion 

was accompanied by folding transverse to the axis of the arch and 

was followed by fracturing on a great scale, faulting, the invasion of 

granodiorite dikes, and widespread hydrothermal metamorphism and 

the deposition of ores of iron, zinc, lead, and copper.

The principal movements along the Barringer fault and the prelava faults of the southern part of the area probably occurred at this 

time.

A prolonged period of erosion ensued. The cover was stripped 

from the granodiorite masses, an irregular topography was developed, and pre-lava enrichment of the zinc ores at Hanover and the 

copper ores at Santa Rita undoubtedly occurred.

At some time in the Tertiary widespread volcanism began, with 

violent explosions that spread coarse and fine volcanic debris over 

the uneven land surface. This material was redistributed by torrential rains to a considerable degree and eventually formed the gravel 

and finer sediments that are now exposed along the southern edge 

of the Santa Rita area and elsewhere. These sediments were covered 

by great sheets of rhyolitic or latitic lava that covered hills and valleys, obliterating the older landscape. After these eruptions there 

were floods of andesitic or basaltic lava, followed by rhyolitic lava. 

Local deposits of fine sand and tuff accumulated between these 

outbursts.

This volcanic period, was followed by faulting, which apparently 

-compensated for the vast transfer of lava from its underground reservoir to the surface and has been intermittently active ever since. 

During its earlier stages it was attended by the intrusion of stocklike masses and dikes of latitic rocks that cut the Tertiary lavas and 

.all the older rocks, but none of these intrusive rocks have been found 

to cut the lavas within the Santa Rita area. After completion of the 

principal movements along these faults, the lavas and the tuff and
64 SANTA EITA MINING AREA, NEW MEXICO

gravel beneath them were eroded from the Fort Bayard arch, with 

the exception of the sand and gravel in the topographic basin south 

of Hanover, which were preserved by local downf aulting.

ORE DEPOSITS

The ore deposits of the Santa Rita area were formed during a 

period of mineralization that may have in part accompanied the 

early stages in the emplacement of the granodiorite stocks but in 

the main was later than the granodiorite. These masses and the 

invaded rocks around them, in consequence of forces that may reasonably be.assigned to final upward movements of the cooling solid 

intrusives, were in many places intensely fractured. To the widespread hydrothermal alteration that immediately followed and that 

may be regarded as an end effect of the intrusions the ore deposits 

are in large measure due. Dikes of granodiorite porphyry invaded 

the stocks and the surrounding rocks about this time, but it is clear 

that mineralization both preceded and continued after the emplacement of these dikes. Thus fracturing, hydrothermal metamorphism, 

the intrusion of the dikes, and the deposition of the ores may all be 

regarded as episodes of an extended period of magmatic invasion.

All the ores were precipitated from heated aqueous solutions. 

Their mineralogic make-up, the place in which they were deposited, 

and the form that they assumed depended on the concentration, 

temperature, and pressure of the solutions and on the character of 

the rocks that were available to receive them. Inasmuch as a great 

variety of rocks, calcareous, argillaceous, and igneous, variously disposed, adjoin the stocks, and inasmuch as fracturing in places 

occurred at long distances from the intrusives, there resulted a 

variety of ore deposits contact deposits, disseminated porphyry 

ores, and veins.

Sedimentary rocks, chiefly calcareous or magnesian, surround the 

Hanover-Fierro stock. During and after the intrusion high temperatures prevailed along the contacts, and solutions circulated 

freely. There formed in consequence around the intrusive mass a 

rude shell, varying in mineral make-up from place to place, made 

up of iron oxides, sulphides, and lime-magnesium-iron silicates.

CONTACT-METAMORPHIC DEPOSITS 

IRON ORES

Historical sketch. According to Kniffen,32

The mine of the Hanover-Bessemer Iron & Copper Co. at Fierra * * * 

is the only operating iron mine in the southwestern part of the United States

' M Kniffen, L. M., Mining and engineering methods and costs of the Hanover-Bessemer 

Iron & Copper Co., Fierro, N. Mex.: U. S. Bur. Mines Information Cir. 6361, 1930.
ORE DEPOSITS 65

[1930]. * * * Nearly all the iron ore is shipped to Pueblo, Colo., a distance 

of 694 miles, where it is smelted by the Colorado Fuel £ Iron Co. The mine 

is not a large producer. * * * In recent years the annual shipments have 

amounted to about 200,000 tons. The property is noteworthy chiefly on account of this long transportation by rail and the economical methods that have 

been developed to make the operation profitable. * * * The large outcrops of magnetite attracted attention for many years, but the lack of transportation made them of no economic value. Soon after the railroad was 

brought to Silver City some "float" was shipped to Pueblo that had been 

hauled from Fierro by ox teams, on the return trip, after bringing supplies to 

Fort Bayard. The Hanover-Bessemer Iron Ore Association was organized 

in 1899, at which time the railroad was built to Fierro. * * * In 1914 the 

Hanover-Bessemer Iron & Copper Co. was incorporated, and a contract was 

made for the sale of the iron ore. A fine-grinding wet-concentration mill was 

.built in 1916. A controlling interest was acquired by the United States Smelting & Refining & Mining Co. in 1919.

Geology. On both sides of the Hanover-Fierro stock, in places 

where the contact of the igneous mass is parallel with the invaded 

strata, are commercially important deposits of magnetite which obviously have been formed by replacement. On the east side of the 

intrusive mass this condition persists throughout a distance of 6,000 

feet; on the west side for about 5,000 feet. On both sides the formations stand at high angles, and from place to place there is strong 

evidence of pilastic deformation of the limestones, as a result of which 

the El Paso limestone has suffered a reduction in thickness. The 

magnetite ores of high grade occur in the lower part of this formation, and in general it may be said that replacement ceased at a 

definite horizon, which is everywhere recognized because of the presence of serpentine. It is believed that the serpentine developed as 

a result of the metamorphism, and that the zone in which it occurs 

represents a chert horizon of the Silver City region. The Bliss 

sandstone also makes ore, but of a distinctly lower grade. Although 

the ore bodies follow the stratification in the main, there are a few 

places where veins in either border extended out into the limestone 

above the serpentine horizon.

It is a noteworthy fact that the magnetite deposits occurring in 

the lower Paleozoic section have replaced magnesian formations 

and that the principal silicates are wollastonite and serpentine, with 

minor amounts of garnet and epidote. On the east side of the intrusive mass the magnetite ores have followed the contact between 

the Bliss sandstone and the El Paso limestone, replacing both formations. The thickness of the ore averages about 40 feet but in places 

may be as great as 200 feet. Here and there alternate beds of 

unreplaced limestone occur; in general the ore exhibits a rude lenticularity. The Bliss sandstone merges upward by gradual increase in calcareous .layers with the El Paso limestone, and no 

clear-cut boundary between the ores of the two formations is to
66 SANTA KITA MINING AREA, NEW MEXICO

be expected. On the west side of the intrusive mass the El Paso 

limestone is thin, either because of strike faults or because of 

plastic flowage. The ore zone occupies the full thickness of such 

of the Bliss sandstone as remains along the igneous contact and all 

of the El Paso formation up to and partly including the ,low-grade 

serpentinized chert layer. In a few places, notably on the west side 

of the granodiorite mass at the north end or the company's property, veinlike bodies of magnetite cut across the serpentine zone into 

the Montoya limestone, which lies stratigraphically above the El 

Paso limestone. Minable ore bodies have replaced the Fusselman 

and Montoya limestones just beneath the Percha shale.

Pyrite, chalcopyrite, and 6halmersite are noteworthy constituents 

of the magnetite ores and are clearly of somewhat later date, as 

proved by their prevailing veinlike distribution through the 

massive magnetite. Sphalerite likewise occurs sporadically in the 

magnetite.

The average partial analysis of the concentrates shipped is as 

follows:

CaO______________ 1.41 

MgO ________________ 13. 38 

Cu _______________ . 37 

S __________________ . 38

Fe ________________ 51.00 

P _________________ . 058 

Si02 _________________ 7. 28 

Mn_________________ . 72 

AU03 _______.1________ 1. 42

Ores of magnetite occur also at the south end of the intrusive mass, 

near Hanover, where they have replaced nonmagnesian limestone 

of Pennsylvanian age. Here ore has been mined in past years for 

a thickness of 50 feet and over a distance of 3,000 feet along the 

contact. Exposures are not good except on the Cupola claim, directly 

south of Hanover station.

North of Santa Rita there is a considerable area where nonmagnesian limestones of the upper part of the Oswaldo formation have 

been converted into magnetite. In this locality the ore is not confined to the contact of the granodiorite but over a considerable 

area has replaced a certain layer of the Oswaldo formation. In the 

early days the ores were shipped for flux, and in 1931 20,000 tons 

was shipped to Pueblo, Colo.

ZINC ORBS

The mines of the New Jersey Zinc Co. at Hanover, which have 

been worked more or less continuously since 1902, are credited with 

an output of 500,000 tons of sphalerite ore, having an average content of 15 percent zinc, and in addition considerable amounts of highgrade carbonate ore, most of which was produced prior to 1918. 

The ores were particularly desirable because they were essentially
OKE DEPOSITS 67

free of lead. An average analysis representing several thousand tons 

of mill heads is as follows:

MgO _____________ 1.81 

C02 ________________ 3. 37 

S ______________ 10.19

Insoluble ____________ 49. 77

Zn_____________.___ 17. 49 

Pb _________________ . 13. 

Fe _________________ 6.19 

Mn __________________ . 94 

CaO________________ 8. 09

The ore was milled at Hanover; the first mill was a' magnetic 

concentrator, the later mill of the flotation type. The mines are 

south and west of the Hanover-Fierro intrusive mass, all within a 

zone of intense alteration, 800 to 1,500 feet wide, that adjoins the 

intrusive.

The typical ore bodies occur in the upper part of the Lake Valley 

limestone and are essentially confined to a massive limestone member about 120 feet thick, locally known as the "white crinoidal 

limestone." This member appears at the surface on the crest of a 

curving anticline which closely parallels the southern lobelike end 

of the intrusive mass on its west and south sides but which because 

of faulting is not continuous.

The ore bodies are typical replacement deposits in limestone 

either upright tabular masses controlled by steeply inclined fractures, some of which are paralleled by granodiorite dikes, or rude 

blanketlike deposits developed especially within the upper part of 

the crinoidal limestone beneath a bed of highly metamorphosed shale, 

which constitutes the basal member of the Pennsylvanian Oswaldo 

formation. The blanketlike deposits on the west side of the intrusive 

mass reach a thickness of 120 feet and are of considerable extent. 

Most of the upright tabular ore bodies are found on the west side 

of the dikes which they accompany. The largest of these bodies 

was 120 feet high, more than 1,000 feet long, and 30 feet in maximum 

width.

The sphalerite in general is found in the outer part of the metamorphic aureole, associated with hedenbergite, ilvaite, and manganese-bearing calcite. Magnetite, on the other hand, is found next 

to the contact of the granodiorite, and in between the magnetite 

and the zinc ores are masses of garnet and epidote carrying disseminated sphalerite. The zinc ores contain greater proportions of lead 

as distance increases from the intrusive mass. Some of the ore 

bodies are jacketed by unusual amounts of galena. Fractures with 

northeast and north trends that traverse this terrane certainly acted 

in places as channels for ore-bearing solutions, but there are reasons 

for believing that replacement of the limestone proceeded quite as 

readily by the passage of aqueous heated solutions with considerable 

freedom through large masses of marbleized limestone, for ,it was
68

observed that the replacement of the limestone either by hedenbergite, garnet, or sphalerite proceeded in very much the same way. 

Places may be observed where solid hedenbergite or garnet has completely replaced limestone along sinuous lines of knifelike sharpness, 

on one side of which appears solid silicate, and on the other pure 

marbleized limestone. In places mixtures of garnet and hedenbergite, one or the other, or both, with sphalerite are too low in grade 

to constitute zinc ore. Between these ore bodies and the granodiorite contact garnetized limestone usually prevails, and the boundary 

of the ore is indefinite against the garnetized rock. In general, 

though not everywhere, the ore grades through lean material to wall 

rock.

The position of the zinc ore bodies south and southwest of the 

granodiorite stock appears to have been controlled by preexisting 

faults or dikes. Here, in striking contrast to the blanket ores that 

lie west of the granodiorite contact and are continuous for long 

distances along the strike of the crinoidal limestone, the ore bodies 

are alined along faults and dikes. Their longer axes are invariably 

normal to the granodiorite contact and roughly parallel either faults 

or dikes. Here, as on the west side of the intrusive, the crinoidal 

limestone is the host rock, and here also the overlying shale has 

acted as a barrier to the upward movement of solutions, for the 

ore terminates abruptly against it and fades away laterally beneath 

it as distance increases from the controlling steeply inclined fissure 

or dike.

Of six ore bodies associated with such faults and dikes onty two 

are reported as carrying minor amounts of ore on the east side of 

the dike.33 Accumulation appears to have been directed along the 

west side of the dikes. Such a structural relation is strong presumptive evidence that the granodiorite dikes were earlier than the ore, 

but of itself it cannot be offered as conclusive evidence.

That pre-ore fractures or dikes directed the movement of solutions is hardly open to question, but it is possible that pre-ore faults 

alone effected the results observed, that the dikes were intruded somewhat later along or near the existing fractures, and that post-ore 

movement has still later occurred along the ancient openings; for 

there is ample evidence of post-ore faulting, both on the surface and 

in the mines.

Inasmuch as sphalerite ore is not found in the dikes, though these 

dikes are epidotized and sericitized, the senior writer is inclined to 

the view that the dikes invaded the ore and are thus later, and that 

the occurrence of ore principally on the west side of the dikes is

33 Schmitt, Harrison, oral communication.
ORE DEPOSITS 69

explained by some phenomenon not connected with the dikes but 

with the fractures that are presumed to have controlled ore deposition.

Zinc ores are not confined to the Lake Valley limestone but have 

been mined from deposits in the overlying Oswaldo and Syrena 

formations, of Pennsylvanian age, on the properties of the Peru 

Mining Co., east of Hanover, and of the Blackhawk Mining Co., 

about a mile south of Hanover.

ORES OF DISSEMINATED CHALCOCITE AT SANTA RITA

At Santa Kita a granodiorite porphyry stock invades Paleozoic 

and Mesozoic sediments and a mass of quartz diorite porphyry. The 

southern boundary of the granodiorite where it cuts the quartz 

diorite porphyry is obscure, for widespread hydrothermal metamorphism has destroyed many of the distinguishing characteristics of 

the invading and invaded rocks, both igneous and sedimentary. The 

granodiorite where unaltered is similar petrographically to the larger 

mass at Hanover and also to the smaller masses at Copper Flat, 

though the latter are somewhat finer grained. The thorough alteration of limestone to silicates, shown at the surface between Hanover

-and Santa Kita, suggests that the two granodiorites are connected at 

moderate depth.

The quartz diorite porphyry is regarded as part of the Fort Bayard laccolith. The crosscutting relations that this rock displays 

south of Santa Rita where it breaks across the Abo, Beartooth, and 

Colorado formations suggests that here or somewhat farther to the 

south beneath the lavas may be the position where the magma rose 

through the basement rocks. Churn drilling indicates that the

-quartz diorite porphyry is at least 945 feet thick. If the intense 

alteration to which the rock has been subjected is taken into account, 

.and .also the fact that many large intrusions vary in minor details 

of mineral composition, there is more to support the view that this 

irock is part of the Fort Bayard laccolith than the view that a 

third intrusive mass is present.

The emplacement of the granodiorite occurred in late Cretaceous

-or early Tertiary time. Owing perhaps to waning upward movements of intrusion, the borders of the solidifying mass, as well as 

the adjoining wall rocks, were intensely fractured. There ensued 

a period of thorough hydrothermal metamorphism, with sulphide 

mineralization and dike intrusion. It is noteworthy that where sulphides are abundant there has been intense fracturing, but that 

where fracturing was, relatively slight mineralization occurs to only 

a minor degree. The ringlike disposition of the ore bodies at Santa
70 SANTA EITA MINING AREA, NEW MEXICO

Rita strikingly illustrates this relation, for the core of relatively unfractured granodiorite is relatively unmineralized. (See fig. 1.)

If the map of the ore bodies illustrated in figure 1 is superimposed 

on a geologic map prepared before excavation by steam shovels had 

appreciably progressed, it becomes clear that much ore was formed 

in the sedimentary rocks adjoining the granodiorite mass. This is7000 6000 5000 4000 3000 2000 IOOOW 0 IOOOE 2000 3000

IOOON

IOOOS

2000

3000

4000

5000

60OO

700O

8000

9OOO

EXPLANATION

JvT]

Pit outline Ore body Stripping limit Waste dump

FIGURE 1. Ore body, stripping limits, pits, and waste dumps at Chino mines. After 

Thorne, H. A., Mining practice at Chino mines, Nevada Consolidated Copper Co.,. 

Santa Kita. N. Mex.: U. S. Bur. Mines Information Circ. 6412, fig. 5, 1931.

particularly true with respect to the ore body on the east side of thestock, where Abo limestone, Beartooth quartzite, and Colorado shale 

all carried ore. Abo limestone and quartz diorite porphyry carried, 

ore at the south end, and considerable Colorado shale was excavated 

on the southwest side. The ore bodies along the northwest border 

lie next to the contact. These facts serve to emphasize the conclusion that circulating solutions sought out those places where frac-
ORE DEPOSITS 71

turing was highly'developed namely, at the borders of the intrusion and made ore irrespective of the host rock.

The granodiorite deformed the sedimentary rocks that it invaded. 

At the northeast side the resulting dip is very local, for the regional 

dip of the Syrena and Oswaldo formations is southward, toward the 

stock. The axis of the anticline indicated by these dips trends 

northwest. A short distance to the east a synclinal depression trends 

in the same direction. These folds and comparable folds that have 

been recognized farther to the west are regarded as due in part to 

the intrusion of magma and quite distinct in time and origin from 

the prominent faults that are regarded as of post-granodiorite age 

and as having suffered, probably, some movement in post-lava time 

(Tertiary).

The value of the ore bodies at Santa Eita is due directly and almost 

entirely to enrichment. Primary mineralization by pyrite and chalcopyrite accompanied the silicification and sericitization of the fractured rocks. This process was carried to great lengths. Colorado 

shale was altered to a porcelainlike siliceous rock that can be distinguished from altered porphyry only by painstaking examination 

with a hand lens. Quartz diorite porphyry in its altered facies is 

distinguished with difficulty from altered granodiorite.

The minerals that have given and still give value to the deposits^ 

particularly in the upper zone, are malachite, azurite, chrysocolla, 

cuprite, and native copper, but chalcocite and chalcocite-coated pyrite are the most abundant minerals. These are generally disseminated through the rocks and in small seams and stringers. Quartz, 

sericite, halloysite, and kaolin are common gangue minerals.

It is well established from regional studies that the enrichment 

beginning in pre-lava time was interrupted by floods of Tertiary lava 

and was resumed after the removal of the lavas by erosion in Quaternary time. It was in this connection that post-lava faulting played 

so important a part, producing the horstlike uplift, already described, 

of the area north of Santa Rita. This uplift brought about the erosion of the lavas from above the Hanover and Santa Rita intrusive 

stocks and initiated a second period of enrichment.

The thickness of the overburden (above the ore bodies) is extremely variable. There is none over the northwestern and northeastern portions of the ore bodies and in small areas elsewhere, but 

it reaches a maximum of about 150 feet over the southern portion. 

The contours of the top and bottom of the ore are very irregular. 

In the main part of the ore bodies the thickness of the ore reaches 

600 feet, but along the margins it decreases to 300 feet and less. 

None of the ore bodies have been fully delimited by drilling, either 

vertically or horizontally.
72 SANTA RITA MINING ABEA, NEW MEXICO

VEINS

The fracturing and hydrothermal metamorphism that followed 

the emplacement of the granodiorite stocks was not confined to the 

immediate vicinity of the large masses now exposed at the surface 

(Hanover and Santa Rita). In the southwestern part of the Santa 

Rita area and extending to Central the quartz diorite porphyry and 

associated sediments are traversed by numerous mineralized fractures that trend northeast. As a group they, are characterized by 

wall-rock alteration and by minerals that strongly suggest an origin 

related to the granodiorite intrusions; and the presence of numerous 

granodiorite dikes supports this view. It is not unreasonable to 

suppose that in depth there are larger masses of which the dikes 

may be apophyses.

Although this region has been prospected for many years, only 

a few of the veins have been worked with profit. Of these the most 

productive occur near and east of Hanover Junction. Here a mineralized fracture zone trending northeast has been developed 

throughout a length of about 4,000 feet. The first development 

was near the north end of the zone on the San Jose claim, located 

in 1875, from which copper, lead, and silver were produced, for 

the most part prior to 1895. Work on the Lucky Bill claim, at the 

south end of the zone, began about 1900, when lead carbonate and 

vanadate ores were discovered. The total production of this claim 

amounted to several hundred thousand dollars.

Lasky 34 says :

Due to the fact that the outcrop on the Groundhog claim, which adjoins 

the San Jos6 on the southwest, was mostly covered with rock debris and the

 exposed parts; of the vein were barren quartz, this claim was not located until 

1900.

The net smelter returns of shipments from the Groundhog up to 1917 were 

about $50,000, representing about 2,000 tons, derived from lead-copper ores 

encountered about 100 feet below the surface at the south end of the claim. 

The mine was sold in 1917, and from then until February 1920, when shipments ceased due to temporary closing of the smelters, the property produced

 6,430 tons of lead-copper carbonate and sulphide ore. During this period, 

under the stimulus of high metal prices, the main shaft was sunk to below 

the 300 level and the property equipped for air drilling.

The mine was idle from February 1920 until the fall of 1924, when it was 

taken over by the Hay ward-Richard Leasing Co. This company deepened the 

shaft to the 400 level and explored the vein on that level. Some small ore 

bodies were stoped south of the shaft, and in the spring of 1928, after courageous drifting northward through a long barren zone, the present extensive 

ore shoot was discovered. In June 1928 a controlling interest was sold to 

the Asarco Mining Co., a subsidiary of the American Smelting & Refining Co.

"* Lasky, S. G., Geology and ore deposits of the Groundhog mine, Central district, Grant 

County, N. Mex.: New Mexico Bur. Mines and Mineral Resources Circ. 2, 1930.
OEE DEPOSITS 73

The total production of the mine to November 1, 1930, was approximately 

323,260 tons of ore. Milling and smelting returns are not available, so the 

net value of this production is not known, but it is estimated at approximately 

$2,250,000. Production from January 1 to November 1, 1930, was 39,512 tons 

of ore which contained 25 to 30 percent of the valuable metals. This is 

indicative of the importance which the property has attained.

Lasky in the paper cited has discussed in detail the geologic features of the Groundhog mine. What follows is a summary of the 

important relations.

Granodiorite dikes have invaded the quartz diorite porphyry (Fort 

Bayard laccolith) along a fracture zone trending N. 35° E., about 

200 feet wide. The quartz diorite porphyry here, as at many other 

places, contains slices and masses of in-faulted or " included " Colorado shale. This is not surprising if the nature of the laccolithic 

intrusion is taken into account. The slices and blocks may be regarded as fragments of displaced roof or floor engulfed in the advance of the magma, the progress of which at many places was crosscutting, at least in detail. Lasky finds that there has been subsequent 

'faulting along most of these shale and diorite contacts, the precise 

date of which it is difficult to establish but which in the main was 

certainly before the eruption of Tertiary lava. The invading granodiorite dikes have in turn been fractured along with their wall 

rocks, and it is within these fractures or fracture zones that the ore 

occurs. Lasky finds also that many of the dike contacts are now 

fault planes. He continues:

Pyrite occurs through the ore in more or less crystalline particles, some of 

which are well developed, and in fine-grained crystalline aggregates. Crystalline pyrite also occurs disseminated1 in some of the wall rock, particularly in 

the quartz diorite.

Sphalerite is in general the most abundant mineral, though, as noted above, 

leady streaks occur in which sphalerite is unimportant. The sphalerite is 

black or deep-brown marmatite. A preliminary microscopic examination shows 

that it contains chalcopyrite as rows of dots and threadlike veins which follow 

a pattern suggestive of grain boundaries. A narrow quartz-chalcopyrite vein 

was noted in one specimen of sphalerite. Chalcopyrite, in addition to the 

above-described microscopic particles, occurs also as megascopic masses in 

the ore.

The galena is both coarse-grained and fine-grained and in all specimens 

examined was the last sulphide deposited.

Gangue is scarce in the ore shoot. It consists mainly of quartz and sericite 

and occurs chiefly in stringers cutting the ore. Quartz combs are common in 

these stringers. In that part of the vein where sulphides are less prominent 

or are absent the vein consists of massive quartz, which at the outcrop is a 

reddish jaspery material.

In general the mineral sequence is as follows: Pyrite, sphalerite, chalcopyrite and quartz, galena, quartz and sericite.

The quartz diorite adjacent to the vein is sericitized, silicified, and pyritized, and generally altered beyond recognition. The granodiorite on the con-
74 SANTA EITA MINING AREA, NEW MEXICO

trary, though older than the ore, is comparatively fresh and at least recognizable, even where in direct contact with massive sulphides. * * *

The difference in degree of alteration between quartz diorite and granodiorite is surprisingly great. Either these rocks are inherently susceptible to alteration to a different degree or else they both were not bathed by the same 

solutions. * * *

Presumably the sill was fractured prior to intrusion of the granodiorite, and 

the rock along this fractured zone was altered by its own concomitant or 

related magmatic juices. These juices may have carried no metals, for the 

pyrite may have resulted from the femic minerals of the rock.

Later intrusions of granodiorite in the form of dikes followed the earlier 

fracturing, and these in turn were fissured and faulted. The granodiorite 

juices were heavily metal-laden, though not so rich in those constituents which 

promote intense rock alteration. These solutions probably furnished the ore, 

which to a very great degree seems only to have filled the available openings. 

The few pyrite specks in the granodiorite probably resulted from alteration of 

the femic minerals and if so are different in origin from the pyrite of the ore.

The vein system described was deeply eroded and blanketed by 

Tertiary lava. Subsequent faulting and erosion have exposed the 

ore deposits at the surface. The principal post-lava fault practically parallels the vein system, dips about 45°, and is downthrown on 

the east about 200 feet. The vein system is cut off by this fault at 

the southwest end, on the Lucky Bill claim.

Lasky says:

Four classes of ore have been mined (1) lead carbonate ore with a little 

copper and silver, (2) secondary copper ore, (3) argentiferous zinc-leadcopper sulphides, and (4) galena ore.

The main ore body occurs as a well-defined shoot within the vein. Early 

work south of the main shaft encountered some small and irregular bodies 

of ore, but as much as 500 tons of ore was seldom in sight at one time until 

the main shoot was discovered. This shoot as thus far developed is about 

1,000 feet long and 40 feet wide at the thickest part. It has been developed

to a depth of 400 feet below the surface, with splendid ore in sight at that 

depth. The top of the shoot is said to be near the third level in general, 

though a prong reached the surface and some high-grade oxidized lead ore 

was mined from it there. It is stated that the southwest end of the shoot 

is about 200 feet or so northeast of the main shaft. Where explored on the 

fourth level this interval is practically barren of sulphides. The northeast 

end of the shoot has not yet been encountered.

Where the shoot was first discovered a 3-inch stringer of sulphide was 

followed for 65 feet before it began to open into a minable ore body.

The primary ore consists of a massive argentiferous mixture of sphalerite, 

galena, pyrite, and chalcopyrite. Locally the ore has a suggestion of banding 

in zincky and leady streaks, some of which are sufficiently pure to be sent 

directly to the smelter. The relationship, if there is any, of chalcopyrite 

to this sernibanding is not apparent.

The primary ore now being mined has the following average composition: 

Silver, 8 ounces per ton; lead, 8 percent; copper, 4 percent; and zinc, 16.5 

percent. The ore to which this analysis refers shows a very incipient secondary copper enrichment, but this is so slight that it can have no more 

than an insignificant effect on grade.
ORB DEPOSITS 75

The present writers suggest, in view of observations at Santa Rita 

and Hanover, that the fracturing and intense alteration of the 

quartz diorite porphyry followed the intrusion of the larger masses

 of granodiorite but somewhat preceded the later granodiorite dike 

intrusions.

The Ivanhoe mine, on the extension of this fracture zone about 

3,000 feet to the northeast, has been worked for lead and copper 

ores. The ore bodies are of the same general type as those just

-described. The lode has resulted from a combination of fissure filling 

and replacement along a contact between a granodiorite dike and 

;shaly limestone.

INDEX

P«ge.

Abo formation, hydrothermal alteration of ___._____ 58, 59 

Abo limestone, copper ore in _ 70 

Abo redbeds, occurrence, character,

and thickness of------ 26-28

section of __-________ 27 

Abstract of report__-________ 1-2 

Acknowledgments for aid _____ 2 3

Barringer fault zone, brecciated granodiorite cut by network 

of quartz veins along_ pi. 6 

features of________ 42,47, 48-50 

Beartooth quartzite, copper ore in__ 70 

occurrence, character, and thickness of__________ 28-30 

section of______________ 29 

Bibliography______________ 10-11 

Bliss sandstone, iron ore in 57-58, 65-66 

occurrence, character, and thickness of __________ 12-14

sections of_____________ 12,13

C a m b r i a n formation, occurrence,. 

character, and thickness of ____-__ 18-19 

Cambrian time, events of _ 60-61 

Carboniferous system, divisions of 19-20 

Carboniferous time, events of- _ 61-62 

Ohalcocite, occurrence and character 

of disseminated ores of, 

at Santa Rita 69-71 

Climate, features of_____ __ 4 

Colorado shale, copper ore in _ 70 

fossils of_____-_______ 31 

occurrence, character, and thickness of__________ 30-31 

Columnar section of formations__ pi. 3 

Contact-metamorphic deposits, features -of^________ 64-69 

Copper Flat, stocks at __ 38-39 

Copper Glance fault, .features of 54-55 

Copper ore, occurrence and character of __:__ 69-75 

Cretaceous or . Tertiary intrusive 

rocks, occurrence and 

character of___ 33-40 

Cretaceous time, events of____ 62-63 

Cretaceous volcanic rocks, occurrence and character of- 32-33

Devonian formation, occurrence, 

character, and thickness of__________ 18-19 

Devonian time, events of_ 61 

Dikes, granodiorite, occurrence and

character of____ _ 39-40 

Tertiary, occurrence and character of 41 

92311 35 6

Page.

El Paso limestone, occurrence, character, and thickness of- 14-17 

replacement of, by magnetite

ore _________ 57-58,66

Faults, features of _________ 46-56 

Field work________________ 2 

Fierro limestone, differentiation of,

into several units __ 19-20 

Folds, features of______:____ 43-46 

Fort Bayard arch, age of_^._ ___ 63

structure of______ 42-44, 46-48, 50 

Fusselman limestone, iron ore in__ 66

occurrence, character, and thickness of __ ___ 15-18

Geographic position of the area 3 

Geologic history____________ 60-64 

Geologic map of Santa Rita quadrangle pi. 1 (in pocket) 

Granodiorite and granodiorite porphyry, occurrence and 

character of 35-40 

Granodiorite dikes, occurrence and

character of_-__- 39-40

Gravel, Tertiary deposits of 31-32, pi. 5

Groundhog fault, features of ___ 51

Groundhog mine, geology of __ 73-74

production of ____ __- 72-73

Hanover-Bessemer Iron & Copper Co.,

iron mine of_ _ 64-65

Hanover, down-faulted block of Tertiary sand and gravel 

near _ __ __ 50

Hanover-Fierro stock, occurrence and

character of ___ 36-38

Hobo fault zone, features of _ 52-53

Igneous rocks, occurrence and character of-__ ____ 32-41

Intrusive rocks, late Cretaceous or 

early Tertiary, occurrence and character of_ 33-40

Iron ores, geology of _ 65-66 

historical sketch of mining of__ 64-65

Ivanhoe mine, features of_-__- 75

Joy fault, features of 55-56 

Kniffen, L. M., quoted_________ 64-65

Lake Valley limestone, colloform 

masses of silicate minerals replacing pi. 6 

occurrence, character, and thickness of____ __ 20-22 

sections of_______ __ 20-22 

zinc ores in 67-69 

Lasky, S. G., quoted _ 72-74

77
78 INDEX

Page.

Lava range, view of___________ pi. 5 

Lavas, Tertiary, occurrence and character of_____ __ 40-41 

Lead, occurrence and character of

ore of _____ 72-75

Madera formation, occurrence, character, and thickness 

of_____________ 23 

Magdaleua group, formations of -_ 22-26 

formations of, sections of _ 24, 25-26 

Magnetite ore, average partial analysis of__________ 66 

Mesozoic formations ___ 28 31 

Metainorphism, effects of______ 56-60 

Mining, history of _ 5-9 

Mirror fault, features of __ 51-52 

Mississippian formation, occurrence, 

character, and thickness of__________ 20-22 

Mississippiau time, events of__ 61 

Montoya limestone, iron ore in_- 57-58, 66 

occurrence, character, and thickness of__________ 14-18

New Jersey Zinc Co., zinc mines of,

at Hanover______ 66-67

Ordovician limestone formations, occurrence and character 

of_____:_______ 14-18 

section of___ _________ 18 

Ore deposits, features of_____ _ 64-75 

Oswaldo formation, hydrothermal

alteration of______ 58-59 

occurrence, character, and thickness of _________ 22-26

zinc ore in_ 69

Paige, Sidney, quoted________ 30

Paleozoic formations__________ 12-28 

Pennsylvania!! formations, occurrence, character, and 

thickness of_______ 22-26 

Pennsylvanian time, events of __ 61 

Perclia shale, alteration of______ 58

occurrence, character, and thickness of___________ 18-19

Permian redbeds, occurrence and

character of______ 26-28 

Permian time, events of______ 62 

Fre-Canihriun time, events of___ 60

Page. 

Production, amount of_ _______ 9-10

Quartz diorite porphyry, occurrence

and character of 33-35 

thickness of 34

Rhyolite, occurrence and character

of____________ 40 

relations of, to gravel, sand, and

tuff ________________ pi. 4 

Romero fault, features of_____ 55

Sandia formation, occurrence, character, and thickness of- 23

Sand, Tertiary, deposits of__ 31-32, pi. 5

Santa Rita stock, occurrence and

character of______ 35-36

Silurian limestone formations, occurrence and character of_ 14-18 

section of- _ _ __ 18

Silurian time, events of________ 61

Silver, occurrence and character of

ore of__________ 72, 74

Stanton, T. W., fossils identified hy_ 31

Stocks, Tertiary, occurrence and

character of_ __ 41

Structure, broad features of_ __ 42-43 

sections showing___ pi. 2 (in pocket)

Syrena formation, hydrothermal alteration of_____ 58 

occurrence, character, and thickness of__________ 22-26 

zinc ore in__________ 69

Tertiary bedded sand and gravel pi. 5 

Tertiary formations, occurrence and

character of_______ 31-32 

Tertiary or Cretaceous intrusive 

rocks, occurrence and 

character of___ 33-40 

Tertiary sand and gravel, downfaulted block of 50 

Tertiary time, events of 63 

Topography of the area.__ 3-4 

Tuff, Tertiary, deposits of__ - 31-32

Vegetation, character of--- 4-5 

Veins, occurrence of ore deposits in_ 72 75

Zinc ore, average analysis of 67 

geology of_________ __ 67-69 

mining of____ ___ _ 66-67

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