The Parral District, Chihuahua, Mexico as related to the silver metallogenic province of northern Mexico

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Authors Valverde, Joaquin Echavez, 1940-

Publisher The University of Arizona.

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Link to Item http://hdl.handle.net/10150/552008 THE PARRAL DISTRICT, CHIHUAHUA, MEXICO

AS RELATED TO THE SILVER METALLOGENIC

PROVINCE OF NORTHERN MEXICO

by

Joaquin Echavez Valverde

A Thesis Submitted to the Faculty of the

DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING WITH A MAJOR IN GEOLOGICAL ENGINEERING

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE

In the Graduate College

THE UNIVERSITY OF ARIZONA

1968 STATEMENT BY AUTHOR

This thesis has been submitted in partial fulfillment of re­ quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg­ ment the proposed use of the material is in the interests of scholar­ ship. In all other instances, however, oermission must be obtained from the author.

SIGNED:

APPROVAL BY THESIS DIRECTOR

This thesis has been approved on the date shown below:

DR. WILLIAM C. PETERS Professor of Mining and Geological Engineering DEDICADO

A la

Memoria de mi

Padre

y

A mi

Madre

con veneracion

O i i i ACKNOWLEDGMENTS

A series of factors has enabled me to.achieve this degree.

The f i r s t fa c to r, and w ithout any doubt the cause of the o th e rs, was the granting of the scholarship, given to me through Ing. Don Manuel

Franco Lopez, Secretary of the Patrimonio Nacional.

I would also like to thank:

Asarco Mexicana, S.A., the sponsor of the scholar­

ship for two years. Asarco authorized the use of the

study made by the author in the summer of 1967 which

appears in this thesis.

American Smelting and Refining Company, for its

collaboration in the compilation of maps and in the

reproduction of the thesis.

The Department of Mining and Geological Engineer­

ing, the head of which is Dr. Willard C. Lacy, including

the professors and graduate students from whom I re­

ceived invaluable help during my studies at the University.

Dr. Edward Wisser, for the loan of several unpublished

reports, which were of great assistance.

I would like to give special thanks to Dr. William C. Peters, who suggested the subject and oriented me in its development. It is not often possible to meet a person with his high human quality.

Lothar and Florecita.

iv TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS...... vii '

LIST OF TABLES...... v iii

ABSTRACT...... ix

I. INTRODUCTION...... 1 Hc o in rHcoco Geomorphology...... Sonoran Basin and Range Province Sierra Madre Occidental Province Sierra Madre Oriental Province.. History of Mining......

II . REGIONAL STRATIGRAPHY...... 7

Precambrian...... 7 Paleozoic...... 10 Cambrian...... 10 Ordovician...... 11 S ilu ria n ...... 11 Devonian...... 12 Mississippi an...... 12 Pennsylvanian...... 12 Permian...... 13 Mesozoic...... 14 T ria s s ic ...... 14 J u ra s s ic ...... 15 Cretaceous...... 16 Cenozoi c ...... 17 T e rtia ry ...... 17 Quaternary...... 17

I I I . TECTONIC SETTING...... 18

S ierra Madre O ccidental...... 18 Sierra Madre Oriental...... 20 • Great Grabens...... 21 Basement C ontrol...... 22 Sequence of the Deformation...... 22

v vi

TABLE OF CONTENTS—Continued

Page

IV. PARRAL DISTRICT...... : ...... 23

In tro d u ctio n ...... 23 Previous Geological Work...... 23 Geomorphology...... 24 General Geology...... 24 S tratig rap h y ...... 25 Geologic History...... ' 32 S tru ctu re ...... 34 Veins...... 35 F a u lts...... 38 Mineralogy...... 38 Sulfide Zone...... 39 Oxide Zone...... 40 Paragenesis...... 40 C la ssific a tio n of the D eposits...... 41 Suggestions for Exploration...... 42

V. METALLOGENIC STUDY...... 44

Tectonic H istory...... 44 Tectonic Concepts Applicable to Metallogeny.... 48 Metal Distribution Pattern ...... 54 Occidental B elt...... 55 Central B e lt...... 55 O riental B elt...... 56 Parras B elt...... 56 Volcanic B elt...... 57 Secondary Alignments...... 58 Explanation of the Ore Deposits...... 59

VI. EXPLORATION APPLICATIONS...... 62

SELECTED BIBLIOGRAPHY...... 65 LIST OF TABLES

Table Page

1. Summary of Vein Systems...... 37

viii ABSTRACT

A general stratigraphic description is given for the states of Sonora and Chihuahua; the geomorphologic characteristics of the provinces comprised within these states is also presented. The tec­ tonic setting is described in relation to the regional pattern of mineralization and is related to the metal!ogenic characteristics of the remainder of Mexico. The Parra! District is used as a specific example of a mineralized portion of the region.

As a result of the correlation of silver mines throughout

Mexico, five metal!ogenic belts are identified by the author and the tectonic control for each belt is presented.

The sig n ifican ce of in te rsec tio n s and junctions w ithin the metal!ogenic belts is discussed in relation to exploration for mineral deposits.

ix CHAPTER I

INTRODUCTION

Geomorphology

Some of the f i r s t geologists to study Mexico and its major geomorphic provinces were: Sapper (1899 and 1904), Aguilera (1906a and 1906b), Burckhardt (1930), and Bose (1906). Later, Ezequiel

Ordonez (1936) made an excellent physiographic analysis in his paper called "Provincias F isio g raficas de Mexico" and provided a c l a s s i f i ­ cation of eleven provinces and nine subprovinces. King (1942) described seven divisions, considering only the norhtern part of Mexico (area lying north of the 20th parallel, or north of the belt of recent volcanoes of Central Mexico). King pointed out that two of these provinces (mesa

Central and Sierra Madre Oriental), with the exception of some differences in surface features, were tectonically very closely related. In the past few years several contributions to this subject have been published:

Alvarez (1949, 1958), Guzman (1950), Gonzalez Reyna (1956a, 1956b), and DeCserna (1956, 1958, 1960, 1961). Special attention should be given to Guzman and DeCserna1s paper, "Tectonic History of Mexico"(1963).

These writers, using the techniques of Harrington (1956) who plots the main morphostructural regions of South America according to internal constitution and external relief, have introduced the latest morpho- tectonic classification (Figure 1). In addition to using Harrington's techniques, Guzman and DeCserna based their geological criteria on the Geologic Map of Mexico (1960) and on the Tectonic Map o f Mexico

1 2

Kms. Approx.

after Guzman and DeCserna

Figure No. I Morphotectonic Provinces of Mexico. 3

(DeCserna, 1961). The geomorphic boundaries of Guzman and DeCserna were drawn on the basis of the physiographic map of Mexico by Raisz

(1959).

This paper makes a study of the area covered by the states of Sonora and Chihuahua, which include parts of three morphotectonic provinces. Those are, from west to east, Sonoran Basin and Range Province,

Sierra Madre Occidental and Sierra Madre Oriental.

Sonoran Basin and Range Province

The Sonoran Basin and Range province is located south of the

United States border and between the Gulf of California and meridian

110°W. It is a region of low mountains and intervening desert basins that resembles the Basin and Range province of the United States (King,

1942). The main structural characteristic of this province is the great abundance of roughly north-south trending, high angle faults which are responsible for dividing the region into fault blocks with attendant interior drainage and basin filling.

Geomorphically, the region consists of highly dissected block- mountains which rise above the level of a semi desert plain (Guzman and DeCserna, 1963).

Sierra Madre Occidental Province

The Sierra Madre Occidental province extends south and south­ eastward from the United S tates border to l a t . 20°N. At l a t . 20°N. begins the trans-Mexico volcanic province. The Sierra Madre Occidental province borders the Sonoran Basin and Range province and the Gulf of California at the northwest and west respectively. The sierra 4

is 950 miles long, with a maximum width of 250 miles at lat. 28°30'N, and a minimum width of 150 miles a t the 22nd p a r a lle l. The general

trend of the province and the individual sierras are northwest-southeast.

The morphological characteristics of this province are the numerous great barrancas or canyons which sometimes reach a mile in depth, formed by erosion of the rivers flowing toward the Gulf o f C alifornia and the P acific Ocean.

The area is composed almost e n tire ly o f igneous rocks and is generally considered to be a volcanic plateau.

Sierra Madre Oriental Province

For a long time the name Sierra Madre Oriental was used to

define the great mountain chain which forms the extreme eastern high area in Mexico. Although several geologists recognized the close similarity

in rocks and structures between the Mesa Central and this province,

it was not until 1963 that they were grouped together (Guzman and DeCserna,

1963). The province extends from the United States to the southern boundary of Mexico. The trans-Mexico volcanic belt is superimposed on the Sierra Madre Oriental between parallels 19° to 20°N. The Sierra

Madre Oriental is the largest province in Mexico. In fact, it is more

than 1100 miles long. The trend of the individual sierras in the province

is northwest-southeast, with the exception of the area around parallel

25°N. where they change in orientation to east-west. This change was

caused by the influence of an isolated positive area during the time

that the sierras were formed. The general trend is thought to be con­

trolled by basement configuration. 5

A major characteristic of this province is the close corre­ lation of the sierras with anticlines, in the zones between the anti­ clines, the synclines are buried beneath a great amount of alluvium.

Another characteristic in the northern part of the province, is the appearance of expanses of desert lands, which are called "bolsones"

Some of these correspond to great grabens (fosas tectonicas) (DeCserna,

1956).

History of Mining

After discovering the Zacatecas district, the Spanish explorers became interested in the reconnaissance of the northern part of Mexico.

It has been reported that Rodrigo del Rio, during an exploration trip, observed the outcrops around what now is Santa Barbara. He compared them to the c h a ra c te ris tic features a t Zacatecas, and found the vein,

"Veta Mina del Agua", in 1563. The first settlement in Santa Barbara was made in the year 1567. By 1575 mining had begun to develop with many difficulties, as is confirmed by Juan de Miranda, a clergyman who reported the following to Dr. Orozco:

Eight leagues beyond (to the north of) the Florida River are the mines of Santa Barbara. Here is located the most distant Spanish settlement of some thirty families. Mills and reduction works' have been extablished. There are many mines and much ore which has a value of four to six ounces per hundredweight. Production of silver is low due to the few Indian workmen, the extreme distance that they live from the mines, and the many wars among them. The mines are well located with all the wood, water, and other necessities. (Griffith, 1948)

Santa Barbara was at this time the home base for several successful expeditions that discovered many new mining districts. By the year 6

1600, Santa Barbara had become the most important city in the old Spanish

Province of Nueva Viscaya which at this time included the present states of Durango, Chihuahua, Sinaloa, Sonora, part of Coahuila, Texas, New

Mexico, and Arizona (Gonzalez Reyna, 1956b).

By the year 1631, Juan Rangel de Biesma, a worker in the Santa

Barbara mine had discovered the vein "La Negrita" (today, La Prieta)

and had founded San Joseph del Real de Parra! (Hidalgo de P a rra !).

During the same period, the Minas Nuevas ore body was discovered. Captain

Francisco de Molina found mineralization in the area now known as San

Francisco del Oro in 1658.

The discoveries increased as time passed, totaling 139 mines

in all the province by 1665 (Gonzalez Reyna, 1956b).

It is well known that the Indians worked mines a long time

before the arrival of the Spaniards. The Indians used the gold and

silver mainly for decorative purposes; their workings were on a small

scale. The Spaniards developed mines discovered near the "Indian

Mines". Their long trips are explained by rumors that they heard

from the Indians about the occurrences of mineralization in other

parts of the country. In fact, Santa Barbara had been worked by

the Indians before Rodrigo del Rio's expedition.

At the present time, the mining industry provides one of

the most important revenues for the State of Chihuahua. Although Sonora

i has been recognized as a potentially very rich land with reference

to minerals, it was not until the last few years that several companies

had begun regional exploration programs throughout the State. CHAPTER II

REGIONAL STRATIGRAPHY

The northern p a rt of Mexico contains rep resen tativ es of almost all geologic series since and including the Precambrian. The sedimentary rocks have been most intensively studied. Petroleum exploration geolo­ gists (Pemex) have contributed a great deal to the correlation of the formations in northern Mexico. Sedimentary rocks are especially important in the Sierra Madre Oriental. In this general area they form a mountain chain without any major cover. In the central-north area of Mexico, the sierras consist principally of sediments. The associated igneous

rocks have been correlated by their structural relations with rocks

near them and have been id e n tifie d in the geologic time sca le . In

the western part of Mexico, in the Sierra Madre Occidental, volcanic

rocks cover extensive areas. The youngest eruptions cover the sediments

and make the interpretation of the stratigraphy quite difficult.

Metamorphic rocks have been studied with increasing detail

in recent years. Isotopic measurements have in some instances brought

forth new ideas and data in the interpretation of the regional geologic

history. The metamorphic complexes are located mainly along the coast

of the Pacific Ocean.

Precambrian

Precambrian rocks crop out in several localities in Sonora.

Figure 2 shows the lo c a litie s . The areas where they have been studied

7 8

114* 110° 108* 106® 104*

• Tucson Polcmgs^ oEI Paso Nogales's------% Cd.JuarezV Cananeao "CabuMono s.Samala^ca §'!?£ . S^Ahu^da 3 u 0 4 Nacozari '1 eCasas Grandes | Carrizoo Presidio . Ojinoyuvj- • Hermosillo

•Navosaigame *\Sahuayacan^amar90o \ \ % Jimenez© \ o Parra I i

% L. V..'

3 00 Kms. 1 Placer de Guadalupe 5 Granito Aibo

2 Caborca 6 Plomosa Mine 3 Cerro del Arpo 7 Santa Rosa Canyon

4 Bamori 8 Mina Linena

modified after Ramirez and Acevedo.

Figure No.2 Map of Outcrops in Sonora and Chihuahua States. 9 are: Caborca-Altar-Bamori (Damon and others, 1962), Altar (Cooper and Arellano, 1946), (Arellano, 1956), Cabullona (Taliaferro, 1933).

They are simply divided in Older and Younger Precambrian. This division was made on the basis of the Mazatzal Revolution 1700 million years ago (Wilson, 1936, 1937).

The Older Precambrian rocks are exposed around the town of

A ltar and the town o f Cabullona. They were described by Cooper and

Arellano in 1946 at Altar, where there is a section 5,355 feet thick composed mainly of sh ale, lim estone, q u a rtz ite and dolom ite. T aliaferro

(1933) called the Older Precambrian rocks Pinal Schist at Cabullona.

In this location the rocks are formed of quartz and micaceous schists representing ancient sedimentary and volcanic rocks. The thickness is unknown (Maldonado, 1954). In southern Arizona the Pinal shist is estimated to be 20,000 feet thick (Wilson, 1962). The Older Precambrian rocks are folded with the axes oriented northeast (Damon and others,

1962).

At the end of Older Precambrian time the Mazatzal Revolution caused major structural deformation which culminated with the emplace­ ment of large plutons of granitic to gabbroic composition (Wilson,

1936, 1937). South of Caborca there is an intrusive body of this age called Granitic Aibo (Damon and others, 1962).

Cooper and Arellano (1946) and Arrellano (1956) have described the Younger Precambrian rocks as a section 6,500 fe e t thick composed of interbedded quartzite, phyllitic shale, limestone and dolomite overlying the Older Precambrian rocks. The younger group retains its sedimentary characteristics and has been very little affected by tectonic deformation. 10

This group might be co rrelated with the Apache group o f Arizona. At

Bamori and Cerro del Arpa (south of Caborca), the Older and Younger

Precambrian formations are separated by a basal conglomerate. The

Older Precambrian beds around Bamori are in situ and there is a general trend to the northwest (Damon and others, 1962).

The thickness of the Younger Precambrian rocks decreases toward the east. In fact, in the northeast part of Sonora, the thickness of the above mentioned rocks is only a few meters and in some other places the Younger Precambrian has been completely removed by erosion (F rie s,

1962).

Paleozoic

Exposures of Paleozoic rocks are more abundant in Sonora than in any other state of Mexico.

Cambrian

The most complete section is exposed in the Altar district.

Gomez and Torres Izabal (Alvarez, 1949) found representative Cambrian fossils. Cooper made a clear classification of the sediments in this area and divided them in several formations (Maldonado, 1954). Each formation was identified by characteristic fossils. All of them together are considered Lower and Middle Cambrian. The Cambrian rocks are composed of schists, limestones, quartzites and dolomites, totalling 3,900 feet in exposed section, with the bottom not observed.

At Cananea, the Cambrian is composed o f white q u arzites which become arkosic and conglomeratic toward the bottom (Valentine, 1936).

These quartzites are considered Lower Cambrian (Maldonado, 1954). 11

In the Cabullona basin, the formation classified as Lower

Cambrian is very similar to that found in Cananea. Also at Cabullona, a sequence of sediments discovered by Taliaferro (1933) is characterized by thin limestone beds that sometimes have small chert bands. This sequence is considered to be Upper Cambrian (Maldonado, 1954).

Ordovician

The sediments of this series are known in two areas in the

central part of Sonora: La Casita and the Sierra de Cobachi (King,

1939). At both places the rocks are composed of massive limestone

and contain Upper Ordovician fauna. The thickness is 150 fe e t. Under­

lying them are black, grey to black limestones with flint concretions,

silicificated shales and thin quartzites beds. Fossils have not been

described, but they are assumed to be Lower Ordovician (Ramirez and

Acevedo, 1957).

At Placer de Guadulupe, Chihuahua (100 kilometers northeast

of Chihuahua City) there is another outcrop of this age. It is predomi­

nantly composed of shaley lim estone with some dolom itic m ottling. Its

average thickness is 1000 feet and it is considered to range in age

from Early to Late (?) Ordovician (Bridges, 1964).

Si 1 uri an

At Cerro de Enmedio (area around Placer de Guadulupe) there

is the best exposed Silurian section named the Solis Limestone (Bridges,

1964). These sediments are mainly limestone. Its average thickness

is 800 feet, and it ranges in age from Late Ordovician to early Middle

Devonian. Maldonado (1954) thinks that in the central part of Sonora, 12 in central Sinaloa and to the east of Sinaloa, the lower part of some limestones associated with quartzite and schists could represent the

S ilu rian .

Devonian

The best exposures of Devonian rocks are near Altar, Cananea, and Cabullona. They are mainly constituted of limestone and dolomite with a thickness that ranges from 330 to 900 feet. At Cananea, the section is considered as Lower Devonian (Maldonado, 1954) and at Altar

(Cooper and A rellano, 1946) and Cabullona (Alvarez, 1949) as Upper

Devonian.

M ississippi an

It is again in the area Altar-Cananea-Cabullona and El Tigre

(25 miles northeast of Nacozari) where we find Mississippi an sediments.

They consist of limestones and have been studied at Altar by Cooper and Arellano (1946), Gomez and Torres Izabal (Alvarez, 1949); at

Cananea by Mulchay and Velasco (Maldonado, 1954); a t Cabullona by

Taliaferro (Maldonado, 1954) at El Tigre by Iml ay (1939).

In the area of Placer de Guadulupe there are two exposures from th is period, composed almost e n tire ly o f s i l t y lim estone and shale.

The thickness ranges from 100 to 180 feet. The age is early Late Devonian (?) to Early Pennsylvanian (Bridges, 1964).

Pennsylvanian

The Pennsylvanian rocks have been identified in several places in northern Mexico, in Sonora, Chihuahua, and Coahuila. 13

In Sonora, the best exposures are near Cananea (Maldonado,

1954), Cabullona (Kellurn, 1944), and El Tigre (Imlay, 1939 and Dunbar,

1939). The rocks are almost entirely limestone with an average thickness of 2,300 feet.

In Chihuahua the Pennsylvanian appears in the Palomas area

(100 kilom eters west of Ciudad Juarez) where i t is composed mostly of lim estone. I t is 4000 fe e t thick (Arch. Pemex, 1952). Pennsylvanian rocks are also present at Placer de Guadalupe. In this place the section has an average thickness of 1,200 feet and is formed almost entirely of limestone. The age varies from Early Pennsylvanian to Early Permian

(Bridges, 1964).

Permian

Permian sediments in Sonora crop out in the Altar, Hermosillo, and El Tigre a re a s. At A ltar the sediments r e s t upon igneous rocks, and the Permian section (500 feet) as classified by Cooper, is composed of limestone (Maldonado, 1954). At 40 and 80 kilometers east-south­ east from Hermosillo there are exposures of Permian rocks. They consist of limestones and are 1100 feet thick (King, 1939). At El Tigre the limestone strata are thin-bedded at the bottom, becoming increasingly thicker-bedded toward the top. It is common to find chert nodules.

The thickness of Permian sediments is 4,000 feet in Santa Rosa Canyon, southeast from El Tigre (Imlay, 1939).

In Chihuahua, the Permian is present in the area of the Plomosa

Mine (Placer de Guadalupe). It is best exposed at Cerro de Enmedio.

The dominant lithology is siItstone and conglomerate but the formation also includes a limestone reef and a rhyolite flow. The maximum thick­ 14 ness is more than 3,300 feet. The age is uncertain, but could range from Wolfcampian into Triassic (Bridges, 1964). There are other Permian outcrops at Sierra del Cuervo (50 kilometers north of Chihuahua City) consisting of limestone with many fusulinids (Arch. Pemex, 1952).

Mesozoic

The Mesozoic rocks have been studied with special interest and in more detail than the others due to the fact that mineral and petroleum deposits are contained in these rocks. They cover a great extent throughout Mexico and in general are of marine o rig in . The

Cretaceous rocks are best known as a consequence of their large out­ cropped areas. The Jurassic is next in extent of outcrop.

Fossils in the Mesozoic rocks are very numerous, especially in certain zones, a fact that has helped in identifying and correlating these formations.

T riassic

The Triassic rocks are recognized in several states of Mexico.

In the north and central part of the Republic they are considered to be sedimentary facies with close similarity to rocks of the same age in New Mexico and Texas.

King (1939) studied the rocks of this age in northern Sonora.

Around Rio Yaqui the sediments are almost entirely continental sediments and co n sist of q u a rtz itic sandstones 3,300 fe e t in thickness. Toward the west the sediments become marine and increase in thickness, reaching

6,800 feet to the west of meridian 111°(Ramirez and Acevedo, 1957). 15

Ju rassic

The Lower Jurassic section is present in the states of Sonora

and Chihuahua along a line oriented northwest which has its northern

extreme near Caborca (Mina Lineha) and the southern end at the border

between Sonora and Chihuahua (Navosaigame and Sahuayacan). The rocks

are formed of impure clay-like sandstone, schist and limestone with

characteristic fossils.

The Middle Jurassic rocks have not been identified in the

northern part of Mexico, probably Chihuahua state was emerging at

.this time.

During the Upper Jurassic, the state of Chihuahua was invaded

by the sea, which was limited at the west by the Sierra Madre Occidental,

at the north until Ciudad Juarez and at the east by the Coahuila Peninsula.

To the south the sea continued through the Durango s ta te and was connected

to the sea that at this time, covered almost all Mexico (Ramirez and

Acevedo, 1957).

Sediments of this period are also present in the Sierra de

Samalayuca (north of Chihuahua state). Villa Ahumada (north of Chihuahua

state) and Placer de Guadalupe. At Sierra de Samalayuca the rocks

have been designated as Oxfordian to Kimmeridgian in age. The section

consists of 2,000 feet of sandstone, shale and sericitic shale and

limestone interbedded with shale (Marquez, Arch. Pemex, 1952). At

Villa Ahumada and Placer de Guadalupe the age of the rocks ranges

from Portland!an to Kimmeridgian. The thickness increases from Villa

Ahumada (650 feet) to Placer de Guadalupe (4,200 feet). The sediments

are characteristically formed of conglomerate, shale, limestone. 16 sandstone, gypsum and coal shales (W ay, 1953, Arch. Pemex). The sediments indicate that this area in Chihuahua was unstable during the Jurassic and the presence of gypsum indicates poor circulation of the waters.

Cretaceous

The Cretaceous sequence of rocks is the most important in the economic life of Chihuahua. Ore bodies are present in these rocks.

There are several types of lithology and the thickness reaches 13,000 fe e t. The sediments were deposited in the Mexican Geosyncline; the source area was emergent at that time in Arizona, New Mexico, West

Texas, Sonora, and part of Chihuahua, and the Peninsula de Coahuila.

In Chihuahua the distribution of the Cretaceous rocks is as follows: in the northern part of the state Upper Cretaceous rocks have been eroded and the sierras show only the Lower Cretaceous. In the central part, the Upper Cretaceous is more apparent; and in the eastern part the Upper Cretaceous appears abundantly in the sierras

(Ramirez and Acevedo, 1957) and the sediments have been strongly deformed.

The Lower Cretaceous strata show an on and off shore relation­ ship during Neocomian tim e; in Aptian time there was a general invasion of fin e e la s tic s and in Albian-Lower Cenomanian the terrigenous sediments were absent (DeCserna, 1956).

The Upper Cretaceous consists of a clastic transgressive succession toward the east, increasing in grain size upward; it is considered a flysch deposit (DeCserna, 1956). 17

Cenozoic

In the Cenozoic Era a great part of the mineralization was formed in Mexico. It is associated with the strong vulcanism which was localized in the eastern and central areas of Mexico.

T ertiary

It was during this time (probably Miocene) when massive eruption of volcanic material took place. The extensive volcanic rocks upwelled . from several fissures along the Sierra Madre Occidental and in the center of Mexico, giving place to very thick accumulations of andesitic flows and andesite tuffaceous material. These rocks, especially the granitic bodies, have a close genetic connection with the emplacement of intru­ sive bodies.

Quaternary

The last manifestation of vulcanism is thought to belong at this time. It is represented by basalt eruptions in several areas of

Mexico. The b a sa lt is manifested as a mesa which has a very long ' extension and variable thickness. These rocks are more often located

in the center of Mexico (trans-volcanic province), but they are present also between the Sierra Madre Occidental and the Sierra Madre Oriental. CHAPTER III

TECTONIC SETTING

A brief description of the tectonic setting of the area was

given in the Geomorphology section. In this section a broader discus­ sion will be presented.

S ierra Madre Occidental

The Sierra Madre Occidental is characterized by a great pile

of volcanic material which has been upfolded into a long, narrow south­

east trending anticline with branching spurs and with superimposed local

anticlines and domes. The volcanic rocks overlie a basement comprised

of pre-Tertiary rocks - including Mesozoic and Paleozoic as well as

those of Precambrian age (Wisser, 1966). King (1939) described the

Tertiary rocks and mentioned the great thickness of Tertiary in the

S ierra Madre O ccidental. The sequence becomes thinner westward. The

volcanics are composed of very different families of rocks and display

considerable variation from place to place in the succession, even in

parts closely adjacent. The dominant rock is andesite. There are also

rhyolite flows, acidic tuffs, breccias and conglomerates. Wisser (1966)

correlated the members of the volcanic sequence by constructing strati­

graphic sections taken both transverse and parallel to the major axis

of the sierra. For constructing the sections he used data collected

by R.E. King (1939) plus his own private reports and his experience

during 40 years in the area. Dr. Wisser concluded from his data that the

18 19 longitudinal sections have very little variation in the lithology of the volcanics along the trend of the Sierra Madre Occidental. In contrast, the transverse sections show a change in lithology and a thinning of the sequence toward the southwest;

The general structure of the volcanic pile has been described by Wisser (1966) as follows:

The principal stru c tu ra l feature is a complex but well-defined elongated uplift which coin­ cides rather closely with the Mesozoic Occidental geanticline; this uplift will be called the main w e lt. On the north the main w elt consists of two north-trending uplifts separated by a long, relatively narrow structural basin. El Tigre lies on the western uplift. Dos Cabezas on the eastern. South of the basin the two uplifts coalesce and the welt veers to the southeast, where i t has a number of cupolas and spurs. The Chinipas structural basin parallels the welt and lies high on its southwest flank. For some distance southeast of Los Angeles the welt may consist of a sin g le ridge, but i t becomes complex again fa rth e r southeast. The San Dimas district lies at the north end of an axial basin, southeast o f which is a cupola (Figure 3).

At the western part of the main welt, in the segment where the welt trends northward, is a series of faults paralelling the trend of the welt. Some of these are "thrusts", others "normal" faults

(King, 1939). Of special interest is the fault closely following the 109th meridian (Figure 3). On the north it is a "thrust", on the south, a "normal" fault. In each segment the upthrown block lies on the east, that is, toward the main welt (Wisser, 1966). Faults with similar characteristics to these located in the Sierra Madre Occidental are also found at the margin of the uplifts in the central Rocky Mountain region and have been described by King, Eardley (1963), Prucha and others (1962), and Wisser (1960). These writers considered the faults 20 to be boundaries of blocks of the crystalline basement that have been elevated by d iffe re n tia l v ertical movement. As a consequence the volcanic cover has been deformed into an anticline or dome.

Sierra Madre Oriental

The State of Chihuahua is located within the province that has been described in the preceding pages as the Sierra Madre Oriental.

Generally, the western half of the area is covered by volcanic material which has the same characteristics as that described in the former paragraph. In the eastern half, sedimentary rocks are dominant and are a distinctive feature of the Sierra Madre Oriental.

The sediments were folded by forces acting approximately east- west, forming structures with a general northwest-southeast trend.

The only exceptions to this trend are the east-west folds located near the 25th parallel. As it has been pointed out before, this change in orientation was due to the presence of a positive area (Peninsula de Coahuila) which modified the regional trend.

Away from the Peninsula de Coahuila the action of the deformation stresses is manifested by fractures, faults and by very gentle folds.

Closer to the pre-Aptian isla n d , the folds become more acute and form recumbent isoclinal folds and overthrusts.

The individual ranges are commonly composed of several a n ti­ clines which change in width and height and are modified by intrusives, o v e rth ru sts, or normal f a u lts . The in tru siv es appear to be situ a te d on the axes of the anticlines.

The age of folding in the Sierra Madre Oriental has been placed by Bose and Cavins (1927) as Lower to Middle Eocene. The c r ite r ia fo r 21 this determination were taken from the piedmont zone of the Sierra Madre

Oriental, where marine Tertiary strata are present. Muir (1936) and

Helm (1940) with more recent studies supported this conclusion. DeCserna

(1956) from additional information obtained during his studies concluded that the folding age is post-Upper-Cretaceous and pre-Upper-Eocene. All of the writers indicate that the longitudinal faults, the overthrusts and the emplacement of granodiorite and monzonite bodies were penecon- temporaneous with the folding of the sediments.

Great Grabens

In the eastern part of Chihuahua, there are several internal hydrographic basins, called in Spanish "bolsones". Some of them are:

Bolson Maijoma, Bolson de los Caballes, Bolson de Gigantes and Bolson de Mapimi (Figure 3). They are oriented more o r less p a ra lle l to the regional trend (NW-SE).

DeCserna (1956) in his tectonic study of the area between Torreon and Monterrey (south and east to our area) classified the bolsones in his area as great grabens (fosas tectonicas) and pointed out that the marginal faults are apparent only on one side of the individual grabens, but added that the marginal faults on the other sides may be covered by alluvium. He thinks that the age of the "bolsones" is contemporaneous or a little later than the basaltic eruption of the San Carlos series, which is Pliocene; he considers that there is a very close relationship between this block faulting and the basaltic magmatism. 22

Basement Control

The general trend of the Sierra Madre Oriental is controlled

by basement folds. Basement in this case is considered as the rocks

formed during the Precambrian and Lower Paleozoic time. DeCserna (1956) described the San Julian Anticline, 100 kilometers southeast of Torreon and considered it a semi-developed tectonic pilar. He compared this anticline to the Harz Mountains in Germany (Stille, 1940) and to the

Bighorn Mountains of the United States (Bucher, 1933). The Villa Juarez

Inlier (near Lerdo City, Durango, southeast corner of Figure 3) repre­ sents a basement fold, but on a minor scale. The presence of intrusives

in some anticlines such as in the Sierra de Mapimi and Sierras de San

Julian, are related to basement structures (DeCserna, 1956). The same

author considers the basement folds, marginal faults and great grabens

as being almost contemporaneous with the intrusions.

Sequence of the Deformation

The folds which are oriented east-west near the 25th parallel

between the cities of Torreon and Monterrey have been classified by

DeCserna (1956) as over thrust folds. These folds are believed to have

been formed by g rav itatio n al movement. According to DeCserna, the

basement folds were formed during a following stage, and the intrusives

formed during a still later stage. CHAPTER IV

PARRAL DISTRICT '

Introduction

The Parra! District is located in the southern part of the

State of Chihuahua almost on the border with the State of Durango

(Figure 4). The three major cities are Hidalgo del Parra!, Santa

Barbara, and San Francisco del Oro. The Parra! district covers an area of about 311 square kilometers.

This chapter is primarily concerned with the district and with an area located roughly to the east of Santa Barbara which was studied by the author (Figure 4) which is called Area A.

Previous Geological Work

Although the mining work began during the 16th century, it was in the early 1900‘s when geological work was started, shortly after the American Smelting and Refining Company formed a unit at

Santa Barbara and began operations.

Among the geologists who have studied the district, there have been several well known scientists. J.E. Spurr, one of the first to study the mines, was followed by Basil Prescott, J.G. Barry, W.M.

Davy, Harrison A. Schm itt, H.E. McKinstry, and T.P. Clendenin. In recent years the district has alos been studied by outstanding members of the geologic profession such as Edward Wisser (1945), G.S. Koch,

Jr. (1956), J.B. Scott (1958), G. Ordonez, A. Giesecke (1960).

23 24

Geomorphology

The Parra! district is located in the transition zone between the Sierra Madre Occidental and the Sierra Matire Oriental and consequently has some of the geomorphic characteristics of both provinces.

The area is composed of large mesas around the towns. Away from the three major c itie s the topography becomes more abrupt; esp ecially toward the north, west, and south. This area of sharp relief is typical of late youth. The average altitude of the district is about

6,400 feet above sea level.

Ore deposits of the Sierra Madre Occidental are mainly of the precious-metal type, in the form of epithermal veins in andesite flows, while the deposits of the Sierra Madre Oriental (table land) are dominantly silver-lead-zinc replacements in limestone. Parra! shows some characteristics of each province: the vein type ore deposits carry, in their higher zones at least, higher silver than do the replacement deposits farther to the east. The Parra! deposits carry higher quantities of zinc and lead than do the precious-metal veins of the western province (Wisser, 1959).

General Geology

The most widespread rocks in the region are sedimentary.

They are composed of interbedded marls and sh ales. In some areas the marls grade into limestone. In the deepest mining levels at

Parra! and Santa Barbara the shale is highly silicified, similar to a fine grained quartzite (Clendenin, 1953). Near intrusive bodies the sediments are strongly folded and intensely altered. The regional 25

dip is, in general, gentle and toward the west. The age is Upper

Aptian-Lower Albian, correlatable with the Upper part of the Trinity

Group in Texas. The sediments are known collectively as the Parra! formation. After deposition, the sediments were folded, uplifted and deeply eroded into a mountainous topography. Around Parra! City there is a conglomerate lying above an irregular surface of the Parra! formation. Wisser (1945) reports a coarse breccia of limestone and quartzite boulders, overlain by water-lain tuff and sandstone in the northwest part of the district.

The next step in the geologic history of the Parra! district is characterized by volcanism which took place in Tertiary time.

The volcanic activity is manifested by a thick andesitic sequence, which rests upon either the Parra! formation or the conglomerate, depending upon whichever was exposed at the time of volcanism.

The andesitic volcanic rocks were later deformed by the injection of acidic dikes (quartz-monzonite, rhyolite, etc.). The mineralization of the district occurred shortly before the dike injection.

The last volcanic manifestation was the eruption of basaltic lavas which form the present day mesas. Alluvial material is found in the arroyos cutting into the mesas and also in flood plains.

Stratigraphy

In the following section a more detailed description of the different types of rocks is presented.

The Parra! Formation. The Parra! formation crops out to

the south of Parra! City. At this location it consists of thin bedded shales, with colors that change from grey to dark grey, and limey 26 shales, of a blue-black color. The individual beds have an average thickness of 2 to 3 inches. Near the Esmeralda Mine, sand lenses have been found. The regional dip around Parra! City is 30° to 65°

W. Many small folds are present and this folding is exaggerated near the intrusive monzonite (Lowther and Marlow, 1956).

At Santa Barbara, at San Francisco del Oro and in Area A (Figure

4) sedimentary rocks are predominantly of the type described above.

At Santa Barbara and San Francisco the formation is folded into an asymmetrical a n tic lin e whose southwest limb dips about 30° west and whose no rth east limb dips about 8° e a st. The fold axis s trik e s

N. 28° W. and plunges 12° N; the axial plane s trik e s N. 33° W. and dips 75° E. (Koch, 1956).

In Area A, the formation is composed o f a sim ilar sequence of sediments. The marls range in color from light grey to black and have a thickness which ranges from 2 to 16 inches. The shale appears in thin beds, in certain areas being as thick as 4 inches. Generally the shale has a yellowish brown color due to the oxidation of pyrite, which is uniformly distributed within it. The average dip throughout the area is 35° toward the west. The regional strike of the beds is north - south. Toward the west the larger size particles increase in the elastics (Echavez, 1967). It is thought to be characteristic of bathyal sedimentary facies in which the depth of sedimentation was g reater than 650 fe e t.

The shales of the Parra! formation are generally very strong, fine grained, and impervious. In general the rock does not require support in mine workings, except when some fracture or fault system 27 changes the rocks primary physical characteristics.

The age of the Parra! formation was for a long time uncertain due to the scarceness of characteristic fossils in the district.

Fried!ander in 1906, was the first and only one to collect, near the

Palmillas mine, dwarf ammonites. These ammonites, although unfortunately in very bad condition, were recognized as characteristic of the deep water facies of Gault-Vraconian (Albian, upper part of Lower Cretaceous) in central Mexico (Burckhardt, 1930). Bose (1906) disagreed: " I t is possible that the Parra! schist belongs to the Upper Jurassic.

I have found th ere a good number of Aptychus, but no ammonites." Ramirez and Acevedo (1957) considered the age o f th is formation as Vraconian

(Upper Albian) and correlated it with the Georgetown formation of

Texas. In September, 1965, a fossil was found in one of the iron baskets used to carry ore to the mill from the San Francisco del Oro mines; the exact place of origin of this fossil is of course unknown: it may have come from either the San Francisco mine or the Clarines mine.

The fo ssil was id e n tifie d by the Laboratorio de Paleontologia de Petroleos

Mexicanos (Paleontology Laboratory of Pemex) as Acanthohoplites aff. aschiltaensis (Anthula) which corresponds to Upper Aptian-Lower Albian

(Escandon, 1967). No fossils were found in Area A during the investi­ gation.

Using the above data, the writer correlated the Parra! formation with the adjacent Kiami chi and Cuesta del Cura formations in Mexico.

The equivalent strata in Texas would be the Fredericksburg and Washita

Groups. This correlation was necessary because the Parra! formation has a thickness greater than 3,300 feet, as measured in the shafts 28 of Santa Barbara and San Francisco. If the correlation is correct, the Parra! formation overlies the La Pena formation (Upper part of

Trinity Group, in Texas).

Conglomerate. Wisser (1945) reports that a coarse bouldery breccia of limestone and quartzite occurs at the base of the volcanic series. Immediately above this breccia, northwest of Parra! City, water-lain tuff and sandstone is present. This breccia could be corre­ lated with a Red Conglomerate that crops out north of San Francisco del Oro, outside of the mapped area (Figure 4)

The area where the conglomerate is exposed is limited. Its strike varies from N. 30° E. near San Francisco, to due east in the more northern areas. The dip varies from 50° to 70° north. The thickness varies from 1.6 to 33 feet, having an average thickness of 3.3 feet. The breccia was probably formed after the Parra! formation was folded and at the beginning of rhyolite extrusion. The conglomerate is composed of fragments which range in size from 1 to 2 inches, although there are some as large as 4 inches. Voids are filled by

sand or by calcareous cement. Shale fragments are elongate with a

5 to 1 relationship between their "a" and "b" axes. The edges of

the fragments are slightly rounded. The small fragments are more

or less rounded. The more abundant fragments are shales, rhyolites,

rhyolite tuff and volcanic glass (Escandon, 1967). Due to the fact

th a t the conglomerate is composed o f rocks th a t are present in the

area, it is classified as intraformational (PettiJohn, 1957).

The volcanic rocks cover a wide area in the district. The

dominant types are andesite and basalt, but there are also minor 29 rh y o lites and d a cites. The andesites are the o ld est and the b asalts appear to have developed from several ejections. The strongest basalt manifestation occurred at the end of the volcanic cycle, forming the top of the mesas.

Andesite. The andesite is found as flows and as intrusive bodies. It is located in close proximity to Parra!, toward the northwest and north, toward the south and southeast of Santa Barbara, and toward the northeast of Area A (Figure 4).

In the Parra! Area, the flow andesite occupies the extreme western portion and the intrusive andesite the central portion. This large intrusive measures 6.2 miles along its north-south axis and

5.6 miles along its east-west axis. The intrusive was classified as biotite-quartz-monzonite porphyry by Schmitt (1931) who said,

Macroscopically the monzonite is light gray in color. It contains prominent feldspar phenocrysts, of which those of plagioclase are the largest, some times being three-eighths inches long. Ferromag- nesian minerals are relatively unimportant. Micro­ scopically the rock is porphyritic in texture; the most abundant phenocrysts are zoned andesine and orthoclase, with minor biotite and argite. A few - large apatite crystals are characteristic. The groundmass is usually xenomorphic.

Giesecke (1960) mapped th is body as an in tru siv e andesite.

The majority of the veins in the Parra! Area occur in this intrusive.

At Santa Barbara, the andesite flows are located toward the south and at Area A they are located toward the northwest. They are parts of the same flow (Figure 4) and are thought to be contempor­ aneous with the flows that are exposed to the northwest of Parra!

City. When fresh, they range in color from light gray to dark blue; 30 when they are altered the color changes to light brown to white, giving the appearance of kaolin. The flows rest unconformably on the shale.

The shale a t the contact shows baking, a lte ra tio n , and s ilic if ic a t io n in zones ranging up to five meters in thickness at the contact. The andesite at the contact is very fine grained and shows vivid colors due to oxidized iron. The andesite assumes a porphyritic texture upward and becomes q u ite massive (S co tt, 1958).

Granite. This type of intrusive crops out at the eastern part of Area A. At some places it appears interbedded with the Parra! formation. It has a white to light grey color due to the abundant quartz. The identification of this rock was megascopic and therefor could be classified as granite-monzonite, or other acid family of intrusive rocks, depending on the plagioclase content. The author's feeling is that these intrusive bodies may be correlated with the big intrusives at Parra! City and have a common origin at depth. There could be a large district-wide batholith, which would be the source of the granite intrusives and dikes.

Rhyolite. Rhyolite appears in the parral area as flows and dikes, esp ecially toward the south of the c ity . Between San Francisco del Oro and Santa Barbara, rhyolite dikes are found which are as much as 780 feet thick. The average thickness of these dikes is between

3 to 10 fe e t. The rh y o lite is pink, brown, and w hite. I t contains about 5 per cent quartz phenocrysts averaging 2mm across in a fine­ grained groundmass. The dikes vary in both dip and strike, but most s trik e north. However, some of the dikes show a S. 70° W. tren d , which is not parallel to any mineralized veins but is almost parallel 31 to the strike of one of the post mineral fault groups. Schmitt (1928) comments that the structure of the dikes indicates a possible intrusive at shallow depth. To the south of Santa Barbara the thyolite dikes intrude the shales and andesites. Because of their hardness the rhyo­ lite dikes are preserved from erosion, being easily distinguished in the fie ld and on air-p h o to s. The dikes are more abundant in the eastern part of Area A. The rhyolite dikes are younger than the mineralized vei n s.

Basalt. The basalt is the youngest group of the volcanic rocks.

Generally it is located in the topographically highest areas forming the mesas, which suggest that the region was subjected to very strong erosion since its extrusion. About 10 kilometers from Santa Barbara, on the road to Parra!, the basalt is found in the valley buried by alluvial material and organic soil. The basalt is dark grey to black in color, hard and dense, and breaks with conchoidal fracture where it does not have a high content of vesicles. Koch (1956) reports that the basalt in the San Francisco del Oro area consists of "85% feldspar and pyroxene, in the ratio of 3:1, 10% olivine phenocrysts, and 5% vesicles, most of which are partly filled with cal cite." The approximate thickness of the basalt lavas are from 130 to 200 feet reaching to 330 feet thick in some mesas.

Alluvium. The alluvium is the youngest sediment in the district.

It is found along the beds of the rivers and arroyos, and in their flood plains. The composition and size of the alluvium particles is highly variable and heterogeneous. Shale, limestone, andesite, and basalt fragments are all present, with the shales being most abundant. 32

Geologic History

Toward the end of Late Jurassic the seas invaded this portion of Mexico. This marine transgression became more extensive toward the end of the Early Cretaceous and marked the beginning of the th ird geotectonic cycle during which the Mexican structural belt developed

(DeCserna, 1960). It is possible that be this time several areas were beginning to be uplifted or were already elevated. These areas were the S ierra Madre O ccidental, Isla de Aldama (in the center of

Chihuahua) and the Peninsula de Coahuila (in Coahuila). These were the main islands close to the study areas. The change in the grain size of the sediments which are coarser in the western part of Area

A and decrease in size toward the eastern, suggest that the Sierra

Madre Occidental was most influential as the origin for the sediments.

The deposition of shales and limestones suggests that the sedi­ mentation conditions were, in general, uniform. The presence of con­ glomerates in some parts of the district shows a regression of the seas and uplift of the continents.

The Parra! Formation was deposited in bathyal conditions.

Its dark coloration and the pyrite content in the limey beds are char­ acteristic of reducing conditions due to the poor water circulation fa r from the shore.

The depositional environment apparently remained similar until the end of the Cretaceous or Pal eocene. By this time metamorphism and granite emplacement occurred in Baja California, site of the former eugeosyncline (DeCserna, 1956). This occasioned erosion of the high­ lands, which occupied the position from the Sierra Madre Occidental 33 to the western half of Guerrero. The flysch wedge deposits of this period proceed outward from the highlands and were deposited in the miogeosyncline. The Hidalgoan orogeny (approximately correlative with the Laramide orogeny of western United States) folded the sediments during the Early Eocene (Guzman and DeCserna, 1963). The folded structures have a close relationship with the pre-Aptian highlands. Near to them the folds are much more deformed. Away from the continental borders the folds are gentle and symmetric, showing less effect of the tectonic forces. In Area A the average dip of the sedimentary rocks is 35° toward the west. From this fact Area A is interpreted as a gentle western limb of an anticline. This area was subjected to a taphrogeny phase during the middle Eocene-01igeocene. The andesitic flows took place in 01igocene-Miocene time. These two events may be related with the two fracture stages proposed by Koch (1956). In the first stage, two sets of complementary shear fractures were formed.

In the second one, the first two sets were re-opened and two additional sets were formed. The mineralization appears to have taken place just after this readjustment. The emplacement of rhyolite dikes was the next geologic event in the district. The preceding rocks were affected a t th is time by the movements o f the blocks. This action occurred perpendicular to the already-formed veins. The sub-aerial erosion proceeded consistently and strongly during Pliocene time pro­ ducing a gently rolling surface upon which the basalt lavas were deposited at the end of Pliocene and Pleistocene time. The actual topography may be very similar to that in Pleistocene time. The alluvium and cultivated soils are of Recent time. 34

Structure

At Parra! City the main structure is a broad, flat dome with a stock in the center (Figure 4) (Schm itt, 193!). The stock may merge on the west with a north-south uplift. North of the stock the uplift forms an arch in cross section and carries the block faulted Veta

Colorado-San Patricio graben along its crest. The block faults are vertical with offsets of up to 1500 feet of dip slip. South of the stock the north-south uplift continues as a horst bounded on the west by the Cabadena fault vein and on the east by the Carmen fault and dyke.

From Santa Barbara to San Francisco del Oro the regional struc­ ture is an anticline. Its characteristics have been described in the Parra! Formation section. The trend of the anticline on the north end of the stru c tu re o f San Francisco del Oro is N. 28° W., with 12° north plunge (Koch, 1956). At Santa Barbara, the south end of the structure has a N. 30° W. trend. The detailed structure is very complex due to numerous drag folds and small fa u lts . The west limb seems to dip more steep ly than does the e a st limb. Examples of reverse movement along the bedding planes or as faults are very common in the underground workings (Scott, 1958).

At Area A the general strike of the sedimentary beds is north- south or N. 15° W. with an average dip of 35° to the west. At some places, especially at the west, this general setting is interrupted by dikes and small intrusive bodies which produce small anticlines as a consequence. Due to the persistent dip of the beds. Area A is interpreted, as the west limb of a regional anticline. This shows that the compressive forces were not very strong in the area. 35

The compressive stresses may be due to the upward movement of the Sierra Madre Occidental which may have been faster during the

Hidalgoan Orogeny. This upward movement could produce horizontal forces in the district which were directed northeast or east. They were deflected in the opposite direction when they abutted against the stable shield (Peninsula de Coahuila). The Parra! stock and Santa

Barbara-San Francisco del Oro anticline was formed after the action of the horizontal forces took place. In the Parra! area the intrusive body reached the surface and a t Santa Barbara and San Francisco del

Oro the deformation of the sediments may have been due to the intrusion of another igneous body which is not from the same origin as that of the Parra! stock but may have been genetically very closely related to i t .

Veins

The veins in the Parra! District are very persistent and para­ llel in strike; dips are directed inward toward the axis of the fracture zone.

Especially in the immediate area of Parra!, the type of wall rock controls the abundance, altitudes and susceptibility of minerali­ zation of the hanging-wall and footwall of each vein. With andesite walls the mineralization is closely confined to the main fault plane.

With shaley limestone walls, however, there is irregular invasion of the walls by the mineralization (Schmitt, 1931).

At Santa Barbara-San Francisco del Oro, the veins fill faults with displacement on the order of a few tens of meters. The general width of the veins range from five feet to ten feet; but in some 36 places ore shoots are as much as 50 feet wide. The veins at San Francisco are in a system of relatively short fractures while at Santa Barbara they are in long and persistent fractures up to 5.5 kilometers long.

All are unusually regular in strike and dip.

The shale on either side of the veins show silicification, silication, pyritization, and in a few places, disseminated sulfide replacement. Sub-parallel stringers of quartz and cal cite are common.

The alteration extends for 3 to 6 feet on either side of the veins at San Francisco and up to 50 feet at Santa Barbara.

The angle between the fracture and the bedding of the shale at San Francisco and Santa Barbara is the most important factor governing vein width. Koch (1956) pointed out that the wide parts of the veins stand at a large angle to the shale bedding. Evidently, the stress that fractured the rock opened wide, persistent vein fractures only where it could not be dispersed by small displacements along favor­ ably oriented bedding planes.

The veins in the Parra! District fall into four fracture systems, each system showing a characteristic strike-dip trend that is different from the other three systems. At San Francisco the veins were classified into groups by Koch (1956), and similarly at Santa

Barbara by Scott (1958). Some of the main veins in the Parra! Area fall into the four-fold classification. In Area A the veins fall

also into some of the four groups; in addition, another set oriented

roughly east-west was identified. The several systems are summarized

in Table 1. 37

Table 1. Summary of Vein Systems

Santa San Area Attitude Parra! Barbara Francisco A* Type

Veta N S 75E Grande Alpha Frisco 10 dip s lip

N S 40-70W Esmeralda Beta Transvaal dip slip

N25E 55-75W Guadalupe Delta Footwal1 11-12 strike slip

N25W 55-75W Mari eta Gamma Cobriza 25-27 strike slip

E W 70S 8-22

*Area A: The numbers in this part correspond to samples taken from veins. The numbers have been l e f t out of Figure 4 fo r security reasons.

Koch (1956) stated that the vein fractures were formed in two stages. A portion of his paper is quoted below:

In the first stage, the fractures of the Frisco and Transvaal sets were opened as a system of two sets of conjugate shear fractures in res­ ponse to a tensional stress directed nearly horizontally at right anales to their strike combined with a compressive stress directed nearly vertically. In the second stage the fractures of the Cobriza and Footwal1 sets were opened as a second system of two sets of con­ jugate shear fractures in response to a ten­ sional s tre ss directed somewhat sim ilarly to the tensional stress of stage one but plunging downward to the east, in fact a direction about normal to the attitude of the Transvaal vein set, combined with a compressive stress directed more nearly horizontally than vertically.... the forces which opened the last set also reopened the earlier formed fractures and made the whole block of ground an especiallyfavor­ able place for ore deposition.

From these several systems Koch (1956) reported the following relative

amounts of ore at San Francisco: Footwal1 33%, Frisco 30%, Cobriza

19%, and Transvaal 18%. 38

Schmitt (1928) suggests that it is-possible that about 3,000 feet of volcanic material covered the sediments at the time of ore deposition. Thus, this thick cap of ejected magma might have been one of the factors to cause compressive stress and set up the conjugate shear fractures.

Faults.

Just after the mineralization period another readjustment took place causing the formation of faults and joints. This reopening has two related sets of faults that fall within the strike trend groups. The f i r s t has an average s trik e of N. 80° E. and contains most of the major faults, while the second with an average strike of N. 45° W. contains both fa u lts and jo in ts . The f if th s e t of veins (E-W) may fall in the first group of the faults. Scott (1958) distinguished three types of faults: (1) quartz-filled faults,

(2) calcite-filled faults, (3) gouge-filled faults. The displace­ ment along the faults is moderate. The strike-slip movement has an average of about 33 feet. The vertical displacement in the Clarines mine has been reported at as much as 300 feet on one fault, but in general it is considerably less. In most cases, a fault zone con­ sists of a crushed zone 3 to 40 feet wide with a center zone 0.3 to

3.3 feet wide filled with quartz, calcite or gouge. Many of the gouge faults have diabase dikes in the central zone (Scott, 1958).

Mineralogy

The veins in the district have a general similarity in mineral composition. The recoverable metals are: gold, silver, lead, copper. 39 and zinc. The main mineral products in order of abundance are: sphalerite and marmatite 14%, galena 6%, chalcopyrite 2%, and p y rite 2% (Koch,

1956). The gangue m inerals are q u artz, cal c ite , f lu o r ite , and a series of "high temperature" silicate minerals.

The m inerals have been divided into two groups. The primary sulfides below the water table and the oxide zone located above it.

At the base o f th is l a s t zone a small amount of secondary su lfid e enrichment is present (Scott, 1958).

Sulfide Zone

The more common m inerals in th is zone are: sp h a le rite , galena, chalcopyrite, pyrite, and arsenopyrite. At San Francisco Koch (1956) reports besides the former minerals, gold, hematite, and scheelite.

Schmitt (1931) mentioned specularite and argentite in the same zone in the Parra! area. In Area A, the above mentioned common minerals are found. Scott (1958) gave the following distribution of the minerals:

Small amounts of b o rn ite, native copper, and hematite are found in the lower levels of some of the veins. The ore minerals sphalerite, galena, and chalcopyrite are found from the top of the sulfide zone to the lowest levels. Gener­ ally the marmatite is quite massive and has a coarse crystal form. Galena occurs in two forms, the first very massive and showing a coarse crys­ ta l form. The second, while massive, has a fin e crystal form and tends to be closely associated with pyrite. Chalcopyrite is rather fine grained and occurs as masses associated with pyrite or arsenopyrite. The arsenopyrite, although in small amounts near the surface, tends to increase with depth and in sane of the lowest workings is very abundant.

As a general rule all the sulfides and gangue minerals become coarser- grained with depth (Koch, 1956; Schmitt, 1928; Scott, 1958). The silver is closely associated with the galena. The highest silver 40

values occur with the fine-grained variety of galena. The gold seems

to be associated with the galena and the chalcopyrite.

Among the gangue minerals located in the sulfide zone the most abundant are quartz 33%, fluorite 11%, and cal cite 9% (Koch,

1956). The quartz ranges from clear colorless to grey and to greenish

in color. Most of the vein quartz is massive and dull in appearance.

It has a comb structure. Calcite is white to colorless. Fluorite

ranges from white to green in color and is fine grained. At the

northern part of Santa Barbara-San Francisco the amount of fluorite

increases and in places becomes the main gangue component. The high

temperature silicates belong to the garnet, pyroxene, and epidote

groups.

Oxide Zone

The water ta b le varies from 165 to 400 fe e t below the su rface.

Near the surface all the veins are oxidized. The oxidized ore is

commonly vuggy, earthy and shows residual boxwork. The secondary

minerals are angles!te, azurite, malachite, cerussite, jarosite,

and limonite. Additional secondary minerals were reported by Schmitt

(1928). These are: bornite, chalcocite, plumbojarosite, mimetite,

pyromorphite, smithsonite, calamine, plattnerite and hisingerite.

Paragenesis

The mineralized solutions possibly emanated from an intrusive

body suspected to be at depth and were introduced into the open fracture

systems. The hydrothermal fluids contained fluorine, gold, silver,

lead, copper, zinc, iron, magnesium, sulfur and perhaps other constituents. 41

Silicate skarn minerals were formed from the constituents of the shale, with the addition of iron and magnesium from the flu id ; quartz and cal c ite were re c ry sta lliz e d , and flu o r ite and su lfid e minerals were deposited.

Koch (1956) suggests that the bulk of the mineral matter at the Frisco mine was introduced at one time and not at different periods. Schmitt (1928) gives three types of sulfide ore: (1) a siliceous lead-silver-zinc type, characterized by massive galena and sphalerite and containing minor amounts of chalcopyrite and pyrite,

(2) a siliceous gold-silver ore, distinguished by the absence of massive sulfides and the presence of silicate minerals such as pyroxene and garnet, (3) a massive sulfide ore with abundant silicate minerals.

With these three types taken into account, Schmitt suggests more than one period of vein filling at Santa Barbara. Scott (1958) thinks that at least two stages of vein filling are represented. His opinion is that the high-temperature silicates with associated sulfides const!tued the initial stage of vein filling; as vein filling progressed, the temperatures dropped, until at a late stage, deposition took place with little or no silicates. Barite appears to be later than the sulfides. A late stage of fluorite is also present. A very late stage of deposition is represented by barren quartz veins that cut the older mineralized veins.

Classification of the Deposits

Allen and Fahey (1957) classified the veins at Santa Barbara as pyrometasomatic replacement deposits due to the presence of bire- fringent garnet associated with the pyroxenes in sane of the sphalerite 42 ore; they also considered that the veins were formed by replacement of shale. Pyrometasomatic deposits, however, seldom have such large amounts of quartz gangue.

Koch (1956), taking into consideration the shallow depth of emplacement, classified the veins as xenothermal, pointing out that the mineralogy is not similar to that of xenothermal deposits.

Scott (1958), following Lindgren's (1933, p. 694) classification, stated that the Santa Barbara deposits should be assigned to the hypothermal class (temperature 300* to 500°c and very high pressure) of hydrothermal deposits.

Taking into consideration the vein characteristics at Santa

Barbara and San Francisco del Oro described in the former paragraphs, these deposits might be considered as leptothermal (Graton, 1933).

The deposit at Parra! seems to agree better with the epithermal classi­ fication. Dr. Wisser (personal communication, 1968) considers the

leptothermal-epithermal range to be correct for the districts.

Suggestions for Exploration

Taking into consideration the persistence of the veins in

strike and depth (some veins are 4.5 miles long and the lowest levels

are 3,300 feet below the surface) the writer has the opinion that it would be in te re stin g to explore the d i s t r i c t in more d e ta il. The

exploration program might be oriented toward the main trend of the

veins (approximately north-south) as well as in a perpendicular direc­

tio n .

On the basis of personal experience during the last summer in

the Santa Barbara area, it is suggested to plan future drill holes in an appropriate manner to cut the veins at some level below 660 feet from the surface (Santa Barbara level equivalent). The objective is taken from the high values present below the 660 level.

It is possible to find within the district other kinds of deposits or, probably, more profitable deposits such as mantos and disseminated mineralization in intrusive bodies. CHAPTER V

METALLOGENIC STUDY

Tectonic History

In the Precambrian and Paleozoic Eras sediments in northwes­ tern Mexico were deposited in an orthogeosynclinal b e lt with two essential parts: a miogeosyncline on the east covering two thirds of Sonora and part of western Chihuahua, and a eugeosyncline on the west occupying extreme western Sonora, the Gulf of California, and part of the Baja California Peninsula.

The hedreocraton was located in the central p a rt o f Mexico and comprised part of northern Sonora, eastern Chihuahua, and an area extending south to Puebla. This Precambrian land was composed of granites and metamorphics.

Another orthogeosyncline of the same age was located at the eastern boundary of the hedreocraton (Huastecan belt). In the area of interest the orthogeosyncline has been called the Jaliscoan belt by DeCserna (1960) (Figure 5). For distinguishing the two different phases in the Jaliscoan belt, DeCserna based his criteria on the rocks and structures in the miogeosyncline, using the earlier studies of King (1939) and Lochman-Balk (1956).

The eugeosyncline, which extended southward and southeastward into Guatemala, was deduced from the presence of metasediments and ophielites of pre-Carboniferous age (Bose, 1905; Webber and Ojeda,

1957) and from the distribution of granitic stocks and batholiths

44 4 5

vv. Huastecan Orthogeosyncline

Ualiscoan Orthogeosyncline

Km s. Approx.

Hedreocraton |:':V:.vi'::| Miogeosyncline

I ■ — ] Eugeosyncline

modified after Guzman and DeCserna.

Figure No. 5 Paleogeographic Map of Mexico During Early Paleozoic. 46

of Middle Paleozoic age in the Sierra Madre del Sur (Late Mississippi an

to Early Pennsylvanian) (Fries, 1962). The metamorphism and the

granite emplacement constitute part of what DeCserna has called the

anatexitic phase of the Jaliscoan geotectonic cycle.

During Middle Pennsylvanian to Late Permian time the sediments were deposited in shallow waters, but at the end of the Permian and

Early Triassic the sediments were gently folded and uplifted, resulting

in block faulting. Fries (1962) named this event the Sonoran Orogeny, which was equivalent in time to Coahuilian Orogeny in the Huastecan

belt and with the late phase of the Appalachian Orogeny of the eastern

United States. The Sonoran Orogeny represented the third phase of

DeCserna*s geotectonic cycle in this orthogeosyncline.

Taphrogenic or block faulting characterizes the fourth phase

in the geotectonic cycle in the area of major interest. Fries (1962)

believed that the first post-Paleozoic (Upper Triassic) sediments

deposited in Sonora, being clastic material, were derived from the

uplifted anticlines and fault blocks formed during and after the

Sonoran Orogeny. The above mentioned sediments overly deformed Paleozoic

rock in angular unconformity.

At the end of the Jurassic a marine transgression began to

take place and became more extensive toward the end of Early Cretaceous;

this obliterated the older structural belts and marked the beginning

of a new orthogeosyncline. DeCserna (1960) has designated this feature

as the Mexican geotectonic belt. It is the best known of the three

geotectonic cycles due to the fact that the rocks and structures

that were deformed during the time of the third cycle are the rocks 47 that we observe today. This belt extends from the United States border to the Guatemalan border covering practically all of Mexico.

During the orthogeosynclinal phase, the eugeosyncline occupied approximately the present site of Baja California, as shown by the d istrib u tio n of graywacke and o p h io lite (Bose and W ittich, 1913;

Beal, 1948; Mina, 1957), whereas the miogeosyncline occupied practically all the rest of the country (Burckhardt, 1930; Imlay, 1944). The a n ate x itic phase of th is cycle took place a t the end of Cenomanian time with the intrusion of great granitic batholiths in Baja California

(Beal, 1948) and in a belt extending about 150 kilometers inland from the coast (DeCserna, 1956, 1957, and 1958; Pantoja, 1959). This intrusive belt now forms the Sierra Madre Occidental. Probably this land began to be uplifted in a uniform manner during the late Jurassic.

During Cenomanian time the u p lif t was more rapid due to the emplacement of the in tru siv e s. The S ierra Madre Occidental seems to be located along the contact of the miogeosyncline and eugeosyncline elements of the Sonoran geotectonic cycle and therefore might have a close relationship.

The anatexitic phase of the latest cycle can be correlated with the Santa Lucian orogeny. Some of the intrusions of the anatexitic phase cut Lower Cretaceous limestones and have produced contact metamorphic iron deposits (E. Mapes, personal communication in DeCserna, 1960).

The uplifted areas were subjected to erosion and the material derived from them was deposited in the miogeosyncline forming the clastic flysch wedge or pre-orogenic sediments, which together with the eugeo- synclinal sediments were folded during Early Eocene time (Bose and 48

Cavins, 1927; Muir, 1936; Helm, 1940; Fries, et.al., 1955; C. Fries

Jr. personal communication to DeCserna, and DeCserna, 1956). This deformation, constituting the orogenic phase of the latest geotectonic cycle, has been named Hidalgoan orogeny. It seems to be approximately correlative with the Laramide orogeny of the western United States

(DeCserna, 1960).

The taphrogenic phase took place during Middle Eocene to

Oligocene. The post orogenic debris or molasse deposits of continental origin accumulated in the central and western parts of Mexico (Salas,

1949; Guzman, 1950; Edwards, 1955; Fries, 1957; DeCserna, 1956 and

1958; Pantoja, 1959), while marine deltaic deposits were laid down in western Baja California (Beal, 1948; Mina, 1957). The continental post-orogenic debris was covered by subsequent volcanics during late

Oligocene-Miocene time. The volcanics in turn were tilted and partly eroded during the Pliocene. Fries (1962) stated that in this epoch there was additional block faulting which involved normal faults.

At this time, there was subsequent magmatic activity consisting largely of igneous extrusives with a few intrusives.

A final volcanic sequence of basaltic composition and of limited distribution is considered to represent the end of the geotectonic cycle and the consolidation of the Mexican stru c tu ra l b e lt (Guzman and DeCserna, 1963).

Tectonic Concepts Applicable to Metal!oqeny

For a long time scientists have tried to explain the difficult processes of mountain building and its related phenomena, proposing a variety of theories that in many cases explain some features but 49 overlook others. With passing of time, the concepts have been refined and coupled with new data obtained in recent years.

The most useful current theory for an explanation of mountain building relative to metal!ogenic belts involves the concept of convec­ tion currents and certain associated features such as ocean ridges, sea floor spreading, island arcs and continental drift. These features and concepts have been summarized in excellent papers by Schmitt

(1966) and by G uilbert and Sumner (1968).

Convection currents are thought to arise from temperature differences between the lower mantle and the base of the crust. At the place of emergence they create a rise or ridge. These features are continuous elements in all of the major ocean basins of the world

(Cook, 1962; Schmitt, 1966). The closest ridge to the subject area, and thus with a very strong influence in the tectonics of Mexico, is located in the vicinity of the Gulf of California. The ridge disappears under the continent and reappears again as an oceanic feature off the coast of Canada. The continental area might be related to the present active zone of the San Andres Fault. It has been correlated or identified by its association with the seismic belt and the high-heat-flow characteristics of the crest (Menard,

1964). The East Pacific Rise, another major feature, is cut by several fractures, oriented roughly East-West and displacing the original position of the crest.

The upward movement of mantle and c ru st o rig in atin g a t the crest of the ridge is thought to involve a displacement of material.

This action has been designated as sea floor spreading. It is 50 supposed by Orowan (1965) that a non-Newtonian type of plastic flow, such as is observed in the hot creep range of metals, must be responsible for the flow phenomenon. The measurements o f higher values of heat flow at the crest of oceanic ridges support the spreading sea floor concept.

It has been pointed out that in the ridges there would be an upwelling of material with a high content of metallic mineralization.

Bostrom and Peterson (1966) collected data showing anomalously high

Fe, Mn, Cu, Co, Ni and Pb contents in bottom sediments on the present

East Pacific Rise crest and on its immediate flanks. Water samples collected far away from the crest (more or less 1200 miles) were relatively clear in both directions from the ridge, but as the samples were taken closer to the crest they began to show metal oxide precipitate, with the metal enrichment being highest in the crestal area. There is a marked correlation between high heat flow and the enrichment areas. It is believed that these precipitates are caused by ascending solutions of deep-seated origin, which are probably related to magmatic processes at depth. The same authors consider the rise of a zone of exhalation from the mantle of the earth, and these emanations could serve as the original enrichment in certain ore-forming processes.

Island arcs and associated trenches are the counterparts of ocean ridges. Guilbert and Sumner (1968) discussed the situation of deep oceanic trenches on the oceanward side of Island arcs, and mentioned that earthquake foci deepen on the continent side of the arc down to 400 miles (700 kilometers). An example of an island arc is the island chain of Japan, with oceanic deeps to the east. 51 extending south past the Phi Hi pines, then east past Indonesia. Oliver and Isacks (1967) in their studies of island arcs have found that the oceanic crust is apparently dragged downward under island arcs by convective movement of the earth's mantle.' This serves to explain the consumption of crust in a way complementary to its formation along oceanic ridges.

Continental drift is very closely related with what Schmitt

(1966) has named transverse orogeny. This orogeny consists of series of faults, lineaments or belts oriented approximately east-west and

appears in several parts of the continent. The more interesting lineaments fo r our study are the Texas, Parras and Mexico City Belts

(Figure 6). The Texas lineament is correlatable with the Murray frac tu re zone. The Mexico City lineament (tran s-v o lcan ic axis) is correlatable with the Clarion fracture. The Parras lineament may be correlatable with another ocean fracture without a specific name; this lineament crosses the Hawaiian Islands and there it is known as the Molokai fra c tu re zone. The name Parras lineament is proposed for our area. Schmitt (1966) has suggested that this system may be a fault zone of continental proportions along which a drifting of the continents occurred in the area from northern Chile to the northwest. These transverse lineaments seem to have been reactivated a t various times since the Precambrian and seem to have a deep-seated o rig in .

This enormous mass movement may be re la te d to driving movements of the earth's core and geoidal compensation as well as convection c u rre n ts. 52

Waso.tch Mendocino Pioneer •• Mucr.ay.-----.v San Andreo

Molokai- Parras Clarion Miles

Eosle r

...... Faults or bound­ aries of struc­ tural zones. ------Axis of deep.

Crest of East Pacific Rise (Menard.) modified after H. A.Schmitt

Figure No.6 Transverse Lineaments. 53

It appears that in certain epochs the internal forces of the earth have been stronger than at other times. This suggests a cyclic factor, in association with orientations of the magnetic pole.

This periodic reactivation may be associated with DeCserna's geotectonic cycle in Mexico which consists of the following points:

(1) an orthogeosynlinal phase (eu-and miogeosynclines) with or with­ out initial magmatic activity, (2) an antexitic phase consisting of batholith emplacement with attendant regional metamorphism in the eugeosyncline and deposition of a clastic or flysch wedge over the mi ogeosyncline, (3) an erogenic phase consisting principally of the folding and thrusting of the sediments of the miogeosyncline together with the clastic or flysch wedge against the foreland, and

(4) a taphrogenic or block-faulting phase accompanied by ( a) accumulation of post-orogenic debris or molasse, (b) subsequent magmatic activity consisting largely of igneous extrusions with fewer intrusions, and

(c) final magmatic activity consisting of igneous extrusions. The interval of time involved in these four phases is a function of the time required for an orthogeosyncline to become consolidated.

The geotectonic cycle appears to be related to the rotation of the earth's core, which in certain positions and certain times has more influence on convection movements.

The S ierra Madre Occidental seems to follow G u illu ly 's theory

(Guilluly, 1965) in its formation. This author suggested that the eugeosyncline sediments of Phanerozoic age were deposited on an oceanic crust while the miogeosyncline developed on a continental crust, and 54

that the junction between them was somehow the favored site for retention

of plutons within the crust. The accumulation of the intrusive mass

is explained as an ensim atic segment of the cru st th a t became welded

to the continent, "an event unique in Phanerozoic history", (Guilluly,

1965).

The source for the granitic bodies, some of which have roots

50 kilometers deep (Pakiser, personal communication to Guilluly, in

Guilluly, 1963) and which are concentrated at the boundary of the eu-

and miogeosyncline it is believed by Guilluly (1965) to be due to the movement of sialic masses that have been brought together by convection

currents at the edge of the miogeosyncline and that the plutons were

derived from them by syntexis and palingenesis as the eugeosyncline was crowded ag ain st i t .

The junction o f the b e lts on the orthogeosyncline seems to

have been a reactivated belt along the Phanerozoic period and to

be the direct source and cause of the formation of the Sierra Madre

Occidental and mineral deposits in it.

Metal Distribution Pattern

The d is trib u tio n o f s ilv e r deposits in Mexico can be categorized

into five main belts (Figure 7). Among these belts, one in particular

is especially conspicuous and easy to distinguish. This belt is

located in the Sierra Madre Occidental and here will be called Occidental

Belt. Two more belts are roughly parallel to the first one, and

are designated as the Central and Oriental belts. Two additional

transverse belts run in an east-west direction. The northern belt 55 generally coincides with the 25th parallel. This will be called

Parras Belt. The southern belt is located near Mexico City. The main characteristic of this latter belt is the abundance of basalt, therefor it is designated as the Volcanic Belt.

The term belt refers to a wide zone that can vary from 50 to 250 kilom eters or more in w idth.

Occidental Belt

It is easier to distinguish the Occidental Belt than the rest of the belts due to the great concentration of deposits. This zone constitues a straight line from Nogales, Sonora in the north down to the city of Colima and probably continues into the Pacific

Ocean.

Some of the main mines located along this belt from north to south are: Ocampo (A-3)1, Candamena (A-5), Uruachic (A-6), Batopilas

(A-ll), Dolores (A-12), Tamazula (A-25), Topi a (A-26), San Dimas

(A-27), Concordia (A-56), and Etzatlan (A-45). Cananea (A-57) is located at the junction of this belt with the Central Belt.

Central Belt

The Central Belt is recognized approximately 70 kilometers to the east of Nogales; it extends south passing through Parra! CA­

TS, A-14, A-15, A-16), Zacatecas (A-65), Guanajuato (A-36, A-37,

A-38), and Taxco (A-39). Cananea (A-57) in the north, seems to belong to this belt. Although the concentration of mines in this belt is not as intense as in the Occidental belt, the well known districts

1. The terms within the parentheses are the classification and identification of the mine or district in Figure 7. 56 along it speak for themselves.

The Central Belt has a trend more eastwardly in the north portion and for this reason it intersects the Occidental Belt in

Southern Arizona. These two belts are, in addition, intersected in Arizona by the Texas Lineament (Figure 7).

Oriental Belt

The Oriental Belt is probably the least conspicuous from the standpoint of deposits along it, but this may be due to the lack of exploration. In the states of Queretaro and Hidalgo the deposits are very clearly aligned along the belt. For this reason we should not underestimate the importance of the belt in future exploration.

The deposits that belong to this belt are: Sierra de Los

Lamentos (A-24), S ierra Mojada (A -l), Melchor Ocampo (A-66), Noche "

Buena (A-67), Mazapli (A-68), Concepcion del Oro (A-69), Charcas

(A-52), and Pachuca (A-41) and Real del Monte (A-42).

The Concepcion del Oro District is located at the intersection of this belt with the Parras Belt. Pachuca-Real del Monte District

is at the intersection of this belt with the Volcanic Belt.

The Central and O riental B elts, in an opposite re la tio n sh ip

to the junction of the Occidental and Central Belts in Arizona, come

to join in the states of Morelos and Oaxaca, the junction having

a climax in the Pacific Ocean, probably not far from Puerto Angel

(Figure 7).

Parras Belt

The Parras Belt runs roughly east-west passing close to the

city of La Paz in Baja California, into the gulf, and reappearing north 57

of Culiacan, where it intersects the Occidental Belt. Farther east it cuts the Central Belt near Cuencame, Durango (A-35). The Oriental

Belt is intersected by the Parras Belt at Concepcion del Oro; the

Parras Belt continues east into the Gulf of Mexico.

The deposits located along this belt are: Tamazula (A-25),

Topi a (A-26), Santiago Papasquiaro (A-29), Promontorio (A-30), Velardena and Pedricena (A-34), Cuencame (A-35), and Concepcion del Oro D istrict

(A-66, 67, 68, 69).

Volcanic Belt

The Volcanic Belt is located near the 20th parallel. The main feature is a thick sequence of recent basaltic lavas, which masks all evidence of underlying mineral deposits. The Volcanic

Belt passes south of Guadalajara, along Lake Chapala. Where this belt intersects the Oriental the very important Pachuca mining district is located. The belt goes into the Gulf of Mexico and appears to emerge in the Yucatan Peninsula near the city of Campeche.

Very few mines are located within the Volcanic Belt due to the thick basalt cover. Mines that bear mention, however are: Ayutla

(B-40) and Atemajac de Brizuela (D-167) around the intersection of the Occidental and the Volcanic Belts; Jerecuaro (D-lll), El Oro

(A-46), Tlalpujahua (A-47), and Angangeo (A-48) around the intersection formed with the Central Belt. Pachuca-Real del Monte (A-40) is located, as has been mentioned before, at the intersection with the Oriental

Belt. 58

Secondary Alignments

Considering the state of Chihuahua in some detail, it appears that there is a close relationship between the sedimentary structure, the marginal fault on each side of the bolsones, the intrusive bodies and the location of the mining districts (Figure 3).

The author has identified six interesting lineaments which are more or less parallel. Another observation is that the distance between the first two lineaments is greatest in the western part and decreases toward the east.

These lineaments, for simplicity of identification, will be called A, B, C, D, E and F. The letter A identifies the first belt on the west. The letter F, the last one on the east. The rest of the letters correspond in respective order to the rest of the lineaments between the two f i r s t mentioned.

Lineament A includes ten mines which are from north to south:

San Pedro Corralitos, Casas Grandes, San Joaquin, Cusihuiriachi,

Magisstral, Satevo, Parra!, San Francisco del Oro, Talamantes and

Santa Barbara. This lineament appears to be part of the Central

Belt described before.

Lineament B is located 70 kilometers to the east of Lineament

A. Lineament B contains eleven mines. They are: Los Borregos,

Cononia Enriquez, Terrenates, Coyami to, Ojo de Laguna, Sierra del

Cuervo, Terrazas, Santa Eulalia, Naica, Almolaya and Los Reyes.

Lineament C is located 45 kilometers to the east of Lineament

B. Lineament C has six mines: La Union, Las Damas, Sierra de Gomez,

El Morrion, Amargosa and La Ojuela. 59

Lineament D is 35 kilometers to the east of Lineament C.

The mines are: Samalayuca, La Gloria, Placer de Guadalupe, Plomosas,

C arrizalillo, Siete Tinajas, and Los Organos.

Lineament E is 32 kilometers to the east of Lineament D.

There are along Lineament E six mineral deposits, which are: Los

Lamentos, Laguna Salada, Tosesihua, Las Vigas, La Perl a, and Jaco.

Lineament F is approximately 25 kilometers to the east of

Lineament E. This lineament only has two mines; these mines are:

Aurora and Cuchillo Parado. Some other lineaments can be traced but the author considers the lineaments described as the more conspicuous.

Explanation of the Ore Deposits

In the preceding section, some of the main tectonic concepts applicable to the explanation of the mineralization pattern were given. These concepts can now be applied to our specific area and to the large mineralization belts across Mexico.

The source of the minerals has not been defined as yet, but what is clear is that they come from a deep origin (Guilbert and

Sumner, 1968). This source may be located in some place in the mantle.

The previously described mineralized belts and lineaments have several common features which are described below.

The excess of mineralization in the Occidental Belt is probably due to the combination of two favorable conditions at the time of the formation of the Sierra Madre Occidental. These two conditions were the accumulation of the sialic masses at the boundary of the eu-and mio geosyncline of Phanerozoic age, due to convection currents

(Guilluly, 1965). This boundary corresponds with what now is the 60

Sierra Madre Occidental. Probably this boundary may be considered also as a deep-suture which during certain times has suffered more intensive activation, giving, as a result, a tapping action for ore sources at depth.

At the time of the accumulation of the sialic material, i t is logical to assume that some ore was taken from the mantle (?); it follows that later, with the action of incompletely known processes such as syntexis (?), the ore deposits were emplaced. These deposits are located especially along the crest of the main welt (Wisser,

1966).

A reason for mineralization along the Central and Oriental

Belts appears to be that these two mobile belts were reactivated during Phanerozoic time and can be considered as related to deep- fractures. These two belts coincidently are found along the borders of DeCserna's hedreocraton (Figure 5). From this "coincidence" we can suggest that these two belts have been reactivated since Precambrian time, resulting in the deposition along them of very important ore bodies such as Pachuca, Taxco, Guanajuato, Zacatecas, Parra!, etc.

The Parras and Volcanic Belts are correlateable with the

Molokai and Clarion-Rivera fault zones of world-wide extent. It has been pointed out by Guilbert and Sumner (1968) that these fault zones are almost certainly related to the Texas Zone. These zones extend to great depths in the crust also and may act as tapping channelways

from deep ore sources.

The secondary lineaments are considered to be the result of basement faulting during the Eocene, which in turn was a consequence 61 of the position of granitoid intrusives along the Pacific coast of

North America emplaced at the end of Jurassic time. This magmatic activity culminated in the eastern margin of the Cordillera with basement faulting (Lindgren, 1933; S tille, 1940). This compression flowing toward the east caused the uplift of Paleozoic rocks in the

Sierra Madre Occidental area and originated small basement folds.

When the uplift was large enough in the west, tension in the external part of the basement led to faulting (DeCserna, 1956).

The reduction in distance between the secondary lineaments is caused by the increasing frequency of the basement folds which were controlled by the roots of the craton; in other words, the basement folds, far from the craton are wide and symmetrical but as they approach the craton, the frequency increases, thus bringing their axes closer to each other. When these folds were subsequently faulted the intrusive bodies and mineralized solutions used the fracture planes to rise to the surface. The secondary lineaments support DeCserna's (1956) ideas, who suggested that the Mapimi (La Ojuela), Concepcion del Oro and Catorce mines are located over basement faults. The basement fault-mineral belts concept is shown in Figure 3. CHAPTER VI

EXPLORATION APPLICATIONS

We have passed the time in history in which most ore bodies were discovered in outcrop and when it was possible to see their characteristics manifested on the surface. The people who made such discoveries were not geologists; they were.explorers.

In recent years the United States, Russia, Australia,.and

Canada have increased their mineral production from discoveries of new ore bodies. These countries have used scien tific exploration methods for these discoveries, selecting for exploration some specific areas, which have more probability to be mineralized than other areas.

These areas have been called metal!ogenic belts. In Mexico it is now time to start with scientific and systematic exploration along the metal!ogenic belts, the main characteristics of which were described in the two former sections.

Each of these belts constitutes a potential site for mineral deposits. It is the opinion of the author that each one of the belts has the same intensity of mineralization, with the possible excep­ tion of the Occidental Belt which was affected by two mineralization processes.

The mineralization content of each belt increases when there is an intersection of two belts and even more mineralization may occur at the intersection of three belts (Occidental, Central and

Texas Belts). This triple-intersection occurs only in southern

62 63

Arizona and probably is unique in the American Continent. It can be used to explain the great concentration of ore bodies in this specific area. At this place the Central Belt is correlatable with the Wasatch-Jerome Belt and a little bit to the east the Oriental

Belt is correlatable with the Front Range Belt of the southwestern

United States.

A very interesting intersection occurs near Ciudad Juarez,

Chihuahua, where the Texas Lineament intersects the Oriental Belt.

It is interesting because the Texas Lineament has been proposed by several geologists as a very favorable site for the location of porphyry copper deposits (Guilbert and Sumner, 1968). The possi­ bilities of success in this search will be increased at the inter­ section with the Oriental Belt.

The Cananea mine occurs at the junction of the Occidental and

Central Belts. It is interesting to note that a junction of belts can be as important as on intersections.

Where the Parras Belt cuts the other belts, important mining districts are located: Topi a is at the intersection with the Occidental

Belt; El Oro and Inde are at the Central Belt. Parra! and Zacatecas, districts along the Central Belt, would also be considered within the influence area of Parras Belt. If this assumption is correct, this could explain the east-west fractures in Parra! District.

Another very important area is located along the Volcanic Belt.

Between the cities of Morelia and Pachuca we have the junction of three belts, a similar factor found in southern Arizona. The belts are the

Volcanic, Central and Oriental lineaments and if the geological rules 64 are the same we can find the same concentration of mineral deposits as in southern Arizona. The mode of occurrence of the minerals will not necessarily be the same as that in Arizona.

Another junction occurs in the state of Oaxaca. This junction involves the Central and Occidental Belts; the intersection is located in the Pacific Ocean not far from Puerto Angel.

The reason that the extension of the belts into the oceans has been mentioned is because in future years there will be a necessity to explore these belts along the bottom of the oceans for the purpose of mining under-sea mineral deposits. The under-sea area of greatest interest under Mexican control is near Puerto Angel. SELECTED BIBLIOGRAPHY

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Fries, J r . , C., Hibbart, C.W., and Dunkle, O.H., 1955, Early Cenozoic vertebrates in the red conglomerate at Guanajuato, Mexico. Smithsonian Misc. Coll., V. 123, no. 7.

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______, 1966, Yacimientos de plata de Mexico, Inst, de Geol. U.N.A.M., map.

Graton, UC., 1933, The depth-zones in ore deposition: Econ. Geol., v. 28, No. 6, p. 513.

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-T" I 1 14 1 1 V no- 10 9 * 1 0 8

GEOLOGIC SETTING OF ORE DEPOSITS IN CHIHUAHUA, MEXICO JOAQUIN E C H A V E Z.I968 Geology compiled by Ramirez and Acevedo, 1956- Geologic settir of ore deposits by Carlos and Luis Garcia Gutierrez, 1964.

FIGURE No. 3b

k ilo m e te rs

LEGEND

Quaternary ------C o n ta cts | k» | Cretaceous upper Inferred Contacts no~l Cretaceous-lower ------Faults — -I— Anticlines j Jurassic-upper ---- 1—- Synclines T riassic — P— O v ertu rn ed Fold River I mem | Perm ian • - Arroyo I' N* 1 Pennsylvanian » Astronomical Control Station |iy-car| Perm ian & Carboniferous <» City » Town • Ranch jSiiiii Igneous Intrusive ------Paved Road ——— Improved Dirt Road Igneous Extrusive ------Dirt Road ------Railroad + International Border + -4-4 State Borders

Types of ore deposits □ Manto deposits O Disseminations In sandstone A Metasomatk replacement of Igneous and sedimentary rocks O Fissure and/or fault type deposits O Pyrometamorphlc deposits O Secondary deposits

r - - '* ------'•kN. r*-*" □ Tres Morios

. wmam m i*- / H&S’ ^ (o U

oo

o lO o

26*56 aEI Paso

.dhtht^ahua

miles 9_ 500 kilometers 1000 (O io o oi Jimenez* .Palmilla to Mexico 27' City l- mme_ ^"^ rral :o Del Oro ___jta Barbara M s E3 Azules o kilometers

INDEX MAP

26°53

(after Giesecke, I960)

San Fco Del Oro

26*50 LEGEND

j Andesite intrusive Veins

L v i Andesite flows 7>— 1 Rhyolite dikes

[L.... 1 Rhyolite flows —------Faults

1 i ■ j Shale, Limestone ^ ^ ^ Main arroyos

Basalt Contacts and dips

Granite llllU# Town

^ 2 3 Aluvium • (81 X Mine

(l) Frisco South (g) La Paz

@ Granadena (Tp) Hidalgo

(§) Remedies (T T ) Esmeralda

(4) Cobriza (@ La Prieta (after Koch,jr. and Kierans,I956) Area "A" (after Echavez,l967) (§) Mina del Agua (|3) El Vesubio 26*47 (6) Alejandria (j4 Veta Grande 26*471

® Tecolotes (f5) Vesper

@ Coyote ([6) S. Patricio

GEOLOGIC MAP

Portions of the Parral District, Chihuahua,

MEXICO

scale 1 : 50,000 Compiled by J. Echavez, 1968

Figure No. 4

26° 44' 102° 100° 98° 96° 88° 117° 116° 115° 114° 113° 112° 111° IIOe 109° 108° 107° 106° 104° 103° 86°

Clossifio- Clossrfio- C tossifio- " Nome or C ount/ . .S to le Nrsnse or C o u n ty N am e or C o u n t y S t o l e County Stot • Nome or County jStofe C la ssific­ C la s s ific ­ otion .S lo ts otion atron Nome or County, Stole Nome or County Slate atio n atio n P - >1 twmdgtq do C^Nw 0 - 71 Hgo 0 248 Son Juen Vieio Lo Forteleze 02-354 Cei Villa Coronado Chih 0 -142 Tosquiiio Mme Tasaial Sen. E - 55 Son Aren Nepewueeeo Chlh E - 157 9 - 32 lUleRueU* 0 - 72 07-143 Mgo 0 -249 Cuyomecolco, Cuicolldn 07-333 Sierro de lo Cor bower o Son. Reoliio Col Lo Higuora Chih Zones do Cttoncio y Sonto Ro*o E - 56 Chih C -158 Tloponcmgo Oo p 9 • >3 Pont epee Ch* 07- 73 Lo* Ang*ti* 0 -144 Hgo 0 250 Jumllehuoco 0 356 Puertoc.ro Chih Aclopon E - 57 La* Torres Chih E - 1 59 Tocomaxftohuoco Oo* 6 - »R Cegeeete Chit 07- 74 Cabal li to* Hgo 0 -251 Mimiepec y Los T#,ocotes D 357 Oiv.soderos Chih 0 -145 HuOSCO E - 58 Zono de los Yedros y Tunas E •160 Coicoydn Oo * 0 - 33 Am ego Chit 07- 75 Oconpo Mgo 0 252 Numiho Pg* 0 -146 Aguo Blanco 0 356 P.n.io E - 59 Torohumoro Chih. E - 161 Son Miguel Peros Rebeco 9 - id Tgegisco ngo 0 -253 Coltodo de Lo Rosa Oo R Chit 0 - 76 Villa Hidalgo Dgo 0 -147 M lllpic 0 359 Tbnuco E - 60 Bollezo: Guopeoori Chih •162 Hgo 07-254 Son Mateo E Mmo Sonlo Morgor.ta 0 0 F 9 - 37 Chicewucele Chi# 0 - 77 Son Bortolo y Guadalupe MontoAo 0 -148 Cuautopoc 07-360 Son E - 61 Dgo D -255 Cocooiepec Lo Sol*dad. Lo* Olivos Chih E -163 0 o x 9 - i d Aeoceyegue Poevenir Chit Hgo 0 - 78 Son Lun del Cordero Dgo 0 -149 Municipio de Tepeii del Rio D -361 Zona de Polmo Son E - 62 Roocevolles Ch.h E - 164 Tlocofepee Hgo 0 -256 Sonto Ines Don 9 • id Chguerrie y EJ Pxvurvr Chu 07- 79 Bello Vino Dgo 0 -ISO TolCOyuCO 0 362 Am or il los Son E - 63 Zono di Volsequ.llo Chih E -165 Hgo 0 257 Voldef lores E - 64 Ofln 0 * Mazapo de Modero Chi# 07- 80 Son Gregono 0 -151 Mumcipio de Apam 0 -363 Mozoton Son Adorgos, Soli,Hero, etc Chih E -166 Yosonotii Chi* Jol C7-256 Sto Cruz Mimiepec 07-364 Son Juon de Dios Son E - 65 El Cormen * dt Mutuzmtio 07- 8 1 Sauces 0 -152 Dos Reyes Ogo E - 167 Tocohuo Oon Chih Jol 0 -259 Joluzo 07-365 Chipionero Son. E - 66 Copalqum 8 - 4 2 Sen Pedro 07- 8 2 Son Nicola's Dgo 0 -153 Dgo E -1 66 Lo Providenc e 0 0 B Chih JO I 0 -260 Sto Color,no Ti|qu,opon Palmar Son E - 67 Zono de Metal** 8-43 Ceeee Grondo- 0 83 Son Lucas Ogo 0 -154 •ifttlohuocan D -366 Ogo. E - 169 Jolteptc Oo x Chih 0 -261 El Vorgel * ^44 aosoemr 0 - 8 4 Conefo Bufos de Coneto Ogo 0 - 155 Teocoi tiche Jol 07-367 C.eneguifo, Lo* Toios, v.dolln Son. E - 6 8 Tohuehueto Ogo E - 1 70 Teoz ocooico n fl. Son E - 69 Pot 7470 8 ' 45 Le Escondido Chih 0 - 8 3 Son Lorenzo Ogo 0 -156 Encornocion Jol 07-262 Zono de Guelovio y Son juonico 0 7 368 BoRoncrte Ogo E - 17 1 Cohuocud 0 o * 8 - 4 4 Mugdelono y Klondyk* Chih 0 86 JO 1 0 *263 Zono de Guerggoti Petopo y El Borno 07-369 Son Jose de P.mos Son E - 70 Municipios de Lerdo y Gomez Polocio -172 - PeAon Blonco Dgo 0 157 Comonjo LO Compechono Ogo E Yuguf i Chih. JO 1 07-264 Zono de Guichicovi Son E - 7 1 Norolol 0 - 4 7 C errlze 0 - 8 7 G uornom ey Ogo 0 -158 Son Diego 0 -370 Polo Blanco Ogo E - 173 El Piojo 0 o x 9-48 Tocachi Chih Jol 0 -265 Son Miguel Chlmolopo Son E - 72 Sionon •174 07 88 Guadalupe Victoria 0 -159 Alengui HO 0 -371 Ague Col.onto Dgo. E Ayoqueico Hq . Chih 0 -266 Plan Mmo 6-49 M etochic 0 89 Sonlo Clara 0 -1 6 0 Jol 0 372 Torcon Son. E - 73 Guosimillos y Bojodo Ogo. E -175 Rio Duice Oo* Chih Jol 0 -267 Son Pedro Cootlon Son. E - 74 Birimee 6 - SO Cheiomo 07- 90 Ventonos Ogo 0 -161 At eng o 07-373 Las Leio* Ogo. £ - 1 76 Totomochopo Oo* Jol 67- Si Leo Vtgei Chih 0 - 91 Negros y Picochos 0 - 162 Zonos de Son Joaquin y Pomoso 0 -268 Lo CompoRio 07-374 Borronco* Son E - 75 Coneios Dgo E - 177 Son Bernardo Mimiepec 87- S 2 Son Nicolds Chih 0 - 92 Mumcipio de Du'ongo Dgo 0 -163 Cuoutlo Jol 07-269 Yogono 0 -373 Rio Chico Son E - 76 Min,lo* Ogo E -178 Nuxao Oo* 0 -270 Cootecos Altos 97- 5 3 Morcova Chih 07- 93 Ogo 0 -164 Jol 0 -376 Rosiros Son E - 77 Llonitos Ogo. E -179 Guojolotipoc Oa « 9? 5 4 Petrero, Mpio de Ocampo Chih Jol 07-2 7 1 Zono de Ouechopo y Lochidovo 0 -9 4 Vento Verde Ogo 07-165 JuChi llo'n 0 -377 Tobeio Son. E - 78 Son Andres de lo Sierra Ogo E • I 80 Guild On r 9 3 3 Or. Belieone Dominguez Chih 0 - 95 Ammos 0 -1 6 6 Son Martin H-dolgo Jol 0 -272 Lochigollo 0 -378 Mumcipio de Nuotobompo Son E - 79 Borronco Hondo Ogo E • 181 Magdalena Tetipoc Oo* 97* 56 Rose lei Chih 07- 9 6 Cajon Ogo 07-167 Aiemoioc de Bnzueio Jol 0 273 Mimtequillo 0 -379 Son Francisco Son. E - 80 Borrstero* Ogo. E -182 Guelovi lo Om uol 9 - 5 7 Juhmes : Chonoii. Guadalupe, etc Chih 07- 97 Comi tolpo Dgo D -168 Jocoiepec 0 -274 Zona de Imioltepec 0 -380 V.llogran Tamp* E - 81 Sauces Ogo E - 183 Ixtepeji On, 9 - 5 6 Espfritu Sonto Chih 0 - 98 Mezuuiiol Ogo 0 -169 Mpio de Chopolo Jol 0 -275 Tlocuilolepec 0 -381 Jimenez Tamps E - 82 Boil* Ogo E -184 Sosolo Oo* 9-59 Lot Animas y Sonto Roto Chih 07- 99 Matoio'n Ogo D -170 El Limon Jol 0 -276 Jolopan 07-382 Municipio de Ciudad Victoria Tomp* E - 83 Huohuopom y Son Francisco Ogo E -185 T lo xi 1 o Oa * Chih Union de Tula Jol 0 - 6 0 Botuchique 0 • 100 Son Po’nciO Ogo 0 -171 0 27 7 Huouchmongo 0 -383 Bustamante Tempi E - 84 Gavi lanes Ogo E -186 Jolt tonguts Oo* 0 - 6 1 El Limon Chih 07-10 1 Bufo del Leon Ogo 0 -172 Son Rofoel Jol 0 -278 Son Pedro 0 -364 PolmiHos lamps E - 85 Potnllos Ogo E - 187 Yoreni 0 o* Eiutlo Jol 07- 62 Cobrizo, Aguo Colienli Chih 07-102 Dr Hernandez Aivo'ez Lo Providenc-o G'o 0 -1 7 3 0 279 Villa Jua'rez 0 -385 X.colencoM Ton.pi E - 86 Ogo E -1 8 8 Ou.otepec Oo* 97- 6 i Uruopo Chih 0 103 Son Felipe D -174 El Grullo Jol 0 -280 Chignohuopan 0 -386 Antique Morelos Tempi E - 87 Guadalupe Victoria Ogo E - 169 Mocuiltionguis Oa x. Tonoyo ) * 6 4 Lluvio de Oro Chih 0 -104 Leon Veio de lot Gigomet Gio 0 -175 Jol 02-281 location 0 -387 Los Mmos y Zomelohuocon Ver. E - 8 8 Hueiomolo Ogo E -190 C ocoiotepec Oo* 0 -176 T-oxcocuesco ,0 - 6 5 Bosuchic Chih 0 - 105 Tierro Blonco G »o Jol 0 -282 Ahuocolldn 0 -388 Tolofilo Vcr E - 89 T lochiquera Gio E - 19 1 Zono de Taboo, Zola go. Too L o r^o y 0 -177 Son Gabriel Jo 1 9-66 fhatrero Chih 0 -106 Arteogo Glo 0 283 Zopotitldn D -389 Aclopon Ver E - 90 Santa Rosa Gto. Vtlio Aha Oo, 0 178 Ouifupon Jol - 29° 9-67 Nonoavo t 0 - 107 Cuero mo ro G to 0 -284 Coetzolo 0 390 Chocoman Ver. E - 91 Dolores Hidolgo: S Anton de las Mmos Gto. E -192 Lolopa Oa* 0 .179 Mpio de Cihuo'Ion ^P7- 6 6 Boquinochic Chih 0 108 Municipio de IrapuO'O G'o Jol 0 -285 Xochiopuico 0 -391 Sonto Rito Zoc. E - 92 Victoria Gto E - .93 Toleo de Costro Oo* Chih 0 - *80 Copolo U * 69 Santa Ana 0 -109 Mumcipio de Son Miguel de Allende G'o JO 1 0 -286 Zocopoomllo 07-392 Municipio de Rio Grande Zac E - 93 Gallo Gro. E -194 Zono de Zocotepec - Joyocoiepec Oo* Chih 0 -161 Zopo'iltic zono oeto Sierro del Nevada Jot 0 -2 6 7 Tenem* lo 0-70 Cerro# do Sant^ Ana 0 -110 Comonfort 0 -393 Jimenez del Teui Zoc E 94 Ajuchitldn Gro E -195 Lochiguiri Oo* 0 -182 Tonilo Jol Dill £L° 0 -288 Imcomoslitlon 0 -394 Volporaiso Zoc. E - 95 Zono de Tlochopo y Son Vicente Gro E -196 E co.epee Tuspon j 0l Oulces Nombres 0 -289 Ajoiullo 0 -395 Zac E - 96 Jocotitldn - N oil epee Gro E - 197 Oo* Tecolilldn j 0i Lo Union 0 29v Chilchoilo 0 -396 Monte Escobedo Zoc E - 97 Coxco t Ion G r o E - 198 Zono de Zono epee Oo* Son Lucos Manuel M Oieguez j 0 i 0 -291 TeoMoco 0 -397 Cuauhtemoc Zee. E - 98 Tioimelec Gro E - 199 Cuyooco Pue Tiopehuolo, zono de Los Froquos J,lotion de los Dolores Joi 0 -292 izucor de Matamoros 0 -398 Villa Gonzalez Ortega Zoc E 99 Teteio del Rio Gro E -200 Zoutla Pue Coizomoio Sierra de Ahu, |uiio Jol 0 29 3 Ch. naut lo Tomellu 0 -399 Nona de Son Miguel Zoc E -100 xochipalo G ro E -201 Tlotlouquitepec El Rosono Pue Mpio de Pedro Ascencio Aiquicros Srorro de Teeozotion Met 0 294 Cooyuco D -400 Teui de Gonzalez Onego Zoc E -101 Jocala H go. E -202 Litres Los Tojos Pue Cue’zoio Inopantongo m,, 07-295 Tehuilzmgo 0 -401 Municipio de Jolpo Zoc E - 102 Piso*lores Hgo E -203 Son Nicolas Buenos Aires Pue Ocotepec Me, 0 -296 Zono de Imcomilpo 0 402 Juch.piic Roncho de Cedros, Jesus Mono Zoc E -103 Hgo E -204 Tehuocdn Pue Buenovisfc de Cuellor Pmohuo, Teiup, lea Nor c hitiito Me> 0 -297 Piamtlo D -403 Mumcipio de Noch xtlon Zoc. E 104 Molango Hgu E -205 Tulcmgo Pue Nohvidod Omorepec Me'. 0 -298 Acalldn E 105 S Seboiiion Socorro, Oeicubndoro,Roluge Jol E -206 AhuOCOtldn Crc Almoloyo de Alqu,c,ros 07-299 Tollman S Morcos, Animas, Providence NvilluCO E - 1 Delf mo 8 Calif E -106 Magdalena Jol. E -207 Mumcipio de Jolpon Oro. Zono de Choncmqo y Nul# * lo Ocuilon Me« 0 -300 Vizorrdn Tepozdn E - 2 Sonto Mono e.coht. E -107 Tequila A|uslodero, Color,no, El Tojo, etc Jol. E -208 Esconeio 0 ro Sierro de Peto Mon Solitre Me> 07-301 Mumcipio de Colon E - 3 Son 6or|0 8 Calif E -108 Colot Ion Son Morlm Jol. E -209 Bucoreii Q,0 Mp.o de Generoi Hehodoro Cos• • no Un,dn Mei 0 -302 Mumcipio de Huimilpon E - 4 S-erro del Carmen Cooh E -109 Municipio de Logos de Moreno Jol E -210 Moconi Qro Mpio de Leonordo Brovo Villa Victoria M,ch 07-303 Municipio de Amealco E - 5 Santa Eleno Cooh E -110 Mascoto Jol E -2U Soforere* e Guadalupe Qro Chichihuolco Zones de Cbpo'O y Lobo M.ch 0 -304 Refugio E - 6 Monel ova Montes de Gloria Cooh E - H I Rur.ficocion Jol E -2 12 Aiuch.lldn La Lui Oro Mp.o de Mochitlon Zones de Crude y Aguoli Mich 0 -305 Sonto Domingo E - 7 Pdnuco Cooh E -112 Zono de Topolpo y Peruleros Jol. E -2 13 Sfo Rosa Jaurequ Cerrd del Charapo Qro. Mp.o de Chi lopo Municipio de Uruopon Mich 0 -306 Guadalupe E - 8 Condole Cooh E -1 13 Zonal de Tamozulo y Nancilitlo Jol E -214 Ahuolulco S.L P Xochihuf ue*ion Nuevo Urecho Mich 0 307 Villa Juortz E - 9 Mumcipio de Torreon Cooh. E 1 14 Acombay Me*. E -2 15 Sonto Morio del Rio S.LP Municipio de Atoyoc de Aivortz Huomqueo Mich 0 -308 Villa Reyes E - 10 Jimulco Cooh E -1 15 Son Felipe del Progreso Me, E -216 Cordm oi S L P Dos Commos Tocdmboro Huoungucho M cn 0 -3C9 Ocoroni E - II C ooh E - 1 16 Real de Arriba Me, E -2 i 7 Zono de Cerro Alto y Cobr i zo Sm Villa Madera M ch 0 310 Portezuelo y Teloche Mp.o de Coyuco de Benitez E - 12 Municipio de Saltillo Cooh. E -11 7 Real de Abgjo Me* E -2 18 Mun.c.p.o de Moiatlbn Sin. Mumcipio de Morelia Mien 0 3 1 I Guerco Mumcipio de Acopulco E - -13 Son Anlomo Cooh E - lie Son Simon de Guerrero Sm Chore Mch Mb, E -2 19 Copolo Ouechultenonqo 0 -312 Huerto E - 14 Solosuchiopo E -1 19 Tlotlqyo Mb, E -220 PI om o Son Zopotit ion Municipio de Cuitzec Mich 07-3 I 3 Son Lorenzo E - 15 Sierro de Corcay E -120 Mich E -221 El Anl.monio Son Municpio de Morovorio Met Polo Blonco Aflomoioemq v E - 16 Bismarck Ch.h. E -12 l Cerro Verde y Sonto Niho Mich E 2 22 Alii: Lot Toios Son Mpio de Moniolieper Tuipon Mich E - 17 Bornai y Conejos Chih E -122 Coocol man Lo Purist mo Mich Terrenole y Slo Viv.ono Son Ocampo Mich E -223 E - 18 Guadalupe Brovos Ch.h E -123 A gut III lo Mich E 224 C.nlai de Plata Son ] ! l Onzelle'n Zildcuoro Mich Elo'o i E - 19 Lolita, Son Bias Chih. E -124 M.ch E 225 Cocdspera Son Muehuetio Ben.to JuOrei Mict Pueblo Buevo Joiobo, Meioles E - 20 Cuatro Amigos Ch.h E -125 An© de Rosales Son Cristobal Mich E -226 Sierro de Guadalupe Son Son Miguel Ctui de Commas Mict Camacho E - 2 1 Son Jooqui'n, Dos Carlos, El Nopal Ch.h E -126 Tzitno Mmitos, Lo Troncho M.ch £ -227 Fronleroi Son Esplnlu Sonto Mict -320 Escumopo E - 22 Lo Mojina Ch.h E -127 ndoporopeo M.ch E -2 2 8 Cerro Colorado y Cobrizo Son T,quicheo Mich -3 2 1 Puerto Penasco E - 23 Gjmoga Aurora. Giocondo Chih. E -128 Querendoro M.ch. E -229 Sonto Roeolia Son 1 ! 1 i M.ocol ion Me r 0 -322 Son Antonio E - 24 Guoynopo: Lo Concordia Ch.h E -129 E -230 Bobiconora Son xochitepec Cerro de Jamillepec Mar -323 Batura E - 25 Temdsochic Chih Guiiorro, etc Mich. E -231 Volemuelo Son Toutepec Mar 07-324 ZoAi E - 26 Yopochc Chih. E -130 Chopotuoto Equtdod, Lo Potna, Son E -2 32 Pilores de Teros Son Zones de Amocuzoc y Pueme d e li’io Mor 07-325 Juarez E - 27 S.srro Rica Chih. Nicoids, etc. M.ch E -2 33 Huochmero Son Joiutlo Mor. 0 - 326 Felicias E - 28 Tutuoco S’o Bn'gido, Cerro Boludo Chih E -131 Tuzontlo M.ch E -2 3 4 Corbd Son HuouMo Sonto Ana, e’e Mor 0 -327 Sombrerelillo E - 29 Rosario Ch.h E -132 Zonos de Potdmboro y Porongueo Dolores, E -235 Roydn Son Milpillos No, 0 - 326 Son Milano E - 30 Zono de General Trios Ch.h Solud, Trimdod, etc M.ch E -236 Horcasitas Son i 5 Mo 10,1 No, 0 - 329 Oquitoa E - 3l El Limon, Son Agustm, Gorochic Ch.h E -133 i Mich E -2 37 Reoliio Son Fronlol No, 0 -330 Sonto Terete E - 32 Tetomoo Chih E -134 ChurumuCO Mich E -2 38 Son Fehpe Son Ruiz No, 07-331 Lo Jojoba E - 33 Loreto Son Jose, Guadalupe Ch. h E -135 Teponohuoxllo Noy E -2 39 Cobrizo Son Pozolillo No, 0 332 Ague Zarea E - 34 Boiopiliilos Chih. E -l 36 Rosa Morodo Noy E -2 4 0 Sierra de Oposuro Son Son Nicolas No y 0 -333 Esperonzo E - 35 Monte'do Ch.h E -137 Aguopan Nay E -2 4 1 Granados Son Tepic, Mpio de Nor 07 334 Cerro B anco E - 36 Los Ovat«s 7 Ch»h E - 136 Estonzuelo Noy E -242 Huaiabai Son Refugio Noy 0 -335 Noco E - 37 Borronco de Tororecuo o del Cob'# C hih E - 139 Chimoltilldn Noy E 243 Bocodehuochic: Colorado, Daguiro, etc Son Mirovolles Noy -336 Ague Prieto E - 38 Corichic Ch.h E -140 Acuiilopilco Valenciono Noy E 244 Son Franco Son Zenos de l o Cos'eilona , CoopiMo No, 0 -337 Ploceres E - 39 Bocobunochic Ch.h E - H 1 Santo Maria dll Oro Noy E - 2 4 5 Surro de Monterrey y Son Lun Son Jaio Nay 0 -338 Cordoveno E - 40 Son Froncuco de Borja Ch.h. E - 142 Compound , Hu.cic.lo Concepcion Noy E -246 Zono de WHlord Son I ml i on del Rio Aurora, Lo Florida No, 0 -}39 Chuotero E - 41 Sotevc Son Miguel Ch.h. E - 143 AhuocoHdn El Bondo Noy E -247 ZuMol* Son Sobmos H doigo Sto Ro-ollo, Rosono N _ 0 -340 Ronguillo E - 42 Comorgo LO Amorgoso.Chonote, E -144 Barrancas Noy E -2 48 Zono de A.game Son Zono dt Doctor Cos N L 0 - 341 Son Pedro Poionlos, lie Ch.h E -145 Vollic.llo N L E 249 Ttcoror. Son - 24" Ge-erci Escoqedo M no Son Jose N L 0 -342 Son Miguel E - 43 Topago y Lo M,Honor.o Chih E - 146 I guana N L 6* -250 Surro de Uvolomo Son Los Bomones N L 07-343 Mmo Cerro Prieto E - 44 Septentnon Chih E -147 Poros N L E -25. Zono de S Morcioi Mmo Grande Son Sierro de Ai'ende N L 0 -344 Zono de Huocoponchi E - 45 Temores y Sonto Barbara Ch.h E 148 Mmo Cerro de Enmedio, Son Antonio N L E 252 Zone del Mun.cp.o de Guoymo* Son Cohhuolo Dos 07-345 Rio Boidio E - 46 Cerocohui Ch.h E -149 Zono de Abosoio e Hidolgo: Cormen N.L E -253 8 or oy tea Son Silocoyoooon Dorn 0 -346 Bocuochilo E - 47 Boiosegocn.c Ch.h E -I 50 Garcia N L E -254 Miguel Auto Zoc S,locoyoop.i lo Guodotape. Pro» Pence. etcOoi 0 -347 Sonto Eleno E - 48 C .oncgu.ro Chih E -15 1 Zeno de Guadalupe y Judrez N L E -255 Alborrodo Zoc Miitepec Oom 0 -348 Son Juon (I ) E - 49 T ubores E -152 Sierro de Linares N L £ -256 Sc n Alto Zoc Temauim'epec Oom 0 349 Veldes E - 50 Huopolo.no Ch.h E - 153 Aromberri La Reformo N L E -257 Zoc Yoic'epec Oom 0 -350 Sierro de Cornelia • E - 51 La Govilono Chih E -154 Doctor Arroyo (Sierra de) N L E -258 Villa de Cos Zoc Chi spo de Diaz Oom 0 7-351 Mmos de M homuco y Los Nidos E - 52 Voile de Zaragoza Ch.h E - 155 M.er y Noriega N L E 259 Villanueva Zoc Dimcuiii Oom 0 352 Son Juan (2) E - 53 Real de Morelos Los Arneros.Los Bronces Ch h E -156 iguoltepec On* E -260 V illo Gorcu) Lo Soltdod Zoc Los Cues Oom 0 -353 Sierrilo E - 54 Z de Bobongome Real de La Dura, Los Chorcos. etc. Ch.h

\— 22“

ECONOMIC CLASSIFICATION SILVER Progreso WITHOUT ECON VALUE SECONDARY ECON VALUE UNKNOWN

Closjiftc- Clossrfio ClOSSrfiO Nome or County Stole County Classific­ Nome or County State CiO SSlflO 01 on Name or County S to le otion State ation otlon

A - 1 Sierro Moiado. Cooh A? S3 Cerro de Son Pedro Su.lepec Colo, Dolores, Lo Luz etc Mas Paros. Angusl.os, Escendido.Ger.boldl GuOdoKOZOf: • ? - 2 El Souz Chit, A - 54 Cosold: Lo Condeiono, etc Zocuolpon An.mos, Blanco, El Aloe tin, Tepentitldn Coroco, Cuitzinilo.olc A - 3 Ocampo Cn.ranara*, Sto Margorila, etc. Chih A?- 55 Son Ignacio etc Mb* C - 37 See Nicoltfs del Ore Aire, Lo Pen. Car cal Ian ------20 ® A7- 4 CenchaAo- Chib A - 56 Concordia Huetomo Dolores, etc. Mich. C - 38 Cam pa M erode Reformo, etc General Anton,a P Santos A 5 Condom* Ao CMh. A - 57 Coneeee Tlalquitenongo. Mor C - 39 Real del Limon Mumcipio de Chois A - 6 Urvechic Cblh. A - 56 Alamos y Aduono Huojlcori El T.gre, etc. Nay C - 4 0 Teloleopon Cor on, 11 o, Ptler, etc Los Papas, Cosielo, Chigulte, etc A - 7 Moggonchic Chih. A * 35 CholchUnifies: La Plato, Zorogoze, Cerrolvo El Cormen, Porven.r C - 41 Mumcipio de Cl Fuerte a - e Polmoreio Chih. Mliogro, etc. Barrodo'n, etc N L. C? 4 2 Azuloques Reoliio, Mimas, Cchodos, An.mos, etc A - 9 Goozopores Aguo Nuevo, Guerra ol Teona,etc Chih. At- 60 None 0e 5. Pantoledn,Trinidad, Sto. Fe. Cerrolvo Nigueros N.L. C - 4 3 Sinaloa Rone he lo Joyo A7- 10 Urique Gohodo Colorado, Du ices Nombres, etc. Chih A - 6l Sembierete. Pobelldn, Veto Negro, Tov.che: Son Froncisguilo, etc. Oo., C - 44 Xitlngo Bocubirile A - 1 1 Botoeiio* Carmen, Pprfirio D'oz.Lo* Toro*, ProoRo, Toceyos, etc. El Doctor Lo Luz, America, El C - 45 Acomisllo Mocorilo Son Nestor, ete. Chih At- 62 Nieves: Sonia Celorlno, Volenelona, Burro, Viboro, etc. Oro. C - 46 Zono do lo D.cho Soyai.la Son Jose, Son Luis A - 12 Dolores Chih Hueco, El Zope^ete. ^oc. Son Jooquin Son Cristobal, etc Oro. C • 47 Ch.loanclngoiMpio de) Delt.no, Cuhocen lMpio de) y Tepuche ^ rre e ir A - 13 Son Francitco del Oro, Son Ignacio, Sen A - 63 Frosnllio: A score. Son Josd, 5. Roloel,etc. Zoc. Bf- 52 Pmol de Amoles Borronco, Gochu- Po'nuco Costa R,co, El Toro, etc Polrkio, etc Chih A - 6 4 El Bote Zoc. Oro C - 48 Nicoles Flores Plomosos _ I9‘ A - 14 Some Barbara Chih. A - 65 Zacatecas: Son Acaclo, Ovebrodillo, B7- 53 Moctezumo: Mineral El Sobino SL.P C7- 49 Bonanza: Son Judas, Sto E lone, etc A - 15 Hidolgo dll Forrel Agu loriRo, Lo PrieW,elc Chin • El Goto, Barones, etc. Zoc. 8-54 Son Jose" de Groc'o Los Muertos, C?- 5 0 Ism.quilpon(Mpio do) Piiiquito Mom oho, tic . A - 16 Minoi Nunes Chih. A - 6 6 He Ichor Ocampo: El Trebd, El Caidn,etc. Zoc Loreto, etc Sin. C7- 51 El Atonal Altar Lo Estoril, El Tigre, etc A - 17 Chih. A - 67 Noche Bueno, Avalos Zoc 67 - 55 Bed.roguoio S Jose, Ledesma, etc Sm C - 52 Tope no no: Emestino.Sgnlo Niho.etc Tubutamo Gran Republics A7- 18 Milpillos lo Reino Chih 8 - 68 Moiop.l: Alborroddn, Avalos,S.Ellgio,etc. Zoc. 8 - 5 6 Gvoddupe de los Reyes Lo Estoca, etc. Sin. C? 55 OmitlEn de Juerez Sonc ignorode, liohone, etc. A - 19 (A»ihuKidchic Buenos Aires.El Burro, Rosono C - 5 4 AKioietco: Cecullecoe, El Grullo, Nogales Plane hot do Plata P.omonleno, tit. Chih. La La jo, etc. Urique. etc Zoc. B - 58 Nocozeri de Gordo Sort Sonto Cruz A 20 Apuilei Sir den Mmmoi de Sie tetblie CMh. 8 - 59 Condeiono Zoc C - 55 Amece: E slen cie, etc A - 21 Aquiles Serdon Sonto Domingo. Chih. 8 - 1 Ocampo Cooh. 8 - 6 0 Zoc. C7- 5 6 Zono do Geochinengo y Nov,dad Magdalena Berrendo.Benmie, AT- 22 BT- 2 Cue ft* Cldnogos: Lo Pur.'iimo Erin, etc Mumcipio de Aldomo Chih Cooh. 8 - 6 1 Veto Grande Ouebrod.lla.Com.cerioe, C - SF Oesmor anode AT - 23 Nomlquipo Lo Prioceso Chih. e r - s Son Buenaventura Cooh. Cualo Ctumoliltibn, Oje de Ague, Sonto Ana Nome or County Stole Son Roberto, etc Zac. C - 5 6 AT- 24 Son Vicente, etc. Sierra de Lei Lominlot Chih 8 - 4 Muzqulz Cooh. 8 - 62 Sonto Rosa Zoc. Trincheros C -161 Morelos A - 25 Tomozulo, Mpio. do Le Asuncion y Sobinal Bromodor Joro Viejo Dgo B»- 5 Chih. 8 7 - 63 P.nos Nona, Candelaria, El Ale, C - 5 6 C - 162 Zoc J A»- 26 Topio Modrvgodo, Lo Colero, etc. Ogo. BT- 6 Son Pedro Cerrellle* Chih. El R elug,o, ole Zoc. C7- 6 0 Awtle'n Bocoochic In grata. Pur,CO, etc C - 163 Guodolupe Lo Fe, Lo Comoro, etc Zoc 1 A - 27 Son Oimoi Lo Condelorio, BT- 7 Mpio. do Nutvo Casas Grand** Chih C - 61 Costmiro Coelllle Arizpe Gronodifoi, Oro Blanco, etc C - 164 Lo Blonco B ilbao El Cobeio’n Zoe) Copellllo, etc. Ogo Chih Bevispe: Son Jose' BT- 8 Guoyeeplte C - 1 Casio A** C7- 6 2 PS hue we: Sierro do Ptomo Zinc C - 165 Oro Calient# Guonoiuol. Ho, A - 28 Tayoltlta Chih. Ogo BT- 9 Helsope: El Latraro, Yopachle c - 2 Tegezeio y As, on toe: S. Mali os, etc . A«s. C - 6 3 hi I open dot Ore: Angeles, Animas. Boceroc. Dolores, Lo Viejo, etc Le Concopcien Zoc 1 A»- 29 Santiago Poposquioro Dgo ■ - 10 La Colero Chih. c - 3 Zono oe Ensenada (ol SE) BCor.l Cols Opuie: Son Ignacio, Trimdod, etc C - 166 Norio de los Angeles Socovon,Son Joot Zoc ' A - 3 0 Chih. Municipio do Arleego Cumpos: Consliluc,on. Conut,Ho, etc C - 167 Promonterie Ogo 8 - II LO RdpdbHca c - 4 Comedo B-CoM C7- 6 4 Pthdn Btonco Compoh.o, Fresnillito^cZoc A - 31 El Oro: La Candela, El Salvador, etc. Dgo Chih. Bonomtchi: Son Poscuol.etc C7- 168 Villo Hidolgo B - If C? 5 Cocochilos An,me Sole, Chiveto.etc. 8 CoM C - 6 5 Oropeo Le Chine, etc. Zoc A»- 32 Indo: Lo Colorado, El Ague, etc. Dgo. B r- 13 Moris Chih. c - 6 S Antonio, El Tnunto: Aelmes. C ?- 6 6 Le Amieled Jet vile Opodepe: Sietro del Socorro C - 169 M eiqu.tol del Oro Zee A - 33 Moptnrf. Frowonlorio, Lo Ojuele, etc. Ogo. B - 14 Chinlpa* Chih. Bebelomo, etc • CoM C7 6 7 Huepoc: Lo Loiuelo A 34 Velordeno y Ptdncpfto Ofo BT- 15 R/o Plato Chih. C?- T Castehoe Cooh C - 6 6 Bovi dears D - 1 Rincon de Romos Ags A - 35 Cuencomd: Santa Ana, etc. Dgo B - 16 Yoqulve: Perletrencle Chih. C - 8 Romos Arizpe Cooh Moctezumo. Colorado, Arcuillat, ttc 0 - 2 Mumcipio de Aguoscolienies Ag» 0 - 5 A - 36 Lo lu z : Son Jeon, Refugio, Majfamor BT- 17 ZZpuri: Son Retool, Son Martin, etc Chih. C7- 9 Vieeeo Melemeree Cooh C7- 6 » No cor, Chico Mumcipio de T.,uonq B Col.l Son Pedro Gllmenene, ole. D - 4 Tecolo Gto. 8 - IS Gnodolupo y Cel*#-. Sonto Luc Clneo de Moya Chih C • 7 0 Acdponeto (Mpio. de). Sierra de Topochi: Broncos,Corricito, etc. BCei.1 D - 5 Son Ignoc.o A - 37 Guanajuato: Volant tana, Reyes, B t- I 9 Plomooos i Sonto Domingo Ch.h C - I I Sonto Domingo Ch.h. tseejiceri, Le Colorado Nay Uies: Amor,lies, El Toje, Ole B Col.l Cato, Msllado, etc. D - 6 Son Juon Glo. B - 2 0 Mono el Benovtdee y Sen Carles Ch.h. C - 12 Lo Fortune Chih C7- 7 | Mi Mme N»7 Hermesillo Gurguz, Sto. Fo, etc B Col if AT* 38 El Cube, Per fie, VIIHipondo, etc Gto. 8 - 21 Sierro de Almeloye Chlh. C - 13 Modern Ch.h C - 7 2 El-topi Iota: Tonomecho, Los Toies,itcNoy. Mine Grondo 0 - 7 Jocoi.ioe B.Col.1 Lot V.'rgenes A - 39 Toiea: Amo lea. Pedragel, See - 2 2 Municipio de Allende Chih. C - 14 Ceyeme Chih. C - 7 3 Le Yeste Noy Villa Pesquero 0 - 8 a Coi.t Cayelame, etc. Gro - 2 3 ewonocwvt: Fermy, Predllecse Sto. Ane Dgo C - 13 Cechtlle Porede Chih. C7- 7 4 Lemeezee Voiledores ML. Botuc D - 9 Islo de Son Mor cos BColrf 0 - 10 Mulegb AT- 4 0 Mineral Le Reformo Mgo. - 2 4 tbnunil' Zopote, Oopo*e,etc Ogo. C - id Guerrero. AHegrecie, EecendidoAtc. Chih C7- > 3 Mines V lejos N.L. Suoqui Chico Elvira 8 Col if A - 41 Pochuoa: Ardvole, Copula, See - 25 Otdez ^ C - I f We Tlnte, Terrozes.Oeecubridere C - 7 6 Vilieldamo Borbal kin N L. Boconere D l l Islo de Cerrolvo BColrf Goll.no* Rataot, Barren, Vizcaino, ete. M^o. - 26 Tepehuoees me,lies,Le Seder,to. 3 Vicente Chih. C7- 7 7 Ae*e Leguos ML. Sohuonpo: Lo Trimdod, Colon, etc D - 12 8 CoM A - 42 Rool del Menlo: Cebrere, E so o eo V - 27 Pdnuto de Coronado °G®.- C - 18 Pines AM os Sente N.ho, etc Chih. C - 7 8 Sol,nos Victoria ML. Arivtchi 0-13 Tode* Sonrot e cei.i D.l.celled, etc. " 9 0 . - 28 Aevno y Arzoto 0,0 C - i f Lee Azuies Chih. C • 79 Santa Cotor.no N l_ Soyopo D - 14 Sonliogo BCol.1 A - 4 3 El Chlaa: Son MerciM. Pobelldn, etc. Hg* : 29 Son Juan do Suedolupe Potrocinto, etc Dgo C - 2 0 Jimenez Cerro de H e Ane Chih C7- 60 Monterrey La M.tre, Coloredo, S. Pw*o M L. Sen Jovier Lo Nehuile 0 - 15 Cedumo* 8 Col.l distribution p a t t e r n o f s il v e r A 44 Zlmepen Lome da Taro, Santo Blhe, - 30 Sierro de Remfrez: Sonto Domingo. C - 21 Sen Berner do Ota. C7- 61 Sentiego ML. Tocoripo Som e Domingo D? 16 Son Jose dot Co bo ecohf ludltro SeRoro, etc. Mgo. Colover. I e, etc 05° C - 22 Sen Pedro del Gelle: PeAo.es, C7- 6 2 (Meena N.L Los Broncos Le ProvMonCie 0 - 17 Zone do Villa Acuhe Cooh Sen Rofeel A - 43 E 'td h a i Cermet,#, Cenctnolle - 31 X.chu «** Dto C - 63 Genewl Z aragoza El Moldn.Victoria N.L Lo Colorado 0? 18 Z 0/0*070 Cooh. DEPOSITS AND METALLOGENIC BELTS Mozota, etc. Jol. - 32 Coyuco de Celeldn C * 23 Birimee. Ceeches, Porl.lle Dee eg- 64 Teoiomelce Oo» Suoqui Grondo: D - 19 Nava Cooh A - 46 El Oe: Sen Acoclo, Sen Retool, - 33 Tetipoc: Cuadv.ilo, Peder de O.oe etc 6 re C?- 2d Rodee Ote C7- 65 Ejutlo Oes. Zone do Onavas y GuedeitMO 0 - 2 0 Obeyes Cooh El Arco, Esperonzo, ete. BUv © to 0-21 Sen Felipe Cooh Kilometers - 34 iguelo Gre. C - 23 Lee Ceiereder CT- 6 6 6. Martin Oe loe Coosecoe, Lee Ocelee Oe» YStCOrO Joaquin Echavez V A - 47 Tlolpuiohuo Sam ira, Ocotos, AzSaco, C - 2d AreecoK C - 6 7 0 - 22 Jubrez Cooh t- 35 Zumpengo del Rio 6re O f Terete del O e Espeteroi-HMMzfee, Me Pee Nwerio Estrtliot, etc Mich i 36 Cordonol Hge C -,27 Joceislile Dgo C - 6 6 TrziuNon Pue D7k 2 J La Male Cooh Ouir-ego 1968 A 48 - a * SC A L Angonguio Cormin, Cotingdn, He. Mich 57 •oloRos Carolina, Borronco, iguono C7- 29 Teiemee Euroha Ogo. c i«Jb Miooe, zone de Le Precieee hbnes Hue vos 0 - 2 4 Escobedo Cooh. A - 49 ixlldn de Judrez, Notividod, Xidcui, y Miohuelle'e Pee C - 29 Gonerol Simon Bel.rer ©g« Son N,colds 0 - 25 Melemeree Cooh. Oom C7- g o 0 - 26 C#ek Heeiet.poeu.lle LoModoia, etc J C * 30 Pee big Nuevo: Lae An.mos D th Rfo 8lance Dolores,Loe Reyes, etc Ore Son Carlos Generoi Coped# 4 - 50 Figure No, 7 C erorci El Refugio, Lo Luz, Meriles, Tolpo de Allende Avenjeez J C .- SI Nembre de Ows Le Glorie Ogo. C - 61 Mtem.ller: Ague Frio Ore Hdotge 0 - 2 7 Arteogo Cooh veiencieno, etc SLR Ayuile. Loe Reyes, e tc J C - 32 Muleree Dgo C - S2 Carre del Burozna Ore. 0 2 8 Municipio do Montana do Cot. A - 51 Mnihuoie LO Poz, Sente Fe, etc. S. l_R Temoscoiiepec Gochup.no, Veto Negro, C*- 33 Sen Juen de le Chrce y Ocampo fit* C7- 9 3 venegos y Cedroi SUP 0 • 29 Munrerp.o de M,met,item Col A - 52 Cnarcos Cerro do Sonto hid*, otc. S.LR Beeor.e, ete Mdi C>* 3 4 See Lute do le Pee Gto C - 6 4 S LP 0 - 3 0 Mu me. pro do Coqemelle'n Col Compilation of silver deposits by Gonzalez Reyna, 1966

88° 102° 101° 100°