Exploration and development at the LaNegra Mine, Maconi, Queretaro, Mexico

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Authors Gaytán Rueda, José Eligio, 1940-

Publisher The University of Arizona.

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EXPLORATION AND DEVELOPMENT AT THE LA NEGRA MINE,

MACONI, QUERETARO, MEXICO

by

Jos£ Eligio Gaytcin Rueda

A Thesis Submitted to the Faculty of the

DEPARTMENT OF MINING AND GEOLOGICAL ENGINEERING

In Partial Fulfillment of the Requirements For the Degree of

MASTER OF SCIENCE WITH A MAJOR IN GEOLOGICAL ENGINEERING

In the Graduate College

THE UNIVERSITY OF ARIZONA

1 9 7 5

STATEMENT BY AUTHOR

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

Brief quotations from this th e s is are allowable without specia l p e rm iss io n , provided that accurate acknowledgment of source is m ade. Requests for perm ission for extended quotation from or reproduction of th is 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 judg­ment the proposed use of the material is in the in te res ts of scholar­sh ip . In all other in s ta n c e s , however, perm ission must be obtained from the au tho r .

SIGNED:

APPROVAL BY THESIS DIRECTOR

This th e s is has been approved on the date shown below:

WILLIAM C. PETERS /dateProfessor of Mining and Geological Engineering

DEDICADO

A mi esposa:

Blanca Rosa

A mis h ijos:

Jo s6 Eligio

Juan Rafael

Javier Andres

ACKNOWLEDGMENTS

Various factors have enabled the writing of th is th e s is . The

f irs t , and without doubt the cause of the o th e rs , was the granting of a

scholarship by Industrias P en o les , S .A . , through Ing. Pedro Sanchez

M ejorada, at present Director of the Division of New Projects and De­

velopment, who has advised me in the development of the th e s is and

throughout my professional caree r . For th is , I would like to give him

. specia l th a n k s .

I would a lso like to thank Industrias Pefloles, S .A . , the spon­

sor of the scholarship for one year . Penoles has authorized the incor­

poration in the th es is of a ll information obtained as a resu lt of the

s tudies conducted by me during the two years (1970-72) during which I

acted as res iden t geologist at the La Negra mine.

I am grateful to Ing. Manuel C astilldn Bracho, Subdirector of

Exploration, and In g . Gustavo Aguilar Arzate, D ivisional M anager, for ■

the help received from them in the development of my presen t a c t iv i t ie s .

Overall, I express my gratitude to the Mining Division of

Penoles , d irected by Ing . Carlos.Sierra Valdes, and e sp ec ia l ly to Ing.

Eduardo Garcia Guerrero, General M anager, Ing. Luis Corrales Velasco

and Ing. Carlos M adrazo, D ivisional Managers of the Mining D ivision,

for the help received from them during my residence at the La Negra

mine.

I would like to express my appreciation to the Department of

Mining and Geological Engineering and to Dr. Willard C . Lacy , its

chairman during the student period, and espec ia lly to Dr. William C.

P e te rs , who advised me during my s tu d ie s , and Dr. Thomas J . O 'Neil

and Dr. Charles E . G la s s .

TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS . . ............... v iii

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • x

1. INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Geographic Setting . . . . . . . . . . . . . . . . . . . . . . . . . . 2H istorical Information ............... 4

2 . REGIONAL tz? E (Z) l_i (2) . . . . . . . . . . . . o . . . . . . . . . . . . . . . 6

Physiography and Geomorphology . . . . . . . . . . . . . . . . . 6Lithology and Stratigraphy. . . . . . . . . . . . . . . . . . . . . . 8

Sedimentary Rocks . . . . . . . . . . . . o . . . . . . . . . . . 9Las Trancas Formation . . . . . . . . . . . . . . . . . . 9El Doctor Formation . . . . . . . . . . . . . . . . . . . . 9

Cerro Ladrdn F a c ie s . . . . . . . . . . . . . . . . . 9El Sacavdn Facies . . . . . . . . . . . . . . . . . . 10San Joaquin Facies . . . . . . . . . . . . . . . . . 10La Negra Facies . . . . . . . . . . . . . . . . . . . 10

Soyatal Formation . . . . . . . . . . . . . . . . . . . . . 11M ezcala Formation . . . . . . . . . . . . . . . . . . . . 11El Morro Conglomerate . . . . . . . . . . . . . . . . . . 11Surficial Deposits . . . . . . . . . . . . . . . . . . . . . 12

Igneous Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . 12Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3 . GEOLOGY . . . . . o . . . . . . . . . . . . . . . . . . . . . . . . . 14

Sedimentary Roc ks . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Igneous Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Metamorphic Rocks . . . . . . . . . . . . . . . o . . . . . . . . . . 15

4 . ORE-BODY DEVELOPMENT . . . . . . . . . . . . . . . . . . . . . . . . . 21

Old Mine Workings . . . . . . . . . . . . . . . . . . . . . . . . . . 21Preproduction Development Work . . . . . . . . . . . . . . . . . 23Mining and Sampling Methods . . . . . . . . . . . . . . . i, . . . 27Scale of Operation and Life of the Mine . . . . . . . . . . . . . 32Ore Grade and Tonnage. . . . . . . . . . . . . . . . . . . . . . . . 34

vi

vii

TABLE OF CONTENTS—Continued

Page

5. ECONOMIC GEOLOGY............... 37

Ore Control ............... 38Lithologic Factors ..................... 38Stratigraphic Factors . . . . . . . . . . . . . . .. . . . . . . . 39Structural Factors . . . . . . . . . . . . . . . . . . . . . . . . 39Chemical F a c t o r s .................................... 39D ensity and Textural Factors . . . . . . . . . . . . . . . . . 40

Ore M ineralogy. ............... 40Mineral Paragenesis and Zoning ............... 41Ore G enesis . ̂ . 44

6. EXPLORATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

Exploration Program at Depth . . . . . . . . . . . . . . . . . . . . 52System atic Exploration at the Mine . . . . . . . . . . . . . . . . 54Results and Costs of the Exploration at Depth

and at the Mine . . . . . . . . . . . . . . . . . . . . . . . . . . . 55Geologic In terpreta tion. . . . . . . . . . . . . . . . . . . . . 58Ore R e s e r v e s ............................... . . . . . . . . . . . . . . 59Results of Exploration a t the Mine . . . . . . . . . . . . . 62Cost of Exploration at Depth and at the Mine . . . . . . 62

Exploration in Socavdn El Alacrdn . . . . . . . . . . . . . . . . . 63

7. SUMMARY AND CONCLUSIONS. . . . . . . . . . . . . . . . . . . . . . 66

APPENDIX A: ORE RESERVE ESTIMATE FOR LA NEGRA AND EL ALACRAN ORE BODIES, EXPLORATION PROGRAM, 1964-67. . . . . . . . . . . . . . . . . . . . 69

APPENDIX B: ORE RESERVE ESTIMATE FOR THE LOWER PART OF LA NEGRA ORE BODY FOUND DURING FIRST STAGE OF EXPLORATION PROGRAM AT DEPTH,1972 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

APPENDIX C: SUMMARY OF DIAMOND DRILL HOLE LOGGING. . 85

REFERENCES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

LIST OF ILLUSTRATIONS

Figure Page

1. Location of the La Negra m ine , Quer^taro, M ex ico . 3

2o Physiographic provinces y Estados Unidos M exicanos . . . . . 7

3 . Regional geology of the La Negra d is tr ic t . . . . . . . . in pocket

4. Local geology of the La Negra area . . . . . . . . . . . . in pocket

5. Geologic map of sublevel 2317 (7), plan v i e w ................ 17

6. Geologic map of sublevel 2295 (3), plan view . . . . . . . . . . 18

7. Geology and sampling maps of sublevel 2266 (Cono) . . . . . 19

8. Geologic map of sublevel 2170, plan view . . . . . . . . . . . . 20

9. Composite map of the old mine workings of theLa Negra mine . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

10. Longitudinal and cross sections of the La Negraore body . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

11. Sublevel p repara tion , firs t stage . . . . . . . . . . . . . . . . . . 25 '

12. Sublevel preparation, second s ta g e . . . . . . . . . . . . . . . . . 26

13. Ore haulage and mining system , isometric drawing. . . . . . . 29

14. Isom etric.projection of the La Negra ore body . . . . . . . . . . 30

15. Map.showing sampling method, diamond drill h o le s ,and pocket of mineral at the footwall, sublevelNo. 5 (elevation 2317 m) . . . . . . . . . . . . . . . . . . . . . 33

16. Ore reserve estim ate of the La Negra ore body. . . . . . . . . . 35

17. Variation of m etallic contents at depth, based onaverage a s s a y s , IQO-m intervals . . . . . . . . . . . . . . . . .43

18. Plan view showing target zone No. 1 . . . . . . . . . . . . . . . . 49

viii

ix

LIST OF ILLUSTRATIONS--Continued

Figure Page

19. Cross section of the La Negra ore body explorationprogram between elevation 2,000 and 2,100 m . . . . . . . . 50

20. Generalized geologic map along Socavdn La Negraand El A la c rc in ................................................... 51

21. Plan view showing the mineralized zones in te rsec tedwith the horizontal diamond drill holes betweenelevation 2,000 and 2,100 m . . . . . . . . . . . . . . . . . . . 56

22 . Cross section of the La Negra ore bodies I and I I . . . . . . . . 57

23. Longitudinal projection of the La Negra ore body II,ore reserve estimate map . . . . . . . . . . . . . . . . . . . . . 60

24. Longitudinal projection of small pocket of m ineralization at the footwall of the La Negra ore body II, ore reserve estimate map . . . . . . . . . . . . . . . . . . . . . . . . 61

ABSTRACT

The La Negra mine, located in the central part of the Mexican

Republic, belongs to the Lower Range subprovince of the Sierra Madre

Oriental province. - The La Negra ore body is an epigenetic and typ ically

metasomatic or pyrom eta somatic deposit where the m ineralization is

p resen t as m assive su lf ides , with silver as h e s s i te , lead as g a le n a ,

copper as chalcopyrite , and zinc as m arm atite .

The exploitation method is a combination of sublevel and long

hole b las ting . The in itia l ore reserves have been estim ated a t 1 ,368 ,427

metric tons , averaging 254 g/m etric ton Ag, 1.4% Pb, 1.52% Cu, and

3.3% Zn. The life of the mine was estim ated to be about 12 years at

the production rate of 120,000 metric tons per year . Actually, th is pro­

duction has been increased to 156,000 metric tons per year and the life

of the mine is s t i l l considered to be 12 years because the ore reserves

have a lso been increased by 30 percent since the continuation of the

ore body at depth has been loca ted . The author considers that the p o s ­

s ib il i t ie s for more ore at depth and in other areas in the v icinity of the

mine are h ig h .

x

CHAPTER 1

INTRODUCTION

This paper describes certa in a sp ec ts of the La Negra mine, the

la te s t mine to be brought into operation by the group Industries P eh o les ,

S.A. The mine started operating in January 1971. Although at this t im e ,

June 1973, other mines are under development, none of these is in opera­

tion y e t .

It is not unrea lis tic to say tha t La Negra is the most modern,

m edium -size, underground mining operation in M exico. The operation is

highly m echanized, with a consequent high degree of efficiency and pro­

ductiv ity . The geologic setting is such that p o ss ib il i t ie s for additional

ore are favorable and it is apparent that it will be a larger mine in the

near fu ture . In spite of the fact that the area has been subjected to in­

tensive prospecting activ ity for over a century, as w itnessed by num-.

erous prospects and small abandoned m ines, the La Negra ore body can

be considered to be a completely new discovery with all its ore reserves

untouched .

Approximately 15 years before Peholes took in te res t in the a rea ,

various mining companies had turned down the property because of nega­

tive r e s u l t s . The exploration of the La Negra mine is a good example of

su ccess through in te res t in areas with evidence of mining operations or

in old mining d is tr ic ts no matter how many geologists or mining com­

panies have studied the a rea . The most important thing is the economic

sense of the geologist that permits him to see the real importance behind

apparently insignificant or small geologic fea tu res .

The La Negra area is a typical contact m etasomatic zone where

every meter of tac ti te - lim estone con tact is a potentially good exploration

target for m assive sulfide ore bodies and where similar targets occur

within the tac ti te zone and the tac ti te - in tru s iv e con tac t.

Since the beginning of operations, the La Negra mine has been

a su ccess in all re sp e c ts , including discovery, m etallurgical operation

in spite of the complexity of the o res , effective and low -cos t mining,

and exploration during the first two operating years . In that.tim e,

500,000 metric tons of additional ore reserves were found, and the same

or better resu lts are expected with current and future exploration pro­

gram s.

Geographic Setting

The sta te of Quer6taro is located in the southern portion of the

great central p lateau of Mexico . The distance from Mexico City to the

c ity of Q uer6taro, cap ita l of the s ta te , is 215 km (Fig. 1). The La Negra

mine is s ituated in the Maconi mining d is tr ic t in the northeastern part of

the s ta te of Quer6taro in the eas te rn portion of the Sierra Gorda de

Guanajuato. At th is point, the boundary between the s ta te s of Querdtaro

and Hidalgo is the Moctezuma River. The neares t— and very small—

town is M aconi, municipality of C aderey ta . The population of th is town

is about 700. The d is tance from Maconi to the mine is 5 km by an un­

paved road. The Zimapan mining d is tr ic t in the s ta te of Hidalgo is 7 km

e a s t of the La Negra mine, but no communication ex is ts between the two

because of the depth of the Moctezuma River canyon and the general

/ \ J \ STATE OF

( STATE OF \

C- QUERETARO

jTo son M,'9ua/

GRAPHIC SCALE

0 5batz±c±±at

To L e o n o n d Cd. J o o’re z

10 15~ tm n m T r m m l

'ft'ent/e - ' J

x " > < :

K I L O M E T E R S

E X P L A N A T I O N

■ Paved roads Dir t roods

Rail rood River State boundary- > — Internat ional boundary

\

S°n- T V X A NEGRAy / Maconi

SAN LUIS POTOSI

G.ity \ ( Q u e r e ta r o ^

V

STATE OF HIDALGO

Figure 1. Location of the La Negra m ine, Q uer^ ta ro , Mexico

ruggedness of the topography„ The a c c e ss road to the La Negra mine is

shown in Figure .1. The neares t railroad point is San N icolas sta tion near

Q u e r ita ro , 120 km d is tan t . The average altitude of the d is tr ic t is 2 ,000

m, which gives it a temperate climate; the average annual temperature is

19°C. The rainy seaso n , from July to September, accounts for most of

the .500 mm of average yearly ra in fa ll .

H istorica l Information

The very old, small workings sca ttered over San N icolas Moun­

tain were discovered and explored during the Colonial period . These

workings furnished oxidized lead o re , carrying s i lver , for the several

sm elters at M aconi, where large masonry hydraulic blowing towers and

large slag p iles bear w itness to the extent of their operations (Fink,

1952).

After, the Colonial period, in the late 1879 's , the mine and

smelter were operated by Victor Beaurang, consul general of Belgium to

M exico. His son continued operating the properties after Beaurang*s

death and then sold them to Oscar and Thomas Braniff in the early 1 9 0 0 's .

In 1904, the Braniffs sank severa l shafts on the outcrop of the ore body

and drove the La Blanca Tunnel, 326 m long. They cut some m ineraliza­

tion at depth but m issed the main ore body. The main reason for stopping

the operations in the early years of the Revolution was tha t they were .

unable to trea t the deeper unoxidized complex sulfide ore by gravity con­

centration methods (McCarthy, 1953).

In 1950, C ia . Minera Acoma, S .A ., acquired the properties

from the Braniffs. C ia . Minera Acoma did a limited magnetometer survey

and carried out a diamond drilling program without su ccess fu l r e s u l ts .

Their lack of su ccess may have been due to a. very poorly planned ex­

ploration program. As a consequence , the project was abandoned by

C ia . Minera Acoma . Eloy Vallina and Antonio Guerrero took over the

p roperties , and Peholes subsequently acquired them (Sanchez M ejorada,

1960). The Exploration Department of Peholes developed an extensive

geologic and diamond drilling program, with very su ccess fu l re su l ts ,

and discovered the main ore body, the La Negra, and the El Alacrdn,

which is 500 m north of La Negra.

CHAPTER 2

REGIONAL GEOLOGY

Physiography and Geomorphology

The Maconi mining d is tr ic t belongs to the Lower Range sub­

province of the Sierra Madre Oriental province , which is limited to the

e a s t by the Gulf C oasta l province, to the w est by the Central M eseta

province, and to the south by the Neovolcanic Plateau p rov ince„ The

Sierra Madre Oriental province c o n s is ts of Jurassic and Cretaceous

sedimentary rocks, mostly lim estone, folded into an tic lines and syn-

c l i n e s , forming evenly sculptured elongate ridges „ The Lower Range

subprovince is para lle l to the High Sierras on the eas t; both belong to

the Sierra Madre Oriental province (Fig. 2). In con trast to the High

Sierras, the subprovince is lower in altitude and the va lleys are wide

and detritus fi lled . The transition to the Central M eseta is gradual

(Raisz, 1964). This is a general descrip tion , but locally the topography

is abrupt and the valleys are narrow. The g rea tes t re lie f is about 1,200

m, with an average re lie f of 400 m. Near the La Negra mine, the slopes

along the Moctezuma River are nearly vertica l and the difference in a l t i ­

tude is in the order of 1,000 m.

In the Maconi d is tr ic t , the topography is very rugged , with

very high, scarped mountains of irregular shape and s teep s lo p e s . The

main rivers in the region are the Moctezuma and Tollman in the eas te rn .

part and the Extorax in the w estern part . Intermittent streams with swift

currents due to the steep slopes are charac teris tic in the d is tr ic t . The

GRAPHIC SCALES

MILES

PittedTheLa Negro Mine%\Veo

r ‘ * + J 3

Figure 2. Physiographic provinces, Estados Unidos Mexicanos

drainage system is para lle l and is included in the hydrographic basin of

the Moctezuma River.

The upper portions of the high mountains are formed by the

w ea th e r-re s is tan t, m assive limestone of the Cerro Ladrbn fa c ie s , giving

these hills a very prominent shape. The limestone in the Cerro del

Espolbn form vertica l slopes of about 100 m at the contact with the

sha les and m arls . Maconi Valley is carved in soft sh a le s , m arls, and

th in-bedded lim estones . Differential erosional effects give the terrain a

very abrupt topography.

Litholoqy and Stratigraphy

The different type of rocks that crop out in the Na Negra d is ­

tr ic t a re , from a lithologic point of view , sedimentary and igneous and

represent an incomplete geologic interval from Jurassic to Q uaternary .

The stratigraphic sequence of the exposed geologic formations (Fig. 3,

in pocket) is summarized as follows (Carbonell, 1970):

Quaternary <j"

Tertiary _ <

Upper

C re taceous« L

Lower <_

U nconformitySurficial deposits

A ndesitic , b a sa l t ic and rhyolitic flows , granodioriti and dioritic intrusive rocks

U nconformityEl Morro Conglomerate

Unconformity —

M ezcala Fm.

Soyatal Fm.

El Doctor Fm.

M a r ls , m udstone, sandstone , and limestoneLimestone, m a r ls , and sha lesLa Negra fac ies San Joaquin fac ies El Socavdn fac ies Cerro Ladrbn fac ies

Limestone

■ U nconform ity---------- -------------------- ------Ju rass ic <j Upper<j Las Trancas Fm. Sha les , a rk o s e , grayw acke, and

*- L limestone

Sedimentary Rocks

Four different sedimentary form ations, Las Trane a s , El D octor,

Soyatal, and M ezcala , are p resent in the region. They have been in­

truded by plutonic rocks of intermediate composition and are overlain by

a Tertiary conglomerate and surficial d eposits . The lithologic sequence

sta rts with the Upper Jurassic and continues to the Quaternary. A gen­

eral description of the sequence follows (Bodenlos, 1956; Segerstrom,

1956, 1961; Carbone 11, 1970).

Las Trane as Formation

The Las Trancas Formation is the o ldest found in the region and

is Late Jurassic in a g e . It is exposed as a belt trending northwest-

sou theast from Cerro del Palmito to Bucareli (Fig. 3). The maximum ob­

served th ickness is 200 m. At the bottom of the formation is a thin bed

(30-60 cm) of g ray ish-green arkose; the matrix is a rg i l la c eo u s . A thin

gray bed, 50 cm th ic k , of graywacke concordantly overlies the a rk o se .

The top of the formation is composed of thin beds of reddish shale in te r­

bedded with thin , dark-gray l im esto n es , 10 cm th ick .

El Doctor Formation

The El Doctor Formation is in con tact with the Las Trancas For­

mation in an angular unconformity. The age of this formation is Early

Cretaceous (Albian-Cenomanian). The to ta l th ickness of the formation

ranges from 150 to 1,500 m. It is divided into four lim estone fac ie s .

Cerro Ladr6n F a c ie s . The Cerro Ladr6n fac ies is the lowest

unit of the El Doctor limestone and is the most conspicuous lithologic

. un it. It is a great calcareous mass with thick beds of gray lim estone.

10

The th ickness ranges from 10 cm to 2 m„ There are len ticu lar fragments

of dark chert interbedded with the limestone b e d s . The lithology of th is

facies is not uniform, and it can be subdivided into three subfacies: (1)

a subfacies with rud is tid s , (2) a subfacies of lithified limestone m uds,

and (3) a subfacies of fine-grained conglomerate „ The Cerro Ladr6n crops

out in the upper part of the El Doctor ran ge , in the cen tra l and northeast­

ern part of the mapped area (Fig. 3).

El Socav6n F a c ie s . The El S oca von fac ies is res tric ted to a

zone located between the San Joaquin fac ies to the northeast and the

Cerro Ladr6n fac ies to the southw est. These beds of limestone e la s t ic s

are exposed in a belt 1 to 3 km wide.

San Joaquin F a c ie s . The San Joaquin facies is composed of

thick beds of very compact, d e n se , dark-gray lim estone, with an abun­

dance of chert nodules. In general, i ts composition is similar to that of

the overlying La Negra fac ies , but it was deposited at le s s depth. It is

present in a belt 1 to 2 km wide. The San Joaquin fac ies interfingers with

the La Negra fac ies to the northeast and with the El Socavdn facies to the

southw est. The presence of small primary folds in monoclinal areas sug­

ges ts that deposition of the sediments took place over a sea floor with

enough inclination to cause underwater sliding of the unconsolidated

sedim ents . The th ickness of the fac ies is about 60.m. It is correlated

with the Tamaulipas or Aurora limestone in the northeastern part of

Mexico . The facies crops out as small bands south and northwest of the

San Joaquin area (Fig. 3).

La Negra F a c ie s . The La Negra fac ies is found over a larger

area than any of the other fac ies of the El Doctor Formation. It is a very

11

fine grained lim estone. Thin members of red shale interbedded with the

limestone beds are 10 to 30 cm thick; thin beds and len ses of black chert

are a lso p resen t, mainly at the bottom of the formation. The total th ick ­

ness of the La Negra beds appears to be riot greater than 300 m. This

facies is correlated with the C uesta del Cura limestone (Albian-

Cenomanian) of northeastern Mexico. It is believed tha t these sediments

were deposited in the deepest part of a neritic zone. The fac ies crops

out mainly in the El Doctor, Cerro de los Lirios, Cerro San N ico la s ,

La Negra, Cerro Quemado, and Cerro de los Chinos a reas (Fig. 3) .

Soyatal Formation

The Soyatal Formation is a dark-gray limestone of Late C reta­

ceous age . The limestone is interbedded with yellowish shale and gray

to light-reddish marls; i t does not contain black chert . Age of the for­

mation is Turonian. It crops out mainly in the Maconi and San Joaquin

areas and in the northeastern part of the mapped area (Fig. 3).

M ezcala Formation

The M ezcala Formation is composed mainly of yellowish-brown,

ligh t-gray , and greenish-gray clay marls in beds 5 cm to 1.2 m th ick .

Gray limestone beds, 30 cm thick, mudstone, and sandstone , 40-60 dm

th ick , are found interbedded with the m arls . These beds have been

strongly folded.

El Morro Conglomerate

The El Morro Conglomerate is composed of coarse c la s t ic rocks

with a reddish calcareous c lay matrix. This conglomerate overlies all

the lower formations with an angular unconformity. It is found as sm all.

12

iso la ted outcrops in the a rea . The age of the conglomerate is Tertiary

(Eocene-Oligocene).

Surficial D eposits

C las tic deposits of Ple istocene to Holocene age are p resent as

alluvial te r ra c e s , a lluvial d e p o s i ts , ta lu s , ca liche , and reddish residual

sediments „

Igneous Rocks

. The largest intrusive mass p resen t in the area is of granodio-

ritic composition. This intrusive mass crops out in the Deconf, El

Yonthe, D ivisadero, and La Negra areas (Fig. 3). D ifferentiated parts of

the same intrusion are a lso found in the area as stocks of quartz diorite

and as a small mass of d iorite . Andesite, dac ite , and rhyolite dikes are

a lso p resen t. The age of these intrusive bodies is middle Tertiary .

The extrusive rocks found in the area are mainly flows and tuffs

of different composition, expelled during the Oligocene and Pliocene.

These rocks are exposed near Bucareli and in the M esa de Ramirez and

M esa del Hormiguero areas (Fig. 3).

Structure

In general, the sedimentary sequence shows a northwest-

sou theast trend and dips from 40°-70Q SW, The top of the Las Trane as

Formation, composed of thin beds of sha le , crops out in a 4 km-wide

b e lt .

The intrusive rocks are exposed as s tocks, d ik es , and s il ls

of differing com positions. The sedimentary rocks were t il ted from their

original position by these intrusive bodies; hence , faulting and folding

' ' 13

are mainly re la ted to intrusive a c t iv i ty . The Maconi Valley is carved in

sha les and marls of Late Cretaceous a g e „ In a structural se n se , this

valley is a sync line , with the m assive limestone of the Cerro Ladrdn

fac ies exposed on the flanks of th is sync line in Cerro del Espoldn to the

w est and in Cerro de los Lirios to the e a s t . The sha les and marls of the

Soyatal Formation and perhaps the M ezcala Formation crop out in a syn-

cline in the Maconi Valley overlying the limestone of the Cerro Ladrdn

fac ie s .

CHAPTER 3

LOCAL GEOLOGY

The El Doctor range is composed in i ts upper part of m assive

limestone of the Cerro Ladrdn fac ie s . The slopes of the range and the

valley are composed of the lim estones, sh a le s , and marls of the Soyatal

Formation. The general strike of the beds is northw est-sou theast with

dips of about 50° SW. There are various outcrops of plutonic rocks that

have been c la ss if ied as monzonite, d io r ite , and quartz d iorite . It is

common to find metamorphic h a lo s . In the La Negra a rea , the outcrops

are represented by sedimentary ro c k s , which constitu te 85 percent of

the to ta l outcrops, igneous rocks 7 percent and metamorphic rocks 8

percen t.

Sedimentary Rocks

The limestone presen t in the area is the La Negra fac ies of the

El Doctor Formation. It is dark gray and thin bedded. The general strike

of the beds is N. 20°-40o W. and the dip ranges from 20° to 60° SW.

Folding is local and occurs mainly near the intrusive b o d ie s . Near the

contact zone, metamorphic minerals have been developed, including

w o llas ton ite , garnet, epidote, diop s ide , and v e su v ia n i te . There are

two systems of faults and fractures; the principal system is oriented

north-w est and the secondary system trends n o r th -ea s t , normal to the

La Negra intrusive body.

14

15

Igneous Rocks

Igneous rocks represent 7 percent of the La Negra area . The

intrusive rock in the vicin ity of the La Negra mine has a predominantly

dioritic composition. The b iggest dioritic mass exposed at the surface

has been emplaced as a stock with branching s i l ls and d ik es . It crops

out in an elongate form whose major axis s trikes N. 75° E. Other small

m asses of diorite are exposed at the surface in different orientations

but mainly N. 20° W. These small m asses have been emplaced as s i l ls

and dikes of porphyritic tex ture .

Metamorphic Rocks

Metamorphic rocks represent 8 percent of the La Negra area

and are predominantly t a c t i t e . This con tac t metasomatic rock is in a

more s tr ic t sense a g a rn e t i te , because it is almost entirely composed

of garnet of the green and brown varie ty , grossularite and andradite, in

tha t order. In minor proportions w ollas ton ite , epidote, diop s ide , and

vesuvianite are p resen t.

These rocks represent a transit ion zone from igneous (diorite)

to sedimentary (limestone) rock and have been formed by contact meta­

morphic effects of the intrusion into the lim estone. The th ickness of

th is zone ranges from 20 to 200 m e te rs . The rocks mentioned above are

also found in the mine workings where they have the same charac te r is ­

t ic s . Another metamorphic rock, hornfels, is not p resen t in the surface

but has been found in the mine. Hornfels is found as len se s of medium

size at the contact between the limestone and the in trus ion . It is a

fine-grained , very hard , white rock. The primary cons tituen t, w ollas­

ton ite , amounts to 94 percent. Garnet amounts to an .accesso ry 6 p e rc e n t .

16

Accordingly, the rock can be c la ss if ied as ca lc ic s i l ic a te hornfels

(Quezadas, 1972).

The metamorphic mineral spurrite is found in small bands in te r­

bedded with the marmorized l im estone . This is common in the hanging

wall very c lo se to the ore body. The spurrite is blue with white and

yellowish sh ades . Its chemical components are 25.4 percent 8102 and

62.0 percent CaO; the formula is 2Ca2*Si04-CaCO s .

The local geology is shown in Figure 4 (in pocket) . As can be

observed, it is a typical con tact metasomatic a rea . Intrusive bodies of

dioritic composition, p resen t as stocks and d ikes , are surrounded by the

metasomatic zone, which is a tac ti te composed of green and brown garnet

(grossularite and andradite , in that order) as e s se n t ia l m inerals . Near

the contact zone, the intrusive body is more s iliceous and the biotite is

a ltered to ch lorite . Surrounding the con tact metasomatic zone is the La

Negra limestone in which an area of about 50 m has been changed to

hornfels due to the effects of the in trusion . This white hornfels is com­

posed mainly of wollastonite and quartz , which makes it a very hard

rock. Interbedded with the hornfels, thin bands of tac ti te are found as

well as spurrite; th is is better observed in the mine w ork ings. Outside

of the metamorphosed limestone is the fresh , gray La Negra lim estone.

Some maps with the geology of the mine workings are included (Figs. 5

through 8).

In some sublevels the hanging wall of the ore body is limited by

a fault con tac t, as shown in Figure 7. Another in teres ting thing has been

observed: the green garnet is more c lose ly assoc ia ted with the mineral­

iza tion and the brown garnet is near the contact with the in trusion .

5000

17

3 L i m e s t o n e

3 T o c t i t e

23 Hi gh grode O r e P a s s

M a n w a y

F r a c t u r e

— V e r t i c a l F r a c t u r e s

N - 5100

0 10 20 35Lmi1 iix j kr t l — . — LmxmxiirniiK.mH.Dod

M E T E R S

i : 5 0 0

Figure 5 . G e o lo g ic map of s u b l e v e l 2317 ( 7 ) , p l a n v iew

18

\ ! / ODH D i a m o n d D r i l l H o l e i p r o i e c f e d fo Cut t hei S - T T f n n f n r i A n r o i 10 0 m E X P L A N A T I 0 N

'■^'a A 'X 'a 'X 'X . . I n t e r s e c t i on p o in t of mi ne r a l i z a t i on i ndi ca t ed wi t h d i amond dr i l l ho le No. 2 , dr i l l ed L i m e s t o n e

T a c t i t e

Q Z x n D i o r i t ®

L3 H i g h gradeLow grade Or e P a s s

Manway

F a u l t

F r a c t u r e

Ve r t i c a l F r a c t u r e s

G R A P H I C S CAL E

0 10 bnat—fanut . btii

1 : 500

N - S I O O

Figure 6 . G e o lo g ic map of s u b le v e l 2295 (3), p l a n v iew

19

N-5100

5 0 °

MW

MW85°

80°

75°

60°

70°o

LU

E X P L A N A T I O N

1 1 . l..B L imes tone

i 'L~ ' d T act i te

I - - . •• *• • ] Low grade

High grade

Head samples

© Ore Pass

^ MW Manway

) 8 5®Fault

G R A P H I C S C A L Eo iou = w =u =

20

ham35

80°

E T

1 : 5 0 0

Frac tu re

Vert ical Fractures

i 40° Str ike and Dip

Figure 7 . G eo logy and sam p l in g maps of s u b l e v e l 2266 (Cono)

5000

5 0 0

V e r f i c o l F r o c f u r e s

Figure 8. Geologic map of sublevel 2170, plan view

CHAPTER 4

ORE-BODY DEVELOPMENT

Old Mine Workings

The early workings at La Negra consis ted of a se r ies of open

cuts and short adits a ll the way up the c liff of the outcrop of the d e p o s i t ,

a d istance of 85 meters vertica lly above the La Negra patio leve l. These

sm all, scattered workings were operated during the Colonial period.

During the time of the Braniffs, about 1904, three adits were driven and

several shafts were sunk below the outcrop (Fig. 9). The first one was

the La Negra ad it , at 2,352 m elevation , from which drifts and c rosscu ts

were driven to determine the extent of the ore body. This adit is the

only one that was driven into the ore body; the other two adits m issed

i t . The second adit was driven 1 5 .4 m below the f i r s t . This adit did not

in te rsec t the ore body and encountered only scan t m ineralization in the

foot w a ll. Two shafts connect the first and second ad its ; one is 38 .9 m

deep and the other is about 25 m deep . The third adit driven was La

Blanca, 152 m vertica lly below the first ad it , on the La Negra leve l.

La Blanca is too far from the ore body and passed into the foot wall of

the intrusive m ass; it did cut some low m ineralization in its present

face , and th is was mistakenly thought to correspond to the same ore

body exposed in the number one adit on the La Negra lev e l. The length

of the La Blanca adit is 325 m.

21

22

Surfoce workings

Level 1 (La Negro) E-2352

Level 2, E - 2 2 3 7Level 3, E- 2 2 2 5

Lo Blanco adit, E - 2 2 0 0

BONANZA

SOTOL

Ore body, Level

Ore body, Level

Ore body, Level

N 5100

i n

UJ

N 500 0

/ // /

Figure 9. Composite map of the old mine workings of the La Negra mine

23

During P eno les1 1960 exploration program, a fourth adit was

driven 49 m below number one ad it . This is now known as level number

3. This adit in te rsec ts the ore body, and some drifts and c rosscu ts were

driven in order to determine the width and length of the ore body at that

e levation .

Preproduction Development Work

Compania Minera La Negra y Anexas, S .A . , wholly owned by

Industries Penoles , S .A . , started the development work of the La Negra

mine in the middle of. 1968. As explained above, some mining was done

before Penoles took over the p roperties . All of these mine working were,

and s t i l l a re , of great use in the preparation and exploitation of the m ine .

The first part of the exploitation stage was planned in the upper

part of the ore body, from elevation 2,266 to 2,383 m (Fig. 10), and the

second part from elevation 2,100 (the lowest limit of the ore body during

the exploration stage of 1967) to 2 ,200 (La Blanca leve l) . With th is

knowledge, a main ad it , Socavdn Principal, was driven at 2,000 m e le ­

vation . The length of Socavon Principal is 1 ,538 m, and its c ross s e c ­

tion is 4 by 4 m eters. It was driven perpendicular to the general strike

of the ore body in order to cut it in case of a continuation of m ineraliza­

tion at th is leve l, but it only found the lime stone - ta c t i te contact with no

economic m ineralization. The main reason for the tunnel was to provide

for haulage of the ore coming from the mine workings (Figs. 11 and 12).

The Socavdn Principal La Negra is connected with the mine workings by

an ore p a s s , Chorreadero G eneral, which is paralle l to the dip of the

CROSS SECTION TO N 15° W

LONGITUDINAL SECTION TO N 7 5 ° E LEVEL 1

LEVEL 1

L E V E LE-2 3 0 0

60 80

LA BLANCA LEVEL

1 : 2000E-2200E - 2 2 0 0

LA BLANCA LEVEL

E X P L A N A T I O N

T o c t i t e

L i m e s t o n e

O r e b o d y

E - 2 1 0 0

Figure 10. Longitudinal and cross sections of the La Negra ore body

3,5

COCO

CL

UJCL

LUO

oe>5?

LuCtO

O, o

vc 6^

Nee"93 ^X.V

1%

v - ^ ° 0

26

SUBLEVEL (OPEN CUT)

S U B L E V E L (OPEN CUT)

P I L L A R

P IL L A R

P I L L A R /

SU B L E V E L /

S U B L E V E L

S U B L E V E L

S U B L E V E L

//

Scale 1 : 500

Figure 12. S ub leve l p r e p a r a t io n , s ec o n d s t a g e

27

ore body. In this ore p a s s , at the La Blanca leve l, there is a minus 20

inch grizzly in order to control the size of the ore fragm ents .

The total inclined length of the ore pass is about 400 m ete rs ,

and its section is 4 by 4 m e te rs . In order to have better efficiency in

the transportation of the miners and the mine equipment, a vertica l se r ­

vice shaft of one compartment has been driven from the Socav6n Princi­

pal La Negra to level number 3. The to ta l depth of th is shaft is 300 m,

and it has a cross section of 3 .5 by 3 .5 m ete rs .

Mining and Sampling Methods

Due to the irregular form of the ore body, a combination of d if­

ferent mining methods has been chosen in order to obtain the h ighest re ­

covery feasib le with low cost and to have the best control over the

dilution of the ore (Cardona, 1968).

There are two sec tions of the ore body which are similar in

w id th , length, and to n n ag e , so it is poss ib le to use the same mining

method in both sec t io n s , with ju s t a lit t le varia tion . The most economic

and appropriate method is a combination of sublevel and long hole b la s t ­

ing m ethods. The decis ion to use th is method was based on the follow­

ing physical charac te ris tics of the ore body: width, d ip , and hardness

of the w a lls . In general, the method is as follows (F igs. 11 and 12).

From the general ore p ass (Chorreadero General) and each 10 vertical

m eters, c rosscu ts are driven to the hanging w all. Then drifts of 3 .5 by

3.5 meters in cross section are driven along th is contact between the

s il ica ted limestone and the mineralized zone, both north and south to

the limits of economic m ineralization. This is easy to do because the

28

hanging wall is very sharply defined and the m ineralization ends at the

contact with the lim estone , which is b a rren . The next step is to open

the drifts to the full width of the ore body. Once the sub levels are com­

p lete ly enlarged to the ore l im its , the remaining p illars between sub-

levels are about 6 m in th ickness (the final height of the sublevels is

about 4 m ). These pilla rs are then drilled with vertical and inclined drill

holes positioned according to geological and sampling cross sections

which are drawn to plan ore breakage and to control dilution as much as

p o ss ib le . These p illars are then broken by b las ting , according to a pro­

duction program previously planned, starting in the same section of the

general ore pass and going line by line (separation between each line is

1.5 m) to the north and south up to the mineralization lim its .

To take advantage of the form of the upper part of the ore body,

which will be mined out f i rs t , it has been planned to u s e , in longitudinal

cross sec tion , the form of an inverted cone. In cross sec tio n , the zone

to be mined first is tabu lar. The slope of the north and south sides of

the cone is 45 deg rees . The main reason for adopting th is form is for

eas ie r and cheaper exploitation. The broken ore from the p i l la rs , which

represen ts 60 percent of the mine production, falls by gravity into the

main ore p a s s . The broken ore that comes from the preparation of the

sublevels represents 40 percent of the mine production; th is is hauled

to the main ore p a s s . This ore fa lls to the 2 ,000-m eter lev e l, passing

through a minus 20-inch grizzly in s ta lled on the 2 ,200-m eter leve l.

At 20 m below the Socav6n Principal, at the 1 ,980-m eter lev e l,

there is a jaw crusher to reduce the ore to minus 5 inches (Figs. 13 and

14). The crushed ore is then transported by an inclined conveyor (+ 17

29

ORE MINED

BROKENORE

o GENERAL ORE PASSae

coGRIZZLY

GENERAL ORE PASS

FEEDER

CRUSHER 24 x 36

CONVEYOR BELT

ORE POCKET

TRUCK LOADING POINT

E - 2 0 0 0

To the plant

S c a le 1 : 1 0 0 0

Figure 13. Ore h a u lag e and mining s y s t e m , i s o m e t r i c d rawing

30

*:)v‘

1 : 3 300

GRAPHIC SCALE

50 100 150 200 250

EX PL A N A T ION

V L V 3 L I M E S T O N E

ORE BODY

T A C T I T E

E - * X I N T R U S I V E b o d yMETERS

Figure 14. I so m e t r i c p ro je c t io n of the La N eg ra ore body

31

degrees) to the ore bin , which is 20 m above the. Socavdn Principal.

From th is point the mineral is transported by trucks to the flotation p lan t,

about 2 .5 km d is tan t .

The 10-meter separation between each sublevel was planned in

order to have a maximum ore dilution of 10 percent. The larger the se p ­

aration, the greater the dilution because of the irregularities of the ore

body .

The lower section of the ore body has been planned to be mined

by the same method, with minor differences according to its shape. Two

general haulage levels have been p ro jec ted . One, at the 2 ,150-m eter

e levation to mine the orebody section from th is level to 2 , 200 m, will

be done by driving sublevels each 10 vertica l meters (Fig. 10). The

other general haulage level has been projected at the 2 ,100-m eter e le ­

vation to mine the ore body section between th is level and the 2 ,15 0 -

meter level by the same method of su b leve ls . Both the 2150 and 2100

levels will be connected with the general ore pass by another inclined

ore p a ss in order to transport the broken ore from the sublevels and p i l ­

la rs . The a cc ess to these general levels will be from the service shaft.

The northern section of the ore body, called the "Dog Nose"

(Fig. 10) will a lso be mined by sublevels but with a different type of

equipment because of the width of the ore body in th is section is about

2 m eters.

The middle sec tion , from the 2200 level to 2266, needs more

exploration in order to define the form of th is narrow m ineralized section

better and to choose the bes t mining method (Fig. 10).

32

Two sampling methods are used in the m ine . Once each drift

has been finished in a section of 3„5 by 3 .5 meters to the hanging w all,

a se ries of diamond drill holes (size EX) are drilled every 5 m toward

the footwall in order to determine the ore l im its . This is n ecessa ry due

to the irregularity of the ore body and a lso because the mineralization

toward the footwall gradually decreases in value in such a way that the

limit of the stopes must be determined by a ssa y (Fig. 13). The other

sampling method used is to cut channel samples in the b ack , fa c e s , and

w alls of the su b leve ls , as they are n e ed e d . Because of the hardness of

the rock, it has been found convenient to use a d isk with a diamond c u t­

ting edge, driven by a pneumatic motor. The channels are 2 .5 inches

wide and about an inch deep . The separation of the samples is from 1.5

to 2 m. From the combination of these two methods, sampling maps are

made (Fig. 15), which are used to aid management in controlling m ining,

dilution, combination of grades and in calculating ore tonnage and aver­

age grades.

Scale of Operation and Life of the Mine

The annual production of the mine was planned to be 120,000

metric tons of ore per year . Actually (June 1973) , the annual production

has been increased to 156,000 metric tons per year . According to the

ore reserves and the annual production originally estim ated , the life

of the mine was calcu lated to be about 12 y e a r s . Ore r e s e rv e s , how­

ever, have been incremented by small d islocated bodies in the hanging

wall and footwall of the main ore body. More important is the fact that

exploration for other ore bodies at depth and for a continuation of the

33

-5100

5 0 0

G R A P H I C S C A L E

10

SAMPLENo.

WIDTHMETERS

AVER AGE ASSAYSA9

g / tPb%

Cu%

zn%

5 - 1 4 . 0 0 3 5 0 2 8 0 . 5 0 3 55 - 2 9 . 5 0 4 00 3 . 3 0 . 7 0 2 . 75 - 3 6 5 0 6 00 h_ 4. 0 0 .80 4 . 05 - 4 3 . 25 150 _ 0 . 6 OTZ5 0 : 35 - 5 5 . 00 500 _ 4 , 0 0 . 6 0 5 . 05 - 6 12 . 0 0 550 3 .5 0 .60 6 . 05 - 7 2 . 0 0 90 ^ 0 : 5 0 . 3 0 0 . 65 - 8 8 . 2 5 390 2 . 0 0 . 4 0 3 . 0- p - 9 5 . 5 0 3 40 1 .8 0 . 5 0 3 . 55 - 10 7 . 5 0 12505 - H 9 . 50 580 _ 2 7 0 6 0 3 .05 - 12 10 . 00 TfrO . 0 . 5 0 4 .05 -13 13 00 1300 6 . 5 0 .80 5 . 05 - 1 4 1.5 , 2 5 6 00 4 . 0 0 . 8 0 4 65 - 1 5 3 . 75 40 0 3 .0 0 . 4 0 4 . 05 - IB 2 . 00 50 0 . s 0 . 30 1.0 "5 " 17 3 . 7 5 400 3 , 5 0 . 50 4 . 0 —& -18 7 . 5 0 150 1 5 0 25^ 1.05 -19 _ 1 , 5 0 2 50 i.o 0 . 3 0 1 5| - | o 5 , 150 2 . 0 0 -19 1.0r - n 4 . 00 300 1 .5 0 .40 1 .25 - 2 2 14 . 00 ISO 1 .0 0 . 3 0 1.25 - 23 1 3 . 0 0 450 2 9 0 . 7 0 2 . 9

- 5 " ^ T 4 9 . 0 0 100 0^.8 0 . 4 0 0 . 95 - 2 5 33 . 5 0 550 3 5 0 . 80 3 . 35 - 2 6 7. 00 88 0.7 0 . 20 1 0 _5 - 2 7 500 4 0 0 . 7 5 4 25 - 28 9 .50 1 25 . 1 2 0 . 3 5 1 . 05 - 2 9 24 .50 5 80 4 0 0 .82 4 . 5 _

0 . 9 0 35 7 . 2b -31 IB . 00 no _ 1 0 0 .40 1 . 55 - 32 3 0 . 0 0 4 75 3. 5 0 .77 3 . 75-33 . J 50 TTO rrrro 2.15 - 34 ~2 1 .50 180 1.2 0 . 4 0 2 . 45 - 3 5 2 0 . 0 0 370 2 . 8 0 . 7 0 2 . 85 - 3 6 6 .75 120 0.85 0 . 3 5 1 . 5

E X P L A N A T I O N

b.1 ■ 1 i 3 L imestone

E H 3 = lH 3 T a c t i l e

L_ ■ ■ '- •■■'..J] Low mineral izat ion

5 - 2

e

<s>H.

3 High mineral izat ion

- Head samples

Ore Pass

Manway

h Diamond Dril l Holes, (Horizontal)

Figure 15. Map showing sampling method, diamond drill ho les , and pocket of mineral at the footwall, sublevel No. 5 (elevation 2317 m)

34

La Negra ore body to the north and a lso at depth is in progress with good

r e s u l t s , which will be mentioned in Chapter 6.

Ore Grade and Tonnage

The exploration program conducted by Penoles at La Negra,

started in 1964 and fin ished in 1967 after discovery of two ore b o d ie s ,

La Negra and El A lacrin , and the outlining of the ore r e s e rv e s . During

those 3 y e a r s , 40 diamond drill holes were drilled in the La Negra area

and 14 in the El Alacr&n a rea . Of the 40 in La N egra , 25 in te rsec ted the

ore body and 15 were barren or in te rsected low-grade m ineralization . All

of the 14 drilled in El Alacr&n in te rsec ted m ineralization.

The ore reserve map (Fig. 16) is included here and the re la ted

detailed calcu lations are given in Appendix A, but only in regard to the

La Negra ore body, since th is is the main subject of the study . The ore

reserves of El Alacr&n will only be included in the summary of the ore

reserve estimate and only in a general form „

The ore reserves and average a s sa y s in both of the ore bo d ies .

La Negra and El Alacr&n, using 10 percent mining dilution are:

W eighted Average Assays

Metric TonsAg

g/MTPb%

Cu%

Zn%

La Negra 790 ,568 .9 335 2.1 1.28 4 .6

El Alacr&n 577 ,858 .2 115 trace 1.86 1.5Total 1 ,3 68 ,42 7 .1 254 1.4 1.52 3 .3

The in itia l exploration of the La Negra ore body covers only a

vertica l range of 275 m from the surface (elevation = 2 ,375 m) to

LONGITUDINAL SECTION OF T H E L A NEGRA ORE BODY

P 31P- 26 \ Bo r r a n

P 28SN - 6

E - 2 3 0 0o P | 4 ° p - |6 ■' B a r r e n.5.00m

22 p̂ ieV 23 a V \2 4 a

15 B] 26

20

5.00 m

/ MO o P lS B a r r e n

P 10

P 2125

B a r r e n

I . I O n VE - 2 2 0 0

4 .5 0 mEXPLANATION

No. 1429

P 35

very low m ine­ra l izat ion

^ Proven Ore10.00 m P -3030

P 34Probable OreBarren

3 2 34

P 1533

1.50 m L.E - 2 1 0 0P 36

DIAMOND 1 A S S A Y S

DRILL HOLE NUMBER

M E T E R SINTERVAL

C /ton A<J

%Pb

%Cu

%Z n

P -5 1 0 0 606 4 2 0 70 5 2P - 6 1 5 . 0 0 425 2 5 0 40 5 4P - 7 1 4 40 603 3 3 0.60 5 2P- 8 8 . 00 203 1 3 3.30 1.5P - 9 II . 80 575 2.9 0.50 5 2P - II 8 . 30 403 1.9 0.90 2.2P - 18 10 . 20 501 5 4 0.30 10.4P - 23 8 50 601 5.6 0.80 9.0P - 24 10 , 00 . 430 2 0 0 50 4 1P - 26 0 80 ■ 506 2.8 0 40 4.0P - 2 8 10 00 314 2 4 0 90 3 0P - 29 . 1 5 . 0 0 712 5.4 3 90 10.4P - 3 1 17. 75 282 1.8 0.40 2.9P - 32 1 . 10 646 8 0 0.80 9.9P - 3 3 1 . 05 112 1.2 101 4 6P - 34 32 90 [ 646 8.0 0.80 9.9P - 3 6 2 . 10 354 2.0 0.56 9.2P - 39 6 . 00 535 2 3 3.17 9.3P - 4 0 7. 10 171 1.2 075 1.70 6 00 530 4 3 0.40 7 2b L j l -70 585 5 7 0 60 9.3c _ 7 . 10 455 3 4 0 46 5.7d 6 . 7 0 267 1 .0 0 10 1 1.1d 10 0 0 332 7.1 0 50 6 6e 12 80 336 4 7 0 50 4 2f 2 65 351 2.1 0 56 3 1a 2 00 30 2 2 3 0 30 .3 2 _h 8 00 4 78 2 4 0 50 1 3 2i .. 6 00 525 3 3 0 50 ̂ 6 j__j 10. 00 3 16 4 0 0.70 4 0S - l _ _ 2 . 3 0 . . 326 2.6 0 83 3.8No. 14 1 6. 15 162 0 9 0 60

f ' . ' -No 15 A 3. 10 554 8 9 1.00No 15 B _ 4 . 15 151 - 3.30 1 -

G R A P H 1 C S C A L E

0 20 60 100

M E T E R S

I!2000

Figure 16. Ore reserve estim ate of the La Negra ore body GJC n

the 2,100 meter e levation , because at that time it was very difficult and

expensive to explore deeper. This would have required very long h o les ,

and the angle of in tersection with the ore body would have been too

a c u te .

During the subsequent de ta iled exploration s ta g e , very p leasan t

surprises have been encountered. In some p la c e s , the ore body is short­

er than expected but in most it is larger and wider. Consequently , actual

ore reserves have been found to be 20 percent above the original e s t im ate .

Density of the rock was ca lcu la ted according to the formula,

Density = W e i g h t / V o l u m e , and i t was found to be 3 .7 5 . The rock sample

was weighed and then submerged in a graduated te s t tube containing

w ater. The difference between the water level before and after the add i­

tion of the rock is the volume of the rock sample .

A summary and deta iled estim ate of the ore reserves found b e ­

tween 1964 and 1967 are given in Appendix A.

CHAPTER 5

ECONOMIC GEOLOGY

The La Negra ore body occurs in the outer limits of the contact

metasomatic zone (Fig. 10), between the limestone and the ta c t i te . The

hanging wall of the ore body is very sharply defined; the mineralization

ends in the contact of garnet tac tite with a white s i l ica ted limestone

with abundant w ollastonite and ore mineralization does not continue into

the lim estone. The tac ti te is found on the footwall of the ore body. The

highest values of the ore are found at the contact with the lim estone ,

while the grade decreases gradually toward the footwall. Because of

t h i s , it is difficult to define the exact limit of the economic m ineraliza­

tion by v isua l observation . The limit has been defined by diamond drill

holes and supporting laboratory t e s t s . All of the tac ti te zone is m ineral­

ized , but its grade is too low to be considered o re , except for the

hanging-w all portion. The intrusive rock (diorite) is found at the inner

contact of the tac ti te z o n e . The general strike of the ore body is N .

15° W at the surface; as it in creases in depth, the strike changes to

N . 45° W . at 250 m below the su rface . The average dip is 60° SW

(Fig. 10).

In cross sec tion , the ore body is represented by two large

le n s e s , one above the 2 ,200-m eter level and a second below this e le ­

vation . These two lenses are connected in a short and narrow w aistlike

interval where the average ore th ickness is only about 2 m eters . The

ore body is in general concordant with the limestone bedding, and it is

37

believed tha t the reduction in width is due to the strong folding in the

limestone in th is s e c t io n . The average width of the ore body is about 11

m e te rs . In a longitudinal projection (Fig. 10), the ore body has an hour­

g la ss shape . The minimum strike leng th , 20 m e te rs , occurs at the La

Blanca level (elevation 2,200 m). Both above and below th is leve l, the

length of the ore body in c re a se s , reaching 150 meters a t the 2 ,300-m eter

lev e l. The known vertica l range of the ore body was 280 meters before

the exploration program of 1971, but the lower part was s t i l l undeter­

mined, since no exploration had yet been done below the main haulage

ad it . Another important charac ter is tic of the ore body is that its southern

part is wider and richer than the northern part between leve ls 2,200 and

2 ,300 , whereas ju s t the opposite occurs from the 2 ,300-m eter level to

the surface (Figs. 5, 6, and 7).

Ore Control

There are severa l factors tha t could have controlled the c ircu­

lation of mineralizing solutions and the subsequent ore emplacement.

The most important ones are the lithology, stra tigraphy, s tructure ,

chem istry , and density and texture of the host rock.

Litholoaic Factors

There are two important types of alteration of the limestone;

one is where the limestone was transformed to a tac t i te near the ore

body and the second is in the hanging wall of the ore body where the

limestone has been mainly s ilic if ied and rec rysta ll ized with development

of w o lla s to n i te . This suggests that the lim estone, which is now altered

39

to t a c t i t e , was an argillaceous limestone and that the second limestone

was re la tive ly pure.

Stratigraphic Factors

The ore body is at the contact between limestone and t a c t i t e .

It a lso conforms very c lose ly to the limestone bedding, and the ore body

dips with the flank of the fold at 50o-80° W . Every change in dip of the

limestone is a lso noted in the ore body.

Structural Factors

The major structural control of the ore body seems to have been

folding. The La Negra ore body is controlled by gentle folds of the lime­

stone b e d s . It is found along plunging noses of secondary an tic lina l

flexures in one flank of a local broad fold (Sanchez M ejorada , 1968).

In another structural a sso c ia t io n , thick lenses of mineral are

found in the concavities of the limestone beds pointing toward the tac ti te

zo n e , while the ore body is short and narrow where opposite conditions

occu r.

Chemical Factors

Chemical action was an important factor in the emplacement of

the ore body. The metasomatic effect caused by the intrusion of the

diorite brought about the rec rysta l l iza tion , recombination, and the for­

mation of new m in era ls . The new m in era ls , formed mainly in the tac ti te

zone, include green and brown varie ties of g a rn e t , diop s id e , and perhaps

vesu v ian ite . This new mineralogy and i ts arrangement in the tac ti te zone

changed the texture and density , thus increasing its perm eability , which

40

favored the passage of the mineralizing solutions to replace the minerals

of the tac ti te zone. This chemical ac tion , which made the rock more

favorable to m ineralization, is regarded as "ground p repara tion ." In the

outer limits of the tac ti te zone, a hard, dense , s ilc if ied limestone is

p resen t. In th is rock, the metamorphic and metasomatic effects caused

s il ic if ica tion of the lim estone, making it more dense and impermeable.

These rocks constitu ted a seal or barrier to the advances of the mineral­

izing solutions c irculating within the tac ti te z o n e .

Density and Textural Factors

As has been shown in the description of the chemical fac to rs ,

the texture and density of the host rock were important factors in ore

control. Change in density and texture plus the increased permeability

of the rock are consequences of the chem ical factors already described .

The se lec tive position of the ore body and of some m ineralized lenses

delimited by the s il ic if ied limestone as well as the occurrence of some

small bodies of limestone with no m ineralization at a ll within the center

of the ore body i l lu s tra tes the se lec tiv ity of the mineralizing solutions

in the zones of more perm eability . Furthermore, where the tac tite is .

fine grained, dense , and only slightly fractured, ore is very low in

g rad e . .

It can be considered that chemical factors have apparently been

the most important ones of the ore control factors a lready mentioned.

Ore Mineralogy

The La Negra ore body is of very complex mineralogy. The

economic metals in the ore body include s i lv e r in h e s s i t e , Ag2Te, a very

41

elusive mineral detectable only by a very detailed petrographic study

(W illiams, 1968), lead in ga lena , zinc in m arm atite, and copper occur­

ring almost exclusively in chalcopyrite . Silver and lead are c lo se ly a s ­

soc ia ted . Silver (hessite) is found as small blebs arranged in cleavage

planes of galena c ry s ta l s . The economic m ineralization is found as m as­

sive sulfides a sso c ia ted with the following non-ore su lfides: p y r i te ,

p resent in very minor proportion and arsenopyrite and pyrrhotite in great

proportion. Some schee lite and traces of gold have been found.

The highest values of m ineralization are found ju s t at the con­

tac t of the tac ti te with the lim estone. Toward the footwall, m ineraliza­

tion in the tac ti te is not as m assive as at the contact; ac tually , it is

d issem ina ted . In th is zone , bes ides p y r i te , arsenopyrite , and pyrrhotite ,

certain gangue minerals are found, including c a lc i t e , quartz , d iopside,

epidote, se r ic i te , ch lorite , and garnets (the green and brown varieties ',

grossularite and andradite , in that order).

Mineral Paragenesis and Zoning

The following paragenetic sketch is a compilation of deta iled

petrographic studies made by Institu te de G eologia, UNAM, 1966;

Guilbert, 1966; Geologia y M ineria, S .A . , 1967). These studies have

been based on the investigation of seven ore samples taken from differ­

ent diamond drill h o le s . These samples were studied in thin section

under the polarizing m icroscope. X-ray diffraction and fluorescence

analysis were a lso made .

According to these s tu d ies , the paragenetic sequence shows

that after the formation of the ca lc ic s i l ic a te s (diopside and garnets) .

42

the sulfides were deposited as follows „ Pyrite appears as the o ldes t,

pyrrhotite is partially contemporaneous with pyrite but mostly younger.

Arsenopyrite came after all of the pyrite but is s t i l l included in the

depositional time of the pyrrho tite . Marmatite and chalcopyrite are

sim ultaneous. Galena overlaps the m arm atite-chalcopyrite but continues

beyond the general se q u en c e . The paragenetic sequence can be crudely

sketched as follows:

Pyrite ..................

Pyrrhotite 1— ...................... —

Arsenopyrite

Marmatite „ - — , ,

Chalcopyrite ̂ r

Galena ,

The mineral sequence was completed by secondary m ineralization of c a l -

c ite , which under high pressure conditions was deposited in the in ter­

s t ice s not occupied by the sulfides .

In the study of samples by X-ray diffraction and fluorescence

a n a ly s is , s i lver , camium, t in , m anganese , and zirconium were detected

in small portions. Silver is p resent a sso c ia ted with galena and cadmium

with m arm atite. Based on the sampling of diamond drill holes and mine

workings the following mineral zonation can be e s tab l ish ed . Andradite

is found in greater proportion than grossularite near the in trusion , and

the reverse situation is found near the limestone co n tac t . Lead and

silver decrease in depth and a lso toward the intrusive m ass . Copper

and zinc increase at depth and toward the intrusion (Fig. 17).

43

2300 m

2200 m

2100 m

2000 m

0 U I C R O PAg

Cu

PbH

NHH

Zn

L A NEGRA ORE BODY

Relative scale for si lver 100 gm. per metric - ton equivalent to 1.0 % for base metal.

G R A P H I C S S C A L E S

VERTICAL0 25hrmrinnnj

50rbmrr

100HORIZONTAL

o 1% 2% _ tnc

3 %nsabr:

4 %--1

m e t e r s 100 200 300 400

Figure 17. Variation of m etallic contents at d e p th , based on average a s s a y s , 100-m intervals

44

Common mineral a sso c ia t ions are: pyrrho tite -chalcopyrite ,

g a le n a -h e ss i te , and marmatite-cadmium. Arsenopyrite is found in g rea t­

est concentration either where the lead -s i lv e r values are high or where

the copper-marmatite is high. Pyrite, in g e n e r a l / i s erratic and occurs

in very minor concentrations .

Ore G enesis

The La Negra ore body is. an epigenetic deposit a sso c ia ted with

an intrusion of dioritic com position. This intrusion is the origin of all

the metamorphic and metasomatic effects in the ad jacent limestone and

the typical metasomatic or pyrometasomatic ore body i ts e l f .

The age of the intrusive body has been determined by the K-̂ Ar

method, in Teledyne Iso topes , W estwood Laboratories in the United

States of America. The resu lts of the analysis are:

SpecimenIsotopic Age

(m.y.)Rad — 6

SccAr XI0 %ArRad

%K

KA 71-61 38.8 + 0 .82m5.51 73 3.51

Whole rock 38.6 ± 0 . 8 5.49 70 3.53

The constants used for the age calculation were X = 4 .72 x 10~10 and

y~^ , x e = 0. 585 x , and y - ̂ and = 1.19 x 10*^ atom percent

of natural po tassium . The error indicated for the reported ages takes

into account a ll sources of analy tical errors.

The samples submitted for the age determination were co l­

lec ted from two different lo ca tio n s , one from the Socavdn Principal La

Negra at an elevation of 2,000 m (approximately 380 m below surface

45

and from the La Blanca adit at 2 , 200-meter elevation approximately 180

m below su rface ) .

This study has determined that the age of the intrusion is 38.7

+ 0 .8 m .y . Based on th is determination and with the consideration that

the intrusion was the source of mineralizing solutions which formed the

known ore bod ies , the age of both can be considered about the sam e.

According to th is a g e , both the intrusion and the ore body were formed

in the middle Tertiary period.

The thermal and high pressure effects caused by the intrusive

mass can be considered as the first stage of the ore-body formation.

During th is s ta g e , the limestone was recrysta ll ized and changed to

marble and the whole metamorphic halo was developed around the intru­

sive m a s s . During th is s tag e , there was no addition of new elements

but simple re c rysta lliza tion and rearrangement of the already existing

m inerals.

The second stage of the ore -body formation was characterized

by the addition of hydrothermal fluids coming from the intrusive m a s s .

The main consituent of these fluids was s i l ic a , which in contact with

the limestone gave rise to l im e-s i lica te gangue m inerals, such as gar­

ne t, w o lla s to n ite , d iopside, e t c . As a consequence of th is p ro c e s s , a

metasomatic aureole was formed surrounding the in trusive m a s s . The

resulting type of rock is known as tac t it e or skarn, composed mainly of

g a rne t . The two s tages already described acted as "ground prepara tion ,"

which is described by Park and MacDiarmid (1964) as any prem etalization

process that increases the perm eability, causes a favorable chemical

change , or induces b ritt leness in the rocks which may develop an area

46

that will localize deposition from the pre bearing f lu id s . Such a change

makes the country rock more receptive or more reactive to the ore bear­

ing so lu t io n s .

The third stage is characterized by the introduction of mineral­

izing solutions v The m etallic constituen ts replaced the ca lc ic s i l ic a te s

of the t a c t i t e , giving r ise by th is p rocess to the ore body. This p rocess

was res tr ic ted mostly to the outer limits of the tac ti te zone at the con­

tac t with the s ilic if ied lim estone. This limestone is very d e n s e , fine

g ra ined , and very hard, containing no mineralization a t a l l . The miner­

a liza tion of economic grade in th is case is in the tac ti te and it ends

abruptly in contact with the s ilic if ied limestone at the hanging wall; to ­

ward the foot wall it gradually decreases in the direction of the intrusive

c o n ta c t . The concentration of high-grade mineralization in the tac ti te

zone ends at the contact with the s ilic if ied lim estone, and the absence

of mineralization in the limestone zone suggests that the tac ti te has a

higher permeability and more favorable chemical properties due to the

"ground preparation" p ro c e s s . The difference in time between the firs t

and second s tages could have been sm all. However, between the second

and third s t a g e s , the difference in time could have been longer in order

for the "ground preparation" process to take p lace . It is poss ib le that

ju s t after the mineralizing process a la s t pulse of the fluids brought

some ca lc ic solutions which now filled the intergranular spaces not o c ­

cupied by the su lf ides .

Considering the se lec tiv ity of m ineralization in the ta c t i te , the

original type of rocks was probably a se ries of limestone beds with local

d ifferences; the a ltered zone where the tac ti te is p resen t could have

47'

been an argillaceous limestone which was favorable to the formation of

the ca lc ic s i l ic a te s of Fe and AL The s il ica ted limestone in the hanging

wall of the ore body could have been derived from a pure limestone which

came in contact with siliceous solutions from the intrusive m a s s , giving

rise to the formation of a pure ca lc ic s i l ic a te , such as w o lla s to n i te .

The impermeability, h a rd n e s s , and high density of the limestone as well

as the envisioned fault zone could indicate a textural and structural

limit of m ineralization in the hanging wall where the mineralizing so lu ­

tions stopped and, because of lower temperature and p ressu re , the c a l ­

c ic s i l ic a te s were replaced by the minerals in solution (Gaytan Rueda,

1971).

CHAPTER 6

EXPLORATION

Exploration target No. 1 at the La Negra mine has been planned

in order to place a limit on the ore body at depth. This exploration can

be divided in two s t a g e s , with the first from the e levation of 2,000 to

2,100 meters and the second deeper than the elevation of 2,000 meters

(Figs. 18 and 19). In order to understand the exploration program, the

following charac ter is tics of the ore body and its geologic interpretation

are mentioned below.

1. As the ore body goes deeper, i ts general strike becomes more

w esterly . Thus, its strike at the surface (elevation 2,352 m ),

which is N . 15° W . , changes gradually at depth to N . 45° W.

at an e levation of 2,150 m (Fig. 20).

2. A longitudinal section of the ore body shows tha t its lower por­

tion tends to rake to the northwest (Fig. 10).

3. The average dip of the ore body is 60° SW; if th is were con­

tinuous a t depth it would project to an elevation of 2,000 m at

the location of the crusher (Fig. 18).

4. Due to the preference of the ore body emplacement to the outer

part of the tac t it e zone, the tac ti te - l im e stone contact is the

target for exploration.

5. As observed in cross sec tion (Fig. 10), the ore body known to ­

day shows very definite zones which are repeated with analogous

48

L I M E S T ON E

I------------------- 1 T A C T I T E

I * * *1 DIOR I T E

I j HIGH G R A D E

F A U L T

DIAMOND DRILL HOLES

P R O J E C T E D ORE BODY E L E V A T I O N 2 1 0 0 m

L C r u s h e r \ \ \

Figure 18. P lan v ie w showing t a rg e t zone N o . 1

SECTION N 8 0 ° W LOOKING N 1 0 ° E

LA NEGRA ORE BODY

3 Limestone

3 Tact i le

T a c t i l e3 Diori te ELEVATION 2100 m

•J High grade

-o Diamond dri l l holes

20

SOCAVON (Adit) x LA NEGRADIAMOND DRILL STATION

P r o p o s e d DDK

E L E V A T I O N 2 0 0 0 m

Figure 19. Cross section of the La Negra ore body exploration program between elevation 2,000 and 2100 m

Ref

eren

ce

Line

To

S vr

f oc

e51

M E 5 T 0 N Ei n f e r r e d

SERVICE SHAF THOIST

X

D D H T D. 112 .00 m

a/ > / MINERALIZED CONTACT THE LA NEGRAORE BODY II

m iLIMESTONE

E L A b ^ C R ORE BOD

ERALIZ&D ZONE 9 .30 mLOW GRADE < 2 0 0 9 / t Ag

TACTI

xxx\x>ux v x\ v

\ x x x x xX X X X

EXPLORATION DRIFT TO THE N ^ T H LEVE L 3 . _ / .

- - « / Xx * ' X e s 0 x

x / x ^ x x / X X6

X x X x ■?P L A N A T I O N'-'W iy xw / x x x / x X ORE BODY x

/ x X / , , X X X /

X

X \X w X X \

i n Limestone

T cc t i+e

I x x x j Dior i te

!"<,% = / cLol Ore bodyV # A NCRUSHER '

I Fa u 11

■ v W f ^ h i /) / .

X HOIST x x x X

1 : 2 000% ......... Q L " s u r f a c

LEVEL 3 ELEVATION 2 3 0 0 m

G R A P H I C S C A L E

4 0 8 0

E

ORE BOELEVATIBfhk 2352 m

Fracture

Vertical Fracture

1, 2, 3, 4 Mineral ized zones, mainly copper.Average Assays > 1 %

Figure 20 . G e n e ra l i z e d g eo lo g ic map along Socavdn La Negra and El Alacrdn

c h a ra c te r is t ic s . There are two zones where the width is more

than 10 m and a lso two narrow z o n e s , From the surface to e le ­

vation 2,266 m , the average width of the ore body is 13.5 m;

from elevation 2,266 to 2,200 m, the ore body is very narrow

with an average width of 2 .0 m; from elevation 2,200 to 2,120■ r

m , the average width of the ore body is 18.5 m; from elevation

2,120 to 2,100 m again the ore body is very narrow, averaging

2.0 m in w id th .

6. There is one mineralogic charac teris tic which has to be taken

into account during the exploration. The values of lead and

s ilver decrease at depth, while copper-zinc increase ; th e re ­

fore, it could be expected to have a deeper ore body where the

copper-zinc values would be higher than those of lead and

s ilver (Fig. 17).

The geology of the Socavdn La Negra shows one radical change

in rela tion to that of the upper l e v e l s . Based in the projection of the

lime s to n e - tac ti te contact from the upper part of the ore body, where the

average dip is 60° SW, there is a horizontal d isplacem ent of the contact

at the elevation of the Socavdn La Negra (2,000 m, amounting to 120 m

toward the southw est. This displacem ent could have been caused by

faulting or by a change in dip of the lim estone, due to the intrusive m ass

(Figs. 18 and 19).

Exploration Program at Depth

As already mentioned, the lower limits of the La Negra ore body

found during preliminary exploration were at e levation 2,100 m. The

53

exploration was suspended mainly because of technical prob lem s. Due

to the topography and dip of the ore body, it was very difficult to find a

place to project a drill hole of moderate length to in te rsec t the ore body

and at an angle s t i l l a cc ep tab le . So the problem of exploring at greater

depth was left to be continued when conditions were more favorab le , as

is now the case with the Socavdn La Negra.

The actual exploration program has been divided in two s tages :

f i r s t , to find the continuation of the ore body between elevations 2,100

m to .2,000 m (Fig. 19) and, second, if the ore body is found there , to

search for i ts downward extension by means of a deep drilling p ro jec t .

In the exploration program, our target for drilling is zone No. 1

(Fig. 18), from elevation 2,000 to 2,100 m. Projecting the surface geo l­

ogy, it is believed that the intrusive ("C"), which appears in the Socavdn

La Negra (Fig. 18), is the same as marked "A" at the surface (Fig. 4).

If th is is t r u e , the contact zone marked "No. 1" is our drilling ta rg e t .

According to th is in terpretation, the ore body has to be d isp laced in two

direction: to the north and to the w est (Fig. 18). Based on th is in terpre­

ta t ion , one diamond drilling sta tion has been p laced in order to drill 12

diamond drill holes (Fig. 18). The holes will be drilled with AX b i ts ,

inner diameter 3 .09 cm.

The design of the second stage of the exploration program must

await the resu lts of the first o n e .

54

DH No. Bearing InclinationApproximate Length (m) Obiective

1 N 65 W 0° 220.00 To cut the ore body at e levation 2,005 m

2 " N 83 W 0 45.00 To check the lim e- s to n e - ta c t i te con­ta c t

3 N 85 W 0 180.00 Same as DDH 1

4 N 60 E 0 40.00 Same as DDH 2

5 S 57 E 0 50.00 Same as DDH 2

6 N 80 W 0 200.00 Same as DDH 1

7 N 50 W 0 250.00 Same as DDH 1

8 N 80 W +32 170.00 To cut the ore body at e levation 2,075 m

9 N 80 W +52 175.00 To cut the ore body at e levation 2,100 m

10 N 85 W +32 165.00 To cut the ore body at e levation 2,050 m

11 N 70 W +20 190.00 Same as DDH 8

12 N 85 W +20 185.00 Same as DDH 10

System atic Exploration at the Mine

Due to the charac te ris tic irregularity of the ore body, it has

been- n ecessa ry to design a program of system atic exploration with d ia ­

mond drill holes from the mine workings. The purpose of th is system atic

exploration is to look for other ore bodies near the main one in both

d irec tions , toward the hanging wall (limestone) and to the footwall

( tac ti te ) . Another purpose is to find d is loca ted bodies or pockets or ore

that may branch from the.main ore body.

55

According to the geology of each su b le v e l , diamond drill holes

will be projected toward the hanging wall and toward the footwall. In

the first c a s e , the purpose is to explore for possib le m ineralized zones

replacing the limestone b e d s . The reason for this exploration is based

on the fact that at the surface there are some small mine workings in the

limestone beds; a l s o , two small zones of regular m ineralization in

limestone beds have been found by DDE #6 (officially recorded as. LN-

7-71) (Figs. 21 and 22). The exploration toward the footwall is of in ­

te re s t because a ll the tac ti te zone is m ineralized, although the grade is

low. This can be explained by the fact that the tac ti te zone was the con­

duit of the ore-bearing solutions and some m ineralization was deposited

th e re . This factor makes the tac ti te zone favorable for small ore b od ies ,

predominantly with copper-bearing mineralization due to the proximity

of the intrusive mass and therefore higher tem pera ture . Small amounts

of chalcopyrite are p resent a ll along the tac ti te zone where its back­

ground can be considered as 0.2% Cu.

Besides diamond drill exploration in the su b lev e ls , it is pro­

jec ted to drive an exploration heading to the north from level No . 3 to

in te rsec t the narrow m ineralized zone shown on Figure 6. The purpose

is to continue with th is drift along the contact toward tha t direction for

a t le a s t 200 m, looking for other ore bodies similar to those of La Negra

and El Alacrdn.

Results and Costs of the Exploration a t Depth and at the Mine

The first stage of the exploration program to find a continuation

of the La Negra ore body between e levations 2,000 and 2,100 m has

56

\ T0 . 232. 55 m

L I M E S T O N E

T A C T I T E

D I O R I T E

HI GH G R A D E

LOW G R A D E

H 5̂ _ F A U L T

DIAMOND DRILL HOLES

G R A P H I C S C A L E 0 „ 20k m u u i j iyyvmrv-lS M A L L POC KET

OF M I N E R A L

i ooo

,P R O J E C T E D ORE BODY ELEVATION 2100 m

X / '

65°

55°

•CRUSHI

57

THE L A NEGRA ORE BODY I

Sublevel 2170

Sublevel 21 502 15 0 mE L E V A T I O N

T D 167.20 m

FTHE L A NEGRA OR E B O D Y I I '

E L E V A T I O N 2 1 0 0 m

I D . 1 6 4 . 2 5 m

Limestone/FAULT

T D 183 .0 0 m

Diori te

High grade0«°Low grade

Diamond dri l l holes.FA U LT " B

Fault

T. D.2 2 2 . 4 0 m

LU 20 4 0 7 0

/•:) r<iE L E V A T I O N 2 0 0 0 m

SOCAVON (Ad i t )L A N E G R A - D I A M O N D D RILL STATION

FAULT AS M A L L POCKET OF M I N E R A L

Figure 22. C ro s s s e c t io n of the La Negra ore bod ies I and II

58

been very success fu l (Figs. 21 and 22). There have been minor va ria ­

tions from the original exploration program as to bearing and inclination

of the drill h o le s . The eight most important drill holes are described in

Appendix C . The differences in strike and inclination between these

holes and the planned holes are due to drill-hole dev ia tio ns .

Geologic Interpretation

As can be seen on Figures 21 and 22, there has been a great

d isplacem ent of the lower portion of the ore body (from 2,000 to 2,100

m) in relation to the upper section (above elevation 2 ,100 m ). Two

faults that have been identified are believed to be responsib le for th is

d isp lacem ent, as shown in Figure 22. Both faults are be lieved to be

postm ineral, but we have proved fault "A" to be older than fault "B"

because the first has been d isp laced by the second. It is poss ib le that

a longitudinal d isplacem ent could have been caused by fault "A" and

that a subsequent horizontal and vertica l d isplacem ent could have been

caused by fault "B". Fault zone "A" is about 10 m wide; it is apparent

in sublevel 2,150 as a strongly oxidized belt in the sulfide ore body.

When this fault is observed out of the mineralized zone—mainly in the

lim estone—-it is only a few centim eters wide and the oxidation is not

very strong. Fault "B" d isp laces the ore body; there fo re , it is safe to

conclude that both faults are postm ineral.

One important thing that must be mentioned is that DDE No.

LN-7-71 cuts two mineralized zones in limestone (F igs. 21 and 22)

which can be considered as a good indication of subs tan tia l tonnages

of lime stone-ore rep lacem ents, away from the tac ti te zone.

Ore Reserves

The first stage of the exploration program co nsis ted of 12 d i-

mond drill h o le s , to taling 2,028 m drilled . It outlined the continuation

of the La Negra ore body from elevation 2,000 m (Socavdn La Negra) to

e levation 2,121 m. The tonnage found and its average a s s a y , using

a 10 percent dilution, are:

Average Assays

Metric Tons Ag (g/ton) Pb (%) Cu (%) Zn (%)

300,800 383 2 .6 0 .73 4 .4

This ore reserve estim ate map is shown in Figure 23.

Besides some small m ineralized veins located toward the foot-

wall of the main ore body, a small pocket of ore was found. This small

pocket was found with DDH L N -7 -7 1 . Ore reserves between elevations

2,000 and 2,030 m, as shown in vertica l projection (F igs. 21 and 22)

are estim ated , after 10% dilution, as:

Average Assays

Metric Tons Ag (g/ton) Pb (%) Cu (%) Zn (%)

33,400 296 1.6 1 .44 1.6

This ore reserve estimate map is shown in Figure 24.

The positive resu lts obtained in th is first stage of exploration

give rise to a well-founded expectation for continuation of the ore body

at depth . The second stage of the exploration.will aim to prove th is .

A summary and deta iled estimate of the ore reserves found are shown in

Appendix B.

60

4 m 1 0 m 5 m 4 mr

9 m 4 m

zCL,

E - 2 I O O m

N - 1 5 - 7 216 m. 10 m

2m .I A L N - 2 3 - 7 ;

L N - 2 2 - 7 2

3 m6mN - 2 4 - 7 2

P - 3 8

7 m 7 mL N - 1 - 7 1

. L N - 7 -E - 2 0 0 0

3 m 7 m 3 m7 m

\ \ \ j P R O V E N O R EE X P L A N A T I O N

Di a mo n d Drill H o l e

N u m b e r

M E T E R S A S S A Y S

I N T E R V A L g / t o nAq . ; t % %

Z nLN - 1 - 7 1 — 6 8 0 . 0 1 0 6 2 0 . 0 7L N - 3 - 7 1 — 6 1 0 . 4 2 0 . 1 7 1 . 3 0L N - 7 - 7 1 7 . 5 0 7 8 0 . 2 5 1 . 2 8 4 . 0 7L N - 1 5 - 7 2 1 8 . 0 0 6 4 4 4 . 0 0 0 . 7 0 5 . 6 0L N - 2 1 - 7 2 1 0 . 0 0 5 9 3 4 . 7 9 0 . 5 3 5 . 3 8L N - 2 2 - 7 2 — B a r r e nL N - 2 3 - 7 2 4 . 0 0 4 7 8 3 0 7 0 9 5 5 . 8 6L N - 2 4 - 7 2 7 . 0 0 2 0 0 1 . 2 5 0 . 7 0 3 . 0 0

[ 3 Z J P R O B A B L E ORE

G R A P H I C S C A L E

0 10 20 30

M E T E R S

1: 1 000

Figure 23. Longitudinal projection of the La Negra ore body II, ore reserve estimate map

61

E - 2 1 0 0 m

E - 2 0 0 0 m

E X P L A N A T I O N

D i a mo n d M E T E R S A S S A Y SDril l Ho l e

I N T E R V A L 2 / T o n % % %N u m b e r A g Pb Cu Zn

L N - 7 - 7 1 8 . 0 0 3 2 9 1 . 8 0 1 . 6 0 1 . 8 0

1 : 1 0 0 0

G R A P H I C S C A L E

P R O V E N O R E

P R O B A B L E O R E f T V0 1 0 2 0 3 0Vmrrrrv r i --------------W in n rry j ~

6 0=d

M E T E R S

Figure 24. Longitudinal projection of small pocket of m ineraliza­tion at the footwall of the La Negra ore body II, ore reserve estim ate map

Results of Exploration at the Mine

Exploration at the mine as well as the exploration in the area at

depth has been su c c e s s fu l . Two small pockets of ore have been found;

one in the hanging wall in the north portion of the main ore body, from

sublevel No. 3 to sublevel No. 4 (Fig. 6), and the other one in the foot-

wall of the southern portion , from sublevel No., 3 to sublevel No. 7

(Figs. 5, 6, and 15). The calcu la ted tonnage of these provides an in ­

crement of 85,000 metric tons of ore assay ing 390 g / to n Ag, 3% Pb,

0.75% C u , and 2% Zn. This increment in tonnage is from level 2266

to 2352, so similar resu lts in the lower portion of the ore body can be

expected . This area,, from level 2100 to 2200, is now being prepared

for m ining.

Since the exploration drift to the north, loca lized in level No.

3, did not cut mineralization where it was e x p ec ted , it was decided to

continued exploration with diamond drill h o les . The first hole in ter­

sec ted a mineralized zone, as shown in Figure 19. Although th is zone

is low in tenor, because it has been proved that the m ineralization con­

tinues toward the north and far from the main ore body, it is in teresting

from the exploration point of view . Once th is m ineralized contact has

been loca ted , exploration toward the north will continue with the drift.

Cost of Exploration at Depth and at the Mine

The to ta l cost of the diamond drill hole exploration programs in

the mine area and at depth are given below and are compared with the

ore reserves found.

63

AssaysExplora­tionProgram Metric Tons

Ag(g/ton)

Pb(%)

Cu(%)

Zn(%)

M etersDrilled

Cost(pesos)

Mine- 85,000 390 3.0 0 .75 2.1 1,130 352,000

At depth 334,200 374 2.6 0.81 4.1 2,028 831,000

Total 419,200 377 2 .6 0 .79 3 .8 3,158 1,183 ,000

.Total Cost _ .1,183 ,..QQ.Q. — $2.82 Pesos (M exican)/ton Tons Found 419,200

Exploration in Socavon El Alacr^n

As can be seen on the surface geologic maps (F igs. 4, in

pocket and Fig. 20), two ore bodies are localized along the lime s tone-

tac ti te con tac t. La Negra and El A la c r in . The second one is about 650 m

northeast of the f i rs t . Between these ore bod ies , the favorable zone for

mineralization is the l im estone-tac ti te c o n ta c t . Both mines are now

connected by the Socavdn El Alacrdn at e levation 2,000 m , 350 m below

the old La Negra workings and 200 m below the El Alacrdn outcrop. As

th is level has been driven almost para lle l to the lime s to n e - tac t i te con­

ta c t , it will be used as an exploration level with diamond drill s ta tions

every 125 m on both s id e s . Two exploration programs have been planned

for two different t a r g e ts . The first program will explore the 1 ime stone-

tac ti te contact looking for ore bodies similar to those of La Negra and

El Alacrcin. The second will explore the tac ti te zone toward the intrusive

mass looking for copper sulfide bodies of high grade and re la tive ly small

tonnage or of lower grade and large to n n ag e .

64

There are three reasons why these po ss ib i l i t ie s are co n s id ered .

F irs t , in theory, as chalcopyrite is a rather high temperature mineral, it

is expected to find higher values c loser to the intrusive mass and at

depth. Second, sampling of the tac ti te between La Negra and El Alacrctn

has proved the exis tence of severa l zones where copper values are of

1 percent or more (Fig. 20). Third, in a ll the tac ti te zone, chalcopyrite

is present in d issem inated form, with an average a s sa y of about 0.2%

Cu. Therefore, the poss ib le exis tence of a large low-grade copper ore

body can be hypothesized .

The La Negra mine is similar to the Antamina mine, which is

located in Peru in the northern part of the Andean Cordillera (Petersen,

1959). The most important ch arac te ris tics of the Antamina mine that are

similar to those of the La Negra mine are:

1. The ore deposit is pyrom etasomatic.

2. The contact metasomatic zone is composed mainly of tac tite

with garnet in its brown and green v a r i t ie s , showing the same

zonation as La N eg ra . The brown variety is p resen t near the

intrusive mass and the green variety near the lim estone.

3. The type of intrusion is about the same as the one of the La

Negra mine, and the limestone is M esozoic in age .

4 . The form of the ore body is like Chimenea; the ve rtica l dimen­

sion is longer than the other two.

5. Folding and lithology seem to have been the main control for

ore deposition .

65

6. It is a polymetallic ore body where copper is p resen t as ch a l-

copyrite , lead as galena , zinc as sp h a le r i te , and has some

si lv e r . In Antamina, the principal mineral is cha lcopyrite ,

then sp h a le r i te , and lead and silver are p resen t in small

amounts. This sequence is different than that at La Negra.

7. As in La Negra, copper increases toward the ta c t i te , and lead

ju s t the opposite .

8. The tac ti te was formed f i rs t , then the m etallic m inerals .

CHAPTER 7

SUMMARY AND CONCLUSIONS

The La Negra ore body occurs in the outer limits of the contact

metasomatic zone, ju s t between the tac ti te and the lim estone. The La

Negra ore body is an epigenetic and typically metasomatic or pyrometa-

somatic deposit. M ineralization is p resen t as m assive su lf ides , in

which silver is presen t as h e s s i te , lead as ga lena, copper as cha lco -

p y r i te , and zinc as m arm atite . Andradite is found in greater proportion

than grossularite near the intrusive m ass , and the reverse s ituation is

found near the limestone contact.

Common mineral a sso c ia tio ns are: pyrrhotite-chalcopyrite ,

g a le n a -h e s s i te , and m armatite-cadmium.

An increase in copper m ineralization in relation to that of lead

and silver toward the intrusive mass ind icates the p o ss ib i l i t ie s of higher

copper values that way and that the lead and silver m ineralization is

mostly present near the limestone zone.

Among the ore control factors the most important one is chem­

ic a l , because the process of "ground preparation" is considered as the

first step in fac ilita ting the passage of the mineralizing solutions .

Structure is a lso important, because the emplacement of the La Negra

ore body is controlled by the gentle folds of the limestone b e d s , along

plunging noses of secondary an tic lina l flexures in one flank of a local

broad fo ld . '

66

67

During the first year and a half of m ining, additional ore re ­

serves have been found, at depth and in the ore body i ts e l f , which

account for 30 percent of the original ore reserves e s t im a te d . Two small

mineralized zones have been in te rsec ted the DDH No. 7 in the limestone

zo n e .

Results of sampling the tac ti te zone along the socavbn between

the La Negra and El.Alacrctn ore bodies have proved the ex is tence of

several zones where copper values are 1 percent or m ore. The diamond

drill hole from the exploration drift to the north on level No. 3 cut some

lea d -s i lv e r mineralization ju s t in the tac ti te - lim estone con tac t, about

200 m away from the La Negra ore body . It is believed that the p o s s i ­

b ili t ie s for more ore a t depth and in other areas are very good.

From all these findings, the following conclusions and recom­

mendations are m ade.

All around the La Negra area is a very in teresting prospective

zone, mainly where intrusive bodies are p resent as s to c k s , d ik es , and

s i l l s .

From the zonatioh of grossularite and andradite and the charac ­

te r is t ic that high grades of lead and silver are found near the limestone

c o n ta c t , it can be concluded that the presence of the first ind icates

that the limestone contact is c lose and thus it is an indication of a

probable good exploration target for le a d -s i lv e r ore d e p o s i ts .

The common mineral a sso c ia tio n between pyrrhotite and c h a l-

copyrite shows a very good poss ib ili ty to use the electrom agnetic geo­

physical method for exploring for copper d ep o sits .

68

The relative increase of copper values toward the intrusive

mass and its rather high temperature of formation, as well as the good

copper values found by sampling the tac ti te zone along the Socav6n El

Alacrcin, are indications that copper ore deposits could ex is t toward the

intrusive m a s s . It is recommended that the tac ti te - in tru s ive contact be

explored with diamond drill holes from the Socav6n El A lacrdn.

It is recommended that de ta iled stratigraphic and structural

mapping in the area be done to look for folding and secondary antic linal

flexures of the limestone beds a sso c ia ted with in tru s io n s .

The fact that the system atic exploration in the mine was su c ­

cess fu l shows that this method should be continued in the future through­

out the mine. The positive resu lts of the exploration between the 2100

and 2000-meter levels give rise to a recommendation to explore deeper

than the 2000-meter leve l. .

In tersection of two mineralized zones in the limestone zone by

DDH No. 7 would indicate that the limestone zone is a good.target for

exploring for replacement ore d e p o s i ts .

F inally , it is recommended that exploration from the explora­

tion drift on level No. 3 be continued.

APPENDIX A

ORE RESERVE ESTIMATE FOR

LA NEGRA AND EL ALACRAN ORE BODIES,

EXPLORATION PROGRAM, 1964-67

69

70

Summary

Without Dilution

La Negra Ore Body I

Metric TonsAg

gr/tonPb%

Cu%

Zn%

Proven Ore 576 ,551 .5 403 2 .8 1.30 5.1

Probable Ore 142 ,147 .5 360 2.9 1.93 5.1Proven plus Probable Ore 718 ,699 .0 394 2.8 1.42 5.1

El Alacrcin Ore Body

Proven Ore 525 ,325 .7 128 Tr 2.07 1.7

Total, La Negra plus El Alacrcin 1 ,2 4 4 ,0 2 4 .7 282 1 .6 1.69 3 .7

With 10% Dilution

La Negra Ore Body I

Proven Ore 634 ,206 .6 363 2 .5 1.17 4 .6

Probable Ore 156,362.3 324 2 .6 1.74 4 .6

Proven plus . Probable Ore 790 ,568 .9 355 2 .5 1.28 1 .5

El Alacrcin Ore Body

Proven Ore 577 ,858 .2 115 Tr 1.86 1.5

Total, La Negra plus El Alacrin 1 ,3 6 8 ,4 2 7 .1 254 1.4 1.52 3.3

Note tha t although no geologic data about the El AlacrSn ore

body is included in th is t h e s i s , the ore reserve estim ate is in this sum­

mary because it is considered as a portion of the La Negra mine.

. ' Width Ag Pb Cu Zn l/2 B a s e H eight Area Width VolumeBlock Location m g /to n % % % ' m m m D ensity M etric Tons

1 XR 0 SOC 5 SOC 5

6.0011.70

-11.70

530585585

4.35.75.7

0.400.600.60

7.29 .39.3

25.00 8.00 200.00 9.80 1,960.00 3.75 7,350.000

Average 2 9 . 40 / 9 . 80 574 5.4 0.56 8.9

2 SOC 5 SOC 5 XR 0 P 11 XR 0 P 24

11.7011.70

7.10 8.30' 6.70

10.00

585585455403267430

5.75.7 3.4 1.9 1.0 2.0

0.600.600.460.900.100.50

9.39.3 5.7 2.2 1.1 4.1

27.50 16.00 440.00 9.25 4 ,070 . 00 3.75 15,262.500

Average 5 5 . 5 0 / 9 . 8 0 475 3.6 0.55 5.9

3 SOC 5 P 31 P 24

11.7017.7510.00

585282430

5.71.8 2.0

0.600.400.50

9.32.94.1

30.00 6.00 180.00 13.15 2 ,367.00 3.75 8, 876.250

Average 39 . 45 / 13 / 15 409 3.0 0.48 5.1 •

4 SOC PP XR 0 P 31

10.0012.8017.75

332336282

7.14.71.8

0.500.500.40

6.64.22.9

29.00 2.50 72.50 13.50 978.75 3.75 3, 670.313

Average 4 0 . 55 / 13 . 50 311 4.0 0.46 4.2

5 XR 0 P 28'. P 26

7.1010.00

0.80

455314506

3.42.42.8

0.460.900.40

5.73 . 04 .0 •

39.00 5.00 195.00 5.95 1,160.25 3.75 4 , 350.938

Average 17 . 9 0 / 5 . 9 5 379 . 2 .8 0.70 4.1 •

6 XR 0 P 11 XR 0 P 24 P7y No. P 28

7.10 8.30 6.70

10.00 13 14.40

10.00

455403267430603314

3.41.91,02.03.32.4

0.460.900.100.500.600.90

5.72.21.1

. 4 . 15.23.0

24.00 21.50 516.00 ' 9 .40 4 ,850 . 40 3.75 18,189.000

Average 5 6 . 5 0 / 9 . 4 0 433 2.4 0.60 3.8

Block Width Ag Pb ■ Cu Zn l /2 B a s e H eight Area Width VolumeN o . Location m g /to n % % % m m m2 m m3 D en sity M etric Tons

7 P 24 10.00 430 2.0 0.50 4.1P 31 17.75 282 1.8 0.40 2.9P 9 11.80 575 2.9 0.50 5.2P7y No. 13 14.40 603 3.3 0.60 5.2

Average 53 . 95 / 13 . 50 459 2.5 0.49 4.2

8 P 31 17.75 282 1.9 0.40 2.9P 6 15.00 425 2.5 0.40 5.4P 9 11..80 575 2.9 0.50 5.2

Average 44 . 55 / 14 . 85 408 2.3 0.43 4.4

9 P 31 17.75 , 282 1.8 0.40 2.9XR 0 12.80 336 4.7 0.50 4.2P 23 8.50 601 5.6 0.80 9.0P 6 15.00 425 2.5 0.40 5.4

Average 54 . 05 / 13 . 50 385 3.3 0.49 4.9

10 P 26 0.80 506 2.8 0.40 4.0XR 0 2.65 331 2.1 0.56 3.1S 1 2.30 326 2.6 0,83 3.8

Average 5 . 7 5 / 1 . 9 0 . 353 2.4 0.64 3.5

11 XR 0 2.65 331 2.1 0.56 3.1P 26 0.80 506 2.8 0.40 4.0P 28 10.00 314 2.4 0.90 3.0XR . 0 2.00 302 2.3 0.30 3.2

Average 15 . 45 / 3 . 85 325 2.4 0.74 3.1

12 P 28 10.00 314 2.4 0.90 3.0P7y No. 13 14.40 603 3.3 0.60 5.2XR 0 8.00 478 2.4 0.50 3.2XR 0 2.00 302 2.3 0.30 3.2

Average 3 4 . 40 / 8 . 60 472 2.8 0.65 4 , 0

15.50 16.50 255.75 13.50 3 ,452 .625 3 .75 12,947.344

15.00 6.50 97.50 14.85 1 ,447.875 3 .75 5,429.531

20.00 16.50 330.00 13.50 4 ,455 .000 3 .75 .16 ,706 .250

48.00 27.00 1 , 296 . 00 1.90 2 ,462 .40 3 .75 9 , 234 . 000

50.50 34.00 1 ,717 .00 3.85 6 ,610 .45 3 .75 24,789.188

20.50 46.50 953.24 8.60 8 , 197 . 95 3 .75 30,742.313

■"~3DO

Width Ag Pb Cu Zn l/2BaseBlock Location m g/ton °/c % °/c m

13 P7yNo. 13 14.40 603 3.3 0.60 5.2 12.50P 9 11.80 575 2.9 0.50 5.2XR 0 8.00 525 3.3 0.60 6.1XR 0 8.00 478 2.4 0.50 3.2

Average 4 2 . 20 / 10 , 55 557 3.0 0.55 5.0

14 P 9 11.80 575 2.9 0.50 5.2 17.00P 6 15.00 425 2.5 0.40 5.4XR 0 10.00 316 4.0 0.70 4.0XR 0 8.00 525 3.3 0.60 6.1

Average 44 . 80 / 11 . 20 458 3.1 0.53 5.2

15 P 6 15.00 425 2.5 0.40 5.4 51.00P 23 8.50 601 . 5.6 0.80 9.0XR 0 10.00 316 4.0 0.70 4.0

Average 33 . 50 / 11 . 15 437 3.7 0.59 5.9

16 XR 0 12.80 336 4.7 0.50 4.2 60.00XR 0 10.00■ 316 4.0 0.70 4.0P 23 8. 50 601 5.6 0.80 9.0

Average 3 1 . 30 / 10 . 45 402 4.7 0.65 5.4

17 No. 1 2.30 326 2.6 0.83 3.8 94.00.XR 0 2.65 331 2.1 0.56* 3.1

. P 5 1.00 606 4.2 0.70 5.2Average 5 . 95 / 2 . 00 375 2.6 0.69 3.7

18 XR 0 2.65 331 . 2.1 0.56 3.1 50.00XR 0 2.00 302 2.3 0.30 3.2P 5 1.00 • 606 4.2 0.70 5.2

Average 5 . 6 5 / 1 . 9 0 369 2.5 0.49 3.5

19 XR 0 2.00 302 2.3 0.30 3.2 29.00XR 0 8.00 478 2.4 0.50 3.2P 5 1.00- 606 4.2 0.70 5.2

Average 11 . 00 / 3 . 65 . 458 2.5 0.48 3.4

H eight Area Width Volumem m2 m m3 D ensity M etric Tons

47.50 593.75 10.55 6 ,264.063 3.75 23,490.236

49.50 841.50 11.15 9 , 424 . 80 3.75 35,343.000

4.50 229.50 11.15 2 ,558.925 3.75 9,595.500

5.00 300.00 . 10.45 3 ,135 .00 3.75 11,756.250

6.00 564.00 2.00 1 ,128 .00 3.75 4 , 230.000

7.00 350.00 1.90 665.00 . 3.75 2,493.750

10.50 304.50 3.65 1,111.425 3.75 4 ,167 .844

<1co

Block N o. Location

Widthm

Agg/ton

Pb%

Cu%

Zn7c

l/2B asem

Heightm

Aream2

Widthm

Volumem3 D ensity Metric Tons

20 XR 0 XR 0 P 18 P 5

8.00 8.00

10.20 ' 1.00

478525501606

2.43.35.4 4.2

0.500.600.300.70

3.2 6.1

10.45.2

23.00 23.00 529.00 6.80 3,597.20 3.75 13,489.500

Average 2 7 . 20 / 6 . 80 505 3.9 0.46 6.8

21 XR 0 XR 0 P 18

8.0010.0010.20

525316501

3.3 4.05.4

0.600.700.30

6.14.0

10.4

24.00 8 . 0 0 192.00 9.40 1,804.80 3.75 6,768.000

Average 2 8 . 2 0 / 9 . 4 0 442 4.3 0.53 6.9

22 XR 0 P 8 P 18

10.008.00

10.20

316203501

4.01.35.4

0.705.300.30

4.01.5

10.4

24.00 12.50 300.00 9.40 2 ,820.00 3.75 10,575.000

Average 2 8 . 2 0 / 9 . 4 0 . 351 3.7 1.86 5.6

23a P 5 P 18 No. 15

1.0010.20

3.10

606501554

4.25.48.9

0.700.301.00

5.210.4

1.1

40.00 6.50 260.00 4.75 1,235.00 3.75 4,631.250

Average 1 4 . 30 / 4 . 75 520 6.1 0.48 8.0

23b P 5 P 18 No. 15

1.0010.20

4.15

606 . 501

151

4 . 25.4

0.700.303.30

5.210.4

41.00 9.00 369.00 5.10 1,881.90 3.75 7,057.125

Average 1 5 . 35 / 5 . 10 413 3.9 1.14 7.2

24a ' P 18 P 8 No. 15

10.208.003.10

501 203

. 554

5.41.38.9

0.30 5.30 I .00

10.41.51.1

29.00 7.50 217.50 7.10 1,544.25 3.75 5,790.938

Average 2 1 . 3 0 / 7 . 1 0 397 4.4 2.28 5.7

24b P 18 P 8 No. 15

10.208.004.15

501203151

5.41.3

0.305.303.30

10.41.5

29.00 11.00 319.00 7.45 2 , 376.55 3.75 8,912.06

Average 22 . 3 5 / 7 . 4 5 329 2.9 2.65 5.3

Block Width ’ Ag Pb Cu Zn l/2B ase HeightN o. Location m g/ton % % % m m

25 P 5 1.00 606 4.2 0.70 5.2 70.00 12.00No. 15 4.15 151 - 3.30 -P 32 1 .10 646 8.0 0.80 9.9

Average 6 . 2 5 / 2 . 1 0 311 2.1 2.44 2.6

26 No. 15 4.15 151 — 3.30 - 68.00 6.50P 8 8.00 203 1.3 5.30 1.5P 32 1.10 646 8.0 0.80 9.9

Average 1 3 . 25 / 4 . 40 223 1.4 4.30 1.7

27 P 32 1.10 646 8.0 0.80 9.9 55.00 9.50No. 14 16.15 162 0.9 0.60 0.6P 40 7.10 171 1.2 0.75 1.7

. Average 24 . 3 5 / 8 . 1 0 186 1.3 0.65 1.3

28 P 32 r . i o 646 8.0 0.80 9.9 46.00 , 19.50P 29 15.00 712 5.4 3.90 10.4No. 14 16.15 162 0.9 0.60 0.6

Average 32 . 25 / 10 . 75 434 3.2 2.14 5.5

29 P 40 7.10 171 1.2 0.75 1.7 40.00 10.00No. 14 16.15 162 0.9 0.60 0.6P 34 32.90 254 1.7 1.12 3.9

Average 56 . 15 / 18 . 70 217 1.4 0.92 2.7

30 No. 14 16.15 162 - 0.9 0.60 0.6 40.00 14.00P 39 6.00 535 2.3 3.17 9.3P 34 32.90 254 1.7 1.12 3.9

• Average 55 . 05 / 18 . 35 258 1.5 1.19 3.5

31 No. 14 16.15 162 0.9 0.60 0 . 6 46.00 15.00P 29 15.00 712 5.4 3.90 10.4P 39 6.00 535 2.3 3.17 9.3

Average ■ 37 . 15 / 12 . 40 444 2.9 2.35 6.0

Area Width Volumem2 m m2 D ensity M etric Tons

840.00 2.10 1 ,764.00 3.75 6 ,615.00

442.00 4 .40 1,944.80 3.75 7 , 293.00

522.50 8.10 4 ,232 .25 3.75 15,870.93

897.00 10.75 9 ,642 .75 3.75 36,160.31

400.00 18.70. . 7 , 480.00 3.75 28,050.000

560.00 18.35 10,276.00 3.75 38,535.000

690.00 12.40 8 ,556.00 3 .75 32,085.000

-<!c n

Block Width N o. Location m

Agg/ton

Pb '%

Cu%

Zn%

l/2 B a sem

32 . P 34 . P 39

P 36

32.906.002.10

254535354

1.72.32.0

1.123.170.56

3.99.39.2

70.00

Average 41 . 0 0 / 1 3 . 6 5 300 1.8 1.39 5.0

33 P 39 6.00 535 2.3 3.17 9.3 . 102.00P 33 1.05 112 1.2 1.01 4 . 6P 36 2.10 354 2.0 0.56 9.2

Average 9 . 1 5 / 3 . 0 5 445 2.1 2.32 8.7

34 ' P 39 6.00 535 2.3 3.17 9.3 60.00P 29 15.00 712 5.4 3.9 10.4P 33 1.05 112 1.2 1.01 4.6

Average 2 2 . 05 / 7 . 35 635 4.4 3.56 9 . 8

PROVEN ORE

Without Dilution 403 2.82 1.30 5.13

With 10% Dilution 363 2.54 1.17 4.62

A XR 0 12.80 336 4.7 0.50 4.2 62.005.00 ? ? ? ?

' XR 0 10.00 316 4.0 o .‘70 4.0Average 2 7 . 8 0 / 9 . 25 . 327 4.4 0.59 4.1

B 5.00 ? ? ? ? 12.50XR 0 10.00 316 4.0 0.70 4.0P 8 8.00 . 203 1.3 5.30 1.5

5.00 ? ? ? ?Average 2 8 . 00 / 7 . 00 266 2.8 2.74 2.9

H eight Area Width Volumem m m3 D ensity M etric Tons

13.50 945.00 13.65 12,899.25 3.75 48,372 .188

19.00 1 ,938.00 3.05 5 ,910.90 3.75 22,165.875

21.50 1 ,290.00 7 .35 9 ,481 .50 3 .75 35,555.625

576,551.491

634,206.640

7.00 434.00 9 .25 4 ,014.500 3.75 15,054.375

26.00 325.00 7 .00 2,275.000 3.75 8 , 531 .350

■<]C D

Block Width Ag Pb Cu ZnN o. Location m g/ton % % %

C P 5 1.00 606 4.2 0.70 5.21.10 646 8.0 0.80 9.91.10 ? 9 ? ?

Average 3 . 2 0 / 1 . 0 5 627 6.2 0.75 7.7

D 5.00 ? ? ? . ?P 8 8.00 203 1.3 5.30 1.5P 32 1.10 646 8.0 0.80 9.9

1,10 ? ? ? ?Average 15 . 20 / 3 . 80 257 2.1 4.76 2.5

E 1.10 ? ? ? ?P 32 1.10 646 8.0 0.80 9 .9P 40 7.10 171 1.2 0.75 1.7

4 .50 ? ? ? ?Average 1 3 . 8 0 / 3 . 4 5 235 2.1 0.76 2.8

F P 32 1.10 646 8.0 0.80 9.91.10 ? ? ? ?

10.00 ? ? ? ?P 29 15.00 712 5.4 3.90 10.4

Average 2 7 . 2 0 / 6 . 8 0 707 5.6 3.69 10.4

G . 4 .50 ? ? ? ?P 40 . 7.10 171 1.2 0.75 1.7P 34 32.90 254 1.7 1.10 3.9

20.00 ? ? ? ?Average 64 . 50 / 16 . 10 239 1.6 1.04 3.5

H 20.00 ? ? ? ?P 34 32.90 254 1.7 1.10 3.9P 36 2.10 354 2.0 0.56 9.2

1.50 ? ? ? ?'Average 5 6 . 50 / 14 . 10 260 1.7 1.07 4.2

l/2 B a sem

70.00

68 .00

55.00

51.00

32.50

50.00

H eight Area Widthm m2 m

Volumem3 D ensity M etric Tons

4.50 315.00 1.05 330.750 3.75 1 ,240 .31

10.00 680.00 3.80 2 ,584.000 3.75 9 , 690 .000

10.00 550.00 3.45 1 ,897.500 3.75 7 ,115 . 62

12.50 637.50 6.80 4 ,335 .000 3.75 16,256.250

15.00 - 487.50 16.10 7 ,848.750 3.75 29,432.813

15.00 750.00 14.10 10,575.000 3.75 39/656.250

■V]

S I

Block Width N o. Location m

Agg/ton

Pb%

Cu%

Zn%

l/2B asem

Heightm

Aream2

Widthm

Volumem ̂ Density Metric Tons

I P 29 15.00 10.00

P 33 1.05

712?

112

5.4?

1.2

3.90?

1.01

10.4?

4.6

62.00 •7.50 465.00 8.70 4 , 045 . 500 3.75 15,170.625

Average 2 6 . 05 / 8 . 70 673 5.1 3.71 10.0

PROBABLE ORE

Without Dilution • 360 2 .9 1.93 5.1 142,147.501

With 10% Dilution 324 2 .6 1.74 4.6 156,362.250

SUMMARY

Without Dilution

Proven Ore Probable Ore

403360

2 .82 .9

1.30 1.93

5.15.1

576.551.5142.147.5

■ Proven plus Probable Ore 394 2 .8 1.42 5.1 718,699.0

With 10% Dilution

Proven Ore Probable Ore

3 63 324

2 .52 .6

1.171.74

4 . 64.6

634,206.64156,362.25

Proven plus Probable Ore 355 2 .5 1.28 4 . 6 790,568.89

APPENDIX B

ORE RESERVE ESTIMATE FOR THE LOWER PART OF

LA NEGRA ORE BODY FOUND DURING FIRST STAGE

OF EXPLORATION PROGRAM AT DEPTH, 1972

79

80

Summary

La Negra Ore Body II

Without Dilution

Proven Ore

Probable Ore

Proven plus Probable Ore

Metric Tons

171,000

102,500

273,500

Agq/ ton

434

413

426

Pb%

2.9

2 . 8

Cu%

0.81

0.83

2.9 0.81

With 10% Dilution

Proven Ore 188,100

Probable Ore 112,700Proven plusProbable Ore 300,800

391 2 .6 0.73

372 2.6 0.75

383 2.6 0.73

Small Pocket of Ore at Footwall of Main Ore Body

Without Dilution

30,330

With 10% Dilution

329 1.8 1.60

33,360 296 1.6 1.44

Zn%

4.9

4 .9

. 4 .9

4 .4

4 .4

4 .4

1 . 8

1 . 6

Block WidthN o . Location m

Ag Pb . Cu 2n l/2 B a se Height Area Width Volumeg /to n % . % % m m m2 m m ̂ D en sity Metric Tons

1 LN-21-72 LN-15-72

. LN-23-72

10.0018.00

4.00

593644478

4.794.003.07

0.530.700.95

5.385.805.86

87.50 8.25 721.88 10.67 7,702 . 46 3.75 28,884.23

Average 32 .00 / 10 . 67 607 4.13 0.68 5.68

2 LN-15-72LN-24-72LN-23-72

18.007.004.00

644200478

4.001.253.07

0.700.700.95

5.803.005.86

55.50 12.00 666.00 9.67 6,440.22 • 3 .75 24,150.82

Average 29 . 00 / 9 . 67 514 3.20 0.73 5.13

3 LN-23-72 LN-24-72 LN- 7-71

4.007.00 7.50

478200

78

3.071.250.25

0.95 0.70 1.28

5.863.004.07

77.00 16.50 1,270.50 6.17 7,839 . 00 3.75 29,396.25

Average 18 . 50 / 6 . 17 21 1.23 1.00 4.05

4 LN-23-72LN-21-72

4.00 10.00

3.00 10.00

478 593

■ ??

3.074.79

??

0.950.53

?9

5.865.38

?9

87,50 10.00 875.00 6.75 5 , 906.25 3.75 22,148.44

Average 27 . 00 / 6 . 75 560 4.30 0.65 5.52

5 LN-23-72 LN- 7-71

4.00 7.502.00 7.00

47878??

3.070.25

??

0.951.28

??

5.864.07

?9

77.00 10.00 770.00 5.12 3,942 . 40 3.75 14,604.00

Average 20 . 50 / 5 . 12 217 1.23 1.17 4.69

6 LN-21-72LN-15-72

10.0018.0016.00

9.00

593644

??

4.794.00

??

0.530.70

??

5.385.80

??

38.00 10.00 380.00 13.25 5,035 . 00 3.75 18,881.25

Average 53 . 00 / 13 . 25 625 4 .28 0.64 5.65

Block Width ' Ag Pb Cu ZnN o. Location m g/ton % % %

7 LN-15-72 18.00 694 4.00 0.70 5.80. LN-24-72 7.00 200 1.25 0.70 3.00

16.00 ? ? ? ?6.00 ? ? ? ?

Average 4 7 . 00 / 11 . 75 519 3.23 0.70 5.01

8 LN-24-72 7.00 200 1.25 0.70 3.00LN- 7-71 7.50 . 78 0.25 1.28 4.07

6.00 ? ? ? ?7.00 ? ? ? ? '

Average 27 . 5 0 / 6 . 8 7 137 0.73 1.00 3.53

9 LN-21-72 10.00 593 4.79 0.53 5.3810.00 ? .

? ? ?9.00 ? ? ? ? .

9.00 ? ? ? ?Average 3 8 . 00 / 9 . 50 593 4.79 0.53 5.38

10 LN-23-72 4.00 478 3.07 0.95 5.863.00 ? ? ? ?2.00 ? ? •? ?

Average 9 . 0 0 / 3 . 0 0 478 3.07 0.95 5.86

11 LN- 7-71 7.50 78 0.25 1.28 4.077.00 ? ? ? ?7.00 ? ? ? ?7.00 9 ? ? ?7.00 ' ? ? ? ?

Average 3 5 . 00 / 7 . 00 78 0.25 1.28 4.07

PROVEN ORE

• Without Dilution 434 2.9 0.81 4.9

With 10% Dilution 391 2.6 0.73 4 . 4

l/2 B a sem

28.50

54.00

10. 00

10. 00

16.75

H eight . Area Width Volumem m2 m m3 D ensity M etric Tons

10.00 285.00 11.75 3 , 348 . 75 3.75 12,557.81

10.00 540.00 6.87 3 ,709 .80 3.75 11,892.50

10.00 100.00 9.50 950.00 3.75 3 ,562 . 50

4.00 40.00 3.00 120.00 3.75 .450.00

10.00 167.50 7.10 1 ,189 .25 3.75 4 , 459.69

170.987.50

188.100.50 S

Block N o. Location

Widthi , m

Agg/ton

■ Pb%

Cu%

Zn ’ %

l/2 B a sem

Heightm

Area Widthm

Volumem̂ Density Metric Ton

12 Block N o. 4

3.004.00

10.00

?560

?

?4.30

?'

?0.65

?

?5.52

?93.00 . 14.00 1,302.00 5.67 7 ,382.34 3.75 27,663.78

Average 17 . 00 / 5 . 67 560 4.30 0.65 5.52

13 Block N o. 6

16.00 4.00 . 9.00.

10.00

?. ?

625 . ?

??

4.28?

??

0 ."64 ?

??

5.65?

37.00 12.00 444.00 9.75 4,329 . 00 3.75 16,233.75

Average 39 . 0 0 / 9 . 7 5 625 4.28 0.64 5.65

14 Block No.. 7

16.0010.00

6.003.00

??

519?

??

3.23?

??

0.70?

??

5.01?

28.00 16.50 462.00 8.75 4 ,042 . 50 3.75 15,159.38

Average 3 6 . 00 / 8 . 75 519 3.23 0.70 5.01

15 Block N o. 8

3.006.003.007.00

??

137?

??

0.73?

??

1.00?

?■?

3.53?

65.00 16.00 1, 040.00 4.75 4 ,940 . 00 3.75 18,525.00

Average 19 . 00 / 4 . 75 137 0.73 1.00 3.53

16 Block N o. 5

6.003.003.00

?217

? '

?1.23

?

?1.17' ?

?4.69

?88.00 17.00 1,496.00 4.00 5 , 984.00 3.75 22,440.00

Average 12 . 0 0 / 4 . 0 0 217 1.23 1.17 4.69

17 Block N o. 9

4.004.009.009.00

??

593?

??

4.79?

??

0.53?

??

5.38?

10.00 10.00 100.00 6.50 650.00 3.75 2,437.50

Average 2 6 . 00 / 6 . 50 593 4.79 0.53 5.38

PROBABLE OREWithout Dilution 413 2 .8 0.83 4 .9 102,459,41With 10% Dilution 372 2 .6 0.75 4 .4 112,700.00

Block Width ■ N o. Location m

Agg/ton

Pb%

Cu%

2n%

l/2B asem

Heightm

Area Widthm

Volumem3 Density Metric Tons

18 LN-7-71 2.00 2.005.005.00

??

329?

??

1.807

?7

1.60?

??

1.80 . ?

33.00 30.00 990.00 3.50 3 , 465.00 3.75 .12,993.75

Average . 14 .00/3 .50 329 1.80 1.60 1.80

19 LN-7-71 5.005.005.005.00

. ??

• 329 ?

??

1.807

??

1.607

??

1.80?

30.00 2 1 . 0 0 630.00 • 5.00 3,150 . 00 3.75 11,812.50

Average 20 . 0 0 / 5 . 0 0 329 1.80 1.60 1.80

20 LN-7-71 5.005.002 . 0 0 2 . 0 0

??

329?

??

1.80?

??

1.60?

?7

i . ' s o?

30.00 14.00 420.00 3.50 1, 470.00 3.75 5 , 512.50

Average 14 . 00 / 3 . 50 329 1.80 1.60 1.80

SMALL POCKET

Without Dilution 329 1.80 1.60 1.80 30,328.75

With 10% Dilution 296 1.60 1.44 1.60 33,361.62

APPENDIX C

SUMMARY OF DIAMOND DRILL HOLE LOGGING

85

Table C - l . DDH N o . LN-1 -7 .1 , D iam ond D rill S ta t io n N o . 1

Coordinates: N 5077.E 4859.

Elevation: 2,005 m

9050

Bearing: N64W Inclination: 0°

Core Size: Lotal Length:

AX232.55 m

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

0 14.00 99 Diorite quartz , chlorite , epidote14.00 34.00 100 Tactite brown garnet34.00 89.30 100 Diorite quartz , chlorite89.30 114.00 99 Tactite brown garnet , pyrite

114.00 115.25 100 Tactite brown ga rne t , chalcopyrite 66 0.03 1.26 0.33115.25 124.00 95 Tactite brown garnet124.00 128.90 99 Tactite green garnet 124 0.36 0.61 1.76128.90 149.00 99 Tactite green garnet149.00 150.90 99 Tactite green garnet 160 0.08 0.79 0.07150.90 152.90 100 Tactite green garnet152.90 154.05 100 Tactite green garnet 68 0.01 0.62 0.07154.05 198.90 99 Tactite green & brown garnet , very low

galena, chalcopyri te , marmatite198.90 230.60 99 Calcite very low galena, chalcopyrite,

marmatite , pyrrhotite

230.60 232.55 99 Limestone marble

Note that from 120.45 to 131.60 m, probable fault zone (oxidized t a c t i t e ) .

Table C - 2 . DDH No'. L N - 3 -7 1 , D iam ond D rill S ta t io n N o : 1

Coordinates: N E

Elevation: 2,

5077. 4859. 005 m

9050

Bearing: S85W Inclination: 0°

Core Size: Total Length:

AX167.05 m

From To RecRock Type

Ag PbAlteration and Minerals g / ton %

Cu%

Zn.% •

0 20.00 100 Diorite quartz , chlorite

20.00 35.00 99 Tactite brown & green ga rne t , low chalcopyrite chalcopyrite

35.00 95.50 99 Diorite quartz95.50 96.50 99 Tactite brown & green garnet96.50 98.60 99 Tactite brown & green garnet,

marmatite130 0.70 0.83 2.51

98.60 100.60 99 Tactite brown & green garnet100.60 103.00 99 Tactite brown & green g a rne t ,

chalcopyrite .40 0.10 1.00 0.20

103.00 128.00 99 Tactite brown & green garnet128.00 135.30 99 Tactite green garne t , c a l c i t e ,

chalcopyri te , marmatite53 0.35 0.70 1.70

135.30 140.30 99 Tactite green ga rne t , calci te

140.30 145.00 99 Tactite green ga rne t , c a l c i t e , marmatite

61 0.42 0.17 2.30

145.00 167.05 100 Limestone marble

Table 0 - 3 . DDH No. L N -7-71 , Diamond Drill Station No. 1

Coordinates: N 5077.90 Bearing: N76W Core Size: AXE 4859.50 Inclination: 0° Total Length: 221.55 m

Elevation: 2, 005 m

From To Rec Ag Pb Cu Znm m % Rock Type Alteration and Minerals g / ton % % %

0 10.50 100 Diorite quartz , chlorite10.50 29.85 99 Tactite brown garnet29.85 74.30 100 Diorite quartz74.30 85.75 98 Tactite brown & green garnet

85.75 88.05 100 Diorite quartz88.05 91.05 100 Tactite green garnet91.05 97.75 99 Diorite quartz , chlorite97.75 98.75 100 Tactite green garnet98.75 100.35 100 Tactite green garnet , chalcopyrite 87 2.13

100.35 109.85 99 Tactite green garnet109.85 114.50 99 Tactite chalcopyri te , marmatite 64 0.11 1.07 1.98114.50 123.30 99 Tactite galena, chalcopyri te , marmatite 329 1.81 1.60 1.80123.30 147.80 50 Tactite oxidation z o n e , fault ? 65 0.30 0.32 0.38147.80 156.40 98 Tactite marmatite 67 0 .2 0 - 0.80 3.06156.40 160.35 100 Tactite green ga rne t , mainly chalco­

pyrite , and marmatite99 0.34 2.22 6.10

160.35 194.80 100 Limestone marble

Table C -3 . DDHNo. LN-7-71—Continued

Fromm

Tom

Fee% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

194.80 197.25 100 Tactite green garnet, galena, chalcopyri te , marmatite

318 1.60 0.89 2.60

197.25 198.60 100 Limestone marble198.60 200.60 100 Tactite green garnet , marmatite 42 0.20 0.29 5.10200.60 221.55 100 Limestone marble

Table C -4 . DDK No. LN-15-72, Diamond Drill Station No. 1

Coordinates: N E

Elevation: 2,

5077. 4859. 006 m

9050

Bearing: N78W Inclination: +34°

Core Size: Total Length:

AX164. 75 m

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

0 9.75 100 Diorite quartz9.75 41.80 99 Tactite brown & green ga rne t , wollastonite

41.80 68.00 99 Diorite chlori te , wollastonite68.00 72.00 100 Tactite green garnet72.00 73.00 100 Diorite fresh73.00 77.00 100 Tactite green garnet77.00 78.70 100 Diorite fresh78.00 81.50 100 Tactite green garnet81.25 83.60 100 Tactite low galena, chalcopyri te ,

marmatite106 0.70 0.23 0 .50

83.60 85.05 100 Tactite good galena, chalcopyrite, marmatite

447 3.50 1.28 1 .50

85.05 99.20 99 Tactite green garnet99.20 101.90 100 Tactite low g a le n a , chalcopyri te ,

marmatite57 0.40 0.06 1 .10

101.90 119.80 100 Hornfels wollastonite119.80 121.20 100 Tactite low g a le n a , chalcopyrite ,

marmatite146 0.90 0.50 3 .00

Table 0 4 . DDE No. LN-15-72—Continued

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

121.20 124.15 100 Hornfels wollastonite

124.15 125.35 100 Tactile good galena, chalcopyri te , marmatite

1550 14.00 0.94 11.7

125.35 125.95 100 Limestone marble

125.95 127.80 100 Tactile good galena, chalcopyrite 1033 4.7 0.35 4.80127.80 129.15 100 Limestone marble129.15 149.65 100 Tactile good galena, chalcopyri te,

marmatite644 4.00 0.70 5.80

149.65 164.75 99 Limestone marble

Table C -5 . DDH No. LN-21-72, Diamond Drill Station No. 1

Coordinates: N E

Elevation: 2,

5077. 4859. 006 m

9050

Bearing: N78W Inclination: +56°

Core Size: Total Length:

AX167.35 m

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

0 6.40 100 Diorite chlorite6,40 19.00 100 Tactite brown ga rne t , wollastoni te

19.00 67.20 100 Diorite wollastonite67.20 77.10 100 Tactite green garnet, wollastonite77.10 78.60 100 Diorite chlorite78.60 80.70 100 Tactite green garnet80.70 82.60 100 Diorite chlorite82.60 103.05 99 Tactite green ga rne t , wollastonite

103.05 105.45 100 Tactite good ga lena, chalcopyri te , marmatite

565 4.80 0.58 6.50

105.45 118.55 99 Hornfels wollastoni te118.55 120.65 100 Tactite c a l c i t e , g a le n a , chalcopyri te ,

marmatite284 1.60 0.22 4.30

120.65 126.15 100 Limestone marble126.15 127.45 100 Tactite low galena, chalcopyrite ,

marmatite162 0 .80 0.14 8.10

127.45 129.35 100 Limestone marble

129.35 136.65 99 T ac t i te , good ga lena, chalcopyri te , marmatite

593 4.8 0.53 5.40

Table 0 5 . DDE No. LN-21 -72 — Continued

From To Rec Ag Pb Cu Znm m m Rock Type Alteration and Minerals g / ton % % %

139.65 167.35 100 Limestone marble

Table 0 6 , DDH No. IN -22 -72 , Diamond Drill Station No. 1

Coordinates: N E

Elevation: 2,

5077. 4859. 006 m

9050

Bearing: N85W Inclination: +32°

Core Size: Total Length:

AX154.70 m

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Ag Pb g / ton %

Cu Zn% %

0.00 5.50 100 Diorite fresh

5.50 26.65 98 Tactile brown & green garnet •

26.65 68.80 99 Diorite quar tz , chlorite

68.80 99.90 97 Tactile green garnet , c a l c i t e , low chalcopyrite

99.90 154.70 98 Limestone marble

Table C -7 . DDH No. LN-23-72, Diamond Drill Station No. 1

Coordinates: N E

Elevation: 2,

5077. 4859. 006 m

9050

Bearing: N66W , Inclination: +23°

Core Size: Total Length:

AX217.05 m

Fromm

Tom

Rec% Rock Type Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

0.00 4.95 100 Diorite fresh4,95 12.80 99 Tactite brown garnet

12.80 22.25 100 Diorite chlorite22.25 53.00 99 Tactite brown garnet53.00 89.90 99 Diorite quartz , chlorite89.90 98.65 100 Tactite brown garnet98.65 103.55 100 Tactite green garne t , chalcopyrite 243 0.56 2.00 0.60

103.55 118.85 99 Tactite green garnet118.85 122.20 99 Tactite green garnet 140 0.42 0.61 1.40122.20 124.00 100 Tactite green garnet , calci te124.00 138.00 100 Limestone marble138.00 156.25 98 Tactite green garnet , calci te

156.25 168.80 99 Tactite oxidized zone, f a u l t?168.80 186.40 100 Tactite green garnet , calci te

186.40 195.20 100 Tactite green ga rne t , good galena, chalcopyri te, and marmatite

478 3.10 0.95 5.90

195.20 217.05 100 Limestone marble

Table C -8 . DDH No. LN-24-72, Diamond Drill Station No. 1

Coordinates: N E

Elevation: 2,

5077. 4859. 006 m

9050

Bearing: N76W Inclination: +22°

Core Size: Total Length:

AX183.00 m

Fromm

Tom

Rec% Rock Types Alteration and Minerals

Agg/ ton

Pb%

Cu%

Zn%

0.00 5.65 100 Diorite fresh5.65 38.20 98 Tactite brown garnet

38.20 69.55 99 Diorite guartz69.55 78.15 100 Tactite brown & green garnet78.15 80.65 100 Diorite chlorite80.65 84.60 100 Tactite brown & green garnet84.60 88.90 100 Diorite quartz , chlorite88.90 114.00 98 Tactite green garnet

114.00 116.00 100 Tactite green garnet , low galena, chalcopyrite

100 1.00 0.25 1.00

116.00 121.00 100 Tactite green garnet121.00 124.00 100 Tactite green garnet , low galena,

chalcopyri te , and marmatite120 0.80 0.30 1.50

124.00 136.35 99 Tactite green garnet136.35 148.30 99 Tactite green ga rne t , fair galena,

chalcopyr i te , and marmatite200 1.25 0.70 3.00

148.30 156.00 100 Tactite green garnet156.00 183.00 100 Limestone marble

REFERENCES

Bodenlos, A. J „ , 1956, Notas sobre la geologia de la Sierra Madre enla seccidn Zimapdn-Tamazunchale . Estratigrafia del Cenozoico y del Mesozoico a lo largo de la carretera entre Reynosa, Tamps, y Mdxico, D .F . Tectonica de la Sierra Madre Oriental, vulcanismo en al Valle de Mdxico: Int. Geol. C o n g . , Mexico, 20th, Excursiones A-14 and C -6 , p . 293-309.

Carbonell , M. P . , 1970, Bosquejo geolbgico de la Sierra de Querdtaro. Mineria prehispdnica en la Sierra de Querdtaro, in Boletin y Mapa Geoldgico de la Secretaria del Patrimonio Nacional: Consejo de Recursos Naturales No Renovables, p . 13-16.

Cardona, J. A . , 1968, Control dilucidn del mineral de-la mine La Negra: unpublished report, Industrias Peholes , S .A . , La Negra, Querdtaro, Mexico.

Fink, W. N . , 1952, Report on La Negra properties: unpublished report, Industr ias Penoles , S. A . , Mexico, D .F .

Gaytdn Rueda, J. E . , 1971, Geologia del depbsito mineral de La Negra y general idades sobre exploracibn y sistema de explotacidn: National Convention of the Asociacidn de Ingenieros de Minas Metalurgis tas y Geblogos de Mdxico, IX Biannual, Hermosillo, Sonora, Memoirs, p . 367-378.

Geologia y Mineria, S .A . , 1967, Estudios petrogrdficos de la mina La Negra: unpublished report, Industrias Penoles , S .A . , Mexico, D .F .

Guilbert, J. M . , 1966, Petrographic s tudies on La Negra mine: un­published report, Industr ias Peholes , S .A . , Mexico, D .F .

Inst i tu te de Geologia , Universidad Nacional Autdnoma de Mdxico, 1966, Estudios petrogrdficos de la mina La Negra: unpublished report , Industrias Peholes , S .A . , Mexico, D .F .

McCarthy, J. C . , 1953, La Negra mine, El Doctor d is t r ic t , Querdtaro: unpublished report, Industr ias P eho les , S . A . , Mexico, D .F .

Park, C. F . , J r . , and MacDiarmid, R. A . , 1964, Ore deposi ts : W. H. Freeman and C o . , San Francisco.

Petersen, U . , 1959, Geologia del Yacimiento de Antamino, Ancash,Peru: unpublished report, Cerro de Pasco C o r p . , La Oroya, Peru.

97

98

Q u e z a d a s , A. G . , 1972, Estudios petrogr^ficos de la mina La Negra: unpublished report # Industr ias Peholes , S .A . , Mexico, D.F .

R a isz , E . , 1964, Map and descriptions of the landforms of M exico .Physiographic Provinces: prepared for the Geography Branch of the Office of Naval Research , Washington, D . C .

Sanchez Mejorada , P . , 1960, Report on La Negra mine, El Doctor min­ing d is tr ic t , Municipality of Caderey ta , Gro: unpublished report, Industr ias Peh o les , S. A . , Mexico, D . F .

Sanchez Mejorada , P. , 1968, Geology of La Negra mineral deposi t . State of Quer^taro, Mexico. Paper presented at the Intl.Cong . of the Geological Society of America, Mexico City, M exico .

Segerstrom, K. , 1956, Estratigrafia y tectdnica del Cenozoico entreMdxico, D .F . y Zimapdn, E g o . Estratigrafia del Cenozoico y Mesozoico a lo largo de la carretera entre Reynosa, Tamps. y Mdxico, D .F . Tectonica de la Sierra Madre Oriental, vulcanis mo en el Valley de Mdxico: In tl. Geol. C on g . , Mexico, 20th , Excursiones A-14 and C - 6 , p . 311-323.

Segerstrom, K. , 1961, Estratigrafia del area Bernal-Jalpan, Estado de Querdtaro: Asociacidn Mexicana de Geoldgos Petroleros Bul l . , v . 13, nos . 5 and 6, p . 183-206.

Wil l iams, S. A . , 1968, Petrographic studies on La Negra mine: unpub­l ished report, Industr ias Peholes , S .A . , Mexico, D .F .

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