Exploration and development at the La Negra Mine, Maconi, Queretaro, Mexico
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Authors Gaytán Rueda, José Eligio, 1940-
Publisher The University of Arizona.
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Link to Item http://hdl.handle.net/10150/554937 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 thesis has been submitted in partial fulfillment of re quirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judg ment the proposed use of the material is in the interests of scholar ship. In all other instances, however, permission must be obtained from the author.
SIGNED:
APPROVAL BY THESIS DIRECTOR
This thesis has been approved on the date shown below:
WILLIAM C. PETERS /date Professor of Mining and Geological Engineering DEDICADO
A mi esposa:
Blanca Rosa
A mis hijos:
Jos6 Eligio Juan Rafael
Javier Andres ACKNOWLEDGMENTS
Various factors have enabled the writing of this thesis. The
first, and without doubt the cause of the others, was the granting of a
scholarship by Industrias Penoles, S.A., through Ing. Pedro Sanchez Mejorada, at present Director of the Division of New Projects and De velopment, who has advised me in the development of the thesis and
throughout my professional career. For this, I would like to give him
. special thanks.
I would also like to thank Industrias Pefloles, S.A., the spon
sor of the scholarship for one year. Penoles has authorized the incor
poration in the thesis of all information obtained as a result of the
studies conducted by me during the two years (1970-72) during which I
acted as resident geologist at the La Negra mine. I am grateful to Ing. Manuel Castilldn Bracho, Subdirector of Exploration, and Ing. Gustavo Aguilar Arzate, Divisional Manager, for ■
the help received from them in the development of my present activities.
Overall, I express my gratitude to the Mining Division of
Penoles, directed by Ing. Carlos.Sierra Valdes, and especially to Ing.
Eduardo Garcia Guerrero, General Manager, Ing. Luis Corrales Velasco
and Ing. Carlos Madrazo, Divisional Managers of the Mining Division,
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 especially to Dr. William C.
Peters, who advised me during my studies, and Dr. Thomas J. O'Neil and Dr. Charles E. Glass. TABLE OF CONTENTS
Page
LIST OF ILLUSTRATIONS ...... viii
ABSTRACT ...... • x
1. INTRODUCTION ...... 1 Geographic Setting ...... 2 Historical Information ...... 4
2 . REGIONAL tz? E (Z) l_i (2) ...... o...... 6
Physiography and Geomorphology ...... 6 Lithology and Stratigraphy...... 8 Sedimentary Rocks ...... o...... 9 Las Trancas Formation ...... 9 El Doctor Formation ...... 9 Cerro Ladrdn Facies...... 9 El Sacavdn Facies ...... 10 San Joaquin Facies ...... 10 La Negra Facies ...... 10 Soyatal Formation ...... 11 Mezcala Formation ...... 11 El Morro Conglomerate ...... 11 Surficial Deposits ...... 12 Igneous Rocks ...... 12 Structure ...... 12
3 . GEOLOGY .....o...... 14
Sedimentary Rocks...... 14 Igneous Rocks ...... 15 Metamorphic Rocks ...... o...... 15
4. ORE-BODY DEVELOPMENT ...... 21
Old Mine Workings ...... 21 Preproduction Development Work ...... 23 Mining and Sampling Methods ...... i, .. . 27 Scale of Operation and Life of the Mine ...... 32 Ore Grade and Tonnage...... 34
vi vii TABLE OF CONTENTS—Continued
Page
5. ECONOMIC GEOLOGY...... 37
Ore Control ...... 38 Lithologic Factors ...... 38 Stratigraphic Factors ...... 39 Structural Factors ...... 39 Chemical Factors ...... 39 Density and Textural Factors ...... 40 Ore Mineralogy...... 40 Mineral Paragenesis and Zoning ...... 41 Ore Genesis . ^ . 44
6. EXPLORATION ...... 48
Exploration Program at Depth ...... 52 Systematic Exploration at the Mine ...... 54 Results and Costs of the Exploration at Depth and at the Mine ...... 55 Geologic Interpretation...... 58 Ore R eserv es ...... 59 Results of Exploration at the Mine ...... 62 Cost 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 mine, Quer^taro, Mexico . 3 2o Physiographic provinces y Estados Unidos Mexicanos ..... 7
3. Regional geology of the La Negra district ...... in pocket 4. Local geology of the La Negra area ...... in pocket
5. Geologic map of sublevel 2317 (7), plan v iew ...... 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 the La Negra mine ...... 22
10. Longitudinal and cross sections of the La Negra ore body ...... 24
11. Sublevel preparation, first stage ...... 25' 12. Sublevel preparation, second stage...... 26
13. Ore haulage and mining system, isometric drawing...... 29
14. Isometric.projection of the La Negra ore body ...... 30
15. Map.showing sampling method, diamond drill holes, and pocket of mineral at the footwall, sublevel No. 5 (elevation 2317 m) ...... 33
16. Ore reserve estimate of the La Negra ore body...... 35
17. Variation of metallic contents at depth, based on average assays, 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 exploration program between elevation 2,000 and 2,100 m ...... 50
20. Generalized geologic map along Socavdn La Negra and El Alacrcin ...... 51
21. Plan view showing the mineralized zones intersected with the horizontal diamond drill holes between elevation 2,000 and 2,100 m ...... 56
22 . Cross section of the La Negra ore bodies I and II...... 57 23. Longitudinal projection of the La Negra ore body II, ore reserve estimate map ...... 60
24. Longitudinal projection of small pocket of mineralization 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 typically metasomatic or pyrom eta somatic deposit where the mineralization is present as massive sulfides, with silver as hessite, lead as galena, copper as chalcopyrite, and zinc as marmatite.
The exploitation method is a combination of sublevel and long hole blasting. The initial ore reserves have been estimated at 1,368,427 metric tons, averaging 254 g/metric ton Ag, 1.4% Pb, 1.52% Cu, and
3.3% Zn. The life of the mine was estimated to be about 12 years at the production rate of 120,000 metric tons per year. Actually, this pro duction has been increased to 156,000 metric tons per year and the life of the mine is still considered to be 12 years because the ore reserves have also been increased by 30 percent since the continuation of the ore body at depth has been located. The author considers that the pos sibilities for more ore at depth and in other areas in the vicinity of the mine are high.
x CHAPTER 1
INTRODUCTION
This paper describes certain aspects of the La Negra mine, the latest mine to be brought into operation by the group Industries Peholes,
S.A. The mine started operating in January 1971. Although at this time,
June 1973, other mines are under development, none of these is in opera tion y et. It is not unrealistic to say that La Negra is the most modern, medium-size, underground mining operation in Mexico. The operation is highly mechanized, with a consequent high degree of efficiency and pro ductivity. The geologic setting is such that possibilities for additional ore are favorable and it is apparent that it will be a larger mine in the near future. In spite of the fact that the area has been subjected to in tensive prospecting activity for over a century, as witnessed by num-. erous prospects and small abandoned mines, 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 interest in the area, various mining companies had turned down the property because of nega tive results. The exploration of the La Negra mine is a good example of success through interest in areas with evidence of mining operations or in old mining districts no matter how many geologists or mining com panies have studied the area. 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 features. The La Negra area is a typical contact metasomatic zone where every meter of tactite-limestone contact is a potentially good exploration target for massive sulfide ore bodies and where similar targets occur within the tactite zone and the tactite-intrusive contact.
Since the beginning of operations, the La Negra mine has been a success in all respects, including discovery, metallurgical operation in spite of the complexity of the ores, effective and low-cost mining, and exploration during the first two operating years. In that.time,
500,000 metric tons of additional ore reserves were found, and the same or better results are expected with current and future exploration pro grams.
Geographic Setting
The state of Quer6taro is located in the southern portion of the great central plateau of Mexico . The distance from Mexico City to the city of Quer6taro, capital of the state, is 215 km (Fig. 1). The La Negra mine is situated in the Maconi mining district in the northeastern part of the state of Quer6taro in the eastern portion of the Sierra Gorda de
Guanajuato. At this point, the boundary between the states of Querdtaro and Hidalgo is the Moctezuma River. The nearest—and very small— town is Maconi, municipality of Cadereyta. The population of this town is about 700. The distance from Maconi to the mine is 5 km by an un paved road. The Zimapan mining district in the state of Hidalgo is 7 km east of the La Negra mine, but no communication exists between the two because of the depth of the Moctezuma River canyon and the general / \ J \ STATE OF SAN LUIS ( STATE OF \ POTOSI C- QUERETARO \ j To son M, '9ua/'ft'ent/e - ' J S°n- T V X A NEGRA y / Maconi x " > < : STATE OF HIDALGO To Leon ond Cd. J o o’re z GRAPHIC SCALE 0 5 10 15 batz±c±±at ~ tmnmTrmml G.ity \ ( Q u e r e ta r o ^ KILOMETERS V
EXPLANAT ION
■ Paved roads Dirt roods Rail rood River State boundary - > — International boundary
Figure 1. Location of the La Negra mine, Quer^taro, Mexico ruggedness of the topography„ The access road to the La Negra mine is shown in Figure .1. The nearest railroad point is San Nicolas station near
Queritaro, 120 km distant. The average altitude of the district is 2,000 m, which gives it a temperate climate; the average annual temperature is
19°C. The rainy season, from July to September, accounts for most of the .500 mm of average yearly rainfall.
Historical Information
The very old, small workings scattered over San Nicolas Moun tain were discovered and explored during the Colonial period. These workings furnished oxidized lead ore, carrying silver, for the several smelters at Maconi, where large masonry hydraulic blowing towers and large slag piles bear witness 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
Mexico. His son continued operating the properties after Beaurang*s death and then sold them to Oscar and Thomas Braniff in the early 1900's.
In 1904, the Braniffs sank several shafts on the outcrop of the ore body and drove the La Blanca Tunnel, 326 m long. They cut some mineraliza tion at depth but missed the main ore body. The main reason for stopping the operations in the early years of the Revolution was that they were . unable to treat the deeper unoxidized complex sulfide ore by gravity con centration methods (McCarthy, 1953).
In 1950, Cia. Minera Acoma, S.A., acquired the properties from the Braniffs. Cia. Minera Acoma did a limited magnetometer survey and carried out a diamond drilling program without successful results.
Their lack of success may have been due to a. very poorly planned ex ploration program. As a consequence, the project was abandoned by
Cia. Minera Acoma . Eloy Vallina and Antonio Guerrero took over the properties, and Peholes subsequently acquired them (Sanchez Mejorada, 1960). The Exploration Department of Peholes developed an extensive geologic and diamond drilling program, with very successful results, 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 district belongs to the Lower Range sub province of the Sierra Madre Oriental province , which is limited to the east by the Gulf Coastal province, to the west by the Central Meseta province, and to the south by the Neovolcanic Plateau province„ The
Sierra Madre Oriental province consists of Jurassic and Cretaceous sedimentary rocks, mostly limestone, folded into anticlines and syn- clines, forming evenly sculptured elongate ridges „ The Lower Range subprovince is parallel to the High Sierras on the east; both belong to the Sierra Madre Oriental province (Fig. 2). In contrast to the High Sierras, the subprovince is lower in altitude and the valleys are wide and detritus filled. The transition to the Central Meseta is gradual
(Raisz, 1964). This is a general description, but locally the topography is abrupt and the valleys are narrow. The greatest relief is about 1,200 m, with an average relief of 400 m. Near the La Negra mine, the slopes along the Moctezuma River are nearly vertical and the difference in alti tude is in the order of 1,000 m.
In the Maconi district, the topography is very rugged, with very high, scarped mountains of irregular shape and steep slopes. The main rivers in the region are the Moctezuma and Tollman in the eastern . part and the Extorax in the western part. Intermittent streams with swift currents due to the steep slopes are characteristic in the district. The GRAPHIC SCALES
MILES
Pitted The %\Veo La Negro Mine
r ‘ * + J 3
Figure 2. Physiographic provinces, Estados Unidos Mexicanos drainage system is parallel and is included in the hydrographic basin of the Moctezuma River. The upper portions of the high mountains are formed by the weather-resistant, massive limestone of the Cerro Ladrbn facies, giving these hills a very prominent shape. The limestone in the Cerro del Espolbn form vertical slopes of about 100 m at the contact with the shales and marls. Maconi Valley is carved in soft shales, marls, and thin-bedded limestones. 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 dis trict are, from a lithologic point of view, sedimentary and igneous and represent an incomplete geologic interval from Jurassic to Quaternary. The stratigraphic sequence of the exposed geologic formations (Fig. 3, in pocket) is summarized as follows (Carbonell, 1970):
Quaternary _ Cerro Ladrbn facies ■ Unconformity ------Jurassic Four different sedimentary formations, Las Trane as, El Doctor, Soyatal, and Mezcala, are present in the region. They have been in truded by plutonic rocks of intermediate composition and are overlain by a Tertiary conglomerate and surficial deposits. The lithologic sequence starts 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 oldest found in the region and is Late Jurassic in age. It is exposed as a belt trending northwest- southeast from Cerro del Palmito to Bucareli (Fig. 3). The maximum ob served thickness is 200 m. At the bottom of the formation is a thin bed (30-60 cm) of grayish-green arkose; the matrix is argillaceous. A thin gray bed, 50 cm thick, of graywacke concordantly overlies the arkose. The top of the formation is composed of thin beds of reddish shale inter bedded with thin, dark-gray limestones, 10 cm thick. El Doctor Formation The El Doctor Formation is in contact with the Las Trancas For mation in an angular unconformity. The age of this formation is Early Cretaceous (Albian-Cenomanian). The total thickness of the formation ranges from 150 to 1,500 m. It is divided into four limestone facies. Cerro Ladr6n Facies. The Cerro Ladr6n facies is the lowest unit of the El Doctor limestone and is the most conspicuous lithologic . unit. It is a great calcareous mass with thick beds of gray limestone. 10 The thickness ranges from 10 cm to 2 m„ There are lenticular fragments of dark chert interbedded with the limestone beds. The lithology of this facies is not uniform, and it can be subdivided into three subfacies: (1) a subfacies with rudistids, (2) a subfacies of lithified limestone muds, and (3) a subfacies of fine-grained conglomerate „ The Cerro Ladr6n crops out in the upper part of the El Doctor range, in the central and northeast ern part of the mapped area (Fig. 3). El Socav6n Facies. The El S oca von facies is restricted to a zone located between the San Joaquin facies to the northeast and the Cerro Ladr6n facies to the southwest. These beds of limestone elastics are exposed in a belt 1 to 3 km wide. San Joaquin Facies. The San Joaquin facies is composed of thick beds of very compact, dense, dark-gray limestone, with an abun dance of chert nodules. In general, its composition is similar to that of the overlying La Negra facies, but it was deposited at less depth. It is present in a belt 1 to 2 km wide. The San Joaquin facies interfingers with the La Negra facies to the northeast and with the El Socavdn facies to the southwest. The presence of small primary folds in monoclinal areas sug gests that deposition of the sediments took place over a sea floor with enough inclination to cause underwater sliding of the unconsolidated sediments. The thickness of the facies 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 Facies. The La Negra facies is found over a larger area than any of the other facies of the El Doctor Formation. It is a very 11 fine grained limestone. Thin members of red shale interbedded with the limestone beds are 10 to 30 cm thick; thin beds and lenses of black chert are also present, mainly at the bottom of the formation. The total thick ness of the La Negra beds appears to be riot greater than 300 m. This facies is correlated with the Cuesta del Cura limestone (Albian- Cenomanian) of northeastern Mexico. It is believed that these sediments were deposited in the deepest part of a neritic zone. The facies crops out mainly in the El Doctor, Cerro de los Lirios, Cerro San Nicolas, La Negra, Cerro Quemado, and Cerro de los Chinos areas (Fig. 3) . Soyatal Formation The Soyatal Formation is a dark-gray limestone of Late Creta ceous age. The limestone is interbedded with yellowish shale and gray to light-reddish marls; it 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). Mezcala Formation The Mezcala Formation is composed mainly of yellowish-brown, light-gray, and greenish-gray clay marls in beds 5 cm to 1.2 m thick. Gray limestone beds, 30 cm thick, mudstone, and sandstone, 40-60 dm thick, are found interbedded with the marls. These beds have been strongly folded. El Morro Conglomerate The El Morro Conglomerate is composed of coarse clastic rocks with a reddish calcareous clay matrix. This conglomerate overlies all the lower formations with an angular unconformity. It is found as small. 12 isolated outcrops in the area. The age of the conglomerate is Tertiary (Eocene-Oligocene). Surficial Deposits Clastic deposits of Pleistocene to Holocene age are present as alluvial terraces, alluvial deposits, talus, caliche, and reddish residual sediments „ Igneous Rocks . The largest intrusive mass present in the area is of granodio- ritic composition. This intrusive mass crops out in the Deconf, El Yonthe, Divisadero, and La Negra areas (Fig. 3). Differentiated parts of the same intrusion are also found in the area as stocks of quartz diorite and as a small mass of diorite. Andesite, dacite, and rhyolite dikes are also present. 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 Mesa de Ramirez and Mesa del Hormiguero areas (Fig. 3). Structure In general, the sedimentary sequence shows a northwest- southeast trend and dips from 40°-70Q SW, The top of the Las Trane as Formation, composed of thin beds of shale, crops out in a 4 km-wide belt. The intrusive rocks are exposed as stocks, dikes, and sills of differing compositions. The sedimentary rocks were tilted from their original position by these intrusive bodies; hence, faulting and folding ' ' 13 are mainly related to intrusive activity. The Maconi Valley is carved in shales and marls of Late Cretaceous age„ In a structural sense, this valley is a sync line, with the massive limestone of the Cerro Ladrdn facies exposed on the flanks of this sync line in Cerro del Espoldn to the west and in Cerro de los Lirios to the east. The shales and marls of the Soyatal Formation and perhaps the Mezcala Formation crop out in a syn- cline in the Maconi Valley overlying the limestone of the Cerro Ladrdn facies. CHAPTER 3 LOCAL GEOLOGY The El Doctor range is composed in its upper part of massive limestone of the Cerro Ladrdn facies. The slopes of the range and the valley are composed of the limestones, shales, and marls of the Soyatal Formation. The general strike of the beds is northwest-southeast with dips of about 50° SW. There are various outcrops of plutonic rocks that have been classified as monzonite, diorite, and quartz diorite. It is common to find metamorphic halos. In the La Negra area, the outcrops are represented by sedimentary rocks, which constitute 85 percent of the total outcrops, igneous rocks 7 percent and metamorphic rocks 8 percent. Sedimentary Rocks The limestone present in the area is the La Negra facies 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 bodies. Near the contact zone, metamorphic minerals have been developed, including wollastonite, garnet, epidote, diop side, and vesuvianite. There are two systems of faults and fractures; the principal system is oriented north-west and the secondary system trends north-east, 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 vicinity of the La Negra mine has a predominantly dioritic composition. The biggest dioritic mass exposed at the surface has been emplaced as a stock with branching sills and dikes. It crops out in an elongate form whose major axis strikes N. 75° E. Other small masses of diorite are exposed at the surface in different orientations but mainly N. 20° W. These small masses have been emplaced as sills and dikes of porphyritic texture. Metamorphic Rocks Metamorphic rocks represent 8 percent of the La Negra area and are predominantly tactite. This contact metasomatic rock is in a more strict sense a garnetite, because it is almost entirely composed of garnet of the green and brown variety, grossularite and andradite, in that order. In minor proportions wollastonite, epidote, diop side, and vesuvianite are present. These rocks represent a transition zone from igneous (diorite) to sedimentary (limestone) rock and have been formed by contact meta morphic effects of the intrusion into the limestone. The thickness of this zone ranges from 20 to 200 meters. The rocks mentioned above are also found in the mine workings where they have the same characteris tics. Another metamorphic rock, hornfels, is not present in the surface but has been found in the mine. Hornfels is found as lenses of medium size at the contact between the limestone and the intrusion. It is a fine-grained, very hard, white rock. The primary constituent, wollas tonite, amounts to 94 percent. Garnet amounts to an.accessory 6 percent. 16 Accordingly, the rock can be classified as calcic silicate hornfels (Quezadas, 1972). The metamorphic mineral spurrite is found in small bands inter bedded with the marmorized limestone. This is common in the hanging wall very close to the ore body. The spurrite is blue with white and yellowish shades. Its chemical components are 25.4 percent 8102 and 62.0 percent CaO; the formula is 2Ca2*Si04-CaCOs . The local geology is shown in Figure 4 (in pocket) . As can be observed, it is a typical contact metasomatic area. Intrusive bodies of dioritic composition, present as stocks and dikes, are surrounded by the metasomatic zone, which is a tactite composed of green and brown garnet (grossularite and andradite, in that order) as essential minerals. Near the contact zone, the intrusive body is more siliceous and the biotite is altered to chlorite. Surrounding the contact 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 intrusion. 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 tactite are found as well as spurrite; this is better observed in the mine workings. Outside of the metamorphosed limestone is the fresh, gray La Negra limestone. 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 contact, as shown in Figure 7. Another interesting thing has been observed: the green garnet is more closely associated with the mineral ization and the brown garnet is near the contact with the intrusion. 5000 iue . elgc a o sbee 2317 sublevel of map Geologic 5. Figure 1 2 35 20 10 0 Lmi1 iixj iixj Lmi1 krtl— . E S R E T E M LmxmxiirniiK.mH.Dod — ( i:500 7 ), ln view plan Vertical Fractures — 23 Toctite 3 Limestone 3 Fracture Fracture Man way High Ore Pass Pass Ore grode N 5100 - 17 18 \ ! / ODH Diamond Drill Holei proiecfed fo Cut the i S-TT f nnf nri A nr o i 100 m EXPLANA T I 0 N '■^'a A'X' a 'X'X.. Intersection p o in t of mineralization indicated with diamond drill hole No. 2 , drilled Limestone Tactite QZ x n Diorit® L3 H i g h grade Low grade Ore P a s s Manway Fault Fracture Vertical Fractures GRAPHIC SCALE 0 10 bnat—fanut . btii 1 : 500 N-SIOO Figure 6. Geologic map of sublevel 2295 (3), plan view 19 N-5100 5 0 ° MW MW 85° 80° 75° 60° 70° o 5000 LU EXPLANATION 1 1 . l..B Limestone i 'L~'d T act ite GRAPHI C SCALE I--. •• *• • ] Low grade o io 20 35 High grade u = w =u = ham E T Head samples 1 : 500 80° © Ore Pass Fracture ^ MW Manway Vertical Fractures ) 8 5® Fault i40° Strike and Dip Figure 7. Geology and sampling maps of sublevel 2266 (Cono) 5 0 0 Verficol Frocfures Figure 8. Geologic map of sublevel 2170, plan view CHAPTER 4 ORE-BODY DEVELOPMENT Old Mine Workings The early workings at La Negra consisted of a series of open cuts and short adits all the way up the cliff of the outcrop of the deposit, a distance of 85 meters vertically above the La Negra patio level. These small, 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 adit, at 2,352 m elevation, from which drifts and crosscuts 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 missed it. The second adit was driven 15.4m below the first. This adit did not intersect the ore body and encountered only scant mineralization in the foot wall. Two shafts connect the first and second adits; one is 38.9 m deep and the other is about 25 m deep. The third adit driven was La Blanca, 152 m vertically below the first adit, on the La Negra level. La Blanca is too far from the ore body and passed into the foot wall of the intrusive mass; it did cut some low mineralization in its present face, and this was mistakenly thought to correspond to the same ore body exposed in the number one adit on the La Negra level. The length of the La Blanca adit is 325 m. 21 22 Surfoce workings Level 1 (La Negro) E-2352 BONANZA Level 2, E-2237 Level 3, E- 2225 Lo Blanco adit, E-2200 SOTOL Ore body, Level Ore body, Level Ore body, Level N 5100 i n UJ N 5000 // // Figure 9. Composite map of the old mine workings of the La Negra mine 23 During Penoles1 1960 exploration program, a fourth adit was driven 49 m below number one adit. This is now known as level number 3. This adit intersects the ore body, and some drifts and crosscuts were driven in order to determine the width and length of the ore body at that elevation. 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 properties. All of these mine working were, and still are, of great use in the preparation and exploitation of the mine. 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 level). With this knowledge, a main adit, Socavdn Principal, was driven at 2,000 m ele vation. The length of Socavon Principal is 1,538 m, and its cross sec tion is 4 by 4 meters. It was driven perpendicular to the general strike of the ore body in order to cut it in case of a continuation of mineraliza tion at this level, but it only found the lime stone -tactite contact with no economic mineralization. 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 pass, Chorreadero General, which is parallel to the dip of the LONGITUDINAL SECTION CROSS SECTION TO N 75° E TO N 15° W LEVEL 1 LEVEL 1 E-2300 LEVEL 60 80 LA BLANCA 1: 2000 E-2200 LEVEL E-2200 LA BLANCA LEVEL EXPLANATION T o c t i t e Limestone Ore body E- 2100 Figure 10. Longitudinal and cross sections of the La Negra ore body 3,5 CO CO CL UJ CL OLU o e> 5? Lu O Ct ,o O v -^ °0 1%vc 6^ X.V e"93 ^ Ne 26 SUBLEVEL (OPEN CUT) SUBLEVEL (OPEN CUT) / / SUBLEVEL PILLAR SUBLEVEL PILLAR SUBLEVEL PILLAR / SUBLEVEL / Scale 1 : 500 Figure 12. Sublevel preparation, second stage 27 ore body. In this ore p a ss, at the La Blanca level, there is a minus 20 inch grizzly in order to control the size of the ore fragments. The total inclined length of the ore pass is about 400 meters, and its section is 4 by 4 meters. In order to have better efficiency in the transportation of the miners and the mine equipment, a vertical ser vice shaft of one compartment has been driven from the Socav6n Princi pal La Negra to level number 3. The total depth of this shaft is 300 m, and it has a cross section of 3.5 by 3.5 meters. Mining and Sampling Methods Due to the irregular form of the ore body, a combination of dif ferent mining methods has been chosen in order to obtain the highest re covery feasible with low cost and to have the best control over the dilution of the ore (Cardona, 1968). There are two sections of the ore body which are similar in width, length, and tonnage, so it is possible to use the same mining method in both sections, with just a little variation. The most economic and appropriate method is a combination of sublevel and long hole blast ing methods. The decision to use this method was based on the follow ing physical characteristics of the ore body: width, dip, and hardness of the walls. In general, the method is as follows (Figs. 11 and 12). From the general ore pass (Chorreadero General) and each 10 vertical meters, crosscuts are driven to the hanging wall. Then drifts of 3.5 by 3.5 meters in cross section are driven along this contact between the silicated limestone and the mineralized zone, both north and south to the limits of economic mineralization. This is easy to do because the 28 hanging wall is very sharply defined and the mineralization ends at the contact with the limestone, which is barren. The next step is to open the drifts to the full width of the ore body. Once the sublevels are com pletely enlarged to the ore limits, the remaining pillars between sub- levels are about 6 m in thickness (the final height of the sublevels is about 4 m). These pillars 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 possible. These pillars are then broken by blasting, 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 limits. To take advantage of the form of the upper part of the ore body, which will be mined out first, it has been planned to use, in longitudinal cross section, the form of an inverted cone. In cross section, the zone to be mined first is tabular. The slope of the north and south sides of the cone is 45 degrees. The main reason for adopting this form is for easier and cheaper exploitation. The broken ore from the pillars, which represents 60 percent of the mine production, falls by gravity into the main ore pass. The broken ore that comes from the preparation of the sublevels represents 40 percent of the mine production; this is hauled to the main ore pass. This ore falls to the 2,000-meter level, passing through a minus 20-inch grizzly installed on the 2,200-meter level. At 20 m below the Socav6n Principal, at the 1,980-meter level, 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 BROKEN ORE o GENERAL ae ORE PASS co GRIZZLY GENERAL ORE PASS FEEDER CRUSHER 24 x 36 CONVEYOR BELT ORE POCKET TRUCK LOADING POINT E -2000 To the plant Scale 1 : 1 000 Figure 13. Ore haulage and mining system, isometric drawing 30 * :)v‘ EX PL A N A TION 1 : 3 300 V L V 3 LIMESTONE ORE BODY GRAPHIC SCALE 50 100 150 200 250 TACTITE METERS E-* X INTRUSIVE body Figure 14. Isometric projection of the La Negra ore body 31 degrees) to the ore bin, which is 20 m above the. Socavdn Principal. From this point the mineral is transported by trucks to the flotation plant, about 2.5 km distant. The 10-meter separation between each sublevel was planned in order to have a maximum ore dilution of 10 percent. The larger the sep 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 projected. One, at the 2,150-meter elevation to mine the orebody section from this level to 2 ,200 m, will be done by driving sublevels each 10 vertical meters (Fig. 10). The other general haulage level has been projected at the 2,100-meter ele vation to mine the ore body section between this level and the 2,150- meter level by the same method of sublevels. Both the 2150 and 2100 levels will be connected with the general ore pass by another inclined ore pass in order to transport the broken ore from the sublevels and pil lars. The access to these general levels will be from the service shaft. The northern section of the ore body, called the "Dog Nose" (Fig. 10) will also be mined by sublevels but with a different type of equipment because of the width of the ore body in this section is about 2 meters. The middle section, from the 2200 level to 2266, needs more exploration in order to define the form of this narrow mineralized section better and to choose the best mining method (Fig. 10). 32 Two sampling methods are used in the mine. Once each drift has been finished in a section of 3„5 by 3.5 meters to the hanging wall, a series of diamond drill holes (size EX) are drilled every 5 m toward the footwall in order to determine the ore limits. This is necessary due to the irregularity of the ore body and also because the mineralization toward the footwall gradually decreases in value in such a way that the limit of the stopes must be determined by assay (Fig. 13). The other sampling method used is to cut channel samples in the back, faces, and walls of the sublevels, as they are needed. Because of the hardness of the rock, it has been found convenient to use a disk with a diamond cut 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 mining, 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 estimated, the life of the mine was calculated to be about 12 years. Ore reserves, how ever, have been incremented by small dislocated 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 AVER AGE ASSAYS SAMPLE WIDTH A9 Pb Cu zn No. METERS g /t % % % 5 - 1 4.00 350 2 8 0.50 3 5 5 - 2 9.50 4 00 3.3 0.70 2.7 5 -3 6 5 0 6 00 h_ 4. 0 0 .80 4.0 5 - 4 3 .25 150 _ 0.6 OTZ5 0:3 5 -5 5 .00 500 _ 4,0 0.60 5.0 5 -6 12 .00 550 3 .5 0 .60 6.0 5 -7 2 .00 90 ^ 0:5 0.30 0.6 5 - 8 8 .25 390 2 . 0 0.40 3.0 -p-9 5.50 3 40 1 .8 0.50 3.5 5 - 10 7.5 0 1250 5 - H 9 . 50 580 _ 2 7 0 6 0 3 .0 5 - 12 10 . 00 TfrO . 0.50 4 .0 5 -13 13 00 1300 6.5 0 .80 5.0 5-14 1.5 , 2 5 6 00 4.0 0.80 4 6 5-15 3 . 75 400 3 .0 0.40 4.0 5 - IB 2 . 00 50 0 .s 0 .30 1.0 " 5 " 17 3 .75 400 3,5 0 . 50 4.0— & -18 7 .50 150 1 5 0 25^ 1.0 5 -19 _ 1 ,50 2 50 i.o 0.30 15 |-|o 5 , 150 2.0 1.0 r - n 4. 00 300 1 .5 0 -19.40 1 .2 5 -2 2 14 . 00 ISO 1.0 0.30 1.2 5 - 23 13.00 450 2 9 0.70 2.9 -5"^T4 9.00 100 0^.8 0.40 0.9 5 -2 5 33 .50 550 3 5 0 .80 3.3 5 -2 6 7. 00 88 0.7 0 . 20 10 _ 5-2 7 500 4 0 0.75 4 2 5 - 28 9 .50 1 25 . 12 0.35 1 . 0 5-29 24 .50 580 4 0 0 .82 4.5 _ 0.9 0 35 7.2 b -31 IB .00 no _ 10 0 .40 1 . 5 5 -32 30.00 475 3.5 0 .77 3.7 5-33 . J 50 TTO rrrro 2.1 5 -34 ~2 1 .50 180 1.2 0.40 2.4 5-35 20 .00 370 2.8 0.70 2.8 5-36 6 .75 120 0.85 0.35 1 . 5 -5100 EXPLANA T I ON b.1 ■ 1 i3 Limestone E H 3 = l H 3 Tactile L_ ■ ■ '- •■■'..J] Low mineralization 3 High mineralization 5-2 - Head samples 5 0 0 e Ore Pass GRAPHIC SCALE Figure 15. Map showing sampling method, diamond drill holes, and pocket of mineral at the footwall, sublevel No. 5 (elevation 2317 m) 34 La Negra ore body to the north and also at depth is in progress with good results, which will be mentioned in Chapter 6. Ore Grade and Tonnage The exploration program conducted by Penoles at La Negra, started in 1964 and finished in 1967 after discovery of two ore bodies, La Negra and El Alacrin, and the outlining of the ore reserves. During those 3 years, 40 diamond drill holes were drilled in the La Negra area and 14 in the El Alacr&n area. Of the 40 in La Negra, 25 intersected the ore body and 15 were barren or intersected low-grade mineralization. All of the 14 drilled in El Alacr&n intersected mineralization. The ore reserve map (Fig. 16) is included here and the related detailed calculations are given in Appendix A, but only in regard to the La Negra ore body, since this 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 assays in both of the ore bodies. La Negra and El Alacr&n, using 10 percent mining dilution are: Weighted Average Assays Ag Pb Cu Zn Metric Tons g/MT % % % La Negra 790,568.9 335 2.1 1.28 4.6 El Alacr&n 577,858.2 115 trace 1.86 1.5 Total 1,368,427.1 254 1.4 1.52 3.3 The initial exploration of the La Negra ore body covers only a vertical range of 275 m from the surface (elevation = 2,375 m) to A S S AYS DIAMOND 1 METERS DRILL HOLE C /ton % % % INTERVAL LONGITUDINAL NUMBER A Figure 16. Ore reserve estimate of the La Negra ore body GJ Cn the 2,100 meter elevation, because at that time it was very difficult and expensive to explore deeper. This would have required very long holes, and the angle of intersection with the ore body would have been too acute. During the subsequent detailed exploration stage, very pleasant surprises have been encountered. In some places, 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 estimate. Density of the rock was calculated according to the formula, Density = W eight/Volume , and i t was found to be 3.75. The rock sample was weighed and then submerged in a graduated test tube containing water. The difference between the water level before and after the addi tion of the rock is the volume of the rock sample . A summary and detailed estimate of the ore reserves found be 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 tactite. The hanging wall of the ore body is very sharply defined; the mineralization ends in the contact of garnet tactite with a white silicated limestone with abundant wollastonite and ore mineralization does not continue into the limestone. The tactite is found on the footwall of the ore body. The highest values of the ore are found at the contact with the limestone, while the grade decreases gradually toward the footwall. Because of this, it is difficult to define the exact limit of the economic mineraliza tion by visual observation. The limit has been defined by diamond drill holes and supporting laboratory tests. All of the tactite zone is mineral ized, but its grade is too low to be considered ore, except for the hanging-wall portion. The intrusive rock (diorite) is found at the inner contact of the tactite zone. The general strike of the ore body is N. 15° W at the surface; as it increases in depth, the strike changes to N. 45° W. at 250 m below the surface. The average dip is 60° SW (Fig. 10). In cross section, the ore body is represented by two large lenses, one above the 2,200-meter level and a second below this ele vation. These two lenses are connected in a short and narrow waistlike interval where the average ore thickness is only about 2 meters. The ore body is in general concordant with the limestone bedding, and it is 37 believed that the reduction in width is due to the strong folding in the limestone in this section. The average width of the ore body is about 11 m eters. In a longitudinal projection (Fig. 10), the ore body has an hour glass shape. The minimum strike length, 20 m eters, occurs at the La Blanca level (elevation 2,200 m). Both above and below this level, the length of the ore body increases, reaching 150 meters at the 2,300-meter level. The known vertical range of the ore body was 280 meters before the exploration program of 1971, but the lower part was still undeter mined, since no exploration had yet been done below the main haulage adit. Another important characteristic of the ore body is that its southern part is wider and richer than the northern part between levels 2,200 and 2,300, whereas just the opposite occurs from the 2,300-meter level to the surface (Figs. 5, 6, and 7). Ore Control There are several factors that could have controlled the circu lation of mineralizing solutions and the subsequent ore emplacement. The most important ones are the lithology, stratigraphy, structure, chemistry, 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 tactite near the ore body and the second is in the hanging wall of the ore body where the limestone has been mainly silicified and recrystallized with development of wollastonite. This suggests that the limestone, which is now altered 39 to tactite, was an argillaceous limestone and that the second limestone was relatively pure. Stratigraphic Factors The ore body is at the contact between limestone and tactite. It also conforms very closely 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 also 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 beds. It is found along plunging noses of secondary anticlinal flexures in one flank of a local broad fold (Sanchez Mejorada, 1968). In another structural association, thick lenses of mineral are found in the concavities of the limestone beds pointing toward the tactite zone, while the ore body is short and narrow where opposite conditions occur. 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 recrystallization, recombination, and the for mation of new m inerals. The new m inerals, formed mainly in the tactite zone, include green and brown varieties of garnet, diop side, and perhaps vesuvianite. This new mineralogy and its arrangement in the tactite zone changed the texture and density, thus increasing its permeability, which 40 favored the passage of the mineralizing solutions to replace the minerals of the tactite zone. This chemical action, which made the rock more favorable to mineralization, is regarded as "ground preparation." In the outer limits of the tactite zone, a hard, dense, silcified limestone is present. In this rock, the metamorphic and metasomatic effects caused silicification of the limestone, making it more dense and impermeable. These rocks constituted a seal or barrier to the advances of the mineral izing solutions circulating within the tactite zone. Density and Textural Factors As has been shown in the description of the chemical factors, 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 chemical factors already described. The selective position of the ore body and of some mineralized lenses delimited by the silicified limestone as well as the occurrence of some small bodies of limestone with no mineralization at all within the center of the ore body illustrates the selectivity of the mineralizing solutions in the zones of more permeability. Furthermore, where the tactite is . fine grained, dense, and only slightly fractured, ore is very low in grade. . It can be considered that chemical factors have apparently been the most important ones of the ore control factors already mentioned. Ore Mineralogy The La Negra ore body is of very complex mineralogy. The economic metals in the ore body include silver in hessite, Ag2Te, a very 41 elusive mineral detectable only by a very detailed petrographic study (Williams, 1968), lead in galena, zinc in marmatite, and copper occur ring almost exclusively in chalcopyrite. Silver and lead are closely as sociated. Silver (hessite) is found as small blebs arranged in cleavage planes of galena crystals. The economic mineralization is found as mas sive sulfides associated with the following non-ore sulfides: pyrite, present in very minor proportion and arsenopyrite and pyrrhotite in great proportion. Some scheelite and traces of gold have been found. The highest values of mineralization are found just at the con tact of the tactite with the limestone. Toward the footwall, mineraliza tion in the tactite is not as massive as at the contact; actually, it is disseminated. In this zone , besides pyrite, arsenopyrite , and pyrrhotite , certain gangue minerals are found, including calcite, quartz, diopside, epidote, sericite, chlorite, 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 detailed petrographic studies made by Institute de Geologia, UNAM, 1966; Guilbert, 1966; Geologia y Mineria, S.A., 1967). These studies have been based on the investigation of seven ore samples taken from differ ent diamond drill holes. These samples were studied in thin section under the polarizing microscope. X-ray diffraction and fluorescence analysis were also made . According to these studies, the paragenetic sequence shows that after the formation of the calcic silicates (diopside and garnets). 42 the sulfides were deposited as follows „ Pyrite appears as the oldest, pyrrhotite is partially contemporaneous with pyrite but mostly younger. Arsenopyrite came after all of the pyrite but is still included in the depositional time of the pyrrhotite. Marmatite and chalcopyrite are simultaneous. Galena overlaps the marmatite-chalcopyrite but continues beyond the general sequence. The paragenetic sequence can be crudely sketched as follows: Pyrite ...... Pyrrhotite 1— ...... — Arsenopyrite Marmatite „ - — , , Chalcopyrite ^ r Galena , The mineral sequence was completed by secondary mineralization of cal- cite , which under high pressure conditions was deposited in the inter stices not occupied by the sulfides . In the study of samples by X-ray diffraction and fluorescence analysis, silver, camium, tin, manganese, and zirconium were detected in small portions. Silver is present associated with galena and cadmium with marmatite. Based on the sampling of diamond drill holes and mine workings the following mineral zonation can be established. Andradite is found in greater proportion than grossularite near the intrusion, and the reverse situation is found near the limestone contact. Lead and silver decrease in depth and also toward the intrusive mass. Copper and zinc increase at depth and toward the intrusion (Fig. 17). 43 0 U I C R O P Ag Pb H N H 2300 m H Cu Zn 2200 m 2100 m LA NEGRA ORE BODY 2000 m Relative scale for silver 100 gm. per metric - ton equivalent to 1.0 % for base metal. GRAPHICS SCALES 0 25 50 100 o 1% 2 % 3% 4 % VERTICAL hrmrinnnj rbmrr HORIZONTAL _ tnc nsabr: --1 meters 100 200 300 400 Figure 17. Variation of metallic contents at depth, based on average assays, 100-m intervals 44 Common mineral associations are: pyrrhotite-chalcopyrite, galena-hessite, and marmatite-cadmium. Arsenopyrite is found in great est concentration either where the lead-silver values are high or where the copper-marmatite is high. Pyrite, in general/is erratic and occurs in very minor concentrations . Ore Genesis The La Negra ore body is. an epigenetic deposit associated with an intrusion of dioritic composition. This intrusion is the origin of all the metamorphic and metasomatic effects in the adjacent limestone and the typical metasomatic or pyrometasomatic ore body itself. The age of the intrusive body has been determined by the K-^Ar method, in Teledyne Isotopes, Westwood Laboratories in the United States of America. The results of the analysis are: Isotopic Age Rad — 6 Rad Specimen (m.y.) SccAr XI0 %Ar %K 2m KA 71-61 38.8 + 0.8 5.51 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~^ , xe = 0. 585 x , and y- ^ and = 1.19 x 10*^ atom percent of natural potassium. The error indicated for the reported ages takes into account all sources of analytical errors. The samples submitted for the age determination were col lected from two different locations, 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 surface). This study has determined that the age of the intrusion is 38.7 + 0.8 m .y. Based on this determination and with the consideration that the intrusion was the source of mineralizing solutions which formed the known ore bodies, the age of both can be considered about the same. According to this age, 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 this stage, the limestone was recrystallized and changed to marble and the whole metamorphic halo was developed around the intru sive mass. During this stage, there was no addition of new elements but simple re crystallization and rearrangement of the already existing minerals. The second stage of the ore -body formation was characterized by the addition of hydrothermal fluids coming from the intrusive mass. The main consituent of these fluids was silica, which in contact with the limestone gave rise to lime-silicate gangue minerals, such as gar net, wollastonite, diopside, etc. As a consequence of this process, a metasomatic aureole was formed surrounding the intrusive mass. The resulting type of rock is known as tact it e or skarn, composed mainly of garnet. The two stages already described acted as "ground preparation," which is described by Park and MacDiarmid (1964) as any premetalization process that increases the permeability, causes a favorable chemical change , or induces brittleness in the rocks which may develop an area 46 that will localize deposition from the pre bearing fluids. Such a change makes the country rock more receptive or more reactive to the ore bear ing solutions. The third stage is characterized by the introduction of mineral izing solutions v The metallic constituents replaced the calcic silicates of the tactite, giving rise by this process to the ore body. This process was restricted mostly to the outer limits of the tactite zone at the con tact with the silicified limestone. This limestone is very dense, fine grained, and very hard, containing no mineralization at all. The miner alization of economic grade in this case is in the tactite and it ends abruptly in contact with the silicified limestone at the hanging wall; to ward the foot wall it gradually decreases in the direction of the intrusive contact. The concentration of high-grade mineralization in the tactite zone ends at the contact with the silicified limestone, and the absence of mineralization in the limestone zone suggests that the tactite has a higher permeability and more favorable chemical properties due to the "ground preparation" process. The difference in time between the first and second stages could have been small. However, between the second and third stages, the difference in time could have been longer in order for the "ground preparation" process to take place. It is possible that just after the mineralizing process a last pulse of the fluids brought some calcic solutions which now filled the intergranular spaces not oc cupied by the sulfides. Considering the selectivity of mineralization in the tactite, the original type of rocks was probably a series of limestone beds with local differences; the altered zone where the tactite is present could have 47 ' been an argillaceous limestone which was favorable to the formation of the calcic silicates of Fe and AL The silicated 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 mass, giving rise to the formation of a pure calcic silicate, such as wollastonite. The impermeability, hardness, and high density of the limestone as well as the envisioned fault zone could indicate a textural and structural limit of mineralization in the hanging wall where the mineralizing solu tions stopped and, because of lower temperature and pressure, the cal cic silicates 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 stages, with the first from the elevation 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 characteristics of the ore body and its geologic interpretation are mentioned below. 1. As the ore body goes deeper, its general strike becomes more westerly. 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 elevation of 2,150 m (Fig. 20). 2. A longitudinal section of the ore body shows that its lower por tion tends to rake to the northwest (Fig. 10). 3. The average dip of the ore body is 60° SW; if this were con tinuous at 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 tact it e zone, the tactite-lime stone contact is the target for exploration. 5. As observed in cross section (Fig. 10), the ore body known to day shows very definite zones which are repeated with analogous 48 LIMESTONE I------1 T ACTITE I* * *1 DIOR ITE I j HIGH GRADE FAULT DIAMOND DRILL HOLES PROJECTED ORE BODY ELEVATION 2100 m LCrusher \\\ Figure 18. Plan view showing target zone No. 1 SECTION N 80° W LOOKING N 10° E LA NEGRA ORE BODY 3 Limestone 3 Tactile Tactile 3 Diorite ELEVATION 2100 m •J High grade -o Diamond drill holes 20 Reference Reference Line SOCAVON (Adit) x LA NEGRA DIAMOND DRILL STATION P r o p o s e d DDK ELEVATION 2000 m Figure 19. Cross section of the La Negra ore body exploration program between elevation 2,000 and 2100 m To S vr f oce w i m MINERALIZED / > / / , , X X / X X X , , / X x / iue 0 Gnrlzdgooi mp ln ScvnL er ad ElAlacrdn and Negra La Socavdn along map geologic Generalized 20. Figure x x / ORE BODY II CONTACT THE A NEGRALA X X x / x CRUSHER ' R BD x ORE BODY X x X x x HOIST x LVTO 20 m 2300 ELEVATION 3 LEVEL v ■ fh i / Wf^h ) . / O H N^TH H T ^ N TO THE EE 3 _ . 3 LEVEL EXPLORATION DRIFT x x ^ x / x N A # V 6 % X / « - - * x 0 s e X ' * x ...... " L Q /. ORE BO ELEVATIBfhk m 2352 X / surfac X w X X\ X w X D D H D 120 m 112.00 D.T TACTI LIMESTONE ERALIZ&D ZONE 9.30 m ERALIZ&D 9.30 ZONE X \ -' yx iy 'W '- O GAE 20 t Ag /t 9 <200 LOW GRADE d e r r e f n i \x>ux v x\ v v \x>ux x\ v x x x x x x \ x X X X X X M E 5 xxx 0 E N 0 T RPI SCALEGRAPHIC 0 8 0 4 E 1 : 2 000 x xj x Ix !"<,% =/Ll r body Ore /cLol = n Limestone n i a LN TION PLANA Fa u 11 I X HOIST , , , Mnrlzd zones, Mineralized 4 3, 2,1, a ny copper.mainly vrg Asy >1% 1 > Assays Average etcl FractureVertical Fracture Diorite Tccti+e x X SERVICE L R C ^ b A EL R BOD ORE X SHAFT x ■? 51 characteristics. There are two zones where the width is more than 10 m and also two narrow zones, From the surface to ele 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 min width. 6. There is one mineralogic characteristic which has to be taken into account during the exploration. The values of lead and silver decrease at depth, while copper-zinc increase; there fore, it could be expected to have a deeper ore body where the copper-zinc values would be higher than those of lead and silver (Fig. 17). The geology of the Socavdn La Negra shows one radical change in relation to that of the upper levels. Based in the projection of the lime stone-tactite contact from the upper part of the ore body, where the average dip is 60° SW, there is a horizontal displacement of the contact at the elevation of the Socavdn La Negra (2,000 m, amounting to 120 m toward the southwest. This displacement could have been caused by faulting or by a change in dip of the limestone, due to the intrusive mass (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 elevation 2,100 m. The 53 exploration was suspended mainly because of technical problems. 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 intersect the ore body and at an angle still acceptable. So the problem of exploring at greater depth was left to be continued when conditions were more favorable, as is now the case with the Socavdn La Negra. The actual exploration program has been divided in two stages: first, 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 its downward extension by means of a deep drilling project. 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 geol 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 this is true, the contact zone marked "No. 1" is our drilling target. According to this interpretation, the ore body has to be displaced in two direction: to the north and to the west (Fig. 18). Based on this interpre tation, one diamond drilling station has been placed in order to drill 12 diamond drill holes (Fig. 18). The holes will be drilled with AX bits, inner diameter 3.09 cm. The design of the second stage of the exploration program must await the results of the first one. 54 Approximate DH No. Bearing Inclination Length (m) Obiective 1 N 65 W 0° 220.00 To cut the ore body at elevation 2,005 m 2 " N 83 W 0 45.00 To check the lime- stone-tactite con tact 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 elevation 2,075 m 9 N 80 W +52 175.00 To cut the ore body at elevation 2,100 m 10 N 85 W +32 165.00 To cut the ore body at elevation 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 Systematic Exploration at the Mine Due to the characteristic irregularity of the ore body, it has been- necessary to design a program of systematic exploration with dia mond drill holes from the mine workings. The purpose of this systematic exploration is to look for other ore bodies near the main one in both directions, toward the hanging wall (limestone) and to the footwall (tactite). Another purpose is to find dislocated bodies or pockets or ore that may branch from the.main ore body. 55 According to the geology of each sublevel, diamond drill holes will be projected toward the hanging wall and toward the footwall. In the first case, the purpose is to explore for possible mineralized zones replacing the limestone beds. The reason for this exploration is based on the fact that at the surface there are some small mine workings in the limestone beds; also, two small zones of regular mineralization 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 terest because all the tactite zone is mineralized, although the grade is low. This can be explained by the fact that the tactite zone was the con duit of the ore-bearing solutions and some mineralization was deposited there. This factor makes the tactite zone favorable for small ore bodies, predominantly with copper-bearing mineralization due to the proximity of the intrusive mass and therefore higher temperature. Small amounts of chalcopyrite are present all along the tactite zone where its back ground can be considered as 0.2% Cu. Besides diamond drill exploration in the sublevels, it is pro jected to drive an exploration heading to the north from level No . 3 to intersect the narrow mineralized zone shown on Figure 6. The purpose is to continue with this drift along the contact toward that direction for at least 200 m, looking for other ore bodies similar to those of La Negra and El Alacrdn. Results and Costs of the Exploration at Depth and at the Mine The first stage of the exploration program to find a continuation of the La Negra ore body between elevations 2,000 and 2,100 m has 56 \T0. 232.55 m LIMESTONE TACTITE DIORITE HIGH GRADE LOW GRADE H 5^ _ FAULT DIAMOND DRILL HOLES GRAPHIC SCALE 0 „ 20 SMALL POCKET kmuuij iyyvmrv-l OF MINERAL i ooo ,PROJECTED ORE BODY ELEVATION 2100 m X/' 65° 55° •CRUSHI 57 THE LA NEGRA ORE BODY I Sublevel 2170 Sublevel 2150 ELEVATION 2 15 0 m T D 167.20 m THE LA NEGRA ORE BODY II' ELEVATION 2100 m F ID. 164.25 m Limestone /FAULT T D 183 .00 m Diorite 0«° High grade Low grade Diamond drill holes .FA U LT " B Fault T. D. 222.40 m LU 20 4 0 70 /•:) r FAULT A SOCAVON (Adit) SMALL POCKET OF MINERAL LA NEGRA-DIAMOND DRILL STATION Figure 22. Cross section of the La Negra ore bodies I and II 58 been very successful (Figs. 21 and 22). There have been minor varia tions from the original exploration program as to bearing and inclination of the drill holes. 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 deviations. Geologic Interpretation As can be seen on Figures 21 and 22, there has been a great displacement 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 responsible for this displacement, as shown in Figure 22. Both faults are believed to be postmineral, but we have proved fault "A" to be older than fault "B" because the first has been displaced by the second. It is possible that a longitudinal displacement could have been caused by fault "A" and that a subsequent horizontal and vertical displacement 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 limestone—-it is only a few centimeters wide and the oxidation is not very strong. Fault "B" displaces the ore body; therefore, it is safe to conclude that both faults are postmineral. One important thing that must be mentioned is that DDE No. LN-7-71 cuts two mineralized zones in limestone (Figs. 21 and 22) which can be considered as a good indication of substantial tonnages of lime stone-ore replacements, away from the tactite zone. Ore Reserves The first stage of the exploration program consisted of 12 di- mond drill holes, totaling 2,028 m drilled. It outlined the continuation of the La Negra ore body from elevation 2,000 m (Socavdn La Negra) to elevation 2,121 m. The tonnage found and its average assay, 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 estimate map is shown in Figure 23. Besides some small mineralized 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 LN-7-71. Ore reserves between elevations 2,000 and 2,030 m, as shown in vertical projection (Figs. 21 and 22) are estimated, 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 results obtained in this 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 this. A summary and detailed estimate of the ore reserves found are shown in Appendix B. 60 4 m 10m 5m r 4m 9 m 4 m z CL, E-2IOO m N - 15-72 16 m. 10 m 2m . IALN-23-7; L N - 2 2 - 7 2 N - 2 4 - 7 2 6m 3m P- 3 8 7m 7m L N - 1-71 .LN-7- E- 2000 3m 7m 3m7m \ \ \ j PROVEN ORE EXPLANAT ION Diamond METERS A S S A Y S [ 3 Z J PROBABLE ORE Drill Hole g / ton % Number INTERVAL Aq. ; t % Zn LN -1 -7 1 — 68 0 . 0 1 0 62 0 . 0 7 LN -3 - 71 — 61 0 . 4 2 0 . 17 1 . 30 LN -7 - 71 7 . 5 0 78 0 . 2 5 1 . 2 8 4 . 0 7 GRAPHIC SCALE LN -15-72 1 8 . 0 0 6 4 4 4.00 0 . 70 5.60 0 10 20 30 LN-21-72 1 0.00 593 4 . 7 9 0 . 5 3 5 . 3 8 LN-22-72 — B a r r e n M E T E R S LN-23-72 4 . 00 4 7 8 3 0 7 0 95 5 . 8 6 LN-24-72 7 . 00 2 0 0 1 . 2 5 0 . 7 0 3 . 0 0 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 NATION Diamond METERS A S S A Y S Drill Hole 2 /T o n %% % Number INTERVAL Ag Pb Cu Zn L N - 7 - 7 1 8 . 0 0 329 1.80 1.60 1 .8 0 1 : 1 000 PROVEN ORE GRAPHIC SCALE PROBABLE ORE f T V 0 10 20 30 60 Vmrrrrv ri ------W in n rry j ~ =d METERS Figure 24. Longitudinal projection of small pocket of mineraliza tion at the footwall of the La Negra ore body II, ore reserve estimate map Results of Exploration at the Mine Exploration at the mine as well as the exploration in the area at depth has been successful. 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 calculated tonnage of these provides an in crement of 85,000 metric tons of ore assaying 390 g/ton Ag, 3% Pb, 0.75% Cu, and 2% Zn. This increment in tonnage is from level 2266 to 2352, so similar results in the lower portion of the ore body can be expected. This area,, from level 2100 to 2200, is now being prepared for mining. Since the exploration drift to the north, localized in level No. 3, did not cut mineralization where it was expected, it was decided to continued exploration with diamond drill holes. The first hole inter sected a mineralized zone, as shown in Figure 19. Although this zone is low in tenor, because it has been proved that the mineralization con tinues toward the north and far from the main ore body, it is interesting from the exploration point of view. Once this mineralized contact has been located, exploration toward the north will continue with the drift. Cost of Exploration at Depth and at the Mine The total 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 Assays Explora tion Ag Pb Cu Zn Meters Cost Program Metric Tons (g/ton) (%) (%) (%) Drilled (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 (Mexican)/ton Tons Found 419,200 Exploration in Socavon El Alacr^n As can be seen on the surface geologic maps (Figs. 4, in pocket and Fig. 20), two ore bodies are localized along the lime stone- tactite contact. La Negra and El Alacrin. The second one is about 650 m northeast of the first. Between these ore bodies, the favorable zone for mineralization is the limestone-tactite contact. Both mines are now connected by the Socavdn El Alacrdn at elevation 2,000 m, 350 m below the old La Negra workings and 200 m below the El Alacrdn outcrop. As this level has been driven almost parallel to the lime stone-tactite con tact, it will be used as an exploration level with diamond drill stations every 125 m on both sides. Two exploration programs have been planned for two different targets. The first program will explore the 1 ime stone- tactite contact looking for ore bodies similar to those of La Negra and El Alacrcin. The second will explore the tactite zone toward the intrusive mass looking for copper sulfide bodies of high grade and relatively small tonnage or of lower grade and large tonnage. 64 There are three reasons why these possibilities are considered. First, in theory, as chalcopyrite is a rather high temperature mineral, it is expected to find higher values closer to the intrusive mass and at depth. Second, sampling of the tactite between La Negra and El Alacrctn has proved the existence of several zones where copper values are of 1 percent or more (Fig. 20). Third, in all the tactite zone, chalcopyrite is present in disseminated form, with an average assay of about 0.2% Cu. Therefore, the possible existence 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 characteristics of the Antamina mine that are similar to those of the La Negra mine are: 1. The ore deposit is pyrometasomatic. 2. The contact metasomatic zone is composed mainly of tactite with garnet in its brown and green varities, showing the same zonation as La Negra. The brown variety is present near the intrusive mass and the green variety near the limestone. 3. The type of intrusion is about the same as the one of the La Negra mine, and the limestone is Mesozoic in age. 4. The form of the ore body is like Chimenea; the vertical 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 present as chal- copyrite, lead as galena , zinc as sphalerite, and has some silver. In Antamina, the principal mineral is chalcopyrite, then sphalerite, and lead and silver are present in small amounts. This sequence is different than that at La Negra. 7. As in La Negra, copper increases toward the tactite, and lead just the opposite. 8. The tactite was formed first, then the metallic minerals. CHAPTER 7 SUMMARY AND CONCLUSIONS The La Negra ore body occurs in the outer limits of the contact metasomatic zone, just between the tactite and the limestone. The La Negra ore body is an epigenetic and typically metasomatic or pyrometa- somatic deposit. Mineralization is present as massive sulfides, in which silver is present as hessite, lead as galena, copper as chalco- pyrite, and zinc as marmatite. Andradite is found in greater proportion than grossularite near the intrusive mass, and the reverse situation is found near the limestone contact. Common mineral associations are: pyrrhotite-chalcopyrite , galena-hessite, and marmatite-cadmium. An increase in copper mineralization in relation to that of lead and silver toward the intrusive mass indicates the possibilities of higher copper values that way and that the lead and silver mineralization is mostly present near the limestone zone. Among the ore control factors the most important one is chem ical, because the process of "ground preparation" is considered as the first step in facilitating the passage of the mineralizing solutions . Structure is also important, because the emplacement of the La Negra ore body is controlled by the gentle folds of the limestone beds, along plunging noses of secondary anticlinal flexures in one flank of a local broad fold. ' 66 67 During the first year and a half of mining, additional ore re serves have been found, at depth and in the ore body itself, which account for 30 percent of the original ore reserves estimated. Two small mineralized zones have been intersected the DDH No. 7 in the limestone zone. Results of sampling the tactite zone along the socavbn between the La Negra and El.Alacrctn ore bodies have proved the existence of several zones where copper values are 1 percent or more. The diamond drill hole from the exploration drift to the north on level No. 3 cut some lead-silver mineralization just in the tactite-limestone contact, about 200 m away from the La Negra ore body. It is believed that the possi bilities for more ore at depth and in other areas are very good. From all these findings, the following conclusions and recom mendations are made. All around the La Negra area is a very interesting prospective zone, mainly where intrusive bodies are present as stocks, dikes, and sills. From the zonatioh of grossularite and andradite and the charac teristic that high grades of lead and silver are found near the limestone contact, it can be concluded that the presence of the first indicates that the limestone contact is close and thus it is an indication of a probable good exploration target for lead-silver ore deposits. The common mineral association between pyrrhotite and chal- copyrite shows a very good possibility to use the electromagnetic geo physical method for exploring for copper deposits. 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 tactite zone along the Socav6n El Alacrcin, are indications that copper ore deposits could exist toward the intrusive mass. It is recommended that the tactite-intrusive contact be explored with diamond drill holes from the Socav6n El Alacrdn. It is recommended that detailed stratigraphic and structural mapping in the area be done to look for folding and secondary anticlinal flexures of the limestone beds associated with intrusions. The fact that the systematic exploration in the mine was suc cessful shows that this method should be continued in the future through out the mine. The positive results of the exploration between the 2100 and 2000-meter levels give rise to a recommendation to explore deeper than the 2000-meter level. . Intersection 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 deposits. Finally, 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 Ag Pb Cu Zn Metric Tons gr/ton % % % Proven Ore 576,551.5 403 2.8 1.30 5.1 Probable Ore 142,147.5 360 2.9 1.93 5.1 Proven 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 1,244,024.7 282 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 1,368,427.1 254 1.4 1.52 3.3 Note that although no geologic data about the El AlacrSn ore body is included in this thesis, the ore reserve estimate 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 Height Area Width Volume Block Location m g/ton % % %' m m m Density Metric Tons 1 XR 0 6.00 530 4.3 0.40 7.2 25.00 8.00 200.00 9.80 1,960.00 3.75 7,350.000 SOC 5 11.70 585 5.7 0.60 9.3 SOC 5 -11.70 585 5.7 0.60 9.3 Average 29.40/9.80 574 5.4 0.56 8.9 2 SOC 5 11.70 585 5.7 0.60 9.3 27.50 16.00 440.00 9.25 4,070.00 3.75 15,262.500 SOC 5 11.70 585 5.7 0.60 9.3 XR 0 7.10 455 3.4 0.46 5.7 P 11 8.30' 403 1.9 0.90 2.2 XR 0 6.70 267 1.0 0.10 1.1 P 24 10.00 430 2.0 0.50 4.1 Average 55.50/9.80 475 3.6 0.55 5.9 3 SOC 5 11.70 585 5.7 0.60 9.3 30.00 6.00 180.00 13.15 2,367.00 3.75 8,876.250 P 31 17.75 282 1.8 0.40 2.9 P 24 10.00 430 2.0 0.50 4.1 Average 39.45/13/15 409 3.0 0.48 5.1 • 4 SOC PP 10.00 332 7.1 0.50 6.6 29.00 2.50 72.50 13.50 978.75 3.75 3,670.313 XR 0 12.80 336 4.7 0.50 4.2 P 31 17.75 282 1.8 0.40 2.9 Average 40.55/13.50 311 4.0 0.46 4.2 5 XR 0 7.10 455 3.4 0.46 5.7 39.00 5.00 195.00 5.95 1,160.25 3.75 4,350.938 P 28'. 10.00 314 2.4 0.90 3.0 P 26 0.80 506 2.8 0.40 4.0 • Average 17.90/5.95 379 . 2.8 0.70 4.1 • 6 XR 0 7.10 455 3.4 0.46 5.7 24.00 21.50 516.00 ' 9.40 4,850.40 3.75 18,189.000 P 11 8.30 403 1.9 0.90 2.2 XR 0 6.70 267 1,0 0.10 1.1 P 24 10.00 430 2.0 0.50 .4.1 P7y No. 13 14.40 603 3.3 0.60 5.2 P 28 10.00 314 2.4 0.90 3.0 Average 56.50/9.40 433 2.4 0.60 3.8 Block Width Ag Pb ■ Cu Zn l/2 B a s e Height Area Width Volume No. Location m g/ton % % % m m m2 m m3 Density Metric Tons 7 P 24 10.00 430 2.0 0.50 4.1 15.50 16.50 255.75 13.50 3,452.625 3.75 12,947.344 P 31 17.75 282 1.8 0.40 2.9 P 9 11.80 575 2.9 0.50 5.2 P7y No. 13 14.40 603 3.3 0.60 5.2 Average 53.95/13.50 459 2.5 0.494.2 8 P 31 17.75 282 1.9 0.40 2.9 15.00 6.50 97.50 14.85 1,447.875 3.75 5,429.531 P 6 15.00 425 2.5 0.40 5.4 P 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 2.9 20.00 16.50 330.00 13.50 4,455.000 3.75 .16,706.250 XR 0 12.80 336 4.7 0.50 4.2 P 23 8.50 601 5.6 0.80 9.0 P 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 4.0 48.00 27.00 1,296.00 1.90 2,462.40 3.75 9,234.000 XR 0 2.65 331 2.1 0.56 3.1 S 1 2.30 326 2.6 0,83 3.8 Average 5.75/1.90 . 353 2.4 0.64 3.5 11 XR 0 2.65 331 2.1 0.56 3.1 50.50 34.00 1,717.00 3.85 6,610.45 3.75 24,789.188 P 26 0.80 506 2.8 0.40 4.0 P 28 10.00 314 2.4 0.90 3.0 XR . 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 3.0 20.50 46.50 953.24 8.60 8,197.95 3.75 30,742.313 P7y No.13 14.40 603 3.3 0.60 5.2 XR 0 8.00 478 2.4 0.50 3.2 XR 0 2.00 302 2.3 0.30 3.2 Average 34.40/8.60 472 2.8 0.65 4,0 ■"~3 DO Width Ag Pb Cu Zn l/2Base Height Area Width Volume Block Location m g/ton °/c % °/c m m m2 m m3 Density Metric Tons 13 P7yNo. 13 14.40 603 3.3 0.60 5.2 12.50 47.50 593.75 10.55 6,264.063 3.75 23,490.236 P 9 11.80 575 2.9 0.50 5.2 XR 0 8.00 525 3.3 0.60 6.1 XR 0 8.00 478 2.4 0.50 3.2 Average 42.20/10,55 557 3.0 0.55 5.0 14 P 9 11.80 575 2.9 0.50 5.2 17.00 49.50 841.50 11.15 9,424.80 3.75 35,343.000 P 6 15.00 425 2.5 0.40 5.4 XR 0 10.00 316 4.0 0.70 4.0 XR 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 51.00 4.50 229.50 11.15 2,558.925 3.75 9,595.500 P 23 8.50 601 . 5.6 0.80 9.0 XR 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 60.00 5.00 300.00 . 10.45 3,135.00 3.75 11,756.250 XR 0 10.00■ 316 4.0 0.70 4.0 P 23 8. 50 601 5.6 0.80 9.0 Average 31.30/10.45 402 4.7 0.65 5.4 17 No. 1 2.30 326 2.6 0.83 3.8 94.00. 6.00 564.00 2.00 1,128.00 3.75 4,230.000 XR 0 2.65 331 2.1 0.56* 3.1 . P 5 1.00 606 4.2 0.70 5.2 Average 5.95/2.00 375 2.6 0.69 3.7 18 XR 0 2.65 331 . 2.1 0.56 3.1 50.00 7.00 350.00 1.90 665.00 . 3.75 2,493.750 XR 0 2.00 302 2.3 0.30 3.2 P 5 1.00 • 606 4.2 0.70 5.2 Average 5.65/1.90 369 2.5 0.49 3.5 19 XR 0 2.00 302 2.3 0.30 3.2 29.00 10.50 304.50 3.65 1,111.425 3.75 4,167.844 XR 0 8.00 478 2.4 0.50 3.2 P 5 1.00- 606 4.2 0.70 5.2 Average 11.00/3.65 . 458 2.5 0.48 3.4 <1 co Block Width Ag Pb Cu Zn l/2B ase Height Area Width Volume No. Location m g/ton % % 7c m m m2 m m3 D ensity Metric Tons 20 XR 0 8.00 478 2.4 0.50 3.2 23.00 23.00 529.00 6.80 3,597.20 3.75 13,489.500 XR 0 8.00 525 3.3 0.60 6.1 P 18 10.20 501 5.4 0.30 10.4 P 5 ' 1.00 606 4.2 0.70 5.2 Average 27.20/6.80 505 3.9 0.46 6.8 21 XR 0 8.00 525 3.3 0.60 6.1 24.00 8.00 192.00 9.40 1,804.80 3.75 6,768.000 XR 0 10.00 316 4.0 0.70 4.0 P 18 10.20 501 5.4 0.30 10.4 Average 28.20/9.40 442 4.3 0.53 6.9 22 XR 0 10.00 316 4.0 0.70 4.0 24.00 12.50 300.00 9.40 2,820.00 3.75 10,575.000 P 8 8.00 203 1.3 5.30 1.5 P 18 10.20 501 5.4 0.30 10.4 Average 28.20/9.40. 351 3.7 1.86 5.6 23a P 5 1.00 606 4.2 0.70 5.2 40.00 6.50 260.00 4.75 1,235.00 3.75 4,631.250 P 18 10.20 501 5.4 0.30 10.4 No. 15 3.10 554 8.9 1.00 1.1 Average 14.30/4.75 520 6.1 0.48 8.0 23b P 5 1.00 606 4.2 0.70 5.2 41.00 9.00 369.00 5.10 1,881.90 3.75 7,057.125 P 18 10.20 . 501 5.4 0.30 10.4 No. 15 4.15 151 3.30 Average 15.35/5.10 413 3.9 1.14 7.2 24a ' P 18 10.20 501 5.4 0.30 10.4 29.00 7.50 217.50 7.10 1,544.25 3.75 5,790.938 P 8 8.00 203 1.3 5.30 1.5 No. 15 3.10 . 554 8.9 I .00 1.1 Average 21.30/7.10 397 4.4 2.28 5.7 24b P 18 10.20 501 5.4 0.30 10.4 29.00 11.00 319.00 7.45 2,376.55 3.75 8,912.06 P 8 8.00 203 1.3 5.30 1.5 No. 15 4.15 151 3.30 Average 22.35/7.45 329 2.9 2.65 5.3 Block Width ’ Ag Pb Cu Zn l/2Base Height Area Width Volume No. Location m g/ton % % % m m m2 m m2 Density Metric Tons 25 P 5 1.00 606 4.2 0.70 5.2 70.00 12.00 840.00 2.10 1,764.00 3.75 6,615.00 No. 15 4.15 151 - 3.30 - P 32 1.10 646 8.0 0.80 9.9 Average 6.25/2.10 311 2.1 2.44 2.6 26 No. 15 4.15 151 — 3.30 - 68.00 6.50 442.00 4.40 1,944.80 3.75 7,293.00 P 8 8.00 203 1.3 5.30 1.5 P 32 1.10 646 8.0 0.80 9.9 Average 13.25/4.40 223 1.4 4.30 1.7 27 P 32 1.10 646 8.0 0.80 9.9 55.00 9.50 522.50 8.10 4,232.25 3.75 15,870.93 No. 14 16.15 162 0.9 0.60 0.6 P 40 7.10 171 1.2 0.75 1.7 . Average 24.35/8.10 186 1.3 0.65 1.3 28 P 32 r.io 646 8.0 0.80 9.9 46.00 , 19.50 897.00 10.75 9,642.75 3.75 36,160.31 P 29 15.00 712 5.4 3.90 10.4 No. 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 10.00 400.00 18.70.. 7,480.00 3.75 28,050.000 No. 14 16.15 162 0.9 0.60 0.6 P 34 32.90 254 1.7 1.12 3.9 Average 56.15/18.70 217 1.40.92 2.7 30 No. 14 16.15 162 - 0.9 0.60 0.6 40.00 14.00 560.00 18.35 10,276.00 3.75 38,535.000 P 39 6.00 535 2.3 3.17 9.3 P 34 32.90 254 1.7 1.12 3.9 • Average 55.05/18.35 258 1.51.19 3.5 31 No. 14 16.15 162 0.9 0.60 0.6 46.00 15.00 690.00 12.40 8,556.00 3.75 32,085.000 P 29 15.00 712 5.4 3.90 10.4 P 39 6.00 535 2.3 3.17 9.3 Average ■ 37.15/12.40 444 2.9 2.35 6.0 - 32 . P 34 32.90 254 1.7 1.12 3.9 70.00 13.50 945.00 13.65 12,899.25 3.75 48,372.188 . P 39 6.00 535 2.3 3.17 9.3 P 36 2.10 354 2.0 0.56 9.2 Average 41.00/13.65 300 1.8 1.39 5.0 33 P 39 6.00 535 2.3 3.17 9.3 . 102.00 19.00 1,938.00 3.05 5,910.90 3.75 22,165.875 P 33 1.05 112 1.2 1.01 4.6 P 36 2.10 354 2.0 0.56 9.2 Average 9.15/3.05 445 2.1 2.32 8.7 34 ' P 39 6.00 535 2.3 3.17 9.3 60.00 21.50 1,290.00 7.35 9,481.50 3.75 35,555.625 P 29 15.00 712 5.4 3.9 10.4 P 33 1.05 112 1.2 1.01 4.6 Average 22.05/7.35 635 4.4 3.56 9.8 PROVEN ORE Without Dilution 403 2.82 1.30 5.13 576,551.491 With 10% Dilution 363 2.54 1.17 4.62 634,206.640 A XR 0 12.80 336 4.7 0.50 4.2 62.00 7.00 434.00 9.25 4,014.500 3.75 15,054.375 5.00 ? ? ? ? ' XR 0 10.00 316 4.0 o .‘70 4.0 Average 27.80/9.25 . 327 4.4 0.59 4.1 B 5.00 ? ? ?? 12.50 26.00 325.00 7.00 2,275.000 3.75 8,531.350 XR 0 10.00 316 4.0 0.70 4.0 P 8 8.00 . 203 1.3 5.30 1.5 5.00 ? ? ? ? Average 28.00/7.00 266 2.8 2.74 2.9 ■<] CD Block Width Ag Pb Cu Zn l/2 B a se Height Area Width Volume No. Location m g/ton % %% m m m2 m m3 Density Metric Tons C P 5 1.00 606 4.2 0.70 5.2 70.00 4.50 315.00 1.05 330.750 3.75 1,240.31 1.10 646 8.0 0.80 9.9 1.10 ? 9 ? ? Average 3.20/1.05 627 6.2 0.75 7.7 D 5.00 ? ? ? . ? 68.00 10.00 680.00 3.80 2,584.000 3.75 9,690.000 P 8 8.00 203 1.3 5.30 1.5 P 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 ?? ? ? 55.00 10.00 550.00 3.45 1,897.500 3.75 7,115.62 P 32 1.10 646 8.0 0.80 9.9 P 40 7.10 171 1.2 0.75 1.7 4.50 ? ? ? ? Average 13.80/3.45 235 2.1 0.76 2.8 F P 32 1.10 646 8.0 0.80 9.9 51.00 12.50 637.50 6.80 4,335.000 3.75 16,256.250 1.10 ???? 10.00 ?? ? ? P 29 15.00 712 5.4 3.90 10.4 Average 27.20/6.80 707 5.6 3.6910.4 G . 4.50 ???? 32.50 15.00 - 487.50 16.10 7,848.750 3.75 29,432.813 P 40 . 7.10 171 1.2 0.75 1.7 P 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 ? ??? 50.00 15.00 750.00 14.10 10,575.000 3.75 39/656.250 P 34 32.90 254 1.7 1.10 3.9 P 36 2.10 354 2.0 0.56 9.2 1.50 ? ? ?? 'Average 56.50/14.10 260 1.7 1.07 4.2 ■V] SI Block Width Ag Pb Cu Zn l/2B ase Height Area Width Volume No. Location m g/ton % % % m m m2 m m^ Density Metric Tons I P 29 15.00 712 5.4 3.90 10.4 62.00 •7.50 465.00 8.70 4,045.500 3.75 15,170.625 10.00 ? ? ? ? P 33 1.05 112 1.2 1.01 4.6 Average 26.05/8.70 673 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 403 2 .8 1.30 5.1 576.551.5 Probable Ore 360 2.9 1.93 5.1 142.147.5 ■ Proven plus Probable Ore 394 2 .8 1.42 5.1 718,699.0 With 10% Dilution Proven Ore 3 63 2.5 1.17 4.6 634,206.64 Probable Ore 324 2.6 1.74 4.6 156,362.25 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 Ag Pb Cu Zn Metric Tons q/ton % % % Proven Ore 171,000 434 2.9 0.81 4.9 Probable Ore 102,500 413 2.8 0.83 4.9 Proven plus Probable Ore 273,500 426 2.9 0.81 . 4.9 With 10% Dilution Proven Ore 188,100 391 2.6 0.73 4.4 Probable Ore 112,700 372 2.6 0.75 4.4 Proven plus Probable Ore 300,800 383 2.6 0.73 4.4 Small Pocket of Ore at Footwall of Main Ore Body Without Dilution 30,330 329 1.8 1.60 1.8 With 10% Dilution 33,360 296 1.6 1.44 1.6 Block Width Ag Pb . Cu 2n l/2 B a se Height Area Width Volume No. Location m g/ton % . % % m m m2 m m^ Density Metric Tons 1 LN-21-72 10.00 593 4.79 0.53 5.38 87.50 8.25 721.88 10.67 7,702.46 3.75 28,884.23 LN-15-72 18.00 644 4.00 0.70 5.80 . LN-23-72 4.00 478 3.07 0.95 5.86 Average 32 .00/10.67 607 4.13 0.68 5.68 2 LN-15-72 18.00 644 4.00 0.70 5.80 55.50 12.00 666.00 9.67 6,440.22 • 3.75 24,150.82 LN-24-72 7.00 200 1.25 0.70 3.00 LN-23-72 4.00 478 3.07 0.95 5.86 Average 29 .00/9.67 514 3.20 0.73 5.13 3 LN-23-72 4.00 478 3.07 0.95 5.86 77.00 16.50 1,270.50 6.17 7,839.00 3.75 29,396.25 LN-24-72 7.00 200 1.25 0.70 3.00 LN- 7-71 7.50 78 0.25 1.28 4.07 Average 18.50/6.17 21 1.23 1.00 4.05 4 LN-23-72 4.00 478 3.07 0.95 5.86 87,50 10.00 875.00 6.75 5,906.25 3.75 22,148.44 LN-21-72 10.00 593 4.79 0.53 5.38 3.00 ■ ? ? ? ? 10.00 ? ? 9 9 Average 27 .00/6.75 560 4.30 0.65 5.52 5 LN-23-72 4.00 478 3.07 0.95 5.86 77.00 10.00 770.00 5.12 3,942.40 3.75 14,604.00 LN- 7-71 7.50 78 0.25 1.28 4.07 2.00 ? ? ? ? 7.00 ? ? ? 9 Average 20 .50/5.12 217 1.23 1.17 4.69 6 LN-21-72 10.00 593 4.79 0.53 5.38 38.00 10.00 380.00 13.25 5,035.00 3.75 18,881.25 LN-15-72 18.00 644 4.00 0.70 5.80 16.00 ? ? ? ? 9.00 ? ? ? ? Average 53.00/13.25 625 4.28 0.64 5.65 Block Width ' Ag Pb Cu Zn l/2 B a se Height . Area Width Volume No. Location m g/ton % %% m m m2 m m3 Density Metric Tons 7 LN-15-72 18.00 694 4.00 0.70 5.80 28.50 10.00 285.00 11.75 3,348.75 3.75 12,557.81 . LN-24-72 7.00 200 1.25 0.70 3.00 16.00 ? ? ? ? 6.00 ? ? ? ? Average 47.00/11.75 519 3.23 0.70 5.01 8 LN-24-72 7.00 200 1.25 0.70 3.00 54.00 10.00 540.00 6.87 3,709.80 3.75 11,892.50 LN- 7-71 7.50 . 78 0.25 1.28 4.07 6.00 ? ? ? ? 7.00 ? ? ? ? ' Average 27.50/6.87 137 0.73 1.00 3.53 9 LN-21-72 10.00 593 4.79 0.53 5.38 10.00 10.00 100.00 9.50 950.00 3.75 3,562.50 ? 10.00 ? . ?? 9.00 ??? ? . 9.00 ? ? ? ? Average 38.00/9.50 593 4.79 0.535.38 10 LN-23-72 4.00 478 3.07 0.95 5.86 10.00 4.00 40.00 3.00 120.00 3.75 .450.00 3.00 ??? ? 2.00 ? ? •? ? Average 9.00/3.00 478 3.07 0.95 5.86 11 LN- 7-71 7.50 78 0.25 1.28 4.07 16.75 10.00 167.50 7.10 1,189.25 3.75 4,459.69 7.00 ? ? ? ? 7.00 ? ? ?? 7.00 9 ??? 7.00 ' ? ? ? ? Average 35.00/7.00 78 0.25 1.284.07 PROVEN ORE • Without Dilution 434 2.9 0.81 4.9 170.987.50 With 10% Dilution 391 2.6 0.73 4.4 188.100.50 S Block Width Ag ■ Pb Cu Zn ’ l/2 B a se Height Area Width Volume No. Locationi , m g/ton % % % m m m m^ Density Metric Ton 12 Block 3.00 ? ? ? ? N o. 4 4.00 560 4.30 0.65 5.52 93.00 . 14.00 1,302.00 5.67 7,382.34 3.75 27,663.78 10.00 ? ?' ? ? Average 17.00/5.67 560 4.30 0.65 5.52 13 Block 16.00 ? ? ? ? N o. 6 4.00 . . ? ? ? ? 9.00. 625 4.28 0 ."64 5.65 37.00 12.00 444.00 9.75 4,329.00 3.75 16,233.75 10.00 . ? ? ? ? Average 39.00/9.75 625 4.28 0.64 5.65 14 Block 16.00 ? ? ? ? No.. 7 10.00 ? ? ? ? 6.00 519 3.23 0.70 5.01 28.00 16.50 462.00 8.75 4,042.50 3.75 15,159.38 3.00 ? ? ? ? Average 36.00/8.75 519 3.23 0.70 5.01 15 Block 3.00 ? ? ? ?■ N o. 8 6.00 ? ? ? ? 3.00 137 0.73 1.00 3.53 65.00 16.00 1,040.00 4.75 4,940.00 3.75 18,525.00 7.00 ? ? ? ? Average 19.00/4.75 137 0.73 1.00 3.53 16 Block 6.00 ? ? ? ? N o. 5 3.00 217 1.23 1.17 4.69 88.00 17.00 1,496.00 4.00 5,984.00 3.75 22,440.00 3.00 ? ' ? ' ? ? Average 12.00/4.00 217 1.23 1.17 4.69 17 Block 4.00 ? ? ? ? N o. 9 4.00 ? ? ? ? 9.00 593 4.79 0.53 5.38 10.00 10.00 100.00 6.50 650.00 3.75 2,437.50 9.00 ? ? ? ? Average 26.00/6.50 593 4.79 0.535.38 PROBABLE ORE Without Dilution 413 2.8 0.83 4.9 102,459,41 With 10% Dilution 372 2 .6 0.75 4.4 112,700.00 Block Width Ag Pb Cu 2n l/2B ase Height Area Width Volume ■ No. Location m g/ton % % % m m m m3 Density Metric Tons 18 LN-7-71 2.00 ? ? ? ? 2.00 ? ? 7 ? 5.00 329 1.80 1.60 1.80 . 33.00 30.00 990.00 3.50 3,465.00 3.75 .12,993.75 5.00 ? 7 ? ? Average . 14.00/3 .50 329 1.80 1.60 1.80 19 LN-7-71 5.00 . ? ? ? ? 5.00 ? ? ? ? 5.00 • 329 1.80 1.60 1.80 30.00 21.00 630.00 • 5.00 3,150.00 3.75 11,812.50 5.00 ? 7 7 ? Average 20.00/5.00 329 1.80 1.60 1.80 20 LN-7-71 5.00 ? ? ? ? 5.00 ? ? ? 7 2 . 0 0 329 1.80 1.60 i.'so 30.00 14.00 420.00 3.50 1,470.00 3.75 5,512.50 2 . 0 0 ? ? ? ? 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 No. LN-1-7.1, Diamond Drill Station No. 1 Coordinates: N 5077. 90 Bearing: N64W Core Size: AX E 4859. 50 Inclination: 0° Lotal Length: 232.55 m Elevation: 2,005 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0 14.00 99 Diorite quartz, chlorite , epidote 14.00 34.00 100 Tactite brown garnet 34.00 89.30 100 Diorite quartz, chlorite 89.30 114.00 99 Tactite brown garnet, pyrite 114.00 115.25 100 Tactite brown garnet, chalcopyrite 66 0.03 1.26 0.33 115.25 124.00 95 Tactite brown garnet 124.00 128.90 99 Tactite green garnet 124 0.36 0.61 1.76 128.90 149.00 99 Tactite green garnet 149.00 150.90 99 Tactite green garnet 160 0.08 0.79 0.07 150.90 152.90 100 Tactite green garnet 152.90 154.05 100 Tactite green garnet 68 0.01 0.62 0.07 154.05 198.90 99 Tactite green & brown garnet, very low galena, chalcopyrite, marmatite 198.90 230.60 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 tactite). Table C-2. DDH No'. LN-3-71, Diamond Drill Station No: 1 Coordinates: N 5077. 90 Bearing: S85W Core Size: AX E 4859. 50 Inclination: 0° Total Length: 167.05 m Elevation: 2, 005 m From To Rec Ag Pb Cu Zn. Rock Type Alteration and Minerals g/ton % % % • 0 20.00 100 Diorite quartz, chlorite 20.00 35.00 99 Tactite brown & green garnet, low chalcopyrite chalcopyrite 35.00 95.50 99 Diorite quartz 95.50 96.50 99 Tactite brown & green garnet 96.50 98.60 99 Tactite brown & green garnet, 130 0.70 0.83 2.51 marmatite 98.60 100.60 99 Tactite brown & green garnet 100.60 103.00 99 Tactite brown & green garnet, 40 0.10 1.00 0.20 chalcopyrite . 103.00 128.00 99 Tactite brown & green garnet 128.00 135.30 99 Tactite green garnet, calcite, 53 0.35 0.70 1.70 chalcopyrite, marmatite 135.30 140.30 99 Tactite green garnet, calcite 140.30 145.00 99 Tactite green garnet, calcite, 61 0.42 0.17 2.30 marmatite 145.00 167.05 100 Limestone marble Table 0 -3 . DDH No. LN-7-71, Diamond Drill Station No. 1 Coordinates: N 5077.90 Bearing: N76W Core Size: AX E 4859.50 Inclination: 0° Total Length: 221.55 m Elevation: 2, 005 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0 10.50 100 Diorite quartz, chlorite 10.50 29.85 99 Tactite brown garnet 29.85 74.30 100 Diorite quartz 74.30 85.75 98 Tactite brown & green garnet 85.75 88.05 100 Diorite quartz 88.05 91.05 100 Tactite green garnet 91.05 97.75 99 Diorite quartz, chlorite 97.75 98.75 100 Tactite green garnet 98.75 100.35 100 Tactite green garnet, chalcopyrite 87 2.13 100.35 109.85 99 Tactite green garnet 109.85 114.50 99 Tactite chalcopyrite, marmatite 64 0.11 1.07 1.98 114.50 123.30 99 Tactite galena, chalcopyrite,marmatite 329 1.81 1.60 1.80 123.30 147.80 50 Tactite oxidation zone, fault ? 65 0.30 0.32 0.38 147.80 156.40 98 Tactite marmatite 67 0.20- 0.80 3.06 156.40 160.35 100 Tactite green garnet, mainly chalco 99 0.34 2.22 6.10 pyrite , and marmatite 160.35 194.80 100 Limestone marble Table C-3. DDHNo. LN-7-71—Continued From To Fee Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 194.80 197.25 100 Tactite green garnet, galena, 318 1.60 0.89 2.60 chalcopyrite, marmatite 197.25 198.60 100 Limestone marble 198.60 200.60 100 Tactite green garnet, marmatite 42 0.20 0.29 5.10 200.60 221.55 100 Limestone marble Table C-4. DDK No. LN-15-72, Diamond Drill Station No. 1 Coordinates: N 5077. 90 Bearing: N78W Core Size: AX E 4859. 50 Inclination: +34° Total Length: 164. 75 m Elevation: 2, 006 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0 9.75 100 Diorite quartz 9.75 41.80 99 Tactite brown & green garnet, wollastonite 41.80 68.00 99 Diorite chlorite, wollastonite 68.00 72.00 100 Tactite green garnet 72.00 73.00 100 Diorite fresh 73.00 77.00 100 Tactite green garnet 77.00 78.70 100 Diorite fresh 78.00 81.50 100 Tactite green garnet 81.25 83.60 100 Tactite low galena, chalcopyrite, 106 0.70 0.23 0.50 marmatite 83.60 85.05 100 Tactite good galena, chalcopyrite, 447 3.50 1.28 1.50 marmatite 85.05 99.20 99 Tactite green garnet 99.20 101.90 100 Tactite low galena, chalcopyrite, 57 0.40 0.06 1.10 marmatite 101.90 119.80 100 Hornfels wollastonite 119.80 121.20 100 Tactite low galena, chalcopyrite , 146 0.90 0.50 3.00 marmatite Table 0 4 . DDE No. LN-15-72—Continued From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 121.20 124.15 100 Hornfels wollastonite 124.15 125.35 100 Tactile good galena, chalcopyrite, 1550 14.00 0.94 11.7 marmatite 125.35 125.95 100 Limestone marble 125.95 127.80 100 Tactile good galena, chalcopyrite 1033 4.7 0.35 4.80 127.80 129.15 100 Limestone marble 129.15 149.65 100 Tactile good galena, chalcopyrite, 644 4.00 0.70 5.80 marmatite 149.65 164.75 99 Limestone marble Table C-5. DDH No. LN-21-72, Diamond Drill Station No. 1 Coordinates: N 5077. 90 Bearing: N78W Core Size: AX E 4859. 50 Inclination: +56° Total Length: 167.35 m Elevation: 2, 006 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0 6.40 100 Diorite chlorite 6,40 19.00 100 Tactite brown garnet, wollastonite 19.00 67.20 100 Diorite wollastonite 67.20 77.10 100 Tactite green garnet, wollastonite 77.10 78.60 100 Diorite chlorite 78.60 80.70 100 Tactite green garnet 80.70 82.60 100 Diorite chlorite 82.60 103.05 99 Tactite green garnet, wollastonite 103.05 105.45 100 Tactite good galena, chalcopyrite, 565 4.80 0.58 6.50 marmatite 105.45 118.55 99 Hornfels wollastonite 118.55 120.65 100 Tactite calcite, galena, chalcopyrite, 284 1.60 0.22 4.30 marmatite 120.65 126.15 100 Limestone marble 126.15 127.45 100 Tactite low galena, chalcopyrite, 162 0.80 0.14 8.10 marmatite 127.45 129.35 100 Limestone marble 129.35 136.65 99 Tactite, good galena, chalcopyrite, 593 4.8 0.53 5.40 marmatite Table 0 5 . DDE No. LN-21-72—Continued From To Rec Ag Pb Cu Zn m 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 5077. 90 Bearing: N85W Core Size: AX E 4859. 50 Inclination: +32° Total Length: 154.70 m Elevation: 2, 006 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0.00 5.50 100 Diorite fresh 5.50 26.65 98 Tactile brown & green garnet • 26.65 68.80 99 Diorite quartz, chlorite 68.80 99.90 97 Tactile green garnet, calcite, low chalcopyrite 99.90 154.70 98 Limestone marble Table C-7. DDH No. LN-23-72, Diamond Drill Station No. 1 Coordinates: N 5077. 90 Bearing: N66W, Core Size: AX E 4859. 50 Inclination: +23° Total Length: 217.05 m Elevation: 2, 006 m From To Rec Ag Pb Cu Zn m m % Rock Type Alteration and Minerals g/ton % % % 0.00 4.95 100 Diorite fresh 4,95 12.80 99 Tactite brown garnet 12.80 22.25 100 Diorite chlorite 22.25 53.00 99 Tactite brown garnet 53.00 89.90 99 Diorite quartz, chlorite 89.90 98.65 100 Tactite brown garnet 98.65 103.55 100 Tactite green garnet, chalcopyrite 243 0.56 2.00 0.60 103.55 118.85 99 Tactite green garnet 118.85 122.20 99 Tactite green garnet 140 0.42 0.61 1.40 122.20 124.00 100 Tactite green garnet, calcite 124.00 138.00 100 Limestone marble 138.00 156.25 98 Tactite green garnet, calcite 156.25 168.80 99 Tactite oxidized zone, fault? 168.80 186.40 100 Tactite green garnet, calcite 186.40 195.20 100 Tactite green garnet, good galena, 478 3.10 0.95 5.90 chalcopyrite, and marmatite 195.20 217.05 100 Limestone marble Table C-8. DDH No. LN-24-72, Diamond Drill Station No. 1 Coordinates: N 5077. 90 Bearing: N76W Core Size: AX E 4859. 50 Inclination: +22° Total Length: 183.00 m Elevation: 2, 006 m From To Rec Ag Pb Cu Zn m m % Rock Types Alteration and Minerals g/ton % % % 0.00 5.65 100 Diorite fresh 5.65 38.20 98 Tactite brown garnet 38.20 69.55 99 Diorite guartz 69.55 78.15 100 Tactite brown & green garnet 78.15 80.65 100 Diorite chlorite 80.65 84.60 100 Tactite brown & green garnet 84.60 88.90 100 Diorite quartz, chlorite 88.90 114.00 98 Tactite green garnet 114.00 116.00 100 Tactite green garnet, low galena, 100 1.00 0.25 1.00 chalcopyrite 116.00 121.00 100 Tactite green garnet 121.00 124.00 100 Tactite green garnet, low galena, 120 0.80 0.30 1.50 chalcopyrite, and marmatite 124.00 136.35 99 Tactite green garnet 136.35 148.30 99 Tactite green garnet, fair galena, 200 1.25 0.70 3.00 chalcopyrite, and marmatite 148.30 156.00 100 Tactite green garnet 156.00 183.00 100 Limestone marble REFERENCES Bodenlos, A. J„, 1956, Notas sobre la geologia de la Sierra Madre en la 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. Cong., 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, Industrias Penoles, S. A., Mexico, D.F. Gaytdn Rueda, J. E ., 1971, Geologia del depbsito mineral de La Negra y generalidades sobre exploracibn y sistema de explotacidn: National Convention of the Asociacidn de Ingenieros de Minas Metalurgistas 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 studies on La Negra mine: un published report, Industrias Peholes, S.A., Mexico, D.F. Institute 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 district, Querdtaro: unpublished report, Industrias Peholes, S.A., Mexico, D.F. Park, C. F., Jr., and MacDiarmid, R. A., 1964, Ore deposits: W. H. Freeman and Co., San Francisco. Petersen, U., 1959, Geologia del Yacimiento de Antamino, Ancash, Peru: unpublished report, Cerro de Pasco Corp., La Oroya, Peru. 97 98 Quezadas, A. G. , 1972, Estudios petrogr^ficos de la mina La Negra: unpublished report # Industrias Peholes , S.A., Mexico, D.F . Raisz, E. , 1964, Map and descriptions of the landforms of Mexico. 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 min ing district, Municipality of Cadereyta, Gro: unpublished report, Industrias Peholes, S. A., Mexico, D .F. Sanchez Mejorada, P. , 1968, Geology of La Negra mineral deposit. State of Quer^taro, Mexico. Paper presented at the Intl. Cong. of the Geological Society of America, Mexico City, Mexico. Segerstrom, K. , 1956, Estratigrafia y tectdnica del Cenozoico entre Mdxico, D.F. y Zimapdn, Ego. 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: Intl. Geol. Cong., 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 Bull., v. 13, nos. 5 and 6, p. 183-206. Williams, S. A., 1968, Petrographic studies on La Negra mine: unpub lished report, Industrias Peholes, S.A., Mexico, D.F. .0 3 4 1 P 8 E 9 7 9 / MS' 3G 99*39'30 37'30" 35,00" 32 "30" 30'00" 99°27'30" E X P L A N A T I 0 N 2330 21o5l00" so de Rarty'rAz SEDIMENTARY ROCKS Surficiol Deposits Q u a l QUATERNARY (^RQuol A Co. Grande Km U < i l X v - del H orm iguerth-vX El Morro Conglomerate (Not Shown in map) T m T m v TERTIARY Angular Unconformity __ . c^^XQualX 1 Soyatal - Mezcala Formations . K s s m £ - V ^ ^ J c a r e l i 21o2l30' Kssm La Negro Facies ...... K m ualA LoF Nedios ’CRETACEOUS 2325 - t ^ ^ j \ A Kisj \ Co. de la Go Mina ' jC. | \ \ Son Joaquin Facies ...... El Doctor Formation 1 \ r f El Socovdn Facies .... Kis k,W- . Cerro Ladrdn Facies . . . Kil K s s m . / /C o de los Medios Angular Unconformity Las Trancas Formation Jst JURASICO I y Kssm 21 °00' 00 IGNEOUS ROCKS Kssm ^ u 0y t \ ^ 21°00‘00" ■j\Ki" Intrusive Rocks .... T i • C .Juarez _y Co. PitoReal y Pita Real Diorife, Granodiorite, Quartzdiorite Kssm ^a Guadalupe y rTERTIARY □ Goxe . - -x _ ( ' j / v / . / y X Y La Palma 2320 EIVidrioT " ...... \ Son Luis' Qual ) Mina Grande, / > . Jy XT £> Yon the i \ V \ Extrusive Rocks . . . . . T e / ( y / ' < ^ : ' / / El A bra \ y Son Juan Teflo Flows and Tuffs of different composition XL. Providencia x C Divisodero N y / y ytored°nes4 Kssm ^ j f / V y " : \ j / /IlerraWorodas % y f W ¥ > 5 ? - -Z./I Kssm V* y Aparfadero El Rincdn / J Kisi V A . y y \ f / " ' ' ’ \ S x \ kiU Kin X-. x \ Jst / V " Kssm Co de losC Quito sue bo. Anticlinal Axis .... J < Kisj X / Q u a l x. Los Planes 57'30" Synclinal A x is ...... Sta.Mdnico0 "01 X S Geologic Contoctc / J Kssm CristoRey Fault Showing dip U = Up D = Down U f 6 0 ° 2315 Strike and dip of beds . 4 5 ° \ El Aguocat Kssm jg ^ a .a Mine Workings / Sto\VEntierro Kssm S: S.Cristoba O’. Paved Rood Son Joaquin Unpaved Rood . . 55 00 . La Pferla 5500 Trail Kisj ! \ ssm^\ ^ \K ssm K Streams and Rivers . A U G, Km II k A iir y rr— Kssm La R u d q \ Co. El Grifo Mesa Los T ro je s ^ . X El Zopilote 1 Qual 2310 “35 / i - j -J> X Kin Jquqi 'Kin f K ssm ./ Kssm K ssm . GRAPHIC SCALE o r / > Kisj- / KinX XIQua I r / \ / - z 5 0 0 0 1 2 r n i — =bc m o ir toon - toonomtt. K I LOMETERS i)//L o s Trejos A- 52'30" Kil J / Kin „ \ r 0 \ Kil Co. del Rjlm ito' i X La Ventana / ' 0/>y Kssm X y y / Aa l z - > SonJo x " " r La B ecerra " / OCTOR / ...... V Kin / Coloradas 2305 Socovdn El Cobre ,K NEGR4 ,y mo pcho-.. 20° 50'00" . A6- dcom Catos |EI ^s-.Qual Co. V igos , % V / / ) / - - - 20°50'00" ^Kssm yypolif; los Lirios Kssm ^Te^ " /d>~Te y K ssm \ -- L agunita Kin ] y : 99°39'30" 99°27 30 4 3 0 440 DIB. TEC 583 80-84 Fig 3 - Regional Geology of the Lo Negro D is tric t. Jose E. Gay ton Ruedo, MS. Thesis, Dept of Mining ond Geological Engineering, 1974 c w 1116 E X P L A N A T I O G r a v e l . GRAPHIC SCALE 50 TOO 200 4 0 0 L i m e s t o n e it= ~ T'l'I I'l'l i M i ■ i k i k J =d I L 0 M E T E R E-4000 T ac tile Diorite Mineralization E-5000 Caliche X y Stream N- 6000 z Geologic contact Strike and dip § K Mine workings . V v ACRAN I V E-6000 % N-5000 N- 5000 (Adit) 3 yf ! \ \ 46° l : 7, J / 38? / i f ' } / I V N /24? ; , ¥ J 0»° / X N- 4000 N-4000 7 ' Ji U E-4000 E- 5000 DIB TEC. 583-80 84 Fig 4 - Local Geology of the Lo Negro Area. Jose E. Goyto'n Ruedo, M S. Thesis, Dept of Mining and Geological Engineering, 1974.H. Manway 10 h Diamond Drill Holes, (Horizontal)