THE GEOLOGY OF SANTA ANA, A NEWLY DISCOVERED EPITHERMAL
SILVER DEPOSIT, PUNO PROVINCE, PERU
By
Christian Ríos Vargas
___________________
A Manuscript Submitted to the Faculty of the
DEPARTMENT OF GEOSCIENCES
In Partial Fulfillment of the Requirements
For the Degree of
MASTER OF SCIENCE
In the Graduate College
THE UNIVERSITY OF ARIZONA
2008
1
STATEMENT BY THE AUTHOR
This thesis has been submitted in partial fulfillment of requirements for the
Master of Science degree at The University of Arizona and is deposited in the Antevs
Reading Room to be made available to borrowers, as are copies of regular theses and
dissertations.
Brief quotations from this manuscript are allowable without special permission,
provided that accurate acknowledgment of the 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 Department of Geosciences when the proposed use of the material is in the
interests of scholarship. In all other instances, however, permission must be obtained
from the author.
__________________________________________
(author’s signature)
_____________
(date)
APPROVAL BY RESEARCH COMMITTEE
As members of the Research Committee, we recommend that this thesis be accepted as
fulfilling the research requirement for the degree of Master of Science.
Eric Seedorff
__________________________________________
Major Advisor (type name)
(signature)
_____________
(date)
Mark D. Barton
__________________________________________
(type name)
(signature)
_____________
(date)
Spencer R. Titley
__________________________________________
(type name)
(signature)
_____________
(date)
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ACKNOWLEDGMENTS
I would like to express my gratitude to Eric Seedorff, for his time, editorial
comments, and assistance in translation throughout the writing of this thesis. I would like
to thank Mark D. Barton and Spencer R. Titley for their comments and suggestions on
previous versions of the thesis.
I would like to thank Mr. David Lowell for his financial support via the Lowell
Scholarship, and Bear Creek Mining for their financial support during my stay in the
United States, and especially to Andrew Swarthout for motivating me to come here.
I would like to thank to the people that motivated me in general. Thanks to Cesar
Rios, David Volkert, and Mike McClave for their comments on the paper. I thank Greg
Corbett for the use of some of his figures and for giving me some papers before arriving
in the U.S. I thank Edwin Gutierrez for his patience in helping me understand the
MineSight Software. I thank Luis Romero for his time helping me with some figures and
maps. I thank Rene Tonconi for his help with some figures and photos. I thank Doug
Kriener and Brad Christoffersen for their help with language and grammar issues in some
parts of the paper.
My most special thanks goes to Carolina, my wife. Thank you for your
understanding, unconditional love, and never ending support.
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DEDICATION
Dedicated to my loved ones – the people who support and believe in me.
To my wife Carolina, the most special person in my life,
To my newborn Ana Camila, the one who inspires me to be responsible and who
motivates me to work to my full potential,
To my father (El Abuelo), mother, and my sister for their love, support
and education throughout my life.
To God, the One that gave sense to my life.
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TABLE OF CONTENTS
LIST OF ILLUSTRATIONS……………………………………………………...8
LIST OF TABLES………………………………………………………………..10
ABSTRACT……………………………………………………………………….11
INTRODUCTION………………………………………………………………...13
EXPLORATION HISTORY……………………………………………………..16
METHODS………………………………………………………………………..17
Geologic mapping………………………………………………………………..17
Rock chip sampling……………………………………………………………....17
Trenching…………………………………………………………………………18
Geophysical surveying…………………………………………………………...18
Drilling and logging……………………………………………………………...18
Petrography………………………………………………………………………19
Soil sampling……………………………………………………………………..19
Geologic modeling……………………………………………………………….19
EXPLORATION OPERATIONS……………………………………………….20
REGIONAL GEOLOGY AND TECTONICS………………………………….23
DISTRICT GEOLOGY…………………………………………………………..25
GEOLOGY OF ANOMALY B AREA OF THE SANTA ANA DEPOSIT…..27
Overview…………………………………………………………………………27
Rock types……………………………………………………………………….27
Mesoscopic characteristics……………………………………………………..27
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TABLE OF CONTENTS-Continued
Petrography……………………………………………………………………...28
Structural geology…………………………………………………………………28
Mineralization……………………………………………………………………..29
Mode of occurrence………………………………………………………………29
Mineralogy……………………………………………………………………….30
Wall-rock alteration………………………………………………………………..32
Alteration in andesitic lava flows………………………………………………...32
Alteration in dacite dike…………………………………………………………..33
GEOLOGY OF ANOMALY A……………………………………………………34
GEOPHYSICAL CHARACTERISTICS………………………………………...35
SOIL SAMPLES…………………………………………………………………. .36
GEOLOGIC INTERPRETATIONS AND DISCUSSION………………………37
Structural interpretation…………………………………………………………...37
Parageneses………………………………………………………………………..38
Geochemical environment………………………………………………………...40
Influence about fluid sources……………………………………………………...41
Classification and distinctive characteristics of Santa Ana……………………….42
Comparison of Santa Ana with other epithermal polymetallic vein deposits…….43
Pachuca-Real del Monte…………………………………………………………43
Peripheral zones of Butte………………………………………………………...43
Laykakota………………………………………………………………………..44
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TABLE OF CONTENTS-Continued
RESOURCE ESTIMATION……………………………………………………..45
Assembly of drilling and geologic data…………………………………………..45
Defining 3-D solid………………………………………………………………..45
Geostatistical analysis…………………………………………………………….45
Grade interpolation and resource estimation……………………………………..46
OTHER ECONOMIC IMPUTS…………………………………………………47
Infrastructure……………………………………………………………………..47
Mining……………………………………………………………………………47
Metallurgy………………………………………………………………………..47
ECONOMIC POTENTIAL………………………………………………………48
CONCLUSIONS………………………………………………………………….49
REFERENCES……………………………………………………………………51
FIGURE CAPTIONS…………………………………………………………….58
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List of Illustrations
FIGURE 1. Location map of the Santa Ana deposit…………………………………… 63
FIGURE 2. Location map of Anomaly A and Anomaly B…………………………...… 64
FIGURE 3. Photographs of old workings ……………………………………………… 65
FIGURE 4. Geologic map of Anomaly B………………………………………………. 66
FIGURE 5. Detailed geological map of East Breccia………………………………….. 67
FIGURE 6. Photographs of trenches at Anomaly B……………..................................... 68
FIGURE 7. 3D Interpretation of induced polarization and resistivity survey………….. 69
FIGURE 8. Interpretation of 3D induced polarization and resistivity section.……….... 70
FIGURE 9. Representative photograph of drill core…………………………………… 71
FIGURE 10. Photomicrographs of lavas………………………………………….……. 72
FIGURE 11. Photomicrographs of opaque mineralogy ……………………...…………73
FIGURE 12. Location map of soil samples, Anomaly B………………………………. 74
FIGURE 13. Projection of drill holes to plan view, MineSight® Software…………… 75
FIGURE 14. Projection of drill holes to section view, MineSight® Software……….… 76
FIGURE 15. Solid shape from different views, MineSight® Software…………..….… 77
FIGURE 16. Histogram of Ag assay values…………………..…..………………….… 78
FIGURE 17. 3-D Block model, plan view……………………………………………… 79
FIGURE 18. 3-D Block model, section view……………………………………………80
FIGURE 19. Photographs of drill core…………………………….…………………… 81
FIGURE 20. Stratigraphic column, Puno. ……………………………...…..………….. 82
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FIGURE 21. Surface photographs……………………………………………………… 83
FIGURE 22. Sketch of geological relationships including dilational splays………….....84
FIGURE 23. Conceptual geological model for Santa Ana……………………………....85
FIGURE 24. Comparison of three phases of metallurgical test results……………….... 86
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List of Tables
TABLE 1, Diagnostic Minerals and Textures of Various States of pH, Sulfidation
and Oxidation State…………………………………………………………………… 87
TABLE 2, Resource Estimate Determined with MineSight® Software……………….. 88
TABLE 3, Drill holes results, Phase 1…………………………………….…………… 89
TABLE 4, Drill holes results, Phase 2…………………………………………………. 90
TABLE 5, Drill holes results, Phase 3…………………………………………………. 91
TABLE 6, Drill holes results, Phase 3, continued…………………………………...…. 92
TABLE 7, ALS Shaker Test results………………………………………………….… 93
TABLE 8, Plenge Bottle Roll Test results…………………………………………….... 94
TABLE 9, McClelland Bottle Roll Test results……………………………………….... 95
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Abstract
The Santa Ana project is an epithermal silver vein deposit in the Andes
discovered in 2006 by geologists of Bear Creek Mining. It comprises seven claims that
cover an area of 6,300 hectares. The main property anomaly is located 4 km south of the
village of Huacullani and about 120 km south of Puno, southeastern Perú, South
America. The mineralogy and geometry of the veins of this deposit show similarities with
certain intermediate sulfidation epithermal deposits, such as Pachuca mine in Mexico.
The characteristics of the Santa Ana deposit are known primarily from outcrop
mapping, rock chip and soil sampling, and drilling. Mineralization is hosted by andesitic
lava flows of the Oligocene to Miocene Tacaza Group and associated dacitic dikes. The
veins contain sphalerite, galena, pyrite, minor chalcopyrite, and argentite and a late
carbonate. Most silver occurs as argentite that overgrows sphalerite. The veins are
bordered by chlorite-pyrite-illite alteration envelopes of assemblages are products of from
these structures.
Mineralization is localized mainly along two trends: north-south and east-west.
Most of the mineralized veins strike north to northeast and dip 15º to 60º west. The
principal veins range in width from centimeters to 2 meters, although the total width of a
mineralized interval, including zones of stockwork veins, breccias, and open- space
filling structures can be up to 40 meters. The highest silver values occur in areas of openspace filling that may represent dilatant flexural zones associated with variations in strike
of the veins. Fluidized breccia dikes, hydrothermal magnetite veins (at depths >170m),
11
and illite-pyrite alteration are present at Santa Ana, which some workers regard as
evidence of a magmatic fluid component.
Santa Ana has characteristics in common with other Ag-Zn-Pb polymetallic vein
deposits of southern Perú. The mineralogy of Santa Ana has similarities with Pachuca,
Hidalgo, Mexico, the outer zones of Butte, Montana, and Laykakota, Perú, but the quartzpoor character and lack of evidence for adularia at Santa Ana are distinctive. A resource
estimate based on the first 50 drill holes, made using MineSight® software is ~48 million
tonnes containing ~40 million ounces of contained Ag at an average grade of ~30 g/t Ag
and demonstrates that Santa Ana has the potential to be a bulk-minable deposit.
Metallurgical testing indicates the potential for cyanide leaching of ores at Santa Ana,
which is economically favorable and thus strongly encourages further exploration and
possible future development of the deposit.
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Introduction
The mineralogy, wall-rock alteration, and structure of epithermal deposits provide
key information necessary to understand their genesis (Simmons et al., 2005), and the
location, size, grade, and metallurgical characteristics of deposits are important factors
relevant to their economic viability (e.g., Hoal et al., 2006). The Santa Ana project,
located about 120 km south of Puno in the Miocene andesite-dacite arc terrane
constructed on the Altiplano in the Andes of southeastern Perú (Fig.1), is an epithermal
silver vein deposit discovered in 2006 by geologists of Bear Creek Mining with
similarities to certain intermediate sulfidation epithermal deposits. Mineralization is
structurally controlled in andesitic lava flows of the Eocene to Miocene Tacaza Group
and dacitic dikes, which are altered to chlorite-pyrite-illite assemblages. Elevations in the
area vary between 3800 and 4300 m above sea level (~14,000 ft).
Epithermal deposits, as originally defined, are products of hydrothermal activity
at shallow depths and low temperatures (Lindgren 1922, 1933). Deposition normally
takes place within about 1 km of the surface in the temperature range of <100 to 320° C.
During formation of these deposits, fluids can reach the surface as hot springs.
Epithermal deposits are more common in areas of active volcanism, including volcanic
arcs. Epithermal deposits are important hosts of precious metals but also contain other
metals, such as Cu, Pb, Zn, and Bi. Comparison of the hydrothermal evolution of major
silver veins in Tertiary volcanic rocks reveals contrasting thermal histories, sulfidation
states, and degree of hydrolysis associated with ore fluids (e.g., Tayoltita and Guanajato,
13
Mexico; Graybeal et al., 1986). Vein assemblages indicate little restriction on the
availability of sulfur and other constituents. Vein temperatures for ore-grade
mineralization fall into a narrow range. In all deposits economic amounts of precious
metals are deposited at 250º - 300º C from solutions containing 10-2 to 10-3 total sulfur at
pH = 4-6 (Graybeal et al., 1986).
The Andes are a major producer of precious metals (Anonymous, 1972; Noble et
al., 1989, 1999; Noble and Vidal, 1994), and Perú is particularly known for its silver
production (Kamilli et al., 1977). Polymetallic veins in the Andes are sulfide - rich veins
containing sphalerite, galena, silver and sulfosalt minerals in a carbonate and quartz
gangue. Regional faults, fault sets, and fractures are important ore controls. The Miocene
volcanic arc in the Peruvian Andes is an important metallogenic province for precious
metal epithermal vein deposits such as Caylloma (Echavarria et al., 2006), Arcata
(Candiotti et al., 1990), Orcopampa (Gibson et al., 1990, 1995), and the recently
discovered Corani deposit. Veins largely form by several phases of open-space fillings of
faults, but some degree of wall-rock replacement, particularly in breccia fragments, is
usually present (Colqui, Perú; Kamilli et al., 1977). Veins commonly have complicated
parageneses and may exhibit spatial zoning with silver overlying base metal assemblages,
although superposition is also common.
Santa Ana is a structurally controlled, Ag-rich vein deposit with mineralogic
similarities to intermediate-sulfidation deposits (Table 1) such as Pachuca, Hidalgo,
Mexico, but the quartz-poor character and lack of evidence for adularia at Santa Ana are
distinctive. Certain characteristics may indicate proximity to an intrusion that could be a
source of metals for the deposit. The size, grade, and metallurgical properties of the ores
14
are economically favorable for possible future development of the deposit, thus
supporting further exploration of the deposit.
The purpose of this paper is to describe the geology of this new volcanic-hosted
silver-polymetallic deposit, to compare its characteristics with other epithermal deposits,
and to make a preliminary resource estimate. I first describe the geologic setting of the
region and the district that contains the Santa Ana deposit, then document the methods
that Bear Creek Mining followed to make this discovery. I summarize the results of my
field work and describe the structure and mineralogy of the deposit. I compare Santa Ana
with other silver - polymetallic deposits and offer speculations on its origin. Finally, I use
data of the first 50 drill holes to make a resource estimate of the deposit with MineSight®
software to evaluate the economic potential of the Santa Ana deposit.
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Exploration History
The earliest work done at Santa Ana dates back to colonial times. Similar to many
of the early discoveries in Latin America, it was mined by the Spanish in the 1600’s.
Some miners returned in the earliest 1980’s, in which small workings mostly mined
narrow, structurally controlled high-grade zones.
In 2004, geologists of Bear Creek Mining Corporation became aware of these old
workings and took eight chip samples that returned values of up to 200 grams per tonne
of silver in a “crestone” structure (term used for vein-breccias with hackly texture).
Samples from rock chips returned values of 20-35 grams per tonne. Consequently, Bear
Creek decided to begin serious exploration during the second half of 2004. The areas
containing the most significant geochemical anomalies were given names designated by
letters (e.g., Anomaly A, Anomaly B, etc.). Anomaly A, Anomaly B and Anomaly C (1
km south of the main Anomaly B) (Fig. 2) contain some of the small mine workings that
were dug in the 1980’s (Fig. 3). Little is known about mining close to the Huacullani
District but “comuneros” (indigenous people who live in Huacullani, the closest village
to the project) said that people used to mine a gray colored mineral (supposed to be lead).
The focus of exploration completed to date has been on Anomaly B. Bear Creek
geologists started grid sampled (50 x 50 meters) in the Anomaly B zone, taking 446
samples that averaged 83 grams per tonne. Later, four trenches were dug totaling 160 m
in length. Three phases of drilling have been completed since then. More recently,
increasing attention has been focused on Anomalies C and A.
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Methods
Geologic mapping
Detailed mapping was completed at a scale of 1:2500 (meters) in 2004 (Fig. 4). A
more detailed map was made at a scale of 1:1000 for the main structural trend called
“East Breccia” because of the abundant structures present there (Fig. 5). Mapped
observations were plotted on two layers: one for structures and the other for outcrops and
alteration. Outcrops and mineralized structures where drawn in layers using Provisional
South American 1956 map datum recorded on a Garmin GPS 12.
Rock chip sampling
Sampling was done in an area of 2.8 kilometers long by 600 meters wide. A total
of 582 samples were taken in the area (“Anomaly A” and “Anomaly B” areas, see Fig.2),
with an average of 85.4 g/t silver. Samples include chip samples from outcrops and
structures. Samples were taken randomly (spaced 1.5 – 2 m) on outcrops. In the case of
structures, samples were collected continuously along a channel line perpendicular to the
structure. The footwalls and hanging walls were also considered for sampling of
structures. Each sample was described in the field; they later were recorded in an Excel
spreadsheet.
17
Trenching
Trenching was done in order to check if the silver anomalies continue between
structures (Fig. 6). Four trenches were completed for a total of 224 m. Each sampled
interval was 1.5 – 2 m long. They were taken in a channel (25 – 30 cm wide) across the
different outcrops. Each sample was described and recorded in Excel spreadsheet.
Geophysical surveying
Geophysical exploration was performed by Valdor Geophysics in early 2005.
Valdor used induced polarization and resistivity (IP/Res), differential GPS and Total
Field Magnetic (TFM) methods covering 1.2 km of strike length along the north-south
corridor trend. Each section line (100 m spacing between lines) was interpreted in the
Lima office for future consideration of drill holes (Fig. 7 and Fig. 8)
Drilling and logging
Drilling occurred in three phases. Forty-two shallow core drill holes for a total of
5033.6 meters were drilled as of May 31, 2007 (Bear Creek is still drilling the project).
Holes were drilled with a L-250 model drill rig. Each HQ core interval was placed in a
carboard box and then was taken by truck to the field camp for geologic logging and
preparation of analytical samples. Logging attempted to distinguish different type of host
18
rocks ore and gangue minerals, characteristics of the structures, and alteration. Each box
of core was photographed (Fig. 9).
Petrography
Petrographic examination of 13 thin sections was done in order to identify the
main ore minerals and alteration products, paragenetic sequences, and textures relevant to
likely metallurgical behavior. Photos were taken (Fig. 10, 11).
Soil sampling
Soil samples were made in a grid of 50 x 50 meters in the northern and southern
parts of Anomaly B (Fig. 12). Samples were collected from the B soil horizon in 1 x 1 x
0.8-meter pits dug with a pickax. Samples were then seived and then placed in a special
bag for analysis.
Geologic modeling
A 3-D solid was constructed using Mintec MineSight® software. Drilling and
geologic information from the first 50 drill holes were imported (Fig. 13, 14) to develop a
3-D solid of the initial shape of the deposit (Fig. 15). The data were then subjected to
geostatistical analysis (Fig. 16), and a 3-dimensional block model (Fig. 17, 18) was
constructed that resulted in a possible resource estimate (Table 2).
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Exploration Operations
Trenching
Four trenches were excavated in the Anomaly B area with the following results:
Trench
Total meters sampled (2m/sample)
Location
Ag average grade (ppm)
1
126
East Breccia
23.66
2
24
West Breccia
80.13
3
4.5
close to W Breccia
80.67
4
6
north of W Breccia
106.50
Drilling
There have been three phases of drilling at Santa Ana since its discovery in 2006.
This paper is based on the first 42 drill holes (5033.6m) that Bear Creek completed as of
May 31, 2007. (See drill core samples Fig. 19A-F).
First phase: Eleven extremely widely spaced holes (more than 250 m apart on average)
were drilled by the contractor, Bradley, during June 2006. A total of 1120 m of HQ core
were drilled. The holes confirmed the possible bulk tonnage potential of the property and
provided the first strong evidence for mineralization controls.
20
These holes (e.g., SA-2) indicated that the type and degree of alteration of lavas
and dike were similar at the surface and at depth. Small volcanic breccias (autobreccias?) were found in a few holes (e.g., SA-3) with the same alteration patterns:
feldspars are altered to illite-sericite, and mafics are chloritized. Similar patterns were
found in all holes. Disseminated pyrite is present in amounts of <1% to 2% in a few
holes. Crackle breccias in drill holes correlate with the surface projection of crestones,
the vein-breccias that exhibit a hackly texture. The degree of fracturing, abundance of
barite, and abundance of jarosite correlate with presence of silver mineralization, though
they are not necessarily indicative of economic values. Most of the holes had an azimuth
between 100º and 300º, with a dip of -60º (to the E or W) and a depth of 100m. Sulfides
are predominantly oxidized in the upper 60 m, but in a few holes mixed zones appear
beginning at 40 m (e.g., SA-2). See Table 3 for silver values.
Second phase: Twenty-three additional holes were drilled before the end of 2006,
totaling 3191 m in this phase. Deeper holes were drilled (171.40m in drill hole SA-19A).
Holes were drilled mainly oriented between 130º and 180º with dips of -60º. Holes
oriented in a scissor pattern were drilled from some platforms (e.g., SA-3, SA-3A, SA3B, SA-3C). Lavas, volcanic breccias, and dikes were also found in this phase, with
similar characteristics and alteration patterns as in the first phase. The structures (veinlets
and veins, from mm up to 30 cm) observed dip at low angles (between 45 and 15º) to the
drill core axis. Oxidation persists to approximately 60 m. Good silver grades are related
to degree of fracturing, presence of barite, and presence of chalcedonic silica + carbonate
infill (see Fig. 19C). See Table 4 for results.
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Third phase: This paper considers holes drilled through SA-39A (as on May 31, 2007),
but drilling continued at least through all of 2008. Characteristics of host rocks and
alteration observed in this phase were similar to earlier phases. Lavas are intercalated
with volcanic breccias; both are clay – chlorite altered, and both are cut locally by the
dacitic dike. The best mineralization is restricted to low-angle centimetric structures and
dilational open-space filling. Barren Puno sandstones also were encountered in this phase
of drilling (drill hole SA-30A at 32m) for the first time. It is not clear yet what controls
the presence of these sedimentary rocks, but maybe there presence is related to a
secondary structure and associated uplift and erosion on the north-northeastern side of the
project.
Some important results are shown in Table 5 and Table 6.
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Regional Geology and Tectonics
The Santa Ana deposit is located in a Miocene andesite-dacite arc terrane
constructed on the Altiplano as part of the Andes in southeastern Perú. Southeastern Perú
contains rocks that range from Paleozoic clastic sedimentary rocks to Recent volcanic
rocks, including immense volcanic centers that produced Late Miocene to Pliocene
Barroso pyroclastic rocks. There are different opinions about the importance of the
Cenozoic strike-slip faulting in southeastern Perú, especially in the Altiplano area (Herail
et al., 1996; Horton, 1996). Paleozoic sedimentation started with marine sandstones of
Ordovician age, which are overlain by Siluro-Devonian marine shales.
Early tectonic activity in the region occurred mainly in two phases. Early
Hercynian tectonism (Late Devonian) was characterized by tectonic compression, which
formed the folds that are responsible for the angular discontinuity between Lower
Devonian rocks and the overlying deltaic sedimentary rocks of the Mississippian Ambo
Group (INGEMMET, 1995). A minor disconformity between Mississippian sedimentary
rocks and overlying Permian sedimentary rocks is a result of strong folding north of Lake
Titicaca that formed during Late Hercynian orogenesis. The Paleozoic closed with the
basic volcanism of the Iscay Group (270 Ma).
Mesozoic sedimentation started with deposition of Lower Jurassic to Lower
Cretaceous rocks in the Yura basin, which was filled with terrigenous sediments of the
Yura and Lagunillas Groups. In the lower to middle Cretaceous, the site of deposition
23
shifted to the east from the Yura basin to the Putina basin, which continued into the lower
Tertiary as the Puno Group (INGEMMET, 1995).
Three phases of calc-alkaline volcanism developed in the Tertiary in the western
Cordillera (INGEMMET, 1995), forming rocks of the Tacaza Group (upper Oligocene to
lower Miocene), Sillapaca Group (middle Miocene), and Barroso Group (upper Miocene
to Pliocene) (Fig. 20). Volcanism continued until the Quaternary.
In southeastern Peru, Andean orogenesis started in the Santonian with the
Peruvian orogeny. Folds were formed in the Yura basin during epeirogeny and erosion
that define the Incaic orogeny, which started a phase of molasse facies deposition of the
Puno Group in the Altiplano that continued until the Oligocene (INGEMMET, 1995).
Five phases of the Neogene Quechuan orogeny are recognized on the basis of
stratigraphy and geochronology (INGEMMET, 1995): post- Puno/ pre-Tacaza (~30 Ma);
intra-Tacaza and pre-Palca (~22 Ma); post-Palca to post-Puno (~16 Ma); and post-Maure
to pre-Barroso (~7 Ma); and overthrusting of the Ayabaca Shale (<7 Ma).
Mineralization occurs along a wide belt that trends northwest-southeast
(INGEMMET, 1995). Paleozoic rocks are mineralized with W, Mo, and Sb near posttectonic Permian intrusive rocks. Tertiary mineralization is principally associated with
outcrops of the Tacaza Group, west of the Alto de Cabanillas. The principal metals
associated with the Tertiary mineralization are silver, lead, and zinc, with minor copper
and gold.
24
District geology
The Santa Ana deposit contains continental sedimentary rocks that have been
assigned to the Puno Group, mineralized volcanic lava flows and auto-breccias of the
Tacaza Group, a pre-ore Cenozoic dacitic subvolcanic intrusive dome and dike, and postore pyroclastic rocks of the Barroso Group.
The Puno Group consists of a broad accumulation of arkosic red sandstones and
conglomerates with rounded clasts of fluvial origin. Shales, mudstones with intercalations
of calcareous beds, and evaporites are present locally. The Puno Group was deposited
between the Upper Cretaceous and the early Oligocene (83 - 35 Ma). In the Santa Ana
area, sandstones of the Puno Group are observed in the northeastern part of Anomaly B
(Fig. 2) and in drill hole SA-30A at 32 m. To date, sedimentary rocks of the Puno Group
are barren of mineralization.
The Tacaza Group of Oligocene-Miocene age is composed of andesitic lavas that
commonly were deposited discordantly on Mesozoic rocks or rocks of the Puno Group.
Locally, however, rocks of the Tacaza Group were deposited on Paleozoic rocks. The
Tacaza Group is one of the main hosts for epithermal deposits across Perú (e.g., Corani
deposit in Puno; Yanacocha district in Cajamarca). In the Santa Ana area, the Tacaza
Group is the principal host of silver mineralization. Lavas of the Tacaza Group dip 15º to
60º west. The Tacaza Group is overlain by the Cenozoic tuffs of the Barroso Group.
25
The dacitic quartz-feldspar porphyry seems to be one of the Cenozoic intrusions
that occur in southeastern Perú. It is present in Santa Ana in the Anomaly B area as a
crescent-shaped dike and in the Anomaly A area as a lava dome (Fig. 21B).
The Barroso Group of Mio-Pleistocene age is related to volcanic centers that
closed the effusive and explosive volcanic Tertiary sequence in the Peruvian Andes.
Lithologically the Barroso is composed of andesitic, trachyandesitic, and dacitic lavas,
breccias, agglomerates, and tuffs. The lavas are mostly basaltic andesites or hornblende
andesites. Some rocks of the Barroso Group are of interest because they host epithermal
Au-Ag mineralization. In the area of Santa Ana, a tuff of the Barroso Group is in the
western part of the Anomaly B (Fig. 2) overlies mineralization. No silver anomalies have
been found in the Barroso Group.
26
Geology of Anomaly B Area of the Santa Ana Deposit
Overview
Anomaly B is the most important area of mineralization at Santa Ana (Fig. 2 and
Fig. 21a). It is located approximately at 8158000 North and 466000 East UTM grid
coordinates using the PSAD 56 map datum (zone 19). Colonial workings are present
(approximately 50 small workings) (Fig. 3). Anomaly B comprises a zone of 1,300 m
north - south by 500 m east - west. Recent drilling has shown that this area has been
extended by at least 200 m in both directions and still remains open in all directions.
Rock types
Mesoscopic characteristics: The main outcrops are andesitic lavas of the Miocene
Tacaza Group that are cut by a Cenozoic dacitic dike that is related to a dome located 1.5
km to the north-northeast. Felsic tuffs of the Barroso Group overlie the mineralized lavas.
Between the lava flows, it is common to find volcanic breccias (mostly monolithic
autobreccias but apparently locally including heterolithic breccias). Volcanic breccias
have been observed mostly found in drill holes. Hydrothermal intrusive(?) breccias have
been reported in recent drilling, although they were observed since the beginning of
exploration on a dump in the southern part of the area before any holes were drilled (A.
Swarthout, pers. commun., 2005) and at the end of drill hole SA-2A.
Petrography: These three samples (see Fig. 10) correspond to a porphyritic
volcanic rock with microgranular to microcrystalline matrix. Plagioclase occurs as
27
phenocrysts and in a microcrystalline matrix, with different shapes from subhedral to
anhedral crystals and sizes up to 2,6 mm. Quartz, located in the groundmass, comprises
approximately 5% of a sample, and is up to 0.3 mm in size. Accessory minerals present
in the sample are zircon, sphene, and apatite. Hydrothermal minerals are observed and are
described further below.
Structural geology
The main structures observed are vein-faults, and fracture sets that exhibit
negligible or indeterminate offset of geologic markers. Where mineralized, bedding faults
are observed, the faults exhibit a normal sense of displacement. Two main orientations of
faults and fracture sets have been observed at Santa Ana: north-south and east-west.
The majority of veins, vein–breccias, and crestones (vein-breccias that exhibit a
hackly texture) have north-south strikes. Veins can be from 20 cm to 1.5 m wide at the
surface, although open space fillings and stockworks related to the veins can mineralized
over widths of up to 40 m. In drill core, vein-breccias occur in zones with intense
crackling and/or shearing with chorite-illite-pyrite alteration, typically 10 cm to 3 m
wide. Similar widths of mineralization occur with the crestones. Mineralization also
occurs parallel to bedding in the lavas (15 – 60º to the west). Some north-south structures
vary in strike to north-northeast (015°-045°), creating dilational zones. Some northnortheast to northeast-striking fractures can be considered splays or horsetails on the
main east-west structures (Fig. 22). The old workings continue south of Anomaly B (for
at least 1 km), where surface sampling is getting silver assays as high as 90 ppm.
28
The east-west trending structures are present as veins, veins-breccias, and lesser
crestones. These structures divide the north-south trend structures into blocks.
Mineralization
Mode of occurrence: Main structures in the area are the “East Breccia”, the
“Northwest Breccia” (Fig. 21a) with a predominantly trend of north-south, and the “EastWest Structure” in the southern part of Anomaly B (Fig. 22). These structures are
considered to be hydrothermal - tectonic breccias that are moderate to strongly chloritized
in parts. At the surface, breccias contain jarosite or argentojarosite?, barite, manganese
oxides (presumably an alteration product of carbonates such as rhodochrosite or
manganoan calcite), pyrite, primary magnetite, ,and hematite after oxidation of
magnetite.
A dacitic quartz-feldspar porphyry dike occurs in a dilational zone between both
“crestones” (Fig. 4). At the surface, the dike is anomalous in silver (from 2 ppm to 21
ppm), but at depth high grade structures occur at the dike - lava contact or inside the dike,
with values up to 1000 ppm silver. Some old colonial workings (rich structures) are
present at the contact lava - dike. The dike can only be seen in an area of 600 m long by
15 m wide. Lavas are present in most of the area, and they are moderately fractured and
can have values up to 31 ppm silver, even when they are not close to the vein-breccias.
Jarosite (argentojarosite?), barite, and manganese after carbonates can be seen in those
fractures. Volcanic breccias (autobreccias) intercalated with the lavas contain the same
amount of Ag mineralization, with values up to one ounce Ag if there is no structure
nearby.
29
To the east of Anomaly B, the same Tacaza lavas are exposed but no important
mineralization has been found. The truck route on the extreme eastern end of Anomaly B
may coincide with a major fault that is controlling the eastern limit of mineralization.
Only some spots of manganese can be seen in the eastern part of this Anomaly, but no
important structures have been recognized to date.
Outcrops samples in this area (335) average 43g/t Ag and mineralized structures
(78 samples) average 237 g/t Ag. Also, 25 samples taken from dumps average 154 g/t,
but these samples are not included in the general average of 85.4 g/t Ag. Silver anomalies
correlates with lead (0.37% average), zinc (0.32% average), and barium (up to 4200 ppm)
anomalies.
Mineralogy and texture: Veins that cut the lavas of the Tacaza Group are
composed of galena, sphalerite, rutile, magnetite, hematite, chalcopyrite, argentite, and
pyrite. At the microscopic scale, galena fills the open space and microfractures of the
gangue minerals (e.g., as micro-veinlets in barite). In part it replaces hematite, pyrite,
chalcopyrite, and sphalerite (Fig. 11a, 11b, 11c). Galena also fills some holes in
sphalerite. Sphalerite can be found disseminated and in the cleavages of the alteration
minerals. Magnetite is disseminated and is intergrown with rutile. Rutile is associated
with magnetite and can be present as a weak alteration to leucoxene. Hematite is present
as radial aggregates and is included in gangue minerals (Fig. 11c), and in this way its
distribution is dispersed. There is also secondary hematite after magnetite. In few cases,
hematite can be observed replacing sphalerite. Chalcopyrite fills the interstices of the
gangue minerals. Argentite is present as veinlets filling the microfractures, and it replaces
30
sphalerite and galena (Fig. 11e). Pyrargyrite is possibly present as a dark ruby silver
mineral. Pyrite is disseminated between the gangue minerals.
At the surface, structures are in most cases veins-faults filled with barite-jarositemanganese-clay, and it is difficult to distinguish any silver mineral, although some people
reported seeing argentite and pyrargyrite on some dumps (G. Corbett, D. Volkert, A.
Swarthout pers. commun., 2007) At depth in the mixed sulfide-oxide zone (below 40m
depth in many cases), it is easier to see sphalerite, galena, and a little chalcopyrite. Silver
grades increase when light green sphalerite and galena occur with carbonate (ankerite?)
in veins that are at low angles to the core axis and when these reduced polymetallic
minerals are mixed with specular hematite. A positive correlation has also been observed
between vein width and silver grade in certain areas, but this is not a general correlation.
There is also a positive relation between silver grade and barite that occurs as invasivebrecciated open-space fillings in the andesitic lavas.
Quartz content increases with depth (generally deeper than ~60 m), where it has
been observed that chalcedonic silica (low-temperature quartz) that is typical of upper
zones changes to a comb quartz texture at depth. This change, however, has been
observed only in certain drill holes (e.g., DDH-15, DDH-15A).
Broadly, the mineralogic zoning will be an oxide zone of jarosite-manganesehematite-barite in the first 20 m, an oxide-mixed zone from ~20 to ~80 m with oxides,
carbonate, and intermediate sulfidation minerals , and a sulfide zone beginning at ~80100 m, where pyrite, low-iron sphalerite, galena, argentite, tetrahedrite(?), plus secondary
hematite appear together in some holes. Pyrite is present as 1-2% disseminated grains in
the host rock (lava), and there is not a clear increase in abundance except close to
31
structures (in the alteration halo) or in the structure (10-20%, e.g., DDH-SA6 @ 170 m).
Hydrothermal magnetite is present (e.g., DDH-SA6) in very few parts of the area (it may
be detected where the chargeability geophysical anomaly increased, e.g., DDH-SA6).
The more abundant sulfide mineral in the host rock is pyrite, and in the structures are
sphalerite and pyrite, follow by galena.
Pyrite is a mineral that is present as 1-2% disseminated in the host rock (lava) and
there is not a clear increase of it until it is close to structures (as alteration halo) or part of
the structure (10-20%, e.g., DDH-SA6 @ 170 m). Hydrothermal magnetite is present
(e.g., DDH-SA6) in very few parts of the area (it may be detected where the chargeability
geophysical anomaly increased, e.g., DDH-SA6). The more abundant sulfide mineral in
the host rock is pyrite, and in the structures are sphalerite and pyrite, follow by galena.
Wall-rock alteration
Alteration in andesitic lava flows: The main hydrothermal minerals observed in
the andesitic lavas of the Tacaza Group (Fig. 4) are illite-sericite as a product of alteration
of the plagioclase phenocrysts (Fig. 10), chlorite after ferromagnesian minerals, and
calcite associated with chlorite and possibly originating from alteration of ferromagnesian
minerals. Quartz is also present in trace amounts, giving the samples the common district
propylitic assemblage: chlorite-sericite-calcite-quartz. Rocks seem to be more intensely
bleached (illite-pyrite-chlorite) adjacent to structures, but this occurs for a few
centimeters on each side. In the northwestern part of this area, there is a slight increase in
kaolin close to the old workings, where values can be as high as 20 ppm Ag.
32
Alteration in dacite dike: The dike presents the same alteration as the lavas. Its
feldspars are altered to illite- sericite and its mafics are altered to chlorite. Pyrite and
primary magnetite are disseminated in the dike.
Surface mapping, sampling, and logging show few spatial variations in alteration.
In Anomaly B, veins of barite-jarosite-manganese, 10 cm to 2 m wide with illite-pyritechlorite halos in the northern and western parts of the area (more typical maybe in
crestones), with a more chlorite-clay-pyrite halos in the rest of the area. Illite may be
dependent of a supergene effect, and it clearly evident in some dumps and old workings
in the northern and west parts of the area. Adularia has not been observed either on the
surface or in drill holes to date. Quartz is found in minor quantities on some old dumps,
but very little quartz was mapped at the surface.
Veins, vein-breccias and open space fillings and stockworks wall rocks in Santa
Ana are mainly altered to chlorite-pyrite assemblages, although structures in core show
more abundant illite or other phyllosilicates near the surface, probably due to weathering
effects. Some structures are bleached for up to 1.5 m from structures in the upper parts of
the drill core, but this halo disappears at depths of 20 to 30 m. The only obvious change
in alteration is that halos of chlorite-pyrite alteration increase in width when the structure
is wider.
33
Geology of Anomaly A
This area is located north of Anomaly B (see Fig. 2 and Fig. 21A-B), and it is
about 800 m long by 300 m wide. Anomaly A is composed of lavas of the Tacaza Group
with the same clay-chlorite alteration as observed in Anomaly B. Anomaly A contains a
quartz feldspar porphyry (QFP) dome that is the root for the dike that crops out in
Anomaly B (see Fig. 21 and Fig. 4). The dome is outcropping with the same clay-chlorite
alteration seen in Anomaly B.
Most of the barite, jarosite, manganese structures are oriented north-south to
north-northeast, with sub-vertical dips. Many structures are located in the edges of the
dome, although others can be found in the center cutting the dome, with values up to 100
ppm silver. High dump values were also taken with results of 118, 160, 311 and 768 ppm
in silver. This area is considered as an important prospective area due to the number of
old workings present. Weak increase of silica and pyrite in the bottom parts of the dacite
dome are important in this area. Further deep holes should be drilled here to test for
possible increases in the grade of mineralization with depth and for the presence of a
possible mineralized porphyry copper/ copper-gold deposit at depth.
34
Geophysical Characteristics
Geophysical surveys consisting of ground magnetics, induced polarization, and
resistivity were completed in 2005. These surveys define an area of sulfide mineralization
underlying the geochemical anomaly, interpreted to contain >5% sulfides) (Bear Creek
Annual Report 2006).
The IP response suggests that vertical continuity is good and that the
mineralization is open to the south, where strongly anomalous silver was found in
outcrops at the limits of the sampling grid. Three chargeability anomalies are outlined by
the induced polarization-resistivity survey (Fig. 7). The chargeability responses range
from weak (7mV/V) to strong (20mV/V) with respect to the background. The
chargeability response increases from surface to depth, suggesting differences through
leaching (VDG del Peru SAC, 2005).
A hole (SA-6) drilled in the area of one of the strongest induced polarization
targets (Fig. 8) found 5% pyrite as disseminated grains and veinlets of pyrite + weak
secondary magnetite veinlets at 140 m. No direct evidence of a porphyry deposit was
observed.
35
Soil Samples
Soil samples were collected in two phases in 2006 and 2007. Samples were
collected on a grid of 50 by 50 m. Both phases of sampling were conducted only at
Anomaly B. The first phase was done in the south-southwestern to southern part of
Anomaly B in a 1000 m x 1250 m area, and the second phase was in the northern part in
an area of 750 m x 500 m (Fig. 12).
Bear Creek got good values (e.g., 12 ppm silver in soil sample # 51136) in a few
areas that are coincident with buried structures, the presence of which has been confirmed
by drilling (e.g., structures in new holes SA-44, SA-44A).
36
Geologic Interpretations and Discussion
Structural interpretation
Many ore deposits are localized by major thoroughgoing structures that may
display variable activity histories, especially if the structural setting provides dilational
sites for the enhanced flow of hydrothermal fluid (Corbett, 1994; Corbett and Leach,
1998).
Santa Ana is a structurally controlled ore deposit. Veins at Santa Ana formed
during an episode of extension, as interpreted from the presence of normal faults and the
great thickness of some open-space filling veins and related extension fractures. In the
southern part of Anomaly B, a prospect-scale jog occurs where north-south striking
structures change in orientation southward to northeasterly striking structures. A second
jog occurs further to the south, where there is a transition from northeasterly striking
structures to north-northeasterly striking structures at Anomaly C (800 m south of
Anomaly B; see Fig. 2). Such a variation within mineralized fractures would be
consistent with a component of dextral strike-slip movement that might facilitate the
development of ore shoots within flexures (Corbett, 2007) (Fig. 22), which is consistent
with good Ag grades in drill holes SA-3, SA-4, SA-12, and SA-15.
Normal fault movement parallel to bedding in volcanic rocks is interpreted to be
due to a collapse of the lava flows on the western margin (Corbett, 2007; possible border
of a diatreme?), where there are hydrothermal breccias (e.g., SA-38, SA-38A, SA-2A;
Photo 19A). Alternatively, bedding-parallel flow could have been promoted by bedding
37
plane shear due to a component of uplift or doming within the north-south structural
corridor (east side of Anomaly B), although no evidence has been found to support such
uplift. The hydrothermal breccias are characterized by slab-like breccia clasts, which are
typical of environments characterized by collapse Corbett, 2007; Corbett and Leach,
1998). A common character in most holes at the southern part is the low-angle (15-25°)
between the millimeter- to centimeter-scale structures and the 60-70° inclination of the
drill holes. This sheeted character shows a dilatant character (Photo 23) due to the normal
bedding movement, and these sites localize polymetallic sulfides, carbonate minerals, and
high-grade silver values (Fig. 23A).
The east-west striking structures present in the area divide the north-south
trending structures into blocks. Mineralized structures exploit the east-west shears and
north-northeast trending splay faults, which may be indicative of a component of sinistral
strike-slip movement on the east-west structures in the area of the Spanish mine workings
(Corbett, 2007) (Fig. 22).
Paragenesis
From the study of drill core and thin sections, hydrothermal minerals are
interpreted to have been deposited in the following sequence: hematite – pyrite –
sphalerite-argentite-galena and carbonates. Four different stages can be inferred.
Stage I: Intrusive dome, dikes, tectonic breccias are interpreted to have formed
above the magma chamber, which may have increased the permeability of the rocks for
future flow of mineralized fluids. Fluidized breccias with a milled matrix (Fig. 19B) and
38
possibly intrusion-related hydrothermal breccias (Fig. 19A) that may border a possible
diatreme (Ríos, 2007 ) also may have influenced ground preparation. These ground
preparation features are coincident with the district-scale, weak to moderate intensity of
propylitic alteration in the area.
Stage II: Barite, low-temperature quartz and specular hematite are interpreted to
have formed prior to the main economic mineralization event but after tectonic
brecciation. Specular hematite can be difficult to distinguish from galena when it is finegrained. Hematite has a red streak (Fig. 19E), whereas boxwork after galena leaves a
crimson red color (Fig. 19D).
Stage III: This is the main stage of deposition of ore minerals in the area, as
economic minerals overgrow barite and quartz. Pyrite, chalcopyrite, sphalerite, argentite,
galena are interpreted to be deposited in this stage. Hydrothermal activity may also have
promoted chlorite-pyrite-illite(?) envelopes on some of the main veins and breccias.
Hydrothermal-tectonic breccias formed in this stage.
Stage IV: Carbonates and amethystine quartz were deposited at the end of the
hydrothermal system. Carbonate developed in the upper portion of the hydrothermal
system perhaps from bicarbonate waters, and the mixing of these waters with rising ore
fluids may have promoted precious metal deposition (Corbett and Leach, 1998). This
could be an important control for silver mineralization at Santa Ana.
39
Geochemical environment
The mineralogy of the silicates and sulfides at Santa Ana record the near-neutral
pH and intermediate-sulfidation state of the ore-forming solution. Local gold anomalies
(e.g., 0.097 ppm Au in DDH SA-6, 120m) are spatially associated with specular hematite
and may also occur at deeper levels in the hydrothermal system, where hairline magnetite
veins are present at the southern part of Anomaly B, the site of the highest IP anomaly in
the area.
Fluid inclusion data for epithermal silver-polymetallic vein deposits exhibit a
wide range of salinities (1-20 wt % NaCl equiv), although fluid inclusion data are not
available for Santa Ana. Fluids of moderate to high salinity are capable of transporting
significant quantities of silver and base metals (e.g., Seward and Barnes, 1997). The
epithermal deposits that have fluids of moderate to high salinities are either rich in base
metals or contain precious metals with subordinate amounts of base metals, such as
Fresnillo, Durango, Real de Guadalupe, Guerrero, and La Guitarra, Mexico (Simmons,
1991; Albinson et al., 2001). The high salinities in fluid inclusions could be interpreted to
be derived from either a magmatic source or interaction with evaporites. Much of the
Altiplano of southern Peru, including Santa Ana, is underlain by the Puno Group. The
Puno Group locally contains evaporites, so fluids with elevated salinities could have been
generated at Santa Ana because of interaction of ore fluids with evaporites.
40
Inference about fluid sources and causes of ore deposition
Mixing between fluids of different compositions can be a viable mechanism of
precious metal precipitation, as supported by some fluid inclusion data, extensive isotopic
data, and numerical simulations (e.g., Robinson and Norman, 1984; Mancano and
Campbell, 1995; Hayba, 1997). Ore fluids in epithermal deposits may contain a
significant magmatic fluid component; for example, ore fluids in bonanza parts of the
Comstock Lode appear to have had a significant (30-75%) magmatic component (Taylor,
1973; Vikre, 1989; Simmons, 1995). Santa Ana is interpreted to have a significant
magmatic component also because of the presence of hydrothermal magnetite veins,
hypogene (specular) hematite (typical of deeper parts in polymetallic vein systems), and
illite-pyrite alteration (Corbett, 2007). Ore minerals may have been precipitated at Santa
Ana by dilution and cooling and, to a lesser extent, from changes in oxidation state and
pH (Simmons et al., 2005).
Dilational zones are interpreted to have acted as sites for mixing of ore fluids with
bicarbonate waters because of its high grade and mineralogy (base metals-argentite with
carbonates; Photo 17, 18, 19, and 24). The quartz-poor character in Santa Ana may be
due of a suppression of precipitation of SiO2 during cooling as a consequence of fluid
mixing during ore deposition (M. Barton, pers commun., 2008).
41
Classification and distinctive characteristics of Santa Ana
Many classification systems exist for classifying precious metal deposits,
including by the sulfidation state of the contained minerals (Simmons et al., 2005). The
term sulfidation is used in ore petrology to describe the stabilities of sulfur-bearing
minerals in terms of sulfur fugacity (e.g., Barton and Skinner, 1979; Hedenquist et al.,
1994; Einaudi et al., 2003), and some authors use a three-fold classification of deposits
into low-, intermediate-, and high-sulfidation deposits (e.g., Sillitoe and Hedenquist,
2003; Simmons et al., 2005).
Santa Ana is here classified as intermediate sulfidation epithermal silver polymetallic deposit. Intermediate sulfidation state minerals present at Santa Ana are
pyrite, chalcopyrite, Fe-poor sphalerite, hematite-pyrite, magnetite-pyrite (Table 1).
Other examples of intermediate-sulfidation deposits (e.g.,) include Arcata, Peru
(Candiotti et al., 1990); San Cristóbal, Bolivia (Buchanan, 2000); the Comstock Lode
(Vikre, 1989) and Tonopah (Nolan, 1935; Bonham and Garside, 1979) in Nevada;
Creede, Colorado (Barton et al., 1977); and Pachuca-Real del Monte (Dreier, 2005),
Fresnillo (Simmons et al., 1988), and Tayoltita, Mexico (Smith et al., 1982). Santa Ana is
notable for its relatively quartz-poor character. Santa Ana also has similarities with the
carbonate – base metal Au-Ag deposits of the southwestern Pacific rim (Corbett and
Leach, 1998), such as Kelian, Indonesia (van Leeuwen et al., 1990).
42
Comparison of Santa Ana with other epithermal polymetallic vein deposits
Pachuca-Real del Monte, Hidalgo, México: Pachuca is an underground mine that
has been active since 1550 (Geyne et al., 1963; Dreier, 1976, 1982, 2005). This deposit is
hosted in calc-alkaline volcanic and hypabyssal rocks ranging in composition from
basaltic andesite to rhyolite. Alteration is characterized by the presence of quartz,
epidote, chlorite, adularia, albite, calcite, and pyrite, but quartz, adularia, and pyrite occur
as alteration envelopes around the veins. Orebodies are contained in a series of east-west,
northwest-southeast and north-south trending, fault-hosted veins. Productive ore zones
occur where there are changes in vein strike and dip (Simmons et al., 2005). The veins
range in width from 0.5 to 5 m, although vein-filling fractures can span zones up to 35 m
wide. Quartz, chalcopyrite, galena, and sphalerite are the common vein minerals. Silver
occurs mainly in acanthite. Fluid inclusion homogenization temperatures range from 210°
to 305° C, with salinities of 0 to 6 wt percent NaCl equivalent.
Santa Ana shows similar structural control and a mixing environment between
magmatic water and bicarbonate waters at similar depths in the system. Adularia was not
seen in Santa Ana but low-temperature quartz suggests the influence of meteoric waters
or boiling in the deposit.
Peripheral zones of Butte, Montana, USA: Peripheral zones of Butte show a
similar mineralogy to Santa Ana (McClave, 2007). The presence of quartz, rhodochrosite,
carbonates, sphalerite, pyrite with silver minerals in open-space filling veins are shared
43
by both deposits, implying that a porphyry copper deposit could be located possible
below the volcanic dome at Santa Ana.
Laykakota, Peru: Laykakota, located in Puno, was an important mine in the
1600’s. Mineralization is hosted by andesitic lavas of the Tacaza Group and occurs in
parallel, northeast-striking veins that dip to the east (INGEMMET, 1993). Veins are
between 1.5 and 5 m wide.. The ore minerals are galena, sphalerite, chalcopyrite, and
pyrite with barite and manganese. This deposit is significant for its relative proximity to
Santa Ana.
44
Resource Estimation
Assembly of drilling and geologic data
Fifty-five drill holes were used in the construction of a 3-D solid (Fig. 13, 14).
The total length of these drill holes is 9928 m. A database was constructed that contains
all the relevant data for each hole, such as drill hole locations and orientations, as well as
assays of each analyzed interval. The solid was constructed on the basis of silver values,
because silver is the most important metal economically in the deposit (Tables 3, 4, 5,
and 6). The dip angles of the mineralized structures were also taken into consideration.
Defining 3-D solid
Vertical sections and horizontal plans were made every 5 m using MineSight®
software. Both sets of slices were combined for construction of the 3-D solid. The shape
of the interpreted mineralized volume took into account the strike and dip of the
structures, constraints from field geology, the grades of the drill hole, and my
interpretation of grade continuity (Fig. 15). Two codes were used to differentiate
mineralized material from waste. Grades were interpolated only inside the volume of the
solid that defined the limit of mineralized material.
Geostatistical analysis
Conventional statistics and geostatistics were used to analyze silver assays from
holes drilled at the Santa Ana deposit. Using a cut-off grade of 18.50, the arithmetic mean
grade is 27.3 g/t. A variogram analysis for the deposit was done for silver to determine
45
the spatial continuity of the mineralization in the zones and to determine the parameters
for the grade interpolation of the block model. It was determined the variogram 3-D
considering horizontal grade of 30º and vertical grade of 22.5º. The variograms were
modeled using a single structure spherical model. The histogram shows that the average
grade is 27.3 g/t (Fig 16).
Grade interpolation and resource estimate
The 3-D block model is based on the shape of the 3-D solid and geostatistical
analysis of the data. The 3-D block model for mineral resource estimation was built with
blocks of 10 x 10 x 10 m (Fig. 17, 18). The block model was interpolated using the
kriging method. The ellipsoidal search parameters for the interpolation process were 100
(major) x 40 (minor) x 90 m (vertical).
Mineral resources, in order of decreasing level of confidence, are assigned to the
measured, indicated, and inferred categories (e.g., JORC, 2004). Because this model of
Santa Ana is based on only 55 drill holes that are widely spaced, this estimate is
considered a to represent a combination of the indicated and inferred resources. Future
drilling and geologic logging will provide new geologic insights and additional assay
data, which will eventually permit a better estimate of mineral resources in the future.
The total indicated and inferred resources from all zones in the deposit at a cut-off grade
of 18.50 g/t are 47.71 million tonnes of mineralized material grading 27.3 g/t of Ag,
totaling 41.9 million ounces of contained Ag. Additional drilling and economic inputs are
required before an ore reserve can be obtained.
46
Other Economic Inputs
Infrastructure
Infrastructure in Santa Ana is optimal because of the location of the property.
The deposit is close to a paved highway and to Desaguadero (a medium to large city for
the Altiplano). Water for a potential future mining operation can be taken from a large
river (Limancota) located 10 km north of the project. A power line needs to be
constructed from Santa Ana to an electrical sub-station located ~40 km away, which is
connected to the national grid. Construction will be relatively easy because the area has
moderate topography, typical of relief throughout this part of the Altiplano.
Mining
At this moment Santa Ana is viewed potentially as an open pit operation. Highgrade veins at depth may be amenable to underground mining, concurrent with or after
open pit mining. Future drilling will clarify this issue.
Metallurgy
Two phases of metallurgical leach tests have been done to see if the material from
Santa Ana is amenable to conventional cyanide leach recovery.
The first phase tested ten samples (representing both high- and low-grade
material) form different parts of five different core drill holes. The samples were crushed
to 70% passing 2mm. Three tests were made from these samples. The first tests were
performed by the ALS-Chemex laboratory in Lima and were cyanide-soluble shake tests.
The tests show that 55.5% leachable silver can be recovered (see results in Table 7). The
47
second tests were made in the Plenge metallurgical test laboratory in Lima and were
longer term, bottle roll tests performed on finely ground material. Results from the test
showed 85% recovery of silver of (see results in Table 8). Finally, the third tests were
made at McClelland Laboratories, Inc., in Sparks, Nevada, in which bottle roll tests were
performed on the un-ground course reject material. The average recovery of silver was
71% (see results in Table 9). Results from the three laboratories are summarized in Fig.
24.
The second phase of metallurgical testing was initiated with the objective of
evaluating samples in conventional heap leaching with and without pulp agglomeration.
The average silver recovery was 64.6%, achieved for the conventional column tests,
although in a conventional, commercial heap leach situation, the overall long-term silver
recovery should exceed 70% according to McClelland Laboratories. Ongoing
metallurgical optimization tests will be needed to establish the most economic crush size
for the heap leach. Standard flotation of lead and zinc will also be checked by future
metallurgical testing.
Economic Potential
An impressive resource has already been defined at Santa Ana, even though the
solid model was based on only 55 drill holes (as on May 31, 2007). The degree of
continuity of mineralization at Santa Ana may be an issue, which further drilling will
address. The metallurgical behavior of the material, based on heap leach tests performed
to date, also are encouraging. Hence further exploration of Santa Ana is certainly
warranted.
48
Conclusions
Santa Ana is a recent discovery of silver-polymetallic mineralization in the
Peruvian Andes. The Ag-Zn-Pb mineralization occurs in vein-breccias and open space
fillings related to extensional zones hosted by andesites of the Tacaza Group. Veins
contain sphalerite, galena, pyrite, minor chalcopyrite, and argentite and a late mixed
(MgCa) carbonate and are thus of intermediate sulfidation in character. Most Ag occurs
as argentite that overgrows sphalerite. Mineralization is spatially associated with
propylitic alteration (chlorite, pyrite) which was cut by veins that have chlorite-pyriteillite(?) (sericite?) envelopes. The deposit is notable because the veins are relatively
quartz-poor, and adularia has not been observed. High silver values in drill core occur
where carbonates and chalcedony occur with base metals. Silver may have been
deposited in an environment where CO2-bearing magmatic waters mixed with meteoric
waters.
Supergene processes in Santa Ana affect the upper 80 m of the deposit, which is
responsible for the possible presence of argentojarosite and may have contributed to
making the deposit more amenable to heap leaching.
There may be a spatial association with a porphyry system at depth, as is inferred
for some intermediate deposits. Quartz-poor character of Santa Ana makes this
intermediate epithermal deposit unusual in its style and should be taken in consideration
in future subdivisions in epithermal deposit types. The lack of adularia, although rare in
this deposit type, is not unique to Santa Ana because some deposits in Philippines and
Papua New Guinea contain sericite rather than adularia, indicating higher temperatures
and limited boiling which could be the result of greater depth of formation. An estimate
49
of the resource that was based on the first 55, widely separated drill holes contained 41
million ounces of silver in 47 million tonnes of mineralized material with an average
grade of 27.3 g/t Ag. There is good potential to increase the size of the resource with
further drilling, and certain key, non-resource economic inputs (such as infrastructure,
metallurgical performance, and amenability to open-pit mining) appear to be favorable.
50
References
Albinson, T., Norman, D.I., Cole, D.R., and Chomiak, B., 2001, Controls on formation of
low-sulfidation epithermal deposits in Mexico: Constraints from fluid inclusion
and stable isotope data, in Albinson, T., and Nelson, C. E., eds., New mines and
discoveries in Mexico and Central America: Society of Economic Geologists
Special Publication 8, p. 1-32.
Barton, P.B., Jr., and Skinner, B.J., 1979, Sulfide mineral stabilities, in Barnes, H. L., ed.,
Geochemistry of hydrothermal ore deposits, 2nd Edition: New York, John Wiley
and Sons, p. 278-403.
Barton, P.B., Jr., Bethke, P.M., and Roedder, E., 1977, Environment of ore deposition in
the Creede mining district, San Juan Mountains, Colorado: Part III. Progress
toward interpretation of the chemistry of the ore-forming fluid for the OH vein:
Economic Geology, v. 72, p. 1-24.
Bear Creek Mining Corporation, 2008. Retrieved March 20, 2008, Web site:
http://www.bearcreekmining.com
Candiotti de los Ríos, H., Noble, D.C., and McKee, E.H., 1990, Geologic setting and
epithermal silver veins of the Arcata district, southern Perú: Economic Geology,
v. 85, p. 1473-1490.
Corbett, G.J., 2007a, Comments on the controls to mineralization at the Santa Ana
project, Perú: Unpublished report to Bear Creek Mining Corporation.
Corbett, G.J., 2007b, Comments on the controls to mineralization at the Santa Ana
project, Perú: Unpublished report to Bear Creek Mining Corporation.
51
Corbett, G.J., 2007c, Low sulphidation epithermal Au-Ag: Exploration implications of
varying styles: Unpublished paper.
Corbett, G.J., and Leach, T.M., 1997, Southwest Pacific Gold-Copper Systems: Structure,
Alteration and Mineralization: Short Course Manual, p. 135-156.
Corbett, G.J., and Leach, T.M., 1998, Southwest Pacific Gold-Copper Systems: Structure,
Alteration, and Mineralization: Society of Economic Geologists Special
Publication 6, 236 p.
Dreier, J.E., 1976, The geochemical environment of ore deposition in the Pachuca-Real
del Monte district, Hidalgo, Mexico: Unpublished Ph. D. thesis, University of
Arizona, 116 p.
Dreier, J.E., 1982, Distribution of wall rock alteration and trace elements in the PachucaReal del Monte district, Hidalgo, Mexico: Mining Engineering, v. 34, p. 699-704.
Dreier, J.E., 2005, The environment of vein formation and ore deposition in the PurísimaColon vein system, Pachuca Real del Monte district, Hidalgo, Mexico: Economic
Geology, v. 100, p. 1325-1347.
Echavarria, L., Nelson, E.P., Humphrey, J., Chávez, J., Escobedo, L., and Iriondo, A.,
2006, Geologic evolution of the Caylloma epithermal vein district, southern Perú:
Economic Geology, v. 101, p. 843-863.
Einaudi, M.T., Hedenquist, J.W., and Inan, E.E., 2003, Sulfidation state of fluids in active
hydrothermal systems: Transitions from porphyry to epithermal environments:
Economic Geology Special Publication 10, p. 285-313.
Gagliuffi Espinoza, P.M., 2007, Estudio microscópico de doce (12) muestras de rocas
procedentes del Proyecto Santa Ana: Unpublished report to Bear Creek Mining.
52
Gemmell, J.B., 2006, Low- and intermediate-sulfidation epithermal deposits: Centre for
Ore Deposit Research, University of Tasmania, p. 57-63.
Gemmell, J.B., 2006, Exploration implications of hydrothermal alteration associated with
epithermal Au-Ag deposits: Centre for Ore Deposit Research, University of
Tasmania, p. 1-4.
Gibson, P.C., Noble, D.C., and Larson, L.T., 1990, Multistage evolution of the Calera
epithermal Ag-Au vein system, Orcopampa district, southern Peru: First results:
Economic Geology, v. 85, p. 1504-1519.
Geyne, A.R., Fries, C., Jr., Segerstrom, K., Black, R.F., and Wilson, I.F., 1963, Geology
and mineral deposits of the Pachuca-Real del Monte district, State of Hidalgo,
Mexico: Consejo de Recursos Naturales No Renovables Publication 5E, 203 p.
Graybeal, F.T., Smith, D.M., Jr., and Vikre, P.G., 1986, The geology of silver deposits, in
Wolf, K.H., ed., Handbook of strata-bound and stratiform ore deposits, v.14, p. 1184.
Hayba, D.O., 1997, Environment of ore deposition in the Creede mining district, San
Juan Mountains, Colorado: Part V. Epithermal mineralization from fluid mixing
in the OH vein: Economic Geology, v. 92, p. 29-44.
Hedenquist, J.W., Matsuhisa, Y., Izawa, E., White, N.C., Giggenbach, W.F., and Oaki,
M., 1994, Geology, geochemistry, and origin of high sulfidation Cu-Au
mineralization in the Nansatsu district, Japan: Economic Geology, v. 89, p. 1-30.
53
Herail G., Baby P., Blanco J., Bonhomme M., Soler P., 1996, The Tupiza, Nazareno and
Estarca basins (Bolivia): strike-slips faulting and related basins in the Cenozoic
evolution of the southern branch of the Bolivian orocline: Tectonophysics
259:201-12.
Horton B., 1996, Sequence of Late Oligocene-Miocene fold-thrust deformation and
development of piggyback basins in the Eastern Cordillera, southern Bolivia: Int.
Symp. Andean Geodyn., 3rd, Saint-Malo, France, ORSTOM, p. 383-86.
Instituto Geológico, Minero y Metalúrgico, 1993, Geología de la Cordillera Occidental y
Altiplano al Oeste del Lago Titicaca – Sur del Perú: INGEMMET, Boletín 42, p.
72-127
Instituto Geológico, Minero y Metalúrgico, 1995, Geología del Perú: Lima,
INGEMMET. Primera Edición, p. 20-43.
John, D.A., 2001, Miocene and early Pliocene epithermal gold-silver deposits in the
northern Great Basin, western United States: Characteristics, distribution, and
relationship to magmatism: Economic Geology, v. 96, p. 1827-1853.
JORC, 2004, Australasian Code for Reporting of Mineral Resources and Ore Reserves
(The JORC Code), 2004 Edition, The Joint Committee of the Australasian
Institute of Mining and Metallurgy: Australian Institute of Mining and
Metallurgy, Australian Institute of Geoscientists, and Minerals Council of
Australia, 20 p.
Kamilli, R.J. and Ohmoto, H., 1977. Paragenesis, zoning, fluid inclusion and isotopic
studies of the Finlandia vein, Colqui district, central Peru: Economic Geology, v.
72, p. 950, 982.
54
Lewis, R., 1956, The geology and ore deposits of the Quiruvilca district, Perú: Economic
Geology, v. 51, p. 41-63.
Lindgren, W., 1922, A suggestion for the terminology of certain mineral deposits,
Economic Geology, v. 17, p. 292-294.
Lindgren, W., 1933, Mineral deposits: New York, McGraw-Hill, 930 p.
Mancano, D. P., and Campbell, A. R., 1995, Microthermometry of enargite-hosted fluid
inclusions from the Lepanto, Philippines, high-sulfidation Cu-Au deposit:
Geochimica et Cosmochimica Acta, v. 59, p. 3909-3916.
McClave, M.A., 2007, Property report for the Santa Ana project for Bear Creek Mining
Corp.: Unpublished report to Bear Creek Mining.
Noble, D.C., and McKee, E.H., 1999, The Miocene metallogenic belt of central and
northern Peru: Society of Economic Geologists Special Publication 7, p. 155-193.
Noble, D.C., and Vidal, C.E., 1994, Gold in Peru: Society of Economic Geologists
Newsletter 17, no. 1, p. 7-13.
Noble, D.C., Eyzauirre, V.R., and McKee, E.H., 1989, precious-metal mineralization of
Cenozoic age in the Central Andes of Peru: Circum-Pacific Council for Energy
and Mineral ResourcesvEarth Science Series, v. 11, p. 207-212.
Nolan, T. B., 1935, Underground geology of the Tonopah mining district, Nevada,
Nevada University Bulletin, v. 29, no. 5, 49 p.
Petersen, U., Mayta, O., Gamarra, L., Vidal, C.E., and Sabastizagal, A., 2004,
Uchucchacua: A major silver producer in South America: Economic Geology
Special Publication 11, p. 243-257.
Ríos, C.C., 2007, Santa Ana drilling: Unpublished memorandum to Bear Creek Mining.
55
Robinson, R. W., and Norman, D. I., 1984, Mineralogy and fluid inclusion study of the
southern Amethyst vein system, Creede mining district, Colorado: Economic
Geology, v. 79, p. 439-447.
Seward, T. M., and Barnes, H. L., 1997, Metal transport by hydrothermal ore fluids, in
Barnes, H. L., ed., Geochemistry of hydrothermal ore deposits, 3rd Edition: New
York, John Wiley and Sons, p. 435-486.
Sillitoe, R.H., and Hedenquist, J.W., 2003, Linkages between volcanotectonic settings,
ore-fluid compositions, and epithermal precious metal deposits: Economic
Geology Special Publication 10, p. 315-343.
Sillitoe, R.H., 2004, Musings on future exploration targets and strategies in the Andes:
Economic Geology Special Publication 11, p. 1-14.
Simmons, S. F., 1991, Hydrologic implications of alteration and fluid inclusion studies in
the Fresnillo district, Mexico: Evidence for a brine reservoir and a descending
water table during the formation of hydrothermal Ag-Pb-Zn orebodies: Economic
Geology, v. 86, p. 1579-1601.
Simmons, S. F., 1995, Magmatic contributions to low-sulfidation epithermal deposits, in
Thompson, J. F. H., ed., Magmas, fluids, and ore deposits: Mineralogical
Association of Canada Short Course, v. 23, p. 455-477.
Simmons, S. F., Gemmell, J. B., and Sawkins, F. J., 1988, The Santo Niño silver-leadzinc vein, Fresnillo district, Zacatecas, Mexico: Part II. Physical and chemical
nature of ore-forming solutions: Economic Geology, v. 83, p. 1619-1641.
56
Simmons, S.F., White, N.C., and John, D.A., 2005, Geological characteristics of
epithermal precious and base metal deposits: Economic Geology 100th
Anniversary Volume, p. 485-522.
Smith, D. M., Jr., Albinson, T., and Sawkins, F. J., 1982, Geologic and fluid inclusion
studies of the Tayoltita silver-gold vein deposit, Durango, Mexico: Economic
Geology, v. 77, p. 1120-1145.
Taylor, H.P., Jr., 1973, O18/O16 evidence for meteoric hydrothermal alteration and ore
deposition in the Tonopah, Comstock lode, and Goldfield mining districts,
Nevada: Economic Geology, v. 68, p. 747-764.
van Leeuwen, T.M., Leach, T.M., Hawke, A.A., and Hawke, M.M., 1990, The Kelian
disseminated gold deposit, East Kalimantan, Indonesia: Journal of Geochemical
Exploration, v. 35, p. 1-61.
VGD del Peru, 2005, Geophysical report on induced polarization and magnetic surveys,
Santa Ana Project. Unpublishd report to Bear Creek Mining.
Vikre, P.G., 1989, Fluid-mineral relations in the Comstock lode: Economic Geology, v.
84, p. 1574-1613.
57
Figure Captions
Fig. 1. Location map of the Santa Ana deposit. Map shows location within Puno
Province, southeastern Perú (Bear Creek Mining Corporation, 2008).
Fig. 2. Location map of Anomaly A and Anomaly B. Upper green square encloses
Anomaly A; below it is Anomaly B. The area now considered a new anomaly, Anomaly
C, is 800 m south of Anomaly B (Bear Creek unpublished data, 2005).
Fig.3. Photographs of old workings. Top photograph shows southern part of Anomaly B,
with dumps visible in the distance. Bottom photograph shows close up of old workings
(Photos by C. Ríos, R. Tonconi).
Fig. 4. Geologic map of Anomaly B. Area mapped at a scale of 1:2500 (Bear Creek
Mining Corporation, 2008).
Fig. 5. Detailed geological map of eastern side of Anomaly B (Bear Creek unpublished
data, 2005). Geology, with a focus on structural measurements in the vicinity of the East
Breccia, was mapped at a scale 1:1000.
Fig. 6. Photographs of trenches at Anomaly B. Top and bottom photographs show
trenches in southern and northern parts of Anomaly B, respectively (Photos by R.
Tonconi).
58
Fig. 7. Interpretation of 3D induced polarization and resistivity survey. Plan view
(VALDOR GEOFISICA, unpublished data, 2005).
Fig. 8. Interpretation of 3D induced polarization and resistivity section. Section is along
Line 7400 in Anomaly B (VALDOR GEOFISICA, unpublished data, 2005).
Fig. 9. Photographs of representative drill core box. View shows two boxes of core
totaling 6.40 m in length (Photo by C. Ríos).
Fig. 10. Photomicrographs of lavas. Phenocrysts of plagioclase are altered to illitesericite, and ferromagnesian phenocrysts are altered to chlorite, constituting a propylitic
type of alteration. Calcite may be associated with chlorite, possibly originating from the
alteration of ferromagnesian minerals. All the minerals are enclosed in a microgranular to
microcrystalline matrix composed of plagioclase, quartz, and chlorite. (Photos by P.
Gagliuffi).
Fig. 11. Photomicrographs of opaque mineralogy. A. Drill hole SA-03 (80.60m),
hematite (hm) being replaced by sphalerite (ef), chalcopyrite (cp) can be observed as little
grains between the gangue minerals (GGs) and the sphalerite. B. Drill hole SA-03
(80.60m), galena (gn) replacing sphalerite. C. Drill hole SA-03 (80.60m), galena and
sphalerite replacing anhedral crystals of hematite. D. Drill hole SA-11 (6.60m), veinlet of
sphalerite that is partially replaced by galena. E. Drill hole SA-17 (66.45m), proustite
59
associated with argentite replacing sphalerite, with galena replacing all minerals. F. Drill
hole SA-05 (38.40m), sphalerite replacing hematite. Right side: hematite filling holes in
the gangue (Photos by P. Gagliuffi).
Fig. 12. Location map of soil samples, Anomaly B (Bear Creek unpublished data, 2007).
Fig.13. Projection of drill holes to plan view, MineSight Software (Figure by C. Ríos, E.
Gutierrez). Yellow color: 20g/t Ag average. Green Color: 20-40g/t Ag. Red Color: more
than 40g/t Ag.
Fig. 14. Projection of drill holes to section view, MineSight Software (Figure by C. Ríos,
E. Gutierrez).Yellow color: 20g/t Ag average. Green Color: 20-40g/t Ag. Red Color:
more than 40g/t Ag.
Fig. 15. Solid shape from different views, MineSight Software. A. Looking north, 3D
view. B. Looking west, 3D view. C. N-S, Plan view (Figure by C. Ríos, E. Gutierrez).
Yellow color: 20g/t Ag average. Green Color: 20-40g/t Ag. Red Color: more than 40g/t
Ag.
Fig. 16. Histogram of Ag assay values (Figure by C. Ríos, E. Gutierrez).
Fig. 17. 3-D Block model, plan view (Figure by C. Ríos, E. Gutierrez). Yellow color:
20g/t Ag average. Green Color: 20-40g/t Ag. Red Color: more than 40g/t Ag.
60
Fig. 18. 3-D Block model, section view (Figure by C. Ríos, E. Gutierrez). Yellow color:
20g/t Ag average. Green Color: 20-40g/t Ag. Red Color: more than 40g/t Ag.
Fig. 19. Photographs of drill core. A. Hydrothermal breccia with intense illite-pyrite
alteration, SA-38A, 11.2m. B. Pyrite-bearing fluidized breccia dyke, SA-6, 138.7m. C.
Typical polymetallic Ag mineralization characterized by early quartz overprinted by
galena and light green sphalerite with later carbonate gangue, SA-15, 97.9m. D. Crimson
hematite developed from weathering of galena, SA-15A, 115.5m. E. Banded quartzbarite-sulfide-carbonate vein with argentite within the carbonate vein portion, SA-2A,
75.7m. F. Chlorite shear with interlayered barite, SA-36A, 123m (G. Corbett,
unpublished report, 2007).
Fig. 20. Stratigraphic column, Puno (INGEMMET, 1993).
Fig. 21. Surface photographs, A. Anomaly B, left side (dark color): East Breccia, right
upper part: post mineral Barroso tuff. B. Anomaly A, right center: QFP dome (Photos by
C. Ríos).
Fig. 22. Sketch of geological relationships including dilational splays. (G. Corbett,
unpublished report, 2007).
61
Fig. 23. A. Conceptual geological model for Santa Ana. Figure illustrates the creation of
dilatancy within the pre-existing sheeted fractures where ore fluids (orange) have mixed
with bicarbonate waters to promote Ag deposition (red). Lower Ag grade mineralization
(orange) occurs in the absence of the fluid mixing environment. B. Dilational zone with
galena-sphalerite and later carbonate in drill core SA-29, 114.4m.
Fig. 24. Comparison of three phases of metallurgical test results (M. McClave,
unpublished report, 2007).
62
Ríos, Figure 1, Location map of Santa Ana.
63
Ríos, Figure 2, Location map of Anomaly A and Anomaly B.
64
Ríos, Figure 3, Photographs of old workings, southern part of Anomaly B.
65
Ríos, Figure 4, Geologic map of Anomaly B.
66
Ríos, Figure 5, Detailed geological map of East Breccia.
67
Ríos, Figure 6, Photographs of trenches at Anomaly B.
68
Ríos, Figure 7, Interpretation of 3D induced polarization and resistivity survey.
69
Ríos, Figure 8, Interpretation of 3D induced polarization and resistivity section.
70
Ríos, Figure 9, Representative photograph of drill core.
71
Ríos, Figure 10, Photomicrographs of lavas.
.
72
Ríos, Figure 11, Photomicrographs of opaque mineralogy.
A
B
C
D
E
F
73
Ríos, Figure 12, Location of soil samples, Anomaly B, scale 1:2500
74
Ríos, Figure 13, Projection of drill holes to plan view, MineSight® Software.
75
Ríos, Figure 14, Projection of drill holes to section view, MineSight® Software.
76
Ríos, Figure 15, 3-D Solid shape from different views, MineSight® Software.
A
B
C
77
Ríos, Figure 16, Histogram of Ag assay values.
.
78
Ríos, Figure 17, 3-D Block model, plan view.
79
Ríos, Figure 18, 3-D Block model, section view.
80
Ríos, Figure 19, Photographs of drill cores, Anomaly B.
A
B
C
D
E
F
81
Ríos, Figure 20, Stratigraphic column, Puno.
82
Ríos, Figure 21, Surface photographs.
A
B
83
Ríos, Figure 22, Sketch of geological relationships including dilational splays.
84
Ríos, Figure 23, Conceptual geological model for Santa Ana.
A
B
85
Ríos, Figure 24, Comparison of three phases of metallurgical test results.
100.0%
90.0%
80.0%
70.0%
60.0%
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
1
2
3
4
5
Recovery McClelland - Calced Heads
86
6
7
Recovery ALS
8
9
Recovery Plenge
10
Table 1. Diagnostic Minerals and Textures of Various States of pH, Sulfidation and Oxidation State. Used to Distinguish
Epithermal Ore-Forming Environments (Giggenbach, 1997, Einaudi et al., 2003) (the use of hyphens between minerals
indicate an equilibrium assemblage for which all phases need to be present)
Acid pH
Neutral pH
Alunite, kaolinite (dickite), pyrophyllite
Quartz-adularia ± illite, calcite
residual, vuggyquartz
High sulfidation
Intermediate sulfidation
Low sulfidation
Pyrite-enargite, ± luzonite, covellite-
Tennantite, tetrahedrite, hematite-
Arsenopyrite-loellingite-pyrrhotite,
digenite, famatinite, orpiment
pyrite-magnetite, pyrite, chalcopyrite,
pyrrhotite, Fe-rich sphalerite-pyrite
Fe-poor sphalerite-pyrite
Oxidized
Reduced
Alunite, hematite-magnetite
Magnetite-pyrite-pyrrhotite, choritepyrite.
87
Table 2. Resource Estimate Determined with MineSight Software (50 drill holes)
Category
Indicated and Inferred
Mtonnes
Silver (g/t)
47.7
27.3
Based on 18.50 g/t cut-of grade, 70% Ag recovery.
88
Silver (Million Oz)
41.8
Table 3. Drill holes results, Phase 1.
Azimuth
(degrees)
Inclinatio
n
(degrees)
Total
Depth
(m)
105
-65
101.00
0
-60
99.50
305
-50
96.00
SA-05
includes
280
-50
99.00
SA-07
includes
SA-10
145
-60
100.00
30
-70
80.50
SA-11
172
-65
75.50
Drill
Hole
#
SA-02
includes
SA-03
includes
and
SA-04
From
(m)
To
(m)
0
28
48
50
72
4
22
42
0
0
56
0
22
48
52
34
96
60
80
10
38
52
40
16
66
52
32
72
0
36
12
54
89
Silver
(grams Lead
per
(%)
tonne)
52
34.2
nil
6
133.7
nil
48
87.1
0.5
10
199
0.6
8
102.6
1.2
6
112
0.7
16
87.1
0.6
10
43.5
1.3
40
77.8
0.3
16
140
0.3
10
68.4
0.2
52
56
0.5
10
127.5
0.7
24
82.2
0.1
Hole TDs in 72 g/t silver
12
189.7
0.4
18
34.2
0.4
Interval
(m)
DTH
Zinc
(%)
0.6
1.3
1.1
0.8
2.6
0.3
0.4
0.8
0.6
0.7
0.4
0.7
0.9
0.3
0.2
0.7
Table 4. Drill holes results, Phase 2.
Drill Hole
#
Azimuth
(degrees)
Inclinatio
n
(degrees)
Total
Depth
(m)
SA-3A
includes
and
SA-10B
includes
SA-10C
includes
SA-12
includes
and
SA-13
includes
and
and
SA-13A
includes
0
-75
106
86
86
0
-70
100
70
-70
152
225
-70
169
SA-15
includes
280
-60
150
SA-15A
includes
and
SA-16
includes
and
100
-70
148
303
-70
153
SA-17
270
-60
152
SA-19
123
-60
124
includes
From
(m)
To
(m)
48
48
78
24
38
0
76
2
16
42
10
38
58
78
8
8
106
0
34
114
136
4
4
104
6
12
36
72
2
116
2
58
72
106
72
90
62
52
86
80
48
22
48
82
42
60
82
44
20
166
44
40
122
146
128
16
120
114
18
48
76
74
128
40
98
76
90
Interva
l
(m)
DTH
58
24
12
38
14
86
4
46
6
6
72
4
2
4
36
12
60
44
6
8
10
124
12
16
108
6
12
4
72
12
38
40
4
Silver
(grams
per
tonne)
84.2
125.8
91.7
86.1
163.1
38.4
285.0
89.0
172.0
418.0
40.2
131.0
573.0
112.0
35.3
64.3
30.5
37.2
113.3
50.8
56.6
32.0
66.7
82.8
35.0
116.3
88.3
100.0
31.6
55.8
41.0
23.3
88.5
Lead
(%)
Zinc
(%)
0.6
1.0
0.5
0.3
0.4
0.2
1.0
0.4
1.0
0.7
0.2
0.2
0.7
0.1
0.1
0.2
0.1
0.4
1.2
0.2
0.3
0.3
0.2
0.5
0.3
1.0
0.9
0.6
0.3
0.5
0.2
0.2
0.2
1.0
1.0
1.2
0.2
0.2
0.3
1.1
0.3
0.7
0.2
0.2
0.2
0.3
0.3
0.2
0.2
0.2
0.5
1.1
0.3
0.3
0.6
0.4
0.8
0.4
0.6
0.4
0.8
0.7
1.1
0.3
0.4
0.3
Table 5. Drill holes results, Phase 3.
Drill Hole
#
Azimuth
(degrees)
Inclination
(degrees)
Total
Depth
(m)
SA-29
includes
270
-50
218
SA-29A
includes
and
SA-29B
90
-45
166
90
-75
173
270
-40
185
280
-40
213
includes
and
SA-30
includes
and
includes
SA-31
includes
and
and
SA-31A
includes
SA-32A
100
-60
141
105
-60
156
From
(m)
To
(m)
Interval
(m)
DTH
44
80
150
200
2
24
60
34
66
68
88
18
64
70
86
124
124
112
104
168
206
68
40
66
48
150
72
102
30
94
80
94
152
130
68
24
18
6
66
16
6
14
84
4
14
12
30
10
8
28
6
Silver
(grams Lead
per
(%)
tonne)
38.4
0.2
73.2
0.3
218.1
0.5
37.7
2.0
66.4
0.2
119.5
0.4
286.3
0.2
27.0
0.2
35.9
0.2
82.5
0.4
82.4
0.2
59.0
0.2
102.5
0.4
145.2
0.4
153.0
0.6
48.4
0.3
77.0
0.1
62
116
158
4
86
32
98
120
160
94
92
102
36
4
2
90
6
70
81.3
97.0
180.0
24.9
83.7
48.3
91
0.3
0.2
0.6
0.1
0.3
0.5
Zinc
(%)
0.6
0.7
0.7
1.0
0.5
1.0
0.1
0.5
0.5
1.0
0.4
0.3
0.8
0.9
1.1
0.6
0.3
0.4
0.2
1.0
0.2
0.3
0.8
Table 6. Drill holes results, Phase 3, continued.
Azimuth
(degrees)
Inclination
(degrees)
Total
Depth
(m)
270
-60
257.2
90
-60
257.0
includes
SA-35B
180
-60
242.0
includes
SA-36
300
-60
204.9
120
-60
210.0
270
-60
210.5
90
-70
215.2
270
-60
161.0
90
-60
224.0
135
-60
200
300
-60
223.0
120
-60
190
Drill
Hole
#
SA-35
includes
and
and
SA-35A
includes
SA-36A
includes
SA-37
includes
SA-37A
includes
and
and
SA-38
includes
SA-38A
includes
SA-38B
SA-39
and
and
SA-39A
includes
From
(m)
To
(m)
Interval
(m)
DTH
0
82
116
188
44
58
98
130
180
204
0
138
184
14
52
138
146
10
116
46
66
100
42
56
130
178
60
78
34
180
54
90
114
0
104
196
0
66
140
244
94
140
192
50
68
100
162
220
208
100
210
208
34
66
188
158
190
130
48
110
108
194
64
154
182
126
90
216
188
78
106
144
14
164
214
120
72
154
244
12
24
4
6
10
2
32
40
4
100
72
24
20
14
50
12
180
14
2
44
8
152
8
24
4
66
12
182
8
24
16
30
14
60
18
120
6
14
92
Silver
(grams
per
tonne)
29.5
122.5
84.9
90.0
35.3
30.8
78.0
36.4
182.1
1532.0
18.8
37.8
65.0
46.0
39.7
34.2
61.5
17.6
101.6
100.0
32.0
72.8
45.9
140.8
114.2
96.0
51.8
138.0
30.3
164.5
53.8
53.4
90.0
12.6
14.0
17.5
53.4
325.0
51.9
Lead
(%)
Zinc
(%)
0.3
1.0
0.6
0.1
0.2
0.2
0.6
0.2
0.4
2.4
0.2
0.2
0.3
0.2
0.5
0.2
0.1
0.1
0.3
0.6
0.2
0.3
0.4
1.3
0.6
1.0
0.3
0.6
0.3
1.3
0.7
1.0
0.9
0.3
0.1
0.1
0.7
1.2
0.5
0.5
0.9
1.0
0.1
0.3
0.4
0.6
0.3
0.4
2.4
0.5
0.3
0.3
0.3
0.9
0.3
0.2
0.3
0.3
1.5
0.4
0.6
0.8
2.0
1.3
1.4
0.5
0.7
0.5
1.5
1.1
1.8
1.7
0.3
0.1
0.3
1.1
3.1
0.3
Table 7. ALS Shaker Test.
Measured Cyanide Soluble Residual
Shaker Ag
Hole
Sample Head Ag (g/t)
Ag (g/t)
Cyanide (%) Recovery
16
2205
54
32.0
0.22
59.2%
16
2209
172
75.6
0.20
43.9%
3A
58537
238
137.7
0.19
57.9%
3A
58542
78
56.1
0.22
71.9%
13
58775
145
72.7
0.21
50.1%
13
58795
57
16.4
0.10
28.8%
14
58929
161
96.9
0.21
60.2%
14
58942
52
33.0
0.24
63.4%
15
59083
52
31.1
0.21
59.8%
15
59142
114
72.0
0.21
63.2%
Average
112.3
62.4
0.20
55.5%
.
93
Table 8. Plenge Bottle Roll Test.
Sample
Grind
2205
2209
58537
58542
58775
58795
58929
58942
59083
59142
57%-200M
52%-200M
51%-200M
60%-200M
49%-200M
56%-200M
54%-200M
49%-200M
52%-200M
46%-200M
Average
NaCN *Head: Residue:
g/t Ag
g/t Ag
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
0.10
57.4
165.5
226.8
83.9
133.8
71.0
164.9
57.7
52.7
119.9
113.4
8.7
46.8
8.1
12.5
15.1
13.9
31.0
13.5
8.2
4.9
16.3
94
Extraction
%
84.9
71.7
96.4
85.1
88.7
80.4
81.2
76.6
84.4
95.9
84.5
Reagents: kg/t
NaCN
1.0
1.8
3.8
2.9
1.1
4.8
1.9
2.5
1.2
1.9
2.3
CaO
2.4
2.6
1.8
1.7
2.4
1.7
2.1
1.9
2.6
1.3
2.1
Table 9. McClelland Bottle Roll Test.
Calculated
SAMPLE Head Ag (g/t)
2205
57.89
2209
156.55
58537
220.08
58542
75.82
58775
123.75
58795
70.94
58929
159.96
58942
61.12
59083
53.14
59142
109.06
Average
108.83
Residue:
g/t Ag
15.33
61.33
34.67
17.67
37.67
32.33
49.33
18.33
17.67
13.67
29.80
Extraction
%
73.5%
60.8%
84.2%
76.7%
69.6%
54.4%
69.2%
70.0%
66.7%
87.5%
71.3%
95
NaCN
Consumption kg/t
0.20
0.98
3.18
2.26
0.37
4.13
1.42
2.00
0.34
1.52
1.64
Lime
Consumption
kg/t
4.7
6.1
3.7
3.0
5.2
2.1
4.9
3.7
5.9
2.7
4.2