PREPARED BY: LUIS NAVARRETE, ERICK GUERRERO, ALEJANDRO PASQUEL & BRYAN CHAVARRIA
October 1th – October 4th
International Field Trip Report
Cajamarca, Perú 2017
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Contents Summary ..............................................................................................................................................................2
1. Introduction .................................................................................................................................................3
Objectives .........................................................................................................................................................3
Participants ......................................................................................................................................................3
Itinerary ............................................................................................................................................................3
2. Regional Setting ...........................................................................................................................................3
3. Yanacocha ....................................................................................................................................................4
4. La Zanja ........................................................................................................................................................7
5. Porphyry-Epithermal Transition ..................................................................................................................9
6. Conlusions ................................................................................................................................................. 10
7. Acknowledge ............................................................................................................................................. 10
8. References ................................................................................................................................................. 10
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Summary The SEG Student Chapter – Escuela Politécnica Nacional organized a geological fieldtrip to visit
Yanacocha and La Zanja high epitermal deposits, which we could learn about the principal
characteristics and exploration tools for high sulphidation epithermal deposits and porphyry-
epithermal transition. Twelve people attended this field trip: nine students and three industry
participants who helped guide students during the visit. Financial support was provided by Stewart
R. Wallace Funding; allowing nine students to travel by land to reach Cajamarca (Peru) from Quito
(Ecuador). Every day the participants were given a mine tour and an excellent presentation of the
deposits. After that, the group visited the core shack and learned about advanced argillic
assemblages, hydrothermal breccias, patchy and wormy textures and quartz-tourmaline breccias.
The Yanacocha District in Cajamarca region of northern Peru lies the countries most mineralized
belt. This Miocene belt continues to the north within the Azuay-El Oro districts (e.g El Mozo, Tres
Chorreras, Chaucha). In an overview geology we can see similarities with the south of Ecuador so
there is great hidden potential in the southern Ecuadorian Miocene volcanism that needs more
studies to contrast and know the extent of Miocene volcanism.
Image 1. Participants at Mirador Yanacocha. Left to Right: Elena Angulo, Osman Poma (Industry Advisor), Willmer
Merino (Cornerstone Geologist), Richard Pilco (Yanacocha Geologist), Bryan Chavarría, Belén Vela, Jhonny Lozada,
Milton Gonzaga, Luis Miguel Navarrete, Alejandro Pasquel, Erick Guerrero, Dayana Yaguana and Fausto Villegas
(Cornestone Geologist),
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1. Introduction
Objectives
• Acquire specific field experience and new skills for field exploration of epithermal and
porphyry deposits.
• Learn about Porphyry-Epithermal Transition (e.g. Yanacocha).
• Provide facilities to students to access big projects.
• Access to geological information that allow us to conduct studies in ore deposits.
Participants
Name Affiliation
Jhonny Lozada SEG - Escuela Politécnica Nacional
Belén Vela SEG - Escuela Politécnica Nacional
Dayana Yaguana SEG - Escuela Politécnica Nacional
Alejandro Pasquel SEG - Escuela Politécnica Nacional
Bryan Chavarría SEG - Escuela Politécnica Nacional
Erick Guerrero SEG - Escuela Politécnica Nacional
Milton Gonzaga SEG - Escuela Politécnica Nacional
Elena Angulo SEG - Escuela Politécnica Nacional
Luis Miguel Navarrete SEG - Escuela Politécnica Nacional
Wilmer Merino Cornerstone Resources
Fausto Villegas Cornerstone Resources
Osman Poma Industry Advisor
Itinerary TIME ACTIVITY TRANSPORT
DAY 1: September 28 20H00 Travel Quito – Huaquillas Bus
DAY 2: September 29 08H00 Travel Huaquillas – Tumbes Travel Tumbes – Chiclayo
Taxi Bus
DAY 3: September 30 17H00 Travel Chiclayo – Cajamarca Bus
DAY 2: October 1 Sun 09H00 Visit to Cumbemayo Bus
DAY 3: October 2 Mon 08h00 • Limatambo Clinic
• Newmont for issuing of fotocheck access badges
• Tour historical Cajamarca
DAY 4: October 3 Tue 06H45 All day tour of Yanacocha Newmont Bus
Day 5: October 4 Wen 05H00 Visit to La Zanja Buenaventura Bus
Day 6: October 5 Thu 22H00 Travel Cajamarca – Chiclayo Bus
Day 7: October 6 Fri 06H00 10H00 19H00
Travel Chiclayo – Piura Travel Piura – Huaquillas Travel Huaquillas - Quito
Bus Bus Bus
Day 8: October 7 Sat 06h00 Arrive to Quito
2. Regional Setting The Yanacocha and La Zanja epithermal gold deposits are part of the extensive Miocene
metallogenic belt of central and northern Peru. The Yanacocha district occur within the central
Andean orogenic belt, a northwest-trending region of deformation that encompasses the entire
western half of Peru (Teal and Benavides, 2010). The northeast trending belt 30 to 40 km wide and
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200 km or more long that encompasses the mineral deposits in the Cajamarca region has been
named the Chicama-Yanacocha structural corridor (Quiroz, 1997 in Gustafson et al., 2004).
The Tertiary volcanic sequences comprise together the Calipuy Group, wich is divided in the Llama
Volcanics, Porculla Formation and Huambo Formation that overlay unconformably the Cretaceous
Basement, wich consists of sedimentary rocks intensely folded and thrusted (Pinto, R., 2002).
Figure 1. Generalized geologic map of the Cajamarca region, northern Peru, showing location of mineral deposits. From
Gustafson et al., 2004.
Rivera & Santisteban (2011) think that this small lineaments of NE direction are product of the main
regional fault of Andean strike (NW-Peruvian Andes) direction, it means that this lineaments are
secondary structural expressions of the great movements of the fault of Andean strike direction
that usually have an associated strike slip component. The convergence of these small NE direction
faults with regional Andean fault (NW) faults constitute favorable sites for the hydrothermal -
magmatic manifestations.
3. Yanacocha The Yanacocha District has produced 34 Moz Au with 44.7 Moz Au mined and is the largest gold
producer in South America. It is developed within a tectonic setting of extensional continental
margin arc and genetically related to andesite-dacite tuffs and domes.
The district contains at least ten distinct near-surface, high sulphidation epithermal deposits
formed in the middle Miocene (12.5–11.8 Ma) Yanacocha volcanic complex (Gustafson et al., 2004).
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This disseminated bodies of Yanacocha District have trends E-W, northwest and northeast
directions.
Figure 2. Yanacocha district schematic stratigraphic column showing mineralized horizons by deposit and volcanic
sequences. From Teal and Benavides, 2010.
The Cretaceous Basament within the Yanaocha district consist of folded and thrusted sequences of
Farrat Formation sandstones of the Lower Cretaceous Goyllarisquiza Group. This oldest rocks are
overlain by a Tertiary volcanic pile divided in three sequences: The lower andesite sequence consist
of an intercalated sequence of block and ash flow tuffs, flow sequences with rare associated flow
domes, and an upper zone dominated by ignimbrites; The Yanacocha pyroclastic sequence consists
of a variable progression of lithic to lithic crystal tuffs. The upper andesite sequence consists of
intercalated andesitic to dacitic flows and ignimbrites dominated by multiple flow dome complexes
in its upper portion (summarized of Teal and Benavides, 2010; figure 2).
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The high sulphidation epithermal deposit of Yanacocha contains many alterations zones described
in the Figure 3, by sericite and silica pyrophyllite zones below the Ultimate Oxide Pit Crest line as
seen in the cross section, the upper zone of the district is described by massive silica and propylitic
zones, in the central part of the cross section in the diatreme is observed an Argillic zone with some
propylitic zones. In the lower part there are fresh intrusions, also Diaspore and Sericite/ Illite-
Smectite remanents.
The mineralization of the Yanacocha District, the mayority concentration of Au (ppm) is located
principally in the Oxide Zone, while for the concentration of Cu is increasing as we reach the deep
zone with sulphides. The concentrations in ppm is described in the Figure 3.
Currently they are mining the Oxide zone and remains of rocks near the zone, in the future they
hope to mine the gold/copper sulphides in the lower zone.
Figure 3.Description of lithology and alteration interpretation maps of Yanacocha complex.
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Chaquicocha Deposit open pit was also observed, and soon this mine is going to be an underground
mine. It is constituted of phreatic breccias with a N40E control. Chaquicocha has a potential of 500k
ounces Au in oxides and 250k ounces Au in sulfides. Structural control is responsible for
hydrothermal breccias emplacement and high grade mineralization (resources of 3 Moz Au and a
cut off ranges from 3 g/t to 6 g/t Au).
Figure 4. Hydrotermal breccia with clast of gray silica filled with alunite and native sulfur. Chaquicocha deposit.
4. La Zanja La Zanja district consists of San Pedro Sur and Pampa Verde high sulphidation epithermal deposits,
with a quartz-alunite alteration. The two deposits contains gold reserves of more than 500,000 oz
of gold. The mineralization is hosted within tuff sequences of Oligocene and is associated with the
emplacement on intermineral domes that enrich the mineralization (gold), this mineralization has
ages between 11 and 13 Myr.
This epithermal deposits are in the Cenozoic Belt (36-5 Ma) and Upper Cretaceous – Paleocene Au-
Ag Epithermals Metallogenic Belt within which porphyry type mineralization was found. The NE, N-S
structures are the most important in the region because this trends are intermineral.
These deposits have been developed during Tertiary calc-alkaline volcanism of dacite to andesite
composition. Stratigraphically these rocks correspond to the Calipuy Group.
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The cryptolithic tuffs favored by the primary permeability (porosity) and secondary permeability
(intense fracturing), are the most favored rock for gold mineralization. The structural trend NW and
E-O, control mineralization in San Pedro Sur and Pampa Verde deposits. In Pampa Verde deposit,
through the reactived structural system and mineralizers favored by a NE structural control
increased the gold content.
The highest mineral content is associated to silica cores. The contact between dome and tuff has
the greatest expression of grade. The grade in La Zanja is 0.71 g/t Au and have been produced 973
oz Au.
Image 2. Participants at La Zanja. Left to Right: Dayana Yaguana, Alejandro Pasquel, Bryan Chavarría, Luis Miguel
Navarrete, Elena Angulo, Jhonny Lozada, Erick Guerrero, Camilo Ruiz (Buenaventura Geologist), Fausto Villegas
(Cornestone Geologist), Milton Gonzaga, Osman Poma (Industry Advisor), Willmer Merino (Cornerstone Geologist) and
Belén Vela.
The Castrejon Project a copper and molybdenum breccia pipe porphyry-style deposit is also part of
this district, it is located 7 km southwest of San Pedro Sur. Comprise andesitic lavas and tuffs with
three intrusives of different composition (diorite feldspar, monzonitic quartz and monzodioritic
porphyries) that are intruded by hydrothermal breccias and late andesitic dykes. This quartz-
tourmaline breccia associated with a phyllic alteration is mineralized of molybdenum and copper.
The highest value molybdenum in the surface is 2500 ppm. The hydrothermal breccia of quartz-
tourmaline (figure 5) is enriched with Cu-Mo-Au; and could be related to the quartz monzonitic
porphyry to which mineralization is associated. The resources indicated in sulphides are: 50 Mt @
0.31% Cu, 0.12% Mo, 0.13 g/t Au, 5.62 g/t Ag.
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Figure 5. Quartz-tourmaline breccia of Castrejón Project.
5. Porphyry-Epithermal Transition The transition between porphyry and epithermal environments is exposed at Perol and
Huaylamachay, La Zanja, and especially Tantahuatay and Yanacocha (Gustafson et al., 2004).
La Zanja staff prepared to us a presentation about it, which was very helpful for us to understand
the porphyry-epithermal transition and the related textures (e.g. patchy, wormy).
Characteristics of Alteration Textures from Porphyry-Epithermal Transition
Patchy Wormy
Texture of irregular white shapes or patches within a light gray silica matrix, this patches are mainly pyrophyllite, alunita, kaolinite and diaspora. In some cases can be observed ¨ghost of crystals¨. Generally the patchy texture is destructive and is associated with an extreme acid leaching. This is formed above or peripherally on the top of possible porphyries. The patchy could be a connection or transition between the overlap of a high sulphidation system and the porphyry environment.
Consists of granular quartz with discontinuous and contorted shapes associated with advanced argillic alteration. Wormy texture overlap the top of A quartz veins and they could mark the bottom of high epithermal systems. A wormy texture consist in rounded patches of Pyrofillite-Diaspore / Alunite in a silicificated matrix with stronger anomaly of Molibdene.
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Figure 3. Patchy texture at La Zanja. Patches of pyrophyllite and minor alunite.
6. Conclusions Yanacocha have a multiple epitermal mineralization centers with a high sulphidation marked,
alteration zones very well defined and a good estimation in mineralization concentration of gold in
oxide zones and copper in sulphide zones.
The Yanacocha and La Zanja epithermal gold deposits are part of the extensive Miocene
metallogenic belt of central and northern Peru that continues to the north within the Azuay-El Oro
districts in Ecuador. In an overview geology similar characteristic features with the south of Ecuador
could be identified, so we think there is great hidden potential in the southern Ecuadorian Miocene
volcanism that needs more studies to contrast and know the extent of Miocene volcanism.
7. Acknowledge The Escuela Politécnica Nacional - Society of Economic Geologists Students Chapter would like to
express their sincere thanks to the respective people to make this fantastic fieldtrip happen. A
special thanks to Camilo Ruiz, Hernan Tanabe, Roberto Andia, Jose Cabrera (Compañia de Minas
Buenaventura S.A.A.) and Dale Finn, Sean McCann, Richard Pilco, Lucia Campos, Imer Pizan
(Newmont – Yanacocha SRL) for the help during the preparation of the field trip. Financial support
was provided by Stewart R. Wallace Funding; allowing nine students to travel by land to reach
Cajamarca (Peru) from Quito (Ecuador). Finally, the EPN-SEG Student Chapter would like thank the
generosity of Cornerstone Resources, to support us with the accommodation expenses of our SEG
Student Chapter Members.
8. References Gustafson, L., Vidal, C., Pinto, R. and Noble, D., 2004, Porphyry-epithermal transistion, Cajamarca
region, northern Perú: Society of Economic Geologists Special Publication 11, p. 279–300.
Pinto, R., 2002, Transicion de un sistema de alta sulfuracion a un sistema porfirítico de alto nivel en
depósito Kupfertal, distrito minero de Yanacocha, Cajamarca, Perú: Unpublished Ingeniero Geólogo
thesis, Lima, Peru, Universidad Nacional Mayor de San Marcos, 62 p.
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Rivera, R., & Santisteban, A., 2011, Control Estructural, Producción y Reservas en las Franjas
Metalogenéticas del Norte del Perú. VII Congreso Internacional de Exploraciones – ProExplo 2011.
Teal, Lewis, and Alberto Benavides. "History and geologic overview of the Yanacocha mining
district, Cajamarca, Peru." Economic Geology 105.7 (2010): 1173-1190.