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.