Magmas associated with Au-Cu deposits in the Hualgayoc Mining District, Northern Peru

1Department of Earth Sciences, University of Ottawa, Ontario, Canada; 2Gold Fields La Cima, Lima, Peru; 3Compania de Minas Buenaventura S.A.A., Lima, Peru; 4Regulus Resources Inc., Lima, Peru

Introduction1

Geological setting2 U-Pb zircon ages4

Lithology and alteration 3

Zircon as records of magmatic processes

6

7 Magmatic oxygen fugacity calculated from amphibole composition

AknowledgementsReferences

8 Summary

M Viala1, K Hattori1, P Gomez2, J Trujillo3, K Heather4

Magmas source and evolution

5 0,00007

Ì

Cajamarca

HualgayocMina Congas

La CarpaGaleno

Michiquillay

Cerro CoronaCerro CoronaTantahuatay

Sipan

Yanacocha

La Zanja

Peru

25 Km

E 0,00008E

9200,000 N

9300,000 NÌ

Cajamarca

LEGEND

PRECAMBRIAN METAMORPHIC ROCKS

PALEOZOIC INTRUSIVE ROCKSPALEOZOIC METASEDIMENTARY ROCKS

TRIASSIC JURASIC CARBONATES

CRETACEOUS CARBONATESJURASSIC VOLCANIC ROCKS

UPPER CRETACEOUS BATHOLITH

OLIGO-MIOCENE VOLCANIC ROCKS

PALEOCENE SEDIMENTARY ROCKS

OLIGO-MIOCENE INTRUSION

QUATERNARY

MIOCENE VOLCANIC ROCKS

Cerro Corona

MAJOR FAULTS

CHICAMA-YANACOCHASTRUCTURAL CORRIDOR

PORPHYRY Au-CuDEPOSIT

HIGH SULFIDATION Au-AgDEPOSIT

Yanacocha

PeruPeru

25 km

N

Tantahuatay

TOWN AND VILLAGE

Hualgayoc

20°

7°

40°30°

56°

35°

30°

24°

30°

10°

25°

40°

30°

45°

30°

8°

12°

30° 30°

18°

28°

N

9250000

9255000

000557

000067

000567

24°

4 km

Alluvial (Quaternary)

Postmineral tu�Postmineral rhyodaciteAndesite domePyroclastic rocksQuartz-phyric dacite Quartz-diorite porphy-Porphyritic diorite

LimestoneSandstone

BeddingFaultVeins (Ag, Cu)Porphyry Au-Cu

High-sul�dation Au

Massive pyrite-enargite

Mio

cene

Cret

aceo

us

San Miguel [c] Tantahuatay [g]

Co. Corona [e]

LEGEND

Sill Coymolache [b]

AntaKori

Co. Hualgayoc [a]

Co. San Jose [d]

Co. Jesus [h]

Co. Cienaga [f]

San Nicolas [i]

Co. Quijote [j]

Cerro Jesus

San Jose

San Miguel

Cerro Corona

Anta porphyry 1

Choro Blanco

Coymolache

Las Gordas

Caballerisa

Cienaga north

San Nicolas

Tantahuatay Igneous Rocks

Anta porphyry 2

Calipuy rhyolite

Hualgayoc

Cienaga south

Calipuy andesite

N

9250000

9255000

000557

000067

000567

LEGEND13.5-15 Ma

11-13.5 Ma

9-10 Ma

Cerro Corona

9 10 11 12 13 14 15 16

Age (Ma)

Tantahuatay

2km

Coymolache Sill

Pl

Bt

Hbl

1cm

[b]

Cerro Hualgayoc rhyodacite

BtQz

Pl1cm

[a]

Cerro Corona – Phase 3 (strong Kfs+Bt alteration)

Hbl

Bt

Pl

QzKfs-Qz veinlets

1cm

[e]

San Jose (weak Kfs alteration)

Pl

Secondary Bt

Kfs

1cm

[d]

San Miguel Diorite (weak Chl alteration)

Pl

Chl after Hbl

1cm

[c]

San Jose (strong WM alteration)

Pl (WM) Py

1cm

Hbl replacedby WM

[d]

1cm

AlnFe-O-OH

Prl

Cerro Cienaga (intense Aln+Prl alteration)

[f]

Tantahuatay intrusive rock (strong WM+PRL alteration)

QzPy

1cmWM + Prl

1cm

Py+Qz

[g]

Ccp+PyMag

Hem

Chl

2cm

High-grade ore with Ccp, Py, Mag and Hem – Cerro Corona.

[e]

500 um200 um

-16

-15

-14

-13

-12

-11

-10

-9

800 840 880 920 960 1000 T (°C)

-8

Log

fO2

FMQ NNO

FMQ +3

Coymolache amphiboles

San Nicolas amphiboles

Legend: Yanacocha amphiboles (Longo, 2005)

Porphyry �eld

1

1.2

1.4

1.6

0

2

4

6

8

10

[La]

cn/[

Sm] cn

[Dy]cn/[Yb]cn

b)

Hbl fractionation Garnet

fracti

onation

Bulk rock

0

5

10

15

20

0

20

40

60

80

100

120

Sr/Y

Y

d)

Alte

rati

on

Hbl fractionation

Bulk rock“Adakit”-like field

Normal arc field

1

10

100

La

Ce

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

a) Bulk rock

Hualgayoc rhyodacite Sill Coymolache San Miguel San Jose

San Miguel Andesite Cerro Jesus Cerro Quijote

Cerro Corona Cerro Caballerisa Cerro Choro Blanco

Calipuy rhyolite formation AntaKori porphyry 2

San Nicolas AntaKori porphyry 1 Cerro Cienaga

Legend:(color corresponds to age grouping; red, green and blue from oldest to youngest; Fig. 4)

6000

8500

11000

13500

16000

500

600

700

800

900

Crys

talli

zatio

n te

mp.

(°C

)

Hf

b)

Magma crystallization

Zircon

100

1000

10000

0

0.4

0.8

1.2

1.6

2

Th/U

∑REEs +Y

c)

Mag

fr

actio

natio

n

Magma evolution Zircon

0

0.2

0.4

0.6

0.8

1

0

100

200

300

400

500

600

Ce/C

e*

Eu/Eu*

e) Zircon

6000

8500

11000

13500

16000

0

10

20

[Yb]

cn/[

Dy] cn

Hf

d)

Hbl

frac

tiona

tion

Magma evolution

Zircon

LaCe

PrNd

PmSm

EuGd

TbDy

HoEr

TmYb

.001

.01

.1

1

10

100

1000

10000

Median zircon value of each intrusions

Zircon �eld

Lu

a)

Legend: Zircon (15-13.5 Ma intrusions)

Zircon (13.5-11 Ma intrusions)

Zircon from Cerro Hualgayoc(10-9.5 Ma)

Trend

Abbreviations: Bt: biotite – Hbl: hornblende – Pl: plagioclase – Qz: quartz – Chl: chlorite – Kfs: potassic feldspar – Cpx: clinopyroxeneAnh: anhydrite – Aln: alunite – Prl: pyrophyllite – Py: pyrite – Ccp: chalcopyrite – Mag: magnetite Hem: hematite – WM: white mica

0.0

0.5

1.0

1.5

2

0

10

20

30

40

La/Y

b

Yb

Hbl fractionation

Bulk rock

Porphyry Au-Cu deposit

High-sul�dation Au deposit

Porphyry Au-Cu mineralization

Ag±Cu veins

The Hualgayoc mining district in the Peruvian Cordillera is located 30km north of the Yanacocha high-sul�dation Au deposits. The district hosts numerous Au-Cu deposits, including epithermal, skarn and porphyry. This study examine the igneous rocks associated with and without mineralization.

Fig. 1: Regional geological map of the Cajamarca province, from Cerro Corona technical report (2004).

Cretaceous sedimentary rocks were intruded by dioritic rocks, including the Cerro Corona porphyry, and overlain by andesitic to rhyolitic �ows, domes and tu�. Mineral deposits include the Cerro Corona porphyry Cu-Au mine, Tantahuatay high-sul�dation Au mine, and the AntaKori Cu skarn deposit.

Fig. 2: Simpli�ed geological map of the Hualgayoc district, modi�ed after S. Canchaya, J. Paredes and R. Tosdal (1996), cited by Gustafson et al (2004). Letters in brackets correspond to panel #3. •Gustafson, L. B., Vidal, C. E., Pinto, R., & Noble, D. C. (2004). Porphyry-epithermal transition, Cajamarca region, northern

Peru. Society of Economic Geologists, 11, 279-299.

•Longo, A. A. (2005). Evolution of volcanism and hydrothermal activity in the Yanacocha mining district, northern Peru. Unpublished PhD. Thesis at the Oregon State University.

•Ridolfi, F., Renzulli, A., & Puerini, M. (2010). Stability and chemical equilibrium of amphibole in calc-alkaline magmas: an overview, new thermobarometric formulations and application to subduction-related volcanoes. Contributions to Mineralogy and Petrology, 160(1), 45-66.

•Sisson, T. W., & Grove, T. L. (1993). Experimental investigations of the role of H2O in calc-alkaline di�erentiation and subduction zone magmatism. Contributions to Mineralogy and Petrology, 113(2), 143-166.

We thank Gold Fields Cerro Corona mine sta� for their logistic support during our �eld work; Buenaventura and Regulus Resources Inc. for their help with sampling; Samuel Mor�n, Glenn Poirier and Alain Mauviel for their analytical assistance; and Je�rey Hedenquist for his advice on the project. The project was supported by a Natural Science and Engineering Council of Canada Discovery Grant to K.H.

Igneous activity in the district was previously considered to have started in the Paleocene. Our U-Pb zircon ages indicate nearly continuous magmatism from 14.8 to 9.7 Ma with a hiatus between 11 and 10 Ma.

Intrusions in the eastern and northern part of the district formed between 15 and 13.5 Ma. Some are associated with mineralization (e.g., Cerro Corona, e in Fig. 2) whereas others appear to be barren (e.g., Coymolache, b in Fig. 2).

Magmatism from 13.5 to 11 Ma was focused in the Tantahuatay and AntaKori areas, consisting of porphyritic intrusions and volcanic rocks (largely Calipuy Formation). The Cerro Hualgayoc rhyodacite dome (Fig. 2, a) at 9.7 Ma appears to represent the �nal magmatic activity in the area.

All intrusions have a nearly �at pattern from middle to heavy REEs, with [Dy]cn/[Yb]cnranging from 1.4 to 1.1 (Figs. 5a, b), suggesting similar magma source containing amphibole.

Younger rocks show higher La/Yb (Fig. 5c) and lower [Dy]cn/[Yb]cn, suggesting amphibole fractionation.

Weak Eu anomalies (0.8-1.1) for all rocks re�ect essentially no Pl fractionation.

High Sr/Y ratios (40-90) and low Y (5-16ppm) (Fig. 5d) re�ect high water contents in parental magmas, which suppressed Pl crystallization (Sisson and Grove, 1993). Phenocrysts of Bt and Hbl support this interpretation.

A similar REE pattern for zircon re�ects a similar parental magma composition.

In 13.5-11 Ma magmas, Hbl and Mag crystallized with zircon (Fig. 6c, d), whereas Hbl and Mag crystallized before zircon in 15-13.5 Ma magmas.

Most zircons compositions indicate weak negative Eu anomalies (Eu/Eu*=0.4-0.8) and moderate to very high Ce anomalies (Ce/Ce*=50-600), re�ecting oxidized parental magmas (Fig. 6e).

The oxygen fugacity of barren Coymolache sill and barren San Nicolasintrusion were calculated following the method of Ridol� et al. (2010). The results indicate oxidized values (FMQ +1.6 to +2.9) (Fig. 8). These values are similar of those from Yanacocha, calculated using the amphibole compositions presented by Longo

Fig. 3: Representative photographs of hand samples from several intrusions.

Fig. 4: Average and 2σ values of U-Pb zircon ages.

Fig. 8: [Top] Unaltered amphibole from the San Nicolas (left) and Coymolache (right) intrusions. Red circles are areas for the analylsis. [Bottom] Calculated crystallization temperature (°C) vs. magmatic oxygen fugacity.

• Parental magmas in the district were hydrous, moderately to highly oxidized and originated from garnet-free, amphibole-bearing subcontinental lithospheric mantle or lower crust. Amphibole fractionation was the major cause for the compositional variation.

• Mineralized and barren intrusions are similar in composition and contemporaneous, suggesting similar magma sources and evolution.

• The mineralization requires other factors, including geometry of the intrusion and the depth of emplacement.

Dominant rocks are hornblende (Hbl) ± Biotite (Bt) porphyritic diorite with magnetite (Mag) micro-phenocrysts, suggesting relatively oxidized parental magmas. Volcanic rocks include rhyodacite domes north of Cerro Corona, and the andesitic to rhyolitic Calipuy formation which hosts part of the Tantahuatay and AntaKori deposits.

Alteration includes K feldspar (Kfs) + Bt + Mag at Cerro Corona (e in Fig. 2), and locally in the San Jose intrusion (d in Fig. 2), weak to moderate chlorite (Chl) ± epidote (Ep) alteration in San Miguel (c in Fig. 2) and Cerro Quijote intrusions (j in Fig. 2); intense WM alteration in the San Jose and Cerro Jesus intrusions (h in Fig. 2); and pyrophyllite (Prl) ± alunite (Aln) at Cerro Cienaga (f in Fig. 2) and Tantahuatay plus AntaKori (g in Fig. 2) deposits.

Fig. 5: Bulk rock geochemistry (cn: chondrite-normalized).

Fig. 6: zircon trace-elements geochemistry.