-
Oxidized, Water-rich Magmatism in the Hualgayoc Au-Cu Mining Camp, Northern Peruvian Cordillera
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 dates4
Lithology and alteration 3
Bulk rock composition5
Zircon composition6 7
8 Magma oxygen fugacity estimated using Ce4+/Ce3+ in zircon
Ce and Eu anomaly in zircon
AknowledgementsReferences
9 Implication for exploration 10 Summary and on-going work
M Viala1, K Hattori1, P Gomez2, J Trujillo3, K Heather4
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 km25
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 tuffPostmineral rhyodaciteAndesite domePyroclastic rocksQuartz-phyric dacite Quartz-diorite porphyry Porphyritic diorite
LimestoneSandstone
BeddingFaultVeins (Ag, Cu)Porphyry Au-Cu
Oxide AuMassive pyrite-enargite
Mio
cene
Cret
aceo
us
San Miguel
Tantahuatays
Co. Corona
LEGEND
Sill Coymolache
AntaKori
Co. Hualgayoc
Co. San Jose
Co. Jesus
Co. Cienaga
San Nicolas
Co. Quijote
9 10 11 12 13 14 15 16
Hualgayoc
Calipuy rhyolite
AntaKori porphyry 2
Calipuy andesite
Cienaga north
Sill Coymolache
AntaKori porphyry 1
Cerro Corona
San Miguel
Cienaga south
San Jose
Jesus
Tantahuatayigneous rocks
Ma
Sill Coymolache
Pl
Bt
Hbl
1cm
Cerro Hualgayoc rhyodacite
BtQz
Pl1cm
Cerro Corona – Phase 3 (strong potassic alteration)
Hbl
Bt
Pl
QzKfs-Qz veinlets
1cm
San Jose (weak potassic alter-ation)
Pl
Bt
Kfs
1cm
San Miguel Diorite (weak chlorite alteration)
Pl
Chl after Hbl
1cm
N
9250000
9255000
000557
000067
000567
LEGEND13.5-15 Ma
11-13.5 Ma
9-10 Ma
San Jose (strong white mica alteration)
Pl (WM) Py
1cm
Hbl (WM)
1cm
QzFe-O-Oh
WM
Zorro (intense acidic alteration)
1cm
AlnFe-O-Oh
Prl
Cerro Cienaga (intense alunite + pyrophyllite alteration)
Tantahuatay intrusive rock (in-tense white mica alteration)
QzPy
1cm
WM
Tantahuatay intrusive rock (strong white mica+pyrophyllite alteration)
QzPy
1cmWM + Prl
1cm
Py+Qz
Ccp+PyMag
HemChl
2cm
High-grade ore with Ccp, Py, Mag and Hem – Cerro Corona.
Pyrite+enargite vein – Tantahuatay
Choro Blanco Caballerisa
CC phase 1
Mineralized intrusions
CC phase 4CC phase 6
San Miguel
Coymolache San Nicolas
Apparently barren intrusions
-18
-17
-16
-15
-14
660 680 700 720 740 760
Log
fO2
T (C°)
Max. s
olubili
ty of
Au in
magm
a
Median zircon values
FMQ
FMQ +
1
FMQ +
2
-19
-18
-17
-16
-15
-14
-13
600 650 700 750 800
Log
fO2
T (C°)
Max.
solub
ility of
Au in
mag
ma
All zircons
FMQ
FMQ +
1 FM
Q +2
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu.001
.01
.1
1
10
100
1000
10000Rock/Chondrites
a)
Median zircon value of each intrusions
Zircon field
Inherited core from Cerro Hualgayoc
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8600
700
800
900
T°(C
)
Th/U
c)
HualgayocCoymolache
San Miguel San JoseCienagaCerro Corona
CaballerisaChoro Blanco
Cerro Jesus
Las GordasSan Nicolas
0 5 10 15 200
20
40
60
80
100
Sr/Y
Y
“Adakite”-like rocks
Normal arc rocks
d)
1
10
100
Rock/chondrite
La PrCe Nd
PmSm
EuGd
TbDy
HoEr
TmYb
Lu
a)
.001 .01 .1 1 10 100 1000.01
.1
1
10
100
1000
10000
(Sm
/La)
N
La
Hydrothermal zircon field
b)
50 60 70 800
10
20
30
40
50
60
70
Mg-
#
SiO2
b)
HualgayocCoymolache
San Miguel
Cerro Corona
Caballerisa
Choro BlancoSan NicolasCerro Quijote
1.0 1.2 1.4 1.6 1.81
2
3
4
5
(La/
Sm) N
(Dy/Yb)N
c)
San J
ose
Caba
lleris
a
Co C
oron
a 1
San M
iguel
Chor
o Blan
co
Co C
oron
a 4
Co C
oron
a 6
Cien
aga
Co C
oron
a 5
Jesu
s
Hualg
ayoc
Las G
orda
s
Coym
olach
e
San N
icolas
0
200
400
600
800
Ce4+
/Ce3
+
Porphyry Au-Cu mineralization
High-sulfidation style mineralization
Apparently barren
c)1000
0.1 0.3 0.5 0.7 0.90
500
Ce4+
/Ce3
+
Eu/Eu*
a)
6000 8000 10000 12000 140000
500
1000
Hf
Magma evolution
Ce4+
/Ce3
+
b)
50 60 70 800
1
2
3
4
5
6
7
Th
SiO2
e)
The Hualgayoc mining district in the Peruvian Cordillera is located 30km north of the Yanaco-cha high-sulphidation Au deposit. The district hosts numerous Au-Cu deposits.This study characterizes the igneous rocks in the district to evaluate the features associated with Au-Cu fertile magmas.
Fig. 1: Regional geological map of the Cajamarca province, from Cerro Corona technical
Cretaceous sedimentary rocks were intruded by dioritic rocks, including the Cerro Corona porphyry, and overlaid by andesitic to rhyolitic flows, domes and tuffs. Mineral deposits include the Cerro Corona porphyry Cu-Au mine, Tantahuatay high-sulfidation Au mine, and the AntKori Cu skarn deposit
Fig. 2: Simplified geology of the Hualgayoc mining district, after S. Canchaya, J. Paredes and R. Tosdal (1996), cited by Gustafson et al. (2004) and modified.
The dominant phase of intrusive rocks in the district is hornblende±biotite porphyritic diorite with magnetite micro-phenocrysts, suggesting relatively oxidized parental magmas. Volcanic rocks include rhyodacite domes north of Cerro Corona, and the andesitic to rhyolitic Calipuy formation which partially hosts the Tantahuatay and AntaKori deposits.Weak to medium chlorite±epidote alteration affects the San Miguel and Cerro Quijote intrusions. Intense white mica alteration occurs in the San Jose and Cerro Jesus intrusion and rocks within the Tantahuatay and AntaKori deposits. Acidic alteration forming pyrophylite±alunite is present in Cerro Cienaga intrusion and within the Tantahuatay and AntaKori deposits. Potassic alteration forms K-feldspar + biotite + magnetite occurs at Cerro Corona, and locally in the San Jose intrusion.
REEs are mostly +3, but Ce can be +4 under oxidized conditions and Eu +2 under re-duced conditions. Zircon readily incorpo-rates Ce4+ into the Zr4+ site. Therefore, the Ce and Eu anomaly in zircon may be used to evaluate magmatic redox state. All zircons have consistently low anomalies of Eu (Eu/Eu*=0.5-0.7) (Fig. a) and variable Ce4+/Ce3+ (10-900). Ce4+/Ce3+ appears to in-crease with magma evolution (fig.b).
All mineralized intrusions including the Cerro Corona porphyry have high median Ce4+/Ce3+ values (360-625) while all appar-ently barren intrusion have low median Ce4+/Ce3+ values (200-290), except the San Miguel intrusion (~ 500) (Fig. c).
•Botcharnikov, R. E., Linnen, R. L., Wilke, M., Holtz, F., Jugo, P. J., & Berndt, J. (2011). High gold concentrations in sulphide-bearing magma under oxidizing conditions. Nature Geoscience, 4(2), 112.•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.•Sisson, T. W., & Grove, T. L. (1993). Experimental investigations of the role of H2O in calc-alkaline differentiation and subduction zone magmatism. Contributions to mineralogy and petrology, 113(2), 143-166.•Smythe, D. J., & Brenan, J. M. (2016). Magmatic oxygen fugacity estimated using zircon-melt partitioning of cerium. Earth and Planetary Science Letters, 453, 260-266.•Zajacz, Z., Candela, P. A., Piccoli, P. M., Wälle, M., & Sanchez-Valle, C. (2012). Gold and copper in volatile saturated mafic to intermediate magmas: Solubilities, partitioning, and implications for ore deposit formation. Geochimica et Cosmochimica Acta, 91, 140-159.
We thank Gold Fields Cerro Corona mine staff for their logistic support during our field work; Buenaventura and Regulus Resources Inc. for their help with sampling; Samuel Morfin, Glenn Poirier and Alain Mauviel for their analytical assistance; and Jeffrey Hedenquist for his advice on the project. The project was supported by Natural Science and Engineering Council of Canada Discovery Grant to K.H.
The magmatic oxygen fugacity of the intrusions calculated following the method of Smythe and Brenan (2016) show moderately oxidized values, FMQ +0.5 to +2, independent of the association with mineralization. Mineralized Cerro Corona porphyry intrusions appear to be less oxidized with median value of FMQ +0.8 to +1.3.Experimental data shows maximum solubility of Au in andesitic melt at around FMQ +1.5 and decreases at higher and lower fO2 (Botcharnikov et al. 2010). In contrast, the solubility of Cu in melt increases with increasing oxidation conditions (Zajacz et al. 2012). The median fO2 value of magmas from the Hualgayoc mining district, FMQ +1.28, correspond to the condition for relatively high Au solubility and appears to be consistent with the abundant Au mineralization in the district including the high Au/Cu ratio, ~1.7 x10-4, of the Cerro Corona deposit.
Zircon grains from mineralized intrusions have higher Ce4+/Ce3+ than most zircon grains from barren intrusions. This suggests that the Ce anomaly in zircon can be used to identify intrusions that may be potentially Au-Cu fertile within a district. Our results also suggest that Au-fertile districts are characterized by moderate magma oxidation conditions (FMQ +1 to +2). This may be useful to identify potentially fertile districts.
Au-Cu mineralization in the district is associated with hydrous, moder-ately oxidized magmas that originate from amphibole-bearing source rocks, with little to no crustal assimilation. Contemporaneous em-placement of mineralized and barren intrusions in the district suggest that oxidized magma do not necessarily produced Cu and Au mineral-ization. The mineralization requires other factors including focused in-jections of magmas and hydrothermal activity to concentrate the metals to economic values.On-going work includes more U-Pb zircon dating, and trace element analysis of zircon and bulk rocks to evaluate any differences for magmas associated with high-sulfidation Au deposits, skarn and por-phyry Au-Cu deposits.
The igneous activity in the district was previously thought to range from Paleocene to Miocene in age. New U-Pb zircon ages obtained in this study indicate that igneous activity ranged from 14.8Ma to 9.7Ma, similar to that at the Yanacocha high-sulfidation Au deposit. Most intrusions formed between 14 and 15Ma. Some are associated with mineralization (Cerro Corona) whereas others appear to be barren (Coymolache). Magmatic activity from 13.5 to 11 Ma is focused in the Tantahuatay and AntaKori areas, and consists of porphyritic intrusions and the Calipuy volcanic formation.Late magmatism at 9-10Ma consists of barren rhyodacite-rhyolite domes near Cerro Corona.
All the intrusions have similar Mg-# (0.30-0.55) and SiO2 (59-65 wt%) except the early phase of the Cerro Corona intrusive complex with Mg-# (0.65), and the Cerro Hualgayoc rhyolite which shows high SiO2 content (70 wt%) (fig.b).
All intrusions show listric-shaped REE pattern (Fig. a), and low [Dy]n/[Yb]n ratio (1.4-1.1) (Fig. c), reflecting preferential retention of middle REEs by amphibole in the source. Intrusions show a weak Eu anomaly (0.8-1.1) reflecting essentially no plagioclase fractionation.
All intrusions except Cerro Quijote show an “adakitic”-like geochemical signature with high Sr/Y ratios (40-90) and low Y (5-16ppm) (Fig. d). High Sr/Y can be explained by high water contents in parental magmas that suppress plagioclase crystallization (Sisson and Grove, 1993). This is consistent with the presence of phenocrysts of biotite and hornblende in most intrusions.
Low Th content in samples (3-7 ppm) indicates essentially no assimilation of siliciclastic rocks during magma ascent through the thick continental crust (Fig. e).
Sharp oscillatory zoning and low light REEs concentration in zircons confirm magmatic origin (fig. b).
Zircon grains from all intrusions show a similar REE pattern with relatively flat middle to heavy REEs, weak negative Eu anomaly and high Ce anomaly. In con-trast, inherited cores show con-cave-shaped heavy REEs profile and a strong negative Eu anomaly, suggesting the derivation from the basement rocks (fig. a).
The Ti-in-zircon thermometer yielded crystallization temperatures between 620-720 C° except the San Nicolas in-trusion which appears to have crystal-ized at higher temperature (720-800 C°) (fig.b).