©2005 Society of Economic Geologists, Inc.

Economic Geology, v. 100, pp. 979–1003

Geology, Mineralization, Alteration, and Structural Evolution of

the El Teniente Porphyry Cu-Mo Deposit
JAMES CANNELL,†,* DAVID R. COOKE,
Centre for Excellence in Ore Deposits, University of Tasmania, Private Bag 79, Hobart, Tasmania 7001, Australia

JOHN L. WALSHE,
CSIRO Division of Exploration and Mining, 26 Dick Perry Ave., Kensington, Perth, Western Australia 6151, Australia

AND HOLLY STEIN

AIRIE Program, Department of Geosciences, Colorado State University, Fort Collins, Colorado, 80523-1482, and
Geological Survey of Norway, Leiv Eirikssons vei 39, 7491 Trondheim, Norway

Abstract
El Teniente is a typical porphyry Cu-Mo deposit—in terms of its alteration and sulfide assemblage zonation,
association with felsic intrusions, and predominance of quartz vein-hosted copper mineralization. It is anom-
alous in size, with >94 million metric tons (Mt) of contained fine copper making it the world’s largest known
porphyry Cu deposit. There is an intimate spatial and temporal association between all stages of mineralization
and latest Miocene to early Pliocene felsic intrusions at Teniente.
Most of the copper was emplaced during the late magmatic stage (5.9–4.9 Ma), contemporaneously with in-
trusion of the dacite porphyry dike and dacite pipes into a mafic to intermediate sill-stock complex. Mineral-
ization of the late magmatic stage is mainly hosted by a quartz-anhydrite–dominated stockwork associated with
K-feldspar alteration in the dacites and Na-K-feldspar, biotite, and propylitic alteration of the mafic intrusive
package. Minor copper-mineralized hydrothermal biotite-cemented breccias formed at this time. The late
magmatic stage was followed by two stages of mineralized phyllic alteration, referred to as the principal hy-
drothermal (4.9–4.8 Ma) and late hydrothermal (4.8–4.4 Ma) stages, during which thicker, Cu-rich veins were
emplaced. A 1,200-m-wide breccia pipe, the Braden Breccia, formed during the late hydrothermal stage and
appears to have destroyed a large amount of ore from the center of the deposit.
The late magmatic and principal hydrothermal vein stages have predominantly concentric and radial vein
orientations centered on the Braden Pipe. Most of the concentric veins are shallowly dipping, whereas the ra-
dial veins are subvertical. We present a model in which vein distributions were controlled by the local stress
regime generated by the intrusion of a large, deep magma chamber that is interpreted to be the source of the
dacites, the Braden Pipe, and ultimately, the copper and molybdenum mineralization. The late hydrothermal
veins are steeply inward dipping and concentric to the Braden Pipe. In contrast to the late magmatic and prin-
cipal hydrothermal vein stages, radial veins and shallow-dipping concentric veins are rare, consistent with for-
mation during a stage of subsidence due to relaxation of intrusion-induced stresses. Resurgence of the magma
chamber reactivated the steep concentric structures in a reverse sense, and a build up of magmatic and/or fluid
pressure resulted in explosive brecciation and fluidization, producing the Braden Pipe. A predominantly late
set of northeast-trending faults, associated with movements on the district-scale Teniente fault zone, is the only
evidence for far-field stresses exceeding local stresses in the deposit.

Introduction “breccia deposit” in keeping with the other large Miocene

THE EL TENIENTE Cu-Mo porphyry deposit is located in the copper deposits of the central Chile belt (Los Pelambres,
Andean Cordillera in the central Chile porphyry belt (Fig. 1). Atkinson et al., 1996; and Río Blanco, Serrano et al., 1996).
Central Chile is one of the world’s most richly endowed cop- Skewes et al. (2002) documented a variety of magmatic-hy-
per provinces, with more than 180 million metric tons (Mt) of drothermal breccia pipes interpreted to have formed over
copper identified in five late Miocene-Pliocene porphyry Cu several million years that, together with abundant fine biotite
deposits (Fig. 1). El Teniente, owned by CODELCO, is the veinlets, host the majority of the copper in the deposit. Ac-
world’s largest underground copper mine, containing 12.4 bil- cording to Skewes et al. (2002) the oldest mineralized biotite
lion metric tons (Gt) at 0.62 percent Cu (current resource breccias and associated alteration formed before and after the
plus past production totals 94.4 Mt of Cu; Camus, 2002) and 7 Ma Sewell Tonalite. They also argued that the dacite por-
7.8 Gt at 0.018 percent Mo (1.4 Mt of pure Mo). phyry had a late to postmineralization timing, either remov-
Recently, Skewes et al. (2002) argued that El Teniente ing preexisting copper mineralization or remobilizing it into a
should not be considered a porphyry Cu deposit but rather a stockwork.
In this paper we document and interpret the geologic his-
† Corresponding author: e-mail, j_cann@yahoo.com
tory, mineralization, alteration, geochronology, and structural
*Current address: Lane Xang Minerals Limited, Sepon Copper Project, framework of El Teniente. We have based the study on log-
Laos. ging of 20 km of drill core, combined with petrography from

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980 CANNELL ET AL.

2002), which formed in a tholeiitic arc setting overlying thin

continental crust (Kay et al., 1999; Charrier et al., 2002). The
contact between the two units is structural or locally uncon-
formable (Thiele et al., 1991; Godoy et al, 1999). Charrier et
al. (2002) suggested that deposition of the Coya-Machali For-
mation is related to crustal extension, and an increase in con-
vergence rates between the Nazca and South American plates
led to tectonic inversion, followed by deposition of the Farel-
lones Formation.
The Coya-Machali and the Farellones Formations in the
Teniente district were intruded by a series of calc-alkaline fel-
sic to intermediate intrusions between 12 and 7 Ma. These
are termed the Teniente plutonic complex, and include the
Sewell Tonalite and/or diorite intrusive complex (dated be-
tween 8.9 and 7 Ma; Cuadra, 1986; S. Kay and A. Kurtz, 1995,
unpub. report for CODELCO; Kurtz et al., 1997). The
youngest intrusions known from the district occur within the
Teniente deposit. They include the dacite and latite por-
phyries (5.67 ± 0.19–4.82 ± 0.09 Ma: Maksaev et al., 2004)
and lamprophyre dikes (3.8–2.9 Ma: Cuadra, 1986; Maksaev
et al., 2004).
Mapping by O. Rivera and M. Falcón (1998, unpub. report
for CODELCO) identified four remnant volcanic centers
with ages of 11 to 9 Ma in the Teniente district. They are as-
sociated with subvolcanic andesitic intrusions and lie on a
northwest–north-northwest–trending lineament termed the
Codegua fault (Fig. 2). This structural feature is apparent in
FIG. 1. Locality map—El Teniente is located in the central Chilean late local- to regional-scale aeromagnetic maps, but surface ex-
Miocene-Pliocene porphyry-Cu belt. Also shown is the approximate bound- pressions are difficult to find. Based on the aeromagnetic
ary between the Southern volcanic zone (SVZ) and the nonvolcanic flat-slab
segment (modified from Serrano et al, 1996; Camus, 2002). Other giant por- data, the Codegua fault is interpreted to be a basin-bounding
phyry copper-molybdenum deposits occur at Los Pelambres and Río Blanco- structure that has undergone significant vertical movement
Los Bronces, and copper-molybdenum porphyry prospects occur at Vizca- and has caused accumulation of volcanic debris to the south
chitas and Rosario de Rengo. (P. Gow, pers. commun., 2000). Northwest-trending arc-
transverse structures, such as the Codegua fault, have influ-
enced the formation of Miocene volcanotectonic basins
approximately 200 thin sections. Logged drill holes were cho- throughout central Chile (Rivera and Cembrano, 2000;
sen mainly from three cross sections with additional drill Rivera and Falcón, 2000). These structures are believed to
holes selected to gain information from as much of the de- have formed due to reactivation of north-northwest–west-
posit as possible. We provide a temporal analysis of the struc- northwest–trending Mesozoic basement structures during
tural evolution of the deposit, based on a structural database the development of the Andean Cordillera (Rivera and Cem-
compiled by mine geologists (4,337 vein orientation measure- brano, 2000; Rivera and Falcón, 2000).
ments from underground exposures). We provide evidence El Teniente is situated close to the intersection between
that supports the conventional porphyry Cu model con- the Codegua fault and the Teniente fault zone (Fig. 2). The
structed progressively by previous workers (Howell and Mol- Teniente fault zone is a 14-km-long zone of anastamosing
loy, 1960; Camus, 1975; Cuadra, 1986). Apart from its ex- faults trending northeast–east-northeast, which are associated
treme size, El Teniente shows many features typical of with strongly developed unmineralized argillic alteration
porphyry Cu deposits, and we argue that it should be classi- (Agua Amarga prospect: Camus, 1975; Cuadra, 1986; R.
fied as such. We use our results here to demonstrate how the Floody and C. Huete, 1998, unpub. report for CODELCO).
shallow emplacement of a composite felsic intrusive complex
has controlled the hydrothermal and structural evolution of Deposit Geology
El Teniente, in contrast to the mineralized breccia model of
Skewes et al. (2002). Mine andesites
The principal host rocks at El Teniente are the mine an-
Geologic Setting desites, traditionally grouped as part of the Farellones For-
The mid-late Miocene Farellones Formation hosts El Te- mation (Fig. 3). The textural and geochemical features of the
niente. It is a flat-lying sequence of arc-related volcanic and mine andesites have been obscured by widespread, pervasive,
volcaniclastic rocks located trenchward of the current vol- texturally destructive biotite alteration, and they have been
canic front (Fig. 1). The Farellones Formation is underlain by interpreted in different ways by previous workers. Lindgren
the Coya-Machali Formation (23–15 Ma; O. Rivera, 1999, and Bastin (1922) described the host rocks as intrusive an-
unpub. for CODELCO; Godoy et al., 1999; Charrier et al., desites, and Howell and Molloy (1960) described them as

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 981

thick, massive andesite flows of the Farellones Formation,

with rare intercalated breccia lenses. A. Skewes (1998, 1999,
unpuplished reports for CODELCO) and Skewes et al.
(2002) described them as crystal-supported gabbroic intru-
sions, cut by a complex of biotite-matrix hydrothermal
breccias.
Based on detailed core logging and thin section petrogra-
phy we have reclassified the rock units (Table 1) and logged
their occurrence in drill core in several cross sections through
the deposit (e.g., Fig. 4). In agreement with Lindgren and
Bastin (1922) and Skewes et al. (2002), we interpret the mine
andesite package as a sill and stock complex containing crys-
tal-supported, feldspar ± hornblende-phyric to aphanitic an-
desite sills (Fig. 5A). The sills have intruded andesitic lava
flows (Fig. 5B) and volcaniclastic units (Fig. 5D) of the Farel-
lones Formation. Microprobe analyses indicate that the pla-
gioclase phenocrysts are strongly calcic (An46–An92, mostly
between An60 and An85: Skewes, 1997, 1998, unpuplished re-
ports for CODELCO; Skewes et al., 2002; Cannell, 2004).
The distribution of the mine andesites in section 83 is
shown in Figure 4. On the east side of the dacite porphyry,
the andesite porphyry sill complex is the predominant host
rock to mineralization below the 2,200-m level. The andesitic
sill complex is at least 450 m thick in this section. Fine-
grained andesite porphyry concordantly underlies a volcanic
breccia zone on the east side of the dacite porphyry. Clasts of
andesite porphyry in the volcanic breccia (Fig. 5D) suggest
that the andesite porphyry unit is either partly extrusive or
was uplifted and eroded after emplacement. The presence of
amygdales and rare domains of intermingled sediment and
andesite on the upper margins of the fine-grained andesite
porphyry (interpreted to be peperite) support a shallow in-
trusive origin for the igneous units. Based on textural and
mineralogical similarities we correlate the andesite porphyry
in the Teniente mine with mafic to intermediate subvolcanic
rocks described and mapped to the east of Teniente (andesite
intrusions in Fig. 2) and around the Agua Amarga prospect to
the west of the mine (R. Morel and C. Spronhle, 1992,
unpub. report for CODELCO; Skewes et al., 2002). The sur-
rounding Farellones Formation consists of subhorizontal,
predominantly fine-grained, undifferentiated volcaniclastic
units, volcanic breccias (Fig. 5D), and coherent volcanic
flows. On the western side of the dacite porphyry, the fine-
grained andesite porphyry cuts the volcanic and/or volcani-
clastic sequence discordantly. Apparently subvertical, sube-
quigranular stocks intruded the sill complex on the periphery
of the ore deposit. The host sequence is cut by vertical, thin,
fine-grained, porphyritic andesite dikes and late-stage hy-
drothermal biotite-matrix breccias (up to 30-m apparent
thickness; Fig. 5C; see below). In contrast to the conclusion
of Skewes et al. (2002), the biotite breccias in section 83 are
volumetrically minor (Fig. 4), and most of the wall rocks, al-
though altered and veined, are not brecciated.
Nine samples of altered mine andesites were analyzed for
their major and trace element compositions (Table 2). Altered
FIG. 2. Geology of the Teniente district. A northwest-trending lineament mine andesites have SiO2 contents between 46 and 57 wt per-
of relict eruptive centers occurs along the postulated Codegua fault within a cent (Table 2; Camus, 1975; Villalobos, 1975; Skewes et al.,
volcano-sedimentary basin. El Teniente occurs close to the intersection of
the Codegua fault with the northeast-trending Agua Amarga fault, part of the 2002) and trace element ratios that classify them geochemi-
Teniente fault zone. Modified from O. Rivera and M. Falcón (1998, unpub- cally as gabbro or diorite (Fig. 6, Table 2). However, due to
lished report for CODELCO). the large extent of the Teniente alteration system (>4 × 3

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982 CANNELL ET AL.

FIG. 3. Geology of Teniente level 6 (2,165 m), showing the locations of sections 83 and 124. This plan has been modified
from the geologic data, based on underground mapping, contained in the mine database (data courtesy of CODELCO).

TABLE 1. Lithofacies of the Farellones Formation and Mine Andesite Sill and Stock Complex, El Teniente

Lithotype Distribution/ occurrence Features Interpretation

Crystal-poor Rare; mainly occurs on Porphyritic, 20 to 30% fine- to coarse-grained plagioclase Coherent volcanic flow
euhedral andesite unit west side of section 83 phenocrysts and rarely preserved hornblende; fine
groundmass, + amygdales
Crystal-poor Predominant unit above Less coherent, subhedral to anhedral plagioclase crystals; Volcaniclastic origin
anhedral unit 2,200-m elevation in mine fine-grained to aphanitic groundmass, occasionally with
quartz grains and feldspar crystals
Horizontal Thin horizontal units in volcani- Contain abundant polylithic subrounded clasts up to tens of Volcaniclastic breccias
breccia zones clastic zones; abundant in centimeters wide
section south of Braden Pipe
Coarse-grained Stocks/sills; locally Porphyritic crystal rich (30–50% plagioclase phenocrysts) sub- Sill/stock intrusive
andesite porphyry >450 m thick, sills up to to euhedral to equant plagioclase phenocrysts, coarse grained complex
100 m thick (>2 mm long phenocrysts), crystal- to groundmass-supported;
rare hornblende crystals and amygdales; heterogeneous
complex, variation in phenocryst size, and abundance
Fine-grained Spatially associated and As above but phenocrysts <2 mm, up to 60% of rock; can Sill complex
andesite porphyry typically surrounding the be fine-grained equigranular; ± amygdales ± autobrecciated
coarse andesite porphyry unit margins
Gabbro One stock on far west Equigranular, coarse grained Stock
side of section 83
Diorite Porphyry Subvertical stocks and Medium- to coarse-grained, crystal rich, 40 to 70% equant Stock and dikes
dikes <10 m wide to anhedral interlocking plagioclase phenocrysts; light gray
Andesite dikes Subvertical dikes <5 m 20 to 40% phenocrysts, coarse- to fine-grained phenocrysts Dikes (low level of
thick, sharp contacts (± polycrystalline aggregates) in a fine groundmass of alteration suggests
interlocking/ aligned microliths late timing)
Biotite Breccias Subvertical breccia zones (one Composed of polylithic, andesitic to leucocratic clasts some Hydrothermal breccias
in section 83 is inclined 30°), of which are altered and veined; matrix composed of biotite, associated with
typically <5 m (up to 30 m) quartz, anhydrite, sulfides; can be well mineralized intrusion of the dacite

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 983

FIG. 4. Geologic cross section 83 (located at 1000N), showing the interpreted distribution of lithofacies of the mine an-
desite sill and stock complex and the biotite breccias, based on logging of 14 drill holes in this section (drill holes labeled as
DDH 1293, etc.). A number of thin porphyritic andesite dikes cut the sequence but are too thin to be shown at this scale.
The distribution of the felsic intrusions, supergene zone, and colluvium in this section was obtained from the mine database,
courtesy of CODELCO, and is based on more drill holes than those indicated. The dashed line represents the limits of >0.5
percent Cu mineralized ore shell. Additional geologic cross sections are contained in Cannell (2004). In the supergene zone
anhydrite has been dissolved and the feldspars are altered to kaolinite. Rock textures are mostly preserved in this zone.

km), no fresh rocks have been identified to date that are un- age distributions, with peaks at 6.46 ± 0.11 to 6.11 ± 0.13 and
ambiguously equivalent to the Teniente mine andesites. The 5.67 ± 0.19 to 5.48 ± 0.19 Ma (Table 3). Maksaev et al. (2002)
major elements (including K, Na, Ca and Si) are likely to have interpreted the older ages to be inherited from previously
been mobile during the processes of potassic alteration, hence crystallized zircons and the younger ages to be the ages of
the primary mine andesite compositions are not known. final crystallization, whereas Maksaev et al. (2004) inter-
preted the older ages to be the intrusion ages and the younger
Felsic to intermediate intrusions and the Braden Pipe ages to relate to hydrothermal activity.
A series of felsic to intermediate intrusions were emplaced The dacite pipes (5.50 ± 0.24 Ma: Table 3; Figs. 3, 4) and
into the andesitic host rocks (Table 3). The premineralization the dacite porphyry dike (5.28 ± 0.10 Ma: Table 3; Fig. 3) are
plagioclase-hornblende-phyric Sewell Tonalite (Fig. 3) is the plagioclase (±quartz, biotite) phyric porphyries with an aplitic
oldest felsic to intermediate intrusion in the deposit (Table 3). groundmass. They are temporally and spatially related to Cu-
Two textural varieties are identified (Camus, 1975; Guzman, and Mo- bearing veins and potassic alteration (Camus, 1975;
1991), an inner equigranular phaneritic phase and an outer Villalobos, 1975; Zúñiga, 1982; Guzman, 1991). Ossandón
porphyritic phase (Table 3). In section 124, the biotite-pla- (1974) and Rojas (2002) have identified discrete intrusive
gioclase-K-feldspar-phyric gray porphyry intruded the Sewell phases of the dacite porphyry dike based on phenocryst sizes,
Tonalite (Table 3, Fig. 3). Thin, cylindrical to irregular felsic abundances, proportions, and form (Table 3). K-feldspar is a
intrusions occur in the north and east of the deposit (Fig. 2). rare phenocryst phase in all of the dacite intrusions but is lo-
These were previously termed quartz diorite and/or tonalite cally abundant in the groundmass. Quartz phenocrysts are
apophyses (e.g., Camus, 1975; Cuadra, 1986), however based also uncommon in the dacites (typically <2%), but quartz is
on their mineralogy and geochemistry (see below) in this abundant in the groundmass (approx 20%). Rare primary (?)
study they are reclassified as dacite pipes. anhydrite occurs as a fine groundmass constituent. The
U-Pb SHRIMP dating of zircons by Maksaev et al. (2002, dacites locally have igneous breccias, characterized by wall-
2004) has shown that the porphyritic phase of the Sewell rock clasts in an igneous dacitic groundmass, at their contacts
Tonalite, the gray porphyry, and thedacite pipes have bimodal (Skewes et al., 2002).

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FIG. 5. Lithotypes of the mine andesite sill and stock complex. A. Coarse-grained, crystal-rich andesite porphyry, with >40
percent subhedral plagioclase phenocrysts. Crystal to groundmass supported (ET112A, DDH1698, 14.6 m). B. Coarse-
grained, porphyritic crystal-poor andesite, euhedral to subhedral plagioclase phenocrysts, interpreted to be a coherent an-
desite flow (Ten, level 6). Late magmatic veins with dark-colored biotite halos cut the lighter colored, pervasive early mag-
netite alteration assemblage. C. Biotite breccia containing subrounded felsic and mafic clasts (ET69, DDH1689, 42.4 m). D.
Volcaniclastic breccias. Top, monomictic breccia containing subangular andesite porphyry clasts in a secondary biotite-rich
matrix (ET649, DDH1698, 18.9 m). Bottom, monomictic breccia composed of subangular dark- to light-gray aphanitic clasts,
some with curviplanar edges, in a gray aphanitic matrix containing fine biotite-altered mafic crystals (ET786, DDH1409,
293.7 m).

The Braden Pipe is a massive, late to postmineralization brec- sorted, polymictic breccia with a rock flour-matrix and both
cia pipe with low copper grade that occurs in the center of the stratified and unstratified facies. The breccia contains abun-
deposit. It has an inverted cone shape, is 1,200 m wide at sur- dant, subrounded to subangular, phyllic-altered wall-rock
face, with 60º to 80º inward-dipping walls (R. Floody, 2000, fragments that contain truncated veins. Clasts of the Marginal
unpub. report for CODELCO). A lower contact was inter- Breccia are scarce within the Braden Breccia (R. Floody,
sected 1,400 m below surface in the deepest drill hole, which 2000, unpub. report for CODELCO), suggesting that the
passes into an underlying latite stock. The Braden Pipe is made original spatial extent of the Marginal Breccia was probably
up of two principal breccia facies, the mineralized Marginal similar to its present day distribution.
Breccia and the largely barren Braden Breccia (dated by K/Ar Plagioclase-phyric latite dikes are the youngest altered intru-
on sericitic clasts at 4.7 and 4.6 Ma, respectively: Cuadra, 1986). sions in the deposit, dated at 4.8 Ma (Table 3). They are seric-
The Marginal Breccia is a <1- to 60-m-thick monomictic, itized and occur as northwest- to west-trending dikes or as ring
clast-supported breccia unit that occurs as a rim around the dikes <15 m thick that occur concentrically around the Braden
Braden Pipe (Fig. 3). This breccia has tourmaline-rich ce- Pipe (Cuadra, 1986). Pebble dikes, typically <2 m wide, con-
ment, with accessory sulfates, sulfides, and sulfosalts and is taining rounded sericitized clasts also occur as incomplete ring
associated with local angular wall-rock clasts with phyllic dikes around the Braden Pipe. The youngest known intrusions
(quartz, sericite, chlorite) alteration. The Braden Breccia in the deposit, and in the Teniente district, are thin northeast-
occurs in the central part of the Braden Pipe and is a poorly trending lamprophyre dikes (3.8–2.9Ma: Table 3).

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TABLE 2. Whole-Rock Geochemistry of the Mine Andesites

Andesite
Coarse andesite porphyry Fine andesite porphyry Gabbro dike

ET765 ET671 ET640 ET742 ET777 ET407 ET756 ET768 ET263

DDH1689, DDH1306, DDH1565, DDH1314, DDH1981, DDH1423, DDH1317, DDH1530, DDH1529,
272.8 m 208.2 m 451.6 m 33.8 m 221.0 m 506.6 m 12.2 m 655 m 195.1 m

SiO2 (wt %) 49.3 46.22 51.03 50.23 53.18 54.59 53.46 50.91 53.58
TiO2 0.98 1.17 1.26 1.11 1.02 0.93 1.04 0.96 1.05
Al2O3 18.62 20.71 20.18 19.26 17.31 17.8 17.84 18.08 18.58
Fe2O3 6.27 6.23 6.22 8.54 9.5 8.83 5.19 10.13 7.9
MnO 0.05 0.04 0.06 0.05 0.08 0.06 0.03 0.16 0.06
MgO 6.42 4.5 4.16 4.69 5.5 3.58 5.39 6.02 3.93
CaO 7.12 7.2 7.54 6.88 6.5 5.86 5.98 7.49 6.98
K2O 3.76 3.42 2.39 2.41 1.85 2.3 3.49 2.67 1.23
Na2O 2.31 4.38 3.11 2.82 1.95 3.34 2.93 1.44 2.65
P2O5 0.2 0.23 0.27 0.25 0.22 0.22 0.24 0.18 0.22
LOI 4.74 5.07 3.14 3.44 2.87 2.66 4.19 2.15 3.74
Total 99.77 99.17 99.36 99.68 99.98 100.17 99.78 100.19 99.92

Ti (ppm) 22541 20503 14328 14448 11091 13789 20923 16007 7374
P 873 1004 1178 1091 960 960 1047 786 960
Cr 97 38 24 15 103 6 107 151 8
Ni 47 25 17 17 45 8 42 59 8
Rb 173 175 103 139 103 121 204 131 74
Sr 425 491 528 453 358 523 471 351 480
Ba 291 346 307 83 142 269 147 175 114
Sc 30 34 33 30 27 23 31 31 30
V 332 332 372 274 240 232 291 279 278
Nb 2 2 3 2 4 3 4 2 3
Zr 65 70 95 90 140 96 137 95 84
Th 2 2 3 2 5 3 4 4 2
Y 15 16 18 22 19 18 19 16 18
La 11 10 10 6 12 16 12 7 7
Ce 25 28 25 20 31 25 30 14 18
Nd 15 14 14 13 18 14 17 9 12
Cu 7085 15600 4526 395 278 149 525 125 1976
Zn 50 48 52 52 58 53 26 68 48
Mo 25 94 12 3 2 3 1 2 3
Pb 3 10 4 4 3 4 3 2 5

Notes: Samples were analyzed by X-ray fluorescence (XRF) at the University of Tasmania; total iron reported as Fe2O3

The dacite porphyry, dacite pipes, and latite dikes are all
geochemically similar, classified as calc-alkaline dacites
(61–68 wt % SiO2: A. Skewes, 1998, 2000, upub. reports for
CODELCO; Rojas, 2002; Skewes et al., 2002; Table 4), al-
though data for dacite pipes from Villalobos (1975) span an
SiO2 range from 50 to 67 wt percent. The Sewell Tonalite
samples vary from 60 to 66 wt percent SiO2 (Guzman, 1991;
Reich, 2000; Table 4). There is no consistent trend to more
felsic or mafic compositions through time. A single analysis of
altered gray porphyry indicates 51 wt percent SiO2 (Table 4),
consistent with a basaltic composition. The sample contains
abundant volatile components due to hydrothermal alteration
(loss on ignition of 11 wt %), and it is possible that SiO2 re-
moval occurred during potassic alteration, producing the
anomalously low silica content.
Vein and Alteration Paragenesis
Based on our detailed observations throughout the de-
FIG. 6. Zr/TiO2 vs. SiO2 plot for least altered El Teniente mine andesites, posit, copper and molybdenum mineralization at El Te-
showing the compositional fields of Winchester and Floyd (1978). The
coarse-grained andesite porphyries and the gabbro are more mafic than the
niente is hosted mostly within a vein stockwork in the mine
fine-grained andesite porphyries and the andesite dike. Abbreviations: Ab = andesites and dacite intrusions. This contrasts with Skewes
alkali basalt, Bsn/Nph = basanite, nephelinite, TrAn = trachyandesite. et al. (2002) who concluded that mineralization is predom-

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986 CANNELL ET AL.

TABLE 3. Petrography and Geochronology of Felsic to Intermediate Intrusions, El Teniente

Intrusion Subtype Location Mineralogy Texture Age References1

Sewell Equigranular Stock in southeast Plagioclase, hornblende, Equigranular 7.4 ± 1.0 to 7.1 ± 1.5 Ma Sewell diorite/
Tonalite corner of deposit biotite, K-feldspar, (K/Ar, Cuadra, 1986) tonalite of
quartz, sericite, chlorite, Camus (1975),
epidote Faunes (1981),
Guzman (1991),
Porphyritic Outer carapace Plagioclase, biotite, Porphyritic, 6.15 ± 0.16 and 5.59 ± Kurtz et al. (1997)
to stock K-feldspar, quartz, 30 to 50% 0.17 Ma (SHRIMP
sericite, chlorite, phenocrysts, U-Pb on zircon,
anhydrite aplitic groundmass Maksaev et al., 2004)

Gray Intruded the Plagioclase, biotite, Porphyritic, 6.46 ± 0.11 and 5.67 ± Cuadra (1992),
porphyry Sewell Tonalite K-feldspar (perthite), inequigranular 0.19 Ma (SHRIMP Skewes et al. (2002)
near its contact anhydrite groundmass U-Pb on zircon;
with mine Maksaev et al., 2004)
andesites 5.1–6.0 Ma (K/Ar on
biotite; Cuadra, 1992).

Dacite Various (>6) pipes Plagioclase (An16-–0), Porphyritic, 6.28 ± 0.16 and 5.50 ± Quartz diorite/
pipes east of dacite quartz, biotite 30 to 50% 0.24 Ma, 6.11 ± 0.13 tonalite apophyses
porphyry. also has phenocrysts in phenocrysts, and 5.48 ± 0.19 Ma of Villalobos (1975),
intruded Sewell quartz-plagioclase- groundmass is (SHRIMP U-Pb on Camus (1975),
Diorite along K-feldspar, groundmass aplitic (<0.12 mm), zircon; Maksaev Guzman (1991),
contacts? to coarse grained et al., 2004)
(up to 0.5 mm)

Dacite Euhedral Northern end of Plagioclase (An7-–39), Euhedral 5.28 ± 0.1 Ma (SHRIMP Ossandon (1974),
porphyry 1,500- × 200-m quartz, biotite pheno- phenocrysts, U-Pb on zircon; Skewes et al. (2002),
Dacite dike crysts in quartz- aplitic groundmass Maksaev et al., 2004) Rojas (2002)
plagioclase-K-feldspar, 4.7–4.5 Ma (K/Ar on
groundmass biotite, Cuadra, 1986,
Subhedral Central portion Subhedral 1992)
of Dacite dike phenocrysts, coarse
groundmass
Igneous Contacts of all Plagioclase, K-feldspar, Wall-rock xenoliths Undated Ossandon (1974),
breccia intrusive units biotite, quartz pheno- <20% Rojas (2002)
above crysts in quartz-feldspar-
biotite groundmass

Latite dikes Concentric to Plagioclase (An30-–70), Porphyritic, 4.82 ± 0.09 Ma, (SHRIMP Riveros (1989)
Braden Pipe and quartz, biotite pheno- 30 to 50% pheno- U-Pb on zircon;
northeast-trending crysts in quartz- crysts, very fine Maksaev et al., 2004)
thin dikes plagioclase-K-feldspar aplitic groundmass 5.3 (± 0.7)–4.8 (± 0.6) Ma
groundmass, sericitized (<0.02 mm) (K/Ar on biotite, sericite,
plagioclase; P. Cuadra,
1992, unpub. report for
CODELCO)

Lamprophyre Northeast- Hornblende, pyroxene, Fine-grained, 3.85 ± 0.18 Ma (Ar40/Ar39 Cuadra (1986)
dikes trending thin dikes olivine, plagioclase porphyritic on hornblende;
Maksaev et al., 2004)
3.8 and 2.9 Ma (K/Ar:
Cuadra, 1986)

1 Table supplemented with information from the following unpublished reports for CODELCO: J. Ojeda, E. Hernandez, G. Ossandon and A. Enrione

(1980); P. Cuadra (1992); A. Skewes (1997)

inantly breccia hosted. The 0.5 percent Cu contour in the around the Braden Pipe. There is a zoned distribution of
Teniente level 6 outlines a wedge-shaped zone approxi- sulfide minerals, with bornite occurring in the center of the
mately 2.5 km long, 1.8 km wide (Fig. 3) and more than 800 deposit at the southern end of the dacite dike, passing out-
m deep, with high-grade hypogene zones (>1.2% Cu, for ward to an intermediate annular domain characterized by
100s of meters) localized around intrusive centers (e.g., Es- chalcopyrite and finally to a pyrite (±pyrrhotite inclusions)
merelda, sub-6). High grades also occur in the supergene domain occurring on the periphery (Camus, 1975; Cuadra,
zone, which locally extends down deeper around the dacite 1986, A. Arevalo and R. Floody, 1995, unpub. report for
porphyry due to higher fracture intensities (Skewes et al., CODELCO).
2002). Higher molybdenum grades (>0.03% Mo) occur lo- Alteration and vein assemblages at El Teniente were di-
cally around the dacite intrusions and as a concentric ring vided by previous workers into four stages: the late magmatic,

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 987

TABLE 4. Geochemistry of the Felsic to Intermediate Intrusions at El Teniente

Gray
Sewell Tonalite Dacite porphyry Dacite pipes porphyry Latite porphyry Lamprophyre

CE52 ET720 ET811 ET585 ET789 ET769 ET701 ET534 ET820 ET779 ET782 ET788 ET452 ET754
2 km DDH DDH DDH DDH DDH DDH DDH DDH DDH DDH DDH DDH DDH
S of 1463, 1291, 1525, 1505, 1297, 1889, 1676, 1680, 1981, 1079, 1068, 855, 1314,
Sewell 423.1 m 423.7 m 33.2 m 3.0 m 299.0 m 215.8 m 458.4 m 316.7 m 346.6 m 435.6 m 1012.9 m 387.7 m 386.6 m

(wt %)
SiO2 59.9 61.12 65.47 67.62 64.66 66.14 1889 735 50.83 64.27 65.89 68.41 55.64 55.78
TiO2 0.69 0.55 0.38 0.36 0.35 0.39 0.38 0.36 0.44 0.31 0.31 0.34 0.77 0.85
Al2O3 16.26 17.35 16.85 16.87 15.92 17.21 16.32 16.77 12.91 15.72 16.35 17.18 15.81 17.57
Fe2O3 7.54 2.61 0.68 0.89 0.63 1.88 1.04 1.31 3.76 1.78 2.1 1.34 4.88 5.64
MnO 0.15 0.03 0.01 0.01 0.01 0.01 0.02 0.01 0.03 0.07 0.03 0.01 0.11 0.08
MgO 2.78 1.87 0.93 0.98 0.89 0.84 1.23 1.03 1.94 0.74 0.78 0.8 3.12 3.71
CaO 3.4 3.6 3.21 1.35 3.31 3.12 3.82 2.94 8.56 4.89 2.03 2.71 6.67 5.86
K2O 2.12 3.81 2.59 3.36 2.81 2.63 2.22 3.06 6.67 4.21 4.92 0.98 1.78 1.5
Na2O 5.8 4.82 6.03 5.47 6.29 5.61 5.72 5.42 2.13 1.35 4.02 7.09 3.55 4.51
P2O5 0.18 0.34 0.14 0.13 0.14 0.13 0.14 0.14 0.21 0.12 0.13 0.13 0.25 0.28
LOI 1.04 3.74 3.29 2.15 4.17 2.07 4.7 2.33 10.99 6.66 3.47 1.04 7.17 4.27
Total 99.86 99.84 99.58 99.19 99.18 100.03 99.55 99.27 99.47 100.12 100.03 100.03 99.75 100.05

(ppm)
Ti 12,709 22,841 15,527 20,143 16,846 15,767 13,309 18,345 39,987 25,239 29,495 5,875 10,671 8,993
P 786 1,484 611 567 611 567 611 611 916 524 567 567 1,091 1,222
Cr 39 15 6 7 6 5 10 6 18 5 4 4 76 73
Ni 14 10 4 5 3 1 6 4 2 2 3 41 45
Rb 54 203 65 84 61 51 85 72 209 160 140 32 42 28
Sr 407 608 773 486 611 771 627 782 536 228 331 711 736 956
Ba 464 524 628 657 485 712 417 854 692 564 742 238 376 414
Sc 13 8 5 5 4 3 5 4 9 3 4 3 14 14
V 175 103 66 75 72 63 79 72 203 56 52 66 141 148
Nb 3 3 2 3 2 3 2 2 3 2 2 2 3 4
Zr 114 107 91 91 85 93 94 94 78 99 87 100 125 133
Th 10 2 3 4 4 2 2 4 3 2 5 4 3 2
Y 12 8 4 4 4 4 5 3 9 4 3 4 9 8
La 12 16 13 11 9 12 14 11 37 15 13 7 14 15
Ce 25 37 30 24 29 30 27 26 72 29 27 16 37 41
Nd 14 18 14 12 13 14 12 12 33 11 12 8 21 23
Cu 107 1,136 1,387 5,215 5,806 623 2,460 4,625 10,100 18 1,426 6 46 47
Zn 123 36 17 28 27 17 41 32 34 35 26 34 102 76
Mo 78 12 8 52 38 2 161 47 255 1 22 4 2 2
Pb 52 3 6 5 12 4 6 9 9 4 2 16 12 7

Notes: Samples were analyzed by X-ray fluorescence (XRF) at the University of Tasmania; total iron reported as Fe2O3

principal hydrothermal, late hydrothermal, and “postuma” A phyllic (tourmaline + sericite, chlorite, magnetite) alter-
stages (Villalobos, 1975; Cuadra, 1986, Skewes et al., 2002). ation assemblage formed adjacent to the Sewell Tonalite. It is
We have modified this basic paragenesis by adding a prem- locally associated with thick, barren quartz veins (type 1b,
ineralization stage and by combining the postuma stage with Table 5). No copper or molybdenum mineralization was asso-
the late hydrothermal stage (Table 3). We have also identified ciated with this phyllic alteration.
multiple vein generations within each of the main paragenetic
stages, as described below. Late magmatic stage (type 2 veins)
Emplacement of quartz-anhydrite-sulfide stockwork veins
Premineralization stage (type 1 veins) and extensive potassic alteration occurred during the late
A magnetite + quartz + anhydrite + actinolite + calcic pla- magmatic stage, synchronous with intrusion of the dacite.
gioclase (An 94–An 40) ± epidote alteration assemblage pre- The relative proportion of copper introduced during the late
dates mineralization at El Teniente (Skewes et al., 2002; Fig. magmatic stage (and the principal hydrothermal and late hy-
7A; Cannell, 2004). This assemblage varies from pervasive to drothermal stages) was estimated systematically during core
vein controlled and occurs in association with magnetite logging. In the holes examined in this study, approximately 60
veinlets (type 1a). Primary plagioclase phenocrysts have been percent of the copper in the logged drill holes was introduced
partially replaced by fine disseminated magnetite (Fig. 7B). during the late magmatic stage.
Remnants of this early magnetite alteration assemblage are Type 2a veins are rare, wavy-edged quartz veins that con-
preserved in andesitic units throughout the mine but are best tain minor chalcopyrite and bornite. They are the earliest
preserved on the deposit margins. formed veins in the felsic intrusions at Teniente (Table 3).

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988 CANNELL ET AL.

FIG. 7. Alteration styles at El Teniente. A. Fine andesite porphyry showing early magnetite alteration, which produced
abundant secondary magnetite (typically 10–30 vol % of the rock) and variable amounts of actinolite. Note that primary ig-
neous textures are preserved (ET604, DDH1565, 117.5 m, crossed polars). B. Late magmatic vein, on the left of the photo,
with a biotite ± rutile halo that has preferentially altered the groundmass of early magnetite-altered mine andesite (right side
of the dashed line). This is visible at the hand-sample scale in Figure 5B. Magnetite dusting in the plagioclase phenocryst is
preserved (ET91, DDH1689, 236.4 m, plane-polarized light). C. Biotite-altered mine andesite. Aggregates of chalcopyrite, bi-
otite, anhydrite, and rutile have replaced a primary mafic mineral (hornblende?; ET671, DDH1306, 208.3 m, plane-polarized
light). D. Thin, diffuse brown biotite veinlets (+ minor anhydrite, chlorite, sulfides) and intense, texturally destructive biotite
alteration that has overprinted the plagioclase phenocrysts and groundmass crystals. Groundmass magnetite has been altered
to biotite ± rutile and sulfides. Biotite also occurs as a halo around the crosscutting late magmatic vein (ET664, DDH1306,
107.7 m, plane-polarized light). E. Pervasive alteration assemblage from the transitional potassic-propylitic zone (>300 m from
dacite porphyry). Green-brown biotite is intergrown with clots of chlorite, sulfide (pyrite and chalcopyrite), and anhydrite
(clear). Sericite needles and/or chlorite fans are intergrown with the disseminated and vein-hosted sulfides (ET62, DDH1738,
428.2 m plane-polarized light). F. Chalcopyrite + quartz + anhydrite principal hydrothermal vein with a phyllic halo. Note that
the phyllic halo is zoned from inner sericite to outermost chlorite (ET44, DDH1738, 186.1 m). Abbreviations: act = actino-
lite, anh = anhydrite, bt = biotite, chl = chlorite, cpy = chalcopyrite, mag = magnetite, plag = plagioclase.

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 TABLE 5. Summary of Vein Paragenesis, Alteration, and Mineralization1

Abundance Associated intrusions,

Vein type Mineralogy Features Cu Mo VA alteration, sulfides

Premineralization stage

1a veins Magnetite, Ca plagioclase, quartz, Thin, to several centimeters thick; diffuse veins with - - R Early magnetite alteration; related to
actinolite, anhydrite early magnetite alteration halo Sewell Tonalite?

1b veins Quartz ± tourmaline, sericite, chlorite Quartz veins (dikes) up to 8 m thick - - R Early phyllic alteration (sericite, chlorite,

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tourmaline); related to Sewell Tonalite?

Late magmatic (LM) stage

Anhydrite- Anhydrite breccias, veins + chalcopyrite Similar to type 2d anhydrite breccias, includes biotite or A C R Early - Associated with potassic
sulfide-biotite (±biotite, tourmaline, feldspar) tourmaline; includes biotite-bearing vein types gray alteration (biotite, Na-K-
breccias porphyry feldspar), grading to distal
2a veins Quartz ± chalcopyrite, bornite, anhydrite Wispy, wavy-edged, thin, rare veins in dacite intrusions C - R Main propylitic alteration (chlorite,
sericite, magnetite, epidote)
dacite
2b veins Chlorite, sulfide, anhydrite, quartz-biotite- Abundant, zoned veins, with Na-K-feldspar halos; 1 mm C R A Type 2 distal (sericite-chlorite
porphyry
Na-K-feldspar, anhydrite, quartz halo to 4 cm thick; temporal overlap with type 2c and 2d veins stable), and type 2 chlorite veins
dyke +
predominate in peripheral zones
pipes
2c veins Quartz, anhydrite, sulfide (±K-feldspar, Abundant, submillimeter to 4 cm thick; ±biotite halo C R A of deposit
chlorite, biotite)
Contains bornite, chalcopyrite,
2d breccias Anhydrite breccias (±sulfide) Crackle breccia; associated with contacts of dacite C - R molybdenite
intrusions; ±Na-K-feldspar or biotite halo

989
2e veins Quartz, sulfide (±anhydrite) Thick (5 mm–3 cm), continuous, straight-edged; typical C C C Late
sulfide (+ molybdenite) seam and /or selvage; ±biotite
or phyllic halo
2 chlorite Sulfide, chlorite (±anhydrite, quartz, Thin (<5 mm), abundant in propylitic zone; + chlorite, C R C
veinlets sericite, biotite) sericite halo; commonly form central seam in reopened
veins (e.g., type 2b)

Principal hydrothermal (PH) stage

3 veins Quartz, anhydrite, sulfide Thick (up to 4cm) chalcopyrite-rich veins, minor gangue A C C Phyllic halos + pervasive alteration; sulfides
EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE

quartz and anhydrite; well developed sericite, chlorite, are chalcopyrite, pyrite, molybdenite (bornite
quartz halos absent); concentrated distally from dacite dike

Late hydrothermal (LH) stage Second phyllic (±illite) alteration stage,

related to intrusion of Braden Breccia and
4a breccias Tourmaline, anhydrite, sulfide “Crackle breccia” and veins; pale sericite halo, tourmaline C - R latite dikes; veins are concentrated close to
(±gypsum, quartz) rimming walls; related to Marginal Breccia (?) these intrusions

4b veins Anhydrite, chalcopyrite, bornite <2 cm thick; sericite ± chlorite halo; similar to type 3 C R R Sulfides are chalcopyrite, bornite, pyrite,
(±quartz, tourmaline, gypsum) veins, but they cut type 4a, and can contain bornite tennantite-tetrahedrite, molybdenite, (+ minor
sphalerite, galena, enargite, stibnite); gangue
4c veins Carbonate (±various gangue Sericite, chlorite halo; up to tens cm thick, variable vein C A C minerals are anhydrite, quartz, tourmaline,
and sulfides) mineralogies; include anhydrite breccias gypsum, carbonate, barite

4d veinlets Gypsum, chlorite (± various minerals) Gypsum-chlorite dominated; typically hin, chlorite, - - R Expostuma stage (Cuadra, 1986)
tsericite halo; occur inside and outside the Braden Pipe.

1A relative scale of the estimated vein abundance (VA) and Cu and Mo Abundance for each vein stage is indicated: A = abundant, C = common, R = rare, - = absent
989
990 CANNELL ET AL.

Unidirectional solidification textures (UST; Shannon et al., in time with intrusion of the dacites. In general, type 2c veins
1982; Kirkham and Sinclair, 1988; Fig. 8A), also containing cut type 2b veins (Fig. 8B) and the dacite contacts. Type 2b
copper sulfides, occur in some of the dacite pipes, and we and 2c veins comprise the bulk of the late magmatic stock-
infer a similar timing for the unidirectional solidification tex- work. Late-stage type 2e veins are up to 2 cm wide and typi-
tures and the type 2a veins. They are both interpreted to have cally contain molybdenite. They have parallel walls, inward-
formed within a partly solidified igneous melt. grown quartz crystals, central sulfide seams, and peripheral
The oldest mineralized veins in the andesitic wall rocks are sulfide selvages (Fig. 8E).
zoned, mineralogically complex type 2b veins with Na-K- There are some late magmatic vein types that are spatially
feldspar halos (Fig. 8B-C, Table 3). The veins contain Cu-Fe restricted to specific parts of the deposit. Type 2 chlorite (in-
sulfides, biotite, anhydrite, and quartz and typically show termediate argillic) veins are thin chlorite-sulfide–dominated
more than one stage of opening and sulfide precipitation (Fig. veins that reopened earlier late magmatic stage veins locally.
8D). Type 2c veins are quartz-dominated veins (Fig. 8B), lo- Biotite-(or tourmaline) anhydrite sulfide-bearing veins and
cally with biotite halos. They are more continuous than type breccias are concentrated adjacent to the gray porphyry in
2a or 2b veins. Anhydrite ± copper sulfide-cemented crackle section 124. Type 2 distal veins are chlorite-sericite–bearing
breccias (type 2d) formed within the mine andesites at the late magmatic veins that are concentrated at the margins of
contacts with the dacites. Both type 2b veins and type 2d the deposit. These are interpreted to be temporally equiva-
breccias cut and are cut by individual dacite intrusions, indi- lent to the biotite-bearing type 2 veins in the core of the sys-
cating multiple vein- and breccia-forming events overlapping tem. The mineralogy of some late magmatic veins varies with

FIG. 8. Vein styles at El Teniente. A. Unidirectional solidification textures (UST) at the contact of a dacite pipe, with crys-
tal orientations perpendicular to the intrusion walls. The dacite has cut a broad, diffuse type 2b vein in the mine andesites
(ET697, DDH1889, 174.5 m). B. Wavy type 2b veins with pale Na-K-feldspar halos cut by straight type 2c quartz veins
(ET102, DDH1689, 299.2 m). C. Andesite porphyry, cut by a thick type 2b chlorite + sericite + anhydrite + quartz vein (A),
with a dark-gray biotite-rich selvage (B), and a pale-gray to white Na-K-feldspar halo (C; ET265, DDH1529, 233.6 m). D.
Photomicrograph of a type 2b chalcopyrite-sericite vein with a halo of Na-K-feldspar, quartz, chalcopyrite (opaque, poikolit-
ically enclosing quartz and feldspar), and anhydrite, which has overprinted biotite-altered andesite. Note the two generations
of chalcopyrite and the partial replacement of early chalcopyrite + Na-K-feldspar by chalcopyrite + sericite (ET705,
DDH1463, 61.3 m, crossed polars). E. Type 2e quartz vein, with straight sides, crystals perpendicular to the vein walls, and
a central chalcopyrite seam, cut by a type 3 chalcopyrite-quartz with a thin phyllic halo (ET172, DDH1300, 165.6 m). F. Late
hydrothermal type 4a tourmaline breccia composed of intergrown tourmaline and chalcopyrite around the vein walls, filled
by anhydrite, and associated with phyllic alteration of the wall rock (ET520, DDH1418, 332.1 m). Abbreviations: cpy = chal-
copyrite, ser = sericite, UST = unidirectional solidification texture (comb quartz layer).

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 991

depth. In the potassic alteration zone (see below), type 2b Subvertical, polylithologic, matrix-supported biotite brec-
veins are predominant at depth, whereas type 2c veins are cias (A. Skewes, unpub. report for CODELCO, 1997; Skewes
abundant at elevations above 2,000 m (Figs. 9A, 10A). At et al., 2002) occur predominantly at the contacts between the
higher elevations, late magmatic veins also contain chlorite felsic intrusions and andesitic wall rocks (Fig. 4). Rounded to
and sericite distal to the dacite intrusions (Fig. 10C). subangular clasts of biotite-altered andesite and felsic intru-

FIG. 9. A. Distribution of late magmatic vein styles in section 83. Type 2d anhydrite breccia zones are localized around
the contacts of the dacite pipes and rarely the dacite porphyry. Type 2b veins are predominant at depth where they are as-
sociated with the vein-controlled and pervasive Na-K-feldspar alteration assemblage. Type 2c quartz veins are predominant
at higher elevations. The thin vertical zone of anhydrite breccia at 1000E is presumably associated with a dacite pipe located
off section to the south. Type 2 distal and chlorite veins are predominant at the periphery of the deposit. B. Abundance of
late magmatic veins in section 83. High densities of late magmatic veins (up to 50 veins/m core) occur close to the dacite por-
phyry and locally around the dacite pipes. Late magmatic veins decrease in abundance away from the dacite porphyry, to in-
tensities of 10 to 20 veins/m core in the propylitic zone. Note that it can be difficult to distinguish late magmatic and princi-
pal hydrothermal veins in the transitional potassic-propylitic zone due to the similarity in vein mineralogy, and reopening and
alteration of late magmatic veins by later principal hydrothermal veins. C. Domains of late magmatic stage vein and/or al-
teration assemblages in section 83. The proximal potassic domain (see Table 6) occurs within 100 to 400 m of the dacite por-
phyry, in which the veins are biotite bearing and disseminated sulfides (bornite and chalcopyrite) are stable with respect to
biotite (e.g., Fig. 7C). In the transitional potassic-propylitic zone, the late magmatic alteration and vein assemblages are
sericite ± chlorite bearing (e.g., Fig. 7E). The outermost propylitic domain is marked by a decrease in vein and alteration in-
tensity, an increase in the abundance of chlorite in the alteration assemblage, and pyrite (± minor pyrrhotite inclusions) to
chalcopyrite ratios >5. Biotite grades from brown and Ti rich in the proximal potassic zone to green and Ti poor in the tran-
sitional and propylitic domains.

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992 CANNELL ET AL.

FIG. 10. A. Distribution of late magmatic vein styles in section 124. See (B) for drill hole numbers. This section contains
an irregular zone of intense Na-K-feldspar alteration that has affected 100 percent of the rock volume localized around a
dacite pipe. Around this Na-K-feldspar–altered zone are type 2d anhydrite breccias and domains of vein-controlled to per-
vasive Na-K-feldspar alteration. Type 2 distal and chlorite veins are abundant in the propylitic zone and at higher levels.
Richly mineralized anhydrite-sulfide breccias occur adjacent to the gray porphyry. The breccias contain biotite below 2,100
m and tourmaline and sericite at higher levels. Note that the distribution of the geologic units in this section was obtained
from the mine database, courtesy of CODELCO, and is based on more drill holes than indicated in (B). B. Abundance of
late magmatic veins in section 124. High vein densities occur close to the dacite porphyry (west of the section) and locally
around and downdip from the dacite pipes. Late magmatic veins are less abundant at the eastern edge of the section outside
the 0.5 percent Cu ore shell boundary. C. Domains of late magmatic stage vein and/or alteration assemblages in section 124.
The proximal potassic zone is localized around the dacite porphyry (to the west of the section) and includes zones of intense
pervasive Na-K-feldspar alteration. The transitional potassic-propylitic zone occurs in the higher levels of the section. The
propylitic domain occurs on the periphery of the deposit. Potassic-altered zones also occur around the gray porphyry where
it has intruded the Sewell Tonalite and around the dacite pipe at 1300E. Abbreviations: bx = breccia, tourm = tourmaline.

sions (Fig. 5C) are set in dark-gray, hydrothermal cement cally difficult to distinguish from the altered mine andesites
composed of biotite, anhydrite, quartz, feldspar, Cu-Fe sul- (e.g., Skewes et al., 2002). Most of the late magmatic, princi-
fides, molybdenite, and chlorite. The biotite breccias are lo- pal hydrothermal and late hydrothermal stage veins cut the

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 993

breccia bodies. There are, however, rare examples of (1) trun- halos in the northern sector (Ossandón, 1974; Camus, 1975).
cated quartz veins contained within some clasts, (2) discrete At the northern end of the dacite porphyry, the K-(±Na)
clasts of quartz veins, and (3) variable intensities of biotite al- feldspar alteration assemblage passes laterally northward to a
teration within adjacent clasts. These features are interpreted propylitic assemblage of chlorite, epidote ± magnetite,
to indicate that formation of the biotite breccias postdated the hematite, pyrite, sericite, and calcite (Ossandón, 1974).
earliest stages of late magmatic veining and alteration at El Domains of intense, pervasive domains of Na-K-feldspar
Teniente. One biotite breccia in section 83 (Fig. 4) cuts the alteration occur in the andesites adjacent to some of the
dacite porphyry obliquely, and the common occurrence of fel- dacite pipes, extending up to 50 m away, and, to a lesser de-
sic clasts in this breccia implies that it formed after the dacite. gree, the dacite porphyry. The Na-K-feldspar–altered zones
Our detailed logging shows that although the breccias contain are composed of massive anhedral gray quartz and sodic
significant amounts of disseminated copper and molybdenum feldspar (Ab44–96, predominantly Ab61–96), and lesser anhydrite,
sulfides, they only host a minor portion (<10%) of the ore in rutile, sulfides, and minor biotite. Minor pervasive alkali
the logged drill holes at El Teniente. feldspar (Or13–96) was detected, and staining indicates the ex-
Late magmatic vein types are systematically zoned around istence of variable amounts of K-feldspar in the assemblage.
the dacite intrusions, and their development varies with Apart from these localized zones, potassium metasomatism
depth (Figs. 9A, 10A). The intensity of late magmatic veins is in the andesites has caused intense, texturally destructive,
highest within 300 m of the dacite porphyry and locally pervasive biotite alteration of the groundmass and mafic phe-
around the dacite pipes (Figs. 9B, 10B). Based principally on nocrysts, in many cases leaving the plagioclase phenocrysts
the vein and alteration mineral assemblages, three late mag- unaltered (Fig. 7B). The biotite-altered zone is laterally ex-
matic domains can be distinguished: (1) proximal potassic tensive, extending up to 1 km away from the dacites. In-
zone (biotite bearing), (2) transitional potassic-propylitic zone tensely biotite altered andesites are composed only of dark-
(biotite-sericite-chlorite bearing), and (3) propylitic zone brown biotite, rutile, anhydrite, and Cu-Fe sulfides (Fig.
(chlorite bearing, Figs. 9C, 10C). The features of these zones 7C-D). Early, microscopic biotite veinlets (Skewes et al.,
are summarized in Table 6. 2002; Fig. 7D) and late magmatic stage veins with biotite
Within the dacite intrusions, potassic (-sodic) alteration as- halos are abundant locally (Fig. 7B).
sociated with the late magmatic stage is characterized by hy- With increasing distance from the dacite porphyry (typi-
drothermal K-(±Na-) feldspars. The feldspars are white in cally >300 m), hydrothermal chlorite and sericite occur to-
hand specimen, and staining or thin section petrography is re- gether with hydrothermal biotite. The abundance of these
quired to discriminate orthoclase and albite. Primary biotite phases increases outward toward the propylitic alteration
is partially to completely altered to chlorite ± carbonate. Phe- zone, whereas biotite abundance decreases outward (Fig.
nocryst and groundmass plagioclase show weak to strong se- 7E). Biotite in the transitional alteration zone has a distinctive
lective alteration to sericite ± carbonate. The K-(±Na) green-brown color typical of low titanium biotite when
feldspar alteration assemblage is developed pervasively at the viewed in plane-polarized light (electron microprobe analyses
southern end of the dacite porphyry and is restricted to vein indicate <0.25 wt % Ti; Cannell, 2004). Low Ti biotite

TABLE 6. Characteristics of the Potassic, Transitional Potassic-Propylitic and Propylitic Alteration Zones at El Teniente

Potassic zone Transitional potassic-propylitic zone Propylitic zone

Location Proximal to dacite porphyry and Distal from dacite porphyry, and Deposit periphery, near and extends
locally around dacite pipes >2,200-m elevation beyond the 0.5 percent Cu limit

Dominant pervasive Biotite alteration assemblage Transitional potassic-propylitic Propylitic assemblage

alteration assemblage assemblage

Other alteration types Pervasive Na-K-feldspar alteration Pervasive phyllic alteration, vein Rare phyllic (phengitic sericite),
controlled Na-K-feldspar alteration early magnetite ± epidote

Dominant vein/breccia type Type 2a-2e, type 2 biotite-anhydrite- Type 2 distal, type 2f chlorite, type 3 Type 2f chlorite, type 2 distal
sulfide breccias, biotite breccias

Vein intensity High Medium-high Low

Vein gangue mineralogy Biotite, Na-K-feldspar, Sericite, chlorite, rare Chlorite, pyrite ±sericite, magnetite,
(ubiquitous quartz, anhydrite) rare sericite, chlorite. Na-K-feldspar, magnetite Na-K-feldspar

Sulfides Chalcopyrite and bornite Chalcopyrite and pyrite Pyrite ± chalcopyrite pyrrhotite
inclusions

Phyllosilicate mineral Biotite Sericite and chlorite Chlorite ± sericite

intergrown with sulfides

Cu and Mo grades High Cu (>1%) and Mo (>0.01%) High-moderate Cu (mostly >1%), Low Cu (<0.5%), and Mo (<0.01%)
moderate Mo (mostly 0.01–0.03%)

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compositions are consistent with a lower temperature of for- alteration only occurs as centimeter-scale halos around type 3
mation (Engel and Engel, 1960; Le Bel, 1979). Pyrite veins, except on the west side of section 83 (Fig. 11).
(±pyrrhotite inclusions) and magnetite are abundant in the
transitional zone, whereas bornite is absent. Chlorite ± Late hydrothermal stage (type 4 veins)
sericite typically occur as rims around sulfide grains (Fig. 7E). The late hydrothermal stage is a second phyllic stage spatially
The transitional alteration assemblage grades out to a and temporally associated with the Braden Pipe and related
propylitic alteration assemblage within the andesitic country latite intrusions. Of all of the vein types, only late hydrothermal
rocks, outboard from the 0.5 percent Cu contour. Mafic min- veins cut the Braden Pipe, providing temporal constraints on
erals are selectively altered to chlorite, magnetite, epidote, the formation of the final stage of the vein paragenesis.
and hematite. This assemblage also has filled amygdales in Late hydrothermal veins have a diverse mineralogy, includ-
the propylitic zone (Villalobos, 1975). ing Cu-Fe, Mo, and base metal sulfides and sulfosalts (Table
The dacite intrusions have an intimate spatial association 5). Gangue minerals include quartz, anhydrite, tourmaline,
with the pervasive alteration assemblage, with the vein inten- gypsum, carbonates, and barite. Clay minerals and pyrophyl-
sity, and with the vein styles (Figs. 9, 10). In particular, in- lite were also reported from this stage (Camus, 1975). PIMA
tense pervasive Na-K-feldspar alteration and abundant type analyses (Cannell, 2004) indicate that sericite of the late hy-
2b veins and 2d breccias (up to 30% of the rock volume) drothermal stage is more illitic than that of the principal hy-
occur at the contacts of some of the dacite pipes resulting in drothermal stage. Kaolinite was detected in only one of more
high copper (±Mo) grades localized around the pipe contacts. than 50 samples analyzed.
Although the dacite porphyry dike typically does not display Type 4a veins and crackle breccias contain tourmaline, an-
such an obvious relationship to mineralization, the large-scale hydrite, and chalcopyrite (Fig. 8F, Table 5) and are inter-
zoning of alteration assemblages, vein intensity, vein styles, preted to be associated with the Marginal Breccia facies of
and sulfide mineralogy around the southern end of the dike, the Braden Pipe. They are cut by type 4b quartz-chalcopy-
and the temporal overlap between veining and intrusion sug- rite-anhydrite (±bornite) veins that are mineralogically and
gest that alteration and mineralization are genetically associ- texturally similar to type 3 veins. Type 4c veins are miner-
ated with the dike. alogically variable, typically containing carbonates, sulfates,
sulfides (including abundant molybdenite), and sulfosalts
Principal hydrothermal stage (type 3 veins) (Table 5). Type 4c veins occur in some of the larger faults ob-
Late magmatic stage veins are overprinted by principal hy- served underground. Type 4b and 4c veins are less abundant
drothermal stage veins and associated phyllic alteration halos. in the Braden Pipe than in the adjacent mine andesites. Spec-
Principal hydrothermal (type 3) veins are typically thick (2 tacular crystal caverns containing gypsum crystals up to 6 m
mm–3 cm) and chalcopyrite-rich (±molybdenite, ± pyrite at long occur within the Braden Pipe. These are attributed to
the periphery of the deposit). They have well-developed phyl- stage 4c hydrothermal activity. The youngest veins are thin,
lic alteration halos from 3 mm to 5 cm thick (Fig. 7F). Quartz typically unmineralized type 4d gypsum-chlorite veins.
and anhydrite are the predominant gangue minerals. Al- Late hydrothermal veins are less abundant than principal
though principal hydrothermal veins have lower abundances hydrothermal veins, and we estimate that they host approxi-
(typically <10 veins/m of core) than the late magmatic veins, mately 10 percent of the copper in the logged drill holes. The
our visual estimate is that principal hydrothermal veins host density of late hydrothermal veins and the intensity of alter-
approximately 30 percent of the copper in the logged core. ation are greatest within 100 to 200 m of the Braden Pipe and
In addition to alteration halos around principal hydrother- decrease away from the pipe and with depth. South of the
mal veins, intense, texturally destructive phyllic alteration oc- Braden Pipe, thin latite dikes are locally associated with richly
curs in discrete domains in the higher levels of the mine at mineralized type 4c breccia zones and domains of pervasive
Teniente. These intensely phyllic altered intervals are com- phyllic alteration.
posed of sericite (up to 80%), quartz (5–25%), variable chlo-
rite (0–15%), and minor anhydrite, rutile, and sulfides (up to Structural Evolution
5%). Infrared absorption analysis using a portable infrared A diversity of vein arrays has been documented in porphyry
spectrometer (PIMA) indicates that the white mica from the deposits. Stockwork orientations can be described as random
principal hydrothermal stage varies of the principal hy- (e.g., “A” veins from El Salvador: Gustafson and Hunt, 1975)
drothermal stage varies from slightly paragonitic to slightly or sheeted, in which one or more preferred orientations exist
phengitic muscovite. (Laramide deposits of Arizona: Heidrick and Titley, 1982; Ti-
Estimated densities of principal hydrothermal veins and in- tley, 1990; Cadia Hill; Holliday et al., 2002). A sheeted vein
tensities of alteration are shown for sections 83 and 124 in system indicates that far-field stresses exceeded the stresses
Figures 11 and 12, respectively. Intensity of phyllic alteration localized by magma emplacement and, as a consequence, the
and densities of principal hydrothermal veins are highest in veins are predominantly orientated parallel to the regional
the upper levels of the deposit, where they overprint the tran- fabric (Titley, 1990; Tosdal and Richards, 2001). Some de-
sitional potassic-propylitic zone. In these domains, pervasive posits show domains of preferred vein orientation that
phyllic alteration affected up to 100 percent of the rock vol- formed in response to displacement along master faults (e.g.,
ume locally (Zúñiga, 1982; Figs. 11B, 12B). The intensity of Chuquicamata: Lindsay et al., 1995). Concentric and radial
phyllic alteration and the density of principal hydrothermal vein and dike patterns in several porphyry Cu and Mo de-
veins decrease with increasing depth and with increasing posits from the American Southwest (Titley, 1990; Tosdal and
proximity to the dacite porphyry. Below 2,150 m, phyllic Richards, 2001), from “D” veins at El Salvador (Gustafson

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FIG. 11. A. Abundance of type 3 (principal hydrothermal) veins in section 83. Type 3 veins are only weakly developed
near the dacite porphyry, especially at depth. Principal hydrothermal veins are more abundant away from the dacite porphyry
and vertically upward, reaching a maximum of >20 veins/m core in the transitional zone. B. Intensity of phyllic alteration in
section 83, which approximately correlates with abundance of principal hydrothermal veins. Intensity of phyllic alteration in-
creases away from the dacite porphyry and also increases vertically, forming zones of pervasive alteration (solid colors) above
2,100 m RL. Below this level the phyllic alteration assemblage occurs as vein halos (lines and dashes). Chalcopyrite-rich type
3 veins do not have phyllic halos where they occur adjacent to the dacite porphyry at depth. Abbreviation: PH = principal
hydrothermal.

and Hunt, 1975), and from various epithermal deposits (Ry- A review of the available structural data from El Teniente
tuba, 1994, and references therein) have been described. was undertaken to ascertain the dominant vein and fault ori-
El Teniente was previously described as structurally entations and to relate them to the observed paragenesis, in-
isotropic, composed of a stockwork of randomly oriented trusive history, and district-scale structures. Vein and fault
veins, with the exception of a zone extending for ~200 to 300 data were compiled from geotechnical reports and structural
m around the Braden Pipe that is composed of radial and maps. No new measurements were collected for this study,
concentric veins centered on the pipe (e.g., Cuadra, 1986). and the data are paragenetically constrained to the late mag-
Subvertical strike slip and reverse faults occur in the deposit matic, principal hydrothermal or late hydrothermal stages as
with a late hydrothermal vein fill, but these faults only have mapped by El Teniente mine geologists. In total, 4337 vein
meter-scale displacements and can be traced for a maximum and fault measurements were utilized in this study from four
of 800 m (Cuadra, 1986; I. Garrido, 1995, unpub. report for mining areas (Quebrada Teniente, Sub-6, Esmerelda, and
CODELCO). There is a preferred northeast orientation for Regimiento). Where possible, the data are split into a late hy-
some faults, tourmaline-anhydrite breccia zones, latite, and drothermal domain (where late hydrothermal veins predomi-
lamprophyre dikes, and thick quartz veins (type 1b). Based on nate over principal hydrothermal veins) within approximately
this preferred orientation of geologic features, the northeast 200 to 300 m of the Braden Pipe and a principal hydrother-
Teniente fault zone (Fig. 2) has been implicated in the gene- mal domain (where late hydrothermal veins are rare) located
sis of the deposit (Garrido et al., 1994). The north-north- outboard of the late hydrothermal domain.
west–trending dacite porphyry dike and the northwest-trend-
ing dacite pipes and associated igneous and anhydrite Vein stages
breccias to the northeast of the Braden Pipe (Skewes et al., The preferred structural orientations for the Teniente
2002) are subparallel to the Codegua fault (Fig. 2). paragenetic stages are summarized in Table 7. Data for late

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FIG. 12. A. Abundance of type 3 (principal hydrothermal) veins in section 124. Type 3 veins are most abundant in the
transitional zone of section 124. Type 3 veins do not occur at depth to the west of the section, proximal to the Braden Pipe.
B. Intensity of phyllic alteration in section 124. Pervasive phyllic alteration is restricted to levels above 2,200 m, within the
transitional zone. Abbreviation: PH = principal hydrothermal.

magmatic and principal hydrothermal veins are plotted in Thick type 1b quartz veins have predominantly northeast
stereonets in Figure 13A and B, respectively. Figure 13C and trends, parallel to the Teniente fault zone. Northwest- and
D plot the same structures in polar coordinates, relative to the east-trending veins are also present (Fig. 14). The late mag-
radial angle from the geographic center of the deposit. In polar matic and principal hydrothermal vein stockworks, which
coordinates, a radial vein anywhere in the deposit has a north- contain most of the copper in the deposit, have broadly con-
south strike; a concentric inward-dipping vein anywhere in the centric and radial orientations centered approximately in the
deposit will have an east-west strike and a dip to the south. middle of the deposit, where the Braden Pipe is now situated
(Fig. 14). The concentric veins are shallowly dipping (pre-
dominantly 40°–60°) toward the pipe in the mine areas to the
TABLE 7. Summary of Vein Types at El Teniente (based on analyses of vein north of the Braden Pipe. They dip steeply (>60°) toward the
orientations and timing relationships)
Braden Pipe in the eastern sector and less steeply in the south
Vein type Orientations Comments of the deposit. Radial veins are subvertical and are more
abundant in the principal hydrothermal domain than in the
Type 1b Variable in mine, Premineralization, associated late hydrothermal domain. In all of the mine areas, shallowly
northeast in district with Sewell Tonalite? dipping (<40°) vein populations are present. The preferred
Type 2 (LM) Concentric dipping Associated with dacites; alignment of the late magmatic and principal hydrothermal
and 3 (PH) (40°–80°) and radial Type 2 veins are scattered, veins in subvertical radial and inward-dipping concentric ori-
(subvertical), broad Type 3 veins are more focused
data scatter entations with respect to the center of the deposit is shown in
Figure 13C and D.
Type 4a-c (LH) Concentric, Reverse faults common,
typically >70° associated with Braden Pipe
Most of the late hydrothermal structures have a consistent
steeply inward dipping (>70º) concentric orientation with re-
Type 4c, d (LH) Northeast trending, Mainly faults (strike slip),
subvertical lesser veins, parallel to the
spect to the Braden Pipe (Fig. 15), illustrated in the stereonet
Teniente fault zone data (Fig. 13F). fault orientations in the deposit (Figs. 13H,
16) have a similar orientation. In contrast to late magmatic
Type 4 (LH) N ± 30° LH veins that do not fit into
sets 3 or 4 and principal hydrothermal veins, radial and shallow-dipping
concentric veins and faults are rare.
Abbreviations; LH = late hydrothermal, LM = late magmatic, PH = prin- A series of planar northeast- to east-northeast–trending,
cipal hydrothermal subvertical late hydrothermal structures (Figs. 14G, 16) are

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FIG. 14. Orientations of major (i.e., >50 m long) type 1b premineralization

quartz veins and late magmatic (LM) and principal hydrothermal (PH) struc-
tures. Data for this figure, and for Figures 16 and 17, were obtained from
1:1000 and 1:5000 mapping by Teniente mine geologists (listed in Fig. 13).
Stereonets indicate the dominant orientations (solid lines) and subdominant
FIG. 13. Contoured stereonets showing poles to vein and fault orientations orientations (dashed lines) of veins measured by mine geologists during
for El Teniente. Contour intervals are % data/1% area. A and B. Late magmatic structural mapping. The dominant preferred orientation in the stereonets for
(n = 463) and principal hydrothermal (n = 1,176) veins, respectively. Note the the late magmatic and principal hydrothermal veins is approximately con-
broad scatter of data for both datasets. C and D. Late magmatic (n = 463) and centric to the Braden Pipe in all but the stereonet for late magmatic veins
principal hydrothermal (n = 1,176) veins, respectively, plotted in polar coordi- from Regimiento. Similarly, the major structures have mostly concentric and
nates, relative to the radial angle from the geographic center of the deposit. radial orientations. The dotted line concentric to the Braden Pipe is the ap-
The radial angles assigned to the mine areas are Quebrada Teniente +25º, Sub- proximate boundary between the late hydrothermal (LH) domain (within ap-
6 mine –20º, Esmerelda late hydrothermal domain –35º, Esmerelda principal prox 300 m of the pipe) and the principal hydrothermal (PH) domain, which
hydrothermal domain –50º, Regimiento –200º. Note the concentration of shal- occurs farther out from the pipe. The rotated grid indicates the mine coordi-
low to steep inward dipping concentric veins and subvertical radial veins for nates relative to magnetic and UTM north. Block-cave mining areas (e.g.,
both polar datasets. E. Late hydrothermal veins (n = 1,272), with consistently, Sub-6 mine) are denoted by dotted lines and contain most of the mapped
steep dips, and variable strike. F. Late hydrothermal veins (n = 1,272) plotted structural features shown here. Abbreviations: asl = above sea level, LH =
in polar coordinates. Note the tight cluster of steeply inward dipping orienta- late hydrothermal, LM = late magmatic, PH = principal hydrothermal.
tions concentric to the Braden Pipe. G. faults (n = 1,602), which have a con-
sistently steep dip. The set of northeast-trending faults is visible in this dataset.
H. faults (n = 1,602) plotted in polar coordinates. Despite the presence of
northeast-trending faults, the faults are predominantly steeply inward dipping
and concentric to the Braden Pipe. Structural information was compiled for parallel to the Teniente fault zone (Fig. 2). Northeast-trend-
this study from unpublished CODELCO geotechnical reports on individual ing structures are mainly latest stage faults and include the
mine areas by A. Morales and J. Pereira (1996), A. Morales and J. Seguel “falla P,” “falla D2,” and the “falla ten-sur” anastomosing fault
(1998), O. Quezada (1998), A. Russo (1999), A. Brzovic (1999, 2000), and systems, the most continuous in the deposit (Cuadra, 1986).
Duarte (2000). The structural data were collected by the mine geologists dur-
ing routine structural mapping or from strategically selected lines of detail,
Some late magmatic and principal hydrothermal veins also
where all the structures are measured that cross a horizontal line on the wall of occur in this orientation, implying that it was weakly devel-
a drive. All data provided courtesy of CODELCO, El Teniente division. oped during the main stages of veining and mineralization.

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FIG. 15. Orientations of late hydrothermal major concentric structures FIG. 16. Orientations of northeast-trending major structures, which are
and stereonets showing the orientations of late hydrothermal veins. See Fig- parallel to the district-scale Teniente fault zone. See Figure 14 for detailed
ure 14 for detailed explanation. All of the stereonets of late hydrothermal explanation. Most of the northeast-trending structures formed during and
veins indicate a predominant orientation concentric and steeply inward dip- after the late hydrothermal stage; however, the anisotropic zone adjacent to
ping to the Braden Pipe. Abbreviations: asl = above sea level, LH = late hy- the Sewell Tonalite includes some late magmatic and principal hydrothermal
drothermal, LM = late magmatic, PH = principal hydrothermal. veins. The stereonets plot all the faults in the deposit, predominantly with
orientations concentric to the pipe. Some of the stereonets (Regimiento, Es-
merelda) show a weak northeast-trending (or radial) secondary orientation.
Other structures are predominantly north trending (±30°) and do not fit with
Another minor set of late hydrothermal structures is predom- the above sets. Abbreviations: asl = above sea level, LH = late hydrothermal,
PH = principal hydrothermal.
inantly north trending (Table 7, Fig. 16).
There is a pronounced structural anisotropy where struc-
tural sets coincide. For example, in the Quebrada Teniente
mine area, concentric late hydrothermal structures occur not have a sheeted orientation, suggesting that during vein
parallel to the east-northeast–trending structures. In the formation, far-field stresses were less important than local-
Regimiento, Sub-6, and Esmerelda mine areas these struc- ized stresses around the felsic intrusive body. The late mag-
tures are oriented obliquely to each other, resulting in a scat- matic and principal hydrothermal vein orientations have an
tered vein and fault array. overall inward-dipping concentric and radial distribution cen-
tered in the middle of the deposit, coincident with the loca-
Structural model tion of the Braden Pipe (Fig. 17A), suggesting that they
We propose a structural model based on the observed ori- formed in response to intrusion of a large pluton at depth and
entations and paragenesis of the veins and faults. Previous au- doming of the overlying volcano-sedimentary sequence (e.g.,
thors (e.g., Garrido, 1994) inferred that the northeast-trend- Acocella et al., 2000). The scatter of vein orientations may be
ing Teniente fault zone was active during the period of due to local fluid pressures exceeding stresses induced by the
formation of the late magmatic and principal hydrothermal intruding magma (e.g., Burnham, 1979). During the late
stockwork. However, the vein stockwork at El Teniente does magmatic stage, the dacite porphyry dike and pipes intruded

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 999

from the deep magma chamber into the mine andesites, and
perturbations in the stress field caused by these high-level in-
trusions resulted in greater vein densities proximal to their
margins (Figs. 9B, 10B).
A change in stress conditions led to the generation of con-
centric, subvertical fractures above the magma chamber dur-
ing the late hydrothermal stage. The lack of radial veins in this
stage implies that magma pressure was low, and it is inter-
preted that structures associated with the late hydrothermal
stage formed during a subsidence event associated with
magma withdrawal (e.g., Koide and Bhattacharji, 1975; Fig.
17B). Previously formed, steeply inward dipping reverse and
outward dipping normal concentric faults would have been
reactivated with opposite sense, allowing for central subsi-
dence (Acocella et al., 2000).
In this model, resurgence occurred in the deep magma
chamber during the late hydrothermal stage, associated with
uplift, fracture reactivation (Fig. 17C), and generation of re-
verse faults. Latite porphyry dikes, Marginal Breccia zones,
and pebble dikes were emplaced into dilational cone sheets
above the magma chamber. Fluid and/or magmatic pressures
associated with the resurgent magma eventually exceeded the
lithostatic stress resulting in explosive fragmentation, fluidiza-
tion, and ultimately formation of the Braden Breccia. This
brecciation was possibly phreatomagmatic (e.g., Sillitoe,
1985), although direct evidence for this process (i.e., juvenile
clasts) is lacking. The breccia pipe utilized the concentric
fractures generated during the Marginal Breccia phase, re-
sulting in the characteristic funnel-shaped Braden Breccia
partially bordered by the earlier formed Marginal Breccia (R.
Floody, 2000, unpub. report for CODELCO). The Braden
Pipe is located close to the center of the deposit, indicating
that the locus of the intruding magma and related stresses did
not change markedly from the late magmatic and principal
hydrothermal stages to the late hydrothermal stage.
During and after these stages of intrusion and withdrawal,
minor northeast-trending faults and veins were generated
(Fig. 17C) due to movements along the Teniente fault zone.
These structures, as well as the north-northwest–northwest
trend of the dacite intrusions, are the only features associated
with far-field stresses that exceeded localized stresses induced
by the intruding magma.
FIG. 17. Schematic structural model of El Teniente system. A. The vein Discussion
stockwork emplaced during the late magmatic and principal hydrothermal
stages was subjected to stresses associated with initial intrusion of a large plu- Age of mineralization
ton inferred to lie below the current level of the mine. Radial veins are more
abundant peripherally (in the principal hydrothermal domains). Faults are Re-Os dating of molybdenite using a double Os spike (Stein
rarely preserved from the late magmatic stage, probably due to reactivation et al. 2001; Markey et al. 2003) was used to address the age of
and overprinting during the principal hydrothermal and late hydrothermal
stages. B. A period of magmatic quiescence and subsidence followed, ac-
mineralization at El Teniente. Cannell et al. (2003) and Can-
companied by magma withdrawal, in which steeply dipping normal concen- nell (2004) presented Re-Os age data generated at Colorado
tric fractures were developed. C. A stage of resurgence of the magma cham- State University for molybdenite samples collected from El
ber is inferred, and uplift was facilitated by reactivation of the concentric Teniente during this study. Our high-precision Re-Os ages
fractures with a reverse sense. Latite dikes, pebble dikes, Marginal Breccia range from 5.89 to 4.70 Ma (Fig. 18).
zones, and late hydrothermal veins were emplaced into these extensional
concentric fractures, until explosive brecciation and formation of the Braden Maksaev et al. (2004) reported nine Re-Os ages for molyb-
Pipe caused instantaneous depressurization and cooling of the magma. Only denites from El Teniente (Table 3, Fig. 18) and interpreted
minor alteration and veining followed this event, largely confined to concen- five episodes of mineralization (6.30 ± 0.03, 5.60 ± 0.02,
tric fractures inside and at the edges of the pipe overprinting the Marginal 5.01–4.96, 4.89 ± 0.08 to 4.78 ± 0.03, and 4.42 ± 0.02 Ma).
Breccia-Braden Breccia contact (R. Floody, 2000, unpub. report for
CODELCO) and northeast-trending fractures related to movements along
These Re-Os ages correlate well with their U-Pb ages for the
the Teniente fault zone. Abbreviations: LH = late hydrothermal, LM = late felsic intrusions and 40Ar-39Ar ages for biotite and sericite
magmatic, PH = principal hydrothermal. (Table 3, Fig. 18). Maksaev et al. (2004) therefore concluded

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FIG. 18. Summary of geochronological data from El Teniente. Blank-corrected Re-Os ages on molybdenite are from Can-
nell et al. (2003) and Cannell (2004). Samples are from molybdenite-bearing veins and breccias, some with coexisting chal-
copyrite and molybdenite. Errors shown include the uncertainty in the decay constant for 187Re. Other Re-Os data are from
Maksaev et al. (2004) as indicated and are not constrained paragenetically, beyond an association with biotite or sericite al-
teration. U-Pb zircon ages for the intrusions are from Maksaev et al. (2004). Note that the Sewell Tonalite, the gray porphyry,
and two samples from the dacite pipes have bimodal age distributions. We have followed the interpretation of Maksaev et al.
(2002), whereby the early ages for these four units are inferred to be inherited from previously crystallized zircons, whereas
the younger ages represent the ages of final crystallization. This contrasts with the interpretation of Maksaev et al. (2004),
who interpreted the older ages to be the intrusion ages and the younger ages to be hydrothermal overgrowths. Biotite and
sericite Ar40/Ar39 and K-Ar ages are from Maksaev et al. (2004), Cuadra (1986), and P. Cuadra (unpub. report for
CODELCO, 1992), respectively. These are significantly younger than the U-Pb and Re-Os ages, due either to resetting dur-
ing intrusion of the late dacite (Maksaev et al., 2004) or the lower closure temperature of the K/Ar isotope system (Cannell,
2004). The type 2e molybdenite-bearing vein dated at 4.82 to 4.80 Ma may have been reopened, allowing molybdenite pre-
cipitation during the principal hydrothermal or late hydrothermal stage, given that the age is significantly younger than the
other late magmatic veins. The K-Ar age determination for the phaneritic Sewell diorite is from Cuadra (1986).

that mineralization at El Teniente was sourced directly from 0.24, and 5.48 ± 0.19 Ma, respectively, SHRIMP U-Pb zircon
the felsic intrusions. data of Maksaev et al., 2002, 2004; Table 3; Fig. 18). Other
Based on the Re-Os age determinations of Cannell et al. Re-Os molybdenite ages for the late magmatic stage cluster
(2003), early-late magmatic vein-hosted molybdenite miner- around 5.0 Ma and are approximately 300,000 yr younger
alization is interpreted to have occurred at 5.89 Ma, similar to than the dacite porphyry dike (5.28 ± 0.10 Ma: Maksaev et al.,
the youngest U-Pb ages determined for the gray porphyry, 2004). This may be due to the limited number of U-Pb analy-
the Sewell Tonalite porphyritic phase, and two age determi- ses of the multiphase dacite intrusions (i.e., there may be an
nations from dacite pipes (5.67 ± 0.19, 5.59 ± 0.17, 5.50 ± as yet undated dacitic phase that correlates temporally with

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 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 1001

these 5.0 Ma ages). Alternatively, molybdenite mineralization porphyry dike, and the gray porphyry appear to have acted as
may be related to a deep magma chamber below the level of fluid conduits and focused veining, brecciation, and high-
the mine and was not synchronous with high-level felsic grade mineralization proximal to their contacts. The pervasive
intrusion. alteration assemblages, sulfide assemblages, and the mineral-
A change to sericite-stable veins of the principal hydrother- ogy and densities of the late magmatic veins all vary system-
mal stage occurred at approximately 4.95 to 4.90 Ma (Fig. atically, both outward and upward from the dacite porphyry
18). The principal hydrothermal stage appears to have had a to the periphery of the deposit.
short duration (<100,000 yr) constrained by intrusion of the We interpret the predominance of concentric and radial
latite dikes (4.82 ± 0.09 Ma: Maksaev et al., 2004) and the vein orientations in all stages of mineralization at El Teniente
Braden Pipe (Fig. 18). to indicate that emplacement of a large pluton below the ex-
The late hydrothermal stage mineralization persisted until posed levels of the mine localized stresses and controlled vein
at least 4.70 Ma (Fig. 18), and some hydrothermal activity formation throughout the life of the hydrothermal system,
persisted until 4.37 ± 0.05 Ma based on 40Ar/39Ar and K-Ar from early stages of stockwork development to later stages of
dates from Cuadra (1986), P. Cuadra (unpub. report for brecciation, to form the Braden Pipe. This pluton is inter-
CODELCO, 1992), and Maksaev et al. (2002, 2004). In total, preted to have sourced both the felsic intrusions and miner-
mineralization, alteration, and cooling of the hydrothermal alizing fluids. We speculate that episodes of magma intrusion
system at El Teniente spanned at least 1.5 m.y., from 5.9 to and withdrawal, coupled with decreasing depths and pres-
4.4 Ma, coincident with the emplacement of the dacite and sures due to tectonic uplift and concomitant erosion (e.g.
latite intrusions (U-Pb ages of 5.7–4.8 Ma: Maksaev et al., Kurtz et al., 1997) could account for differences between the
2002, 2004) and the Braden Pipe. three main stages of mineralization at Teniente.
Timing and origin of copper mineralization Conclusions
Skewes et al. (2002) proposed that copper at El Teniente El Teniente is a typical, albeit enormous, Cu-Mo porphyry
was initially deposited with widespread brecciation and bi- deposit. It is characterized by multiple phases of weakly to
otite alteration and was either remobilized or removed by the strongly altered felsic intrusions. It has an alteration paragen-
later intrusive events. Several points from the current study esis and distribution typical of other porphyry Cu deposits
are incompatible with this model. We have observed no tex- (e.g., Lowell and Guilbert, 1970). Its vein paragenesis is sim-
tural evidence for the remobilization of early-formed copper ilar to El Salvador (Gustafson and Hunt, 1975). A large, late-
sulfides associated with the intrusion of the dacite porphyry. stage breccia pipe cuts the mineralization, similar to deposits
Skewes et al. (2002) argued that the dacite porphyry is low such as Batu Hijau (Garwin, 2002). Two distinctive features of
grade compared to the mine andesites because it postdated El Teniente are worthy of note. First, of the 14 vein stages, all
the biotite breccias and copper mineralization. This study has but the first two and the last (premineralization stage and
shown that biotite breccias locally cut the dacites (e.g., Fig. type 4d; Table 5) contain Cu-Fe sulfides, indicating that dur-
5C). Furthermore, the low copper grade of the dacite por- ing every paragenetic stage copper was carried in the fluid,
phyry (a feature common to many porphyry Cu deposits: e.g.; and conditions existed to cause precipitation of Cu-bearing
Sillitoe, 2000), may simply reflect its intramineral timing, the sulfides from the fluids. Second, despite the location of El Te-
presence of, as yet unidentified, late mineral dacite porphyry niente at the intersection of two district- to regional-scale
phases that have diluted grade, or a lack of a suitable physic- fault zones, far-field stresses do not appear to have influenced
ochemical gradient to precipitate copper or molybdenum in vein development. Instead we suggest that stresses localized
the central, hottest parts of the system. Based on our drill above a deep-seated magma body produced the observed
core observations, we conclude that the biotite breccias and vein array and influenced resurgence and withdrawal of
associated widespread biotite alteration are temporally and magma.
spatially linked to the dacite intrusions and are not a discrete Our interpreted geologic evolution of El Teniente is sum-
hydrothermal event that preceded dacite emplacement by up marized as follows. The deposit formed during the final stages
to several million years as suggested by Skewes et al. (2002). of a prolonged period of intrusive activity within a Miocene-
Our detailed logging of the mine andesites confirms that Pliocene magmatic arc (e.g., Kay et al., 1999; Charrier et al.,
breccias, including biotite- and anhydrite-cemented breccias 2002). Volcanic and volcaniclastic rocks of the Farellones For-
and the Marginal Breccia facies of the Braden Pipe, typically mation were intruded by a mafic to intermediate sill-stock
host high-grade ore at El Teniente. However, the breccias are complex approximately 11 to 9 Ma. This was followed by in-
volumetrically minor in comparison to the several cubic kilo- trusion of the Sewell Tonalite (part of a 9–7 Ma intrusive
meters of felsic intrusions and andesitic host rocks that con- complex), which was associated with minor premineraliza-
tain the pervasively developed vein stockwork that hosts the tion-stage alteration and veining.
bulk of the ore at El Teniente. During the latest Miocene, a large, deep-seated, felsic plu-
Geochronology confirms the findings of Howell and Molloy ton was emplaced. Fluid exsolution from the crystallizing plu-
(1960), Camus (1975), Villalobos (1975), and Cuadra (1986) ton led to the formation of abundant mineralized late mag-
that the mineralization, veining, and alteration at El Teniente matic stage veins and lesser biotite-cemented breccias,
are temporally linked to felsic intrusions. Vein overprinting together with widespread biotite alteration of the wall-rock
relationships indicate that the late magmatic stage vein- package. The parent pluton controlled stresses in the deposit
hosted mineralization overlapped with the multistage dacite (Fig. 18A) and was the source for high-level felsic intrusions
intrusions. The dacite pipes, the southern end of the dacite dated between 5.7 and 5.3 Ma (Maksaev et al., 2002, 2004).

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1002 CANNELL ET AL.

Late magmatic-stage mineralization continued until approxi- Camus, F., 1975, Geology of the El Teniente orebody with emphasis on wall-
mately 4.95 to 4.90 Ma and was followed by the short lived rock alteration: ECONOMIC GEOLOGY, v. 70, p. 1341–1372.
Camus, F., 2002, The Andean porphyry systems: Hobart, Tasmania, Univer-
(<100,000 yr) principal hydrothermal stage. During the prin- sity of Tasmania, CODES Special Publication 4, p. 1–38.
cipal hydrothermal stage chalcopyrite-rich veins with phyllic Cannell, J., 2004, El Teniente porphyry copper-molybdenum deposit, central
halos were emplaced, which host approximately 30 percent of Chile: Unpublished Ph.D. thesis, Hobart, University of Tasmania, 317 p.
Teniente’s copper resource. Cannell, J., Cooke, D.R., Stein, H.J., and Markey, R.J., 2003, New para-
genetically constrained Re-Os molybdenite ages for El Teniente Cu-Mo
Relaxation of the magma-induced stresses led to a stage of porphyry deposit, central Chile [abs]: Society for Geology Applied to
subsidence, possibly due to withdrawal of the magma cham- mineral Deposits (SGA), Athens, 2003, Abstracts with Programs, v. 1, p.
ber (Fig. 17B). As a result, steeply dipping concentric veins 255–258.
and normal faults formed during the late hydrothermal stage. Charrier, R., Baeza, O., Elgueta, S., Flynn, J.J., Gans, P., Kay, S.M., Munoz,
Latite porphyries and the Braden Pipe were emplaced ap- N., Wyss, A.R., and Zurita, E., 2002, Evidence for Cenozoic extensional
basin development and tectonic inversion south of the flat-slab segment,
proximately 4.8 Ma (Fig. 17C), associated with further late southern central Andes, Chile (33°–36°S.L.): Journal of South American
hydrothermal-stage veining and alteration. Explosive breccia- Earth Sciences, v. 15, p. 117–139.
tion and formation of the Braden Breccia apparently depres- Cuadra, P., 1986, Geocronología K-Ar del yacimiento El Teniente y areas
surized the parent pluton and terminated igneous activity. adyacentes: Revista Geológica de Chile, v. 27, p. 3–26.
Mostly late stage northeast-trending faults and minor miner- Duarte, P.O., 2000, Caracterización geológica y geotécnica del pórfido
dacitico El Teniente: Unpublished Honours thesis, Santiago, Universidad
alized veins formed due to movements along the Teniente de Chile, 80 p.
fault zone (Fig. 17C). The waning stages of the hydrothermal Engel, A.E., and Engel, C.G., 1960, Progressive metamorphism and graniti-
system continued until approximately 4.4 Ma. The last stage zation of the major paragneiss, northwest Adirondack Mountains, New
in the evolution of El Teniente was intrusion of thin postmin- York: Geological Society of America Bulletin, v. 71, p. 1–57.
Faunes, A., 1981, Caracterización de la mineralogía metalica y alteración en
eralization lamprophyre dikes at 3.8 Ma. un sector del Stock Tonalitico del yacimiento El Teniente: Unpublished
Honours thesis, Santiago, Universidad de Chile, 175 p.
Acknowledgments Garrido, I., Riveros, M., Cladouhos, T., Espineira, D., and Allmendinger, R.,
This work was conducted as part of the senior author’s 1994, Modelo geológico estructurál del yacimiento El Teniente: Congreso
Ph.D. dissertation at the University of Tasmania, which was Geológico Chileno, 7th, Concepción, 1994, Actas, v. 2, p. 1553–1558.
Garwin, S., 2002, The geological setting of intrusion-related hydrothermal
part of the Australian Mineral Industry Research Assocation systems near the Batu Hijau porphyry Cu-Au deposit, Sumbawa, Indone-
(AMIRA)-funded Giant Ore Deposits Systems project sia: Society of Economic Geologists Special Publication 9, p. 333–366.
(P511). We thank all of the other members of the P511 re- Godoy, E., Yañez, G., and Vera, E., 1999, Inversion of an Oligocene volcano-
search team, particularly Peter Hollings, Peter Frikken, Glen tectonic basin and uplifting of its superimposed Miocene magmatic arc in
the Chilean Central Andes: First seismic and gravity evidences: Tectono-
Masterman, Paul Gow, and Gem Midgley, our AMIRA indus- physics, v. 306, p. 217–236.
try sponsors, and also the AMIRA research coordinator, Joe Gustafson, L.B., and Hunt, J.P., 1975, The porphyry copper deposit at El Sal-
Cucuzza. The senior author received an Australian Research vador, Chile: ECONOMIC GEOLOGY, v. 70, p. 857–912.
Council (ARC) APA-I postgraduate research scholarship, Guzman, C.G., 1991, Alteración y mineralización de los Pórfidos Dioriticos
which is gratefully acknowledged. We also thank the ARC for del sector centrál, yacimiento El Teniente: Unpublished honours thesis,
Santiago, Universidad de Chile, 143 p.
additional funding through the Special Research Centre and Heidrick, T.L., and Titley, S.R., 1982, Fracture and dike patterns in Laramide
Linkage grant schemes. The Re-Os work was funded by NSF plutons and their structural and tectonic implications; American South-
grant EAR-0087483 (H Stein). Supintendencía de Geología west, in Titley S.R., ed., Advances in geology of porphyry Cu deposits,
El Teniente, CODELCO-Chile, and CODELCO Central are southwestern North America: Tucson, University of Arizona Press, p.
thanked for providing additional financial and logistical sup- 73–91.
Holliday, J.R., Wilson, A.J., Blevin, P.L., Tedder, I.J., Dunham, P.D., and
port. Francisco Camus and Jorge Skármeta are thanked for Pfitzner, M., 2002, Porphyry Au-copper mineralization in the Cadia dis-
organizing access to El Teniente and for their support and trict, eastern Lachlan fold belt, New South Wales, and its relationship to
helpful discussions. Patricio Zuñíga, Ricardo Floody, Rodrigo shoshonitic magmatism: Mineralium Deposita, v. 37, p. 100–116.
Morel, and all of the other geologists and engineers from El Howell, F.H., and Molloy, J. S., 1960, Geology of the Braden orebody, Chile,
South America: ECONOMIC GEOLOGY, v. 55, p. 863–905.
Teniente, and also Alex Losada, Ron Berry, and Jocelyn Mc- Kay, S.M., and Kurtz, A., 1995, Magmatic and tectonic characterization of
Phie are thanked for many useful conversations and for their the El Teniente region: Internal report, Superintendencía de Geología, El
assistance onsite. Thanks to reviewers R. Tosdal, R. Sillitoe, Teniente, CODELCO, 180 p.
and A. Skewes, and also to M. Hannington, for their detailed Kay, S., Mpodozis, C., and Coira, B., 1999, Neogene magmatism, tectonism,
critiques of the paper and comments that have helped to im- and mineral deposits of the central Andes (22° to 33° latitude): Society of
Economic Geologists Special Publication 7, p. 27–59.
prove the quality of this manuscript. Kirkham, R.V., and Sinclair, W.D., 1988, Comb quartz layers in felsic intru-
sions and their relationship to porphyry deposits: Canadian Institute of
August 4, 2004; July 15, 2005 Mining and Metallurgy, v. 39, p. 50–71.
Koide, H., and Bhattacharji, S., 1975, Formation of fractures around mag-
REFERENCES matic intrusions and their role in ore localization: ECONOMIC GEOLOGY, v.
Acocella, V., Cifelli, F., and Funiciello, R., 2000, Analogue models of collapse 70, p. 781–799.
calderas and resurgent domes: Journal of Volcanology and Geothermal Re- Kurtz, A., Kay, S.M., Charrier, R., and Farrar, E., 1997, Geochronology of
search, v. 104, p. 81–96. Miocene plutons and exhumation history of the El Teniente region, central
Atkinson, W.W., Souviron, S., Vehrs, T.I., and Faunes, A., 1996, Geology and Chile (34–35ºS): Revista Geológica de Chile, v. 24, p. 75–90.
mineral zoning of the Los Pelambres porphyry Cu deposit, Chile: Society Le Bel, L., 1979, Magmatic and hydrothermal micas in the environment of
of Economic Geologists Special Publication 5, p. 131–155. the Cerro Verde-Santa Rosa porphyry Cu, Peru, in Robert, J. L., ed., Les
Burnham, C.W., 1979, Magmas and hydrothermal fluids, in Barnes, H.L., Micas; Chimie et cristallochimie: Paris, Masson, p. 35–41.
ed., Geochemistry of hydrothermal ore deposits: New York, Wiley-Inter- Lindgren, W., and Bastin, E.S., 1922, Geology of the Braden mine,
science, p. 71–136. Rancagua, Chile: ECONOMIC GEOLOGY, v. 17, p. 863–905.

0361-0128/98/000/000-00 $6.00 1002

 EL TENIENTE Cu-Mo PORPHYRY DEPOSIT, CHILE 1003

Lindsay, D.D., Zentilli, M., and Rojas de la Rivera, J., 1995, Evolution of an Rytuba, J.J., 1994, Evolution of volcanic and tectonic features in caldera set-
active ductile to brittle shear system controlling mineralization at tings and their importance in localization of ore deposits: ECONOMIC GE-
Chuquicamata porphyry copper deposit, northern Chile: International Ge- OLOGY, v. 89, p. 1687–1696.
ology Reviews, v. 37, p. 945–958. Serrano, L., Vargas, R., Stambuk, V., Aguilar, C., Galeb, M., Holmgren, C.,
Lowell, D., and Guilbert, J.M., 1970, Lateral and vertical alteration-mineral- Contreras, A., Godoy, S., Vela, I., Skewes M.A., and Stern C.R., 1996, The
ization zoning in porphyry ore deposits: ECONOMIC GEOLOGY, v. 65, p. late Miocene to early Pliocene Rio Blanco-Los Bronces copper deposit,
373–408. Central Chilean Andes: Society of Economic Geologists Special Publica-
Maksaev, V., Munizaga, F., McWilliams, M., Fanning, M., Mathur, R., Ruiz, tion 5, p. 119–130.
J., and Thiele, K., 2002, El Teniente porphyry Cu deposit in the Chilean Shannon, J.R., Walker, B.M., Carten, R.B., and Geraght, E.P., 1982, Unidi-
Andes: New geochronological time frame and duration of hydrothermal ac- rectional solidification textures and their significance in determining rela-
tivity [abs]: Geological Society of America Abstracts with Programs, v. 34, tive ages of intrusions at the Henderson mine, Colorado: Geology, v. 10, p.
no. 6, p 336. 293–297.
Maksaev, V., Munizaga, F., McWilliams, M., Fanning, M., Mathur, R., Ruiz, Sillitoe, R.H., 1985, Ore-related breccias in volcanoplutonic arcs: ECONOMIC
J., and Zentilli, M., 2004, New chronology for El Teniente, Chilean Andes, GEOLOGY, v. 80, p. 1467–1514.
from U-Pb, 40Ar/39Ar, Re-Os, and fission-track dating: Implications for the ——2000, Gold-rich porphyry deposits: Descriptive and genetic models and
evolution of a supergiant porphyry Cu-Mo deposit: Society of Economic their role in exploration and discovery: Reviews in Economic Geology, v.
Geologists Special Publication 11, p. 15–54. 13, p. 315–345.
Ossandón, G., 1974, Petrografía y alteración del Pórfido Dacitico, yacimiento Skewes, A., Arévalo, A., Floody, R., Zúñiga, P.H., and Stern, C.R., 2002, The
El Teniente: Unpublished honours thesis, Santiago, Universidad de Chile, giant El Teniente breccia deposit: Hypogene copper distribution and em-
112 p. placement: Society of Economic Geologists Special Publication 9, p.
Reich, M.H., 2000, Estudio petrográfico, mineraloquímico y geoquímico de 299–332.
los cuerpos intrusivos de Sewell y La Huifa en el sector del yacimiento El Thiele, R., Beccar, I., Levi, B., Nystrom, J., and Vergara, M., 1991, Tertiary
Teniente, VI Región, Chile: Unpublished Honours thesis, Concepción, Andean volcanism in a caldera-graben setting: Geologische Rundschau, v.
Universidad de Concepción, 95 p. 80, p. 179–186.
Rivera, O., and Cembrano, J., 2000, Modelo de formación de cuencas Titley, S.R., 1990, Evolution and style of fracture permeability in intrusion-
volcano-tectónicas en zonas de transferencia oblicuas a la cadena Andina: centered hydrothermal systems, in Titley S.R., ed., The role of fluids in
el caso de las cuencas Oligo-Miocenos de Chile central y su relación con crustal processes: Washington DC, National Acadamic Press, p. 50–63.
estructuras WNW-NW (33°00'-34°30' LS) [abs]: Congresso Geológico Tosdal, R.M., and Richards, J.P., 2001, Magmatic and structural controls on
Chileno, 9th, Puerto Varas, Chile, 2000, Actas, 5 p. the development of porphyry Cu ± Mo ± Au deposits: Reviews in Eco-
Rivera, O., and Falcón, M., 2000, Las Formaciones Farellones, Coya- nomic Geology, v. 14, p. 157–181.
Machalí y Abanico en los aldredores del yacimiento El Teniente: Villalobos, J., 1975, Alteración hidrotermal en las andesitas del yacimiento El
Sequencias de cuencas volcano-tectonicas transversales del Oligo-Mioceno Teniente, Chile: Unpublished Ph.D. thesis, Santiago, Universidad de Chile,
de Chile central (33°45'-34°30' LS): Congresso Geológico Chileno, 9th, 125 p.
Puerto Varas, Chile, 2000, Actas, 5 p. Zúñiga, P., 1982, Alteración y mineralización hipógenas en el sector oeste del
Riveros, M., 1989, Geología del pórfido latitico sector sur yacimiento El yacimiento El Teniente: Unpublished Honours thesis, Santiago, Universi-
Teniente: Unpublished Honours thesis, Santiago, Universidad de Chile, dad de Chile, 107 p.
133 p.
Rojas, A., 2002, Petrografía y geoquímica del pórfido dacitico Teniente,
yacimiento El Teniente, Provincia de Cachapoal, VI Región, Chile:
Unpublished Honours thesis, Concepción, Universidad de Concepción,
118 p.

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