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Abstract

Antamina, the world’s largest copper-zinc skarn deposit, entered production in 2001. This paper describes the development of the geologic model for the feasibility study (1996–1998). Antamina is located in the eastern part of the Western Cordillera of northern Peru at latitude 9° 32′ S and longitude 77° 03′ W and 4,200 to 4,800 m in elevation.

Antamina has a long history of exploration and is a case study of successful creation of an orebody from a mineral resource. While small-scale mining is recorded intermittently since 1860, the first serious exploration was not begun until a century later by Cerro de Pasco Corporation (1952–1970), followed by a Minero Peru-Geomin (Romania) partnership, which conducted a feasibility study (1970–1976) with a reserve of 128.6 million metric tons (Mt) at 1.6 percent Cu and 1.3 percent Zn.

Privatization of the project was won by Compañía Minera Antamina in 1996. This consortium undertook a major exploration program and completed a full feasibility study in 1998 that defined a minable, open-pittable resource of 500 Mt at 1.2 percent Cu, 1.0 percent Zn, 0.03 percent Mo, and 12 g/t Ag within a global resource of 1,500 Mt. Production is by open pit and flotation at 70,000 t/d, producing 270,000 t of copper and 162,000 t of zinc in concentrates per year. This makes Antamina the seventh largest copper and the third largest zinc mine in the world.

Antamina is located in the polymetallic belt of central Peru, which comprises copper, zinc, silver, lead and gold deposits related to mid to late Miocene calc-alkaline stocks. The regional geologic setting comprises Late Jurassic to Late Cretaceous siliciclastic to carbonate sequences in a northwest-trending foreland fold-thrust belt of mid-Eocene age, the Incaic II deformation phase. Antamina is hosted by calcareous siltstone and mudstone of the Late Cretaceous Upper Celendin Formation. Skarn mineralization forms a shell over and around a quartz monzonite porphyry stock of late Miocene age, which itself hosts subeconomic porphyry copper-molybdenum mineralization. The skarn body is approximately 2,500 m long in a northeasterly direction and up to 1,000 m wide, with a known vertical extent of 1,000 m. The skarn consists mainly of andraditic garnet. It is symmetrically zoned around the intrusion from proximal brown garnet endoskarn and exoskarn outward to green garnet exoskarn, with peripheral wollastonite-diopside exoskarn. Significant copper mineralization is hosted by endoskarn. Retrograde chlorite skarn and hydrothermal breccia are minor.

Metals are zoned laterally from a central copper-only zone to a peripheral copper-zinc zone. Chalcopyrite is distributed throughout all skarn zones. Appearance of sphalerite approximately coincides with the transition from brown to green garnet. The copper-zinc zone thins at depth and originally appears to have closed over the top of the intrusion, although most of it has been eroded. The main copper mineral in the wollastonite-diop-side skarn is bornite, and this zone also has elevated gold values. Silver, lead, and bismuth values are highest in the outer part of the copper-zinc zone and adjacent marble. Molybdenite occurs in the intrusion and adjacent skarn, as well as being abundant in the wollastonite-diopside skarn. Sulfides were deposited during the late prograde and retrograde phases and occur disseminated interstitial to garnet; as irregular massive sulfide zones; and as veinlets. The deposit was unroofed by glaciation and is exposed in a glacial valley; hence there is no significant oxidation or enrichment.

Antamina is an oxidized calcic copper skarn related to a calc-alkaline quartz monzonite porphyry stock containing subeconomic porphyry copper-molybdenum mineralization. The outer zinc zone is unusually well developed. Features that appear to have contributed to Antamina’s world-class status include a possible mantle origin of the intrusions, the basin-margin setting of the host sedimentary rocks, favorable structural preparation, limited retrograde alteration, and partial preservation of the intrusion roof zone.

Introduction

The Antamina deposit, the world’s largest skarn deposit of both copper and zinc, entered production in 2001. The deposit has a long exploration history and is a case study of successfully creating an ore deposit from a mineral resource. This paper describes development of the geologic model for Antamina made during the feasibility study (1996–1998) and is based on the results of extensive diamond drilling, geologic mapping, and mineralogic studies. This geologic model was the basis for the resource calculation and production decision. Parts of this work have been described previously by Redwood (1998, 1999, 2003) and O’Connor (1999). Research initiated during the feasibility study was described by Love and Clark (1998a, b) and Love et al. (2000, 2001, 2003a, b, 2004).

Antamina is located in the central Andes of northern Peru at latitude 9° 32′ 17″ S and longitude 77° 03′ 51″ W, between 4,300 and 5,073 m in elevation, and 270 km north of Lima and 130 km east of the Pacific Ocean (Fig. 1). The topography is characterized by steep northwest trending ridges, deep canyons, and short glacial valleys with lakes. Politically, Antamina lies in the District of San Marcos, Province of Huari and Department of Ancash. The nearest town is San Marcos, 10 km to the west at an elevation of 2,964 m (Fig. 1). The altitude zone is subalpine with annual precipitation of approximately 960 mm, an average annual temperature of 6°C, and a temperature range of −° to +16°C. There is a mild rainy season between October and April, while the rest of the year is drier with more extreme temperatures and some snow. The vegetation zone is wet Páramo or high-altitude tall grassland transitional to Puna high-altitude grassland, with the land used for grazing and subsistence farming.

Fig. 1.

Location of Antamina, Peru.

Fig. 1.

Location of Antamina, Peru.

History

Copper was mined at Antamina in pre-Spanish times (Raimondi, 1873) and the deposit name means copper mine, derived from anta meaning copper in Quechua and the Spanish mina or mine. Antamina is only 10 km east of the ruins of one of the oldest civilizations in the Americas at Chavín de Huántar (ca. 3,000−2,200 yr B.P.), where gold and silver artefacts have been found (Fig. 1). However, Antamina is not mentioned in any of the Spanish colonial mining records.

The first description of Antamina was by the Italian naturalist Antonio Raimondi who visited the area in November 1860 as part of a study of the mineral deposits of the Ancash Department for Henry Meiggs, who planned a railway. The first known operator was Carlos Pflucker who in 1859 to 1860 dug a 25-m-deep shaft and an adit but had abandoned them by the time Raimondi visited and described several other mines. Argentiferous galena from one mine was being smelted at Juproc, 5 km to the southwest (Fig. 2), to produce lead ingots weighing about 34 kg and containing 24 oz of silver (Raimondi, 1873, p. 542–548). The smelter used local coal and quenual wood, and the ruins can still be seen.

Fig. 2.

Geology of the Antamina district (after Glover, 1997).

Fig. 2.

Geology of the Antamina district (after Glover, 1997).

In 1903, Vicente Lezameta started mining at Antamina and produced copper mat with a grade of 32 percent. He returned in 1912 to 1914 and made an unsuccessful attempt to leach copper (Diez Canseco, 1920). With the start of the Great War in 1914 there was a search for new copper deposits by Cerro de Pasco Copper Corporation and several well-known geologists visited Antamina, including E. Diez Canseco (Diez Canseco, 1920), Donald J. McLaughlin, and J. L. Glidden. A. H. Means visited in 1925 for Northern Peru Mining and Smelting Company (Asarco), which drilled eight diamond holes totaling 780 m in search of porphyry copper mineralization. The peripheral silver, lead, and zinc vein deposits, such as Fortuna, Rosita de Oro, and Casualidad (Fig. 3), were mined on a small scale after World War II and were in production in 1948 to 1949 when Bodenlos and Ericksen (1955) mapped them for the U.S. Geological Survey; they were mined intermittently until 1998.

Fig. 3.

Geology of the Antamina copper-zinc skarn deposit, showing locality names (after Hathaway, 1997).

Fig. 3.

Geology of the Antamina copper-zinc skarn deposit, showing locality names (after Hathaway, 1997).

The first significant exploration of Antamina was carried out by Cerro de Pasco Corporation between 1952 and 1970 (Terrones, 1958; Petersen, 1965). The company focused on the Laberinto zone (Fig. 3) where the steep slopes on the east side of the valley allowed easy underground access by means of adits on several levels. They drilled 32 diamond holes for a total of 3,200 m, of which 18 were from surface and the rest underground. They drifted and crosscut 4,300 m, drove raises totaling 220 m, and dug 19 trenches for 2,064 m. The objective was a high-grade copper deposit and they defined over 1 Mt at >3 percent Cu plus a lower grade reserve of 10 Mt (Terrones, 1958; Petersen, 1965).

Antamina was expropriated from Cerro de Pasco Corporation on October 30, 1970, and transferred to the state company, Empresa Minera del Perú S.A. (Minero Perú), which in 1973 formed the Empresa Minera Especial Antamina SRL in partnership with Geomin (49%), the mining agency of the government of Romania. This consortium carried out a systematic exploration program resulting in a full feasibility study. The work consisted of 100 diamond drill holes totaling 12,000 m on a grid in the Taco area (Fig. 3), 920 m of new underground development, rehabilitation of 3,300 m of old workings, and metallurgical testwork, with a pilot plant at Catac, 120 km from the property (Fig. 1). The feasibility study, completed in 1976, anticipated an initial open pit producing 10,000 t/d of ore for seven years, followed by 20,000 t/d for 13 yrs. The initial study was revised in 1978, 1979, and 1982 at lower production rates of 2,500 to 5,000 t/d, with the objective of limiting capital investment.

Due to its inability to finance the project, Empresa Minera Especial Antamina was disbanded in December 1981 and the project reverted to Minero Perú. In 1992, Minero Perú attempted to market Antamina, and the following year the property was transferred to Empresa Minera del Centro del Perú S.A. (Centromín Perú) to become part of its privatization package. The reserves (proven and probable) were 128.6 Mt at 1.61 percent Cu, 1.33 percent Zn, 17.7 g/t Ag, and 0.04 percent Mo, with a resource (“prospective and potential reserves”) of 542.2 Mt.

Exploration and mine development

The public bid on July 12, 1996, was won by Inmet Mining Corporation and Rio Algom Ltd., both of Canada, in a 50–50 joint venture. Compañía Minera Antamina S.A. was formed and the contract signed on September 6, 1996. The successful offer comprised US$20 million in cash on signing, a work commitment of US$13.5 million over two years, followed by a decision to exercise the option to acquire 100 percent by making an investment commitment of US$2.5 billion within five years from the date of signing. Thirty percent of any unspent difference was to be paid to Centromín at the end of the fifth year. Between August 1996 and July 1997, a major exploration program was carried out to define reserves, and a full feasibility study was completed in March 1998. A total of 103,704 m of diamond drilling was carried out in 271 holes, and a 230-m drift for bulk metallurgical sampling was excavated. A reverse-circulation drill program was carried out for condemnation purposes (3,410 m) and geotechnical drilling also completed. Detailed geologic maps were made, airborne magnetic and radiometric surveys were purchased, and ground magnetic and induced polarization (IP) surveys were carried out.

Subsequent to the feasibility study, Inmet sold its interest in Antamina on July 13, 1998 to Noranda Inc. and Teck Corporation. Mitsubishi Corporation bought 10 percent on March 25, 1999. Current ownership of Antamina is BHP-Billiton plc (Rio Algom Ltd.) 33.75 percent, Noranda Inc. 33.75 percent, Teck Cominco Ltd. 22.5 percent, and Mitsubishi Corporation 10 percent.

The feasibility study defined a resource (measured, indicated and inferred) of 990 Mt at 1.2 percent Cu, 1.0 percent Zn, 0.03 percent Mo, and 13 g/t Ag at a cutoff of 0.7 percent Cu equiv. This is contained within a global resource (all categories, 0 percent Cu equiv cutoff) of 1.5 Bt, which is open at depth. The deepest hole cut 722 m at 1.7 percent Cu and 1.35 percent Zn, which also remains open at depth. A pit was designed around the measured and indicated resource of 760 Mt to give a diluted minable resource of 500 Mt at 1.2 percent Cu, 1.0 percent Zn, 0.03 percent Mo, and 12 g/t Ag. Based on this resource, an open-pit mining operation of 70,000 t/d for 20 yrs, with an average stripping ratio of 2.7 to 1, was planned. The decision to develop the project was announced on September 16, 1998. Construction was completed on May 31, 2001, and the first copper-zinc concentrate was shipped on July 12, 2001. Commercial production was achieved on October 1, 2001, four months ahead of schedule. The total construction cost was US$2,148 million. Payment of US$111.5 million, the balance of the investment commitment, was made to Centromín on August 5, 2002. Subsequent to the feasibility study, the revised proven and probable mineral reserve was 559 Mt at 1.24 percent Cu, 1.03 percent Zn, 0.029 percent Mo, and 13.71 g/t Ag (0.7% Cu equiv cutoff; Compañía Minera Antamina press release, Canada Newswire, Antamina project update, November 27, 2000).

The ore is treated by flotation to produce 1.3 Mt of concentrate per year, making Antamina the third largest concentrate producer in the world (after the Chuquicamata and Escondida mines). Planned annual metal production is 270,000 t (600 Mlb) of copper and 162,000 t (360 Mlb) of zinc. Average annual production for the first 10 yrs was planned to be 306,000 t (675 Mlb) of Cu and 283,000 t (625 Mlb) of Zn, making Antamina the world’s seventh largest copper producer and the third for zinc. Six concentrates are produced, copper-low bismuth, copper-high bismuth, zinc, molybdenite, lead-bismuth, and bornite, with planned recoveries of 93 percent Cu, 77 percent Zn, 45 percent Mo, and 75 percent Ag. The concentrates are transported 300 km by pipeline to a new port at Punta Lobitos in Huarmey (Fig. 1). Average cash costs per pound of copper, net of byproduct credits, were projected at US$0.35/lb. In the first full year of production (2002), Antamina boosted Peru’s gross domestic product by 1.4 percent and increased mining exports, which account for more than half the country’s exports, by 30 percent. The mine increased Peruvian copper production by 35 percent and zinc output by 50 percent. Peru now ranks as the world’s third largest zinc producer and fifth largest copper producer.

Regional Geology

Antamina is located in the easternmost part of the Western Cordillera, east of the Cordillera Blanca (Fig. 1). The regional geology has been described by Cobbing (1985), Cobbing et al. (1996), Jaillard and Soler (1996), and Benavides-Cáceres (1999), and the following summary is based on their work. The Eastern Cordillera, which lies east of Antamina, is Paleozoic and older in age, formed of late Precambrian schists (Marañon Complex) in the north and thick early Paleozoic marine sedimentary rocks in the south. The Western Cordillera is Mesozoic and Tertiary and constitutes the Andean orogenic belt (sensu stricto). It is formed of Mesozoic, ensialic, extensional, marginal basins related to eastward subduction and extends the length of the Andes (Western trough). The basin is bounded by Precambrian craton to both east (Marañon Complex) and west (Arequipa Massif in southern Peru and Outer Shelf High offshore northern Peru). A western sub-basin, the Huarmey basin, has up to 9,000 m of submarine volcanic rocks of mainly basaltic and andesitic composition, the Casma Group, with no observed base. While the oldest volcanic rocks date from the Triassic in northern Peru, the main volcanism was Albian. This sub-basin was closed in the mid-Cretaceous Mochica tectonic phase and was intruded along its axis by the Late Cretaceous Coastal batholith granitoids, which crop out in the western parts of the Western Cordillera to the coast.

An eastern sub-basin, the Chavin basin, was separated from the Huarmey basin by a horst, the Santa belt, with a thinner sedimentary sequence. Sedimentation took place between the Late Jurassic and Late Cretaceous (Table 1). The oldest sedimentary rocks are dark slate and quartzite of the Late Jurassic Chicama Formation, which crop out in the western parts of the sub-basin. These are followed upward by thick deltaic sandstone, shale, and coal, with a thin marine limestone (Early Cretaceous Goyllarisquisga Group), and then by a marine transgressive sequence of thick marine carbonate (Early to Late Cretaceous Pariahuanca, Chulec, Pariatambo, Jumasha, and Celendin Formations; Table 1). The sub-basin was not affected by the closure of the Huarmey basin in the mid Cretaceous, but uplift resulted in molassic red-bed sedimentary rocks (Casapalca Formation) to the east in the Chavin basin during the Late Cretaceous and Paleocene. The Antamina deposit is hosted by the Celendin Formation on the eastern platform of the Chavin basin. The basin is bounded to the east by a basement high (Marañon high) with a much thinner Mesozoic sedimentary sequence and farther east by Mesozoic sandstone and carbonate deposited in an external foreland basin (Eastern basin) onlapping the Brazilian Shield, which forms the Subandean zone fold-thrust belt.

Table 1.

Stratigraphy of the Antamina District

PeriodEpochAgeAge (Ma)GroupFormationThickness (m)Lithology
Santonian87.5−84Celendin115–225Marl, nodular limestone, thinly bedded, fossiliferous; Antamina deposit
LateConiacian88.5−87.5
Turonian91−88.5
Cenomanian97.5−91Jumasha200–800Gray limestone, massive, thickly bedded 1–2 m, micritic, poorly fossiliferous, dolomitic in parts
Pariatambo100–200Dark-gray marl and limestone, bituminous, thinly bedded
Albian113−97.5Dark-gray chert nodules abundant at top
Chulec100–200Thinly bedded shelly limestone, marl, yellow-cream color
CretaceousEarlyPariahuanca54–210Massive shelly limestone, 1-to 2-m beds, calcareous sandstone at base
Aptian119−113Yellowish color
Farrat20White sandstone
Barremian124−119GoyllarisquisgaCarhuaz1,300– 500Shale, silty shale, thin quartz sandstone beds, brown-purplish; disconformable
Hauterivian131−124Gray shales and coal at base
Santa150–341Blue-gray shelly limestone, 0.1-to 1-m beds, chert nodules, parts dolomitic
Valanginian138−131Chimu600–685Quartz sandstone, white; dark shale and coal at base
Berriasian144−138Oyon100Shale, siltstone, sandstone, coal; important thrust plane
JurassicLateTithonian152−144Chicama>1,500Gray slate, quartzite, sandstone
PeriodEpochAgeAge (Ma)GroupFormationThickness (m)Lithology
Santonian87.5−84Celendin115–225Marl, nodular limestone, thinly bedded, fossiliferous; Antamina deposit
LateConiacian88.5−87.5
Turonian91−88.5
Cenomanian97.5−91Jumasha200–800Gray limestone, massive, thickly bedded 1–2 m, micritic, poorly fossiliferous, dolomitic in parts
Pariatambo100–200Dark-gray marl and limestone, bituminous, thinly bedded
Albian113−97.5Dark-gray chert nodules abundant at top
Chulec100–200Thinly bedded shelly limestone, marl, yellow-cream color
CretaceousEarlyPariahuanca54–210Massive shelly limestone, 1-to 2-m beds, calcareous sandstone at base
Aptian119−113Yellowish color
Farrat20White sandstone
Barremian124−119GoyllarisquisgaCarhuaz1,300– 500Shale, silty shale, thin quartz sandstone beds, brown-purplish; disconformable
Hauterivian131−124Gray shales and coal at base
Santa150–341Blue-gray shelly limestone, 0.1-to 1-m beds, chert nodules, parts dolomitic
Valanginian138−131Chimu600–685Quartz sandstone, white; dark shale and coal at base
Berriasian144−138Oyon100Shale, siltstone, sandstone, coal; important thrust plane
JurassicLateTithonian152−144Chicama>1,500Gray slate, quartzite, sandstone

Notes: Based on Benavides (1956), Cobbing et al. (1996), and Wilson (1963); time scale from Anon (1998)

The Chavin basin was deformed by the Incaic II folding phase in the middle Eocene (43−42 Ma). There was extensive folding and reverse faulting throughout the basin, and formation of a foreland fold-thrust belt in the eastern part, the platform along the boundary with the Marañon high (Marañon fold-thrust belt or imbricated zone; Wilson et al., 1967; Mégard, 1984). Antamina is located in this fold-thrust belt.

Following the deformation, an erosional surface developed across the Chavin and Huarmey basins and Coastal batholith, on which up to 3,000 m of subaerial volcanic rocks accumulated during the Tertiary (Calipuy Group) in a belt 40 km wide, forming the Cordillera Negra (Fig. 1). During the Miocene there were four short compressive pulses (Quechua I, II, III, and IV) at ca. 17, 10 to 9, 7 to 5, and 2 Ma, separated by tectonically neutral or extensional periods (McKee and Noble, 1982; Sébrier and Soler, 1991). In the mid-to late Miocene, the Cordillera Blanca batholith was intruded in the eastern part of the Western trough to form the Cordillera Blanca (ca. 13.7−6.3 Ma; Cobbing, 1998; Fig. 1). Concurrently there was widespread magmatism (medium to high K calc-alkaline) across the Western and Eastern Cordilleras to form small stocks, including that at Antamina (Sébrier and Soler, 1991).

Metallogeny

Antamina lies in the eastern part of the polymetallic belt of central Peru, which is located in the Western Cordillera between lat 6° and 14° S and limited at both ends by transverse, arc-normal structures. Mineralization comprises zinc, lead, silver, copper, and gold, mainly in hydrothermal deposits related to calc-alkaline high-level intrusions of mid-to late Miocene age (Soler et al., 1986; Noble and McKee, 1999; Petersen, 1999). The belt was traditionally known for major zinc, lead, and silver mines at Cerro de Pasco, Milpo, Casapalca, and Morococha (Peterson, 1965). Porphyry copper and copper-gold deposits also occur at Toromocho, Michiquillay, La Granja, and Cerro Corona (Noble and McKee, 1999), and in the past decade the belt has become a major gold producer with discovery of high-sulfidation epithermal deposits like Yanacocha (Harvey et al., 1999) and Pierina (Volkert et al., 1998). The deposits of the belt are characterized by large amounts of ancillary metals, including bismuth, cadmium, selenium, tellurium, antimony, indium, mercury, germanium, tin, tungsten, molybdenum, and arsenic (Soler et al., 1986).

Antamina Geology

The Antamina deposit is 2,500 m long, in a northeasterly direction, and up to 1,000 m wide (Fig. 3). The minable reserve is located in the widest, northern part. The orebody is located between elevations of 4,350 and 3,900 m, to which depths the reserves are calculated. However, the entire mineralized skarn has a vertical extent of >1,000 m between outcrops as high as 4,650 m and the bottom of the deepest drill hole at 3,632 m. The shape of the outer limit of the skarn body shows no significant change with depth.

Geomorphology and overburden

The Antamina deposit underlies a 4,000-m long, 600 m-deep, U-shaped glacial valley, which is surrounded by concordant mountain peaks at 4,600 to 4,700 m in elevation (max 5,073 m), remnants of the Puna land surface (Figs. 46). The head of the valley had a cirque lake, Lake Antamina, which was drained before mining (Figs. 36). The cirque was formed during a young glacial advance and is separated from the main valley father downstream by a rock ridge, Taco ridge (Figs. 3, 5). Mineralization crops out on Taco ridge and continues beneath Lake Antamina; it then strikes east and crops out on the valley side east of the lake (Oscarina zone; Figs. 3, 6), with an offshoot continuing east through the ridge to Rosita de Oro (Figs. 3, 6). Southwest of Taco ridge, the deposit continues beneath the Antamina valley to crop out along the southern slope of the valley as far as the Usu Pallares hanging valley (Figs. 3, 5).

Fig. 4.

Oblique air photograph looking northeast along the Antamina valley in 1997 before mining. The skarn deposit crops out on Taco ridge (with drill roads) southwest of the lake and continues southwest beneath the valley, then along the southern edge of the valley to the Usu Pallares hanging valley (lower right with drill roads). From Taco ridge, the deposit continues diagonally under the lake and crops out on the eastern side of the head of the valley (Oscarina) and through the ridge (where the road cuts) to Rosita de Oro. The skarn deposit is hosted by indurated calcareous sediments of the Upper Celendin Formation, which crops out along the valley sides. The highest peaks (Cerro Contonga, 5,073 m, foreground left) are Jumasha Formation limestone.

Fig. 4.

Oblique air photograph looking northeast along the Antamina valley in 1997 before mining. The skarn deposit crops out on Taco ridge (with drill roads) southwest of the lake and continues southwest beneath the valley, then along the southern edge of the valley to the Usu Pallares hanging valley (lower right with drill roads). From Taco ridge, the deposit continues diagonally under the lake and crops out on the eastern side of the head of the valley (Oscarina) and through the ridge (where the road cuts) to Rosita de Oro. The skarn deposit is hosted by indurated calcareous sediments of the Upper Celendin Formation, which crops out along the valley sides. The highest peaks (Cerro Contonga, 5,073 m, foreground left) are Jumasha Formation limestone.

Fig. 5.

View looking west over the Antamina deposit in 1997 before mining, to show the oxidized outcrop of the skarn on Taco ridge left of the lake. The skarn continues beneath the lake to the Oscarina area on the valley side, from where the photograph was taken. Upper Celendin Formation calcareous sedimentary rocks underlie the valley sides and are overlain by Jumasha Formation limestone, which forms the Cerro Contonga peak (5,073 m). The Cordillera Blanca is in the distance.

Fig. 5.

View looking west over the Antamina deposit in 1997 before mining, to show the oxidized outcrop of the skarn on Taco ridge left of the lake. The skarn continues beneath the lake to the Oscarina area on the valley side, from where the photograph was taken. Upper Celendin Formation calcareous sedimentary rocks underlie the valley sides and are overlain by Jumasha Formation limestone, which forms the Cerro Contonga peak (5,073 m). The Cordillera Blanca is in the distance.

Fig. 6.

View of Antamina deposit, looking south in 1998 before mining. The skarn deposit can be seen cropping out at Taco (right of the lake), Laberinto (valley side below the anticline), and Oscarina (valley side above the lake) as far as Rosita (pass on left). The Antamina anticline (right) is a prominent culmination in one of the lower sheets of the thrust duplex in Upper Celendin Formation that hosts Antamina.

Fig. 6.

View of Antamina deposit, looking south in 1998 before mining. The skarn deposit can be seen cropping out at Taco (right of the lake), Laberinto (valley side below the anticline), and Oscarina (valley side above the lake) as far as Rosita (pass on left). The Antamina anticline (right) is a prominent culmination in one of the lower sheets of the thrust duplex in Upper Celendin Formation that hosts Antamina.

The valley contains two moraines representing two stages of glaciation. The older moraine is pyritic and the younger is limonitic and, in places, the two are separated by a ferricrete layer. The lower valley slopes are mantled by lateral moraine, talus, and colluvium. In the Laberinto and Oscarina areas (Fig. 3), ferricrete is up to several meters thick, with slope-parallel layers resting on pyritic bedrock. The upper, steep valley sides are either bare rock or covered by talus deposits and, locally, thin soil. Lake Antamina has a U-shaped bathymetric profile, with steep sides, a flat 50-m-deep bottom, and >32 m of soft, bedded, silt-clay lake sediments. The main valley has pyritic moraine on bedrock, overlain by thin peaty sediments. Overburden thickness is up to 36 m. At the southwestern end of the valley there are rock-fall deposits, with blocks up to 25 m in size.

The preglacial topography is interpreted as the Puna surface (younger than 14.5 Ma) at around 4,700 m, with peaks >5,000 m. A shallow river valley probably existed at Antamina, formed as a headwater during the Valley (post-14.5 to pre-6 Ma) and Canyon (post-6 Ma) periods (Wilson et al., 1967; Tosdal et al., 1984). During the main Pleistocene glaciation, ice accumulation carved out the Antamina valley and internal hanging valleys. The Antamina deposit was probably unroofed during the first glaciation, which exposed the fresh sulfides in the older moraine. In the following interglacial period there was oxidation of exposed sulfides forming ferricrete. This oxidation zone was partly removed by the second cirque glacier, as shown by the limonitic moraine formed during this stage.

Stratigraphy

The Antamina deposit is hosted by the Upper Celendin Formation, over which the Jumasha Formation has been thrust from the west (Figs. 2, 4, 5, 7). To the west, the Carhuaz Formation is in thrust contact with the Celendin and Jumasha Formations (Figs. 2, 7). East of Antamina, the Celendin Formation forms the core of a gently southeast plunging regional synclinorium (Fig. 7).

Fig. 7.

Long section A-A′ through the Antamina skarn deposit, showing district geology and structure (after Glover, 1997). Location of section is shown in Figure 2.

Fig. 7.

Long section A-A′ through the Antamina skarn deposit, showing district geology and structure (after Glover, 1997). Location of section is shown in Figure 2.

The Jumasha Formation comprises several hundred meters of massive, pale-gray, cliff-forming limestone with 36 to 51 percent CaO (Table 2). It is overlain by the Lower Celendin Formation, a thin (100 m?) transitional unit of interbedded limestone and calcareous siltstone with 53 to 54 percent CaO (Table 2).

Table 2.

Limestone Analyses from Antamina District

Jumasha Fm.Lower Celendin Fm.Upper Celendin Fm.
Sample no.6520165202LS03LS04LS01LS02LS0565203652046520565206
SiO2 (%)18.232.830.470.2013.5619.8727.6233.8028.1515.7038.63
TiO2 (%)0.120.120.020.020.180.310.460.480.500.320.56
Al2O3 (%)1.880.650.200.174.026.658.539.348.495.0910.48
Fe2O3 (%)0.530.290.190.181.813.143.843.602.391.614.34
MnO (%)0.010.010.010.020.040.050.070.050.030.030.09
MgO (%)7.021.111.510.812.432.662.742.702.302.242.89
CaO (%)35.8251.4453.4454.5041.5635.3529.2024.0826.9139.4018.03
Na2O (%)0.05<0.010.060.030.200.320.490.650.610.250.25
K2O (%)0.110.250.040.020.660.571.531.401.470.572.22
P2O5 (%)0.070.080.000.020.070.080.100.180.150.100.21
LOI (%)34.2441.7143.6643.6934.4728.2723.8428.7726.3232.6720.68
Total (%)98.0898.4999.8199.7999.8499.8999.9399.0597.3297.9898.38
C total9.5611.960.060.030.080.060.055.716.509.105.07
CO2 (%)34.2042.4243.3043.5133.8228.1623.4720.2322.9132.3017.82
SO3 totaln/an/a0.210.130.842.621.51n/an/an/an/a
Jumasha Fm.Lower Celendin Fm.Upper Celendin Fm.
Sample no.6520165202LS03LS04LS01LS02LS0565203652046520565206
SiO2 (%)18.232.830.470.2013.5619.8727.6233.8028.1515.7038.63
TiO2 (%)0.120.120.020.020.180.310.460.480.500.320.56
Al2O3 (%)1.880.650.200.174.026.658.539.348.495.0910.48
Fe2O3 (%)0.530.290.190.181.813.143.843.602.391.614.34
MnO (%)0.010.010.010.020.040.050.070.050.030.030.09
MgO (%)7.021.111.510.812.432.662.742.702.302.242.89
CaO (%)35.8251.4453.4454.5041.5635.3529.2024.0826.9139.4018.03
Na2O (%)0.05<0.010.060.030.200.320.490.650.610.250.25
K2O (%)0.110.250.040.020.660.571.531.401.470.572.22
P2O5 (%)0.070.080.000.020.070.080.100.180.150.100.21
LOI (%)34.2441.7143.6643.6934.4728.2723.8428.7726.3232.6720.68
Total (%)98.0898.4999.8199.7999.8499.8999.9399.0597.3297.9898.38
C total9.5611.960.060.030.080.060.055.716.509.105.07
CO2 (%)34.2042.4243.3043.5133.8228.1623.4720.2322.9132.3017.82
SO3 totaln/an/a0.210.130.842.621.51n/an/an/an/a

Notes: Samples prefixed by 65 analyzed by Intertek Testing Services Bondar Clegg and Co. Ltd., Vancouver; analyses by X-ray fluorescence on borate bead; loss on ignition (LOI) gravimetric at 1,000°C; total carbon by Leco; total Fe as Fe2O3; samples prefixed by LS analyzed by Fuller Company, Bethlehem, Pennsylvania; K2O and Na2O by flame atomic absorption; Mn reported as Mn2O3; LOI at 900°C; SO3 total by Leco induction furnace; trace pyrite in samples 65201, LS01, LS02, LS05, and 65205

The Antamina skarn is developed in the Upper Celendin Formation, formed of fine-grained calcareous siltstone or claystone and argillaceous limestone with 18 to 42 percent CaO (Table 2). The Upper Celendin is several hunderd meters thick in the Antamina area due to structural thickening by thrusting, but due to the lack of marker beds the true thickness is unknown. The Upper Celendin is recessive weathering and forms rounded topography with little outcrop. However, at Antamina, there is a 3,000-m-wide thermal aureole around the intrusion, which indurated the sedimentary rocks beyond the skarn zone, resulting in atypical cliffs (Figs. 47). As a result, the nonrecessive host rocks were originally considered to belong to the Jumasha Formation (Wilson et al., 1967). The key field evidence is provided by indurated beds traceable laterally from the deposit into the typical, soft-weathering Upper Celendin Formation. Where unaltered and unweathered, the Upper Celendin Formation is medium to dark gray, medium hard, and highly calcareous. Outcrops commonly have a beige color and, in road cuts, exhibit spheroidal weathering. The rock fractures in a characteristic blocky pattern with rough fractures. Bedding is poorly developed on a scale of 1 to 3 m and is enhanced by the effects of the thermal metamorphism. The rock is generally structurally featureless but may have slumped intervals up to tens of meters thick or concordant bedding on a centimeter scale. Other minor features include nodular beds, brachiopod shell debris, brown shale intercalations, crossbedded laminated siltstone or fine-grained sandstone interbeds, stromatolitic beds, and a distinctive dark-gray to black facies with wavy, centimeter-scale bedding (bioturbation or slumping), abundant shells, and bands of black chert nodules. Stylolites are commonly observed in drill core, where they are marked by scapolite concentrations when thermally metamorphosed.

Karst features, including solution cavities and carbonate deposited as stalactites, stalagmites, flowstone, and travertine terraces in stream beds, are well developed in the Jumasha and Lower Celendin limestones. The Upper Celendin is much less susceptible to karstic weathering and no karst features are seen at surface in the mine area. However, underground cavities in Celendin limestone with high water flow were encountered during drilling in the Laberinto, Valley, and south Taco areas (Fig. 3).

Structure

Antamina is located in the northwestern-trending Marañon fold-thrust belt, which is generally only 10 km wide but in the Antamina area attains 40 km (Fig. 2). The northeast-vergent thrust sequence developed during the middle Eocene Incaic II phase (43−42 Ma; Mégard, 1984). The structural setting of Antamina was clarified by mapping carried out by Glover (1997, 1998a-c), Hathaway (1997,1998a, b), and Redwood (1997; Figs 23, 7). The deposit is located in a transition zone between deep-water clastic sedimentary rocks with upright folding to the west and shelf carbonate with fold-thrust deformation to the east (Fig. 7). A series of 50° to 60° southwest-dipping thrust ramps developed at this tectonic transition and brought successively deeper parts of the stratigraphy into contact with the carbonate sequence (Figs. 4, 7). The structure is inferred to represent a major fault zone and to be a reactivated basin-margin fault.

The Antamina skarn deposit is located within a thrust duplex formed by at least six flat-lying thrust sheets of the Upper Celendin Formation, with Pariatambo Formation rocks in some of the lower sheets (Fig. 7). The sole thrust is not exposed but the roof thrust is partly preserved on the highest peaks as imbricate sheets of flat-lying Jumasha limestone. The latter has been thrust eastward over the Celendin Formation. Within the duplex, a prominent culmination in one of the lower thrust sheets forms the Antamina anticline (Fig. 6). To the west, the duplex is cut by the Antamina thrust, a thrust ramp fault with a 50° southwest dip, which juxtaposes Jumasha limestone against the Upper Celendin Formation (Figs. 45, 7). The thrust appears to be younger and out of sequence but is likely to have undergone reactivation as a normal fault (Fig. 7).

The Antamina intrusion and skarn are controlled by three northeast-striking lateral thrust ramps that are downthrown to the northwest, resulting in different structural levels on either side of the Antamina valley (Fig. 8). A tear fault is exposed at the head of the valley beneath a thrust flat. The hanging wall formed a flexure over the ramp resulting in strata locally plunging 20° northwest, opposite to the regional fold plunge. These lateral ramps are interpreted to mark the site of an old basement structure that during reactivation propagated upward through the deformed platform sequence of the fold-thrust belt.

Fig. 8.

Schematic block diagram of the Antamina copper-zinc skarn deposit, showing localization of intrusion and mineralization along lateral ramp, looking southeast (after Glover, 1997).

Fig. 8.

Schematic block diagram of the Antamina copper-zinc skarn deposit, showing localization of intrusion and mineralization along lateral ramp, looking southeast (after Glover, 1997).

Porphyry intrusion and skarn mineralization accompanied a minor extensional event, which may be correlated with the Quechua II phase. Localized extension on the southeastern side of the Antamina valley was accommodated by listric fault reactivation of frontal thrust ramps and by strike-slip movement along lateral thrust ramps. Several minor intrusive sheets were controlled by the listric faults. Within both the skarn and intrusions there are abundant zones of brittle deformation and slickensided fracture surfaces. However, no significant postmineral fault displacements have been identified.

Porphyry stock

The skarn deposit is developed around the Antamina intrusion (9.8 Ma; McKee et al., 1979; 10.34−10.27 Ma; Love et al., 2003a), a multiphase, quartz monzonite porphyry. Numerous intrusive phases were identified during core logging, with relative ages being shown by grouping them as early-, inter-, late-and postmineral in timing, in addition to several dike phases (Sillitoe, 1997). All the quartz monzonite porphyry phases contain phenocrysts of plagioclase, quartz, biotite, orthoclase, and lesser hornblende; some have megacrysts of orthoclase up to 10 cm long. Intrusions within each relative age group tend to have evolved to more potassic compositions, as shown by orthoclase phenocrysts or megacrysts in the later phases. Early mineral intrusions form the central part of the stock, with inter-and late mineral intrusions emplaced around the margins. A late mineral intrusion forms the main Valley and Usu Pallares dikes (Fig. 3).

The intrusive bodies comprise broad northeast-trending dikes that converge to form a stock at depth. The roof of the intrusion and some overlying skarn are preserved, with out-crop widths of 70 to 800 m. At the 3,900-m level, the intrusion forms an almost circular stock 800 m in a northeast direction by 750 m across. The stock has a northeastern-trending spur at the northeastern end of the Lake zone (350 m long × 150 m wide) and a southwestern-trending spur below the valley to the southwest (500 m long × 50–170 m wide). In total, the intrusions are 1,700 m long at this level. Exoskarn forms a shell 400 to 300 m wide around the intrusions.

Porphyry copper-molybdenum mineralization

The Antamina stock is overprinted by porphyry copper-molybdenum mineralization, but the grades are typically less than the cutoff (0.7% Cu equiv) and no resource was calculated. Where the intrusion has grades exceeding the cutoff, it is transformed to endoskarn and was included within the skarn domain in the geologic model.

The early, inter-, and late mineral intrusive phases were affected by potassic alteration, which decreases progressively in intensity as the phases become younger. In core, the potassic alteration is characterized by fine-grained, red-brown hydrothermal biotite in the groundmass and metastable black biotite phenocrysts. Thin sections also show K-feldspar in the groundmass, as coronas to plagioclase, and in veinlets. A-and B-type quartz veinlets containing pyrite, chalcopyrite, and molybdenite accompany the potassic assemblage. Veinlet density is highest in the oldest intrusions and decreases progressively as they become younger.

Phyllic alteration is poorly developed although widespread. It is generally characterized by weak to moderately intense alteration of plagioclase, biotite (magmatic and hydrothermal), and porphyry groundmass. The altered plagioclase has a pale to strong green, beige, or white color. The alteration assemblage includes sericite, muscovite, clay, chlorite, and calcite. The sericitic alteration is sporadically developed, and remnants of preexisting magmatic and potassic alteration minerals are abundant. Silicification may occur, typically as a selvage to D-type quartz-pyrite veinlets, which are abundant only in the Oscarina area (Fig. 3), where they are narrow (1 cm) and parallel. An unusual variety of phyllic alteration is found locally, typified by leached quartz phenocrysts in a strongly silicified groundmass, with purple to colorless fluorite found in veinlets and as fillings of the leached quartz vugs.

There is no definable zone of propylitic alteration at Antamina, although chlorite and calcite are present in parts of the phyllic alteration assemblage and, locally, the biotite is chloritized.

Hydrothermal alteration has been dated at 10.18 to 9.75 Ma (Love et al., 2003a).

Skarn Geology

The skarn is remarkably well zoned symmetrically outward from the Antamina stock as follows (Fig. 9): (1) brown garnet endoskarn with chalcopyrite; (2) brown garnet exoskarn with chalcopyrite; (3) green garnet exoskarn with chalcopyrite and sphalerite; (4) wollastonite-diopside exoskarn with bornite, sphalerite, and anomalous bismuth; and (5) recrystallized limestone and marble with veins or mantos of wollastonite-green garnet skarn with zinc, lead, and silver.

Fig. 9.

Cross section B-B′ of the Antamina copper-zinc skarn deposit, showing zonation of skarn and metals. Line of section is shown in Figure 3. All Cu present as chalcopyrite except for bn = bornite.

Fig. 9.

Cross section B-B′ of the Antamina copper-zinc skarn deposit, showing zonation of skarn and metals. Line of section is shown in Figure 3. All Cu present as chalcopyrite except for bn = bornite.

Garnet endoskarn

Endoskarn is readily identifiable on the basis of brown garnet pseudomorphic of a porphyry igneous texture, and the presence of porphyry relics. The outer contact zone tends to be a hybrid, plagioclase-rich monzonite porphyry (contaminated by limestone assimilation) with abundant xenoliths of marble or garnetite. Endoskarn forms a minor part of the total skarn and is typically developed only over a few meters at the margins of certain intrusions. The inner limit of garnet development in the stock is gradational, with plagioclase and groundmass minerals being selectively replaced. Postmineral intrusions crosscut the garnetite and have sharp contacts.

Endoskarn is most abundant in the roof of the intrusion, in upper levels in the Lake and Taco areas (Fig. 3), and porphyry with as little as 5 to 20 percent garnet carries good copper grade (>1% Cu). This roof zone is interpreted as comprising numerous narrow, discontinuous dikes in limestone, with pervasive garnet replacement of limestone and pervasive to partial garnet development in the intrusion. In such zones, the partly garnetized intrusions are grouped as brown garnet skarn for the purposes of the geologic model. Antamina is unusual in having ore in the endoskarn, which is not simply porphyry copper mineralization.

Garnet exoskarn

The main skarn variety is massive garnet skarn or garnetite. The color is consistently zoned from deep red-brown closest to the intrusion (mapped and logged as brown garnet skarn) to apple green near the marble contact (green garnet skarn). The color zonation is a continuum and there is no sharp contact between the colors. Some garnet crystals are also color zoned, and veinlets of one color of skarn can be seen cross-cutting the other. Microprobe analyses show no significant compositional differences between the two color types and both can be classified as andradite (grossular 0–28%, andradite 72–100%; Table 3; R. Lehne, pers. commun., 1996; Love et al., 2000). The garnets tend to be zoned from grossular-rich cores to andradite-rich rims, reflecting a decrease in aluminum and an increase in ferric iron. The endoskarn garnets are distinctive in composition, being richer in aluminum and lower in ferric iron, and are of grandite composition (grossular 33–58%, andradite 37–62%; Love et al., 2000).

Table 3.

Garnet Analyses

MineralBrown garnet skarnGreen garnet skarn
Analyses35 points46 points
SiO2 (%)34.06–35.3634.17–35.69
CaO (%)31.60–33.7531.02–34.28
FeO (%)25.68–28.3220.83–28.88
Al2O3 (%)0.87–2.140.10–5.95
MgO (%)0.00–0.110.02–0.39
MnO (%)0.13–0.870.10–1.24
TiO2 (%)0.00–0.110.00–1.08
MineralBrown garnet skarnGreen garnet skarn
Analyses35 points46 points
SiO2 (%)34.06–35.3634.17–35.69
CaO (%)31.60–33.7531.02–34.28
FeO (%)25.68–28.3220.83–28.88
Al2O3 (%)0.87–2.140.10–5.95
MgO (%)0.00–0.110.02–0.39
MnO (%)0.13–0.870.10–1.24
TiO2 (%)0.00–0.110.00–1.08

Notes: Samples from drill hole CMA-001 at 269.40 m (brown garnet skarn) and 35.0 m (green garnet skarn); analyses carried out by electron microprobe in 1996 at the Ruhr-Universitaet Bochum (R. Lehne, pers. commun., 1996)

Most of the brown garnetite and all of the green garnetite are exoskarn, as shown by remnant bedding features clearly visible both underground and in surface outcrops. Some garnetite contains small, elongate vugs oriented parallel to the relict bedding. Both types of garnet are andradite. Some green diopside is associated with the green garnet skarn (Love et al., 2000) but is usually difficult to distinguish in core. The texture of the garnetite varies from fine (<1mm) to coarse grained (>10 mm) and from massive and hard to vuggy with euhedral crystals. The massive, fine-grained garnetite occurs in the Oscarina area (Fig. 3) and is a hard, microgranular aggregate of garnet, diopside, and wollastonite cut by sheeted quartz veinlets but with low metal values because of its low permeability. The medium-grained garnetite is commonly disaggregated in drill core and crumbly underground. The disaggregation, more common in brown garnetite, appears to be due to dissolution of minor interstitial calcite during retrograde hydrothermal activity. The coarse-grained garnetite is of medium hardness and is generally vuggy and easy to drill. The porosity of garnetite is explained by the volume reduction, resulting from the change of limestone to garnet. For this reason the garnet is euhedral and the garnetite has an inherent porosity that makes it a good ore host.

Magnetite exoskarn

Zones of massive magnetite, up to several meters wide, occur in the garnetite. The magnetite formed relatively early and is cut by chalcopyrite veinlets. It also occurs as pseudomorphs after tabular and/or bladed specular hematite crystals, which indicates either a decrease in oxygen fugacity or an increase in temperature of the hydrothermal fluid over time.

Wollastonite-diopside exoskarn

This exoskarn comprises white, fibrous wollastonite with diopside and coarse-grained pink and green garnet. The diopside has an unusual mineral habit consisting of large (up to 20 mm), circular crystals with radial texture, cross fractures, and a dull brown-green color. Retrograde alteration products include vesuvianite, calcite, quartz, and steatite. Apatite, fluorite, muscovite, ilvaite, epidote (allanite), cordierite, and sphene are also sporadically developed. The diopside-wollastonite skarn is located on the margins of the deposit and is best developed in the south Laberinto area (Figs. 3, 6). Bornite is associated with the diopside-wollastonite skarn and was introduced after prograde skarn formation together with trace chalcopyrite in interstitial sites and quartz veinlets. Geochemically this marginal zone is enhanced in both gold and bismuth.

Marble

Limestone adjacent to the exoskarn is recrystallized to coarse, equigranular marble of white to light-gray color. Marble formation was accompanied by bleaching of the precursor limestone. The marble zone is typically 200 to 250 m wide, although it can narrow to as little as 10 m. The marble adjacent to the exoskarn contact has narrow skarn zones (green garnet, wollastonite, sulfides) controlled by bedding or fractures for up to tens of meters into the marble. These skarn veins often have ore-grade lead, zinc, and silver. The inner marble zone typically contains disseminated scapolite as small, oblate black crystals. In certain areas, notably at the head of Lake Antamina (Fig. 3), there is a zone of selective skarn alteration in marble and/or limestone beyond the exoskarn contact. This is controlled by bedding permeability and porosity, with stromatolitic limestone beds altered to garnet but micritic limestone interbeds unaltered. Outboard from the main marble zone, there may be a zone of selective marble formation within the limestone that is controlled by bedding porosity-permeability. Traces of disseminated and fracture-coating pyrite occur in the marble and limestone for distances of up to 4,000 m from the edge of the skarn. This represents a pyrite halo around the deposit, similar to that around many porphyry copper deposits.

Hornfels

Hornfels is preserved in some marginal parts of the deposit, notably on the peaks east of Laberinto (Fig. 3). The early hornfels tends to be biotite rich, whereas later hornfels is pyroxene rich and replaced by garnetite.

Retrograde skarn

Retrograde alteration of garnetite is variably developed outward from veinlet selvages, stockworks, and breccias, and as a pervasive replacement. Where pervasive, the retrograde alteration was logged as chlorite skarn, a rock that is typically disaggregated. Retrograde alteration commonly comprises hydrothermal breccias in which clasts of garnetite and vein quartz occur in a matrix of retrograde minerals, including sulfides. The clasts are angular to subrounded with little displacement; exotic clasts are absent. Breccias are controlled by steep fractures, but were not separated during resource modeling because they do not form discrete, mappable bodies. Retrograde assemblages include chlorite, epidote, actinolite, quartz, calcite, sericite, clay, and pyrite. Chalcopyrite is abundant and molybdenite commonly occurs in quartz veinlets.

Sulfide and Metal Distribution

Sulfide mineralization postdates garnetite formation and occurs in three forms: (1) interstitial to garnet crystals, (2) massive sulfide zones, and (3) crosscutting veinlets. There are two main stages of sulfide mineralization, prograde and retrograde. In the prograde stage, sulfide minerals occur with minor calcite as late additions to prograde skarn, as evidenced by a lack of accompanying retrograde alteration. The main sulfide minerals are chalcopyrite and pyrite, with the addition of sphalerite in the zinc zone. Pyrrhotite also occurs locally. Sulfide minerals are a major component of the retrograde skarn, where they are dominated by pyrite and chalcopyrite. The massive sulfide zones are irregular in shape and size, varying from a few centimeters to 10 m in thickness. Underground they are irregular and amorphous in shape, rather than forming veins or replacements of limestone beds; hence, there is extreme variability of ore grades over distances of only a few meters (e.g., between twinned drill holes). A single drill hole may repeatedly intersect zones of massive sulfides interspersed with garnetite. Metal distribution shows a symmetrical lateral zonation outward from (1) a central molybdenum zone with low copper, (2) followed by the principal copper zone, (3) an outer copperzinc halo, (4) with a discontinuous marginal copper (bornite)-zinc-bismuth zone, and (5) a peripheral silver-leadzinc zone (Fig. 9).

Chalcopyrite-rich mineralization

Chalcopyrite is distributed throughout the garnet endoskarn and exoskarn where it constitutes a copper-only zone, approximately coincident with the extent of the proximal brown garnet (endo-and exoskarn), and a copper-zinc zone, which approximates the more distal green garnet zone. Copper contents are similar in both zones. In the upper levels of the deposit, the copper-only zone reaches 600 m in width, whereas at depth the zone is only 100 to 350 m wide (Fig. 9). A high-grade copper zone (>2% Cu) occurs beneath the eastern side of the Lake zone (Fig. 3) from surface to the 4,000-m level. Drill intersections in this zone include 120 m at 4.72 percent Cu and 268 m at 3.30 percent Cu. Chalcopyrite was introduced during the early mineralization stages as interstitial, veinlet, and massive zones in garnetite, and appreciable amounts were also introduced during the retrograde stage in the chlorite skarn. Chalcopyrite also occurs in the stock as porphyry-type mineralization in veinlet and disseminated form but the grade is subeconomic.

Bornite-rich mineralizaton

Bornite occurs in the wollastonite-diopside skarn and locally in outer parts of the green garnet skarn (Fig. 9). The main bornite area is on the eastern side of the skarn in the south Laberinto area (Fig. 3), where it occurs over a strike length of about 400 m and widths of up to 160 m (Fig. 9). Bornite is present only at the higher levels of the deposit, and the base of the bornite-rich zone deepens to the southwest (Fig. 9). On the western side of the valley (Fig. 2), bornite occurs locally in narrow zones (up to 30 m) in wollastonite-diopside and green garnet skarn, both at the marble contact and in the marble itself. In the southern valley, bornite zones are present in both the eastern and western contact zones but are largely absent at Usu Pallares (Fig. 3).

Sphalerite-rich mineralizaton

Sphalerite occurs in the outer zone of the deposit, approximately coincident with the green garnet and the wollastonite-diopside skarn, where it accompanies chalcopyrite to form a copper-zinc halo (Fig. 9). The copper-zinc halo is defined by values of greater than 0.5 percent Zn, a natural statistical break in grade. Copper grades remain the same as those in the copper-only zone. In general the copper-zinc halo is wider in the upper part of the deposit and narrows at depth; it probably continued over the top of the skarn deposit prior to partial erosion. In the upper levels of the deposit, the width of the zone is typically 100 to 200 m, whereas at depth it averages 20 to 50 m but attains 350 m along structures (Fig. 9). There are also some sphalerite-rich intervals within the copper zone, which occur as inward-directed extensions of the copper-zinc halo and as discrete zones, one of which, in the lake area (Fig. 3), is spatially confined to the margin of a single intrusive phase. Finally, sphalerite is present in veins and mantos in marble in the outer zone associated with wollastonite-green garnet skarn with lead and silver.

Silver

Geochemical plots show that silver forms two populations. The copper zone has consistent silver values of 7 to 8 g/t. The good Ag/Cu correlation suggests that the silver occurs as a solid solution in chalcopyrite. The outer parts of the copper-zinc zone and the outer zone of veins and mantos in marble have higher silver values associated with galena, bismuth sulfosalts, proustite, and late-stage tennantite in veinlets (Fig. 9).

Molybdenum

While the overall molybdenum content of the deposit is low, molybdenum grade is locally high. Molybdenite is present in quartz veinlets in porphyry, in garnet endoskarn, and in exoskarn proximal to the intrusion (Fig. 9). Molybdenite is also abundant in the wollastonite-diopside skarn where it tends to occur as coarse disseminated flakes. Molybdenum contents in these skarn types are greater than 0.05 percent Mo and, locally, >0.1 percent. The remainder of the skarn has grades of <0.02 percent Mo.

Bismuth

Bismuth distribution was modeled in detail since it incurs a smelter penalty in copper concentrate. There are high bismuth zones (>15 ppm; metallurgical cutoff) at the northern and southern extremities of the deposit, between which it forms an outer zone near to the limestone contact. These bismuth-rich zones are mainly in the green garnet and wollastonite-diopside skarn but also in the brown garnet exoskarn at the deposit extremities. Bismuth values are mostly >100 ppm but can reach thousands of ppm. The upper levels of the outer bismuth zone tend to be wide (typically 200 m), but they narrow at depth (commonly as little as 10 m). The rest of the deposit has irregular, patchy bismuth enrichment zones (15–40 ppm), interspersed with zones with <15 ppm. The copper and copper-zinc ores are each divided into low and high bismuth types. The bornite ore always contains high bismuth contents (Fig. 9). The most common bismuth minerals are bismuthinite and cosalite (Pb2Bi2S5), but wittichenite (Cu3BiS3), cuprobismutite (Cu10Bi12S23), aikinite (PbCuBiS3), kobellite (Pb22Cu4(Bi, Sb)30S69), and native bismuth also occur. These bismuth species are included and intergrown with pyrite, sphalerite, chalcopyrite, and bornite.

Lead

Galena is present in outer zones of the green garnet skarn, where values attain thousands of parts per million, and in the outer zone of veins and mantos in marble, associated with zinc and silver (Fig. 9).

Gold

Elevated gold values occur in the outer copper-zinc-bismuth zone at Usu Pallares and southern Laberinto (Figs. 3, 9). Average grades are on the order of 0.1 to 0.2 g/t Au. The longest Au-bearing intercept is 180 m at 0.25 g/t, including 15.3 m at 0.94 g/t and a maximum value of 1.49 g/t over 3.1 m. Gold is associated with the wollastonite-diopside skarn, but gold was identified in only two samples as small inclusions (max 10 μm) of native gold and electrum in chalcopyrite. Elsewhere gold values are low (isolated intervals of 0.1–0.2 g/t, with uncommon higher values) in the main skarn body at the northern end of the Lake zone in the copper (chalcopyrite) zone.

Oxidized and Enriched Zones

Skarn deposits, like Antamina, are generally not susceptible to development of supergene enrichment due to their low pyrite contents, low acid-generating capacity, and high neutralization capacity combined with low fracture permeability. In addition, the relatively young age of both deposit formation and unroofing, glacial erosion, as well as the wet climate are unfavorable factors for supergene enrichment. A thin supergene profile, partly eroded, overlies the dominantly hypogene Antamina ore. Nevertheless, the restricted oxidized zone was defined as a separate domain in the geologic sections because of its potential to cause metallurgical problems during flotation.

Oxidation is inferred to have taken place in the late Pleistocene interglacial period, following unroofing of the deposit by glaciation, and was partly removed during the second stage of cirque glaciation. There is minor, ongoing, postglacial oxidation. The oxidized zone varies from zero to 20 m in thickness, with locally fracture-controlled zones penetrating downward for up to 100 m in the Lake zone.

Oxidation was defined as the presence of visual limonite (jarosite, goethite, and minor hematite) and/or oxide copper (chalcanthite, cuprite, malachite, neotocite, and tenorite). The amount of these minerals is normally minor and abundant sulfide minerals remain. At the base of oxidation, native copper may occur over a short interval (tens of centimeters). There is usually a zone, a few meters thick, of supergene copper sulfides (chalcocite, covellite, and digenite) below the oxidized zone. This incipient enrichment extends to depths as great as 140 m along fractures. The copper sulfide minerals coat hypogene sulfide minerals but do not cause significant replacement. Copper contents are not significantly increased by supergene processes, and for this reason the zone was not separated for reserve estimation purposes. Supergene zinc minerals, such as hemimorphite and smithsonite, are present only locally in the oxidation zone, where manganese oxide minerals, such as pyrolusite, psilomelane, and possibly manganite, are also present in small amounts.

Deposit Model

Antamina is a typical calcic copper skarn as defined by Einaudi et al. (1981). The outward zonation from garnet through wollastonite to marble and the garnet and pyroxene mineralogy are typical of copper skarns. The outer zinc zone is unusually well developed, with exceptionally high, economic zinc grades. Copper skarns often have minor sphalerite in the outer zone but it is generally low grade. The lack of manganese, including johannsenitic pyroxene (Love et al., 2000), distinguishes Antamina from typically reduced and distal zinc skarns. Magnesian skarn is also absent due to a lack of dolomite in the host rocks. The mineral assemblage that characterizes the skarn is relatively oxidized as befits its intimate association with porphyry copper-molybdenum mineralization of subeconomic grade. The high molybdenum contents and presence of minor fluorite suggest an approach to a calk-alkaline porphyry molybdenum system.

There is only minor retrograde alteration, a feature that is atypical in copper skarns. The lack of retrograde assemblages may help to explain the marked homogeneity of the deposit and the preservation of the peripheral zinc zone.

The localized outer zone with wollastonite and bornite is typical of many copper skarns and reflects an outward decrease in iron and sulfur activities. However, the occurrences of diopside and elevated bismuth and gold contents in parts of the outer zone are both features common to some distal, reduced gold skarns. The high bismuth and molybdenum contents are typical of deposits of the polymetallic belt of central Peru. Molybdenum is common in other deposits in the vicinity of Antamina, as are tin and tungsten, although the last two metals are absent at Antamina.

Notable and perhaps unusual factors that may have contributed to the large size of the Antamina deposit include: (1) most of the skarn is mineralized (in most skarns, only a small percentage is mineralized but in this case >90%); (2) remarkably homogenous metal grades with little variation of mineralogy or grade with depth; (3) lack of significant retrograde alteration; (4) well-developed structural preparation of the host rocks, allowing complicated intrusive geometry and high intrusion to limestone contact area; and (5) shallow erosion of the system preserving flat-lying skarn bodies in the roof zone of the intrusion as well as steep skarn bodies along the sides.

Antamina is part of a belt of small mineralized intrusions of mid-to late Miocene age, which includes the Cordillera Blanca batholith located 50 km west (Fig. 1) and dated at 13.7 to 6.3 Ma (Cobbing, 1998). This batholith is mantle derived, with no contamination by continental crust, as shown by the Sr-Nd isotope values (Petford et al., 1993). The magma source is interpreted to be new basaltic material underplated at the base of the crustal keel (Atherton and Petford, 1993). This origin contrasts with that of the Miocene magmas elsewhere in the central Andes, which formed during crustal thickening, with extensive crustal contamination and assimilation (e.g., Redwood and Rice, 1997). The Antamina intrusion may thus have a similar mantle-derived origin to the Cordillera Blanca batholith, consistent with the copper-molybdenum signature and lack of tin and tungsten.

Antamina has some similarities with the Magistral deposit that is situated in the same belt 160 km to the northwest (Fig. 1), which has an inferred resource of 190 Mt at 0.83 percent Cu and 0.062 percent Mo (Perelló et al., 2001). Magistral is hosted by the same sedimentary sequence, has a similar structural setting in the Marañon fold-thrust belt, is related to a porphyry copper-molybdenum–bearing intrusion (albeit older: 15 Ma), and has similar garnet zoning. Unlike Antamina, however, the porphyry stock hosts a resource, the deposit is smaller, lacks zinc, and has an epithermal overprint (Perelló et al., 2001).

There is a remarkable similarity between the geologic setting of Antamina and that of the Ertsberg district copper-gold skarns and the Grasberg porphyry copper-gold deposit, Papua province, Indonesia (Mertig et al., 1994; Meinert et al., 1997). These major deposits are gold rich compared to Antamina and have magnesian skarn assemblages as a result of the dolomitic host rocks. The depositional setting of the host sedimentary rocks at both the Antamina and Ertsberg-Grasberg deposits, a basin margin of a craton, is similar. This situation gave rise to optimal sedimentary facies, comprising calcareous siltstone and mudstone, rather than shelf carbonate or deep-water mudstone. In addition, basin-margin faults contributed to sedimentary facies with enhanced permeability (e.g., slump structures), and fault reactivation as thrust ramps facilitated intrusion and fluid pathways for skarn formation.

References

Anon
,
1998
,
1998 Geologic time scale
 :
Boulder, Colorado
,
Geological Society of America
.
Atherton
,
M.P.
Petford
,
N.
,
1993
,
Plutonism and the growth of Andean crust at 9o S from 100 to 3 Ma
:
International Symposium on Andean Geodynamics, 2nd, Oxford, England, 1993
 ,
Paris
,
Editions de l’Orstom
, p.
331
333
.
Benavides
,
V.E.
,
1956
,
The Cretaceous system in northern Peru
:
Bulletin of the American Museum of Natural History
 , v.
108
, p.
353
494
.
Benavides-Cáceres
,
V.
,
1999
,
Orogenic evolution of the Peruvian Andes: The Andean cycle
:
Society of Economic Geologists Special Publication
 
7
, p.
61
107
.
Bodenlos
,
A.E.
Ericksen
,
G.E.
,
1955
,
Lead-zinc deposits of the Cordillera Blanca and northern Cordillera Huayhuash, Peru
:
U.S. Geological Survey Bulletin
 
1017
,
166
p.
Cobbing
,
E.J.
,
1985
,
The tectonic setting of the Peruvian Andes
, in
Pitcher
,
W.S.
Atherton
,
M.P.
Cobbing
,
E.J.
Beckinsdale
,
R.D.
, eds.,
Magmatism at a plate edge: The Peruvian Andes
 :
Glasgow
,
Blackie and Son
, p.
3
12
.
Cobbing
,
E.J.
1998
,
The Coastal batholith and other aspects of Andean magmatism in Peru
:
Boletín de la Sociedad Geológica del Perú
 , v.
88
, p.
5
20
.
Cobbing
,
J.
Sánchez
,
A.
Martínez
,
W.
Zárate
,
H.
,
1996
,
Geología de los cuadrángulos de Huaraz, Recuay, La Unión, Chiquián y Yanahuanca
:
Instituto Geológico Minero y Metalúrgico [Perú] Boletín
 
76
,
281
p.
Diez Canseco
,
E.
,
1920
,
Apuntes sobre la región cuprífera de Antamina
:
Informaciones y Memorias de la Sociedad de Ingenieros del Perú
 , v.
24
, p.
111
123
.
Einaudi
,
M.T.
Meinert
,
L.D.
Newberry
,
R.J.
,
1981
,
Skarn deposits
:
Economic Geology 75th Anniversary Volume
 , p.
317
391
.
Glover
,
J.K.
,
1997
,
Structural and stratigraphic setting of the Antamina deposit
:
Preliminary evaluation, executive summary
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
4
p.
Glover
,
J.K.
1998a
,
Geological aspects and implications for exploration of the on-site structural investigations in the Poderosa mine area, Antamina project
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
8
p.
Glover
,
J.K.
1998b
,
Structural and lithological controls of mineralization and alteration, Antamina copper-zinc skarn deposit, summary report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
6
p.
Glover
,
J.K.
1998c
,
Phase III structural study: Structural and lithological controls of mineralization and alteration, Antamina copper-zinc skarn deposit
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
13
p.
Harvey
,
B.
Myers
,
S.A.
Klein
,
T.
,
1999
,
Yanacocha gold district, northern Peru
:
Pacific Rim Congress, Bali, Indonesia, 1999, Proceedings
 , p.
445
459
.
Hathaway
,
L.
,
1997
,
Geological surface mapping and structural interpretation at Antamina, Peru
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
35
p.
Hathaway
,
L.
1998a
,
Geotechnical field trip report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
7
p.
Hathaway
,
L.
1998b
,
Geotechnical field trip report II
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
6
p.
Jaillard
,
E.
Soler
,
P.
,
1996
,
Cretaceous to early Paleogene tectonic evolution of the northern Central Andes (0–18o S) and its relations to geodynamics
:
Tectonophysics
 , v.
259
, p.
41
53
.
Love
,
D.A.
Clark
,
A.H.
,
1998a
,
Re-evaluation of the oregenetic model for the Antamina Cu-Zn(-Ag) skarn, interim report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
36
p.
Love
,
D.A.
Clark
,
A.H.
1998b
,
Revision of the ore-genetic model for the Antamina Cu-Zn(-Ag) skarn, 1998 final report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
50
p.
Love
,
D.A.
Clark
,
A.H.
Schwarz
,
F.P.
,
2000
,
The Antamina deposit, An-cash, northern Peru: Anatomy and petrology of a giant copper-zinc skarn [abs.]
:
Geological Society of America Abstracts with Programs
 , v.
32
, no.
7
, p. A137.
Love
,
D.A.
Clark
,
A.H.
Strusievicz
,
O.R.
Lee
,
J.K.W.
,
2001
,
The regional tectonic setting of the giant Antamina Cu-Zn skarn deposit, north-central Peru [abs.]
:
Geological Society of America Abstracts with Programs
 , v.
33
, no.
6
, p.
A358
.
Love
,
D.A.
Clark
,
A.H.
Ullrich
,
T.D.
Archibald
,
D.A.
Lee
,
J.K.W.
,
2003a
,
40Ar-39Ar evidence for the age and duration of magmatic-hydrothermal activity in the giant Antamina Cu-Zn skarn deposit, Ancash, north-central Peru [abs.]
:
Geological Association of Canada-Mineralogical Association of Canada-Society of Economic Geologists, Joint Annual Meeting
 ,
Vancouver
,
British Columbia
, Abstracts Volume, v.
28
,
CD-ROM
.
Love
,
D.A.
Clark
,
A.H.
Lipten
,
E.J.H.
,
2003b
,
Genesis of the Antamina Cu-Zn skarn deposit, Ancash, Peru
:
Congreso Geológico Chileno, 10th
 ,
Concepción
,
CD-ROM
,
1
p.
Love
,
D.A.
Clark
,
A.H.
Glover
,
J.K.
,
2004
,
The lithologic, stratigraphic and structural setting of the giant Antamina copper-zinc skarn deposit, Ancash, Peru
:
Economic Geology
 , v.
99
, p.
887
916
.
McKee
,
E.H.
Noble
,
D.C.
,
1982
,
Miocene volcanism and deformation in the western Cordillera and high plateaus of south-central Peru
:
Geological Society of America Bulletin
 , v.
93
, p.
657
662
.
McKee
,
E.H.
Noble
,
D.C.
Scherkenbach
,
D.A.
Drexler
,
J.W.
Mendoza
,
J.
Eyzaguirre
,
V.R.
,
1979
,
Age of porphyry intrusion, potassic alteration, and related skarn mineralization, Antamina district, northern Peru
:
ECONOMIC GEOLOGY
 , v.
74
, p.
928
930
.
Mégard
,
F.
,
1984
,
The Andean orogenic period and its major structures in central and northern Peru
:
Journal of the Geological Society
 , v.
141
, p.
893
900
.
Meinert
,
L.D.
Hefton
,
K.K.
Mayes
,
D.
Tastran
,
J.
,
1997
,
Geology, zonation, and fluid evolution of the Big Gossan Cu-Au skarn deposit, Ertzberg district, Irian Jaya
:
Economic Geology
 , v.
92
, p.
509
534
.
Mertig
,
H.J.
Rubin
,
J.N.
Kyle
,
R.
,
1994
,
Skarn Cu-Au orebodies of the Gunung Bijih (Ertsberg) district, Irian Jaya, Indonesia
:
Journal of Geochemical Exploration
 , v.
50
, p.
179
202
.
Noble
,
D.C.
McKee
,
E.H.
,
1999
,
The Miocene metallogenic belt of central and northern Peru
:
Society of Economic Geologists Special Publication
 
7
, p.
155
193
.
O’Connor
,
K.
,
1999
,
Yacimiento polimetálico de Antamina: Historia, exploración y geología
:
ProExplo 99, Congreso Internacíonal de Prospectores y Exploradores, 1st
 ,
Lima, Peru
,
1999, Primer volumen de monografías de yacimientos minerales peruános. Historia, exploración y geología, Volumen Luis Hochschild Plaut, Instituto de Ingenieros de Minas del Perú
,
13
p.
Perelló
,
J.
García
,
A.
Ramos
,
P.
Glover
,
K.
Neyra
,
C.
Muhr
,
R.
Fuster
,
N.
Caballero
,
A.
,
2001
,
The Magistral porphyry-skarn Cu-Mo deposit, Ancash, Peru
:
ProExplo 2001, Congreso Internacíonal de Prospectores y Exploradores, 2nd
 ,
Lima, Peru
,
2001
,
Instituto de Ingenieros de Minas del Perú, CD-ROM
,
3
p.
Petersen
,
U.
,
1965
,
Regional geology and major ore deposits of central Peru
:
Economic Geology
 , v.
60
, p.
407
476
.
Petersen
,
U.
1999
,
Magmatic and metallogenic evolution of the Central Andes
:
Society of Economic Geologists Special Publication
 
7
, p.
109
153
.
Petford
,
N.
Atherton
,
M.P.
Halliday
,
A.N.
,
1993
,
Miocene plutonism in N. Peru: Implications for along-strike variations in Andean magmatism (9–22o S)
:
International Symposium on Andean Geodynamics, 2nd, Oxford, England, 1993
 ,
Paris
,
Editions de l’Orstom
, p.
427
430
.
Raimondi
,
A.
,
1873
,
El departamento de Ancachs [sic] y sus riquezas minerales
 :
Lima, Peru
,
Enrique Meiggs
,
651
p.
Redwood
,
S.D.
,
1997
,
Reinterpretation of the structural evolution of Antamina
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
4
p.
Redwood
,
S.D.
1998
,
The Antamina copper-zinc skarn deposit, northern Peru [abs.]
:
Geological Association of Canada, Mineral Deposits Division Congress, Quebec, 1998, Abstract Volume, Carrefour in Earth Sciences
 , v.
23
, p.
A153
.
Redwood
,
S.D.
1999
,
The geology of the Antamina copper-zinc skarn deposit, Peru
:
The Gangue
 , v.
60
, p.
1
, 3–7.
Redwood
,
S.D.
2003
,
The development of the geological model of the Antamina copper-zinc skarn deposit, northern Peru
:
Congreso Geológico Chileno, 10th, Concepción, 2003, CD-ROM
 ,
1
p.
Redwood
,
S.D.
Rice
,
C.M.
,
1997
,
Petrogenesis of Miocene basic shoshonitic lavas in the Bolivian Andes and implications for hydrothermal gold, silver and tin deposits
:
Journal of South American Earth Sciences
 , v.
10
, p.
203
211
.
Sébrier
,
M.
Soler
,
P.
,
1991
,
Tectonics and magmatism in the Peruvian Andes from late Oligocene time to the Present
:
Geological Society of America Special Paper
 
265
, p.
259
278
.
Sillitoe
,
R.H.
,
1997
,
Comments on the geological model for the Antamina copper-zinc skarn deposit, Peru
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
7
p.
Soler
,
P.
Grandin
,
G.
Fornari
,
M.
,
1986
,
Essai de synthèse sur la métallogénie du Pérou
:
Géodynamique
 , v.
1
, p.
33
68
.
Terrones
,
A.J.
,
1958
,
Structural control of contact metasomatic deposits in the Peruvian Cordillera
:
American Institute of Mining, Metallurgical and Petroleum Engineers
 , v.
211
, p.
365
372
.
Tosdal
,
R.M.
Clark
,
A.H.
Farrar
,
E.
,
1984
,
Cenozoic polyphase landscape and tectonic evolution of the Cordillera Occidental, southernmost Peru
:
Geological Society of America Bulletin
 , v.
95
, p.
1318
1332
.
Volkert
,
D.F.
McEwan
,
C.J.A.
Garay
,
E.
,
1998
,
Pierina Au-Ag deposit, Cordillera Negra, north-central Peru [ext. abs.]
:
Pathways ’98, Cordilleran Roundup. 15th, 1998
 ,
Vancouver, Canada
,
Extended Abstracts Volume
, p.
33
35
.
Wilson
,
J.
,
1963
,
Cretaceous stratigraphy of central Andes of Peru
:
Bulletin of the American Association of Petroleum Geologists
 , v.
47
, p.
1
34
.
Wilson
,
J.
Reyes
,
L.
Garayar
,
J.
,
1967
,
Geología de los cuadrángulos de Mollebamba, Tayabamba, Huaylas, Pomabamba, Carhuaz y Huari
:
Servicio de Geología y Minería [Perú], Boletín
 
16
,
95
p.

Acknowledgments

This article is the result of a tremendous amount of work carried out for the Antamina feasibility study by a joint Inmet-Rio Algom team, and I thank all who contributed. Particular thanks are due to John Kapusta, Ian Pirie, Frank Balint, Leo Hathaway, Brian Brodsky, Alex Ascencios, Rainer Lehne, Manuel Pacheco, José Salas, and Nick Bircham. Special thanks are also due to Richard Sillitoe, the late Keith Glover, David Love, and Stephen Zuker. Other Peruvian geologists deserve credit for their dedicated hard work: Javier Carnero, Julio Carreón, Ivo Cornejo, Ignacio Couturier, Ricardo Gallegos, Manuel Geldres, José Luis Igreda, Santiago Linares, Carlos Luna, Joel Melgar, Julio Pacheco, Ruber Palomino, Carlos Pari, Orlando Pariona, Ernesto Pizzaro, Manuel Prado, Gilberto Ramos, Reynaldo Ríos, Percy Rondón, Iván Salazar, Michael Sánchez, Luis Taboada, Andrés Ticona, Ricardo Vega, and Carlos Vela. The figures were drafted by José de la Luz Cornejo. Economic Geology reviewers Gerry Ray, Lluís Fontboté, and Rainer Lehne, and editors Richard Sillitoe and José Perelló, greatly improved the manuscript. Permission to publish was granted by Compañía Minera Antamina, Rio Algom Ltd. (BHP-Billiton), Noranda, Teck Cominco, and Inmet.

Figures & Tables

Fig. 1.

Location of Antamina, Peru.

Fig. 1.

Location of Antamina, Peru.

Fig. 2.

Geology of the Antamina district (after Glover, 1997).

Fig. 2.

Geology of the Antamina district (after Glover, 1997).

Fig. 3.

Geology of the Antamina copper-zinc skarn deposit, showing locality names (after Hathaway, 1997).

Fig. 3.

Geology of the Antamina copper-zinc skarn deposit, showing locality names (after Hathaway, 1997).

Fig. 4.

Oblique air photograph looking northeast along the Antamina valley in 1997 before mining. The skarn deposit crops out on Taco ridge (with drill roads) southwest of the lake and continues southwest beneath the valley, then along the southern edge of the valley to the Usu Pallares hanging valley (lower right with drill roads). From Taco ridge, the deposit continues diagonally under the lake and crops out on the eastern side of the head of the valley (Oscarina) and through the ridge (where the road cuts) to Rosita de Oro. The skarn deposit is hosted by indurated calcareous sediments of the Upper Celendin Formation, which crops out along the valley sides. The highest peaks (Cerro Contonga, 5,073 m, foreground left) are Jumasha Formation limestone.

Fig. 4.

Oblique air photograph looking northeast along the Antamina valley in 1997 before mining. The skarn deposit crops out on Taco ridge (with drill roads) southwest of the lake and continues southwest beneath the valley, then along the southern edge of the valley to the Usu Pallares hanging valley (lower right with drill roads). From Taco ridge, the deposit continues diagonally under the lake and crops out on the eastern side of the head of the valley (Oscarina) and through the ridge (where the road cuts) to Rosita de Oro. The skarn deposit is hosted by indurated calcareous sediments of the Upper Celendin Formation, which crops out along the valley sides. The highest peaks (Cerro Contonga, 5,073 m, foreground left) are Jumasha Formation limestone.

Fig. 5.

View looking west over the Antamina deposit in 1997 before mining, to show the oxidized outcrop of the skarn on Taco ridge left of the lake. The skarn continues beneath the lake to the Oscarina area on the valley side, from where the photograph was taken. Upper Celendin Formation calcareous sedimentary rocks underlie the valley sides and are overlain by Jumasha Formation limestone, which forms the Cerro Contonga peak (5,073 m). The Cordillera Blanca is in the distance.

Fig. 5.

View looking west over the Antamina deposit in 1997 before mining, to show the oxidized outcrop of the skarn on Taco ridge left of the lake. The skarn continues beneath the lake to the Oscarina area on the valley side, from where the photograph was taken. Upper Celendin Formation calcareous sedimentary rocks underlie the valley sides and are overlain by Jumasha Formation limestone, which forms the Cerro Contonga peak (5,073 m). The Cordillera Blanca is in the distance.

Fig. 6.

View of Antamina deposit, looking south in 1998 before mining. The skarn deposit can be seen cropping out at Taco (right of the lake), Laberinto (valley side below the anticline), and Oscarina (valley side above the lake) as far as Rosita (pass on left). The Antamina anticline (right) is a prominent culmination in one of the lower sheets of the thrust duplex in Upper Celendin Formation that hosts Antamina.

Fig. 6.

View of Antamina deposit, looking south in 1998 before mining. The skarn deposit can be seen cropping out at Taco (right of the lake), Laberinto (valley side below the anticline), and Oscarina (valley side above the lake) as far as Rosita (pass on left). The Antamina anticline (right) is a prominent culmination in one of the lower sheets of the thrust duplex in Upper Celendin Formation that hosts Antamina.

Fig. 7.

Long section A-A′ through the Antamina skarn deposit, showing district geology and structure (after Glover, 1997). Location of section is shown in Figure 2.

Fig. 7.

Long section A-A′ through the Antamina skarn deposit, showing district geology and structure (after Glover, 1997). Location of section is shown in Figure 2.

Fig. 8.

Schematic block diagram of the Antamina copper-zinc skarn deposit, showing localization of intrusion and mineralization along lateral ramp, looking southeast (after Glover, 1997).

Fig. 8.

Schematic block diagram of the Antamina copper-zinc skarn deposit, showing localization of intrusion and mineralization along lateral ramp, looking southeast (after Glover, 1997).

Fig. 9.

Cross section B-B′ of the Antamina copper-zinc skarn deposit, showing zonation of skarn and metals. Line of section is shown in Figure 3. All Cu present as chalcopyrite except for bn = bornite.

Fig. 9.

Cross section B-B′ of the Antamina copper-zinc skarn deposit, showing zonation of skarn and metals. Line of section is shown in Figure 3. All Cu present as chalcopyrite except for bn = bornite.

Table 1.

Stratigraphy of the Antamina District

PeriodEpochAgeAge (Ma)GroupFormationThickness (m)Lithology
Santonian87.5−84Celendin115–225Marl, nodular limestone, thinly bedded, fossiliferous; Antamina deposit
LateConiacian88.5−87.5
Turonian91−88.5
Cenomanian97.5−91Jumasha200–800Gray limestone, massive, thickly bedded 1–2 m, micritic, poorly fossiliferous, dolomitic in parts
Pariatambo100–200Dark-gray marl and limestone, bituminous, thinly bedded
Albian113−97.5Dark-gray chert nodules abundant at top
Chulec100–200Thinly bedded shelly limestone, marl, yellow-cream color
CretaceousEarlyPariahuanca54–210Massive shelly limestone, 1-to 2-m beds, calcareous sandstone at base
Aptian119−113Yellowish color
Farrat20White sandstone
Barremian124−119GoyllarisquisgaCarhuaz1,300– 500Shale, silty shale, thin quartz sandstone beds, brown-purplish; disconformable
Hauterivian131−124Gray shales and coal at base
Santa150–341Blue-gray shelly limestone, 0.1-to 1-m beds, chert nodules, parts dolomitic
Valanginian138−131Chimu600–685Quartz sandstone, white; dark shale and coal at base
Berriasian144−138Oyon100Shale, siltstone, sandstone, coal; important thrust plane
JurassicLateTithonian152−144Chicama>1,500Gray slate, quartzite, sandstone
PeriodEpochAgeAge (Ma)GroupFormationThickness (m)Lithology
Santonian87.5−84Celendin115–225Marl, nodular limestone, thinly bedded, fossiliferous; Antamina deposit
LateConiacian88.5−87.5
Turonian91−88.5
Cenomanian97.5−91Jumasha200–800Gray limestone, massive, thickly bedded 1–2 m, micritic, poorly fossiliferous, dolomitic in parts
Pariatambo100–200Dark-gray marl and limestone, bituminous, thinly bedded
Albian113−97.5Dark-gray chert nodules abundant at top
Chulec100–200Thinly bedded shelly limestone, marl, yellow-cream color
CretaceousEarlyPariahuanca54–210Massive shelly limestone, 1-to 2-m beds, calcareous sandstone at base
Aptian119−113Yellowish color
Farrat20White sandstone
Barremian124−119GoyllarisquisgaCarhuaz1,300– 500Shale, silty shale, thin quartz sandstone beds, brown-purplish; disconformable
Hauterivian131−124Gray shales and coal at base
Santa150–341Blue-gray shelly limestone, 0.1-to 1-m beds, chert nodules, parts dolomitic
Valanginian138−131Chimu600–685Quartz sandstone, white; dark shale and coal at base
Berriasian144−138Oyon100Shale, siltstone, sandstone, coal; important thrust plane
JurassicLateTithonian152−144Chicama>1,500Gray slate, quartzite, sandstone

Notes: Based on Benavides (1956), Cobbing et al. (1996), and Wilson (1963); time scale from Anon (1998)

Table 2.

Limestone Analyses from Antamina District

Jumasha Fm.Lower Celendin Fm.Upper Celendin Fm.
Sample no.6520165202LS03LS04LS01LS02LS0565203652046520565206
SiO2 (%)18.232.830.470.2013.5619.8727.6233.8028.1515.7038.63
TiO2 (%)0.120.120.020.020.180.310.460.480.500.320.56
Al2O3 (%)1.880.650.200.174.026.658.539.348.495.0910.48
Fe2O3 (%)0.530.290.190.181.813.143.843.602.391.614.34
MnO (%)0.010.010.010.020.040.050.070.050.030.030.09
MgO (%)7.021.111.510.812.432.662.742.702.302.242.89
CaO (%)35.8251.4453.4454.5041.5635.3529.2024.0826.9139.4018.03
Na2O (%)0.05<0.010.060.030.200.320.490.650.610.250.25
K2O (%)0.110.250.040.020.660.571.531.401.470.572.22
P2O5 (%)0.070.080.000.020.070.080.100.180.150.100.21
LOI (%)34.2441.7143.6643.6934.4728.2723.8428.7726.3232.6720.68
Total (%)98.0898.4999.8199.7999.8499.8999.9399.0597.3297.9898.38
C total9.5611.960.060.030.080.060.055.716.509.105.07
CO2 (%)34.2042.4243.3043.5133.8228.1623.4720.2322.9132.3017.82
SO3 totaln/an/a0.210.130.842.621.51n/an/an/an/a
Jumasha Fm.Lower Celendin Fm.Upper Celendin Fm.
Sample no.6520165202LS03LS04LS01LS02LS0565203652046520565206
SiO2 (%)18.232.830.470.2013.5619.8727.6233.8028.1515.7038.63
TiO2 (%)0.120.120.020.020.180.310.460.480.500.320.56
Al2O3 (%)1.880.650.200.174.026.658.539.348.495.0910.48
Fe2O3 (%)0.530.290.190.181.813.143.843.602.391.614.34
MnO (%)0.010.010.010.020.040.050.070.050.030.030.09
MgO (%)7.021.111.510.812.432.662.742.702.302.242.89
CaO (%)35.8251.4453.4454.5041.5635.3529.2024.0826.9139.4018.03
Na2O (%)0.05<0.010.060.030.200.320.490.650.610.250.25
K2O (%)0.110.250.040.020.660.571.531.401.470.572.22
P2O5 (%)0.070.080.000.020.070.080.100.180.150.100.21
LOI (%)34.2441.7143.6643.6934.4728.2723.8428.7726.3232.6720.68
Total (%)98.0898.4999.8199.7999.8499.8999.9399.0597.3297.9898.38
C total9.5611.960.060.030.080.060.055.716.509.105.07
CO2 (%)34.2042.4243.3043.5133.8228.1623.4720.2322.9132.3017.82
SO3 totaln/an/a0.210.130.842.621.51n/an/an/an/a

Notes: Samples prefixed by 65 analyzed by Intertek Testing Services Bondar Clegg and Co. Ltd., Vancouver; analyses by X-ray fluorescence on borate bead; loss on ignition (LOI) gravimetric at 1,000°C; total carbon by Leco; total Fe as Fe2O3; samples prefixed by LS analyzed by Fuller Company, Bethlehem, Pennsylvania; K2O and Na2O by flame atomic absorption; Mn reported as Mn2O3; LOI at 900°C; SO3 total by Leco induction furnace; trace pyrite in samples 65201, LS01, LS02, LS05, and 65205

Table 3.

Garnet Analyses

MineralBrown garnet skarnGreen garnet skarn
Analyses35 points46 points
SiO2 (%)34.06–35.3634.17–35.69
CaO (%)31.60–33.7531.02–34.28
FeO (%)25.68–28.3220.83–28.88
Al2O3 (%)0.87–2.140.10–5.95
MgO (%)0.00–0.110.02–0.39
MnO (%)0.13–0.870.10–1.24
TiO2 (%)0.00–0.110.00–1.08
MineralBrown garnet skarnGreen garnet skarn
Analyses35 points46 points
SiO2 (%)34.06–35.3634.17–35.69
CaO (%)31.60–33.7531.02–34.28
FeO (%)25.68–28.3220.83–28.88
Al2O3 (%)0.87–2.140.10–5.95
MgO (%)0.00–0.110.02–0.39
MnO (%)0.13–0.870.10–1.24
TiO2 (%)0.00–0.110.00–1.08

Notes: Samples from drill hole CMA-001 at 269.40 m (brown garnet skarn) and 35.0 m (green garnet skarn); analyses carried out by electron microprobe in 1996 at the Ruhr-Universitaet Bochum (R. Lehne, pers. commun., 1996)

Contents

GeoRef

References

References

Anon
,
1998
,
1998 Geologic time scale
 :
Boulder, Colorado
,
Geological Society of America
.
Atherton
,
M.P.
Petford
,
N.
,
1993
,
Plutonism and the growth of Andean crust at 9o S from 100 to 3 Ma
:
International Symposium on Andean Geodynamics, 2nd, Oxford, England, 1993
 ,
Paris
,
Editions de l’Orstom
, p.
331
333
.
Benavides
,
V.E.
,
1956
,
The Cretaceous system in northern Peru
:
Bulletin of the American Museum of Natural History
 , v.
108
, p.
353
494
.
Benavides-Cáceres
,
V.
,
1999
,
Orogenic evolution of the Peruvian Andes: The Andean cycle
:
Society of Economic Geologists Special Publication
 
7
, p.
61
107
.
Bodenlos
,
A.E.
Ericksen
,
G.E.
,
1955
,
Lead-zinc deposits of the Cordillera Blanca and northern Cordillera Huayhuash, Peru
:
U.S. Geological Survey Bulletin
 
1017
,
166
p.
Cobbing
,
E.J.
,
1985
,
The tectonic setting of the Peruvian Andes
, in
Pitcher
,
W.S.
Atherton
,
M.P.
Cobbing
,
E.J.
Beckinsdale
,
R.D.
, eds.,
Magmatism at a plate edge: The Peruvian Andes
 :
Glasgow
,
Blackie and Son
, p.
3
12
.
Cobbing
,
E.J.
1998
,
The Coastal batholith and other aspects of Andean magmatism in Peru
:
Boletín de la Sociedad Geológica del Perú
 , v.
88
, p.
5
20
.
Cobbing
,
J.
Sánchez
,
A.
Martínez
,
W.
Zárate
,
H.
,
1996
,
Geología de los cuadrángulos de Huaraz, Recuay, La Unión, Chiquián y Yanahuanca
:
Instituto Geológico Minero y Metalúrgico [Perú] Boletín
 
76
,
281
p.
Diez Canseco
,
E.
,
1920
,
Apuntes sobre la región cuprífera de Antamina
:
Informaciones y Memorias de la Sociedad de Ingenieros del Perú
 , v.
24
, p.
111
123
.
Einaudi
,
M.T.
Meinert
,
L.D.
Newberry
,
R.J.
,
1981
,
Skarn deposits
:
Economic Geology 75th Anniversary Volume
 , p.
317
391
.
Glover
,
J.K.
,
1997
,
Structural and stratigraphic setting of the Antamina deposit
:
Preliminary evaluation, executive summary
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
4
p.
Glover
,
J.K.
1998a
,
Geological aspects and implications for exploration of the on-site structural investigations in the Poderosa mine area, Antamina project
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
8
p.
Glover
,
J.K.
1998b
,
Structural and lithological controls of mineralization and alteration, Antamina copper-zinc skarn deposit, summary report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
6
p.
Glover
,
J.K.
1998c
,
Phase III structural study: Structural and lithological controls of mineralization and alteration, Antamina copper-zinc skarn deposit
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
13
p.
Harvey
,
B.
Myers
,
S.A.
Klein
,
T.
,
1999
,
Yanacocha gold district, northern Peru
:
Pacific Rim Congress, Bali, Indonesia, 1999, Proceedings
 , p.
445
459
.
Hathaway
,
L.
,
1997
,
Geological surface mapping and structural interpretation at Antamina, Peru
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
35
p.
Hathaway
,
L.
1998a
,
Geotechnical field trip report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
7
p.
Hathaway
,
L.
1998b
,
Geotechnical field trip report II
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
6
p.
Jaillard
,
E.
Soler
,
P.
,
1996
,
Cretaceous to early Paleogene tectonic evolution of the northern Central Andes (0–18o S) and its relations to geodynamics
:
Tectonophysics
 , v.
259
, p.
41
53
.
Love
,
D.A.
Clark
,
A.H.
,
1998a
,
Re-evaluation of the oregenetic model for the Antamina Cu-Zn(-Ag) skarn, interim report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
36
p.
Love
,
D.A.
Clark
,
A.H.
1998b
,
Revision of the ore-genetic model for the Antamina Cu-Zn(-Ag) skarn, 1998 final report
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
50
p.
Love
,
D.A.
Clark
,
A.H.
Schwarz
,
F.P.
,
2000
,
The Antamina deposit, An-cash, northern Peru: Anatomy and petrology of a giant copper-zinc skarn [abs.]
:
Geological Society of America Abstracts with Programs
 , v.
32
, no.
7
, p. A137.
Love
,
D.A.
Clark
,
A.H.
Strusievicz
,
O.R.
Lee
,
J.K.W.
,
2001
,
The regional tectonic setting of the giant Antamina Cu-Zn skarn deposit, north-central Peru [abs.]
:
Geological Society of America Abstracts with Programs
 , v.
33
, no.
6
, p.
A358
.
Love
,
D.A.
Clark
,
A.H.
Ullrich
,
T.D.
Archibald
,
D.A.
Lee
,
J.K.W.
,
2003a
,
40Ar-39Ar evidence for the age and duration of magmatic-hydrothermal activity in the giant Antamina Cu-Zn skarn deposit, Ancash, north-central Peru [abs.]
:
Geological Association of Canada-Mineralogical Association of Canada-Society of Economic Geologists, Joint Annual Meeting
 ,
Vancouver
,
British Columbia
, Abstracts Volume, v.
28
,
CD-ROM
.
Love
,
D.A.
Clark
,
A.H.
Lipten
,
E.J.H.
,
2003b
,
Genesis of the Antamina Cu-Zn skarn deposit, Ancash, Peru
:
Congreso Geológico Chileno, 10th
 ,
Concepción
,
CD-ROM
,
1
p.
Love
,
D.A.
Clark
,
A.H.
Glover
,
J.K.
,
2004
,
The lithologic, stratigraphic and structural setting of the giant Antamina copper-zinc skarn deposit, Ancash, Peru
:
Economic Geology
 , v.
99
, p.
887
916
.
McKee
,
E.H.
Noble
,
D.C.
,
1982
,
Miocene volcanism and deformation in the western Cordillera and high plateaus of south-central Peru
:
Geological Society of America Bulletin
 , v.
93
, p.
657
662
.
McKee
,
E.H.
Noble
,
D.C.
Scherkenbach
,
D.A.
Drexler
,
J.W.
Mendoza
,
J.
Eyzaguirre
,
V.R.
,
1979
,
Age of porphyry intrusion, potassic alteration, and related skarn mineralization, Antamina district, northern Peru
:
ECONOMIC GEOLOGY
 , v.
74
, p.
928
930
.
Mégard
,
F.
,
1984
,
The Andean orogenic period and its major structures in central and northern Peru
:
Journal of the Geological Society
 , v.
141
, p.
893
900
.
Meinert
,
L.D.
Hefton
,
K.K.
Mayes
,
D.
Tastran
,
J.
,
1997
,
Geology, zonation, and fluid evolution of the Big Gossan Cu-Au skarn deposit, Ertzberg district, Irian Jaya
:
Economic Geology
 , v.
92
, p.
509
534
.
Mertig
,
H.J.
Rubin
,
J.N.
Kyle
,
R.
,
1994
,
Skarn Cu-Au orebodies of the Gunung Bijih (Ertsberg) district, Irian Jaya, Indonesia
:
Journal of Geochemical Exploration
 , v.
50
, p.
179
202
.
Noble
,
D.C.
McKee
,
E.H.
,
1999
,
The Miocene metallogenic belt of central and northern Peru
:
Society of Economic Geologists Special Publication
 
7
, p.
155
193
.
O’Connor
,
K.
,
1999
,
Yacimiento polimetálico de Antamina: Historia, exploración y geología
:
ProExplo 99, Congreso Internacíonal de Prospectores y Exploradores, 1st
 ,
Lima, Peru
,
1999, Primer volumen de monografías de yacimientos minerales peruános. Historia, exploración y geología, Volumen Luis Hochschild Plaut, Instituto de Ingenieros de Minas del Perú
,
13
p.
Perelló
,
J.
García
,
A.
Ramos
,
P.
Glover
,
K.
Neyra
,
C.
Muhr
,
R.
Fuster
,
N.
Caballero
,
A.
,
2001
,
The Magistral porphyry-skarn Cu-Mo deposit, Ancash, Peru
:
ProExplo 2001, Congreso Internacíonal de Prospectores y Exploradores, 2nd
 ,
Lima, Peru
,
2001
,
Instituto de Ingenieros de Minas del Perú, CD-ROM
,
3
p.
Petersen
,
U.
,
1965
,
Regional geology and major ore deposits of central Peru
:
Economic Geology
 , v.
60
, p.
407
476
.
Petersen
,
U.
1999
,
Magmatic and metallogenic evolution of the Central Andes
:
Society of Economic Geologists Special Publication
 
7
, p.
109
153
.
Petford
,
N.
Atherton
,
M.P.
Halliday
,
A.N.
,
1993
,
Miocene plutonism in N. Peru: Implications for along-strike variations in Andean magmatism (9–22o S)
:
International Symposium on Andean Geodynamics, 2nd, Oxford, England, 1993
 ,
Paris
,
Editions de l’Orstom
, p.
427
430
.
Raimondi
,
A.
,
1873
,
El departamento de Ancachs [sic] y sus riquezas minerales
 :
Lima, Peru
,
Enrique Meiggs
,
651
p.
Redwood
,
S.D.
,
1997
,
Reinterpretation of the structural evolution of Antamina
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
4
p.
Redwood
,
S.D.
1998
,
The Antamina copper-zinc skarn deposit, northern Peru [abs.]
:
Geological Association of Canada, Mineral Deposits Division Congress, Quebec, 1998, Abstract Volume, Carrefour in Earth Sciences
 , v.
23
, p.
A153
.
Redwood
,
S.D.
1999
,
The geology of the Antamina copper-zinc skarn deposit, Peru
:
The Gangue
 , v.
60
, p.
1
, 3–7.
Redwood
,
S.D.
2003
,
The development of the geological model of the Antamina copper-zinc skarn deposit, northern Peru
:
Congreso Geológico Chileno, 10th, Concepción, 2003, CD-ROM
 ,
1
p.
Redwood
,
S.D.
Rice
,
C.M.
,
1997
,
Petrogenesis of Miocene basic shoshonitic lavas in the Bolivian Andes and implications for hydrothermal gold, silver and tin deposits
:
Journal of South American Earth Sciences
 , v.
10
, p.
203
211
.
Sébrier
,
M.
Soler
,
P.
,
1991
,
Tectonics and magmatism in the Peruvian Andes from late Oligocene time to the Present
:
Geological Society of America Special Paper
 
265
, p.
259
278
.
Sillitoe
,
R.H.
,
1997
,
Comments on the geological model for the Antamina copper-zinc skarn deposit, Peru
 :
Lima, Peru
,
Compañía Minera Antamina
,
unpublished report
,
7
p.
Soler
,
P.
Grandin
,
G.
Fornari
,
M.
,
1986
,
Essai de synthèse sur la métallogénie du Pérou
:
Géodynamique
 , v.
1
, p.
33
68
.
Terrones
,
A.J.
,
1958
,
Structural control of contact metasomatic deposits in the Peruvian Cordillera
:
American Institute of Mining, Metallurgical and Petroleum Engineers
 , v.
211
, p.
365
372
.
Tosdal
,
R.M.
Clark
,
A.H.
Farrar
,
E.
,
1984
,
Cenozoic polyphase landscape and tectonic evolution of the Cordillera Occidental, southernmost Peru
:
Geological Society of America Bulletin
 , v.
95
, p.
1318
1332
.
Volkert
,
D.F.
McEwan
,
C.J.A.
Garay
,
E.
,
1998
,
Pierina Au-Ag deposit, Cordillera Negra, north-central Peru [ext. abs.]
:
Pathways ’98, Cordilleran Roundup. 15th, 1998
 ,
Vancouver, Canada
,
Extended Abstracts Volume
, p.
33
35
.
Wilson
,
J.
,
1963
,
Cretaceous stratigraphy of central Andes of Peru
:
Bulletin of the American Association of Petroleum Geologists
 , v.
47
, p.
1
34
.
Wilson
,
J.
Reyes
,
L.
Garayar
,
J.
,
1967
,
Geología de los cuadrángulos de Mollebamba, Tayabamba, Huaylas, Pomabamba, Carhuaz y Huari
:
Servicio de Geología y Minería [Perú], Boletín
 
16
,
95
p.

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