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Economic GeologyVol. 98, 2003, pp. 1575–1605 Porphyry-Style Alteration and Mineralization of the Middle Eocene to Early Oligocene Andahuaylas-Yauri Belt, Cuzco Region, Peru JOSÉ PERELLÓ,† Antofagasta Minerals S.A. Ahumada 11, Oficina 602, Santiago, Chile VÍCTOR CARLOTTO, Departamento de Geología, Universidad Nacional San Antonio Abad del Cuzco. Avenida de la Cultura, Cuzco, Perú ALBERTO ZÁRATE, PEDRO RAMOS, HÉCTOR POSSO, CARLOS NEYRA, ALBERTO CABALLERO, Minera Anaconda Perú S.A. Avenida Paseo de la República 3245, Piso 3, San Isidro, Lima 27, Perú NICOLÁS FUSTER, AND RICARDO MUHR Antofagasta Minerals S.A. Ahumada 11, Oficina 602, Santiago, Chile Abstract Originally known for its Fe-Cu skarn mineralization, the Andahuaylas-Yauri belt of southeastern Peru is rapidly emerging as an important porphyry copper province. Field work by the authors confirms that mineralization in the belt is spatially and temporally associated with the middle Eocene to early Oligocene (~48–32 Ma), calc-alkaline Andahuaylas-Yauri batholith, a composite body with an areal extent of ~300 × 130 km emplaced into clastic and carbonate strata (e.g., Yura Group and Ferrobamba Formation) of Jurassic to Cretaceous age. Batholith emplacement included early-stage, mafic, cumulate gabbro and diorite between ~48 and 43 Ma, followed by pulses of granodiorite and quartz monzodiorite at ~40 to 32 Ma. Coeval volcanic rocks make up the middle Eocene to early Oligocene Anta Formation, a sequence of >1,000 m of andesite lava flows and dacite pyroclastic flows with interbedded volcaniclastic conglomerate. Sedimentary rocks include the red beds of the Eocene to early Oligocene San Jerónimo Group and the postmineralization late Oligocene to Miocene Punacancha and Paruro formations. Eocene and Oligocene volcanic and sedimentary rocks are interpreted to have accumulated largely in both transtensional and contractional synorogenic basins. New and previously published K-Ar and Re-Os ages show that much of the porphyry-style alteration and mineralization along the belt took place during the middle Eocene to early Oligocene (~42–30 Ma). Thus, batholithic magma emplacement, volcanism, and sedimentation are inferred to have accompanied a period of intense deformation, crustal shortening, and regional surface uplift broadly synchronous with the Incaic orogeny. Supergene mineralization is inferred to have been active since the Pliocene on the basis of geomorphologic evidence and a single K-Ar determination (3.3 ± 0.2 Ma) on supergene alunite. The belt is defined by 31 systems with porphyry-style alteration and mineralization, including 19 systems grouped in 5 main clusters plus 12 separate centers, and by hundreds of occurrences of magnetite-rich, skarntype Fe-Cu mineralization. Porphyry copper stocks are dominated by calc-alkaline, biotite- and amphibolebearing intrusions of granodioritic composition, but monzogranitic, monzonitic, quartz-monzonitic, and monzodioritic stocks occur locally. Hydrothermal alteration includes sericite-clay-chlorite, and potassic, quartz-sericitic, and propylitic assemblages. Calcic-potassic and advanced argillic alteration associations are locally represented, and calc-silicate assemblages with skarn-type mineralization occur where carbonate country rocks predominate. Porphyry copper deposits and prospects of the belt range from gold-rich, molybdenum-poor examples (Cotabambas), through deposits carrying both gold and molybdenum (Tintaya, Los Chancas), to relatively molybdenum-rich, gold-poor end members (Lahuani). Gold-only porphyry systems are also represented (Morosayhuas). Gold-rich porphyry copper systems are rich in hydrothermal magnetite and display a positive correlation between Cu and Au in potassic alteration. The bulk of the hypogene Cu (-Au, -Mo) mineralization occurs in the form of chalcopyrite and bornite, in intimate association with early-stage potassic alteration which, in many deposits and prospects, is variably overprinted by copper-depleting sericite-clay-chlorite alteration. Most porphyry copper systems of the belt lack economically significant zones of supergene chalcocite enrichment. This is due primarily to their relatively low pyrite contents, the restricted development of quartzsericitic alteration, and the high neutralization capacities of both potassic alteration zones and carbonate country rocks as well as geomorphologic factors. Leached cappings are irregular, typically goethitic, and contain copper oxide minerals developed by in situ oxidation of low-pyrite, chalcopyrite (-bornite) mineralization. Porphyry copper-bearing stocks emplaced in the clastic strata of the Yura Group and certain phases of the Andahuaylas-Yauri batholith may develop appreciable supergene chalcocite enrichment in structurally and lithologically favorable zones. † Corresponding author: e-mail, [email protected] 0361-0128/01/3394/1575-31 $6.00 1575 1576 PERELLÓ ET AL. A model for the region suggests that the calc-alkaline magmas of the Andahuaylas-Yauri batholith and subsequent porphyry-style mineralization were generated during an event of subduction flattening which triggered the crustal shortening, tectonism, and uplift assigned to the Incaic orogeny. Shortening of the upper crust would have impeded rapid magma ascent favoring storage of fluid in large chambers which, at the appropriate depth in the uppermost crust, would have promoted large-scale porphyry copper emplacement. Geodynamic reconstructions of the late Eocene to early Oligocene period of flat subduction in the central Andes suggest that emplacement of the Andahuaylas-Yauri batholith took place at an inflection corridor in the subduction zone broadly coincident with the position of the present-day Abancay deflection. Similarly, evidence from southeastern Peru suggests that the Andahuaylas-Yauri belt may be continuous with the late Eocene to early Oligocene porphyry copper belt of northern Chile and that the process of subduction flattening in southern Peru also may have taken place in northern Chile between ~45 and 35 Ma. Introduction THE ANDAHUAYLAS-YAURI belt (Bellido et al., 1972; Santa Cruz et al., 1979; Noble et al., 1984) covers an area of approximately 25,000 km2 in southern Peru and extends for about 300 km between the localities of Andahuaylas in the northwest and Yauri in the southeast (Fig. 1a). Until the late 1980s, the Andahuaylas-Yauri belt had received only limited geologic scrutiny and was mainly known for its copper-bearing, magnetite skarn deposits (Terrones, 1958; Bellido et al., 1972; Sillitoe, 1976, 1990; Santa Cruz et al., 1979; Einaudi et al., 1981; Aizawa and Tomizawa, 1986), best exemplified by Tintaya, Atalaya, Las Bambas, Katanga, and Quechua. For most researchers, these occurrences were considered to be copper skarns associated with barren intrusions (e.g., Einaudi et al., 1981; Noble et al., 1984), although potassic alteration in host porphyritic stocks had been described and characterized as such (Yoshikawa et al., 1976; MMAJ, 1983; Noble et al., 1984). During the late 1980s, regional work complemented by detailed geologic studies at Tintaya and Katanga (Carlier et al., 1989), followed by grass-roots exploration in the region during the 1990s, confirmed the presence of porphyry-style alteration and mineralization (e.g., Fierro et al., 1997) and resulted in the discovery of additional, potentially economic porphyry copper deposits (Table 1) at Antapaccay (Jones et al., 2000), Los Chancas (Corrales, 2001), and Cotabambas (Perelló et al., 2002), as well as porphyry-skarn mineralization at Coroccohuayco (BHP Company Limited, 1999). Zinc-rich, Mississippi Valley-type mineralization was also discovered in the region (Carman et al., 2000) adding to the metallogenic diversity of the belt. This paper describes the salient geologic features of a number of porphyry Cu (-Au, -Mo) deposits and prospects of the Andahuaylas-Yauri belt that help to define this region as a new porphyry copper province. It also provides new geochronologic data to constrain the age of the porphyry-style alteration and mineralization in the belt and establishes regional correlations and comparisons with nearby porphyry copper provinces. However, the paper is not designed to cover in full the complex geology of this still poorly understood region. Detailed geologic descriptions can be found in Marocco (1978) and Carlotto (1998) for the area under study, and in Clark et al. (1990) and Sandeman et al. (1995) for nearby southeastern Peru transects. The paper focuses on systems for which the bulk of the mineralization is of porphyry type and excludes those deposits in which skarn-type mineralization is the dominant style. Descriptions of the latter can be found elsewhere (Terrones, 1958; Santa Cruz et al., 1979; Aizawa and Tomizawa, 1986; Fierro et al., 1997; Zweng 0361-0128/98/000/000-00 $6.00 et al., 1997). Following a short review of the regional geologic setting of the Andahuaylas-Yauri belt, the main geologic features of several deposits and prospects are described. The paper concludes with a section in which regional metallogenic aspects are reviewed. Methods Except for those deposits and prospects with published descriptions (e.g., Tintaya, Antapaccay, Los Chancas), much of the work represents the product of more than three years of exploration by the authors, including both regional (1:25,000 scale) and detailed (1:5,000 scale) mapping. Field work was complemented by thin section petrographic studies to characterize rock types, alteration assemblages, and dominant vein styles at each prospect. Rock names for the main batholith intrusions and porphyry copper-bearing stocks follow the nomenclature of Streckeisen (1976, 1978) and are based on point counts (1,500 points) for modal proportions of key silicates. Unless otherwise stated, the K-Ar ages reported here were determined at the geochronology laboratory of the Geological Survey of Chile, Santiago and followed standard procedures and techniques (e.g., Dalrymple and Lamphere, 1966; Steiger and Jaeger, 1977; Baksi, 1982). All ages are referred to the geological time table of Haq and van Eysinga (1987). Regional Setting The Andahuaylas-Yauri belt is located at a distance of ~250 to 300 km inland from the present-day Peru-Chile trench (Fig. 1). The region is underlain by thick sialic crust (50 to 60 km; James, 1971), and straddles the transition zone between the southern, normal subduction regime of southern Peru and northern Chile and the northern, flat subduction zone of central and northern Peru (Cahill and Isacks, 1992). It is located immediately southeast of the Abancay Deflection (Marocco, 1978). The region encompasses parts of the intermontane depressions between the Eastern and Western Cordilleras and the northern extremity of the Altiplano (Fig. 1b; Carlier et al., 1996; Chávez et al., 1996). The western part of the belt is characterized by a rugged, mountainous topography where ranges and snow-capped peaks above 4,500 m are incised by deep (>2,000 m), steep-sided canyons. These canyons constitute the main drainage system of the region and include the Santo Tomás, Urubamba, Apurímac, Vilcabamba, Mollebamba, and Antabamba rivers, all of which drain toward the Amazon basin. The eastern and southern parts of the region are characterized by the gently undulating topography of the ~4,000 m-high plateaus that extends into the Altiplano of Bolivia (Fig. 1b). 1576 1577 PORPHYRY-STYLE ALTERATION AND MINERALIZATION, ANDAHUAYLAS-YAURI BELT, PERU Lima 100 75 50 125 150 75° 65° 70° BR A PERU 80° 10° 70° 60° 50° 40° ZIL 0° M Cuzco A AC 10° 600 BOLIVIA Y 15° PE Puno RU e dg La Paz N az ca Ri - 40° CH 50° IL E Arica R idge NCH Oligocene Crust CHILE TRE ne st ce Cru o E e rly en Ea leoc a P m/yr 8.5 c a 30° Arequipa Middle-Late Eocene Crust 20° 20° Lake Titicaca da di LEGEND Calama r Pe 125 Benioff Zone Contours (km) 175 200 Elevation > 3 km Study Area 75° 65° 70° A: Lima AC: Abancay AMAZON CRATON AC A Andahuaylas M Cuzco Y: Yauri M : Machu Pichu Y 15° 50 Puno Arequipa La Paz Precambrian and Paleozoic terranes with Grenville basement 60 PACIFIC OCEAN Contour on Moho (km) Arica Altiplano 70 Western Cordillera 50 Calama PA TE MP RR EA AN N E 20° Eastern Cordillera 0 b 250 FIG. 1. Sketch maps showing the location of the study area in the context of main geologic, geophysical, topographic, and physiographic features of the Central Andes. a. Area with average elevation >3,000 m and depth contours of the subducted slab after Cahill and Isacks (1992). Oceanic features from Jaillard et al. (2000). b. The study area relative to main regional physiographic provinces (Jaillard et al. 2000), contours of crustal thickness (James, 1971), and main Precambrian basement units (Ramos and Aleman, 2000). 0361-0128/98/000/000-00 $6.00 1577 500 km Chávez et al. 1998) are probable extensions of the Marañón massif exposed farther north and are interpreted by Ramos and Aleman (2000) to constitute remnants of perigondwanan terranes attached to the Amazonian Craton in the Early Paleozoic (Fig.000 m of volcanic and clastic rocks of the Mitu Group (Permian to Early Triassic. n.. The Western basin. The Eastern basin.a. and supergene copper oxides (Cárdenas et al..42 0. 1997). with hypogene chalcocite and bornite. It contains a sedimentary pile (Middle Jurassic to Late Cretaceous) in excess of 4.. limestone. 1990. 1986. 1989) and northern Chile (San Bartolo.a. which have similarities to the red bed deposits from the Bolivian Altiplano (e.. 2)..01 <0. 2 and 4).08 Deposit 1BHP Main reference Jones et al. Coutand et al.68 1. 1999.500 m.39 0. with a total thickness of approximately 800 m (Fig. 1982. with a total thickness of ~4. 1993). These units unconformably overlie the Mesozoic and early Cenozoic sequences described above. 1978. 1996). (2002) Corrales (2001) Billiton corporate website: <www.. Carlotto et al.89 1. 1992). 1b). sedimentary.. black shale. Paleozoic rocks in the region include >10. and volcanic microconglomerate) strata interbedded with tuffaceous horizons near the top. TABLE 1... up to several meters thick. Farther south.000 m of volcanosedimentary. Tejada (pers. from the upper tuffaceous horizons of the Soncco Formation (Fig. Jaillard et al. made up of red bed terrigenous (sandstone.01 Los Chancas 200 1. 3)..com> Precambrian and Paleozoic basement Precambrian gneisses at Río Pichari. Pecho.g. and continental rocks of Cambrian(?) to Early Permian age (Marocco. 1996). 1993. 1999). commun. including the sedimentary San Jerónimo Group and the dominantly volcanic Anta Formation (Figs. Carlotto.. respectively. The top of the sequence contains the massive micritic limestone.. Fornari et al. The northeastern edge of this basin.g. Fierro et al. The San Jerónimo Group (Eocene to early Oligocene) consists of two main formations (Kayra and Soncco.23 n. Noblet et al. Carlotto et al. n.a..12 0.. 1981). 1993.00 0. Cárdenas et al.. The age of these rocks is Late Jurassic to Paleocene (Fig. Sillitoe. 4).1578 PERELLÓ ET AL. 1999). n. the lower horizons of the Tiwanaku Formation and the Berenguela and Turco formations. The Anta Formation is a >1.57 1.16 0. marine. basal sandstone of the Soncco Formation includes horizons of stratiform copper mineralization. Corocoro. and in the Salar de Atacama area of northern Chile (upper Purilactis Group. pelitic sandstone.00 Eocene to early Oligocene stratigraphy Two main units characterize the Eocene to early Oligocene stratigraphy of the region. 3. Carlotto et al. 1996a. Mpodozis et al. shale.. (2000). The upper part of the pre-Andean basement is dominated by >1. 4). corresponds to the present-day Western Cordillera. Hérail et al. Geologic Resources for Main Deposits of the Andahuaylas-Yauri Belt Tonnage (× 106) Cu (%) Au (g/t) Mo (%) Tintaya district Antapaccay Coroccohuayco Ccatun Pucara Quechua Tintaya 383 155 24 300 139 0. Marocco and Noblet. conglomeratic. n.a.a.83 Ma. 1994.16 n. where it is overlain by the volcanic horizons of the Tacaza Group (Klinck et al. 1982). Travisany. Mesozoic and Cenozoic stratigraphy The Mesozoic and Cenozoic stratigraphy of the region is chiefly made up of Jurassic and Cretaceous sedimentary sequences deposited in a paleogeographic setting dominated by two main basins (Western and Eastern Peruvian basins) separated by the Cuzco-Puno basement high (Fig.36 <0. Sedimentation is interpreted to have taken place initially in a fluvial environment that progressed into structurally controlled. Jaillard.4 Ma and 30. 1990. coincident with the Andahuaylas-Yauri region. also known as Putina basin (Jaillard. with a total thickness of ~ 2. Alonso. 1994). 1993. (2002) Perelló et al. BHPBilliton. pull-apart basins (Córdova. 1987. is made up of several sequences of Late Cretaceous marine clastic and carbonate rocks. 1978). ~130 km northwest of Cuzco (Carlotto..9 ± 1.84 ± 0. Clark et al. 1978. also known as the Arequipa basin (Vicente et al. and an upper part with abundant limestone (Vicente et al. 0. 1992. 4. 2003) BHP Billiton (2003)1 Perelló et al.62 0.. Jaillard and Santander. Jaillard and Santander. Kraemer et al. in the Puna of northwestern Argentina (Geste and Quiñoa formations. Jaillard and Soler. and an upper member of fluvial conglomerate with 1578 .. 1992).000 m sequence characterized by a lower member with andesite lava flows and dacite pyroclastic flows locally interbedded with alluvial conglomerate.. (2002) BHP (1999) BHP (1999) E. Cotabambas Area Azulccacca Ccalla 24 112 0. The San Jerónimo Group is equivalent to the Puno Group of the Peruvian Altiplano southeast of the study region (Fig.39 0.a. 2002). 1998. and nodular chert of the Ferrobamba Formation (Marocco. The Cuzco-Puno high includes ~900 m of terrigenous red beds interbedded with shale. and gypsum (Carlotto et al. Fig.. n. 1994). 1986.500 m thick with a lower part dominated by turbidites. 0361-0128/98/000/000-00 $6. Fig.44 0. The age of the San Jerónimo Group is constrained by stratigraphic relations (it unconformably overlies strata with plant fossils of Paleocene to early Eocene age) and on K-Ar and ArAr ages of 29. red bed sequences are known in the Altiplano of Bolivia (e.. made up of Early Jurassic limestone and Middle to Late Jurassic quartz arenite and shale. 1979). a middle part with quartz arenite.a. 1997). 3). includes the Lagunillas and Yura groups (Marocco.600 m (Jaillard et al. 2001). Between Cuzco and Sicuani. b b: Mainy volcanic rocks (Mitu Gp. 2. and equivalent units) Miocene to Pliocene h a nc om a c 73°30´ t Chalhuanca ul rí Fa ac a mb ni 14°30´ Andahuaylas m Machu Pichu lt 14°00´ 13°30´ ío pu au i ca C us alhuanc a 13°00´ R A h cc ua n a -H eF uit oq P Ch Lakes PORPHYRY-STYLE ALTERATION AND MINERALIZATION.) Yauri 71°30´ S ic ua Fault Ay av ir iF au lt Putina Basin Sicuani ul t 11 Fa Reverse Fault Porphyry Cu cluster/deposit 71°00´ Syncline Anticline Early Paleozoic basement (undifferentiated) Late Paleozoic to Early Triassic basement a: Mainy granitoids.) b b: Red bed sequences (San Jerónimo and Puno Gps.00 1579 Figure. Ferrobamba Fm.0361-0128/98/000/000-00 $6. 6 Alicia 7 Cristo de los Andes 8 Katanga 9 Portada 10 Winicocha lt 17 7 A Cotabambas R ecord 2 1 bo m m ba ta o C 73°00´ 14 u Curahuasi Ta m Fa 16 F ault 13 a A ban ca y F Abancay 15 Mo lleb amba lt Lima ta mbo F a ult is 1 2 3 4 5 12 Fau Eocene to early Oligocene Andahuaylas-Yauri Batholith Eocene to early Oligocene continental rocks a: Volcanic and sedimentary sequences (Anta Fm.) a Pomacanchis rur Urcos Accha lt ul Paruro co-U lt Cu z Fa u ul t Yau ri Fault Fa FIG. with additions after Pecho (1981) and this study. modified and greatly simplified after Carlotto (1998). ANDAHUAYLAS-YAURI BELT. Geologic map of the study area.-2 Morosayhuas Cotabambas Chaccaro Ferrobamba Chalcobamba 11 12 13 14 15 Tintaya Los Chancas Peña Alta Leonor Panchita 16 Lahuani 17 Trapiche 72°30´ 0 F ault 5 4 3 Cuzco a chay ult 6 Fa 25 8 Velille 50 km 72°00´ 9 Santo Tomás ba s rco sF au Pa t oF a ul t 10 Livitaca Mesozoic to early Cenozoic marine sedimentary sequences (Yura and Lagunillas Gps. and equivalent units) Pliocene shoshonitic volcanic rocks Oligocene to Miocene continental sedimentary rocks (Paruro. Punacancha Fms.) a Oligocene to Miocene subaerial volcanic rocks (Tacaza and Sillapaca Gps. PERU 1579 . 1997. 2 and 4. 1990. flood plains and alluvial fans in structurally controlled basins (Carlotto et al. 1990. small shoshonitic volcanic centers of Pliocene to Quaternary age occur in the region (Figs. Jaillard (1994). 1998).100 m-thick) formations (Fig. The Anta Formation andesites and conglomerates are interpreted to be stratigraphic equivalents of the San Jerónimo Group red beds (Fig.4 Ma.5 and 37.1580 LATE CRETACEOUS (MAASTRICHTIAN) PERELLÓ ET AL. Carlier et al. Its age is constrained to middle Eocene to early Oligocene by stratigraphic relations and K-Ar geochronology (Carlier et al. 1997).1 Ma (Carlotto. 1990. NE BORDER OF THE WESTERN (AREQUI PA) BASIN EASTERN (PUTINA) BASIN CUZCO-PUNO HIGH W E PU A F A H EARLY-LATE (TURONIAN) CRETACEOUS F H M HU HU S CH PALEOZOI C BASEMENT M S ? MIDDLE (BAJOCIAN) -LATE (TITHONIAN) JURASSIC G CH ? F P ? YURA GP... Oligocene and Miocene volcanic rocks in the region and nearby areas are largely dominated by the calc-alkaline sequences of the Western Cordillera (Inner-Western Cordillera of Sandeman et al.500–5. Carlotto.9 ± 1. are interpreted to reflect topographic rejuvenation of the source regions in response to increasing regional tectonic uplift. 1996. Late Oligocene to Miocene stratigraphy The late Oligocene to Miocene sedimentary deposits of the region include the Punacancha (1. 4). 4). 100 km FIG.. 1998). as well as a K-Ar age of 10. and a basaltic horizon from the upper part of the unit yields a K-Ar whole rock age of 29... 1580 .. The Tacaza Group consists dominantly of trachyandesite. 2000)..1 ± 0.. Carlotto. Sandeman et al. 1995) and Altiplano.5 Ma for a tuffaceous horizon near the base of the Paruro Formation (Carlotto et al. interbedded andesite and basaltic andesite flows (Fig. 1995)... They are dominated by coarsening-upward red shale and sandstone. 3. with shoshonitic rocks being important in the Santa Lucía area. 1996a. Sedimentation is interpreted to have taken place in a fluvial environment with braided rivers. with 0361-0128/98/000/000-00 $6. Jaimes et al. L FERROBAMBA A AYAVACAS M MARA H HUANCANE S SORAYA HU HUAMBUTIO G GRAMADAL AA ANTA-ANTA P PISTE PU PUQUIN CH CHUQUIBAMBILLA 0 50 L LAGUNILLAS GP. Shoshonitic volcanism in the Santa Lucía area took place between ~32 and 24 Ma (Fig. 1996.4 ± 1.9 ± 1.. with alluvial and fluvial conglomerates dominated by volcanic and plutonic clasts at the top. and Carlotto (1998). Carlotto.. a series of scattered.000 m thick) and Paruro (>1. (1994. 1990. southeast of Yauri (Clark et al. 4). The age of these sequences is based on stratigraphic relations and fossil flora. Main stratigraphic units and correlations after Vicente et al. In addition to these. 1998). and rhyolite tuff (Klinck et al. with sedimentation in a piggy-back style basin environment (Carlotto. Clark et al. Wasteneys.00 gypsum and conglomerate being characteristic in the upper parts of the sequences. 1997). 1997. Southwest of Cuzco. Sandeman et al. The coarsening-upward characteristics of the sequence. two biotite-rich dacitic flows from the middle part of the formation have returned K-Ar ages of 38. Wasteneys. 1998). with the erosion products of the Anta Formation feeding the San Jerónimo basin located to the northeast. Schematic paleogeographic reconstruction of the backarc basin of southern Peru during the Mesozoic and the earliest Cenozoic. See text and Figure 8 for dominant rock types of each sequence. 1995). 1998). andesite. 4. Jaillard et al. 1986. Romero et al. and include the Tacaza (Oligocene) and Sillapaca (Miocene) groups. (1982). 2002). note the spatial and temporal relationships between batholithic plutons. with additions after Carlier et al. and D simplified after Sandeman et al. Columns A. commun. B. 60 55 50 40 37 34 30 28. ANDAHUAYLAS-YAURI BELT. volcanic rocks of the Anta Formation. 1996) and this study. (1989.8 PLEISTOCENE 0 Age (Ma) MIOCENE LATE MIDDLE EARLY LATE EARLY LATE MIDDLE OLIGOCENE EOCENE 0361-0128/98/000/000-00 $6. sedimentary. Summary stratigraphic columns for representative Eocene to present-day volcanic. 4.PLIOCENE 1581 PALEOCENE ? LATEST TOQUEPALA PLUTONISM/ VOLCANISM ATASPACA PLUTONS MOQUEGUA FM HUAYLILLAS FM CHUNTACALA FM CAPILLUNE FM BARROSO GP AMBATO GP B WESTERN CORDILLERA ANDAHUAYLASYAURI BATHOLITH PUNO GP ANTA FM TACAZA GP SANTA LUCIA FM SILLAPACA GP BARROS O GP ? ? ? EARLY TER TIARY REDBED S KAYRA FM Red bed Copper SAN JERONIMO GP SONCCO FM PUNACANCHA FM PARURO FM SANTO TOMAS IGNIMBRITES CUZCO-SICUANI VOLCANOE S C WESTERN CORDILLERA/ ALTIPLANO D EASTERN CORDILLERA 15° PERU PICOTANI GP QUENAMAR I GP MACUSANI FM ARCO-AJA FM C A B BOLIVIA CHILE D 70° Dominantly mafic cumulate calc-alkaline intrusions Dominantly intermediate compositioncalc-alkaline intrusions Dominantly “syenogranitic” intrusions Peraluminous monzogranitic intrusions Evaporites Dominantly mollasic sedimentation Mixed dacitic/basaltic-andesitic or lamprophyric volcanism Dominantly rhyolitic to rhyodacitic volcanism Dominantly dacitic volcanism Dominantly andesitic volcanism Apparent non-volcanic interval FIG.00 EARLY A ARC FRONT PORPHYRY-STYLE ALTERATION AND MINERALIZATION. (1995) and references therein and A.H. Column C for the study area compiled after Carlotto (1998). PERU 1581 . In column C. Clark (pers. and the sedimentary red bed sequences of the San Jerónimo Group. and intrusive units of the study area and nearby southeastern Peru transects..5 24 20 16 11 10 5 1. In general terms. and diorite) followed by rocks of intermediate composition (monzodiorite.. Contact aureoles within country rocks are extremely irregular in shape. 1993). as no involvement of pre-Mesozoic basement is apparent. Clark et al. The batholith is composed of a multitude of intrusions that crop out discontinuously for >300 km between the towns of Andahuaylas in the northwest and Yauri in the southeast. Early-stage cumulate rocks are exposed mainly along the northern border of the batholith (Fig. The Andahuaylas-Yauri batholith The northeastern border of the Western Cordillera in the study area is underlain by large bodies of intrusive rocks collectively known as the Andahuaylas-Yauri batholith (Carlier et al. (1996). confirm a middle Eocene to early Oligocene age (~48-32 Ma) for the bulk of the batholith (Fig. 0361-0128/98/000/000-00 $6. 1996. Altiplano. 1998). 4. 5) between Curahuasi and Limatambo (Carlier et al. represent the terminal stage (see below).. Carlotto (1998). 5). 1999).. Mendívil and Dávila.. 1981). 1986). 4). Subvolcanic rocks of dominantly granodioritic/dacitic composition. Cabrera et al. however. 1991. elsewhere in the Puno region a second effusive event. it may be speculated that the temporal overlap of the Oligocene to Miocene volcanism of the Western Cordillera. 1990). 1999).1582 PERELLÓ ET AL.and high-angle thrusts locally accompany the most intense deformation and folding. 1990. northwest-trending folds with dominantly northerly vergence (Fig. Although some exceptions exist (Marocco. that considerable time overlap existed between the more mafic and the more felsic intrusions of the younger group (Fig. 1998). however. 4). particularly in the southern quadrangles of the region (Pecho. The intrusions of the intermediate stage are lighter gray in color. quartz diorite. gabbrodiorite. Carlotto.. Rocks from Santa Lucía yield ages of between ~22 and 14 Ma (Clark et al. 1989. Sillapaca Group rocks include mainly dacite flows with subordinate andesite in the southeastern part of the study region (Carlotto. (1989. It is also known locally as the Abancay (Marocco. 1990. olivine gabbro.. Tacaza-equivalent pyroclastic flows intercalated with the molassic Moquegua Formation commenced at ~26 Ma (A. In addition.. 1989. returns ages of between ~14 to 12 Ma (Klinck et al. 1978) or Apurímac batholith (Pecho. 1975. The geochronologic data support the inference by Bonhomme and Carlier (1990) that cumulate rocks are older (~48-43 Ma) and that intermediate composition rocks are younger (~40-32 Ma). 1998). together with a number of ages obtained during the course of the present study.00 Structural geology The structure of the region is. This style has similarities to thin-skinned fold-thrust belts elsewhere (e. The limit between the Western Cordillera and the Altiplano is characterized by two main northwest-trending fault systems (Limatambo-Ayaviri and Abancay-Yauri) with exposed 1582 .. where petrologic work by Carlier et al. These intrusions are part of a larger alkalic magmatic province that also includes the basanites. 1996) determined that they constitute typical calcalkaline cumulates crystallized at the bottoms of shallow magma chambers.g.g. 1996. 1995) would also apply to the Andahuaylas-Yauri region. troctolite. equigranular to slightly porphyritic textures. Ligarda et al. display mediumto coarse-grained. size. 5b). Its width varies between ~25 km in the Tintaya area and ~130 km along the Chalhuanca-Abancay transect (Fig. They are regularly distributed throughout the region and constitute the main mass of the batholith. and granodiorite) (Fig. Carlotto. and trachytes of the Ayaviri region.. Bonhomme and Carlier. 4). 1998). with temperatures of emplacement of ~1. Low. Ferrobamba Formation) and biotite and cordierite hornfels are developed where the more pelitic facies of the Mesozoic formations are present (Carlotto. thereby corroborating the concept that batholith emplacement took place in at least two main stages. Pecho. commun. 1990).. the batholith includes early-stage intrusions of cumulates (gabbro. whereas farther south. In the Andahuaylas-Yauri region. volcanism seems to have been intermittently active since the middle Eocene (Carlier et al. also assigned to the Sillapaca Group. 2).. 2000). (2002). 1994). (1995) that a >350-km-wide arc was episodically active throughout southern Peru during late Oligocene and Miocene times. 1989.. 5c. 2002). similar age (~29 Ma) shoshonitic rocks have been interpreted to be part of uppermost Anta Formation (see above and Carlotto... and Eastern Cordillera (Sandeman et al. with most of the mapped thrusts displaying northerly vergence.. although garnet skarn is typically formed in calcareous rocks (e. thereby implying some degree of temporal overlap with Tacaza rocks (Fig. 1975. following Bonhomme and Carlier (1990). Carlotto. in general terms. regional maps lack the detailed structural data that would help to understand the regional tectonics as a whole. with local pyroxene in the more mafic members. This interpretation is consistent with the suggestion by Sandeman et al. Clark. Sandeman et al. Carlotto et al. phonotephrites. The data also suggest. poorly constrained and understood. The northeastern border of the Western Cordillera is dominated by Mesozoic to Cenozoic sequences that have been moderately to intensely deformed in large. Intense folding in the region typically involves carbonate and shaly sequences (Ferrobamba Formation and equivalent units) that wrap around cores of quartz arenite of the Yura Group. Carlier et al. Fig. 1998). In the Andahuaylas-Yauri region. If the correlations above are accepted (Fig. Bonhomme and Carlier. locally associated with porphyry-style mineralization. 1981. 5a). and possess amphibole > biotite as the dominant ferromagnesian phases.000°C and pressure conditions of ~2 to 3 kbars.. 1995). several K-Ar ages reported by Carlier et al. and Perelló et al. Carlotto et al.. The age of the batholith is constrained by regional stratigraphic relations and geochronologic data (Table 2. along the arc front. Batholith rocks intrude mostly Mesozoic and early Cenozoic marine and continental strata as well as the middle Eocene to early Oligocene Anta Formation (Fig. Other intrusions Post-batholith intrusive activity in the region is characterized by a series of small syenitic stocks that have yielded K-Ar ages of ~28 Ma in the Curahuasi area (Carlotto. 5b). 1998) and subvolcanic dacite plugs and ash-flow tuff in the Santa Lucía area (Fig. 2000. H. The name Andahuaylas-Yauri batholith is used in this paper. with ages between 29 and 26 Ma (Carlier et al. and composition. pers. quartz monzodiorite. 1981. Benavides-Cáceres. 1998. 1996b. 9±1.1±3. 1976).8 LIVITACA 40. Main localities studied are identified for better comprehension (see text for descriptions).3±1.7±1. based primarily on work by the writers with additions after Pecho (1981).5 43.5 24 20 Ma PUNACANCHA FORMATION ANTA Fm SAN JERONIMO Gp STRATIGRAPHY P c PORPHYRY-STYLE ALTERATION AND MINERALIZATION.9 KATANGA 8 9 4 YAURI 71°30´ 31.6±0.8±0.2±1. Displays the main body of the batholith (Fig. ANDAHUAYLAS-YAURI BELT.8±1. Available K-Ar age data relative to volcanism of the Anta Formation and sedimentation of the San Jerónimo Group as in column C of Figure 4. 1998) Batholith Plutons CHALHUANCA ANDAHUAYLAS DIORIT E / GABBRO (CUMULATES) DIORITE MONZODIORITE QUARTZ MONZODIORITE GRANODIORITE (1) (1) 73°30´ a 14°30´ 14°00´ (1) (1) (1) ANDAHUAYLAS-YAURI BATHOLITH 13 72°00´ 35.9 LAS BAMBAS 39. 50 40 37 34 30 28.3±1. c. (1989). and Carlotto (1998).9 43. a.00 EARLY 1583 ? ? (1) (1) (1) CURAHUASI 73°00´ 35.1 39. 2) and the location of the K-Ar age data from the present study (Table 2) and Carlotto (1998). b.4 50 km 72°30´ SANTO TOMAS 34.2 ±0.9 ABANCAY 37.7±0.1(1) POMACANCHIS 14 3 Monzogranite Granodiorite Tonalite Quartz Monzonite Quartz Monzodiorite Quartz Diorite Monzodiorite Diorite / Gabbro CUZCO A 5 6 7 10 11 12 16 17 6 14°30´ 14°00´ 16 11 7 12 17 Curahuasi Livitaca Pomacanchis Katanga Tintaya Cotabambas Las Bambas FIG. PERU 1583 . 5.9(1) COTABAMBAS 35. Distribution and age of the Andahuaylas-Yauri batholith in the study area.1(1) MACHU PICHU (1) K-Ar (Carlotto.7±1.0 1 15 0 5 2 1 Q TINTAYA SICUANI 43.MIOCENE EARLY OLIGOCENE EARLY LATE LATE b EOCENE MIDDLE 0361-0128/98/000/000-00 $6. Composition of the main phases of the Andahuaylas-Yauri batholith on a QAP diagram (Streckeisen. Carlier et al. Evidence from outside the study region (Portugal. (1990) and Sandeman et al. 1990. uplift.00 quences is interpreted to indicate that successive compressive events were modifying the original pull-apart transtensional architecture into contractional basins (Córdova. they place deep cumulate facies of the Andahuaylas-Yauri batholith on top of either younger intrusions of the same batholith or over volcanic horizons of the Anta Formation (Carlotto.1584 PERELLÓ ET AL.. 1998). Cabrera et al.9 31.544 0. This summary suggests that the Incaic orogeny in the study region constitutes a long-lived period of semicontinuous deformation of ~20 to 15 m.833 0.8 ± 0. Sébrier and Soler 1991). 1996. Fluvial sedimentation is thought to have progressed from south to north (Fig.556 0. TABLE 2. %) Age ± 2σ LIVIKAR 02 PORKAR 02 KATKAR 05 COTKAR 01 COTKAR 02 PROGKAR 01 PROGKAR 02 LAHUKAR 01 CHALCOKAR 02 14°18'58" 14°29'34" 14°26'38" 13°45'03" 13°41'11" 14°06'02" 14°00'54" 14°25'08" 14°03'37" 71°44'10" 71°56'02" 71°54'30" 72°21'23" 72°21'14" 72°28'35" 72°28'28" 73°00'45" 72°18'21" Biotite Biotite Biotite Biotite Amphibole1 Biotite1 Amphibole Biotite Amphibole 7. 1992. 1996.504 11. Cuzco-Puno high) into major high-angle reverse faults that favored the uplift of the Andahuaylas-Yauri batholith..g. 1990. Paleogeographic reconstructions (Fig. Chávez et al.9 35. Both are made up of several segments or smaller faults with individual continuous runs of >50 km that display high-angle reverse and strike-slip movements. Farther southeast.9 39. Locally. 1987.9 ± 1. Mégard et al. 1998. 10 to 50-km-wide corridor defined by the Limatambo-Ayaviri and Abancay-Yauri fault systems is occupied by the synorogenic rocks of the Anta Formation and the San Jerónimo Group. is also thought to have been the most important event of compressive deformation in the region.155 10..8 43. 1974. 1975. 1998). percent See Figure 5 for sample location 1 Some degree of alteration to chlorite present lengths of >300 km (Fig. Carlotto.. 1996b) of which the Eocene to early Oligocene (Incaic) and Oligocene to Miocene (Quechua) pulses are the most important.7 ± 0. In the vicinity of the Abancay deflection (Marocco. The bulk of the deformation.751 31 25 13 17 34 26 53 27 36 40. 1978). 6).0 35.8 ± 1. 1986. 40K = 0..581 × 10–10y–1. interpreted to have begun at ~42 Ma (Carlotto.3 ± 1. these structures transpose Paleozoic plutonic rocks over younger cover sequences. see below). northeast-trending synorogenic basins localized at the boundary between the Eastern and Western Cordillera. 1998).1 39..493 0. K-Ar Ages of Various Intrusive Phases of the Andahuaylas-Yauri Batholith Sample no. a contrasting view to that of Clark et al..812 6. apparent and may have accompanied emplacement of the various phases of the Andahuaylas-Yauri batholith in at least two main events. 1992... between the middle Eocene and the early Oligocene.5. Jaillard and Santander. The ~300-km-long. Latitude Longitude Mineral K (%) Radiogenic Ar (nl/g) Ar (at. 1999).212 5. 40Ar/36Ar = 295. 1998) strongly suggests that magmatism. The presence of several progressive unconformities in the sedimentary se0361-0128/98/000/000-00 $6. Important sedimentary.335 1. in the area of Santa Lucía.. λε = 0. 1988. Pecho. 1988.100 6.5 34.331 7.2 ± 0. Farrar et al. Carlier et al. 1998). (1995) for a contiguous transect (13–20°S) farther southeast.516 10.01167 at. Noblet et al. Sébrier et al.. Reactivation of older.171 0.y. Carlier et al.278 1. The Altiplano is characterized by the synorogenic sequences that filled the basins of the San Jerónimo Group and the Punacancha and Paruro formations. important volcanism (Anta Formation) accompanied deposition of the San Jerónimo red bed sequences. and magmatic activity occurred in the Eocene and Oligocene.962 × 10-10y–1.9 37. The two main fault systems are inferred to have been active during Mesozoic time and to have largely controlled the shape and extension of the Cuzco-Puno high in the region (Carlotto. Farther east. 1981. 1991. Marocco and Noblet.7 ± 1. 1979. 1992). Carlotto. 1974. high-angle reverse structures belonging to the southeastern extension of the Abancay-Yauri fault are interpreted to have been associated with a major fold-thrust deformation event (Jaillard and Santander. at ~48 to 43 and ~40 to 32 Ma (Bonhomme and Carlier. Carlotto et al. Carlotto. Benavides-Cáceres. tectonic. they would therefore constitute structures reactivated during Andean deformation (Jaillard and Santander.. folding. 1996b. These sequences display intense synsedimentary deformation structures including tight folding and fault-controlled progressive unconformities (Carlotto. Mégard. Carlotto et al. basin-bounding structures (e.. Porphyry Copper Geology Distribution The Andahuaylas-Yauri belt extends for ~300 km and is defined by 31 prospects and deposits with porphyry-style 1584 .6 ± 0. The red beds of the San Jerónimo Group were deposited in structurally controlled. 1996). 2).041 7. and erosion were all integral components of the Incaic orogeny in the Western Cordillera and Altiplano. also took place during late Eocene to early Oligocene time (~40–32 Ma. Several distinct deformation events and associated shortening and uplift are.271 9. 1987.4 Constants: λβ = 4. near Curahuasi. Tectono-Magmatic Synthesis The main part of the region under consideration seems to have been affected by several Late Cretaceous to Pliocene tectonic events (Marocco. 6) suggest that this northeast-directed deformation was responsible for the development of the basins that accommodated middle Eocene to early Oligocene volcanism and sedimentation.066 7. however. 1984.2 ± 1. 1998) and thus broadly synchronous with the Incaic orogeny of central Peru (Noble et al. Morosayhuas. 1585 . Note the intimate spatial relationship between batholithic plutons. The belt has a known maximum width of 130 km in a northeast-southwest direction. whereas both batholith intrusions and Anta Formation volcanic horizons make up the host rocks of the Morosayhuas cluster farther north (Fig. Los Chancas. whereas the Chuquibambilla and Soraya formations constitute common host rocks where the Yura Group predominates (Fig. Schematic paleogeographic reconstruction of the study area during late Eocene to early Oligocene time. 8). ANDAHUAYLAS-YAURI BELT. 1997. 7a). Wall rocks to the Las Bambas. as at Aurora (Fig. 2001). Portada. including 19 systems grouped in 5 main clusters plus 12 separate porphyry centers (Fig. alteration and mineralization. 7b). Leonor. and Antapaccay was the earlier plutonic phase effectively penetrated by the later porphyry stocks. Within the Mesozoic units.00 intrusions. Fierro et al. Corrales. and Las Bambas clusters and by the Peña Alta. and Aceropata. Leticia. and Winicocha systems.700 m (Fig.800 m. Lahuani. are nevertheless related to smaller plutons and outliers of the same batholith. 6. in the southwestern part of the belt (Los Chancas. are the preferred host rocks (Tintaya deposits. Jones et al. 1997. Katanga. Modified after Carlotto (1998).400 and 4. Main localities are shown for reference. Cotabambas.. However. Fig.1585 PORPHYRY-STYLE ALTERATION AND MINERALIZATION. Host rocks Country rocks for selected porphyry systems of the belt are indicated in Figure 8 and Table 3. and Chaccaro. 8). volcanic rocks of the Anta Formation.. Also shown are the main fault systems and high-angle thrusts that are interpreted to have controlled both uplift of the batholith at the deformation front south of Cuzco (the Cuzco-Puno high) and the San Jerónimo basins. beyond the limits of the belt in the Eastern Cordillera.. 3 systems (Leonor. and the sedimentary basins of the San Jerónimo Group in this reconstruction. far from the main batholithic 0361-0128/98/000/000-00 $6. it is apparent that lower Ferrobamba Formation horizons. porphyry Cu-Mo mineralization is exposed at elevations as low as 2. Isolated systems. A salient feature of the belt is the spatial distribution of porphyry copper stocks around the edges of the main intrusions that make up the Andahuaylas-Yauri batholith. 2002).. PERU 71° 73° MACHU PICHU Ri o A p ur Ab ANDAHUAYLAS an ca y im Fau ac Fault ault Limatambo F CUZCO lt ABANCAY C ot ab URCOS am ba s F a ult 14° 14° Po CHALHUANCA SICUANI ma LIVITACA ca s Fa av ir ult i Fa ul t a: CONGLOMERATES b: VOLCANIC ROCKS MAIN PLUTONS OF ANDAHUAYLAS-YAURI BATHOLITH hi ault uri F b ANTA FORMATION Ay nc a Ya SANTO TOMAS SAN JERONIMO GROUP BASINS YAURI MESOZOIC ROCKS 50 km PALEOZOIC BASEMENT SEDIMENT PROVENANCE 71° 73° FIG. Of these. 2000). with deposits exposed at elevations between 3. as exemplified by the Katanga. Only at Panchita. Alicia. near their contact with the Mara Formation. Leticia. The Cotabambas cluster is restricted to diorite and granodiorite of the AndahuaylasYauri batholith (Perelló et al. 7a) are excluded from this review due to a lack of data. such as those of the Tintaya cluster and Trapiche. Zweng et al. 7b). and Tintaya clusters include either intrusive batholithic rocks or sedimentary rocks preserved as roof-pendants in the batholith. l. (3) syn. Cotabambas. 9). The Aurora prospect is also shown for reference. and Panchita). the stocks generally range from ~0. Distribution of the porphyry copper deposits and prospects referred to in this study. a. together with other separate deposits and prospects.25 to 0. and Tintaya. Katanga. 7.1586 PERELLÓ ET AL. Fig. owing to (1) post-mineralization moraine cover (Katanga). such as the “rootless” nature of the stocks at Chabuca and 1586 .s. 9). Las Bambas. Moreover. Numbers in parentheses are keyed to the section of Figure 7b. IN SE T 5000 A A´ R 17 25 ON FO MOROSAYHUAS CLUSTER 9 29 30 CT I 4500 SE 6 3 24 4000 32 LLOCLLACSA (21) 18 19 2 23 31 14 16 26 28 13 33 11 5 27 22 7 3500 MAKI (22) COTABAMBAS CLUSTER 10 20 QENCO (27) CHA-CHA (11) 12 21 8 1 15 CHILCACCASA (12) HUACLLE (15) CCALLA (7) LETICIA (20) 3000 ACEROPATA (1) b AZULCCACCA (5) CCARAYOC (8) 4 50 km 2500 CHACCAR O (10) CHALCOBAMBA (9) FERROBAMBA (14) 14° ALICIA (2) LOS CHANCAS (18) PEÑA ALTA (24) SULFOBAMBA (29) LAS BAMBAS CLUSTE R LEONOR (19) CRISTO DE LOS ANDES (6) PANCHITA (25) KATANGA CLUSTER LAHUANI (17) A WINICOCHA (33) MONTE ROJO (23) PORTADA (26) SAN JOSE (30) TRAPICHE (32) KATANGA (16) TINTAYA (31) 50 km a TINTAYA CLUSTER ANTAPACCAY (3) 15° COROCCOHUAYCO (13) QUECHUA (28) FIG. 71° A´ 72° 73° AURORA (4) 13° Elevation meters a. (2) late mineral dikes (Cotabambas and Tintaya. In general. and (4) textural and compositional similarities between porphyry copperbearing stocks and wall rocks (Winicocha.and cylinder-like geometries. but also include the much smaller examples of the Morosayhuas cluster where the stocks can be as small as 150 × 50m. the form of the stocks 0361-0128/98/000/000-00 $6. Chalcobamba. b.6 km2. Morosayhuas.to post-mineralization faults (Cotabambas and Antapaccay. Simplified section A-A´ displaying the distribution of the systems relative to present-day elevation above sea level. Fig. Geometry Porphyry copper-bearing stocks of the Andahuaylas-Yauri belt are centered on multiple-pulse porphyritic intrusions (Table 3) that commonly display both dike.00 is difficult to determine. Illustrates the location of the main clusters at Morosayhuas. In plan view. other systems seem to have developed complex geometries from the outset. as at Qenqo. as at Lahuani and Peña Alta. 1990). 10c). The size. with respect to the main stock. plagioclase and orthoclase in microfelsitic aggregates. which locally contain interstitial biotite. and the Peña Alta and Quechua composite stocks. which may or may not include postmineral intrusions. shape and location of inter. Chaccaro. Katanga.g. and Morosayhuas clusters.. Perelló.. Las Bambas. Similarly. Los Chancas. In most cases.. Fig. but are cylindrical in shape at Alicia and irregular at Morosayhuas and Chaccaro. with biotite being more abundant at Alicia. In some deposits. inter. and microdioritic dikes. and alteration products to the main intrusions. Schematic diagram illustrating the tentative location of selected porphyry systems of the belt relative to the main Mesozoic to Cenozoic stratigraphic units of the region and the Andahuaylas-Yauri batholith. Typical cylindrical host intrusions include Los Chancas (Corrales. At Alicia. like the major intrusions of the Andahuaylas-Yauri batholith..PORPHYRY-STYLE ALTERATION AND MINERALIZATION. Other important phenocryst populations are largely dominated by plagioclase (30 to 80 vol %) and subordinate quartz “eyes” and orthoclase (~10 vol % each) (Fig. Zweng et al. Peña Alta. Although it is difficult to assign precise petrographic names to altered and mineralized intrusive rocks. Panchita. 1997) and the bedding-parallel attitude of the multiple sills at Quechua (J. making distinction between them difficult. Antapaccay. 1997). Portada. Antapaccay.. through two at Ccalla (Cotabambas) and Chabuca (Tintaya). they tend to possess weaker versions of the same alteration and mineralization types. Chaccaro. 1997. whereas later-mineral intrusions occupy peripheral positions in association with late-stage dome and dike swarms of dacitic composition (Fig. and in the Cotabambas and Tintaya clusters. 1997). Systems dominated by tabular. the monzonitic nature of some stocks in the Katanga cluster (MMAJ. 2002. Trapiche. 10c). Zweng et al. Lahuani. 1997. 8. Quechua. PERU LABRA/ CHUQUIBAMBILLA Fms WINICOCHA CRISTO DE LOS ANDES PEÑA ALTA COTABAMBAS ALICIA LAHUANI YURA Gp SORAYA/ HUALHUANI Fms LOS CHANCAS MURCO/MARA/ HUAMBO Fms QUECHUA FERROBAMBA/ ARCURQUINA/ AYAVACAS Fms TINTAYA ANTAPACCAY CHACCARO NEOCOMIAN . Alicia. whereas younger. and Tintaya. Katanga. the earliest inter-mineral phases are centrally located with respect to the main-phase stock. ANDAHUAYLAS-YAURI BELT.. the Chabuca deposit) the dikes cut the early-stage porphyry stock and related mineralization almost at a 90-degree angle and extend far beyond mineralized zones (Zweng et al.. Inter-mineral dikes of roughly the same composition as that of the main stocks are present at Cotabambas. Cristo de los Andes. Las Bambas. in the Tintaya cluster. and Alicia (Fig. Jones et al. Groundmass mineralogy is dominated by quartz. These later intrusions vary from one central phase at Alicia (Fig. with dacite and/or granodiorite predominanting (Fig. are commonly dominated by andesitic. and up to six phases have been described at Antapaccay (Jones et al. Cristo de los Andes. and Peña Alta. with plan dimensions of between 300 and 600 m. Morosayhuas. compositionally and texturally distinct phases occur at Tintaya. and the dominantly quartz monzonitic to monzonitic composition of the Tintaya cluster. typically calc-alkaline in composition (Carlier et al. Postmineral mafic dikes are common at Tintaya (Fierro et al. 9a) and at Tintaya (e. and Cotabambas clusters. Two phases are apparent at Los Chancas and Lahuani. 9c). data. Amphibole dominates at Cristo de los Andes.. 2000. including Quechua (Fierro et al.. 2003). 1983). Coroccohuaycco (Fierro et al.. Los Chancas. exert a marked influence on the geometry of both the main stocks and the mineralized zones in porphyry deposits of the belt. In most deposits. however.to late-mineral phases are dike-like in form. Proportions of biotite to amphibole vary greatly among the different systems.TITHONIAN ANDAHUAYLAS . dike-like geometries include the Cotabambas (Fig. Zweng et al. These younger phases. 9). and in the Tintaya.. 0361-0128/98/000/000-00 $6. the cylinder-like. 9a). 9c). 2000).to late-mineral porphyry intrusions constitute integral parts of all systems in the belt. the bulk of the mineralization seems to be genetically associated with one single phase of intrusion. However. Later inter-mineral and younger phases display different compositions and textures. Bonhomme and Carlier. and the Morosayhuas and Cotabambas clusters (Table 3). dacitic. as at Alicia... Earliest inter-mineral porphyries exhibit similar textures. Peña Alta. Composition Porphyry copper-bearing stocks of the belt are. the monzogranitic composition of Panchita. 1989. unpub. and are characterized by much weaker alteration.to late-mineral intrusions. 1997. and in the Las Bambas and Katanga clusters. 1997. as at Ccalla at Cotabambas. Chaccaro.00 1587 Biotite and amphibole are by far the most abundant ferromagnesian phenocrysts in all the porphyries studied. Exceptions include some quartz monzodioritic stocks at Cotabambas (Perelló et al. Modification of 1587 . 2001). inter. in addition to lacking significant hydrofracturing. 2002). Portada. although pyroxene is also present locally at Katanga. compositions. Katanga. most of the porphyry-related intrusions studied possess an intermediate composition. Fierro et al. 10c). inter-mineral intrusion occupies a central position (Fig. to at least three at Antapaccay.YAURI BATHOLIT H KATANGA SAN JERONIMO Gp PALEOCENE EOCENE-EARL Y OLIGOCENE PUNACANCHA Fm CACHIOS/ PISTE Fms PELITE LAGUNILLAS Gp SANDSTONE CONGLOMERATE QUARTZITE GYPSUM LIMESTONE ANDESITE FIG.TURONIAN PUQUIN/ ANTA-ANTA Fms LAS BAMBAS MOROSAYHUAS ANTA/ KAYRA/ SONCCO Fms CHILCA/ QUILQUE Fms MAASTRICHTIAN BAJOCIAN . Lahuani. Mara.A. diorite pluton Undifferentiated Ferrobamba Fm Undifferentiated Ferrobamba Fm Lower Ferrobamba Fm Lower Ferrobamba Fm Lower Ferrobamba. diorite pluton Lower Ferrobamba Fm Wall rocks Early potassic overprinted by quartz-sericitic Early potassic and calcicpotassic overprinted by sericite-clay-chlorite and peripheral quartz-sericitic Early potassic? overprinted by quartz-sericitic and local advanced argillic Early potassic overprinted by sericite-clay-chlorite Early potassic overprinted by quartz –sericitic Early potassic overprinted by sericite-clay-chlorite Early potassic overprinted by intense quartz-sericitic and local advanced argillic Early potassic and calcicpotassic overprinted by sericite-clay-chlorite and local quartz-sericitic and advanced argillic Early potassic with peripheral quartz-sericitic Early potassic Early potassic and calcicpotassic overprinted by sericite-clay-chlorite and local quartz-sericitic Early potassic overprinted by sericite-clay-chlorite Early potassic overprinted by sericite-clay-chlorite Early potassic overprinted by quartz-sericitic Early potassic overprinted by albite-rich sericiteclay-chlorite Early potassic overprinted by sericite-clay-chlorite Ore-related hydrothermal alteration Trace chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite. magnetite-rich N. . dacite an mafic dikes Three phases: andesite dikes Mid.and late mineral intrusions Microdiorite and dacite stocks Upper Soraya Fm Soraya Fm Upper Ferrobamba Fm Chuquibambilla Fm Upper Ferrobamba Fm Chuquibambilla and Soraya Fms Lower Anta Fm. granodiorite stock Several phases: dacite and andesite dikes Two phases: dacite and andesite dikes Several phases: andesite dikes Several phases: andesite and quartz monzonite dikes Two phases: granodiorite and dacite dikes Several phases: diorite. Several phases: dacite and andesite dikes Several phases: dacite and andesite dikes. Large intermineral. sericite-rich Inter-mineral.A.A.A.5 km Minor exoskarn Dominant: exoskarn N.00 Six phases: monzonite to quartz monzonite One phase?: quartz monzonite One phase: granodiorite to quartz monzodiorite Several phases: dacite Several phases: dacite and/or granodiorite Antappacay (Tintaya) 1588 One phase: dacite Winicocha Cristo de los Andes Peña Alta Lahuani Chaccaro Alicia Two phases: granodiorite to quartz monzonite One phase: granodiorite and/or dacite One phase: dacite One phase: rhyodacite to dacite One phase: dacite One phase: dacite/ rhyodacite Los Chancas Qenco/Maki One phase: (Morosayhuas) diorite and quartz diorite San José (Katanga) Katanga (Katanga) Ferrobamba (Las Bambas) Chalcobamba (Las Bambas) Ccalla (Cotabambas) Several phases: monzonite and dacite Two main phases: dacite Two phases: monzonite Chabuca (Tintaya) Quechua (Tintaya) Mineralized intrusion(s) Deposit or prospect (cluster) N.A. Contact breccias and pebble dikes Pebble dikes Large postmineral diatreme Pebble dikes Hydrothermal breccias Distal skarn at 1–2 km Minor exoskarn. Inter-mineral. N. Distal skarn at 1–2 km Present: exo>endoskarn Dominant: exo>endoskarn Important: exo>endoskarn Dominant: exo>endoskarn Distal skarn at 2–3 km Locally important exoskarn Minor exoskarn Dominant: exo>endoskarn Skarn mineralization 1588 PERELLÓ ET AL. and upper Soraya Fms Diorite and granodiorite plutons Lower Ferrobamba Fm. molybdenite Chalcopyrite Chalcopyrite ~ bornite Chalcopyrite > bornite Trace chalcopyrite Chalcopyrite Chalcopyrite Chalcopyrite > bornite Chalcopyrite ~ bornite Chalcopyrite > bornite Chalcopyrite Bornite ~ chalcopyrite Chalcopyrite > bornite Ore mineralogy Absent Copper oxides and chalcocite blanket Minor copper oxides Minor copper oxides Minor copper oxides Minor copper oxides Copper oxides and chalcocite blanket Copper oxides and chalcocite blanket Absent Abundant copper oxides Irregular copper oxides Irregular copper oxides Irregular copper oxides and chalcocite blanket Irregular copper oxides and chalcocite N.0361-0128/98/000/000-00 $6. N.A. Contact breccias N.A.A. Geological Features of Selected Porphyry Systems of the Andahuaylas-Yauri Belt Inter.A. Several phases: andesite and microdiorite dikes Several phases: dacite and andesite dikes Several phases: andesite dikes Several phases: andesite dikes One central phase: dacite N.A. distal jasperoids at ~2 km Distal skarn at 2–3 km Distal skarn at 1.to latemineral. sericite-rich Local tourmalinerich dikes N. Irregular copper oxides Supergene mineralization TABLE 3. sericite-rich N. Based on data provided by the Metal and Mining Agency of Japan (1983) and mapping by the writers.00 1589 . c. b. ANDAHUAYLAS-YAURI BELT. 0361-0128/98/000/000-00 $6. 2000 and Fierro et al. 9. Schematic cross section through the San José porphyry system at Katanga displaying the distribution of the main geologic units and the location of the supergene enrichment zone. d.. Main geologic attributes of selected porphyry copper systems of the Andahuaylas-Yauri belt. a. Displays the cluster at Cotabambas and the structurally controlled nature of the stocks at Ccalla and Azulccacca.1589 PORPHYRY-STYLE ALTERATION AND MINERALIZATION. PERU a b ALICIA ANTAPACCAY 71°20´ ANTAPACCAY NORTH 71°59´ 14°05´ 15°00´ Late-mineral Diatreme Late Porphyry 200 m Late Porphyry Main Porphyry Main Porphyry Pre-mineral Diorite Skarn Skarn Reverse Fault Zone of Intense Stockwork Veining Anticline c ANTAPACCAY SOUTH d COTABAMBAS 500 m SAN JOSE 72°22´ Cerro Saiwa 4400m HUACLLE 4300m ? 4200m 4100m 13°44´ CCALLA 200 m CCARAYOC AZULCCACCA Late Dome and Dikes 1 km a b a b Porphyry-related Intrusions Andahuaylas-Yauri Batholith a: Diorite b: Granodiorite Skarn Leached Capping Late Andesite Dike Supergene Chalcocite Blanket a: Intersected by Drilling b: Projected Hydrothermal Breccia Main Porphyry Drill Hole FIG. 2002). together with the peripheral. latemineral dome and its dike swarm (simplified after Perelló et al.. 2002).. Illustrates the structurally controlled nature of the porphyry copper systems at Antapaccay and the large postmineral diatreme breccia (simplified after Jones et al. as mapped by the writers. Displays the cylindrical form of the porphyry copper-bearing stock at Alicia and the central location of the late-mineral porphyry dike. 2001) (3) K-Ar (Noble et al. . Distribution of porphyry copper clusters and systems relative to the Andahuaylas-Yauri batholith and Fe-Cu skarn occurrences. c. 10.b ? ? 1590 (1) (1) (1) (1) 14°30´ 14°00´ (1) LOS CHANCAS PANCHITA WNW LAHUANI TRAPICH E a 73°30´ 200 km CHALHUANCA 50 km CRISTO DE LOS ANDES SANTO TOMAS SULFOBAMBA KATANGA ALICIA 72°00´ PORTADA CHACCARO CHALCOBAMBA FERROBAMBA LAS BAMBAS CLUSTER 72°30´ CHILCACCASA CUZCO A 5 10 20 35 71°30´ ANTAPACCAY KATANGA CLUSTER SAN JOSE 90 Q 7 4 6 90 65 11 10 2 3 8 5 1 9 DACITE 60 90 QUECHUA COROCCOHUAYCO TINTAYA CLUSTER SICUANI TINTAYA YAURI RHYOLITE WINICOCHA LIVITACA MONTE ROJO 60 ALICIA CRISTO DE LOS ANDES CHACCARO KATANGA CLUSTER PORTADA PEÑA ALTA PANCHITA WINICOCHA LAS BAMBAS CLUSTER TRAPICHE COTABAMBAS CLUSTER 13°30´ c 1 2 3 4 5 6 7 8 9 10 11 COTABAMBAS CLUSTER AZULCCACCA CCALLA CCARAYOC HUACLLE MAKI QENCO LLOCLLACSA MOROSAYHUAS CLUSTER CHA-CHA MACHU PICHU LETICI A ACEROPATA SSE Skarn Fe-(Cu. Dominant composition of selected porphyry copper-bearing stocks of the belt according to their modal mineral contents on a QAP diagram (Streckeisen. Age distribution of selected porphyry copper deposits and prospects of the belt (Table 4) relative to the Andahuaylas-Yauri batholith and the volcanic and sedimentary stratigraphy of the region. 1978). Au) TRAPICHE LEONOR PEÑA ALTA 73°00´ LAHUANI PANCHITA ABANCAY 73°00´ PORPHYR Y COPPER ALTERATION-MINERALIZ ATION CRISTO DE ANDES SULFOBAMBA CHALCOBAMBA FERROBAMBA LOS CHANCAS 73°30´ ANDAHUAYLAS ANDAHUAYLAS-YAURI BATHOLITH (1) (1) (1) QUECHUA 20 FIG. 1984) KATANGA GRANODIORITE QUARTZ MONZODIORITE MONZODIORITE DIORITE DIORIT E / GABBRO (CUMULATES) (1) K-AR (Carlotto. 1998) PORTADA MIOCENE EARLY OLIGOCENE EARLY LATE LATE EOCENE MIDDLE EARLY 0361-0128/98/000/000-00 $6... STRATIGRAPHY 50 40 37 34 30 28. b. Note the preferred location of the porphyry clusters along the edges of main batholithic bodies.5 PUNACANCHA FORMATION ANTA Fm SAN JERONIMO Gp 24 ALICIA CCALLA CHILCACCASA CHACCARO 20 SAN JOSE MONTE ROJO WINICOCHA OTHER INTRUSION INTER-LATE PHASE PORPHYR Y AND/OR ALTERATION MAIN PHASE ALTERATION (2) Re-Os (Mathur et al.00 PEÑA ALTA TINTAYA (3) TINTAYA (2) Ma P 1590 PERELLÓ ET AL. a. 1975. Plagioclase (both phenocrysts and groundmass) is replaced by a pale-green. The latter was originally termed SCC-type by Sillitoe and Gappe (1984) in the Philippines porphyry copper deposits and is now referred to as intermediate argillic alteration by Sillitoe (2000). magmatic biotite. Calcite. and varied proportions of epidote. and Antapaccay at Tintaya. Ferrobamba. Chalcobamba. In all cases. apatite. Early. including Cotabambas and Chaccaro. the latter of magmatic and/or hydrothermal origin. and chalcopyrite. calcite. Calcic-potassic alteration: Calcic-potassic alteration is represented at Cotabambas. and/or epidote. with important K-feldspar. It generally modifies. San José. Cotabambas. propylitic. biotite. biotite. anhydrite.PORPHYRY-STYLE ALTERATION AND MINERALIZATION. and chlorite. Sillitoe and Gappe. Magmatic pyroxene is altered to aggregates of actinolite-apatite and actinolite-biotite. and calc-silicate types of Meyer and Hemley (1967) and subsequent investigators (Lowell and Guilbert. A-veinlets also occur in copper-poor. plagioclase is variably altered to K-feldspar. Hydrothermal alteration and mineralization Six distinct types of alteration-mineralization are recognizable in porphyry systems of the Andahuaylas-Yauri belt. and K-feldspar. Sericiteclay-chlorite alteration varies in both intensity and mineralogy. chlorite. typically barren biotite seams and veinlets occcur at several systems. 1984). Morosayhuas. but most characteristically at Cotabambas. biotite is accompanied by K-feldspar. actinolite. Amphibole and biotite.to late-mineral bodies is appreciable. Peña Alta. and Quechua. but with some degree of preservation. greasy sericite assemblage which also includes illite and. and clays (illite-smectite). Los Chancas. actinolite. Puerto Rico. smectite. either alone or accompanied by other silicate phases. and Winicocha. Llocllasca. B-type veinlets are characterized by semicontinous centerlines filled by millimeter. locally. chlorite. including Maki at Morosayhuas. Lahuani. biotite. Chile. quartz. Conspicuous magnetite accompanies potassic alteration in gold-rich porphyry systems of the belt. such as those from the Morosayhuas cluster (see below). and Los Chancas. and at Lahuani.. Major quantities of quartz were introduced as either uni. a variety of 0361-0128/98/000/000-00 $6. and as partial replacements of original plagioclase sites. which at Cotabambas and Tintaya constitutes a volumetrically significant alteration mineral. Sillitoe. A-type veinlets carry significant mineralization in the form of chalcopyrite and/or bornite at a number of deposits.00 1591 quartz veinlets. 2002). Gustafson and Hunt. 2000). In common with porphyry systems elsewhere (e. apatite and calcite. Hydrothermal biotite replaces ferromagnesian components. Guilbert and Lowell. and magmatic hornblende is converted to mixtures of clinopyroxene. advanced argillic. and can be compared with the early biotite veins described by Gustafson and Quiroga (1995) at El Salvador. 1995. ANDAHUAYLAS-YAURI BELT. goldbearing porphyry systems. where they contribute minor amounts of chalcopyrite.to centimeter-sized grains of bornite and chalcopyrite. and Katanga clusters. as part of this association. although assemblages defined for systems of the belt always include one or more associations of sericite (finegrained muscovite).and C-type veinlets described by Cox (1985) at Tanamá. characterize potassic alteration in porphyry deposits and prospects of the Andahuaylas-Yauri belt. Calcite is common as a replacement of plagioclase.and B-type veinlets described by Gustafson and Hunt (1975) from El Salvador porphyry copper deposit.or multidirectional veinlets during potassic alteration in all deposits and prospects. An additional. whereas magmatic biotite and amphibole are selectively replaced by needles of actinolite. less commonly. it is a major constituent of the 1591 . sericitic (phyllic). and hornblende. Where overprinting by either quartz-sericitic or sericite-clay-chlorite alteration is intense. In at least five systems. contain appreciable amounts of magnetitebearing veinlets that are similar to the M-type veinlets of Clark and Arancibia (1995) and to the A.. Antappaccay. gives rise to ore-grade CuAu mineralization. Las Bambas. Morosayhuas. Ccalla and Azulccacca at Cotabambas. smectite. less widespread alteration-mineralization type includes the mixed calcic-potassic assemblages observed at several deposits and prospects. potassic alteration is the principal alteration type directly associated with mineralization in Andahuaylas-Yauri porphyry systems (Table 3). such as the Ccalla and Azulccacca centers at Cotabambas. introduced in several generations. The assemblage is characterized by veinlets of quartz. including the Cotabambas. For example. these massive bodies are the only remnants of the early-stage potassic alteration. and Chalcobamba at Las Bambas. Winicocha). Typical assemblages and textures compare closely with the A. Ferrobamba. Chaccaro. San José at Katanga. they are dominated by chalcopyrite and molybdenite. whereas at Peña Alta. with local development of graphic textures and complete destruction of original rock textures. and in some deposits and prospects. Sericite-clay-chlorite alteration: Several deposits and prospects of the belt. and at Cotabambas attains >5 vol percent (Perelló et al. 1970. possess significant sericite-clay-chlorite alteration as part of their ore zones (Table 3). Peña Alta. and Tintaya. In general. Maki. Chile. halloysite. the most intense potassic alteration at Ccalla is dominated by aggregates of quartz and K-feldspar. including the Ccalla and Azulccacca centers at Cotabambas. Gustafson and Quiroga. Gold-rich porphyry copper deposits of the belt. 1974). K-feldspar also occurs in a variety of veinlet types with quartz and biotite. and Winicocha. Magnetite is a common constituent. illite.g. and magnetite are additional minerals in potassic alteration assemblages and are also common constituents of veinlet assemblages. In most deposits and prospects. including Peña Alta and Cotabambas. These make up the potassic. are characteristically replaced by chlorite. calcite. potassic alteration occurs early in the evolution of each system and consists of quartz. It also occurs in the groundmass of porphyry stocks and in veinlets. Las Bambas. and volumetrically minor amounts of clinopyroxene and epidote. This assemblage imparts a pale-green overprint to potassic alteration and gives a soft aspect to the rock (cf. typically magmatic hornblende and. and Peña Alta (Table 3). including Alicia. the quartz veinlets coalesce to form massive bodies of nearly pure quartz. as well as an alteration type characterized by sericite. commonly intergrown with apatite. Tintaya. Alicia. At Alicia and Chalcobamba. PERU ore zones at Cotabambas. Alteration halos to various veinlet sets include K-feldspar. biotite. within the veinlets or as alteration halos. original rock textures. and hornblende as in several systems of the Morosayhuas cluster. and albite. Tintaya. Potassic alteration: With a few exceptions (Morosayhuas. and Las Bambas by intrusion of the inter. and Morosayhuas (Table 3).. At Tintaya (Fierro et al. sericite. Zweng et al. all of the deposits have distal skarn-type assemblages in roof-pendants of Ferrobamba Formation and equivalent units. as at Ccalla. 2002) and Tintaya (Fierro et al. 1983) mines. Hydrothermal breccias Hydrothermal breccias are poorly documented in Andahuaylas-Yauri porphyry systems (Table 3). and Lahuani. and Las Bambas.. they were identified at most deposits and prospects. at Lahuani (Table 3).g. The quartzsericitic assemblages typically comprise white. commun. with or without chalcopyrite.. and as products of prograde (anhydrous) and retrograde (hydrous) events (Table 3). Lahuani. Los Chancas. Winicocha. possibly. diopside.. 2001). At the Ccalla deposit in Cotabambas. common in many porphyry Cu-Mo deposits worldwide (e. Noble et al. 1979. 1958. At Maki and San José. bornite.1592 PERELLÓ ET AL. advanced argillic alteration is superimposed on the porphyry stocks and associated potassic and sericite-clay-chlorite alteration.. halloysite. excluding Cotabambas. In other systems. The presence of jasperoid in several deposits and prospects is evidence that they constitute integral parts of porphyry-centered systems in the region. and actinolite are the characteristic calc-silicate assemblages (Terrones. and specular hematite is a characteristic constituent of the assemblage. Peña Alta. sericite (fine-grained muscovite). Maki. and mixedlayer illite-smectite are common (Cotabambas. Zweng et al. However.. disseminated and veinlet pyrite. D-type veinlets (Gustafson and Hunt. texturally destructive aggregates of quartz. and Winicocha. However. Broad quartz-sericitic alteration halos around potassic cores. Chalcopyrite is locally present in some veinlet assemblages and may constitute monomineralic veinlets with chlorite and quartz. structurally controlled patches of quartz-sericitic alteration abut intermediate argillic assemblages in the upper parts of the system (Perelló et al. As-anomalous jasperoidal mantos resembles the Carlin-style gold environment described around some porphyry centers (Sillitoe and Bonham. distal replacement of calcareous shale by structurally controlled. 1997. Fierro et al.. At San José. 1984. 1970). Llocllacsa. an observation supported by descriptions of Antapaccay (Jones et al. Pyrite is typically present in the form of veinlets and disseminations (Chaccaro. Propylitic alteration: Propylitic alteration in AndahuaylasYauri belt porphyry systems (chlorite. and Morosayhuas. less commonly. San José. although they are inferred at Los Chancas (Corrales. occurring only at Trapiche and Morosayhuas. 1983). which develop quartz-sericitic halos. 2003). In addition. bornite. as at Cotabambas. Maki). centimeter-wide structures with pyrite and quartz. A similar situation is also observed at Cristo de los Andes. accompanied by several percent pyrite. assemblage. as at Cotabambas. Moderate amounts are also present at Cotabambas (Ccalla). 1975) are typically associated with overprinting quartz-sericitic alteration in most systems of the belt where this style of alteration occurs. Lahuani. Moreover. is the dominant Cu and Au contributor. which at Tintaya is reported to contain up to 1 ppm Au (Zweng et al.. Bornite. Lowell and Guilbert. associated mineralization has constituted the main source of Cu-Au ore at the Tintaya (Terrones. 1997). In all systems mentioned above. Santa Cruz et al. rarely survives sericite-clay chlorite alteration. calc-silicate alteration and mineralization occur in endoskarn and exoskarn facies. Santa Cruz et al. Tejada. Las Bambas.. Indeed. Cristo de Los Andes. and it is an important contributor to mineralization at the Las Bambas skarn-porphyry cluster and the Quechua deposit (E. Another expression of the distal environment is the structurally and lithologically controlled.. Advanced argillic alteration: Hypogene advanced argillic alteration is not recognized as a common assemblage in porphyry systems of the Andahuaylas-Yauri belt. Quechua and at the San José deposit in the Katanga cluster (MMAJ. 2002) and contributed to the formation of an irregular chalcocite blanket. Morosayhuas). as at Morosayhuas and at the Chabuca Este deposit at Tintaya (Zweng et al. Calc-silicate alteration: Calc-silicate alteration is represented in many deposits and prospects of the belt. sericite-clay-chlorite alteration.. and halos of green sericite. Peña Alta. 1997). -Mo) mineralization at Tintaya and Las Bambas was introduced during prograde events. Katanga.g. In both cases. whereas at Winicocha it is developed at higher elevations and constitutes the roots of a porphyry copper lithocap. Quartz veinlets include various associations with chlorite and calcite. if present in earlier assemblages. epidote. the rock is completely replaced by fine.. 1592 . and calcite) is found mainly as part of the outer halo confined to noncarbonate wall rocks. in amounts of ~1 vol percent. Where quartz veining is intense and halos coalesce. quartz-sericitic alteration typically overprints earlier-formed potassic or. yellow-brown jasperoid developed in limestone beyond the skarn front at Tintaya. Chaccaro. Garnet. Cristo de los Andes. a common constituent of sericitic alteration in many parts of the world. proximal calc-silicate assemblages and associated skarn-type mineralization are present in most systems of the belt. chalcopyrite contents are lower than in earlier potassic alteration-mineralization. pers. are not widely developed in systems of the Andahuaylas-Yauri belt. epidote. in that it is richer in Pb and Zn (e. 2000. whereas at the smaller Alicia system.00 contact between quartz diorite and volcanosedimentary country rocks.. 1997). Magnetite is variably transformed to martite.. Quechua and. The bulk of the Cu (-Au. and is volumetrically important at Cotabambas. 1997) and Katanga (MMAJ. at Winicocha and Chilcaccasa. and mixed-layer illite-smectite that obliterate original host rock textures. 1981). continuous. Quartz-sericitic alteration: Well-defined zones of quartzsericitic alteration accompany ore in several systems of the belt at San José. but in general. and illite. Tourmaline. Chaccaro). is rarely developed in AndahuaylasYauri porphyry systems.to very fine-grained mosaics of quartz. advanced argillic alteration is intimately associated with transgressive structures. During this study.. whereas at Maki it is controlled by permeability contrasts at the 0361-0128/98/000/000-00 $6. 1990). 1958. sericite-rich alteration that also contains pyrophyllite and kaolinite-group minerals is present at San José. 1979). at distances of ~3 km. typically as chalcopyrite and. is common. Chaccaro. Albite is locally important as a replacement of plagioclase. and Maki (Table 3). Distal skarn mineralization in porphyry-centered systems of the belt is similar to that elsewhere (Einaudi et al. propylitic alteration occurs within porphyry copper ore zones in late-mineral stocks and dikes. D veinlets fill planar. Porphyry stocks constitute the main host to ore where country rocks are dominated by the terrigenous facies of the Yura Group and equivalent units. and fine-grained (dusty) pyrite are typical constituents of the matrices. Although still poorly known. mainly due to intense overprinting by chlorite or quartz-sericitic alteration. K-Ar ages were mainly determined for hydrothermal alteration silicates. or by volcaniclastic and red bed horizons of the Anta Formation. (1976) for Quechua. and (3) porphyry stocks and dioritic country rocks with small amounts of skarn at Antappaccay (Jones et al. 1. The following examples document the variety observed in the belt. at Morosayhuas. through deposits carrying both gold and molybdenum (Tintaya. exfoliated clasts. 2000) including (1) subvolcanic quartz diorite to dacite porphyry stocks. Larger expressions of a similar style of brecciation. and associated with low-grade porphyry-style mineralization. as in the Morosayhuas cluster. by Yoshikawa et al.. and Chalcobamba. and although less well defined. Illite. At the Maki and Qenco centers at Morosayhuas. Dikelike breccias possess strong structural control and conform to pebble dikes as is common in porphyry systems worldwide. 9). Ferrobamba. This is particularly evident where the breccias are cut by mineralized veinlets. Chaccaro. however. as at Cotabambas and San José. Additional geochronologic data available from the literature include the K-Ar ages reported by Noble et al. 2. Other goldbearing porphyry copper systems of the belt include Los Chancas (Corrales. Most of the breccias are volumetrically small. (6) Cu values of up to several hundred ppm.. with that at Antapaccay probably constituting the largest single mass in any porphyry system in the belt (Fig. where quartz eye-bearing rhyodacitic intrusions hosting heavily veined zones with development of “brain rock-type” texture (i. Molybdenum contents are low.. albite-rich. dominantly biotite. As at Antapaccay. 1991. unidirectional solidification texture) are distinctive. 1991. All of these deposits possess gold grades in the 0. although contact (igneous) breccias associated with the emplacement of early and intermineral porphyry stocks are clearly intermineral in timing.3 ppm range (Table 1) and. (2) unidirectional. Sillitoe. the Chabuca deposits at Tintaya (Zweng et al. in a sericitic matrix. despite the fact that country rocks there are dominated by carbonate horizons of the Ferrobamba Formation. They typically consist of centimeter-sized. Cristo de los Andes. Vila and Sillitoe. Ore zone geometry Most Andahuaylas-Yauri porphyry deposits and prospects possess mineralization that is variably hosted by porphyry stocks and their immediate country rocks. chlorite. banded. Chile (Vila and Sillitoe.e. 10b). gold-only (e. 3. gold-bearing quartz-magnetite associations. Muntean and Einaudi.. the presence of both A-type veinlets rich in magnetite and biotite and later. with an average Au grade >0. as at Tintaya. 2002). 1997). Chalcobamba. subrounded lithic clasts supported by volumetrically important matrices of finely comminuted (rock flour) material. they can be considered as members of the Cu-Au clan of porphyry deposits (Sillitoe.1 to 0. Another Mo-bearing center in the belt is Lahuani. although poorly explored. and (7) low Mo contents (<10 ppm). (5) Au values typically averaging between 0. (2) porphyry stocks. Alicia. Significant mineralization. Fierro et al. molybdenum-poor examples (Cotabambas).. <100 ppm. sericite-clay-chlorite alteration.. ANDAHUAYLAS-YAURI BELT. with minor skarn mineralization at Quechua. the porphyry centers possess most of the features that characterize the porphyry gold mineralization of the Maricunga belt. and the new Re-Os ages of Mathur et al. Age of the Andahuaylas-Yauri Belt A reconnaissance K-Ar study has been conducted on 18 systems in the belt (Table 4.g.. 1997). 2002). all the observed breccias postdate main-stage mineralization. Fierro et al. Antappaccay (Jones et al. are features that compare closely with the porphyry gold mineralization at Refugio (Muntean and Einaudi. 2000.. and Los Chancas. The Ccalla and Azulccacca centers at Cotabambas are the best examples of the gold-rich category of porphyry copper deposits (Perelló et al. as at Cotabambas. (2001) for Tintaya (Fig. tens of centimeters in size. gold-poor end-members (Lahuani). 2002). but higher grade volumes are present (e. 1593 . sheeted veinlets dominated by dark gray.4 ppm. Fierro et al. Los Chancas and Tintaya are reported to contain appreciable molybdenum grades (Table 1) and would therefore constitute members of the Cu-Au-Mo category of Cox and Singer (1986). 2000). Ore seems to be evenly distributed between porphyry stocks and wall rocks where intrusions of the AndahuaylasYauri batholith constitute the dominant country rock. 10). include rounded to subrounded. is also hosted by both porphyry stocks and wall rocks at Ferrobamba and San José. as at Lahuani..3 and 1 ppm. Zweng et al. 2001). Most mapped hydrothermal breccias are either dike-like in form or occur as narrow zones at intrusive contacts. Los Chancas and Quechua. associated with main stage potassic alteration and mineralization as at Panchita. (1984) for Tintaya and Chalcobamba.g. Los Chancas).00 1593 molybdenum-rich.. 2000). Antappaccay. Portada. to relatively 0361-0128/98/000/000-00 $6. banded quartz-magnetite veinlets typically cutting the former.3 ppm and appreciable volumes averaging >0. Where such alteration proved unsuitable for K-Ar dating.PORPHYRY-STYLE ALTERATION AND MINERALIZATION. 2002) of the belt. because smaller. 2000) porphyry systems are interpreted to be present in the Morosayhuas cluster and at the isolated Winicocha system. Goldonly porphyry systems. Fig. Mineralized skarns are present in country rocks where porphyry stocks intrude carbonate rocks of the Ferrobamba Formation and equivalent units. (3) moderate to intense. Metal contents Porphyry copper deposits and prospects of the Andahuaylas-Yauri belt range from gold-rich. Ccalla. as at Winicocha. are present in at least two areas at Morosayhuas and Winicocha. 2000. Cristo de los Andes. The Tintaya cluster further exemplifies the diversity of mineralization styles and ore hosts.. (4) quartz-magnetite-biotite veinlets of A type. PERU 1997. the Ferrobamba and Chalcobamba systems at Las Bambas. Where best studied. Peña Alta. Monte Rojo. including (1) skarns at the various Chabuca deposits and Coroccohuayco. Alicia. 8 Amphibole2 0.2 Ma for Tintaya (Mathur et al.747 11.916 17 31.608 10.753 0.00 inferred to have occurred almost simultaneously along a ~130-km-wide..392 9.162 6. it is suggested that a distinct. typically 1594 . Thus. late Eocene to earliest late Oligocene porphyry copper event in the belt (Noble et al. commun.8 ± 1.231 31 29. however.0 Secondary biotite1 6. Consequently.8 35. Katanga. locally.2 ± 0.9 Magmatic biotite1 Amphibole2 Secondary biotite2 Secondary biotite Secondary biotite1 Whole rock (sericite2) Secondary biotite Secondary biotite Secondary biotite Secondary biotite Biotite 5.410 6 35.9 ± 0.0 Secondary biotite1 6.557 7.. Dilles.692 10. % See Figures 7 and 10c for sample location and plots 1 Some degree of alteration to chlorite present 2 Mid. Overall.7 ± 0. with minimum ages between approximately 35 and 30 Ma. and the high neutralization capacities of both potassic alteration zones and carbonate country rocks.985 9.962 × 10-10y-1. The K-Ar age of 35. the data confirm the presence of a widespread.9 Ma (Table 4.9 ± 0.810 7 38 23 11 21 29 19 27 21 30 25 35. pers. Supergene Effects The depth of partial to complete oxidation of sulfides in porphyry deposits and prospects of the belt is commonly 30 to 50 m but.373 7. extends to 150 m. K-Ar Ages of Alteration Minerals from Selected Porphyry Systems of the Andahuaylas-Yauri Belt Deposit or prospect (cluster) Chilcaccasa (Morosayhuas) Ccalla (Cotabambas) Monte Rojo (Katanga) San José (Katanga) Katanga Pit (Katanga) Ferrobamba (Las Bambas) Chalcobamba (Las Bambas) Sulfobamba (Las Bambas) Chaccaro Los Chancas Alicia Portada Winicocha Lahuani Trapiche Peña Alta Panchita Cristo de los Andes Mineral K (%) Radiogenic Ar (nl/g) Ar (at. with ages ranging between approximately 39.2 ± 1. most cappings are immature. Fig.982 68 33.to late-mineral porphyry phase or hydrothermal alteration event dating was conducted on inter.002 13 35.5. whereas sericitic alteration was dated at Chilcaccasa and Winicocha.9 28.6 ± 0.434 9.7 ± 0. consistently return the youngest ages in the belt and seem to have been active at the end of the metallogenic episode responsible for the Andahuaylas-Yauri belt.and nonporphyry-related mineralization.465 9.7 ± 0. This age range can be expanded further into the middle Eocene when the Re-Os age of 41.482 8.271 18 36. it can be inferred that much of the main-stage potassic alteration in the belt formed between approximately 42 and 35 Ma. biotite) and (2) the K-Ar system offers no way of experimentally testing whether later Ar loss occurred to produce artificially young ages (J.to late-mineral dikes or hydrothermal alteration events.055 7.0 37.374 7. 40K = 0. 40Ar/36Ar = 295.7 ± 0.537 10. If. following Table 4.515 5. during the middle to late Eocene.442 7. i. and San José.e.0 ± 0.9 ± 0. and porphyry-style alteration and mineralization are 0361-0128/98/000/000-00 $6. 10b).328 6.743 10.2 32.375 10 35.g.0 Constants: λβ= 4.8 36.4 ± 1. 300-km-long belt.0 ± 1.9 33. 2003). oxidation tends to be thicker under ridge crests and nearly absent beneath valley floors. Most of the porphyry systems lack economically significant zones of supergene enrichment.1 Ma at Peña Alta and 28.2 ± 0.9 ± 0. on the basis of available K-Ar data.8 39.9 Secondary biotite1 6. 2001) is considered. Fig 10b) for magmatic biotite from a skarn-related intrusion at Sulfobamba further confirms the age range of the belt for both porphyry.2 ± 0.5 ± 1.393 10.737 7. The Katanga cluster and nearby Winicocha system. only those ages from unaltered secondary biotite are taken into account.581 × 10-10y-1. As expected from the rugged topography of much of the region.. TABLE 4. Although both biotite and amphibole ages from this cluster are modified by a chloritic overprint that presumably caused Ar loss.9 Amphibole2 1.1 ± 1.176 0.01167at.146 0. λε= 0.367 9.8 Ma at Winicocha (Table 4.9 Secondary biotite 7.9 35.to late-mineral porphyry stocks and dikes at Trapiche.9 30.5 ± 1.068 1.5 ± 1.664 7. the poorly developed nature of quartz-sericitic alteration.743 7. No sub-belts or age trends are apparent from Figures 7 and 10.. Amphibole was dated from inter. 1984).3 ± 0. %) Age ± 2σ Sericite2 7. All K-Ar dates are considered here as minimum ages because (1) the K-Ar method records cooling rather than crystallization of the dated silicates (e.742 5.. localized plutonic and porphyry copper event took place in the Katanga area during the early Oligocene.1 36. because of the relatively low pyrite contents. the plutons of the area return the youngest ages of the entire Andahuaylas-Yauri batholith.1594 PERELLÓ ET AL. mafic.. Katanga. by ~35 Ma.200 m). To the east of the Andahuaylas-Yauri belt. The age relationship between porphyry copper emplacement. located approximately 300 km from the trench. The porphyry-related skarn mineralization. coeval volcanism of the Anta Formation.. strongly favors a Pliocene or younger age for the supergene processes. the close parallelism of most of the chalcocite blankets to the present surface. Fig.g.. In general. tectonism. ANDAHUAYLAS-YAURI BELT. a close association is observed between porphyrytype alteration-mineralization and the intermediate and late stages of quartz monzodiorite and granodiorite of the batholith (Noble et al.. major thick-skinned compression.. took place at ~40 Ma (Farrar et al. 1984. as at San José. Carlier et al. between 50 and 30 Ma (e. earlystage.. into northern Chile. and syntectonic sedimentation of the San Jerónimo Group red beds are illustrated in Figures 6 and 10. In contrast to some other regions (e. include. For example. 1999) are fundamental to the discussion that follows. pitch limonite. intermediate argillic and quartz-sericitic alteration in both diorite wall rock of the Andahuaylas-Yauri batholith and the porphyry stocks. may be associated either with the same late Pliocene event or with younger topographic rejuvenation events common throughout the region (e.g. gypsum.. Although poorly explored to date. Maksaev and Zentilli.. PERU goethitic in composition. 1995) and geophysical perspectives (James and Sacks. Cristo de los Andes. where a chalcocite blanket formed in quartz-sericitic assemblages althougth the immediate country rocks are dominated by carbonates of the Ferrobamba Formation (MMAJ. supergene alunite from the top part of the leached capping returned a K-Ar age of 3. Slab flattening is. furthermore. 1990. exceptions to the above include those porphyry systems emplaced in rocks other than carbonate horizons of the Ferrobamba Formation and equivalent units. 1996). These models concur in that a period of slab flattening began in southern Peru between 50 and 45 Ma. The recent models for the geodynamic evolution of the Central Andes (southern Peru.y. contain irregular. the presence of appreciable pyrite as a component of intermediate argillic and quartz-sericitic alteration.. most notably in quartzite and sandstone of the Yura Group and certain phases of the Andahuaylas-Yauri batholith (Fig.. cumulate pulses of the Andahuaylas-Yauri batholith are thought to have been generated in the asthenospheric wedge between ~48 and 43 Ma and rapidly ascended into the crust (Bonhomme and Carlier. although other authors consider it to be part of a longer event of at least 20 m. 1979). 1995). whereas in southeastern Peru and northeastern Bolivia it is bracketed between ~41 and 38 Ma (Farrar et al.. (1984). 1992. Both leached cappings and supergene blankets are accompanied by widespread kaolinization of feldspars. 9d). an Incaic event of crustal shortening interpreted to have caused ramping of the (proto-) Cordillera Oriental over the foreland (Sandeman et al. 1995). In the area of study. All were broadly synchronous with the regional thin-skinned shortening and uplift associated with the Incaic orogeny between ~42 and 30 Ma. Cabrera et al. 1988). 2002). 10). Cotabambas (Perelló et al. rather than host-rock composition. and native copper are also present. northern Chile. at the Ccalla deposit at Cotabambas. In central Peru. 11a). northern Chile. Perelló et al. 1999). Similarly. 0361-0128/98/000/000-00 $6. Supergene enrichment blankets located at higher elevations. (1996). chrysocolla.. In all cases. as at Ccalla. Sandeman et al. In particular. Kennan et al. 2002). Las Bambas.. Incaic compression is generally assigned an age between ~42 and 39 Ma (Hammerschmidt et al. Mpodozis et al.. Sillitoe and McKee. Establishment of complete flat subduction conditions at 1595 .. these cappings have developed by in situ oxidation of lowpyrite. typically chalcopyrite-bornite mineralization with total sulfide contents of <3 vol percent and pyrite/copper sulfide ratios of <2:1. as at Tintaya. and associated copper oxide minerals. 1995. involving basement uplift along the Zongo-San Gabán tectonothermal zone.. This is evidenced by the San José prospect at Katanga. and broadened southward. 1999). tenorite. 1999). and is accompanied by varying proportions of covellite. stratigraphically and structurally controlled immature chalcocite blankets developed in quartz-sericitic alteration. became stable at ~42 to 40 Ma. a conclusion supported by additional lines of evidence. Carlier et al. 1983. 1989.. neotocite. within the limits of groundwater penetration. 1988. and Alicia. chalcocite enrichment at Cotabambas occurs in intimate association with pyrite-rich.. 1990) (Fig. the age of the Incaic deformation is generally accepted to be ~41 Ma (Noble et al. Carlotto (1998) and references therein. together with their partial exposure and overall immaturity. 1991). important gossan zones as oxidation products of magnetite and massive sulfides.3 ± 0. sooty chalcocite is the main host for copper in the supergene enrichment zones. martitization of magnetite.. along the arc. Cuprite.00 1595 Discussion Metallogenic implications It is apparent from the regional geology and age relationships described above that mineralization of porphyry type in the Andahuaylas-Yauri belt broadly overlapped with the various pulses of the Andahuaylas-Yauri batholith (Fig. In general. the age of formation of supergene chalcocite blankets and leached cappings in the belt is poorly constrained.PORPHYRY-STYLE ALTERATION AND MINERALIZATION. emplaced into quartzose sandstone of the upper Soraya Formation. Sandeman et al. For example. In general. and Quechua (~4. and uplift assigned to the major Incaic orogeny of the Central Andes. inferred to have produced the crustal shortening. the entire central Andes region at the latitude of the Bolivian orocline is thought to have been undergoing flat subduction (James and Sacks. with some containing appreciable copper in the form of malachite. based on the geological relationships documented in this paper together with data in Noble et al. and northern Bolivia) from both geologic (Clark et al. the small Cristo de los Andes and the large Los Chancas (Corrales.2 Ma or late Pliocene (Perelló et al. Supergene alunite may be locally formed in leached cappings overlying the more pyritic parts of the systems.. in addition. Geodynamic evolution A model for the tectonomagmatic evolution of the Andahuaylas-Yauri batholith and its associated porphyry-style mineralization is formulated here. Thus. In northern Chile. seems to be the most important control on supergene chalcocite formation.g. and removal of anhydrite and. 2002). 2001) systems. 8). 32 Ma) EC moho hos phe re 150 200 c 0 100 200 300 400 500 Distance (km) WC: WESTERN CORDILLERA A : ALTIPLANO EC : EASTERN CORDILLERA ANDAHUAYLAS . INTERMEDIATE. and Eastern Cordillera shown for reference. c : EARLY. b. Volcanism of the Anta Formation (Anta Arc) is important at the Western Cordillera-Altiplano transition.45 Ma) EC A 0 ( sph ere a 0 300 200 100 400 500 Distance (km) ( INITIAL STAGE OF PORPHYRY COPPER EMPLACEMENT ZONGO-SAN GABÁN ZONE (PROJECTED) ANTA ARC WC 0 41 . Sandeman et al. Sandeman et al. 1988.YAURI BATHOLITH a c a. 11. Present-day positions of the Western Cordillera. 1995). followed by the intrusion of the intermediate-composition plutons (between 41 and 38 Ma) that make up much of the present-day body of the batholith. b.38 Ma) EC A Depth (km) 50 moho oce ani 100 c lit hos phe 150 re b 200 0 300 200 100 400 500 600 Distance (km) MAIN STAGE OF PORPHYRY COPPER EMPLACEMENT END-STAGE ANTA ARC WC 0 Depth (km) 50 oce ani 100 c lit A ( 38 . Geodynamic setting largely based on models after Clark et al. Schematic sequence of cross sections illustrating the formation of the Central Andes at the latitude of the Andahuaylas-Yauri belt and contiguous southeastern Peru. and James and Sacks (1999). a. EARLY-STAGE ANTA ARC ? WC ? Depth (km) 50 moho oc ean 100 ic l itho 150 200 50 . between the Eocene and the earliest Oligocene. c. 12 for details). (1995). is shown for reference. Illustrates the main stage of porphyry copper formation along the belt together with the terminal stages of Anta Formation volcanism (38–32 Ma) (see Fig.. Deformation along the Zongo-San Gabán zone. 0361-0128/98/000/000-00 $6. interpreted to have occurred at the craton-orogen interface (Farrar et al.. Displays emplacement of the early phases of the batholith. Altiplano. Synchronous magma ascent and deformation of the uppermost crust (Incaic orogeny) in conjunction with slab flattening is implied.00 1596 . (1990). Clark. Illustrates the middle Eocene (50–45 Ma) magmatic arc along the eastern edge of the Western Cordillera.1596 PERELLÓ ET AL. 1993. AND LATE PHASES b FIG. although. and northeast of Lima the Quicay high-sulfidation gold deposit has been related to magmatism associated with Incaic deformation (Noble and McKee. between ~40 and 35 Ma (Figs. and synorogenic sedimentation. which is inferred to have been fed from magma chambers associated with the Andahuaylas-Yauri batholith.PORPHYRY-STYLE ALTERATION AND MINERALIZATION. Kurtz et al. Kay et al.. 12. The extension of the belt into southeastern Peru is complicated by the presence of the widespread. 11b and c). and erosion (Jordan et al. PERU ~40 Ma is interpreted to have increased deformation and shortening of the upper crust (James and Sacks. therefore. Andesitic Volcanism (Anta Formation) Rapid Uplift 20 km Molasse Deposits Mesozoic Sequences Fold-Thrust Belt 50 km Early-Stage Cumulate Gabbros and Diorites Intermediate-Stage Granodiorites and Quartz Monzodiorites FIG. and El Teniente (Skewes and Stern. Los Bronces-Río Blanco.. 1990. 1984. The following lines of evidence. 1999. The relatively shallow emplacement of the main. Sandeman et al. 1999). synchronous surface uplift and unroofing assisted with the ascent of these smaller. progressive flattening of the subducting slab during the middle Miocene in central Chile resulted in eastward migration of the volcanic front accompanied by intense crustal thickening. 1998). It should also be noted that porphyry copper formation was recurrent and.. 1995). Soler and Bonhomme. deformation.. 1998.. would have eventually given rise to the tectonic and gravitational conditions in the upper crust (e.g. 1994. 13b). an overall geodynamic setting that compares closely with slab flattening and deformation inferred for the AndahuaylasYauri belt during the Incaic orogeny. Los Chancas. Moreover. porphyry copper emplacement. 1990. 1999). 2000) as occurred in nearby transects (Clark et al.. 1993. Although speculative. judging by the similar ages of hydrothermal biotite formation at Lahuani. Trapiche. 10). locally. Noble and McKee. Skewes and Stern. 1999. 10). 1990. apparently. 1994. 1988. Figure 13a displays a hypothetical map of the Wadati-Benioff zone during the late Eocene to Oligocene period of flat subduction in the central Andes as reconstructed by James Porphyry Copper Stock and Sacks (1999).. 14). 6). Petersen. intermediate-stage phases of the batholith.. An example is provided by the arc that formed the Anta Formation south of Cuzco (Fig. 2001) that favored rapid tectonic (surface) uplift and denudation. Petersen. 1999). associated with large-volume magma emplacement.g. Figure borrows from Skewes and Stern (1994) and Sillitoe (1997. 1997). Fig.. Cotabambas. James and Sacks. Kimbrough et al. 1988. intermediate-stage body of the batholith is implied. Clark et al. compressive deformation. the late Eocene to early Oligocene Andahuaylas-Yauri batholith and its associated porphyry copper mineralization appear to have been emplaced at the inflection point between flat subduction to the south and normal subduction to the north. Farther north. ANDAHUAYLAS-YAURI BELT. it never became completely extinct (Carlier et al. 12). 1991. 1983. In the proposed model. To the north. 0361-0128/98/000/000-00 $6. confined magma chambers in the uppermost crust and triggered porphyry copper emplacement at the appropriate depths (Fig.. much younger systems developed in zones that had been the locus of earlier hydrothermal activity. thereby impeding magma ascent and favoring evolution of large magma chambers (e. 1995. volcanism.. In such a geodynamic model. and Leonor (Fig. 1999). Portada. 1999). rapid regional uplift. as in the area of Lahuani. Indeed. The intermediate-stage phases of the Andahuaylas-Yauri batholith. 1995). 1989. Sillitoe. the belt apparently stops at the Abancay Deflection (Fig. Thermal and mechanical gradients. and subsequent intrusion of the more differentiated. Schematic illustration of the spatial and temporal relationships between batholith ascent. uplift. post-Oligocene volcanic cover of the region.00 1597 1597 .. Kay et al. and Panchita (Table 4. Clark et al. which hosts the world class deposits at Los Pelambres. Volcanism seems to have been subdued along the belt during much of the transition from normal to flat subduction.. must have ascended as a large composite unit and presumably reached the depth of porphyry copper formation broadly at the same time over its entire extent. Possible extensions of the Andahuaylas-Yauri belt The northern and southern extensions of the AndahuaylasYauri belt are not well constrained. Clark. late Eocene to Oligocene magmatism is present in central Peru (Noble et al. most reconstructions for late Eocene to early Oligocene magmatism and mineralization imply significant segmentation along the belt at the latitude of the Bolivian Orocline in the central Andes (Sillitoe. this location is remarkably similar to the position of the late Miocene to Pliocene porphyry copper belt of central Chile (Fig. Comparison between the geodynamic settings of the Andahuaylas-Yauri and central Chile porphyry copper belts. b. Note the broad similarities between both settings and the presence of the Zongo-San Gabán zone and the Sierras Pampeanas basement highs in each case. a. 1992. Illustrates the setting of the Andahuaylas-Yauri batholith at the inflection corridor between flat and normal subduction during the late Eocene and the Oligocene.1598 PERELLÓ ET AL.. Ramos et al. (1988) and Kurtz et al. as modeled by James and Sacks (1999). Plutons of the partially unroofed late Tertiary batholith taken from Parada et al. 0361-0128/98/000/000-00 $6. Displays the setting of the central Chile Miocene plutons and late Miocene to Pliocene porphyry copper belt at the inflection of the present-day subduction zone (Cahill and Isacks.SAN GABAN ZONE 15° Puno Arequipa BOLIVIA La Paz PERU CHILE FLAT-SLAB SEGMENT 20° 100 km UA Y Arica 200 PA R AG 100 Calama a 65° 70° 75° ARGENTINA Recent Volcanoes Late Tertiary Batholith Antofagasta 125 CENTRAL VOLCANI C ZONE Benioff Zone Contours (km) 25° Chile T Giant Porphyry Copper deposit rench Sierras Pampeanas Tucumán Copiapó 250 La Serena FLAT-SLAB/ NORMAL SLAB ALONG-ARC PROPAGATION La Rioja 125 FLAT-SLAB SEGMENT 30° 200 LOS PELAMBRES-EL PACHÓN 150 San Juan JUAN F ER NÁNDEZ R ID GE Mendoza Santiago EL TENIENTE b San Luis RÍO BLANCO-LOS BRONCES 100 km SOUTHERN VOLCANI C ZONE 35° 50 100 FIG. 2002). 75° Lima ANDAHUAYLAS-YAURI BATHOLITH 50 5 65°B 70° RA ZI L Cuzco 75 ZONGO . (1997).00 1598 . 13. 35-31) EXPLORADORA (33-32) CHILE SALTA EL SALVADOR (44-41) CHILE Area with Eocene to Oligocene (Incaic) deformation and/or terrigenous sedimentation TREN CH Inner Arc POTRERILLOS (36-35) LA FORTUNA (35-32) CHILE APOLINARIO (35) 30° LOICA (35) 30° ARGENTINA ARGENTINA SANTIAGO SANTIAGO b 500 km 500 km a 80° 70° FIG. (5) SPENCE C EN H POST-EARLY OLIGOCENE VOLCANIC AND SEDIMENTARY COVER SEQUENCES TR QUICAY (38-37) RU PE 10° 10° (30-32) : AGE RANGE MOROSAYHUAS (35) COTABAMBAS (36-35) LIMA LAS BAMBAS (36-35) N ECTIO ? FL Y DE NCA ABA ZONGO-SAN GABAN LOS CHANCAS (32) KATANGA (33-30) BOLIVIA TINTAYA (42. based on U-Pb (zircon) dating by Richards et al. 1999. 0361-0128/98/000/000-00 $6. Clark et al. synorogenic sedimentation in Chile (Mpodozis et al. data. (1999). 14. if real (see text for discussion). (3) TOQUEPALA. (2) QUELLAVECO.. Perelló. (1995).. Their definition of inner arc includes the inner arc domain and parts of the inner Cordillera Occidental of Clark et al.. Rojas et al. Zappettini et al. is masked by younger volcanic and sedimentary cover sequences. PERU 80° 70° MIDDLE EOCENE-EARLY OLIGOCENE PORPHYRY COPPER DEPOSIT SELECTED DEPOSIT OF THE LATE PALEOCENE-EARLY EOCENE BELT BRAZIL PERU (1) CUAJONE.. Geologic elements borrowed from Maksaev and Zentilli (1988). 1999. (1996). According to James and Sacks (1999). and Conchi. and Chimborazo. (1997). Petersen (1999). Hernández et al. (1999). 1999. Maksaev (1990). Cornejo et al. All other ages are for hydrothermal alteration assemblages. Asterisks indicate ages of intrusions at La Escondida. Perelló et al. Schematic illustration of the Andahuaylas-Yauri belt and its possible northward and southward extensions. and high electrical conductivity.ESCONDIDA NORTE-ZALDIVAR (38-35*. 2001). and J. J. 1999. Coutand et al. 1999. 1999) is shown for reference. Zaldívar. unpub. 35-33) LA PAZ (1) (2) SANTA LUCIA (32-30) ATASPACA (40) (3) TICNAMAR (41) QUEEN ELIZABETH (36) BRAZIL PER U 20° (4) 20° QUEBRADA BLANCACOLLAHUASI-UJINA (35-32) LIMA ESPERANZATELEGRAFO (42-41) ? EL ABRA-CONCHI (37-36) BOLIVIA (5) CHUQUICAMATAMM-TOMIC (34-31) GABY (42-40) LA PAZ CENTINELAPOLO SUR (44) SALTA TACA-TACA (34-33) CHIMBORAZO (39-38*) ESCONDIDA . Telégrafo. (1997). ANDAHUAYLAS-YAURI BELT. Sillitoe (1988. The extension of the belt into northern Chile. Polo Sur. (1990. (2001). (1996). high degree of crustal deformation. Tomlinson et al.1599 PORPHYRY-STYLE ALTERATION AND MINERALIZATION. a. (1998) and references therein. Perelló. (inset) Relationship between Eocene to early Oligocene (Incaic) porphyry copper mineralization. The location of the inner Arc in Bolivia and southeastern Peru (sensu James and Sacks. 1987. data for Esperanza (2000). b.. unpub. Clark et al. 2000) and Argentina (Jordan and Alonso. features that they consider to have been inherited from the period of flat subduction beneath the central Andes during late Eocene to early Oligocene time. Petersen et al. Kraemer et al. (2001). Segmentation along the belt is apparent at the Abancay Deflection. Gustafson et al. Noble and McKee (1999). 1990). the inner arc is characterized by high heat flow. 1998).00 1599 . Adelman and Görler. Cuadra et al. (1990) and Sandeman et al. Clark (1993). (4) CERRO COLORADO. However. imply that late Eocene to early Oligocene deformation and magmatism occurred in the area and that the extension of the belt into Chile is represented at Ataspaca and. This association is remarkably similar to that described for the San Jerónimo Group in the Andahuaylas-Yauri belt near Cuzco. Available geochronologic data confirm that much of the porphyry alteration and mineralization in the belt formed between ~40 and 35 Ma. Furthermore. skarn-type Fe-Cu mineralization. seems to have taken place during a well-defined interval of ~10 to 12 Ma duration (cf. although the complete spectrum of age ranges between ~42 and 28 Ma (middle Eocene to earliest late Oligocene). might have occurred essentially simultaneously along the late Eocene magmatic arc of southern Peru and northern Chile. Goldonly porphyry systems with similarities to the gold porphyries of the Maricunga belt of northern Chile also occur. and sedimentation extended eastward as far as the Altiplano and Eastern Cordillera of Bolivia (Farrar et al. 1999).. 14b) suggests that Eocene to Oligocene Incaic compression. i. molybdenum-rich counterparts. Kay and Mpodozis. and denudation is widely accepted (Maksaev and Zentilli.to 39-Ma magmatic and hydrothermal activity recorded at Ataspaca (Clark et al. Gold-rich members of the belt do not possess any unique features that distinguish them from gold-poor. On the contrary. no such along-arc migration is apparent in the late Eocene to early Oligocene porphyry copper belt of northern Chile. Magmatism and Incaic deformation in the Santa Lucía area are interpreted to have occurred along the same crustal discontinuity that chaneled the deformational front in the Andahuaylas-Yauri belt near Cuzco (Jaillard and Santander. uplift. The data also support the broad inference that gold-rich and goldpoor members of the belt formed synchronously. alteration. 3. Summary and Conclusions The Andahuaylas-Yauri belt is defined by 31 deposits and prospects with porphyry-style alteration and mineralization. sericite-clay-chlorite. as shown in Figure 14a. Kraemer et al.. 1988. 1600 . 2002). Porphyry stocks are dominated by multiphase. These observations suggest that there may have been continuity between the Andahuaylas-Yauri and the northern Chile porphyry copper belts during middle (–late) Eocene to early Oligocene time (~45–30 Ma. 2001). Maksaev. molybdenum-poor examples. 1999. and advanced argillic alteration types. 3 and 6). calcic-potassic. Indeed. Interruption of the belt at the latitude of the Arica deflection may be apparent. the Cuzco-Puno high (Figs. 1990) and was broadly coeval with the ~30-Ma flows interbedded in San Jerónimo Group redbeds. the ~45. Santa Lucía. 14).. the interruption may be attributable to the changing tectonomagmatic framework in response to along-arc flat subduction propagation in southern Peru during the late Eocene to Oligocene (James and Sacks.and pyroxene-bearing alteration assemblages in addition to potassic alteration.e. 1990). through systems containing both gold and molybdenum. No sub-belts or age trends are apparent in the data. 2003).to 35-Ma magmatism. 1. and was accompanied by the synorogenic. 2002) may be considered as a more modern analog (Fig. Soler and Bonhomme.and amphibole-bearing intrusions of dacitic and granodioritic composition. and given that a genetic association between the late Eocene to early Oligocene porphyry copper belt of northern Chile and Incaic compression. quartz-sericitic. shortening. except perhaps for their appreciably higher contents of hydrothermal magnetite and the presence of amphibole. Fig. Hydrothermal alteration is typical of porphyry ore deposits elsewhere and includes potassic. 1987. A salient feature of the belt is the spatial association of porphyry stocks and related mineralization with the Andahuaylas-Yauri batholith. irrespective of size. much of the porphyry copper mineralization there. 1992). 2002) and across the border into northernmost Chile (García et al.e. perhaps triggered by fast convergence (Pardo Casas and Molnar. during the late Eocene.. 13). Clark et al. gold-depleted endmembers. in the Andahuaylas-Yauri belt (Fig. Magmatism at Santa Lucía was active in the early Oligocene (~30–32 Ma. Sempere et al.. Alternatively. current knowledge (Fig. 2. near the border with Chile. Southeasterly extensions of the regional late Eocene to early Oligocene structures present in the Andahuaylas-Yauri region appear to extend into southeastern Peru (Sempere et al. propylitic. In the Tarata district. country rocks. molasse-type sedimentation of the Puno Group (Portugal. Calc-silicate assemblages with skarn-type mineralization occur where carbonate country rocks of the Ferrobamba Formation predominate. 1999). 1990) between ~45 and 35 Ma. Maksaev and Zentilli. irrespective of their locations. 4. and mineralization of the Katanga area. 1990). 1992). Important thin-skinned deformation of fold-thrust belt type took place during the late Eocene (~40 Ma) in the Santa Lucía area. 1997) and as far south as 26°S in the Puna of northwestern Argentina (Jordan and Alonso. 1990) represents the connection with the late Eocene to early Oligocene porphyry copper belt of northern Chile. probably. broadly simultaneously with emplacement of intermediate-stage phases of the Andahuaylas-Yauri batholith (~40–32 Ma).00 of northern Chile might have also taken place under similar conditions of subduction flattening (Mpodozis and Perelló. Porphyry copper deposits and prospects of the belt range from gold-rich. 1988... and with the ~30... 5. By analogy with the Andahuaylas-Yauri belt. i. which suggest that porphyry mineralization took place during a well-defined interval of time along the 130-km-wide. evidence from the belt does not support any apparent connection between metallogenesis and crustal properties (Titley. 1999.. subduction flattening. 1992. calc-alkaline. however. and enhanced by the widespread younger volcanism that mantles much of the region. Coutand et al. 1987.. and porphyry stock compositions.1600 PERELLÓ ET AL. biotite. accompanied by hundreds of occurrences of magnetite-bearing. 10). 300-km-long belt. Alonso. Jaillard and Santander. Although the rapidly changing metallogenesis of the Miocene to Pliocene magmatic belt of central Chile (Kay et al. to relatively molybdenum-enriched. a large composite body of calc-alkaline intrusions of middle Eocene to early Oligocene age (~48–32 Ma). 1974. it is here speculated that late Eocene to early Oligocene porphyry copper mineralization 0361-0128/98/000/000-00 $6. v.. 35. 1982. R. Perú. 2003 REFERENCES Adelman. and dessication [abs]: Geological Society of America. Salta.G. Brimhall and Mote. 1999. V.. Aizawa. 1999. ANDAHUAYLAS-YAURI BELT. D. Flores.. O. 1992. 190. and Christophe Noblet for their contributions on various aspects of the geology of the belt. p. Vallenas. Sociedad Geológica del Perú.. McBride. v. Rodriguez. Chávez. Major cumulative supergene chalcocite enrichment blankets are absent from porphyry systems of the AndahuaylasYauri belt because of the low pyrite contents.. and Gil. F.I.. Volumen Especial 1. in González Bonorino. Informe Final 19841988.. 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Extended Abstracts volume.. V. W.. Lorand. Victor Torres. 1999. T. crustal thickening.. Prospecting of Coroccohuayco copper deposit. V. and synorogenic clastic sedimentation associated with the compressive Incaic orogeny between ~40 and 32 Ma. no. Extended Abstracts. p. Geology and Ore Deposits of the Central Andes: Society of Economic Geologists Special Publication 7. 1989. Cárdenas. responsibility for the opinions expressed and any errors is ours alone. June 17.P. 1999: Melbourne. 155–159.00 1601 that led to numerous improvements. Under the appropriate conditions.. Geomorphologic and geochronologic evidence from the region indicates that the formation of chalcocite blankets has occurred at least since the late Pliocene. although producing immature blankets. Eduardo Tejada.. J. 1997). E. Perelló et al. v. p..L. Acknowledgments We would like to thank Gabriel Carlier.. 189–199. press release. Lima. Benavides-Cáceres. p. 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