geology, petrography and geochemistry of igneous rocks related to mineralized skarns in the nw...

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Geology, petrography and geochemistry of igneous rocks related to mineralizedskarns in the NW Neuquén basin, Argentina: Implications for Cordilleranskarn exploration

Josefina Pons a,⁎, Marta Franchini a, Lawrence Meinert b, Leopoldo López-Escobar c, Laura Maydagán a

a Centro Patagónico de Estudios Metalogenéticos-Consejo Nacional de Investigaciones Científicas y Técnicas, Facultad de Ingeniería, Universidad Nacional del Comahue, Buenos Aires 1400,

8300 Neuquén, Argentinab Department of Geosciences Smith College, Northampton, MA 01062, United Statesc Grupo Magmático, Instituto GEA, Universidad de Concepción, Casilla 160-C, Concepción-3, Chile

a b s t r a c ta r t i c l e i n f o

Article history:

Received 15 January 2010Received in revised form 19 May 2010Accepted 20 May 2010Available online 27 May 2010

Keywords:

Igneous rocksMineralized CuFeAu skarnsNW Neuquén BasinArgentina

Five mineralized Cu, Au, and Fe skarns and related igneous rocks of the Andes Cordillera of NW Neuquén(Paleogene Campana Mahuida, Caicayén and Cerro Nevazón) and SW Mendoza (Neogene Vegas Peladas andHierro Indio) provinces of Argentina (34–38°S) are reviewed to demonstrate that geochemical signatures ofigneous rocks can be used to predict the metal potential of skarn prospects of the Andes Cordillera ofArgentina. These igneous rocks are calc-alkaline, metaluminous, and derived from a sub-arc mantle sourcewithout residual garnet. They were emplaced at shallow depths. The Vegas Peladas, Hierro Indio, and CerroNevazón igneous rocks have similar major and trace element contents, and are typical of primitive, I-typeplutons associated with Fe skarns worldwide. The Vegas Peladas and Hierro Indio plutons are, however, lessreduced and they have lower Ni concentration than the Cerro Nevazón rocks, whose skarns have higher Auconcentrations. In the Caicayén district, small skarns with sub-economic Cu concentrations and abundantpyrite are associated with porphyry copper style alteration in igneous rocks that underwent amphibolefractionation. Their chemical compositions are intermediate between the most primitive plutons associatedwith Fe skarns and the most evolved plutons associated with Cu skarns, both with high fO2. At CampanaMahuida a small porphyry copper deposit and associated Cu skarns are linked to andesite dikes and plutonwith similar SiO2 contents but richer in incompatible trace elements (K, Rb, Sr, Ba, La, Ce, and Th) than theMendoza, Cerro Nevazón and Caicayén igneous rocks. This suggests that their parental magmas evolved in anopen system and were contaminated with crustal material, thus resulting in the strongest fractionation ofamphibole and accessories phases. These intrusions share many features with typical Cu skarns-relatedplutons.

© 2010 Elsevier B.V. All rights reserved.

1. Introduction

There are 28 mineralized skarns in the Andes segment between34° and 38°S known as Cordillera Principal of SW Mendoza and NWNeuquén (Méndez et al., 1995; Franchini and Dawson, 1999;Franchini, 2005; Franchini et al., 2007a, b, Pons et al., 2009). Theyare related to Andean Cordillera plutons that are part of a magmaticbelt of calc-alkaline rocks caused by eastward subduction of the Nazca(Farallon) plate beneath South America (Davison and Mpodozis,1991; Franchini et al., 2003; Pons et al., 2007). Their ages decreasefrom Paleogene, between 36° and 38°S, in NW Neuquén to Neogenebetween 34 and 36°S, in SW Mendoza (Fig. 1; Franchini et al., 2003,2007b; Pons et al., 2007).

Skarn size and economic importance range from outcrops withonly exploratory trenching and sampling to small deposits (e.g.,Hierro Indio and Vegas Peladas; Zanettini, 1999; Franchini andDawson, 1999; Franchini et al., 2007a, 2007b; Pons et al., 2009) thathave been mined for Fe and Cu in the early 1900s. Some of thesemineralized skarns are related to porphyry copper deposits (e.g.,Campana Mahuida; Sillitoe, 1977; Franchini and Malvicini, 1998;Chabert and Zanettini, 1999) or porphyry-style alteration andmineralization (Caicayén District; Casé and Malvicini, 1999; Franchiniet al., 2000). Other examples are enriched in precious metals (e.g., Agat Cerro La Virgen and Aguas Amarillas skarns; Angelelli, 1984;Franchini and Dawson, 1999, or Au at Cerro Nevazón; Franchini et al.,1999).

This paper is a review of the geology, petrography and geochem-istry of igneous rocks related to mineralized skarns in NW Neuquén(Campana Mahuida, Cerro Nevazón and Cerro Caicayén; Franchiniet al. 2003; Franchini 2005; Franchini et al., 2007a; Table 1) and SW

Ore Geology Reviews 38 (2010) 37–58

⁎ Corresponding author. Tel./fax: +54 299 4485344.E-mail addresses: [email protected], [email protected] (J. Pons).

0169-1368/$ – see front matter © 2010 Elsevier B.V. All rights reserved.doi:10.1016/j.oregeorev.2010.05.006

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Mendoza (Vegas Peladas and Hierro Indio; Franchini et al., 2007b;Pons et al., 2007; Pons et al., 2009; Table 1), including the maincharacteristics of each deposit. The compositions of Neuquén andMendoza igneous rocks (Appendices A-D) are compared to thesubduction-related plutons associated with Fe, Au, Cu and Zn skarnsin other parts of the world (Meinert, 1995) to address the relationshipbetween pluton composition and the metal content of associatedskarns. Interestingly, although the igneous rocks from NW Neuquénand SW Mendoza seem to have formed from similar mantle-generated magmas, differences in the evolutionary trends of thesemagmas correlate with the styles of alteration and mineralization inthe resulting skarns. Thus, the geochemical signatures of igneousrocks can be useful in predicting the metal potential of the numerousskarn prospects of the Andes Cordillera of western Argentina, evenwhere outcrops are limited.

2. Setting

The study areas are located in the Andes Cordillera, in the segmentbelonging to the actual Southern Volcanic Zone (Fig. 1; SVZ, 33°–46°S;Hildreth and Moorbath, 1988; Tormey et al., 1991; Ferguson et al.,1992) where the thickness of continental crust decrease from thenorth (Northern SVZ) between 33° and 34°30′S (65–60 km; Hildrethand Moorbath, 1988 and references therein) to the south (55 km;Transitional SVZ between 34.5° and 37°S) and Southern SVZ between37° and 46° (42–35 km; López Escobar, 1984; Tormey et al., 1991;Ramos et al., 2004). In this region, Mesozoic and Cenozoic sedimen-tation and magmatism were superimposed on a Paleozoic basementof accreted continental and oceanic terranes (Mpodozis and Ramos,1998). A significant feature is the NW-trending Cortaderas lineament,220 km in length (36°S; Ramos and Kay, 2006), that correlates with achange in the structure of the underlying continental crust andmantlelithosphere (Ramos and Kay, 2006). This lineament separates tworegions with differences in the geometry of the subducting slab andcrustal rheology and marks the southern limit of a Miocene shallowsubduction zone. North of the lineament, Neogene backarc magma-tism changes from an early Miocene non-arc-like chemistry, to a late

Miocene arc-like chemistry and then back to a Pliocene non-arcchemistry (Kay et al., 2006). South of the lineament, Neogene backarcmagmatism is absent (Kay et al., 2006) and the region wascharacterized by a constant normal subduction with little fluctuationsin the position of arc front from the Cretaceous to the Quaternary(Ramos and Kay 2006).

3. Geological framework of NW Neuquén and SW Mendoza

The CampanaMahuida, Nevazón and Caicayén districts are locatedin the Cordillera Principal of NW Neuquén, along the westernboundary of the Thrust Belt segments of the Chos Malal and AgrioFold Belts defined by Bracaccini (1970) and Ramos (1978) (Fig. 2). Theregion is characterized by a series of E-verging folds and relatedthrusts which developed a complex thrust front that is bounded to theeast by an area of gentle folding. These fold belts are bordered on theNW and SE, respectively, by the Cordillera del Viento anticline and theLoncopué graben, an extensional structure filled with Plio-Pleistocenebasalts (Ramos, 1999). The Agrio and Chos Malal Fold Belts consist of7000 m of Jurassic and Cretaceous sedimentary rocks that uncon-formable overlie Permian–Triassic volcaniclastic basement (theChoiyoi Group; Fig. 2). The structures of the area have a N–Sorientation and are dominated by folds with complex faults. Thisarea was affected by Paleogene magmatism which cuts the fold andfault structures (e.g., Cerro Negro, Cerro Mayal, Cerro Caicayén,Collipilli, Franchini et al., 2003).

The Vegas Peladas and Hierro Indio prospects are located in thefold and thrust belt of Malargüe (34°–36°S; Kozlowski et al., 1993;Mingramm et al., 1993), in the central-south Andes segment knownas Cordillera Principal of SW Mendoza province (Fig 2; Ramos,1993). During the Late Triassic–Early Tertiary, this region locatedeast of the arc–trench system, was characterized by a series of fault-bounded depressions, and the tectonic regime was dominated byextension and subsidence with local episodes of uplift, folding, anderosion (Gulisano and Gutiérrez-Pleimling, 1995). These basinswere filled with more than 6000 m of Late Triassic to Paleocenemarine and continental sedimentary rocks that unconformablyoverlie the Permian–Triassic volcaniclastic basement of the ChoiyoiGroup (Fig. 2). Compressional tectonics began in the Tertiary(Gulisano and Gutiérrez-Pleimling, 1995) forming the thick-skinnedMalargüe fold and thrust Belt (Kozlowski et al., 1993). Thiscompression was followed by widespread volcano-plutonic activity,represented in this segment by three magmatic cycles (Ramos andNullo, 1993): the Late Eocene to Early Oligocene Molle Group(Haller et al., 1985; Nullo, 1985), the widespread Miocene HuincánFormation (Nullo, 1985; Bouza, 1991; Baldauf et al., 1992), andyoung Pleistocene volcanism (Ramos and Nullo, 1993). TypicalCordilleran I-type plutons were emplaced into the Mesozoic–Cenozoic sedimentary sequences along the main (N–S) thrust faultsand folds (Ramos and Nullo, 1993).

4. General characteristics of mineralized skarns and associatedigneous rocks

4.1. The Cerro Nevazón skarns

Three mineralized skarn bodies occur at the contact of thePaleogene (60.1±1.6 to 56±1.7 Ma) igneous rocks with the Jurassicmicritic limestone siltstone and sandstone and Cretaceous black shale(Table 1). The skarns are similar to Au-rich skarn deposits elsewhere(Franchini et al., 1999; Table 1). The igneous rocks consist of threestocks and numerous sills and dikes and crop out along the easternboundary of the Cordillera del Viento (Fig. 2), between Cajón delMedio and Cajón Grande creeks. The stocks intruded the core of ananticline and occur as three discontinuous outcrops with an ellipticalshape, elongated in the N–S direction; these may be apices of a single

Fig. 1. Location map of the skarn prospects associated with Paleogene (CampanaMahuida, Cerro Nevazón and Caicayén) and Neogene (Vegas Peladas and Hierro Indio)igneous rocks and of other volcanic centers from the Southern Volcanic Zone segment(SVZ) and Transitional Southern Volcanic Zone (TSVZ, modified from López Escobar,1984; Tormey et al., 1991; Franchini et al., 2003).

38 J. Pons et al. / Ore Geology Reviews 38 (2010) 37–58


Table 1

Synthesis of the main characteristics of skarns from Cerro Nevazón, Campana Mahuida, Caicayén, Vegas Peladas and Hierro Indio districts.

Deposits name Latitude Longitude Province Size and grade Host rocksAge and lithology

Ore forming intrusionAge, composition and alteration

Skarn mineralogy Ore mineralogy References

Prograde Retrograde

Cerro NevazónAu skarn

36°47′S36°49′S

70°29′W NWNeuquén

Up to 162 ppm As, 58 ppmsiltstone (Lotena F.), micriticlimestone (La Manga F.) andsandstone (Tordillo F.) andCretaceous micritic blackshale (Vaca Muerta F.)

Upper Jurassic silstone(Lotena F.), micriticlimestone (La Manga F.)and sandstone (TordilloF.) and Cretaceousmicritic black shale (VacaMuerta F.)

56–60.1 Ma K/Ar and 40Ar/39Arages calc-alkaline gabbro-dioritestock, andesite dikes act, bio, fdspyx, scp, gart(Ad31–66 Pi11-3),qtz ep, amph, qtz in bx

Inner zone: gart±pyx±scp±ido±ttn±qtz±cal±sulfides(up to 4%)Intermediate zone: pyx±scp±gart±ttn±qtz±cal±sulfides (8%)Outer zone: wo±scp±pyx±gart±sulfides(10%) scp(Me34–61)Npyx(Hd7–79Jo0.3-6)Ngart(Ad17–98 Pi1–3)Nwo, ido, qtz

amph,ep, cal,qtz, chl,preh

poNpy, cp, mt,,asp, sl, mo, mc,electrum

Franchini and Innes(1997), Franchini etal. (1999),Franchini et al.(2003)

Campana Mahuidaporphyry Cu–Cuskarn

38°14′S 70°32′W NWNeuquén

0.05% Cu; 0.3 g/t Au o.p. Upper Jurassic silstone(Lotena F.), micriticlimestone (La Manga F.)and sandstone (TordilloF.)

61±1.4 Ma (SHRIMP U–Pb ageof zircon calc-alkaline andesitedikes with potassic, propylitic,phyllic alteration gart(Ad37–85),act,ep, pyx(Hd16–25 Jo4)

gart(Ad46–98 Pi2–17), pyx, ep, qtz act, chl,qtz, cal,silica–py

py, mt, hm, cp, mc,bn, mo,

Franchini andMalvicini (1998)and referencesthere in

Caicayén porphyryCu–Cu skarn

37°27′S 70°27′W NWNeuquén

0.02–4.6% Cu; 0.1–1.1%Znupto 0.3 g/t Au; up to 10 g/t Ag;8.5–100 ppm As; up to168 ppm Pb, up to100 ppmA. o.p.

Upper Jurassic black shale(Lotena F.), micritic andalgal limestoneinterbedded with nodulargypsum (La Manga F.).

44.7 Ma K–Ar in whole-rockcalc-alkaline quartz andesiteand andesite sills and dikes withpotassic, propylitic, phyllicalteration ep, gart(Ad45–90Pi),pyx (Hd18–39Jo), qtz

Inner zones: gart(Ad95–97 Pi2),pyx(Hd28–60 Jo3–6) qtzOuter zone: pyx(Hd28–60)±sulfides±qtz

ep,clzep, chl,cal,qtzsd,silica,py

py, po, mt, sl, mc,cp, hm

Franchini andMalvicini (1998),and referencesthere in, Franchiniet al. (2000),Llambías andRapela (1989)

Vegas PeladasFe skarn

35°20′S 69° 57′W SWMendoza

39–69.5% Fe260 ppm Cu2.9 ppm Ag

Lower to Middle Jurassicshales, limestone, andmudstone–wackestone(Puchenque and CalabozoFs.)

15.19±0.24 Ma Rb–Sr calc-alkaline diorite to tonalitestocks, dikes, Ort87–93, Ort87–93act, ep, fds, qtz, ttn, cal, chl

Inner zone: gart(Ad31–89 Pi0–2),pyx±qtzDistal veins: gart(Ad96–100)±pyx (Hd72–29 Jo1–4)

Ab96–98,ep, cal,qzt, act,chl, ttn,Feoxides

mtNhmNpy≫Ncp Pons et al. (2007),Pons et al. (2009)and referencesthere in;

Hierro IndioFe skarn

34°59′S 69°47′W SWMendoza

0.450 m.t. with 63% Fe op Lower Cretaceousfossiliferous limestone(Vaca Muerta F.) andcalcareous shale (ChachaoF.)

15 Ma 40Ar/39Ar in plagioclasecalc-alka porphyritic andesite totrachyte sills and microgranulardiorite stock zo, clz, ido, bio, qtz,cal ep, flap

gart(Ad32-96 Pi0.5-1.8) NNpyx,ap±Fe oxides

ep, cal,qzt,amph,chl, flap,op

mtNhm, py, cpmal, az, cris

Angelelli (1984),Elizalde andGonzalez Laguinge(1954), Franchini etal. (2007b), Rigal(1942), Zanettini(1999)

Abreviations: act=actinolite, ad=andradite, ap=apatite, asp=arsenopyrite, bio=biotite, bn=bornite, bx=breccia, chl=chlorite, clz=clinozoisite, cp=chalcopyrite, ep=epidote, F=formation, Fs=formations, flap=fluorapatite,gart=garnet, hd=hedenbergite, hm=hematite, ido=idocrase, jo=johannsenite, mc=marcasite, mo=molybdenite, mt=magnetite, m.t.=million tons, o.p.=open pit mine, po=pyrrhotite, preh=prehnite, py=pyrite,pyx=pyroxene, qtz=quartz, scap=scapolite, sl=sphalerite, wo=wollastonite.

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underlying pluton (Fig. 3A). Their texture varies from equigranular toseriate to porphyritic near margins. They range in modal compositionfrom gabbro to quartz diorite, with diorite being the most common.Dioritic and quartz dioritic rocks contain normally zoned plagioclase(Anb50) (64–74%), clinoamphibole (15–20%), biotite (5–10%), andquartz (4–18%), with accessory magnetite, minor ilmenite, apatite,titanite and traces of zircon. In some dioritic samples, clinoamphibolecontains relic enstatite (Wo2.5–3 En71–73Fs24–25) and augite (Wo42–43En42–43Fs14–15) cores. The gabbro stock contains plagioclase(AnN50), pyroxene (both enstatite and augite, with reaction rims ofamphibole–biotite–magnetite), olivine partially replaced by idding-site, and accessory magnetite, minor ilmenite and apatite. The modalcompositions of dikes and sills are similar to the diorite and gabbrostocks but they have porphyritic textures.

Near the intrusive rocks, the sedimentary siltstone is recrystallizedto zoned hornfels (Fig. 3A). The skarn system also is zoned around thegabbro and diorite–tonalite plutons (Table 1). Sulfides (see Table 1)

are present in all the prograde skarns zones and show an increasefrom 4% at the inner zone to 15% at distal zone of the exoskarn.Pyrrhotite is the most abundant metallic mineral, locally reaching40 vol.% and is along with electrum (AuNAg) and silver.

4.2. The Campana Mahuida and Caicayén skarns

The Campana Mahuida and Caicayén skarns (Table 1) have beenclassified as typical Cu skarns related to porphyry copper deposits(Franchini and Malvicini, 1998; Franchini et al., 2000). At CampanaMahuida, Cu skarns and a porphyry Cu deposit are hosted in aPaleogene porphyry stock (61.0±1.4 Ma) and associated dikes atthe contact with Jurassic sandstone and limestone (Table 1; Fig. 3B).These igneous rocks were emplaced along stratigraphic contacts andpreexisting faults, although the faults have been active after theemplacement (Chabert and Zanettini, 1999). In outcrop, andesiteand quartz–andesite dikes have sharp contacts with the

Fig. 2. Geologic map of the Cordillera Principal of SWMendoza and NWNeuquén provinces with the location of the Campana Mahuida, Cerro Nevazón, Caicayén, Vegas Peladas, andHierro Indio districts in the framework of the Upper Cretaceous–Miocene intrusive and extrusive igneous rocks of western Argentina (modified after Zappettini, 1998). C:Carboniferous; E: Paleogene; FTB: Fault and thrust belt; J: Jurassic; K: Cretaceous; N: Neogene; P: Permian; Q: Quaternary; T: Triassic.



sedimentary rocks. In subsurface, andesite forms a stock-like body1.400 m long in a NNE direction and 400 m wide and hosts theporphyry Cu deposit. The dikes are porphyritic with a fine-grained

matrix. They contain normally zoned plagioclase, clinoamphibole,minor quartz, with accessory magnetite, apatite, titanite and tracesof zircon. These rocks are contemporaneous with two dioritic stocks

Fig. 3. 3-D images (Google Earth-2010) of the Cerro Nevazón, Campana Mahuida and Caicayén regions showing the location of igneous rocks, hornfels, silica–pyrite replacements,mineralized skarns, and porphyry Cu alteration-mineralization (modified after Casé, 1996; Franchini and Malvichini, 1998; Franchini et al., 2003; Franchini et al., 2007a).

41J. Pons et al. / Ore Geology Reviews 38 (2010) 37–58


(60.7±1.9 Ma; K/Ar in amphibole; Franchini et al., 2003) that cropout to the north at Cerro Pedregoso and Tres Puntas (Fig. 3B). Theporphyry copper deposit is characterized by a potassic core and aphyllic halo surrounded by a large propylitic zone. Argillic alterationpatches occur within the phyllic zone. The main hypogene coppermineral is chalcopyrite that is spatially related to the potassicalteration zone. Several mineralized skarn and silica–pyrite bodies(Fig. 3B) occur within the phyllic and propylitic halos of theporphyry Cu deposit. Skarns and silica–pyrite outcrops extenddiscontinuously in an area 2.5 km×0.3 km, approximately 1 to2.5 km SSE of the potassic core of the deposit. Within the phyllichalo and associated with the porphyry Cu, alteration of thesedimentary protolith formed silica–pyrite bodies with Cu and Auanomalies and relic skarn clots. In the outer propylitic zone a Cuskarn occurs in the contact with andesitic dikes (Table 1).

At Caicayén, a series of skarn and replacement deposits occur aslenticular bodies (averaging 40 m thick) at the contact of Paleogeneplutons (44.7±2 Ma,) and the Jurassic sedimentary rocks (Figs. 2 and3C) surrounding a porphyry-style alteration and mineralization(Table 1). The plutons have intruded already formed structures(folds) and are considered to be late-tectonic relative to the main

deformational event of the areas (Llambías and Malvicini, 1978;Minniti et al., 1986; Llambías and Rapela, 1989; Franchini et al., 2003).Seismic lines reveal the close association between the fold whereplutons have been intruded and deep structures (thrust faults) thataffected the Pre-Jurassic basement at depth (Minniti et al., 1986). Theplutons consist of several porphyritic sills (175–300 m thick) oftonalite that crop out to the S and SE of twomain tonalite stocks. Theycontain normally zoned plagioclase (An20–52), amphibole pheno-crysts, and quartz with accessory titanomagnetite, apatite, andtitanite. Porphyry-style alteration and mineralization occurs in a3 km2 zone and consists of: 1) a potassium silicate core; 2) a propyliticzone; 3) a phyllic halo superimposed upon the potassic and propyliticzones, and 4) a narrow, structurally controlled kaolinite–montmoril-lonite–sericite zone east of the potassic core (Casé, 1996; Casé andMalvicini, 1999). Concentrations of sulfides, magnetite, and gold arelocated within the potassic and phyllic zones. Copper and goldanomalies have been identified in exposures within the potassic andphyllic halos (Placer Dome Exploration Inc, 1993, 1994; Gencor,1995). Zoned Cu skarns occur near the potassic core and 800 m southof the potassic halo where massive silica±pyrite also replaceslimestone.

Fig. 4. 3-D images (Google Earth-2010) of the (A) Vegas Peladas and (B) Hierro Indio prospects showing the location of igneous rocks, hornfels and Fe skarns (modified afterFranchini et al., 2007b and references there in; Pons et al., 2009).



4.3. The Vegas Peladas and Hierro Indio Skarns

Mineralized skarns in the Vegas Peladas and Hierro Indio districts(Table 1) have been classified as Fe skarns (Franchini et al., 2007b;Pons et al., 2009). They are similar to other iron skarns located in thesame belt of SW Mendoza (Franchini and Dawson, 1999; Franchiniet al., 2007b).

The Vegas Peladas iron skarn is hosted in the Jurassic shale,mudstone–wackestone, and limestone at the contact with aMiocene (Rb–Sr 15.2±0.2 Ma; Table 1; Figs. 2 and 4A) pluton.The diorite pluton is the oldest igneous rock and forms the LasMinas Hill (Fig. 4A). Its composition ranges from diorite to tonalite,with diorite being the most widespread variety. Diorite and tonalitecontain zoned plagioclase, pyroxene, amphibole (edenite–magnesiohornblende), biotite, and quartz, with accessory magne-tite, minor titanite, and apatite, and traces of zircon. The texturevaries from microporphyritic to glomerophyritic. The skarn issuperposed on a metamorphic halo with several types of hornfels

(800 m wide). Magnetite and hematite are the main iron oreminerals and occur as massive orebodies and veins associated withretrograde alteration.

The Hierro Indio iron skarn is hosted in Cretaceous limestone andcalcareous siltstone (Table 1) at the contact withMiocene (11±1 Ma;Table 1; Figs. 2 and 4B) plutons. These igneous rocks consist of a smalltonalite–granodiorite stock and numerous dacite sills and dikes thatintrude the sedimentary rocks in the core of a syncline structure(Fig. 2). The igneous bodies are aligned with the N–S trend and formthe hills of the area. They contain phenocrysts of magnesiohastingsiteand zoned plagioclase (Or1–2Ab53–66) with interstitial quartz andmagnetite, titanite, apatite, and zircon as accessory. The magnesio-hastingsite commonly has relic clinopyroxene cores. The borders ofthe stocks, sills and dykes have more porphyritic textures than thecore. Skarn mineralization is associated with andesite sills thatintrude out from the roof of the main diorite pluton (Fig. 4B). It isexposed in four areas of open pits, the largest of which had originally atotal surface area of 45,000 m2 Magnetite is associated with pyroxene

Fig. 5. Total alkali–silica classification (Middlemost, 1994; Bellieni et al., 1996) with the alkali–subalkali limit (Irvine and Baragar, 1971) of least-altered (A–B) Campana Mahuida,Cerro Nevazón, and Caicayén, and (C–D) igneous rocks Vegas Peladas and Hierro Indio. The compositional fields of other igneous rocks associated with Fe, Cu, Au and Zn skarns (afterMeinert, 1995) are shown for comparison.



and garnet skarn zones and hematite is related to the retrogradealteration of the exoskarn.

5. Chemical composition of igneous rocks

5.1. Major elements

In the (Na2O+K2O) vs. SiO2 diagram of Middlemost (1994)(Fig. 5A–D), the Neuquén igneous rocks are subalkaline and most plotin the diorite and tonalite fields. Two samples from CampanaMahuidafall in the granodiorite field whereas three samples of Caicayénigneous rocks plot in the monzonite field, probably due to albite andphyllic alteration. The igneous rocks from SW Mendoza are alsosubalkaline and plot in the diorite–granodiorite fields; only onesample from Hierro Indio plots in the monzonite field due its sodicalteration. When compared with plutons associated with base metaland gold skarns, all the samples fit well in the field of typical plutonsassociated with Fe and Au skarns though the most evolved plutonsfrom Caicayén and Campana Mahuida (granodiorite and monzonite)

are closer to the Cu and Zn skarn fields. According to the AFM diagramof Irvine and Baragar (1971) (Fig. 6A–D), the Mendoza and Neuquénigneous rocks are subalkaline with a calc-alkaline affinity. The samecharacteristics are exhibited by most plutons associated with skarndeposits (Meinert, 1995).

As shown in Fig. 7A–D, except for the CamapanaMahuida intrusiverocks, all other igneous rocks have similar K2O contents and plot in thefields of low and medium K2O, like the K2O contents of plutonsassociated with Fe and Au skarns. For similar SiO2 ranges, theCampana Mahuida igneous rocks have higher wt.% K2O than the restof intrusions from Mendoza and Neuquén, also, a stock sample withthe lowest SiO2 have higher K2O than all other skarns-related plutons.These igneous rocks define a trend similar to the less K2O-enrichedplutons associated with Zn and Cu skarns (Meinert, 1995) (Fig. 7A–B).

In the MgO vs. SiO2 diagram (Fig. 7E–H), most Cerro Caicayénplutons have MgO values similar to those of intrusive rocks associatedwith Cu and Zn skarns, meanwhile the Campana Mahuida values aresimilar to those of igneous rocks from Au and Cu skarns. CerroNevazón, Vegas Peladas and Hierro Indio igneous rocks show a wide

Fig. 6. AFM diagramswith calc-alkaline-tholeiitic boundary line from Irvine and Baragar (1971) of least-altered (A–B) CampanaMahuida, Cerro Nevazón, and Caicayén igneous rocksand; (C–D) Vegas Peladas and Hierro Indio. The compositional fields of other igneous rocks associated with Fe, Cu, Au and Zn skarns (after Meinert, 1995) are shown for comparison.



range of SiO2 as well as MgO contents. The trend they defined in theMgO vs. SiO2 diagram is similar to that of those intrusive rocksassociated with Fe and Au skarns. However, for similar SiO2 contents,the majority of the Vegas Peladas and Hierro Indio plutons have lowerMgO than typical Au skarns-related plutons.

In Fig. 8A–D, the A/CKN range of the Caicayén igneous rocks (0.88–1.1) is greater than those from Campana Mahuida (0.83–0.84),Nevazón (0.80–0.95), Vegas Peladas (0.85–0.95) and Hierro Indio

(0.6–0.9) igneous rocks. According to these data, they are metalumi-nous and plot near the line dividing the metaluminous andperaluminous fields, similar to plutons associated with Fe, Au, Cuand Zn skarns. A/CKN ratios greater than 1 in some Caicayén intrusiverocks are considered to be due either to alkali-element leaching andmicaceous alteration (samples C7 and C12 with high alkali contents,App. 3) or less silicic sills with more calcic plagioclase (samples C11and C-42, App. 3).

Fig. 7. (A–D) K2O vs. SiO2 with the high, normal, and low K2O boundary from Le Maitre (1989); and (E–I) MgO vs. SiO2 diagrams of Campana Mahuida, Cerro Nevazón, and Caicayén(A–B, E–F) and the Vegas Peladas and Hierro Indio igneous rocks (C–D, G–H). The compositional fields of other igneous rocks associated with Fe, Cu, Au and Zn skarns (after Meinert,1995) are shown for comparison.



The metaluminous character of most analyzed igneous rocks fromNeuquén and Mendoza combined with the presence of widespreadamphibole phenocrysts and accessory magnetite and titanite aretypical features of I-type or magnetite-series rocks with intermediatefO2. In the FeO/(Fe2O3+FeO) vs. SiO2 diagram, however, mostNevazón intrusives have FeO/(Fe2O3+FeO) ratios less than 0.4(Fig. 8E–F). These low ratios are not observed either inCampana Mahuida nor in Caicayén igneous rocks, which exhibitFeO/(Fe2O3+FeO) ratios in the 0.4–0.7 range. The presence ofilmenite as grains and also as exsolution lamellae within magnetite,combined with low Mg/(Mg+Fe2+) ratios in biotite (Franchini et al.,2003), suggest that the Cerro Nevazón igneous rocks are significantlymore reduced than those from CampanaMahuida and Caicayén. Thesedifferences are also shown in Fig. 8E–F, where Campana Mahuida andCaicayén samples plot well within the fields of Cu and Zn skarns-related plutons with high fO2, but Cerro Nevazón rocks plot close tothe Fe and Au fields, both represented by plutons that form undermore reduced conditions (Meinert, 1995).

5.2. Trace and rare earth element signatures

Fig. 9A–D shows the Rb–Sc relationship for igneous rocks fromNeuquén and Mendoza and plutons associated with Fe, Au, Cu, and Znskarns. The Rb and Sc values of the Neuquén and Mendoza igneousrocks are similar to those of primitive plutons associated with Feskarns, with the lowest Rb values and variable Sc values. In the V vs. Nidiagram (Fig. 9E–H; Appendix 1), igneous rocks from Cerro Nevazónshow the highest Ni contents whereas the rest of igneous rocks showmore Ni dispersion and lower values. The Sc and Ni depletion in theCampana Mahuida, Caicayén and Mendoza igneous rocks suggest thatthese rocks underwent a higher degree of mafic mineral fractionation(clinopyroxene+olivine) than did the Cerro Nevazón igneous rocks,which coincide with their depletion in olivine and clinopyroxene.

When LILE are comparedwith the less mobile HFSE, it is possible toanalyze the crystallization and differentiation processes and theirrelationship to a particular skarn type. For example, in the Rb/Sr vs. Zrdiagram (Fig. 10A–D), most of the Neuquén rocks plot in the field of

plutons associated with Au and Fe skarns. On the other hand, most ofthe Mendoza igneous rocks plot in the field of Fe skarns. In the Ba vs.Zr diagram (Fig. 10E–H), the Neuquén and Mendoza intrusive rocksplot in the field of plutons associated with Fe skarn, far from the Ba-enrichment trend observed in intermediate-composition plutonsassociated with typical Zn and Cu skarns. Ba depletion in Neuquénand Mendoza igneous rocks may reflect their low K-feldspar andbiotite contents, as Ba can substitute K in both minerals. Two samplesof the Hierro Indio igneous rocks that have high values of Zr also havehigher amphibole content than other rocks. In magmas of interme-diate-composition Zr behaves as a compatible element (Rollinson,1993).

The trace element patterns of the Neuquén and Mendoza igneousrocks normalized to N-MORB (Pearce, 1983, 1996) are typical of acalc-alkaline, continental arc, with high Th, Ce and Zr, low Ti, Y, and asignificant Nb depletion (Fig. 11A–B). Their Y and Zr contents close to1 indicate the lack or scarce residual garnet in the source rocks(Fig. 11A–B). The Mendoza igneous rocks are richer in incompatibleelements (Th, Nb, Ce) than the Neuquén intrusions with the exceptionof the Campana Mahuida igneous rocks that have the highest Thvalues. Campana Mahuida and Caicayén rocks are depleted in Nd, Sm,Yb, and Y in comparison with the other samples. Taking into accountthat these elements have high amphibole/liquid distribution coeffi-cients, their depletion may indicate the fractionation of amphibole(Pearce 1996). The trace element patterns normalized to continentalcrust (Taylor and McLennan, 1985; Fig. 11C–D), show that all theNeuquén igneous rocks have the strongest Nb negative anomalieswith respect to the Mendoza igneous rocks, and the highestenrichment in the low field strength elements (LFSE) like, Rb, Ba,and Sr of the Campana Mahuida igneous rocks with respect to theother samples (Fig. 11C–D).

The rare earth elements normalized to chondrite (Boynton, 1989)patterns also reflect the differences between these three igneous rockgroups (Fig. 11E). The pattern of the Campana Mahuida igneous rockshas the highest La/Yb ratio, due to its enrichment in the LREE anddepletion in HREE, and also exhibits the highest negative Eu anomaly.In contrast, the pattern of the Cerro Nevazón igneous rocks has the

Fig. 7 (continued).



Fig. 8. Aluminum saturation index of least-altered (A–B) Campana Mahuida,Cerro Nevazón, and Caicayén; and (C–D) Vegas Peladas and Hierro Indio igneous rocks and (E–F) the Feoxidation state — FeO/(Fe2O3+FeO) vs. SiO2 diagrams of the igneous rocks from NW Neuquén. The compositional fields of other igneous rocks associated with Fe, Cu, Au and Znskarns (after Meinert, 1995) are shown for comparison.



lowest La/Yb ratios of the Neuquén rocks, being depleted in the LREEin comparison to the other groups of rocks. The Caicayén pattern isintermediate in LREE compared to the previous groups, but it is alsodepleted in HREE. The REE patterns of the Mendoza igneous rocks aresub-parallel to that of the Cerro Nevazón rocks but they are enrichedin all the REE with respect to the Neuquén igneous rocks.

6. Discussion

Most of the Neuquén and Mendoza plutons intruded along themain structures of the study areas and several lines of evidenceindicate that they were emplaced at relatively shallow depth. The fivedistricts have igneous rocks with contrasting textures, from fine-

Fig. 9. (A–D) Rb vs. Sc diagrams; and (E–H) V vs. Ni diagrams illustrating trace element content of igneous rocks from Campana Mahuida, Cerro Nevazón, Caicayén, Vegas Peladas,and Hierro Indio. The compositional fields of other igneous rocks associated with Fe, Cu, Au and Zn skarns (after Meinert, 1995) are shown for comparison.



grained granular, seriate, to porphyritic. The porphyritic rocks are themost common type associated with mineralization (i.e., at Caicayén,Campana Mahuida, Hierro Indio and Vegas Peladas), and containplagioclase and amphibole phenocryts (1–5 mm), with only localquartz (i.e., Caicayén) in a microgranular to aphanitic matrix. Thistexture suggests at least two different cooling rates for the magmasand, together with the presence of hornfels suggest a large thermalcontrast between magmas and host rocks (Llambías, 2003), which istypical of brittle and epizonal environments. Similar ratios ofphenocrysts to aplitic matrix (1:1) in CampanaMahuida and Caicayénporphyries indicate that after 50% of melt crystallization, the systemwas significantly undercooled, probably as a result of pressurequenching to hydrostatic conditions, like in other porphyry copperdistricts (i.e., Yerington, Dilles, 1987; Seedorff et al., 2005).

The plutons associated with Neuquén and Mendoza skarns shareseveral geochemical and petrographic features with most intrusiverocks associated with Fe, Au, Cu and Zn skarns worldwide: they arecalc-alkaline and metaluminous, with N-MORB normalized traceelement patterns (Pearce, 1996) characteristics of calc-alkalinemagmas derived from a sub-arc mantle source (Figs. 6A–D and11A–E; Kay and Mpodozis, 2002). But in terms of trace and rare earthelements there are significant differences among the plutons.

The Cerro Nevazón plutons are similar to igneous rocks from VegasPeladas and Hierro Indio. All are emplaced north of the Cortaderaslineament that marks a change in Mesozoic to Holocene structure ofthe underlying continental crust and mantle lithosphere to the northand south (Ramos and Kay, 2006). They are mafic to intermediate incomposition (diorite to granodiorite). They are also the mostprimitive, being Mg-rich, K- and Si-poor rocks and their trace(Fig. 7A–H) and rare earth element patterns (Figs. 8A–H, 9A–H and11A–E) are similar to the primitive igneous rocks associated with ironskarns (cf. Meinert, 1995; Figs. 7A–H and 11A–E). However, the CerroNevazón igneous rocks have higher Ni values and lower fO2 than theMendoza igneous rocks, similar to igneous rocks associated withreduced Au skarns (Figs. 7A–H, 6E–F and 11A–E). As Ni substitution islargely restricted to olivine, the highest values of Ni are consistentwith the presence of this mineral in the Cerro Nevazón igneous rock.The REE pattern of these rocks are similar (enriched in the LREE with

respect to the HREE) except that the Cerro Nevazón igneous rockshave slightly lower values of total REE (Fig. 11). They have negativeanomaly of Nb, typical of volcanic arc magmas where the Nb isretained within amphibole and minor phases, such as titanite andrutile, in the subducting plate and its overlying lithospheric mantle(Pearce and Peate, 1995). The higher Nb anomaly in Cerro Nevazóncould indicate higher accessory mineral fractionation.

The Campana Mahuida and Caicayén igneous rocks are locatedsouth of the Cortaderas lineament. Igneous rocks from Caicayén andmost igneous rocks from Campana Mahuida have similar major, traceand rare earth element values relative to the more evolve igneousrocks associated with Cu skarns (Figs. 5–11). As shown in their Rb/Srratios which are very sensitive to the degree of differentiation(Meinert, 1995), the Campana Mahuida plutons are the most evolvedof the Neuquén igneous rocks, being enriched in the incompatibleelements. This is also reflected in the Campana Mahuida REE patternby the negative Eu anomaly due to the fractionation of feldspar andthe highest enrichment in LREE relative to HREE. The lowest values ofHREE in Campana Mahuida could indicate the fractionation ofaccessory phases, such as zircon and rutile that have high affinityfor HREE (Rollinson, 1993: Fig. 11B, D–E). Both igneous rocks aredepleted in Yb probably due to the fractionation of amphibole(Rollinson, 1993) during magmatic ascent.

The chemical differences among the analyzed plutons are bestvisualized in the La/Yb vs. Rb/Cs diagram (Fig. 12A), that shows threedifferent trends. The wide range of Rb/Cs ratios is the maincharacteristic of the Campana Mahuida, Cerro Nevazón, Vegas Peladas,and Hierro Indio igneous rocks. Since Rb and particularly Cs are highlyincompatible trace elements, this wide range cannot be attributed to asimple crystal fractionation process. The variable concentration of Csseems to be themain cause of the wide range of Rb/Cs ratios. Since Cs iscompatible with fluid phases, the interaction of the magmatic systemwith crustal fluids could explain the variable concentrations of thiselement. Constant La/Yb in Cerro Nevazón and the Mendoza intrusionsmay be caused by fractionation of minerals with similar solid/liquiddistribution coefficients for heavy and light REE (e.g., olivine±plagioclase±orthopyroxene). These three trends emerge from thefield of basalts from the central province of the Southern Volcanic Zone

Fig. 9 (continued).



of the Andes (TSVZ–SSVZ; 35–41°.5′S; Hickey-Vargas et al., 1986;Tormey et al., 1991). This suggests that the subcrustal sources andprocesses that gave rise to theprimarymagmasof TertiaryMendozaandNeuquén igneous groups are similar to those that gave rise to basaltsfrom theQuaternary TSVZ of theAndes (Morris andHart, 1983; Futa andStern, 1988). Thus, the subcrustal sources and processes can bemodeledby approximately 10%melting of a peridotiticmantle source enriched inalkalis (among them Cs coming from subducted pelagic sediments;Morris and Hart, 1983; Futa and Stern, 1988) and alkaline

earth elements due to fluids coming from the subducted oceanic slab(López-Escobar et al., 1977, 1995). Also the REE patterns normalized tochondrite for all these rocks indicate that in the generation of theparentalmagmabymantle partialmelting, the participation of garnet asa residual phase would be rare to absent. The initial 87Sr/86Sr ratio of0.7043 and preliminary 147Sm/144Nd (0,123) and 143Nd/144Nd (0,513)ratios for the Vegas Peladas igneous rocks (Pons, 2007) are alsoconsistent with a mantle source for these rocks without crustalcontamination (Faure 1986; Hall, 1996).

Fig. 10. (A–D) Rb/Sr vs. Zr; and (E–H) Ba vs. Zr diagrams illustrating trace element content of igneous rocks from Campana Mahuida, Cerro Nevazón, Caicayén, Vegas Peladas, andHierro Indio. The compositional fields of other igneous rocks associated with Fe, Cu, Au and Zn skarns (after Meinert, 1995) are shown for comparison.



The La/Yb, La/Sm and Sm/Yb, ratios of the Cerro Nevazón rocksare similar to other Paleogene rocks located NW of Neuquén(Fig. 12C, D; Kay et al., 2006). The Cerro Nevazón igneous rockshave lower Sm/Yb ratios than the Neogene Mendoza igneous rocks,suggesting that they were emplaced in a relatively thinnercontinental crust (∼30 km; Franchini et al. 2003). Sm/Yb ratios ofVegas Peladas and Hierro Indio intrusions plot in the fields of otherNeogene igneous rocks (from NW Neuquén and SW Mendoza).Nevertheless, the variability in the Sm/Yb for similar La/Sm ratiosshown in Fig. 12D, with the lowest values of Sm/Yb for the Neogeneigneous rocks from NW Neuquén and the highest values for thosefrom SW Mendoza points to a small increase in crustal thicknessfrom south (30 km; NW Neuquén) to north (50 km; SW Mendoza)during Neogene arc, similar to the increase observed in theQuaternary Volcanic Arc between the 35° and 37° SL (AntucoVulcano and Planchon Peteroa Volcanic Group; Hildreth andMoorbath, 1988; Tormey et al., 1991).

The geochemical signatures of the CampanaMahuida and Caicayénrocks differ from the typical signatures of other Paleogene igneousrocks (Fig. 12B; Kay et al., 2006 and references therein) in their wideLa/Yb ratio and their dispersion of La/Sm and Sm/Yb ratios. Thesegeochemical differences of the Campana Mahuida and Caicayénigneous rocks would be mainly controlled by 1) the interaction ofsubcrustal magmas, as the parental magmas rose, with crustalmaterials having different La, Sm, and Yb concentrations (Franchiniet al., 2003) or/and 2) fractional crystallization: with different degreesof amphibole fractionation, with a solid/andesitic liquid distributioncoefficient b1 for La and N1 for Yb, which would in turn causedifferent degrees of Yb depletion.

7. Conclusions

The Neuquén and Mendoza igneous rocks emplaced in the NWof the Neuquén basin represent an example of magmatic activitythat took place during the formation of Paleogene to Neogenevolcanic arcs of the Andes. They are granitoids derived from similarmagmas and share several geologic and petrographic features, but

they have some differences that are related to their associatedskarns.

The Vegas Peladas andHierro Indio igneous rocks have similarmajorand trace element contents, and are typical of primitive, I-type plutonsassociated with Fe skarns worldwide. Likewise, they share severalgeologic, petrographic and geochemical features with the PaleogeneCerro Nevazón igneous rocks, for which a mantle source with scarce orno residual garnet has been suggested. The Vegas Peladas and HierroIndio plutons are, however, less reduced and they have lower Niconcentration than the Cerro Nevazón rocks, whose skarns have higherAu concentrations. In the Caicayén district, small skarns with sub-economic Cu concentrations and abundant pyrite are associated withporphyry copper-like alterations in igneous rocks that underwentamphibole fractionation. Their chemical compositions are intermediatebetween the most primitive plutons associated with Fe skarns and themost evolved plutons associated with Cu skarns, both with high fO2. Inthe case of Campana Mahuida, a small porphyry Cu deposit and Cuskarns are associated with andesite dikes and plutons with similar SiO2

contents, but are richer in incompatible trace elements (K, Rb, Sr, Ba, La,Ce and Th) than the Mendoza, Cerro Nevazón and Caicayén igneousrocks, suggesting that their parentalmagmas evolved in an open systemand were contaminated with crustal material and have strongestfractionation of amphibole and accessories phases. These intrusionsshare many features with typical Cu skarn-related plutons.

Consequently, these examples illustrate the role of magmaevolution, of associated skarns and related deposits, and they mayturn out to be of use in large scale prospecting. Another interestingfeature is the chemical differences between the igneous rocks locatednorth of the Cortaderas lineament (Vegas Peladas, Hierro Indio andNevazón) and the igneous rocks located south of the lineament(Caicayén and Campana Mahuida). This may reflect differences insource regions or tectonic processes.

Acknowledgements

The authors express their appreciation to the Argentinean NationalInstitution for Scientific and Technical Research (CONICET) and theFacultad de Ingeniería of the Universidad Nacional del Comahue, for

Fig. 10 (continued).



Fig. 11. (A–B)Whole-rock trace element concentrations average normalized to N-typeMORB (Pearce, 1996) showing differences in the Nb and Ti anomalies; (C–D)whole-rock traceelement concentrations average normalized to continental crust (Taylor and McLennan, 1985); and (E) whole-rock REE concentrations average normalized to average chondrite(Boynton, 1989) for the Neuquén and Mendoza igneous rocks.



funding these studies. LLE also acknowledges the contribution of theCONICYT-Chile, Líneas Complementarias Project No. 800-0006.Special thanks are due to the two anonymous reviewers for their

excellent contributions that helped us revise this manuscript. Finally,we wish to thank to Nigel J. Cook for his careful examination anddedication as Editor.

Fig. 12. (A) Diagram of La/Yb vs. Rb/Cs with the arrows showing the different trends among Campana Mahuida, Cerro Nevazón, Caicayén, Vegas Peladas, and Hierro Indioigneous rocks: 1) the Nevazón, Vegas Peladas and Hierro Indio trend, characterized by relatively constant La/Yb and variable Rb/Cs ratios; 2) the Campana Mahuida trend,characterized by variable La/Yb and Rb/Cs ratios, with the La/Yb ratio increasing as the Rb/Cs ratio increases, and finally 3) the Caicayén trend, characterized by relativelyconstant and low Rb/Cs and variable La/Yb ratios; (B–C) La/Yb vs. SiO2; and (D–E) La/Sm vs. Sm/Yb ratios diagrams for the Paleogene and Neogene igneous rocks from NWNeuquén and SWMendoza, respectively, with those fields of other igneous rocks from the Paleogene and Neogene volcanic arcs located in the same Andean segment (SVZ, datafrom Kay et al., 2006). The last diagram illustrates the relationship between REE patterns and crustal thickness (Hildreth and Moorbath, 1988).



Appendix A. Whole rock, trace and rare earth element compositions of representative igneous rock suites from Cerro Nevazón.

Facies Tonalite Gabro Tonalite Diorite Diorite Gabro Tonalite Tonalite Diorite Gabro Diorite Diorite Tonalitestock stock stock sill stock sill stock stock stock stock stock stock stock

Sample 18,523 15,920 15,918 15,914 18,534 18,527 15,906 18,540 15,751 15,919 15,772 15,800 15,902

wt.%

SiO2 59.99 50.83 58.83 56.86 53.29 50.63 59.43 57.47 55.38 50.12 55.64 56.91 59.04TiO2 0.51 0.72 0.58 0.66 0.73 0.74 0.52 0.62 0.63 1.02 0.78 0.65 0.62Al2O3 17.06 19.87 18.62 18.67 18.06 20.93 18.29 17.79 18.57 19.08 18.11 18.07 17.46FeO 2.94 3.92 2.5 3.12 5.3 5 3.6 4.04 3.2 5.16 4.2 4.26 5.32Fe2O3 3.01 1.19 2.41 3.59 2.79 3.20 2.14 2.58 3.59 4.20 2.94 2.74 0.87MnO 0.12 0.09 0.03 0.13 0.15 0.15 0.08 0.09 0.09 0.14 0.12 0.13 0.16MgO 2.74 4.45 2.61 3.11 5.55 4.96 2.52 2.81 3.77 5.27 3.37 3.31 2.38CaO 5.87 10.41 8.18 7.94 8.54 9.5 5.78 7.4 8.56 9.44 7.33 7.07 6.06Na2O 3.55 2.89 4.29 4.02 2.91 2.8 4.06 3.54 3.35 2.84 3.36 3.12 3.48K2O 1.45 0.87 0.3 0.24 0.65 0.72 2.09 1.39 0.67 0.77 1.69 1.36 1.45P2O5 0.23 0.09 0.15 0.3 0.21 0.09 0.15 0.21 0.2 0.26 0.19 0.23 0.2L.O.I. 1.9 4.1 1.2 0.9 0.8 0.6 1.4 1.4 1.3 0.8 1.6 1.5 2C 0.05 0.31 0.07 0.01 0.02 0.01 b0.1 0.01 0.2 0.03 0.03 0.02 0.2S 1.21 0.01 1.02 0.03 0.05 0.03 0.11 1.22 0.01 0.01 0.01 0.03 0.02Total 99.81 99.98 100.08 99.99 100.05 99.98 100.6 99.92 99.78 99.77 99.91 99.92 99.76

ppm

Ni 26 29 b20 21 28 b20 b20 29 23 35 b20 26 28Cr 23.94 23.94 30.79 30.79 30.79 41.05 30.79 17.10 51.31 30.79 17.10 27.36 34.21Sc 10 18 10 10 20 19 b10 13 14 23 16 14 10Ba 319 157 126 120 173 174 475 330 181 158 309 306 351Rb 75.2 19.2 5.4 6 31.7 16 49.1 37.7 26.3 29.3 66.8 48.6 76.4Sr 401.4 481 470.9 406.1 384.6 459.7 518.4 505.2 463.9 448.5 372.8 342.8 462.6Zr 141.5 67.4 104.8 83.7 75.7 64.2 154.6 148.4 105.1 72.5 105.3 101.7 185.1Y 20.5 14.6 16.1 13.9 13.3 14.2 23 23.8 15.6 15.8 16.9 15.7 16.5Nb 4.6 2 3 2.6 1.9 1.7 4.6 4 3.3 2.1 3.4 3.3 6.2Ga 21.2 18.4 18.9 19.7 20.4 18.9 21.2 20.4 20.9 20 22.2 20.9 22.8Bi b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 0.1 b0.1 b0.1Co 14 14 6 13 28 25 9 15 12 22 15 20 12Cs 2 0.9 1.1 1.7 1.5 1.2 2.7 0.5 1.2 1.8 1.7 2.4 5.9Hf 2.7 1.3 2 1.6 1.4 1.3 3 2.7 2 1.4 2 2 3.1Sn b1 1 1 b1 b1 b1 b1 b1 b1 b1 1 0.2 1Ta 0.3 b0.1 0.1 0.1 b0.1 b0.1 b0.1 0.1 0.2 b0.1 0.2 0.2 0.3Th 5.2 1.5 2.6 2.4 2.3 1.3 4.6 2.6 2.7 1.6 4.1 4.4 3.8U 1.4 0.3 1.5 0.5 0.6 0.4 1.1 0.9 0.6 0.4 0.7 0.7 1.2V 116 163 104 118 222 211 112 148 152 225 218 183 160W b0.5 b0.5 b0.5 0.6 b0.5 b0.5 0.7 b0.5 1.9 b0.5 3.2 1.3 1.7La 16 10 11 7 10 7 15 14 8 8 10 13 12Ce 30 22 28 13 19 13 32 31 16 15 20 25 24Pr 3.92 2.8 4.12 1.95 2.28 1.84 4.14 4.01 2.32 2.22 2.84 2.92 3.53Nd 13 11 15 8 9 8 16 16 9 9 11 11 13Sm 3.44 2.47 3.47 2.31 2.43 2.24 4.22 4.25 2.7 2.67 3.07 2.92 3.2Eu 0.91 1.04 1.42 0.75 0.81 0.76 1.14 1.15 0.88 0.81 0.94 0.92 0.97Gd 4.76 3.58 4.57 2.96 3.25 2.96 5.87 5.52 3.51 3.51 3.94 3.85 3.87Tb 0.61 0.44 0.56 0.41 0.43 0.41 0.73 0.73 0.49 0.51 0.54 0.52 0.51Dy 2.93 2.11 2.51 2.07 2.17 2.03 3.47 3.56 2.27 2.44 2.6 2.4 2.49Ho 0.66 0.48 0.57 0.47 0.49 0.48 0.8 0.82 0.57 0.59 0.61 0.55 0.58Er 2.19 1.53 1.92 1.56 1.62 1.52 2.49 2.55 1.81 1.84 1.94 1.79 1.8Tm 0.28 0.19 0.23 0.2 0.2 0.19 0.32 0.31 0.22 0.22 0.24 0.22 0.24Yb 2.23 1.52 1.85 1.68 1.57 1.58 2.7 2.58 1.79 1.69 1.91 1.86 1.95Lu 0.25 0.17 0.23 0.19 0.18 0.18 0.31 0.29 0.21 0.19 0.22 0.21 0.24

These samples correspond to Franchini et al. (2003).Notes: Major-element, trace-element analyses and FeOwere determined by inductively coupled plasma emission spectroscopy (ICPES), inductively coupledmass spectroscopy (ICP-MS), and dichromate titration, respectively, in ACME Analytical Laboratories LTD, Vancouver, Canada.

Appendix B. Whole rock, trace and rare earth element compositions of representative igneous rock suites from Campana Mahuida.

Facies Andesite dyke Dacite dyke Dacite dyke

Sample 3138 3117 3110

wt.%

SiO2 57.26 62.24 63.54TiO2 0.72 0.52 0.53Al2O3 16.81 16.10 16.50FeO 3.34 3.46 1.06Fe2O3 2.27 0.00 1.26MnO 0.14 0.07 0.05



(continued)

Facies Andesite dyke Dacite dyke Dacite dyke

Sample 3138 3117 3110

wt.%

MgO 3.62 2.03 2.22CaO 6.77 5.83 6.08Na2O 3.50 3.22 3.57K2O 1.95 2.96 2.51P2O5 0.20 0.25 0.20L.O.I. 2.80 2.80 2.10C 0.30 0.29 0.02S 0.01 1.14 0.79Total 97.42 100.91 99.17

ppm

Ni b20 b20 b20Cr 44.47 51.31 47.89Sc 13.00 6.00 7.00Ba 350.00 442.00 501.00Rb 41.88 92.31 66.88Sr 604.20 308.30 638.80Zr 91.10 146.30 144.90Y 12.60 10.40 11.00Nb 3.02 3.86 4.07Ga 15.50 13.30 14.80Bi 0.10 0.10 0.10Co 14.00 5.70 5.70Cs 0.70 1.60 1.00Hf 3.60 4.30 4.40Sn 2.80 2.80 2.70Ta 0.20 0.30 0.30Th 6.80 9.70 9.20U 1.60 2.20 2.20V 159.00 75.00 91.00W 1.40 4.20 4.40La 16.20 21.90 22.80Ce 34.10 43.20 44.50Pr 4.57 5.26 5.53Nd 16.70 17.50 18.80Sm 3.30 2.90 3.20Eu 0.83 0.57 0.81Gd 3.22 2.84 2.98Tb 0.43 0.36 0.36Dy 2.53 1.93 2.15Ho 0.40 0.33 0.32Er 1.21 0.95 1.00Tm 0.18 0.14 0.15Yb 1.11 1.00 0.93Lu 0.17 0.16 0.17

These samples correspond to Franchini et al. (2003). Notes: Major-element, trace-element analyses and FeO were determined by inductively coupled plasma emission spectroscopy(ICP-ES), inductively coupled mass spectroscopy (ICP-MS), and dichromate titration, respectively, in ACME Analytical Laboratories LTD, Vancouver, Canada.

Appendix C. Whole rock, trace and rare earth element compositions of representative igneous rock suites from Caicayen.

Facies Tonalite sill Tonalite sill Tonalite sill Tonalite sill Tonalite sill Tonalite sill

Sample C-4 C-5 C-7 C-12 C-11 C-42

wt.%

SiO2 59.38 61.93 60.57 61.72 59.01 59.01Al2O3 18.7 17.77 20.36 20.78 19.35 19.27TiO2 0.42 0 0.36 0.3 0.52 0.56Fe2O3 3.68 2.87 0.32 1.62 2.21 2.35FeO 2.7 1.73 1.63 1.2 2.76 2.62MnO 0.06 1.44 0.07 0.04 0.1 0.08CaO 3.61 3.15 5.13 4.97 6.88 6.5MgO 1.34 1.44 1.12 1.15 1.96 1.95K2O 1.22 0.88 0.52 0.65 1.02 1.26Na2O 6.83 5.97 8.01 7.07 2.34 2.89P2O5 0.14 0 0.11 0.12 0.15 0.14L.O.I. 4.4 2.73 1.33 1.3 1.43 2.19H2O+ 0.68 1.67 0.44 0.02 0.54 1.01Total 99.89 101.58 99.97 99.84 98.45 99.83

Appendix B (continued)

(continued on next page)



(continued)

Facies Tonalite sill Tonalite sill Tonalite sill Tonalite sill Tonalite sill Tonalite sill

Sample C-4 C-5 C-7 C-12 C-11 C-42

ppm

Ni 2 2 3 2 4 4Cr 61.6 61.6 65 n.a. n.a.Sc 7 7 6 5 13 12V 76 65 58 64 109 108Ba 138.8 268.9 146.2 102.6 326.7 283.8Rb 34.1 75 6.8 18.6 34.9 36.3Sr 419.5 471.4 504.8 523.1 459.4 435.6Zr 74.3 82.9 59.8 87 134.9 73.8Y 11.8 12.3 10.7 9.7 13.6 13.2Nb 2.8 2.8 2.2 2.3 3.4 2.4Ga 17.1 17.1 16.3 17.1 17.2 16.6Cu 4 91 6 97 7 11Mo b2 3 b2 b2 b2 b2Pb b5 10 9 b5 9 10Zn 19 324 79 17 35 45As b5 5 b5 b5 6 b5La 13 13.8 14.4 33.8 12.4 13.2Ce 25.5 27.5 26.1 65.2 25.8 21.5U 1 1.2 1.3 1.8 1.2 1Th 3.6 3.8 3.1 5.3 4.5 5.3Cs 6.6 11 3.5 19.7 2.6 3.1Hf 1.9 2.1 1.6 2 3.2 1.9Nd 14.6 16.3 13 23.6 14 3.2Sm 2.9 3.2 2.2 3.3 2.9 0.9Eu 1.1 1.1 0.9 1 0.9 0.9Gd 2.9 3.3 2.6 2.5 3.1 2.9Tb 0.4 0.5 0.4 0.4 0.5 0.5Yb 1.4 1.4 1.1 1.1 1.5 1.4Lu 0.3 0.3 0.2 0.2 0.3 0.3

These samples correspond to Franchini et al. (2003). Notes: Major-element, trace-element analyses and FeO were determined by inductively (ICP-ES), inductively coupled massspectroscopy (ICP-MS), and dichromate titration, respectively, in ACME Analytical Laboratories LTD, Vancouver, Canada.

Appendix D. Whole rock, trace and rare earth element compositions of representative igneous rock suites from Hierro Indio and VegasPeladas districts.

District Hierro Indio Vegas Peladas

Rock Tonalite Tonalita Andesita-dyke Andesita-dyke Tonalite Tonalite Diorite Diorite Tonalite Diorite Diorite Diorite Diorite Tonalite

Sample *2601 *2602 *2622 85703 *2629 *2652 *2653 2628 2696 *2626 *2630 2638 2686 VP21 G

SiO2 58.6 62.7 63.6 58.8 57.4 57.7 54.9 55.9 58.2 55.8 55.9 56.2 57.8 59.5Al2O3 17.5 18.2 18.5 19.3 18.5 18.1 19.0 18.9 18.4 18.7 18.7 17.9 17.5 17.6TiO2 0.8 0.6 0.5 0.7 0.8 0.9 0.8 0.7 0.8 0.9 0.9 1.0 0.7 0.7Fe2O3 3.2 1.7 3.9 2.8 7.9 7.6 9.2 8.7 8.0 8.3 8.4 8.3 7.4 7.0MnO 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.1 0.1 0.1CaO 9.6 8.2 5.3 7.4 7.2 6.3 7.4 7.3 6.6 7.8 7.4 7.6 7.2 6.2MgO 3.9 1.7 0.9 2.2 2.9 3.2 3.1 3.0 2.8 3.0 3.1 4.2 3.8 2.9K2O 0.7 0.4 1.7 1.8 1.3 2.0 1.1 1.5 1.4 1.2 1.2 1.1 1.8 2.0Na2O 5.3 6.1 5.4 6.6 3.7 4.0 3.9 3.5 3.6 3.9 3.9 3.2 3.3 3.7P2O5 0.3 0.3 0.2 0.3 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.2 0.2 0.2L.O.I. 1.1 0.3 2.6 1.6 0.9 1.9 1.2 1.2 1.1 0.8 1.0 1.2 1.0 0.9Total 101.1 100.3 102.6 101.6 100.8 101.9 101.2 101.2 101.1 100.8 101.0 101.2 101.0 100.9

ppm

Ni 33 3 2 n.a. 3 9 3 1.5 1.8 3 3 28 24 2.5Cr 125 3 3 n.a. 4 10 10 b0.001 b0.001 18 5 0.004 0.015 0.002Sc 18 9 7 7 14 12 16 11 11 16 16 23 n.a. n.a.Ba 294 261 504 672 313 394 256 399 377 263 268 307 412 405.2Rb 14 8 31 43 47 69 38 60.2 45.5 34 44 61 57.8 62.8Sr 672 718 693 526 603 601 601 662.7 613.6 643 607 538 621.7 555.8Zr 194 239 240 165 137 147 124 172.4 130.5 117 127 139.9 147.6 156.7Y 19 21 23 22 21 18 21 20.5 20.3 20 20 25.3 21.1 21.6Nb 11 12 10 6 6 6 5 4.1 4.4 5 5 5.3 4.7 6.2Ga 22 24 22 19 18 22 23.8 22.8 19 19 21.6 21.6 17.5Bi b0.1 n.a. n.a. 0.1 b0.1 n.a. b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1 b0.1Co b3 b3 4 15 11 12 17.8 17.8 12 17 22.6 23.6 17Cs 0.1 n.a. n.a. 0.8 1.8 n.a. 1.5 1.1 1.3 1.3 1.9 1.9 2 4.3Hf 5 n.a. n.a. 4.3 3.6 n.a. 2.8 5.4 3.9 3.3 3.5 4.1 3.9 4.8Sn n.a. n.a. n.a. n.a. n.a. n.a. n.a. 3 2 n.a. n.a. 3 2 b1Ta 0.6 n.a. n.a. 0.5 0.3 n.a. 0.2 0.3 0.4 0.2 0.2 0.4 0.4 0.5Th 7 8 7 6.5 4 6 3 5.1 4.2 3 3 4.1 6 5.7

Appendix C (continued)



(continued)

District Hierro Indio Vegas Peladas

Rock Tonalite Tonalita Andesita-dyke Andesita-dyke Tonalite Tonalite Diorite Diorite Tonalite Diorite Diorite Diorite Diorite Tonalite

Sample *2601 *2602 *2622 85703 *2629 *2652 *2653 2628 2696 *2626 *2630 2638 2686 VP21 G

ppm

U 3 3 3 1.8 0.9 3 0.6 1.2 0.9 0.6 0.8 1.7 1.1 1V 132 68 40 n.a. 116 120 126 121 126 125 117 209 142 102W 0.6 n.a. n.a. 1.1 0.6 n.a. 0.7 0.1 0.3 0.2 0.6 0.5 0.4 0.3La 17.5 25 30 15 18.8 17 16 13.1 17.9 15.3 17.3 14.7 18.7 19.1Ce 39.6 57 63 38.4 41.4 45 36.9 29.6 40 34.1 39.4 34.5 39.9 45.8Pr 5.06 n.a. n.a. 4.99 5.18 n.a. 4.6 3.98 5.25 4.31 5.01 4.47 4.99 5.58Nd 22.3 28 24 22.3 21 b22 21.5 18.9 23.1 18.1 22.2 19.3 22 24.8Sm 4.3 n.a. n.a. 4.6 4.3 n.a. 4.3 3.8 4.5 4 4.2 4.5 4.6 5Eu 1.28 n.a. n.a. 1.24 1.27 n.a. 1.45 1.32 1.18 1.23 1.25 1.26 1.13 1.23Gd 3.17 n.a. n.a. 3.45 3.09 n.a. 3.41 4.02 4.51 3.26 3.29 4.98 3.88 4.18Tb 0.56 n.a. n.a. 0.67 0.66 n.a. 0.72 0.55 0.54 0.61 0.64 0.72 0.6 0.68Dy 3.52 n.a. n.a. 3.57 3.57 n.a. 3.99 3.28 3.18 3.41 3.46 4.18 3.56 3.9Ho 0.62 n.a. n.a. 0.63 0.63 n.a. 0.79 0.66 0.63 0.63 0.79 0.8 0.68 0.8Er 1.81 n.a. n.a. 1.81 2 n.a. 1.99 2.2 1.92 1.76 1.76 2.62 2.22 2.05Tm 0.3 n.a. n.a. 0.31 0.37 n.a. 0.32 0.29 0.24 0.28 0.28 0.33 0.27 0.31Yb 1.72 n.a. n.a. 1.88 1.95 n.a. 2.13 1.94 1.82 1.62 1.81 2.23 2 2.05Lu 0.26 n.a. n.a. 0.33 0.32 n.a. 0.31 0.33 0.32 0.26 0.27 0.35 0.27 0.36

These samples correspond to Franchini et al. (2007b) and Pons et al. (2007). *Major and trace elements from the analytical data of Universidad de Sao Pablo, Brasil and the REEanalyses from ACME Analytical Laboratories LTD, Vancouver, Canada. The rest of the analyses are from ACME Analytical Laboratories LTD, Vancouver, Canada.

Appendix D (continued)

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geology, petrography and geochemistry of igneous rocks related to mineralized skarns in the nw...

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