Journal of South American Earth Sciences 82 (2018) 239e260

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Journal of South American Earth Sciences

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Mineralogy, structural control and age of the Incachule Sb epithermal veins, the Cerro Aguas Calientes collapse , Central Puna

* Natalia Salado Paz a, ,Ivan Petrinovic b, Margarita Do Campo c, Jose Affonso Brod d, Fernando Nieto e, Valmir da Silva Souza f, Klauss Wemmer g, Patricio Payrola a, Roberto Ventura f a Instituto de Bio y Geociencias del NOA (IBIGEO), Universidad Nacional de Salta-CONICET, Av. Bolivia 5150, Salta 4000, Argentina b Centro de Investigaciones en Ciencias de la Tierra (CICTERRA), Universidad Nacional de Cordoba-CONICET, Cordoba X5016GCA, Argentina c Instituto de Geocronología y Geología Isotopica (INGEIS), Universidad Nacional de Buenos Aires- CONICET, Ciudad Universitaria C1428EHA CABA, Argentina d Facultade de Ci^encias e Tecnologia (FC), Universidade Federal de Goias, Brazil e Dpto de Mineralogía y Petrología e I.A.C.T, Universidad de Granada-CSIC, Avda. Fuentenueva s/n, 18002 Granada, Spain f Instituto de Geociencias, Universidade de Brasília, Campus Universitario Darcy Ribeiro, Asa Norte, CEP 70910-900, Brasília, DF, Brazil g University of Goettingen, Geoscience Centre, Goldschmidtstraße 3, 37077 Goettingen, Germany article info abstract

Article history: The Incachule Sb epithermal veins is located near to the N-E rim of the Cerro Aguas Calientes collapse Received 28 March 2017 caldera (17.5e10.8 Ma), in the geologic province of Puna, Salta- Argentina. It is hosted in felsic Received in revised form volcanic rocks with continental arc signature. The district includes twelve vein systems with minerali- 23 June 2017 zation of Sb occurring in hydrothermal breccias and stockwork. The veins are composed of -sulfide Accepted 9 July 2017 with pyrite, stibnite and arsenopyrite. All around the veins, wall rocks are variably altered to clay Available online 26 August 2017 minerals and sulfates in an area of around 2.5 km wide by more than 7 km long. The hydrothermal alterations recognized are: silicic, phyllic and argillic. Keywords: Collapse caldera The veins are characterized by high contents of Sb, As, and Tl and intermediate contents of Pb-Zn-Cu, fl Hydrothermal breccia and traces of Ag and Au. Homogenization and ice-melting temperatures of uid inclusions vary from 34 Epithermal 125 Cto189 C and 2.4 Cto0.8 C. The isotopic data indicated a range of d S 3.04‰ to þ0.72‰ Low sulfidation consistent with a magmatic source for sulfur. We present the firsts K-Ar ages for hydrothermal illite/smectite mixed layers (I/SR1, 60% illite layers) and illite that constrain the age of the ore deposit (8.5e6.7 ± 0.2 Ma). The data shown here, let characterized the Incachule district as a shallow low sulfidation epithermal system hosted in a collapse caldera. Our data also indicate that mineralization is structurally controlled by a system related to the 10.3 Ma collapse of Aguas Calientes caldera. The interpreted local stress field is consistent with the regional one. © 2017 Elsevier Ltd. All rights reserved.

1. Introduction 2002; Sillitoe, 2008). This applies particularly to the Central Puna (~24S), which is one of the largest ore districts with silver, lead, In the Puna geological province profuse magmatic activity copper and gold mineralizations in epithermal veins (Sureda et al., occurred during the Miocene, giving place to different kinds of 1986; Pelayes, 1981; Sillitoe, 2008; Zappettini, 1999; Ramallo et al., volcanic and subvolcanic forms comprising stratovolcanoes, cal- 2011). Previous studies were focused on the mineralogy of the ore deras, and domes. Several metallogenetic major episodes, in some deposits, with the goal of defining whether or not they were of the cases of economic interest, are linked with that magmatic activity epithermal type (Arganaraz~ and Sureda, 1979; Morello, 1968). (Coira, 1983; Caffe, 1999; Kay and Mpodozis, 2001; Chernicoff et al., However, those studies did not explore the genetic linkage between the mineralization and specific volcanic episodes and/or volcanic centers. * Corresponding author. In the case of the Incachule mine, located in the Central Puna E-mail address: [email protected] (N. Salado Paz). http://dx.doi.org/10.1016/j.jsames.2017.07.002 0895-9811/© 2017 Elsevier Ltd. All rights reserved. 240 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

(Fig. 1), previous works interpreted the mineralization as epi- 2. Regional geological setting thermal, and related it with the activity of the Quevar volcano (JICA, 1993; Zappettini, 1999; Chernicoff et al., 2002). In this study, we The Cerro Aguas Calientes collapse caldera hosts a Sb mineral- present new data suggesting a temporal and spatial link between ization and is located in the geological province of Puna (Turner and the mineralization of the Incachule area and the cerro Aguas Cal- Mendez, 1979), on the trace of the Calama-Olacapato-El Toro ientes collapse caldera and with the local and regional tectonic Lineament, a major strikeeslip fault system oriented NWeSE and framework. oblique to the NeS tectonics trends of the central (Mon, The relationship between epithermal deposits and collapse 1979; Salfity, 1985). The products of the collapse caldera cover an has been cited for various examples globally, where those area of 1700 Km2, with a late stage of resurgence in the caldera landforms are important structural traps for localization and dis- center that uplifts 1000 m the outcrops of the intracaldera with tribution of ore deposits. In the case of the geological province of respect to outflow caldera . The caldera has 15 km in the Puna, hydrothermal activity hosted in collapse caldera were diameter with the major axis oriented N30E in a left-lateral mentioned for northern Puna (Coira, 1999), but the relationship of transpressive setting (Petrinovic et al., 2010). magmatism and structure of the caldera remains as a matter of In Fig. 1 we summarize the geological background of the area. debate. Regarding the Central Puna (~24S), the first references that Thus, the stratigraphic of the studied area comprises the links the origin of polymetallic veins with posthumous volcanic Neoproterozoic-Lower (marine activities and collapse caldera correspond to Petrinovic (1999) for low grade metasedimentary sequences, Turner, 1960) and a low the Aguas Calientes and to Riller et al. (2001) for the Negra Muerta Paleozoic plutonic-volcano-sedimentary marine sequence calderas. However, studies aimed to understand the relationship (Omarini et al., 1984; Coira et al., 2001; Viramonte et al., 2007). between magmatic and/or collapse caldera event structures Northward of the study area, Cretaceous-Paleocene continental (doming, subsidence, resurgence) and the hydrothermal- sedimentary sequences of the Salta Group crop out (Turner, 1960). mineralization episodes responsible for the Incachule ore district The Cretaceous Pirgua Subgroup is the best exposed unit of the have not yet been done. Salta Group in the area of the Piedra Caída-Cajon creeks (Vilela, The aim of this study is to characterize the mineral association of 1969). To the north and west of the study area, younger continen- the hydrothermal alteration halos and the mineralized zones, to tal sedimentary sequences, the Pastos Grandes Group occurs constrain the main features of the mineralizing fluids, based on (Turner, 1972). Miocene- volcanic rocks of dacitic-andesitic geochemical analyses of fresh and altered rocks and ore minerals, composition, generally showing high contents, crop out as well as on isotopic and fluid inclusions data. We discuss a genetic extensively in the study area. They comprise ignimbrites originated model for the Sb veins mineralization and its relation with the from cerro Aguas Calientes collapse caldera, ignimbrites and caldera collapse and their structure. from central eruptions of Quevar and Tuzgle and Incachule is the first ore deposit in Central Puna for which the volcanic rocks from minor eruptive centers (Petrinovic et al., 1999), genetic linkage with collapse caldera is investigated, thus the un- such as the domes and subvolcanic bodies of Concordia, El Morro, derstanding of the processes that originate this deposit can be Organullo, and Rupasca (Fig.1), with ages ranging between 12.1 and useful to understand the relationship of mineralized systems with 13.5 Ma obtained on biotite using the K-Ar method (JICA, 1993; caldera events or structure in similar mineral ore deposits in the Petrinovic et al., 1999). The latest records of volcanic activity in Central Andes. the area correspond to the monogenetic basaltic centers of the Negro de Chorrillos and San Jeronimo, which were dated (K/Ar

Fig. 1. A- Regional geological map of the study area. Modified from Blasco et al. (1996), Petrinovic et al. (1999), and Petrinovic et al. (2010). N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 241 whole rock) by Aquater (1980) at 0.2 ± 0.08 Ma and 0.78 ± 0.1 Ma, a laminated structure consisting of 2 cm-long sheets (Fig. 2C). respectively, and the explosive rhyolitic centers in with Phyllic alteration affects the Verde , surrounding the ages between 1.15 and 0.5 Ma (Coira and Paris, 1981; Petrinovic and silicic alteration halos as an elliptical zone (Fig. 3H). The alteration Colombo Pinol,~ 2006). is intense to moderate and pervasive. According to Petrinovic et al. (2010) the evolution of the Aguas Argillic alteration is located in the northwest and south borders Calientes collapse caldera comprises two caldera-forming episodes of the phyllic alteration halo. In the field it can be identified by its that occurred at 17.15 Ma and 10.3 Ma. Both caldera collapses are whitish and yellowish colours. This zone shows intense and quite similar in shape, location and characteristics. The 17.5 Ma pervasive alteration (Fig. 3H). produced a thick intra-caldera ignimbrite (Verde Ignimbrite) without an evident and associated extra-caldera facies (Petrinovic 4. Material and methods et al., 2010). At Cerro Verde hill evidence of a local contractions of the caldera moat (tectonic/volcanic resurgence) and postcaldera Fifty five samples were collected in representative outcrops of volcanism can be observed (Fig. 1). hydrothermal altered rocks and mineralized breccias. We per- The 10.3 Ma collapse event (Chorrillos and Tajamar Ignimbrites formed standard petrographical analyses from 38 rock samples and from Petrinovic et al., 2010) was accompanied by base and 15 samples representative of the mineralization to determine li- precious-metal mineralization (Salado Paz, 2014), in a conspicuous thology and the primary and secondary (alteration) mineralogy. volcano-tectonic framework. The veins of Pb-Ag-Zn are hosted in Eight representative samples were chosen for mineralogical study the NNE caldera border and Sb veins crops out near to the oriental by reflectance spectrometry analyses (SWIR) with the equipment caldera border (Petrinovic et al., 2010; Salado Paz, 2014). These PIMA II SP (Portable Infrared Mineral Analizer), which employed veins are posthumous to the last resurgence event (Petrinovic et al., wave lengths between 1200 and 2600 nm, in the SEGEMAR labo- 2010). Both mineralizations are close to each other (~4 Km), so is ratory, Buenos Aires. This methodology is particularly sensitive for suggested that they form part of the same system, formed at minerals that contain certain molecules and radicals, including 2 2 different depths (Coira and Paris, 1981). H2O, OH ,NH3,CO3 ,SO4 , which produce diagnostic absorption features at certain wavelengths in the SWIR spectra (Pontual et al., 3. Geology of the Sb-Au deposits 1997). For the case of ammonium-containing minerals, the spectra have depression in the region between 1900 and 2200 nm The mineralization of the Incachule district occurs in vetiform (Thompson et al., 1999). bodies which strikes between N 290 and N330, are 600 m in The mineralogical composition of the<2 mm sub-fraction was length and have thicknesses between 2.5 and 5 m. This deposit is tested in 8 samples by X-ray diffraction (XRD) using an X'Pert Pro hosted in the 17.3 Ma intracaldera facies (Verde Ignimbrite) and diffractometer (CuKa radiation, 40 kV, 40 mA) (Departamento de also in the younger Chorrillos and Tajamar ignimbrites (10.3 Ma) Físico Química, UNC, Argentina), and a PANalytical X'Pert Pro (Fig. 2A). diffractometer (CuKa radiation, 45 kV, 40 mA) equipped with an The intra-caldera rocks show hydrothermal alteration associ- X'Celerator solid-state linear detector (Department of Mineralogy ated with the mineralization, evidenced by light colours and the and Petrology, University of Granada). Clay sub-samples (<2 mm) presence of veinlets on fracture planes. The mineralization is placed were prepared in accordance with the guidelines of Moore and between the eastern collapse rim and the resurgent dome of the Reynolds (1997). Afterwards, four representative samples (I 12B, I last caldera cycle (Fig. 2B); there are no outcrops westward of the 30, I8, I31A), were chosen for detailed study with a scanning elec- resurgence that attested the continuity of the mineralization to the tron microscopy (SEM), employing polished thin sections using western caldera rim. The geothermal system that produced the back-scattered electron imaging and X-ray dispersive (EDS) anal- mineralization is still active, it has migrated southward given place ysis carried out with a ZEISS DSM 950 equipment (Scientific In- to the present Incachule geothermal field, that depicts similar strument Centre, University of Granada, CIC) and Thermo Electron characteristics than the old one (Fig. 2C). This is particularly evident NORAM NSS-100 (LaSem Universidad Nacional de Salta). Moreover, from the observation of a deep negative gravimetric anomaly five samples representative of the mineralized zones were studied (12Mgal), close to the present geothermal field (Gotze€ et al., 1988). with a JEOL superprobe JXA-8230electron probe micro analyser Two types of mineralization have been distinguished: 1- (EPMA) (Instituto de Geociencias,^ Universidade de Brasília). Mineralized hydrothermal breccias (Fig. 3A and B). 2- Quartz with Atomic concentration ratios were converted into formulae ac- sparse mineralization, stockworks formed by veinlets of sulfurs cording to stoichiometry. Accordingly, the structural formulae of inside the silicificated wall rock (Fig. 3C and D). The hydrothermal dioctahedral micas and illite/smectite mixed-layers were calculated breccias are the mineralized structure most important, where the on the basis of 22 negative charges (O10 (OH)2). In the cases of sulfurs minerals are disseminated in the matrix. The zone of sulfates-phosphates structural formulae were calculated on the stockworks mineralization and veinlets are near to the mineralized basis of 11 negative charges ((O4)2 (OH) 6). bodies breccias. Both mineralization styles are composed of pure Chemical analyses of major, minor and trace elements were stibnite, arsenical pyrite, marcasite and pyrite in a gangue of quartz performed for twenty two rock samples from hydrothermal alter- and chalcedony with breccia, massive, lattice bladed and colloform ation and mineralized zones with FRX and ICP-MS and acidic textures (Fig. 3E, F and 3G). digestion for the metals at ACMELABS laboratories (Canada). In The hydrothermal alteration zones around the veins are present order to study the mobility of elements during the alteration pro- in an area a 7 by 2.5 km direction N-S elongated band (JICA, 1993; cesses and to identify the elements that could be used as path- Zappettini, 1999; Salado Paz, 2014). Three halos of hydrothermal finders of Au anomalies; we compared our results with previous alteration could be distinguished: silicic, phyllic and argillic analyses of unaltered Verde and Tajamar ignimbrite from Petrinovic (Fig. 2A). Silicic alteration affects the and the pyroclastic et al. (1999). dykes of the Verde ignimbrite and also the pyroclastic dykes of the A total of 163 microthermometric analyses on fluid inclusions in Chorillos ignimbrite. The alteration reaches up to 15 m in thickness, quartz from the mineralized veins were performed on four selected from mineralized veins to wall rock, making the wall rock highly rocks using a Linkam fluid inclusion cooling-heating stage at the competent (Fig. 3A and B). Moreover, siliceous sinter up to 20 cm in Fluid Inclusion Laboratory of the Universidad Nacional del Sur, thickness crops out close to the mineralized zone. The sinter shows Bahía Blanca, Argentina. 242 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

Fig. 2. A- Geological map of the area of Incachule mine depicting the hydrothermal alteration zones. The silicic zone is very small and could not be represented in this scale. B- Cross section W-E and relationship between epithermal breccias, dome resurgence and edge collapse caldera C- Cross section N-S from Incachule mine area, indicating the outcrops from fossil and actual sinters.

Sulfur isotopic compositions were determined on handpicked Schumacher (1975). The age calculations were based on the con- sulfides at the Geochronology Laboratory of the Institute of Geo- stants recommended by the IUGS quoted in Steiger and Jager€ sciences, University of Brasilia, by LA-MC-ICP-MS (Laser Ablation- (1977). Potassium was determined in duplicate using a BWB XP Multi Collector-Inductively Coupled Plasma Mass Spectrometry). flame photometer. The samples were dissolved in a mixture of HF In order to determine the structural controls on hydrothermal and HNO3 according to the technique of Heinrich and Herrmann alteration and mineralized zones we collected structural data in (1990). The analytical error for the K/Ar age calculations is given fault veins of hydrothermal breccias in a total of 40 stations and in on a 95% confidence level (2s). stockwork veins. In the first case, two types of data were obtained: a-faults with kinematic indicators (fault plane, dip, slickensides and 5. Results step), and b-faults without kinematic indicators (fault plane and dip). For vein stockworks, we measured average thickness, strike 5.1. Petrography and mineralogy of hydrothermal alteration and dip. Stereonet (Allmendinger, 2002) and FaultKinwin freewere package were used for the interpretation of statistical data 5.1.1. SEM and optical microscopy (Allmendinger, 2001). Four volcanic rocks, representative of the silicic alteration (I30, K/Ar ages were determined on <2 mm size fractions at the I31A), phyllic to argillic transition alteration (I12B) and argillic Geoscience Centre of the University of Gottingen€ by the following alteration zones (I8) were studied with SEM and optical procedure: The argon isotopic composition was measured in a microscopy. Pyrex glass extraction and purification line coupled to an ARGUS VI Sample I30 contains primary of potassium multi-collector noble gas mass spectrometer operating in static and biotite, strongly replaced by secondary phases and showing mode. The amount of radiogenic 40Ar was determined by isotope abundant dissolution voids. Potassium feldspar is replaced by illite/ dilution method using a highly enriched 38Ar spike from smectite mixed-layers (I/S) or, less frequently, by micron-scale N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 243

Fig. 3. A-Outcrops of hydrothermal breccias. B- Hydrothermal breccia with altered clasts and chalcedonic matrix. C- Outcrops of disseminate veins. D- Stibnite crystal from disseminate veins. E-Texture lattice bladed in quartz from vein. F- Stibnite crystal in colloform quartz texture. G- Pure crystal of stibnite in massive quartz texture. H- Hydrothermal alteration in host rocks. intergrowths of I/S and kaolinite. It could also depict replacement the interlayer sites of I/S. Pyrite and rutile occurs as anhedral in- by quartz in the borders and overgrowth of secondary potassium clusions in altered phenocrysts. Minor tiny euhedral or anhedral Fe feldspar. Biotite is mostly replaced by I/S and secondary potassium sulfates-phosphates (destinezite?), depicting some substitution of feldspar (Fig. 4B and C), I/S and kaolinite frequently occur as P and/or S for As, also occur as secondary phases (Fig. 4B and C). irregular laths, up to 10 mm long, with open spaces between them, Sample I31A depict a pervasive replacement by secondary quartz, and radial morphology (Fig. 4A and B). K is the prevailing cation in chalcedony and adularia. The primary mineralogy is no longer 244 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

Fig. 4. BSE images (A-C and F-I), optical microscopy (DeE) and SE (J, K) BSE images (AeI) and SEM (J,K) and A-Illite with radial morphology and oxides of Ti inclusion (I30 sample).

B- Biotite replaced by I/S with potassic inclusion (I30 sample). C- Biotite replaced by I/S and potassic feldspars with SO4AsFe inclusions (I30 sample). D- Chalcedony and quartz in pervasive silicic alteration zone (sample I31A). E Rhombic crystals of adulary from silic alteration (sample I31A). F- biotite replaced by Kln þ I/S with TiO2 inclusion

(sample I12). G- Potassic feldespars replaced by Kln þ I/S, with FeO2 inclusion, illite and sulfates (sample I12). H- SO4FePbAs filling void in a rock matrix composed of quartz, potassic feldspar and biotite (sample I12). I- Potassic feldspar fromthe matrix altered to I/S plus kaolinite, patches of secondary FeAsO and sulfates-phosphates are also observed (sample I12). J- Handpicked crystals of jarosite from argillic alteration zone(I8 sample). K- Crystals of alunite from argillic alteration sample (I8 sample). Mineral abreviations: I/S: illite- smectite mixed-layers; Kln: kaolinite. Ox: oxides; Ill: illite; Bt: biotite; Kfs: K-feldespars; Jrs: jarosite; Aln: alunite; Chc: chalcedony; Adl: adulary; Qz: quartz. recognizable, but the volcanic texture is preserved. Quartz and H) and less frequently to quartz. Biotite also depicts abundant chalcedony are abundant, it occurs in grains up to 500 mm in size fractures and open spaces along cleavage planes, and is profusely (Fig. 4D). Adularia conform rhombic crystals up to 25 mm in size and altered to micron-scale intergrowths of kaolinite and I/S (Fig. 4F). also constitute veins and veinlets (Fig. 4E). The rock presents veinlets and fractures filled with complex as- Sample I12B is composed by phenocrysts of biotite and potas- semblages of sulfates, phosphates, arseniates and zoned oxides sium feldspar and accessory in a groundmass replaced by indicating successive and sometimes cyclic changes in fluid phyllosilicates. Potassium feldspar crystals show abundant frac- composition (Fig. 4G, H and I). The zones that appear whitest in BSE tures and are pervasively altered to kaolinite or to micron-scale images are those showing the highest lead contents in EDS. Rutile intergrowths of kaolinite and I/S, but also to illite (Fig. 4F, G and and iron oxides, and less commonly Fe-As oxide and scarce As-Ce N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 245 phosphate were also identified. These phases also occur as thin 5.1.3. Mineral composition coatings around primary crystals, rimming voids, forming irregular The I/S from silicic halo (I30) depicts higher substitution along patches, as well as disseminated or depicting dendritic textures in illitic and Tschermack compositional vectors than in the sample the groundmass, in close association with phyllosilicates (Fig. 4H corresponding to the phyllic alteration halo (I12B). In both cases K is and I). the prevailing cation in the interlayer site, with minor Na and Ca Sample I8 is entirely composed by secondary minerals such as (Table 2). Many analyses show high Al and low K contents, probably opale, jarosite and alunite. The jarosite and alunite occur in fine- due to contamination resulting from fine intergrowths of I/S and grained euhedral and subhedral crystals associated with kaolinite kaolinite below the resolution of the EDS. On the other side, sample (Fig. 4 J and K). I12B contains secondary illite in addition to I/S, the two phases depict a clear contrast in compositional diagrams, as illite shows less illitic and less Tschermack substitution than I/S (Fig. 5). The EDS analyses for sulfates from phyllic alteration halo (I12B) 5.1.2. Clay minerals and associated secondary minerals indicate intermediate members of the alunite supergroup depicting The clay minerals assemblages occurring in the different alter- chemically variable zones that frequently are too thin to be ation zones were studied by SWIR, XRD and SEM, results are shown analyzed individually with the EDS. The analytical results agree, in Table 1. within reasonably limits, with the general formula for this super- The clay minerals identified in the argillic alteration halo were group: DG3(TO4)2(OH,H2O)6 (Jambor, 1999), In this case D is occu- kaolinite þ I/S associated with alunite, jarosite, and opale. Ac- þ þ pied by K and minor Na, and divalent Pb, G is typically A13 or Fe3 , cording to XRD data in most of the samples kaolinite and I/S are in þ þ þ and T is S6 ,P5 or As5 . A substantial part of the analysis corre- similar proportions in the clay fraction XRD, although less spond to the plumbojarosite-jarosite family, the hinsdalite-corkite frequently it only contains, kaolinite (samples I 24, I38, I34). The series or the beudantite group (Table 2), but others depict com- SWIR study identified reflection in 1461 nm indicating alunite plex chemical composition corresponding to intimate mixtures or containing ammonium ions in some samples (I7, I8) (Godeas, 2010). solid solutions among more than two compositional end-members. The phyllic alteration halo is characterized by a clay assemblage of illite þ (I/S) þ smectite, associated with pyrite and quartz (I17, I19A, I26, I27, I20, I12). The reflections of I/S in the region between 5.2. Geochemistry of the wall rock 16 and 172q in XRD patterns indicate R1 order and illite contents of 60e75%, depending of the sample (Moore and Reynolds, 1997). All the rocks in the mineralized area are altered to a variable Some samples from silicic alteration halo present kaolinite (I30, degree, so in order to analyze the mobility of elements during the I31A) associated with quartz and adularia. The SWIR study also hydrothermal alteration we included in the plots representative identified reflections in 1912, 2013 and 2112 nm indicating the analyses of unaltered rocks from two caldera cycles taken from presence of buddingtonite (I33, I29) and reflections in 1554, 1410, Petrinovic et al. (1999) (Table 3). 2180, 2228 nm indicating illite (I9) with ammonium ions (peaks in The unaltered rocks plot within the and / 1912 and 2013 nm), (Pontual et al., 1997). dacites fields in the diagram of Winchester and Floyd (1977)

Table 1 Mineralogy of altered rocks based on XRD, SWIR, and SEM-EDX studies. 246

Table 2 Structural formulae for illite, I/S, kaolinite, intergrows of illite plus kaolinite, and sulfates according to EDX data.

illite illite illite illite illite illite I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S I/S

Si 3,31 3,28 3,30 3,24 3,27 3,23 3,25 3,52 3,46 3,49 3,25 3,30 3,17 3,23 3,33 3,51 3,40 3,51 3,53 3,50 3,51 3,47 3,48 3,46 3,48 AlIV 0,69 0,72 0,70 0,76 0,73 0,77 0,75 0,48 0,54 0,51 0,75 0,70 0,83 0,77 0,67 0,49 0,60 0,49 0,47 0,50 0,49 0,53 0,52 0,54 0,52 AlVI 1,82 1,88 1,76 1,87 1,87 1,88 1,93 1,69 1,64 1,71 1,90 1,90 1,95 1,87 1,88 1,69 1,70 1,66 1,68 1,69 1,61 1,66 1,67 1,74 1,69 Fe 0,11 0,09 0,15 0,11 0,11 0,08 0,11 0,17 0,18 0,15 0,14 0,12 0,14 0,17 0,18 0,14 0,13 0,19 0,17 0,17 0,18 0,18 0,15 0,13 0,16 Mg 0,08 0,05 0,09 0,06 0,05 0,04 0,07 0,18 0,18 0,19 0,05 0,08 0,04 0,04 0,01 0,20 0,24 0,18 0,19 0,19 0,23 0,19 0,21 0,18 0,17 Mn 0,00 0,01 0,01 0,00 0,00 0,02 0,00 0,01 0,01 0,00 0,00 0,00 0,01 0,00 0,01 0,00 0,01 0,00 0,01 0,01 0,01 0,00 0,01 0,00 0,00 .Sld a ta./Junlo ot mrcnErhSine 2(08 239 (2018) 82 Sciences Earth American South of Journal / al. et Paz Salado N. Ti 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,00 0,02 0,01 0,00 0,01 0,00 0,00 0,01 0,01 0,02 0,00 0,00 0,00 0,00 0,01 0,02 0,00 0,00

S oct. 2,01 2,04 2,02 2,04 2,03 2,01 2,11 2,04 2,03 2,06 2,08 2,11 2,13 2,08 2,07 2,03 2,10 2,03 2,03 2,05 2,04 2,04 2,07 2,06 2,03 K 0,66 0,58 0,65 0,59 0,64 0,73 0,45 0,54 0,57 0,51 0,46 0,32 0,43 0,47 0,48 0,53 0,49 0,56 0,51 0,53 0,59 0,54 0,51 0,52 0,54 Na 0,01 0,03 0,03 0,02 0,02 0,03 0,01 0,01 0,00 0,00 0,01 0,02 0,00 0,01 0,01 0,02 0,02 0,00 0,00 0,00 0,00 0,00 0,01 0,01 0,00 Ca 0,03 0,03 0,03 0,04 0,02 0,02 0,02 0,01 0,02 0,01 0,03 0,05 0,03 0,04 0,01 0,02 0,01 0,02 0,03 0,00 0,01 0,02 0,00 0,01 0,04

S int. 0,74 0,67 0,74 0,69 0,70 0,79 0,49 0,55 0,61 0,52 0,54 0,44 0,49 0,56 0,51 0,58 0,53 0,59 0,57 0,54 0,61 0,59 0,52 0,54 0,61

I/S I/S I/S Kln Kln Kln Kln Kln Kln Kln Kln I/S þ Kln I/S þ Kln I/S þ Kln I/S þ Kln I/S þ Kln I/S þ Kln I/S þ Kln I/S þ Kln

Si 3,52 3,45 3,51 3,23 3,22 3,12 3,12 3,23 3,22 3,24 3,18 3,28 3,23 3,27 3,27 3,28 3,16 3,23 3,13 AlIV 0,48 0,55 0,49 0,77 0,78 0,88 0,88 0,77 0,78 0,76 0,82 0,72 0,77 0,73 0,73 0,72 0,84 0,77 0,87 AlVI 1,67 1,75 1,71 2,14 2,14 2,06 2,04 2,04 2,12 2,15 2,20 2,06 2,09 2,04 2,06 1,98 2,14 1,90 1,94 Fe 0,14 0,12 0,13 0,10 0,08 0,19 0,22 0,17 0,11 0,06 0,05 0,10 0,08 0,09 0,10 0,13 0,08 0,18 0,21 Mg 0,18 0,19 0,18 0,01 0,02 0,02 0,01 0,03 0,02 0,04 0,00 0,05 0,04 0,06 0,04 0,06 0,01 0,13 0,11 Mn 0,00 0,00 0,00 0,01 0,00 0,00 0,01 0,00 0,00 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,01 0,00 0,00 Ti 0,00 0,00 0,01 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,00 0,01 0,00 0,00 0,01 0,00 0,00 0,00 0,00

S oct. 2,01 2,06 2,03 2,24 2,23 2,28 2,27 2,24 2,25 2,24 2,24 2,22 2,22 2,20 2,21 2,18 2,24 2,21 2,26 K 0,54 0,49 0,53 0,02 0,06 0,04 0,06 0,01 0,02 0,04 0,05 0,04 0,10 0,14 0,08 0,18 0,13 0,25 0,15 Na 0,03 0,01 0,00 0,01 0,01 0,00 0,02 0,02 0,01 0,01 0,01 0,03 0,00 0,00 0,01 0,01 0,00 0,00 0,00 Ca 0,03 0,03 0,03 0,02 0,02 0,01 0,00 0,02 0,01 0,01 0,01 0,02 0,03 0,02 0,03 0,03 0,01 0,02 0,02

S int. 0,64 0,54 0,57 0,06 0,10 0,07 0,08 0,07 0,05 0,07 0,08 0,12 0,16 0,19 0,14 0,24 0,14 0,27 0,20

Formulae Pb-Jrs Hinsdalite-corkite Beudantite?

(n:6) (n:4) (n:3) e 260

D Kþ 0,05 0,02 0,13 2 0,53 1,25 0,74 Na 0,00 0,01 0,01 Mg 0,01 0,01 0,03 Pb Mn 0,00 0,00 0,00

G Al 0,04 1,82 0,09 3þ Fe 2,90 0,34 2,85 Ti 0,00 0,01 0,00 þ TS6 1,96 1,30 1,09 þ 5P 0,01 0,65 0,03 þ As5 0,03 0,04 0,42 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 247

Fig. 5. Compositional diagrams for micaceous phases. Red circles: sample I30, yellow crosses: sample I12B. Mineral abreviations: I/S: illite-smectite mixed-layers; Kln: kaolinite. Composition expressed in atoms per formula unit (a.p.f.u). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

(Fig. 6A). The altered rocks plot within rhyodacite/ and The alteration index AI ¼ 100*(MgO þ K2O)/ rhyolite fields showing similar or higher SiO2 contents than the (MgO þ K2O þ Na2O þ CaO) defined by Ishikawa et al. (1976), unaltered rocks (Fig. 6A). quantifies K or Mg enrichment or depletion relative to Ca and Na. Normalized rare earth elements (REE) patterns of unaltered The AI increase as a result of formation of K feldspars and/or K rocks are characterized by an enrichment of LREE and relatively flat phyllosilicates (muscovite or illite), and decrease due to calcareous HREE patterns. Such features are common in calc-alkaline rocks of alteration. In the other hand, the carbonate-chlorite-pyrite index the Andes. Altered rocks depict similar REE patterns, although, they CCPI ¼ 100*(MgO þ FeO)/(MgO þ FeO þ Na2O þ K2O) from Large show slight depletion in LREE and stronger depletion in HREE et al. (2001), measures total alkali depletion, relative to Mg and (Fig. 6B) relatively to fresh volcanic rock. Fe enrichment associated with formation of secondary chlorite, Unaltered rocks show negative correlations between CaO, Fe2O3, pyrite, dolomite or siderite. Na2O, MgO and SiO2 in Harker plots, and positive correlations be- The unaltered volcanic rocks (first and second collapse caldera tween K2O and SiO2, all typical of magmatic differentiation trends. event) have AI values between 40 and 60 and CCPI values between The altered rocks show more scattering in Harker plots, suggesting 40 and 60 reflecting high primary concentrations of alkalis, Fe and element mobility, although broad negative correlations between Mg. On the other hand, the altered rocks have AI > 90 and CCPI <40, Fe2O3,Al2O3, MgO and SiO2 and positive correlations between K2O the trend showed by these rocks is consistent with the alteration of and SiO2 could be observed. Na2O shows a slight negative corre- mafic minerals (mainly biotite) and and the formation lation with SiO2, whereas CaO and SiO2 show no correlation (Fig. 6 of secondary K-micas (illite-muscovite, I/S) and K-feldspars C). (adularia) (Fig. 7A). Combining the AI index defined by Ishikawa et al. (1976) with In order to compare base and transition metal concentrations the carbonate-chlorite-pyrite index from Large et al. (2001) in a between unaltered and altered rocks, metal abundances were boxplot allows the recognition of the main minerals that were plotted against K2O contents, as the geochemistry of the altered respectively destroyed and formed as a result of the hydrothermal rocks suggest that the hydrothermal fluids associated with the process. These indices were used in some massive sulfur ore de- mineralization have high concentration of K2O. The concentrations posits and were also applied in epithermal ore deposits (Gemmell of base metals (Pb, Zn) are noticeably lower in the altered rocks and Large, 1992; Gemmell, 2007). from the Incachule ore deposits than in the fresh volcanic rocks Table 3 248 Geochemical analysis of major, minor and trace elements of altered and unaltered rocks. Concentration of trace elements expressed in ppm.

Sample *9173 *891114 *9243 *941207 *941209 *941210 *941214 *89114 *891113 *941212 *9175 *9178 *941211 *941216 *941217 *941218 I1

Wt% SiO2 66,22 66,42 64,99 65,32 65,21 64,47 66,43 64,97 67,17 63,71 65,86 62,25 65,98 65,97 66,1 66,96 70,69 TiO2 0,61 0,56 0,69 0,64 0,72 0,74 0,69 0,62 0,58 0,69 0,61 0,7 0,62 0,71 0,76 0,66 0,65 Al2O3 15,98 16,07 15,76 16,16 16,49 16,11 15,89 15,89 15,65 17,37 15,97 17,05 16,29 15,84 15,7 16,26 15,02 Fe2O3 4,58 4,22 4,73 4,75 5,08 5,17 5,17 4,78 4,3 4,95 4,45 5,06 4,46 4,95 5,04 4,14 1,01 MnO 0,06 0 0 0,06 0,09 0,01 0,04 0,04 0 0,04 0,05 0,06 0,03 0,04 0,04 0,02 0,01 MgO 3,05 1,73 2,52 2,37 0,96 2,69 1,41 2,37 1,68 2,05 2,22 2,63 1,88 2,78 2,7 2,41 0,31 CaO 2,74 3,41 4,35 3,85 4,2 3,89 2,99 3,57 2,86 3,88 3,4 4,94 3,38 2,74 2,68 2,66 0,14 Na2O 2,6 3,11 2,91 3,08 3,05 2,96 2,73 2,96 2,59 3,19 3,15 3,24 2,97 2,96 2,83 2,81 0,28 K2O 3,98 4,3 3,77 3,52 3,95 3,7 4,37 4,54 4,98 3,88 4,02 3,8 4,15 3,77 3,9 3,84 7,98 P2O5 0,18 0,17 0,27 0,25 0,25 0,26 0,27 0,26 0,19 0,24 0,26 0,28 0,24 0,24 0,25 0,25 0,07 Total 100 99,99 99,99 100 100 100 99,99 100 100 100 99,99 100 100 100 100 100,01 99,86 .Sld a ta./Junlo ot mrcnErhSine 2(08 239 (2018) 82 Sciences Earth American South of Journal / al. et Paz Salado N. ppm As 8,16 20,4 15,7 22,3 11,4 10,3 15,1 3,33 4,48 890,1 Ba 589 604 575 556 589 562 525 664 629 612 550 574 591 545 584 654 682 Be 4,72 4,95 5,83 3,35 3,15 3,08 2,88 6,34 5,2 3,98 6,14 5,7 3,38 3,46 2,23 1,17 2 Bi 0,3 0,03 0,03 0,65 0,36 0,3 0,13 0,02 0,09 0,2 Cd 0,19 0,35 0,19 0,22 0,29 0,2 0,12 0,16 0,18 0,1 Co 47,7 28,4 32 46,7 29,7 25,6 19,6 56 39,6 34,5 36,5 43,6 24,8 22,8 19,1 31,2 0,5 Cr 67,4 68 74,8 80 86,5 81,2 75,4 70,8 65,9 129 67,6 90,3 71,5 73,5 70,6 77,4 Cs 18,3 17 22,7 9,54 78,6 9,8 10,8 11,1 7,93 62,5 Cu 14,4 53,8 20,5 12,7 10,5 19,2 10,8 16,5 97,6 23,4 18 15,1 3,91 12,5 12,2 9,9 3,6 Ga 21,6 22,3 21 21,7 23,8 22,1 20,9 21 21,3 20,6 Ge 1,5 2,05 1,64 1,36 1,43 1,69 1,41 1,55 1,37 Hf 4,31 4 4,55 3,97 4,36 4,7 3,79 4,33 5,09 4,2 In 0,05 0,05 0,05 0,05 0,05 0,04 0,05 0,04 0,04 Mo 1,35 2,53 2,33 1,9 11 3,91 2,27 2,29 3,3 1,1 Nb 16,7 16,7 16,9 15,6 16,2 16,3 15,6 18,9 17,1 16,7 17,9 16,6 16,3 15,7 17,2 16,7 16,4 Ni 22,5 30,5 12,5 27,3 30,4 25,8 27,6 25,1 18,3 59,2 11,3 15,7 25,8 25 24,3 30,7 1,3 Pb 26,9 25,2 22,2 22,6 22,1 23 23,3 24,1 31,8 5,3 Rb 171 191 178 159 182 171 188 220 235 193 183 172 203 162 167 174 543,3 Sb 0,72 0,42 0,28 1,76 1,03 1,82 0,61 0,57 0,29 9,6 Sn 4,12 2,76 2,85 3,18 4,16 3,81 3,02 2,14 2,6 4 Sr 231 305 332 299 298 299 269 307 248 323 265 329 268 257 229 218 136,2 Ta 2,77 2,43 2,29 2,16 2,52 2,31 2,3 2,2 1,94 1,3 Th 14,7 15,8 16,3 15,4 16,1 17,4 17,5 16,2 16,8 12,1

U 5,68 6,22 7,15 4,62 6,75 7,93 6,28 6,68 6,25 8,8 e V 98,1 89,9 112 91,8 89,3 101 72,8 109 90,8 97,1 96 113 83,9 102 92 101 87 260 Y 19,3 20,6 16,6 20,87 20 20,6 18,6 22,9 22,5 19,7 20,7 18,7 21,5 17,7 19,8 25,3 9,8 Zn 56,4 70,9 60,2 79,7 74,4 65,3 65,7 78,8 39,5 61,3 77,5 88,8 55,8 47 60 64,1 3 Zr 146 181 150 160 146 166 146 207 165 162 200 159 165 134 161 191 141,8 La 37,6 40,66 42,76 35,49 40,51 41,99 35,67 44,61 40,44 37,26 43,24 39,3 41,21 37,94 38,67 46,55 24,4 Ce 71,7 77,9 79,8 68,6 74,3 79,3 69,1 86,5 77,7 73 82,6 74,5 81,2 71 75,3 90,8 49,3 Pr 7,95 8,59 8,29 7,57 8,16 8,51 7,57 9,44 8,8 7,95 8,95 7,89 8,9 7,91 8,23 10,04 5,57 Nd 28,43 31,85 29,76 27,58 29,08 30,08 27,4 34,33 31,5 29,57 32,32 29,92 32,19 27,65 30,41 36,79 21,3 Sm 5,47 6,07 5,42 5,34 5,45 5,56 5,32 6,43 5,75 6,01 6,06 5,26 5,94 5,47 5,84 7,1 3,4 Eu 1,26 1,42 1,28 1,27 1,25 1,26 1,2 1,34 1,26 1,3 1,3 1,34 1,28 1,14 1,22 1,52 0,85 Gd 4,44 4,65 4,16 4,4 4,22 4,54 4,16 5,55 4,59 4,57 4,61 4,21 4,7 4,21 4,65 5,76 1,98 Tb 0,63 0,68 0,57 0,66 0,61 0,66 0,62 0,75 0,71 0,64 0,74 0,64 0,69 0,59 0,66 0,85 0,32 Dy 3,65 3,77 3,2 3,66 3,61 3,43 3,34 4,26 4 3,67 3,86 3,41 3,9 3,34 3,85 4,6 1,44 Ho 0,71 0,77 0,65 0,75 0,71 0,72 0,67 0,83 0,79 0,72 0,81 0,67 0,8 0,68 0,75 0,93 0,28 Er 1,79 1,84 1,59 1,95 1,76 1,8 1,74 2,17 1,97 1,86 1,99 1,79 1,94 1,73 1,92 2,37 0,88 Tm 0,27 0,3 0,28 0,3 0,26 0,29 0,26 0,32 0,32 0,27 0,34 0,28 0,28 0,27 0,29 0,38 0,12 Yb 1,75 1,94 1,73 1,98 1,71 1,92 1,77 2,36 2,03 2 2,14 1,79 2,01 1,92 2,07 2,51 0,89 Lu 0,27 0,29 0,25 0,29 0,28 0,28 0,26 0,3 0,32 0,28 0,32 0,26 0,31 0,27 0,3 0,35 0,13 Au 2,1 Ag 300 Tl 2,2 ^ 0 ^ 0 Sample I9A I7A I24 I19A I12A I12B I20 I26 I30 I38 IS CV2 I34 Wt% SiO2 73,43 72,76 74,71 69,93 71,59 65,31 70,08 67,82 71,13 67,71 61,21 59,1 65,93 TiO2 0,5 0,48 0,72 0,64 0,57 0,79 0,58 0,74 0,57 0,73 0,68 0,58 0,76 Al2O3 12,86 12,27 15,59 14,46 12,67 16,7 13,95 16,21 13,92 16,38 15,41 13,81 16,98 Fe2O3 1,42 1,96 1,45 1,84 3,09 2,63 2 1,6 1,73 2,08 5,36 4,3 2,56 MnO 0,01 0,02 0,01 0,01 0,01 0,01 0,01 0,01 0,01 0,01 0,07 0,1 0,01 MgO 0,81 1,22 0,11 0,57 0,93 1,05 0,4 0,77 0,57 0,57 2,5 3,17 0,94 CaO 0,08 0,16 0,33 0,06 0,29 0,42 0,28 0,11 0,07 0,11 4,48 5,16 0,41 Na2O 0,2 0,2 0,04 0,42 0,41 0,52 0,32 0,57 0,39 0,59 2,47 1,82 0,5 K2O 7,56 8,31 7,23 8,2 5,13 7,66 7,14 8,28 8,54 7,65 3,58 3,12 7,06 .Sld a ta./Junlo ot mrcnErhSine 2(08 239 (2018) 82 Sciences Earth American South of Journal / al. et Paz Salado N. P2O5 0,12 0,07 0,21 0,07 0,17 0,12 0,15 0,18 0,12 0,14 0,2 0,24 0,16 Total 99,88 99,86 99,9 99,85 99,85 99,83 99,51 99,86 99,86 99,85 99,81 99,81 99,85 ppm As 169,7 76 3075,5 3124,2 7147,2 540,8 5584,2 495,5 1241 233,2 1,7 31,4 317,5 Ba 543 529 31 638 445 680 546 632 590 676 586 580 634 Be222 2 3 32 233423 Bi 1,3 0,4 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,2 0,1 0,3 0,2 Cd 0,1 0,1 0,1 0,1 0,4 0,1 0,1 0,1 0,1 0,1 0,1 0,1 0,1 Co 3,9 5,7 1,1 1,1 6,4 2,7 2,7 1,5 1,3 1,7 13,3 9,2 3,4 Cr Cs 58,2 75,7 23,8 163,2 181,2 242,8 162 160,7 273,8 158,5 55,5 24,3 174,6 Cu 2,9 6,3 7 5,4 16,2 6,5 7,5 6,7 6 11,6 18,4 12,2 11,5 Ga 16,4 15,2 19,2 20 16,6 21,4 18,1 21,2 19,8 22,4 20,8 27,9 22,5 Ge Hf 3,7 3,4 3,9 4 3,9 4,4 3,4 4,4 4,2 3,8 4,5 3,9 4,4 In Mo 4,6 0,8 1,8 3,8 3,9 0,7 11,3 2,4 4,3 2,3 1 0,3 1,1 Nb 14 13,8 16,2 14,4 12,7 17,3 13,7 16,7 14,7 17,4 16,5 14,2 18,3 Ni 7,8 12,1 4,1 2,7 12,7 6,1 5,8 3 4 4,5 24,8 19,3 8,4 Pb 8,9 3,9 12,9 11,4 57,7 9,2 8,5 7,9 5,9 9,5 3,7 21,1 10,7 Rb 463,5 545,6 23,3 534 363,6 586,4 440,3 573,8 619,1 575,9 182,7 142,4 489 Sb 6,1 2,4 268,5 38,5 97,7 18,7 2000,0 20,1 44,3 18,5 0,4 0,3 9,8 Sn235 5 2 34 333323 Sr 54,4 58,4 39,7 106,5 46,9 67,4 58,1 63,7 54,3 66,6 345 277,7 68

Ta 1,4 1,3 1,4 1,3 1,1 1,5 1,2 1,5 1,3 1,6 1,3 1,3 1,4 e 260 Th 13,2 13,2 12,9 11,6 11,6 13,6 10,5 15,5 13,2 16 14,3 14,4 16,3 U 6,2 5,3 5,6 4,3 8 7 3,9 5,5 10 9,8 5,6 5,3 6,3 V 72 78 91 95 84 114 88 107 77 108 100 79 105 Y 13,2 11,5 8,8 11,6 10,5 11,4 11,1 11,2 11,8 12,5 20,2 16,4 13,6 Zn 14 23 22 8 53 27 6 7 4 6 72 70 23 Zr 126,4 124,1 139,4 130,4 130,9 146,2 117,4 146,8 135,4 146,5 133,9 129 153 La 30,3 28,6 25,5 30,6 28,1 27,1 30,9 29,4 28,4 30,3 35,3 32,5 37,8 Ce 59,3 55 48,3 56,9 55,8 51,5 60,1 56,6 53,7 60,7 70,2 66 76,1 Pr 6,24 5,97 5,12 6,05 6,09 5,76 6,27 6,43 5,5 6,52 7,51 7,09 7,84 Nd 22,7 22,3 18,1 22,5 21,5 21,6 23,7 25,2 20,2 25,5 27,9 24,8 29,2 Sm 3,68 3,6 3,38 4,15 4,17 4,32 4,53 4,94 3,74 4,24 5,04 4,37 4,87 Eu 0,75 0,72 0,95 1 0,91 1,02 1,04 1,07 0,84 1,13 1,19 0,99 1,23 Gd 2,76 2,53 2,33 2,79 2,94 2,99 3,15 3,42 2,61 3,68 4,03 3,94 3,77 Tb 0,44 0,39 0,34 0,45 0,45 0,46 0,49 0,51 0,41 0,49 0,65 0,58 0,52 Dy 2,18 1,86 1,62 2,13 2,1 2,09 2,18 2,29 2 2,53 3,49 3,12 2,75 Ho 0,43 0,36 0,28 0,41 0,36 0,4 0,41 0,39 0,4 0,42 0,68 0,58 0,48 249 Er 1,25 1,06 0,74 1,07 0,97 1,15 1,04 1,11 1,1 1,13 1,88 1,56 1,34 Tm 0,19 0,15 0,12 0,17 0,17 0,18 0,17 0,18 0,19 0,16 0,28 0,23 0,18 (continued on next page) 250 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

(Fig. 7B). The Cu concentration is high in two samples from unal- tered rocks. On the contrary, altered rocks depict higher abun- dances of Tl, As, Sb and Cs than the unaltered rocks. It is remarkable that several altered rocks display gains in Ag and Au.

5.3. Ore mineralization

The opaque minerals identified under the chalcographic mi- croscope were pyrite, arsenian pyrite, stibnite and marcasite. These minerals occur in veinlets as stockworks and as massive accumu- lations in the cement of hydrothermal breccias. Microscopically fine grained sulfide minerals occur as discrete aggregates in the matrix of the silicified breccia clast. Averages of mineral compositions are given in Table 4. Stibnite is the most abundant ore mineral, it forms euhedral crystals up to 3.5 cm in size and subhedral to anhedral crystals of variable sizes (between 100 and 300 mm) but always show larger grain sizes than the other sulfides (Fig. 8 A, B). Pyrite occurs in tiny euhedral crystals up to 20 mm(Fig. 8 C, D), as small inclusions in biotite (Fig. 8 E), as anhedral mosaic, and forming veinlets in the breccia cement and silicified breccia clast. Arsenical pyrite occurs scarcely as anhedral disseminated crystals in the breccia cement and forming veinlets (Fig. 8 F). The veins are characterized by high contents of Sb, As and Tl, and intermediate contents of Ag, Pb-Zn-Cu and traces of Au. Whereas, hydrothermal breccias in some cases depict high Ag/Au ratios (Table 5). Some samples from stockworks (I30v) and hydrothermal breccia (I12v) have higher Cu-Pb-Zn concentration compare with other samples.

5.3.1. Fluid inclusions Microthermometric measurements were done in quartz veinlets associated with the mineralization. The studied fluid inclusions consist of primary biphasic inclusions (liquid þ vapor), with pre- dominant liquid phase, showing ovoid, irregular and regular shapes, less than 15 mm in size. Homogenization temperatures ranging from 125 to 189 C, with an average of 157.64 C, and freezing temperatures from 0.8 to 2.4 were determined. Fluid salinities between 1.5 and 4.5 wt% NaCl equivalent where estimated for the inclusions showing the lower freezing temperatures, from last ice melting temperatures using the equations of Bodnar (1993), whereas a mode salinity of 1.5 wt% NaCl equivalent was obtained (Table 6).

5.3.2. Sulfur isotopes Sulfur isotopic compositions were measured in hypogene stib- nite, pyrite, and arsenopyrite, free of mineral inclusions, from the veins and hydrothermal breccias. The range of d34S obtained, from 7.10e2.88‰ (Table 7), is compatible with a magmatic source for d34

I24 I19A I12A I12B I20 I26 I30sulfur (Ohmoto I38 and IS Rye, 1979). CV2 The S I34 values of the ore-forming fluid, 3.04 to þ0.72‰, was calculated from the d34S values of the sulfide minerals for which the appropriate temperature of forma- tion were reasonably estimated by fluid inclusion data employing 0 ^

A the empirical equation from Ohmoto and Rye (1979). I7 5.4. Structural analysis

The major mineralized structures are the hydrothermal-breccias 0 ^ A emplaced along the strike slip faults, having a northwest trending ) (N330) with left-lateral component and 50 to 80 dip. However, some faults have E-W trending with high dip angle (80-90: I42, I47). Just a few are located on normal faults with a strike slip continued ( component (P63, I49, I46) and NW-SE, E-W or NE-SW trend (Fig. 9). The hydrothermal-breccia veins form mineralized lenticular Sample I9 YbLuAuAgTl 1,25 0,19 7,9 100 1,09 0,9 0,17 0,9 10 0,8 0,8 0,12 0,5 10 1,12 2,7 0,16 9,5 200 1,1 3,1 0,17 1,5 10 1,2 0,17 5,8 0,5 0,15 10 1,09 0,8 0,5 0,17 10 1,16 9,5 0,9 0,17 1,2 10 1,1 0,16 11,7 1,07 400 4,8 0,27 1 1,69 10 2,2 0,23 1,49 0,5 10 0,2 0,16 1,22 0,5 100 0,1 0,6 10 0,7 Table 3 Ridgway et al., 1990 bodies with quartz and laminated chalcedony, commonly separated N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 251

Fig. 6. Major and trace elements data for altered (triangle) and unaltered whole rocks of the Cerro Aguas Calientes collapse caldera, first collapse event (square) and second collapse caldera (rhombus). A- Total silica versus Zr/TiO2 diagram (Winchester and Floyd, 1977). B- Spider diagram for rare earth elements. C-Harker variation diagrams showing the variations of major and trace elements of altered and unaltered rocks of Cerro Aguas Calientes collapse caldera. 252 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

Fig. 7. A- AI vs CCPI binary diagram, discriminating altered rocks from Incachule mine from the least altered ignimbrite host rocks. B-Cu, Sb, Pb, Cs, Zn, As, Ag, Au, Tl contents versus

K2O variation diagrams. N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 253

Table 4 Compositions of stibnite and pyrite according to EMPA.

Element(Wt%) Stibine n:54 Pyrite n:50

Average Maximum Minimum Average Maximum Minimum

As 0,22 0,57 0,10 1,17 15,10 0,00 S 28,23 29,40 26,51 50,01 54,00 37,40 Bi 0,06 0,17 0,00 0,11 0,21 0,02 Ag 0,01 0,07 0,00 0,01 0,05 0,00 Fe 0,02 0,11 0,00 45,24 47,07 36,31 Co 0,01 0,05 0,00 0,05 0,11 0,01 Ni 0,01 0,05 0,00 0,01 0,04 0,00 Cu 0,01 0,05 0,00 0,01 0,04 0,00 Zn 0,01 0,06 0,00 0,01 0,05 0,00 Sb 71,95 74,25 69,02 0,11 0,69 0,00 Cd 0,01 0,05 0,00 0,01 0,04 0,00 Au 0,00 0,00 0,00 0,00 0,00 0,00 Pb 0,01 0,09 0,00 0,01 0,06 0,00 Total 100,55 103,26 97,00 96,73 101,28 74,99

Fig. 8. Chalcographic photomicrographs of the main ore minerals. A- Euhedral crystal of stibnite (10X). B- Anhedral crystal of stibnite (20X). C- Small crystal of pyrite as anhedral mosaic (20X). D- Abundant subhedral crystals of pyrite in quartz matrix (20X). F- Tiny inclusions of pyrite in biotite (20X). G- Arsenical pyrite in veins and crystal (20X). Mineral abbreviations: Py: pyrite; Stb: stibnite; Apy: arsenical pyrite.

Table 5 Trace metal contents in veins (breccias) and disseminated mineralization.

Sample Au Ag Sb Pb Zn Cu Tl As Ag/Au

Stockworks ppm ppm ppm ppm ppm ppm ppm ppm

I30v 0,08 25,67 2000,00 7995,59 154,30 691,46 4,64 520,00 320,87 I31Av 0,24 3,46 727,13 439,67 11,60 29,42 15,55 2135,90 14,41 Breccias ppm ppm ppm ppm ppm ppm ppm ppm I2v 0,23 1514,28 3,33 13,90 15,54 19,22 1292,50 1,00 I7v 0,97 7,98 117,76 9,93 39,60 11,34 3,66 2644,50 8,24 I3v 0,11 0,14 88,68 2,94 17,90 8,41 8,17 5871,80 1,29 I9v 0,14 0,16 10,78 4,41 1,70 5,21 2,21 798,30 1,11 I12v 0,06 25,65 2000,00 8033,28 149,40 699,02 4,40 505,90 415,71 I33v 0,00 0,73 2000,00 0,01 25,90 17,17 35,54 308,30 3650,00 2NS034a 0,18 2,3 1400 300 500 12,78 2NS035a 0,54 2,5 600 400 500 4,63 2NS036a 0,77 1,3 25800 400 500 1,69 2NS041a 1,55 20,4 900 400 800 400 13,16

a Data from Jica (1995). by slivers of foliated altered wall rock. These breccias are composed chalcedony or quartz. of non-rotated variable sized (0.5e3.7 cm) angular clasts of altered Kinematic indicators such as slickensides, steps, and quartz wall rock and chalcedony rich fragments (in some cases foliated) slickenfibres are commonly observed along altered wall rock with jigsaw textures, enclosed in a hydrothermal matrix of slivers, with a main plunge of 120e145 and 15-45 dip (Fig. 9). 254 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

Table 6 Fluid inclusion data.

Mineral size (mm) shape L:V Mean Th (C) Mean Tm (C) Salinity (%NaCl eq) Measures

Quartz 5 ovoid 8:2 185,2 2 Quartz 5 regular 8:2 186,2 2 Quartz 5 ovoid 9:1 172,5 1 Quartz 5 ovoid 7:3 170,5 3 Quartz 5 irregular 6:4 182,4 1 Quartz 5 irregular 8:2 168,2 2 Quartz 7 ovoid 7:3 152,8 0,9 1,57 9 Quartz 10 tabular 6:4 179,7 1,2 2,07 4 Quartz 60 irregular 7:3 139,3 0,5 0,88 5 Quartz 10 tabular 8:2 182,5 1,3 2,24 12 Quartz 12 ovoid 7:3 152,3 2,4 4,03 5 Quartz 15 irregular 6:4 156,2 1,2 2,07 2 Quartz 60 regular 6:4 135,8 0,9 1,57 1 Quartz 30 tabular 8:2 165,5 1,8 3,06 8 Quartz 7 tabular 8:2 150,1 2,4 4,03 3 Quartz 10 irregular 8:2 146,4 0,9 1,57 5 Quartz 12 ovoid 9:1 148,2 0,8 1,40 5 Quartz 15 ovoid 8:2 132,8 0,4 0,70 2 Quartz 20 irregular 8:2 134,5 0,6 1,05 4 Quartz 10 ovoid 8:2 132,1 1,1 1,91 9 Quartz 7 tabular 9:1 173,6 0,2 0,35 8 Quartz 6 tabular 8:2 135,1 0,8 1,40 7 Quartz 5 tabular 8:2 128,4 8 Quartz 5 tabular 7:3 125,4 5 Quartz 5 ovoid 8:2 152,5 1 Quartz 10 ovoid 8:2 156,6 0,7 1,22 6 Quartz 12 irregular 8:2 149 0,2 0,35 9 Quartz 10 irregular 7:3 166,8 0,7 1,22 16 Quartz 15 irregular 8:2 159,8 0,3 0,53 2 Quartz 30 irregular 6:4 173,9 0,1 0,18 1 Quartz 20 tabular 7:3 179,2 0,6 1,05 3 Quartz 15 ovoid 8:0 159 0,1 0,18 14 Quartz 10 ovoid 7:3 169,8 0,3 0,53 9 Total 163

Table 7 5.5. K-Ar ages Sulfur isotopes data data for sulfide minerals. The d34S values of the ore-forming fluid were calculated using the empirical equation worked out by Ohmoto and K-Ar analyses were performed for two clay fractions from rocks Rye (1979). of the phyllic alteration zone (Table 8 A). Sample I20A, which d34 ‰ d34 ‰ fl Sample S mineral S uid contains disseminated mineralization, and whose <2 mm fraction is I20-Stb 6.72 2.66 composed of I/S R1 (y 60% illite layers) and kaolinite yield a date of I33-Stb 7.10 3.04 8.5 ± 0.2 Ma. Sample I12B, which contains vein breccia minerali- IE1-Stb 5.52 1.46 < m y zation and whose 2 m fraction is composed of I/S R1 ( 60% illite IE2-Stb 2.01 2.05 ± Ia50-Py 1.40 0.76 layers) and illite yielded an age of 6.7 0.2 Ma. Ia50-Apy 1.82 0.34 Therefore, K-Ar ages constrain the hydrothermal mineralization I33-Py 2.39 0.23 process at the Incachule mine to the Miocene (Tortonian- I33-Apy 2.88 0.72 Messinian).

6. Discussion The hydrothermal breccias are emplaced along the same fault planes as the previous pyroclastic dykes from the 10.3 Ma collapse 6.1. Mineralogy characteristics and physical-chemical variation cycle. The Chorillos ignimbrite pyroclastic dykes have N330 trend, up to 2 m width and a maximum length of 200 m. Some of the The typical models of epithermal deposits focus on the changes dykes have sigmoid shapes. However, in some cases the hydro- of minerals assemblages, physical and geochemical parameters, thermal breccias cut pseudo-parallel or obliquely the pyroclastic their variations with depth can be used to determinate the level of dyke, showing different strikes (Fig. 10A and B and C). erosion in each case (Buchanan, 1981; Hayba et al., 1985; Heald The minor mineralized structures are stockworks zones or et al., 1987). However, the type and distribution of secondary fi veinlets with sul des (I39, I47), that are located close to the hy- mineral assemblages produced by hydrothermal alterations drothermal breccias (I12, I7, I8). All veins show a similar trend depend of many variables, including fluid composition, tempera- (N 330.) and 70-85 dip, similar to those of the mineralized faults ture, composition and permeability of the primary rocks, position (Fig. 10 D). The stockworks include pyrite-quartz and stibnite veins of the water table, deep boiling zone and structural controls of fluid with competent altered host rocks, up to 10 cm wide and up to flow. This complex interaction makes it hard to interpret the gen- 80 cm long. esis. Such is the case of and near surface systems where Other structures not related with the mineralization were cooling, boiling and condensations processes are present. observed in the area, like reverse (I51, I71) and normal (I48, I49) Three main mineral assemblages were identified in the Inca- faults. chule ore deposits. Quartz, adularia and illite, associated with N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 255

Fig. 9. Detailed map with structural data. Stereograms for each data point, plane faults and striaes. stibnite, pyrite and arsenical pyrite constitute one group. The sec- crystallization processes. Some cyclic textures of I/S þ Kln and I/S ond group is represented by chalcedony, I/S and smectite, and the observed in sample I12B, suggest compositional fluctuations in the þ þ þ þ last group comprise kaolinite, alunite, jarosite, marcasite and . fluid, with variations in K /H ,Ca2 /H and Si/Al ratios. Kaolinite The first association suggests that boiling had occurred (Dong and associated with Pb-sulfates (I12B) was also observed, indicating þ Morrison, 1995; Hedenquist, 1990) thereby increasing pH and K / acid conditions, as this mineral assemblage is stable at low pH. The þ H with the precipitation of adularia and K-micas associated with acid alteration produced by this mechanism is superficial, rarely sulfides. The association is characteristic of low temperature and extending even 50 m below the surface, and are generally not compatible with the values determined by fluid inclusion in this preserved in ore deposits (Hedenquist et al., 2000). However, in the work (~158 C). Then, the cooling of the fluid let attain silica Incachule mine part of the superficial system is preserved. Probably saturation and precipitation of chalcedony, I/S (R1) and smectite because the arid climate prevailing since the late Miocene in the suggesting a temperature range between 80 and 120 C central Puna (Quade et al., 2014) reduced weathering erosion and (Hedenquist, 1990; Pollastro, 1993; Inoue, 1995). The last mineral supergenesis in the Incachule ore deposits. assemblages are formed by oxidation of H2StoH2SO4 giving place Although precious metals are not present in noticeable to argillic alteration zone characterized by the occurrence of amounts, the ammonium ion contained in some minerals phases of kaolinite, opal, alunite and other complex-sulfates. These sulfates the mineralized zone (buddingtonite, brammalite and alunite) is an (hinsdalite, coorkite, jarosite, alunite, plumbojarosite, beudanite) indicator sensitive to the presence of Ag and Au (Ridgway et al., are common in the supergene zone of pyrite bearing deposits. 1990), so it is considered an excellent pathfinder in mining and However, these minerals can also form by hypogenic processes in geothermal exploration for this area. hydrothermal altered zone, as occurs in present hot springs and geothermal zones (Raymahashay, 1969; Dutrizac and Jambor, 6.2. Geochemical changes, and alteration mineralogy and type of 2000). In the Incachule area the association of the acid suite min- mineralization erals with silica sinters as well as the occurrence of hydrothermal breccias point to an origin by steam-heated acid-sulfate waters at The compositions of the altered and fresh caldera rocks are temperatures <120 C, near the water table, in the shallowest similar, with a wider range of SiO2 in altered rocks, indicating epithermal environment. Neither Fe-oxides, cellular textures nor that most of the altered rocks were enriched in Si during fluid- fi secondary sul de that could indicate supergenic processes were rock interaction. Evidence for enrichment of Si can be seen in observed. Moroever, pyrite crystals are not altered nor stibnites the intense silicic alteration and quartz stockworks in the fi have insigni cant alteration. The occurrence of jarosite- altered rocks. All the rocks exhibit similar REE patterns char- plumbojarosite in several samples (I12B, I8, I7 and I38, I50) in- acterized by a gently dipping pattern from LREE to HREE. dicates oxidation of H2S when the vapor phase generated by boiling However altered rocks are depleted in HREE relatively to the of the deep waters interacts with the atmosphere just above the fresh ones, suggesting its mobility during the interaction with water table (Simmons et al., 2005). Moreover, textures observed in hydrothermal fluids. Although REE are commonly considered BSE images indicate that alteration mainly proceed by dissolution- immobile during water-rock interactions, there are numerous 256 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260

Fig. 10. Relationship between pyroclastic dykes and breccia veins. A- Breccia cutting pyroclastic dyke. B- Breccia cutting pyroclastic dyke with horizontal strike. C- Stereographic diagram from strike plane of faults (without striae data) in breccia zone and veinlets stockwork data in schematic cross section.

Table 8 concentration in altered rocks suggesting significant secondary fi < m Analytical results of K/Ar analyses of the ne fractions ( 2 m) of hydrothermally addition during water-rock interactions, in coincidence with the altered rocks. wide occurrence of secondary K-rich phyllosilicates and adularia in Sample K2O (Wt%) 40 Ar(nl/g) 40 Ar (%) Age (Ma) altered rocks. Al2O3 shows lower contents in altered rocks and I12 7.42 1.603 25.85 6.69 ± 0.26 negative correlation with SiO2. Altered rocks have higher Tl, As, Sb, Cs, Au and Ag contents I20 5.04 1.388 28.12 8.51 ± 0.20 than unaltered ones; moreover, these elements show a positive correlation with K2O, indicating that hydrothermal fluids were enriched in such elements. The enrichment in Sb, As and Tl is a well-known pathfinder in epithermal Au-Ag deposits (Taylor, studies which show that REE can be mobilized during hydro- 2007), and typical of shallow environment epithermal deposits thermal alteration (Oreskes and Einaudi, 1990; Taylor and Fryer, (Henley et al., 1984; Hayba et al., 1985; Heald et al., 1987; 1983; Cathelineau, 1987; Lottermoser, 1992). In the case of the Hedenquist, 1986; Berger and Silberman, 1985; Hedenquist Incachule ore deposits, the mobility of REE appears to increase et al., 2000). The altered rocks depict lower Pb and Zn contents in the late stages of the hydrothermal process (phyllic and than the fresh volcanic rocks, indicating leaching of these ele- argillic zones), probably as a consequence of the increase in ments by acid fluids (Brookins, 1988). Sample I12A represents an fl uid/rock ratios. exception, as it shows gains of Pb. However, it corresponds to the During the hydrothermal alteration, the host rocks lost NaO2, outer zone of the phyllic alteration halo close to the contact with CaO, Fe2O3 and MgO indicating mobility and leaching of these el- the Verde Ignimbrite. The higher Pb content of this sample along fl ements by hydrothermal uids, consistent with the widespread with their clay mineral assemblage, consisting of illite þ I/S and alteration of primary biotite and K-feldspar observed at the optical lacking kaolinite suggests alteration by fluids with intermediate microscope and SEM scale. On the other hand, K2O shows higher N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 257

þ to high alkaline/H activity ratios, conditions under which In this work we observed that all mineralization of Sb have a kaolinite is not stable (Inoue, 1995). The mobility of Pb is also structurally control with the NW-SE dilatational structure, as the indicated by the occurrence of sulfates, arseniates, and phos- pyroclastic dykes of the second event eruption of the collapse phates of Pb-Fe at SEM scale in samples corresponding to the caldera (Figs. 9 and 10). The relationships between hydrothermal phyllic-argillic transition (I12B) and silicic alteration zones (I30). breccias that cut pyroclastic dykes pseudo-parallel or obliquely, These secondary minerals are formed through oxidation of the indicate that they was formed later. Also, there are faults with strike base metal sulfides by acid hydrothermal fluids (Silberman and NW-SE outside collapse caldera without mineralization, suggesting Berger, 1985). that the Incachule mineralization is structural and genetically The breccias and stockworks zones show Ag/Au ratios and metal associated with the collapse caldera. association typical of low sulfidation ore deposits (Hedenquist The collapse caldera rim, despite being a permeable zone, does et al., 2000; Sillitoe and Hedenquist, 2003; Simmons et al., 2005). not present mineralization. However, there are NW-SE hydrother- Higher Pb, Zn, Cu and Ag contents in vein samples I12v and I30v, mal veins emplaced into the caldera moat, close to the oriental could be indicating a vertical zonation in the epithermal system as caldera rim, due to the intense breaking of the rocks in the fault and suggested by Coira and Paris (1981). According to the micro- the rheological contrast between precaldera (granitic rocks) and thermometric study of fluids inclusions the epithermal mineral- intracaldera rocks (ignimbrites). Others minor structures, as the izing fluids at Incachule were dilute (<2 wt% NaCl equivalent) and stockworks zone, show a similar trend (N330) to the hydrothermal had low temperatures, with a 157.5 C average. This data is breccias evidencing the same stress field. concordant with JICA (1993) who determinate an average tem- The last-collapse cycle of the Aguas Calientes caldera (10.3 Ma, perature of 166 C in quartz. As regards of the origin of sulfur, the >100 km3) probably erupt all its magma to the surface quickly, as d34S of pyrite arsenopyrite and stibnite indicate a predominance of predicted in theoretical models (Gualda et al., 2013), attesting that magmatic sulfur (d34S values near 0‰, Ohmoto and Rye, 1979) the longevity of the could not be up to hundreds (Table 7). of thousands years (Wilson and Charlier, 2009). Notwithstanding, the hydrothermal activity related with caldera systems may begin millions of years after the volcanism (Branney and Acocella, 2015). 6.3. Relationship with collapse caldera and age of the Taking into account these considerations, we have delineated an mineralization evolution model for the Inacachule ore deposits. The hydrothermal system started after the eruption of the Mineralization is frequently hosted in permeable zones of the Tajamar ignimbrite, when a deformation episode produced the calderas, commonly at the collapse margins or in fault/fracture contractional/resurgent stage of the cerro Aguas Calientes that planes into the caldera structure. These are zones of weakness that could have driven the hydrothermal activity. Then, the fluids were could be related with pre-caldera stages in a radial pattern or at the channeled in weakness zones produced by fault planes and pyro- postcaldera stages. Commonly they follow a radial to concentric clastic dykes (Fig. 11). We estimate that a further increase in local pattern (Lipman, 1997), but if regional tectonics drives the collapse and/or regional deformation caused the reactivation of NW struc- of the caldera, as suggested by Petrinovic et al. (2010), minerali- tures, allowing the sudden release of hydraulic pressure and pro- zation will be tectonically hosted. Aguas Calientes collapse caldera ducing the hydrothermal breccias (Salado Paz et al., 2013; Salado is emplaced on the Calama-Olacapato-Toro strike-fault zone, which Paz, 2014), which are hosted in the same trend as the pyroclastic acts as trigger of caldera-forming eruptions (Petrinovic et al., 2010).

Fig. 11. Evolution scheme of collapse caldera, tectonic events and mineralized veins. 258 N. Salado Paz et al. / Journal of South American Earth Sciences 82 (2018) 239e260 dykes of the caldera. This means that the regional and local stress leaching and lateral dispersion of this element that overprinted field that promoted the collapse and conduit arranges also earlier alteration patterns. controlled the mineralization. So, the transpressive setting inter- The K-Ar ages obtained indicate that alterations are younger preted for the caldera stage probably persisted during the 8.3e6Ma than the last collapse caldera cycle. Notwithstanding, the genetic period with the same style and intensity and probably continued up model outlined in this paper suggests a genetic relationship be- to the in this area (Petrinovic et al., 2006). tween the hydrothermal activity and the structure of the collapse In this way, the two K-Ar ages determined in hydrothermal clays caldera. The hydrothermal fluids related to Au mineralization are the first radiometric ages obtained for epithermal systems of ascended along structures resulting from the same stress field the Central Puna. The older age was obtained for sample I20 (8.51 which governed caldera collapse. Ma), that corresponds to the stockworks mineralization, whereas a Hot spring systems are surface expressions very susceptible to sample representative of the vein zone yielded a younger age erosion, which makes the case of the Incachule mine an excep- (sample I12B, 6.69 Ma). We interpret this temporal variation as two tionally preserved example. different mineralization episodes. In the early stage, the increase of tectonic stress produced boiling generating breccias with jigsaw Acknowledgments texture and not rotated clast, dispersing mineral (stockworks) near to the principal veins with secondary minerals precipitated in This work was funded by grants CONICET PIP 0781, ANPCYT PICT fractures of the host rock (I20). Then, probably new hydraulic 381, CAPES-MINCyT 009/12, ANPCYT PICT 0407, CONICET PIP 0489. fracturing in breccias happened, evidenced by textures consisting The authors thank SEGEMAR, Dra M. Godeas for performing SWIR of clasts of chalcedony immersed in chalcedony hydrothermal spectometry analyses and the Geochronology laboratory from matrix in the breccias (Salado Paz et al., 2013), (I12b). Universidade de Brasilia (Brasil). The help of I. Guerra with the SEM The ages obtained for secondary clay minerals from the Inca- (Centro de Instrumentacion Científica, University of Granada, chule alteration zones are similar to the ages of Cerro Quevar Espana),~ Carlos Gomez eSilvia Blanco (LaSem Universidad Nacional (Wilson et al., 1998), thus supporting previous studies that related de Salta) and Luis Mancini (Universidade de Brasilia) was essential the Incachule ore deposits with the Quevar magmatism (Zappettini, for the present work. The authors would like to acknowledge the 1999). However, the connection between the argillic alteration use of the diffractometers from Departamento de Físico Química, zone and silicic sinter demonstrates that Incachule is hosted and UNC, Argentina, y Departamento de Mineralogía y Petrología de la related with post-magmatic activity from the Aguas Calientes Universidad de Granada. We thank the two anonymous reviewers, collapse caldera. 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