Porphyry Indicator Zircons (PIZs): Application to exploration of Porphyry Copper Deposits

Keywords: Zircon, Porphyry Indicator Minerals (PIMs), Eocene to Oligocene metallogeny belt, Northern Chile, Porphyry Copper Deposit, non-mineralized intrusive body

Magmas with a high oxidation state (FMQ +1 to +2), a high-water content (≥ 4 wt % H2O) and a high degree of fractionation are necessary to form porphyry copper deposits (PCDs). Different proxies, such as Fe 3+ /Fe 2+ ratio of whole-rock, minerals indicative of high oxygen fugacity (fO2) and water content as well as geochemical signatures of whole-rock (e.g. high Sr/Y and V/Sc ratios) are commonly used to trace these magmatic conditions. However, these proxies are of limited use for rocks hosting porphyry copper mineralization because the hydrothermal fluids associated with ore deposits obliterate the primary minerals and their initial geochemical signatures. Zircon is a common accessory mineral of igneous rocks that retains its original chemical composition from the time of crystallization, therefore provides information related to parental magmas. Several studies on PCDs worldwide have investigated the geochemical characteristics of zircons (e.g., Hf concentration, Ce 4+ /Ce 3+ , Eu/Eu*) as indicators of a high oxidation state, high magmatic water content and high degree of magma fractionation. Here, the petrographic and geochemical characteristics of zircons collected from Chuquicamata, Mirador, Esperanza and Escondida PCDs, located in the upper Eocene to lower Oligocene metallogenic belt of northern Chile, were determined in order to validate the use of zircon as a tracer for porphyry fertility. Our results show that zircon collected from all studied PCDs crystallized from monzogranitic to granodioritic magmas at temperatures below 750°C and show euhedral morphologies mainly characterized by prismatic forms of type {110} and pyramidal forms of type {101}. Most zircons from PCDs have Hf concentrations > 8,750 (ppm) and Ce/Nd > 1, Eu/Eu* > 0.4, 10,000x(Eu/Eu*)/Y > 1, (Ce/Nd)/Y > 0.01, Dy/Yb < 0.3, Th/U < 1 -> 0.1. From this group of geochemical values measured on zircon, we propose the Porphyry Indicator Zircon concept (PIZ), where each zircon from PCDs must comply with the previously mentioned geochemical framework. Our results show that studied PCDs have abundant zircons with PIZ characteristic (>54%); at Mirador and Esperanza porphyries the PIZ proportion exceeding 70 %.

On the other hand, the non-mineralized intrusive bodies have no zircons with PIZ characteristics.

Therefore, these results combined with previously published studies from other porphyry belts worldwide, validate zircons as an indicator of metallogenic fertility and its use as a porphyry indicator mineral and a potential exploration tool in search for PCDs.

Introduction

In northern Chile and southern Peru, porphyry copper deposits (PCDs) form in subduction zones linked to silica-rich calc-alkaline intrusions (e.g. [START_REF] Sillitoe | Porphyry copper systems[END_REF][START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF][START_REF] Richards | The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny[END_REF][START_REF] Chambefort | Anhydrite-bearing andesite and dacite as a source for sulfur in magmatic-hydrothermal mineral deposits[END_REF][START_REF] Chambefort | Amphibole geochemistry of the Yanacocha Volcanics, Peru: Evidence for diverse sources of magmatic volatiles related to gold ores[END_REF][START_REF] Loucks | Distinctive composition of copper-ore-forming arcmagmas[END_REF]. These magmas are characterized by high oxidation state (FMQ +1 to +2;Richard, 2015;[START_REF] Sun | The formation of porphyry copper deposits[END_REF], high water content (≥ 4 wt % H2O), and high sulfur and metal contents [START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF]2011;[START_REF] Richards | High Sr/Y magmas reflect arc maturity, high magmatic water content, and porphyry Cu±Mo±Au potential: Examples from the Tethyan arcs of central and eastern Iran and western Pakistan[END_REF][START_REF] Loucks | Distinctive composition of copper-ore-forming arcmagmas[END_REF]. They also generally record a high degree of fractionation [START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF][START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF]2011).

Several studies identified magmatic conditions necessary to form a PCD [START_REF] Sillitoe | Porphyry copper systems[END_REF][START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF][START_REF] Richards | The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny[END_REF][START_REF] Seedorff | Porphyry deposits: Characteristics and origin of hypogene features[END_REF][START_REF] Chambefort | Anhydrite-bearing andesite and dacite as a source for sulfur in magmatic-hydrothermal mineral deposits[END_REF]. For example, the oxidation state of the magma is evaluated from the Fe 3+ /Fe 2+ ratio of whole-rock, the composition of Fe-Ti oxides and the presence of minerals indicative of high oxygen fugacity (fO2), such as magnetite, hematite, and anhydrite [START_REF] Ishihara | Magnetite-series and ilmenite-series granitic rocks[END_REF][START_REF] Daniels | Oxygen fugacity constraints on the southern African lithosphere[END_REF][START_REF] Sun | The link between reduced porphyry copper deposits and oxidized magmas[END_REF]. The water content in the melt is estimated by the presence of minerals indicative of high H2O, such as hornblende and biotite [START_REF] Rutherford | The May 18, 1980, eruption of Mount St. Helens: 3. Stability and chemistry of amphibole in the magma chamber[END_REF][START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF]. Finally, the degree of magma fractionation is evaluated based on the Hf concentration and the Sr/Y, V/Sc and Th/U ratios of whole-rock [START_REF] Bea | Residence of REE, Y, Th and U in Granites and Crustal Protoliths; Implications for the Chemistry of Crustal Melts[END_REF][START_REF] Baldwin | Discrimination of productive and nonproductive porphyritic intrusions in the Chilean Andes[END_REF][START_REF] Lang | Isotopic and geochemical characteristics of Laramide magmatic systems in Arizona and implications for the genesis of porphyry copper deposits[END_REF][START_REF] Rohrlach | Multi-million-year cyclic ramp-up of volatiles in a lower crustal magma reservoir trapped below the Tampakan copper-gold deposit by Mio-Pliocene crustal compression in the southern Philippines[END_REF][START_REF] Richards | Adakite-like rocks: Their diverse origins and questionable role in metallogenesis[END_REF][START_REF] Chiaradia | Why large porphyry Cu deposits like high Sr/Y magmas?[END_REF][START_REF] Loucks | Distinctive composition of copper-ore-forming arcmagmas[END_REF]. However, these proxies are not widely applicable to intrusive bodies related to PCD's, since the hydrothermal fluids associated with ore deposits commonly obliterate the primary minerals and alter the whole-rock geochemical composition [START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF][START_REF] Richards | The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny[END_REF][START_REF] Seedorff | Porphyry deposits: Characteristics and origin of hypogene features[END_REF][START_REF] Sillitoe | Porphyry copper systems[END_REF]. In this context, the petrographic and geochemical characteristics of various mineral species including accessory, alteration and ore minerals (e.g. zircon, apatite, epidote, jarosite, rutile, tourmaline, magnetite, pyrite and chalcopyrite) have been evaluated to trace each stage of the magmatic/hydrothermal evolution related to the formation of a PCD [START_REF] Averill | The application of heavy indicator mineralogy in mineral exploration, with emphasis on base metal indicators in glaciated metamorphic and plutonic terrain: in[END_REF][START_REF] Kelley | Porphyry Cu indicator minerals in till as an exploration tool: example from the giant Pebble porphyry Cu-Au-Mo deposit, Alaska, USA[END_REF][START_REF] Deditius | Trace metal nanoparticles in pyrite[END_REF][START_REF] Nadoll | Geochemistry of magnetite from porphyry Cu and skarn deposits in the southwestern United States[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF][START_REF] Bouzari | Hydrothermal alteration revealed by apatite luminescence and chemistry: a potential indicator mineral for exploring covered porphyry copper deposits[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. These distinctive characteristics have been used to differentiate between intrusive bodies related to PCDs from non-mineralized intrusive bodies [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Canil | Trace elements in magnetite from porphyry Cu-Mo-Au deposits in British Columbia, Canada[END_REF]Bouzari et al., 2018;[START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Because some of these minerals can persist in the surficial environment despite weathering and transport [START_REF] Pisiak | Magnetite as an indicator mineral in the exploration of porphyry deposits: a case study in till near the Mount Polley Cu-Au deposit[END_REF], they have the potential to be used as porphyry indicator minerals (PIMs) in detrital sedimentary record.

Zircon [ZrSiO4] is a common accessory mineral of intermediate to felsic igneous rocks that shows a remarkable resistance to high-temperature diffusive re-equilibration [START_REF] Cherniak | Rare-earth diffusion in zircon[END_REF]Watson & Cherniak, 1997;[START_REF] Cherniak | Diffusion in zircon[END_REF]. It can retain its primary chemical and isotopic composition from the time of crystallization [START_REF] Cherniak | Rare-earth diffusion in zircon[END_REF], thus providing chemical information related to parental magmas. During its crystallization, zircon incorporates trace and radiogenic elements of variable valence, which tend to replace to Zr 4+ (e.g. Sn 4 + , Th 4 + , U 4 + , Hf 4+ ) and Si 4+ (e.g. Ge 4+ and Ti 4+ ) [START_REF] Finch | Structure and chemistry of zircon and zircon-group minerals[END_REF][START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF].

Zircon can also incorporate rare earth elements (REE), leading to an increase of zircon/melt partition coefficients from light to heavy REE (e.g. [START_REF] Sano | High mass resolution ion microprobe analysis of rare earth elements in silicate glass, apatite and zircon: lack of matrix dependency[END_REF] during crystallization. In particular, the Ce 4+ (0.97 Å) and Eu 3+ (1.066 Å) oxidized ions are preferably incorporated into the zircon structure, whereas the Ce 3+ (1.143 Å) and Eu 2+ (1.25 Å) reduced ions tend to be excluded (Hoskin and Schalteger, 2003). Thus, occurrence of Ce positive (Ce 4+ /Ce 3+ > 120) anomaly and lack of significant negative Eu anomaly (Eu/Eu* > 0.3) in zircon have been linked to a high oxidation state of magma (e.g. [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF]. Also, high trace elements ratios, such as, Eu/Eu* (> 0.3), (10,000x Eu/Eu*)/Y (> 1) and (Ce/Nd)/Y (> 0.01) measured in zircon are related to high-water content in magma at epizonal depth [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. A hydrous melt during early stages of cooling tends to crystallize garnet and hornblende whereas the crystallization of plagioclase is inhibited (Alonso-Perez et al. 2009;[START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF][START_REF] Richards | High Sr/Y magmas reflect arc maturity, high magmatic water content, and porphyry Cu±Mo±Au potential: Examples from the Tethyan arcs of central and eastern Iran and western Pakistan[END_REF][START_REF] Chiaradia | Why large porphyry Cu deposits like high Sr/Y magmas?[END_REF][START_REF] Bissig | High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia[END_REF]. This can generate high Y and REE (HREE) depletion and Eu enrichment in the residual melt [START_REF] Chiaradia | Why large porphyry Cu deposits like high Sr/Y magmas?[END_REF][START_REF] Loucks | Distinctive composition of copper-ore-forming arcmagmas[END_REF]. Finally, the high Hf concentration (e.g. [START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF], low Th/U ratio values (> 1) [START_REF] Xiang | U and Th contents and Th/U ratios of zircon in felsic and mafic magmatic rocks: Improved zircon-melt distribution coefficients[END_REF][START_REF] Kirkland | Zircon Th/U ratios in magmatic environs[END_REF] and the preferred incorporation of high REE (HREE) over medium REE (MREE) [START_REF] Davidson | Amphibole "sponge" in arc crust?[END_REF][START_REF] Richards | Adakite-like rocks: Their diverse origins and questionable role in metallogenesis[END_REF] measured in zircon are linked to a considerable degree of magma fractionation. In the case of REE content low Dy/Yb ratio values (< 0.3) have been documented in zircons from porphyry fertile plutons [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. These geochemical signatures obtained from zircon have been proposed to differentiate between mineralized intrusive bodies type copper porphyry from nonmineralized intrusive bodies [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Studies carried out on the Oyu Tolgoi, Mongolia [START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF], Bajo la Alumbrera, Argentina [START_REF] Buret | From a longlived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)[END_REF] and Boddington, Australia [START_REF] Lu | Zircon fingerprinting of magmatic-hydrothermal systems in the Archean Yilgarn Craton: Geological Survey of Western Australia[END_REF] porphyries, discuss the co-crystallization effects of other minerals, such as apatite, titanite, amphibole and plagioclase on the measured fertility indicator in zircon.

In this paper, we present the petrographic characteristics (microscopic observations and cathodoluminescence) and geochemical signatures (Electron Microprobe Analysis [EMPA] and Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry [LA-ICP-MS]) of zircons collected from four porphyry copper deposits located in the Upper Eocene -lower Oligocene porphyry belt of Northern Chile. These are the Chuquicamata, Mirador, Esperanza and Escondida deposits (Fig 1a). This study is aimed at validating zircon crystals as an indicator of metallogenic fertility and its use as a porphyry indicator mineral (PIM) and a potential exploration tool in search for buried PCDs.

Studied Porphyry Copper Deposits

The studied zircons were collected from four porphyry copper deposits from the Upper Eocenelower Oligocene metallogenic belt located in the Precordillera of Northern Chile. The four deposits are Chuquicamata (Ossandón et al., 2001;[START_REF] Rivera | Update of the geologic setting and porphyry Cu-Mo deposits of the Chuquicamata District, northern Chile[END_REF][START_REF] Barra | Timing and formation of porphyry Cu-Mo mineralization in the Chuquicamata district, northern Chile: new constraints from the Toki cluster[END_REF], Mirador [START_REF] Perelló | Wealth creation through exploration in a mature terrain: The case history of the Centinela district, northern Chile[END_REF], Esperanza [START_REF] Perelló | Discovery and geology of the Esperanza porphyry copper-gold deposit, Antofagasta region, northern Chile[END_REF][START_REF] Sillitoe | Porphyry copper systems[END_REF] and Escondida [START_REF] Padilla-Garza | Geology of the Escondida porphyry copper deposit, Antofagasta region, Chile[END_REF][START_REF] Hervé | Geologic overview of the Escondida porphyry copper district, Northern Chile[END_REF] (Fig. 1a). These porphyry deposits have been extensively studied for decades, with the exception of Mirador. Emplacement of these deposits occurred during E-W-directed contraction, crustal shortening, and uplift related to the Incaic tectonic phase (Maksaev and Zentelli, 1999). These deposits display the typical hydrothermal alteration zones previously defined for PCDs of Northern Chile [START_REF] Lowell | Lateral and vertical alteration-mineralization zoning in porphyry ore deposits[END_REF][START_REF] Sillitoe | Porphyry copper systems[END_REF] with a well-developed potassic alteration zone with abundant quartz-vein stockwork overprinted by quartz-chlorite and phyllic alterations zones hosting the sulfide mineralization. The propylitic alteration zone is always observed as a peripheral halo.

The Chuquicamata PCD located 15 km north of the city of Calama (Fig 1a) is the largest deposit in the Chuquicamata District. The Cu-Mo mineralization is mainly hosted by the Chuquicamata Intrusive Complex (CIC) that intruded to the Paleozoic and Triassic volcanic and Triassic granodioritic rocks of the Collahuasi Group and Granodiorita Helena, respectively [START_REF] Rivera | Update of the geologic setting and porphyry Cu-Mo deposits of the Chuquicamata District, northern Chile[END_REF]. The largest and oldest unit of the CIC is the East porphyry (35.2 ± 0.4 and 34.6 ± 0.3 Ma;[START_REF] Ballard | Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by ELA-ICP-MS and SHRIMP[END_REF] (Fig 1b), which is of granodioritic composition, with phenocrysts of plagioclase, quartz, biotite, hornblende and titanite in a coarse-grained groundmass of quartz and K-feldspar. The East porphyry is cut by smaller bodies that also belong to the CIC, which are the granodioritic West porphyry (34.1 ± 0.3 Ma; [START_REF] Ballard | Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by ELA-ICP-MS and SHRIMP[END_REF], the Banco porphyry of monzogranitic composition (34.0 ± 0.3 Ma; [START_REF] Ballard | Two ages of porphyry intrusion resolved for the super-giant Chuquicamata copper deposit of northern Chile by ELA-ICP-MS and SHRIMP[END_REF] and the granodioritic Fino porphyry. The potassic zone is characterized by pervasive and veinlet-controlled K-feldspar alteration and recrystallized biotite. Much of the ore occurs with an important overprint of phyllic alteration, and to a lesser extent, a chlorite-sericite alteration. The propylitic zone is composed mainly of chlorite, and to a lesser extent epidote, calcite and pyrite and is found both in the porphyry intrusions and wall rocks (see Ossandón et al. (2001), [START_REF] Rivera | Update of the geologic setting and porphyry Cu-Mo deposits of the Chuquicamata District, northern Chile[END_REF] and Barra et al. (2012), among others for more details).

The Mirador PCD is located 40 km SSW of the city of Calama (Fig 1a). There are few published studies about this deposit [START_REF] Perelló | Wealth creation through exploration in a mature terrain: The case history of the Centinela district, northern Chile[END_REF][START_REF] Riquelme | Supergene and exotic Cu mineralization occurs during periods of landscape stability in the Centinela Mining District, Atacama Desert[END_REF]. The mineralization in the Mirador PCD is related to two porphyritic bodies that intruded the Jurassic sedimentary rocks from the Caracoles Group and granodioritic rocks dated at 45.5 ± 1.1 Ma [START_REF] Perelló | Wealth creation through exploration in a mature terrain: The case history of the Centinela district, northern Chile[END_REF].

The main and oldest mineralized unit corresponds to a granodioritic porphyry dated between 40.6 ± 1.1 and 41.6 ± 2.4 Ma (Internal data from Antofagasta Minerals) which contains phenocrysts of plagioclase, quartz, biotite and hornblende in a coarse-grained groundmass of quartz and K-feldspar. This porphyry is cut by a younger and smaller body of similar composition, which is 39.6 ± 0.8 Ma in age (Internal data from Antofagasta Minerals). Both intrusions differ by their texture and their particular association of ore and alteration minerals.

The main hydrothermal alteration that affects these porphyries corresponds to the potassic alteration that consists of K-feldspar, biotite and anhydrite, overprinted by a chlorite-sericitequartz mineral assemblage. Locally and structurally controlled, weak phyllic alteration characterized by the presence of quartz-sericite-pyrite is superimposed on all the other alterations [START_REF] Perelló | Wealth creation through exploration in a mature terrain: The case history of the Centinela district, northern Chile[END_REF].

The Esperanza deposit, also located in the Centinela Mining District (Fig 1a), is geologically similar to the Mirador porphyry described above. The Cu-Mo mineralization in the Esperanza PCD occurs with two granodioritic porphyry intrusive bodies corresponding to an early and a main phase dated at 42.1 ± 0.8 Ma and 41.3 ± 0.3 Ma, respectively (Internal data from Antofagasta Minerals), which intruded the Upper Cretaceous volcanic-sedimentary sequence of the Quebrada Mala Formation [START_REF] Perelló | Discovery and geology of the Esperanza porphyry copper-gold deposit, Antofagasta region, northern Chile[END_REF]. Both porphyries have the same composition and vary just slightly in texture, the early phase having a finer-grained texture. However, they vary in the intensity of the hydrothermal alteration and the content of quartz-vein. The earliest porphyric intrusion is characterized by a more intense potassic alteration and quartz-magnetite veinlets, whereas the main and late phase is characterized by the presence of a fine texture and hydrothermal breccias bodies [START_REF] Perelló | Discovery and geology of the Esperanza porphyry copper-gold deposit, Antofagasta region, northern Chile[END_REF][START_REF] Sillitoe | Porphyry copper systems[END_REF] (Fig. 1c). The potassic alteration containing K-feldspar, biotite and quartz with abundant hydrothermal magnetite and anhydrite is centered on the early porphyry and the Quebrada Mala Formation rocks [START_REF] Perelló | Discovery and geology of the Esperanza porphyry copper-gold deposit, Antofagasta region, northern Chile[END_REF]. It laterally grades to intermediate argillic alteration dominated by quartz, chlorite and greenish sericite and also contains illite and smectite. Both alterations assemblages are overprinted by a weak phyllic alteration, mainly developed in andesitic rocks, destroying the original texture of the rocks. The propylitic alteration is only observed at the margins of the deposit.

The Escondida PCD located 170 km SE of the city of Antofagasta (Fig 1a) is the largest deposit in the Escondida Mining District. The Cu-Mo mineralization in this deposit is associated with a granodioritic-monzonitic porphyric intrusive, known as the Escondida stock [START_REF] Padilla-Garza | Geology of the Escondida porphyry copper deposit, Antofagasta region, Chile[END_REF][START_REF] Hervé | Geologic overview of the Escondida porphyry copper district, Northern Chile[END_REF] that intrudes the Paleozoic and late Cenozoic volcanic rocks from La Tabla and Augusta Victoria Formations, respectively (Fig. 1d). The Escondida Stock was dated at 38-37 Ma [START_REF] Richards | A revised late Eocene age for porphyry Cu magmatism in the Escondida area, northern Chile[END_REF][START_REF] Padilla-Garza | Hypogene evolution of the Escondida porphyry copper deposit[END_REF], and is composed of phenocrysts of plagioclase, quartz, biotite and hornblende in a coarse-grained groundmass of quartz and Kfeldspar. At depth, this body is cut by a biotite-bearing granodiorite dated at 35.4 ± 1 Ma, which is related to a low grade hypogene copper mineralization [START_REF] Hervé | Geologic overview of the Escondida porphyry copper district, Northern Chile[END_REF], whereas the west part of deposit is cut by a barren quartz-rich biotitic rhyolitic dome dated at 37.5 ± 1 Ma [START_REF] Padilla-Garza | Geology of the Escondida porphyry copper deposit, Antofagasta region, Chile[END_REF][START_REF] Hervé | Geologic overview of the Escondida porphyry copper district, Northern Chile[END_REF]. The potassic alteration zone developed in the early granodioritic porphyry as well as in the host rocks characterized by K-feldspar, biotite and quartz. The chlorite-sericite-quartz and phyllic alteration assemblages overprinted the potassic and propylitic alterations. The latter occurs in the vicinity of the deposit and it is composed of epidote and smaller amounts of chlorite, montmorillonite and pyrite [START_REF] Padilla-Garza | Geology of the Escondida porphyry copper deposit, Antofagasta region, Chile[END_REF].

The advanced argillic alteration is mainly controlled by fractures and affects both the wall-rock as well as the whole deposit [START_REF] Padilla-Garza | Geology of the Escondida porphyry copper deposit, Antofagasta region, Chile[END_REF].

Sampling and methodologies

A total of 10 samples of approximatively 5 kg each were selected for zircon petrographic and geochemical analysis. These samples were collected from different hydrothermal alteration zones within the Chuquicamata, Mirador, Esperanza and Escondida PCDs. The location and geological information for each sample is given in Table 1.

All collected samples were first crushed and sieved to a < 0.5 mm grain size. From this material zircons were separated by conventional separation procedures, using a Wilfley vibrating water table, heavy liquids (Tetrabromoethane, 2.98 g/cm 3 and Diiodomethane, 3.31 g/cm 3 ) and magnetic separation (inclination 20° and > 1.2 Amps) at the Géosciences Environnement Toulouse (GET) laboratory, France. Representative zircon grains from the four deposits were hand-picked from the nonmagnetic fraction using a binocular microscope, mounted in epoxy resin disks, and then polished to approximately half-grain thickness. Due to sample and laboratory constraints we analyzed ~ 10 grains per sample based on the grain number used in similar studies (e.g. [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF], even if recent studies suggest to use 50 grains per sample [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF][START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF] to generate a more robust geochemical database. A transmitted polarized light microscope and a Cambridge Image Technology Ltd. MK 4A model cold cathodoluminescence (CL) stage mounted on a petrographic microscope at the Mineral Deposit Research Unit (MDRU) of the University of British Columbia (UBC) were used to observe the petrographic and CL characteristics of the zircon grains, such as morphology and internal textures. For cathodoluminescence studies, the samples were irradiated in a vacuum chamber with an electron beam of approximately 15 kV and a current set at 350 to 500 μA.

Petrographic studies of zircon grains under transmitted light and CL showed that most grains did not have inclusions and inclusions that could be identified were small in size (< 20 µm). The areas with inclusions were avoided during the analysis.

Electron-probe microanalysis of zircon was conducted using a fully automated CAMECA SX-50 instrument at the Department of Earth, Ocean and Atmospheric Sciences of the UBC, operating in the wavelength-dispersion mode with the following operating conditions: excitation voltage, 15 kV; beam current, 20 nA; peak count time for Si and Zr, 20 s; background count-time for Si and Zr, 10 s; peak count time for Hf and U, 100 s; background count-time for Hf and U, 50 s; spot diameter, 5 µm. Data reduction was done using the 'PAP' φ(ρZ) method [START_REF] Pouchou | PAP'j (rZ) procedure for improved quantitative microanalysis[END_REF]. For the elements considered, we used the following standards, X-ray lines and crystals: silicon, SiKα, TAP; zircon, ZrLα, PET; Hf metal, HfLα, LIF; UO2 glass, UMα, PET.

Three standard deviations (99.7% confidence level) were used for the calculation of detection limits that are shown in Appendix 1.

LA-ICP-MS analyses were carried out in the Pacific Centre for Isotopic and Geochemical Research of the UBC using a Resonetics m50-LR 193 nm excimer laser coupled to an Agilent 7700x ICPMS with laser diameter of approximately 34 μm. The ablation time was 40 s with He gas flow (750 ml/min He and 2ml/min N2). The calibration was made with NIST610 and NIST612 silicate glasses as external standards, primary and secondary, respectively. The Zr concentrations obtained by EPMA from the same zircon grains were utilized as internal standards. The basaltic BCR2-G, Plesovice and 9500 zircon masses were used as quality controls. The data reduction was performed by means of Iolite software [START_REF] Paton | Iolite: Freeware for the visualization and processing of mass spectrometer data[END_REF], from which the elemental concentrations using NIST610 and NIST612 silicate glasses for external standardization was determined. Intervals for data reduction were chosen based on the flattest part of the 90 Zr plateau, typically between ~2 s after the laser was turned on and before around 2 s before the laser was turned off. During the reduction of the data, a careful check throughout the depth of the profile of each laser-ablated area using a multi-element mass spectrometry was realized to eliminate any possible impurities that may have been encountered. This was done by assessing the 90 Zr profile, inspecting for depressions and examining for spikes of other masses that indicated the presence of inclusions. Additionally, spot analyses affected by contamination due to small inclusions or cracks into the zircons were discarded by applying filtering mechanisms namely the 'clean zircon' standard [START_REF] Zou | Insight into zircon REE oxy-barometers: A lattice strain model perspective[END_REF]; La < 0.1 ppm) and the LREE-I index (Bell et al., 2016; LREE-I (Dy/Nd + Dy/Sm) < 30) (Appendix 2). If the elemental concentrations of LA-ICP-MS data were below detection limits, for the purpose of displaying the data graphically, values of half a detection limit were used. A large number of zircon grains are sector zoned, showing a highly heterogeneous distribution of elements [START_REF] Jackson | the application of laser ablation-inductively coupled plasma-mass spectrometry to in situ U/Pb zircon geochronology[END_REF]2013;[START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF]. Accordingly, in each zircon grain two ablations (spots) were analyzed, one in the core and one at the margin to check for significant differences in geochemical compositions between these two areas in individual grains. Additionally, grains of more than 100 µm in length were selected to verify compositional variations and more than two ablations were then performed.

Results

Petrographic characteristics of zircon from studied PCDs

Zircon coming from different copper porphyry deposits present very slight differences with respect to their petrographic characteristics. The size of the crystals varies between 85 and 200 µm (axial axis), the smallest zircons corresponding to those from Chuquicamata and the largest one to those from Escondida (Fig. 2, Table 2). We first estimated the aspect ratio of the zircons (which corresponds to the length/width ratio) and related it to the cooling rate of the magma [START_REF] Corfu | Atlas of zircon textures[END_REF]. Elongated crystals (aspect ratio close to 5) are associated with rapid magma cooling at shallow levels, whereas equidimensional crystals (aspect ratio close to 1) are associated with slow magma cooling at greater depths [START_REF] Corfu | Atlas of zircon textures[END_REF]. In our crystal the aspect ratio varies between 1.5 and 6 (Fig. 3 andTable 2). About 80% of the zircons from Chuquicamata and Esperanza PCDs present an aspect ratio between 1.5 and 3.0, whereas the aspect ratios found at Mirador and Escondida PCDs are more variable, with only about 55% of the grains exhibiting values between 1.5 and 3 (Fig. 3. Table 2). Aspect ratio in our zircons indicate a majority of slightly elongated crystals pointing to rapid magma cooling at shallow level for our PCDs.

Our morphological studies are based on the three-dimensional morphology of the grain surface.

Petrographic studies of transmitted light and CL showed the morphology of external and internal grains, which allows tracing changes in the grain's morphology during crystal growth. Our zircons show external euhedral morphology and typical zoning in accordance with those described as igneous zircons [START_REF] Corfu | Atlas of zircon textures[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]Fig. 2). For the morphological characterization of zircons, we used the typological classification diagram developed by [START_REF] Pupin | Zircon and granite petrology[END_REF], in which zircon crystals are classified according to the relative development of the prismatic forms {100} vs. {110} and the pyramidal forms {211} vs. {101}. [START_REF] Pupin | Zircon and granite petrology[END_REF] proposed a direct relationship defined by the A index (I.A) between the development of pyramidal faces and magma composition, though the Al/Na+K ratio. The development of prismatic faces is controlled by the T index (I.T), related to the crystallization temperature. From these relationships, [START_REF] Pupin | Zircon and granite petrology[END_REF] proposes a petrogenetic classification that assign average values of A index (XI.A) and T index (XI.T) from populations of zircons to a given magmatic origin (composition and temperature). Appendix 1 shows an example of recognition of the main morphology of zircon grains using transmitted light and CL images for each studied porphyry, as well as associated calculations of XI.A and XI.T values when possible.

Zircon collected from studied PCDs mainly show prismatic forms of type {110} with less development of type {100} and pyramidal forms mainly of type {101} with less development of type {211} (Fig. 4; Table 2; Appendix 1). In agreement with the typological classification [START_REF] Pupin | Zircon and granite petrology[END_REF], the investigated zircons mainly correspond to subtypes S8, S4 and S9, with a respective percentage for each subtype greater than 10% of the total population of a given PCD (Fig. 4; Table 2). In some cases, i.e. Chuquicamata and Esperanza, the percentage of subtype S8 exceeds 40% of the total population (Fig 4a andc). Chuquicamata porphyry also contain S7 and S5 subtypes, while Escondida porphyry contain zircons of S3 and S5 subtypes, these subtypes representing less than 10% of zircon population in both cases. We note that Mirador porphyry is the only one to contain zircons of P2 subtype, which are exclusively formed by pyramidal forms of type {101} (Fig 4b). Among the analyzed zircons from all studied deposits, the XI.A varies between 449 and 505, whereas the XI.T varies between 371 and 379 (Table 1; Appendix 1). The lowest XI.A and highest XI.T values were calculated for the zircons coming from Chuquicamata PCD, whereas the highest XI.A and lowest XI.T values were calculated for zircons coming from Mirador and Escondida PCDs, respectively (Table 2;Appendix 1 With respect to the internal structures, the zircon grains display zoned, weakly zoned or unzoned cores and strongly oscillatory zoned rims, which are typical of igneous zircons (Fig. 2). This zoning is reflected through slight variations in the luminescence color into the grain varying from translucent green, green and yellowish green that could be related to geochemical variations in the grain. In some grains we observed interruptions of the internal structures by cracks (e.g. Fig. 2m). In addition, in a large number of grains we recognized fluid-, gas-and/or mineralinclusions, these last characteristics being more frequently reported for apatite than for zircons and other minerals (Figs. 2e, g, k, h andi). The reabsorption textures were poorly observed (Fig. 2m andj), and inherited cores are not recognized in this study. The investigated zircons do not differ significantly between the different investigated PCD's either in terms of petrography or with respect to the type of hydrothermal alteration they are associated with.

Geochemical signatures of zircon from studied PCDs

Ti-in-Zircon Temperature

The temperature of zircon crystallization was estimated from its titanium content using the equation proposed by [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF], whose calibration assumes crystallization under conditions of saturation of quartz and rutile (aTiO2 = 1 and aSiO2 = 1). The experimental calibration is for a pressure of 1 GPa (10 kbars) and although Ti-in-zircon is pressure sensitive [START_REF] Ferriss | Computational study of the effect of pressure on the Ti-in-zircon geothermometer[END_REF], we can ignore the effects of this because the PCDs solidified at shallow crustal levels, i.e., 1~5 km (Dilles, 1987;[START_REF] Richards | Tectono-magmatic precursors for porphyry Cu-(Mo-Au) deposit formation[END_REF][START_REF] Sillitoe | Porphyry copper systems[END_REF] and studied zircon, likely crystallized over a limited pressure range (<1-3 kbars, e.g., [START_REF] Seedorff | Porphyry deposits: Characteristics and origin of hypogene features[END_REF]. Because the rocks are intensely altered the aSiO2 and aTiO2 in whole rock cannot be estimated and the temperature correction for the Ti-in-zircon thermometer proposed by [START_REF] Schiller | Application of Ti-in-zircon thermometry to granite studies: problems and possible solutions[END_REF] cannot be applied. Alternatively, we estimated the aSiO2 and aTiO2 from the mineral association observed in the different samples. All samples contain primary magmatic quartz, so the aSiO2 = 1. In some samples, Ti oxides (e.g. titanite) and Fe-Ti oxides (titano/magnetite-hematite) of possible hydrothermal and/or magmatic origin are present [START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF], which pleads for an aTiO2 < 1. Previous studies for zircons coming from other PCDs in the same region attributed an aTiO2 = 0.7, in accordance with the general presence of other Fe-Ti oxides [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF]. We therefore assumed an aSiO2 of 1 and an aTiO2 of 0.7 for our PCDs. Note that, variation of the aTiO2 by 0.3 and/or a variation of the Ti-in-zircon as a function of sector zoning [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF], would lead to errors of about 15 °C to 20 °C, so the errors of the calculated temperatures in the model are ±30 °C (2σ).

With the assumptions mentioned above, Figure 5 shows variations in the temperature of zircon crystallization estimated from the titanium content [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF] versus the Hf concentration (ppm). The temperature varies between 605 °C and 794 °C, although 90% of the data fall between 738 °C and 637 °C, with a median value (x) of 685 °C (Table 3; Appendix 2).

The zircon with the highest formation temperatures are found in the Escondida deposit (x > 697 °C for all samples), whereas zircon with lower formation temperature are found in Chuquicamata (x: 677 °C), Mirador (x: 672 °C) and Esperanza (x: 677 °C) deposits. The Hf concentration in zircons varies between 7,780 and 13,400 ppm, with a median value of 10,610 ppm. Escondida and Mirador deposits samples exhibit the highest (x:11,510 ppm) and lowest (x: 10,070 ppm) concentrations, respectively (Table 3; Appendix 2). No significant differences are found between core and margin in zircons and for both zircon's crystallization temperatures and Hf concentration among the studied PCDs. Zircons from the different hydrothermal alteration zones of a given PCD also exhibit the same lack of significant differences. The temperature of zircon crystallization from all porphyries fall mainly between 738 °C and 637 °C and this temperature range is consistent with zircon crystallization at near-eutectic conditions close to the solidus of hydrous granite [START_REF] Fu | Ti-in-zircon thermometry: Applications and limitations[END_REF]. High Hf values are similar to values reported in zircons from other porphyry copper mineralized systems [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF]. Only, Escondida shows a decrease in crystallization temperature associated with increasing Hf concentration. This characteristic is also reported in zircon from El Salvador Porphyry (Chile) and could be related to a higher degree of fractionation [START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF].

REE Patterns of zircon

The abundances of the rare earth elements (REE) measured in zircons from the four selected PCDs were normalized to the chondrite values of [START_REF] Mcdonough | The composition of the Earth[END_REF]. REE patterns of zircons from all studied PCDs show similar shapes. They all evidence low light REE (LREE) and elevated heavy REE (HREE) contents with distinctive large positive Ce and small negative Eu anomalies (Fig. 6). There is no significant difference in the REE patterns of zircons collected from different hydrothermal alteration zones nor differences observed between core and margin.

The zircons studied herein are consistent with those published for porphyry deposits elsewhere [START_REF] Belousova | Igneous zircon: trace element composition as an indicator of source rock type[END_REF][START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF]. Thus, zircons from arc magma intrusions typically have similar overall patterns but vary slightly by the size of Ce and Eu anomalies. In PCDs, the Ce anomaly is typically larger and the Eu anomaly is typically smaller in magnitude compared to those from non-mineralized intrusions [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF]Shen et al., 2012;[START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF].

Geochemical signatures of zircon

Variation in the concentration of trace elements measured in zircons has been used as a relatively useful tool to differentiate between zircons that come from porphyry fertile intrusive bodies from those that are unrelated to porphyry mineralization [START_REF] Belousova | Igneous zircon: trace element composition as an indicator of source rock type[END_REF][START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. High Ce/Nd (> 1), Eu/Eu* (> 0.4), (Ce/Nd)/Y (> 0.01) ratios and low Dy/Yb (< 0.3) and Th/U (< 1) ratios have been documented in zircons originating from PCDs worldwide [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Variations of these ratios can be explained in terms of the oxidation state, water content and/or degree of fractionation (co-crystallizing assemblage) of magmas.

Figure 7 shows the relationship between (Ce/Nd)/Y and Eu/Eu * ratios calculated for the study sites. The (Ce/Nd)/Y ratio varies between 0.004 and 4.118 (Table 3; Appendix 2), but the majority of the analyzed zircon (80%) in this study have values between 0.01 and 0.16 (Fig. 7).

Most zircons coming from Mirador, Esperanza and Escondida porphyries shows (Ce/Nd)/Y ratio > 0.01, with median values > 0.026 in in all cases (Table 3). Zircons collected from Chuquicamata porphyry present a greater dispersion in (Ce/Nd)/Y ratio, with some values < 0.01 (Fig. 7). Zircons with a (Ce/Nd)/Y ratio > 0.01 indicate crystallization from a magma with a relatively high-water content (≥ 4 wt % H2O) [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. The Eu anomalies (Eu/Eu*) were calculated from the normalized values of the Sm and Gd concentrations. The Eu/Eu* ratio is defined as EuN/(SmN x GdN) 1/2 , where the abundance of the elements were normalized to the chondrite values of [START_REF] Mcdonough | The composition of the Earth[END_REF]. In zircons from the studied PCDs this anomaly varies between 0.22 and 0.93 (Table 3; Appendix 2). Zircons coming from Mirador present highest Eu/Eu* ratios, with a median value > 0.6, whereas zircons coming from Esperanza, Chuquicamata, and Escondida, with exception of zircons from propylitic alteration, present the relatively lower Eu/Eu* ratio values with a median value > 0.44 (Fig. 7 and Table 3). The Eu/Eu* ratios > 0.4 in zircon indicate crystallization in a magma with a high oxidation state (FMQ +1 a +2) and/or a relatively high-water content (≥ 4 wt % H2O) [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. The possible effects of accessory mineral phases co-crystallisation on Eu anomaly in zircon are discussed below (see section 5.3). The Chuquicamata and Escondida porphyries contains a significant number of zircons with Eu/Eu* ratio values < 0.4 (Fig. 7 and Table 3). For both cases these zircons were taken from samples with propylitic alteration, which develops in the margins of the intrusive bodies.

A positive correlation for the zircons of the four studied deposits is observed between the Dy/Yb and Th/U ratios (Fig. 8). The Dy/Yb ratio ranges between 0.097 and 0.305 and most zircons (99%) present Dy/Yb ratio values < 0.3 (Table 3; Appendix 2). The Dy/Yb ratio is a proxy for the MREE content relative to the HREE (e.g. Dy, Yb, [START_REF] Davidson | Amphibole "sponge" in arc crust?[END_REF]. Dy/Yb ratio values < 0.3 suggest that the zircons formed in magmas with a higher HREE content with respect to MREE, which can be widely attributed to amphibole fractionation [START_REF] Davidson | Dy/Dy*: Variations arising from mantle sources and petrogenetic processes[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF][START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF], although the garnet fractionation can also play an important role in the HREE behavior (Alonso-Perez et al., 2009;[START_REF] Bissig | High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia[END_REF][START_REF] Rottier | Origin and evolution of magmas in the porphyry Au-mineralized Javorie volcano (Central Slovakia): evidence from thermobarometry, melt inclusions, and sulfide inclusions[END_REF]). The Th/U ratio in the studied zircons ranges between 0.15 and 1.09, with only few zircon grains from Chuquicamata and Escondida deposits with Th/U ratios > 1 (Fig. 8; Table 3; Appendix 2). In fact, 95% of the zircons analyzed in this study have Th/U ratios between 0.1 and 1 (Fig. 8). Th/U ratios between 0.1 and 1 suggest zircons formation in fractionated magmas. Th and U are mainly incompatible with major rock forming minerals (e.g. [START_REF] Bea | Residence of REE, Y, Th and U in Granites and Crustal Protoliths; Implications for the Chemistry of Crustal Melts[END_REF]. Both are compatible with zircon (Hoskin et al., 2000;[START_REF] Hanchar | Rare earth element behaviour in zircon-melt systems[END_REF], but Th is still less compatible than U and therefore will tend to remain in the residual melt [START_REF] Kirkland | Zircon Th/U ratios in magmatic environs[END_REF], The high degree of fractionation of magma can be evident by the positive correlation between both ratios.

Discussion

Shape, temperature and crystalline textures of zircons from PCDs

The morphology of zircon grains analyzed in this study can be related to cooling rates, magma composition and temperature of the melt from which they crystallized [START_REF] Pupin | Zircon and granite petrology[END_REF][START_REF] Corfu | Atlas of zircon textures[END_REF]. The studied zircon grains are slightly longer than wider (Fig. 3), which indicates that they formed as a result of relatively rapid cooling [START_REF] Corfu | Atlas of zircon textures[END_REF], similarly to zircons described in other PCDs (example, El Teniente; [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF]. The zircon crystals mainly present a morphology of prismatic forms of type {100} (see section 4.1), probably favored by a growth blocking effect produced by the adsorption of protons. These protons are provided in the growth environment by water molecules, hydrous complexes, and by elements such as U, Th, P, Hf and Y [START_REF] Benisek | Factors controlling the development of prism faces in granite zircons: a microprobe study[END_REF][START_REF] Vavra | Systematics of internal zircon morphology in major Variscan granitoid types[END_REF], whose concentrations increase with the degree of melt fractionation [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF]. A relatively high degree of fractionation would explain the high U, Th, and Hf concentrations measured in zircons from our PCDs. The calculated XI.A and XI.T values [START_REF] Pupin | Zircon and granite petrology[END_REF][START_REF] Belousova | Zircon crystal morphology, trace element signatures and Hf isotope composition as a tool for petrogenetic modelling: examples from eastern Australian granitoids[END_REF], indicate crystallization at relatively low temperatures (668 ° to 689 °C) from monzonitic to granodioritic magmas with a relatively high Al concentration with respect to the alkalis (Fig. 9a; Table 2; Appendix 1). The results provided by XI.A are consistent with the lithologies from which the zircon samples were taken. The temperatures estimated from XI.T are in agreement with the temperatures calculated from the Ti-in-zircon thermometer (Fig. 9b), which mainly range between 738 and 637 ± 30 °C. This strengthens our hypothesis (see section 4.1) that aSiO2 and aTiO2 are close to 1 and 0.7 respectively in our PCDs. The temperatures determined are thus consistent with crystallization of zircons under eutectic conditions near the hydrous granite solidus and similar to those reported in other copper porphyry systems worldwide [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF].

The internal texture of our zircons exhibits zoned, weakly zoned or unzoned cores and strongly oscillatory zoned rims. The origin of zoned oscillation in zircon grains is a consequence of the oscillatory distribution of trace elements, mainly high field strength elements (HFSE), such as Zr, Nb, Hf, REE, U, Th and Ta [START_REF] Hoskin | Rare earth element chemistry of zircon and its use as a provenance indicator[END_REF][START_REF] Corfu | Atlas of zircon textures[END_REF][START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF]. High concentrations of these elements were measured in studied zircons (Table 3), whose distribution into crystals can be controlled by cation substitution, diffusion, and melt polymerization at the zircon/melt interface [START_REF] Hoskin | Rare earth element chemistry of zircon and its use as a provenance indicator[END_REF][START_REF] Corfu | Atlas of zircon textures[END_REF][START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. The increase in oscillatory textural in studied zircon can be due to rapid magma cooling and crystal growth rate relative to the slow diffusion rate of HFSE ions in the melt boundary layer around the growing crystal, that is to say, the faster the growth rate relative to the HFSE diffusion rate, the greater the complexity of oscillatory growth banding [START_REF] Hofmann | Sub-micron-scale trace-element distributions in natural zircons of known provenance: implications for Ti-in-zircon thermometry[END_REF]. Thus, the internal texture observed in our zircons can confirm the rapid magma-cooling rate already inferred from the morphological analysis. These textures are similar to those documented by [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF] in zircons from different PCDs worldwide. However, from cathodoluminescence analysis complemented with microscopic observations used in this research, it was not possible to observe mottled textures [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF]; El Teniente PCD), which would indicate modification by the circulation of hydrothermal fluids. This could be due to the fact that the zircons in Teniente crystallized earlier at a higher temperature with respect to our zircons [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF]. Finally, the low LREE content, i.e. lower than the MREE content (Fig. 6), also suggests that zircons are not geochemically altered (Bell et al., 2016).

Geochemical signatures of zircon as indicator of metallogenic fertility

Geochemical signatures from zircons have been used to differentiate between intrusive bodies related to PCD's from non-mineralized intrusive bodies [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] proposed the Ce 4+ /Ce 3+ ratio calculated in zircon as an indicator of the magma oxidation state. Ce 4+ /Ce 3+ ratios > 300 were estimated in zircons coming from porphyry copper systems at the El Abra-Chuquicamata metallogenic belt [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] and El Teniente mine [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF], Chile. For the Central Asian Orogenic Belt, Ce 4+ /Ce 3+ ratios > 120, were estimated for zircons collected from PCDs of Bozshakol, Nurkazghan, Kounrad, Borly, Aktogai, and Koksai, Kazakhstan; Baogutu and Tuwu-Yyong, China; and Erdenet, Mongolia [START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF]. In the present study, it was not possible to calculate this ratio, because the La and Pr concentrations, two essential parameters for calculating the Ce anomaly (Ce/Ce*), were mainly too low (La below the detection limit: LOD). The low La concentration in most of the zircon (< LOD and < 0.01) is also indicative of the lack of chemical contamination by small inclusions [START_REF] Zou | Insight into zircon REE oxy-barometers: A lattice strain model perspective[END_REF]). An alternative is to use the Ce/Nd ratio as a proxy for the Ce anomaly [START_REF] Chelle-Michou | Zircon petrochronology reveals the temporal link between porphyry systems and the magmatic evolution of their hidden plutonic roots (the Eocene Corocco-huayco deposit, Peru)[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Zircons that crystallize from more oxidized magmas tend to have high Ce/Nd values (> 1). The zircons coming from four studied PCDs indeed show Ce/Nd ratios > 1 (Table 3), which indicate zircons crystallization from a magma with a high oxidation state (FMQ +1 to +2; [START_REF] Richards | The oxidation state, and sulfur and Cu contents of arc magmas: implications for metallogeny[END_REF][START_REF] Sun | The formation of porphyry copper deposits[END_REF]. However, recent studies discuss the use of this proxy as a valid oxy-barometer [START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF][START_REF] Zhong | Can magmatic zircon be distinguished from hydrothermal zircon by trace element composition? The ef-fect of mineral inclusions on zircon trace element composition[END_REF][START_REF] Zou | Insight into zircon REE oxy-barometers: A lattice strain model perspective[END_REF]. [START_REF] Zou | Insight into zircon REE oxy-barometers: A lattice strain model perspective[END_REF] based on the positive correlation between high Ce/Nd ratio and low La values, notably suggests that Ce/Nd ratio could be dominated by La contents rather than oxygen fugacity. In our zircons, no positive correlation is found between Ce/Nd and La values. Therefore, we think Ce/Nd ratio measured in zircon can be used as a possible indicator of oxidation state of magma.

If initial U content were known, calculations of FMQ could be performed with the newly proposed magmatic oxy-barometer using Ce, U, and Ti contents of magmatic zircons [START_REF] Loucks | New magmatic oxybarometer using trace elements in zircon[END_REF].

The depth of the Eu anomaly (Eu/Eu*) can be associated with the oxidation state and/or water content of the magma [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF] and also, may be affected by co-crystallization of amphibole, apatite, titanite, plagioclase, and garnet [START_REF] Buret | From a longlived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)[END_REF][START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF][START_REF] Lu | Zircon fingerprinting of magmatic-hydrothermal systems in the Archean Yilgarn Craton: Geological Survey of Western Australia[END_REF]. Eu/Eu* ratios > 0.4 were estimated in zircons from porphyry copper systems in the El Abra-Chuquicamata metallogenic belt [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El Teniente [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF] and El Salvador, Chile; Yanacocha, Peru and Yerington and Butte, USA [START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF]. Eu/Eu* ratios > 0.3 have been measured in zircons coming from different PCDs worldwide, in Batu Hijau, Indonesia; Tampakan, Philippines; Sar Cheshmeh and Sungun Iran; Dexing, Jiama, Qulong, Nannihu and Yuchiling, China [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Our zircons generally show Eu/Eu* values > 0.4 (Figs. 7 and 10; Table 3), similar to those observed in zircons from different porphyries also located in Northern Chile, whereas in the associated non-mineralized intrusive bodies, Eu/Eu* ratios < 0.4 are found, such as for Pajonal-el Abra, Los Picos and Fortuna complexes [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] and precursor non-mineralized intrusive body to El Salvador PCD [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF] (Fig. 10a andb). The high oxidation state of the magmas transforms the Eu 2+ to Eu 3+ . Trivalent Eu cannot be incorporated into the plagioclase structure but can be incorporated into the zircon structure as Eu 3+ [START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF] leading to a ratio > 0.4. Another hypothesis to explain the Eu/Eu* ratios > 0.4 in zircons is related to the fractionation of garnet and hornblende, this latter observed as phenocrysts in most of the studied samples. The presence of garnet and hornblende in the lower-crustal residuum indicates highwater content in the magma (≥ 4 wt % H2O; Alonso-Perez et al., 2009;[START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF]Richard, 2011;[START_REF] Bissig | High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia[END_REF][START_REF] Rottier | Origin and evolution of magmas in the porphyry Au-mineralized Javorie volcano (Central Slovakia): evidence from thermobarometry, melt inclusions, and sulfide inclusions[END_REF]. This condition inhibits early plagioclase crystallization at high temperature and pressure, which yields Eu/Eu* values closer to unity in evolved hydrous melts [START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF][START_REF] Richards | High Sr/Y magmas reflect arc maturity, high magmatic water content, and porphyry Cu±Mo±Au potential: Examples from the Tethyan arcs of central and eastern Iran and western Pakistan[END_REF][START_REF] Richards | Adakite-like rocks: Their diverse origins and questionable role in metallogenesis[END_REF][START_REF] Chiaradia | Why large porphyry Cu deposits like high Sr/Y magmas?[END_REF][START_REF] Loucks | Distinctive composition of copper-ore-forming arcmagmas[END_REF]. Also, when magma cooled at temperatures close to solidus (close or slightly below the crystallization temperature of zircon) (Figs. 5 and9), a significant amount of plagioclase begins to crystallize [START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF][START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF]. Additionally, the albite plagioclase is more common in PCDs with respect to anorthite plagioclase, the Eu being least compatible in the latter, so the onset of plagioclase crystallization in the PCDs, should not have a major effect on the Eu/Eu* ratio in the residual melt.

Other ratios measured in zircon that can be related to a high-water content in magma are the (Ce/Nd)/Y and (10,000xEu/Eu*)/Y ratios [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. In these magmas, early garnet and hornblende crystallization depletes the Y concentration in the residual melt (Alonso-Perez et al. 2009;[START_REF] Richards | Geologic evolution of the Escondida area, northern Chile: A model for spatial and temporal localization of porphyry Cu mineralization[END_REF][START_REF] Richards | High Sr/Y magmas reflect arc maturity, high magmatic water content, and porphyry Cu±Mo±Au potential: Examples from the Tethyan arcs of central and eastern Iran and western Pakistan[END_REF][START_REF] Chiaradia | Why large porphyry Cu deposits like high Sr/Y magmas?[END_REF][START_REF] Bissig | High Sr/Y Magma Petrogenesis and the Link to Porphyry Mineralization as Revealed by Garnet-Bearing I-Type Granodiorite Porphyries of the Middle Cauca Au-Cu Belt, Colombia[END_REF]). Therefore, we expect higher Eu/Eu*/Y and (Ce/Nd)/Y ratios in zircons from PCDs zircons than in zircons from non-mineralized intrusive bodies (lower water content). Ratios of (10,000xEu/Eu*)/Y > 1 and (Ce/Nd)/Y > 0.01 have been documented by [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF] in zircon from different PCDs at Batu Hijau, Indonesia; Tampakan, the Philippines; Sar Cheshmeh, and Sungun, Iran; Dexing, and Jiama, Qulong Nannihu and Yuchiling, China. For Chile, zircon grains from Radomiro Tomic, El Abra, and Opache PCDs, show (Ce/Nd)/Y > 0.01 ratios, whereas Fortuna, Los Picos and the Pajonal-el Abra intrusive Complex tend to exhibit (Ce/Nd)/Y < 0.01 ratios (Fig. 10b andc). The majority of zircon grains from Chuquicamata, Mirador, Esperanza and Escondida PCDs also show (Ce/Nd)/Y > 0.01 ratio values (Fig. 7 and10). This ratio therefore seems pertinent to discriminate between zircons that come from PCDs from those non-mineralized intrusive bodies ones.

The REE patterns found in the studied zircons indicate that these crystals have low LREE concentrations, with the exception of Ce (Fig. 6), whereas the MREE to HREE tend to increase (Fig. 6). This is due to the increase of the zircon/melt partition coefficient from La to Lu as the ionic radius decreases (e.g. [START_REF] Sano | High mass resolution ion microprobe analysis of rare earth elements in silicate glass, apatite and zircon: lack of matrix dependency[END_REF]. The Dy/Yb ratio may be an indicator of the content of MREE with respect to HREE (Dy, Yb, [START_REF] Davidson | Amphibole "sponge" in arc crust?[END_REF]2013) related to the degree of magma fractionation. Low Dy/Yb ratio < 0.3 were found in studied PCDs by [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Zircons grains from Chuquicamata, Mirador, Esperanza and Escondida PCDs also show Dy/Yb ratio values < 0.3 (Fig. 8 and Fig. 10c andd). This value can be mainly related to the early crystallization of hornblende that tends to preferentially incorporate MREE over HREE [START_REF] Davidson | Amphibole "sponge" in arc crust?[END_REF]2013). Therefore, the fractionation degree of hornblende in hydrous magmas should decrease the Dy/Yb ratio values in the residual magma [START_REF] Davidson | Amphibole "sponge" in arc crust?[END_REF]2013;[START_REF] Richards | Adakite-like rocks: Their diverse origins and questionable role in metallogenesis[END_REF][START_REF] Lu | Fluid flux melting generated post-collisional high-Sr/Y copper-ore-forming water-rich magmas in Tibet[END_REF] and therefore also in the zircons. On the other hand, zircons coming from non-mineralized intrusive bodies tend to present Dy/Yb ratios > 0.3 (Fig. 10c andd), indicating low water content and low degree of fractionation.

The Hf concentration and Th/U ratio measured on zircons from intrusive bodies have also been linked to the degree of magma fractionation [START_REF] Xiang | U and Th contents and Th/U ratios of zircon in felsic and mafic magmatic rocks: Improved zircon-melt distribution coefficients[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Kirkland | Zircon Th/U ratios in magmatic environs[END_REF], however, in both cases geochemical thresholds could not be defined. The studied zircons have high Hf concentration (from 7,780 ppm to 13,400 ppm) above Hf concentration reported for zircons from crustal rocks [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF] and similar to zircons from other PCDs, such as El Abra, Opache, Chuquicamata and Radomiro Tomic; Chile [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El Salvador, Chile; Yanacocha, Peru and Yerington and Butte, USA [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF] (Fig. 10a). Also, Hf concentrations tend to be higher than the one reported by zircons from non-mineralized intrusive bodies from Chuquicamata and El Salvador Mining Districts [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF]: Dilles et al., 2015) (Fig 10a). Only the Hf concentration in zircons from El Teniente porphyry tends to be relatively lower than in the aforementioned ore deposits [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF], which can be related to the generation of the magma for this ore deposit in a large relatively shallow magma chamber mainly composed of mantle-derived mafic magmas. El Teniente porphyry being the final product of magmatic differentiation (Stern et al., 2011), the zircons then formed in a less differentiated magma, as corroborated by high Th/U values (close to 1) and leads to relatively higher crystallization temperatures for the zircons [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF]. Therefore, excluding the particular case of Teniente, we define a lower geochemical threshold of 8,750 ppm (corresponding to the 95 percentile) for Hf concentrations in zircons coming from PCDs.

The Th/U ratio ranges between 1 and 0.1 (Fig. 8) (Table 3), in agreement with values published for others PCDs, such as El Abra, Opache, Chuquicamata and Radomiro Tomic [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El Salvador [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF], El Teniente; Chile [START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF] (Fig. 10d), Bozshakol, Nurkazghan, Kounrad, Borly, Aktogai, and Koksai; Kazakhstan, Baogutu and Tuwu-Yyong; China, and Erdenet; Mongolia [START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF]. Zircons from rocks with lesser degree of magma fractionation tend to present Th/U ratio values > 1, such as the non-mineralized intrusive of the Chuquicamata and El Salvador Mining Districts [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF] (Fig 10 d). Thus, Th/U values ranging between 1 and 0.1, define a geochemical range for porphyry mineralized bodies.

Porphyry Indicator Zircon (PIZ)

The zircons collected from Chuquicamata, Mirador, Esperanza and Escondida PCDs display similar geochemical and morphological characteristics to zircons coming from other porphyry copper deposits worldwide, all formed from calc-alkaline magmatic intrusions in convergent margins [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Muñoz | Zircon trace element and O-Hf isotope analyses of mineralized intrusions from El Teniente ore deposit, Chilean Andes: constraints on the source and magmatic evolution of porphyry Cu-Mo related magmas[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Geochemical characteristics are high Hf concentrations, high Ce/Nd, Eu/Eu*, (10,000xEu/Eu*)/Y, (Ce/Nd)/Y ratios, intermediate Th/U ratios and low Dy/Yb ratios. This study supports zircon as a reliable porphyry fertility indicator mineral as previously proposed (e.g. Bouzari et al., 2011;[START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF][START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF]. It also establishes a group of geochemical indicators for zircons summarized conceptually as Porphyry Indicator Zircon (PIZ). In our framework, a 'PIZ' zircon, needs to comply with each of the following geochemical values: Hf > 8,750 (ppm), Ce/Nd > 1, Eu/Eu* > 0.4, 10,000 x (Eu/Eu *)/Y > 1, (Ce/Nd)/Y > 0.01, Dy/Yb < 0.3 and Th/U < 1 -> 0.1.

For the studied zircons that diverge from these geochemical thresholds (see section 5.2), the presence of ante-crystals inherited from precursors intrusive, zircons from host rock [START_REF] Miller | Zircon growth and recycling during the assembly of large, composite arc plutons[END_REF] and/or of accessory minerals might explain their behavior [START_REF] Buret | From a longlived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)[END_REF][START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF]. Accessory minerals notably tend to crystallize contemporaneously with zircons, competing for trace elements, such as REE, available in the melt (e.g. apatite, titanite; [START_REF] Buret | From a longlived upper-crustal magma chamber to rapid porphyry copper emplacement: Reading the geochemistry of zircon crystals at Bajo de la Alumbrera (NW Argentina)[END_REF][START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF]. In the studied PCDs, the observed titanite would be of hydrothermal origin and not magmatic, which is corroborated by relatively high Ta (> 0.2 ppm) and Nb (> 1 ppm) values measured in zircons [START_REF] Loader | The effect of titanite crystallisation on Eu and Ce anomalies in zircon and its implications for the assessment of porphyry Cu deposit fertility[END_REF] Table 3). Also, apatite was recognized in many studied PCD samples [START_REF] Pizarro | Trazadores mineralógicos como indicadores de denudación de sistemas mineralizados tipo pórfido cuprífero en el relleno sedimentario de cuencas adyacentes[END_REF]. Petrographic observations and geochemical analysis suggest that much of the apatite crystallized relatively late, after the crystallization of plagioclase (Sr/Y ratios < 1; [START_REF] Pan | Apatite trace element and halogen compositions as petrogenetic-metallogenic indicators: Examples from four granite plutons in the Sanjiang region, SW China[END_REF] or may have precipitated directly from hydrothermal fluid (in the latter case with high Ca and Low Mn and Na contents [START_REF] Bouzari | Hydrothermal alteration revealed by apatite luminescence and chemistry: a potential indicator mineral for exploring covered porphyry copper deposits[END_REF]. Thus, apatite crystals have crystallized after zircon. Although in some zircon grains we observed small apatite inclusions, suggesting a co-crystallization between both minerals [START_REF] Lee | Using zircon trace element composition to assess porphyry copper potential of the Guichon Creek batholith and Highland Valley Copper deposit, south-central British Columbia[END_REF], which may have a minor influence on zircon trace-element compositions (e.g.

LREE, Th and U).

In our study, 94% and 71% of the zircon grains from Mirador and Esperanza porphyries, respectively, comply with PIZ characteristics (Fig. 11 and Table 3). Whereas for Escondida and Chuquicamata porphyries, the percentages of zircons with PIZ characteristics are relatively lower, 64% and 54%, respectively (Fig. 11). The latter may be related to the fact that very few zircons with PIZ characteristics were found in the propylitic alteration zone both in Chuquicamata and Escondida porphyries, 33% and 15%, respectively (Table 3), while that the potassic and phyllic hydrothermal alteration zones of studied all porphyries have zircon percentages with PIZ characteristics < 56% (Table 3). The lower PIZ percentages in propylitic alteration zones may be due the localization of this zone at the periphery of the intrusive body.

Therefore, these zircons may have crystallized in an earlier stage of the magmatic evolution with a lower oxidation state, and/or lower degree of fractionation compared to the magmas that originated from the central zone of the intrusive body. The other option is that since they are peripheric rocks, they may likely to incorporate zircons coming from the wall-rocks [START_REF] Miller | Zircon growth and recycling during the assembly of large, composite arc plutons[END_REF].

The Fortuna and Los Picos Complexes [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], and non-mineralized Intrusive Pre-El Salvador [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF] don't have zircons with PIZ characteristic, only the Pajonal-El Abra Complex, exhibits 3% of PIZ [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] (Fig. 11). In addition to the deposits studied, a lot of other porphyries located in Eocene-Oligocene metallogenic belt from Northern Chile have over 54% of their zircons with PIZ characteristic, with the exception of the El Abra PCD (only 33%; Fig. 11). From this, we suggest that PIZ can be considered as an effective indicator for copper porphyries (Fig. 11). Because the zircon can persist in the surficial environment despite weathering and transport (e.g. [START_REF] Thomas | Detrital-zircon geochronology and sedimentary provenance[END_REF], and also can be retrieved from a wide range of exploration materials, such as soils, regolith and glacial, fluvial or/and alluvial sediments, they can be used as a tool for the exploration of PCDs and the selection of promising areas. This might be particularly useful when PCD is buried and where minerals of hydrothermal alteration have been extensively weathered to clays during surface processes.

Additionally, our results provide the basis for the fertility assessment of detrital zircons from sedimentary sequences adjacent to worldwide PCDs metallogenic belts.

Conclusions

The petrographic and geochemical characteristics of zircons from the Chuquicamata, Mirador, Esperanza and Escondida porphyry copper deposits located in the Eocene-Oligocene metallogenic belt from Northern Chile, were used to validate zircon as an indicator of metallogenic fertility and evaluate its use as an indicator mineral for copper porphyry deposits.

The conclusions can be summarized as follows:

• The zircons from porphyry copper deposits (PCD) crystallized from monzonitic to granodioritic magmas at temperatures that vary mostly between 637 °C and 738 °C, as indicated by Ti-in-zircon thermometer and morphological analysis.

• The zircons from different PCDs show euhedral morphologies mainly characterized by prisms {110} and pyramidal faces {101} defined as subtype S8, S9 and S4.

• The zircons from different PCDs present high Hf concentrations (> 8,750 ppm), high Ce/Nd (> 1), Eu/Eu* (> 0.4), (10,000xEu/Eu*)/Y (> 1), (Ce/Nd)/Y (> 0.01) ratios, intermediate Th/U (< 1 -> 0.1) ratios and low Dy/Yb (< 0.3) ratios, whose geochemical values can be linked with a high oxidation state (FMQ +1 to +2), a high water-content (≥ 4 wt % H2O) and a high degree of fractionation in the magma. These geochemical characteristics define the Porphyry Indicator Zircon (PIZ).

• PIZ can be used as a porphyry indicator mineral and as an effective exploration tool in search for buried PCDs in detrital sedimentary record. Escondida. The dashed vertical and horizontal lines separate fertile from non-fertile fields for porphyry copper deposits worldwide; fertile intrusions having Ce/Nd)/Y > 0.01 and Eu/Eu* > 0.4 ratios [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. Escondida. The dashed vertical line separates fertile from non-fertile fields for porphyry copper deposits worldwide; fertile intrusions having Dy/Yb ratio < 0.3 [START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. studied PCDs (see Appendix 1). b) Temperatures were calculated using the Ti-in-zircon thermometer, assuming an activity in the melt for aSiO2 = 1 and aTiO2 = 0.7 [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF]. [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El Salvador [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF], Chuquicamata, Mirador, Esperanza, Escondida (This work). Nonmineralized intrusive bodies: Pajonal-El Abra, Los Picos and Fortuna intrusive Complexes [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] and non-mineralized intrusive pre-El Salvador PCD [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF] The fine dashed vertical and horizontal lines separate fertile from non-fertile fields for porphyry copper deposits worldwide [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF][START_REF] Dilles | Zircon compositional evidence for sulfur-degassing from ore-forming arc magmas[END_REF][START_REF] Shen | Oxidation condition and metal fertility of granitic magmas: zircon trace-element data from porphyry Cu deposits in the Central Asian Orogenic Belt[END_REF][START_REF] Lu | Zircon compositions as a pathfinder for porphyry Cu±Mo±Au deposits[END_REF]. The coarse dashed vertical lines separates fertile from non-fertile fields for porphyry copper deposits, these geochemical value were calculated from zircons coming from studied PCDs. [START_REF] Mpodozis | Cenozoic tectonics and porphyry copper systems of the Chilean Andes[END_REF]. PCDs: El Abra, Opache, Chuquicamata, Radomiro Tomic [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El Salvador (Lee et al., 2017), Chuquicamata, Mirador, Esperanza, Escondida (This work). Nonmineralized intrusive bodies: Pajonal-El Abra, Los Picos and Fortuna intrusive Complexes [START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF] and non-mineralized intrusive pre-El Salvador PCD [START_REF] Lee | Magmatic evolution of granodiorite intrusions at the El Salvador porphyry copper deposit, Chile, based on trace element composition and U/Pb age of zircons[END_REF].

Figure Captions

) Ch07-2_1, c) Ch18-2_1, d) Ch18-2_2, e) M01-2_3, f) M01-3_4, g) M01-4_3, h) M03-3_3, i) Esp01-1_2, j) Esp01-4_3, k) Esp03-2_2, l) Esp03-4_1, m) Esc03-1_2, n) Esc06-1_2, o) Esc06-4_1, p) Esc09-

  ). High XI.A values (values close to 800) are associated with alkalis-rich magmas whereas low XI.A values (values close to 100) are associated with Al-rich magmas. For XI.T index, the high values (XI.T values close to 800) are associated with magmas that crystallized at relatively high temperatures (900 °C), whereas the low values (XI.T values close to 100) are associated with magmas that crystallized at relatively low temperatures (550 °C) (Appendix 1).

Fig. 1 .

 1 Fig. 1. Location, geology, hydrothermal alterations and sampling of the studied PCDs. a) Location of Chuquicamata, Mirador, Esperanza and Escondida DPCs in metallogenic belts from Northern Chile and Southern Peru, b) Chuquicamata map (Modified from Ossandón et al 2001), c) Esperanza map (Modified from Perelló et al 2004), d) Escondida map (Modified from Hervéet al., 2012; Riveros et al., 2014).

Fig. 2 .

 2 Fig. 2. Cathodoluminescence (left) and transmitted light (right) microscopic images of representative zircon grains collected from studied PCDs. a) Ch04-2_1, b) Ch07-2_1, c)

  4_2. The white circles represent the size and position of the ablation into the grains for measurement of trace elements. Parentheses indicate subtypes from typological classification diagram of[START_REF] Pupin | Zircon and granite petrology[END_REF].

Fig. 3 .

 3 Fig. 3. Aspect ratio histogram (length/width) of zircons coming from PCDs. a) Chuquicamata, b) Mirador, c) Esperanza, d) Escondida. n, number of analyzed crystals.

Fig. 4 .

 4 Fig. 4. Zircon morphology from PCDs, schematically illustrated in the typological classification diagram of Pupin (1980). a) Chuquicamata, b) Mirador, c) Esperanza, d) Escondida. (Appendix 1 shows as were estimated the subtypes different using transmitted light and CL images and as were calculated XI.A and XI.t from zircons collected from each samples) Fig. 5. Hf content (ppm) vs. crystallization temperature of zircons. Temperatures were calculated using the Ti-in-zircon thermometer, assuming an activity in the melt for aSiO2 = 1 and aTiO2 = 0.7 (Ferry and Watson, 2007). a) Chuquicamata, b) Mirador, c) Esperanza, d) Escondida.

Fig. 6 .

 6 Fig. 6. Chondrite-normalized REE patterns for zircons coming from porphyries copper deposits. a), b) and c) Chuquicamata, d) and e) Mirador, f) and g) Esperanza, h), i) and k) Escondida. Chondrite values are from McDonough and Sun (1995).

Fig. 7 .

 7 Fig. 7. Zircon (Ce/Nd)/Y vs. Eu/Eu* ratio plot. a) Chuquicamata, b) Mirador, c) Esperanza, d)

Fig. 8 .

 8 Fig. 8. Zircon Dy/Yb vs. Th/U ratio plot. a) Chuquicamata, b) Mirador, c) Esperanza, d)

Fig. 9

 9 Fig. 9. a) Index A (Al / Na + K) vs Temperature (Modified from Pupin, 1980). b) Hf content (ppm) vs. crystallization temperature of zircons. a) Temperatures were calculated using the average values of T index (XI.T) from zircons collected from each sample coming from all

Fig. 10 .

 10 Fig. 10. Trace elements measured in zircons from PCDs and non-mineralized intrusive bodies. PCDs: El Abra, Opache, Chuquicamata, Radomiro Tomic[START_REF] Ballard | Relative oxidation states of magmas inferred from Ce (IV)/Ce (III) in zircon: application to porphyry copper deposits of northern Chile[END_REF], El

  . a.) Zircon Hf (ppm) vs. Eu/Eu* plot. b) Zircon (Ce/Nd)/Y vs. Eu/Eu* plot. c) Zircon (Ce/Nd)/Y vs. Dy/Yb plot. d) Th/U vs Dy/Yb. Porphyry Indicator Zircon (PIZ: Hf > 8,750 (ppm), Cd/Nd > 1, Eu/Eu* > 0.4, 10,000 x (Eu/Eu*)/Y > 1, (Ce / Nd)/Y > 0.01, Dy/Yb < 0.3 y Th/U < 1 -> 0.1.

Fig. 11 .

 11 Fig. 11. Percentage of PIZ and zircon without PIZ characteristic on PCDs and nonmineralized intrusive bodies from Northern Chile (Modified from Mpodozis and Cornejo,

Acknowledgments

This work was partly funded by CONICYT (Chilean Commission on Science and Technology), by means of a Doctorados Nacionales scholarship No. 21150393 and FONDECYT Project No. 1170992, by the IRD (Institut de Recherche pour le Développement, France) by means of the grant ARTS-IRD No. 862271K and the Laboratoire Mixte International (LMI) Cuivre et Pediments (COPEDIM) and by the MDRU research project Discovery Tools for Buried Copper Deposits in the Atacama Desert, Chile. We thank Sergio Pichott, Sergio Rivera and José Perelló for allowing access and sampling at Chuquicamata and Centinela Mining Districts and to Dr.

Karl Riveros for providing samples from Escondida deposit. Also, we acknowledge the collaboration of Edith Czech on the EPMA and Marghaleray Amini on the LA-ICP-MS analyses.

Additionally, we would like specially to thank to the Dr. Sébastien Carretier and Dr. Peter Winterburn, both Directors of two last mentioned projects, for having contributed to the training of the first author as a researcher, at this moment Peter rest in peace. We gratefully acknowledge the editor Professor Rui Wang and the constructive comments and suggestions from Dr. Yongjun Lu and an anonymous reviewer.

 [START_REF] Mcdonough | The composition of the Earth[END_REF]. Temperature (Ti-in-zircon thermometer; [START_REF] Ferry | New thermodynamic models and revised calibrations for the Ti-in-zircon and Zr-in-rutile thermometers[END_REF]. % of PIZ by samples. In this study to eliminate the anomalous values, we worked with a confidence interval of σ2 (95% of the data) and the values equal to 0 or negative were eliminated.

Appendix captions

Appendix 1. Example of recognition of the main morphology of zircon grains using transmitted light and CL images for each studied porphyry and calculations of XI.A and XI.T values using [START_REF] Pupin | Zircon and granite petrology[END_REF] [START_REF] Pupin | Zircon and granite petrology[END_REF]