Zia Steven Kahou

Stéphanie Duchêne

Stéphanie Brichau

Eduardo Campos

Guillaume Estrade

Marc Poujol

Janogithan Kathirgamar

Hugo Testa

Mathieu Leisen

Sandrine Choy

Philippe De Parseval

Rodrigo Riquelme

Sébastien Carretier

Mineralogical and chemical characterization of supergene copper-bearing minerals: examples from Chile and Burkina Faso

Keywords: in situ and exotic supergene copper mineralization, Atacama Desert, Gaoua Cu-Au district, black chrysocolla, chrysocolla, pseudomalachite

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Introduction

Supergene copper mineralization (SCM) is produced by the interaction between sulfides and supergene processes and was originally defined by [START_REF] Ransome | Copper deposits near Superior, Arizona[END_REF] as sulfide oxidation and leaching of ore deposits in the weathering environment, and any attendant secondary sulfide enrichment. In order to form supergene copper mineralization, specific tectonics, climate and geomorphologic conditions are required. Tectonics controls the uplift needed to lower the groundwater table and raise the deep-seated ore deposits towards more oxidizing environments were the oxidation and leaching of sulfides may occur. On the other hand, climate controls water availability, and therefore the leaching of sulfides and remobilization of copper-bearing solutions in the supergene environment towards the locus where supergene copper-bearing minerals precipitate. Then, favorable geomorphologic conditions prevent major erosion and removal of the supergene mineralized bodies [START_REF] Hartley | Controls on supergene enrichment of porphyry copper deposits in the Central Andes: A review and discussion[END_REF][START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. Two types of SCM have been recognized: 1) in situ deposits, which are produced by nearly vertical descending Cu-bearing aqueous solutions and precipitation of SCM within or near the leached cap [START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]; and 2) exotic deposits, which are originated by lateral migration of Cu-bearing solutions from the parental deposit, without direct link with the original source of metal (Fig. 1, Münchmeyer, 1996;[START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. In order to better understand the genesis of in situ and exotic SCM deposits and the parameters controlling their formation, mineralogical and geochemical characterization are required. To the best of our knowledge, apart from the work of Chavez (2000) who described in detail the zoning and distribution of copper oxide minerals in SCM in general, all the previous studies have been focused on the description of single SCM deposits and the characterization of the secondary Kbearing minerals that are genetically linked to the precipitation of copper-bearing minerals [START_REF] Alpers | Middle Miocene climatic change in the Atacama Desert, northern Chile: Evidence from supergene mineralization at La Escondida[END_REF][START_REF] Bouzari | Anatomy, Evolution, and Metallogenic Significance of the Supergene Orebody of the Cerro Colorado Porphyry Copper Deposit, I Región, Northern Chile[END_REF][START_REF] Cuadra | Oxide mineralization at the radomiro tomic porphyry copper deposit[END_REF][START_REF] Kahou | First U-Pb LA-ICP-MS in situ dating of supergene copper mineralization: case study in the Chuquicamata mining district, Atacama Desert, Chile[END_REF][START_REF] Marsh | 40Ar/39Ar Geochronology of Cu-Au and Au-Ag Mineralization in the Potrerillos District, Chile[END_REF]Mote et al., 2001a). Furthermore, most of these studies have been carried out in the Atacama Desert and southwest USA. However, SCM can be observed all around the world (Fig. 2A) and were therefore formed under various climatic and tectonic conditions (e.g. Atacama Desert, SW of U.S.A, northern Mexico, Mongolia, Papua New Guinea, Philippines, western and central Africa, etc…). Here we present a comparison of SCM deposits in two contrasting geological and climatic settings, the Atacama Desert and the southwestern region of Burkina Faso.

For decades, the Atacama Desert represents an ideal location to study SCM because of the presence of world-class examples of both in situ (Chuquicamata, Salvador, Cerro Colorado, Zaldivar-Escondida Norte, etc.) and exotic (Mina Sur, Damiana, Tesoro, etc.) SCM formed within an active continental margin under hyperarid climate resulting from the interaction between the uplift of the Andean mountain and the intensification of the Humboldt Current [START_REF] Garreaud | Andean uplift, ocean cooling and Atacama hyperaridity: A climate modeling perspective[END_REF]. In this area, we focused our study on Zaldivar and Gaby in situ SCM and Mina Sur, Damiana and El Cobre exotic SCM, all formed during the Eocene to Miocene epochs. As a contrasted example, we also studied the in situ SCM of Gaoua, in Burkina Faso, emplaced during the Cenozoic, and located in a passive tectonic margin under a much wetter climate (i.e. sub-humid to Sahelian climate).

In more details, we carried out an intensive mineralogical and mineral chemistry studies of the oxidized copper ores using optical microscopy and SEM to describe the textural features together with EPMA and LA-ICPMS analyses for a chemical characterization. All the acquired data were then combined in order in order to better constrain the main factors controlling the genesis of SCM. The mineralogical characterizations show that Atacama Desert and SW Burkina Faso underwent similar processes during the SCM formation and preservation despite geodynamic differences. Our new chemical study confirms and implements previous ones [START_REF] Chávez | Supergene Oxidation of Copper Deposits: Zoning and Distribution of Copper Oxide Minerals[END_REF][START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF][START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF] by pointing out that exotic SCM deposits were formed under uninterrupted oxidizing conditions while in situ SCM deposits show changes in the redox conditions during their formation.

Geological Background

The Atacama Desert is worldwide known to host some of the world's largest porphyry copper deposits, e.g. Escondida, Chuquicamata and Collahuasi. Most of these deposits are located in the Precordillera, a near N-S trending pre-Andean mountain range that extends over 800 kilometers and corresponds to a former magmatic arc formed during the Incaic orogeny (Fig. 2B; [START_REF] Mpodozis | The Andes of Chile and Argentina. Geology of the Andes and its Relation to Hydrocarbon and Mineral Resources[END_REF][START_REF] Amilibia | The role of inherited tectono-sedimentary architecture in the development of the central Andean mountain belt: Insights from the Cordillera de Domeyko[END_REF][START_REF] Mpodozis | Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes[END_REF]. This mountain range contains most of Chile's porphyry copper deposit and is made up of Late Paleozoic to Eocene blocks, delimited by inverted normal and strike-slip faults [START_REF] Scheuber | Magmatic arc tectonics in the Central Andes between 21° and 25°S[END_REF]. In the Atacama Desert, the emplacement of hydrothermal alteration and hypogene mineralization was synchronous with the formation of the Precordillera [START_REF] Sillitoe | Andean Copper Province: Tectonomagmatic Settings, Deposit Types, Metallogeny, Exploration, and Discovery[END_REF] while supergene alteration occurred at least ~ 11 m.y. after the last hydrothermal event [START_REF] Sillitoe | Age of supergene oxidation and enrichment in the Chilean porphyry copper province[END_REF].

The Mina Sur exotic copper deposit (Fig. 2B) is located within the Chuquicamata mining district, the second biggest Cu producer in the world. Geological, petrological and tectonic features of the Chuquicamata porphyry copper as well as the Mina Sur exotic copper deposits have been discussed in detail by previous authors [START_REF] Dilles | The geology of the Fortuna Granodiorite Complex, Chuquicamata district, Northern Chile: relation to porphyry copper deposits[END_REF][START_REF] Mortimer | Emplacement of the Exotica orebody, Chile[END_REF][START_REF] Mpodozis | Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes[END_REF][START_REF] Newberg | Geochemical implications of chrysocolla-bearing alluvial gravels[END_REF][START_REF] Ossandón | Geology of the Chuquicamata Mine : A Progress Report[END_REF][START_REF] Rivera | Update of the Geologic Setting and Cu-Mo Deposits of the Chuquicamata District, Northern Chile[END_REF][START_REF] Sillitoe | Andean Copper Province: Tectonomagmatic Settings, Deposit Types, Metallogeny, Exploration, and Discovery[END_REF] and are only briefly summarized here. In response to the uplift of the Precordillera, several forearc basins were formed during the Late Tertiary [START_REF] Scheuber | Tectonic Development of the North Chilean Andes in Relation to Plate Convergence and Magmatism Since the Jurassic[END_REF] including the Calama basin, which hosts the Mina Sur exotic copper deposit. The basement of this basin is represented by a metamorphic Paleozoic complex, extensively faulted and brecciated and by a Permian to Carboniferous Igneous complex [START_REF] Ossandón | Geology of the Chuquicamata Mine : A Progress Report[END_REF][START_REF] Rivera | Update of the Geologic Setting and Cu-Mo Deposits of the Chuquicamata District, Northern Chile[END_REF]. The Calama formation and the El Loa group [START_REF] Tomlinson | Geologia de la Precordillera Andina de Quebrada Blanca -Chuquicamata, Regiones I y II (20°30[END_REF], both made of continental sedimentary to volcano-sedimentary erosional gravels [START_REF] May | Eocene to Pleistocene lithostratigraphy, chronostratigraphy and tectono-sedimentary evolution of the Calama Basin, northern Chile[END_REF][START_REF] May | Tectonic signatures in arid continental basins: an example from the Upper Miocene-Pleistocene, Calama Basin, Andean forearc, northern Chile[END_REF] lie above this basement. An ignimbrite flow deposited on top of the gravels was dated at 8.4 ± 0.4 Ma by K/Ar on biotite [START_REF] Mortimer | Emplacement of the Exotica orebody, Chile[END_REF], which gives a minimum depositional age for these gravels. The exotic copper mineralization, which comprises copper silicates, copper phosphates, copper carbonates and copper halides is observed either filling fractures on the bedrock or the empty spaces available between the gravels.

The Damiana exotic copper deposit originates from the lateral migration of copper solutions from the Salvador porphyry copper deposit, within the El Salvador Mining District (Fig. 2B). This mining district has been well studied by [START_REF] Gustafson | The porphyry copper deposit at El Salvador, Chile[END_REF], [START_REF] Cornejo | El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework[END_REF], [START_REF] Gustafson | Multiple Centers of Mineralization in the Indio Muerto District, El Salvador, Chile[END_REF] and Mote et al. (2001b). The district is located near the Sierra Castillo fault, which represents the southern segment of the Domeyko fault system. The Domeyko fault system is a near N-S trending major zone of deformation in the Precordillera, related to the emplacement of some of the most important porphyry copper deposits in the Atacama Desert [START_REF] Mpodozis | Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes[END_REF]. The bedrock of the mining district is made of a Paleocene rhyolitic dome complex, named the Cerro Indio Muerto, which has been intruded by hypogene mineralized porphyries [START_REF] Cornejo | El Salvador, Chile Porphyry Copper Deposit Revisited: Geologic and Geochronologic Framework[END_REF]. The exotic copper mineralization in the Damiana deposit is filling fractures that are present in the Early Cretaceous volcanoclastic rocks a.k.a. the Llanta formation [START_REF] Bissig | Andean uplift and climate evolution in the southern Atacama Desert deduced from geomorphology and supergene alunite-group minerals[END_REF][START_REF] Rojas | Damiana": Uno de los yacimientos tipo" Exoticos" de El Salvador[END_REF]. This mineralization is also within the gravels (i.e. Atacama Pediplain), filling paleochannels around the Cerro Indio Muerto. Finally, ignimbrite flow and tuff, dated at 11.6 ± 0.5 Ma and 12.5 ± 0.5 Ma respectively [START_REF] Sillitoe | A chronology of landform evolution and supergene mineral alteration, southern Atacama Desert, Chile[END_REF], cover the Atacama pediplain and yield a minimum age for the deposition of the pediment.

The El Cobre exotic deposit is linked to the Potrerillos porphyry copper deposit located approximately 30 Km to the southeast of El Salvador deposit, in the Potrerillos mining district (Fig. 2B; [START_REF] Bissig | Contrasting Landscape Evolution and Development of Supergene Enrichment in the El Salvador Porphyry Cu and Potrerillos-El Hueso Cu-Au Districts, Northern Chile[END_REF]. Previous studies discussed the geology as well as the structural features of the Potrerillos porphyry copper deposit [START_REF] Bissig | Contrasting Landscape Evolution and Development of Supergene Enrichment in the El Salvador Porphyry Cu and Potrerillos-El Hueso Cu-Au Districts, Northern Chile[END_REF][START_REF] Marsh | 40Ar/39Ar Geochronology of Cu-Au and Au-Ag Mineralization in the Potrerillos District, Chile[END_REF], indicating that this deposit is linked to the Sierra Castillo fault and is hosted by Jurassic to Cretaceous marine and volcano-sedimentary rocks. Hypogene mineralization of the Potrerillos porphyry copper deposit were emplaced during the late Eocene (~36-35 Ma; [START_REF] Marsh | 40Ar/39Ar Geochronology of Cu-Au and Au-Ag Mineralization in the Potrerillos District, Chile[END_REF]. At El Cobre exotic deposit, copper mineralization was deposited within the fractured and brecciated Paleocene andesitic and rhyolitic volcanic rocks [START_REF] Bissig | Contrasting Landscape Evolution and Development of Supergene Enrichment in the El Salvador Porphyry Cu and Potrerillos-El Hueso Cu-Au Districts, Northern Chile[END_REF], which provide therefore a maximum age for their deposition.

The Zaldivar and Gaby in situ SCM are also located within the Precordillera of northern Chile (Fig. 2B). Zaldivar is part of the Escondida cluster, which represents the biggest copper district in the world whilst Gaby is located ~ 100 Km south of Chuquicamata and ~ 43 Km east of Spence porphyry copper deposit. The formation of both deposits is linked to the compressional and transtensional movements of the Domeyko fault system, related to the Incaic orogenic event [START_REF] Mpodozis | Cenozoic Tectonics and Porphyry Copper Systems of the Chilean Andes[END_REF]. Country rocks at Zaldivar is made of the La Tabla formation [START_REF] Urzua | Geology, geochronology, and structural evolution of La Escondida copper district[END_REF], a set of Early Permian rhyolite to dacite ignimbrite and volcanic rocks. The latter are intruded by granodiorite to dacite porphyries, related to the Incaic magmatism ( between 41 Ma and 30 Ma; [START_REF] Maksaev | Fission Track Thermochronology of the Domeyko Cordillera, Northern Chile: Implications for Andean Tectonics and Porphyry Copper Metallogenesis[END_REF]. At Gaby, basement rocks are represented by the Carboniferous Quebrada Escondida metavolcanic-sedimentary rocks and the Permian Pampa Elvira granodiorite complex. This basement is intruded by two Eocene porphyries, the dike-like Gaby and Crowded porphyries. In both deposits, a well-developed supergene alteration profile is observed with a 120-500 m-thick supergene copper orebody at Zaldivar and a 250 m-thick copper oxide orebody at Gaby [START_REF] Aguilar | Discovery and Geology of the Undeveloped Codelco's Gaby Copper Deposit[END_REF][START_REF] Perelló | Geologic Controls on Hypogene Mineralization at the Zaldívar Porphyry Copper-Gold-Molybdenum Deposit, Escondida District, Northern Chile[END_REF]. Both deposits lie beneath thick gravels pediment and comprises copper silicates as predominant Cu-bearing minerals, together with copper sulfates, copper phosphates and black-copper oxides.

The Gaoua porphyry Cu-Au district in southeastern Burkina Faso (Fig. 2C), is located within the West African craton (WAC) which consists of an Archean core, juxtaposed to Paleoproterozoic greenstone belts also known as the Boromo-Goren greenstone belt [START_REF] Baratoux | Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2-2.0Ga), western Burkina Faso[END_REF]. The deposition of the Paleoproterozoic greenstone belt of the WAC took place during the Eburnean orogeny, around 2.25 to 2.15 Ga ago [START_REF] Baratoux | Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2-2.0Ga), western Burkina Faso[END_REF]. These Boromo-Goren greenstone belt consists of volcanic to plutonic rocks affected by a greenschist facies regional metamorphism. These volcanoplutonic rocks were intruded by granitoids, emplaced from ca. 2250 Ma to 2060 Ma, and deformed successively by three deformation stages [START_REF] Béziat | Gold metallogeny in the Birimian craton of Burkina Faso (West Africa)[END_REF][START_REF] Baratoux | Juvenile Paleoproterozoic crust evolution during the Eburnean orogeny (∼2.2-2.0Ga), western Burkina Faso[END_REF][START_REF] Baratoux | Tectonic evolution of the Gaoua region, Burkina Faso: Implications for mineralization[END_REF]. At a local scale, the Gaoua district is located at the southwestern margin of the Boromo Belt (Fig. 2C). The basement of the Gaoua porphyry copper deposit comprises a thick-sequence of mafic rocks (i.e. gabbro, basalt, andesite), followed by calc-akaline intrusive bodies (diorite, granodiorite, dolerite, granite, rhyolite). All the series underwent a regional greenschist-facies metamorphism [START_REF] Baratoux | Tectonic evolution of the Gaoua region, Burkina Faso: Implications for mineralization[END_REF]. Hypogene copper mineralization is hosted by the greenschist facies volcanic flows and quartz-diorite intrusions (Le [START_REF] Mignot | The Paleoproterozoic Copper-Gold Deposits of the Gaoua District, Burkina Faso: Superposition of Orogenic Gold on a Porphyry Copper Occurrence?[END_REF]. This mineralization appears as veins, hydrothermal breccia filling or is disseminated within quartz-diorite porphyry stocks at Mont Biri, Diénémara, Gongondy and Bousséra (Fig. 2D; Le [START_REF] Mignot | The Paleoproterozoic Copper-Gold Deposits of the Gaoua District, Burkina Faso: Superposition of Orogenic Gold on a Porphyry Copper Occurrence?[END_REF]. The supergene copper ore of the Gaoua district is linked to the Tertiary history of the West African craton. During the Cenozoic, the onset of a hot and wet tropical climate, in alternation with dry seasons, in this tectonically stable craton and in addition to the low denudation rates in the region (2-20 m Ma -1 ; Beauvais and Chardon, 2013) allowed for the formation of large and flat erosion surfaces a.k.a pediplains or regolith. These pediplains, which result from chemical and mechanical alteration of the bedrock (i.e. Birimian greenstone belts, [START_REF] Gunnell | Radiometric ages of laterites and constraints on long-term denudation rates in West Africa[END_REF], sometimes overlie supergene mineralization of various economic importance, i.e. manganese at Tambao, and copper at Gaoua [START_REF] Chardon | West African lateritic pediments: Landform-regolith evolution processes and mineral exploration pitfalls[END_REF]. However, to the best of our knowledge no studies have been published about the recognition and/or the characterization of the in situ SCM from the Gaoua porphyry Cu-Au district.

Analytical Procedures

Samples from five Cu-deposits in northern Chile and one Cu-Au deposit in Burkina Faso have been collected during a sampling campaigns in 2018 (i.e. Mina Sur, Damiana, El Cobre for exotic SCM) or were provided by mining geologists (i.e. Zaldivar, Gaby and Gaoua for in situ SCM). Mineralogical studies were carried out at the Géosciences Environnement Toulouse (GET, Université de Toulouse, France) using a polarizing microscope NIKON JLV 500 on polished thin sections. Backscattered electron images (BSE) as well as qualitative data were obtained using the JEOL JSM 6360 LV Scanning Electron Microscope (SEM) coupled to an energy dispersive spectrometry (EDS) analysis system at the GET laboratory. The analytical conditions used were 15kv for the acceleration voltage, 50 µm for the beam size while a tungsten filament was used as the electron source. Quantitative analyses as well as major element distribution maps were carried out at the Centre de Micro-Caractérisation Raimond Castaing (Université de Toulouse, France) using the CAMECA SXFive Electron Probe Micro-Analyzer (EPMA) on polished thin sections. The analytical conditions for the profiles were 2 µm for the beam size, 10 nA for the current intensity and an acceleration voltage of 15 keV. Data are reported in ESM 1. For the maps, the analytical settings were 100 nA for the current intensity, an acceleration voltage of 15 keV, a dwell time of 900 ms and a varying step size of 4 and 5 µm. Chemical studies, i.e. traces and REE elements analyses, were carried out at the GET laboratory using a Thermo-Fisher Element-XR, High Resolution Inductively Coupled Plasma Mass Spectrometry (HR-ICPMS) coupled to an ESI NWR213UC 213 nm laser ablation system (ns-LA). Tuning of the instrument as well as mass calibration were performed on NIST SRM 610 glass reference material, i.e. 238 U + / 232 Th + between 0.95 and 1.05, oxide production < 0.5 % and a sensitivity > 20000 cps/ppm for 238 U. Laser ablation were carried out using a laser fluence of 3 J/cm 2 , a repetition rate of 10 Hz and a 20 µm spot size. Ablated materials were transported in helium (450 mL/min) which was used as carrier gas. Each laser spot was ablated during 40s with 10s of background collection and 40s for the "wash-out". The isotopes monitored are 139 La, 140 Ce, 141 Pr, 146 Nd, 147 Sm, 151 Eu, 157 Gd, 159 Tb, 163 Dy, 165 Ho, 167 Er, 169 Tm, 173 Yb, 175 Lu. The internal and external calibration procedure suggested by [START_REF] Longerich | Laser ablation inductively coupled plasma mass spectrometric transient signal data acquisition and analyte concentration calculation[END_REF] was used. The following standards were used: NIST SRM 610 reference glass as primary standard and 91500 zircon (as a proxy for the black chrysocolla and chrysocolla, see [START_REF] Wiedenbeck | Three Natural Zircon Standards for U-Th-Pb, Lu-Hf, Trace Element and Ree Analyses[END_REF] as well as Durango apatite (as a proxy for pseudomalachite, see [START_REF] Mcdowell | A precise 40Ar-39Ar reference age for the Durango apatite (U-Th)/He and fission-track dating standard[END_REF] as secondary, quality control standards (see [START_REF] Kahou | First U-Pb LA-ICP-MS in situ dating of supergene copper mineralization: case study in the Chuquicamata mining district, Atacama Desert, Chile[END_REF]. External measurement was carried out at the beginning and the end of each analytical session and each 15 spot analyses. Data reduction was carried out using the Iolite data reduction software [START_REF] Paton | Iolite: Freeware for the visualisation and processing of mass spectrometric data[END_REF]. Operating conditions, traces and REE concentrations obtained on black chrysocolla, chrysocolla and pseudomalachite are reported in ESM 2.

Textural and chemical characterization of supergene copper mineralization 4.1 Textural features of SCM

To summarize the following description of the ore samples and the mineralogical assemblages, a synthetic paragenetic sequence is presented in Fig. 3.

The Mina Sur exotic SCM

The ore body at Mina Sur is ca. 2.2 km long, 1.2 km wide with a maximum thickness of about 110 m [START_REF] Mortimer | Emplacement of the Exotica orebody, Chile[END_REF] and lies 2 Km south of the world-class Chuquicamata porphyry copper deposit. The copper mineralization is mainly composed of chrysocolla and atacamite that fill fractures in the bedrock as well as the porosity in the overlying sedimentary cover [START_REF] Mortimer | Emplacement of the Exotica orebody, Chile[END_REF][START_REF] Münchmeyer | Exotic deposits -products of lateral migration of supergene solutions from porphyry copper deposits. Andean copper deposits : new discoveries, mineralization, styles and metallogeny[END_REF]. Macroscopic scale observations of the samples selected for this study (Fig. 4A) show that the copper mineralization is mainly composed of chrysocolla either under the form of black Mn-rich angular millimeter size clasts (a.k.a black chrysocolla or copper pitch; see [START_REF] Throop | Nature and Origin of Black Chrysocolla at the Inspiration Mine, Arizona[END_REF], or as millimetric turquoise to pale green Mn-poor bands coating both the black chrysocolla and the sedimentary clasts. Chrysocolla bands are intercalated with green micrometer size thin-bands of pseudomalachite. Atacamite, a copper chloride showing an acicular texture, is also present in small proportion. Under plane polarized light, black chrysocolla appears as black clasts, showing locally a concentric banding texture with black to brownish color variations (Fig. 4B). The chrysocolla bands (Fig. 4B) are made of microcrystalline aggregates with a strong birefringence in plane-polarized light [START_REF] Campos | Understanding Exotic-Cu Mineralisation: Part I -Characterisation of Chrysocolla[END_REF][START_REF] Foote | On solid solutions in Minerals. IV. The composition of amorphous minerals as illustrated by chrysocolla[END_REF][START_REF] Menzies | Understanding Exotic-Cu Mineralisation: Part II -Characterisation of Black Copper ("Cobre Negro[END_REF][START_REF] Sun | the nature of chrysocolla from inspiration mine[END_REF][START_REF] Thompson | Chrysocolla pseudomorphs from Ray, Arizona[END_REF]. Pseudomalachite has an emerald-green to dark green color (Fig. 4B) and a low pleochroism in planepolarized light [START_REF] Berry | On pseudomalachite and Cornetite[END_REF][START_REF] Shoemaker | Refinement of the crystal structure of pseudomalachite[END_REF]. Atacamite displays thin black prismatic crystal in cross-polarized light (Fig. 4C) and appears as overgrowths around the chrysocolla and pseudomalachite bands. Backscattered electron imaging (Fig. 4D) shows a more complex textural association between these minerals as chrysocolla and pseudomalachite display intergrowth textures. In some places, crystals of chrysocolla crosscut some pseudomalachite bands. Such textural relationships have been interpreted as resulting from dissolution-precipitation of pseudomalachite by chrysocolla [START_REF] Crane | Formation of chrysocolla and secondary copper phosphates in the highly weathered supergene zones of some Australian deposits[END_REF]. Finally, atacamite is present as prismatic crystals that grew on top of other mineral phases or also as filling available voids. Textural observations clearly shown that atacamite formed after chrysocolla and pseudomalachite.

The Damiana exotic SCM

At the scale of the outcrop, mineralization in both gravels (Fig. 5A) and bedrock fractures (Fig. 5B) appear as a homogeneous, cryptocrystalline blue-greenish mass. In hand specimens, chrysocolla is the most abundant copper mineral, followed, to a lesser extent, by copper wad, a term mainly used by miners to refer to a mixture of Mn, Fe, Cu oxyhydrates [START_REF] Fam | Eventos de mineralizacion Exotica de Cu en el distrito de Chuquicamata, II region Chile[END_REF][START_REF] Menzies | Understanding Exotic-Cu Mineralisation: Part II -Characterisation of Black Copper ("Cobre Negro[END_REF]Mote et al., 2001a;[START_REF] Pincheira | Las fases de cobre negro en yacimientos exoticos: nuevos antecedentes mineralógicos, texturales y composicionales[END_REF].

In the ore found in the Damiana bedrock, optical microscopy observations confirm that chrysocolla predominates over copper wad and pseudomalachite. In the fractures, chrysocolla appears as greenish and heterogenous fillings. Sometimes, chrysocolla appears as micrometric concentric bands (Fig. 5C). Copper wad precedes chrysocolla and appears as thin coatings in fractures with a brown to dark brown color and a low pleochroism. Pseudomalachite was the last mineral to crystallize. It shows a thin coating texture under SEM, indistinguishable under the petrographic microscope and occurs as overgrowths on chrysocolla (Fig. 5D). Backscattered electron imaging shows a clear paragenetic sequence characterized by 1) copper wad showing colloform texture deposited as thin coatings within the bedrock fractures 2) massive chrysocolla is found within fractures in the bedrock usually on top of copper wad and 3) pseudomalachite filling the empty spaces left (Fig. 5D). In the Damiana gravels, the SCM is deposited in the available empty spaces within the gravels (Fig. 5E). Chrysocolla is the dominant copper phase with lesser amounts of copper wad, pseudomalachite, microcrystalline quartz and apatite. Under plane polarized light, chrysocolla appears as millimetric greenish layers coating the gravels clasts. The texture is relatively homogeneous, with a low pleochroism and a strong relief (Fig. 5E). Pseudomalachite shows green to dark green color in plane polarized light, strong relief with a millimeter crystal size (Fig. 5E). Finally, quartz appears as euhedral micro-crystals, with low relief and birefringence (Fig. 5E). SEM-EDS analyses have shown a precipitation sequence characterized by chrysocolla precipitation coeval with colloform apatite, followed by the crystallization of pseudomalachite and microcrystalline quartz at a later stage (Fig. 5F). BSE images of chrysocolla displays either homogeneous texture or micrometer-scale banded texture, linked to variable Si/Cu ratios as shown by SEM-EDS analyses.

The El Cobre exotic SCM

At the scale of the outcrop, mineralization appears as massive cryptocrystalline light-blue to darkblue masses filling the fractures. It may also be present as thin coating on the edge of some fractures (Fig. 6A,B). Chrysocolla is the most abundant Cu-bearing mineral, followed by minor copper wad and traces of pseudomalachite.

Under a petrographic microscope, a common paragenetic sequence is easily distinguishable for the filling of the fractures: first, copper wad is deposited as thin coatings covering the edges of the fractures, followed by the precipitation of chrysocolla (Fig. 6C). Finally, pseudomalachite and microcrystalline quartz are the last mineral phases to be deposited. At El Cobre, chrysocolla occurs mostly as cluster of concentric micrometer-scale laminae (Fig. 6C). Under SEM, chrysocolla shows a fairly homogeneous texture (Fig. 6D). Pseudomalachite crystallizes as concentric spherulitic and mammillary texture (as shown by SEM images, Fig. 6D) filling open spaces, impregnating bedrock fractures and overgrowing chrysocolla. 4. 1.4 Zaldivar in situ SCM The SCM at Zaldivar porphyry copper deposit extends over a thickness of about 500 m under the piedmont gravels [START_REF] Monroy | Nueves antecedentes geologicos del porfido cuprifero Zaldivar II Region, Chile[END_REF]. At a macroscopic scale, the in situ SCM appears as emerald green to dark-green masses surrounding angular to sub-angular black clasts (Fig. 7A). The green to dark-green masses are made of brochantite and pseudomalachite while the black clasts are made of dark chrysocolla. Brochantite is the most abundant mineral phases whereas pseudomalachite and chrysocolla are less abundant. Under plane polarized light, both types of brochantite show a weak pleochroism (Fig. 7B). Prismatic-crystal shaped brochantite displays zoning characterized by a silica-rich core surrounded by druse crystal growth (Fig. 7B). Pseudomalachite occurs as light-green to green masses filling spaces similarly to brochantite (Fig. 7B). Chrysocolla is observed, under plane polarized light, as light-to darkbrown masses surrounding the clasts and filling the empty spaces or as coating the breccias (Fig. 7B). Chrysocolla displays a strong relief and shows a massive texture with syneresis cracks (Fig. 7C). SEM images clearly exhibit textural relationship between the copper-bearing minerals. Brochantite displays a markedly druse-crystal shape with micrometer-scale size (Fig. 7C) while pseudomalachite and brochantite show intergrowth textures (Fig. 7C). However, locally, brochantite seems to develop at the expense of a former assemblage of chrysocolla and pseudomalachite (Fig. 7C). Occasionally, pseudomalachite masses display homogeneous texture, without impurities. Copper wad forms micrometer-scale thin concentric bands coating pseudomalachite crystals (Fig. 7D).

Gaby Sur in situ SCM

In hand and core-logging samples, copper oxide mineralization appears either as veins (filling fractures) or disseminated within the porphyry (Fig. 8A). Chrysocolla is the most common mineral phases, followed by minor amounts of black copper oxides, brochantite and atacamite. Under the petrographic microscope, chrysocolla appears as light-to dark-green masses filling empty spaces (Fig. 8B). Under plane polarized light, chrysocolla shows a strong relief without cleavage. Chrysocolla presents no outward crystal form, although sometimes crystalline in internal structure (Fig. 8B). Copper wad is observed, under plane polarized light, as dark brown to black amorphous masses. Under SEM, chrysocolla displays a relative homogeneous texture with a lot of internal cracks and/or fractures (Fig. 8C). Copper wad is filling fractures and empty spaces and exhibits a colloform texture (Fig. 8C). Brochantite clearly shows the direct replacement of sulfides (Fig. 8D) displaying impregnations and disseminations within the sulfides relicts and as coatings at the edges of the altered sulfides. Finally, atacamite coats both chrysocolla and brochantite as highlighted by SEM images (Fig. 8D).

Gaoua in situ SCM

SCM is disseminated inside the porphyries or fills some veins in association with primary sulfides. In hand samples, oxidized copper ore displays homogeneous light-to dark-blue masses filling veins (Fig. 9A). Under the petrographic microscope, these light to dark blue masses can be identified as chrysocolla, which is the most abundant oxidized Cu-bearing minerals (Fig. 9B). Under plane polarized light, chrysocolla appears as green to dark-green heterogeneous masses mainly found within fractures or as coating (Fig. 9B). Pseudomalachite and copper oxides (i.e. cuprite) are present in lesser amounts while no copper wad and atacamite have been found (Fig. 9C). Pseudomalachite is found as inclusions within the chrysocolla internal texture (Fig. 9D) while copper oxides exhibit a square granular shape due to corrosion and occurs as thin coatings as well as impregnating silica clasts as illustrated in Fig. 9D. Chrysocolla seems to replace cuprite and fills the empty spaces between the quartz crystals (Fig. 9D). 4.2 Chemical compositions of the main Cu-bearing minerals 4.2.1 Mineral chemistry Quantitative major and minor element distributions of the studied SCM are reported in ESM 1.

In the exotic deposits (i.e. Mina Sur, Damiana or El Cobre), chrysocolla shows slightly variable proportion of CuO (~ between 50-55 wt. % at Mina Sur, 35-45 wt. % at Damiana and ~ 52 wt. % at El Cobre) and SiO 2 (values between ~ 40-50 wt. % at Mina Sur, 45-50 wt. % at Damiana and ~35-45 wt. % at El Cobre) as well as a variable proportion of H 2 O (average between 0-10 wt. %). Al 2 O 3 , CaO, K 2 O, MgO, FeO are also found as trace elements (Fig. 10A). Black chrysocolla (Fig. 10B), which is only found at Mina Sur, is distinguished from chrysocolla by a higher amount of MnO (up to 6 wt.%) and H 2 O (10-20 wt.%) and a lower content in SiO 2 (20-40 wt.%) and CuO (~ 45-50 wt.%). Pseudomalachite displays more homogeneous composition with high CuO (~ 68.4 wt. % at Mina Sur, between 63-70 wt. % at Damiana and ~ 67 wt. % at El Cobre) and P 2 O 5 contents (average 24.2 wt. % at Mina Sur, 23-27 wt. % at Damiana and 27-28 wt. % at El Cobre) and low H 2 O contents (5-10 wt. %) in all exotic deposits (Fig. 10C). Silica, aluminum, iron and calcium are also present as trace elements.

The compositional data obtained for the in situ SCM (i.e. Zaldivar, Gaby and Gaoua) are listed in ESM 1 and displayed in Fig. 10D for chrysocolla. At Zaldivar, the chemical composition of chrysocolla is consistent with previously published analyses [START_REF] Newberg | Geochemical implications of chrysocolla-bearing alluvial gravels[END_REF][START_REF] Pinget | Supergene enrichment and exotic mineralization at Chuquicamata[END_REF] and display high SiO 2 (~ 43 wt. %) and CuO (~ 51 wt. %) contents with a low water content (~ 4 wt. %). Brochantite contains high proportion of Cu (CuO ~ 78 wt. % and 84 wt. %), and sulfate (SO 3 ~ 11-20 wt. %) while water was below the detection limits. Pseudomalachite shows CuO contents between 21-24 wt. %, P 2 O 5 between 67-69 wt. % and H 2 O contents between 5-8 wt. %. Chrysocolla is composed of CuO (~ 50 wt. %), SiO 2 (average between 39-47 wt. %) and variable water contents (average between 0-15 wt. %).

At Gaby, chrysocolla presents high CuO (~ between 45-58 wt. %) and SiO 2 contents (~ between 28-42 wt. %) and a varying proportion of H 2 O (~ between 3-12 wt. %). Low concentrations of CaO (< 1 wt. %) is also found in chrysocolla. Brochantite, which replaces ancient sulfides, reveals high CuO (~ between 76 and 100 wt. %) and SO 3 (~ between 17-40 wt. %) contents. These wide range of values does not agree with the published values for brochantite [START_REF] Mrose | Evidence for the identity of Kamarezite with Brochantite, Cu4(SO4)(OH)6[END_REF] but rather highlights the ongoing replacement of sulfides relicts by brochantite and other Cu-phosphate minerals. EPMAanalyses carried out on atacamite show homogeneous Cl (~ 12-15 wt. %) and CuO concentrations (74-77 wt. %) and significant quantities of SiO 2 (up to 5 wt. %), emphasizing the presence of chrysocolla or silica impurities within the atacamite.

Finally, for the Gaoua deposit, EPMA analyses reveal that chrysocolla presents chemical compositions that are similar to those of the Atacama Desert. The SiO 2 and CuO contents vary from 35 wt. % to 48 wt. % (average ~ 41 wt. %) and from 41 wt. % to 51 wt. % (average ~ 46 wt. %) respectively while the Al 2 O 3 contents can reach ~ 1.5 wt. %. In Gaoua, intra-layer compositional profiles of chrysocolla show a relatively homogeneous chemical composition with SiO 2 and CuO ranging from 35 wt. % to 45 wt. % and 43 wt. % to 51 wt. %, respectively. Low K 2 O, CaO and Na 2 O contents have also been detected. Pseudomalachite chemical analyses show high CuO (~ 67 wt. %) and P 2 O 5 (~ 21 wt. %) contents with minor amounts of SiO 2 (~ up to 2 wt. %). Aluminum, calcium and magnesium are present as trace elements.

In order to better characterize the chemical homogeneity of the Cu-bearing minerals (i.e. chrysocolla and pseudomalachite), distribution maps of Si, Cu and P were built for both type of deposits (i.e. exotic and in situ). At Mina Sur, silica, copper and phosphorous show a fairly homogeneous distribution in both minerals (Fig. 11A,B,C) although low-Cu and high-Si spots demonstrate the presence of impurities and/or mineral inclusions. At Damiana and El Cobre, elemental distribution maps show that the distribution of Si, Cu and P are rather homogenous in both chrysocolla and pseudomalachite with the exception of the micro-cracks as seen in Fig. 12A-F. Nevertheless, a faint concentric zoning can be observed in pseudomalachite at El Cobre (as shown in Fig. 12B,D,F), which underlines concentric mineral layering and reveals the crosscutting relationship between chrysocolla and pseudomalachite. For chrysocolla and pseudomalachite from Zaldivar, elemental distribution maps are homogeneous for P, Si and Cu and show a faint zoning for Si, Cu and P in the copper wad (Fig. 13A,C,E). Finally, for the Gaby deposit, distribution maps for Si and Cu at the boundaries between chrysocolla and copper wad, show growth bands within the copper wad contrasting with the homogenous distributions within the chrysocolla (Fig. 13B,D).

Rare earth elements

Results are presented in ESM 2 for REE and in Fig. 14. Except for Damiana and El Cobre, all the chrysocolla and pseudomalachite samples have REE concentrations above the detection limits.

REE data of chrysocolla from exotic (Fig. 14A) and in situ (Fig. 14B) SCM have been plotted in a chondrite-normalized spider diagram [START_REF] Mcdonough | The composition of the Earth[END_REF]. Most of the chrysocolla from both exotic and in situ deposits, show a flat pattern for all the REE with a slightly depleted spectrum for HREE, a strong negative Ce-anomaly and a small negative Eu-anomaly. Chrysocolla from the in situ SCM of Zaldivar appears as an outlier, with notably lower REE contents and a strong positive Ceanomaly. Chrysocolla from Gaby and Gaoua has REE contents that are ten times higher than those from Zaldivar, with a strong negative Ce-anomaly. REE contents of chrysocolla from Mina Sur are ten times lower than any other exotic deposits without a markedly negative Ce-anomaly. Chrysocolla from Damiana displays LREE contents ten times higher than those from Mina Sur and El Cobre. Black chrysocolla from Mina Sur show a strong negative Ce-anomaly, a flat HREE spectrum with HREE contents that are ten times higher than chrysocolla from the same deposit.

With the exception of Damiana, the REE patterns for pseudomalachite found in the exotic and in situ SCM show high LREE and HREE concentrations when compared to REE contents of chrysocolla and black chrysocolla (Fig. 14C,D). The REE spectrum at El Cobre shows concentrations up to ten times higher than those obtained at Damiana and Mina Sur, especially for LREE. For Mina Sur and El Cobre, LREE spectrum show a strong negative Ce-anomaly while LREE data at Damiana show an almost flat spectrum without any noticeable negative Ce-anomaly. In spite of their distinct, negative Ce-anomaly, REE contents from El Cobre are more Ce-rich that those from Damiana and Mina Sur. Compared to the LREE spectrum, the HREE spectrum from Mina Sur and Damiana shows a slight enrichment while at El Cobre, the HREE displays a slight depleted spectrum (Fig. 4C). The notable exception is the pseudomalachite REE pattern from the Zaldivar deposit (Fig. 14D), which shows a HREE depleted spectra compared to LREE and a weak negative Eu-anomaly. We also note that the LREE contents in pseudomalachite from Zaldivar are systematically an order of magnitude higher than pseudomalachite from Mina Sur and Damiana.

Discussion

Physicochemical controls for the SCM formation

In all the studied in situ and exotic SCM, chrysocolla is by far the most abundant copper-bearing mineral and predominates over copper wad, atacamite and pseudomalachite.

In the in situ SCM deposits, the mineral parageneses are almost similar with minor copper wad at Zaldivar and Gaby, which precedes abundant chrysocolla in the three deposits, followed by lesser amount of pseudomalachite at Zaldivar. At Gaoua, cuprite is the main second stage mineral followed by pseudomalachite. This paragenetic sequence suggests that all these deposits have undergone the similar processes of in situ supergene oxidation. In detail, at Zaldivar and Gaby, textural and mineralogical features show that copper sulfides were replaced by oxidized sulfate-Cu minerals (Fig. 7C and Fig. 8C). The oxidation process is accompanied by a lower pH [START_REF] Anderson | Characteristics of leached capping and techniques of appraisal[END_REF] and a loss of copper (i.e. by downward or lateral migration) as shown by the lower copper contents in sulfate minerals compared to supergene sulfides. The main thermodynamic constraints for abundant chrysocolla precipitation are pH and H 4 SiO 4 0 (aq) activity [START_REF] Crane | Formation of chrysocolla and secondary copper phosphates in the highly weathered supergene zones of some Australian deposits[END_REF][START_REF] Yates | Complexation of copper with polymeric silica in aqueous solution[END_REF]. Chrysocolla precipitates when the pH exceed ~ 5 [START_REF] Yates | Complexation of copper with polymeric silica in aqueous solution[END_REF]. Precipitation of chrysocolla is thus commonly explained by changing conditions from acid (pH < 5) to neutral or low-alkaline (pH < 9) due to the neutralization of the acidic copper solutions during fluid-rock interaction [START_REF] Newberg | Geochemical implications of chrysocolla-bearing alluvial gravels[END_REF]. It also means that most of the minerals that contributes to lowers the pH (i.e. pyrite and chalcopyrite) are leached or do not have the capacity to increase the pH. As suggested by [START_REF] Crane | Formation of chrysocolla and secondary copper phosphates in the highly weathered supergene zones of some Australian deposits[END_REF], when H 4 SiO 4 0 (aq) is the dominant species in the copper solution, chrysocolla will precipitate at a pH ~ 7. Inversely, when H 2 PO 4 -(aq) is the dominant species in the copper solutions, pseudomalachite will precipitate. This can explain the precipitation of pseudomalachite at Zaldivar and Gaoua. Generally, cuprite crystallizes as replacement of the primary sulfides [START_REF] Schwartz | Paragenesis of the oxidized ores of copper[END_REF] and is rapidly oxidized to hydrate the copper phases. In Fig. 9D, chrysocolla seems to replace cuprite which confirms the assumption of [START_REF] Schwartz | Paragenesis of the oxidized ores of copper[END_REF].

In the exotic SCM (i.e. Mina Sur, Damiana, El Cobre), the same paragenetic sequence is clearly observed: small amount of copper wad, followed by abundant precipitation of chrysocolla and pseudomalachite. At Mina Sur atacamite appears as overgrowths on chrysocolla. At Damiana, apatite growth is coeval to the first phase of chrysocolla. At Damiana and El Cobre, pseudomalachite and microcrystalline quartz are linked to the second crystallization stage event. Except for Mina Sur characterized by the presence of reworked angular clasts of black chrysocolla linked to mechanical transportation or in situ breaking, all three deposits show mineral textures resulting from the deposition of copper transported in solution from a source (i.e. porphyry copper deposits) to a sink (i.e. the adjacent basins). This requires a progressive neutralization of the mineralizing fluids originating from the upstream oxidizing ore from porphyry copper deposits [START_REF] Münchmeyer | Exotic deposits -products of lateral migration of supergene solutions from porphyry copper deposits. Andean copper deposits : new discoveries, mineralization, styles and metallogeny[END_REF][START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. According to [START_REF] Newberg | Geochemical implications of chrysocolla-bearing alluvial gravels[END_REF][START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF], chrysocolla can precipitate as soon as the pH reaches value between ~ 5 and 9 with an optimum value of ~7. Chrysocolla is formed by the interaction between a copper-rich fluid and SiO 2 [START_REF] Yates | Complexation of copper with polymeric silica in aqueous solution[END_REF]. Copper comes from the porphyry while SiO 2 can come from either the porphyry host rocks or from the gravels present in the basins (e.g. altered feldspars). Finally, the good porosity and permeability of the host gravels will favor the precipitation of chrysocolla.

The paragenetic relationship between chrysocolla and pseudomalachite records pH variation. Figure 7 from [START_REF] Crane | Formation of chrysocolla and secondary copper phosphates in the highly weathered supergene zones of some Australian deposits[END_REF] and Figure 10 from [START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF] have shown that a slight variation of the pH in copper-rich solutions can lead to the saturation of either chrysocolla or pseudomalachite together with the H 4 SiO 4 0 (aq) activity. This could explain the alternation of chrysocolla and pseudomalachite observed at Mina Sur and the presence of second stage pseudomalachite at Damiana and El Cobre. The fact that, in both in situ or exotic SCM, pseudomalachite has been found as thin bands or as thin coatings around chrysocolla, implies that the chemistry of copper-rich solutions from the parental porphyry is not constant but has changed according to the pH variation and the H 4 SiO 4 0 (aq) and H 2 PO 4 -(aq) ions activity.

At Damiana and El Cobre, the last mineral to precipitate was the microcrystalline quartz. [START_REF] Bustillo | Silicification of Continental Carbonates[END_REF] has shown that microcrystalline quartz is stable at pH < 9 whereas at pH > 9, calcite is broadly stable. At pH between 5 and 9, chrysocolla and pseudomalachite tend to co-precipitate. When the mineralizing fluids is depleted in copper, microcrystalline quartz can precipitate [START_REF] Dold | Geochemical modeling of the exotic mineralization of the Exotica deposit at Chuquicamata, Chile[END_REF]. The meaning of microcrystalline quartz precipitation can be discussed in terms of a silicification process [START_REF] Bustillo | Silicification of Continental Carbonates[END_REF], favored by the silica content, temperature, host-rock permeability and pH. Highly silica oversaturated solutions will lead to poorly-ordered silica phases (e.g. opal and amorphous silica) while slightly saturated solutions conduct to more ordinated forms (i.e. quartz and chalcedony). This transition may reflect a dilution of the silicification process as shown by [START_REF] Thiry | Interpretation of palaeoweathering features and successive silicifications in the Tertiary regolith of inland Australia[END_REF] and highlighted by [START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF] at Tesoro Central exotic copper deposit. Indeed, the transition from chrysocolla to microcrystalline quartz, observed in our samples, could be a proof of a silicification process.

The fact that no copper carbonates were observed in both type of deposits could be explained by either the combination of high H 4 SiO 4 0 (aq) activity and a pH maximum value of ~ 9 for the copperrich solutions or by the fact that the fluid was too depleted in copper after chrysocolla and pseudomalachite formation to promote copper carbonates precipitation. Ultimately, when the climate become more arid (or hyperarid), atacamite, a copper salt highly soluble in fresh water, started to crystallize. This is well exemplified by the atacamite needles overgrowing pseudomalachite at Mina Sur (Fig. 5D) linked to salt-rich water circulation in the hyperarid conditions of the Atacama Desert [START_REF] Reich | Atacamite formation by deep saline waters in copper deposits from the Atacama Desert, Chile: evidence from fluid inclusions, groundwater geochemistry, TEM, and 36Cl data[END_REF]. The fact that atacamite was not found at Gaoua can be explained either by the absence of saline fluids which could have promoted the formation of atacamite or salt minerals (e.g. gypsum, anhydrite), or by their late destabilization in the context of modern semi-arid climatic conditions (the West African Craton never experienced a hyperarid climate; [START_REF] Séranne | Early Oligocene stratigraphic turnover on west Africa continental margin: a signature of the Tertiary greenhouse to icehouse transition?[END_REF].

As observed in most of the deposits, chrysocolla and copper wad show concentric banding texture which suggests chemical variations of the mineralizing fluids as already mentioned by [START_REF] Nelson | Carbon Isotope Evidence for Microbial Involvement in Exotic Copper Silicate Mineralization, Huinquintipa and Mina Sur, Northern Chile[END_REF] and [START_REF] Campos | Understanding Exotic-Cu Mineralisation: Part I -Characterisation of Chrysocolla[END_REF]. The banding textures observed within chrysocolla have also been explained by [START_REF] Nelson | Carbon Isotope Evidence for Microbial Involvement in Exotic Copper Silicate Mineralization, Huinquintipa and Mina Sur, Northern Chile[END_REF] as the result of biogenic processes, suggesting bacterial involvement in the formation of in situ (i.e. at Gaby) and exotic (i.e. at Mina Sur, Damiana and El Cobre) SCM.

REE concentration in supergene copper minerals

Beside the presence of oxidized copper rich minerals such as silicates, phosphates and sulfates, the existence of oxidizing conditions in the studied localities is supported by the geochemical characterization of the supergene copper minerals (chrysocolla and pseudomalachite) where REE spectra (Fig. 14) are characterized by Ce-anomalies. As shown by [START_REF] Goldschmidt | The principles of distribution of chemical elements in minerals and rocks. The seventh Hugo Müller Lecture[END_REF] and [START_REF] Braun | Cerium anomalies in lateritic profiles[END_REF], Ce is the only LREE to present two oxidation states (Ce 3+ and Ce 4+ ) in a low-T environment. This makes Ce highly sensitive to redox processes. In fact, the oxidation state of Ce is mainly controlled by the pH. At low pH, water could reduce Ce 4+ to Ce 3+ whereas if the pH value increases, Ce 3+ is oxidized to Ce 4+ [START_REF] Bouchaud | pH-distribution of cerium species in aqueous systems[END_REF]. [START_REF] Bouchaud | pH-distribution of cerium species in aqueous systems[END_REF] have also shown, by experimental studies, that Ce 3+ and Ce 4+ are soluble in meteoric water at neutral to alkaline pH values. Additionally, Estrade et al. (2019 and references therein), have shown that the precipitation of Ce, either as Ce 4+ or Ce 3+ , within supergene environments, is linked to the depth of the supergene column. In the upper part of the column, within more oxidizing and higher pH, Ce 4+ precipitates in Ce-rich minerals such as cerianite (CeO 2 ) or associated with Mn-and Fe-oxyhydroxydes. Consequently, the supergene copper minerals will display negative Ce-anomaly due to the Ce 4+ consumption by cerianite or Mn-Fe oxyhydroxydes. This is the case for chrysocolla and pseudomalachite presented in this study who recorded negative Ce-anomaly, except for chrysocolla from Zaldivar. Conversely, in the lower part of the supergene column, under low pH and reduced conditions, Ce 3+ predominates over Ce 4+ and no Cerich minerals such as cerianite or Mn-Fe oxyhydroxydes can precipitate. Therefore, Ce will be available in the environment and captured by Cu-rich supergene minerals that will consequently display positive Ce-anomaly as seen for example for chrysocolla at Zaldivar. Similarly, [START_REF] Decrée | Rare earth element fractionation in heterogenite (CoOOH): implication for cobalt oxidized ore in the Katanga Copperbelt (Democratic Republic of Congo)[END_REF] have shown that REE spectrum in heterogenite (a supergene cobalt mineral, CoOOH) can display negative Ceanomaly when this mineral co-precipitates with Mn-and Fe-oxides in the upper part of the oxidation profile and positive Ce-anomaly when heterogenite forms in the deeper part of the oxidation profile. The negative Ce-anomalies in exotic copper deposits will further support continuous oxidizing conditions. By contrast, the REE patterns from in situ supergene copper minerals (i.e. chrysocolla and pseudomalachite), which show both positive and negative Ce-anomalies, might reflect changes in the redox conditions during the leaching process, above the porphyry, both in time (reducing to oxidizing conditions) and space, i.e. from oxidizing conditions at the top (with Ce 4+ predominates) toward reducing conditions at depth (with Ce 3+ predominates).

If we focus on the REE concentration processes for both in situ and exotic deposits, the REE distribution within chrysocolla and pseudomalachite are heterogenous. Pseudomalachite from El Cobre and Zaldivar contains ten times more REE than those from the other deposits. Furthermore, REE patterns of chrysocolla are contrasted, as the REE contents in Damiana are ten times higher compared to those from Mina Sur, while the REE contents of Zaldivar are ten times lower than those from Gaby and Gaoua. Indeed, in supergene environments, the REE-bearing minerals control the budget and the distribution of the REE. The weathering of the primary REE-bearing minerals (i.e. zircon, monazite and xenotime) will induce either the redistribution of the REE within the newly formed supergene copper minerals (e.g. chrysocolla and pseudomalachite) or the consumption of the REE by secondary REEbearing minerals (i.e. allanite, bastnesite, rhabdophane; [START_REF] Braun | REY-Th-U Dynamics in the Critical Zone: Combined Influence of Reactive Bedrock Accessory Minerals, Authigenic Phases, and Hydrological Sorting (Mule Hole Watershed, South India)[END_REF]. For instance, the absence of secondary REE-bearing minerals at El Cobre and Zaldivar could explain the high REE concentrations found in pseudomalachite from both deposits whereas possible precipitation of apatite and rhabdophane (i.e. two secondary phosphate REE-bearing minerals) in the other deposits (i.e. at Mina Sur and Damiana) could explain the low REE contents in pseudomalachite. Similarly, the low REE content in chrysocolla at Mina Sur and Zaldivar (Fig. 14A,B) could be explained by the precipitation of secondary REE-bearing silicates minerals (e.g. allanite, bastnesite) that trapped the REE. 5.3 Necessary conditions for the genesis and preservation of oxidized SCM

In the Atacama Desert of northern Chile and in southwestern Burkina Faso, tectonics (i.e. Incaic orogeny in Northern Chili and Eburnean orogeny in Burkina Faso) and climatic (i.e. semi-arid to arid climate) settings were combined to favor supergene alteration of porphyries and the formation of thick in situ supergene copper orebodies [START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF][START_REF] Sillitoe | Age of supergene oxidation and enrichment in the Chilean porphyry copper province[END_REF] and/or exotic-Cu deposits [START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF], 2018;[START_REF] Hartley | Controls on supergene enrichment of porphyry copper deposits in the Central Andes: A review and discussion[END_REF][START_REF] Münchmeyer | Exotic deposits -products of lateral migration of supergene solutions from porphyry copper deposits. Andean copper deposits : new discoveries, mineralization, styles and metallogeny[END_REF][START_REF] Riquelme | Supergene and exotic Cu mineralization occur during periods of landscape stability in the Centinela Mining District, Atacama Desert[END_REF][START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. To produce an oxidized supergene copper mineralization, three conditions are necessary. First, tectonic uplift will bring the primary porphyry stock and hypogene sulfides close to the earth surface where oxidizing conditions, controlled by the level of water table, prevail. Second, under favorable climatic conditions, the oxidation of sulfides will produce acidic solutions which will transport copper down and laterally, in the subjacent area, to form an oxidized copper ores when copper solution reach saturation [START_REF] Fernández-Mort | A genetic model based on evapoconcentration for sediment-hosted exotic-Cu mineralization in arid environments: the case of the El Tesoro Central copper deposit, Atacama Desert, Chile[END_REF][START_REF] Reich | Geological and Economic Significance of Supergene Metal Deposits[END_REF]. Finally, once the supergene column is formed, favorable climatic conditions as well as moderate erosion rate can favor SCM preservation. The fact that, although both areas have experienced different tectonic styles, the supergene copper minerals from northern Chile and SW Burkina Faso are identical and share the same chemical compositions implies that they both underwent similar climatic evolutions, i.e. from semi-arid to arid, during the mineralization processes. However, if Northern Chile has evolved towards a hyperarid climate for the past ~10 m.y., responsible for the formation of atacamite, the SW Burkina Faso area has only experienced a semi-arid climate since the Eocene [START_REF] Monsels | Bauxite deposits in Suriname: Geological context and resource development[END_REF]. According to [START_REF] Hartley | Controls on supergene enrichment of porphyry copper deposits in the Central Andes: A review and discussion[END_REF], who published a compilation of supergene copper deposits ages in the Atacama Desert, the formation of in situ SCM took place between 36 Ma and 6 Ma. More recently, [START_REF] Riquelme | Supergene and exotic Cu mineralization occur during periods of landscape stability in the Centinela Mining District, Atacama Desert[END_REF] and [START_REF] Kahou | First U-Pb LA-ICP-MS in situ dating of supergene copper mineralization: case study in the Chuquicamata mining district, Atacama Desert, Chile[END_REF] have published ages between ca. 25-12 Ma and ca. 19 Ma for the formation of the Centinela and Mina Sur exotic copper deposits respectively, i.e. ages that are within the range found for the in situ SCM. As stated by [START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF] and [START_REF] Sanchez | Exhumation history and timing of supergene copper mineralisation in an arid climate: New thermochronological data from the Centinela District, Atacama, Chile[END_REF], in Chile, the processes necessary for the formation of well-developed oxidized SCM profile can take anything from a million to ten millions of years and ceased at the onset of hyperaridity. In SW Burkina Faso, the age of the SCM deposit is unknown but the phases responsible for the exhumation of the porphyry towards oxidizing conditions were contemporanous with lateritization/bauxitisation processes, i.e. between 59 Ma and 3 Ma [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation: The West African example: Cenozoic cratonic denudation[END_REF][START_REF] Gunnell | Radiometric ages of laterites and constraints on long-term denudation rates in West Africa[END_REF]. These exhumation phases were controlled by evolving weathering conditions and took place at rates lower than 20 m/m.y. [START_REF] Beauvais | Modes, tempo, and spatial variability of Cenozoic cratonic denudation: The West African example: Cenozoic cratonic denudation[END_REF]. The comparison between Chilean and African SCM suggest that the preservation of the supergene deposits is due to a favorable combination of slow erosion rates and aridity.

Another necessary factor for the genesis of oxidized SCM can be related to evaporation process. In the southern part of the Atacama Desert, a stable isotope study by [START_REF] Bissig | Andean uplift and climate evolution in the southern Atacama Desert deduced from geomorphology and supergene alunite-group minerals[END_REF] has shown that meteoric waters were affected by high evaporation rates to favor the deposition of supergene alunite. In the same manner, Fernández-Mort et al. ( 2018) also highlighted that evapoconcentration was the main parameter to form the exotic SCM of Tesoro Central. Although no isotope studies have been carried out in this study, this evaporation process can be involved in the formation of both in situ and exotic SCM deposits from Chile but also in the in situ SCM from Burkina Faso. 5.4 Oxidized SCM characterization: key for an exploration success Oxidized SCM are the result of supergene alteration of hypogene sulfides, namely pyrite and chalcopyrite from any sulfide-rich deposit. This supergene alteration produces a vertical zonation consisting on a Fe-and Al-rich leached cap depleted in Cu, followed by an oxidized horizon moderately enriched in copper (up to 1 wt. % of Cu) and at the bottom a secondary sulfide enrichment zone, highly enriched in copper (up to 2 wt. % of Cu) formed below the paleo water table [START_REF] Chávez | Supergene Oxidation of Copper Deposits: Zoning and Distribution of Copper Oxide Minerals[END_REF][START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. As stated by Chavez (2000), the distribution of oxidized copper minerals can be used as exploration keys. For example, as shown by our study, the broad distribution of chrysocolla within in situ SCM are interpreted as characteristic of a geochemically mature supergene system and the formation of a well-developed in situ oxidized SCM. In fact, both types of oxidized SCM represent an important target for numerous exploration and mining companies as their exploitation is environmentally friendly compare to process required for the recovery of copper from sulfide ore. As a result, mineralogical characterization of SCM can provides some useful keys to better improve the metallurgical treatment.

To date, mapping exploration program combined with geophysical and geochemical studies, successfully located oxidized and enriched porphyry copper deposits buried beneath piedmonts gravels. Moreover, geomorphological and sedimentological studies are powerful tools to discover new in situ and exotic SCM. As proposed by [START_REF] Riquelme | Supergene and exotic Cu mineralization occur during periods of landscape stability in the Centinela Mining District, Atacama Desert[END_REF], the exploration of these deposits, buried under gravels and ignimbrite, needs to take into consideration both the landscape evolution and the depositional history of the piedmont gravels. The study of the landscape and the piedmont evolution has also been presented as a major guide for the exploration of supergene ore by [START_REF] Chardon | West African lateritic pediments: Landform-regolith evolution processes and mineral exploration pitfalls[END_REF] in Burkina Faso. When the conditions are favorable, supergene alteration of porphyry copper deposit also leads to the deposition of exotic SCM, hosted within piedmont gravels or underlying bedrock fractures. The presence of exotic copper deposits is indicative of the existence of primary copper porphyry deposits somewhere upstream and can be used as exploration tool. Although in some cases, the source of these deposits are known (e.g. Chuquicamata porphyry for Mina Sur and Salvador porphyry for Damiana, see Munchmeyer, 1996), the sources of some exotic-Cu deposits remain unknown (e.g. Tesoro and Lagarto exotic-Cu deposits; Munchmeyer, 1996;[START_REF] Sillitoe | Supergene Oxidized and Enriched Porphyry Copper and Related Deposits[END_REF]. Therefore, the mineralogical and geochemical characterization of the supergene copper minerals should be implemented during exploration strategies. For instance, the predominance of chrysocolla over copper wad in an exotic-Cu deposit is indicative of a lateral migration of copper-rich solutions within a radius of 2 to 6 km around the primary porphyry copper deposit. When combined with mass-balance calculation model and geomorphology, mineralogical studies can assess the geochemical maturity of the oxidized ore of the porphyry copper deposit and the directions followed by the copper solutions from the primary copper deposits to the sink [START_REF] Alpers | Paleohydrologic evolution and geochemical dynamics of cumulative supergene metal enrichment at La Escondida, Atacama Desert, northern Chile[END_REF]Mote et al., 2001b). Consequently, an integrated study involving geomorphology, sedimentology and geochronological together with a mineralogical and geochemical characterization of the oxidized SCM must be taken into account for enhanced exploration success. 6. Conclusions Supergene copper mineralization from three exotic and two in situ Cu-deposits from the Atacama Desert in Northern Chile and the Gaoua in situ Cu-Au district in Burkina Faso have been studied in details. Mineralogical and chemical characterization of these SCM provide new insights on the genesis of these deposits. Chrysocolla, which precipitates after copper wad, is the main Cu-bearing minerals and shows similar textures and chemical compositions in both in situ and exotic SCM. Precipitation of chrysocolla reflects the progressive evolution of the mineralizing fluids from acidic (pH < 5) to neutral or low-alkaline (pH < 9) conditions during fluid-rock interaction. Chrysocolla is then followed by the crystallization of pseudomalachite in exotic deposits due to changes of both pH and H 2 PO 4 activity of the Cu-bearings fluids (i.e.). Geochemical analyses emphasize the strong oxidizing conditions required for the formation of oxidized SCM and show that REE distribution and Ce-anomaly are linked to the pH evolution, the depth of the supergene column and the presence of primary and secondary REEbearing minerals. The fact that almost the same mineralogy and geochemical patterns are observed on six different deposits, on different location and geodynamic context, point out the fact that the processes involve in the formation of these deposits are very similar, i.e. progressive neutralization of the acidic copper solutions that lead to chrysocolla precipitation at neutral pH, high H 2 PO 4 -(aq) activity together with low H 4 SiO 4 0 (aq) activity that permit pseudomalachite formation, and silicification process that lead to the late crystallization of microcrystalline quartz.

The role of regional and local controls on the formation and preservation of supergene mineralization is now well-understood and requires a subtle balance between tectonics, climate and geomorphology. The formation of such deposits requires several steps with first the exhumation and weathering of the primary porphyry deposit to ensure surface oxidizing processes and a preservation favored by an environment characterized by moderate erosion and rain fall to prevent mechanical abrasion and leaching of the newly formed deposits and finally, a possible key role played by evaporation processes. This equilibrium has been achieved in both Northern Chile and SW Burkina Faso where similar mineralization processes have been involved to form SCM.

Captions

Fig. 1 Fig. 2 Fig. 3 Fig. 4 Fig. 5 Fig. 6 Fig. 8 Fig. 9 ESM 1 ESM 2

 1234568912 Fig. 1 Schematic representation of the relationships between hypogene porphyry copper mineralization

Acknowledgments: We would like to thank the geologists from CODELCO-Chile for providing access to the Mina Sur and Damiana open-pit mines. We also want to thank geologists from the Zaldivar and Gaby copper mines for giving us samples. We thank Didier Béziat, Athanase Naré, Naba Séta and Pascal Ouiya who helped us to have access to samples from the Gaoua Cu-Au district. Special thanks to Fabienne de Parseval, Thierry Aigouy, Sophie Gouy, Aurélie Marquet and François-Xavier d'Abzac who helped during thin sections preparation, SEM, EPMA and LA-ICP-MS analyses. This work was supported by the program funding of the Institut Carnot ISIFoR and the TelluS Program of CNRS/INSU. We acknowledge the LMI Copedim, an IRD research program, the Université Paul Sabatier (Toulouse, France) as well as Universidad Católica del Norte (Antofagasta, Chile). Finally, we want to gratefully acknowledge the Society of Economic Geologists Foundation for the Hugh McKinstry fund (SRG 20-15) received by Zia Steven Kahou.

Highlights