Laura Gemmrich

Lisard Torró
email: lisardtorro@hotmail.com

Joan Carles Melgarejo

Oscar Laurent

Jean Vallance

Cyril Chelle-Michou

Thierry P A Sempere

Trace element composition and U-Pb ages of cassiterite from the Bolivian tin belt

Keywords: Central Andes, geochemical composition, high-tech metals, critical elements, U-Pb geochronology

The Bolivian tin belt is a metallogenic province in the Eastern Cordillera of the Andes known for its Sn, W, Ag and base metal deposits. Cassiterite, which is a major constituent in many magmatic-hydrothermal ore deposits from the Bolivian tin belt, can incorporate dozens of elements within its crystal lattice, making it a useful geological tracer mineral, and also a potential host of critical elements. New U-Pb dating of cassiterite yields Late Triassic (Kellhuani deposit) and Late Oligocene to earliest Miocene (Viloco, Huanuni and Llallagua deposits) ages. These ages confirm that Sn mineralization in the Bolivian tin belt occurred at least in two separate events during two major magmatic episodes apparently triggered by mantle upwelling, decompression melting and basalt

Man crip Wi ho Track Change

Click here to access/download;Manuscript Without Track Changes;0_Gemmrrich et al_BTB_V3.doc 2 production promoting high heat flow into the overlying crust. The composition of studied hydrothermal cassiterite yields some geochemical trends that are attributed to its distance to the causative intrusion and/or level of emplacement. For example, cassiterite is generally enriched in Nb and Ta and yields higher Ti/Zr and Ti/Sc ratios in samples from xenothermal ore deposits located adjacent to intrusive complexes relative to shallow xenothermal and epithermal ore deposits. Therefore, these geochemical trends in cassiterite are useful tracers pointing to magmatic-hydrothermal centers. REE distribution in cassiterite was likely influenced by boiling processes, which resulted in tetrad-type irregularities. Cassiterite from the Bolivian tin belt is unattractive as a source for Nb (interquartile range [IQR] 4.84-0.037 ppm), Ta (IQR 0.0924-0.0126 ppm) and Ge (IQR 3.92-0.776 ppm). Some deposits, however, contain cassiterite relatively enriched in In (IQR 96.9-9.78 ppm, up to 1414 ppm) and Ga (IQR 92.1-3.03, up to 7437 ppm), that could constitute an attractive supplementary source for these elements in addition to sulfide minerals in the same deposits.

Introduction

Cassiterite, a tin oxide mineral (SnO2) of the rutile group and the primary Sn ore mineral, can incorporate a wealth of elements in minor and trace concentrations within its structure. Typical elements that are present in significant, although variable, amounts within its crystal lattice include Fe, Ti, Mn, Al, Nb, Ta and U, which substitute for Sn cations. Innovation in analytical chemistry (i.e., ICP-MS and micro-PIXE; e.g., [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF][START_REF] Serranti | Trace-element distribution in cassiterite and sulfides from rubané and massive ores of the Corvo deposit, Portugal[END_REF] further allows the determination of other elements found in trace amounts in cassiterite such as those of the rare earth elements (REE), Be and In amongst others. Some of these elements (e.g., Nb, Ta, W, REE, Be and In) are considered high-tech metals critical to the global economy [START_REF] Skirrow | Critical commodities for a hightech world: Australia s potential to suppl global demand[END_REF]European Commission 2017;[START_REF] Schulz | Critical mineral resources of the United States Economic and environmental geology and prospects for future supply[END_REF]).

The broad range of P-T-X conditions in which cassiterite forms, its strong physical and chemical resistance and its plethora of chemical constituents including both compatible and incompatible elements makes this mineral useful as a petrogenetic indicator (Murciego et al. 1977;[START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF][START_REF] Serranti | Trace-element distribution in cassiterite and sulfides from rubané and massive ores of the Corvo deposit, Portugal[END_REF][START_REF] Jiang | Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit, Yunnan, China: Implication for migmatitic-hydrothermal fluid evolution and ore genesis[END_REF]Chen et al. 2019). Furthermore, the moderate U 4+ and low Pb 2+ contents and high Pb isotope closure temperature (up to 860ºC; [START_REF] Zhang | The closure of U-Pb system in cassiterite and its reliability for dating[END_REF]) in cassiterite makes it suitable for U-Pb dating (e.g., [START_REF] Zhang | Combined zircon and cassiterite U Pb dating of the Piaotang granite-related tungsten tin deposit, southern Jiangxi tungsten district, China[END_REF][START_REF] Zhang | Neoproterozoic tin mineralization in South China: Geology and cassiterite U Pb age of the Baotan tin deposit in northern Guangxi[END_REF][START_REF] Guo | Genesis of tin-dominant polymetallic deposits in the Dachang district, South China: insights from cassiterite U-Pb ages and trace element compositions[END_REF][START_REF] Neymark | In situ LA-ICPMS U Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF][START_REF] Chen | The genetic association between quartz vein-and greisentype mineralization at the Maoping W Sn deposit, Southern Jiangxi, China: Insights from zircon and cassiterite U Pb Ages and cassiterite trace element composition[END_REF][START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF][START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF][START_REF] Moscati | U Pb geochronology of tin deposits associated with the Cornubian Batholith of southwest England: Direct dating of cassiterite by in situ LA-ICPMS[END_REF][START_REF] Zhao | U-Pb Ages, O isotope compositions, Raman spectrum, and geochemistry of cassiterites from the Xi ao copper-tin polymetallic deposit in Gejiu District, Yunnan Province[END_REF][START_REF] Legros | The world-class Nanling metallogenic belt (Jiangxi, China): W and Sn deposition at 160 Ma followed by 30 m.y. of hydrothermal metal redistribution[END_REF][START_REF] Lehmann | Monazite and cassiterite U-Pb dating of the Abu Dabbab rare-metal granite, Egypt: Late Cryogenian metalliferous granite magmatism in the Arabian-Nubian Shield[END_REF][START_REF] Mao | Combined zircon, molybdenite, and cassiterite geochronology and cassiterite geochemistry of the Kuntabin tintungsten deposit in Myanmar[END_REF].

The Bolivian tin belt, in the Central Andes, is one of the largest tin metallogenic belts worldwide and in 2019 accounted for about 6% of the global tin production; in addition, it produced about 5% of silver and 1.5% of tungsten globally (U.S. Geological [START_REF] Survey | [END_REF]. Despite massive tin production since early 1900s, by when most Bolivian great tin deposits had been discovered, Bolivia is estimated to contain > 8% of the orld s tin reserves (Arce-Burgoa and Goldfarb 2009; U.S. Geological Survey 2020). However, a detailed survey on the geochemical composition of cassiterite from this metalliferous belt has never been conducted. Furthermore, the age of the magmatism along the Bolivian tin belt is relatively well constrained through U-Pb zircon dating, but dispersion of K-Ar and Ar-Ar mica and feldspar dates reveals a complex thermal history (Ahfeld 1967;[START_REF] Clark | The Bolivian Tin Province; notes on the available geochronological data[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Clark | Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru[END_REF][START_REF] Sugaki | K Ar ages of tin-polymetallic mineralization in the Oruro mining district, central Bolivian tin belt[END_REF][START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF][START_REF] Cordani | Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods[END_REF]. This is especially the case in the northern segment of the Bolivian tin belt, where plutons of Triassic age cluster. As previous geochronological studies on tin deposits were mainly based on K-Ar and Ar-Ar dating of hydrothermal mica, some questions remain in respect of their reliability. In this study we determine the geochemical composition and U-Pb dates of cassiterite grains from nine deposits/districts of the Bolivian tin belt with a threefold aim: i) to refine the geochronology of tin mineralization in this region, ii) to constrain the mechanisms that control minor and trace element concentrations in cassiterite crystallized at contrasting conditions within the xenothermal (i.e., polymetallic high-temperature [~300-500ºC] vein-type deposits emplaced in the sub-epithermal environment; [START_REF] Buddington | High-temperature mineral associations at shallow to moderate depths[END_REF][START_REF] Imai | Geologic structure and mineralization of xenothermal vein-type deposits in Japan[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF] and epithermal environments, and iii) to assess their potential as source of high-tech byproducts.

Geological setting

Geological setting of the Bolivian Andes

The ore deposits dated in this paper are located in the northern and central segments of the Bolivian Eastern Cordillera. These segments are parts of the northwest limb of the Bolivian Orocline [START_REF] Isacks | Uplift of the central Andean plateau and bending of the Bolivian orocline[END_REF], and, more precisel , of its southernmost portion, i.e. close to the oroclinal core hinge . This broad region therefore shares many geological characteristics with adjacent Peru, and the descriptions and comments in this section are often envisioned from this point of view.

The Bolivian Andes present a marked morphotectonic partition that reflects differences in geological history, paleostructural domains and current crustal structure. These domains are, from west to east, the Western Cordillera, the Altiplano and the Eastern Cordillera. Furthermore, a deformed Subandean Belt serves as a tectonic transition between the Eastern Cordillera and the nearly undeformed Amazonian Lowlands to the northeast and east.

The Western Cordillera corresponds to the present-day location of the main magmatic arc related to subduction processes. It is characterized by a ~100 km-wide belt of volcanoes sitting on a high-altitude surface, which reflects a considerable crustal thickness beneath (e.g., James 1971a,b;[START_REF] Isacks | Uplift of the central Andean plateau and bending of the Bolivian orocline[END_REF][START_REF] Kono | Mountain building in the Central Andes[END_REF]Lamb and Hoke 1997). At the latitudes of Bolivia, the Western Cordillera however extends also in adjacent Northern Chile. It is mostly composed of Late Miocene to recent intermediate to felsic igneous rocks that intruded in and extruded over Jurassic and Cretaceous sedimentary and volcanic rocks. The igneous rocks from the Western Cordillera belong to the magnetite series and record a high contribution of a mantle component [START_REF] Ishihara | The granitoid series and mineralization[END_REF]Sugaki et al. 1988a).

The upper crustal structure of the Altiplano varies significantly. It seems likely that its lower crust has been thickened through ductile flow from the overthickened crust along both the Western and Eastern cordilleras [START_REF] Husson | Thickening the Altiplano crust by gravity-driven crustal channel flow[END_REF]. Much of the current Altiplano surface is covered by recent sedimentary and volcanic deposits; it is strongly suspected that its eastern fringe corresponds to the buried western fringe of the Eastern Cordillera, and thus constitutes a transitional strip between the two domains. In particular, this transition is confirmed by the observation that many magmatic phenomena that affected the Altiplano also affected the crust of the western Eastern Cordillera, along which products of coeval and related magmatism are commonly observed (see below).

The scope of this paper is focused on the Eastern Cordillera since it hosts the Bolivian tin belt. The Eastern Cordillera was formed by inversion and substantial shortening of a Triassic rift system [START_REF] Sempere | Discussion of Sediment accumulation on top of the Andean orogenic wedge: Oligocene to late Miocene basins of the eastern Cordillera, southern Bolivia (Horton, 1998)[END_REF][START_REF] Sempere | Late Permian Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics[END_REF]. This protracted compressional to transpressional deformation has developed since the Eocene and/or Oligocene in relation to the formation of the Bolivian Orocline (e.g., [START_REF] Farrar | Zongo-San Gabán zone: Eocene foreland boundary of the Central Andean orogen, northwest Bolivia and southeast Peru[END_REF][START_REF] Sempere | Late Oligocene-Early Miocene major tectonic crisis and related basins in Bolivia[END_REF][START_REF] Roperch | Counterclockwise rotation of late Eocene Oligocene fore-arc deposits in southern Peru and its significance for oroclinal bending in the central Andes[END_REF], and the ensuing erosion has resulted in the exposure of mainly Ordovician and Silurian strata, which as a whole may be over ~10 km thick.

The almost exclusively marine stratigraphic set formed by the Ordovician to Devonian strata is so thick that it raises the question of the geotectonic context in which this succession accumulated, and, indirectly, that of the time at which subduction was initiated at the latitude of Bolivia and Peru. Both present-day territories were part of supercontinents Rodinia and Pannotia; Laurentia separated from the latter at the latitudes of Peru and Bolivia through the opening of the Iapetus Ocean during the latest Neoproterozoic [START_REF] Scotese | Late Proterozoic plate tectonics and palaeogeography: A tale of two supercontinents, Rodinia and Pannotia[END_REF], which implies that what was to become the Central Andean margin is very likely to have been passive at least in the earliest Paleozoic. A subduction-arc geochemical signature is however unambiguously noted in Carboniferous plutons of Peru [START_REF] Mi Kovi | Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids[END_REF], which provides a minimum age for the onset of subduction at these latitudes.

The overall geological evolution of Bolivia has been summarized by [START_REF] Sempere | Phanerozoic evolution of Bolivia and adjacent regions[END_REF], who divided the stratigraphic record into a number of supersequences that reflect major changes in tectonic context. This preliminary understanding has been refined since that time, in particular thanks to new data from Bolivia and especially Peru. The Carboniferous arc orogeny that developed along at least the Eastern Cordillera of Peru was followed in the Permian by the extensional collapse of the resulting overthickened crust [START_REF] Mi Kovi | Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids[END_REF].

Extensional conditions considerably increased in the Middle to Late Triassic, and resulted in the development of a major back-arc rift system [START_REF] Sempere | Late Permian Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics[END_REF][START_REF] Spikings | Characterisation of Triassic rifting in Peru and implications for the early disassembly of western Pangaea[END_REF]. During the Mitu time interval (~240 220 Ma), such an intense extension and associated mantle-derived mafic magmatism are likely to have generated an anomalously high heat flow. Late Triassic crustal anatexis is documented in several areas of contiguous E and SE Peru (see [START_REF] Kontak | Eocene tectono-thermal rejuvenation of an upper Paleozoiclower Mesozoic terrane in the Cordillera de Carabaya, Puno, southeastern Peru, revealed by K-Ar and 40 Ar/ 39 Ar dating[END_REF]); in the NW-trending segment of the Eastern Cordillera of Bolivia, anatexis is recorded by the Zongo-Yani batholith (Fig. 1A), which consists of two-mica granite plutons that are commonly foliated; the peraluminous composition points to an anatectic origin, and the foliation indicates extensional shearing conditions during magma emplacement. In the Cuticucho-Samaini area, which is located ~25 km north of the Milluni Sn-Zn deposit (Fig. 1A), the Zongo-Yani batholith locally displays facies that range from pervasively foliated to weakly foliated, whereas its composition varies from monzogranite to syenogranite [START_REF] Farrar | The age of the Zongo pluton and the tectonothermal evolution of the Zongo-San Gabán Zone in the Cordillera Real, Bolivia[END_REF]).

U-Pb zircon dating yielded dates of 222.2 9.1/+7.7 and 225.1 4.4/+4.1 Ma on the pervasively and weakly foliated facies, respectively (the weighted mean of these dates is 224.5 4.0/+3.6 Ma). The U-Pb work confirmed that zircons from this pluton had been recycled by anatexis, and these dates are based on lower intercepts in the respective concordia diagrams [START_REF] Farrar | The age of the Zongo pluton and the tectonothermal evolution of the Zongo-San Gabán Zone in the Cordillera Real, Bolivia[END_REF]); all zircons that [START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF] attempted to date by the U-Pb method were also found to be discordant and gave 206 Pb/ 238 U dates between 263 and 226 Ma for the Zongo pluton.

The Triassic rifting led to the subsequent accumulation of a stratigraphic succession that ranges well into the Jurassic [START_REF] Sempere | Late Permian Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics[END_REF]. After an apparently long sedimentation hiatus, deposition resumed at ~100 Ma; a significant increase in subsidence took place at ~90 Ma, reflecting the coeval growth of the main magmatic arc [START_REF] Sempere | Kimmeridgian? to Paleocene tectonic evolution of Bolivia[END_REF][START_REF] Demouy | Spatial and temporal evolution of Liassic to Paleocene arc activity in southern Peru unraveled by zircon U-Pb and Hf in-situ data on plutonic rocks[END_REF]. The latest Cretaceous to Eocene stratigraphic record mainly consists of red beds forming a monotonous succession that may be several km thick [START_REF] Sempere | Stratigraphy and chronology of Late Cretaceous Early Paleogene strata in Bolivia and northwest Argentina[END_REF][START_REF] Horton | Paleogene synorogenic sedimentation in the Altiplano plateau and implications for initial mountain building in the central Andes[END_REF], interpreted as a classical foreland basin (e.g., [START_REF] Decelles | Early to middle Tertiary foreland basin development and the history of Andean crustal shortening in Bolivia[END_REF].

Arc migration is best recorded in southern Peru. Mamani et al. (2010) and [START_REF] Demouy | Spatial and temporal evolution of Liassic to Paleocene arc activity in southern Peru unraveled by zircon U-Pb and Hf in-situ data on plutonic rocks[END_REF] showed that in this large region the arc, from a position currently offshore, migrated northwards between ~130 and ~45 Ma to occupy a position that coincides with the Andahuaylas-Yauri batholith south of Cuzco; the arc has migrated back south ards since 31 30 Ma (Mamani et al. 2010). Because the position of the arc is largely controlled by the dip angle of the subducted slab, the latter back-migration must have implied a widening of the asthenospheric wedge, which in turn involved mantle upwelling and thus decompression melting, and therefore the production of large amounts of basaltic magma (Mamani et al. 2010). This logical chain is confirmed by the widespread existence of basaltic magmatism of alkaline to shoshonitic composition centered over most of the Altiplano of southern Peru and Bolivia, between ~31 and ~22 Ma in southern Peru (Kontak et al. 1996;[START_REF] Sandeman | An integrated tectono-magmatic model for the evolution of the southern Peruvian Andes (13°-20°S) since 55[END_REF], and between ~28 and ~21 Ma across the Bolivian Altiplano [START_REF] Soler | Magmatic constraints upon the evolution of the Bolivian Andes since Late Oligocene times[END_REF]; [START_REF] Fornari | Ar-Ar dating of Late Oligocene-Early Miocene volcanism in the Altiplano[END_REF] detected a diachronic onset of mafic volcanism from ~29 Ma in the southern Peruvian Altiplano to ~21-20 Ma in the southernmost Bolivian Altiplano. The cumulated thickness of basaltic flows may locally be >2 km [START_REF] Baldellón | Sucesión estructural de la zona Serranía de las Minas[END_REF], which eloquently illustrates the magnitude of the related mantle upwelling and thus anomalous heat flow. The available dataset concerning this segment of the Bolivian Orocline suggests that mafic magmatism extended beneath the entire Altiplano of southern Peru and Bolivia as well as adjacent areas, and that it has continued through the Neogene and Quaternary, at least episodically at the surface.

In the Bolivian Altiplano, these mafic lavas occur as flows, sills, dikes and small intrusive stocks; thick and extended flow breccias are common and suggest that many volcanic centers were active at that time [START_REF] Fornari | Ar-Ar dating of Late Oligocene-Early Miocene volcanism in the Altiplano[END_REF]. Near the triple junction of Bolivia, Peru and Chile, the mafic Abaroa Formation yielded whole-rock 40 Ar-39 Ar dates comprised between 28.0 ± 0.1 and 27.3 ± 0.1 Ma [START_REF] Fornari | Ar-Ar dating of Late Oligocene-Early Miocene volcanism in the Altiplano[END_REF]).

In the central Bolivian Altiplano, basaltic sills yielded whole-rock 40 Ar-39 Ar plateau dates of 24.2 ± 0.4 and 23.8 ± 0.1 Ma; the latter date was obtained on a >100 m-thick mafic sill characterized by plagioclase phenocrysts up to 3 cm in size [START_REF] Fornari | Ar-Ar dating of Late Oligocene-Early Miocene volcanism in the Altiplano[END_REF]. About 75 km to the SSE, a ~1-km-thick section of red beds includes >15 basalt levels; lava flows near the base and top of the section yielded whole-rock 40 Ar-39 Ar dates of 23.5 ± 0.1 and 23.6 ± 0.1 Ma, respectively, whereas a mafic dyke cutting several flows and sills yielded a plateau date of 23.5 ± 0.1 Ma; these coinciding dates over a stratigraphic thickness of ~1 km indicate, again, that the corresponding mafic magmatism was extremely productive at that time (~23.5 Ma in this case), and thus involved considerable mantle upwelling, resulting decompression melting and a very high heat flow into the overlying crust.

Crustal thickening in the NW-trending region of the Bolivian Orocline has developed since ~30 Ma [START_REF] Picard | Direction and timing of uplift propagation in the Peruvian Andes deduced from molecular phylogenetics of highland biotaxa[END_REF]Sempere et al. 2008 and references therein). The onset of crustal thickening thus coincided with the widespread development of mafic magmatism during the Late Oligocene and earliest Miocene.

Unlike igneous rocks from the Western Cordillera, silicic intrusive and volcanic rocks from the Eastern Cordillera of both Mesozoic (mostly ca. 225-200 Ma) and Tertiary (ca. 45-12.0 Ma) ages belong to the S-type, ilmenite series and resulted from sediment melting in a thickened continental crust with up to 30% of mantle component [START_REF] Sugaki | Geological study on the polymetallic hydrothermal deposits in the Oruro district, Bolivia[END_REF][START_REF] Morgan | Petrochemistry of Late Miocene peraluminous silicic volcanic rocks from the Morococala Field, Bolivia[END_REF][START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF][START_REF] Mlynarczyk | The role of collisional tectonics in the metallogeny of the Central Andean tin belt[END_REF][START_REF] Maffione | Bending and growth of the Central Andean plateau: Paleomagnetic and structural constraints from the Eastern Cordillera (22-24°S[END_REF].

The morphotectonic provinces are juxtaposed by a succession of parallel, north to south trending mineralized belts of Paleogene and Neogene ages. The Western Cordillera mostly comprises porphyry-type Cu-Mo-Au-Fe deposits, the Altiplano, polymetallic vein-and replacement-type Cu-Pb-Zn-Ag deposits and sedimentary Cu deposits, and the Eastern Cordillera, porphyry-type Sn-W-Ag deposits and associated polymetallic mineralization [START_REF] Petersen | Metallogenic Provinces in South America[END_REF][START_REF] Sillitoe | Relation of metal provinces in western America to subduction of oceanic lithosphere[END_REF][START_REF] Sillitoe | Andean mineralization: A model for the metallogeny of convergent plate margins[END_REF][START_REF] Clark | Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru[END_REF][START_REF] Mlynarczyk | The role of collisional tectonics in the metallogeny of the Central Andean tin belt[END_REF][START_REF] Fontboté | Ore deposits of the Central Andes[END_REF]). The existence of metallogenic provinces (clusters of ore deposits with similar characteristics) in the Central Andes suggests control by regional or large scale geologic environments or processes, which in the region were governed by the quasi-continuous subduction along the western margin of the South American plate over the last ca. 300 My [START_REF] Clark | Longitudinal variations in the metallogenetic evolution of the central Andes: A progress report[END_REF][START_REF] Clark | Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru[END_REF][START_REF] Sillitoe | Andean mineralization: A model for the metallogeny of convergent plate margins[END_REF][START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF][START_REF] Mlynarczyk | The role of collisional tectonics in the metallogeny of the Central Andean tin belt[END_REF]Wörner et al. 2018a,b;[START_REF] Fontboté | Ore deposits of the Central Andes[END_REF]. In this convergent tectonic scenario, shortening, thickening and uplift favored the accumulation of magma in the upper crust, which was responsible for the magmatic-hydrothermal activity that formed the metalliferous deposits along metallogenic provinces [START_REF] Fontboté | Ore deposits of the Central Andes[END_REF]). This W to E zonation reflects the constraining character of the source regions and the decrease in the role of subduction-related processes evidenced by difference in granitoid type and series [START_REF] Mlynarczyk | The role of collisional tectonics in the metallogeny of the Central Andean tin belt[END_REF].

Geological setting of the Bolivian Tin Belt

The deposits selected for this study are distributed along the Bolivian segment of the Bolivian tin belt. The Bolivian tin belt is restricted to the Eastern Cordillera and stretches for about 900 km from ~150 km NNW of Lake Titicaca in Peru (e.g., the San Rafael world-class Sn deposit) through Bolivia to NW Argentina (e.g., the Pirquitas Ag-Zn-Pb-Sn deposit; Fig. 1A). It has an arc shape with contrasting orientations in its northern half (running NW-SE) and southern half (running N-S), both segments connecting in the so-called elbo of the Andes , Bolivian orocline or Arica deflection [START_REF] Ahlfeld | Metallogenetic epochs and provinces of Bolivia[END_REF][START_REF] Maffione | Bending and growth of the Central Andean plateau: Paleomagnetic and structural constraints from the Eastern Cordillera (22-24°S[END_REF]).

The Bolivian tin belt is genetically connected to two major periods of magmatism related to the Andean orogeny: the first is linked to intrusions of granitic plutons of Triassic to Jurassic ages and the second is related to plutonic, sub-volcanic and volcanic eruptive complexes of Oligocene to Miocene ages [START_REF] Turneaure | The Bolivian tin-silver province[END_REF][START_REF] Sillitoe | Porphyry tin deposits in Bolivia[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Lancelot | U/Pb radiochronology of two granitic plutons from the Eastern Cordillera (Peru): Extent of Permian magmatic activity and consequence[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Clark | Occurrence and age of tin mineralization in the Cordillera Oriental, southern Peru[END_REF][START_REF] Clark | Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru[END_REF][START_REF] Clark | Delayed inception of ore deposition in major lithophile-metal vein systems: The San Rafael tin and Pasto Bueno tungsten deposits[END_REF][START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Kontak | Geochronological data for Tertiary granites of the southeast Peru segment of the central Andean tin belt[END_REF][START_REF] Kontak | Eocene tectono-thermal rejuvenation of an upper Paleozoiclower Mesozoic terrane in the Cordillera de Carabaya, Puno, southeastern Peru, revealed by K-Ar and 40 Ar/ 39 Ar dating[END_REF][START_REF] Mlynarczyk | The role of collisional tectonics in the metallogeny of the Central Andean tin belt[END_REF][START_REF] Maffione | Bending and growth of the Central Andean plateau: Paleomagnetic and structural constraints from the Eastern Cordillera (22-24°S[END_REF][START_REF] Mi Kovi | Tectonomagmatic evolution of Western Amazonia: Geochemical characterization and zircon U-Pb geochronologic constraints from the Peruvian Eastern Cordilleran granitoids[END_REF][START_REF] Reitsma | Reconstructing the Late Paleozoic Early Mesozoic Plutonic and Sedimentary Record of South-East Peru: Orphaned Back-arcs Along the Western Margin of Gondwana[END_REF][START_REF] Betkowski | Geochemical and textural characterization of phosphate accessory phases in the vein assemblage and metasomatically altered Llallagua tin porphyry[END_REF][START_REF] Cordani | Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods[END_REF]. The Triassic granite intrusions were interpreted as typical of rift-related magmatism in a back-arc setting [START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Kontak | The rift-associated Permo-Triassic magmatism of the Eastern Cordillera: A precursor to the Andean orogeny[END_REF][START_REF] Kontak | Eocene tectono-thermal rejuvenation of an upper Paleozoiclower Mesozoic terrane in the Cordillera de Carabaya, Puno, southeastern Peru, revealed by K-Ar and 40 Ar/ 39 Ar dating[END_REF][START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF]Miskovic et al. 2009;[START_REF] Reitsma | Reconstructing the Late Paleozoic Early Mesozoic Plutonic and Sedimentary Record of South-East Peru: Orphaned Back-arcs Along the Western Margin of Gondwana[END_REF]. The now-inverted rift system had an axis coinciding with the axis of the current Eastern Cordillera [START_REF] Sempere | Late Permian Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics[END_REF]. In the Cordillera Real, at the core of the Eastern Cordillera and the northern portion of the Bolivian tin belt, the oldest dated granitoids belong the Huato, Illampu, Yani, Huayna Potosí, Zongo and Taquesi plutons and the youngest, to the Illimani, Quimsa Cruz and Santa Vera Cruz plutons (ca. 26-23 Ma; Fig. 1A). In the Peruvian segment of the Bolivian tin belt, known as the Cordillera de Carabaya, the oldest granitoids (San Gabán, Coasa, Limbani and Aricoma plutons; Fig. 1A) have a Triassic age . At the northern end of the Bolivian tin belt, the Nevado de Allincapac peralkaline volcano-plutonic complex comprises gabbros, diorites and nepheline syenites dated between 175 and 181 Ma [START_REF] Stewart | Age Determinations from Andean Peru: A Reconnaissance Survey[END_REF][START_REF] Kontak | Eocene tectono-thermal rejuvenation of an upper Paleozoiclower Mesozoic terrane in the Cordillera de Carabaya, Puno, southeastern Peru, revealed by K-Ar and 40 Ar/ 39 Ar dating[END_REF], and the youngest dated granitoids (San Rafael and Santo Domingo plutons) and their volcaniclastic equivalents of the Picotani Group [START_REF] Sandeman | Lithostratigraphy, petrology and 40 Ar/ 39 Ar geochronology of the Crucero Supergroup, Puno Department, SE Peru[END_REF]) are of Late Oligocene age. South of the Cordillera Real, caldera complexes and huge volumes of Late Pliocene and Miocene (and up to recent) ignimbrite deposits of dacite and rhyolite composition formed as a result of changes in mantle melt productivity induced by the south-migrating subduction of the aseismic Juan Fernández Ridge and sporadic lowercrust and subcontinental lithospheric mantle delamination (de Silva and Kay 2018 and references therein).

Compared to the Chilean and NW-Argentinian part of the Central Andes, rock suites in the Bolivian tin belt present higher abundance of Sn and sustained enrichment trends controlled by fractional crystallization [START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF]. Despite being distinctly enriched in Sn, igneous rocks of Miocene porphyry systems in the Bolivian tin belt show concentrations of Ta, Zr and TiO2 comparable to average upper crust and overall moderately fractionated rhyodacite and dacite bulk composition. In stark contrast, quartz-hosted melt inclusions in these rocks yield highly fractionated rhyolitic compositions and enrichment in incompatible elements such as Ta, B, Cs, Li and Sn at concentrations comparable to those of tin granite systems worldwide [START_REF] Dietrich | Bulk rock and melt inclusion geochemistry of Bolivian tin porphyry systems[END_REF][START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF]. These authors propose that highly fractionated melts, chemically linked to the tin mineralization, mixed with primitive melts within magma chambers previous to shallow emplacement as sub-volcanic intrusions or volcanic eruption. Mio-Pliocene lithophile-rich obsidian glasses in felsic peraluminous tuffs in the Macusani area, in the Carabaya Cordillera in SE Peru, are representative of these highly evolved igneous rocks portions [START_REF] Pichavant | The Macusani glasses, SE Peru: evidence of chemical fractionation in peraluminous magmas. In: Mysen BO (ed) Magmatic Processes: Physicochemical Principles[END_REF](Pichavant et al. , 1988a,b;,b;[START_REF] Cheilletz | Stratigraphy and geochronology of the Macusani ignimbrite field: chronometer of the Mio-Pliocene geodynamic evolution of the Andes of SE Peru[END_REF][START_REF] Poupeau | Fission-track dating of 15 macusanite glass pebbles from the Macusani volcanic field (SE Peru)[END_REF][START_REF] Sandeman | Lithostratigraphy, petrology and 40 Ar/ 39 Ar geochronology of the Crucero Supergroup, Puno Department, SE Peru[END_REF][START_REF] Nupen | Mineral resource estimates for the Falchani lithium project in the Puno district of Peru. Prepared for Plateau Energy Metals Inc. under the Guidelines of National Instrument 43[END_REF].

Subsequent hydrothermal redistribution of Sn from igneous rocks magmatically enriched in this element led to enhancement of Sn concentrations. In this model, Sn inheritance from source and host rocks is discarded.

Nevertheless, source sedimentary sequences played an important role in magma evolution by providing B and Corg that depressed the solidus temperature of fractionating melts and induced a low oxidation state necessary for magmatic enrichment and hydrothermal redistribution of tin, respectively [START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF][START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF]Dietrich et al. 2000). In addition, the high concentration of B and other volatile elements in melt inclusions in tin porphyries from the Bolivian tin belt led [START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF] to conclude that the most likely crustal source was the Lower Paleozoic meta-sedimentary sequences.

Mineral deposits from the northern and southern halves of the Bolivian tin belt show contrasting ages and levels of emplacement [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF][START_REF] Sillitoe | Porphyry tin deposits in Bolivia[END_REF][START_REF] Clark | Longitudinal variations in the metallogenetic evolution of the central Andes: A progress report[END_REF][START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF][START_REF] Kontak | Genesis of the giant, bonanza San Rafael lode tin deposit, Peru: Origin and significance of pervasive alteration[END_REF][START_REF] Slater | Origin of a multi-stage epithermal Ag-Zn-Pb-Sn deposit: the Miocene Cortaderas breccia body, Pirquitas mine, NW Argentina[END_REF]). In the northernmost part, the ore deposits are mainly of Sn-W vein-and manto -(stratabound mineralization) type related to batholiths of Triassic and Oligocene age, whilst in the southernmost segment of the belt, mineralization is Miocene, usually shallower and appears as Sn, Sn-W and Sn-polymetallic veins formed in the epithermal and xenothermal environments (Fig. 1). The mineralized stocks and adjacent wall rocks usually present vertically and laterally zoned hydrothermal alteration, with abundant quartz -tourmaline -muscovite assemblages at high-temperature mineralization centers grading outward to phyllic, propylitic and, occasionally, silicified, advanced argillic lithocaps [START_REF] Sillitoe | Porphyry tin deposits in Bolivia[END_REF][START_REF] Sillitoe | Advanced argillic lithocaps in the Bolivian tin-silver belt[END_REF]Harlaux et al. 2020;[START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF]. Lithocaps are only found in the southern part of the Bolivian tin belt, where volcanic domes genetically linked to the mineralization are only shallowly eroded [START_REF] Sillitoe | Advanced argillic lithocaps in the Bolivian tin-silver belt[END_REF]. Detailed descriptions of deposits from the Bolivian tin belt are given by [START_REF] Ahlfeld | Los yacimientos minerales y de hidrocarburos de Bolivia[END_REF], [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF], [START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF] and [START_REF] Arce-Burgoa | Metalliferous Ore Deposits of Bolivia. SPC Impresores: La Paz Arce-Burgoa O, Goldfarb RJ[END_REF].

Methodology Studied samples and their localities

The studied cassiterite crystals belong to nine ore deposits/districts distributed along the Bolivian segment of the Bolivian tin belt (Fig. 1A-B).

Milluni-Kellhuani district

The Milluni-Kellhuani Zn-Cu-W-Bi district is located in the northernmost part of the La Paz department and sits at the northern part of the Cordillera Real, ~ 5 km south of the Triassic Huayna-Potosí granite [START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF][START_REF] Cordani | Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods[END_REF]. Vein and stratabound mineralization are hosted in Silurian quartzites of the Catavi Formation.

Mineralization consists primarily of early quartz, tourmaline and cassiterite (Sn-W stage) and later sulfides such as chalcopyrite, sphalerite, pyrrhotite and pyrite (sulfide stage; [START_REF] Lehmann | Formation of the strata-bound Kellhuani tin deposits, Bolivia[END_REF]. Fluid inclusions in cassiterite from the Milluni mine yielded trapping temperatures of 410-500ºC (corrected for depositional pressures of 0.5-1 kbar) and salinities of 5-25 wt% NaCl equiv. [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF]).

In the central part of the district, the Chacaltaya granite porphyry stock, which shows extreme hydrothermal alteration (greisenization), intruded the Paleozoic metasedimentary rocks [START_REF] Lehmann | Formation of the strata-bound Kellhuani tin deposits, Bolivia[END_REF]. Mineralization in the greisen is mostly composed of cassiterite accompanied by fine-and medium-grained quartz, muscovite, tourmaline, fluorite and siderite. K-Ar dating of greisen muscovite yielded a date of 210 ± 6 Ma [START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF].

The analyzed cassiterite crystals belong to two samples of quartz-cassiterite veins from the Kellhuani deposit (Kell A and Kell B) about 3 km east of the granite porphyry. Crystals are dark red in color, euhedral and subhedral and have sizes typically larger than 500 m and exceptionally up to 5 mm across (Fig. 2A); some contain inclusions of pyrrhotite and are intergrown with quartz and tourmaline.

Viloco -Rosario de Araca district

The Viloco Rosario de Araca district is located in the La Paz department, 70 km SE of La Paz, on the southwestern flank of the Quimsa Cruz Cordillera in the southern segment of the Cordillera Real. NE-trending peribatholitic veins are hosted by Ordovician quartzites of the Amutara Formation close to their contact with the Oligocene Quimsa Cruz granodiorite and porphyritic monzogranite batholith (Everden et al. 1977;[START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF][START_REF] Artiaga | The Viloco Sn-W-Mo-As deposits, Bolivia: geolog and mineralog[END_REF]. K-Ar dating of igneous biotite and muscovite from the Quimsa Cruz batholith yielded dates between 23 and 26 Ma [START_REF] Ahlfeld | Geología de Bolivia[END_REF]Cordani 1967 in Clark and[START_REF] Clark | The Bolivian Tin Province; notes on the available geochronological data[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF]). U-Pb zircon dates in the Quimsa Cruz batholith at Mina Argentina and Mina Viloco are 25.65 ± 0.41 and 26.02 ± 0.41 Ma, respectively [START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF].

Vein mineralogy comprises early high-temperature cassiterite, wolframite, löllingite and pyrrhotite associated with quartz-tourmaline gangue and a second lower temperature sulfide stage with arsenopyrite, sphalerite, galena, chalcopyrite and stannite in association with sulfosalts and carbonate gangue minerals [START_REF] Sugaki | Geological study on the ore deposits in the La Paz district, Bolivia[END_REF][START_REF] Artiaga | The Viloco Sn-W-Mo-As deposits, Bolivia: geolog and mineralog[END_REF]. Fluid inclusions in cassiterite crystals from the Araca deposit yielded salinities of 23-35 wt% NaCl equiv. and homogenization temperatures (Th) of 340-489ºC [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF]. Cassiterite from this district is world renowned for its large, highly lustrous, black to caramel-color, twinned and euhedral crystals of gem quality.

Cassiterite crystals studied from this district belong to seven samples collected from the Viloco deposit (Vil 1-540d, . In the studied samples, cassiterite is the dominant phase and appears as dark euhedral and subhedral fractured crystals more than 500 m and up to 5 cm across (Fig. 2B). Twining is a common feature of most cassiterite grains. Crystals present sharp edges in contact with an assemblage of quartz and corroded pyrite-marcasite after pyrrhotite (Fig. 2C). Small sulfide veinlets, less than 200 m in idth and containing chalcopyrite and arsenopyrite, cut cassiterite grains.

San José -Itos district (Oruro city)

The San José and Itos mines are located on the western side of the city of Oruro, 200 km SE of La Paz, and sit close to the contact between the Altiplano and the Eastern Cordillera. Metallic mineralization is genetically associated to a Miocene dome and volcanic complex intruding into and extruding over Paleozoic shales and sandstones (Chace 1948a,b;[START_REF] Redwood | K-Ar dating of Miocene magmatism and related epithermal mineralization of the northeastern Altiplano of Bolivia[END_REF][START_REF] Sugaki | K Ar ages of tin-polymetallic mineralization in the Oruro mining district, central Bolivian tin belt[END_REF]. K-Ar dating of biotite, sericite and K-feldspar in rhyodacite domes yielded dates between 15 and 19 Ma [START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Redwood | K-Ar dating of Miocene magmatism and related epithermal mineralization of the northeastern Altiplano of Bolivia[END_REF]). Mineralization appears as Ag-Sn-rich veins and disseminations hosted by domes of 16.1 Ma [START_REF] Redwood | K-Ar dating of Miocene magmatism and related epithermal mineralization of the northeastern Altiplano of Bolivia[END_REF] and hydrothermal breccias of the homonymous San José and Itos stocks [START_REF] Sillitoe | Porphyry tin deposits in Bolivia[END_REF][START_REF] Sugaki | Sulfur isotope reconnaissance of Bolivian hydrothermal deposits[END_REF]).

Mineralization occurred in three stages. The first stage is Sn-rich and composed of euhedral quartz, As-rich pyrite, cassiterite and arsenopyrite. The second stage is sulfosalt-rich and comprises franckeite and cylindrite coatings over previous assemblages. The third stage is composed of sphalerite and stannite-group minerals partially replaced by franckeite and Ag-rich sulfosalts (stephanite, andorite), acanthite and galena as open-space infilling and associated to kaolinite, dickite and alunite [START_REF] Sillitoe | Porphyry tin deposits in Bolivia[END_REF][START_REF] Pastor | The San José-Itos mines, Oruro, Bolivia: Structure and Ag-Sn mineralization[END_REF]. Bismuth-rich andorite and ramdohrite and Sb-rich bismuthinite are also found in the San José mine [START_REF] Keutsch | Metalliferous paragenesis of the San José mine, Oruro, Bolivia[END_REF]. Fluid inclusions in cassiterite from the Oruro district yielded Th of 389-474ºC and salinities of 8.9 to 26.3 wt% NaCl equiv. [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF].

Here studied cassiterite crystals are from six samples collected from the Itos (It-180b, It-250b and It-250d) and San José (1233, 1241 and 1433) mines. Cassiterite forms massive aggregates of crystals ranging in size from a few tens of microns up to 500 m. Most aggregates are highly corroded and show abundant porosity that draws secondary spongy textures (Fig. 2D). Cassiterite aggregates occur usually assembled with quartz, pyrite-marcasite, arsenopyrite and late sulfosalts such as jamesonite that replaced the previous sulfide assemblage. Locally, euhedral cassiterite crystals are intergrown with quartz (Fig. 2E).

Poopó district

The Poop deposit is located 48 km S of Oruro and 240 km SE of La Pa , near the border bet een the Altiplano and the Eastern Cordillera delineated b the NNW SSE striking Poop regional fault. The Sn-Ag low-sulfidation epithermal mineralization consists of a vein system extending along the N-S striking Poopó-Uyuni fault system.

Veins are hosted by Silurian black shales and sandstones of the Llallagua, Uncía and Belén Formations that were intruded by Miocene dacite porphyry stocks and covered by associated ignimbrite deposits [START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF]. Conspicuous cataclastic textures and occurrence of several stages of breccia cementation by hydrothermal minerals suggest that ore mineralization was coeval with the tectonic activity of the Poopó-Uyuni fault (Torres et al. 2019).

The mineralogy of the deposit consists primarily of quartz, sulfides (sphalerite, wurtzite, pyrite and marcasite), cassiterite, which locally amounts to about 10% of the vein assemblage, and a plethora of Ag-Pb-Cu sulfosalts (Torres et al. 2019). Cassiterite crystallized at two stages during the formation of the deposit: the first one, with quartz and sphalerite-pyrite (Zn-Sn stage) and the second one, along with tin sulfides and sulfosalts (Sn stage).

Analyzed cassiterite grains are from sample Poo-St-1c, which was collected from the Santo Toribio vein system, and belong to the first generation crystallized during the Zn-Sn stage. In the studied samples, cassiterite appears as small aggregates of crystals with sizes between a few tens of microns and 1 mm. Cassiterite is often intergrown with pyrrhotite that has been pervasively replaced by an assemblage of pyrite and marcasite along with siderite (Fig. 2F).

Huanuni district

The Huanuni Sn-W-Pb-Ag-Zn world-class district, located in the homonymous city in the Oruro department, 275 km SE of La Paz, is the largest tin producer in Bolivia and in 2018 its production accounted for over half the total tin production of the country. This deposit is considered to be mesothermal or xenothermal [START_REF] Cacho | Mineralogy and distribution of critical elements in the Sn W Pb Ag Zn Huanuni deposit[END_REF].

Mineralization is mostly hosted by Silurian quartzites, shales and siltstones of the Llallagua, Uncía and Cancañiri Formations, which are discordantly overlain by pyroclastic series of the Miocene Morococala Formation [START_REF] Koeppen | The Morococala volcanics: Highly peraluminous rhyolite ash flow magmatism in the Cordillera Oriental, Bolivia[END_REF]. Paleozoic rocks were intruded by Miocene porphyric dikes peripheral to the mineralized area, which are thought to be genetically connected to the hydrothermal mineralization [START_REF] Redwood | The Metallogeny of the Bolivian Andes[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF][START_REF] Cacho | Mineralogy and distribution of critical elements in the Sn W Pb Ag Zn Huanuni deposit[END_REF]. Cassiterite-rich veins are restricted to the central area of the deposit, in the Pozokoni hill, and tin concentration decreases towards the periphery in the Zn-Pb-Ag La Suerte and Bonanza mines, which are rich in sphalerite, galena and sulfosalts.

Hypogene mineralization in the Pozokoni area comprises three stages. The first stage consists of quartz, basemetal sulfides and cassiterite. The second stage records abundant crystallization of schorl and, akin the first stage, is also rich in base-metal sulfides as well as Co-Ni minerals, late chamosite and siderite followed by native bismuth, wolframite and cassiterite. The third stage is characterized by stannite and sphalerite. There was, in addition, ample crystallization of supergene minerals dominated by phosphates, sulfates and carbonates rich in Fe, Cu and Pb [START_REF] Cacho | Mineralogy and distribution of critical elements in the Sn W Pb Ag Zn Huanuni deposit[END_REF]. Fluid inclusions in quartz from quartz-cassiterite veins yielded Th up to 425ºC and salinities up to 26 wt% NaCl equiv. (Sugaki et al. 1988b;[START_REF] Müller | A fluid inclusion reconnaissance study of the Huanuni tin deposit (Bolivia), using LA-ICP-MS micro-analysis[END_REF][START_REF] Arce-Burgoa | Metalliferous Ore Deposits of Bolivia. SPC Impresores: La Paz Arce-Burgoa O, Goldfarb RJ[END_REF].

Studied cassiterite grains belong to six samples collected from the Pozokoni hill mine area (Hua240, Hua240-1a, Hua240-1b, Hua240-3c, Hua-MU-7b and Hua-MU-8). Cassiterite is the most abundant phase in the studied samples and appears as large (>1 to 5 mm) subhedral and anhedral crystals often forming centimetric aggregates with abundant porosity (Fig. 2G). Twinning is a common feature of Huanuni cassiterite. The edges of the cassiterite crystals are usually sharp in contact with quartz and irregular in contact with marcasite-pyrite and pyrrhotite. In addition, cassiterite crystals are wrapped by stannite, which also lines fractures and voids within cassiterite.

Llallagua district

The Llallagua district is located next to the homonymous city, 300 km SE of La Paz and 80 km SE of Oruro. It is one of the orld s largest porph r -tin deposits with a historical production exceeding 500,000 t of tin [START_REF] Ahlfeld | Los yacimientos minerales y de hidrocarburos de Bolivia[END_REF]. The deposit lies in the hydrothermally altered La Salvadora stock, which is composed mostly of porphyry breccias. The stock is pervasively altered to tourmaline in the central areas and at depth grading upwards and outwards to intense sericitization and finally to chloritization and argilitization [START_REF] Betkowski | Geochemical and textural characterization of phosphate accessory phases in the vein assemblage and metasomatically altered Llallagua tin porphyry[END_REF]). The stock is cut by igneous and hydrothermal breccias. Tin mineralization appears disseminated and in quartz-cassiterite-sulfide veins restricted to early, high-temperature stages [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF]. In veins, cassiterite is assembled with pyrrhotite and apatite (Turneaure 1935;[START_REF] Gordon | The mineralogy of the tin mines of Cerro de Llallagua, Bolivia[END_REF]Kempe et al. 2008). Fluid inclusions in cassiterite and quartz yielded salinities up to 8.2 and 26 wt% NaCl equiv., respectively, and Th up to 593ºC [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF]. Analyzed cassiterite grains are from sample LL-4, which was collected from the Siglo XX mine. In the studied sample, cassiterite occurs as anhedral, fractured and corroded relatively large crystals, with sizes in the range between 200 and 500 m, often showing simple twinning (Fig. 2H). Cassiterite grains are intergrown with quartz, tourmaline and small pyrite crystals with cores replaced by marcasite.

Colquechaca deposit

The Ag-(Zn-Sn-Pb) Colquechaca deposit is located in the Hermoso hill in Colquechaca, northern Potosí department, 465 km SW of La Paz and 96 km N of Potosí. Mineralized veins are hosted by the Miocene Colquechaca volcanic complex in which a stratovolcano of andesitic to dacitic composition was intruded by a series of porphyritic rhyodacitic and quartz-latite domes. The volcanic complex is emplaced over metasedimentary Ordovician (Amutara Formation) and Silurian (Cancañiri and Uncía Formations) series and the discordantly overlying Jurassic (Ravelo Formation), Jurassic-Cretaceous (Kondo and Kosmina Formations) and Cretaceous (Tarapaya Formation) sedimentary series (Martínez and Vargas 1990;[START_REF] Claure | Mapas temáticos de recursos minerales de Bolivia, Hoja Uncía[END_REF][START_REF] Díaz | Facies y ambientes sedimentarios de la Formación Cancañiri (Silúrico inferior) en La Cumbre de La Paz, norte de la Cordillera Oriental de Bolivia[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF]. K-Ar dating of igneous biotite, K-feldspar and plagioclase yielded dates in the range between 19.8 and 22.6 Ma [START_REF] Ahlfeld | Los yacimientos minerales y de hidrocarburos de Bolivia[END_REF][START_REF] Thormann | Investigaciones preliminares sobre la geotectónica y metalogénesis de la zona Challapata-Caxata[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF].

Xenothermal vein mineralization hosts a cassiterite-and stannite-rich zone along with tourmalinization in the innermost part of the deposit, which grades outwards to a sulfide-and Ag-sulfosalt-rich domain with phyllic alteration [START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF].

Analyzed cassiterite grains are from two samples collected from the Hilarion vein in the Cerro Ánimas area (Colq6a and 1353). Cassiterite grains form mostly anhedral crystals of appro imatel 400 m across (Fig. 2I). The edges of these crystals are sharp in contact with quartz and tourmaline and more irregular in contact with sulfides (pyrite, sphalerite and galena). Local leather-shaped radial aggregates of cassiterite appear in contact with most massive, anhedral cassiterite crystals (Fig. 2J).

Huari Huari district

The Huari Huari xenothermal vein deposit is located 25 km NE of Potosí in the Potosí department, 400 km SW of La Paz. Vein and much restricted stratabound metallic mineralizations are hosted by slates and quartzites of the Ordovician San Benito and Silurian Cancañiri and Uncía Formations, which are unconformably overlain by Cretaceous sandstones of the La Puerta Formation. The sedimentary sequence was intruded by small dacite domes and stocks of alleged Miocene age [START_REF] Sugaki | Geological study on the polymetallic ore deposits in the Potosi district, Bolivia[END_REF]Torró et al. 2019a).

Polymetallic veins are mostly of the fissure-filling type and NNE-oriented. Vein mineralogy consists primarily of an early assemblage of quartz, cassiterite and pyrrhotite followed by an assemblage dominated by base-metal sulfides (sphalerite, galena) and pyrite and a final stage dominated by Ag-Pb sulfosalts (Torró et al. 2019a).

Analyzed cassiterite grains belong to three samples collected from the Antón Bravo vein (2018hh15, 2018hh2b and 2018hh3a). In the studied samples, cassiterite is rare and mostly of the needle tin" variety (i.e., small micrometric acicular crystals) forming radial aggregates up to 500 m in si e. Nevertheless, in the deepest parts of the Antón Bravo vein, cassiterite appears as subhedral crystals in assemblage with quartz and a complex paragenesis of sulfides and sulfosalts (Fig. 2K).

Ánimas -Chocaya -Siete Suyos district

The Ánimas -Chocaya -Siete Suyos district is located about 150 km S of Potosí in the Potosí department, 520 km SW of La Paz. This district sits in the western flank of the Eastern Cordillera, close to the triple junction that is drawn by the Eastern Cordillera, the Western Cordillera and the Altiplano. Mineralization is genetically associated with the Miocene Chocaya volcanic caldera complex, which is 9 km in diameter and conformed of a pile of lava and pyroclastic deposits of dacitic composition intruded by a central dome of the same composition. The volcanic complex is hosted by Ordovician sandstones and slates unconformably overlain by Oligocene-Miocene sandstones and tuffs of the Quehua Formation [START_REF] Ahlfeld | Los yacimientos minerales y de hidrocarburos de Bolivia[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Arce-Burgoa | Metalliferous Ore Deposits of Bolivia. SPC Impresores: La Paz Arce-Burgoa O, Goldfarb RJ[END_REF]Torró et al. 2019b). Reported K-Ar dates in the area are of 13.8 ± 0.2 Ma (unweighted mean value) for biotite from unaltered volcanic rocks, and of 12.5 ± 0.2 Ma for a sericitized sample (whole-rock age; [START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF].

Mineralization in the district occurs as banded and massive oxide and sulfide ore vein infillings [START_REF] Sugaki | Geological study on the polymetallic ore deposits in the Potosi district, Bolivia[END_REF]. Torró et al. (2019b) Analyzed cassiterite grains are from the 10 vein in the Siete Suyos mine (2018-7S2 and 1380) and from the Colorada vein in the Ánimas mine (2018-An12 and Ani5c). The studied grains are subhedral and anhedral and range in si e from 100 to 600 m. Often, small cr stals of cassiterite form aggregates up to 1 mm across. These aggregates are intergrown with quartz, sulfides and sulfosalts in hexagonal arrangements (Fig. 2L) after hexagonal pyrrhotite (see Torró et al. 2019b).

Analytical methods

A total of 32 thick sections belonging to nine deposits from the Bolivian tin belt were selected: two for Kellhuani, seven for Viloco, six for San José-Itos (Oruro), one for Poopó, six for Huanuni, one for Llallagua, two for Colquechaca, three for Huari Huari and five for Ánimas -Chocaya -Siete Suyos.

Petrography (optical microscope, SEM and SEM-CL)

Mineralogy and textures in thick polished sections were studied by optical microscopy using reflected light in order to select the optimal cassiterite specimens for subsequent geochemical analysis. A selection of the polished sections was also examined with an environmental scanning electron microscope (SEM) Quanta 200 FEI, an XTE 325/D8395 (Thermo Fisher Scientific, Waltham, MA, USA) equipped with an INCA Energy 250 EDS microanalysis system at the Centres Científics i Tecnològics of the University of Barcelona (CCiT-UB). Operating conditions were 20 keV accelerating voltage and 5 nA in backscattered electron (BSE) mode.

Electron probe microanalysis (EPMA)

A total of 268 analyses of cassiterite (major and minor elements) were carried out using a five-channel JEOL JXA-8230 electron probe microanalyzer (EPMA; Jeol Ltd., Tokyo, Japan) at the CCiT-UB, operated at 20 kV acceleration voltage, 20 nA beam current, and ith a beam diameter of 5 m. Anal tical standards and lines used for analyses were: ZrO2 (Zr, L ), Nb2O5 (Nb, L ), SnO2 (cassiterite, L ), FeO (Fe, K ), Ta2O5 (Ta, L ), MnO (rhodonite, K ), TiO2 (rutile, K ). The EPMA data are reported in Supplementary Table S1.

Laser ablation -inductively coupled plasma -sector field -mass spectrometry (LA-ICP-SF-MS)

A total of 330 analyses of cassiterite trace element concentrations and U-Pb isotopic compositions were carried out at ETH Zürich, Switzerland, by laser ablation inductively coupled plasma sector field mass spectrometry (LA-ICP-SF-MS) using a RESOlution S-155 (ASI/Applied Spectra) 193 nm ArF excimer laser system attached to an Element XR (Thermo) sector-field ICP-MS. We have used a laser repetition rate of 3 Hz, a spot diameter of 43 m and a laser energ densit on sample of about 3.5 J•cm 2 . The sample surface was cleaned before each analysis by three pre-ablation pulses. Ablation was performed in a dual-volume, fast-washout S-155 ablation cell (Laurin Technic) fluxed with carrier gas consisting of about 0.5 L•min 1 He and make-up gas consisting of about 1 L•min 1 Ar and 2 mL•min 1 N2. The ablated aerosol was homogenized via flushing through a squid device before being introduced in the plasma.

The ICP-MS instrument is equipped with a high capacity (80 m 3 •h 1 ) interface pump to achieve, in combination with jet sampler and normal H-skimmer cones, a detection efficiency (based on U in NIST SRM612 glass) in the range of 2% [START_REF] Guillong | Evaluating the reliability of U Pb laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) carbonate geochronology: matrix issues and a potential calcite validation reference material[END_REF]). The instrument was optimized for maximum sensitivity on the entire mass range while keeping the production of oxides low ( 248 ThO+/ 232 Th+ 0.15%) and the U/Th ratio at about 1 (on NIST SRM612 glass). The list of analyzed isotopes and corresponding dwell times is provided in Supplementary Table S2. A total of 40 mass scans (~1.04 s sweep time each) were acquired over 40 s measurement (20 s of background measurement followed by 20 s of sample ablation).

For trace element quantification, the resulting intensities were subsequently processed offline with the standalone version 1.3.2 of the SILLS program [START_REF] Guillong | SILLS: A MATLAB-based program for the reduction of laser ablation ICP-MS data of homogeneous materials and inclusions[END_REF]). The USGS GSD-1G glass [START_REF] Guillong | Preliminary characterisation of new glass reference materials (GSA-1G, GSC-1G, GSD-1G and GSE-1G) by Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry using 193 nm, 213 nm and 266 nm wavelengths[END_REF] was used as the primary reference material for trace element quantification and instrumental drift correction using conventional standard-sample bracketing. The Fe concentrations obtained by electron microprobe were used as internal standards for relative sensitivity corrections. The analyzed In intensities on masses 113 and 115 were corrected for interferences by subtracting the contribution of 113 Cd and 115 Sn, respectively, based on the measured 111 Cd and 118 Sn intensities and using natural isotope ratios for Cd and Sn recommended by IUPAC. Because of the very high 118 Sn signal in cassiterite (>5,109 cps) and resulting elevated gas blanks on masses 115 and 118, the extent of the correction is much higher in the case of 115 In than in the case of 113 In, especially since the analyzed cassiterite crystals all show very low Cd concentrations (<1 ppm). Therefore, we only considered the concentrations based on the interference-corrected 113 In intensities. The data are reported in Supplementary Table S3. The analytical reproducibility and accuracy were checked by repeated measurements of the homogeneous NIST SRM610 glass [START_REF] Jochum | Determination of reference values for NIST SRM 610-617 glasses following ISO guidelines[END_REF]) reference material. Reproducibilit ranges from 10 to 15% (2 ) relative for most elements. The quoted uncertainties for each individual anal sis correspond to the internal (2 ) statistical error and analytical reproducibility propagated by quadratic addition. The results are accurate within these calculated uncertainties (Supplementary Table S3).

For U-Pb dating, the measured intensities were subsequently processed offline with the Igor Pro Iolite v2.5 software [START_REF] Hellstrom | Iolite: Software for spatially resolved LA-(quad and MC) ICP-MS analysis. In: Sylvester P (ed) Laser ablation ICP-MS in the Earth sciences: Current practices and outstanding issues[END_REF]), using the VizualAge data reduction scheme [START_REF] Petrus | VizualAge: A novel approach to Laser Ablation ICP-MS U-Pb geochronology data reduction[END_REF].

Background-subtracted intensities were used to calculate isotope ratios, which were corrected for laser-induced Pb/U fractionation (after [START_REF] Paton | Improved laser ablation U-Pb zircon geochronology through robust downhole fractionation correction[END_REF], instrumental mass discrimination and drift by conventional standardsample bracketing, against rutile reference material R10 (using isotope ratios from Luvizotto et al. 2009). No common Pb correction was carried out. U-Pb age calculations and data plotting were performed using the IsoplotR toolkit [START_REF] Vermeesch | IsoplotR: A free and open toolbox for geochronology[END_REF]. The lack of matrix-matched primary reference material most certainly makes the obtained dates inaccurate. Nevertheless, in another session using exactly the same analytical parameters as here (including the use of R10 rutile as primary reference material), we have measured three cassiterite samples of known age from the San Rafael granite, Peru (ca. 24 Ma, samples and unpublished dates courtesy of K. Kouzmanov, University of Geneva, 2020) and obtained a systematic offset of ca. 8% relative on lower intercept dates. This offset is in any case smaller than the relative uncertainty obtained on the cassiterite dates obtained here (13-53% relative), except for samples Kell-A and Kell-B (3-6% relative). For these two samples, a relative uncertainty of 8% was therefore propagated in the uncertainty of the dates by quadratic addition to account for the matrix effects. The data from unknowns and rutile reference material are provided in Supplementary Table S4.

Results

Major-and minor-element composition

The EPMA data of cassiterite grains from the studied Bolivian deposits show a generally restricted range in composition, with SnO2 > 97.7 wt%. Of the other elements, only Fe yields concentrations that are generally above its lower limit of detection (L.O.D.) with maximum concentrations of 2.34 wt%. Iron is particularly high in cassiterite from the Colquechaca deposit, with concentrations systematically higher than 0.5 wt%. The rest of the elements yields values mostly below the respective L.O.D. with some anomalous values for TiO2 (up to 0.92 wt% in a sample from Kellhuani) and Nb2O5 (up to 0.25 wt% in samples from Viloco and Huanuni).

Trace-element composition

Significant effort was made to report only the concentration of elements whose variations respond to solid solutions and not to mixed mineral analyses by analyzing mineral volumes free of obvious inclusions and by selecting only stable signal intervals in LA-ICP-MS spectra (Supplementary Fig. S1). A complete set of box plots showing the concentration of all elements analyzed by LA-ICP-MS is available in Supplementary Figure S2, anda selection of them is shown in Fig. 3. Concentration values will be hereinafter reported as the interquartile range (IQR) unless otherwise specified.

Cassiterite from the Bolivian tin belt shows a relatively wide trace element compositional spectrum, mainly subordinated to W (1987-53.7 ppm) and Ti (918-27.8 ppm) contents. The concentration of high-field-strength elements (HFSE) is relatively low, including Zr (17.0-0.528 ppm), Hf (0.293-0.0455 ppm), Nb (4.84-0.037 ppm) and Ta (0.0924-0.0126 ppm). The highest concentrations of Nb and Ta are found in cassiterite samples from the Kellhuani (60.8-2.26 ppm Nb and 0.639-0.0403 ppm Ta), Llallagua (18.5-0.989 ppm Nb and 0.185-0.0143 ppm Ta) and Viloco (6.19-0.0515 ppm Nb and 0.135-0.0138 ppm Ta) deposits, and the lowest, in cassiterite samples from the Poopó (0.027-0.0126 ppm Nb and 0.0196-0.0133 ppm Ta) and Ánimas -Chocaya -Siete Suyos (0.059-0.00971 ppm Nb and 0.0165-0.00873 ppm Ta) deposits. Manganese concentrations (9.36-1.61 ppm) are consistently lower than Fe concentrations. Maximum Mn concentrations are recorded in samples from the Colquechaca (40.4-3.28 ppm) and Poopó (17.5-8.38 ppm) deposits, and the lowest concentrations, in samples from the Llallagua deposit (<L.O.D.). Most analyzed cassiterite samples from the Bolivian tin belt yield (Fe+Mn)/(Nb+Ta) >> 1 at relatively constant Mn (and Fe+Mn) and variable Nb+Ta (Fig. 4A-B; see also Supplementary Fig. S3). In the Nb vs Ta plot (Fig. 4C), cassiterite samples from the Bolivian tin belt plot mostly around the Nb:Ta = 2:1 ratio line, Nb concentrations being by up to four orders of magnitude higher than Ta concentrations.

Concentrations of Zr and Hf are highest in samples from the Kellhuani (28.5-3.24 ppm Nb and 0.965-0.141 ppm Ta), Huanuni (17.5-1.89 ppm Nb and 0.432-0.0731 ppm Ta) and Llallagua (16.5-3.92 ppm Nb and 0.387-0.0955 ppm Ta) deposits, and lowest in samples from the Ánimas -Chocaya -Siete Suyos (0.059-0.00971 ppm Nb and 0.0165-0.00873 ppm Ta) and Poopó (0.027-0.0126 ppm Nb and 0.0196-0.0133 ppm Ta) deposits. The concentration of both elements yields a relatively good positive correlation mostly at Zr/Hf > 1, Zr concentrations being by up to one order of magnitude higher than Hf concentrations (Fig. 4D). Concentrations of Ti are highest in cassiterite samples from Kellhuani (3065-561 ppm), Huari Huari (1391-383 ppm) and Llallagua (1303-382 ppm) and lowest in samples from Ánimas -Chocaya -Siete Suyos (19.1-4.65 ppm) and Poopó (4.38-2.02 ppm). There is a fairly positive correlation between Ti and Zr at Ti/Zr > 1, similar to most cassiterite worldwide (Fig. 4E). In contrast, Ti does not show clear correlation with U, and Ti/U ratios are normally higher than 1, with a composition similar to global cassiterite in terms of both elements (Fig. 4F). Titanium shows fairly positive correlation with Sc for most samples plotting between the lines defined by Sc:Ti 1:1 and 1:2 ratios in Fig. 4G. Nevertheless, cassiterite compositions for some of the studied deposits align preferably along one or the other, with most samples from the Kellhuani and Viloco deposits lying along the Sc:Ti = 1:2 ratio line and most samples from the Ánimas -Chocaya -Siete Suyos and Poopó deposits lying around the 1:1 ratio line. Finally, there is a strong positive correlation between V and Sc (Fig. 4H).

As for the concentrations of critical metals others than the aforementioned ones (European Commission 2017), In (96.9-9.78 ppm), Ga (92.1-3.03 ppm) and Ge (3.92-0.776 ppm) vary by orders of magnitude in crystals from individual deposits/districts and from deposit to deposit. Gallium and In are distinctively concentrated in cassiterite from the Oruro (801-31.8 ppm In and 377-71 ppm Ga), Huari Huari (889-96.9 ppm In and 438-53.5 ppm Ga) and Ánimas -Chocaya -Siete Suyos (582-174 ppm In and 292-53.1 ppm Ga) deposits. Gallium is also relatively high in the Colquechaca deposit (438-53.5 ppm). The concentrations of In and Ga are consistently very low in the Viloco (63.4-10.0 ppm In and 5.43-1.59 ppm Ga), Kellhuani (30.9-2.15 ppm In and 3.11-0.932 ppm Ga), Llallagua (25-6.5 ppm In and 53.1-23.0 ppm Ga) and Fig. 3) deposits.

REE values show a relative wide dispersion in grains analyzed within individual deposits/districts (Figs. 3 and5, Table 1). Cassiterite samples from Kellhuani (IQR[ REE] = 6.18-2.19 ppm) yield the highest REE concentrations, and samples from the Ánimas -Chocaya -Siete Suyos district (IQR[ REE] = 2.12-1.44 ppm), the lowest REE concentrations. In chondrite-normalized (CN) spider plots (Fig. 5

U-Pb cassiterite geochronology

U-Pb isotopic analyses of cassiterite grains from the Kellhuani, Viloco, Huanuni and Llallagua deposits are presented in Supplementary Table S4 and illustrated in Fig. 6. Spot analyses from the four deposits form Tera-Wasserburg (T-W) isochrons defining lower-intercept dates of 218.3 ± 5.5 Ma (Kellhuani), 24.4 ± 0.4 Ma (Viloco), 24.0 ± 2.4 Ma (Huanuni) and 24.0 ± 5.1 Ma (Llallagua); concordant data is absent. U-Pb isotopic analyses on cassiterite grains from the other studied Bolivian deposits were inconclusive due to too low U contents and/or too high initial Pb.

Discussion

Timing of Sn mineralization in the Bolivian tin belt

Punctuated magmatism and petrogenetically related hydrothermal tin mineralization in the Bolivian tin belt occurred in the Late Triassic, Late Oligocene and Miocene (Ahfeld 1967;[START_REF] Turneaure | The Bolivian tin-silver province[END_REF][START_REF] Clark | The Bolivian Tin Province; notes on the available geochronological data[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Clark | Geologic and geochronologic constraints on the metallogenic evolution of the Andes of southeastern Peru[END_REF][START_REF] Lehmann | The Bolivian tin province and regional tin distribution in the Central Andes: A reassessment[END_REF][START_REF] Sugaki | K Ar ages of tin-polymetallic mineralization in the Oruro mining district, central Bolivian tin belt[END_REF][START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF][START_REF] Neymark | In situ LA-ICPMS U Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF]. Accordingly, the metallogeny of the Bolivian tin belt results from multiple, discrete events that lead to similar anomalous Sn enrichment in a series of mineral deposits of different affiliation within the magmatic-hydrothermal family.

To contextualize our U-Pb cassiterite ages in the framework of the magmatic and metallogenic evolution of the Bolivian tin belt, a geochronologic chart with all available radiometric dates (excluding dates related to exhumation -thermochronology oriented studies, e.g., (U-Th-Sm)/He, fission track) has been produced (Fig. 7).

For some of the studied deposits (Kellhuani, Viloco and Huanuni), our U-Pb cassiterite dates are the first geochronologic data based on ore minerals rather than hydrothermal and/or magmatic mineral phases. This observation is particularly important in the case of the Milluni Kellhuani district and other tin deposits in neighboring areas of the Cordillera Real (Fig. 1A). In the Yani, Sorata, Zongo and Huayna Potosí plutons, there is a large dispersion of radiometric dates (mostly K/Ar and Ar/Ar silicate mineral dates; Fig. 7) from Late Triassic (i.e., the accepted age of host rock crystallization, constrained by U-Pb zircon dating) to dates as young as ca. 35

Ma. This dispersion in radiometric dates probably represents protracted isotopic resetting during the complex thermal history undergone by these rocks (cf. [START_REF] Farrar | Zongo-San Gabán zone: Eocene foreland boundary of the Central Andean orogen, northwest Bolivia and southeast Peru[END_REF][START_REF] Kontak | Eocene tectono-thermal rejuvenation of an upper Paleozoiclower Mesozoic terrane in the Cordillera de Carabaya, Puno, southeastern Peru, revealed by K-Ar and 40 Ar/ 39 Ar dating[END_REF][START_REF] Schildgen | The topographic evolution of the Central Andes[END_REF] but also opens the door to overprinting hydrothermal events connected to mineralization.

Our U-Pb cassiterite date for Kellhuani (218.3 ± 5.5 Ma) agrees, within the limits of the analytical error, with the K/Ar muscovite date at 210 ± 6 Ma reported by [START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF] for the greisen at the Chacaltaya porphyry stock, which is genetically connected to the mineralization in the Milluni-Kellhuani district [START_REF] Lehmann | Formation of the strata-bound Kellhuani tin deposits, Bolivia[END_REF]. In addition, this date agrees with the U-Pb zircon concordia dates of 222.3 ± 2.4 and 220.8 ± 1.9 Ma reported by [START_REF] Cordani | Geochronological systematics of the Huayna Potosí, Zongo and Taquesi plutons, Cordillera Real of Bolivia, by the K/Ar, Rb/Sr and U/Pb methods[END_REF] for two granite samples from the neighboring Huayna Potosí pluton.

In the Viloco deposit, our U-Pb cassiterite date (24.4 ± 0.4 Ma) agrees, within error, with felsic magmatism in the Tres Cruces batholith dated at ca. 22-26 Ma via K/Ar analysis of igneous biotite and muscovite [START_REF] Ahlfeld | Geología de Bolivia[END_REF]Cordani 1967 in Clark and[START_REF] Clark | The Bolivian Tin Province; notes on the available geochronological data[END_REF][START_REF] Evernden | Potassium-argon ages of some Bolivian rocks[END_REF][START_REF] Mcbride | Magmatic and metallogenetic episodes in the northern tin belt, Cordillera Real, Bolivia[END_REF][START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF]. [START_REF] Gillis | Thermochronology, geochronology, and upper crustal structure of the Cordillera Real: implications for Cenozoic exhumation of the central Andean plateau[END_REF] performed U-Pb dating of zircons from the Quimsa Cruz batholith in the Argentina and Viloco mines and obtained dates of 26.2 ± 0.2 and 25.4 ± 0.2 Ma, respectively.

As far as we know, there are no geochronological studies in the Huanuni deposit area. The mineralization has been suggested to be of Late Oligocene -Early Miocene age by analogy with other neighboring mining districts (e.g., San Pablo stock -Japo -Santa Fe, El Poder and Llallagua; Fig. 1A) for which igneous activity connected to tin mineralization has been dated in the range between ca. 25 and 20 Ma (K/Ar mineral and whole rock dates; [START_REF] Everden | Edades absolutas de algunas rocas ígneas en Bolivia por el método potasio-argón[END_REF][START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF][START_REF] Sugaki | K Ar ages of tin-polymetallic mineralization in the Oruro mining district, central Bolivian tin belt[END_REF]. This age bracket encompasses our 24.0 ± 2.4 Ma U-Pb cassiterite date in the Huanuni deposit. The nearby Mororocala ignimbrites (Fig. 1A), in contrast, are much younger according to Ar/Ar dates of ca. 8-6 Ma provided by [START_REF] Koeppen | The Morococala volcanics: Highly peraluminous rhyolite ash flow magmatism in the Cordillera Oriental, Bolivia[END_REF] (see also [START_REF] Morgan | Petrochemistry of Late Miocene peraluminous silicic volcanic rocks from the Morococala Field, Bolivia[END_REF].

The age of the mineralization in the Llallagua deposit has long been a topic of discussion. Reported radiometric dating includes dates as disparate as 43.8 ± 4.7 Ma (Sm/Nd early fluorapatite vein assemblages, [START_REF] Rakovan | Use of surface-controlled REE sectoral zoning in apatite from Llallagua, Bolivia, to determine a single-crystal SmNd age[END_REF], 42.2 ± 4 Ma (Pb/Pb evaporation age in zircon; Kempe et al. 2008), 23.4 ± 2.2 and19.0 ± 1.6 Ma (U-Pb monazite, Kempe et al. 2008;[START_REF] Kohn | U-Th-Pb dating of monazite by single collector ICP-MS: pitfalls and potential[END_REF] and 20.9 ± 0.4 Ma (K/Ar geochronology of the hydrothermally altered porphyry, [START_REF] Grant | K-Ar ages of igneous rocks and mineralization in part of the Bolivian tin belt[END_REF]. U-Pb dating on cassiterite by [START_REF] Neymark | In situ LA-ICPMS U Pb dating of cassiterite without a knownage matrix-matched reference material: Examples from worldwide tin deposits spanning the Proterozoic to the Tertiary[END_REF] yielded a date of 20.0 ± 2.5 Ma, which overlaps within error with our 24.0 ± 5.1 Ma U/Pb cassiterite date thus constraining the tin mineralization event in this deposit to the Early Miocene.

The new geochronologic data presented here, hence, conform to the idea that tin mineralization events in the Bolivian tin belt occurred at least in two separate epochs during the Late Triassic (Norian; Milluni-Kellhuani district) and the Late Oligocene (Chattian) -Early Miocene (Aquitanian; Viloco, Huanuni and Llallagua deposits).

Unpublished cassiterite U-Pb analyses in samples from the San Rafael deposit in Peru yield dates of ca. 24 Ma (pers. comm. M. Harlaux), similar to the Viloco, Huanuni and Llallagua deposits. These ages coincide with major episodes of mantle upwelling, decompression melting and basalt production, and related high heat flow into the overlying crust (see above). Unfortunately, U-Pb measurements of cassiterite grains from deposits located in the southernmost part of the Bolivian tin belt were inconclusive, although previous geochronological data would point to younger mineralization ages of ca. 15-13 Ma (Fig. 7; see also [START_REF] Slater | Origin of a multi-stage epithermal Ag-Zn-Pb-Sn deposit: the Miocene Cortaderas breccia body, Pirquitas mine, NW Argentina[END_REF] for a discussion on the age of the Pirquitas deposit in Argentina based on field relationships). Progressively younger tin-polymetallic mineralization towards the south of the Bolivian tin belt during the Pliocene and Miocene might be related to the southward passage of the subducting Juan Fernández aseismic ridge and associated migrating magmatic flare-up (de Silva and Kay 2018); the latter might however have resulted from the southward migration of the onset of Late Oligocene earliest Miocene major mafic magmatism detected by [START_REF] Fornari | Ar-Ar dating of Late Oligocene-Early Miocene volcanism in the Altiplano[END_REF], possibly as a consequence of the reconstructed migration of this ridge. Separate tectonic events leading to i) crustal melting of volatile-rich, carbonaceous sediments and ii) enhanced magmatic differentiation and sustained heat production enabled by long crustal residence of mantle-derived melts in a thickened crust converged to form one of the largest Sn accumulations on Earth [START_REF] Dietrich | Bulk rock and melt inclusion geochemistry of Bolivian tin porphyry systems[END_REF][START_REF] Lehmann | Boron in the Bolivian tin belt[END_REF].

Controls on minor-and trace-element variations in cassiterite

Due to the tetragonal structure of cassiterite and according to charge, radii and coordination of ions compared with Sn 4+ the following elements are considered to be compatible with cassiterite: Al 3+ , Fe 3+ , Ga 3+ , V 3+ , Cr 3+ , Sc 3+ , Sb 3+ , W 4+ , U 4+ , Zr 4+ , Hf 4+ , Ti 4+ , Nb 5+ and Ta 5+ [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF][START_REF] Mao | Combined zircon, molybdenite, and cassiterite geochronology and cassiterite geochemistry of the Kuntabin tintungsten deposit in Myanmar[END_REF]. Of these elements, the 4+ charged cations (Zr, Hf, Ti, U and W) can directly substitute for Sn 4+ (without readjustments of charge balance) while coupled substitution mechanisms are required for differently-charged cations (e.g., Fe, Mn, Nb, Ta and In; [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF].

Zirconium and Hf have similar geochemical behavior, so they usually maintain a near chondritic Zr/Hf ratio of 35-40 [START_REF] Hoskin | The composition of zircon and igneous and metamorphic petrogenesis[END_REF]. However, in hydrothermal environments and in highly differentiated igneous rocks, deviations from this ratio (i.e., element pair decoupling) can occur [START_REF] Bau | Controls on the fractionation of isovalent trace elements in magmatic and aqueous systems: evidence from Y/Ho, Zr/Hf, and lanthanide tetrad effect[END_REF]. Processes such as metasomatism, crystal fractionation in the presence of zircon, hydrothermal alteration or preferential mobilization of Zr in B-and F-rich fluids have been proposed to cause fractionation of Zr over Hf [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF]. The fact that the studied cassiterite samples yielded Zr/Hf up to 90 agrees with the high activity of B and F during the formation of the mineralization along the Bolivian tin belt, as seen in abundant tourmaline plus fluorite.

Even though Nb and Ta are considered to have similar geochemical behavior, large variations in their concentration and ratio occur in cassiterite. [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF] attribute these variations to processes involving element fractionation during mineral growth due to fluid disequilibrium. However, variations in the concentration of Nb and Ta may also be related to the physical-chemical characteristics of the hydrothermal fluids [START_REF] Zhao | U-Pb Ages, O isotope compositions, Raman spectrum, and geochemistry of cassiterites from the Xi ao copper-tin polymetallic deposit in Gejiu District, Yunnan Province[END_REF][START_REF] Lerouge | Distribution of In and other rare metals in cassiterite and associated minerals in Sn±W ore deposits of the western Variscan Belt[END_REF]. [START_REF] Zhang | Combined zircon and cassiterite U Pb dating of the Piaotang granite-related tungsten tin deposit, southern Jiangxi tungsten district, China[END_REF] noted that cassiterite from high-temperature systems related to highly fractionated Li-F granites and pegmatites has high Nb, Ta and Zr contents (with low Zr/Hf ratios) but low Fe and Mn contents, contrary to cassiterite from low-temperature hydrothermal deposits. On the other hand, isomorphous replacement of Sn3O6 by (Fe,Mn)(Nb,Ta)2O6 is typical of cassiterite in hydrothermal cassiteritequartz veins and greisen deposits (e.g., [START_REF] Möller | Substitution of tin in cassiterite by tantalum, niobium, tungsten, iron and manganese[END_REF][START_REF] Murciego | Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif[END_REF][START_REF] Abdalla | Chemistry of cassiterite in rare metal granitoids and the associated rocks in the Eastern Desert, Egypt[END_REF], whereas isomorphic replacement of 3Sn 4+ by 2(Nb,Ta) 5+ + (Fe,Mn) 2+ is typical of magmatic cassiterite from rare-element granites and pegmatites (e.g., [START_REF] Tindle | Oxide minerals of the Separation Rapids rare-element granitic pegmatite group, northwestern Ontario[END_REF].

Cassiterite grains from the Bolivian tin belt are low in Nb+Ta relative to most cassiterite compiled from the literature, particularly to magmatic cassiterite (Fig. 4A-C, Table 2). Iron and Mn concentrations in cassiterite samples from the Bolivian tin belt fit the composition of most cassiterite described in the literature, with the exception of magmatic cassiterite and cassiterite in greisen mineralizations, which are significantly enriched in Mn. In terms of Fe+Mn and Nb+Ta, cassiterite from the Bolivian tin belt shows limited dispersion without any correlation between the concentrations of Fe+Mn and Nb+Ta (Figs. 4A-B); these observations suggest that neither of the aforementioned substitution mechanisms was significant in the composition of the studied grains. Regarding Nb and Ta systematics, the compositions of cassiterite samples from the Bolivian tin belt lie largely along the Nb:Ta = 2:1 ratio line similar to most cassiterite in hydrothermal occurrences worldwide, whereas most magmatic cassiterite and cassiterite from greisen mineralizations lie rather along the 1:1 ratio line (Fig. 4C). Niobium and Ta are enriched in cassiterite grains from the sediment-hosted Kellhuani and Viloco xenothermal deposits, which formed adjacent to causative intrusive complexes, and the stock-hosted Llallagua xenothermal deposit (Fig. 1B) relative to epithermal and shallow xenothermal deposits formed at lower temperatures and depths (Figs. 1,3).

A decrease in Ti and Ti/Zr in cassiterite grains has been linked to transition from proximal (higher temperature) to distal (lower temperature) locations in intrusion-centered hydrothermal systems [START_REF] Taylor | Geology of Tin Deposits[END_REF][START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF]), which coincides with a higher solubility of Zr in hydrothermal fluids compared to Ti (see also [START_REF] Kessel | The water-basalt system at 4 to 6 GPa: Phase relations and second critical endpoint in a K-free eclogite at 700 to 1400 °C[END_REF].

On the other hand, Sc is said to be transported as F complexes in post-magmatic fluids [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF]. Our samples describe Ti/Zr variations by up to two orders of magnitude and systematically plot above the 1:1 ratio line in Fig. 4E similar to reference data for xenothermal and epithermal deposits. In general, cassiterite samples from the intrusion-proximal Kellhuani and Viloco deposits show higher Ti/Zr and Ti/Sc than samples from the intrusion-distal Ánimas -Chocaya -Siete Suyos and Poopó deposits (Figs. 1B,4E,G). Accordingly, our dataset agrees with a progressive depletion of Ti relative to Zr and Sc in hydrothermal fluids as they evolved or migrated away from the causative intrusive bodies and hence the Ti/Zr and Ti/Sc ratios can be used as tracers to magmatichydrothermal centers.

Cassiterite samples from the Bolivian tin belt yield a fair positive correlation between V and Sc, which has been used to propose a Sc 3+ +V 5+ ⇔ 2Sn 4+ coupled substitution in tin-granite-, greisen-, skarn-and vein-type ores by [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF]. The behavior in hydrothermal systems of elements such as V, In, Ge and Ga regarding cassiterite is poorly understood. [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF] 2 and3) thus supporting this idea. Lerouge et al. (2019) found that sulfides (such as stannite and sphalerite) and rutile associated with In-poor cassiterite contain high amounts of In thus highlighting that In tends to preferentially partition in sulfides rather than cassiterite. This would be also the case in the deposits from the Bolivian tin belt [START_REF] Jiménez-Franco | Mineral chemistry of In-bearing minerals in the Santa Fe mining district, Bolivia[END_REF][START_REF] Cacho | Mineralogy and distribution of critical elements in the Sn W Pb Ag Zn Huanuni deposit[END_REF]Torres et al. 2019;Torró et al. 2019a,b).

The studied cassiterite samples from the Bolivian tin belt show average REE concentrations similar to those of reference data for cassiterite in granite, granite-cupola and greisen mineralizations (Table 1; Fig. 5). Similar to cassiterite from the Bolivian tin belt, cassiterite from granites and granite-cupolas also show positive anomalies in MREE in chondrite-normalized diagrams, particularly Tb (see Zoheir et al. 2019). It is noteworthy that, unlike cassiterite from the Bolivian tin belt, cassiterite compositions reported in the literature normally lack negative Ce anomalies. Broken, unusual REE patterns combining concave and conve tetrads are ackno ledged in tinbearing magmatic-hydrothermal systems probably connected to liquid-vapor REE fractionation [START_REF] Monecke | Unusual rare earth element fractionation in a tin-bearing magmatic-hydrothermal system[END_REF]. Following [START_REF] Monecke | Unusual rare earth element fractionation in a tin-bearing magmatic-hydrothermal system[END_REF], the irregular REE tetrad partition in cassiterite samples from the Bolivian tin belt would reflect generalized fluid immiscibility during the early stages of evolution of the studied deposits concomitant with the crystallization of cassiterite. [START_REF] Kelly | Mineralogy, paragenesis and geothermometry of the tin and tungsten deposits of the Eastern Andes, Bolivia[END_REF] proposed that boiling of the early tin-bearing fluid was an important mechanism for the precipitation of early quartz and cassiterite in Llallagua, and may have played an important role in the location of high grade ore in some shallow deposits of central and southern Bolivia (as also suggested by Chace 1948a,b for the Oruro deposits). These authors suggest that the upward vertical zoning of high grade cassiterite to low grade sulfide-rich tin ore may mark levels of local boiling.

Other plausible mechanisms that might have controlled REE fractionation during the crystallization of hydrothermal cassiterite in Bolivian deposits include i) mixing between magmatic and meteoric waters (as proposed for the San Rafael deposit; Kontak andClark 2002, Harlaux et al. 2020) leading to destabilization of REE chloride and fluoride complexes, which are more stable with increasing atomic number [START_REF] Migdisov | Hydrothermal transport, deposition, and fractionation of the REE: Experimental data and thermodynamic calculations[END_REF]; and ii) partitioning of REE between co-crystallizing phases (e.g., monazite and tourmaline; [START_REF] Jolliff | Mineral recorders of pegmatite internal evolution: REE contents of tourmaline from the Bob Ingersoll pegmatite, South Dakota[END_REF][START_REF] Harlaux | Tourmaline as a Tracer of Late-Magmatic to Hydrothermal Fluid Evolution: The World-Class San Rafael Tin (-Copper) Deposit, Peru[END_REF][START_REF] Sciuba | Chemical composition of tourmaline in orogenic gold deposits[END_REF]). Nevertheless, these alternative or complimentary mechanisms leading to REE fractionation would not reproduce the broken, highly irregular chondrite-normalized REE patterns described here for cassiterite samples from the Bolivian tin belt and therefore we surmise that their impact, if any, was subordinate to that of fluid immiscibility.

Potential of cassiterite from the Bolivian tin belt as a source of critical elements as byproducts

Previous studies on the concentration of high-tech metals in deposits from the Bolivian tin belt have focused mostly on the sulfide mineralization [START_REF] Schwarz-Schampera | Indium: Geology, Mineralogy and Economics[END_REF][START_REF] Ishihara | Inferred indium resources of the Bolivian tin-polymetallic deposits[END_REF][START_REF] Artiaga | The Viloco Sn-W-Mo-As deposits, Bolivia: geolog and mineralog[END_REF][START_REF] Murakami | Trace elements of Indium-bearing sphalerite from tin-polymetallic deposits in Bolivia, China and Japan: A femto-second LA-ICPMS study[END_REF][START_REF] Jiménez-Franco | Mineral chemistry of In-bearing minerals in the Santa Fe mining district, Bolivia[END_REF][START_REF] Cacho | Mineralogy and distribution of critical elements in the Sn W Pb Ag Zn Huanuni deposit[END_REF]Torres et al. 2019;Torró et al. 2019a,b;[START_REF] Poupeau | Fission-track dating of 15 macusanite glass pebbles from the Macusani volcanic field (SE Peru)[END_REF]; summary of reported maximum concentrations of In, Ge and Ga shown in Table 3). In the following lines we assess the potential of cassiterite from the Bolivian tin belt as a source of high-tech, critical elements, chiefly Nb, Ta, In, Ge and Ga, by comparing our results with bibliographic values.

Cassiterite samples from the Bolivian tin belt yielded much lower Nb concentrations than cassiterite from granitehosted, granite cupola, greisen and pegmatite mineralizations worldwide (Table 2). Cassiterite from xenothermal and epithermal mineralizations reported in the literature is also enriched in Nb relative to our values. Likewise, cassiterite from the Bolivian tin belt is strongly depleted in Ta relative to most cassiterite compositions reported in the literature (Table 2). According to our results, cassiterite from the Bolivian tin belt is not likely to make a good resource for these two metals.

Indium concentrations in cassiterite from the Bolivian tin belt are consistent with, and often higher than, previously reported concentrations worldwide. However, it is noteworthy that in most of the studied Bolivian deposits, sulfide minerals, namely sphalerite and stannite, are the main In hosts, often with concentrations at the wt% level (Table 3). On the other hand, there is a close correlation between In enrichment in cassiterite and sulfide minerals in deposits along the Bolivian tin belt (Table 3). Therefore, in some deposits, cassiterite might represent a potential, additional source of In. The metallurgical recovery of In from cassiterite is, as far as we know, poorly developed. Preconcentration of In in slag during the smelting process to obtain tin metal from cassiterite could be expected, just as for Nb and Ta [START_REF] Gupta | Extractive metallurgy of niobium[END_REF], In being separated afterwards by a multistep operation involving sulfuric acid leach of ferrite slag (Tshijik [START_REF] Karumb | The Poopó polymetallic epithermal deposit, Bolivia: mineralogy, genetic constraints, and distribution of critical elements[END_REF].

Gallium contents in cassiterite samples from the Bolivian tin belt are also consistent with and often higher than concentrations reported in the literature (Table 2). Germanium concentrations in the studied samples of cassiterite are systematically very low, particularly if compared to Ge concentrations reported for cassiterite from pegmatites.

With data in hand, cassiterite from the Bolivian tin belt is probably unattractive as source of Ge.

Conclusions

Tin mineralization has been dated directly by U-Pb geochronology on cassiterite samples from the Kellhuani (218.3 ± 5.5 Ma), Viloco (24.4 ± 0.4 Ma), Huanuni (24.0 ± 2.4 Ma) and Llallagua (24.0 ± 5.1 Ma) deposits. The dates are in good agreement with published ages for igneous rocks within the respective districts and confirm that hydrothermal tin mineralization in the Bolivian tin belt occurred mostly in two periods: Late Triassic and Late Oligocene Miocene.

Our new ages closely coincide with two major magmatic episodes that were apparently triggered by mantle upwelling, decompression melting and basalt production, and related high heat flow into the overlying crust. The age obtained for Kellhuani coincides with the culmination of the Mitu rifting episode (~240 220 Ma; [START_REF] Spikings | Characterisation of Triassic rifting in Peru and implications for the early disassembly of western Pangaea[END_REF]. The dates obtained for Viloco, Huanuni and Llallagua have mean values at 24.0 Ma, which overlap with the timing of major and widespread basaltic magmatism in the central Altiplano and probably adjacent regions.

The convergence of highly evolved, peraluminous silicic melts derived in part from the melting of volatile-rich sedimentary series and a sustained heat and fluid contribution from primitive melts stored at intermediate and upper levels of a thickened continental crust enhanced the formation of large tin deposits along the Bolivian tin belt.

The composition of the studied cassiterite samples is relatively homogeneous at the metalliferous belt scale.

Nevertheless, nuances in trace element contents in mineralizations emplaced at different levels within the xenothermal and epithermal environments allow for the identification of some compositional trends. Some deposits formed adjacent to causative intrusive complexes such as Kellhuani, Viloco and Llallagua are typically enriched in Nb and Ta relative to epithermal and shallow xenothermal deposits. In addition, Ti/Zr and Ti/Sc ratios decrease from intrusive-proximal to intrusive-distal locations and therefore can be used to vectorize toward magmatic-hydrothermal centers.

REE abundances are elevated in cassiterite from intrusive-proximal (e.g., Kellhuani, Llallagua) relative to intrusive-distal mineralizations. There is a general, pronounced enrichment in MREE relative to LREE and HREE in chondrite-normalized patterns. REE distribution patterns are likely influenced by boiling processes, which yield characteristic broken REE patterns combining concave and convex tetrads.

The hydrothermal cassiterite from the Bolivian tin belt has low Nb and Ta compared with magmatic cassiterite in rare-metal granites and pegmatites. The concentration of Ge is systematically very low in the studied cassiterite samples. However, some cassiterite samples have relatively high concentrations of In and Ga. Interestingly, the highest In concentrations in cassiterite from the Bolivian tin belt are found in samples from deposits with documented high concentration of this element in sulfide minerals, suggesting that the concentration of In in cassiterite is primarily controlled by its availability in the hydrothermal fluid. In these particular deposits, cassiterite could represent an additional economic source of In. [START_REF] Pollard | Contrasting evolution of fluorine-and boron-rich tin systems[END_REF][START_REF] Heuschmidt | Las áreas prospectivas de Bolivia para yacimientos metalíferos[END_REF] showing the postulated ideal location of the studied deposits. Granite-hosted and granite cupolas: [START_REF] Moore | Geochemistry of some Cornubian cassiterites[END_REF], [START_REF] Lentz | The petrogenesis of tin-and sulfide-lode mineralization at True Hill, southwestern New Brunswick[END_REF], [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF], [START_REF] Murciego | Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif[END_REF], [START_REF] Gorelikova | Classification of tin deposits using trace elements in cassiterites (Far East, Russia)[END_REF][START_REF] Gorelikova | Discriminating geodynamical regimes of tin ore formation using trace element composition of cassiterite: The Sikhote'Alin case (Far Eastern Russia)[END_REF], [START_REF] Abdalla | Chemistry of cassiterite in rare metal granitoids and the associated rocks in the Eastern Desert, Egypt[END_REF], [START_REF] Neiva | Geochemistry of cassiterite and wolframite from tin and tungsten quartz veins in Portugal[END_REF] 2019), [START_REF] Hulsbosch | Tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the Gatumba pegmatite dyke system (NW Rwanda)[END_REF]. Migmatiticrelated: [START_REF] Murciego | Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif[END_REF], [START_REF] Jiang | Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit, Yunnan, China: Implication for migmatitic-hydrothermal fluid evolution and ore genesis[END_REF]. Pegmatite: [START_REF] Murciego | Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif[END_REF][START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF], [START_REF] Wise | Chemical composition of coexisting columbite-group minerals and cassiterite from the Black Mountain pegmatite, Maine[END_REF][START_REF] Hulsbosch | Tracing fluid saturation during pegmatite differentiation by studying the fluid inclusion evolution and multiphase cassiterite mineralisation of the Gatumba pegmatite dyke system (NW Rwanda)[END_REF][START_REF] Kendall-Langley | U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia[END_REF]. Xenothermal and epithermal environment: [START_REF] Murciego | Geochemistry and EPR of cassiterites from the Iberian Hercynian Massif[END_REF], [START_REF] Pavlova | Indium in cassiterite and ores of tin deposits[END_REF], [START_REF] Guo | Genesis of tin-dominant polymetallic deposits in the Dachang district, South China: insights from cassiterite U-Pb ages and trace element compositions[END_REF], [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF], [START_REF] Zhao | U-Pb Ages, O isotope compositions, Raman spectrum, and geochemistry of cassiterites from the Xi ao copper-tin polymetallic deposit in Gejiu District, Yunnan Province[END_REF].

Figure captions

Skarn: [START_REF] Cheng | Controls on cassiterite (SnO2) crystallization: Evidence from cathodoluminescence, trace-element chemistry, and geochronology at the Gejiu Tin District[END_REF]. VMS: [START_REF] Serranti | Trace-element distribution in cassiterite and sulfides from rubané and massive ores of the Corvo deposit, Portugal[END_REF]. Granite-hosted and granite cupolas: [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF], Zoheir et al. (2019). Greisen-type: [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF]. Migmatitic-related: [START_REF] Jiang | Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit, Yunnan, China: Implication for migmatitic-hydrothermal fluid evolution and ore genesis[END_REF].

Table captions

Table 1. Average REE concentrations for Bolivian Tin Belt cassiterite and bibliographic data: Granite-hosted and granite cupolas: [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF], Zoheir et al. (2019). Greisen-type: [START_REF] Plimer | Trace and rare earth elements in cassiterite -sources of components for the tin deposits of the Mole Granite, Australia[END_REF]. Migmatitic-related: [START_REF] Jiang | Trace and rare-earth element geochemistry in tourmaline and cassiterite from the Yunlong tin deposit, Yunnan, China: Implication for migmatitic-hydrothermal fluid evolution and ore genesis[END_REF]. REE division after [START_REF] Samson | The rare earth elements: behaviour in hydrothermal fluids and concentration in hydrothermal mineral deposits, exclusive of alkaline settings. In: Linnen RL, Samson IM (eds) Rare element geochemistry and mineral deposits[END_REF]; LREE: La-Sm; MREE: Eu-Dy; HREE: Ho-Lu. Table 2. Summary of the concentrations of Nb, Ta, In, Ge and Ga in cassiterite grains from the Bolivian tin belt.

Bibliographic data are shown for comparison (references as in Fig. 4).

  Reported radiometric dates are 43.8 Ma (Sm-Nd fluorapatite age; Rakovan et al. 1997), 42.4 Ma (Pb-Pb zircon evaporation geochronology; Kempe et al. 2008), 23.4 and 19.0 Ma (U-Pb monazite; Kempe et al. 2008 -SHRIMP and Kohn and Vervoort 2008 -LA-ICP-MS, respectively). Recent U-Pb cassiterite dating by Neymark et al. (2018) yielded a date of 20.0 ± 2.5 Ma.

  determined a three-stage paragenetic sequence including an early low-sulfidation stage dominated by cassiterite, pyrrhotite, arsenopyrite and high-Fe sphalerite, a second intermediate-sulfidation stage dominated by pyrite, marcasite, sphalerite and stannite and a late intermediate-sulfidation stage dominated by galena and Ag-Pb-Sn sulfosalts. Cassiterite is much abundant in the Siete Suyos deposit and less common in the Ánimas deposit. In the Chocaya deposit, cassiterite is virtually absent (Torró et al. 2019b).

  ), studied cassiterite grains show rather parallel patterns with irregular tetrad distribution, general negative Ce and positive Gd and Tb anomalies and enrichment in MREE relative to LREE and HREE ([ LREE/ MREE]CN between 0.4 and 0.3, [ LREE/ HREE]CN between 1.6 and 0.6, and [ MREE/ HREE]CN between 4.5 and 1.7).

  related the In composition of cassiterite directly to the concentration of this element in the hydrothermal ore-forming fluids. The highest average concentrations of In in cassiterite samples from the Bolivian tin belt are found indeed in Huari Huari and Ánimas -Chocaya -Siete Suyos districts, which are well known for their high concentrations of In (Schwarz-Schampera and Herzig 2002; Torró et al. 2019a,b; Pring et al. 2020; Tables

Fig. 1 .

 1 Fig. 1. (A) Location of the main ore deposits, plutons and volcanic deposits along the Bolivian Tin Belt. Modified from Mlynarczyk and Williams-Jones (2005). (B) Schematic cross-section model of volcanic-and subvolcanichosted epithermal and xenothermal deposits in the Bolivian Tin Belt (inspired in Pollard et al. 1987 and Heuschmidt

Fig. 2 .

 2 Fig. 2. Photomicrographs of representative cassiterite grains for each of the studied Bolivian deposits (reflected light, PPL). (A) Subhedral cassiterite crystals in association with siderite, quartz and basal sections of tourmaline [Kellhuani]. (B) Twinned and fractured euhedral cassiterite crystal in contact with quartz [Viloco]. (C) Fractured subhedral cassiterite crystals with corroded outlines in contact with stannite, sphalerite and pyrrhotite [Viloco]. (D) Massive cassiterite aggregates with abundant secondary porosity in an assemblage of quartz-marcasite [Oruro]. (E) Breccia texture containing small subhedral and anhedral cassiterite grains and pyrite in a micrometric gangue matrix [Oruro]. (F) Subhedral to anhedral cassiterite grains in contact with sphalerite and pyrite-marcasite after pyrrhotite sho ing bird s e e te tures [Poop ]. (G) Massive euhedral to subhedral fractured cassiterite grains [Huanuni]. (H) Massive, twinned cassiterite crystals in an assemblage of quartz and tourmaline [Llallagua]. (I) Breccia-type mineralization with subhedral cassiterite grains along with quartz, pyrite, galena, sphalerite and late siderite [Colquechaca]. (J) Leather-shaped radial aggregates of cassiterite surrounded by massive sphalerite [Colquechaca]. (K) Complex sulfide and sulfosalt assemblage along with corroded and twinned cassiterite crystals [Huari Huari]. (L) Garland-like arrangement of cassiterite, sulfides and sulfosalts wrapping a euhedral hexagonal quartz crystal [Ánimas -Chocaya -Siete Suyos]. Abbreviations: Ara = aramayoite; Cst = cassiterite; Cpy = chalcopyrite; Gn = galena; Mcs = marcasite; Mia = miargyrite; Osc = oscarkempffite; Pyr = pyrargyrite; Po = pyrrhotite; Py = pyrite; Qz = quartz; Sid = siderite; Sl = sphalerite; Stn = stannite; Ttd = tetrahedrite-group; Turm = tourmaline.

Fig. 3 .

 3 Fig. 3. Selected box plots showing element concentrations in cassiterite from the Bolivian Tin Belt (LA-ICP-SF-MS data).

Fig. 4 .

 4 Fig. 4. Correlation binary plots for cassiterite from the Bolivian tin belt. Bibliographic data is shown for comparison.

  , Pavlova et al. (2015), Lerouge et al. (2017), Nascimento and Souza (2017), Zhang et al. (2017), Chen et al. (2019), Cheng et al. (2019), Fuchsloch et al. (2019), Zoheir et al. (2019), Mao et al. (2020). Greisen-type: Plimer et al. (1991), Pavlova et al. (2015), Chen et al. (2019), Cheng et al. (2019), Fuchsloch et al. (

Fig. 5 .

 5 Fig. 5. Chondrite-normalized REE spider diagrams for Bolivian Tin Belt cassiterite represented as individual analyses (A) and as average values for each deposit/district (B). Bibliographic data are shown for comparison.

Fig. 6 .

 6 Fig. 6. Tera-Wasserburg U-Pb concordia plots for cassiterite from the Kellhuani, Viloco, Huanuni and Llallagua deposits.

Fig. 7 .

 7 Fig. 7. Triassic to recent geochronologic chart of the Bolivian Tin Belt, including the new U-Pb cassiterite data presented here. Data are ordered from north to south of the Bolivian Tin Belt. Circled numbers correspond to the following references: 1) Ahfeld and Brainsa (1960); 2) Ahfeld and Schneider-Scherbina (1964); 3) Clark and Farrar (1973); 4) Clark et al. (1983); 5) Clark et al. (2000); 6) Cordani (1967); 7) Cordani et al. (2019); 8) Cunningham et al. (1996); 9) Everden (1961); 10) Everden et al. (1997); 11) Gillis et al. (2006); 12) Grant et al. (1979); 13) Kempe et al. (2008); 14) Kontak and Clark (2002); 15) Kontak et al. (1987); 16) McBride et al. (1983); 17) Redwood and Macintyre (1989); 18) Revollo (1967); 19) Rivas and Carrasco (1968); 20) Thormann (1966); 21) Farrar et al. (1990).

  Figure 1

Figure 2 C

 2 Figure 2

  Figure 6

  Fig e 7_1

Fig e 7_2

  Fig e 7_2

Table 3 .

 3 Maximum reported concentrations of In, Ge, Ga, Nb and Ta in ore minerals and concentrates from deposits in the Bolivian Tin Belt.

	Ta	1
			ppm	EE	L EE	EE	H EE	L EE/	EE CN L EE/H EE CN	EE/H EE CN
			Max.	38.3	13.2	21.3	3.79	0.4		1.6	4.5
		Kellhuani (n=30)	Min.	0.513	0.168	0.266	0.046	0.3		0.6	1.7
			IQR	6.18-2.19 2.28-0.766	3.32-1.14	0.706-0.216	0.4-0.3	1.4-1.0	4.1-2.7
			Max.	35.5	13.5	19.6	2.71	0.4		1.9	5.0
		Viloco (n=81)	Min.	0.351	0.124	0.190	0.0367	0.3		0.3	0.8
			IQR	4.42-1.61 1.55-0.562	2.21-0.865	0.483-0.181	0.4-0.4	1.5-1.0	4.2-2.7
		San José -Itos (Oruro) (n=22)	Max. Min. IQR	13.9 0.498 3.58-1.55 1.30-0.621 5.28 0.182	7.41 0.218 1.96-0.825	1.18 0.0375 0.315-0.137	0.6 0.4 0.4-0.4	2.4 0.9 1.7-1.5	5.3 2.6 4.5-4.0
			Max.	5.50	2.00	3.04	0.467	0.4		1.7	4.7
		Poopó (n=9)	Min.	0.384	0.142	0.209	0.0326	0.3		1.4	4.1
			IQR	3.26-1.98 1.16-0.711	1.83-1.10	0.272-0.178	0.4-0.4	1.6-1.5	4.6-4.4
			Max.	14.6	5.30	8.12	1.21	0.4		1.9	5.1
		Huanuni (n=59)	Min.	0.214	0.0791	0.117	0.0184	0.3		1.5	3.9
			IQR	2.58-1.90 0.977-0.698 1.41-1.04	0.216-0.153	0.4-0.4	1.7-1.6	4.7-4.4
			Max.	11.7	4.03	6.65	0.991	0.4		1.7	4.8
		Llallagua (n=13)	Min.	0.452	0.164	0.251	0.0368	0.3		1.2	3.3
			IQR	3.99-2.30 1.41-0.832	2.21-1.24	0.373-0.198	0.4-0.3	1.6-1.5	4.4-4.2
			Max.	2.57	0.984	1.36	0.253	0.4		1.8	4.5
		Colquechaca (n=5)	Min.	1.73	0.661	0.921	0.144	0.4		1.5	3.6
			IQR	2.47-2.12 0.907-0.784 1.33-1.14	0.203-0.197	0.4-0.4	1.7-1.5	4.5-3.9
			Max.	21.3	8.01	11.5	1.73	0.4		1.9	5.0
		Huari Huari (n=9)	Min.	1.74	0.644	0.954	0.145	0.3		1.3	3.9
			IQR	3.76-1.99 1.38-0.715	2.06-1.10	0.317-0.186	0.4-0.4	1.6-1.5	4.6-4.0
		Ánimas -Chocaya -Siete Suyos (n=17)	Max. Min. IQR	4.66 0.0636 2.12-1.44 0.784-0.543 1.14-0.769 1.68 2.56 0.0234 0.0342	0.421 0.00590 0.197-0.125	0.4 0.3 0.4-0.4	1.6 1.5 1.6-1.5	4.8 4.1 4.4-4.2
		Granite hosted and granite cupolas (n=28)	Max. Min. IQR	447 0.658 164-1.37	356 0.0930 144-0.187	48.0 0.0850 11.2-0.132	42.8 0.260 5.27-0.817	7.9 0.1 3.9-0.3	80.9 0.02 3.0-0.05	10.5 0.1 0.8-0.1
		Greisen-type (n=2)	Max. Min.	12.8 2.19	10.2 0.490	1.10 0.710	1.54 0.990	4.4 0.4		1.7 0.1	0.4 0.4
		Migmatitic-related (n=1)		1.83	1.10	0.350	0.380	1.3		0.7	0.5

Acknowledgments

This study was economically supported by the Peruvian CONCYTEC-FONDECYT-World Bank project 107-2018-FONDECYT-BM-IADT-AV and the Catalan project 2017-SGR-00707. We gratefully acknowledge Pura Alfonso (Polytechnic University of Catalonia) for providing cassiterite samples from the Llallagua deposit. The Bolivian State Mining Company (Corporación Minera de Bolivia COMIBOL) granted its permission to the authors to access the Huanuni mine and to perform the necessary sampling; J.C. Ayaviri, J. Araca, R. Condori, N.

Guevara and all individuals at COMIBOL are cordially thanked for their kind and efficient help during field work.

The help and hospitality extended by the miners from mining cooperatives during sampling and field work are most gratefully acknowledged. We appreciate the technical support by Xavier Llovet (CCiT-UB) during the acquisition of EPMA data, and by Peter Tollan (ETH) during the acquisition of LA-ICP-MS data. We are grateful to Daniel Kontak, Matthieu Harlaux, and Editor-in-Chief Bernd Lehmann for their constructive comments which significantly improved the manuscript.

Supplementary material

Supplementary Table S1. EPMA data for spot analyses of cassiterite grains from the Bolivian Tin Belt. Supplementary Table S2. LA-ICP-MS combined trace element and U-Pb isotopic analyses on cassiterite -Metadata. Supplementary Table S3. Trace-element LA-ICP-MS data for spot analyses of cassiterite grains from the Bolivian Tin Belt. Supplementary Table S4. U-Pb LA-ICP-MS data for spot analyses of cassiterite grains from the Bolivian Tin Belt. Supplementary Figure S3. Ternary diagrams representing cassiterite analyses from Bolivian Tin Belt and bibliographic data. The centered ternary plot (C) is used to accentuate compositional variation in unbalanced compositional data by centering the data-set on its average and visualizing the transformed data with a standard ternary balance scheme. References given in Fig. 4 S3 Click here to access/download Supplementar Material Supplementar Table S3 -CST-LAICPMS DATA. ls S le e a Table S4 Click here to access/do nload Supplementar Material Supplementar Table S4 -U_Pb LA-ICP-MS. ls

Supplementary