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Log-normal probability plots for boron data from Lower Paleozoic sedimentary rocks of the Cordillera Real, Bolivia (1), for the Triassic tin granite-related hydrothermal system from the Chacaltaya area, Cordillera Real, Bolivia (2), the Miocene tin porphyry systems of Llallagua, Chorolque and Cerro Rico de Potosi (3), and for quartz-hosted melt inclusions from the Llallagua, Chorolque and Cerro Rico de Potosi tin porphyries (4). The composite Lower Paleozoic boron population (n 112) (crosses) can be divided into two subpopulations (circles) with a geometric mean of 130 and 45 ppm B, corresponding to pelitic (shale) and psammitic (siltstone/sandstone) samples, respectively. The sample population from the Chacaltaya tin system (n 52) can be divided into two subpopulations with a mean of 10,000 and 210 ppm B, corresponding to the inner hydrothermal halo with very strong quartztourmaline alteration (quartz-muscovite-tourmaline-cassiterite greisen , and pelitic rock units partially transformed into tourmalinite), and the outer halo with chloritic alteration. The tin porphyry sample population (n 45) breaks down into two subpopulations with 6500 and 285 ppm B, corresponding to quartz-tourmaline alteration in core zones, and phyllic alteration in higher and peripheral parts of porphyry intrusions/breccia pipes. The nuclear-reaction analysis/ SIMS boron data from quartz-hosted melt inclusions (n 12) de®ne a geometric mean of 225 ppm B
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Tourmaline alteration and high boron contents are typical features of the magmatic-hydrothermal systems of the Bolivian tin
province. The average boron content in melt inclusions of quartz phenocrysts from tin porphyry systems is 225 ppm (1σ-variation
range: 110–420 ppm; n=12) and suggests a magmatic boron input to the hydrothermal tin systems, and...
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... The most likely explanation for this is the preferential mobilization of Zr in B-and F-rich fluids causing fractionation of Zr over Hf in hydrothermal cassiterite (Cheng et al. 2019). However, at Ayawilca, there is a lack of B and F species, which is a significant difference compared with many other Sn(-polymetallic) magmatic-hydrothermal deposits (Pollard et al. 1987;Xiang et al. 2020;Lehmann 2021), including those in the Central Andean tin belt (Kelly and Turneaure 1970;Lehmann et al. 1990Lehmann et al. , 2000Cacho et al. 2019;Torres et al. 2019;Harlaux et al. 2020), in which the occurrence of tourmaline + fluorite ± topaz in hydrothermal alteration assemblages is ubiquitous. ...
The Ayawilca deposit in Pasco, Peru, represents the most significant recent base-metal discovery in the central Andes and one of the largest undeveloped In resources globally. As of 2018, it hosts an 11.7 Mt indicated resource grading 6.9% Zn, 0.16% Pb, 15 g/t Ag, and 84 g/t In, an additional 45.0 Mt inferred resource grading 5.6% Zn, 0.23% Pb, 17 g/t Ag, and 67 g/t In, and a separate Sn-Cu-Ag inferred resource of 14.5 Mt grading 0.63% Sn, 0.21% Cu, and 18 g/t Ag. Newly obtained U–Pb dates for cassiterite by LA-ICP-MS (22.77 ± 0.41 and 23.05 ± 2.06 Ma) assign the Ayawilca deposit to the Miocene polymetallic belt of central Peru. The polymetallic mineralization occurs as up to 70-m-thick mantos hosted by carbonate rocks of the Late Triassic to Early Jurassic Pucará Group, and subordinately, as steeply dipping veins hosted by rocks of the Pucará Group and overlying Cretaceous sandstones-siltstones of the Goyllarisquizga Group. Relicts of a distal retrograde magnesian skarn and cassiterite (stage pre-A) were identified in the deepest mantos. The volumetrically most important mineralization at Ayawilca comprises a low-sulfidation assemblage (stage A) with quartz, pyrrhotite, arsenopyrite, chalcopyrite, Fe-rich sphalerite, and traces of stannite and herzenbergite. Stage A sphalerite records progressive Fe depletion, from 33 to 10 mol% FeS, which is compatible with the observed transition from low- to a subsequent intermediate-sulfidation stage (B) marked by the crystallization of abundant pyrite and marcasite. Finally, during a later intermediate-sulfidation stage (C) sphalerite (up to 11 mol% FeS), galena, native bismuth, Cu-Pb-Ag sulfosalts, siderite, Mn-Fe carbonates, kaolinite, dickite, and sericite were deposited. This paragenetic evolution shows striking similarities with that at the Cerro de Pasco Cordilleran-type polymetallic deposit, even if at Ayawilca stage C did not reach high-sulfidation conditions. The occurrence of an early retrograde skarn assemblage suggests that the manto bodies at Ayawilca formed at the transition between distal skarn and skarn-free (Cordilleran-type) carbonate-replacement mineralization. Mineral assemblages define a T-fS2 evolutionary path close to the pyrrhotite-pyrite boundary. Buffering of hydrothermal fluids by underlying Devonian carbonaceous phyllites of the Excelsior Group imposed highly reduced conditions during stage A mineralization (logfO2 < − 30 atm). The low fO2 favored efficient Sn mobility during stages pre-A and A, in contrast to other known ore deposits in the polymetallic belt of central Peru, in which the occurrence of Sn minerals is minor. Subsequent cooling, progressive sealing of vein walls, and decreasing buffering potential of the host rocks promoted the shift from low- (stage A) to intermediate-sulfidation (stages B and C) states. LA-ICP-MS analyses reveal significant In contents in Fe-rich sphalerite (up to 1.7 wt%), stannite (up to 1908 ppm), and chalcopyrite (up to 1185 ppm). The highest In content was found in stage A sphalerite that precipitated along with chalcopyrite and stannite, thus pointing to the early, low-sulfidation assemblage as prospective for this high-tech metal in similar mineral systems. Indium was likely incorporated into the sphalerite crystal lattice via Cu⁺ + In³⁺ ↔ 2 Zn²⁺ and (Sn, Ge)⁴⁺ + (Ga, In)³⁺ + (Cu + Ag)⁺ ↔ 4 Zn²⁺ coupled substitutions. Indium incorporation mechanisms into the stannite and chalcopyrite crystal lattices remain unclear.
... 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 (Sugaki et al. 1981;Morgan et al. 1998;Lehmann et al. 2000;Mlynarczyk and Williams-Jones 2005;Maffione et al. 2009). ...
... Despite being distinctly enriched in Sn, igneous rocks of Miocene porphyry systems in the Bolivian tin belt show concentrations of Ta, Zr, and TiO 2 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 Lehmann et al. 2000). 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. ...
... Nevertheless, source sedimentary sequences played an important role in magma evolution by providing B and C org that depressed the solidus temperature of fractionating melts and induced a low oxidation state necessary for magmatic enrichment and hydrothermal redistribution of tin, respectively (Lehmann et al. 1990Dietrich 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 Lehmann et al. (2000) to conclude that the most likely crustal source was the Lower Paleozoic metasedimentary sequences. ...
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 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.
... The causative intrusions of the NYT Sn-Pb-Zn-Ag belt are stronglyevolved and reduced. Tin was not incorporated in minerals rich in ionically-compatible Ti-rich minerals such as titanite due to the low fO 2 and hence became enriched during fractional crystallization with the progressive consumption of Ti-rich phases (Lehmann, 1987;Lehmann, 1990;Lehmann et al., 1990;Lehmann et al., 2000;Müller and Halls, 2005), These granites exsolved magmatic-hydrothermal fluids to produce vein-type Sn-Pb-Zn-Ag deposits that are zoned away from causative granite stocks from proximal high-T (~480 • C: Li et al., 2019b) Snrich ore bodies to distal Ag-rich ore bodies which, due to infiltration of meteoric water and fluid-rock interaction under low-sulfidation conditions, formed at lower temperatures (~160 • C : Li et al., 2019b). ...
The metal and sulfur fertility of granite magmas that formed in post-subduction settings, the key processes that led to their contrasting associated polymetallic mineral deposits, and their post-subduction source remain obscure. The Yidun Terrane, eastern Tibet, extends for 500 km and can be divided into the northern Yidun Terrane (NYT) and southern Yidun Terrane (SYT) based on distinctive magmatic source affinities and related mineral deposits. The NYT has several 103–93 Ma granite plutons and associated magmatic-hydrothermal vein-type Sn–Pb–Zn–Ag polymetallic deposits, such as the giant Xiasai deposit. In contrast, the SYT granites host the Xiuwacu porphyry Mo–W deposit (88–84 Ma) and several porphyry or porphyry–skarn-type Cu–Mo deposits (85–78 Ma), such as Relin, Hongshan and Tongchanggou. The contrasting nature of the causative Cretaceous post-subduction granites and their source is determined from their whole-rock and isotope geochemistry, zircon trace-element concentrations, and biotite and amphibole mineral chemistry. Based on these parameters, the NYT Sn–Pb–Zn–Ag deposits are associated with highly fractionated, reduced ilmenite-series granites derived from a relatively dry magma that formed via mixing between amphibolite-derived and greywacke- and orthogneiss-derived metasomatized crustal melts. In contrast, the SYT Mo–W deposits are associated with strongly- to moderately-evolved and fractionated, oxidized intermediate-series granites. The SYT Cu–Mo deposits are related to more hydrous and less fractionated magnetite-series granites. The granites associated with both Mo–W and Cu–Mo deposits in the SYT were generated by partial melting of metasomatized ancient mafic-intermediate lower continental-crust with variable contributions of metasomatized mantle components. However, there is only evidence for the presence of garnet as a residual phase in the magmatic source of the SYT Cu–Mo-bearing granites. The different magma sources were important in determining the redox state of the Yidun granite magmas, providing a fundamental control on the behaviour of metals and sulfur in fractionating melts and dictating the contrasting polymetallic compositions of causative magmatic-hydrothermal fluids and resultant mineral deposits. The source regions of the granites are thus the primary control on the spatial distribution of the Sn–Pb–Zn–Ag, Mo–W, and Cu–Mo belts in the Yidun Terrane. Although not derived during subduction, as for most Cenozoic porphyry systems, the Yidun deposits are indirectly related to subduction via the metasomatism and fertilization of the mantle lithosphere and lower crust during the earlier subduction phase. The anomalous preservation of Cretaceous porphyry systems in the Yidun Terrane relates to their proximity to the margin of the Yangtze Craton, whose thick buoyant lithosphere inhibited exhumation and erosion.
... Porphyry tin mineralization was mainly reported from the central Andean tin belt in the eastern Cordillera of Bolivia (Sillitoe et al., 1975;Lehmann et al., 1990Lehmann et al., , 2000. The Cenozoic Bolivian porphyry tin systems are generally in small stocks and volcanic complexes of rhyodacitic composition, characterized by pervasive hydrothermal overprint, stockwork-like brecciation, and hydrothermal breccias, and mineralization occurs both disseminated and in complex vein systems (Sillitoe et al., 1975;Grant et al., 1977;Lehmann et al., 1990;Dietrich et al., 2000). ...
The Yanbei tin porphyry district with a total resource of about 250, 000 t Sn is hosted in the Lower Cretaceous Mikengshan volcanic basin in the southeastern part of the Nanling Range. There are several tin deposits of greisen, stockwork and vein styles associated to the intrusive center of the 8 x 8 km large Mikengshan volcano-plutonic complex. LA-ICP-MS U-Pb dating of cassiterite yielded ages of 130.4 ± 4.0 Ma, 132.0 ± 1.5 Ma and 133.5 ± 1.7 Ma for the Yanbei deposit, 135.9 ± 1.5 Ma and 136.7 ± 1.4 Ma for the Taoxiba deposit, and 135.1 ± 4.0 Ma for the Kuangbei deposit. These data overlap within error and indicate that the three deposits belong to a same tin mineral system. Combined with the previous geochronological data, we propose a scenario for the porphyry tin mineral system in the Mikengshan basin. Dacitic to rhyolitic volcanic and subvolcanic rocks formed at ca. 140 Ma, and were shallowly intruded by highly evolved magmas which released magmatic-hydrothermal fluids to form veinlet-disseminated and greisen ore in the granitic rocks, and more distal stockwork and vein tin mineralization in the volcanic and subvolcanic envelope. The porphyry tin deposits in the Mikengshan volcanic basin are part of the 145-135 Ma tin metallogenic event in South China. The Early Cretaceous volcanic basins in the eastern part of the Nanling Range are promising targets for tin exploration.
... The world-class San Rafael Sn (-Cu) deposit (>1 Mt Sn at average grade of 2%) is located in the northern part of the Central Andean tin belt extending from southeast Peru to Bolivia and northern Argentina. This classic metallogenic province hosts hundreds of Sn-W deposits, which contain widespread tourmaline alteration and high B contents (Lehmann et al., 2000). Mineralization at San Rafael consists of a northwest-trending cassiterite-quartz-chloritesulfide vein-breccia system hosted by a late Oligocene (ca. 25 Ma) peraluminous granitic complex and by Ordovician metasediments of the Sandia Formation ( Fig. 1A; Kontak and Clark, 2002;Mlynarczyk et al., 2003). ...
We present a high-resolution in situ study of oxygen and boron isotopes measured in tourmaline from the world-class San Rafael Sn (-Cu) deposit (Central Andean tin belt, Peru) aiming to trace major fluid processes at the magmatic-hydrothermal transition leading to the precipitation of cassiterite. Our results show that late-magmatic and pre-ore hydrothermal tourmaline has similar values of δ18O (from 10.6‰ to 14.1‰) and δ11B (from −11.5‰ to −6.9‰). The observed δ18O and δ11B variations are dominantly driven by Rayleigh fractionation, reflecting tourmaline crystallization in a continuously evolving magmatic-hydrothermal system. In contrast, syn-ore hydrothermal tourmaline intergrown with cassiterite has lower δ18O values (from 4.9‰ to 10.2‰) and in part higher δ11B values (from −9.9‰ to −5.4‰) than late-magmatic and pre-ore hydrothermal tourmaline, indicating important contribution of meteoric groundwater to the hydrothermal system during ore deposition. Quantitative geochemical modeling demonstrates that the δ18O-δ11B composition of syn-ore tourmaline records variable degrees of mixing of a hot Sn-rich magmatic brine with meteoric waters that partially exchanged with the host rocks. These results provide thus direct in situ isotopic evidence of fluid mixing as a major mechanism triggering cassiterite deposition. Further, this work shows that combined in situ δ18O and δ11B analyses of tourmaline is a powerful approach for understanding fluid processes in dynamic magmatic-hydrothermal environments.
... Indeed, Li (and B) enrichments of hundreds up to several thousand μg/g reported in melt inclusions of dacitic to rhyolitic magmatic rocks have been invoked as easily mobilized by meteoric waters and thus as potential sources of Li in brines (Hofstra et al. 2013;Benson et al. 2017, Neukampf et al. 2019. Such melt inclusions are also known from Andean magmas (Lindsay et al. 2001;Schmitt et al. 2002;Dietrich and Lehmann 2000;Lehmann et al. 2000;Grocke et al. 2017). The heat of the active magmatic arc drives abundant hydrothermal systems that sample volcanic and Pz-basement rocks (e.g. ...
We investigate the Li isotope composition and the Li concentrations of metamorphic and sedimentary rocks of the Palaeozoic (Pz) basement in the Central Andes and follow the trace of the Li in the Cenozoic volcanic rocks at the active continental margin. The average Li isotope composition of Pz-basement closely resembles global averages of upper crustal rocks with overlapping, but higher average Li content in the Pz-basement. Lithium isotope composition and content in the Cenozoic volcanic rocks of the Central Volcanic Zone (CVZ) range from mantle-like signatures to Pz-basement compositions with high δ⁷Li values and high Li contents. Evolutionary trends of the Li isotope composition in the CVZ volcanic rocks can be explained by assimilation of the Pz-basement. At a margin-wide scale, the abundance of Li in the CVZ volcanic rocks is higher than that of the Cenozoic volcanic rocks of the active Andean arc north and south of the CVZ. The CVZ volcanic and Pz-basement rocks are considered to be the primary source of Li in world-class Li-deposits in evaporates of the Altiplano-Puna high plateau and its western slope between ca 27° and 20° S. These deposits define the so-called “Lithium-Triangle”, between southern Bolivia, NW Argentina and NE Chile. The pivotal processes of extraction of Li from its primary rock sources and of Li migration from the source rocks to the deposits still await detailed investigation.
... Tin granites are often peraluminous (prior to the often widespread muscovitization which produces a hydrothermal peraluminous overprint), and their primary peraluminous nature relates to a general S-type character due to partial melting of pelitic source material in a post-collisional environment (Sylvester, 1998). The pelitic source material is seen in specific isotope signatures (O, Hf, Nd, Sr), but also reflected in elevated boron contents of the melts and associated hydrothermal systems with abundant tourmaline (Lehmann et al., 2000b). This situation seems to apply for many granites in the major tin belts, such as the Southeast Asian tin belt (Cobbing et al., 1986;Yang et al., 2020), parts of South China (Mao et al., 2019), the Central Andean tin belt (Ericksen et al., 1990;Lehmann et al., 1990), and Cornwall (Jackson, 1979;Müller et al., 2006). ...
... The undiluted metal inventory then would be available for the small melt fractions produced during flatslab subduction, for instance in transtensional strike-slip zones in the general compressive regime. (Kay and Mpodozis, 2001;Lehmann et al., 2000b) Such a model could also apply to the 5-10 Ma Cu porphyry segments of central Chile/NW Argentina and Peru, where present-day flat slab subduction of the Nazca ridge to the north and the Juan Fernandez ridge to the south has shut down major volcanism in these two arc segments (Skewes and Stern. 1995;James and Sacks, 1999; J o u r n a l P r e -p r o o f Hampel, 2002 The accessory mineral zircon mirrors the bulk rock composition and carries not only valuable age information, but also information on melt source, degree of melt evolution, redox state and even hydrothermal overprint. ...
About 85% of all historically mined tin of about 27 million tonnes Sn is from a few tin ore provinces within larger granite belts. These are, in decreasing importance, Southeast Asia (Indonesia, Malaysia, Thailand, Myanmar), South China, and the Central Andes (Bolivia, southern Peru). Primary tin ore deposits are part of magmatic-hydrothermal systems invariably related to late granite phases (tin granites, pegmatites, tin porphyries), and may become dispersed by exogenic processes and then eventually form placer deposits within a few km from their primary source, due to the density of cassiterite, its hardness and chemical stability. Alluvial placer deposits were usually the starting point for tin mining, and have provided at least half of all tin mined.
The small-volume and late granite phases in spatial, temporal and chemical relationship to tin ore deposits are highly fractionated. Systematic element distribution patterns in these granite phases and their associated much larger multiphase granite systems suggest fractional crystallization as the main petrogenetic process controlling magmatic evolution and magmatic tin enrichment. Oxidation state controls the bulk tin distribution coefficient, with low oxidation state favoring incompatible behavior of divalent tin. Low oxidation state is also mineralogically expressed by accessory ilmenite (FeO TiO2) as opposed to accessory magnetite (FeO Fe2O3) in more oxidized melt systems. This difference in the accessory mineralogy and hence metallogenic potential (tin-bearing ilmenite-series versus barren magnetite-series granites), can be easily detected in the field by a hand-held magnetic susceptibility meter.
The hydrothermal system is a continuation of the magmatic evolution trend and necessary consequence of the crystallization of a hydrous melt. The exsolved highly saline aqueous fluid phase, enriched in boron and/or fluorine plus a wide metal spectrum, can be accomodated and stored by the intergranular space in crystallized melt portions, or accumulate in larger physical domains, accompanied by focused release of mechanical energy (brecciation, vein formation), dependent on emplacement depth (pressure). The hydrothermal mobility of tin is largely as Sn²⁺-chloride complexes; the precipitation of tin as cassiterite involves oxidation. Tin typically characterizes the inner high-temperature part of much larger km-sized zoned magmatic-hydrothermal systems with the chemical signature Sn-W-Cu-As-Bi in the inner part (greisen, vein/stockwork/breccia systems, skarn) and a broader halo with vein- or replacement style Pb-Zn-Ag-Sb-Au-U mineralization of lower temperature. This zoning pattern may also occur telescoped on each other.
Active continental margins are the favorable site for both copper (−gold) and tin (−tungsten) systems. However, the narrowly segmented metal endowment and the episodic nature of ore formation suggest additional controls. These are the build-up of a subduction-derived metal and fluid inventory in the lower continental crust by flat-slab subduction (very little magmatism) for copper‑gold in the main arc, followed by large-scale intracrustal melting during mantle upwelling in the back arc for tin (chemically reduced reservoir rocks) and/or tungsten mineralization (less sensitive to oxidation state).
... In granitoid-related tin-tungsten deposits, tourmaline commonly forms disseminations in veins, greisens, and skarns, aggregates in breccias, and irregular replacements in wall rocks (e.g., Slack, 1996;Lehmann et al., 2000;Codeço et al., 2017;Duchoslav et al., 2017). In most such deposits, tourmaline is paragenetically early and formed prior to the tin and/or tungsten ore minerals, but exceptions exist such as in the giant San Rafael tin-copper vein deposit in Peru where two stages of hydrothermal tourmaline growth occur. ...
Tourmaline group minerals are typically the predominant host of boron in hydrothermal mineral deposits. Boron is a fluid-mobile element whose isotopic composition reflects many factors that are relevant to understanding mineralizing processes, including fluid source(s), fluid-rock interaction, and formational temperature. A new compilation of 2622 published δ ¹¹B values for tourmaline from diverse types of hydrothermal ore deposits is presented here, with the focus (2215 analyses) on seven main types: porphyry Cu-Mo-Au deposits, granite-related Sn-W deposits, IOCG deposits, orogenic Au deposits, stratabound VMS and SEDEX deposits, and sediment-hosted U deposits. The total range of δ ¹¹B values for the seven types is -26.8 to +35.0 ‰. Four (granite Sn-W, orogenic Au, stratabound VMS and SEDEX) have median δ ¹¹B values close to the continental crustal average of about -10 ‰. The median values for IOCG and porphyry Cu-Mo-Au deposits are higher (-3.9 ‰ and -2.1 ‰, respectively), whereas sediment-hosted U deposits have distinctly high δ ¹¹B (median = +25.3 ‰). Importantly, a considerable range of δ ¹¹B values exists for tourmaline within each deposit type, the smallest (17.8 ‰) for granite Sn-W deposits and the largest (48.0 ‰) for IOCG deposits.
The boron isotope variations in tourmaline from different deposits are suggested reflect three levels of controlling factors and how these factors operated is illustrated with selected number of case studies. The primary factor is the composition of the boron source; secondary effects relate to fluid-tourmaline fractionation (equilibrium or Rayleigh). There are commonly also tertiary factors that depend on evolution of the specific deposit. These include fluid mixing, changing water-rock ratio and/or depositional temperature, influences of other boron-bearing minerals, and where relevant, post-ore metamorphism. Separating the effects of these factors is rarely possible from boron isotopes alone. However, the growth of multi-isotope studies of tourmaline and coexisting phases such as mica, as well as developments in modelling/experimentation of boron isotopes and element partitioning, suggest that this limitation will be overcome.
... Such is the case of the magmas associated with Cenozoic tin mineralisation of the Eastern Andes, which mostly resulted from sediment melting in a thickened continental crust. This circumstance explains their distinctive peraluminous and reduced signature, thus belonging to the S-type, ilmenite-series [2,65,66]. ...
... A plausible reason for such feature could be that mineralising fluids in peripheral areas were cooler and less reactive with country rocks than in the central area, thus mobilising a lower proportion of sedimentary or metasedimentary sulphur. The most negative δ 34 S values in similar isotopic zonation patterns have been effectively associated with the occurrence of oxidised magmatic-hydrothermal fluids in the porphyry-to-epithermal environment and with their prospectiveness [66][67][68]. Zonation in the isotopic composition of sulphur in sulphides at any scale (from single-grain to deposit, district or semi-regional scales) is not an uncommon feature in many different types of ore deposits and responds to a few reasons [59,[66][67][68][69][70][71][72][73][74][75]. Such isotopic zonation at a district level in Huanuni constitutes an additional feature that would be necessary to test in future endeavours. ...
... The most negative δ 34 S values in similar isotopic zonation patterns have been effectively associated with the occurrence of oxidised magmatic-hydrothermal fluids in the porphyry-to-epithermal environment and with their prospectiveness [66][67][68]. Zonation in the isotopic composition of sulphur in sulphides at any scale (from single-grain to deposit, district or semi-regional scales) is not an uncommon feature in many different types of ore deposits and responds to a few reasons [59,[66][67][68][69][70][71][72][73][74][75]. Such isotopic zonation at a district level in Huanuni constitutes an additional feature that would be necessary to test in future endeavours. ...
The polymetallic Huanuni deposit, a world-class tin deposit, is part of the Bolivian tin belt. As a likely case for a “mesothermal” or transitional deposit between epithermal and porphyry Sn types (or shallow porphyry Sn), it represents a case that contributes significantly to the systematic study of the distribution of critical elements within the “family” of Bolivian tin deposits. In addition to Sn, Zn and Ag, further economic interest in the area resides in its potential in critical elements such as In, Ga and Ge. This paper provides the first systematic characterisation of the complex mineralogy and mineral chemistry of the Huanuni deposit with the twofold aim of identifying the mineral carriers of critical elements and endeavouring plausible metallogenic processes for the formation of this deposit, by means of a multi-methodological approach. With In concentrations consistently over 2000 ppm, the highest potential for relevant concentrations in this metal resides in widespread tin minerals (cassiterite and stannite) and sphalerite. Hypogene alteration assemblages are hardly developed due to the metasedimentary nature of host rocks, but the occurrence of potassium feldspar, schorl, pyrophyllite and dickite as vein material stand for potassic to phyllic or advanced argillic alteration assemblages and relatively high-temperature (and low pH) mineralising fluids. District-scale mineralogical zonation suggests a thermal zonation with decreasing temperatures from the central to the peripheral areas. A district-scale zonation has been also determined for δ34SVCDT values, which range −7.2‰ to 0.2‰ (mostly −7‰ to −5‰) in the central area and −4.2‰ to 1.0‰ (mainly constrained between −2‰ and 1‰) in peripheral areas. Such values stand for magmatic and metasedimentary sources for sulfur, and their spatial zoning may be related to differential reactivity between mineralising fluids and host rocks, outwardly decreasing from the central to the peripheral areas.
... This possibility can be sustained as long as parental magmas included a component of crustal assimilation; otherwise, sulphur would come from magmas that were generated after partial melting of sedimentary rocks. Such is precisely the case of the magmas associated with Cenozoic tin mineralisation of the Eastern Andean Cordillera, which resulted mostly from sediment melting in a thickened continental crust, and yield a distinctive peraluminous and reduced signature, thus belonging to the S-type, ilmenite-series [51][52][53]. The most likely magmatic source for sulphur and other geological elements for the mineralisation would come from the Late Miocene Morococala volcanic complex (Figure 1, [2]) and associated rocks. ...
The tin-rich polymetallic epithermal deposit of Poopó, of plausible Late Miocene age, is part of the Bolivian Tin Belt. As an epithermal low sulfidation mineralisation, it represents a typological end-member within the "family" of Bolivian tin deposits. The emplacement of the mineralisation was controlled by the regional fault zone that constitutes the geological border between the Bolivian Altiplano and the Eastern Andes Cordillera. In addition to Sn and Ag, its economic interest resides in its potential in critical elements as In, Ga and Ge. This paper provides the first systematic characterisation of the complex mineralogy and mineral chemistry of the Poopó deposit with the twofold aim of identifying the mineral carriers of critical elements and endeavouring to ascertain plausible metallogenic processes for the formation of this deposit, by means of a multi-methodological approach. The poor development of hydrothermal alteration assemblage, the abundance of sulphosalts and the replacement of löllingite and pyrrhotite by arsenopyrite and pyrite, respectively, indicate that this deposit is ascribed to the low-sulphidation subtype of epithermal deposits, with excursions into higher states of sulphidation. Additionally, the occurrence of pyrophyllite and topaz has been interpreted as the result of discrete pulses of high-sulphidation magmatic fluids. The δ 34 SVCDT range in sulphides (−5.9 to −2.8‰) is compatible either with: i. hybrid sulphur sources (i.e., magmatic and sedimentary or metasedimentary); or ii. a sole magmatic source involving magmas that derived from partial melting of sedimentary rocks or underwent crustal assimilation. In their overall contents in critical elements (In, Ga and Ge), the key minerals in the Poopó deposit, based on their abundance in the deposit and compositions, are rhodostannite, franckeite, cassiterite, stannite and, less importantly, teallite, sphalerite and jamesonite.
