Composition Of Tourmaline Research Articles

Tourmaline geochemistry and boron isotopic variations as a guide to fluid evolution in the Qiman Tagh W–Sn belt, East Kunlun, China

The Qiman Tagh W–Sn belt lies in the westernmost section of the East Kunlun Orogen, NW China, and is associated with early Paleozoic monzogranites, tourmaline is present throughout this belt. In this paper we report chemical and boron isotopic compositions of tourmaline from wall rocks, monzogranites, and quartz veins within the belt, for studying the evolution of ore-forming fluids. Tourmaline crystals hosted in the monzogranite and wall rocks belong to the alkali group, while those hosted in quartz veins belong to both the alkali and X-site vacancy groups. Tourmaline in the walk rocks lies within the schorl–dravite series and becomes increasingly schorlitic in the monzogranite and quartz veins. Detrital tourmaline in the wall rocks is commonly both optically and chemically zoned, with cores being enriched in Mg compared with the rims. In the Al–Fe–Mg and Ca–Fe–Mg diagrams, tourmaline from the wall rocks plots in the fields of Al-saturated and Ca-poor metapelite, and extends into the field of Li-poor granites, while those from the monzogranite and quartz veins lie within the field of Li-poor granites. Compositional substitution is best represented by the MgFe−1, Al(NaR)−1, and AlO(Fe(OH))−1 exchange vectors. A wider range of δ11B values from −11.1‰ to −7.1‰ is observed in the wall-rock tourmaline crystals, the B isotopic values combining with elemental diagrams indicate a source of metasediments without marine evaporates for the wall rocks in the Qiman Tagh belt. The δ11B values of monzogranite-hosted tourmaline range from −10.7‰ and −9.2‰, corresponding to the continental crust sediments, and indicate a possible connection between the wall rocks and the monzogranite. The overlap in δ11B values between wall rocks and monzogranite implies that a transfer of δ11B values by anataxis with little isotopic fractionation between tourmaline and melts. Tourmaline crystals from quartz veins have δ11B values between −11.0‰ and −9.6‰, combining with the elemental diagrams and geological features, thus indicating a common granite-derived source for the quartz veins and little B isotopic fractionation occurred. Tourmalinite in the wall rocks was formed by metasomatism by a granite-derived hydrothermal fluid, as confirmed by the compositional and geological features. Therefore, we propose a single B-rich sedimentary source in the Qiman Tagh belt, and little boron isotopic fractionation occurred during systematic fluid evolution from the wall rocks, through monzogranite, to quartz veins and tourmalinite.

Indicator minerals of the Meliadine orogenic gold deposits, Nunavut (Canada), and application to till surveys

The Meliadine Gold District is located about 25 km north of Rankin Inlet, Nunavut (Canada), in the Archean Rankin Inlet greenstone belt. The bedrock is composed of greenschist facies metamorphic rocks. The composition of tourmaline and scheelite is investigated by electron probe micro-analyser (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA ICP-MS). The chemical composition of these indicator minerals from the Meliadine deposits is compared with the composition of grains extracted from till samples along a 2 km transect parallel to the direction of ice flow at the Mustang showing. Tourmaline from the deposit is characterized by a flat rare earth element (REE) pattern having a positive europium anomaly also found in tourmaline grains in till samples down-ice of the Mustang showing. Scheelite from the Mustang showing shows a bell-shaped REE pattern with a negative europium anomaly, which is also found in scheelite from down-ice till samples. Scheelite and tourmaline recovered from till down-ice from the Mustang showing have a composition diagnostic of the gold mineralization. Determining the composition of tourmaline and scheelite in unconsolidated sediments can serve to identify gold mineralization and has the potential to be applied in mineral exploration in the Meliadine Gold District and elsewhere.

Towards Zn-Dominant Tourmaline: A Case of Zn-Rich Fluor-Elbaite and Elbaite from the Julianna System at Piława Górna, Lower Silesia, SW Poland

Tourmalines are a group of minerals which may concentrate various accessory components, e.g., Cu, Ni, Zn, Bi, Ti, and Sn. The paper presents fluor-elbaite and elbaite from a dyke of the Julianna pegmatitic system at Piława Górna, at the NE margin of the Bohemian Massif, SW Poland, containing up to 6.32 and 7.37 wt % ZnO, respectively. Such high amounts of ZnO are almost two times higher than in the second most Zn-enriched tourmaline known to date. The compositions of the Zn-rich tourmalines from Piława Górna, studied by electron micropropy and Raman spectroscopy, correspond to the formulae: X(Na0.733Ca0.013☐0.254)Σ1Y(Al1.033Li0.792Zn0.755Fe2+0.326Mn0.094)Σ3ZAl6(TSi6O18)(BO3)3V(OH)3W(F0.654OH0.344), and X(Na0.779Ca0.015☐0.206)Σ1Y(Al1.061Li0.869Zn0.880Fe2+0.098Mn0.094)Σ3ZAl6(TSi6O18)(BO3)3V(OH)3W(OH0.837F0.163), respectively, with Zn as one of the main octahedral occupants. A comparison with other tourmalines and associated Zn-rich fluor-elbaite and elbaite from the pegmatite indicates that atypically high Zn-enrichment is not a result of Zn-Fe fractionation, but dissolution and reprecipitation induced by a late (Na,Li,B,F)-bearing fluid within the assemblage of gahnite spinel and primary schorl-type tourmaline. This strongly suggests Na-Li-B-F metasomatism of gahnite-bearing mineral assemblages as that is the only environment that can promote crystallization of a hypothetical Zn-dominant tourmaline. The compositions of the Zn-rich fluor-elbaite and elbaite suggest three possible end-members for such a hypothetical tourmaline species: NaZn3Al6(Si6O18)(BO3)3(OH)3(OH), ☐(Zn2Al)Al6(Si6O18)(BO3)3(OH)3(OH) and Na(Zn2Al)Al6(Si6O18)(BO3)3(OH)3O by analogy with other tourmalines with divalent Y occupants, such as schorl/foitite/oxy-schorl and dravite/magnesio-foitite/oxy-dravite.

Geochemistry and boron isotopic compositions of tourmaline from the Paleoproterozoic amphibolites, NE China: Implications for the origin of borate deposit

The Paleoproterozoic metasediments and metavolcanics in the Jiao-Liao-Ji belt, northeastern China, host a large number of borate deposits. To trace the source of boron in these borate deposits, we carried out in situ chemical and boron isotopic studies on tourmalines of amphibolites from the Lieryu Formation of the Liaohe Group in the Jiao-Liao-Ji belt. The petrology and the chemical compositions of tourmalines of amphibolites show that these tourmalines formed by influx of B-rich fluids during different stages of metamorphism. The δ11B values of tourmaline continue to decline during the successive metamorphism. Tourmalines that formed during the prograde metamorphism show higher δ11B values (+9.52∼+10.18‰) than those formed during the peak metamorphism of amphibolite facies (+7.22∼+9.43‰). Subsequently, tourmalines with lower δ11B values formed during the retrograde metamorphism of greenschist facies, which have slightly different boron isotopic compositions in cores (+4.18∼+5.50‰) and rims (+2.66∼+4.66‰), mainly due to the temperature effect. The boron isotopic variations of tourmalines of amphibolites match well with our modeling study of boron isotope. The results suggest that tourmalines may be precipitated from fluids released from dehydration of marine sediments with relative high δ11B values (+9‰) during prograde metamorphism. In the same way, the borate deposits formed from the liberated B-rich fluids that interacted with the Mg-rich carbonates and/or silicates.

Experimental Investigation of Biotite-Rich Schist Reacting with B-Bearing Fluids at Upper Crustal Conditions and Correlated Tourmaline Formation

Fluid–rock interaction experiments between a biotite-rich schist (from Mt. Calamita Formation, Elba Island, Italy) and B-bearing aqueous fluids were carried out at 500–600 °C and 100–130 MPa. The experiments have been carried out in order to reproduce the reaction, which would have produced tourmalinisation of the biotite schist, supposedly by circulation of magmatic fluids issued from leucogranitic dykes. The reacting fluids were either NaCl-free or NaCl-bearing (20 wt %) aqueous solutions, with variable concentration of H3BO3 (0.01–3.2 M). The experimental results show that tourmaline (belonging to the alkali group) crystallise under high-temperature and upper crustal conditions (500–600 °C, 100–130 MPa) when H3BO3 concentration in the system is greater than 1.6 M. The composition of tourmaline is either dravitic (Mg-rich) or schorlitic (Fe-rich), depending if an NaCl-bearing or NaCl-free aqueous solution is used. In the first case, a significant amount of Fe released from biotite dissolution remains in the Cl-rich solution resulting from the experiment. By contrast, when pure water is used, Na/K exchange in feldspars makes Na available for tourmaline crystallisation. The high concentration of Fe in the residual fluid has an important metallogenic implication because it indicates that the interaction between the saline B-rich fluid of magmatic derivation and biotite-rich schists, besides producing tourmalinisation, is capable of mobilising significant amounts of Fe. This process could have produced, in part or totally, the Fe deposits located close to the quartz–tourmaline veins and metasomatic bodies of the Mt. Calamita Formation. Moreover, the super-hot reservoir that likely occurs in the deepest part of the Larderello–Travale geothermal field would also be the site of an extensive reaction between the B-rich fluid and biotite-bearing rocks producing tourmaline. Thus, tourmaline occurrence can be a useful guide during deep drilling toward a super-hot reservoir.

Major and trace element geochemistry of tourmalines from Archean orogenic gold deposits: Proxies for the origin of gold mineralizing fluids?

Orogenic style gold mineralizations in the Archean Hattu Schist belt (E Finland) are present in all major host rock lithologies including epiclastic sedimentary and volcanogenic rocks, as well as felsic intrusives. The gold mineralizations occur as dissemination in altered wall rocks and within hydrothermal quartz veins. Hydrothermal tourmalines are often associated with the gold mineralizations occurring in the quartz veins, as alteration minerals in contacts of the metasedimentary host rocks and quartz veins, but also within mineral assemblages of the metasedimentary and magmatic rocks. We characterize and compare the major, trace and rare earth element chemistry of these tourmalines in order to evaluate their suitability as a petrogenetic tool for tracing the fluid sources of the hydrothermal system. By comparing the chemistry of tourmalines from gold mineralization with those from metamorphic and magmatic host rocks, we test whether tourmaline composition can be used to identify the source rocks of the gold transporting hydrothermal fluids. All analyzed tourmalines belong to the alkali super group and plot along the schorl-dravite join. The hydrothermal tourmalines have Li, Sr and V concentrations comparable to metamorphic tourmalines and clearly distinct from magmatic tourmalines. Because the concentrations of Ni, Pb, Cr, Mn, Ga, Zn and Sn show a wide overlap between magmatic, metamorphic and hydrothermal tourmalines, these elements do not permit to discriminate between different source rocks. The co-variations of many elements in hydrothermal tourmalines, when plotted against Li, show more similarity to metamorphic tourmalines and the whole-rock compositions of metasedimentary and metavolcanic host rocks than to their magmatic counterparts. This indicates that the major and trace element composition of hydrothermal tourmalines in the Hattu Schist Belt is predominantly controlled by the host rocks and local fluid-rock interactions, and does not reflect the distal fluid sources. The effect of local fluid-rock interaction is also manifested by the REE patterns of tourmalines. The magmatic tourmalines have distinct LREE enriched patterns resembling the whole-rock REE patterns of granitic intrusives, while the metamorphic and hydrothermal tourmalines have flat or weakly fractionated patterns similar to metavolcanic and metasedimentary host rocks. Taken together, the tourmaline data suggest that hydrothermal tourmalines associated to gold mineralizing fluids are most likely genetically related to metamorphic rock sources without important contributions of magmatic fluids, and that local fluid-rock interaction exerted a major control on tourmaline chemistry.

Chemical and boron isotopic composition of tourmaline from the Mariinsky emerald deposit, Central Urals, Russia

Tourmaline is abundant at the Mariinsky schist-hosted emerald deposit in the Central Urals, Russia, both in emerald-bearing phlogopite veins (type 1) and later, emerald-free pockets, lenses, and veinlets cutting the phlogopite veins (type 2). The Ca content in tourmaline is influenced by the host rocks (ultramafic and mafic rocks), associated minerals, and minerals crystallized before tourmaline (amphibole, fluorite, margarite). The Na concentration in tourmaline depends on the presence or absence of paragonite, and the association with micas also strongly influences the contents of Li, Zn, Ni, and Co in tourmaline. Type 1 tourmalines associated with phlogopite are relatively depleted in these elements, whereas type 2 tourmalines associated with margarite or paragonite are enriched. Some differences in isomorphic substitutions along with the trace element composition (Zn, V, Sr, Co, REE) may have value in exploration of emerald-bearing and emerald-free veins in schist-hosted emerald deposits. The δ11B values in tourmaline of all types fall in a narrow total range from −11.3 to −8.4‰. These values, combined with a mineralization temperature of 420–360 °C, yield an estimated δ11B fluid composition of −7.4 to −6.8‰ suggesting a mixed source of boron, likely dominated from the granitic rocks surrounding the emerald belt. The narrow range of B-isotope compositions in tourmaline from throughout the Mariinsky deposit suggests a well-mixed hydrothermal system.

Chemical and boron isotopic composition of hydrothermal tourmaline from the Panasqueira W-Sn-Cu deposit, Portugal

Tourmaline is a locally abundant hydrothermal mineral in the wallrocks surrounding the W-Sn-Cu mineralized veins in the Panasqueira deposit (Portugal) and a minor phase within the veins themselves. Tourmaline chemical and boron-isotope compositions have been determined from three settings: (1) pervasive fine-grained tourmalinization zones in wallrocks within 10cm of the veins, (2) coarser tourmaline in wallrock-hosted fault zones, and (3) needle-shaped tourmaline from late-stage vugs in the quartz veins. All tourmalines from Panasqueira have ferromagnesian compositions with significant octahedral aluminum contents and variable X-site vacancies. Tourmaline compositions show significant chemical variations at the grain and sample scale but are homogeneous on the deposit scale. Tourmaline is typically optically and chemically zoned, showing significant increases in Fe and F and decrease in Mg, Ca and Al from core to rim. Moreover, as a general trend, Al increases and Mg decreases with proximity to the vein contact. The observed chemical variation seems to have been controlled mainly by the vectors: FeMg−1; X□AlNa−1(R2+)−1; X□Al(OH)Na−1(R2+)−1F−1; R2+(OH,F)Al−1O−1 and X□Al2O Na−1(R2+)−2(OH,F)−1.The total range in tourmaline δ11B values from the Panasqueira W-Sn-Cu deposit is from −3.7 to −12.7‰, including tourmaline from the three settings. The calculated B-isotope composition of the hydrothermal fluid based on the average tourmaline composition of −9‰ and an estimated alteration temperature in the wallrocks, based on Ti-in-quartz thermometry, of 500°C is −7.1‰. This isotopic composition is permissive of a boron source from local metasediments or an S-type granite, but the high boron concentration in the wallrocks, with >50vol% tourmaline, along with the typical element association of Panasqueira (W, Sn, F, Nb, Ta, Rb) makes a granitic source more likely. Late-stage tourmaline needles in vugs within the mineralized veins show the same patterns and ranges in both chemical and boron isotope composition, suggesting that exsolved magmatic fluids were injected in at least two pulses.The variations in chemical and boron isotopic compositions of tourmaline combined with estimates from Ti-in-quartz thermometry suggest that hydrothermal ore formation is associated with fluid cooling and geochemical fluid-rock interactions.

Age and Origin of the Tsavorite and Tanzanite Mineralizing Fluids In the Neoproterozoic Mozambique Metamorphic Belt

Abstract The genetic model previously proposed for tsavorite- (and tanzanite-) bearing mineralization hosted in the Neoproterozoic Metamorphic Mozambique Belt (stretching from Kenya through Tanzania to Madagascar) is refined on the basis of new Sm-Nd age determinations and detailed Sr-O-S isotope and fluid-inclusion studies. The deposits are hosted within meta-sedimentary series composed of quartzites, graphitic gneisses, calc-silicate rocks intercalated with meta-evaporites, and marbles. Tsavorite occurs either in nodules (also called “boudins”) oriented parallel to the metamorphic foliation in all of the deposits in the metamorphic belt or in quartz veins and lenses located at the hinges of anticlinal folds (Lelatema fold belt and Ruangwa deposits, Tanzania). Gem tanzanite occurs in pockets and lenses in the Lelatema fold belt of northern Tanzania. The Sm-Nd isotopic data for tsavorites and tanzanites hosted in quartz veins and lenses from Merelani demonstrate that they formed at 600 Ma, during the retrograde metamorphic episode associated with the East African Orogeny. The tsavorites hosted in nodules do not provide reliable ages: their sedimentary protoliths had heterogeneous compositions and their Sm-Nd system was not completely rehomogenized, even at the local scale, by the fluid-absent metamorphic recrystallization. The initial 87 Sr/ 86 Sr isotopic ratios of calcite from marble and tanzanites from Merelani fit with the strontium isotopic composition of Neoproterozoic marine carbonates. Seawater sediment deposition in the Mozambique Ocean took place around 720 Ma. The quartz-zoisite O-isotopic thermometer indicates a temperature of formation for zoisite between 385 and 448 °C. The sulfur isotopic composition of pyrite (between –7.8 and –1.3‰ V-CDT) associated with tsavorite in the Lelatema fold belt deposits suggests the contribution of reduced marine sulfate. The sulfur in pyrite in the marbles was likely derived from bacterial sulfate reduction which produced H 2 S. Fluid inclusion data from tsavorite and tanzanite samples from the Merelani mine indicate the presence of a dominant H 2 S-S 8 ±(CH 4 )±(N 2 )±(H 2 O)-bearing fluid. In the deposits in Kenya and Madagascar, the replacement of sulfate by tsavorite in the nodules and the boron isotopic composition of tourmaline associated with tsavorite are strong arguments in favor of the participation of evaporites in garnet formation.

Foitit-magneziofoitit a rózsa-hegyi ércesedésből, avagy a nagybörzsönyi turmalin újravizsgálata

Turmalin jelenléte a nagybörzsönyi ércesedésben már 60 éve ismert. A Rózsa-hegy É-i felén, az ún. rózsabányai ércesedés területén erősen kovásodott kőzet üregeiben, illetve később képződött ásványok (kvarc, kalcit, sziderit, pirrhotin, szfalerit) zárványaiként általában 1 mm-nél rövidebb, színtelen, tűs kristályokat, tűs-sugaras, vagy nemezszerű halmazokat alkot. A korábban készült nedveskémiai elemzés alapján a szakirodalomba drávitként bekerült turmalin az újabb elektron-mikroszondás vizsgálatok alapján zónás, és a foitit-magneziofoitit ásványfajokat képviseli. A vasban és magnéziumban legdúsabb elemzési pontokon mért összetétel (31 anionra számolva): ([]0,63Na0,29Ca0,08)Σ=1,00 (Fe2+1,26Mg0,89Al0,79)Σ=2,94 Al6,00 (Si5,88Al0,12)Σ=6,00 O18 (BO3)3 (OH)4,00, illetve ([]0,45Na0,37Ca0,18)Σ=1,00 (Mg1,55Fe2+0,48Al0,83Ti0,01)Σ=2,87 Al6,00 (Si5,67Al0,33)Σ=6,00 O18 (BO3)3 (OH)4,00. A röntgen-pordiffrakciós felvételből számított rácsállandók: a = 15,901(6) Å; c = 7,190(4) Å, V = 1574(1) Å3. A turmalin hidrotermás oldatból vált ki, melynek hőmérséklete 260°C fölött lehetett. A képződő turmalin kémiáját elsősorban a hidrotermás oldat összetétele határozta meg, ebben a tekintetben a mellékkőzetek összetétele, illetve az uralkodó hőmérséklet- és nyomásviszonyok csak másodrangúak voltak. A kristályokon megfigyelhető kémiai zónásság elsősorban a Fe ↔ Mg helyettesítésből ered. A zónásság oka az lehet, hogy a Fe-gazdag hidrotermás oldatok összetételét a Mg-ban és Ca-ban gazdagabb leszivárgó vizek megváltoztatták. A turmalin tűs habitusa kristálykémiai okokra vezethető vissza, ugyanis a magas Al-tartalom és a viszonylag alacsony Fe+Mg-tartalom a c-tengely irányában való gyors növekedését segítette elő.

Geochemistry and formation of tourmaline nodules in Mashhad leucogranite, Iran

Nodular tourmalines composed of dark cores and white haloes occur in the Mashhad leucogranite. The cores are made up of tourmaline and quartz, and the haloes of quartz, muscovite, microcline and orthoclase. The host granite consists of quartz, plagioclase, microcline, muscovite and biotite. Geochemical analyses show that the studied tourmalines are schorl. They are characterized by oscillatory zoning, increasing concentrations of Ca and Mg from core to rim, moderate Fe/Fe + Mg ratios (56–63), and REE distribution patterns similar to those of the host granite. The tourmalines exhibit high Ti content due to breakdown of biotite. Petrographic and geochemical results show that the formation of tourmaline can be attributed to two stages. In the first stage, bubbles containing vapor-rich liquid, Fe, and B were generated by magma differentiation. During rise and cooling of the magma, core tourmaline was produced with Fe rich schorl composition. In the second stage, the tourmaline composition changed to that of Mg rich schorl because of the decomposition of biotite (biotite is considered as a source of Mg), and the mixing with vapor-rich liquid in bubbles

Use of tourmaline as a potential petrogenetic indicator in the determination of host magma: CRS, XRD and PED-XRF methods

Tourmaline defines a group of complex borosilicate forms as accessory mineral in igneous and metamorphic rocks and they act an important role in the interpretation of the chemical composition changes of the composition of the host fluid of the magma.The variety of tourmaline can be identified by using optical microscopy, X-Ray Diffraction (XRD) and by determining its chemical composition through Polarized Energy Dispersive X-Ray Fluorescence (PED-XRF) methods. However, microscopic investigations and XRD analyses are not quite adequate for detailed determination of tourmaline sub-groups. In addition, the use of chemical composition of tourmaline as a strict indicator of geochemical processes might be a misleading method. In this study, variable tourmaline crystals were collected from three different pegmatitic occurrences in Behrekdag, Yozgat and Karakaya granitic bodies of Central Anatolia to identify their chemical properties through Confocal Raman Spectroscopy (CRS), PED-XRF and XRD analyses.The confocal Raman spectrometry of collected tourmalines from the Behrekdag, Yozgat and Karakaya granites are in the compositions of schorl, schorl and elbaite respectively. The dominant compositional groups of these tourmalines are in the form of schorl. Raman shift values of tourmalines revealed four bands centered at almost 1050, 750, 400 and 300cm−1. The first group of the band arises from SiO stretching, the second from BO stretching and the other two belong to bending modes of OBO and BOAl with symmetrical deformation of SiOSi. The strongest spectra near 360cm−1 should belong to the bonding of AlO. As a result, the confocal Raman studies are more sensitive for identification of tourmaline subgroup compositions and have a quite important in the explaining source of the magma.

Tourmaline-rich features in the Heemskirk and Pieman Heads granites from western Tasmania, Australia: Characteristics, origins, and implications for tin mineralization

Distinctive magmatic-hydrothermal, tourmaline-rich features have developed in the Heemskirk and Pieman Heads granites from western Tasmania, Australia. They are categorized as tourmaline-rich patches, orbicules, cavities, and veins, based on their distinctive morphologies, sizes, mineral assemblages, and contact relationships with host granites. These textural features occur in discrete layers in the roof zone of granitic sills within the Heemskirk and Pieman Heads granites. Tourmaline patches commonly occur below a tourmaline orbicule-rich granitic sill. Tourmaline-filled cavities have typically developed above the tourmaline-quartz orbicules in the upper layer of the white phase of the Heemskirk Granite. Tourmaline-quartz veins penetrate all exposed levels of the granites, locally cutting tourmaline orbicules and cavities.The tourmalines are mostly schorl (Fe-rich) and foitite, with an average end-member component of schorl(45) dravite(6) tsilaisite(1) uvite(0) Fe-uvite(3) foitite(31) Mg-foitite(4) olenite(10). Element substitutions of the tourmalines are controlled by FeMg-1, Al-Y(X)square(R2+Na)(-1), and minor (AlO)-Al-Y(R2+OH)(-1) (where R2+ = Fe2+ + Mg2+ + Mn2+) exchange vectors. Several trace elements in tourmaline have consistent chemical evolutions grouped from tourmaline patches, through orbicules and cavities, to veins. There is a progressive decrease of most transition and large ion lithophile elements, and a gradual increase of most high-field strength elements. These compositional variations in the different tourmaline-rich features probably relate to element partitioning occurring in these phases due to volatile exsolution and fluxing of aqueous boron-rich fluids that separated from the granitic melts during the emplacement of S-type magmas into the shallow crust (4 to 5.5 km).Tourmalines from the Heemskirk Granite are enriched in Fe, Na, Li, Be, Sn, Ta, Nb, Zr, Hf, Th, and rare earth elements relative to the tourmalines from the Pieman Heads Granite, but depleted in Mg, Mn, Sc, V, Co, Ni, Pb, Sr, and most transition elements. These results imply that bulk compositions of the host granites exert a major control on the chemical variations of tourmalines. The trace element compositions of tourmalines from the Sn-mineralized Heemskirk Granite are different from those of the barren Pieman Heads Granite. Trace element ratios (e.g., Zn/Nb, Co/Nb, Sr/Ta, and Co/La) and Sn concentrations in tourmaline can distinguish the productive Heemskirk Granite from the barren Pieman Heads Granite.

Chemical composition and evolution of tourmaline-supergroup minerals from the Sb hydrothermal veins in Rožňava area, Western Carpathians, Slovakia

Tourmaline-supergroup minerals are common gangue minerals in Sb-hydrothermal veins on Betliar – Strakova, Cucma – Gabriela and Rožňava – Peter-Pavol vein deposits in the Rožňava area, Slovakia. Tourmaline-supergroup minerals form relatively large prismatic to radial aggregates of parallel black to greyish-black crystals. Tourmaline-supergroup minerals from Betliar – Strakova and Rožňava – Peter-Pavol are almost homogeneous with intermediate schorl-dravite composition. Cucma – Gabriela tourmaline have distinct zoning with massive core of the schorlitic-to-feruvitic shifting to schorlitic-to-dravitic composition, and dravitic to magnesio-foititic rim. The tourmaline composition is influenced by two main substitutions, namely Ca(Mg,Fe)Na−1Al−1 and X □AlNa−1(Mg,Fe)−1. Betliar – Strakova and Rožňava – Peter-Pavol tourmaline-supergroup minerals exhibit only small extents of the X □AlNa−1(Mg,Fe)−1 substitution. This substitution shifts the composition to magnesio-foitite in Cucma – Gabriela tourmaline. The decrease of Al in the core of Cucma – Gabriela tourmaline crystals is caused by extensive Ca(Mg,Fe)Na−1Al−1 substitution. The unit-cell dimensions of all investigated tourmaline-supergroup minerals indicate an octahedral disorder with the Z (Fe3++Mg) proportion calculated from empirical equations varying between 0.85 and 0.87 apfu (atoms per formula unit). Based on Mossbauer spectra, the Z Fe3+ content varied between 0.25 apfu in Betliar – Strakova tourmaline and 0.45 apfu in Cucma – Gabriela sample. Based on Fe/(Fe + Mg) ratio, Betliar – Strakova tourmaline is slightly enriched in Fe compared to Rožňava – Peter-Pavol, suggesting the impact of the host-rock composition; first are grown in Fe-richer acidic metarhyolitic rocks, latter in metapelites. In Cucma – Gabriela, the variations in Fe/(Fe + Mg) are very likely reflecting the change in fluid composition. Magnesio-foitite is the product of second-stage crystallization forming rims and crack fills. The relatively low Fe3+/Fe2+ ratio suggests only minor proportion of meteoric fluids forming tourmaline.

Tourmalines from the siderite-quartz-sulphide hydrothermal veins, Gemeric unit, western Carpathians, Slovakia: crystal chemistry and evolution

Tourmaline is an important gangue mineral in a large number of Cretaceous siderite-quartz-sulphide hydrothermal veins in the Gemeric Unit, Slovak Ore Mountains, Slovakia, such as Dobsina, Vlachovo, Rožňavske Bystre, Hnilcik, Rakovnica, Novoveska Huta, Gretla, Rudňany, and Bindt. In this study we combine by electron microprobe analysis, powder X-ray diffraction, Mossbauer and optical emission spectroscopy to determine the range of tourmaline compositions in the deposits and constrain the mechanisms of its precipitation. Selected samples from the mentioned deposits belong mostly to the alkali group, schorl to dravite series, rarely dominant X-site vacant foititic tourmaline (Vlachovo and Bindt) and oxy-dravite compositions (Hnilcik) were detected. Rim zones of some schorlitic tourmalines show high concentrations of Ti (up to 2.35 wt.% TiO2, 0.30 apfu; Rožňavske Bystre). The chemical composition is mostly controlled by alkali-deficient X □AlNa−1(Mg,Fe2+)−1 and proton-deficient AlO(Mg,Fe2+)−1(OH)−1 substitutions. Titanium is incorporated into the structure by Y Ti Y (Mg,Fe) Y Al−2, Y Ti Z Mg Y Al−1 Z Al−1, Y TiO( Y AlOH), and X Ca Y Ti Z MgO2 X □−1 Y,Z Al−2(OH)−2 substitutions. Along trace elements, Sr and V attain concentrations of ~80–450 and ~70–320 ppm, respectively. The unit-cell parameter a varies between 15.960 and 15.985 A; variations in c are larger, between 7.177 and 7.236 A indicating the presence of Fe3+ and Mg2+ at Z site. Mossbauer spectroscopy has shown variable Fe3+ proportions (0.17–0.55 apfu) in all samples. The gathered dataset suggests some qualitative considerations on the mechanisms controlling tourmaline compositions at the regional scale. The highest Fe3+ concentrations occur in samples from Rudňany and Gretla in the external part of Gemeric unit, suggesting higher oxidation during longer transport of fluids. We propose that the determined XFe in the samples are correlated with the compositions of the host rocks, as schorlitic to foititic tourmalines occur in veins located in the meta-rhyolites host, and tourmalines with the highest Mg contents occur in metabasalts.

Effect of heat treatment on structure, surface composition, infrared emission and surface electrical properties of tourmaline

Crystal structure, surface composition, infrared emission properties and surface electrical properties of tourmaline from Guangxi of China, when subjected to heat treatment in air atmosphere had been studied by some methods, including X-ray fluorescence spectrum (XRF), X-ray diffraction (XRD) meter, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), energy dispersion spectroscopy (EDS), scanning electron microscope (SEM) and Zeta potential analyzer, etc. Experimental results show that the unit cell of tourmaline would shrink during heat treatment because Fe[Formula: see text] were oxidized. Moreover, the Fe[Formula: see text]/Fe[Formula: see text] inside tourmaline can be raised after treatment. Infrared normal total emissivity of tourmaline reaches 0.87, and infrared radiation energy density is [Formula: see text]. It can maintain excellent infrared emission properties at high temperature. Simultaneously, tourmaline presents negative Zeta potential in the aqueous solution, and its Zeta potential reaches −18.04 mV. Zeta potential of tourmaline was increased to −24.83 mV after heat treatment at 400[Formula: see text]C, and decrease to −11.78 mV after heat treatment at 600[Formula: see text]C. These findings may provide reference data for tourmaline’s application in the field of functional materials.

Multistage Skarn-Related Tourmaline From the Galinge Deposit, Qiman Tagh, Western China: A Fluid Evolution Perspective

Abstract The Galinge skarn deposit, the largest iron polymetallic skarn deposit in the Qiman Tagh metallogenic belt (western China), was formed via multi-stage fluid-rock interactions. It is divided into six ore domains from east to the west. Skarn-related tourmaline is ubiquitous in the V ore domain of the Galinge deposit, occurring both in the altered basaltic andesite (Tour-I) and in the sandstone (Tour-II). The tourmaline composition in both rock types is within the dravite–uvite solid solution. Some Tour-I crystals show compositional growth zoning in which the early stage uvite cores (Gen-1) are overgrown by second-stage dravite rims (Gen-2). Some Tour-I crystals also show overgrowth rims and fracture-infilled textures (Gen-3). Some other Tour-1 tourmalines without clear growth zoning (Others) show an intermediate composition between Gen-2 and Gen-3. The varying composition of the zoned tourmalines records important information about the evolving hydrothermal fluids and host rocks. Gen-1 and Gen-2, displaying a narrow and high range of Fe 2+ /(Fe 2+ + Mg) ratios, are much more equilibrated with mafic host rocks. The alkaline (K + Na) content of tourmalines is associated with the salinities of the ore-forming fluids. The lowest Na + K content of Gen-3 indicates that it may have been equilibrated with a low-salinity fluid environment in which the concentration of metal-chlorite complexes decreased. The Gen-3 stage is considered to be the main ore-forming event. Tour-II have similar Ca/(K + Na + Ca) ratios with Gen-1 and Gen-2 ratios, which indicates that they are contemporarily formed by the same fluid as Tour-I. Through compositional comparison of the tourmalines with those from other hydrothermal deposit types, the Galinge skarn-related tourmalines are overwhelmingly controlled by the MgFe –1 substitution mechanism. This is different from the compositions of tourmalines in porphyry, VMS, and vein-greisen type deposits, which are, respectively, controlled by the Fe 3+ Al –1 , (CaMg)(NaAl) –1 and (NaMg)(□Al) –1 , and (Fe 2+ Fe 3+ )(MgAl) –1 substitution mechanisms. Different tourmaline compositions and substitution mechanisms could be used as guides for mineral exploration.

Changes in tourmaline composition during magmatic and hydrothermal processes leading to tin-ore deposition: The Cornubian Batholith, SW England

To investigate the potential of tourmaline as a geochemical monitor, a comprehensive dataset on major, minor and trace element concentrations as well as Fe3+/ΣFe ratios of tourmaline is presented. The dataset includes samples from five plutonic complexes related to diverse magmatic to hydrothermal stages of the Cornubian Batholith (SW England). Tourmaline composition found in barren and cassiterite-bearing samples include all three primary tourmaline groups and tourmaline species with the general endmembers schorl, dravite, elbaite, uvite, feruvite, foitite and Mg-foitite.Based on textures and compositions, it is possible to distinguish not only between late-magmatic and hydrothermal tourmaline, but also between several formation stages. Hence, tourmaline monitors late-magmatic processes and the partitioning of elements during exsolution of an aqueous phase. For example, in hydrothermal tourmaline Sn is strongly enriched, while Ti, Cr, V and Sc are depleted compared to late-magmatic tourmaline of the same sample. Several tourmaline generations that precipitated from magmatic fluids can be distinguished with differing major and minor elements and REE patterns depending on the composition of the melt from which they were expelled from. Strongly zoned tourmaline allows for unraveling the hydrothermal history of a distinct location including ore precipitation. The precipitation of SnO2 in the study area was probably caused by mixing between acidic, reduced, Sn-bearing magmatic fluids and oxidized meteoric fluids, which is in agreement with London and Manning (1995) and Williamson et al. (2000). Hence, the ability of tourmaline composition to monitor changes in Sn concentration and redox conditions in hydrothermal fluids has potential as an exploration tool.

Source of boron in the Palokas gold deposit, northern Finland: evidence from boron isotopes and major element composition of tourmaline

The recently discovered Palokas gold deposit is part of the larger Rompas-Rajapalot gold-mineralized system located in the Paleoproterozoic Perapohja Belt, northern Finland. Tourmaline is an important gangue mineral in the Palokas gold mineralization. It occurs as tourmalinite veins and as tourmaline crystals in sulfide-rich metasomatized gold-bearing rocks. In order to understand the origin of tourmaline in the gold-mineralized rocks, we have investigated the major element chemistry and boron isotope composition of tourmaline from three areas: (1) the Palokas gold mineralization, (2) a pegmatitic tourmaline granite, and (3) the evaporitic Petajaskoski Formation. Based on textural evidence, tourmaline in gold mineralization is divided into two different types. Type 1 is located within the host rock and is cut by rock-forming anthophyllite crystals. Type 2 occurs in late veins and/or breccia zones consisting of approximately 80% tourmaline and 20% sulfides, commonly adjacent to quartz veins. All the studied tourmaline samples belong to the alkali-group tourmaline and can be classified as dravite and schorl. The δ11B values of the three localities lie in the same range, from 0 to −4‰. Tourmaline from the Au mineralization and from the Petajaskoski Formation has similar compositional trends. Mg is the major substituent for Al; inferred low Fe3+/Fe2+ ratios and Na values (<0.8 atoms per formula unit (apfu)) of all tourmaline samples suggest that they precipitated from reduced, low-salinity fluids. Based on the similar chemical and boron isotope composition and the Re–Os age of molybdenite related to the tourmaline-sulfide-quartz veins, we propose that the tourmaline-forming process is a result of a single magmatic-hydrothermal event related to the extensive granite magmatism at around 1.79–1.77 Ga. Tourmaline was crystallized throughout the hydrothermal process, which resulted in the paragenetic variation between type 1 and type 2. The close association of tourmaline and gold suggests that the gold precipitated from the same boron-rich source as tourmaline.

Provenance and tectonic setting of middle-upper Devonian sandstones in the Qinling Orogen (Shanyang area): New insights from geochemistry, heavy minerals and tourmaline chemistry

Devonian sandstones in the Shanyang area crop out in the southern part of the Qinling Orogenic Belt. Geochemical analyses show that the sandstones are enriched in Zr and have high Th/U and Rb/Sr ratios indicating the sandstones underwent repeated recycling. Zircon, tourmaline, apatite, rutile and anatase are the predominant heavy minerals while minor minerals include spinel, pyroxene, ilmenite and magnetite. The mineral compositions of detrital tourmaline grains indicate that the alkali compositional subgroup dominates; schorl and dravite are the main tourmaline species. A tourmaline composition environment discrimination diagram shows that about 70% grains are consistent with metapelite, metapsammite, and calc-silicates sources and about 30% of grains are from granitoids and associated pegmatites, and aplites. Metamorphic and granitic rocks in the Qinling Complex area are potential provenance. Overall data from geochemistry, heavy minerals and tourmaline chemistry suggests the Devonian sandstones were extensively recycled in a foreland basin setting rather than at a passive continental margin.