Tourmaline Crystals Research Articles

Development of Tourmaline-Bearing Lithologies of the Peraluminous Tusaquillas Composite Granitic Batholith, NW Argentina: Evidence from Quartz and Tourmaline

ABSTRACT Textural and chemical characteristics of quartz and tourmaline found in tourmaline-rich orbicules, greisens, pegmatites, and tourmalinite segregations associated with the peraluminous leucogranitic Tusaquillas Batholith Complex of northwest Argentina exhibit both magmatic and hydrothermal features. Imaging of quartz by optical cathodoluminescence and scanning electron microscopy cathodoluminescence shows three stages of development. Stage-1 quartz, considered magmatic, develops as large grains in pegmatites that have optical cathodoluminescence homogeneity; as anhedral relict grains partially replaced by stage-2 hydrothermal quartz in tourmalinite segregations, orbicules, and greisens; and as idiomorphic grains with irregularly spaced oscillatory zoning seen in scanning electron microscopy cathodoluminescence in orbicules. Stage-2 quartz, interpreted as hydrothermal, partially replaces stage-1 quartz and generation-1 tourmaline in most lithologies. Stage-3 quartz, a late hydrothermal stage, occurs in all lithologies as weakly luminescing quartz in healed quartz fractures with abundant fluid inclusions, commonly associated with the crystallization of irregular late-stage tourmaline. Multiple generations of tourmaline span magmatic to hydrothermal phases of development. In all lithologies, generation-1 tourmaline is compositionally similar: highly aluminous (range of average values of Altotal = 6.31–6.95 apfu), markedly Fe- and X□-rich (XMg = 0.01–0.17, X□= 0.21–0.51), and having variable F and WO (F = 0.00–0.57 apfu, WO = 0.00–0.40). Generation-1 tourmaline is interpreted as magmatic with compositions reflecting the chemical environment of the host lithologies and with compositional zoning patterns characteristic of both closed- and open-system behavior, possibly related to the transition to subsolidus conditions. Similar to generation-1 tourmaline, later-stage generations-2 and -3 tourmaline compositions are highly aluminous (range of average values of Altotal = 6.38–6.79 apfu), markedly Fe- and X□-rich (XMg = 0.00–0.20, X□= 0.28–0.40), and variably F- and WO-enriched (F = 0.07–0.57 apfu, WO = 0.00–0.31), but notably poorer in Ca and Ti (<0.01 apfu). The later-stage tourmaline is considered to have developed during the subsolidus hydrothermal conditions. External chemical contributions to tourmaline compositions from the country rocks appear to be minor to nonexistent. The X-site and W-site occupancies of the late-generation tourmaline implies subsolidus invasive alkaline, saline aqueous fluids with high Na but minimal Ca contents derived from the crystallizing leucogranites and related rocks across the solidus-to-subsolidus transition.

Mass Bias Corrections for Hydrogen and Oxygen Isotope Analysis of Tourmaline by Secondary Ion Mass Spectrometry

ABSTRACT Hydrogen (δ2H) and oxygen (δ18O) stable isotopes are used to trace fluid sources, metals, and contaminants in the environment and Earth's subsurface. Tourmaline-supergroup minerals provide an opportunity to quantify both δ2H and δ18O from the same grain using in situ analytical techniques (e.g., Secondary Ion Mass Spectrometry – SIMS). These minerals occur in a wide variety of geological environments and have a wide range of chemical compositions. However, large differences in chemical composition are problematic during SIMS analysis, as instrumental mass fractionation (IMF) often varies with the chemical composition of the mineral. Therefore, calibration models derived by analyzing tourmalines of different chemical composition must be developed for accurate analysis by SIMS. Hydrogen and oxygen isotope analysis was done on six reference tourmaline samples using a CAMECA 7f SIMS instrument operating at extreme energy filtering. Spot-to-spot repeatability for tourmalines was in the range 4–5‰ and 0.6–1.0‰ for δ2H and δ18O, respectively. There is a strong correlation between IMF and several elements (B, Si, Ca, Fe, and Fe#). Iron content is the most robust predictor of IMF, and we report two calibration curves for the correction of δ2H and δ18O measured by SIMS using reference tourmaline crystals with different Fe contents, ranging from 0.00 to 14.00 wt.% Fe. This is the first calibration curve used to correct for the fractionation of hydrogen isotope ratios in tourmaline as measured by SIMS. Tourmaline-supergroup minerals require a suite of at least three, with a range of Fe content, to ensure accurate and precise H and O analysis by SIMS. Crystallographic orientation effects were not observed for these tourmalines.

Co genetic Cr-bearing tourmaline and emerald in the Novo Cruzeiro pegmatite field (Minas Gerais, Brazil)

The Novo Cruzeiro pegmatite field in Minas Gerais (Brazil), located between Téofilo Otoni and the Jequitinhonha River, belongs to the areas of the EBPP with tourmaline and emerald occurrences. The pegmatites show beside of coloured tourmalines, Cr-rich black tourmaline cogenetic with Cr-bearing emerald. General crystallization conditions of pegmatites show, based on the obtained data, important changes during the final phase of tourmaline crystallisation which caused variations in tourmaline chemistry and reflects differences in the chemistry of the participating fluids. The crystallization of tourmaline ceased and after a period of co-crystallization, emerald was the only formed mineral. The obtained information suggests a crystallization sequence from tourmaline over tourmaline+emerald to emerald. A part of B and Fe may come from the host rock, Be and B from the intrusive granites and Cr from regional mafic to ultramafic rocks like amphibolite or Bt-Qz-schist.

The Chemical and B-Isotope Composition of Tourmaline from Intra-Granitic Pegmatites in the Las Chacras-Potrerillos Batholith, Argentina

ABSTRACT The Devonian Las Chacras-Potrerillos batholith comprises six nested monzonitic to granitic intrusions with metaluminous to weakly peraluminous composition and a Sr-Nd isotopic signature indicating a dominantly juvenile mantle-derived source. The chemically most evolved units in the southern batholith contain a large number of intra-granitic, pod-shaped tourmaline-bearing pegmatites. This study uses in situ chemical and boron isotopic analyses of tourmaline from nine of these pegmatites to discuss their relationship to the respective host intrusions and the implications of their B-isotope composition for the source and evolution of the magmas. The tourmalines reveal a diversity in element composition (e.g., FeO, MgO, TiO2, CaO, MnO, F) which distinguishes individual pegmatites from one another. However, all have a narrow δ11B range of –13.7 to –10.5‰ (n = 100) which indicates a relatively uniform magmatic system and similar temperature conditions during tourmaline crystallization. The average δ11B value of –11.7‰ is typical for S-type granites and is within the range reported for peraluminous granites, pegmatites, and metamorphic units of the Ordovician basement into which the Las Chacras-Potrerillos batholith intruded. The B-isotope evidence argues for a crustal boron source like that of the Ordovician basement, in contrast to the metaluminous to weakly peraluminous composition and juvenile initial Sr and Nd isotope ratios of the Las Chacras-Potrerillos batholith magmas. We propose that the boron was not derived from the magma source region but was incorporated from dehydration melting of clastic metasedimentary rocks higher up in the crustal column.

Geochemistry of tourmaline of elbaite-dravite series from sapphire bearing pegmatites, proterozoic higher Himalayan Crystalline Complex Jammu and Kashmir, India: Implication for evolution of pegmatite melt

Tourmaline of rare elbaite-dravite series has been reported for the first time from the sapphire bearing pegmatite from the Paddar area, Kishtwar District (Jammu and Kashmir), India. The sapphire-bearing pegmatites are hosted by ultramafic rocks of the Higher Himalayan Crystalline metamorphic complex. These pegmatites are dominantly composed of sodic-plagioclase, perthite, tourmaline, and sapphire, whereas microcline, biotite, and muscovite make up the minor phases. The tourmaline from these pegmatites contains high Mg, Ca, Na, and F content as well as low K, Fe, and Cr content. They are classified as alkali tourmaline, characterized by higher Mg/Mg + Fe and Na/Na + Ca ratios. They display complex substitution mechanisms during the crystallization (Li + Al↔Mg, Fe↔Mg, Na↔Ca, B + Al↔Si) and post crystallization alteration by the hydrothermal fluids. The geochemistry of tourmaline suggests that the tourmaline is crystallized from peraluminous, silicious pegmatitic melt (enriched in Al, Li, B, and H2O). This melt was most likely formed through partial melting of the metasediments of Higher Himalaya Crystalline during the M2 phase of regional metamorphism. The pegmatitic melt was injected in the ultramafics, resulting in bimtasomatism reaction evidenced by the development of systematic alteration zones next to the contact. Bimetasomatism results in the diffusion of the Ca and Mg from host rock to pegmatitic melt, and removal of silica from the pegmatitic melt, which leads to the increase of Al in pegmatitic melt. Finally, a saturation of the Al in the melt with a high Mg influx from host rock results in the favourable environment for crystallization of Mg-rich tourmaline and sapphire.

Gem Elbaite as a Recorder of Pegmatite Evolution: In Situ Major, Trace Elements and Boron Isotope Analysis of a Colour-Zoning Tourmaline Crystal

Few studies have focused on gem-quality tourmaline acting as a petrogenetic recorder, and the colour genesis of pink elbaite is still controversial. We carry out in situ major, trace element and boron isotope composition analyses on a single tourmaline crystal. This crystal is characterized by sudden transformation from colourless to pink, which can represent full pegmatite magma evolution. According to the analysis results, all spots are divided into alkali groups according to X-site occupancy and subdivided into elbaite series. The pink part accommodates higher concentrations of volatile and incompatible elements. The result is most consistent with successive pegmatite evolution in which the colourless part crystallized from the early stage, while the pink part crystallized from the late stage. The relatively consistent δ11B value between the colourless and the pink part suggests no fluid exsolution occurred during pegmatite evolution. The slight increase of δ11B values within the pink part and the colourless part may be due to mica crystallization. The combination of (Li++Mn2+) (Al3++Xvac)-1 and the exclusive positive linear relationship of Mn2+ vs. Ti4+ indicate that Mn2+ is the main cause of pink, while Mn2+-Ti4+ intervalence charge transfer also plays an important role.

Tourmaline with ultraviolet optical nonlinearity: Emergent material discovery from mineral

Tourmaline, as an important mineral, has received intensive interest, since it is not only a valuable gemstone, but also is a piezoelectric or pyroelectric material, due to the polar structural configuration. However, its nonlinear optical (NLO) properties were not explored so far, because a transparent crystal with high transmittance is scarce, being essential to optical functional materials. Here, we report a novel ultraviolet (UV) NLO tourmaline crystal with chemical composition NaAl9(BO3)3Si6O21OH for the first time by combining first-principles analysis and experimental measurements. It exhibits a short UV absorption edge, considerable second harmonic generation effect and moderate birefringence, thereby facilitating its phase-matching coherent beam output in the range from visible to UV regions.

Origin and significance of tourmaline-bearing rocks in Boroujerd region, Sanandaj-Sirjan zone, western Iran

Tourmaline minerals are a main petrogenetic tool because of their refractory nature, chemical variability, and extensive occurrence in various geological settings. The Middle-Jurassic Boroujerd igneous rocks are one of the largest bodies that located in the middle part in the Sanandaj-Sirjan Magmatic Arc (SSMA) that introduced into regional metamorphic rocks. They are mostly composed of granitoids (granodiorite, quartz-diorite, and monzogranite) and contain apatite, zircon and tourmaline as abounadant accessory minerals. Tourmalines occur in varying types of mineral assemblages, chemical compositions and individual forms including tourmalinite, quartz-tourmaline vein, as accessory mineral in the more evolved granitoids, and schists. Tourmaline crystal sizes in these rocks varies from very fine to coarse-grained. The colour is brown to black and some crystals displaying a finescale chemical zonation. Tourmaline crystals commonly exhibit cellular features. Based on electron probe microanalysis (EPMA) analyses, schorl is the most abundant type of tourmaline in granitoids but foitite and dravite are common compositions in the pegmatite and schist, respectively. Presence of several tourmaline generations and their compositional trend may indicate time-varying relatively acidic boron-bearing fluids and reflects an anatexic melts influence in their crystallization.

Boron isotope composition of detrital tourmaline: A new tool in provenance analysis

Tourmaline is a borosilicate mineral commonly found in sedimentary rocks worldwide. It is chemically and mechanically stable and, as a host of boron in crustal rocks, it could be a useful indicator of rock sources. Despite this, its potential as a source indicator using the boron (B) isotope has remained largely under-explored. In this study, we propose a new integrated approach to fingerprint the origin of detrital tourmaline grains and test whether the approach is useful for identifying source rocks. Tourmaline grains in modern river sands from Southern Tibet were analyzed for optical properties, major elements, and B isotope composition. The geochemistry of detrital tourmaline in sand from the Nianchu and Pumchu rivers draining the Himalayan ranges is similar, and the B isotope values indicated they were mainly from Himalayan leucogranites. Tourmalines in the Lhasa River sand were derived from two major sources. Grains with high Al, low Mg, and strongly negative B isotope values (−12‰ to −16‰) were interpreted from the Gangdese arc batholith, whereas those with low Al, high Fe, and B isotope values of −2‰ to 2‰ were proposed most likely from Nyaingentanglha orthogneisses. We examined the relationships between tourmaline properties and found that B isotope values are useful as a source indicator. We also established a database of B isotope values for 2724 tourmaline crystals in different types of exposed rock spanning 37 countries, to promote the use of B isotope values in tourmaline in provenance studies.

Magnesio-lucchesiite, CaMg3Al6(Si6O18)(BO3)3(OH)3O, a new species of the tourmaline supergroup

Abstract Magnesio-lucchesiite, ideally CaMg3Al6(Si6O18)(BO3)3(OH)3O, is a new mineral species of the tourmaline supergroup. The holotype material was discovered within a lamprophyre dike that cross-cuts tourmaline-rich metapelites within the exocontact of the O’Grady Batholith, Northwest Territories (Canada). Two additional samples were found at San Piero in Campo, Elba Island, Tuscany (Italy) in hydrothermal veins embedded in meta-serpentinites within the contact aureole of the Monte Capanne intrusion. The studied crystals of magnesio-lucchesiite are black in a hand sample with vitreous luster, conchoidal fracture, an estimated hardness of 7–8, and a calculated density of 3.168 (Canada) and 3.175 g/cm3 (Italy). In plane-polarized light, magnesio-lucchesiite is pleochroic (O = dark brown, E = colorless) and uniaxial (–); its refractive index values are nω = 1.668(3) and nε = 1.644(3) (Canada), and nω = 1.665(5) and nε = 1.645(5) (Italy). Magnesio-lucchesiite is trigonal, space group R3m, Z = 3, with a = 15.9910(3) Å, c = 7.2224(2) Å, V = 1599.42(7) Å3 (Canada) and with a = 15.9270(10) Å, c = 7.1270(5) Å, V = 1565.7(2) Å3 (Italy, sample 1). The crystal structure of magnesio-lucchesiite was refined to R1 = 3.06% using 2953 reflections with Fo > 4σ(Fo) (Canadian sample; 1.96% / 1225 for the Italian sample) The Canadian (holotype) sample has the ordered empirical formula X(Ca0.60Na0.39K0.01)Σ1.00Y(Mg2.02Fe0.622+Fe0.093+Ti0.25V0.01Cr0.01)Σ3.00Z(Al5.31Fe0.693+)Σ6.00[T(Si5.98Al0.02)Σ6.00O18](BO3)3V[(OH)2.59O0.41]Σ3.00W(O0.78F0.22)Σ1.00. The Italian (co-type) material shows a wider chemical variability, with two different samples from the same locality having ordered chemical formulas: X(Ca0.88Na0.12)Σ1.00Y(Mg1.45Fe0.402+Al0.79Fe0.363+)Σ3.00ZAl6[T(Si5.05Al0.95)Σ6.00O18](BO3)3V[(OH)2.90O0.10]Σ3.00W(O0.98F0.02)Σ1.00 (sample 1) and X(Ca0.71Na0.21☐0.08)Σ1.00Y(Mg2.49Fe0.412+Ti0.10)Σ3.00Z(Al5.44Fe0.463+Mg0.09V0.01)Σ6.00[T(Si5.87Al0.13)Σ6.00O18](BO3)3V(OH)3W[O0.61(OH)0.39]Σ1.00 (sample 2). Magnesio-lucchesiite is an oxy-species belonging to the calcic group of the tourmaline supergroup. It is related to lucchesiite by the homovalent substitution YFe ↔ YMg, and to feruvite by the homovalent and heterovalent substitutions YFe ↔ YMg and ZAl3+ + WO2– ↔ ZMg2+ + W(OH)1–. The new mineral was approved by the International Mineralogical Association Commission on New Minerals, Nomenclature and Classification (IMA 2019-025). Occurrences of magnesio-lucchesiite show that its presence is not restricted to replacement of mafic minerals only; it may also form in metacarbonate rocks by fluctuations of F and Al during crystallization of common uvitic tourmaline. High miscibility with other tourmaline end-members indicates the large petrogenetic potential of magnesio-lucchesiite in Mg, Al-rich calc-silicate rocks, as well as contact-metamorphic and metasomatic rocks.

Significant boron isotopic fractionation in the magmatic evolution of Himalayan leucogranite recorded in multiple generations of tourmaline

The late-stage evolution of leucogranite magmas and related magmatic-hydrothermal processes which could lead to rare-metal mineralization are still poorly studied in the Himalayas. Since tourmaline is among the minerals that are present in evolved granites of the Himalayas, the geochemistry of this mineral, and in particular the boron isotopic composition, is a powerful tool to trace evolution processes and sources of these magmas. This study focuses on the analysis of tourmalines in the Gurla Mandhata tourmaline leucogranites (GMTL) from the northwest of the Himalayan orogen. Two generations of tourmaline show clear differences in texture, major element, and B isotopic compositions. Early-stage tourmalines have high-Mg# [Mg/(Mg + Fe) 0.39–0.45] and occur as inclusions in late-stage tourmalines [Mg# <0.34] and other minerals. The δ11B values are in the range of −7 ~ −8‰ for the early-stage tourmaline and in the range of −12 ~ −15‰ for the late-stage tourmaline. The occurrence of tourmalines with contrasting B isotopic compositions from the same leucogranite body (even in a same specimen) can be explained either by mixing of magmas from different sources with different B isotopic compositions or by remarkable B isotopic fractionation during magma differentiation. As indicated by mineral textures and compositions, the mixing of different magma batches can be ruled out as a major cause in the case of GMTL. Alternatively, the bimodal distribution of tourmaline δ11B most likely suggests the occurrence of multiple-stage B isotopic fractionation during the magma evolution. Our modeling based on Rayleigh fractionation shows that this fractionation may have been induced mainly by extraction of fluid at a late magmatic stage, but crystallization of tourmaline may have also played a minor role. Interestingly, a compilation of δ11B values (>260 data points) in magmatic tourmaline from eight Himalayan leucogranite bodies systematically shows a similar bimodal distribution (i.e., with peaks at −7‰ and − 13‰), implying that this significant B isotopic fractionation may be a common scenario during magma evolution of the Himalayan leucogranites. However, multiple magma sources with contrasting B isotopic compositions cannot be fully ruled out for explaining the bimodal distribution of B isotopic composition. Combining our results with SrNd isotopic and other geochemical characteristics of the Himalayan leucogranites, we propose that the granitic magmas with high δ11B originated either from fluid-present melting involving boron-rich fluids, or more probably from dehydration melting of the Greater Himalayan Sequence that had been metasomatized by boron-rich fluids. The geological context implies that these fluids were probably derived from dehydration of mica-rich rocks from the Lesser Himalayan Sequence underlying the Greater Himalayan Sequence.

Fluid mixing as primary trigger for cassiterite deposition: Evidence from in situ δ18O-δ11B analysis of tourmaline from the world-class San Rafael tin (-copper) deposit, Peru

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.

Нано- и микроморфологические доказательства коллоидной структуры содержимого включений кольцевых силикатных кристаллов

The substance released naturally during mechanical opening of growth inclusions of aquamarine, beryl and tourmaline crystals (Transbaikalia, Russia) has been studied by scanning atomic force microscopy (AFM) and electron microscopy (SEM). The liquid part of the substance of the inclusions is a sufficiently concentrated colloidal sol-gel-silicate system. The diffused silicate colloid forms a film, poorly removable from the chip surface, which is reliably detected by AFM and transformed under prolonged exposure to an electron beam into a foam-glass. The latter fact can be used to create sub-micron textures that are stable under normal conditions by electron-beam lithography. The study of quartz and phenacite (Ural, Russia) did not reveal such films. In contrast to aquamarine, the inner walls of cavities of quartz and phenacite inclusions, according to AFM data, are covered with growth hills, grown by the dislocation mechanism. This indicates a relatively low degree of polymerization of the silicate component in the initial hydrothermal mother liquor for quartz and phenacite compared to the degree of polymerization in the mineral-forming media of ring silicate crystals.

Gemmological Characteristics of Gemstone Varieties Found in the Pegmatite of Haramosh Area, Gilgit-Baltistan

Haramosh valley is located in eastern side of Gilgitcity (Fig. 1). Geographically it is located between74°44' 17.37 " E and 35° 51 '8.97 " N. The area is asub range of Karakoram in the south-central region ofthe Rakaposhi–Haramosh mountains. Haramosh valleyis famous for its gemstones which are well known inthe world. The first gem mine was discovered in 1951in the area of Haramosh valley in Gilgit. Theprominent four localities of gem-bearing pegmatitesoccur in the vicinity of the Haramosh peak, Shengusalong Indus river, Haramosh Bulachi village, and thesetting of Khaltoro pasture. Along with glaciers,Hindukush Karakorum and Himalayan ranges host avariety of precious stones (Agheem et al., 2014). Inrecent decade Haramosh valley received moreattention because of the occurrence of a variety ofgems in pegmatite veins. Gemstone varieties related topegmatites are also found in other parts of GilgitBaltistan, like Shigar, Shengus, and Stuk Nala (Kazmiet al., Laurs et al., 1998).Pegmatites are found widelyin Gilgit-Baltistan Pakistan within the mountain rangesof Karakoram (Laurs et al. 1998). These macroliticpegmatite’s are mainly associated with leucogranites inHaramosh Massif, which is famous for recent rapiduplift (Laurs et al., 1998; Zeitler 1985). Variouscrystals of topaz, tourmaline, beryl, and quartz arebeing mined from these macrolitic pegmatite’s (Laurset al., 1998). Famous tourmaline crystal (10cm) ofPakistan is found in Stuk Nala of Nanga ParbatHaramosh Massif (Laurs et al., 1998).

The Tres Arroyos Granitic Aplite-Pegmatite Field (Central Iberian Zone, Spain): Petrogenetic Constraints from Evolution of Nb-Ta-Sn Oxides, Whole-Rock Geochemistry and U-Pb Geochronology

Abundant Li-Cs-Ta aplite-pegmatite dykes were emplaced in the western Central Iberian Zone of the Iberian Massif during the Variscan Orogeny. Their origin and petrogenetic relationships with the widespread granitoids have led to a currently rekindled discussion about anatectic vs. granitic origin for the pegmatitic melts. To deal with these issues, the aplite-pegmatite dykes from the Tres Arroyos area, which constitute a zoned pegmatitic field related to the Nisa-Alburquerque granitic batholith, have been studied. This work comprises a complete study of Nb-Ta-Sn oxides’ mineralogy, whole-rock geochemistry, and U-Pb geochronology of the aplite-pegmatites that have been grouped as barren, intermediate, and Li-rich. The most abundant Nb-Ta-Sn oxides from Tres Arroyos correspond to columbite-(Fe), columbite-(Mn) and cassiterite. Niobium-Ta oxides show a marked increase in the Mn/(Mn+Fe) ratio from the barren aplite-pegmatites up to the Li-rich bodies, whereas variations in the Ta/(Ta+Nb) ratio are not continuous. The probable factors controlling fractionation of Mn/Fe and Ta/Nb reflected in Nb-Ta oxides may be attributed to the crystallization of tourmaline, phosphates and micas. The lack of a progressive Ta/Nb increase with the fractionation may be also influenced by the high F and P availability in the parental pegmatitic melts. Most of the primary Nb-Ta oxides would have crystallized by punctual chemical variations in the boundary layer, whereas cassiterite formation would be related to an undercooling of the system. Whole-rock composition of the distinguished lithotypes reflects similar tendencies to those observed in mineral chemistry, supporting a single path of fractional crystallization from the parental Nisa-Alburquerque monzogranite up to the most evolved Li-rich aplite-pegmatites. The age of 305 ± 9 Ma, determined by LA-ICP-MS U-Pb dating of columbite-tantalite oxides, reinforces the linkage of the studied aplite-pegmatites and the cited parental monzogranite.

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

Mineral assemblages of primary and secondary Be-minerals were examined in intraplutonic euxenite-type NYF pegmatites of the Trebic Pluton, Moldanubian Zone occurring between Trebic and Vladislav south of the Trebic fault. Primary magmatic Be-minerals crystallized mainly in massive pegmatite (paragenetic type I) including common beryl I, helvite-danalite I, and a rare phenakite I. Rare primary hydrothermal beryl II and phenakite II occur in miarolitic pockets (paragenetic type II). Secondary hydrothermal Be-minerals replaced primary precursors or filled fractures and secondary cavities, or they are associated with adularia and quart. (paragenetic type III). They include minerals of bohseite-bavenite series, less abundant beryl III, bazzite III, helvite-danalite III , milarite-agalchanovite-(Y) III, phenakite III, and datolite-hingganite-(Y) III. Chemical composition of the individual minerals is characterized by elevated contents of Na, Cs, Mg, Fe, Sc in beryl I and II; Na, Ca, Mg, Fe, Al in bazzite III; REE in milarite-agakhanovite-(Y) III; variations in Fe/Mn in helvite-danalite and high variation of Al in bohseite-bavenite series. Replacement reactions of primary Be-minerals are commonly complex and the sequence of crystallization of secondary Be-minerals is not defined; minerals of bohseite-bavenite series are mostly the latest. Beryl usually occurs in pegmatites with rare tourmaline, whereas helvite-danalite bearing pegmatites are tourmaline-rich. Abundant tourmaline in pegmatites with helvite-danalite and its scarcity in beryl-bearing pegmatites indicate that early tourmaline crystallization affected activity of Al in the parental medium and thus may have controlled formation of primary Be-minerals (beryl - higher Al, helvite-danalite - lower Al) which crystallized later. Secondary Be-minerals with dominant minerals of bohseite-bavenite series and milarite suggest high activity of Ca in fluids. Variations in chemical composition (Al contents) of bohseite-bavenite series were controlled by the chemical composition of the precursor. High variability of primary magmatic Be-minerals within a single pegmatite district is exceptional and it is constrained by variable activities of Si and mainly Al, divalent cations - Ca, Mn, Fe, Zn and Mg, trivalent cations - REEs, Sc, and B, S and f(O2) in the individual pegmatites.

Considerations About Bi and Pb in the Crystal Structure of Cu-Bearing Tourmaline

Copper- and Mn-bearing elbaitic tourmaline (“Paraíba tourmaline”) sometimes contains significant amounts of Pb and Bi. Their position in the tourmaline crystal structure was studied with correlation analysis and bond valence calculations. Correlations between the F content and the X-site charge allow predicting the X-site occupancy. Three sets of tourmaline analyses were studied: (1) Pb-rich tourmalines from the Minh Tien pegmatite, Vietnam; (2) Cu-, Pb- and Bi-bearing tourmalines from the Mulungu mine, Brazil; (3) Cu- and Bi-bearing tourmalines from the Alto dos Quintos mine, Brazil. Two correlations were plotted: (1) the charge by considering only Na1+, Ca2+ and K1+; (2) the charge by adding Pb2+ and Bi3+ to the X-site charge. When plotting correlations for the Minh Tien tourmalines, the correlation significantly improves by adding Pb2+ to the X site. For the Alto dos Quintos tourmalines, only a slight increase of the correlation coefficient is observed, while such a correlation for tourmalines from Mulungu interestingly shows a slight decrease of the correlation coefficient. Bond valence calculations revealed that Bi3+ and Pb2+ can indeed occupy the X site via BiLi(NaAl)−1, PbLi(NaCu)−1 and possibly PbCu(NaAl)−1 substitutions as seen in the investigated tourmaline samples. At the Y site, Pb4+ can be substituted via PbLi(AlCu)−1, and PbVO(AlVOH)−1, while Bi5+ does not have any stable arrangement in Cu-bearing fluor-elbaite. The occurrence of Pb4+ at the Y site could be one explanation for the results of the correlations of the Mulungu tourmalines. Another explanation could be that during the tourmaline crystallization some additional Bi and Pb came into the pegmatitic system and hence disturbed the correlation between the average X-site charge and the F content. Further plots of such correlations in “Paraíba tourmaline” samples might also help to distinguish between the worldwide localities of these rare and sought-after tourmalines.

In-situ elemental and boron isotopic variations of tourmaline from the Maogongdong deposit in the Dahutang W-Cu ore field of northern Jiangxi Province, South China: Insights into magmatic-hydrothermal evolution

In this paper, we present a systematic investigation of in-situ major, trace elements and boron isotopic variations of tourmaline from the Maogongdong deposit in the Dahutang W-Cu ore field of northern Jiangxi Province, South China, which demonstrates both the magmatic and hydrothermal origin for the formation of the tourmalines. The tourmaline occurs mainly in granites, pegmatites and quartz veins. Five types of tourmaline are identified: (1) disseminated tourmaline in the pegmatites (Tur-P type); (2) isolated and disseminated tourmaline clots in the granites (Tur-R1 type); (3) typical anhedral quartz-tourmaline nodulars in the granites (Tur-R2 type); (4) tourmaline clots in quartz-tungsten-sulfide veins (Tur-Q1 type); (5) euhedral needle-columnar tourmaline crystals in quartz or quartz-sulfide veins (Tur-Q2 type). These tourmalines mostly fall into the alkali group representing schorl-dravite solid solution series. Petrography and chemical discrimination diagrams suggest that the Tur-P, Tur-R1 and Tur-R2 are of magmatic origin and the Tur-Q1 and Tur-Q2 are of hydrothermal origin. Hydrothermal tourmalines have higher Mg/(Mg + Fe) ratios, higher Li, Be, Sn, Rb, Co, Sr, V, Pb, Zn, Ni contents and lower Na/(Na + Ca) ratios, lower Nb, Ta contents than the magmatic tourmalines. The Tur-P show negative Eu anomalies and their REE patterns are equivalent to the muscovite granite. The Eu anomalies in Tur-R1 and Tur-R2 change from negative to positive. Compared with magmatic tourmalines, Tur-Q1 and Tur-Q2 exhibit more pronounced positive Eu anomalies, and a majority of the Tur-Q1 and Tur-Q2 have higher ∑REE contents. Tourmalines from the Maogongdong deposit have a B isotopic composition range from −17.9‰ to −12.3‰. The average δ11B values of the Tur-P, Tur-R1 and Tur-R2 are −13.8‰, −14.8‰ and −14.5‰, respectively. Tourmalines in early hydrothermal veins have similar δ11B values (average −14.6‰), while the tourmalines in later hydrothermal veins have slightly lower δ11B values (average −16.5‰). Boron isotopic variations of tourmaline are controlled by temperature, Rayleigh fractionation and external fluid.

Minerály pegmatitových hnízd z okolí Jablonce nad Nisou (krkonošsko-jizerský pluton) - část I. silikáty

We have studied silicate minerals in pegmatite nests from the Tanvald Granite (4 sites) and the Liberec Granite (1 site) in the vicinity of Jablonec n. Nisou, situated within the Variscan Krkonoše-Jizera Pluton. They contain major quartz, K-feldspar and plagioclase (An0-11), subordinate biotite, muscovite and locally schorl. Accessory phases include garnet (spessartine-almandine), andalusite, Hf-rich zircon and thorite. In addition, zinnwaldite was found in a single sample. The studied pegmatites show simple internal structure including aplitic, granitic and coarse-grained “blocky” units; the central zone commonly contains miarolitic cavity which is sometimes filled by tourmaline. The mineral composition and fractionation degree largely reflect those of the host granite; the more fractionated are pegmatites hosted by the Tanvald Granite. The pegmatite nest from Nová Ves nad Nisou II exhibits distinct mineral assemblage with zinnwaldite, pure albite and lack of biotite and garnet, therefore we suggest here a substantial modification of mineral assemblage by superimposed processes. Moreover, tourmaline (schorl) composition with local increasing of Mg toward rim indicates a possible contamination derived from adjacent rocks during tourmaline crystallization.

New Geosite Candidates at the Western Termination of the Büyük Menderes Graben and their Importance on Science Education

The Buyuk Menderes Graben (BMG) is one of the best-known and the largest geological structure of the West Anatolian Extensional Province. It includes two nature conservation parks and twelve cultural heritage sites within and in its vicinity. Four geologically distinct features/locations within and in the vicinity of the BMG have been previously enlisted as geosite candidates in the provisional Geological Heritage Inventory of Turkey compiled in 2002 by the Turkish Association for the Conservation of the Geological Heritage (JEMIRKO): (1) the horst-graben structure of the Buyuk Menderes region itself, (2) the tafoni from the augen-gneiss from the east of Bafa Lake, (3) the zultanite crystals from the northeast of Ilbir Mountain, and (4) the tourmaline (dravite) crystals from the Camizagili, Cine. In the current study, we are introducing additional three new geosite candidates at the western termination of the BMG with three different main geological subjects. The first one is the Yavansu Fault. Located 2 km south of the Kusadasi village, it has a clearly exposed unique fault surface which is one of the best examples of structural indicators for the WAEP with respect to the normal faulting events. The second one is located in the Hisartepe Volcanics exposed between Kusadasi and Soke, and consists of basaltic lava flows with remarkable prismatic cooling joints and a gorgeous feeder dome reaching up to 150 m height. Final suggestion is the Karina marine fan-delta complex located at the south-eastern border of the Dilek Peninsula National Park. This fan-delta complex is the largest one in the Western Anatolian scale and has remarkable paragon outcrops up to 20 m high between Doganbey and Karina Lagoon.