Composition Of Tourmaline Research Articles

Petrology of Tourmaline-Bearing Blueschist from SW Tianshan, China, and Its Implication in B-Rich Fluid Migration in Subduction Zone

Abstract Boron geochemistry can track fluid–rock interaction during subduction zone metamorphism. Rare tourmaline-bearing blueschists, which are associated with ultrahigh-pressure (UHP) serpentinites are first recognized in SW Tianshan, China. Detailed petrology, whole-rock and mineral chemistry, B isotope analysis, and modeling characterized two consecutive stages of tourmaline crystallization (Tur-I, Tur-II). Tourmaline included in, or intergrown with, garnet and the cores of tourmaline in rock matrixes and veins are Tur-I, which grew during prograde metamorphism at 430°C to 460°C/470°C, ~1.9–2.1 GPa. The rims of tourmaline in rock matrixes and veins are Tur-II, which formed during initial exhumation at 460°C to 490°C, ~2.1–1.7 GPa. Variable δ11B values of tourmaline (+8‰, Tur-I to −2‰, Tur-II) point to a 11B-rich signature of the fluid infiltrating at Stage I. With progressing metamorphism, δ11B decreased in the fluid. The high-δ11B Tur-I (up to +8‰) could not have crystallized from fluid released from the high-pressure metapelites (−12‰ to −7‰) and metabasites (−15‰ to −5‰) surrounding the tourmaline host rocks given the lower δ11B values. Modeling of B isotope fractionation yields the δ11B values of −9‰ to −5‰, −11‰ to −1‰, and +8‰ to +17‰ for the fluids equilibrium with the restitic metapelites, metabasites, and serpentinites, respectively. The tourmaline and whole-rock B isotope data, along with the tourmaline compositions, point to the associated serpentinites as source of the fluid that infiltrated the metamorphic rocks. This fluid was released by the partial dehydration of serpentinites through the reaction antigorite + brucite = olivine + water at forearc depth. We propose that metabasites in subduction zones can acquire 11B-rich signatures through interaction with serpentinite-derived fluids, leading to the formation of robust tourmaline minerals at shallow levels. As a new reservoir of heavy boron, these metabasites can then transport this signature to greater depths.

High-precision U–Pb geochronology of the Lundy igneous complex: implications for North Atlantic volcanism and the far-field Paleocene–Eocene ash record

The Lundy Island (Bristol Channel, UK) granite is a felsic expression of the southernmost igneous centre of the North Atlantic Igneous Province that emplaced millions of cubic kilometres of magma during the Paleogene. The granite's distinctive S-type, peraluminous, two-mica ± garnet ± tourmaline composition has led to the hypothesis that eruptions from the Lundy volcanic centre may be the source of thick felsic ash layers within the early Eocene Fur Formation (Denmark) that act as key marker horizons for the onset and duration of the Paleocene–Eocene Thermal Maximum. This paper presents high-precision zircon U–Pb emplacement ages of 57.24 ± 0.11/0.12/0.13 Ma for the granite and 55.970 ± 0.021/0.030/0.070 Ma for a felsic ‘lundyite’ dyke. Trace and rare earth element patterns indicate close similarities between late-stage Lundy activity and ash layer −33 in Denmark. This ash layer was deposited during the Paleocene–Eocene Thermal Maximum carbon isotope excursion, suggesting that the Lundy volcanic centre is likely to be the source of this key ash horizon and that magmatism at Lundy likely continued into the early Eocene.

Tourmaline geochemical and B isotopic constraints on pegmatite Li mineralization and exploration

Pegmatite–related deposits represent one of the most significant types of mineral deposits housing rare–metal elements such as Li, Be, Nb, Ta, Rb, Cs, and Sn. Although extensively studied for almost two centuries, the mechanism controlling the rare–metal mineralization in pegmatites remains controversial. In addition to the enrichment of rare–metal elements in the source region, differentiation processes (e.g., fractional crystallization and liquid immiscibility) after emplacement may have also contributed to the concentration and mineralization of rare–metal elements. However, compared to fractional crystallization, the role of liquid immiscibility in pegmatite mineralization has received limited attention. In this study, the element and boron (B) isotopic compositions of tourmalines from different textural zones (Zones I–VI) of the rare–metal–mineralized Koktokay No. 3 pegmatite, Altai, NW China, as well as from the altered country rock and the border zone, were analyzed to evaluate the role of liquid immiscibility in the generation of Li–mineralized pegmatites. Tourmalines display a variety of compositions, ranging from schorl and elbaite in the outer zones to elbaite in the inner zones of the Koktokay No. 3 pegmatite. Tourmalines from Zones I–III exhibit no obvious internal textures, whereas some tourmalines from Zones IV–VI have replacement textures or abrupt zonations. The distinction is attributed to the absence and presence of exsolving fluids during their formation, respectively. Tourmalines in Zones I–III and VII–VIII display less variable δ11B values (–15.07 ‰ to –12.21 ‰ and –14.16 ‰ to –13.10 ‰, respectively), reflecting a negligible B isotope fractionation produced by fractional crystallization during the pegmatite evolution. By contrast, tourmalines in Zones IV–VII exhibit more significant variations in δ11B values (–14.83 ‰ to –8.09 ‰) compared to those in Zones I–III and VII–VIII. The high δ11B tourmalines in Zones IV–VII were most likely crystallized from the fluids exsolving from the highly evolved pegmatite–forming magma. Their occurrence indicates the fluid exsolution occurring between zones IV and V, where Li mineralization began in the Koktokay No. 3 pegmatite. The mineralization of rare–metal elements is closely linked to the evolution of magma into a coexisting magma–fluid system. In addition, Li–mineralized pegmatites are characterized by tourmalines with Fe3+Al-1 substitution and higher Zn, Li, Li/Sr, and V/Sc than barren pegmatites. These differences are believed to be due to the higher fO2 and greater extent of magmatic differentiation in Li–mineralized pegmatites compared to the barren ones. These findings provide new insights into using the geochemical compositions of tourmalines as a guide for exploring Li–mineralized pegmatites.

Tourmaline composition probes serpentinite-derived fluid mobility in subduction zones

Serpentinite dehydration in subduction zones plays a pivotal role in geochemical cycling on Earth. A number of geochemical studies on arc magmas have elucidated the contributions of serpentinite-derived fluids to mantle sources. However, due to complex geological overprints during subduction zone processes, discerning serpentinite signatures in exposed metamorphic rocks within fossil subduction zones remains challenging. In this study we address these difficulties through in-situ investigations of tourmaline, the geochemistry of which reflects the host environment as well as potential fluid-induced processes. The presence of zonations in tourmaline makes it an excellent recorder of consecutive geological events. Integrated major and trace elements along with in-situ boron isotopes of tourmaline from the high-pressure Sopron area (Hungary) in the Eastern Alps were used to unravel fluid action sourced from serpentinite. Despite the presence of color zoning, tourmaline in the orthogneiss (Tur-G) has low XMg [Mg/(Mg + Fe)] of ca. 0.3–0.6 and δ11B values of around −11 ‰, along with variable trace element compositions. Petrological observations and geochemical analyses suggest that the inner domains of Tur-G are of igneous origin, while the outer rims are likely affected by subsequent metamorphic events. Tourmaline in metasomatized kyanite-quartzite (Tur-K) veins exhibits distinct geochemical zoning, and preserves metamorphic cores and fluid-induced rims. The inner domains of Tur-K display low XMg (<0.6), relatively high trace element concentrations and δ11B values of less than −10 ‰, whereas the overgrowths exhibit extremely high XMg values (>0.99), low trace element concentrations and high δ11B values reaching up to +21 ‰, clearly indicating the incorporation of serpentinite-derived Mg-11B-rich fluids. Through comparison with other metamorphic and metasomatic tourmalines in (ultra)high-pressure rocks globally, we establish that tourmaline with high XMg > 0.85 and δ11B values >0 ‰ may serve as an effective proxy for detecting serpentinite-derived fluids in subduction zones.

Eight mineral species in one crystal: unique zonation of polychrome tourmaline from the Krutaya vein (Malkhan pegmatite feld, Transbaikalia, Russia)

A unique unusually Mn-rich concentrically zoned polychrome crystal from the cavity of granite pegmatite of the Krutaya vein within the Malkhan pegmatite feld (Transbaikalia) is studied. It consists of six valid and two potentially new mineral species of the tourmaline supergroup. The paper provides the detailed physical, chemical and crystallographic characteristics of minerals. A Mn-richest (up to 9.6 wt. % MnO) dark brown core of the crystal is composed of fuor-tsilaisite, princivalleite and a Mn2+-F-analog of foitite. A greenish yellow intermediate zone consists of Mn-rich fuor-elbaite and darrellhenryite and is followed by a Mn-poor pink zone composed of fuor-rossmanite, rossmanite and their O2--analog. A yellowish green peripheral zone consists of late-generation Mn-bearing fuor-elbaite. The Mn content decreases, while the Li + Al content increases from the center of the dark brown zone to the margin of the crystal approximately to the middle of the pink zone, where the evolution of the tourmaline composition is inverted and this trend becomes opposite. The crystal structure of fuor-tsilaisite is refned on a single crystal extracted from this specimen, R1 = 2.4 %. The mineral is trigonal, space group R3m, a = 15.9595(1), c = 7.14164(7) A, V = 1575.31(3) A3, Z = 3.

Chemical and boron isotopic compositions of tourmaline from the pegmatite in Ke'eryin rare metal orefield, Eastern Tibet: Implications for pegmatitic evolution

Pegmatites occur widely in the Ke'eryin rare metal orefield. The genesis and evolution of the Ke'eryin pegmatites are still in dispute, and morphological and geochemical studies on tourmalines from the Ke'eryin pegmatites are limited. In this study, in-situ analyses of major and trace elements and B isotope were conducted to uncover the origin of tourmaline and the evolution of related pegmatites. Three types of tourmaline from the Ke'eryin barren pegmatite were identified: elongated columnar or needle-columnar tourmaline (Tur-1 type), isolated, disseminated, irregular, and massive tourmaline (Tur-2 type), and long columnar tourmaline (Tur-3 type). Petrographically, the Tur-1 type crystallized at the early stage of pegmatitic crystallization sequence, the Tur-2 type possibly formed at the early- and/or syn-pegmatitic crystallization sequence, whereas the Tur-3 type likely formed at the relatively late crystallization sequence. Compositionally, most tourmalines belong to the alkali group with a few falling in the vacancy group. All the tourmalines show a schorl composition and are of magmatic origin. Chemical variations from the Tur-1 to Tur-3 tourmalines are controlled by magma fractionation and melt compositions rather than crystal chemical effects. Most tourmalines follow the (Na, Mg)(Xvac, Al)−1, (Mg, OH)(Al, O)−1, and (Ca, Mg2)(Xvac, Al2)−1 exchange vectors. The higher contents of Zn, Sn, Li, Be, Nb, and Ta and negative Eu anomalies in the Tur-3 type indicate that it was likely crystallized at a more evolved stage. In combination with textural evidence and tourmaline chemistry, we suggest that the Tur-1 and Tur-2 types were formed at the relatively earlier stage of pegmatite-forming magma and the Tur-3 type was likely formed closer to the end-stage of barren pegmatite crystallization. The B isotopic compositions are relatively homogeneous and display slightly higher in the Tur-3 type, which were likely caused by fractional crystallization during B-rich magma evolution. It can be inferred that the tourmaline in more evolved and/or Li-mineralized pegmatite with magma evolution should have higher Li, Be, Nb, Ta, and Sn contents, implying that tourmaline chemistry may be used as a potential exploration indicator for rare metal mineralization.

Origin of fluids in the Lancangjiang tin belt, southwestern Yunnan Province, China: Evidence from trace element and boron isotopic compositions of tourmaline

The Lancangjiang tin belt is located on the eastern margin of the Tibetan Plateau, which is in the northern part of the Southeast Asian tin belt that contains Sn, W, and base metal ore deposits. Tourmaline alteration and high B contents are typical features of the magmatic–hydrothermal systems in the Lancangjiang tin belt. Our new data for tourmaline intergrown with cassiterite reveal complex geochemical features that provide important insights into the origins of ore-forming fluids in this B-rich tin belt. Most of the tourmaline in the Sn deposits and metamorphic rocks belongs to the alkali-group dravite series, except for some that is part of the X-vacant group. The tourmaline compositions differ among the ore districts, but all exhibit Fe-poor (0.61–1.08 apfu) and Mg-rich (1.43–2.06 apfu) compositions, with Fe/(Fe + Mg) = 0.18–0.46. Most trace elements in the tourmaline occur at low contents (<50 ppm), including the large-ion lithophile elements (e.g., Cs and Ba) and high-field-strength elements (e.g., Nb, Ta, Hf, and Th). However, some trace elements (e.g., Zn, Sr, and V) and Sn have high contents (up to several hundreds or thousands of ppm). The δ11B values of tourmaline from the Sn deposits range from −14.7 ‰ to −11.3 ‰, except for those in the Man Makhsan Sn deposit, which range from −12.0 ‰ to −8.1 ‰. The δ11B values (−14.7 ‰ to −8.1 ‰) and the positive correlation between Sn contents and Nb/Ta, Al/Ga, and K/Cs ratios in the ore-related tourmaline indicate that the exsolved ore-forming fluids were derived from highly fractionated S − type granitic magmas. The fluids were mainly B-, Sn-, and Al-enriched. The low Fe/(Mg + Fe) ratios, high oxygen fugacity, and Al saturation were favorable for cassiterite precipitation, and are proxies for the ore-forming potential of large-scale Sn deposits.

Geochemical characteristic and B isotopic compositions of tourmaline from the Chaqiabeishan Li-rich pegmatite in the Quanji Massif, NW China

The Chaqiabeishan Li-rich pegmatite deposit is located in Tianjun County, Qinghai Province. Due to the complex magmatic evolution, there are still numerous controversies surrounding the diagenetic and metallogenic mechanisms of pegmatites. In this study, we investigated tourmalines from pegmatites in Chaqiabeishan by means of analyzing the in situ major element compositions, trace element contents, and boron isotopes. The collected samples can be classified into two types: pegmatitic tourmaline (Tur 1) and fine tourmaline (Tur 2). Based on the observation of geological characteristics, specimens, and microphotographs, the tourmalines have a basically paragenetic relationship with the predominant lithium-bearing mineral (spodumene), tourmalines and spodumenes would crystallize at a late magmatic stage of the pegmatitic sequence. Both tourmalines have similar geochemical characteristics, and Tur 1 crystallized earlier than Tur 2. The major elements show that both tourmalines belong to the alkali group, schorl series, and Li-poor pegmatite. Additionally, they have ∑(Mg + Fe) values less than 3 apfu, and redundant Al (0.04–0.89 apfu, average of 0.61) in the Y-site occupancy. The trace elements show that both tourmalines are characterized by enrichment in LREE relative to the MREE, with a slight negative Eu anomaly, indicating that they are of magmatic origin. The high Li/Sr ratios ranging from 38.56 to 6292.28 (average of 701.01 ppm) further support the magmatic origin. The δ11B values of all tourmalines range from −13.86 to −12.46 ‰, with an average of −13.14 ‰, indicating that the boron in the pegmatites was derived from S-type granitic magma or Dakendaban Group mica schist basement. The δ11B values of Tur 1 (average of −13.13 ‰), the rim of Tur 1 (average of −12.95 ‰), the core of Tur 1 (average of −13.25 ‰), and Tur 2 (average of −13.19 ‰) show a slight variation, indicating that the tourmalines have a consistent boron source and basically no foreign B-rich fluids involved. In conclusion, the petrological and geochemical characteristics suggest that the pegmatites in Caqiabeishan are likely the direct products of anatexis, and the tourmalines and spodumenes were formed in secondary faults at the late magmatic stage.

Provenance of volcano-sedimentary features using tourmaline and REE compositional analysis, in the Paraná Basin, southern Brazil

The present research focuses on sediments' compositional analysis, in the Paraná Basin, to demonstrate provenance contributions for the volcano-sedimentary features distributed along three regions of the Basin's border. In this context, the analyzed sediments, which are generally attributed to the Botucatu Formation, interact with volcanic lava flows from the Serra Geral Formation, establishing a volcano-sedimentary interaction. Nonetheless, the classic description for the Botucatu Formation comprehends almost ubiquitous fine to medium sandstones, while the herein sedimentary rocks vary from fine-grained to very coarse sediments. The granulometry difference raises questions about unexplained events during the Cretaceous volcanism (Serra Geral Formation) over the Botucatu desert. Accordingly, the studied area is distributed into regions A, B, and C from the center to the eastern of the state respectively, covering the Paraná basin's border where the volcano-sedimentary rocks can be outcropped. The methodologies employed involve the analysis of tourmaline compositions and REE patterns. These analytical tools help identify provenance variations and the development of local processes. As a result, the data indicate the predominance of meta-pelites and metapsammites in region A, while in region C there is a prevalence of granitoids contribution, while region B is a transition area showing contributions of both meta-pelites, metapsammites, and granitoids that are attributed to some units of the Sul-Rio-Grandense Shield.

Dravite of Terny Meteoritic Crater (Kryvyi Rih District)

During mineralogical investigations of breccia and volcanic rocks of the Terny structure (Veseli Terny, Kryvyi Rih), so-called Terny meteoritic crater, the mineral tourmaline, previously unknown here, was found. Tourmaline crystals, with a length from 0.05 to 1.0 mm and more and up to 0.1—0.2 mm wide, are associated with quartz, potassium feldspar, graphite and apatite. The morphology and chemical composition of tourmaline were examined using optical microscope and EPMA in transparent thin sections. The tourmaline crystals are unusually parted along two transverse systems of microcracks oriented obliquely to the prism faces. EPMA reveals that tourmaline is dravite. The specific deformations of dravite and observed mineral associations probably indicate the rock formation under conditions of high pressures and temperatures of impact metamorphism. It is also confirmed by the presence of planar fractures in quartz.

Tracing the ore forming process of Dahenglu copper-cobalt deposit with the rare earth elements and isotopic compositions of tourmaline and calcite

Tracing the ore forming process of Dahenglu copper-cobalt deposit with the rare earth elements and isotopic compositions of tourmaline and calcite

Stable hydrogen isotope compositions of tourmalines from the Sopron metamorphic complex: Metamorphic closure temperature and fluid composition

AbstractStable hydrogen isotope compositions of metamorphic rocks and minerals can provide information on the origin of metamorphic fluids, which is especially important in systems that had experienced multiple metamorphic events. The Sopron orthogneiss-micaschist complex is a good target as it records signs of Variscan and Alpine metamorphic events as well as Variscan granitic magmatism. In this study tourmaline-bearing rocks (pegmatitic orthogneisses and kyanite-chlorite-muscovite schists) of the Sopron metamorphic complex were sampled and their tourmaline grains were analyzed for stable hydrogen isotope compositions (δ2H). The δ2H values (−23 ± 1‰, relative to V-SMOW) are in accordance with a fluid flux from devolatilization of subducted, seawater-containing rocks. Tourmaline-chlorite hydrogen isotope fractionations correspond to about 550 °C, indicating that δ2H values formed close to peak metamorphic temperatures are preserved without retrograde isotope exchange during cooling.

Tin Mineralization in the Triassic Chacaltaya District (Cordillera Real, Bolivia) Traced by In Situ Chemical and δ18O-δ11B Compositions of Tourmaline

Abstract We present a petrographic and geochemical study of tourmaline from the Triassic Chacaltaya Sn-polymetallic district in the Cordillera Real of Bolivia. Tourmaline is associated with greisens, breccias, and veins, which occur around the Triassic Chacaltaya peraluminous granitic stock hosted by Silurian metasedimentary rocks. Three main petrographic types of hydrothermal tourmaline have been identified: pre-ore greisen-related (Tur-1), syn-ore breccia-related (Tur-2), and syn-ore vein-related (Tur-3). The three types of tourmaline belong to the alkali group and have Fe-rich compositions mostly close to the schorl end member. Overlapping Fe/(Fe + Mg) ratios suggest broadly similar compositions of the hydrothermal fluids during the deposition of tourmaline. The most notable differences in minor and trace element contents include relative enrichment in Zn and Li in Tur-1 and relative enrichment in Ca, Sc, V, Cr, Sr, Sn, Y, Cs, Be, and Zr in Tur-3, with Tur-2 showing intermediate compositions between those of Tur-1 and Tur-3. The progressive enrichment in Sn from Tur-1 (avg = 14 ppm) through Tur-2 (avg = 311 ppm) and Tur-3 (avg = 476 ppm) indicates an increase of Sn concentrations in the hydrothermal system coinciding with cassiterite deposition in breccias and veins. The transition from high Li and Zn contents in Tur-1 to elevated Ca, Sr, V, and Cr contents in Tur-3 is interpreted as reflecting interaction between a hydrothermal fluid of magmatic origin and the metasedimentary country rocks. Strong and relatively steady positive Eu anomalies in all tourmaline types suggest dominantly reduced hydrothermal conditions. In situ δ18O and δ11B analyses of greisen-related Tur-1 reveal crystallization in isotopic equilibrium with magmatic water derived from a peraluminous S-type granite. In contrast, higher δ18O values of breccia-related Tur-2 and vein-related Tur-3 indicate crystallization in isotopic equilibrium with a fluid of metamorphic origin or a magmatic fluid that variably interacted with the metasedimentary host rocks. Geochemical modeling reproduces interactions between a fluid of magmatic origin and the host metasedimentary rocks at moderate water/rock ratios between 0.1 and 0.5. We conclude that cassiterite mineralization in the Chacaltaya district was formed primarily through interaction between B-Sn–rich magmatic fluids and the metasedimentary country rocks.

Chemical and boron isotope composition of tourmaline from Koktokay pegmatite, Altay Orogenic Belt, Northwest China: Implications for metallogenic mechanism and prospecting indicator for rare-metal pegmatites

The metallogenesis of Li-rich pegmatites remains contentious and an innovative approach for exploring such deposits is needed. The well-known Koktokay pegmatites in the Altay Orogenic Belt exhibit various mineralization degrees and patterns. In this study, we conducted systematic elemental and boron isotope analyses on five tourmaline samples to decipher the metallogenic mechanism and prospecting indicators of rare metal pegmatites. KKTH2 and KKTH3 were collected directly from the magmatic stage and magmatic–hydrothermal stage of the No. 3 pegmatite, KKTH1 was collected from the Aikoz mine pit, and KKTH4 and KKTH5 were collected from a small operational mine near the No. 3 pegmatite. Unlike the No. 3 pegmatite, this mine produces gem crystals but lacks Li mineralization. All tourmalines belong to the alkali group, whereby KKTH1 and KKTH2 are classified as fluor-elbaite, whereas KKTH3 and KKTH4 are schorl. The tourmaline in KKTH5 shows high Al content (up to 45.30 wt%), classifying as mostly rossmanite–elbaite series, with minor amounts of olenite and liddicoatite.A Rayleigh fractionation model yields a shift in △11B value of 4.8‰ between Zone IV and VI involved more than just magma, as B-isotope fractionation between tourmaline and melt would be <1‰ when temperature drop from 650 °C to 500 °C. It further indicates that different parts of No. 3 pegmatite may have originated from diverse sources.After comparing the δ11B values of tourmaline in this study with other fertile and barren pegmatite globally, we suggest that δ11B values of tourmaline higher than −10‰ is a potentially useful indicator for Li-rich pegmatites because of the likely relationship with marine evaporite or carbonate rocks in the source. Furthermore, we propose that tourmaline with a V/Sc value lower than 1 and a Li/Sr value higher than 100 can be used as indicators for Li exploration. The extent of Li migration from magma into the hydrothermal stage and mineralized in the residual melt correlates with the salinity of magma, which may reasonably explain the less intense wallrock alteration near the No.3 pegmatite. This finding provides new insight into the use of trace elements and boron isotope composition as a guide for exploring Li-rich pegmatites.

Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar

Chemical composition of tourmalines from the Manjaka pegmatite and its exocontact, Sahatany Valley, Madagascar

Geochemistry and Genesis of Magnesium Tourmalines in Jian Forsterite Jade Deposits from Ji’an County, Jilin Province, Northeast China

The Jian forsterite jade, so named because of its enrichment in end-member forsterite, is a new type of jade found in Ji’an County (Jilin Province, Northeast China). Tourmaline is discovered in Jian forsterite jade deposits and is characterized by magnesium enrichment. In this study, three types of magnesium tourmaline were identified from the pegmatite veins (type 1), the contact zone (type 2), and the tourmaline veins in jade (type 3). The results are shown by the main test methods, such as EPMA, Micro-XRF, and LA-ICP-MS. The substitutions of Fe2+−1Mg2+−1, (□Al3+)−1 (Na+Mg2+)−1, (□Al3+2)−1 (Ca2+R2+2)−1, etc. are inferred by the variations in the major element compositions. From type 1 to type 2 tourmaline, the content of Mg, Sr, and Sn gradually increases, the content of Fe, Zn, K, Mn, Sc, Ga, and Co gradually decreases, the content of Ca initially decreases and then increases, and the content of Na initially increases and then decreases. Type 3 tourmaline has significantly higher Si and Al than the first two types, and the content of the remaining elements lies between the above two types. We propose that tourmalines in Jian forsterite jade deposits are typically of hydrothermal origins and are mainly constrained by magnesium, which is related to the contact metasomatic metamorphism of pegmatite-related hydrothermal fluid with the Jian forsterite jade, and the chemical composition of tourmaline indicates the fluid characteristics of gradual serpentinization of Jian forsterite jade.

Detrital zircon and tourmaline unravel polycyclic provenance of sedimentary infill of the Cretaceous Tupanciretã formation, southern Brazil

The recognition and evaluation of polycyclic processes in sedimentary units are critical for proper provenance analysis and sedimentary system interpretation. The chemical composition and textural maturity of detrital tourmalines and zircons allow identification of sediment source areas, transport, and deposition. This study investigates the origin and history of post-Gondwanan sediments of the Tupanciretã Formation in southern Brazil, which lacks provenance studies. The Tupanciretã Formation is in a similar setting of the Bauru Supersequence at the uppermost portion of the Paraná Basin. Detrital zircon ages indicate sediment provenance from the Transamazonian, Grenvillian, and Brasiliano orogenic cycles of the Rio Grande do Sul Shield and younger grains (280-128 Ma) record contribution from the Choiyoi and Serra Geral igneous events, with a maximum deposition age of 127 Ma. Detrital tourmaline chemical analyses points to the Sul-riograndense Shield as the ultimate source, with metapelitic, metapsamitic and granitic origins. The predominant degrees of roundness are well rounded to rounded suggest evidence of sediment recycling from sedimentary units of the Paraná Basin, with important aeolian reworking involved. Zircon U–Pb signatures are compatible with the eastern sector of the Botucatu Formation in Rio Grande do Sul as the immediate source and the northeastern Sul-riograndense Shield as the ultimate source. Intermediate sources between the Sul-riograndense Shield and the Tupanciretã Formation were Gondwanan sedimentary units of the Paraná Basin, with possible participation from the Camaquã Basin.

Chemical and boron isotopic composition of tourmaline from the Yixingzhai gold deposit, North China Craton: Proxies for ore fluids evolution and mineral exploration

Chemical and boron isotopic composition of tourmaline from the Yixingzhai gold deposit, North China Craton: Proxies for ore fluids evolution and mineral exploration

Magmatic–hydrothermal evolution of the Koktokay No. 3 pegmatite, Altai, northwestern China: Constraints from in situ boron isotope and chemical compositions of tourmaline

Lithium–Cs–Ta-enriched (LCT-type) pegmatites are characterized by zoning texture and extreme enrichment of rare-metals. The role of fluids in zonation development and rare-metal mineralization remains a topic of debate. The Koktokay No. 3 pegmatite in northwestern China represents a typical LCT-type pegmatite characterized by economically significant Li–Be–Nb–Ta–Cs mineralization. This pegmatite exhibits a complete evolutionary sequence from outer to inner zones, with diverse rare-metal mineralization. Tourmaline is ubiquitously present in all textural zones of LCT-type pegmatites. In the Koktokay No. 3 pegmatite, the tourmalines exhibit a range of compositions from dravite and schorl to elbaite and rossmanite. The tourmalines in this pegmatite are characterized by significantly enriched light B isotope compositions (δ11B = −14.8‰ to −8.1‰), similar to those typically observed in most pegmatites derived from continental crust sources. The tourmalines in the outer zones have less variable δ11B values (−13.8‰ to −11.5‰) and are interpreted to have crystallized in a viscous magma. The tourmalines in the inner zones exhibit larger variations in δ11B values (−14.8‰ to −8.1‰) than those from the outer zones. The decreasing δ11B values of tourmalines from the outer to inner zones are attributed to the separation of an immiscible fluid phase that preferentially incorporated heavy B isotopes. The occurrence of hydrothermal tourmaline as veinlets indicates the exsolution of fluids in inner zones, with high δ11B values ranging from −10.2‰ to −9.3‰. Therefore, the hydrothermal fluid can be saturated when the magma has been strongly evolved. In addition to fractional crystallization, exsolved fluids play a significant role in the formation of internal zones and rare-metal mineralization in LCT-type pegmatites. The rare-metals are gradually enriched through fractional crystallization of magma, and the fluid contains mobile elements such as Cs that facilitate precipitation of rare-metal minerals.

Chemistry and boron isotope composition of tourmaline as a robust tool to characterize the origin of porphyry molybdenum systems: The case of Donggebi deposit in East Tianshan, China

Tourmaline is a chemically and mechanically stable mineral that commonly occurs in hydrothermal mineral systems, and has been used to trace the mineralization processes of many genetic types of ore deposits. Here we apply tourmaline chemistry and isotopic composition to trace the genesis of a porphyry Mo system for the first time. Tourmaline is widespread in the Donggebi Mo deposit in East Tianshan, NW China, where it occurs in five distinct associations: type PG disseminated in the porphyritic granite, TS as hydrothermal tourmalite in the country rocks (strata), V1 in quartz-molybdenite vein, V2 in quartz-polymetallic sulfide vein, and V3 quartz-calcite-fluorite vein. All the tourmaline types belong to the alkali group, with the V3 being schorl and the other types being dravite and schorl. The PG-type tourmalines partly inherit the features of the porphyritic granite, and are rich in F, Na, Al and Sc, and poor in Fe, Mg, Ca, Sr, Ba, Pb, V and Mo compared to the other types. They have low Fe3+ concentrations and low Fe3+/(Fe3++Fe2+) ratios, suggesting a reducing fluid system. They also display weaker Eu-depletion (with an average (Eu/Eu*)N value of 0.96) than the porphyritic granite, and are considered to be the products of interaction of the reducing fluids and the granites. The average (Eu/Eu*)N values of tourmalines decrease from 6.66 of type V1, 5.65 of type V2, to 4.80 of type V3, indicating that the fluids became progressively less reducing along with sulfide precipitation. The δ11B values of the tourmalines range between −15.9 ‰ and −12.5 ‰, resembling those of S-type granites or clastic sediment-sourced hydrothermal fluids. The tourmaline grains in our study do not display any remarkable δ11B variation from the cores to rims, indicating that the δ11B values of the fluids and their source were relatively constant.