Chemical composition and species attribution of tourmalines from a rare-metal pegmatite vein with scapolite, Sangilen Upland, Tuva

A detailed study of the chemical composition and substitutions in calcium tourmalines from a scapolite-bearing rare-metal pegmatite vein from the Sol’bel’der River basin has shown that their species attribution is determined by occupancy of octahedral site Y. The composition of the yellow tourmaline most abundant in the central part of the pegmatite bodyis rather constant and characterized by the ideal formula Ca(Mg₂Li)Al₆(Si₆O₁₈)(BO₃)₃(OH)₃F. Variations in the chemical composition of zonal tourmaline crystals from the contact part of the pegmatite are controlled by abrupt change in the chemical medium during their formation. The yellow cores of these crystals are close in composition to tourmaline from the central part of the pegmatite vein. The Mg content abruptly decreases toward the crystal margin: Mg²⁺ → Fe²⁺, 2Mg²⁺ → Li⁺ + Al³⁺, and Mg²⁺ + OH → Al³⁺ + O²⁻. The composition of dark green marginal zones in tourmaline is characterized by the ideal formula Ca(Al_1.5Li_1.5)Al₆(Si₆O₁₈)(BO₃)₃ (OH₂O)(F). The results indicate specific formation conditions of pegmatite. The crystallochemical formulas of the studied tourmalines allow us to regard them as new mineral species in the tourmaline group.     

东秦岭花岗伟晶岩中电气石地球化学特征及成矿指示意义

东秦岭地区是我国重要的花岗伟晶岩区及稀有金属成矿区.电气石在东秦岭各类花岗伟晶岩中广泛发育,通常在无矿化伟晶岩、铍矿化及锂矿化伟晶岩中呈黑色-深蓝色.本文旨在通过各类伟晶岩中电气石的对比研究揭示电气石地球化学特征对东秦岭伟晶岩矿化类型的指示作用.本文所研究电气石为作为东秦岭各类伟晶岩贯通矿物的黑电气石系列.在双峰村、碾...     

The use of tourmaline in geochemical prospecting for gold and copper mineralization

Chemical composition, unit cell parameters, and trace elements of tourmalines from Mesozoic gold-quartz-sulphide and gold-bearing copper-porphyry ore-magmatic systems of the Trans-Baikal area and Mongolia show that they belong to the specific schorl-dravite highly ferruginous oxytourmaline series. They are low in alumina (Al₂O₃ = 16–33%) and have MgO contents (up to 10%) and Fe₂O₃ (1%). There is a direct correlation of unit cell parameters (a,c,V) with total iron, which permits composition estimates from X-ray diffraction analyses. As a rule, these tourmalines contain high concentrations of Au, Pb and Cu, which are mainly hosted by inclusions of native gold and ore minerals. The highest As abundances are contained in the tourmalines of the copper-porphyry field.Two trends of isomorphic replacement are related to increasing Fe content of oxyferruginous tourmalines:(1) “Acid leaching” trend (less ferruginous part of the series) Mg + Fe²⁺ + 4Al + 40 4Fe³⁺ + 2 + 4(OH,F); and (2) “conjugate deposition” trend Mg + 1.5Fe²⁺ + 1.5Al + 4(OH,F) 4Fe³⁺ + 4O.These features distinguish tourmalines from gold-bearing systems from schorl-dravites of tin and rare-metal deposits. They may be used in metallogenic analyses, interpretation of the origin of primary and secondary anomalies, and assessment of the type and zonation of ore fields.     

Tourmaline from deposits of the Birgil’da-Tomino ore cluster, South Urals

Tourmalines from the Kalinovka porphyry copper deposit with epithermal bismuth-gold-basemetal mineralization and the Michurino gold-silver-base-metal prospect have been studied in the South Urals. Tourmaline from the Kalinovka deposit occurs as pockets and veinlets in quartz-sericite metasomatic rock and propylite. The early schorl-“oxy-schorl” [Fe_tot/(Fe_tot + Mg) = 0.66?0.81] enriched in Fe³⁺ is characterized by the homovalent isomorphic substitution of Fe³⁺ for Al typical of propylites at porphyry copper deposits. The overgrowing tourmalines of the second and third generations from propylite and quartz-sericite metasomatic rock are intermediate members of the dravite-magnesio-foitite solid solution series [Fe_tot/(Fe_tot + Mg) = 0.05?0.46] with homovalent substitution of Mg for Fe²⁺ and coupled substitution of ^X _? + ^YAl for ^XNa + ^YMg. These substitutions differ from the coupled substitution of ^YAl + ^WO^2? for ^YFe²⁺ + ^WOH^? in tourmaline from quartz-sericite rocks at porphyry copper deposits. At the Michurino prospect, the tourmaline hosted in the chlorite-pyrite-quartz veins and veinlets with Ag-Au-Cu-Pb-Zn mineralization is an intermediate member of the dravite-magnesio-foitite solid solution series [Fe_tot/(Fe_tot + Mg) = 0.20?0.31] with homovalent substitution of Mg for Fe²⁺ and coupled substitutions of ^X _? + ^YAl for ^XNa + ^YMg identical to that of late tourmaline at the Kalinovka deposit. Thus, tourmalines of the porphyry and epithermal stages are different in isomorphic substitutions, which allow us to consider tourmaline as an indicator of super- or juxtaposed mineralization.     

西藏南部花岗岩及有关岩石中的电气石

我国西藏南部,特别是高喜马拉雅地区,广泛分布着第三纪电气石花岗岩。这些岩石及其有关的伟晶岩和混合岩中都富含黑色电气石,显示了明显的区域性岩相学标志。本文对由本区和以北冈底斯地区这类岩石中采集的黑色电气石样品,作了某些物理性质、化学成分和穆斯堡尔效应的研究。     

Stable isotope compositions of tourmalines from granites and related hydrothermal rocks of the Karagwe-Ankolean belt,northwest Tanzania

Tourmaline is a ubiquitous mineral in the Mid-Proterozoic, peraluminous, syn- to post-tectonic granites and aplites and the related hydrothermal rocks of the Karagwe-Ankolean belt in northwest Tanzania. Electron microprobe analysis indicates that tourmalines from all of the intrusive and hydrothermal lithologies: (1) belong to the schorl-dravite solid-solution series; and (2) plot within the field occupied by tourmaline from Li-poor granitoids on the Fe-Al-Mg classification diagram. Oxygen isotope compositions range from +12.2 to +11.6‰ (SMOW) for magmatic tourmalines and from +10.8 to +9.8‰ for those of hydrothermal origin. Hydrogen isotope compositions vary from −79 to − 65‰ (SMOW) for magmatic tourmalines and from −99 to −84‰ for hydrothermal tourmalines. Water contents measured by manometry are constant at 3.0–3.2 wt.%. Within the broad grouping there arc systematic variations in both chemical [particularly Fe_tot/(Fe_tot + Mg ratio)] and isotopic composition that relate to evolving magmatic and hydrothermal conditions. Igneous differentiation [increasing Fe_tot/(Fe_tot + Mg) in magmatic tourmaline] has produced trends with higher δ¹⁸O in quartz, lower δ¹⁸O in tourmaline, and larger Δ_QTZ.−TOUR.-values, that reflect a combination of a reduction of crystallization temperature and an increase of Fe_tot/ (Fe_tot + Mg) in the residual melt. Subsequent cooling and interaction of an exsolved, B-rich magmatic fluid with the pelitic country rocks, resulted in the deposition of hydrothermal tourmaline with increasing Fe_tot/(Fe_tot + Mg) ratios, and progressively lower δ¹⁸O and δD -values.     

The crystal structure of an aluminum-rich schorl overgrown by boron-rich olenite from Koralpe, Styria, Austria

Summary The first natural tourmaline (because tourmaline with ^[4]B has also been synthesized, we distinguish here between natural and synthetic tourmaline) that has been unequivocally demonstrated to contain B as a substituent at the T sites was described from Koralpe, Styria, Austria. This colourless B-rich olenite occurs as rims overgrowing schorl (black crystals up to a few cm) that has not yet been structurally characterized. A crystal structure refinement (R = 0.019) of this Al-rich schorl shows that ^[4]B occurs in the overgrown schorl; the optimized occupants of the atomic positions yield ^X (Na_0.64Ca_0.10K_0.06□_0.20) ^Y (Fe²⁺ _1.72Al_1.08Ti_0.11Zn_0.03□_0.06) ^Z (Al_5.70Mg_0.20Fe_0.08 ²⁺Mn_0.02) (^[3]BO₃)_3.00 ^T (Si_5.76 ^[4]B_0.24)O₁₈ [F_0.11(OH)_3.31O_0.58]. This is the first known (Al-rich) schorl where a structure refinement has detected ^[4]B. Comparing the structure refinements and the chemical composition of the Koralpe schorl and other ^[4]B-bearing tourmalines with tourmalines which contain no ^[4]B, it is of interest that only structure refinements of tourmalines which are low in magnesium and with a higher component of olenite show substantial amounts of ^[4]B; the role of Mg in controlling the amount of ^[4]B is not known, but it seems that an Al-component on the Y site (olenite-component), a boron-enriched environment and special P-T-t conditions are necessary to get tourmaline with substantial amounts of ^[4]B. Received July 7, 2000; revised version accepted June 6, 2001     

Optical absorption spectroscopy of synthetic tourmalines

Tourmaline solid solutions containing Fe, Fe+ Ti, Cr, Ni, Cu, Co, Mn chromophoric centers have been grown hydrothermally at 650° C and 1,5 kbar on natural seeding plates close to the elbaite composition. The newly grown tourmalines were characterized by chemical analyses and optical absorption spectroscopy in the range 26316-5000 cm^-1 at 297 K and in the range 26316-9090 cm^-1 at 77 K. Most characteristic of Fe²⁺, Fe³⁺-bearing specimens is the presence of intensive σpolarized absorption bands caused by exchange-coupled Fe²⁺-Fe³⁺ pairs in Y- and Z-sites of the tourmaline structure. An additional intensive absorption band 12500 cm^-1 (σ-polarisation) appears in some specimens but is not yet found in spectra of natural tourmalines. The colour and spectroscopic properties of the Fe³⁺, Mn³⁺ and Cu²⁺ containing tourmalines are significantly affected by the presence of even the smallest Li-contents. The results suggest that Fe²⁺, Cu²⁺, Co²⁺, Ni²⁺-ions occupy, predominantly, Y-sites of the tourmaline structure, whereas the Cr³⁺-ions seem to enter the smaller Z-octachedra.     

Boron in metapelites controlled by the breakdown of tourmaline and retrograde formation of borosilicates in the Yanai area,Ryoke metamorphic belt,SW Japan

Tourmaline-out isograd formed by the breakdown of tourmaline is defined in the upper amphibolite-facies metapelites in the Yanai area, Ryoke metamorphic belt, SW Japan. The rim composition of tourmaline progressively becomes aluminous with ascending metamorphic grade, and the chemical zoning of tourmaline is controlled by ^X□AlNa_–1Mg_–1 and MgTi^YAl_–2 vectors in low- to medium-grade zones where muscovite is stable, whereas it is controlled by Mg(OH)^YAl_–1O_–1, CaMgO^X□_–1 ^YAl_–1(OH)_–1 and MgTi^YAl_–2 vectors in further higher–grade, muscovite-unstable zones. The size of tourmaline increases drastically where breakdown of muscovite+quartz takes place, probably due to the growth of tourmaline during breakdown of muscovite. On the high-temperature side of the tourmaline-out isograd, depletion of whole-rock boron is observed. Escape of boron-bearing melt or the fluid evolved from the melt during its crystallization probably caused this depletion, although locally trapped, boron-bearing melt or fluid formed irregularly shaped tourmaline and dumortierite during retrograde metamorphism.     

Li-bearing, disordered Mg-rich tourmaline from a pegmatite-marble contact in the Austroalpine basement units (Styria, Austria)

Pale-blue to pale-green tourmalines from the contact zone of Permian pegmatites to mica schists and marbles from different localities of the Austroalpine basement units (Rappold Complex) in Styria, Austria, are characterized. All these Mg-rich tourmalines have small but significant Li contents, up to 0.29 wt% Li₂O, and can be characterized as dravite, with FeO contents of ?~?0.9–2.7 wt%. Their chemical composition varies from ^X (Na_0.67Ca_0.19?K_0.02?_0.12) ^Y (Mg_1.26Al_0.97Fe²⁺ _0.36Li_0.19Ti⁴⁺ _0.06Zn_0.01?_0.15) ^Z (Al_5.31?Mg_0.69) (BO₃)₃ Si₆O₁₈ ^V (OH)₃? ^W [F_0.66(OH)_0.34], with a?=?15.9220(3), c?=?7.1732(2) Å to ^X (Na_0.67Ca_0.24?K_0.02?_0.07) ^Y (Mg_1.83Al_0.88Fe²⁺ _0.20Li_0.08Zn_0.01Ti⁴⁺ _0.01?_0.09) ^Z (Al_5.25?Mg_0.75) (BO₃)₃ Si₆O₁₈ ^V (OH)₃? ^W [F_0.87(OH)_0.13], with a?=?15.9354(4), c?=?7.1934(4) Å, and they show a significant Al-Mg disorder between the Y and the Z sites (R1?=?0.013–0.015). There is a positive correlation between the Ca content and?<?Y-O?>?distance for all investigated tourmalines (r?≈?1.00), which may reflect short-range order configurations including Ca and Fe²⁺, Mg, and Li. The tourmalines have X_Mg (X_Mg?=?Mg/Mg?+?Fe_total) values in the range 0.84–0.95. The REE patterns show more or less pronounced negative Eu and positive Yb anomalies. In comparison to tourmalines from highly-evolved pegmatites, the tourmaline samples from the border zone of the pegmatites of the Rappold Complex contain relatively low amounts of total REE (~8–36 ppm) and Th (0.1–1.8 ppm) and have low La_N/Yb_N ratios. There is a positive correlation (r?≈?0.91) between MgO of the tourmalines and the MgO contents of the surrounding mica schists. We conclude that the pegmatites formed by anatectic melting of mica schists and paragneisses in Permian time. The tourmalines crystallized from the pegmatitic melt, influenced by the metacarbonate and metapelitic host rocks.     

Cu- and Mn-bearing tourmalines from Brazil and Mozambique: crystal structures, chemistry and correlations

Cu- and Mn-bearing tourmalines from Brazil and Mozambique were characterised chemically (EMPA and LA-ICP-MS) and by X-ray single-crystal structure refinement. All these samples are rich in Al, Li and F (fluor-elbaite) and contain significant amounts of CuO (up to ~1.8 wt%) and MnO (up to ~3.5 wt%). Structurally investigated samples show a pronounced positive correlation between the <Y-O> distances and the (Li + Mn²⁺ + Cu + Fe²⁺) content (apfu) at this site with R ² = 0.90. An excellent negative correlation exists between the <Y-O> distances and the Al₂O₃ content (R ² = 0.94). The samples at each locality generally show a strong negative correlation between the X-site vacancies and the (MnO + FeO) content. The Mn content in these tourmalines depends on the availability of Mn, on the formation temperature, as well as on stereochemical constraints. Because of a very weak correlation between MnO and CuO we believe that the Cu content in tourmaline is essentially dependent on the availability of Cu and on stereochemical constraints.     

Development and Re‐Evaluation of Tourmaline Reference Materials for In Situ Measurement of Boron δ Values by Secondary Ion Mass Spectrometry

Six tourmaline samples were investigated as potential reference materials (RMs) for boron isotope measurement by secondary ion mass spectrometry (SIMS). The tourmaline samples are chemically homogeneous and cover a compositional range of tourmaline supergroup minerals (primarily Fe, Mg and Li end‐members). Additionally, they have homogeneous boron delta values with intermediate precision values during SIMS analyses of less than 0.6‰ (2s). These samples were compared with four established tourmaline RMs, that is, schorl IAEA‐B‐4 and three Harvard tourmalines (schorl HS#112566, dravite HS#108796 and elbaite HS#98144). They were re‐evaluated for their major element and boron delta values using the same measurement procedure as the new tourmaline samples investigated. A discrepancy of about 1.5‰ in δ¹¹B was found between the previously published reference values for established RMs and the values determined in this study. Significant instrumental mass fractionation (IMF) of up to 8‰ in δ¹¹B was observed for schorl–dravite–elbaite solid solutions during SIMS analysis. Using the new reference values determined in this study, the IMF of the ten tourmaline samples can be modelled by a linear combination of the chemical parameters FeO + MnO, SiO₂ and F. The new tourmaline RMs, together with the four established RMs, extend the boron isotope analysis of tourmaline towards the Mg‐ and Al‐rich compositional range. Consequently, the in situ boron isotope ratio of many natural tourmalines can now be determined with an uncertainty of less than 0.8‰ (2s).     

喜马拉雅东段库曲岩体锂、铍和铌钽稀有金属矿物研究及指示意义

稀有金属矿物记录了花岗伟晶岩成岩成矿的重要信息。喜马拉雅是全球著名的淡色花岗岩带,库曲岩体位于喜马拉雅东段的特提斯喜马拉雅岩系中。本文调查了库曲岩体的二云母花岗岩、白云母花岗岩、电气石花岗岩和花岗伟晶岩,其中,花岗伟晶岩涉及花岗岩的伟晶岩相和独立伟晶岩脉。库曲岩体产出的稀有金属矿物包括锂辉石、锂绿泥石、绿柱石、铌铁矿-钽铁矿、钇铀钽烧绿石和细晶石,它们主要赋存于似文象伟晶岩、石英-钠长石-白云母伟晶岩、块体长石-钠质细晶岩、块体长石-电气石钠质细晶岩、锂辉石-块体长石-细晶岩、白云母花岗岩的伟晶岩相以及电气石花岗岩内。显微镜观察、电子探针和LA-ICP-MS测试结果显示锂辉石具有四种产状,包括粗粒锂辉石自形-半自形晶、细粒锂辉石-石英镶嵌晶、中细粒锂辉石-钾长石-钠长石-云母镶嵌晶以及发育锂绿泥石的粗粒锂辉石,揭示了其形成时复杂的熔流体动荡结晶环境。绿柱石背散射电子图像（BSE）下呈均一结构和不均一结构（蚀变边、不规则分带和补丁分带）,元素替代机制包括通道-八面体替代、通道-四面体替代以及通道中碱金属阳离子间的置换。铌铁矿族矿物包括原生、蚀变边和不规则分带结构,部分被钇铀钽烧绿石和细晶石交代。与原生铌铁矿相比,蚀变边和不规则分带铌铁矿族矿物总体上富钽贫锰,显示了结晶分异、过冷却引起的过饱和以及流体作用。根据稀有金属矿物揭示的成因信息,独立伟晶岩脉（似文象伟晶岩）、白云母花岗岩的伟晶岩相和电气石花岗岩在岩浆分异程度、经历的演化过程、以及流体活动方面存在差异,很可能是不同期次岩浆活动的产物。库曲岩体绿柱石的Rb和Zn含量、以及铌铁矿族矿物的Sc₂O₃、SiO₂和PbO含量,与已有指示标志存在相关性,作为潜在指示标志仍需开展更多的研究工作。综合含锂辉石伟晶岩的产出、岩浆分异演化程度、多期花岗质岩浆活动、复杂的流体作用以及所属锂丰度高值区等因素,库曲岩体是喜马拉雅东段找锂的有利地段。     

Origin of tourmaline and oxide minerals from the metamorphosed Rampura Agucha Zn-Pb-(Ag) deposit, Rajasthan, India

Summary The sediment-hosted exhalative Rampura Agucha Zn-Pb-(Ag) deposit in Rajasthan, India, contains a number of oxide minerals which have been formed as a result of high-grade metamorphism. Gahnite (Zn_0.66–0.75Fe_0.13–0.24Mg_0.06–0.13Al_1.98–2.01O₄) is a common minor phase in the ores and formed from breakdown of sphalerite and Al-rich silicates. Pyrophanite-ilmenite solid solution (Fe_0.42–0.68Mn_0.32–0.58Ti_0.99–1.01O₃) is very rare and occurs, intergrown with rutile, as a result of unmixing of a Ti-Fe-Mn bearing precursor mineral.Dravite-rich tourmaline with Fe/(Fe+Mg) ratios around 0.02 occurs at the hanging wall contact of the orebody with the paragneisses and is intergrown with the ore minerals. Tourmaline from the stratabound ores is distinguished from schorl-rich tourmaline of two pegmatite samples which show Fe/(Fe+Mg) ratios of 0.43 and 0.62, respectively. It is argued that dravite-rich tourmaline (or another B-rich precursor mineral) is of premetamorphic origin. This dravite-rich tourmaline recrystallized during high-grade metamorphism when the metamorphic fluid, represented by H₂O-CO₂±CH₄-N₂ inclusions, was trapped.Amphiboles, muscovites and biotites from metamorphic rocks of the deposit display radiometric³⁹Ar/⁴⁰Ar cooling ages between 788 and 909 Ma.

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Dravit-reicher Turmalin und Oxide der metamorphen Zn-Pb-(Ag) Lagerstätte Rampura Agucha, Rajasthan, Indien

Zusammenfassung Die sedimentär-exhalative Zn-Pb-(Ag) Lagerstätte Rampura Agucha in Rajasthan, Indien, beinhaltet eine Reihe von Oxidmineralen, die infolge der hochgradigen Regional-metamorphose gebildet wurden. Gahnit (Zn_0.66–0.75Fe_0.13–0.24 Mg_0.06–0.13Al_1.98–2.01O₄) ist eine häufig anzutreffende Phase, die sich aus Sphalerit und Al-reichen Silikatphasen gebildet hat. Pyrophanit-Ilmenit (Fe_0.42–0.68Mn_0.32–0.58 T_0.99–1.01O₃) ist sehr selten und bildet, aufgrund der Entmischung eines Ti-Fe-Mn hältigen Vorläuferminerals, Verwachsungen mit Rutil.Dravit-reicher Turmalin mit einem Fe/(Fe+Mg) Verhältnis um 0.02 bildete sich gleichzeitig mit den Sulfidmineralen am Kontakt des Erzkörpers mit den hangenden Paragneisen der Lagerstätte. Dieser Turmalin unterscheidet sich klar von Schörlreichem Turmalin mit Fe/(Fe+Mg) Verhältnissen von 0.43 und 0.62 von zwei Pegmatiten. Die Herkunft dieses prämetamorphen Dravit-reichen Turmalins (oder dessen Vorgängerminerals) ist unklar. Dieser Turmalin rekristallisierte während der Metamorphose, wobei er das metamorphe H₂O-CO₂±CH₄-N₂-Fluid in Form von primären Einschlüssen einschloß.Amphibol, Muskowit und Biotit wurden mittels³⁹Ar/⁴⁰Ar-Methode datiert und liefern radiometrische Abkühlungsalter zwischen 788 und 909 Ma.

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With 8 Figures     

Tourmalinization related to Late Proterozoic-Early Palaeozoic lode gold mineralization in the Bin Yauri area, Nigeria

Three types of tourmaline occurrence have been identified in the area of Bin Yauri, Nigeria, mesothermal lode-gold mineralization. These are: (1) stratabound tourmalinites in pelitic metasediments, (2) tourmaline in a hydrothermal alteration assemblage within hornfelsed wall rocks, (3) tourmaline in auriferous quartz and quartz-carbonate veins. Although the tourmaline occurrences are all within or close to the contact aureole of a granodiorite intrusion, geochemical characteristics of the tourmalines are broadly similar and reflect a common metasedimentary source. Two stages of tourmalinization are envisaged. The earlier (ca. 1100 Ma) involved syngenetic-diagenetic formation of tourmalinites, while the later (ca. 500 Ma) involved epigenetic (hydrothermal) tourmaline-gold mineralization, possibly derived by dehydration and devolatilization of metasedimentary sequences containing tourmaline-rich rocks or tourmalinites. Electron microprobe analyses indicate that the tourmalines are intermediate members of the schorl-dravite solid solution series. Plots involving FeO, MgO, and/or Al₂O₃ from these analyses are used to constrain the sources and processes of tourmalinization. Two metallogenic implications are derived from this study. One is that, although the tourmalinites are barren of gold and base metal mineralization, their occurrences nevertheless encourages exploration for syngenetic-exhalative massive sulphide deposits in the region. The other implication applies to the potential use of tourmaline in deciphering the physico-chemical conditions of gold-mineralizing fluids in the Bin Yauri area.     

Tourmaline from quartz lenses of the Urtui granite pluton,Strel’tsovka orefield,Ttansbaikal krai

Quartz-tourmaline lenses, around which host granite is impregnated by uraninite, have been found among porphyritic granite with large phenocrysts of the Urtui pluton in the Ttansbaikal krai framing the Strel’tsovka volcano-tectonic structure. Two generations of tourmaline are distinguished. Most individual crystals belong to the first generation attributed to “fluor-schorl”; tourmaline-II attributed to schorl occurs as thin rims overgrowing tourmaline-I. The major type of cation isomorphic substitution in both tourmalines is Fe²⁺ → Mg. The Fe³⁺/Fe_tot value and Li content in the average sample are 2% and 80 ppm, respectively. The high F content, comparatively high Li, low Fe³⁺/Fe_tot value, and character of cation isomorphic substitution indicate that the tourmaline relates to greisens. The combination of these features allows one to distinguish greisen-type tourmaline-bearing rocks. The impregnated uranium mineralization in granite of the Urtui pluton, one of the probable sources of uranium in economic U ore of the Strel’tsovka deposit, is suggested to be caused by greisenization and the formation of quartz-tourmaline lenses.     

Tourmalinites from the stratiform peraluminous metamorphic suite of the Central Namaqua Mobile Belt (South Africa)

Tourmalinites as proximal fades equivalents of stratiform peraluminous metamorphic rocks occur stratigraphically below base metal deposits and above thick metarhyolite horizons. Their premetamorphic protoliths are believed to have originated by tourmaline precipitation from exhalative B-, F- and W-rich brines also transporting aluminous clay colloids and dissolved silica. Tourmaline chemistry is used as an effective petrogenetic sensor. The tourmalines are Al-saturated, alkali-deficient dravite-schorl solid solutions, which are in the compositional range of tourmalines originated by exhalative processes. F-substitution in tourmalines is governed by Fe-F-avoidance. F is relatively enriched in the tourmalines and can potentially be used as a tracer for the source of primary hydrothermal solutions. Ti is introduced into the tourmalines by the substitution scheme Ti+Al^IV=Al_Y+Si. The high Ti-contents of the tourmalines as well as those of coexisting muscovites represent evidence of high-temperature metamorphism. Many tourmalines exhibit continuous zoning, which can partly be attributed to external fluid influx near peak metamorphic conditions.     

Genesis of yellow manganese-rich elbaite from the Canary mining area,Lundazi, Zambia

The most important source of yellow gem elbaite is the Canary mining area in the Lundazi District of eastern Zambia. The tourmaline has been mined since 1983 from both pegmatite and eluvial/alluvial deposits, in colors typically ranging from yellow-green to yellow to orange and brown; much of the orange-to-brown material is heated to attain a ‘golden’ or ‘canary’ yellow color. The elbaite is Mn-rich (up to 9.18 wt% MnO documented in the literature) and contains small amounts of Ti and little or no Fe. The distinctive composition of this tourmaline is probably the result of the early crystallization of abundant schorl from an unusual B-rich, Li-poor pegmatite melt, which depleted Fe while conserving Mn until the late-stage crystallization of gem pockets. The simple mineralogy of the pegmatite consists of feldspars, quartz, and tourmaline; the lack of micas, phosphates, or Li minerals, and the presence of very little garnet, allowed Mn to fractionate to high levels during pegmatite crystallization. The presence of abundant gem tourmaline in a Li-poor pegmatite is highly unusual.     

The Al (Nb,Ta) Ti(in−2) substitution in titanite: the emergence of a new species?

Summary The highest (Nb, Ta) content ever encountered in titanite is reported from the Maríkov 11 pegmatite in northern Moravia, Czech Republic. This dike is a member of a pegmatite swarm of the beryl-columbite subtype, metamorphosed under conditions of the amphibolite facies. The pegmatite carries, i.a., rare tantalian rutile intergrown with titanian ixiolite, titanian columbite-tantalite, fersmite and microlite. Fissures generated in the Nb, Ta oxide minerals during deformation are filled with titanite, formed by reaction of the oxide minerals with metamorphic pore fluids. The titanite displays limited degrees of substitutions Na(Ta > Nb)(CaTi)_–1, (Ta > Nb)₄Ti_–4Si_–1 and AI(OH, F)(TiO)_–1, but an extensive (and occasionally the sole significant) substitution (Al > Fe³⁺)(Ta > Nb)Ti_–2, responsible for widespread oscillatory zoning. This substitution reduces the proportion of the titanite componentsensu stricto, CaTiSiO₄,O, to less than 50 mole % in many analyzed spots. The extreme composition corresponds to (Ca_0.994Na_0.011)(Ti_0.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). However, so far this substitution fails to generate compositions that would define a new species.

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Zusammenfassung Die AI(Nb, Ta)Ti_–2 Substitution im Titanit: Auftauchen einer neuen Mineralspecies? Die höchsten (Nb, Ta) Gehalte, die jemals für Titanit gefunden wurden, werden für den Maríkov II Pegmatit in Nordmähren, Tschechei, berichtet. Der Intrusivgang ist Teil eines Amphibolit-faziell überprägten Pegmatitschwarms vom Beryll-Columbit Subtypus Der Pegmatit führt u.a. seltene tantalbetonte Rutile verwachsen mit titanbetontem Ixiolith, titanbetontem Columbit-Tantalit, Fersmit and Mikrolith. Deformationsbedingte Frakturen in den (Nb, Ta) Oxiden sind mit Titanit, als Folge der Reaktion der metamorphen Porenlösungen mit den Oxidmineralen, verkittet. Titanit zeigt begrenzte Substitutionen Na(Ta > Nb)(CaTi)_–1,(Ta > Nb)₄Ti_–4Si_–1 and Al(OH, F)(TiO)_–1, aber extensive (und gelegentlich einzig bedeutsame) Substitution (Al >> Fe³⁺)(Ta > Nb)Ti_–2, die eine weitverbreitete, oszillierende Zonierung hervorruft. Diese Substitution verringert den Anteil der Titanit-Komponentesensu stricto, CaTiSiO,O, auf weniger als 50 Mol% in vielen Analysen. Die Extremzusammensetzung entspricht Ca_0.994Na_0.11) (T_10.436Sn_0.007Al_0.280Fe³⁺ _0.006Ta_0.199Nb_0.079)Si_0.988O₄(O_0.974F_0.026). Das AusmaB dieser Substitution ist unzureichend, um eine neue Mineralspecies zu definieren.

     

Mineral chemistry and chemical zoning in tourmalines, Pampa del Tamboreo, San Luis, Argentina

Tourmalinites that are distally associated with tungsten deposits of the Pampa del Tamboreo area, San Luis, Argentina, contain tourmalines retaining evidence for its origin and evolution. Tourmaline grains uncommonly contain small grains of detrital tourmaline. Analysis of a single detrital tourmaline grain reveals that it is a Ca-rich “oxy-dravite”. Proximal to the detrital cores there are inner domains of asymmetric tourmaline overgrowths that developed during low grade metamorphism. Volumetrically dominant tourmaline overgrowths in the outer domain are concentrically zoned aluminous dravite and “oxy-dravite” with Al/(Al + Fe + Mg) = 0.71–0.74 and Mg/(Mg + Fe) = 0.64–0.71. Variability of Al is primarily controlled by the deprotonation substitution R + OH⁻ = Al + O²⁻ (where R = Fe + Mg), and is a function of the activity of H₂O. A likely evolutionary scenario is one in which volcanogenic material is altered by hydrothermal fluids in the sea floor resulting in an aluminous and magnesian residuum. With further hydrothermal circulation and incipient metamorphism, boron-rich fluids are expelled from metasedimentary and metavolcanic basement rocks and develop Mg-rich tourmalinites in the aluminous, magnesian host rocks. The tourmalinization process occurs over a range of metamorphic conditions and with fluids of variable activity of H₂O.