Pavel Uher

Nomenclature of the tourmaline-supergroup minerals

Abstract A nomenclature for tourmaline-supergroup minerals is based on chemical systematics using the generalized tourmaline structural formula: XY3Z6(T6O18)(BO3)3V3W, where the most common ions (or vacancy) at each site are X = Na1+, Ca2+, K1+, and vacancy; Y = Fe2+, Mg2+, Mn2+, Al3+, Li1+, Fe3+, and Cr3+; Z = Al3+, Fe3+, Mg2+, and Cr3+; T = Si4+, Al3+, and B3+; B = B3+; V = OH1- and O2-; and W = OH1-, F1-, and O2-. Most compositional variability occurs at the X, Y, Z, W, and V sites. Tourmaline species are defined in accordance with the dominant-valency rule such that in a relevant site the dominant ion of the dominant valence state is used for the basis of nomenclature. Tourmaline can be divided into several groups and subgroups. The primary groups are based on occupancy of the X site, which yields alkali, calcic, or X-vacant groups. Because each of these groups involves cations (or vacancy) with a different charge, coupled substitutions are required to relate the compositions of the groups. Within each group, there are several subgroups related by heterovalent coupled substitutions. If there is more than one tourmaline species within a subgroup, they are related by homovalent substitutions. Additionally, the following considerations are made. (1) In tourmaline-supergroup minerals dominated by either OH1- or F1- at the W site, the OH1--dominant species is considered the reference root composition for that root name: e.g., dravite. (2) For a tourmaline composition that has most of the chemical characteristics of a root composition, but is dominated by other cations or anions at one or more sites, the mineral species is designated by the root name plus prefix modifiers, e.g., fluor-dravite. (3) If there are multiple prefixes, they should be arranged in the order occurring in the structural formula, e.g., “potassium-fluor-dravite.”

Extreme variation and apparent reversal of Nb-Ta fractionation in columbite-group minerals from the Scheibengraben beryl-columbite granitic pegmatite, Maršíkov, Czech Republic

Compositional variation in columbite-group minerals was studied from the beryl-columbite pegmatite at Scheibengraben, Marsikov, Northern Moravia, Czech Republic. The pegmatite consists of five textural-paragenetic units, from the least to the most evolved: volumetrically dominant coarse-grained unit, subordinate graphic and blocky units and a minor cleavelandite unit. Saccharoidal albite unit is rather randomly distributed within the dike. It replaces and/or crosscuts all other units except the cleavelandite unit. Columbite-group minerals are the dominant Nb,Ta-oxide phases in all units. They are associated with other Nb,Ta-oxide minerals: minerals of the pyrochlore subgroup and fersmite in the coarse-grained unit, and minerals of the microlite subgroup, ferrotapiolite and rynersonite in the cleavelandite unit. The extreme Nb-Ta [Ta/(Ta+Nb) = 0.06 to 0.97 (microlite 0.99)] and appreciable Fe-Mn [Mn/(Mn+Fe) = (ferrotapiolite 0.22) 0.35 to 0.90] fractionations in columbite-group minerals differ from those observed in beryl pegmatites examined to date, but they are comparable with those in some highly fractionated, complex, Li-rich pegmatites. High activity of F (facilitated by low contents of B, P and Li in the pegmatite melt) very likely maximized such an extensive Nb-Ta fractionation, over and above differential solubilities of columbite and tantalite in pegmatite melt. The apparent reversal of Nb-Ta and Fe-Mn fractionation found in columbite from the saccharoidal albite unit seems to be an artefact from early units (particularly the coarse-grained one), which were extensively replaced by saccharoidal albite.

Magmatic and post-magmatic Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE oxide minerals in A-type metagranite: an example from the Turčok massif, the Western Carpathians, Slovakia

Abstract An electron microprobe study of Y-REE-Th phosphate, silicate and Nb-Ta-Y-REE accessory-mineral assemblages revealed the compositional variations and evolution in post-orogenic, hypersolvus Permian A-type metagranite from Turčok, in the Gemeric Unit, of the Western Carpathians, eastern Slovakia. Prismatic zircon I and allanite-(Ce) are primary magmatic phases. However, the late-magmatic to early-subsolidus processes led to the formation of a more complex younger assemblage: bipyramidal zircon II, xenotime-(Y), thorite, gadolinite-hingganite-(Y), Nb-Ta-Y-REE oxide phases [fergusonite-(beta)/samarskite-(Y), aeschynite/polycrase-(Y), and Nb-rich rutile?] and possibly monazite-(Ce). However, monazite-(Ce) and the partial alteration of allanite-(Ce), xenotime-(Y) and the Nb-Ta-Y-REEminerals are probably connected with a younger Alpine metamorphic overprint of the granite. Thorite appears as a solid solution in the thorite-xenotime-zircon series; it is also enriched in Al. Fergusonite-(beta)/samarskite-(Y) and especially aeschynite/polycrase-(Y) show increased P, Si and Al contents.

Oxy-schorl, Na(Fe2+2Al)Al6Si6O18(BO3)3(OH)3O, a new mineral from Zlatá Idka, Slovak Republic and Přibyslavice, Czech Republic

Abstract Oxy-schorl (IMA 2011-011), ideally Na(Fe22+Al)Al6Si6O18(BO3)3(OH)3O, a new mineral species of the tourmaline supergroup, is described. In Zlatá Idka, Slovak Republic (type locality), fan-shaped aggregates of greenish black acicular crystals ranging up to 2 cm in size, forming aggregates up to 3.5 cm thick were found in extensively metasomatically altered metarhyolite pyroclastics with Qtz+Ab+Ms. In Přibyslavice, Czech Republic (co-type locality), abundant brownish black subhedral, columnar crystals of oxy-schorl, up to 1 cm in size, arranged in thin layers, or irregular clusters up to 5 cm in diameter, occur in a foliated muscovite-tourmaline orthogneiss associated with Kfs+Ab+Qtz+Ms+Bt+Grt. Oxy-schorl from both localities has a Mohs hardness of 7 with no observable cleavage and parting. The measured and calculated densities are 3.17(2) and 3.208 g/cm3 (Zlatá Idka) and 3.19(1) and 3.198 g/cm3 (Přibyslavice), respectively. In plane-polarized light, oxy-schorl is pleochroic; O = green to bluish-green, E = pale yellowish to nearly colorless (Zlatá Idka) and O = dark grayish-green, E = pale brown (Přibyslavice), uniaxial negative, ω = 1.663(2), ε = 1.641(2) (Zlatá Idka) and ω = 1.662(2), ε = 1.637(2) (Přibyslavice). Oxy-schorl is trigonal, space group R3m, Z = 3, a = 15.916(3) Å, c = 7.107(1) Å, V = 1559.1(4) Å3 (Zlatá Idka) and a = 15.985(1) Å, c = 7.154(1) Å, V = 1583.1(2) Å3 (Přibyslavice). The composition (average of 5 electron microprobe analyses from Zlatá Idka and 5 from Přibyslavice) is (in wt%): SiO2 33.85 (34.57), TiO2 <0.05 (0.72), Al2O3 39.08 (33.55), Fe2O3 not determined (0.61), FeO 11.59 (13.07), MnO <0.06 (0.10), MgO 0.04 (0.74), CaO 0.30 (0.09), Na2O 1.67 (1.76), K2O <0.02 (0.03), F 0.26 (0.56), Cl 0.01 (<0.01), B2O3 (calc.) 10.39 (10.11), H2O (from the crystal-structure refinement) 2.92 (2.72), sum 99.29 (98.41) for Zlatá Idka and Přibyslavice (in parentheses). A combination of EMPA, Mössbauer spectroscopy, and crystal-structure refinement yields empirical formulas (Na0.591Ca0.103□0.306)Σ1.000(Al1.885Fe2+ 1.108Mn0.005Ti0.002)Σ3.000(Al5.428Mg0.572)Σ6.000(Si5.506Al0.494)Σ6.000O18 (BO3)3(OH)3(O0.625OH0.236F0.136Cl0.003)Σ1.000 for Zlatá Idka, and (Na0.586Ca0.017K0.006□0.391)Σ1.000(Fe2+1.879Mn0.015 Al1.013Ti0.093)Σ3.00(Al5.732Mg0.190Fe3+0.078)Σ6.000(Si5.944Al0.056)Σ6.000O18(BO3)3(OH)3(O0.579F0.307OH0.115)Σ1000 for Přibyslavice. Oxy-schorl is derived from schorl end-member by the AlOFe-1(OH)-1 substitution. The studied crystals of oxy-schorl represent two distinct ordering mechanisms: disorder of R2+ and R3+ cations in octahedral sites and all O ordered in the W site (Zlatá Idka), and R2+ and R3+ cations ordered in the Y and Z sites and O disordered in the V and W sites (Přibyslavice).

Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and origin

Sapphires related to alkali basalts from the Cerová Highlands, Western Carpathians (southern Slovakia): composition and origin Blue, grey-pink and pink sapphires from the Cerová Highlands, Western Carpathians (southern Slovakia) have been studied using CL, LA-ICP-MS, EMPA, and oxygen isotope methods. The sapphire occurs as (1) clastic heavy mineral in the secondary sandy filling of a Pliocene alkali basaltic maar at Hajnáčka, and (2) crystals in a pyroxenebearing syenite/anorthoclasite xenolith of Pleistocene alkali basalt near Gortva. Critical evaluation of compositional diagrams (Fe, Ti, Cr, Ga, Mg contents, Fe/Ti, Cr/Ga, Ga/Mg ratios) suggests a magmatic origin for clastic blue sapphires with lower Cr and Mg, but higher Fe and Ti concentrations in comparison to the grey-pink and pink varietes, as well as similar compositional trends with blue sapphire from the Gortva magmatic xenolith. Moreover, blue sapphires show similar δ18O values: 5.1 ‰ in the Gortva xenolith, 3.8 and 5.85 ‰ in the Hajnáčka placer, closely comparable to mantle to lower crustal magmatic rocks. On the contrary, pink and grey-pink sapphires show higher Cr and Mg, but lower Fe and Ti contents and their composition points to a metamorphic (metasomatic) origin.

SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatism

SHRIMP U-Th-Pb zircon dating of the granitoid massifs in the Malé Karpaty Mountains (Western Carpathians): evidence of Meso-Hercynian successive S- to I-type granitic magmatism Representative granitic rock samples from the Malé Karpaty Mountains of the Western Carpathians (Slovakia) were dated by the SHRIMP U-Th-Pb isotope method on zircons. Oscillatory zoned zircons revealed concordant Mississippian magmatic ages: 355±5 Ma in Bratislava granodiorite, and 347±4 Ma in Modra tonalite. The results document nearly synchronous, successive Meso-Hercynian plutonic events from S-type to I-type granites. The Neo-Proterozoic inherited zircon cores (590±13 Ma) were identified in the Bratislava S-type granitic rocks whereas scarce Paleo-Proterozoic inherited zircons (1984±36 Ma) were detected within the Modra I-type tonalites.

Metamorphic vanadian-chromian silicate mineralization in carbon-rich amphibole schists from the Malé Karpaty Mountains, Western Carpathians, Slovakia

Abstract Mineralization, involving vanadian-chromian silicates, has been studied in Lower Paleozoic, carbon-rich amphibole schists with pyrite and pyrrhotite near Pezinok, southwest Slovakia. A detailed electron microprobe study has revealed the presence of V,Cr-rich garnet, clinozoisite, and muscovite, associated with amphiboles (magnesiohornblende, tremolite, actinolite, and edenite), diopside, and albite. The garnet contains 5-19 wt% V2O3, 5-11 wt% Cr2O3, and 2-13 wt% Al2O3 (16-64 mol% goldmanite, 19-36 mol% uvarovite, and 9-59 mol% grossular end-members). The garnet is unzoned or shows V-rich cores and Al-rich rims, or irregular coarse oscillatory zoning with V, Cr, and Al, locally involving Ca and Mn as well. The V,Cr-rich clinozoisite to mukhinite and “chromian clinozoisite” contains 2-9.5 wt% V2O3 and 1.5-11 wt% Cr2O3; the muscovite contains 2.5-8 wt% V2O3 and 0-7 wt% Cr2O3. The mineralization originated from primarily V-, Cr-, and C-rich mafic pyroclastic rocks, affected by volcano-exhalative processes. These rocks were weakly metamorphosed during early Hercynian regional metamorphism (M1), followed by late-Hercynian contact metamorphism (M2) with crystallization of V,Cr-rich silicates, diopside, amphiboles, phlogopite, titanite, albite, quartz, carbonate, pyrite, and pyrrhotite. The youngest Alpine(?) retrograde metamorphic event (M3) is connected with production of V,Cr-poor muscovite, clinochlore, clinozoisite, pumpellyite-(Mg), prehnite, quartz, and carbonates, under prehnite-pumpellite facies conditions.

Rare-element granitic pegmatite of Miocene age emplaced in UHP rocks from Visole, Pohorje Mountains (Eastern Alps, Slovenia): accessory minerals, monazite and uraninite chemical dating

Abstract The granitic pegmatite dike intruded the Cretaceous UHP rocks at Visole, near Slovenska Bistrica, in the Pohorje Mountains (Slovenia). The rock consists mainly of K-feldspar, albite and quartz, subordinate muscovite and biotite, while the accessory minerals include spessartine-almandine, zircon, ferrocolumbite, fluorapatite, monazite- (Ce), uraninite, and magnetite. Compositions of garnet (Sps48-49Alm45-46Grs + And3-4 Prp1.5-2), metamict zircon with 3.5 to 7.8 wt. % HfO2 [atom. 100Hf/(Hf + Zr) = 3.3-7.7] and ferrocolumbite [atom. Mn/(Mn + Fe) = 0.27-0.43, Ta/(Ta + Nb) = 0.03-0.46] indicate a relatively low to medium degree of magmatic fractionation, characteristic of the muscovite - rare-element class or beryl-columbite subtype of the rare-element class pegmatites. Monazite-(Ce) reveals elevated Th and U contents (≤11 wt. % ThO2, ≤5 wt. % UO2). The monazite-garnet geothermometer shows a possible precipitation temperature of ~495 ± 30 °C at P~4 to 5 kbar. Chemical U-Th-Pb dating of the monazite yielded a Miocene age (17.2 ± 1.8 Ma), whereas uraninite gave a younger (~14 Ma) age. These ages are comtemporaneous with the main crystallization and emplacement of the Pohorje pluton and adjacent volcanic rocks (20 to 15 Ma), providing the first documented evidence of Neogene granitic pegmatites in the Eastern Alps. Consequently, the Visole pegmatite belongs to the youngest rare-element granitic pegmatite populations in Europe, together with the Paleogene pegmatite occurrences along the Periadriatic (Insubric) Fault System in the Alps and in the Rhodope Massif, as well as the Late Miocene to Pliocene pegmatites in the Tuscany magmatic province (mainly on the Island of Elba).

Intensive low-temperature tectono-hydrothermal overprint of peraluminous rare-metal granite: a case study from the Dlhá dolina valley (Gemericum, Slovakia)

Abstract A unique case of low-temperature metamorphic (hydrothermal) overprint of peraluminous, highly evolved rare-metal S-type granite is described. The hidden Dlhá dolina granite pluton of Permian age (Western Carpathians, eastern Slovakia) is composed of barren biotite granite, mineralized Li-mica granite and albitite. Based on whole-rock chemical data and evaluation of compositional variations of rock-forming and accessory minerals (Rb-P-enriched K-feldspar and albite; biotite, zinnwaldite and di-octahedral micas; Hf-(Sc)-rich zircon, fluorapatite, topaz, schorlitic tourmaline), the following evolutionary scenario is proposed: (1) Intrusion of evolved peraluminous melt enriched in Li, B, P, F, Sn, Nb, Ta, and W took place followed by intrusion of a large body of biotite granites into Paleozoic metapelites and metarhyolite tuffs; (2) The highly evolved melt differentiated in situ forming tourmaline-bearing Li-biotite granite at the bottom, topaz-zinnwaldite granite in the middle, and quartz albitite to albitite at the top of the cupola. The main part of the Sn, Nb, and Ta crystallized from the melt as disseminated cassiterite and Nb-Ta oxide minerals within the albitite, while disseminated wolframite appears mainly within the topaz-zinnwaldite granite. The fluid separated from the last portion of crystallized magma caused small scale greisenization of the albitite; (3) Alpine (Cretaceous) thrusting strongly tectonized and mylonitized the upper part of the pluton. Hydrothermal low-temperature fluids enriched in Ca, Mg, and CO2 unfiltered mechanically damaged granite. This fluid-driven overprint caused formation of carbonate veinlets, alteration and release of phosphorus from crystal lattice of feldspars and Li from micas, precipitating secondary Sr-enriched apatite and Mg-rich micas. Consequently, all bulk-rock and mineral markers were reset and now represent the P-T conditions of the Alpine overprint.

Foordite-thoreaulite, Sn2+Nb2O6–Sn2+Ta2O6: compositional variations and alteration products

The foordite-thoreaulite series of Sn 2+ -bearing Nb, Ta-oxide phases is a rare constituent of complex, rare-element, Li-Cs-Ta-rich (LCT-family) granitic pegmatites with local low f O 2 environment. In this study, detailed electron-microprobe analyses (EMPA) reveal a broad range of nearly continuous foordite-thoreaulite solid solution: at. Ta/(Ta+Nb) =0.23–0.92. Valence equilibration of the formulae suggests up to 6 at.% of total Sn in Sn 4+ state occupying the octahedral Nb, Ta-populated B -site. Three substitution mechanisms dominate the foordite-thoreaulite chemistry: NbTa −1 , Pb 2+ Sn −1 2+ and Sb 3+ Sn 4+ Sn −1 2+ (Nb, Ta) −1 5+ ; Pb 2+ and Sb 3+ occupy ⩽ 21.5 at. % and ⩽ 7.6 at. % of the A -site position, respectively. Sb shows positive correlation with Ta/(Ta+Nb). Primary large foordite-thoreaulite crystals are compositionaly homogeneous, only areas of secondary alteration show small zones of recrystallized foordite-thoreaulite and grains with diffuse or patchy zoning, variable Nb/Ta ratio and locally increased Pb content. Influx of late-magmatic to hydrothermal fluids and/or alkali elements under higher f O 2 causes breakdown of foordite-thoreaulite and production of cassiterite and numerous Nb, Ta-oxide minerals. At Lutsiro pegmatite, foordite is replaced by mosaic fine-grained aggregate of secondary foordite-thoreaulite + columbite-tantalite + Ta-rich cassiterite. Simpsonite is present in Manono and Maniema pegmatites. Local replacement of foordite-thoreaulite by alkali-bearing Nb-Ta phases is widespread; irregular veinlets and zones of lithiotantite, calciotantite, irtyshite/natrotantite, cesplumtantite, a mineral with composition (Na, Cs) 2 (Pb, Sb 3+ ) 3 Ta 8 O 24 , rankamaite, fersmite, and pyrochlore-group minerals occur.