Search

Spherical crystals in minerals from prismatine-bearing rock from Waldheim, including ultrahigh-pressure (UHP) minerals such as stishovite and coesite, were previously described in uncommon crustal environments. To determine if this was an outlier phenomenon, we searched for equivalent inclusions in other rocks, which we indeed discovered in a Variscan tin-bearing granite sensu stricto from the Erzgebirge/Germany. The identification of more examples of this phenomenon implies a novel, very rapid transcrustal transport mechanism, which, however, is not unique. We demonstrate the unusual occurrence of UHP minerals (moissanite, diamond, lonsdaleite, stishovite, coesite, kumdykolite, and cristobalite-II) in topaz the investigated granitic samples, which reflects the direct interaction of mantle and crust via supercritical fluids or extremely volatile-rich melts. Mostly, the UHP minerals we recognized occur as tiny inclusions in moissanite. The trapping by this mineral prevents a fast reaction in an exogenous environment. [ABSTRACT FROM AUTHOR]

We used presence/absence data of 5,160 red wood ant nests (RWA; Formica polyctena) acquired in a systematic large-scale area-wide survey in two study areas (â350 ha) in the Oberpfalz, NE Bavaria, Germany to explore for the first time the influence of variable (e.g., forest type, tree age) and quasi-invariant factors (e.g., tectonics, geochemical composition of the bedrock) on nest size and spatial distribution for Variscan granites. A combination of the forest type (mature pine-dominated forests (â80-140 years) as main variable factor and the geochemical property of the Variscan granites with their high natural Radon potential and moderate heat production as main quasi-invariant factor could explain the high nest numbers in both study areas. In addition, the spatially clustered distribution patterns of the observed nests suggest a strong interaction between nests and their quasi-invariant environment, especially the directionality of the present-day stress field and the direction of the tectonically formed "Erbendorfer Line". In general, such a combination of variable and quasi-invariant factors can be addressed as particularly favorable RWA habitats. [ABSTRACT FROM AUTHOR]

Much of the Mid-European basement has been consolidated during the Variscan Orogeny and includes large volumes of granitic intrusions. Gamma radiation spectroscopic measurements in three study areas along the western margin of the Bohemian Massif give a record of radiogenic element concentrations in the Variscan granites. Most intrusions of the Fichtelgebirge (except for the Tin Granite) and intrusive complexes in the Bavarian Forest show Th/U ratios exceeding unity, most likely related to abundance of monazite. In contrast, some of the Oberpfalz granites located near the Saxothuringian- Moldanubian boundary (Flossenbürg, Steinwald and Friedenfels types) are characterized by higher uranium concentrations and thus Th/U < 1. The low Th/U ratios here are in agreement with a possible U mobilisation along the Saxothuringian-Moldanubian contact zone observed in previous studies. Heat production rates of granites in the three study areas vary between 3.9 and 8.9 µW/m3, with a mean of 4.9 µW/m3. This classifies the intrusions as moderate- to high-heat-producing granites. Considering the huge volume of granitic bodies in the Variscan crust of the Bohemian Massif, the contribution of in situ radiogenic heat production had to have a major impact and should be considered in further thermal modeling. [ABSTRACT FROM AUTHOR]

The Variscan Rand Granite as defined in this paper is a deformed I-type biotite granite that intruded along the southern-to-southeastern margin of the Central Schwarzwald Gneiss Complex. Former K-feldspar megacrysts (now porphyroclasts) of this K–Mg-rich alkali-calcic granite frequently show zonal crystallographic arrangement of mineral inclusions and are enclosed in a matrix of plagioclase, K-feldspar, quartz, biotite, apatite, zircon, and magnetite. Minor sphene and allanite are mostly altered. K-feldspar is orthoclase with perthitic exsolutions. Myrmekite is common and typically replaces marginal K-feldspar. Both feldspars show cataclastic and incipient ductile deformation that took place within the stability field of biotite (≥ 400 °C) as proven by grey varieties of Rand Granite with stable biotite. At most places, however, the Rand Granite shows a reddish colour, caused by late-stage chloritization of biotite and formation of hematite within K-feldspar. Furthermore, plagioclase became partially altered to sericite. This hydrothermal alteration took place at temperatures below the stability of biotite (< 400 °C). In situ ion probe U–Pb dating on zircon gave a concordant age of 330.9 ± 4.8 Ma (2σ), interpreted as the intrusion age of the Rand Granite. A large number of younger concordant to slightly discordant zircon ages between 309 and 90 Ma are interpreted to be due to episodic Pb loss during hydrothermal alteration. The Rand Granite apparently does not contain zircon domains older than the intrusion age and, furthermore, shows relatively high Zr contents (247–358 µg/g). These characteristics suggest high magma temperatures of at least 850–900 °C. The granitic magma most probably resulted from remelting of K-rich mafic to intermediate rocks in the middle crust at H2O-undersaturated conditions. Low Sr/Y ratios suggest a garnet-free residuum, which is only possible at pressures below ~ 0.9 GPa. [ABSTRACT FROM AUTHOR]

The Variscan granites from the Western Erzgebirge were repeatedly dated by various methods, but no consensus has been reached about their exact intrusion ages. This study presents a multi-dating approach for the four largest intrusions from the Western Erzgebirge (Aue-Schwarzenberg, Bergen, Eibenstock, Kirchberg). We analysed several samples from each pluton/suite with zircon U–Pb CA-ID-TIMS (chemical abrasion-isotope dilution-thermal ionization mass spectrometry) to obtain robust temporal information on their age and tempo of intrusion. These data enable us for the first time to define three intrusive episodes of 1–2 Ma each, separated by quiet periods of several Ma. The Aue-Schwarzenberg suite represents the oldest granites that intruded at ~323–322 Ma followed by the granites from Bergen and Kirchberg 2–4 Ma later. The highly evolved ore-bearing granites from the Eibenstock pluton intruded after a time lag of ~5 Ma at ~315–314 Ma. The new data show that there is a resolvable age difference between the two known granite groups. Granite group 2 (also assigned as younger igneous complex, represented by the Eibenstock pluton) is ≥5 Ma younger than granite group 1 (assigned as older igneous complex, represented by granites from Aue-Schwarzenberg, Bergen and Kirchberg). Protracted magmatism and late-/post-magmatic fluid flow partly reset the U–Pb system of these granites to variable degrees, making a precise and accurate dating of their intrusion ages challenging. Pb loss in zircons is often combined with high common Pb (Pb c). SHRIMP/SIMS (sensitive high mass resolution ion microprobe/secondary ion mass spectrometry) and LA-ICP-MS (laser ablation-inductively coupled plasma-mass spectrometry) on non-CA zircons document that Pb loss and high Pb c is quite variable within zircon grains and may be located in micro-fractures. We demonstrate that chemical abrasion (CA) clearly minimizes or removes both Pb loss and Pb c. Results from prior LA-ICP-MS and SHRIMP dating on non-CA zircons from the same samples considerably helped the interpretation of the CA-ID-TIMS data when Pb loss was not completely erased by CA. In such cases we often had to choose the oldest analyses for mean age calculation in contrast to the common practice of the CA-ID-TIMS community to choose the youngest dates. Rb–Sr and Ar–Ar dating systems revealed age differences between the older group and the younger ore-bearing granites albeit with diverging absolute ages. Most Ar–Ar ages are identical with CA-ID-TIMS ages and would imply rapid cooling. However, samples from the older group have excess Ar that could have led to too old ages. In contrast, Rb–Sr ages for the older granites are 0–7 Ma younger than their intrusions. Fluid induced alteration led to the formation of Li-mica, fluorite and cassiterite (greisenization). For the youngest granite (Eibenstock), Li-mica was used to date the first greisenization. Samples without visible hydrothermal overprint yielded identical Ar–Ar and Rb–Sr ages as severely greisenized samples. This implies re-equilibration due to the hydrothermal overprint for all Ar–Ar and Rb–Sr ages from the Eibenstock pluton. According to Ar–Ar dating, the first ore formation (~315 Ma) is coeval with the CA-ID-TIMS intrusion age of the Eibenstock granite while it is delayed by ~6 (±3) Ma according to Rb–Sr dating (308 ± 3 Ma). [ABSTRACT FROM AUTHOR]

Hyper-solidus fabrics of the early Permian Brocken granite pluton, exposed over an area of c. 160 km² and elongated in NNE–SSW direction, were determined by measuring the anisotropy of magnetic susceptibility (AMS). The Brocken granite pluton consists of five petrographically distinguishable and mappable granitic varieties characterized by a generally paramagnetic behavior with primary biotite, partly altered to chlorite, and secondary tourmaline as the major carrier of the susceptibility. Whereas biotite modal content isolines roughly follow petrographic trends, the tourmaline modal contents do not, hence implying secondary, post-emplacement processes that controlled tourmaline distribution. A few samples with primary and secondary magnetite show ferrimagnetic behavior and are co-axial with the paramagnetic fabrics. The generally low magnetic anisotropies in all granitic varieties are a distinct and challenging feature for determining magmatic flow directions. AMS data indicate the predominance of sub-horizontal fabrics outlining an NNE–SSW trending dome axis interpreted to have resulted from granite sheets stacked syn-magmatically in a high crustal level building up a laccolithic pluton. AMS fabrics together with age data and geophysical indications suggest that the emplacement and distribution of the Brocken granite pluton is structurally controlled by NNE–SSW striking deep fault structures, and only weakly influenced by WNW/NW-trending structures. Late Carboniferous-to-early Permian plutonism in the Harz Mountains evolved in an E–W directed extensional regime, and was accompanied by volcanic activity and development of NW- and NE-trending sedimentary basins. [ABSTRACT FROM AUTHOR]

The Eichigt granite is one of two apical intrusions forming the concealed massif of Eichigt-Schönbrunn in the Erzgebirge-Vogtland metallogenic province of Germany. It represents a peraluminuous, medium-grained, Si-rich biotite monzo- to syenogranite of aluminuous A-type affinity and post-collisional (-orogenic) tectonic setting, which belongs to the group of medium-F, low-P Variscan granites of the Erzgebirge. Mineralogically and geochemically, the Eichigt granite shows the closest affinity to the Gottesberg subvolcanic microgranite/rhyolite complex some 25 km north-east of the massif. The granites contain phenocrysts of quartz and K-feldspar and sporadically accessory topaz and andalusite. A special feature is the presence of accessory primary fergusonite-(Y) and secondary synchysite-(Ce). Minor amounts of quartz, K-feldspar, and siderophyllite likely represent antecrysts, i.e., crystallized from a lesser silicic forerunner magma. These observations attest to the operation of magma mingling during the formation of the Eichigt granite. Calculation of Th-U-total Pb uraninite ages proves that the Eichigt and Schönbrunn granites are coeval and emplaced at about 306 ± 3 Ma (2s), i.e., were formed during the same magmatic episode as the northwesterly Henneberg granite in Thuringia und the microgranite/rhyolith suite at Gottesberg and the Seiffen granite in the Erzgebirge-Vogtland. Geochemical data and mineralogical features do not lend support a genetical relation between the Eichigt-Schönbrunn granites and the spatially associated Sn-polymetallic veins. [ABSTRACT FROM AUTHOR]

Granitic rocks obtained during field excursions of the famed mineralized regions of the Erzgebirge, Germany (mainly tin-bearing), and South China (mainly tungsten-bearing) have been geochemically analyzed and their results are compared with similar (mainly tungsten-bearing) granites in the island-arc setting of Southwest Japan. The studied granitoids all belong to the ilmenite-series. The collision-related Erzgebirge granitoids are rich in K2O and P2O5, have high A/CNK ratios (1.11-1.24, i.e. S type), but are also high in Ga/ Al ratio (i.e., having some A-type characteristics). In South China, the Xihuashan granites, in contrast, are very low in P2O5, and have A/CNK slightly above 1.0 (1.01-1.05), indicative of I type granites. The ( Sn-) W-related granites of southwest Japan have similarly low P2O5 and A/CNK ratios, indicative also of I-type. Both in the Xihuashan and southwest Japan, the tungsten-related granites have high whole-rock δ18O values implying involvement of W-rich crustal rocks. Sn and W contents of the unaltered granites are lowest in the island-arc setting where the related Sn- W deposits are smallest in size relative to the collision and continental margin settings of the Erzgebirge and South China. [ABSTRACT FROM AUTHOR]

We present a comprehensive Li and B isotope study of granites, aplites, and igneous enclaves from the multi-phase Eibenstock granite in the Western Erzgebirge-Vogtland metallogenic province of Germany. The studied samples cover the entire compositional range of the granites from moderately to highly evolved and include variably altered types as obtained by magmatic fractionation, post-magmatic high- to medium-temperature and near-surface low-temperature alteration. Fractionation and alteration processes are unequivocally documented by the chemical variability of the rocks. Despite the marked imprint of these processes on bulk-rock compositions, our granite samples show only little variation in δ7Li (−0.52 to 0.75‰) and δ11B (−17.46 to −14.78‰), with surface samples defining the lower end of the δ7Li range. The narrow range in δ7Li suggests that magmatic fractionation and high-temperature overprint have a very minor effect on δ7Li. The B budget of the samples is dominated by tourmaline, which makes δ11B values insensitive for later high- to medium-temperature overprint or surficial low-temperature alteration. Depending on whether tourmaline crystallized before or after exsolution and loss of magmatic fluids, whole-rock samples have higher or lower δ11B values. Granite enclaves have δ7Li and δ11B values ranging from −1.51 to −0.81‰ and − 14.55 to −13.89‰, respectively. Some samples have chemical and mineralogical evidence for wall-rock interaction during emplacement or later overprint by external fluids. These samples show broader ranges in δ7Li (−2.61 to 2.21‰) and δ11B (−21.58 to −9.85‰). These values show that wall-rock interaction via assimilation and external fluids may affect δ7Li and δ11B to a larger extent than intra-magmatic processes, such as fractional crystallization, fluid-mediated autometasomatic overprinting, or exsolution of fluids from the melt. The offset of δ7Li and δ11B values towards the compositions of the wall rocks reflects the contrasting composition of granite and country rock and the addition of country-rock material to the granite. The magnitude of the offset reflects both the relative contribution of wall-rock derived Li and B to the granite and the magnitude of the difference in the Li and B isotopic compositions between them. • Whole rock δ7Li and δ 11B are essentially unaffected by magmatic fractionation. • Fluid-melt separation may reduce δ7Li and δ 11B in residual melt. • Effect of intra-granitic alteration on δ7Li and δ 11B of granitic rocks is small. • Effects on δ7Li and δ 11B during alteration depend on fluid source. [ABSTRACT FROM AUTHOR]

Abstract: The Krušné hory/Erzgebirge Mountains is one of the best-known provinces of granite magmatism and associated metallogenesis in Europe. Variscan magmatic activity in the Krušné hory/Erzgebirge area spanned the period from 330 to 295Ma. For much of this time, two types of magma were generated and emplaced in close proximity in this province. Strongly peraluminous P-rich (S-type) melts were formed alongside slightly peraluminous P-poor melts (A-type). Two suites of strongly peraluminous P, F, Li, Rb, Cs, U, Sn-rich and Zr, Th, Y, HREE-poor magmas were intruded in rapid succession over a period of about 10Ma (about 330–320Ma) over the entire region of the Krušné hory. Several peraluminous rhyolitic dykes near Gottesberg mark an isolated event at about 295Ma. Slightly peraluminous F, Li, Rb, Cs, Sn, Zr, Y, HREE-rich and P-poor magmas were intruded in several events separated in space and time (325–295Ma). Both magmatic episodes culminated with strongly fractionated subvolcanic granite intrusions, accompanied by explosive brecciation and followed by Sn+W mineralization of greisen type. Successive volcanic eruption of rhyolites and dacites of S-type, and rhyolites of A-type form the fill of the Altenberg-Teplice Caldera (ATC), thus demonstrating the close temporal and spatial relationship between these two types of magma. When these two geochemically distinct types of rock are in direct contact, then the rocks of A-type are always younger. The absolute time difference between the two types can range from less than 1Ma (the first eruption of the Teplice rhyolite versus the Schönfeld dacite in the ATC) to about 15Ma (eruption of rhyolites at Gottesberg versus emplacement of the Eibenstock granite). The assumed protolith of all late-Variscan granites in the area of Krušné hory/Erzgebirge is a mixture of fertile quartzo-feldspathic rocks with micaceous metapelites enriched in LILE and Sn+W. The differences in chemical composition of S- and A-type melts originated from local changes in the proportion of quartzo-feldspathic and pelitic lithologies, different pT-conditions of melting, the degree of melting, and the degree of metamorphic dehydratation of the protolith prior to the melting. [Copyright &y& Elsevier]

Abstract: A world-class fluorite mining district was located NNE of Regensburg at Nabburg-Wölsendorf, Germany. Together with some smaller mining sites near Bach a.d. Donau, Germany, it provided the main part of the domestic fluorite supply until the late 1980s when the last mines were shut down in NE Bavaria. Both fluorite mining districts are separated from each other by the Bodenwöhr Halbgraben and their mineral assemblages are controlled by deep-seated fault zones. The NW–SE-running “Pfahl”, also called the “Great Bavarian Quartz Lode” (=quartz dyke along a deep-seated shear zone), is of structural control for the vein-type U-, Pb-, Zn-, Cu-, Bi, -Co-, Ni-, As-, and Se mineralization in the Nabburg-Wölsendorf District. Another prominent fault structure, the NNW-trending boundary fault of the NE Bavarian Basement, controls vein-type fluorite deposits with minor Cu-, Zn- and Pb sulfides in the Donaustauf District. Concluding from the REE distribution, primary fluorite mineralization was sourced from granitic and gneissic aquifers or intrastratal solutions, giving rise in both fluorite mining districts to similar mineral assemblages. Two fluorite mineralizations can be distinguished from each other in both mining districts. The primary fluorite mineralization evolved in the aftermaths of the granite intrusion, during the Late Carboniferous and the early Permian, whereas the secondary mineralization or remobilization of fluorite took place until post-Middle Jurassic times. Remobilization, related to the paleogeography of each mineral district, was more intensive in the northern district, because of a moderate erosion. In the southern district, erosion cut deeply into the fluorite mineralization and left behind only relics of minerals indicative of fluorite remobilization. The physical–chemical regime of the fluorite mineralization was interpreted, making use of the common phase diagrams which show Eh and pH along the x- and y axes. The temperature of formation was as high as 200°C in both districts. The fluid regime became more acidic and more oxidizing from the north toward the south. This physical–chemical change well accords with the paleogeographic situation when the fluorite mineralization took place during the Permo-Mesozoic and with the supergene alteration during the Miocene and Pliocene when the southern part of the basement was undergoing stronger uplift than the northern part. Gangue minerals, e.g., ferroan carbonate and sulfate minerals are proximity indicators marking the distance of the vein-mineralization relative to the horizontal reference plain and implying a depth zonation (unconformity), whereas minerals and elements originating from the hypogene alteration are proximity indicators relative to the vertical reference plains (veins related to deep-seated lineamentary fault zones). [Copyright &y& Elsevier]

Abstract: Fluorite vein-type deposits occur along the western edge of the Bohemian Massif in SE Germany, from Bayerischer Wald to Frankenwald. They are emplaced in various host rock lithologies, as old as Late Variscan granites and low-grade metasediments of late Paleozoic age. The Nabburg-Wölsendorf mining district in NE Bavaria, Germany, used to be the largest in Germany and one of the most important in the world. A minor proportion of fluorite is also concentrated in the Permo-Mesozoic siliciclastic sediments resting unconformably upon the basement rocks near Pingarten. Fluorite is investigated in the present study for its REE variation, the REE minerals associated with it and its Sm/Nd isotope ratios. The primary blue-black fluorites precipitated from aqueous hydrothermal solutions during early stages without noticeable interaction with wall rocks and were poor in REE and Y. The secondary green, white and yellow fluorites formed from remobilization of older fluorite and through the interaction of more viscous fluids with the wall rocks and they are abundant in REE plus Y. Monazite–(Ce) is the major source for the REE re-deposited into fluorite. In a double cross plot, designed during this study and using the Ce-, Eu anomalies and the skewness (fractionation) of the REE pattern, the geological and hydrological evolution of fluorite vein mineralizations are related to the granite and the unconformity, which is the hydraulic reference plane for the fluorite mineralization. First, blue fluorite formed at considerable depth below the unconformity. Fetid fluorite is exclusive to the deep-seated vein mineralization with abundant uranium minerals. These uranium minerals caused some radiation damage to the lattice of the blue fluorite and turned into black. Based upon the variation of REE in fluorite and the Sm/Nd dating (fluorite age: ca. 270Ma) the Permian paleogeography can be reconstructed. It is suggested that in the Nabburg-Wölsendorf District a NW–SE oriented swell stood out from a vast peneplain. Second, fluorite vein mineralization composed of green, white and yellow fluorite along the western edge of the Bohemian Massif resulted from remobilization associated with an increase in REE and Y relative to the blue and black fluorites and a strong fractionation of LREE vs. HREE. The REE signature of the latter fluorites got increasingly more “unconformity-related” (Eh>0), notwithstanding the fluid source which the mineralizing fluids originated from. The REE patterns, Sr- and Sm/Nd isotopes suggest that mineralizing fluids mainly derived from a granitic source rock with little impact from metasedimentary rocks. Cerite–(Ce) formed during the initial stages of fluorite mineralization when little REE were accommodated in the lattice of blue fluorite. During precipitation of green, white and yellow fluorite, REE minerals failed to continue developing on their own, because REE were increasingly accommodated in the structure of fluorite changing its color from blue via green into white. REE minerals were again formed during supergene alteration of fluorite mineral assemblages, terminating the entire F-REE cycle. Rhabdophane is of supergene origin and indicative of meteoric conditions that are neutral to slightly alkaline. Subsequently, florencite evolved under a more acidic regime of chemical weathering. The distinct data arrays in the cross plots of the Sm-, Nd- and Sr isotopes, likewise, indicate this subdivision into fluorite originating from fluids that interacted with granitic and gneissic rocks at depth and those being formed proximal and distal to the unconformity. [Copyright &y& Elsevier]

The study of re-homogenized melt inclusions in the same growth planes of quartz of pegmatites genetically linked to the Variscan granite of the Ehrenfriedersdorf complex, Erzgebirge, Germany, by ion microprobe analyses has determined high concentrations of Be, up to 10,000 ppm, in one type of melt inclusion, as well as moderate concentrations in the 100 ppm range in a second type of melt inclusion. Generally, the high Be concentrations are associated with the HO- and other volatile-rich type-B melt inclusions, and the lower Be concentration levels are connected to HO-poor type-A melt inclusions. Both inclusion types, representing conjugate melt pairs, are formed by a liquid-liquid immiscibility separation process. This extremely strong and very systematic scattering in Be provides insights into the origin of Be concentration and transport mechanisms in pegmatite-forming melts. In this contribution, we present more than 250 new analytical data and show with ion microprobe and fs-LA-ICPMS studies on quenched glasses, as well as with confocal Raman spectroscopy of daughter minerals in unheated melt inclusions, that the concentrations of Be may achieve such extreme levels during melt-melt immiscibility of HO-, B-, F-, P-, ± Li-enriched pegmatite-forming magmas. Starting from host granite with about 10 ppm Be, melt inclusions with 10,000 ppm Be correspond to enrichment by a factor of over 1,000. This strong enrichment of Be is the result of processes of fractional crystallization and further enrichment in melt patches of pegmatite bodies due to melt-melt immiscibility at fluid saturation. We also draw additional conclusions regarding the speciation of Be in pegmatite-forming melt systems from investigation of the Be-bearing daughter mineral phases in the most HO-rich melt inclusions. In the case of evolved volatile and HO-rich pegmatite systems, B, P, and carbonates are important for the enrichment and formation of stable Be complexes. [ABSTRACT FROM AUTHOR]

Abstract: Cryptomelane, a K–Mn-bearing oxide, is widespread in the lowermost part of the weathering/supergene alteration zone of the Hagendorf Pegmatite, SE Germany. This supergene Mn mineral has been used in the present study for K/Ar dating of weathering and paleohydraulic processes as young as Plio-Pleistocene. Different cryptomelane age data found in the same weathering and paleohydraulic system resulted from continuous hydraulic processes in the weathering system rather than from a stepwise uplift that shaped the landscape in the granitic area of the NE Bavarian Basement. An almost pure cryptomelane mineralization is indicative of the basal zone of supergene alteration, because a complete separation of Mn from Fe can favorably be achieved only in the infiltration zone under slightly reducing conditions or in the percolation zone under slightly oxidizing conditions. Cryptomelane is precipitated under slightly oxidizing conditions from alkaline solutions in the percolation zone and cast as a marker for fluctuating (paleo)water levels. Manganese oxides, uranyl phosphates and silicates were found at different depths in the weathering zone of this granitic terrain. They were dated by different dating methods (K/Ar and U/Pb) and yielded the same age of formation. Consequently, the 4Ma signal of both groups of supergene minerals has geomorphological and paleohydraulic connotation and is related to a unique geomorphological process, the Pliocene peneplanation. Gradual hydraulic adjustments gave rise to the younger Pleistocene age found at shallow depth in the weathering zone. [Copyright &y& Elsevier]

- 40Ar/39Ar dating of recrystallized K-feldspar melt particles separated from partially molten biotite granite in impact melt rocks from the approximately 24 km Nördlinger Ries crater (southern Germany) yielded a plateau age of 14.37 ± 0.30 (0.32) Ma (2σ). This new age for the Nördlinger Ries is the first age obtained from (1) monomineralic melt (2) separated from an impact-metamorphosed target rock clast within (3) Ries melt rocks and therewith extends the extensive isotopic age data set for this long time studied impact structure. The new age goes very well with the 40Ar/39Ar step-heating and laser probe dating results achieved from mixed-glass samples (suevite glass and tektites) and is slightly younger than the previously obtained fission track and K/Ar and ages of about 15 Ma, as well as the K/Ar and 40Ar/39Ar age data obtained in the early 1990s. Taking all the 40Ar/39Ar age data obtained from Ries impact melt lithologies into account (data from the literature and this study), we suggest an age of 14.59 ± 0.20 Ma (2σ) as best value for the Ries impact event. [ABSTRACT FROM AUTHOR]

Abstract: To determine how topographic relief in mountainous regions evolves through time we present a new approach that uses in situ-produced cosmogenic 10Be to quantify (1) spatially averaged denudation rates of small watersheds and (2) local denudation rates of the ridge crests bounding these basins. The technique is applied to two catchments in the Black Forest, a forested mountain range with a local relief of a few hundred meters, which is typical for ranges in central Europe. Both the Acher and the Gutach catchments expose predominantly Carboniferous granite, and only minor amounts of high-grade gneiss and Triassic sandstone. The latter occurs on ridges defining the eastern boundaries of the catchments, above a regional unconformity. In the Acher and northern Gutach watersheds denudation rates of subcatchments derived from 10Be concentrations in stream sediment range from 52 to 87mm/ka and 59 to 91mm/ka, respectively. In contrast, grus samples from the ridge crests bounding both watersheds yield lower denudation rates of 34 to 59mm/ka. The differences in denudation rates for sample pairs from individual subcatchments and adjacent ridge crests reveals that topographic relief is growing at a mean rate of 24±12mm/ka (with the exception of the flat southwestern part of the Gutach catchment, where catchment-wide denudation rates are similar to the rate of ridge crest lowering). The inferred rates of denudation and relief growth are consistent with erosion rates calculated from the known thickness of Triassic to Lower Jurassic sediments, which were once present above the regional unconformity but have been largely eroded during the exhumation of the Black Forest. The onset of exhumation ∼19Ma ago is constrained by thermal modelling of apatite fission track data, which suggest a cooling rate of ∼3°C/Ma. Combined with a geothermal gradient of 30 to 40°C/km this cooling rate yields an average exhumation rate of 75–100mm/ka for the modelled apatite fission track data, which is comparable to spatially averaged denudation rates derived from cosmogenic 10Be. Our new approach may help to determine whether tectonically active mountain ranges are in a topographic steady state, in which rates of rock uplift and denudation are equal, or if such a dynamic equilibrium has not yet been attained. [Copyright &y& Elsevier]

Crystalline rock is one of the host rocks considered for a future deep geological repository for highly active radiotoxic nuclear waste. The safety assessment requires reliable information on the retention behavior of minor actinides. In this work, we applied various spatially resolved techniques to investigate the sorption of Curium onto crystalline rock (granite, gneiss) thin sections from Eibenstock, Germany and Bukov, Czech Republic. We combined Raman-microscopy, calibrated autoradiography and µTRLFS (micro-focus time-resolved fluorescence spectroscopy) with vertical scanning interferometry to study in situ the impact of mineralogy and surface roughness on Cm(III) uptake and molecular speciation on the surface. Heterogeneous sorption of Cm(III) on the surface depends primarily on the mineralogy. However, for the same mineral class sorption uptake and strength of Cm(III) increases with growing surface roughness around surface holes or grain boundaries. When competitive sorption between multiple mineral phases occurs, surface roughness becomes the major retention parameter on low sorption uptake minerals. In high surface roughness areas primarily Cm(III) inner-sphere sorption complexation and surface incorporation are prominent and in selected sites formation of stable Cm(III) ternary complexes is observed. Our molecular findings confirm that predictive radionuclide modelling should implement surface roughness as a key parameter in simulations. [Display omitted] • First reported spectro-microscopic measurement of the highly radiotoxic actinide curium with µm resolution. • Quantification and characterization of Cm(III) interaction with natural rocks considered for nuclear waste disposal sites. • Uptake and speciation of Cm(III) on crystalline rocks is strongly affected by mineralogy and surface topography. • Competition of mineral phases in heterogeneous rocks influences the sorption process. [ABSTRACT FROM AUTHOR]

Abstract: In the 16-km-thick Earth''s crust, 2.4–3.2mguranium/kg is assumed to occur. Thus, uranium is more abundant than iodine, cadmium or selenium. In Central Europe, the vegetation richest in uranium is found on granite weathering soils. Compared to these, the uranium content of the flora is about 25% less on Muschelkalk soils, ∼50% less on Buntsandstein, Keuper weathering soils and gneiss weathering soils, and more than 50% less on Pleistocene sands. Drinking water from Pleistocene sands often contains only 1–10% of the uranium content found in that from granite. Mineral and medicinal waters in Germany contain between <0.015 and 25μgU/L. In all, 39% of the mineral waters analysed store <0.10, 29% 0.10–0.99, 15% 1.0–4.9 and 17% 5–25μgU/L, with 2% of them containing <10μgU/L. The majority of the extremely uranium-rich mineral waters are coming from Thuringia, the adjoining states Hesse, Saxony-Anhalt, and especially from the Black Forest in Baden-Württemberg. The high uranium contents there are delivered to the mineral waters and the food chain by the granite in the subsoil of these areas. Compared to control plants, wild and cultivated plants from the immediate vicinity of uranium waste dumps were found to store normal to eightfold uranium contents. Leafy plants species accumulated much uranium, whereas tubes, thick parts of stalks, fruits and grains stored less uranium. With increasing age of the vegetation, its uranium content decreases significantly. The uranium content of 116 foodstuffs and beverages varies extremely. Vegetable foods accumulate between 0.8μgU/kg dry matter (DM) in margarine, bee honey and pearl barley, 50μgU/kg DM in asparagus, and >100μgU/kg DM in mixed mushrooms. As a rule, sugar-, starch- and fat-rich foodstuffs proved to be uranium-poor (fruits, seeds, flour), whereas leafy vegetables, tea and herbs can be uranium-rich. Animal foodstuffs accumulate lower uranium contents, with 0.7μgU/kg DM in butter and 1.1–1.9μgU/kg DM in condensed and normal cow''s milk, 1.5–3.1μgU/kg DM in pork, beef, chicken and mutton, 3–10μgU/kg DM in fish, and 16μgU/kg DM in hen''s eggs. Prepared food for babies and young children proved to be uranium-poor. However, its uranium content can increase to 50 times that of mother''s or cow''s milk due to its preparations with particularly recommended mineral water that is rich in uranium. Of the uranium ingested by adults, 41% are delivered through beverages, 33% through vegetable and 26% through animal foodstuff. Since the end of the GDR and the reunification of Germany, the uranium intake by adults slightly increased from 2.2 to 3.0μgU/day in men, and from 2.2 to 2.6μgU/day in women. It varied considerably from region to region due to geological effects. The test population on the Pleistocene formation in Northern Germany only took in one third of the uranium amounts taken in Thuringia. Uranium does not accumulate in the body. The apparent absorption rate (7 days) amounted to about 6%, which is extremely high. The uranium content of drinking and mineral waters needs to be publicly controlled. [Copyright &y& Elsevier]

The crystal structures of herderite, CaBePO4[F0.75(OH)0.25], a = 9.7446(4), b = 7.6769(3), c = 4.7633(2) Å, β = 90.667(1)°, V = 356.31(4) ų, P21/a, and Z = 4, from the Mogok Stone Tract, Myanmar, and hydroxyl-herderite, CaBePO4[(OH)0.52F0.48], a = 9.7615(4), b = 7.6680(3), c = 4.7853(2) Å, β = 90.184(1)°, V = 358.18(4) ų, P21/a, and Z = 4, from the Sauberg mine, Morgenröther Zug, Ehrenfriedersdorf, Germany, have been refined to R1 indices of 1.7%, in both cases, using MoK&#x03B1 single-crystal X-ray diffraction data. Herderite from Mogok is associated with complex rare-element beryl-type granite pegmatite. Most herderite-series minerals are the product of late-stage processes in granite pegmatite evolution, typically of an exsolved fluid upon crystallization, and significant F-enrichment in these fluids appears to result in the domination of herderite over hydroxyl-herderite. Herderite is now documented from Mogok, Myanmar; Yichung, China; Brazil; and probably Erongo, Namibia. The pegmatites at Ehrenfriedersdorf, Germany have produced samples at the boundary between herderite and hydroxyl-herderite, if not possibly herderite as well. [ABSTRACT FROM AUTHOR]

Abstract??Granites and primary tin mineralization in the Erzgebirge were dated using (1) conventional U?Pb dating of uraninite inclusions in mica, (2) Rb?Sr dating of inclusions in quartz that represent highly evolved melts, (3) Re?Os dating of magmatic?hydrothermal molybdenite, and (4) chemical Th?U?Pb dating of uraninite. Conventional isotope dilution and thermal ion mass spectrometry and chemical Th?U?Pb dating of uraninite in granites from the Ehrenfriedersdorf mining district provide ages of 323.9???3.5 Ma (2?; Greifenstein granite) and 320.6???1.9 and 319.7???3.4 Ma (2?, both Sauberg mine), in agreement with U?Pb apatite ages of 323.9???2.9 and 317.3???1.6 Ms (2?, both Sauberg mine). Rb?Sr analysis of melt inclusions from Zinnwald gives highly radiogenic Sr isotopic compositions that, with an assumed initial Sr isotopic composition, permit calculation of precise ages from single inclusions. The scatter of the data indicates that some quartz-hosted melt inclusions have been affected by partial loss of fluid exsolved from the melt inclusion. Re?Os dating of two molybdenite samples from Altenberg provides ages of 323.9???2.5 and 317.9???2.4 Ma (2?). Together with age data from the literature, our new ages demonstrate that primary tin mineralization and the emplacement of the large Sn-specialized granites in the Erzgebirge fall in a narrow range between 318 and 323?Ma. Primary Sn mineralization occurred within a short interval during post-collisional collapse of the Variscan orogen and was essentially synchronous over the entire Erzgebirge. In contrast to earlier claims, no systematic age difference between granites of the eastern and western Erzgebirge was established. Furthermore, our data do not support a large age range for Late-Variscan granites of the Erzgebirge (330?290?Ma), as has been previously suggested. [ABSTRACT FROM AUTHOR]

The production of impact melt rocks and glasses is a characteristic feature of hypervelocity impact events on Earth and other planetary bodies. This investigation represents the first detailed study of an unusual series of coherent impact melt rocks intermittently exposed around the periphery of the ~24-km diameter, ~14.5 Ma Ries impact structure, Germany. Optical and analytical scanning electron microscopy (SEM) reveals that the groundmass comprises sanidine, plagioclase, quartz and ilmenite (decreasing order of abundance) with the interstices filled by either fresh or devitrified glassy mesostasis. Primary crystallites display skeletal, dendritic and/or spherulitic textures indicating rapid crystallization from a melt. The mesostasis is characterized by extreme chemical heterogeneity (e.g., FeO and Al2O3 contents from ~1 to ~62–80 wt.%). This is likely due to a combination of crystal–liquid fractionation during rapid cooling and crystallization of an originally incompletely homogenized melt. Vapor phase crystallization of sanidine and cristobalite occurred in miarolitic cavities during late-stage cooling of the impact melts. The most likely protolith for the impact melt rocks are granitic rocks present in the crystalline basement target. The high volatile content of the mesostasis suggests that a large volatile component was retained from this protolith. Field observations together with analytical data and micro-textures indicate that the Ries impact melt rocks were molten at the time of, and after, deposition. Field relations with other impactites also suggest that these rocks were emplaced subsequent to the excavation stage of crater formation and that they are not, therefore, ballistic ejecta. Thus, it is proposed that the Ries impact melt rocks were emplaced as ground-hugging impact melt flows that emanated from different regions of the evolving transient cavity during the modification stage of crater formation. This is consistent with, and in fact predicted, by field relations, which indicate that these rocks overlie unequivocal ejecta. This represents the first recognition of impact melt flows near the rim of a terrestrial impact structure and is consistent with observations of such features on the Moon and Venus. [Copyright &y& Elsevier]

An integral method of data evaluation for chemical dating of accessory uraninite by electron microprobe analysis and electron microscopy is proposed. The internal structure of uraninite grains, the contents of Si, Ca, and Fe, and tests for loss or gain of Pb and U are suitable criteria to decide whether or not a given crystal area was affected by secondary alteration. The method was applied to uraninite from the Kirchberg granite, Erzgebirge, Germany, and an age of 330±5 Ma (±2σ) was constrained. This result supports earlier assumptions that there were at least two events of Hercynian granite magmatism separated by a time gap of about 40 Ma, and that the magmatic evolution of the Kirchberg granite is not related to the formation of the W mineralisation developed in the endocontact of this granite. Secondary alteration of uraninite is probably closely related to the formation of U deposits in the vicinity of the Kirchberg massif which was extensively mined in the past. [ABSTRACT FROM AUTHOR]

For soil chemical analyses, the soil skeleton is normally rejected because this size fraction is considered to have no significant short-term nutritional potential. In order to revise this practice, the short-term potential for ion storage and mobilization of the isolated and cleaned soil skeleton was investigated by model experiments, using undisturbed and homogenized soil samples as references. The study considered two soil profiles in the Black Forest, Germany: one on granite and one on gneiss bedrock. The method allowed for the investigation of soil columns at a water status near field capacity. After the extraction of water soluble ions with deionized water, cation exchange properties were determined by percolation of the soil cores with ammonium chloride (NH4Cl). Moreover, the influence of different carbon dioxide (CO2) partial pressures in the soil air for ion mobilization was studied in a closed percolating system. The first results revealed site-specific ion mobilization potentials of the soil skeleton. Below the A-horizon, the skeleton fraction of the gneiss site plays the dominant role as a source for short-term base cation supply. The fine earth of the corresponding soil horizon had lost this function, since the base saturation was less than 5 %. The skeleton of the granite site had much lower ion mobilization rates, but nevertheless, its importance for ion mobilization must not be neglected. The results of the mineralogical study supported the findings of the model experiments. [ABSTRACT FROM AUTHOR]

The origin and evolution of granites remain a matter of debate and several approaches have been made to distinguish between different granite types. Overall, granite classification schemes based on element concentrations and ratios, tectonic settings or the source rocks (I-, A-, S-type) are widely used, but so far, no systematic large-scale study on Th/U ratio variations in granites based on their source or tectonic setting has been carried out, even though these elements show very similar behavior during melting and subsequent processes. We therefore present a compiled study, demonstrating an easy approach to differentiate between S-, A- and I-type granites using Th and U concentrations and ratios measured with a portable gamma ray spectrometer. Th and U concentrations from 472 measurements in S- and I-type granites from the Variscan West-Bohemian Massif, Germany, and 78 measurements from Neoproterozoic A-type Malani granites, India, are evaluated. Our compendium shows significant differences in the average Th/U ratios of A-, I- and S-type granites and thus gives information about the source rock and can be used as an easy classification scheme. Considering all data from the studied A-, I- and S-type granites, Th/U ratios increase with rising Th concentrations. A-type granites have the highest Th/U ratios and high Th concentrations, followed by I-type granites. Th/U ratios in S- to I-type granites are lower than in A-type and I-type granites, but higher than in S-type granites. The variation of Th/U ratios in all three types of granite cannot be explained by fractional crystallization of monazite, zircon and other Th and U bearing minerals alone, but are mainly due to source heterogeneities and uranium mobilization processes. [ABSTRACT FROM AUTHOR]

The late-collisional Erzgebirge granites (~325-318 Ma) were emplaced at shallow crustal levels in the Variscan metamorphic basement shortly after large-scale extension caused by orogenic collapse. These granites comprise mildly peraluminous transitional I-S-types and strongly peraluminous S-type rocks, which can be subdivided into three major groups: low-F biotite granites; low-F two-mica granites; and high-F, high-P2O5 Li-mica granites. The highest degree of differentiation is reached in the Li-mica granites, which exhibit strongly elevated concentrations of P, F, Li, Rb, Cs, Ta, Sn, W and U; but very low Ti, Mg, Co, Ni, Sr, Ba, Y, Zr, Hf, Th and rare earth elements. Crystal-melt fractionation is the dominant process controlling the bulk composition of all groups of granites. However, metasomatic processes involving late-stage residual melts and high-T orthomagmatic fluids became increasingly more important in highly evolved units and have modified the abundances of mobile elements (P, F, Li, Rb, Cs, Ba, Sr) in the Li-mica granites particularly. Isotopic and geochemical characteristics suggest that the three granite groups cannot be derived from a common precursor magma. Their discrete compositions are source related, and are attributed to melting of quartzo-feldspathic and pelitic crustal lithologies in different proportions. Granites are common in the central European Variscides, but the Erzgebirge is unusual for the predominance of evolved Li-mica granites associated with economically important Sn, W and U deposits. The abundance of Li-mica granites is attributed to a combination of favourable factors: (1) low degrees of anatectic melting of crustal protoliths; (2) wide distribution of fertile lithologies rich in large-ion lithophile elements and ore elements; (3) extended magmatic differentiation by crystal-melt fractionation and subsequent autometasomatism. [ABSTRACT FROM PUBLISHER]

Melt inclusions in granitic rocks are generally crystalline and must be homogenized to glass before analysis. We employ a simple kinetic technique with microthermometry to estimate total volatile contents and P–T conditions of trapping of the melts from their homogenization behaviour. This information complements chemical data from microprobe or ion probe analysis, and can be obtained from inclusions too small for direct analysis. We present here values for volatile contents (as equivalent wt % H2O), trapping temperatures and trapping pressures derived from studies of melt inclusions in some Variscan granites of the Erzebirge, Fichtelgebirge and Oberpfalz, Germany. The volatile concentrations range from 3 to 10 equiv. wt % H2O. Microprobe analysis shows that the most volatile-rich inclusions contain up to 8 wt % F. Estimates of trapping pressures ad temperatures suggest that crystallization began at an emplacement level of 3–6.5 km near 700°C with ‘normal’ biotite and two-mica granites, and ended with topaz–albite granite (∼650°C) and pegmatitic phases down to 520°C. This wide range of trapping temperatures and volatile contents is a general feature of melt inclusions in granites. Many of the granites studied are highly evolved geochemically, but the extreme volatile enrichment typical for these also occurs locally in the ‘unspecialized’ granites. [ABSTRACT FROM AUTHOR]

Presents a study on peraluminous granites of the Erzgebirge-Fichtelgebirge, Germany, which are hosts of various members of the monazite group of minerals that display an unprecendented compositional diversity. Geological background of the Erzgebirge-Fichtelgebirge in Germany; Information on typical reported concentrations of Nd2O3 in monazite-(Ce) from granitic rocks; Discussion pertaining to the study.

Verner and co-authors (Int J Earth Sci (2009) 98:517-532) published geological and structural model of evolution and emplacement of the Plöckenstein pluton in the border area of Austria, Germany and Czech Republic. They used data of other authors, giving no reference as to their source, for interpretations without any discussion of the already published results. [ABSTRACT FROM AUTHOR]

The article describes specimens of a yellow danburite mined from at least two steeply dipping granitic pegmatites using hand tools and explosives in Tanzania. The specimens were loaned by Mark Kaufman of San Diego, California and Werner Radl of Germany. The properties of the cut stones include light-to-medium yellow to orangy yellow and inert to both long- and short-wave ultraviolet radiation. Microscopic examination revealed long, thin, curved growth tubes as well as fingerprints that contain angular liquid inclusions.

• Element concentrations in fluids of granite-water leaching and alteration experiments can be linked to the dissolution processes. • Using hydrochemical data of the experiments, it is possible to predict probable alteration products and paths at low and high temperatures. • Li is mainly contained in phyllosilicates of granitic rocks (highest concentrations in muscovite, biotite) as and in fluid-inclusions in quartz. • Biotite is the main source of lithium in deep crystalline basement waters. • Passive increase of Cl and Li by precipitation of secondary smectite/chlorite explains the correlation between Cl and Li of continental brines. Geothermal energy exploitation in the Upper Rhine Graben (URG) chiefly has targeted faults and fractures within or connected with the crystalline basement, where hot fluids of c. 200 °C circulate at depths of c. 5 km. Formation fluids of the crystalline basement are highly saline, NaCl-dominated brines, whereas shallow crystalline basement water (< 500 m) is only weakly mineralized. In order to contribute to a better understanding of redistribution of elements in fluids and alteration phases during fluid-rock interaction processes we conducted leaching and alteration experiments with granites and monzonites from the Schwarzwald at 70 °C (rock powder, pure water) and 200 °C (texturally intact rock cylinders, 2m-NaCl), respectively, inspired by the P-T-x conditions reported for the URG. The trace element concentrations of the leachates are hereby related to the composition and stability of minerals in the rocks and can be directly linked to the proposed and observed dissolution processes at the different temperatures. In experiments with pure water at 70 °C, representing the recharge or infiltration conditions, water-rock interaction mobilized K, Cl, Fe, Mn, Mg, Cu, Zn, Cr, Sc, V, and Li (dissolution of biotite/chlorite) and Si, Al, K, Ca, Na, Ba, Sc, Pb, Sr, Rb, and Eu (dissolution of plagioclase, K-feldspar, and quartz) into the fluid. According to calculated activity diagrams, alteration at these temperatures may result in the formation of illite, kaolinite, Ca-beidellite, and stilbite. In experiments at higher temperatures of 200 °C, according to reservoir conditions, the net output of most elements was increased, but especially of those contained in feldspar, i.e. K, Ca, Al, Si, Ba, Rb, Cs, and Pb, suggesting that fluid-rock interaction is dominated by feldspar dissolution. This alteration is followed by albitization of feldspar surfaces, chloritization of biotite, and precipitation of illite and hematite. In Si-poor samples, analcime occurs in and around porous reaction zones, in agreement with calculated activity diagrams. The amount of dissolution mainly depends on the temperature and the mineralogy of the rock types, in particular on the anorthite-component of plagioclase. Certain elements (e.g., Na, Fe, Mg, Al) were subsequently incorporated into the solids precipitated during the experiments and thus cannot be considered as conservative. [ABSTRACT FROM AUTHOR]

The sources and critical enrichment processes for granite related tin ores are still not well understood. The Erzgebirge represents one of the classical regions for tin mineralization. We investigated the four largest plutons from the Western Erzgebirge (Germany) for the geochemistry of bulk rocks and autocrystic zircons and relate this information to their intrusion ages. The source rocks of the Variscan granites were identified as high-grade metamorphic rocks based on the comparison of Hf-O isotope data on zircons, the abundance of xenocrystic zircon ages as well as Nd and Hf model ages. Among these rocks, restite is the most likely candidate for later Variscan melts. Based on the evolution with time, we could reconstruct enrichment factors for tin and tungsten starting from the protoliths (575 Ma) that were later converted to high-grade metamorphic rocks (340 Ma) and served as sources for the older biotite granites (323–318 Ma) and the tin granites (315–314 Ma). This evolution involved a continuous enrichment of both tin and tungsten with an enrichment factor of ~15 for tin and ~7 for tungsten compared to the upper continental crust (UCC). Ore level concentrations (>10–100 times enrichment) were achieved only in the greisen bodies and dykes by subsequent hydrothermal processes. [ABSTRACT FROM AUTHOR]

Oxide minerals (Nb–Ta-rich rutile, columbite-group minerals and W-bearing ixiolite) represent the most common host for Nb, Ta and Ti in high-F, high-P2O5 Li-mica granites and related rocks from the Geyersberg granite stock in the Krušné Hory/Erzgebirge Mts. batholith. This body forms a pipe like granite stock composed of fine- to middle-grained, porphyritic to equigranular high-F, high-P2O5 Li-mica granites, which contain up to 6 vol. % of topaz. Intrusive breccia's on the NW margin of the granite stock are composed of mica schists and muscovite gneiss fragments enclosed in fine-grained aplitic and also topaz- and Li-mica-bearing granite. Columbite group minerals occur usually as euhedral to subhedral grains that display irregular or patched zoning. These minerals are represented by columbite-(Fe) with Mn/(Mn + Fe) ratio ranging from 0.07 to 0.15. The rare Fe-rich W-bearing ixiolite occurs as small needle-like crystals. The ixiolite is Fe-rich with relatively low Mn/(Mn + Fe) and Ta/(Ta + Nb) values (0.10–0.15 and 0.06–0.20, respectively). Owing to the high W content (19.8–34.9 wt. % WO3, 0.11–0.20 apfu), the sum of Nb + Ta in the ixiolite does not exceed 0.43 apfu. The Ti content is 1.7–5.7 wt. % TiO2 and Sn content is relatively low (0.3–4.1 wt. % SnO2). [ABSTRACT FROM AUTHOR]