Albite Crystals Research Articles

Unraveling the Magmatic-to-Carbothermal Processes in the Ba-Sr-REE Mineralization of the Sevattur Carbonatites, India

Abstract The Neoproterozoic Sevattur carbonatite complex (India) consists of calcite carbonatite, silicate-poor- and silicate-rich (banded and blue) dolomite carbonatite. The trace element composition of the calcite and ferroan dolomite shows that most of them have magmatic characteristics. The predominance of dolomite carbonatite over calcite carbonatite and the absence of a genetically related silicate suite at Sevattur suggest a dolomitic parental magma derived by the direct melting of the mantle. Regardless of the prevalent magmatic character of the Sevattur carbonatites they host a plethora of Ba-Sr-REE minerals formed throughout the orthomagmatic-to-carbothermal stages under varying activities of ${\mathrm{F}}^{-}$,${\mathrm{CO}}_3^{2-}$, ${\mathrm{PO}}_4^{3-}$and ${\mathrm{SO}}_4^{2-}$. The orthomagmatic stage begins with the crystallization of calcite carbonatite containing xenocrystic diopside, antecrystic Y-bearing calcite (Cal-I), and primary benstonite, apatite, and richterite in a Sr-Mg-rich calcite (Cal-II) matrix. Fractionation of apatite, carbocernaite, and cordylite-(Ce) together with the enrichment of Mg, Fe, Na, and F in late-magmatic stages, forms the dolomite carbonatite. The decomposition of benstonite to norsethite, Ba-Ca carbonate, and strontianite occurs within dolomite carbonatite at the same stage with minimal wall-rock assimilation. Interaction between the xenocrystal clinopyroxenite and the primary magma during late-magmatic stages has resulted in the formation of aegirine and phlogopite in calcite carbonatite. Similarly, the prolonged assimilation of clinopyroxenite by the evolving magma leads to the formation of magnesio-riebeckite and magnesio-arfvedsonite within the banded- and blue carbonatites. The increasing activities of ${\mathrm{PO}}_4^{3-},{\mathrm{SO}}_4^{2-}$and H2O during the carbothermal stage, destabilizes precursor carbocernaite and cordylite-(Ce), resulting in an assemblage consisting of synchysite-(Ce), ancylite-(Ce), daqingshanite, hydroxylbastnäsite-(Ce), ferriallanite-(Ce), monazite-(Ce), and baryte in dolomite carbonatite. In the banded carbonatite, the carbothermal stage is characterized by ferri-winchite, tremolite-actinolite, and phlogopite crystallization. Further contamination and differentiation of the carbothermal fluid have resulted in the crystallization of quartz and albite in blue carbonatite. Phlogopitization within the blue carbonatite and clinopyroxenite results from late K enrichment in the carbothermal fluids.

In situ boro-mullite phase formation in Glass–Ceramic glazes: Anatase–rutile phase transformations and microstructure properties

‘‘Boro-mullite’’ is the name for mullites produced through the synthesis of boron-rich material and playing a critical role in producing high-performance materials. Also, the stability of the anatase phase in the glaze and against temperature has been addressed and improved by many studies. In situ boro-mullite crystals generated using various glass-ceramic glaze compositions that contain TiO2 and their impact on the transformation of anatase into a rutile phase were examined in this study. Additionally, the samples' water absorption, bulk density, apparent porosity and shrinkage, Vickers hardness, and optical properties were evaluated at various Al2O3 and B2O3 amounts at 700 °C, 800 °C, 900 °C, 1000 °C and 1100 °C. X-ray diffraction analysis revealed that as the temperature and Al2O3 ratio rose, it triggered the boro-mullite phase formation. On the other hand, increasing the Al2O3 ratio led to a rise in the samples' sintering temperature and delayed the anatase to rutile phase transformation. Furthermore, the presence of corundum crystals retarded the anatase crystal size growth during the remodelling process of the conversion of anatase to rutile. While the increase in the B2O3 ratio sharpened the peaks of albite crystals, the formation of rutile crystals accelerated with the increase in temperature and caused inhibition of albite formation. The albite phase's presence facilitated the creation of the liquid phase and achieved the 0.010 % water absorption and 0 % apparent porosity values as well the highest bulk density and microhardness with 2.476 g/cm3 and 550 H V. The yellowness (+b∗) values were found to be the highest at 1100 °C where the rutile crystals reached their maximum size. The anatase-rutile conversion is postponed and the increase in the yellowness value is prevented by the glaze's formation of boro-mullite. FESEM-EDS analysis showed that the temperature was the driving force in the transformation of acicular boro-mullite crystal into highly acicular prismatic needle crystal and spherical anatase crystals into the rod shape rutile.

Engineering in ceramic albite morphology by the addition of additives: Carbon nanotubes and graphene oxide for energy applications

Abstract The synthesis of zeolite nanoparticles is studied comprehensively by adding an organic template as a reflux method, extracted from crystals. The zeolite nano-crystals are quite effectively synthesized by incorporating silica, organic template, and alkali metal. The tetrapropylammoniumhydroxide, tetrapropylammoniumbromide and tetraethyl orthosilicate (TEOS) as organic templates are added for the assistance of zeolite (albite) crystals. A cross-linker TEOS is also mixed. Adding carbon nanotubes and graphene oxide made the morphology of albite more interesting. Nucleation time is an important feature for the formation of albite crystals. The albite nano-shaped crystal is developed for instance when reaction time is less than 240 h, after this period crystal size increases with time. Batch 1 of zeolite is prepared with additives for testing its morphology, like surface area, particle size shape, and crystal geometry. The general trend (e.g., pore volume, percentage composition, particle size, geometry) of zeolite nano-crystal is explained by the help of robust techniques such as Fourier transform infrared spectroscopy, X-ray diffraction, Brunauer–Emmett–Teller, energy-dispersive X-ray spectroscopy, and scanning electron microscopy.

Characteristics and formation of rare-metal pegmatites and granites in the Duanfengshan-Guanyuan district of the northern Mufushan granite complex in South China

The Mufushan area, which has abundant rare-metal pegmatites within and around the Mufushan Granite Complex, has become a major target for Ta-Nb-(Li-Be) exploration in South China. The age and origin of the pegmatites and associated rare-metal mineralization are still under debate. Here, we report the in situ U-Pb ages and geochemical characteristics of granites and pegmatites in the Guanyuan and Duanfengshan districts, which are located in the central and northern parts of the Mufushan Complex. Combined zircon, apatite and monazite U-(Th)-Pb dating revealed that biotite, two-mica, and muscovite granites from the Guanyuan and Duanfengshan districts were emplaced at 143–139 Ma, which overlaps with the U-Pb ages of columbite-group minerals (CGM) from different internal zones of the Duanfengshan pegmatites (142–140 Ma). Whole-rock major and trace element compositions and Sr-Nd-Hf isotope data reveal that the granites and pegmatites experienced continuous evolution from biotite, two-mica, and muscovite granites to pegmatite and that the magma originated from the partial melting of mica schists that are abundant in the Mufushan area. Temporal, chemical and mineralogical evidence indicates a genetic link between muscovite granite and Ta-Nb pegmatites. The textures and chemical compositions of CGM from different pegmatites exhibit features typical of magmatic CGM, indicating that fractional crystallization was the driving force that promoted Ta-Nb enrichment. The increasing alumina saturation index [ASI: molar Al/(Ca–1.67P + Na + K)] of pegmatitic melt due to albite crystallization may have been the main factor controlling CGM deposition, explaining why major Ta-Nb mineralization is bound to albite pegmatites. The Duanfengshan and other rare-metal pegmatites in the Mufushan area are derivatives of the most evolved granitic facies (i.e., muscovite granite) of the Mufushan Complex. The Duanfengshan and Renli pegmatite fields indicate that the Early Cretaceous (∼140 Ma) may have been an important, underappreciated epoch for the formation of pegmatite-related rare-metal resources in the Mufushan area and beyond in South China.

Mineral Chemistry of Pyrochlore Supergroup Minerals as Records of Nb Mineralization Processes in NYF-Type Pegmatites: A Case Study of the Emeishan Large Igneous Province, SW China

Alkaline igneous rocks have become a potentially important source of Nb, except for the carbonatites. The metallogenetic mechanism of Nb during the magmatic-hydrothermal evolution of alkaline rocks remains ambiguous. From the perspective of Nb minerals, the mineral chemistry of pyrochlore supergroup minerals provides the mineralogical evidence for indicating the respective contributions of magma and hydrothermal fluids to Nb mineralization. In the Miyi County of the Panzhihua-Xichang (Pan-Xi) area, the central zone of the Permian Emeishan large igneous province (ELIP) in SW China, hundreds of Nb-Y-F mineralized pegmatites (NYF-type) are exposed. This study conducted in situ mineral chemistry analyses on four types of pyrochlores to elucidate the Nb mineralization process. Both Pcl-I and Pcl-II exhibit well-developed oscillatory zoning (OZ), representing magmatic pyrochlore formed through disequilibrium crystallization in an oscillatory environment. Pcl-III, with a homogeneous and less variable composition, is also considered of magmatic origin due to its coherent chemical evolution with Pcl-II. Pcl-IV is considered of hydrothermal origin based on its irregular zoning texture, extremely high Na2O contents, and compositional gap compared with magmatic types. The decrease in TiO2 contents, coupled with the increase in Na2O, F, and Nb2O5 contents from Pcl-I to Pcl-III and from the core to the rim of zoned Pcl-II, indicates that fractional crystallization facilitates the crystallization of albite and the enrichment of volatiles, as well as the precipitation of Nb from the early to late stages. During the magmatic-hydrothermal transition stage, the reductive, Na- and F-enriched fluid transports Nb more effectively, leading to further Nb enrichment in pyrochlore. Consequently, there are two-stage Nb mineralization processes associated with the magmatic-hydrothermal evolution in the Miyi pegmatite, with the primary magmatic ore assemblages being the dominant Nb mineralization, which may be a general model for the mineralization of NYF-type pegmatites.

Albitization evidences of Mesozoic carbonates: petrological study of authigenic albites in the northwest of the Bortziriak Cinco Villas Massif, eastern Basque-Cantabrian Basin

The presence of authigenic Na-feldspars in sedimentary carbonate rocks is unusual and its origin is controversial in terms of genesis and timing. The use of optical microscopy, cathodoluminescence and in situ semi-quantitative EDX analysis techniques, has allowed the identification and characterization of authigenic albite crystals in the Mesozoic pre- and syn-rift carbonates of the northwestern margin of the Bortziriak-Cinco Villas Massif, in the northeastern Basque-Cantabrian Basin (western Pyrenees). The euhedral habit, crystal size, spatial distribution and crosscutting relationships, together with the pure albitic composition, suggest a relatively early replacement origin. Compaction of sediments during burial, besides possible fluid migration linked to the intense syn-rift halokinetic activity, may have been decisive for the mobilisation of cations, and hence, for the albitization of the carbonate rocks.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 3. Mineralogy of lithium-bearing objects: feldspars

Traditionally, feldspars are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — kamyano-mohyla (stone grave) complex of Azov region — Kruta Balka rare-metal deposit — Shevchenkivske rare-metal deposit — rare-metal pegmatites of Inhulsky megablock. Feldspars in the chamber pegmatites of the Volyn are represented by maximum microcline-perthite, rarely by intermediate orthoclase and albite. Widely developed feldspars with close regularity, but different symmetry. The form of discharge is granular aggregates and polyhedral crystals. The outline of potassium feldspar crystals is varied. Crystals of only two morphological types have a clear arrangement: I — early high-temperature bar-like individuals, concentrated in the cavities of the graphic zone; II — columnar pseudohexagonal crystals in sinkholes. Among albite crystals, three morphological types are distinguished, depending on acidity-alkalinity and crystallization temperature. Feldspars of chamber pegmatites are well studied by radio spectroscopic, luminescent and genetic methods. Within the boundaries of the Perzhansky ore complex, multi-grained polygenic microcline-perthite dominates, the structural state of its potassium phase corresponds to a high degree of ordered distribution of Si and Al (maximum microcline). The evolution of the twin structure of potassium feldspars is briefly covered and illustrated. Pure microcline and amazonite (probably the purest on the Ukrainian Shield) were found in the perzhansky metasomatites. Feldspars are the leading minerals of the stone-burial complex of the Azov region, represented by microcline and microcline-perthite. A characteristic feature of the microcline rocks of the complex is the unique giant dendritic crystals of pink microcline. Feldspars in the Kruta Balka rare metal deposit are represented by albite, albite-oligoclase and microcline. Two feldspars — microcline and albite (in the form of perthites in microcline and independent aggregates) were diagnosed in the Shevchenkivske deposit. Microcline makes up 15-20% of the volume of pegmatites and represented by three generations. The mineralogy of feldspars in the pegmatites of the Inhulsky megablock is different. They are represented by monoclinic orthoclase, microcline and plagioclase (mostly albite, occasionally oligoclase). Their content in rocks is mostly >50%, but albite >potassium feldspar. In general, these feldspars have features uncharacteristic of rare-metal pegmatites: 1) high symmetry (monoclinic) and low order (t1 >0,7); 2) microperthite decay structure; 3) the initial and middle stages of monodomainization are manifested. These and other features of minerals are a consequence of the specific origin of pegmatites, which represent a new genetic type of deposits of rare elements — metapegmatites.

Study on characteristics of coal gasification fine slag-coal water slurry slurrying, combustion, and ash fusion

In this study, the effects and mechanisms of coal gasification fine slag-coal water slurry (CGFS-CWS) preparation, combustion and ash fusion (AF) were assessed. As the CGFS content increased, the viscosity of the slurry increased, but the stability of the slurry improved significantly. The improvement in the slurry stability is due to the negative charge on the surface of CGFS is significantly stronger than that coal particles. This stronger charge provides strong electrostatic repulsion, which facilitates particle dispersion. The slurry combustion experiments revealed that the incorporation of CGFS significantly reduced the burnout temperature of the slurry and increased the maximum combustion rate. When the mixing amount was less than 8%, the flammability index, combustion stability index, and comprehensive combustion characteristic index significantly improved. Such finding may be due to the formation of activation centers by the alkali metals in CGFS, which promote combustion reactions. The AF temperature of the CGFS-CWS ash decreased as the CGFS blending amount in the slurry increased. This result is due to the melting-assisting effect produced by the Fe2O3 and sulfate contained in the CGFS ash. Albite crystallization with a lower fusion temperature also appeared in the CGFS-CWS, which may be generated by the reaction of nepheline in coal ash and sodium-containing compounds in CGFS ash at high temperatures.

The Nucleation of Albite Crystals in Natural Volcanic Obsidian Glass

The Nucleation of Albite Crystals in Natural Volcanic Obsidian Glass

Seismic properties across an amphibolite- to greenschist-facies strain gradient (Neves area, eastern Alps, Italy): New considerations for shear zone imaging

Detecting the presence and geometry of crustal shear zones by geophysical methods relies on our understanding of the intrinsic parameters controlling the seismic properties of these deformed rocks, over the range of pressure-temperature conditions expected in the Earth's crust. To this end, we aimed to track changes in P-wave propagation velocity (VP), anisotropy (AVP) and S-wave splitting (AVS) across a natural shear zone using experimental and electron backscatter diffraction methods. Five samples were collected across a meter-scale shear zone developed under amphibolite- to greenschist-facies in the Neves metagranodiorite (Tauern Window, Eastern Alps). With increasing strain, seismic properties show a non-linear evolution resulting from interactions among structural, textural and mineralogical changes. Geometry and magnitude of seismic anisotropy are controlled by the interference of strongly anisotropic phyllosilicates with less anisotropic but more abundant quartz and plagioclase. The amphibolite-facies shear zone margin (> 500 °C) is free of major mineral transformations, and rather characterized by the development of S-C structure, inducing an orthorhombic symmetry to the VP distribution and up to 12 % AVP, with the fast axis parallel to lineation. AVS is maximized (6 %) in the two directions parallel to the C-planes. Further deformation under greenschist-facies (450–500 °C) induces significant crystallization of muscovite, chlorite, and albite. A dominant hexagonal symmetry develops, with a fast VP plane and a fast S-wave polarization plane along the C-planes. AVP and AVS exceed 10 %. The computed elastic tensor of the whole shear zone emphasizes the importance of the strain gradient on the seismic signature of the overall structure. In our model, the bulk seismic properties are dominated by the orthorhombic symmetry of the protomylonitic zone rather than by the ultramylonite core with hexagonal symmetry (C-plane), which may explain why seismic studies of shear zones commonly involve a fast velocity plane oblique to the layer boundaries.

Synthesis of porous silicate materials using sodium fluride as fluxing agent

Foam glass products are very actively used for thermal and chemical protection of oil and gas infrastructure instead of polymer materials. The main trend in foam glass technology is a search for new raw materials. A presence of refractory alumina in the raw materials necessitates the introduction of substances that reduce the melting temperature of silicate masses (fluxes). The aim of this work was to study the processes that occur during the heat treatment of foam glass batches when sodium fluoride NaF is added as a flux. The synthesis of porous materials was carried out by powder method according to the hydrate mechanism based on the interaction between silicate raw materials and an alkali solution. The initial batch compositions were developed, and their heat treatment was performed. TG/DSC analysis showed that NaF does not affect mass change processes, including the removal of physically bound water, crystalline hydrated water from hydrosilicates, chemically bound water, and decomposition of organic and carbonate impurities. There is also an endothermic effect of the “β-quartz→α  -quartz” transition for both compositions. However, there is a sharp endothermic jump in the composition with the NaF addition at temperatures above 600 оC due to exposure to sodium fluoride. It was shown that ions from fluoride dissociation are concentrated in a less polymerized microphase, sharply changing its viscosity properties and the viscosity of the melt as a whole. It was set that most of the silicate mass is in an X-ray amorphous glassy state. The main crystalline phase is α -quartz in an amount of not more than 25%, and albite crystals can also be distinguished. As a result of studying the internal structure and density of the synthesized samples, it was found that the introduction of sodium fluoride significantly accelerates the process of silicate mass melting, which makes it possible to obtain samples with a density of 313 kg/m3 at 750 оC and subsequently leads to the breakthrough of pore walls, pore coalescence, and severe sedimentation of the foam, which complicates manufacturing process of high-quality materials. Thus, the use of sodium fluoride in the synthesis of porous silicate materials can be recommended in a small amount as an active fluxing agent.This research was carried out by the Platov South-Russian State Polytechnic University (NPI) and funded by the Russian Science Foundation under the Agreement No. 19-79-00015 “Understanding some general regularities related to the synthesis of porous materials on the basis of man-made and natural silicates” (led by B. M. Goltsman).

An outer shelf shelly fauna from Cambrian Series 2 (Stage 4) of North Greenland (Laurentia)

AbstractAn assemblage of 50 species of small shelly fossils is described from Cambrian Series 2 (Stage 4) strata in North Greenland, the present day northernmost part of the paleocontinent of Laurentia. The fossils are derived from the basal member of the Aftenstjernesø Formation at Navarana Fjord, northern Lauge Koch Land, a condensed unit that accumulated in a sediment-starved outer ramp setting in the transarctic Franklinian Basin, on the Innuitian margin of Laurentia. Most other small shelly fossil assemblages of similar age and composition from North America are described from the Iapetan margin of Laurentia, from North-East Greenland south to Pennsylvania. Trilobites are uncommon, but includeSerrodiscus. The Australian bradoriidSpinospitellais represented by a complete shield.Obolella crassais the only common brachiopod. Hyoliths, includingCassitella,Conotheca,Neogloborilus, andTriplicatella, are abundant and diverse, but most are represented just by opercula. Sclerites interpreted as stem-group aculiferans (sachitids) are conspicuous, includingQaleruaqia, the oldest described paleoloricate,Ocruranus?,Inughuitoconusn. gen., andHippopharangites. Helcionelloid mollusks are diverse, but not common; they are associated with numerous specimens of the bivalvePojetaia runnegari. The fauna compares best with that of the upper Bastion Formation of North-East Greenland, the Forteau Formation of western Newfoundland, and the Browns Pond Formation of New York, but several taxa have a world-wide distribution. Many specimens are encrusted with crystals of authigenic albite. New species:Anabarella?navaranae,Stenotheca?higginsi,Figurina?polaris,Hippopharangites groenlandicus,Inughuitoconus borealis, andOcruranus?kangerluk.UUID:http://zoobank.org/160a17b1-3166-4fcf-9849-a3cabd1e04a3

Petrology of green polished stone axes of the Jomon period from the Sannai‐Maruyama site, Japan, investigating the origin of source rock

AbstractNumerous green polished stone axes have been excavated from the Sannai‐Maruyama site, one of Japan's largest archeological sites in the Jomon period (5.9–4.2 cal kyr BP). The axes are composed of weakly metamorphosed fine‐grained volcaniclastic rock having a peculiar texture that includes numerous acicular actinolites growing in random directions within a quartz and albite matrix. Cobbles of Aotora stone found along the Nukabira River, Biratori town, southern Hokkaido, are the most likely raw material for these stone axes. Aotora stones have alternate bands of a soft dark‐green picritic layer and a hard SiO2‐rich pale‐green layer. The pale‐green layer has a texture similar to the stone axes. Basaltic and picritic volcanic rocks of the Sorachi‐Yezo Belt occupy the area along the Shidoni River, a tributary of the Nukabira River. Volcaniclastic rocks similar in texture, mineralogy, and bulk rock compositions to the Aotora stone are exposed in the area. These rocks underwent metamorphism under the actinolite‐pumpellyite facies conditions. Their protolith is submarine hyaloclastic rocks that are intercalated with laminated picrite detritus. The stone axes, pale‐green layers of Aotora stone, and those of the volcaniclastic rocks of the Shidoni River area all have high SiO2 (~ 55 wt%), Cr (~ 840 μg/g), and Ni (~ 370 μg/g). The rare earth element patterns with abundant light rare earth elements and depleted heavy rare earth elements of stone axes were also consistent with the pale‐green layers of the outcrop. These pale‐green layers, interleaved with dark‐green layers of picritic detritus, were the likely source rock of the stone axes. The high SiO2 content in the pale‐green layer caused the crystallization of quartz and albite in the matrix, which resulted in high‐quality raw material for making stone axes.

Uranium mineralization associated with late magmatic ductile to brittle deformation and Na–Ca metasomatism of the Pan-African A-type Zabili syntectonic pluton (Mayo-Kebbi massif, SW Chad)

The Mayo-Kebbi massif (Chad) exposes a Neoproterozoic juvenile crustal segment that has been tectonically accreted in the Central African Orogenic Belt and reworked during the Pan-African orogeny. It comprises a syntectonic high-K magmatic suite including the Zabili A-type granitic pluton. The Zabili pluton is made of a highly differentiated granite generated by fractional crystallization of a magma formed by partial melting of a Neoproterozoic juvenile protolith. Syn- to post-magmatic ductile to brittle deformation of the Zabili pluton is associated with metasomatism and deposition of uranium. Primary magmatic U-bearing minerals are zircon, monazite, and uranothorite. Late-magmatic deformation and Na-metasomatism are marked by the development of R’ antithetic shear zones with high-temperature dynamic recrystallization of K-feldspar and Ca-plagioclase phenocrysts coeval with crystallization of albite along deformation bands and grain boundaries, and crystallization of interstitial amphibole, calcite epidote and albite also affected by intracrystalline deformation. At this stage, U-bearing minerals are monazite, uraninite, brannerite (pseudomorphosed in ekanite). This late-magmatic event is dated by U–Th–Pb on monazite at 599 ± 4 Ma. Brittle deformation and Ca-metasomatism are marked by cataclastic zones and veins containing albite, epidote, calcite, chlorite, apatite, metamict zircon, pitchblende, U-silicates, and iron oxides. U-bearing minerals are altered and/or remobilized in ekanite, kasolite, and uranophane. These data suggest that the uranium mineralization hosted by the Zabili pluton records a superposition of processes and traces extreme crustal differentiation of a Neoproterozoic juvenile crustal segment reworked during the Pan-African orogeny.

Tourmaline as a Recorder of Ore-Forming Processes in the Xuebaoding W-Sn-Be Deposit, Sichuan Province, China: Evidence from the Chemical Composition of Tourmaline

The Xuebaoding W-Sn-Be deposit located in the Songpan-Ganze Orogenic Belt (Sichuan Province, China) is a hydrothermal deposit with less developed pegmatite stage. The deposit is famous for the coarse-grained crystals of beryl, scheelite, cassiterite, apatite, fluorite, muscovite, and others. The orebody is spatially associated with the Pankou and Pukouling granites hosted in Triassic marbles and schists. The highly fractionated granites are peraluminous, Li-Rb-Cs-rich, and related to W-Sn-Be mineralization. The mineralization can chiefly be classified based on the wallrock and mineral assemblages as muscovite and beryl in granite (Zone I), then beryl, cassiterite and muscovite at the transition from granite to triassic strata (Zone II), and the main mineralized veins composed of an assemblage of beryl, cassiterite, scheelite, fluorite, and apatite hosted in metasedimentary rock units of marble and schist (Zone III). Due to the stability of tourmaline over a wide range of temperature and pressure conditions, its compositional variability can reflect the evolution of the ore-forming fluids. Tourmaline is an important gangue mineral in the Xuebaoding deposit and occurs in the late-magmatic to early-hydrothermal stage, and can thus be used as a proxy for the fluid evolution. Three types of tourmalines can be distinguished: tourmaline disseminations within the granite (type I), tourmaline clusters at the margin of the granite (type II), and tourmalines occurring in the mineralized veins (type III). Based on their chemical composition, both type I and II tourmalines belong to the alkali group and to the dravite-schorl solid solution. Type III tourmaline which is higher in X-site vacancy corresponds to foitite and schorl. It is proposed that the weakly zoned type I tourmalines result from an immiscible boron-rich aqueous fluid in the latest stage of granite crystallization, that the type II tourmalines showing skeletal texture directly formed from the undercooled melts, and that type III tourmalines occurring in the mineralized veins formed directly from the magmatic hydrothermal fluids. Both type I and type II tourmalines show similar compositional variations reflecting the highly fractionated Pankou and Pukouling granites. The higher Ca, Mg, and Fe contents of type III tourmaline are buffered by the composition of the metasedimentary host rocks. The decreasing Na content (<0.8 atoms per formula unit (apfu)) and increasing Fe3+/Fe2+ ratios of all tourmaline samples suggest that they precipitated from oxidized, low-salinity fluids. The decreasing trend of Al content from type I (5.60–6.36 apfu) and type II (6.01–6.43 apfu) to type III (5.58–5.87 apfu) tourmalines, and associated decrease in Na, may be caused by the crystallization of albite and muscovite. The combined petrographic, mineralogical, and chemical characteristics of the three types of tourmalines thus reflect the late-magmatic to early-hydrothermal evolution of the ore-forming fluids, and could be used as a geochemical fingerprint for prospecting W-Sn-Be mineralization in the Xuebaoding district.

Bohseit z beryl-columbitového pegmatitu D6e v Maršíkově (silezikum, Česká republika)

Bohseite was found in a lenticular body of D6e beryl-columbite granitic pegmatite near Maršíkov, which is hosted by amphibole gneisses of the Sobotín Amphibolite Massif (Silesicum, northeastern part of Czech Republic). Bohseite forms chalky white aggregates up to 1 cm in size, which are hosted by small vugs in the coarse-grained pegmatite. It is associated with small crystals of quartz, adularia, albite, muscovite and epidote. Bohseite is orthorhombic, space group Cmcm with following unit-cell parameters refined from X-ray powder diffraction data: a 23.210(2), b 4.955(2), c 19.428(3) Å and V 2234.5(1.0) Å3. The electron microprobe compositional data of bohseite are presented. Bohseite from Maršíkov contains 14.3 - 42.5 mol. % of bavenite component, up to 0.06 apfu Na and 0.13 - 0.36 apfu F. The association with other beryllium-rich phases (milarite, bertrandite) points to variable activities of Be and Al during hydrothermal stage of evolution of the pegmatite body. The likely source of Be was beryl, which is sometimes completely dissolved and vugs after its crystals are lined by small crystals of above mentioned hydrothermal phases.

Magmatic-hydrothermal evolution of rare metal pegmatites from the Mesoproterozoic Orange River pegmatite belt (Namaqualand, South Africa)

The 450 km long Orange River pegmatite belt intruded the Namaqua Sector of the Mesoproterozoic Namaqua-Natal Province, Southern Africa, at ca. 1 Ga. The western part of the belt is characterized by the occurrence of LCT pegmatites locally mineralized in Li, Ta, Nb, Be and Bi. Most of these mineralized pegmatites display zonation with a quartz-feldspar-muscovite-garnet-beryl-bearing aplite border and wall zone, a quartz-feldspar-spodumene-lepidolite-bearing intermediate zone, and a quartz-K-feldspar core. The pegmatites and their granodioritic country rocks commonly show evidence of albitization and greisenization (i.e. secondary muscovitization). In this study, detailed petrographic observations and the compositions of mica, feldspar, spodumene and Nb-Ta oxide minerals are reported. This information is combined with bulk country rock compositions and new U-Pb zircon and monazite ages plus Sm-Nd isotope compositions of monazite to constrain the origin and magmatic-hydrothermal evolution of weakly and strongly mineralized LCT pegmatites.The Li-Ta-Be Kokerboomrand I pegmatite emplaced at ca. 985 Ma during the main stage of pegmatite emplacement in the Orange River belt and regional strike-slip deformation. It has εNd(t)monazite = −14 ± 3 and potentially formed by partial melting of Paleoproterozoic rocks from the Richtersveld magmatic arc. Alternatively, Mesoproterozoic sediments of the Bushmanland Subprovince may also provide a suitable magma source for the Kokerboomrand I pegmatite.The rare metal contents of muscovite and columbite group minerals (CGM) increase from the weakly mineralized to strongly mineralized pegmatites, suggesting early-stage fractional crystallization or variable partial melting conditions. Mica Nb/Ta values of <14 and K/Rb ratios of <40 can be used as geochemical tools for Li-Ta-(Nb)-Be exploration in the region, and possibly in other pegmatite belts worldwide.Rare metal-bearing minerals crystallized throughout the magmatic-hydrothermal evolution of mineralized pegmatites. During the magmatic-dominated stage I, constitutional zone refining likely induced a decrease of spodumene Fe contents and increase of CGM Ta contents toward the pegmatite core. Stage II marks the pervasive circulation of an immiscible hydrosaline melt. This stage is characterized by the replacement of the primary mineral assemblage by lamellar albite (cleavelandite), (fluor)calciomicrolite and Cs-Ta-rich Li-muscovite and zinnwaldite. Stage III represents the progressive transition from a magmatic-hydrothermal system dominated by a Li-Cs-Ta-rich hydrosaline melt toward a system mainly involving (Li)-Cs-(Ta)-Bi-rich aqueous fluids. This stage is characterized by the crystallization of lepidolite and zero-valence-dominant pyrochlore as well as strong localized greisenization and Bi mineralization.Magmatic-hydrothermal alteration of the immediate country rock of the mineralized pegmatites is marked by the crystallization of albite, Li-Ta-Cs-rich mica, various Nb-Ta oxide minerals, and led to a strong decrease of the whole-rock Nb/Ta ratio plus significant rare metal enrichment.Our findings from the Orange River belt demonstrate that an important role can be ascribed to melt-melt and melt-fluid immiscibility and metasomatism in the formation of pegmatite-related rare metal deposits. Greisens and albitites associated with pegmatites and their immediate country rocks can be considered as favorable targets for Li-Ta mineral exploration. Strong and pervasive metasomatism across the mineralized pegmatites and their country rocks suggests involvement of a parental medium that was highly enriched in water.

Tantalum and niobium mineralization from F- and Cl-rich fluid in the lepidolite-rich pegmatite from the Renli deposit in northern Hunan, China: Constraints of fluid inclusions and lepidolite crystallization experiments

Lepidolite-type pegmatite usually produces tantalum–niobium (Ta–Nb) resources; however, the role of the hydrothermal fluid in the Ta–Nb mineralization remains controversial. The pegmatite dike No. 5 is a lepidolite-rich dike in the Ta–Nb pegmatite deposit in Renli, Hunan, China, with a high-grade Ta2O5 in the lepidolite–quartz core. The fluid inclusions with primary features in the quartz from the core have a relatively high Ths (~270–290 °C) and salinity (~10 wt% NaCleq). The mineral features such as occurrences of pezzottaite and fluornatromicrolite, as well as the assemblage of lepidolite, quartz, and albite, further confirm that the fluid inclusions were entrapped in a Na-, Li-, Cs-, F-, and Cl-rich fluid from which quartz and lepidolite crystallized. These fluid inclusions were inferred to be trapped between 640 °C and 530 MPa and 550 °C and 350 MPa, based on the fluid inclusion isochores and the lepdilite crystallization temperature–pressure (T–P) conditions that were determined via lepidolite crystallization experiments in aqueous solutions with a high fHF and a salinity of 10 wt% NaCl in a hydrothermal diamond-anvil cell. Although the P–T conditions are in accordance with the stability field of spodumene, no spodumene was observed in the No. 5 dike because of the high fHF in the fluid. Such Li-, Cs-, F-, Cl-rich fluids could be an indicator of the final layer liquid in the model of constitutional zone refining or B-type fluid/melt in the immiscibility model. Moreover, it could dissolve the previous magmatic Nb–Ta minerals in the form of (Li, Na, Cs)[Ta(Nb)O(F, Cl)4] with Ta–Nb remaining in the aqueous solution until the deposition of Ta-Nb minerals during the crystallization of lepidolite and albite in lepidolite-qaurtz core in No.5 dike in the Renli deposit.

Formation and evolution of snowball quartz phenocrysts in the Dongping porphyritic granite, Hebei Province, China: Insights from fluid inclusions, cathodoluminescence, trace elements, and crystal size distribution study

Quartz phenocrysts are common in many granites, volcanic rocks, metamorphic rocks and hydrothermal deposits. The Dongping porphyritic granite contains large amounts of rounded to sub-rounded quartz phenocrysts. Minerals in this porphyritic granite show weak but distinct orientation. Dense clusters of fluid inclusions and albite crystals exist in the quartz, showing snowball texture. Two types of snowball quartz are recognized: (1) large snowball quartz phenocrysts containing large albite grains distributed in the core and small albite grains distributed in the mantle, and (2) small snowball quartz crystals containing small albite grains. The granite is characterized by high SiO2 (7.15–73.44 wt%), K2O (4.70–5.10 wt%) and Na2O (4.93–5.21 wt%) contents, low CaO (0.41–0.71 wt%), MgO (0.03–0.05 wt%), Fe2O3 (0.87–0.94 wt%), TiO2 (0.02–0.03 wt%) and ΣREE (7.10–9.80 ppm) contents. The granite has similar mineral and chemical composition with the aplite in the area, and they were derived from the residual melt of the Shuiquangou magma that suffered assimilation fractional crystallization process. Fluid inclusions in the quartz phenocrysts have homogenization temperatures of 260–380 °C and salinities of 1.4–12.4 wt% NaCl equiv. for liquid + vapor type inclusions and 34.1–44.3 wt% NaCl equiv. for brine ones. The quartz phenocrysts exhibit homogeneous cathodoluminescence without growth bands or zoning. The trace element contents in the quartz phenocrysts are extremely low (Ti 3.4–5.1 ppm, Al 13–118 ppm, Li < 0.1 ppm, Ge < 0.5 ppm) compared to published data of igneous quartz, which may result from the crystallizing conditions of quartz and chemical compositions of the magma. Crystal size distributions (CSD) of albite in quartz show that the snowball quartz formed in two stages, whereby an increase in nucleation and growth rates resulted in the core-mantle texture of quartz phenocrysts. The co-existence of low-, high-salinity and melt inclusions indicates that the quartz phenocrysts crystallized rapidly in a fluid-enriched magma. Magmatic flow led to mineral rotation and resulted in the rounded and sub-rounded shapes of the quartz phenocrysts. Fluid exsolved from the magma raised nucleation and growth rates and resulted in the two types of snowball quartz.

Influence of red mud on fresh and hardened properties of self-compacting concrete

Red mud is a waste product from the production of alumina, it currently has limited industrial use. This study proposed to use red mud to partially replace fly ash (12.5, 25 and 50% by weight) in self-compacting concrete (SCC) and the influence of red mud on the fresh and hardened properties and microstructural behaviour of SCC were studied. Slump-flow, T500 and J-ring tests were carried out on fresh SCC mixtures. The hardened properties of red mud SCCs including compressive strength, tensile strength and elastic modulus were studied. Moreover, the chemical composition and microstructural properties of red mud concrete samples were analysed using X-ray diffraction (XRD), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS), respectively. The results show that the mechanical strength of concrete increased with increasing red mud content. SCC samples consisting 50% red mud performed the best for the compressive strength and elastic modulus. The results from microscopic studies indicated that there was a slight improvement in the interfacial transition zone (ITZ) between aggregate and cement paste for red mud concrete compared with control concrete. The XRD results indicated that the chemical composition of cement paste containing red mud showed higher sodium and iron contents. With increasing red mud content, some albite crystals appearing in triclinic shape were also identified by XRD.