Quartz Core Research Articles

Distribution of trace elements in growth zones and sectors of spodumene crystals (Pashki deposit, Nuristan, Afghanistan)

Regular distribution of several trace elements in spodumene crystals of the Pashki pegmatite Li deposits in Afghanistan (Nuristan province) is analyzed using secondary ion mass spectrometry (SIMS). Twenty seven local analyses of 19 elements were carried out in spodumene samples of different generations taken from pegmatites during feld works of 2023. We studied an early generation spodumene crystal from blocky spodumene-quartz-albite pegmatite and two late generation spodumene crystals including an euhedral crystal from a quartz core of pegmatite and a crystal extracted from a mineralized cavity together with quartz crystal, albite, and muscovite. It is found that the Fe, B, and Be content is signifcantly higher in the growth pyramid of the pinacoid face (010) than in the growth pyramid of the prism face (021). From early to late growth zones, the Be, B, Fe, and Mn content increases and the K, Rb and Ti content decreases. The heterogeneity of trace element composition of spodumene crystals thus mostly depends on their sectoriality, which is caused by different crystal chemical conditions of the incorporation of isomorphic trace elements into the mineral structure on faces parallel and perpendicular to the direction of pyroxene chains of Si–O tetrahedra along axis [001] rather than by their zonation. From early to late generations of spodumene, the content of most analyzed trace elements signifcantly decreases corresponding to the ideas about the change in the crystallization fractionation of elements during the evolution of the pegmatite process transiting from the closed to open physicochemical system.

Carbonatite Metasomatism in a Subvolcanic Setting: Breccia at the Badou Carbonatite in the North China Craton and Implications for Magmatic Evolution and Eruptive Style

Abstract The genesis and primary compositions of carbonatite melts are enigmatic owing to their reactivity and resulting contamination in the mantle and crust. This overprints earlier uncontaminated compositions and obscures their origins. The subvolcanic Badou carbonatite in the North China Craton is characterized by brecciated textures and comprises pristine clinopyroxene, mica, and apatite phenocrysts in a mixed, carbonate–silicate matrix. Here, we provide mineralogical, textural, and major and trace elemental results to reveal the mantle derivation of the Badou carbonatite melt, and its compositional modification during interaction with crustal materials. Clinopyroxene and apatite phenocrysts have initial Sr isotopes (0.70920–0.71037) similar to brecciated calcite (0.71028–0.71159) and the whole rock (0.70953–0.71061), indicating a common source. Rare Mg-rich clinopyroxene and mica contain high Cr and Ni contents, recording direct mantle derivation without immiscibility from silicate melts. Abundant feldspars and aegirine, occurring as both phenocrysts and fine-grained matrix, formed an antiskarn at relatively low temperatures indicating extensive silica contamination upon crustal emplacement. Silica contamination is further indicated by britholite-rich apatite rims and relict quartz cores in clinopyroxene. Zircon xenocrysts were partly assimilated, indicated by Zr and Hf enrichment in late-stage silicates, and partly underwent decomposition to baddeleyite in a decreasing silica activity environment. The assimilation process consumed the carbonate melt, forming refractory silicate minerals and CO2 vapor, leading to near-surface gas overpressure with a decrease in magma viscosity. This elevates the potential for explosive activity, which, in turn, provides a positive feedback mechanism for silica assimilation. The complex evolution of the carbonatite melt in the crust might be responsible for the compositional gap between the natural rocks and experimental outcomes, and results in different eruption styles.

Mechanism of beryllium mineralization in a granite-pegmatite system: Constraints from ore geology and beryl mineralogy of the large Arskartor Be-Nb-Mo deposit, southern Chinese Altai

The Arskartor Be-Nb-Mo deposit is the second largest Be deposit in the Chinese Altai, NW China, which hosts over 11,000 tons of BeO resource. The muscovite-albite granite and rare-metal pegmatite in the ore district are spatially and temporally coexisted and both are beryllium mineralized. The muscovite-albite granitic stock can be divided into a barren zone and a Be-mineralized zone. The pegmatite shows an well-developed internal zone including the layered muscovite-quartz-albite zone, (lower) beryl-muscovite-quartz zone, quartz core, (hanging) beryl-muscovite-quartz zone, and muscovite-quartz-microcline zone. Beryl is the dominant Be-bearing mineral and mainly occurs in the Be-mineralized granite, the layered muscovite-quartz-albite and the beryl-muscovite-quartz zones of the pegmatite. Subhedral to euhedral beryl in the Be-mineralized granite is interstitial to or intergrown with rock-forming minerals. In contrast, beryl crystals in the pegmatite are coarser in grain size and more euhedral in shape, and mainly coexist with coarse “booked” muscovite and blocky quartz. Concentrations of Li, Cs and Na/Li ratios of beryl are 184–760 ppm, 218–1996 ppm, and 2.13–21.3, respectively. The progressive variations of incompatible elements compositions and Na/Li ratios are consistent with the fractional crystallization mechanism of the granite-pegmatite system. Paragenesis and internal structure of beryl suggest nonequilibrium crystallization of a relatively incompatible elements and fluxes-enriched late granitic melt, generated the coarse-grained Be-mineralized granite. With the progressive enrichment of incompatible and fluxing elements and decreasing temperature, liquidus overcooling was achieved and generated the aplite and immediate zoned pegmatite that hosts abundant beryl. Moreover, the differentiating pegmatitic melt with varying amounts of aqueous fluids at different melt fractions, likely resulted in heterogeneous distribution of beryllium and subsequent variable amounts of beryl crystallization in different internal zones. The exsolution of aqueous fluids from the residual pegmatitic melt resulted in Mo-mineralization and related hydrothermal alteration. Consequently, both protracted fractional crystallization and subsolidus processes contributed the formation of the Arskartor granite-pegmatite system with Be-polymetallic mineralization.

Phosphate sequence study of Boqueirão pegmatite (Rio Grande do Norte state, Brazil)

O pegmatito Boqueirão localiza-se naProvíncia Pegmatítica daBorborema, no estado do Rio Grande do Norte (Nordeste do Brasil), encontra-se encaixado em metaconglomerados de idade neoproterozóicada Formação Equador. Trata-se de um pegmatito zonado concentricamente, exibindo diferentes zonas caracterizadas por suas mineralogias. As zonas de contato e de parede são compostas essencialmente por quartzo, microclina e moscovita exibindo muitas vezes texturas esqueléticas e gráficas, e,tendo como minerais acessórios a turmalina e a granada. A zona intermediária é dividida em duas subzonas distintas e mostra uma mineralogia diversa exibindo uma complexa associação de fosfatos, berilo, columbita-tantalita e zircão. A zona mais interna é principalmente constituída por um núcleo de quartzo. Além disso, observa-se corpos de substituição típicos, constituídos por albita,situados na parte oriental do corpo. Litofilita - triplilita representa a fase de fosfato mais abundante exibindo exsoluções de sarcopsida e substituição por sicklerita, resultante da alteração por Li- lixiviação, mais conhecida como Série de Quensel-Mason. A ausência de membros da série heterosita-purpurita é notável. Fosfatos primários, tais como montebrasita e triplita são também observados. Subsequentemente, a presença de alluaudita e varulita sugere que o pegmatito foi submetido a metassomatismo sódico.Toda esta assembléia de minerais sofreu uma extensa alteração que levou a cristalização de fosfatos secundários. Dados de microssonda eletrônica em trifilita-litiofilita revelam razões Mn/(Mn + Fe) entre 0,21-0,24 e também até 0,72 que sugerem um magma de origem pouco fracionado; consequentemente, a ferrisicklerita mostra valores de Mn/(Mn + Fe)entre 0,69-0,77, característicos de elevado grau de evolução, sugerindo que o pseudomorfismo foi produzido por uma elevada interação entre rocha/fluido. Alluaudita e varulita também revelam conteúdos de Mn e Fe até 0,71 semelhantes aos fosfatos precursores. Além disso, oito diferentes fosfatos secundários foram identificados substituindo fases primárias, quer como pseudomorfos ou cortando-as. Ocorrem como cristais euédricos de grã fina, esferulíticos ou maciços, com cores vivas facilmente identificados. As fases secundárias ricas em Mn são hureaulita, eosphorita, whiteita, jahnsita e serrabrancaita, enquanto que lipscombita, phosphosiderita e mitridatita correspondem a associação secundária rica em ferro (Fe). A origem supergênica tardia e a entrada fluidos ricos Ca, K e Mg procedentes da rocha hospedeira são sugeridos como responsáveis pela formação destes fosfatos. Não há quaisquer feições que os correlacionem a cristalização do pegmatito. O conteúdo de Háfnio (Hf) de zircões encontrados na zona intermediária tem sido analisado por microssonda eletrônica, e, usado como um poderoso indicador do grau de evolução do pegmatito, juntamente com o conteúdo de Mn dos fosfatos. O conteúdo Hf obtido é baixo chegando até 5% em peso de HfO2, que revela um magma pegmatítico pouco fracionado. Além disso, a presença de silicatos ferromagnesianos que constituem a mineralogia de zonas do pegmatito, como a turmalina rica em Fe, a granada e o berilo verde está de acordo com esta hipótese. Portanto, o Pegmatito Boqueirão corresponde a um pegmatito de elementos raros subtipo berilo-columbita-fosfato.

Compositional zoning of the Otowi Member of the Bandelier Tuff, Valles caldera, New Mexico, USA

Abstract The Otowi Member of the Bandelier Tuff erupted at ca. 1.60 Ma from the Valles caldera (New Mexico, USA). It consists of as much as 400 km3 (dense rock equivalent) of strongly differentiated high-silica rhyolite and shows systematic upward variations in crystallinity, mineral chemistry, and trace element concentrations through its thickness, but the major element composition is almost constant and is near the low-pressure granite minimum. Incompatible trace elements in whole pumice fragments and glasses show well-correlated linear covariations. Upward zoning to lower abundances of incompatible trace elements is accompanied by development of overgrowths on quartz and alkali feldspar, although earlier-formed interiors of quartz and feldspar have near-constant compositions throughout the tuff, modified by cation diffusion in the case of feldspar. Melt inclusions in remnant quartz cores show diverse Pb isotope ratios, pointing to a wide range of distinct protoliths that contributed rhyolitic melt to the Otowi magma. Mineral thermometers suggest a modest temperature gradient through the melt body, perhaps of 40 °C, at the time of eruption. Chemical, textural, and mineralogical variations and volume-composition relations through the tuff are consistent with an origin for zoning by melting of a high-crystallinity cumulate layer beneath cognate supernatant liquid to produce denser, remobilized liquid of accumulative composition (i.e., the “modified mush model”). Melting may have occurred in several episodes. The latest of these episodes, probably thousands of years prior to eruption, introduced new rhyolitic liquid into the system and was associated with a thermal excursion, recorded in core compositions of pyroxene, during which much of the earlier crystal mass was dissolved. This left inherited cores and interiors of accumulated quartz and feldspar mantled with new growth having less-evolved compositions (higher Ti, Sr, and Ba). Changing solubility of zircon during cumulate melting produced a reversal of Zr concentrations. There is no clear petrologic evidence of a recharge eruption trigger; nonetheless, compositional zoning resulted mainly from repeated recharge-induced remobilization of quartz-feldspar cumulate. The Otowi system was built, evolved, and modified by several events over the course of a few hundred thousand years.

Pegmatite fields of São Pedro de Ferros, Antônio Dias and Marilac, Minas Gerais State, Brazil: petrographic characterization

Pegmatites are rocks of granite or metastatic origin with gigantic crystals that are formed in fluid phase of the magmatic liquid enriched with incompatible elements, thats why they can be considered as gemstones and industrial minerals deposits. Both studied areas in the present article were genererated by anatexia process or partial fusion. The Jatobá Mine in the Pegmatitic Field of Ferros-Antônio Dias, in Santa Maria de Itabira, explores the aquamarine gem, a beryl variety, in a pegmatite that is located closer to the granite system of the quartz core and is docked in a gnaisse granitic rock from the Guanhães Complex. The collected sample was denominated like Quartzo alkali feldspar sienite in the Diagram QAPF. The blue color of the beryl is given by the intrusion of Fe. The Duas Cores Mining represents the Pegmatitic Field of Marilac, near Governador Valadares, and the exploration of bi-color tourmaline will begin soon. This mineral is in a very weathered pegmatite, positioned more at the end of the granite system and docked in the mica-schist rock of the São Tomé Formation. The sample was named Tonalite by the QAPF Diagram. The color variation of the explored gem is related to the enrichment of the Li element at the site.

Quartz chemistry fingerprints melt evolution and metamorphic modifications in high-purity quartz deposits

In this paper, statistical quartz chemistry is combined with petrographic observations to improve our understanding of how metamorphism reworks trace elements of igneous quartz. We elucidate the key processes involved in the formation of the pegmatite-type high-purity quartz deposits in Tysfjord, Northern Norway, where produced quartz has the second-best chemical purity in the world. The Tysfjord pegmatites are the largest known intra-plutonic Nb-Y-F type, comprising Paleoproterozoic and Devonian generations. The Paleoproterozoic pegmatites show characteristics of Caledonian deformation and can be divided into a strongly-deformed type and a less-deformed type: primary internal zonation is replaced by quartz core and K-feldspar-rich intermediate zones surrounded by sheared granitic wall zones; quartz has undergone dynamic recrystallization and contains very few fluid inclusions. The Devonian pegmatites are undeformed and the quartz is rich in healed, fluid-inclusion-bearing microcracks.Trace elements in the pegmatite quartz are dominated by Al, Ti, Li, Ge and B, and total concentrations of the five elements are 29 ± 9 μg/g, 35 ± 10 μg/g and 38 ± 12 μg/g for the strongly-deformed, less-deformed and undeformed types, respectively. The quartz chemistry of the Devonian pegmatites is largely heterogeneous and shows significantly increasing Ge and B contents from early- to late-stage quartz, reflecting the fractionation enrichment of Ge and B in the evolved melts. The quartz chemistry of the Paleoproterozoic pegmatites has become homogeneous and is dominated by either Ti or Li and Al, resulting from the metamorphic modifications during the Caledonian overprint. The modifications on quartz took place via volume diffusion or dynamic recrystallization equilibrium, resulting in a resetting of Ti (at low TiO2 activity) and losses of Li and Al. Therefore, the less-evolved pegmatite-forming melts derived from the Paleoproterozoic magmatism and the moderate metamorphic modifications during the Caledonian orogeny are important for the formation of the high-purity quartz deposits. This study manifests that quartz chemistry has the potential to fingerprint igneous and metamorphic mineralization processes in tectonomagmatic terranes.

Modelling the reduction of quartz in a quartz–carbon pellet

Traditional refining of silicon generates carbon dioxide emissions that are released into the atmosphere. An alternative process under experimental exploration uses quartz particles coated in a layer of porous carbon as the raw material, instead of lumps of quartz and carbon. The quartz–carbon pellets are processed at a lower temperature than in an industrial furnace, and hence, different chemical reactions are dominant, reducing the greenhouse gas emissions. The quartz core shrinks as it is consumed, and the carbon is converted to silicon carbide, which can subsequently be processed into silicon. We develop a model for chemical and transfer processes within a single quartz–carbon pellet. We derive governing equations for the concentration of silicon monoxide, carbon monoxide, and carbon dioxide, and conservation equations on the moving quartz interface. Furthermore, we then focus on a reduced model in an industrially relevant distinguished limit, and solve numerically the resulting leading-order system. We show examples of reaction-limited behaviour as well as diffusion-limited behaviour. Both regimes are physically admissible due to the large potential range of the parameters. Finally, we sweep through the parameter space, and characterize the dynamics based on the utilization of the carbon and the silicon yield. We find that the diffusion-limited regime is best for carbon utilization and silicon yield, as the silicon monoxide reacts with the carbon before it is transported out of the pellet.

Gold of the upper horizons of the Berezovsky ore field

The calculation of gold reserves (14–25 tons) in the upper part of the ore field (to a depth of 20 m) was made in the 30s of the twentieth century. Their diligent development was carried out until the 60s of the twentieth century. When conducting engineering and geophysical survey work for industrial and civilian construction in the Rudny Field (in fact, in the territory of the city of Berezovsky) it is possible to clarify the position of well-known and untouched famous golden berets and quartz veins, as well as detect golden-bearing facilities to the minological service of the mines. Modern legislation prohibits the prey of minerals in the territory of cities. The extraction of gold of the upper part of the ore field can be organized subject to sampling from the volumes of construction boilers of gold-containing birch trees, quartz cores, marshallite kaolinite loams of cortical corticals and granite porpherfires. Such a small enterprise should be organized by the owners of the Berezovsky land: a mine or a municipality

Chrysoberyl and associated beryllium minerals resulting from metamorphic overprinting of the Maršíkov–Schinderhübel III pegmatite, Czech Republic

AbstractThe Maršíkov–Schinderhübel III pegmatite in the Hrubý Jeseník Mountains, Silesian Domain, Czech Republic, is a classic example of chrysoberyl-bearing LCT granitic pegmatite of beryl–columbite subtype. This thin pegmatite dyke, (up to 1 m in thickness in biotite–amphibole gneiss is characterised by symmetrical internal zoning. Tabular and prismatic chrysoberyl crystals (≤3 cm) occur typically in the intermediate albite-rich unit and rarely in the quartz core. Chrysoberyl microtextures are quite complex; their crystals are irregularly patchy, concentric or fine oscillatory zoned with large variations in Fe content (1.1–5.3 wt.% Fe2O3; ≤0.09 apfu). Chrysoberyl compositions reveal dominant Fe3+ = Al3+ and minor Fe2+ + Ti4+ = 2(Al, Fe)3+ substitution mechanisms in the octahedral sites. Tin, Ga, and V (determined by LA-ICP-MS) are characteristic trace elements incorporated in the chrysoberyl structure, whereas anomalously high Ta and Nb concentrations (thousands ppm) in chrysoberyl are probably caused by nano- to micro-inclusions of Nb–Ta oxide minerals; especially columbite–tantalite. Textural relationships between associated minerals, distinct schistosity of the pegmatite parallel to the host gneiss foliation and fragmentation of the pegmatite body into blocks as a result of superimposed stress are clear evidence for deformation and metamorphic overprinting of the pegmatite. Primary magmatic beryl, albite and muscovite were transformed to chrysoberyl, fibrolitic sillimanite, secondary quartz and muscovite during a high-temperature (~600°C) and medium-pressure (~250–500 MPa) prograde metamorphic stage under amphibolite-facies conditions. A subsequent retrograde, low-temperature (~200–500°C) and pressure (≤250 MPa) metamorphic stage resulted in the local alteration of chrysoberyl to secondary Fe,Na-rich beryl, euclase, bertrandite and late muscovite.

Particle size distribution: An experimental study using southern African reduction methods and raw materials.

We experimentally created a particle size dataset that is based on reduction sequences and raw materials typical of the Middle and Later Stone Age in southern Africa. The reason for creating this new dataset is that current particle size frameworks are based, almost exclusively, on flint and western European knapping methods. We produced the dataset using knapping methods and raw materials frequently encountered in the southern African archaeological record because we wanted to test whether it has the same distribution as particle size datasets experimentally created in Europe, and to initialise the production of a database for use in the analysis of lithic assemblages from southern African Late Pleistocene deposits. We reduced 117 cores of quartz, quartzite, jasper, chalcedony, hornfels, and rhyolite. The knapping methods selected were unidirectional, discoidal, Levallois recurrent and bipolar flaking. In this article we compare this new particle size distribution dataset with the results obtained from previous experiments. We found that the southern African dataset shows a wider size range distribution, which seems to be explained by differences in knapping methods and raw materials. Our results show that there is overlap between the distribution of the southern African experimental knapping dataset and the sorting experiment conducted by Lenoble on flint artefacts in a runoff context. This article shows that a particle size analysis is not sufficient on its own to assess the perturbation of an archaeological assemblage and must be coupled with other analytical tools.

FIELD TRIP GUIDE TO THE SERIDÓ PEGMATITE PROVINCE

The pegmatites of the Seridó Pegmatite Province show a granitic bulk mineralogical composition, composed of K-feldspar, albite, quartz, muscovite and occasionally biotite. Detailed mineralogical studies of the major minerals are scarce. There is, on the other hand, a relatively larger number of published contributions concerning pegmatite accessory minerals. This field trip guide focus on the mainly occurrence locations of these last minerals, which are group here by their most frequently recovered rare metals and gems: (1) Ta-Nb: Tantalite-columbite is the main mineral group, even though other rare varieties may occasionally be recovered as microlite, tapiolite, strueverite, simpsonite, ixiolite, among others. Their grain size varies from the centimeter to decimeter scale. The mineralization is disseminated (less frequently), in pockets, or as aggregates of crystals, usually associated with "replacement bodies" at the contact between Zone III and the quartz core. They also occur sporadically in Zone II and occasionally in homogeneous pegmatites, as crystals in subcentimeter to centimeter scale, frequently disseminated in the quartz-feldspar-muscovite groundmass. In this case, they display lamellar habit and normally lower Ta concentration. (2) Be: Beryl is the main Be-mineral present. Its grain size varies from centimeter to meter, it is normally prismatic and shows diverse colors (white, green, blue, pink, yellow), with green and white prevailing. It occurs in Zones II, III and IV (quartz core), as well as in association with the "replacement bodies". In homogeneous pegmatites, it occurs as centimetric crystals, disseminated in the groundmass. Some pseudoconical forms are also observed, and contain muscovite and quartz inclusions. The gem varieties (aquamarine, morganite, heliodor) are scarce. Beryl and the Ta-Nb minerals, are the main ores exploited in these pegmatites. (3) Li: Li-minerals recovered from the pegmatites are spodumene, lepidolite and amblygonite. The spodumene prevails over amblygonite and lepidolite, although the reserves of Li are still not completely known. Spodumene occurs in individual crystals or aggregates in decimeter to meter dimensions, rarely forming individualized zones. Lepidolite occurs mainly in albitized pegmatites associated with deep blue tourmalines (named Paraíba Tourmaline). Amblygonite occurs in pockets of decimeter to meter width and may be associated with other phosphates such as lithiophilite, triphylite, siclerite, tavoríte, among others. (4) Sn: Cassiterite is the main Sn-ore, although Sn is also present in the crystallographic structure of Ta-Nb minerals. It is found disseminated in centimeter grain size in the "replacement bodies" or in Zone I of heterogeneous pegmatites, and occurs occasionally in some homogeneous pegmatites. Cu (e.g. djurleite), U (e.g. uraninite) and REE (e.g. xenotime) minerals are considered important resources exploted or as potential for further exploration.

Fluids and Melts at the Magmatic-Hydrothermal Transition, Recorded by Unidirectional Solidification Textures at Saginaw Hill, Arizona, USA

Abstract Fluid exsolution and melt evolution at the magmatic-hydrothermal transition are critical processes driving the metal enrichment of porphyry systems. Coeval fluid and melt inclusion assemblages in unidirectional solidification textures (USTs) at Saginaw Hill—a small, porphyry Cu system in southwestern Arizona—record a dynamic and repetitious process of fluid accumulation and release. The cores of quartz crystals throughout the UST bands host coeval silicate melt and brine inclusions but lack vapor-rich inclusions. This could indicate preferential expulsion of vapor and trapping of high-density brine during episodes of fracturing or the direct exsolution of single-phase high-salinity brine from the silicate melt. In contrast, the rims of UST quartz host abundant coeval brine and vapor inclusions, consistent with liquid-vapor immiscibility at lower pressures compared to the corresponding quartz cores. This transition from dominantly coeval silicate melt inclusions and brine in phenocryst cores to coeval brine and vapor in the rims suggests that the Saginaw Hill system underwent cyclic processes of fluid exsolution, accumulation, overpressure, and decompression at relatively stable temperatures (consistently ~650°C) during UST formation. Melt inclusion data indicate that the melt at this stage was highly fractionated and tended toward muscovite saturation. Metal concentrations in the brine were comparable to or higher than those in fluids reported in world-class porphyry Cu systems and were likely the result of both igneous fractionation and the high chloride content of the exsolved fluids. While limited in scale, Saginaw Hill provides evidence for processes that are predicted to occur at the magmatic-hydrothermal transition during the formation of large, well-mineralized porphyry systems.

Magnesiothermic Reduction of Natural Quartz

In the current work, the metallothermic reduction of natural quartz by magnesium has been studied at 1373 K under different reaction conditions, i.e. quartz type, quartz particle size, Mg:SiO2 mole ratio and reaction time. The microstructure of reaction products was studied to illustrate the reaction progression through scanning and transmission electron microscopy techniques. X-ray diffraction analysis with Rietveld phase quantification was used to calculate the change in the amount of phases at different reaction conditions. The results showed that the Mg:SiO2 mole ratio strongly affects reaction mechanism and product characteristics such as phase content and microstructure. At lower Mg:SiO2 mole ratios, the reaction rate is fast at the beginning and the formation of a product layer consisting of different phases such as MgO, Si, Mg2Si, Mg2SiO4 and MgSiO3 around quartz particles limits the Mg diffusion. This phenomenon is more noticeable for larger quartz particle sizes where Mg should diffuse longer distance towards the quartz core to react with it. At higher Mg:SiO2 mole ratios, a significant amount of Si–Mg liquid alloy is formed during reaction where the high mobility of Mg in this liquid phase and cracking of quartz particles result in significantly higher reaction rate. Here the formation of intermediate phases is not significant and the products would be the mixture of MgO, Mg2Si, and either Si or Mg phases.

Insight into the adsorption and oxidation activity of a ZnO/piezoelectric quartz core-shell for enhanced decontamination of ibuprofen: Steric, energetic, and oxidation studies

• ZnO/quartz was used as a catalyst and adsorbent for the removal of ibuprofen (IBF). • It exhibits receptor sites and adsorption capacity of 38.42 mg/g and 145.6 mg/g. • The adsorption reactions of IBF by ZnO/quartz is of physisorption mechanisms. • 50 mg/L of IBF was oxidized after 80 min (Photocatalyst) and 40 min (Piezo-photocatalyst). • The hydroxyl and superoxide radicals are the main oxidizing species. A natural piezoelectric quartz core was coated with environmentally friendly ZnO nanoparticles (GZn/PQz) for enhanced decontamination of ibuprofen (IBF) by adsorption and advanced oxidation. The adsorption properties were described based on the monolayer model of one energy site. The steric studies demonstrated a decline in active site density (Nm) and the saturation adsorption capacities (Qsat) with increasing temperature, and the best values were achieved at 25 °C (Nm = 38.42 mg/g and Qsat = 145.6 mg/g). The number of adsorbed IBF molecules (n) (>3 and <4) suggested the uptake of 3 or 4 IBF molecules per receptor site in a vertical orientation and by a multimolecular mechanism. The adsorption energy values (−7.93 to −9.5 kJ/mol) suggest physical uptake processes. The thermodynamic functions reflected the exothermic and spontaneous properties of the reactions. GZn/PQz achieved IBF (50 mg/L) oxidation percentages of 100%, 93.8%, and 100% after 80 min (photocatalyst), 360 min (piezoelectric catalyst), and 40 min (piezo-photocatalyst), respectively. Hydroxyl radicals and superoxide radicals are essential oxidizing species during the oxidation of IBF by GZn/PQz. Based on the detected intermediate compounds, the oxidation pathway of IBF by GZn/PQz involved hydroxylation, decarboxylation/demethylation, and ring-opening processes.

Geology and Petrogeochemistry of Lijiapuzi Nb-Ta Granitic Pegmatite Deposit: Implications for Ore Genesis and Prospecting

Most of the rare metal pegmatite deposits in China lie in West, Central and South China, and the Lijiapuzi Nb-Ta deposit is the only pegmatite-type Nb-Ta deposit in Northeast China, therefore a detailed study of the Lijiapuzi deposit is of great importance to the metallogeny and exploration of rare metal deposits in Northeast China. The Nb-Ta bearing pegmatites in Lijiapuzi district are composed of a microcline wall zone, a muscovite (lepidolite)-albite intermediate zone and a quartz core, and the rare metal mineralization mainly occurs in the intermediate zone and is intimately related to the albitization. The lithogeochemical features indicate that Lijiapuzi pegmatoids are rich in silicon and alkaline, poor in calcium, magnesium, titanium and phosphorus, and belong to peraluminous granitoid rocks. The enrichment of large ion lithophile elements (LILEs) and depletion of high field-strength elements (HFSEs), the distinct right-inclined REE pattern with obvious Eu negative anomaly, lower ratio of Nb/Ta and higher ratio of La/Nb and Rb/Sr indicate that the pegmatite was of a crustal origin and formed in relatively extensional tectonic setting of post-orogenesis. The pegmatites in Lijiapuzi area can be divided into two categories, i.e., the NW-trending pegmatites are shorter and thicker, with obvious zoning and localized in the upper part of the near-surface, while the NE-trending pegmatites are longer, thinner, devoid of zoning and localized in the lower part of the district. This probably means that excellent ore prospecting potential exists in the lower part of the Lijiapuzi district.

The Formation of Magmatic-Hydrothermal Features in Sn-Mineralized and Barren Tasmanian Intrusions, Southeast Australia: Insights from Quartz Textures, Trace Elements, and Microthermometry

Abstract Tasmania is the most important tin province in Australia, having been endowed with &amp;gt;0.65 Mt Sn. Some granitic intrusions in western Tasmania have distinctive tourmaline- and quartz-rich magmatic-hydrothermal features, whether they are mineralized (e.g., Heemskirk Granite) or barren (Pieman Heads Granite). The Devonian Heemskirk and Pieman Heads plutons crop out on the western coast of Tasmania and are characterized by similar mineralogical and geochemical compositions and ages. The magmatic-hydrothermal textural features include tourmaline patches, tourmaline orbicules, and tourmaline-muscovite veins, as well as miarolitic cavities and quartz-fluorite-sulfide veins in the Heemskirk Granite. Cathodoluminescence (CL) imaging, laser ablation-inductively coupled plasma-mass spectrometry, and microthermometric analyses of quartz have revealed the physicochemical evolution of the magmatic-hydrothermal fluids from which these tourmaline- and quartz-bearing assemblages precipitated. High Ti quartz (20–28 ppm) in tourmaline patches, orbicules, and cavities typically have homogeneous CL-bright intensity, whereas CL-dark fractures have cut and/or offset the CL-bright and -gray domains that characterize low Ti quartz (3.4–8.5 ppm) from the tourmaline veins. The earliest fluid inclusion assemblages in the quartz-tourmaline orbicules and cavities have a salinity range from 3 to 14 wt % NaCl equiv with intermediate density and were probably trapped at lithostatic pressures of 1.57 ± 0.2 kbar and temperatures of 550° to 570°C, suggesting a depth of 5.9 ± 0.8 km. Prolonged depressurization and cooling may have led to the evolution of a brine (~39 wt % NaCl equiv salinity) from the primary magmatic liquid, which formed halite-bearing hypersaline inclusions in the tourmaline orbicules. Continuous pressure decrease explains the intense brittle failure and fluid migration outward from the apical portions of the pluton, where magmatic fluids partially mixed with and were cooled by external meteoric water. These mechanisms triggered the formation of tourmaline-muscovite-quartz veins and local cassiterite-bearing greisens from a moderate-salinity fluid (~12 wt % NaCl equiv) at temperatures of ~300°C and hydrostatic pressures of 120 bars. Retrograde dissolution textures evident from CL-bright quartz cores surrounded by oscillatory growth zones with gray CL response characterize the low Ti (&amp;lt;1 ppm) and high Al (500–1,000 ppm) quartz from the fluorite-sulfide veins that precipitated from a low-salinity (5.7 wt % NaCl equiv) acidic fluid at temperatures of 200° ± 25°C and hydrostatic pressures of &amp;lt;50 bars. High Sb concentrations (up to 80 ppm) in quartz may be an indicator of low-temperature base metal mineralization related to granitic intrusions. Abundant fluid percolation, protracted fractional crystallization, and high tin concentrations in exsolved hydrothermal fluids may explain why the Heemskirk Granite is well endowed in Sn and base metal deposits, whereas the Pieman Heads Granite is barren.

Telluride Mineralogy of the Deer Horn Au-Ag-Te-(Bi-Pb-W) Deposit, British Columbia: Implications for the Generation of Tellurides

ABSTRACTThe Deer Horn deposit, located 150 km south of Smithers in west-central British Columbia, is an Eocene polymetallic system enriched in Au-Ag-Te with lesser amounts of Bi-Pb-W; the Au and Ag are hosted in Te-bearing minerals and Ag-rich gold (Au-Ag alloy). A quartz-sulfide vein system containing the main zones of Au-Ag-Te mineralization and attendant sericite alteration occurs in the hanging wall of a local, spatially related thrust fault and is genetically related to the nearby Eocene Nanika granodiorite intrusive suite. Tellurium-bearing minerals commonly form isolated euhedral to subhedral grains or composite grains (up to 525 μm in size) of Ag-, Bi-, Pb-, and Au-rich tellurium-bearing minerals (e.g., hessite, tellurobismuthite, volynskite, altaite, and petzite). Panchromatic cathodoluminescence imaging revealed four generations of quartz. Within remnant cores of quartz I, local oscillatory zoning occurs in quartz II. Fine-grained veinlets of quartz III and IV crosscut quartz I and II, showing evidence of at least two deformation events; late-forming veinlets of calcite crosscut all generations of quartz. The tellurides and Ag-rich gold occur in stage III quartz. Three types of fluid inclusions were observed in stage III and IV quartz: (1) aqueous liquid and vapor inclusions (L-V); (2) aqueous carbonic inclusions (L-L-V); and (3) carbonic inclusions (vapor-rich). Primary fluid inclusions related to the telluride mineralization within quartz III were tested with microthermometry, along with a few primary inclusions from quartz IV. Homogenization temperatures are 130.0–240.5 °C for L-V inclusions and 268.0–336.4 °C for L-L-V inclusions. Aqueous carbonic inclusions had solid CO2 melting temperatures from –62.1 to –56.8 °C, indicating the presence of ≈1 to 30 mol.% dissolved methane in these inclusions.The Deer Horn Au-Ag-Te-(Bi-Pb-W) deposit is a reduced intrusion-related gold system characterized by sheeted veins, metal zoning, low salinity aqueous-carbonic fluids, and a genetic relationship to an Eocene granodiorite. Values of δ34S of pyrite vary from –1.6 to 1.6 per mil and are compatible with a magmatic source of sulfur.

Microblade Technology in Quartz during the Mesolithic in Eastern Middle Sweden

Thc authors present a material that has previously not been given much attcntion : microblades and microblade cores of quartz from eastern middle Sweden. The focus is on the technology. core types, geographical distribution and dating. The debate on how to interpret the quartz material ofthe region in cultural tenns and the role of the microblade technology in this discussion, are also dealt with. During recent years, many excavations and special surveys have supplied the archaeologists in easterll middle Sweden with new source material. An increased knowledge of quartz is an important factor in the dcvclopment of this field of research. The authors found it vely helpful to discuss the newly found cores and blades and their technical execution with Kjel knutsson of Uppsala University. Gcnerally speaking, the Mesolithic quartz materials from eastern middle Sweden are dominated by two methods ol'reduction; freehand-platform and bipolar-on-anvil. The latter method regularly produces thin flakcs that resemble microblades. In this articlc, however, focus will be on microblades sensu stricto. It seems that the production of'quartz microblades is more common than previously thought. Early reports from sites such as Sjövreten and Skumparberget are no longer anomalies.

Bulk composition of a zoned rare-earth minerals-bearing pegmatite in the Pikes Peak granite batholith near Wellington Lake, central Colorado, U.S.A.

ABSTRACT A previously undescribed small lenticular (~5 × 5 × 5 m) pegmatite, located near Wellington Lake in the NW part of the 1.08 Ga ‘A-type’ (anorogenic) ferroan Pikes Peak granite batholith, ~15 km SW of the South Platte pegmatite district in central Colorado, is concentrically zoned around a mostly monomineralic quartz core with interconnected miarolitic cavities. Major constituents of the Wellington Lake pegmatite are quartz, perthitic microcline, albite (variety cleavelandite), hematite, and biotite. Accessory minerals include fluocerite, bastnäsite, columbite, zircon (var. ‘cyrtolite’), thorite, and secondary U phases. Fluorite is conspicuously absent, although it is a common phase in the South Platte district NYF-type pegmatites, which are rich in niobium (Nb), yttrium (Y), fluorine (F), and heavy rare-earth elements (HREE). Notable for the Wellington Lake pegmatite are a small quantity of well-developed tabular crystals of fluocerite that reach up to 4 cm in diameter, with sub-mm epitaxial bastnäsite overgrowths, suggesting formation from F- and CO2-bearing solutions rich in light rare-earth elements (LREE), with decreasing a(F-)/a(CO32-) during the last crystallization phase. An Nd-isotope value of εNd1.08Ga = -1.6 for the fluocerite is within the range of εNd1.08Ga = -0.2 to -2.7 of the host coarse-grained, pink K-series Pikes Peak Granite (PPG), indicating that REE and other pegmatite constituents derived from the parental PPG magma. A calculation of total pegmatite composition based on whole-rock chemistry and volume estimates of the different pegmatite zones reveals an overall composition similar to the PPG with respect to Si, Al, Na, and K. Yet the pegmatite is depleted in Fe, Mg, Ca, Ti, Mn, and P, the high-field-strength elements (HFSE; Zr, Hf, Nb, Y, Th), and, most significantly, total REE compared to the PPG. Despite containing the LREE minerals fluocerite and bastnäsite, the lack of a net overall REE enrichment of the pegmatite compared to the PPG reflects the large amount of REE-poor silicate minerals forming the wall, intermediate, and core zones of the pegmatite. The calculated total pegmatite composition suggests that the pegmatite formed by the separation from the PPG magma of an F-poor H2O-saturated silicate melt depleted in REE and HFSE compared to the F-rich melts, which formed the NYF-type HREE-rich (LaN/YbN &amp;lt; 1) pegmatites in the South Platte district. Homogenization temperatures of &amp;lt; 500°C for possibly primary fluid inclusions in large quartz crystals from the core of the Wellington Lake pegmatite are consistent with recent models of pegmatite petrogenesis leading to nucleation controlled mega-crystal growth resulting from supercooling.