Ta Concentrations Research Articles

Fabrication of Tantalum-Doped Titanium-Oxide Electron-Selective Contacts with High Passivation Quality

In this paper, we report on the fabrication of Ta-doped TiO2 (TiO2:Ta) electron-selective contacts and their improved passivation qualities. By using thermal atomic layer deposition, 3.5 nm-thick, undoped TiO2 films and 3.5 nm-thick TiO2:Ta films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed at 150 °C on n-type crystalline silicon substrates with ∼1 nm-thick chemical SiO2 layers. Rutherford backscattering spectroscopic measurements confirmed the Ta concentrations in the films and uniform distributions of Ta atoms in the films. X-ray photoelectron spectrometry measurements implied that Ta atoms rather cause local structural changes than enter substitutionally into Ti sites. After annealing at 130 °C in air, the effective minority carrier lifetime (τ eff) of the TiO2:Ta-passivated samples were significantly higher than those of the samples passivated with undoped TiO2 films. The highest τ eff was obtained for the samples with a relatively low Ta-doping concentration of 1.5 at.%. On the other hand, the passivation quality was degraded by Ta doping with a too high concentration (for example, 18.4 at.%). These results indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Geochemistry and Petrogenesis of Late Ediacaran Rare‐metal Albite Granites of the Arabian‐Nubian Shield

AbstractThe Abu Dabbab albite granite (ADAG), in the central Eastern Desert of Egypt, hosts the most significant rare metal ore deposit in the northern part of the Neoproterozoic Arabian‐Nubian Shield. Here, we report detailed field, petrographic, mineralogical and geochemical investigation of the ADAG, an isolated stock‐like granitic body with sharp intrusive contacts against metamorphic country rocks, probably emplaced at about 600 Ma. The fine‐grained porphyritic upper unit is a preserved remnant of the shallowly‐emplaced apex of the magma chamber, whereas the medium‐grained lower unit crystallized at deeper levels under subvolcanic conditions. The peraluminous leucocratic ADAG shares common geochemical characteristics with post‐collisional intraplate A‐type magmas. In addition to the conspicuous enrichment in Na2O, the ADAG is remarkable for its anomalous concentrations of Ta, Nb, Li, Hf, Ga, Sn, Zn and heavy rare‐earth elements. Nb‐Ta minerals in the ADAG are mixed with Fe‐Mn oxides, forming black patches that increase in abundance toward of the base of the intrusion. Columbite‐tantalite, cassiterite and wolframite are the most important ore minerals. Pronounced negative Eu anomalies (Eu/Eu∗ = 0.10–0.24) reflect extreme magmatic fractionation and perhaps the effects of late fluid‐rock interaction. The ADAG was most likely generated by partial melting of the juvenile middle crust of the ANS as the geotherm was elevated by erosional uplift following lithospheric delamination and it was emplaced at the intersection of lineations of structural weakness. Although formation of the ADAG and its primary enrichment in rare metals are essentially due to magmatic processes, late‐stage metasomatism caused limited redistribution of rare metals. Fluid‐driven subsolidus modification was limited to the apex of the magma chamber and drove development of greisen, amazonite, and quartz veins along fracture systems.

Nb-Ta systematics of Kohistan and Gangdese arc lower crust: Implications for continental crust formation

• Kohistan and Gangdese (garnet) hornblendites and/or garnet gabbros are of cumulate origins. • Amphiboles in these lower crust cumulates have high Nb/Ta but low Nb and Ta concentrations. • Amphibole fractionation will not change Nb/Ta ratio of arc magmas significantly. • Rutile likely plays an important role in Nb/Ta fractionation in continental crust formation. Earth’s continental crust has a lower Nb/Ta ratio than that of its building blocks –basaltic melts from the mantle. This Nb/Ta mass imbalance implies the existence of a complementary high Nb/Ta reservoir in deep crust. Amphibole-rich arc cumulates have been proposed to be one such candidate due to the preferential partitioning of Nb over Ta into amphibole. To test this proposal, we carried out in-situ analyses of amphibole and rutile in the lower crustal rocks from Kohistan arc and Gangdese arc. Petrological observations and geochemical results suggest that these rocks in both Kohistan arc and Gangdese arc are of magmatic origins and formed by crystal accumulation, i.e. of cumulate. The Kohistan garnet-bearing hornblendite cumulates were formed at 952–1009 ℃; the garnet-free hornblendite cumulates in Kohistan arc and Gangdese arc were formed at 941–992 ℃ and 955–1027 ℃, respectively. We find that, although the amphibole of the Kohistan and Gangdese cumulates have high Nb/Ta ratios (average 18.2 and 17.0, respectively), their Nb and Ta concentrations are far lower than mantle-derived volcanics (Nb < 1.1 ppm, Ta < 0.11 ppm). We show that, with such low concentrations of Nb and Ta, amphibole fractionation will not change arc magma Nb/Ta ratios significantly. Instead, the rutile in Kohistan cumulates has high Nb/Ta ratios and high Nb-Ta concentrations. The calculation shows that rutile may play a more important role in Nb/Ta fractionation during arc magma differentiation in thickened arc crust. Our study provides a mineralogical perspective to understand the formation of continental crust, and improves our understanding how Nb or Ta becomes enriched in arc setting.

Genesis of Dulong Sn-Zn-In Polymetallic Deposit in Yunnan Province, South China: Insights from Cassiterite U-Pb Ages and Trace Element Compositions

The Dulong Sn-Zn-In polymetallic deposit in the Yunnan province, SW China, hosts a reserve of 5.0 Mt Zn, 0.4 Mt Sn, and 7 Kt In. It is one of the most important polymetallic tin ore districts in China. Granites at Dulong mining area include mainly the Laojunshan granite (third phase), which occurs as quartz porphyry or granite porphyry dikes in the Southern edge of the Laojunshan intrusive complex. Granites of phases one and two are intersected at drill holes at depth. There are three types of cassiterite mineralization developed in the deposit: cassiterite-magnetite ± sulfide ore (Cst I), cassiterite-sulfide ore (Cst II) within the proximal skarn in contact with the concealed granite (granites of phases one to two and three), and cassiterite-quartz vein ore (Cst III) near porphyritic granite. Field geology and petrographic studies indicate that acid neutralising muscovitization and pyroxene reactions were part of mechanisms for Sn precipitation resulting from fluid-rock interaction. In situ U–Pb dating of cassiterite samples from the ore stages of cassiterite-sulfide (Cst II) and Cassiterite-quartz vein (Cst III) yielded Tera-Wasserburg U–Pb lower intercept ages of 88.5 ± 2.1 Ma and 82.1 ± 6.3 Ma, respectively. The two mineralization ages are consistent with the emplacement age of the Laojunshan granite (75.9–92.9 Ma) within error, suggesting a close temporal link between Sn-Zn(-In) mineralization and granitic magmatism. LA-ICPMS trace element study of cassiterite indicates that tetravalent elements (such as Zr, Hf, Ti, U, W) are incorporated in cassiterite by direct substitution, and the trivalent element (Fe) is replaced by coupled substitution. CL image shows that the fluorescence signal of Cst I–II is greater than that of Cst III, which is caused by differences in contents of activating luminescence elements (Al, Ti, W, etc.) and quenching luminescence element (Fe). Elevated W and Fe but lowered Zr, Hf, Nb, and Ta concentrations of the three type cassiterites from the Dulong Sn-Zn-In polymetallic deposit are distinctly different from those of cassiterites in VMS/SEDEX tin deposits, but similar to those from granite-related tin deposits. From cassiterite-magnetite ± sulfide (Cst I), cassiterite-sulfide ore (Cst II), to cassiterite-quartz vein ore-stage (Cst III), high field strength elements (HFSEs: Zr, Nb, Ta, Hf) decrease. This fact combined with cassiterite crystallization ages, indicates that Cst I–II mainly related to concealed granite (Laojunshan granites of phases one and two) while Cst III is mainly related to porphyritic granite (Laojunshan granites of phase three).

Ocean Circulation Drives the Variability of the Carbon System in the Eastern Tropical Atlantic

The carbon system in the eastern tropical Atlantic remains poorly known. The variability and drivers of the carbon system are assessed using surface dissolved inorganic carbon (DIC), alkalinity (TA) and fugacity of CO2 (fCO2) measured in the 12° N–12° S, 12° W–12° E region from 2005 to 2019. A relationship linking DIC to temperature, salinity and year has been determined, with salinity being the strongest predictor. The seasonal variations of DIC, ranging from 80 to 120 μμmol kg−1, are more important than the year-to-year variability that is less than 50 μμmol kg−1 over the 2010–2019 period. DIC and TA concentrations are lower in the northern part of the basin where surface waters are fresher and warmer. Carbon supply dominates over biological carbon uptake during the productive upwelling period from July to September. The lowest DIC and TA are located in the Congo plume. The influence of the Congo is still observed at the mooring at 6° S, 8° E as shown by large salinity and chlorophyll variations. Nevertheless, this site is a source of CO2 emissions into the atmosphere.

Role of tantalum concentration, processing temperature, and strain-rate on the mechanical behavior of copper-tantalum alloys

Microstructural instability in traditional nanocrystalline metals limits the understanding of the fundamental effect of grain size on mechanical behavior under extreme environmental conditions such as high temperature and loading rates. In this work, the interplay between Ta concentrations and processing temperature on the resulting microstructure of a powder processed, fully dense Cu-Ta alloy along with their tensile and compressive behavior at different strain rates are investigated to probe the possibility of manipulating or tuning microstructurally dependent parameters to control the flow-stress upturn phenomenon. Consequently, the results reveal that there is a crucial length scale, i.e., small grain size and appropriate cluster spacing, below which such upturn is damped out. The observation of changes in flow stress upturn behavior is consistent with the observed changes in measured high-rate plasticity, which enhances below the critical length scale. Furthermore, tension-compression asymmetry also tends to be suppressed in nanocrystalline Cu-Ta alloys, while it becomes evident as the grain size increases to an ultrafine regime. Overall, this work presents a systematic approach to control or engineer reduced high strain rate flow stress upturn behavior in metallic alloys, for high-rate applications.

Petrogenesis and tectonic implications of the Neoproterozoic mafic intrusions in the Bikou Terrane along the northwestern margin of the Yangtze Block, South China

The Neoproterozoic mafic intrusions in the Bikou Terrane along the northwestern margin of the Yangtze Block record crucial information on evaluating the tectonic evolution of the Yangtze Block, South China. However, their petrogenesis and tectonic significance are still poorly constrained. In this paper, we present the results of a comprehensive study of zircon U–Pb geochronology and whole-rock geochemistry from the gabbro-diorites and gabbros of the Bikou Terrane. Zircon U–Pb dating results indicate that these gabbro-diorite and gabbro samples were formed coevally at ca. 880 Ma. The gabbro-diorite samples are calc-alkaline in composition and have intermediate contents of SiO2, Mg#, Ni, and Cr. They are enriched in LREEs, and depleted in HFSEs (i.e., Nb, Ta, Zr, and Hf). They have relatively high ratios of Th/Yb, and low ratios of Nb/Yb, Nb/La, Th/Nd, Th/Zr, and U/Th, indicating that they were derived from partial melting of a mantle wedge source metasomatized by slab-derived melts. The gabbro samples are commonly classified as sub-alkaline tholeiitic rocks, and have constantly low to medium values of MgO, Mg#, Cr, and Ni, with distinct spikes at Th, U, Nb and Ta concentrations. They show an E-MORB-like enriched LREEs, low ratios of Nb/La, Ta/Yb, Th/La, and Nb/Zr, and medium ratios of Nb/Yb and Th/Yb, implying that they were most probably originated from the interaction between the upwelling enriched asthenospheric mantle and the mantle wedge peridotite. This mechanism may be triggered by the slab rollback process in a subduction-related environment. Our new investigations, along with available observations from other scholars, support the persistent subduction-related system along the northwestern margin of the Yangtze Block during the early Neoproterozoic.

Multi-elemental composition and toxicity of bottom sediments from Panama Canal watershed

The Panama Canal is a milestone in the history of interoceanic communication. Despite its importance, environmental data regarding this important ecosystem is scarce. The aim of this work was to quantify trace-element levels in bottom sediments from 11 sites along the Canal watershed using ICP-MS, and in the case of mercury, employing a direct Hg Analyzer. These data were associated with the biological activity of aqueous sediment extracts tested on wild type and mutant strains of Caenorhabditis elegans, measuring physiological and molecular markers. The levels of trace elements in bottom sediments decreased in the order Sr > V > Ba > Cr > Li > Sc > Ce > Ni > Y > Co > Ga > Pb > Rb > Nd > La > Gd > Dy > Sm > Pr > Er > Hf > Yb > U > Th > Eu > Ho > Be > Tb > Tm > Ta > Hg. The Pollution factor and Pollution Load Index showed that 36% of the sites presented strong sediment pollution by V, Li, Pb, and Sr. Moreover, the Comprehensive Ecological Risk Index based on Cr and Ni levels was exceeded in all stations. Toxicity tests revealed that sediment extracts, despite not being highly lethal against C. elegans, did significantly reduce its mobility and activated toxicity mechanisms associated with the expression of metallothionein and oxidative stress-related genes. These last three endpoints were statistically related to Cr, Ta and Ba concentrations in sediments, respectively. Data suggest elements present in sediments from Panama Canal may be impacting benthonic organisms, and therefore, stronger management regulations should be considered in order to ensure its sustainability.

Elemental distribution in core sediments of Podampata coast, eastern Odisha, India: potentiality of rare earth elements and Th exploration

The present study is based on the subsurface distribution of trace elements, rare earth elements, and radioactive elements collected from three core samples in the Podampata region near the Rusikulya river mouth on the eastern coast of Odisha, India. This is the first study of the depth dependence of trace elements within sediments along the eastern coast of India. Elemental abundance and mobility in beach regions depend on the source rock and geomorphic agents. The abundance of trace elements, REEs, and radioactive elements was analyzed using instrumental neutron activation analysis (INAA). The mean concentrations of Al, K, Ti, Mn, Cr, Fe, Zn, La, Ce, Dy, Hf, Ta, and Th exposed in each core are higher when compared to those in the upper continental crust, whereas the values for Co, Rb, Sb, and Ba are lower than the upper continental crustal values. The Th/U ratio is around nine times higher in each core sample and has a positive correlation with the total rare earth elements in the study area. A depth of 2–2.5 m in the core is an economically viable zone for the exploration of REEs and other metals as it is observed to be enriched in heavy minerals. The core samples that are at a greater distance from the river are more compacted, and as a result, the zone of accumulation of the elements progresses to deeper levels with distant from the river mouth.

Improvement in the passivation quality of titanium oxide thin films by doping with tantalum

We demonstrate that the passivation quality of TiO2 electron-selective contacts can be improved by Ta doping. By using atomic layer deposition, 3.5-nm-thick, undoped TiO2 films and Ta-doped TiO2 (TiO2:Ta) films with Ta concentrations of 1.5, 2.8, and 5.5 at.% were formed on n-type crystalline silicon substrates with chemical SiO2 layers. After annealing at 130 °C, the effective minority-carrier lifetime (τeff) of the TiO2:Ta-passivated samples were significantly higher than that of the undoped-TiO2-passivated samples, and the highest τeff was obtained at a relatively low Ta-doping concentration of 1.5 at.%. These indicate that moderate Ta doping improves the passivation quality of TiO2 thin films.

Petrogenesis of the post-collisional rare-metal-bearing Ad-Dayheen granite intrusion, Central Arabian Shield

At Hadhb't Ad-Dayheen, in the central Arabian Shield, a post-collisional igneous complex called the Ad-Dayheen intrusion is exposed. It was emplaced in the Early Ediacaran (613–625 Ma), during the final tectono-magmatic stage of Arabian Shield development. Despite limited and discontinuous ring-shaped outcrops due to alluvial cover and later faulting, three pulses of intrusion can be recognized in the field: an early pulse of monzogranite; a second pulse of syenogranite and alkali feldspar granite; and a final pulse of alkaline and peralkaline granite, mineralized microgranite, and pegmatite. Samples show distinctively low contents of CaO, MgO, and Sr in contrast to elevated concentrations of alkalis, Rb, Nb, Y, Ta, Hf, Ga, Zr and rare-earth elements (REE); these are common characteristics of post-collisional rare-metal-bearing A-type granites. The suite displays positive Nb–Ta anomalies and pronounced negative Eu anomalies (Eu/Eu* = 0.11–0.35). The alkaline/peralkaline granites and microgranite of the Ad-Dayheen intrusion feature disseminated mineralization, whereas mineralization is localized in the pegmatite. The primary magma feeding the Ad-Dayheen intrusion was mostly generated by partial melting of the juvenile crust of the Arabian Shield, with a minor mantle contribution. We argue that an episode of lithospheric delamination led to crustal uplift, erosional decompression, and generation of mantle melts that supplied heat to drive crustal melting. The anatectic deep crustal melts assimilated a F-bearing component that also added rare metals to the magma. Each pulse can be described by a fractional crystallization model, but the parental liquid of each subsequent pulse was first modified by further addition of fluorine and rare metals and loss of CaO, Sr, Ba, and Eu due to fluorite fractionation. Texture and morphology of the ore minerals indicate that mineralization (U, Th, Zr, Nb, Ta, Y, Hf and REE) took place in two stages: a magmatic stage coinciding with emplacement of the intrusion, followed by a hydrothermal stage. The magmatic process enriched the residual melt in high field strength elements (HFSE) and REE. The later hydrothermal stage further localized these elements and increased their concentrations to economic grades. The pegmatite is highly mineralized and contains high concentrations of U (81–179 μg/g), Th (244–600 μg/g), Zr (2397–14,927 μg/g), Nb (1352–2047 μg/g), Ta (96–156 μg/g), Y (828–2238 μg/g), Hf (131–377 μg/g) and ∑REE (1969–4761 μg/g).

Comparative evaluation of lactation performance of West African dwarf and red sokoto goats raised in a hot-humid environment

The milk yield and compositions of twelve lactating does comprising six each of West African Dwarf (Fouta djallon) and Red Sokoto (Maradi) were compared in a 21-week study. The does in their second parity were monitored over a full lactation. The goats received daily basal grass and browse fodder in addition to a concentrate supplement in a 2 × 3 factorial experiment. The does were hand milked and milk yield (g/d) was quantified daily. Milk samples were analyzed weekly for total solids (TS %), butter fat (BF %), solids-not-fat (SNF %), crude protein (CP %) and total ash (TA %). Lactose concentration (LC %) was analyzed daily immediately after sampling. Macro-minerals in milk samples were determined by dry ash extraction method specific for each mineral element. Milk yield was influenced significantly (p&lt;0.05) by both breed and stage of lactation. The WAD produced more milk (97.34 g/d than RS (87.01 g/d). For both breeds, the average mid lactation milk yield (119.04 g/d) was significantly (p&lt;0.05) different than either early (88.35 g/d) or late (69.14 g/d). The highest milk production was by WAD does in mid lactation (125.10 g/d) and the least was by RS in late lactation (47.07 g/d). The TS, BF, SNF, CP and LC concentrations in milk were not influenced (P&gt;0.05) by breed. The TA was significantly (P&lt;0.05) higher in WAD milk (0.89 %) relative to RS milk (0.88 %). Also, stage of lactation significantly (P&lt;0.05) influenced the concentrations of TS, BF, TA and LC in WAD and RS goats milk. Total solids was significantly (P&lt;0.05) higher in late (13.47 %) than in early (12.53 %) lactation for both breeds. The BF and LC in milk followed similar trend, recording 4.45, 3.89 and 4.13 and 3.98 % in late and early stages of lactation respectively. On the other hand, The TA decreased with advancing lactation and the highest value was obtained in the early (0.92 %) than in mid (0.89 %) and late (0.86 %) lactation in both WAD and RS goat milk. TA was highest in WAD milk in early lactation (0.92 %) and least in RS milk in late lactation (0.85 %). All macro minerals were influenced (p&lt;0.05) by lactation stage and breed differences, except potassium (K) and sodium (Na) which were only influenced by the stage of lactation. The milk of both WAD and RS goats yielded more calcium (Ca) than K, which was attributed to the nutrients in the diets.

Tracing anthropogenic sources of Tantalum and Niobium in Bothnian Bay sediments, Sweden

PurposeThis study aims to evaluate temporal trends of Tantalum (Ta) and Niobium (Nb) concentrations in northern Baltic Sea sediments with focus on the potential impact from the Rönnskär sulfide ore smelter, located 15 km east of Skellefteå in northern Sweden. The potential of Ta or Nb to serve as tracers for environmental pollution caused by the electronic waste is compared. Lastly, correlations between Ta and Nb concentrations and those of major redox elements are investigated.MethodsA 35-cm-deep core was collected in the harbor bay (Kallholmsfjärden) outside of the smelter. A secondary 6-m-deep sediment core was collected in the deep Bothnian Bay for comparative purposes. Element screening analysis was conducted the using ICP-SFMS for the Kallhomsfjärden core and a combination of ICP-SFMS and ICP-OES for the Bothnian Bay core. In the final analysis, a 5-step sequential extraction technique was preformed to allow for better prediction of the fate and mobility of Ta and Nb.Results and discussionIn the vicinity of the smelter, Ta concentration increases from 0.42 to 3.8 ppm from the time coinciding with the beginning of electronic waste processing. Conversely, Nb concentration remained stable at background levels throughout the core at 6.33 ± 0.78 ppm. The Nb/Ta ratio thus changed from 14.5 to 1.7, reflecting an increase of anthropogenic input of Ta into the bay sediments. In the pre-industrial part of the sediment, concentrations of both elements follow concentration of aluminosilicates in the core. In recent sediments, however, the anthropogenic Ta exhibits an association with hydrous ferric oxides (HFOs) and organic matter.ConclusionsNotable increases in Ta concentrations began following the beginning of scrap metal and electronic waste processing at the Rönnskär smelter. Anthropogenic Ta introduced in the upper portion of the sediment and are more associated with HFOs and organic material than natural Ta seen in the deeper parts of the core where detrital Ta is most common. Niobium was not affected by the Rönnskär smelter and displayed no notable change to the preindustrial background.

Genesis of the volcanic-related Be-U-Mo Baiyanghe deposit, West Junggar (NW China), constrained by mineralogical, trace element and U-Pb isotope signatures of the primary U mineralisation

The Volcanic-related Be-U-Mo Baiyanghe deposit is located in the Paleozoic Xuemisitan Volcanic Belt in West Junggar (NW China). It is the largest Be deposit in Asia which is dominantly hosted in late Devonian rhyolitic tuff and in the late Carboniferous Yangzhuang granite (313 ± 2 Ma) that were emplaced after the closure of the Junggar oceanic domain. The late Devonian rhyolitic tuff is a strongly fractionated peralkaline A1-type volcanic rock with a major magmatic enrichment in Nb, Y, Th, Be, Ta and U. Highly fractionated REE patterns and significant concentrations of Pb, Nb, Zr, Y, Th and Ta in the primary U mineralisation identified these tuffs as the dominant U and probably Be source for Be-U ore genesis in West Junggar. The primary high U concentrations (6.5 < Umean < 15.0 ppm) were released through volcanic glass devitrification and mobilised by oxidising fluids for the formation of hydrothermal mineralisation. The Yangzhuang granite is to the contrary a moderately fractionated moderate- to high-K calc-alkaline A2-type granite characterised by low magmatic U and Be enrichment (Umean = 2.9 ppm; Bemean = 4.7 ppm), and thus constituted a minor U source for the mineralisation as demonstrated by U release and remobilisation from metamict U-bearing accessory minerals.In the Baiyanghe deposit, structurally-controlled primary U mineralisation was temporally constrained by an in situ U-Pb isotopic minimum crystallisation age of 240 ± 7 Ma on pitchblende. This event represents the hydrothermal stage of U mineralisation that occurred during the early Permian–middle Triassic post-accretion event in West Junggar and paragenetically postdates the Be ore stage (ca. 303–265 Ma). The hydrothermal U mineralisation is mainly characterised by Pb-Nb-Ti-Zr-Mo-rich pitchblende veins associated with calcite and quartz, which crosscut Be-stage fluorite veins. During this episode of crustal extension, the Be-U-Mo ore therefore formed in a two-stage hydrothermal model within the same mineralising event: (i) oxidising meteoric and possibly basinal waters percolated downward into the basement through structures and mixed with CO2-bearing magmatic fluids derived from early generations of mafic dykes that intruded the host rocks in the Baiyanghe area. During the circulation of these thermal solutions along faults and fractured zones, Be was leached mainly from the Devonian rhyolitic tuff during hydrothermal alteration and dominantly transported as fluoride complexes in the fluids. These low-temperature (130–150 °C) ore solutions then reacted with Ca-rich minerals of the host rocks, which resulted in a pH increase that triggered fluorite precipitation in turn promoting Be deposition as bertrandite; and (ii) in a second stage, additional oxidising surface-derived fluids including meteoric waters and possibly basinal brines infiltrated the basement. U was also leached mainly from the late Devonian rhyolitic tuff and likely transported as chlorine and/or uranyl carbonate complexes in the fluids. U precipitated as pitchblende due to fO2 decrease when these low-temperature (120–125 °C) oxidising U-bearing solutions encountered favourable reducing environments mainly represented by dolerite and diabase dykes crosscutting the host rocks and/or carbonaceous shales at the contact with the Devonian rhyolitic tuff. Pitchblende then locally experienced dyke-emplacement related post-ore hydrothermal potassic alteration characterised by abundant illite crystallisation, significant Si gain and in situ relative enrichment of Nb, Ti, Th, and Ta due to strong U and Pb depletion. The primary U mineralisation was then largely oxidised into uranophane due to supergene alteration related to further meteoric water infiltration during late Mesozoic–Cenozoic crustal extension in West Junggar.The characteristics of the volcanic-related hydrothermal Be-U mineralisation in the Baiyanghe deposit show key similarities with Streltsovka (U-Mo-F) and Spor Mountain (Be-U) world-class districts, although Baiyanghe has much smaller resources than the ones in Streltsovka.

Petrogenesis of Neoproterozoic rare metal granite-pegmatite suite in Jiangnan Orogen and its implications for rare metal mineralization of peraluminous rock in South China

Recent studies have demonstrated the Mesozoic explosive metallogeny of rare metals in China; however, Precambrian rare metal mineralization event is rarely reported or studied. The Jiangnan Orogen (JO) is a well-preserved Neoproterozoic orogenic belt in South China, and although it abounds with a huge amount of Neoproterozoic granitoids, lacks the equivalent amount granitic pegmatite. In this study, the geology, mineralogy, whole-rock composition, zircon U-Pb age and Hf isotope compositions of the Fanjingshan granite and surrounding rare metal pegmatites, and bulk composition of sedimentary wall rocks of the Taojinhe Formation in Guizhou province, western Jiangnan Orogen (JO), were studied to reveal the petrogenesis of the granite and pegmatite and the source relationship of the pegmatite with the Paleozoic and Mesozoic rare metal ore deposits in South China. The Fanjingshan granite and pegmatite both show Sn-Ta-Nb mineralization and have consistent zircon U-Pb ages of ca. 830 Ma, indicating the existence of the Neoproterozoic rare metal granite-pegmatite suite in the JO. The geology, mineralogy, whole-rock composition and zircon U-Pb age and Hf isotope study results demonstrate that the Fanjingshan rare metal pegmatite belongs to the Li-P-B-Sn-Ta-Nb granitic pegmatite in the Chemical composition-Mineral assemblage-Structural geology (CMS) classification (Dill, 2016), and has close spatial–temporal and source-differentiation connections with the Fanjingshan granite. The petrography and whole-rock composition studies revealed that the Taojinhe formation was formed by the deposition of mature and immature source materials from acidic igneous rocks in a continental arc setting. Comparison of the Hf isotope compositions of the Fangjingshan granite-pegmatite suite with those of the Fangjinshan Group and the high Li, Sn, Rb, W, Ta and Nb background concentrations in the Taojinhe Formation support the conclusion that the Taojinhe Formation was a contributing source to the granite-pegmatite suite. A comparative study of the Fanjingshan granite with synchronous S-type granitoids revealed that the granitoids in the eastern and western JO have distinct sources and degrees of differentiation, indicating the limited ore-forming potential of the Neoproterozoic granitoids in the eastern JO. The Fanjingshan rare-metal granite-pegmatite suite has consistent Hf isotope model ages of 1.6–2.3 Ga with the Paleozoic and Mesozoic Nb-Ta ± Sn-W ± Be-Li ore deposits in South China, indicating a common origin from the Paleoproterozoic crust and the source inheritance of the western JO from the Cathaysia Block.

The Yichun Ta-Sn-Li Deposit, South China: Evidence for Extreme Chemical Fractionation in F-Li-P-Rich Magma

Abstract The Yichun Ta-Sn-Li deposit occurs within the 9.5-km2 Yashan Igneous Complex, which is made up of felsic, peraluminous intrusions including two-mica, Li-mica, and topaz-lepidolite granites. The topaz-lepidolite granite forms a thin sheet confined to the upper part of the Li-mica granite and is separated from the host metasediments by a marginal pegmatite. The topaz-lepidolite granite is characterized by the presence of snowball textures in which quartz, K-feldspar, and topaz phenocrysts contain albite laths and rare lepidolite and columbite arranged along growth zones. These textures indicate simultaneous crystallization of these phases and attest to the subsolvus character of the topaz-lepidolite granite. Minor and accessory phases in the topaz-lepidolite granite include amblygonite, cassiterite, columbite-tantalite, microlite, wodginite, zircon, monazite, and pollucite. The topaz-lepidolite granite is characterized by low SiO2 (68.6–69.7 wt %), TiO2 (0.01 wt %), Fe2O3(total) (0.15–0.33 wt %), MgO (0.01–0.05 wt %), and CaO (0.15–0.19 wt %), whereas Al2O3 (17.97–18.26 wt %), Li2O (0.90–2.09 wt %), P2O5 (0.43–0.54 wt %), and F (1.09–2.30 wt %) are all very high. Na2O ≫ K2O due to both high Na2O (5.18–6.30 wt %) and low K2O (2.63–3.05 wt %). The topaz-lepidolite granite contains extremely high concentrations of Rb (&amp;gt;3,300 ppm), Cs (&amp;gt;340 ppm), Sn (&amp;gt;140 ppm), and Ta (&amp;gt;120 ppm), with very low Zr/Hf and Nb/Ta. Gaps of &amp;gt;3.5 wt % SiO2 and &amp;gt;2.5 wt % Al2O3 together with large increases in F, Li2O, and P2O5 between the Li-mica and topaz-lepidolite granites are not compatible with an evolution by Rayleigh fractionation processes. It is proposed instead that early crystallization of the Li-mica granite led to the formation of an Si-poor, Al-, Na-, and flux-rich boundary layer whose low viscosity and density allowed effective separation from the remaining melt and crystals. This melt concentrated incompatible elements including tin and tantalum and accumulated in the upper part of the magma chamber where it crystallized the sheet-like bodies of marginal pegmatite and topaz-lepidolite granite. The uppermost part of the topaz-lepidolite granite consists of aplite and overlying quartz lepidolite rock, which is composed mainly of quartz, lepidolite, albite, K-feldspar, topaz, amblygonite, cassiterite, and columbite. Compared to the topaz-lepidolite granite the aplite and quartz-lepidolite rock shows a number of complementary element enrichments and depletions. The quartz-lepidolite rock is enriched in Fe, Mn, K, Rb, Cs, Li, F, Ba, Sr, Ti, Zr, Nb, W, Th, and Sm. The formation of the quartz-lepidolite rock is interpreted to result from separation of an F- and Li-rich alkaline phase, which accumulated beneath the already crystallized marginal pegmatite. Complementary to this was crystallization of the strongly peraluminous sodic aplite with the highest tantalum contents measured in this study.

Geology and genesis of vein-type corundum deposits in the Hafafit-Nugrus area, South Eastern Desert, Egypt

AbstractUnusual deposits formed by corundum are described from two separate pegmatitic veins in the Hafafit-Nugrus area of the South Eastern Desert of Egypt. Other related minerals are described too. The vein-type of corundum at Locality 1 (Vein 1) crosscuts through exposed rocks of an ophiolitic mélange, whereas at Locality 2 (Vein 2), it crosscuts through exposed serpentinised ultramafic rocks. The main minerals in Vein 1 are plagioclase, corundum, grossular, phlogopite, muscovite and clinochlore, while almandine, xenotime-(Y), allanite-(Ce), zircon, Cr-rich spinel, apatite, titanite, fergusonite-(Y), meta-ankoleite, U-rich thorite (uranothorite), carbonate and illite are the accessories. In Vein 2, the main minerals are plagioclase, corundum, phlogopite and chlorite, while clinochlore, euxenite-(Y), Nb-rich rutile, almandine, xenotime-(Y), allanite-(Ce), zircon, spinel, apatite, titanite, kasolite, dickite, illite, carbonate, antigorite and talc are accessories. The two types of corundum veins differ in their concentrations of Th, U, Zr, Nb, Ta, REE, Y and Li in whole-rock compositions. Field observations, mineralogy and chemical analyses of samples from the two veins of corundum deposits, as well as concentrations of chromophore elements in corundum crystals, suggest metasomatic origins. The present study suggests that the two types of corundum veins formed at different ages from different residual magmas that underwentin-situhybridisation with the host rocks.

Inter-annual Variability of the Carbonate System in the Hypoxic Upper Pearl River Estuary in Winter

Hypoxia has become a universal environmental and ecological problem in recent decades. The Pearl River estuary (PRE), the largest estuary in Southern China, is hypoxic year-round in the upper estuary. This study reports the inter-annual variation between 2005 and 2019 in the carbonate system of the hypoxic upper PRE in winter. In January 2005, both DIC and TA concentrations were >3000 umol kg-1 at the upstream-most station and decreased sharply downstream. However, DIC and TA were lower, with concentrations of 2300 and 1950 umol kg-1, respectively, at the upstream-most in January 2019. At salinities >15, both DIC and TA were conservative and reached steady values at the downstream seawater end-member. The upstream-most station was taken as an example to quantify the influences of biogeochemical processes on DIC and TA, including CO2 degassing, organic carbon oxidation, pelagic nitrification, CaCO3 dissolution and benthic release. Among the biogeochemical process, a decrease in CaCO3 dissolution (from 734.4 umol kg-1 in 2005 to 168.9 umol kg-1 in 2019) was the major factor driving the decreases of DIC and TA in 2019. In the context of global change, inter-annual variability in biogeochemical process should receive more attention.

Partitioning of Nb, Ta, Ti, Ce, and La between Granitoid Magmatic Melts and Minerals

Experimental data on the Nb, Ta, Ti, Ce, and La concentrations in felsic magmatic melts of various alkalinity and alumina content upon dissolving ilmenorutile, ferrotapiolite, and loparite in them and the partitioning of these metals between the melt and the mineral at 650–850°C and 100 MPa, which allow one to obtain quantitative characteristics for creating physicochemical models of the genesis of rare metal and rare earth deposits, are presented. It is shown that ilmenorutile and ferrotapiolite are stable in the peraluminous melt. Ilmenorutile is also stable in the subaluminous melt and at 650°C in the alkalized melt, and loparite is unstable in all melts participating in the experiments. The dependences of the content and partitioning of Nb on dissolving ilmenorutile and loparite are similar to each other and to those on dissolving columbite and tantalite. At the same time, the dependence obtained by dissolving ferrotapiolite is similar to that obtained by dissolving microlite and pyrochlore.

Trends in elastic properties of Ti–Ta alloys from first-principles calculations

The martensitic start temperature (M s) is a technologically fundamental characteristic of high-temperature shape memory alloys. We have recently shown [Chakraborty et al 2016 Phys. Rev. B 94 224104] that the two key features in describing the composition dependence of M s are the T = 0 K phase stability and the difference in vibrational entropy which, within the Debye model, is directly linked to the elastic properties. Here, we use density functional theory together with special quasi-random structures to study the elastic properties of disordered martensite and austenite Ti–Ta alloys as a function of composition. We observe a softening in the tetragonal shear elastic constant of the austenite phase at low Ta content and a non-linear behavior in the shear elastic constant of the martensite. A minimum of 12.5% Ta is required to stabilize the austenite phase at T = 0 K. Further, the shear elastic constants and Young’s modulus of martensite exhibit a maximum for Ta concentrations close to 30%. Phenomenological, elastic-constant-based criteria suggest that the addition of Ta enhances the strength, but reduces the ductile character of the alloys. In addition, the directional elastic stiffness, calculated for both martensite and austenite, becomes more isotropic with increasing Ta content. The reported trends in elastic properties as a function of composition may serve as a guide in the design of alloys with optimized properties in this interesting class of materials.