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An alternative approach to separating trapped and radiogenic helium, and assessing the mobility of the latter in He-retentive minerals implemented in the present work, has been developed on the basis of helium extraction patterns obtained via incremental heating of mineral samples. We used these data both to estimate helium mobility in concentrates of various ore minerals (pyrite, magnetite, and hematite) and to assess the contribution of in situ-produced 4He in the total helium budget. The rocks of uranium-ore and gold mineralization of the Salla-Kuolajarvi belt (northern Karelia, Fennoscandian Shield) were used as test materials for the new approach. The method allowed such parameters as diffusivity, activation energy, closure temperature, and the contribution of the trapped helium to be obtained for all samples. The latter was used for the correction of apparent U-Th-He bulk ages. The interpretation of the calculated values was performed taking into account the closure temperatures of the U-Th-He system, as well as the peculiarities of each individual sample. [ABSTRACT FROM AUTHOR]

The mica-bearing schist of the Thracian lithotectonic unit basement represents a granite protolith overprinted by high-grade metamorphism. The zircon population displays Silurian protolith age with inherited older Neoto Paleoprotezoic cores affected by a Carboniferous metamorphism. The Late Cretaceous-Paleogene metamorphic rutile could have resulted from extensive volcanic activity within the Maritsa dextral strike-slip shear zone. The apatite geochemistry has a composition corresponding to low- and medium metamorphic and metasomatic apatite. [ABSTRACT FROM AUTHOR]

Eight granite samples representing the main petrographic and geochemical types of Variscan granites from the Krusné Hory/Erzgebirge area were studied to decipher the distribution of rare-earth-elements (REE) among all rock-forming, minor, and accessory minerals. The chemical composition (REE contents) of minerals was determined using electron microprobe and laser ablation ICP MS, while the quantitative abundance of individual minerals was determined by automated mineralogy (TIMA technology). Monazite and xenotime + zircon are dominant hosts of both LREE and HREE respectively, especially in strongly peraluminous S-type granites. In less-fractionated Ca-richer facies, allanite is also an important carrier of LREE. In slightly peraluminous A-type granites, monazite + fluorite (including its alteration products) dominates as LREE hosts, while fluorite (including its alteration products), with small contributions of zircon and xenotime, hosts the HREE. The importance of rock-forming silicates for REE distribution is limited; the relatively highest contribution was found in plagioclase (up to approx. 15 % of LREE in S-type granites). [ABSTRACT FROM AUTHOR]

This report presents the results of a petrographical and mineralogical (optical microscopy, BSE-EDS image analysis) study of zircon in samples from the Lower Nubian monzogranite. The mineral occurs as smaller grains (< 80 μm) in a fine-grained quartz-feldspar-matrix, coexisting with other accessory minerals including biotite, clinochlore, titanite, and britholite-(Ce). Zircon is also present within biotite and britholite-(Ce), suggesting that it started crystallization at about the same time as these two minerals. Two types of thorite inclusions within zircon are reported in this study. Type 1 is widely distributed throughout the zircon grain, forming crystallites of which each is typically < 1 μm in size. Type 2 is relatively larger (5-15 μm) and occurs only in one part of the grain. For the thorite inclusions, three possible origins are briefly discussed: (1) exsolution of thorite from zircon; (2) dissolution/reprecipitation of zircon; and (3) growth syngenetically with zircon. Of these potential hypotheses, the syngenetic growth model seems more favorable for zircon-thorite intergrowths than the other two hypotheses. Thorite inclusions and their host zircons seem to have grown from magma rather than hydrothermal or supercritical solutions. Here, they have primary textures and consistent chemical compositions that are consistent with whole-rock geochemistry.

The Hemrin Basalt (HB) is an abnormal occurrence because of its genesis, mineralogy, textures, rare native metals content, and odd geographic-geologic-tectonic setting. It occurs as a caprock for few NW/SE trending hills in a nearly flat-lying area. The HB is a high-K calc-alkaline, collision-related, continental-arc basalt and consists of diopside, labradorite and volcanic glass as the predominant constituents displaying rare firework and feathery textures. The accessory minerals in HB comprise small, discrete grains of native Ni, Fe, Cu, and Sn metals, and scattered grains of sulfides (pyrrhotite, pentlandite, molybdenite), oxides (magnetite, ilmenite, Cr-spinel), and apatite. These minerals occur as disseminated individual or composite grains of variable shapes within the groundmass of HB. Vesicle-filling secondary minerals are zeolite, calcite, anhydrite, and gypsum. The native metals were formed under reducing conditions. The reducing conditions were created as a result of assimilation of C- and S-rich sedimentary rocks by the ascending magma from the continental lithospheric mantle through the thick pile of sedimentary formations. The possible C- and S-rich rocks include the carbonates and evaporites of Fatha Formation and the Hemrin Coal Seam within the upper part of Injana Formation hosting the HB and overlying the Fatha Formation, and possibly the petroleum source, reservoir and caprocks forming the sedimentary column underlying the area. Assimilation of S from these rocks created sulfides, while assimilated C resulted in the formation of native metals. [ABSTRACT FROM AUTHOR]

Rare earth elements deposited in ion-adsorption clay-type deposits in Northern Kazakhstan were recognised using mineralogical and geochemical methods. The diversity and mineralogical properties of the Shok-Karagay deposit and Syrymbet ore fields under investigation in this study are closely related to the process of the formation of the deposits as well as the deposits' architecture. A combination of mineralogical research and digital technology (GIS) was used to characterise the deposits. Rare earth elements from the cerium series were found in the following quantities: La (in ppm), 43–200; Ce, 57–206; Sm, 100–300; Eu, 22–100. Yttrium-series elements were found in the following quantities: Y, 31–106; Gd, 100–200; Tb, 100–200; Dy, 0–300; Ho, 0–20; Er, 0–364; Tm, 0.28–0.85; Yb, 2.2–39; Lu, 0–200. The wireframe and block models indicated that the bodies' forms were 1800 m wide, 3500 m long, and 20–40 m thick. The major REE group minerals in both bodies were monazite and xenotime, whereas the minor minerals included yttrium parisite, silicorabdophanite, thorite, and orangite; moreover, ilmenite and titanomagnetite were found. The 3D models that were constructed indicated that the mineralogy and geochemistry of the ore bodies played a determining role in the deposits' architecture. [ABSTRACT FROM AUTHOR]

The natural radiometric data revealed that eU and eTh-contents of mylonite rocks reach up to 464 and 1283 ppm, respectively. The studied mineralised mylonites are enriched in thorite, ishikawite and zircon as well as other accessories (ferrocolumbite, xenotime, fergusonite, synchysite, cassetrite, apatite, fluorite, galena and barite). Ishikawaite is considered as the almost enriched mineral in uranium contents, whereas UO2 ranges from 31.02 to 50.78 wt%. The higher concentrations of UO2 reached up to 15.88 wt% and ThO2 up to 4.32 wt% related to metamictization of columbite. Some zircon crystals possess higher values of HfO2 reached up to 6.38 wt% could be affected by hydrothermal activity. Both xenotime and fergusonite are enriched in HREE (average ∑HRE2O3 31.19 and 14.1 wt%, respectively) whereas synchysite is main LREE bearing mineral (average ∑LRE2O3 55.78 wt%). [ABSTRACT FROM AUTHOR]

Mineral behavior during anatectic metamorphism is a direct factor controlling the chemical and isotopic compositions of melts and residues. However, the mechanism that causes disequilibrium melting remains poorly understood. A combined study of petrological, geochronological and geochemical analyses was carried out on a stromatic migmatite outcrop, the Luoerling migmatite in the North Dabie zone. The in-source leucosomes and leucocratic veins are products of in situ partial melting and later magmatic intrusion, respectively. The finding of Neoproterozoic, Late Triassic and Early Cretaceous zircons suggests that the migmatites have Neoproterozoic protoliths, and experienced eclogite-facies metamorphism during collisional orogeny and anatectic metamorphism in the post-collisional stage. The occurrence of peritectic amphibole suggests that anatectic metamorphism mainly occurs through biotite hydration melting. The occurrence of orthopyroxene and clinopyroxene indicates local dehydration melting under granulite-facies conditions. Leucosomes show considerably higher 87Sr/86Sr i , but lower ε Nd (t) and ε Hf (t) values than the corresponding melanosomes. Such isotopic differences between leucosomes and melanosomes result mainly from the influx of external fluids derived from the surrounding eclogites and gneisses, indicating a coupled dehydration-hydration mechanism in the continental subduction zone. Peritectic and anatectic zircon, monazite, titanite and apatite that formed during anatectic metamorphism exhibit different petrological and geochemical characteristics. Peritectic and anatectic accessory minerals in the leucosomes and leucocratic veins exhibit smaller variations in Nd-Hf isotopes than those in the melanosomes, suggesting that the anatectic melts were homogenized during transport. Differential dissolution and growth of monazite, titanite and apatite affect the Sm-Nd isotopes of residues and melts during anatectic metamorphism. The dissolution of apatite plays a significant role in the hydration melting of metagranite. The continuous dissolution of relict zircon during cooling/transportation of melt results in decreased ε Hf (t) values in anatectic zircon, whereas the incomplete dissolution of relict zircon results in whole-rock Hf-Nd decoupling. The difference in Nd-Hf isotopes among whole-rock and different genetic minerals can distinguish between dehydration and hydration melting. Therefore, this study highlights that a combination of multiple isotope analyses on whole-rock and accessory minerals may be conducive to understanding not only the mechanism and process of disequilibrium melting but also the nature of anatectic metamorphism in collisional orogens. • Leucosomes have higher initial Sr, but lower ε Nd (t)-ε Hf (t) values than melanosomes. • Peritectic/anatectic minerals in leucosome have relatively homogeneous isotopes. • Peritectic/anatectic minerals in melanosome have widely variable isotopes. • Apatite dissolution controls the Sm-Nd isotopes during hydration melting. • Differential dissolution of relict zircon affects Hf isotope of anatectic melts. [ABSTRACT FROM AUTHOR]

The Mangodara district (southwestern of Burkina Faso, West African Craton) consists of a regional-scale Eburnean dome cored by granitoid-gneisses comprising rafts of migmatitic paragneisses and amphibolites of the Paleoproterozoic Birimian series. The occurrence of rare metal-bearing pegmatites in diffuse contact with these migmatitic and granitoid gneisses suggests that they originated from the segregation of a residual melt of these partially molten hosts. In this paper, we constrain the petrogenetic link between pegmatites and their hosts, and the mechanisms of rare metal fractionation in Lithium-Cesium-Tantalum (LCT) vs Niobium-Yttrium-Fluorine (NYF) petrogenetic signatures by the geochemistry of micas, apatite, columbite-group minerals, garnet, and zircon. Titanite-allanite pegmatites (containing titanite, allanite, epidote, zircon, and apatite as accessory minerals) and their evolved equivalent, apatite-zircon pegmatites (richer in apatite, lower K/Rb and Fe/Mn ratio in biotite but Li-depleted) are poorly mineralized metaluminous pegmatites. They display a continuous evolution trend in K/Rb and Fe/Mn in biotite and similar REE patterns in apatite, which favor an origin by segregation of residual melt within tonalitic-trondhjemitic gneiss in the core of the Mangodara dome. Garnet-columbite pegmatites containing REE-bearing phosphates and Zr-U-Th-bearing metamict minerals are mixed LCT + NYF pegmatites. Their micas, slightly enriched in Li, LREE-rich apatite, and Nb–Ta-U-rich garnet, are consistent with an origin by partial melting of a metasedimentary source, with dehydration of biotite (reservoir of Li, Rb, Nb) and dissolution of apatite-monazite (reservoir of REE). Apatite crystals in one garnet-columbite pegmatite reveal an inherited REE signature typical of apatite-zircon pegmatite, which suggests mingling of a LCT pegmatite-forming melt with the residual melt derived from crystallization of metaluminous pegmatites. Garnet-REE pegmatites, containing ilmenite-pyrophanite and euxenite-aeschynite), are NYF pegmatites that should originate from melt segregation within granodioritic gneiss associated with breakdown/entrainment of amphibole (reservoir of REE, Y) and LREE segregation by allanite and phosphates in the source. These data show that the LCT vs NYF signature of pegmatites of the Mangodara district results primarily from the chemical composition of the partially-molten source and the minerals involved in the partial melting reactions, which vary as a function of increasing depth (mica, phosphate, amphibole, garnet). The trace-element signature of anatectic peraluminous pegmatite-forming melt might then be affected by mingling with residual Nb-enriched metaluminous melt. [ABSTRACT FROM AUTHOR]

The causes of metasomatic albitization of host rocks and the formation of the accompanying thorium mineralization in uranium deposits of the Streltsovka ore field located in the Streltsovka volcanic caldera are considered. Data provided by the authors and published data allow us to conclude that the process of hydrothermal albitization does not require additional Na input by the magmatogenic fluids. It could have originated from the host rocks due to pre-ore acid leaching; accessory minerals in the same rocks were a source of Th. The increase in the pH value necessary for the deposition of albite under low-T conditions is ensured by a sharp change in the physicochemical conditions due to seismotectonic impulses. The latter were accompanied by opening of the fault and fracture systems, a decrease in pressure (decompression), and degassing. The alkaline character of the fluids that caused albitization is also emphasized by the behavior of trace and rare-earth elements. It is likely that thorium migrated in a sodium alkaline environment probably in the form of mobile tetra- or pentacarbonates: Na4[Th(CO3)4] or Na6[Th(CO3)5]. [ABSTRACT FROM AUTHOR]

Abstract—Miocene rocks within the eastern slope of the Central Russian Upland are represented by the rocks of the Berekskaya (Oligocene–Miocene), Novopetrovskaya, and Krasnoyaruzhskaya formations, Lamkinskaya and Gorelkinskaya series, and Nizhneusmanskaya subseries. The Berekskaya formation contains sands with interlayers of clays and sandstones; the mineralization points of titanium–zirconium placers are associated with these formations. The deposits of the Novopetrovskaya and Krasnoyaruzhskaya formations were identified in the study area for the first time; the point of Ti and Zr mineralization is associated with sandy varieties, and the ceramic raw materials are related to clays. The rocks of the Lamkinskaya and Gorelkinskaya series have not been previously identified in this area; occurrences of ceramic clays are associated with clay interlayers and units. The rocks of the Nizhneusmanskaya subseries are characterized by an increased content of a heavy fraction; several points of Ti and Zr mineralization have been identified. The most promising placer deposits are the rocks in the Berekskaya formation. Ceramic clays are typical of the Lamkinskaya and Gorelkinskaya rocks and, to a lesser extent, of the Novopetrovsk–Krasnoyaruzhskaya rocks. [ABSTRACT FROM AUTHOR]

The relevance and aim. The study of granitoids confined to the Aleysk Zmeinogorsk complex for the first time revealed the presence of rare accessory minerals of yttrium (priorite, fergusonite) in a sample spot of leucogranites of phase IV. According to the available data, these minerals are of pegmatitic, pneumatolith-hydrothermal and metasomatic origin, however their development at the magmatic stage is considered less common. The aim of the study is to reveal the origin of priorite and fergusonite in the Aleysk Zmeinogorsk leucogranites, as well as to explain the presence of yttrium and accessory rare-earth elements within the only intrusive zone. Research methods involve conventional mineralogical and petrographical methods, identification of accessory minerals and analysis of their composition using crashed samples; analytical studies were performed on an electronic scanning microscope JSM–6510LV (Jeol Ltd) fitted with an energy dispersive spectrometer INCA Energy 350+ in a laboratory of the Geology and Mineralogy Institute of the Siberian branch of the Russian Academy of Science (Novosibirsk) and X-ray fluorescence microscope (the Division for Geology, School of Earth Science and Engineering, TPU). Results. In line with earlier discovered yttrium (xenotime), rare-earth monazite, niobates (columbite, ilmenorutile), rare accessory minerals of yttrium-niobium and yttrium-titanium composition were identified in granitoids of the Aleysk Zmeinogorsk complex. Conclusions. The presence of priorite and fergusonite in a stock of leucogranites of IV intrusive phase allows the assumption that it was formed due to continuous inflow of melting rocks during successive intrusive phases. The inflow of intrusive material from the initial magma chamber served as a favorable condition for the rocks to be saturated with yttrium, rare-earth elements, and rare metals. The accessory minerals of corresponding composition occurred at the final stage of intrusion formation as a result of autometasomatism of its apical parts and selvages.

• We present the first comparison of in situ dating techniques for Apollo samples. • 207Pb/206Pb dates of two impactites are more than 100 Ma older than interpreted 40Ar/39Ar ages. • 40Ar/39Ar dates of Apollo impactites may not date impact-melting events. • Less than 16% of the lunar surface is likely to contain U-Pb datable accessory minerals. • Dating strategies are proposed for the future lunar returned samples. Investigations of Apollo-returned samples radically altered our understanding of lunar history which has important implications for terrestrial habitability and Solar System evolution. Radiometric dating of those samples inspired the hypothesis that Moon experienced a Late Heavy Bombardment (LHB) at ∼3.9 Ga. The LHB concept has come under several recent challenges, including the concern that 40Ar/39Ar step-heating dates of Apollo impactites had been misinterpreted. Ultraviolet laser ablation (UVLAMP) 40Ar/39Ar dates – with their capacity for much higher spatial resolution and thus potential to avoid dating near-ubiquitous clasts in impact melt rocks – should in principle provide more interpretable results. Here we compare new ion microprobe 207Pb/206Pb accessory mineral dates for two Apollo 17 impactites for which UVLAMP 40Ar/39Ar dates had been previously obtained. Our results are consistent with a single accessory phase growth event for each sample, though the two samples yielded statistically different mean ages of ca. 3.974±0.013 and 3.928±0.003 Ga. Both can reasonably be interpreted as dating an impact event, but the 207Pb/206Pb dates are older than the associated 40Ar/39Ar dates by several hundred million years. We interpret that the age differences result from subsequent thermal disturbances. The discordancy between impact ages inferred from lunar impactites using two different radiometric systems suggests caution in acceptance of the LHB hypothesis without the benefit of both larger lunar datasets and more multichronometric studies. Even with such information, our capacity to know the lunar bombardment history is likely limited by compositional and thermal effects which appear to restrict growth of impact-produced accessory minerals to a small fraction of the lunar surface. Using currently available datasets, the LHB hypothesis may be effectively untestable. [ABSTRACT FROM AUTHOR]

The compositional diversity of Archean tonalite-trondhjemite-granodiorite (TTG) rocks is generally attributed to partial melting of mafic rocks at various depths or magmatic differentiation driven by the accumulation of plagioclase and/or amphibole. Our investigation of the approximately 130 km2 Paleoarchean Stolzburg pluton in the Barberton area of South Africa reveals a substantial compositional variability that cannot be explained by those processes. The variable Sr/Y and La/Yb ratios can correspond to high-, medium-, and low-pressure types based on pressure-dependent classification criteria, thus conflicting with partial melting simulations and ruling out the model of variable melting depths for such a small, single pluton. Instead, an integrated study incorporating petrographic analysis, mineral mapping, and thermodynamic simulation suggests that the heterogeneous accumulation of accessory minerals during crystal-melt separation in the magma chamber is the leading cause of the compositional variation of the ca. 3.45 Ga TTG pluton. This study highlights the critical role of accessory minerals in intrinsic magmatic differentiation within individual TTG plutons and advise caution when using bulk-rock compositions of TTGs to infer melt physochemical conditions and tectonic settings. [Display omitted] • Accessory minerals in magma mush can cause the compositional variation of TTGs. • Bulk composition of TTGs cannot be used as parent melt due to crystal separation. • Paleoarchean granites may be the product of magmatic differentiation. [ABSTRACT FROM AUTHOR]

The current study presents mineralogical and geochemical characteristics of pegmatite bodies from the Govedarnika Pb-Zn deposit, situated in Laki district, South Bulgaria. The studied pegmatites are composed mainly of K-feldspar, plagioclase, quartz and accessories of titanite, apatite, allanite and zircon. Intensive hydrothermal alteration resulted in specific mineral assemblage of chlorite, hematite, epidote and carbonates. According to the mineral relationships, it preceded or coincided with the time of base metal ore formation and affected both pegmatites and host metamorphic rocks. Both pegmatite accessories and post-pegmatite hydrothermal silicates often show enhanced contents of some strategic elements such as Sr, Li, V, Ga, Ni and REE. Pilot U-Pb geochronology of titanite from the studied pegmatites yielded a lower intercept age of 39.9±2.3 Ma. [ABSTRACT FROM AUTHOR]

Fluids play a major role in facilitating igneous/metamorphic processes in the Earth’s crust and mantle. In this study, we investigate the nature and composition of fluids in Earth’s interior by studying the lower crustal rocks. We compare accessory minerals (e.g., apatite, monazite, allanite, and titanite), their texture, mineral reactions and composition among regionally distributed metamorphosed mafic and felsic rocks representing the roots of Neoarchean arc magmatism from the Nilgiri Block of the Southern Granulite Terrane in India. Regional trends in accessory minerals show the formation of monazite, allanite, and titanite in the felsic rocks. Apatite is depleted in REEs in all the rock types, irrespective of the difference in their whole-rock chemistry. Textural features and mineral reactions show that these accessory minerals were affected by fluids present in the lower crustal conditions. By comparing our results with those from previous experimental results, we further show that acidic CO2-H2O-HCl-HF fluids stable in lower crustal conditions could have resulted in these chemical and textural features. Dielectric constant of water is high (10–35 compared to lower crustal conditions) in high-pressure and low-temperature conditions of subduction zones and the upper mantle. Such conditions would enhance dissociation of HCl (compared to lower crust) and result in acidic fluids during dehydration reactions in subduction zones and in the upper mantle. Our results have important implications in understanding the nature and composition of fluids in Earth’s interior and would be helpful to model the tectonic and deep geochemical processes in both early and modern conditions in planetary interiors.

Effective retrospective modeling of mineral formation in natural systems should take into account all minerals – rock-forming, secondary in abundance and accessory. In the Ilmeny Mountains (South Urals), the ontogeny of pegmatite bodies (granitic, syenitic, carbonatite, and ultramafic) is complex in time and space. Using several examples, the relative age of accessory minerals in aggregates of rock-forming minerals is considered against the background of a general evolution of formation of pegmatite fields.

In the second part of this study, we analyze how crystallization differentiation can affect concentrations of elements and their ratios in melt inclusions and glasses of rocks in major geodynamic environments. The paper presents analysis of experimental data on the partition coefficient of elements between minerals (olivine, pyroxenes, garnet, amphibole, biotite, sulfide, apatite, spinel, ilmenite, rutile, and zircon) and silicate melts, which were discussed in the first part of this study. It is demonstrated that the crystallization of major minerals only insignificantly affects the ratios of incompatible elements. The partition coefficients of some elements between accessory minerals and melts can be very high, but the effects of crystallization differentiation cannot be significant because of the small amounts of the crystallizing phases. These effects are the most significant for chalcophile elements (Cu, Ni, and others), at the separation of sulfides, and for Nb and Ta, at the crystallization of rutile. Differences in concentrations of various elements and their ratios to Cs concentrations are discussed with reference to various geodynamic environments. The maximum values of the ratios of practically all elements to Cs were found in melts in mid-oceanic ridges. The melts of oceanic islands and backarc basins are characterized by relatively low ratios, without any significant anomalies. The lowest ratios of elements to Cs were found in melts of continental and marginal environments. These melts are also characterized by clearly seen geochemical anomalies that are typical of rocks of the corresponding environments (negative Ta–Nb, positive Pb, and other anomalies). [ABSTRACT FROM AUTHOR]

The orebodies of the Belogorskoe deposit contain various bismuth minerals. Many of them are rare in nature or are rare mineral varieties. Among them are native bismuth, bismuthine, cosalite, gladite (?), jonassonite, a galenobismuthite variety enriched in Ag and Cu, bismite, bismutite, preisingerite, bismoclite, zavaritskite, and a large group of unnamed compounds. One specific feature of the endogenous bismuth mineralization of the deposit is its localization in the low- to medium- temperature hydrothermal alteration products of the early assemblages, especially in large carbonate (with fluorite) pockets in blocks of essentially magnetite ores, where it is closely associated with Au–Ag–Pd–Pt and Mo–W mineralization. A significant amount of Ag in the form of Ag–Bi minerals is also related with the bismuth mineralization of the Belogorskoe deposit. The close geochemical relationship of Bi, Au, and PGE in the processes of mineral formation at the Belogorskoe deposit is also manifested by the presence of the common minerals of these elements, such as jonassonite and the unnamed compound Ru(Pb,Ag)2Bi4. The association of bismuth and molybdenum–tungsten mineralization is a characteristic feature of the ores of some tungsten and molybdenum skarn deposits containing scheelite, molybdenite, and bismuthine as the main minerals. The presence of bismuth and noble-metal mineralization is most characteristic of gold and complex gold-bearing ores of hydrothermal deposits of various types. However, such metals as W, Mo, and Bi, as well as Au, Ag, Pd, and Pt, have no independent industrial role at the Belogorskoe deposit, unlike the deposits of the above-mentioned types, and are accompanying useful components relative to iron ores. Rocks and ores that compose the orebodies of the Belogorskoe deposit are Triassic metalliferous sediments that accumulated in island lagoons as a result of erosion of the lateritic weathering crust of ancient gabbroids, which were metamorphosed and partially regenerated during the Late Cretaceous. This accounts for the enrichment of ores in various metals, including Fe and Mn, and the presence of gold–silver–palladium–platinum, nickel–cobalt, and bismuth mineralization, which (including Bi compounds with Au and PGE) is characteristic of some ultramafic massifs. [ABSTRACT FROM AUTHOR]

Relevance of the research. Accessory niobioum-tantalum mineralization of granitoids is an important additional feature at detecting potential rare-metal ore content of leucogranites, which are the derivatives of the final stage of polyphase Aleisk granitoid massif (D2–3) formation. The aim of the research is to discover the forms of niobium and tantalum occurrence as well as the other corresponding rare elements. It includes investigation of their spread and possibilities for their usage as minerals-indicators for conditions of leucogranite formation. Methods: traditional mineralogical and petrographic studies of accessory mineral composition in artificial crushed samples, the initial weight of which is about 5–8 kg. Analytical investigation of minerals is performed in the Institute of Geology and Mineralogy (SB RAS, Novosibirsk), using an electronic scanning microscope JSM–6510LV (Jeol Ltd) with an energy dispersive spectrometer INCA Energy 350+ (the analyst M.V. Khlestov, junior research scientist). X-ray fluorescent microscope is used (the Division for Geology, School of Earth Science and Engineering, TPU, the analyst M.A. Rudmin, Cand. Sc.). Results. Two forms of niobium and tantalum occurrence are discovered in the leucogranite of the Aleisk massif: 1) structural impurity in titanite, zircon, and apatite; 2) individual minerals of niobium and tantalum – ilmenorutile and columbite. Usually niobium concentrations dominate distinctly over tantalum. The striking feature of chemistry of accessory columbite is its high ferruginosity, and enhanced concentrations of impurity scandium correspond to a rare type – scandium ferrocolumbite. Crystallization of niobium minerals (ilmenorutile and columbite) occurred at the post-magmatic period of leucogranite intrusive formation during the alkali stage of autometasomatism. Notably, ilmenorutile is an older mineral in regard to columbite.

Common rock-forming and accessory minerals in marbles from various localities in Slovenia were studied using scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS). Minerals and their chemical composition were identified in order to verify the variability of mineral assemblages in marbles from different localities in Slovenia. The analysis showed that marbles from Košenjak are the most mineralogically diverse, followed by Pohorje and finally Strojna marbles. Common rock-forming minerals calcite and dolomite are more abundant in Pohorje marbles where calcite contains higher levels of magnesium but no strontium and iron as compared with Strojna and Košenjak marbles. Accessory minerals like quartz, mica, titanite, apatite, rutile, zircon, chlorite group minerals, kaolinite and iron oxides/hydroxides were found in marbles from all localities. Clinopyroxene, amphibole, epidote and smectite group minerals, talc, tungsten-bearing ilmenorutile, psilomelane and bismuth oxides/carbonates, were observed only in marbles from Pohorje, while tourmaline and allanite group minerals, thorite or huttonite, chalcopyrite and synchysite group minerals were detected in marbles from Košenjak and Strojna. Variations in mineral assemblages in marbles from different locations are likely a consequence of different sedimentary environment and conditions and metamorphic grade of marble. These differences indicate that marbles from Košenjak and Strojna are genetically different from those from Pohorje and probably reflect mineral composition of the protolith. Thus, they enable rough distinction between more distant locations, but not between individual sub-localities.

Respirable talc powder (RTP) is a complex mineral mixture of talc along with accessory minerals, including tremolite, anthophyllite, quartz, magnesite, dolomite, antigorite, lizardite, and chlorite. The industrial mining, milling, and processing of talc ore is associated with elevated incidences of fibrotic and neoplastic diseases, which are also seen among workers exposed to RTP in secondary industries and individuals using processed cosmetic talc for personal use. There is controversial evidence of a link between the talc-induced lung diseases and a potential contamination with asbestos fibers. This controversy is fueled by inadequate exposure data and the complex mineralogy and terminology of the accessory minerals. Talc aerosols exhibit a wide range of mineral habits, including particulates and fibrous structures that have dimensional and compositional characteristics related to the development of asbestos-related lung disease. The inhalation toxicology of RTP is based on the analysis of occupational hygiene and animal inhalation studies conducted between the 1940s and the 1990s and more recent mechanistic studies conducted both in vivo and in vitro. The review of talc toxicity studies reveals that the occupational studies provide only equivocal links between any of the components of the aerosols and the development of pulmonary cancer; however, there is substantial evidence of an association between the aerosols and pleural and pulmonary fibrosis and the development of nonmalignant respiratory disease. The animal inhalation and implantation studies appear to be less than optimal, which also appears to be true for the in vivo and in vitro studies. The mechanistic studies have identified the key pathogenic characteristics of asbestos to be long and thin fibers that are durable in lung tissues and fluids. Talc toxicity studies show that talc particles and fibers are durable and can remain in the lung for up to 40 years after the end of exposure. This extended tissue residence is considered to constitute a continuing tissue exposure that is capable of inducing the documented inflammatory and proliferative response. There is less consensus as to whether there is a threshold fiber length effect, as long, thin fibers (>5 μm) form only a small fraction of talc aerosols and the possible role of fibers >5 μm in the translocation from the lung to the pleura and their association with pleural fibrotic and carcinogenic lesions. Long, thin fibers are preferentially deposited in hot spots in the lung, such as airway bifurcations, areas typically associated with the development of lung cancer. The platy structures typical of talc can form oblate structures behaving more as fibers in the air stream, and these have also been shown to deposit preferentially in such locations. The review of the inhalation toxicity of talc provides a plausible explanation for the carcinogenic potential of RTP. [ABSTRACT FROM AUTHOR]

Abstract—The problem of the origin of "white granite" in the Kester harpolith of the Arga–Ynnakh–Khaya Pluton is discussed. The morphology, occurrence, and nature of the intrusive contacts of the Kester harpolith prove its magmatic origin. The petrographic and petrochemical properties of "white granite" allow its identification as a postorogenic rare-metal high-phosphorus granite of the Li-F geochemical type. The magmatic genesis of the "white granite" texture is supported by statistical methods. The composition, typomorphic properties, ontogenetic features internal structure and relationship of accessory minerals indicate that the major accessories of the granite, that is, cassiterite, columbite, tantalite, "wolframoixiolite," zircon, and ferberite, were formed at the late stage of the low-temperature rare-metal granitic melt. The Kester harpolith within the Arga–Ynnakh–Khaya granite pluton and the eponymous tin–rare-metal deposit genetically related to it are a part of the Far East Superprovince of rare-metal granites. [ABSTRACT FROM AUTHOR]

• Granitic rocks from the Yangkou region record crustal anatexis at HP to UHP conditions. • These rocks are derived from partial melting of the underlying granitic gneisses. • The pressure effect on melt composition reflects the key role of accessory minerals during anatexis. • The Nd-Hf isotope variation is due to dissolution of apatite and garnet into anatectic melt. The production of granitic melts by decompressional melting of deeply subducted crustal rocks under high-pressure (HP) to ultrahigh-pressure (UHP) conditions is important for the crust-mantle interaction at convergent plate boundaries. However, little is known on the geochemical composition of natural HP to UHP granitic melts from collisional orogens. This problem is partially resolved here through an integrated study of the Yangkou granitic veins in the Sulu orogen, which provide the excellent records of HP to UHP granitic melts from the deeply subducted continental crust. In trace element composition, these granitic veins show enrichment in LREE and LILE but depletion in HFSE with remarkable negative anomalies of Nb, Ta, P and Ti. They have low Sr/Y (5.92–26.3) and (La/Yb) N ratios (12.7–45.6), which are primarily controlled by the solubility of accessory minerals such as apatite and epidote/allanite in anatectic melts. Phengite in the granitic veins have high Si (3.29–3.42 p.f.u.) and Mg (0.16–0.35 p.f.u.) with Mg# of 37.7–68.1 and calculated pressures of 1.7–3.1 GPa, indicating their crystallization under HP to UHP conditions. Geochemical variables such as K 2 O/Na 2 O, A/CNK and LREE for whole-rock exhibit a positive correlation with pressure, indicating the significant pressure effect on the mineral stability that in turn controls the composition of anatectic melts. Furthermore, the granitic veins can be divided into two groups based on their formation pressures and geochemical compositions. Group I granitic veins formed at low pressures of 1.7–2.4 GPa and exhibit higher SiO 2 and Na 2 O contents, but lower contents of K 2 O, MgO, TiO 2 , P 2 O 5 and most trace elements (e.g., Rb, Ba, LREE) with lower K 2 O/Na 2 O ratios and A/CNK values compared to Group II granitic veins that formed at high pressure of 2.6–3.1 GPa. Zircon from the granitic veins give concordant U–Pb ages of 755 ± 10 to 769 ± 9 Ma with steep HREE patterns for relict magmatic cores and 216 ± 4 to 222 ± 4 Ma with steep to flattened HREE patterns for anatectic rims. In comparison to concordant U–Pb ages of 220 ± 3 to 227 ± 3 Ma for newly grown zircon in the host eclogites, it appears that these granitic veins were crystallized from anatectic melts produced by crustal anataxis during the exhumation of the deeply subducted continental crust. The anatectic rims are characterized by the absence of not only oscillatory zoning in CL images but also Eu anomalies and low U contents, indicating their growth from anatectic melts under HP to UHP conditions. The granitic veins show different Sr–Nd–O isotope compositions from the host UHP eclogites, indicating that the former did not originate from partial melting of the latter. This is also supported by the distinct δ18O and ε Hf (t) values for the Triassic zircon from the granitic veins and eclogites. Instead, there are comparable isotopic compositions between the granitic veins and regional UHP granitic gneisses, indicating that the granitic veins would be derived from partial melting of the underlying UHP granitic gneisses. Group II granitic veins have higher ε Nd (t) values than Group I ones and the granitic gneisses by 3–5 ε Nd unit, indicating that the anatectic melts forming Group II granitic veins are in Nd isotope disequilibrium with their source rocks. This can be caused by the behavior of accessory minerals like apatite and epidote/allanite during crustal anataxis at different pressures. The contributions of apatite together with garnet can also account for the increased Hf isotopes in the anatectic zircon. Therefore, the accessory minerals play a key role in constraining the geochemical features of incompatible-element enriched granitic melts during the crustal anatexis under HP to UHP conditions. [ABSTRACT FROM AUTHOR]

• SIMS U-Pb zircon analyses display the Fanjingshan leucogranite formed at ca. 812 Ma. • W-Sn dominant mineralization is temporally and genetically linked with granitic magmatism. • The Fanjingshan leucogranites produced by crustal remelting marked the latest stage of the Jiangnan Orogeny. The Jiangnan Orogen in China host large volumes of Neoproterozoic igneous rocks and is a well-preserved Neoproterozoic orogenic belt in the South China Block. A series of W–Sn mineralization occurrences and ore deposits are spatially related to Neoproterozoic granites in the orogen. However, the geochronology and petrogenesis of the host Neoproterozoic granites and associated W–Sn mineralization in the western Jiangnan Orogen remain poorly understood. In this study, the U–Pb ages of zircon, cassiterite, and apatite, and the geochemistry of minerals and whole rock of the Fanjingshan (FJS) leucogranites, which are located along the western margin of the Jiangnan Orogen, were used to re-evaluate the Neoproterozoic magmatism that occurred in response to the orogeny and the mechanism of W–Sn mineralization. The FJS leucogranites consist mainly of strongly peraluminous tourmaline–muscovite granites. The leucogranites have a characteristic magmatic and hydrothermal mineral assemblage, including cassiterite, tourmaline and fluorite. Zircon U–Pb dating indicates the leucogranites were emplaced at ca. 812 Ma, which is consistent with apatite U–Pb age. Cassiterite U–Pb dating yields an age of ca. 810 Ma, suggesting the mineralization was coeval with the crystallization of the FJS leucogranites. In multi-element variation diagrams, all samples display sea-gull-shaped rare earth element patterns with significant negative Eu anomalies. The whole-rock geochemical data suggest the leucogranites originated by muscovite dehydration melting of a metasedimentary source. Extensive fractional crystallization and magmatic–hydrothermal interactions, as inferred from extremely low rare earth element contents, low Nb/Ta and Zr/Hf ratios, and a large tetrad effect, lead to the W–Sn enrichment and crystallization of ore minerals, such as cassiterite and scheelite. The compositions of muscovite, apatite, cassiterite and tourmaline, along with the occurrence of quartz veins, also provide information on the nature of the magmatic–hydrothermal processes and mineralization. Our data and those for other S-type granites (840–800 Ma) in the western Jiangnan Orogen, suggest that magmatic–hydrothermal processes had a key role in W–Sn mineralization. The Neoproterozoic FJS leucogranites likely formed in an extensional setting during the final stage of orogenesis. [ABSTRACT FROM AUTHOR]

A group of accessory ore minerals is revealed in rocks of the Galmoenan mafic-ultramafic massif (Koryak Upland, Kamchatka, Russia), represented by native metals (iron, copper, zinc, and silver), iron-nickel and cobalt-iron intermetallic compounds, sulfides (pentlandite, cobaltpentlandite, pyrrhotite, sphalerite, heazlewoodite, millerite, shandite, pyrite, chalcopyrite, and Cu3S2 phase), arsenides (maucherite, nicolite, orcelite, and modderite), and some other minerals. Their chemical compositions, crystal forms, and paragenetic associations are described. Formation of these minerals is attributed to serpentinization of rocks. [ABSTRACT FROM AUTHOR]

The explosive atmospheric electrogenic paragenesis we studied was found to contain over 100 mineral species, varieties, and non-crystalline phases (carbonaceous minerals, phases and compounds, native metals and alloys, carbides, silicides, nitrides, halides, chalcogenides, oxides, silicates and alumosilicates, and oxysalts. The paragenesis is characterized by an abnormally low level of mineralogical organization, which indicates a deep origin of the material in the explosive facies of volcanic eruptions, including carbonaceous minerals, phases, and organic compounds. [ABSTRACT FROM AUTHOR]

Abstract The release of arsenic vapors (As3+) during high-arsenic coal combustion not only raises serious environmental concerns, but also causes catalyst deactivation in selective catalytic reduction (SCR) systems. To illuminate the mechanisms involved in the transformation of arsenic vapors towards less troublesome arsenates (As5+) during coal combustion, the accessory minerals in the high-arsenic coal were identified and the association relationship of these compounds with arsenic in fly ash was estimated. The results showed that Si/Al were the main inorganic elements in high-arsenic coal while the content of Ca was quite low. Ca was mostly transformed into sulfates during coal combustion and the effect of Ca on the arsenic transformation was limited. Al/Fe played a more significant role in arsenic speciation transformation and arsenic in the fly ash was predominantly bound with Al/Fe-oxides as arsenates. It was further confirmed that Al in kaolin/metakaolin showed good capacity on arsenic capture. In addition, few arsenic vapors were captured through the physical adsorption mechanism and the large fraction of As3+ in some fine particles was mostly attributed to the chemical reactions between arsenic vapors and Al-compounds. Meanwhile, a certain amount of arsenic vapors were converted into As 2 O 5 (s) under the influence of SCR catalyst and then carried by flue gas to participate in fly ash. Besides, part of arsenic distributed in the fly ash was through the stabilization of ash matrix in high temperature conditions. The transformation of arsenic from vapors towards particulate arsenic favored arsenic emission control by particulate matter control devices. [ABSTRACT FROM AUTHOR]

The paper presents mineralogical analysis data on very-fine- and fine-grained sand in the composition of Quaternary sediments in the southern part of the Chukchi Plateau. The associations and downcore distribution of rock-forming and accessory minerals in relation to other characteristics are considered. The established climatically controlled mineralogical features, i.e., periodicity of warmings and coolings, can be used to solve a number of genetic problems, stratigraphic subdivision of sediments, and paleoreconstructions. [ABSTRACT FROM AUTHOR]

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A research work was embarked in the area in order to understand the sedimentary geology, remote sensing, geomorphology and petrology of the district Sudhunhoti and Poonch, Azad Jammu and Kashmir, Pakistan. For this purpose the Khirik, Muttail Maira, Thandi Kassi, Kothian, Hill, Maidan, Rhera, Dar, Sairhan, Afsar Market, Gorah, Nakkar bazaar, Gui Nala, Bandia, Mang, Jassa Pir and Thorar areas were mapped and interpreted on Digital Elevtion Model (DEM) in the sub-Himalayas of Pakistan. The area has been mutilated by folding and faulting governed by orogenic forces. The clastic rocks exposed in the area are sandstone, siltstone, claystone and conglomerates. The sedimentary structures include planner bedding, ripple marks and pebble imbrications. The rip ups of siltstone and clay occur at the base of sandstone. The sandstone of Nagri Formation is well exposed in the area. The sandstone contains clasts of volcanics, quartzites, schist and chert. The sandstone of Dhok Pathan Formation is medium to coarse grained. It contains clasts of gneiss, schists, quartzites, granite, carbonate and marble. The sandstone is comprised of mineral quartz (23% to 45%), feldspar (3% to 13%) and the rock fragments of igneous, metamorphic and sedimentary rocks. The accessory minerals in the Nagri Formation sandstone are biotite (1% to 3%), muscovite (up to 2%), tourmaline (few traces) and zircon (1%). The cementing material in the rock is calcite (6% to 18%) and silica (2% to 3%). The modal mineralogical data of the sandstone shows that the sandstone is lithic arenite and lithic graywacke. The modal data reveal that the detritus was derived from the rising Himalayas in north of the

Abstract The role of accessory minerals in the incongruent release of Hf and Pb during continental weathering and its implications for the generation of distinct seawater isotope compositions is subject of debate. While it has been suggested that radiogenic Hf and Pb isotope signatures released during the dissolution of rocks are controlled by the relative abundances of minerals with distinct isotope compositions and differences in their resistance to dissolution there has not been a comprehensive experimental investigation of these processes to date. We carried out systematic sequential leaching experiments on fresh and partly weathered granitic rock samples as well as separated zircons from the Central Aar Granite in Switzerland. Combined with major and rare earth element concentrations our new quantitative experimental data reveal systematic preferential release of radiogenic Nd, Hf and Pb isotopes primarily controlled by dissolution characteristics of the host rock's easily dissolvable accessory and major minerals, in particular apatite and sphene, during weak chemical weathering. Moreover, Pb isotope signatures of incipient weathering conditions, contrary to expectations, indicate initial congruent release of Pb from freshly exposed mineral surfaces that becomes subsequently incongruent. During more advanced chemical weathering stages, as well as enhanced physical weathering conditions, the dissolution of major minerals (i.e. feldspars) becomes dominant for Nd and Pb isotope signatures, whereas Hf isotopes are still dominated by contributions from highly radiogenic accessories. Additional leaching experiments of zircon separates were performed to test the specific role of zircons for Hf isotope compositions of riverine runoff. It is demonstrated that zircon is more efficiently dissolved when physical weathering is enhanced. This increased Hf release originating from partial dissolution of zircons, however, is quantitatively not sufficient to explain less radiogenic Hf isotope signatures in seawater during episodes of enhanced mechanical erosion alone. Moreover, the observed addition of Hf from the more congruent dissolution of the zircon-free fractions of the parent rock due to enhanced physical weathering indicates that these minerals also play an important role in controlling Hf isotope signatures released under deglacial conditions. [ABSTRACT FROM AUTHOR]

The Malanjkhand and Dongargarh granitoids are compared to study the role of accessory minerals (apatite, zircon, titanite and titanomagnetite) to understand crystallization evolution of Palaeoproterozoic granitic magmatism in the Bastar Craton, central India. Two varieties of titanite (magmatic and hydrothermal types) are observed in the Palaeoproterozoic granitoids. Occurrence of zircon, apatite, titanite and titanomagnetite as accessory phases in the Palaeoproterozoic granitoids indicates that the early stage of crystallization of granitic magma was saturated with Zr, P and Ti. Petrography and mineral equilibria reaction suggest that magmatic titanite in the Palaeoproterozoic granitoids was formed due to hydration of amphiboles and biotites which favours high f O2 and f H2O conditions. Apatite composition suggests that it was formed in the granitic magma at nearliquidus to near-solidus temperature (900–1000°C) which increased fugacity ratio log(fH2O/fHF) and also controlled the halogen budget during magma crystallization. Relatively high halogen content in the apatites from the Malanjkhand Granitoid (MG) indicates that the parental magma was enriched in F and Cl compared to Dongargarh Granitoids (DG), implying a dominant role of halogens in metal transportation and hydrothermal mineralization. In MG, apatite was the earliest phase to be crystallized in granitic magma followed by zircon and titanite whereas, in DG, crystallization of zircon was followed by apatite and titanite. Two contemporaneous plutons, DG and MG, represent a unique Palaeoproterozoic granitic magmatism wherein early progressive crystallization is dominated by accessory mineral saturation in a relatively static environment with constant magma composition. [ABSTRACT FROM AUTHOR]

The study presents investigations on an interesting co-mineralization phenomenon (placer ilmenite and ion-adsorption REEs) related to weathering of intermediate igneous rocks in South China. In order to delineate the origin of such co-mineralization from source to sink, a genetic model is proposed as shown in below figure. It demonstrated that the occurrence of placer ilmenite and iREEs co-mineralization depends principally on the specific nature of some intermediate igneous rocks that contain both rich Ti-bearing and REEs-bearing accessory minerals. Strong weathering, in one way, gave rise to residual accumulation of ilmenite at upper horizons, and in the other way, generated secondary enrichment of iREEs through eluviation-illuviation at lower horizons. These two enrichment processes happened independently, and generated mineralization effect at different regolith positions. It caused the ore horizons of placer ilmenite and iREEs developed symbiotically but show somewhat dislocation within the regolith. [Display omitted] • Ore-bearing regolith profiles with placer ilmenite and iREEs co-mineralization in South China were investigated. • A genetic model is proposed to understand the co-mineralization of placer ilmenite and iREEs regulated by weathering of various intermediate igneous rocks. • The importance of comprehensive evaluation is emphasized in future exploration and resource utilization of weathering deposits. The placer type ilmenite and ion-adsorption type rare earth elements (iREEs) deposits are two important weathering-related mineral resources in South China, a global supplier of Ti and REEs critical metals. It was believed that these two deposits are not linked to each other because of their different ore-forming conditions and mechanisms. However, many studies have reported that parts of placer ilmenite deposits, especially for those developed by weathering of intermediate igneous rocks, also contain abundant iREEs resources that have not been noticed before. To elucidate the origin of this interesting co-mineralization phenomenon that is of both scientific and economic significance, we conducted a comparative study of three deposits, including Qinghu (QH), Madi (MD), and Tangcun (TC) from Guangxi Province in the western segment of South China. Investigations showed that although the ore-forming parent rocks from the QH, MD, and TC deposits are intermediate igneous rocks, their corresponding regolith profiles are significantly different in their mineralization characteristics. The diorite-derived QH and tonalite-derived MD deposits showed co-mineralization of ilmenite with iREEs, whereas the pyroxene diorite-derived TC deposit only showed independent mineralization of ilmenite. Evidences from systematic mineralogical and geochemical examinations indicated that the occurrence of ilmenite and iREEs co-mineralization, besides the impact of weathering, may principally regulated by the nature of accessory mineral assemblage in the parent rocks. Specifically, both Ti-bearing (ilmenite, anatase) and REEs-bearing (apatite, titanite) accessory minerals were largely identified in the QH diorite and MD tonalite. Analysis of degree of saprolitization (DOS) and weathering index of granite (WIG) revealed that they have experienced strong weathering, which gave rise to residual accumulation of Ti-bearing minerals (mainly ilmenite) at upper horizons of the regolith profiles, and simultaneously, secondary enrichment of iREEs by eluviation-illuviation process at lower horizons. It explained the ore horizons of placer ilmenite and iREEs developed symbiotically but show somewhat dislocation within the regolith. In contrast, the TC pyroxene diorite was found to be rich only in Ti-bearing minerals but poor in REEs-bearing minerals. It is conductive to develop weathering mineralization of ilmenite rather than iREEs in terms of ore source. Also, there is rich iron oxides and hydroxides in the pyroxene diorite-derived regolith, which might has inhibited REEs eluviation-illuviation and act as the other reason for absence of iREEs mineralization in the TC profile. This study not only provides a genetic model to understand the co-mineralization of placer ilmenite and iREEs ores developed by weathering of intermediate igneous rocks, but also highlights the importance of a comprehensive evaluation in future prior to exploration and resource utilization. [ABSTRACT FROM AUTHOR]

[Display omitted] • The mineral chemistry of beryl, tourmaline, and garnet indicates that the Yamrang Pegmatite is an intermediate-fractionated beryl-columbite subtype REL pegmatite. • Octahedral Fe-Al substitution mechanism is dominant in magmatic beryls while channel-tetrahedral substitution is dominant in hydrothermal beryls. • Yamrang aquamarines are enriched in FeO, up to 1.1 wt%, with Fe2+ as the primary chromophore. • Potential pegmatite evolution indicators for IPF include high alkali, Fe, Mn, and Rb contents in beryl, high Xsps in garnet, and enrichment of Li, Fe, Mn, Zn, Ga, and Nb, alongside depletion of Mg, Ca, Ti, and Ta in schorl. The Ikhabu Pegmatite Field (IPF) in the Nepal Himalaya is a newly discovered rare-element (REL) pegmatite field that hosts the Yamrang pegmatite, the primary source of the famous Nepalese aquamarines. In this contribution, we provide a comprehensive description of the geology of both the IPF and the Yamrang pegmatite, offering insights into the evolutionary stages of the Yamrang pegmatite based on its internal texture and the mineral chemistry of beryl, garnet, and tourmaline. The Yamrang pegmatite is classified as a beryl-columbite subtype of REL pegmatite, exhibiting axial symmetric zonation and is differentiated into five mineralogical-textural zones during magmatic and hydrothermal stages. The magmatic stage involves undercooling, disequilibrium crystallization, and fractional crystallization whereas the hydrothermal stage comprises alkali-enriched fluid exsolution, the formation of miarolitic cavities, and the crystallization of aquamarine. Yamrang aquamarines are enriched in FeO, up to 1.1 wt%, with Fe2+ as the primary chromophore, resulting in their blue color. Two types of beryl have been identified: magmatic beryl in zones 3 and 4 and hydrothermal beryl in miarolitic cavities (zone 5). Magmatic beryls are characterized by their alkali-poor to sodic composition, prismatic to columnar habit, homogeneous texture, and the presence of Fe-Al octahedral substitution. In contrast, hydrothermal beryls belong to the sodic to Li-Cs beryl group, with tabular to acicular habit, weak compositional zoning, and channel-tetrahedral substitution. Yamrang garnet belongs to the almandine-spessartine series, while the tourmalines are Mg-Ca rich dravite-schorl to Fe-Mn rich schorl variety. Alkali-poor to Li-Cs beryl with low REE contents, spessartine garnet (spessartine component, Xsps ∼ 52) with high HREE, and schorl with high Ti but low Li, Pb, and REE contents suggests that the Yamrang Pegmatite is an intermediate-fractionated REL pegmatite. Potential pegmatite evolution indicators for IPF include high alkali, Fe, Mn, and Rb contents in beryl, high Xsps in garnet, and an increase in Li, Fe, Mn, Zn, Ga, and Nb, alongside depletion of Mg, Ca, Ti, and Ta in schorl. The identification of a rare metal pegmatite field in the Nepalese Himalaya reinforces the general rare metal mineralization potential of the entire Himalaya region. [ABSTRACT FROM AUTHOR]

The relevance of the issue is caused by the need to study the rounded micro-grains (globules, spherules) of pseudorutile accessories found in Aleysko-Zmeinogorsk granitoid complex (D2-3). The aim of the study is to study in details occurrence and chemical composition of pseudorutile globules in granitoids being subsequent alumnia-silicate melt differentiates, paragenetic associations, pseudorutile globule formations as altered product of primary ore-for-ming elements - titanium and ferrum. The research methods. Mineralogical samples of 5...7 kg were extracted from both granitoid outcroppings and quarries. Analytical analysis was carried out on electron scanning microscope (ESM) JSM-6510LV (Jeol Ltd) and energy-dispersive spectrometer INCA Energy 350+ in the Laboratory of X-ray Spectrum Analysis, Institute of Geology and Mineralogy, Siberian Branch, RAS (Novosibirsk). The results. The paper introduces new data on formation mechanism of pseudorutile globules. The endogenous genesis of mineral as a product of high-temperature oxidation of drop-liquid native intermetallic compound (Ti-Fe) from melt under reducing conditions is proved. Throughout the mantle magmatic chamber evolution involving deep gaseous fluids (H2, CH4) under conditions of oxygen deficiency the reduction regime was formed being favorable for intermetallide ore compound (Ti-Fe) segregation. Reducing conditions appeared within the melt itself and especially, in final phase melts (3-4). Under conditions of increasing facies pressure of oxygen the liquiddrop intermetallides (Ti-Fe) are subjected to high-temperature oxidation within the early magmatic stage of homogeneous pseudorutile phase with Mn, Si, Al, Ca, K impurities.

We present a numerical model of trace-element oscillatory zoning patterns formed when zircon crystallizes from silicate melt, which is also appropriate for other accessory phases with known partition and diffusion coefficients and saturation conditions. The model accounts for diffusion-controlled accessory mineral growth and the equilibrium crystallization of major mineral phases. Consideration of recent, experimentally determined dependencies of partition coefficients on temperature, we find that thermal changes provide the simplest explanations of oscillatory zoning in accessory minerals. Numerical experiments with different cooling rates explore different crystallization scenarios with and without the precipitation of other phases and/or the interface reaction of phosphorus (P) and yttrium (Y) to form xenotime. However, these processes are monotonically related to growth rate and do not cause oscillations. Minor 3–10 °C variations in temperature do not result in zircon dissolution, but strongly influence zircon growth and lead to variations in coeval Y, Hf, and rare earth element (REE) concentrations of up to a factor of two, comparable to those observed in nature. Such temperature variations may be very common in any igneous body in response to external factors such as replenishment by hotter magmas or convection. More significant temperature fluctuations may result in initial minor dissolution at higher temperatures during a mafic recharge event but with continuous growth afterward. At high temperature (>~850 °C) the amplitude of oscillations is relatively small that confirms observations of both less common oscillatory zoning in hot and dry volcanic rhyolites and abundant oscillations in plutonic zircons and in zircons in cold and wet crystal-rich mushes. Additional oscillations in zircon are modeled in response to oscillations of pressure on the order of ±35–50 bars, causing water concentration fluctuations of ±0.1 wt% in water-saturated melt cells with a gas bubble. These variations cause variations of Zr diffusion and zircon growth rates. Such fluctuations could result from pressure oscillations due to recharge and convection in the magma chamber. All simulated runs generate smoothed oscillatory growth zoning; similar patterns found in nature may not necessarily require post-growth intracrystalline diffusion. [ABSTRACT FROM AUTHOR]

The Pampean aquifer, in south east Argentina, is mainly constituted of loess-like sediments. These are clastic sediments mainly composed of quartz and aluminosilicates and calcrete concretions. Its hydrochemistry is generally studied assuming a chemical equilibrium between mineral phases and the aqueous fluids. The phases forming the matrix of this aquifer are considered to be the reactive phases responsible for the chemistry of the groundwater. In the present study, batch dissolution experiments were performed on calcrete and loess to better understand the source of the Pampean aquifer water chemistry and to measure the benefit of applying water-rock interaction models that use kinetic rate laws instead of thermodynamic equilibria. The different minerals composing the loess and calcrete samples were calculated using quantitative Rietveld refinement of X-ray powder diffraction (XRD) patterns. This analysis showed that the major phases of loess are quartz (~ 30 wt%) and feldspars (~ 70 wt%). The main components of calcrete are calcite (~ 95 wt%) and quartz (~ 5 wt%). Scanning electron microscopy with energy dispersive X-ray microanalysis (SEM/EDXS) was used to provide detailed information about the chemical composition of the powder samples, revealing the presence of traces of minerals like halite, barite and fluorapatite, which were not detected by XRD. The kinetic code KINDIS was used to carry out simulations using the minerals identified previously in their relative proportions to identify the signature of those geochemical phases on water chemistry. Experimental data from batch dissolution experiments were compared to simulated data. This investigation showed that water reached pseudo steady state concentrations due to the presence of fast dissolving phases like halite, barite, gypsum, plant phytolith. These phases appeared to be of major importance in controlling the chemical composition of the Pampean groundwater. Furthermore, this work showed that the KINDIS software can be used on all kinds of aquifers as it is very easy to modify the parameters of the simulation to adapt it to numerous situations. The modeling is a very important tool for thermodynamic and kinetic studies of groundwater chemistry; it enables the prediction of water quality and can help to understand the impact of anthropic or natural contamination on the groundwater. [ABSTRACT FROM AUTHOR]

The formation of accessory allanite, monazite and rutile in amphibolite-facies rocks across the Barrovian sequence of the Central Alps (Switzerland) was investigated with a combination of petrography and geochemistry and related to the known structural and metamorphic evolution of the Lepontine dome. For each of these minerals a specific approach was adopted for geochronology, taking into account internal zoning and U–Th–Pb systematics. In-situ U–Th–Pb dating of allanite and monazite by ion microprobe revealed systematic trends for the ages of main deformation and temperature in the Lepontine dome. Isotope dilution TIMS dating of rutile returns dates in line with this picture, but is complicated by inheritance of pre-Alpine rutile and possible Pb loss during Alpine metamorphism. Allanite is generally a prograde mineral that is aligned along the main foliation of the samples and found also as inclusions in garnet. Prograde allanite formation is further documented by rutile inclusions with formation temperatures significantly lower than the maximum T recorded by the rock mineral assemblage. Allanite ages vary from 31.3 ± 1.1 Ma in orthogneisses in the East to 31.7 ± 1.1 Ma for a Bündnerschiefer and 28.5 ± 1.3 Ma for a metaquartzite in the central area, to 26.8 ± 1.1 Ma in the western part of the Lepontine dome. These ages are interpreted to date the main deformation events (nappe stacking and isoclinal deformation of the nappe stack), close to peak pressure conditions. The timing of the thermal peak in the Lepontine dome is recorded in monazite that grew at the expense of allanite and after a main episode of garnet growth at temperatures of ~ 620 °C. Monazite in the central area yields an age of 22.0 ± 0.3 Ma, which is indistinguishable from the age of 21.7 ± 0.4 Ma from a metapelite in the western part of the Lepontine dome. In the central area some of the classical kyanite‐staurolite-garnet schists directly underlying the metamorphosed Mesozoic sediments contain monazite that records only a pre-Alpine, Variscan metamorphic event of upper greenschist to lower amphibolite-facies conditions dated at ~ 330 Ma. The new age data provide evidence that nappe stacking at prograde amphibolite-facies conditions and refolding of the nappe stack occurred between 32 and 27 Ma, only a few million years after eclogite-facies metamorphism in the Adula-Cima Lunga unit. Amphibolite-facies metamorphism lasted for about 10 My to ~ 22 Ma, allowing for multiple ductile deformation and recrystallization events. The long lasting amphibolite-facies metamorphism requires fast cooling between 20 and 15 Ma in the Central Alps. This fast cooling was not related to an increase in sedimentation rates in the foreland basins, suggesting that tectonic exhumation was responsible for termination of amphibolite-facies metamorphism in the Lepontine dome. [ABSTRACT FROM AUTHOR]

In the Pohorje Mts, mostly outcrops of calcite marble can be found, which in places turn into dolomite marbles.The protolith carbonate rocks contained also detritical minerals, which remained unchanged or formed new mineralsduring metamorphosis. Minerals in the Pohorje marbles that can be seen as crystals with the naked eye or 10x magnifyingloupe and with binocular microscope were investigated. With the aid of Raman microspectroscopy, SEM-EDSanalysis and on the basis of morphological characteristics, the presence of 17 different minerals or group of mineralswas confirmed. The most numerous and also the most significant were, apart from calcite, tremolite, diopside, grossularand epidote. For the first time, vesuvianite and scapolite were described in the Pohorje Mts. Particularly rich, as faras crystal faces are concerned, were the crystals of quartz that contained needle-like amphiboles. Other minerals thatwell supplemented the mineral paragenesis were different minerals of mica and chlorite group, feldspars, magnetite,titanite, pyrite and graphite. The determined mineral association revealed the mineral diversity of Pohorje marbles,offering us a new challenge for the investigation of the characteristics and conditions during the origin of this noblerock, which was highly esteemed already by the Romans, while today it is regaining its value and recognisability.