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Mineralogical and geochemical characteristics of stream sediments collected from 30 stations in the Dahab-Wadi Kid area (southeastern Sinai, Egypt) are presented. The studied sediments contain considerable amounts of heavy minerals, including abundant Fe–Ti oxides, with up to 25.94% index figure that measures the relative abundance of heavy minerals to light minerals. Immaturity of the sediments and nature of Fe–Ti oxide intergrowths, in addition to some non-opaque heavy minerals, indicate multiple provenances with contributions from a variety of Neoproterozoic mafic to felsic intrusions. Appreciable amounts of heavy minerals are derived from schists that belong to the so-called Wadi Kid volcano-sedimentary group. Owing to the considerable contribution of the felsic intrusions represented by within-plate granites, the sediments are enriched in REE-bearing minerals (e.g., monazite, cerianite, La-cerianite and allanite), V-bearing thorite, zircon, and a ZrO2 phase. The majority of Fe–Ti oxides are derived from the mafic intrusions, and they show evidence of pre-, syn- and post-depositional phases of alteration and formation of intergrowths. As to the geochemical signature of the bulk silt fraction, there is remarkable enrichment of LREEs with distinct negative Eu anomaly, and this supports dominance of a provenance dominated by felsic intrusions (i.e., the A-type within-plate granite and associated pegmatites). Also, the felsic provenance is responsible for slight abnormality of ∑U + Th content (up to ~ 37 ppm) and few anomalous samples bear uraniferous zircon and Ce-type monazite. The present paper sheds light on the fertility of the Dahab stream sediments in some economic minerals for possible future exploitation, not for gold only, but for potential REE-bearing minerals that are needed for a wide spectrum of modern technological industries.

The present study deals with the detailed field geology, mineralogy, geochemistry, and spectrometric prospection of rare metals and radioactive minerals associated with granitic pegmatites in the Gabal Um Lassaf- Abu Dob- Um Atelia- Kadabora- Kab El Rakeb area (LDAKK), which are situated in the central Eastern Desert of Egypt. The study area is composed of granodiorites and monzogranites. The latter is dissected by granitic pegmatites with a discriminatory distribution of economically important mineralization (rare-metals and U–Th minerals). The granitic pegmatites display a zoning structure composed of feldspar-rich zones enveloping pockets of mica (mostly muscovite) and all zoning internal quartz core. Microscopically, the monzogranite and granitic pegmatites are composed of potash-feldspar, albite, and quartz with a small amount of biotite and muscovite. The mineralogical investigation of the highly radioactive zones in the granitic pegmatite shows enrichment in kasolite, uranothorite, thorite, xenotime, columbite, zircon, bismuth, and galena. Geochemically, the granitic pegmatites are enriched with high field strength elements (HFSE; Zr, Nb, Th, and U) and ion lithophilic elements (LILE; Rb, and Pb) and depleted in Ba, Sr, and Eu. They are strongly peralkaline to metalumainous except for two samples, which are peraluminous. They are formed by partial melting of metagreywackes at depth. The studied granitic pegmatites could belong to the NYF family (Niobium–Yttrium–Fluorine family) according to the geochemistry of the trace elements. The studied granitic pegmatites show deep negative Eu anomaly and display a strong M-type tetrad effect of rare earth elements. The field spectroscopy measurements showed the localization of the radiometric anomalous associated with the granitic pegmatites, which are intruded in the granitic host rocks. Their eU and eTh contents reached up to 316 and 1367 ppm, respectively. Uranium and thorium occurrences in the investigated granitic pegmatites are related to magmatic (syngenetic) origin with hydrothermal (epigenetic) input. The magmatic mineralization is evidenced by the occurrence of thorite and zircon, whilst the hydrothermal activity is represented by alteration of feldspars and formation of pyrite and iron oxides associated with the radioactive minerals. The high concentrations of uranium and rare metals mineralization in the investigated granitic pegmatites make them a target to exploration and to enlarge the potentiality of the highly mineralized zones.

—Metasomatic alterations in cataclased granites of the Primorsky Complex PR1 in the Southern Siberian Craton are represented by albitization and riebeckitization, accompanied by microclinization, dolomitization and completed by the formation of hydrothermal quartz–carbonate veins. Albitization, epidotization, and carbonatization are occurred in the host metavolcanics. Mineral parageneses and mineral thermometry data indicate the occurrence of hydrothermal–metasomatic processes in the temperature range from 400–500 to 200‒250°С. Calcite deposited at an early stage has values of δ13С –(3.2–3.3)‰ and δ18O +(8.3–9.4)‰, ferruginous dolomite δ13С –(1.6–1.9)‰ and δ18O +(10.6–11.1)‰. The calculated values of δ13C in CO2 contained in the fluid from which calcite was deposited at 450°C (about –0.7 to 0.8‰) indicate marine carbonates as the source of CO2; the calculated values of δ18O in a fluid in equilibrium with calcite (from +5.4 to +6.5‰) show that the fluid underwent isotopic exchange with magmatic silicate rocks at elevated temperatures and a low fluid-rock ratio. The initial (87Sr/86Sr)t ratio in newly formed calcite (0.718087) and dolomite (0.712033) and eNdT = –(7.3–8.2) indicate the leading role of an upper crustal source of material. The maximum U concentration (52 ppm on average) contains albite–biotite–magnetite schists at the contact with altered granites. The U concentrators in metasomatically altered rocks are the crichtonite group minerals, zircon, and thorite.

A new mineral species of the pyrochlore supergroup, hydroxyplumbopyrochlore (IMA2018-145), (Pb1.5,□0.5)Nb2O6(OH), has been discovered in the Jabal Sayid peralkaline granitic complex of the Arabian Shield, Saudi Arabia. It is associated with quartz, microcline, ‘biotite’, rutile, zircon, calcite, rhodochrosite, columbite-(Fe), goethite, thorite, bastnäsite-(Ce), xenotime-(Y), samarskite-(Y), euxenite-(Y), hydropyrochlore and fluornatropyrochlore. Hydroxyplumbopyrochlore usually shows euhedral octahedra, slightly rhombic dodecahedra and cubes or their combination (0.01–0.06 mm). The mineral is pale yellow to pale brown, transparent with white streak, and has adamantine to transparent lustre. It is brittle with conchoidal fracture. No cleavage or parting are observed. It is isotropic and non-fluorescent. The average microhardness is 463.4 kg mm–2. The calculated density is 6.474 g cm–3.Hydroxyplumbopyrochlore belongs to the cubic crystal system and exhibits the space group Fd$\bar{3}$m with unit-cell parameters a = 10.5456(6) Å, V = 1172.8(2) Å3 and Z = 8. Electron microprobe analysis gave (6-point average composition, wt.%): CaO 0.32, SrO 0.16, FeO 0.17, Ce2O3 0.07, Pr2O3 0.02, PbO 51.69, Nb2O5 40.06, SiO2 0.05, TiO2 1.68, Ta2O5 4.74, H2Ocalc 0.95, total 99.90, yielding the empirical formula (Pb1.34Ca0.03Fe0.01Sr0.01□0.61)Σ2(Nb1.75Ti0.12Ta0.12Si0.01)Σ2O6(OH0.53O0.08□0.39)Σ1, where □ = vacancy. The Raman spectrum of hydroxyplumbopyrochlore contains the characteristic bands of O–H vibrations and no bands for H2O vibrations.

Gabal El Fereyid area, represents a promising area for monzogranite and pegmatites hosted rare-metal mineralization. Microscopically, monzogranite and pegmatites consist of K-feldspar, albite, and quartz with few biotite +/– hornblende. The radiometric studies of anomalous pegmatite samples show that their eU-contents reached up to 149 ppm while their eTh-contents reached up to 375 ppm, in contrast the eU and eTh contents of monzogranite range from 1 to 5.7 ppm and from 4.2 to 29.1 ppm, respectively. This indicates strong post-magmatic U-enrichment in the pegmatitic melt, due to the presence of radioactive minerals as thorite, uranothorite, fergusonite, samarskite and ishikawit. U and Th mineralization in pegmatites are discriminated as hydrothermal and magmatic types. Pegmatites show enrichment of large ion lithophile elements (LILE; Pb and Rb,), high field strength elements (HFSE; Y, Zr, Th, U, Nb and Ta) and rare earth elements but depleted in K, P, Sr, Cs, Ba and Ti. Pegmatites indicate moderate to large negative Eu anomaly and show clear W-type tetrad effect of the REE.

The chemical weathering of rocks and minerals on the Earth’s surface leads to the mobilization and redistribution of elements and has (a) significant control on the chemistry of the soil-hydrosphere-atmosphere system, (b) a profound effect on the bioavailability and toxic effects of elements, and (c) applications in mineral exploration among others. In this study, we describe the sequential weathering of spessartine- and pyrope-bearing almandine garnet in metamorphosed banded magnetite quartzite from the Khetri Copper Belt, western India. Based on detailed microtextural relations the following sequence of garnet weathering is proposed: garnet → alumo-goethite1 → alumo-goethite2 → kaolinite ± (monazite + xenotime ± thorite) → haematite. Our study thus reports for the first time the presence of alumo-goethite, kaolinite, monazite, xenotime, and thorite in weathering assemblage of garnet. The sequential chemical weathering of garnet was both grain boundary-controlled and fracture-controlled. Tectonic fractures (developed during exhumation), reaction-induced fractures (developed due to volume expansion), and secondary porosity (developed due to volume reduction) collectively controlled the propagation of weathering. Integrating multiple lines of evidence, e.g., corrugated contact between the weathering phases, presence of pores, relative molar volume changes, and high mobility of most elements it is argued that the weathering progressed through an interface-coupled dissolution-precipitation process. In situ major and trace element measurements and mass balance calculations show that several major (Fe, Na, K, P) and trace elements (Cl, F, alkalis, alkaline earth elements, and first series transition and base metals) were added while Si, Al, Ca, Mg and Mn were lost during the garnet to alumo-goethite transformation. During kaolinitization, all the major elements except Si and Al were lost to the weathering fluid. The alkali and alkaline earth, first series transition elements, base metals excepting Cr were lost during this weathering stage. Phosphorous, REEs, and Th were locally immobilized as monazite, xenotime, and thorite. In the more advanced stages of weathering, kaolinite was replaced by haematite. This stage involved re-addition of several major (except Al and Si) and trace elements. It is seen that although alumo-goethite, kaolinite, and haematite can host significant quantities of several trace elements, alumo-goethite and haematite have a much better potential of immobilizing most trace elements including toxic ones compared to kaolinite in the weathering profile.

Research subject. The article presents results of mineralogical and geochemical investigation of albite-bearing granites with high concentrations of trace elements located in the Western Trans-Baikal region. Methods. The composition of rocks was determined by the methods of classical silicate analysis, X-ray fluorescence and ICP-MS analysis. Microstructural features, relationships and homogeneity of minerals were studied using an electron microscope LEO-1430 equipped with an energy dispersive spectrometer Inca Energy-300. Isotopic compositions of oxygen were carried out using a mass spectrometer Finigan MAT 253 in the mode of a constant helium flow. Results. Ore mineralization is specified by the presence of Nb-bearing and less REE-bearing minerals. The studied rocks were divided into two groups: albitized granites, and deep albitized granites and albitites. These groups differ in terms of the presence of accessory minerals. The deep albitized granites and albitites belong to alkaline riebeckite-albite granites containing Nb-, Zr-, Y- and REE-bearing minerals. These rocks contain Y-bearing minerals - thalenite and yttrialite, with an up to 4 wt % inclusion of Y 2 O 3 in titanite, chevkinite, thorite and monazite. In contrast, the albitized granites contain fewer amounts of Y and HREE along with LREE-bearing minerals (monazite, allanite, fluocerite, samarskit). Conclusion. The selected groups of rocks have been analyzed in terms of their mineral and geochemical characteristics. The main Nb-bearing mineral in albitized granites is columbite. Minerals from albitites are rich in Y and HREE. The isotopic investigation has shown involvement of a magmatic-derived fluid in the rock formation process.

Nowadays zircon is the most common mineral of the geological U-Pb dating method. One of the main barriers of getting properly time-resolved and reliable zircon age data is just the internal heterogeneity of the zircon crystals themselves. For overcoming that limitation we defined a four-step pre-examination protocol to be followed before LA-ICP-MS based local geochronology aimed data collection on zircon. Our studied zircon crystals (Table 1) came from Variscan K-Mg-rich granitoids in southern Hungary (Moragy) and northern Austria (Rastenberg). In previous geochronology-aimed publications (KLOTZLI & PARRISH 1996; KLOTZLI et al. 2004; GERDES 2006; KOROKNAI et al. 2010) the Variscan age of the two magmatic complexes is already determined. Nevertheless, these investigations left open basic questions with respect to the whole history of the intrusions (origin of the different rock types and age of the secondary overprinting effect), mainly because of the ambiguity caused by the overlooked textural heterogeneity of the studied zircon crystals. In order to answer the open questions, we clarified and identified the different geological processes on the basis of their preserved traces in zircon textures from two intrusions using a four-step pre-examination process:1. Zircon crystals of different morphology were hosted by different rock-forming minerals at both localities based on light microscopy: “normal” (S24, S25), “flat” (re-defined from S4 to AB5) and “long” (P5) prismatic zircon crystals. The basis of separation is the position of the c-axis in the crystals (Figure 2). Zircon grains occur with the same frequency in all the rock types of both locations (Moragy, Rastenberg). By morphology, “normal” prismatic zircon crystals are dominant in different granitoid rocks, “flat” prismatic zircon crystals are less frequent, while “long” prismatic zircon crystals occur rarely (Figure 3). Analysis of a limited number of zircon crystals in their undisturbed petrographic position in thin sections showed that the “normal” and “flat” prismatic zircon crystals were present in all rock-forming minerals of granitoid rocks, while the few, “long” prismatic zircon crystals occurred only in quartz and feldspar (Figure 4). 2. Determination of mineral inclusions in zircon based on electron probe microanalyses (EPMA). Multiphase (K-feldspar, albite, quartz) and single-phase inclusions (apatite, feldspar, biotite, quartz, thorite/uranothorite) were found in zircon crystals at both localities (Table 2). From a genetic viewpoint, multiphase inclusions are the most relevant. This inclusion type, consisting of Na-free K-feldspar, albite and quartz and occurring most commonly in “long” prismatic zircon crystals, indicates lower temperature crystallization from Si-rich granite melt, confirming that zircon was crystallizing continuously during the solidification of the rest granitoid magma (Figure 5). 3. Primary and secondary textural patterns of zircon crystals were identified in details on by comparison of the cathodoluminescence (CL) and back-scattered electron (BSE) contrasts using scanning electron microscope (SEM). Four internal texture types of zircon could be distinguished (Figure 6a, b). Primary internal textures are growth zoning ± xenocrystic core and sector zoning. The observed secondary textural feature is convolute zoning. Primary texture types occur in all rock types at both localities, but secondary texture is observable only in zircon crystals from Moragy Complex. 4. Structural state of zircon zones was determined by Raman spectroscopy. We classified three groups of structural state of the individual zircon zones based on the full width at half maximum (FWHM) of the ν3(SiO4) Raman band: I. well crystallized ( 15 cm-1 FWHM). Accordingly, the strongly radiation-damaged zones could be excluded from the LA-dating, because these zircon zones are not too resistant toward to the fluid-driven replacement processes (PUTNIS 2009). In the case of the alteration of previously radiation-damaged zircon zones we have to take into account the possibility of Pb loss during the replacement reaction, which can modify and disturb the precise U-Pb age determination (NASDALA et al. 1998). Our samples are generally characterized by moderate radiation damage, FWHM values were mainly between 5 cm-1 and 15 cm-1 (Figure 7). Having regard to four-step pre-examination of zircon crystals from all rock types (Figure 1) we can conclude, that the areas of the primary textures (growth zoning ± xenocrystic core and sector zoning) represent the effect of the main magmatic event. The age difference between the core and rim of zircon gives the time interval of the main magmatic crystallization. The xenocrystic core can inform us about the crustal origin. The secondary texture (convolute zoning, fluid-mediated reactions) reflects the imprint of any post-magmatic event in zircon crystals (Figure 8).Having collected these pieces of information one can mark the promising spots (areas of some ten micrometer in diameter) in zircon crystals from both localities for reliable and geologically well interpretable age data determination (Table 3). With the help of the four-step pre-examination of zircon crystals the yield of the age data was: zircon core 80%, growth and sector zoning 94%-os, convolute zoning 100%.

The N-S trending Central-Aldan magnesiocarbonatite province is located in the Aldan-Stanovoy shield (South Yakutia, Russia). Several apatite-dolomitic carbonatite occurrences were studied: Seligdar, Muostalaah, Ust-Chulman and Birikeen. Mineralogical and petrographic investigations indicate intense hydrothermal-metasomatic alteration and metamorphism, which are reflected in the evolution of the mineral parageneses. The primary minerals are fluorapatite, magnetite, ilmenite, dolomite, K-feldspar, phlogopite and accessory zircon, titanite, baddeleyite and thorite. The hydrothermal-metasomatic minerals are quartz, calcite and siderite aggregates with haematite, monazite-(Ce), xenotime-(Y), rutile-(Nb), barite-(Sr), anhydrite, ancylite-(Ce) and rare sulphide mineral phases. Alkaline rocks associated with the Muostalaah complex, were also studied. The following U-Pb ages have been obtained (Ma): 1930 ± 7 for Muostalaah alkaline basic rocks, 1906 ± 6 for Muostalaah carbonatites, and 1880 ± 13 and 1878 ± 17 for Seligdar and Ust-Chulman carbonatites, respectively.

The stream sediments of Wadi El Reddah (North Eastern Desert, Egypt) are geochemically and mineralogically investigated. Their content of radioactive and other heavy minerals is mainly represented by thorite, uranothorite, zircon, monazite, xenotime, columbite, fergusonite, and unknown rare earth elements (REEs) bearing minerals as well as cassiterite. Special emphasis on REE content of thorite, uranothorite, zircon and xenotime has been done to correlate them with the increase of uranium contents in these sediments. The key evidence for the presence low-temperature alteration processes includes the presence of some zircon crystals as remnants after complete dissolution of the overgrowth zircon in severe acidic environment, the sulphur content, biogenic minerals, occurrence of unusual minerals as cassiterite pore filling in zircon, variation in the REEs content from the surrounding granites to the stream sediments and the abundance of monazite in the surrounding granites. Most minerals are partially and/or completely altered, which indicated by the pseudomorphism of zircon by xenotime, thorite, and uranothorite.

The main deposits of the Bafq district (Choghart, Se Chahun and Chadormalou deposits) are magnetite-apatite ore bodies with Early Cambrian age, hosted by Early Cambrian volcano-sedimentary rocks, showing lava flow structure with miarolitic cavities and occasional brecciation. The texture and geochemistry (trace elements and O-isotope) of the studied magnetite crystals show three types of magnetite with different proportions in different parts of the district and the deposits. These are primary ignious magnetite and high-temperature hydrothermal magnetite in the massive parts of the deposits and foam-like magnetite in the veins or in the fractures of the massive part. The lack of zonation, high Ti/Fe ratios and δ18O values (2‰ ) than the massive magnetites. The magmatic origin for the main part of the ores in the Bafq is more plausible. Contamination of the primary magmas of the Bafq magmatic rocks with crustal phosphorus and evaporate units was the major agent for triggering iron-rich melt immiscibility from the original magma. Concentration of volatiles in the iron-rich melt involving in crystallization of the primary magnetite and nucleation of the aqueous fluid bubbles on magnetite surfaces led to ascending the buoyant fluid bubble-magnetite aggregates. This caused continuation of the magmatic magnetite microlites growth from the iron-rich magmatic-hydrothermal fluid and formed high-temperature hydrothermal magnetite. Formation of hypersaline fluid due to crystallization of iron-rich melt at shallow depth led to crystallization of titanite (and Th-U-REE-bearing minerals) and sodic-calcic alteration related to magnetite mineralization. Microscopic evidence (replacement of magnetite by hematite and filling of fractures of thorite by magnetite) show that degassing continued at shallow depth, which led to re-crystallization of the primary magnetites and formation of the foam-like magnetites.

The Mocambo Granitic Massif is an A-type granite located in the northeastern part of Goias State, near the city of Monte Alegre de Goias. It belongs to the Pedra Branca Suite, which is itself part of the Goias Tin Province, a group of stanniferous granites that exhibit similar geochemical features, including to a greater or lesser degree of rare earth elements enrichment. The parent rock in the Mocambo Granitic Massif is a coarse porphyritic pink biotite granite. Thin section observations coupled with electron microprobe analyses reveal the presence of several REE-bearing minerals: allanite, fergusonite (Ce), fergusonite-(Y), zircon and apatite as accessory minerals, and xenotime-(Y), bastnasite-(Ce), thorite, monazite-(Ce) and hingganite-(Y) as secondary (hydrothermal) minerals. Fergusonite and hingganite are identified in this massif for the first time. This work investigates the forms of occurrence and enrichment of rare earth elements in the Mocambo Granitic Massif, in the parent rock, as well as in greisen, saprolite and soil, with emphasis placed on the rare earth elements adsorbed on clay minerals, and the entire process of transport and fractionation of these elements from the fresh rock until adsorption. The results show enrichment of rare earth elements (with the exception of Ce) in soils in comparison to rock, especially in the clay fraction. Moreover they suggest that these elements are mostly adsorbed on clay minerals, mostly kaolinite and illite, which are identified in the X-ray patterns. The surface oxidation of Ce3+ to Ce4+ on surfaces and the probable formation of Ce oxides cause this element to present a smaller quantity of exchangeable ions. The presence of cerianite grains in one superficial soil sample shows that Ce is mostly found in the Ce4+ state in the soil profile. The Mocambo Granitic Massif displays substantial enrichment in REEY, 555–1229 ppm for the parental granite and 569 ppm for the greisen, and the exchangeable REEY concentrations in the soils horizons, more than 600 ppm, in particular, representing a potential target for an ion-adsorption-type rare earth elements deposit.

The world-class Sn-Nb-Ta Madeira deposit is located in the Pitinga mine (northern Brazil). The deposit is associated with the albite-enriched granite facies of the A-type Madeira Granite (∼1820 Ma). The mine commercially extracts tin (cassiterite), Nb and Ta (U-Pb-pyrochlore and columbite). Fluorine (cryolite), Y, REE (xenotime), Zr (zircon), U (U-Pb-pyrochlore and zircon) and Th (thorite) are potential byproducts. This work presents a detailed study of thorite mineralization in the albite-enriched granite subfacies: the albite-enriched granite core, the albite-enriched granite border and associated pegmatites. The Madeira deposit is revealed in this work to be among the largest Th deposits in the world, with 164 Mt of homogeneously dispersed ore, average grade of 759 ppm ThO2 in the rock, and higher concentrations (up to 1.8 wt% ThO2) in small pegmatites (average of ∼0.51 wt% ThO2). Thorite compositions are either close to the thorite pole or correspond to relatively limited substitutions in the thorite-zircon-xenotime-coffinite solid solution system. The concentration of Fe in thorite ranges from 0.11 wt% to 29.56 wt% Fe2O3, and in many cases is considered to be of structural nature, as well as part of the content of F (up to 6.02 wt% F). Thorites of all subfacies were strongly affected by hydrothermal alteration related to F-rich, low-temperature aqueous fluids. The hydration of thorite allowed the introduction of M3+ cations (Y, REE, Fe, and Al) and F, and caused losses in Si and Th contents (average of ∼48 wt% ThO2). The alteration also created a Fe-rich halo in thorite, with associated secondary minerals, likely Th-Fe-hydroxyfluorides and Y-Th-Fe-fluorcarbonates. The Th/U average ratios in bulk-rock are 1.85 in the albite-enriched granite border, 3.82 in the albite-enriched granite core, and 19.85 in the associated pegmatites. This variation reflects a pattern of magmatic evolution, with higher availability of U in earlier stages and U depletion in later stages. In Pitinga, the Th and U mineralization are divided into different minerals formed at distinct stages of magma evolution. This feature is related to fluorine enrichment and high alkalinity of the magma that strongly inhibited the early crystallization of zircon, as well as columbite, and favored the early appearance of U-Pb-pyrochlore. When crystallization of hydrous silicates reduced alkalinity, crystallization of zircon (from a magma depleted in U, Nb, Ta and LREE) became intense, accompanied by thorite and xenotime.

The role of magmatic differentiation is considered for the formation of the Ulan-Tologoi Ta–Nb–Zr deposit (northwestern Mongolia) related to the eponymous alkali granite pluton. Data are presented on the structure of the pluton, the composition of its rocks, and distribution of rare metal mineralization. The ores of the pluton include alkali granites with contents of ore elements exceeding the normative threshold for Ta (>100 ppm). The rare metal mineralization includes pyrochlore, columbite, zircon, bastnaesite, monazite, and thorite, which are typical of all alkali–salic rocks; however, their amount varies depending on the REE content of the rocks. The pluton was formed ~298 Ma ago under the influence of a mantle-crustal melt source.

Abu Furad is in the Central Eastern Desert, Egypt. It comprises metasediments, metavolcanics, metagabbros, syn- to late-orogenic granites, and post-orogenic granites, in addition to numerous dykes and veins of different shapes and composition invading all the older rocks cropping out in the study area. Field, petrographic, mineralogical, and chemical investigations led to the classification of Abu Furad granites as quartz diorite, tonalite, granodiorite, and syenogranites.Major oxide and trace element data revealed that the syn- to late-orogenic granites and post-orogenic granites are peraluminous. Syn- to late-orogenic granites originated from calc-alkaline volcanic arc–related magma; while the post-orogenic granites (syenogranite) are highly fractionated, calc-alkaline granite from a within plate regime. Radiometrically, the studied quartz diorite, tonalite, and granodiorite had lower uranium and thorium contents and higher eU/eTh ratios than the syenogranites. This may indicate that the syn- to late-orogenic rocks originated from sources depleted in these elements. The average eTh/eU ratio of syenogranites was higher than that of average continental crust, suggesting that the syenogranites are relatively depleted in U. The studied altered syenogranites were strongly enriched in U and Th compared to the Earth’s crust. On the other hand, the average of eU in pegmatites is lower than the global average for uraniferous pegmatites. The most recorded accessory minerals in the altered syenogranites were thorite, fergusonite, samarskite, columbite, zircon, monazite, xenotime, apatite, fluorite, sphene, atacamite, and malachite, in addition to chromium and nickel inclusions.

The El Garra El Hamra complex is a small high-level plug (with associated volcanics) that was emplaced along an ENE-WSW trending dextral strike-slip fault corresponding to the Guinean-Nubian lineament. Owing to continued movement along this fault, the intrusion split into two parts that were displaced horizontally by approximately 580 m. The intrusion consists mainly of syenites (fresh and altered) and granites (altered) that are locally overlain by alkaline trachyte and rhyolite and are hosted by Nubian sandstones. The fresh syenites are composed of perthitic K-feldspars, albite, alkali pyroxenes (aegirine-augite and aegirine) and secondary alkali amphiboles (arfvedsonite and riebeckite). Accessory minerals include opaques, apatite, zircon, xenotime-(Y) and bastnasite-(Ce). Calcite and hematite are alteration products. Geochemically, the syenites are peralkaline; their CIPW norms classify them as ranging between syenite and quartz syenite in compositions. They were emplaced in a within-plate tectonic setting along the Guinean-Nubian lineament (Kalabsha), close to the extension of the Chephren-Kom Ombo trend (a branch of the Trans-African Shear Zone). They were evolved from a magma compositionally similar to Ocean island basalt (OIB). Numerous dextral and sinistral strike-slip faults cut the intrusion and may have facilitated the circulation of fluids that altered them hydrothermally. These faults developed during or shortly after emplacement of the intrusion or perhaps during subsequent reactivation of the Guinean-Nubian and Trans-African shear zones and were accompanied by dykes that range in compositions from intermediate to acidic composition; most of which strike ENE-WSW. Hydrothermal alteration of the syenites locally led to extreme enrichment in rare metals (e.g. LREE, HREE, Zr, Hf, Th, U, Nb and Be) as the minerals zircon, gittinsite, bastnasite-(Ce), parisite-(Ce), monazite–(Ce), REE-rich fluorapatite, chevkinite-(Ce), xenotime-(Y), pyrochlore, columbite-(Fe), Nb-rutile and thorite. Fluorite and barite are important gangue minerals.

Thorium deposit related to alkaline / peralkaline magmatism is the dominant thorium source. The ore-forming thorium mechanism related to the alkaline / peralkaline magmatism, however, has been long fascinated. The Younusisayi Th deposit, hosted in Early Paleozoic alkali-feldspar granite in the South Altyn complex, is an example to explore the Th mineralization processes in magmatic-hydrothermal systems. Zircon U-Pb dating shows that the weakly and strongly mineralized alkali-feldspar granites are emplaced at 445.7±1.8 Ma and 439.0±1.3 Ma, respectively. The U-Pb ages of apatite that occurs concomitantly with thorite in the weakly and strongly mineralized alkali-feldspar granites are 442±11 Ma and 438±14 Ma, respectively, indicating Th mineralization temporally related to the magmatism. Four population of fluorite exhibit distinct occurrences, the fluorite Ia and Ib are in intergrowth with thorite, but the fluorite IIa and IIb are not. Notably, four population of fluorite are differentiated by their Th+U and HREE concentrations, fluorite Ia and Ib show higher Th+U contents and lower HREE contents than fluorite IIa and IIb. Th was extracted by magma during emplacement. As a strong incompatible element, thorium will not be enriched in rock forming minerals. In the process of magmatic evolution, Thorium is gradually enriched in the post-magmatic fluid which contains abundant volatile component. Thorium can be transported as F-Th complexes in F-rich fluids. As temperature decreased, thorium precipitated in the form of thorite, and fluorite Ia and Ib crystallized with a low HREE content. F from decomposition of F-Th complex, reacts with HREE in the fluid to form F-HREE complex, which increases the HREE content in the fluid. Therefore, the fluorite IIa and IIb which formed in the late stage of mineralization have obviously higher contents of HREE. We proposed that the Younusisayi deposit, with an average grade of 0.4 wt% ThO2, formed in a post collisional extensional environment during the early Paleozoic. The Younusisayi deposit is best classified as a magmatic-hydrothermal deposit. Our results demonstrate the usefulness of geochemistry of fluorite for trace the ore-forming process, thus Establishing ore formation models.

The Zhaibei Granite in Jiangxi Province, southern China, hosts an ion-adsorption light rare earth element (LREE) deposit. Recently, heavy REE (HREE) ores have also been reported from weathered crusts of the granitic rocks. In this study, petrological, geochemical, and mineralogical characteristics of the Zhaibei pluton were analysed to establish the genesis of this REE deposit. The pluton contains coarse-grained biotite syenogranite and minor hornblende–biotite–quartz monzonite in its central zone, medium-grained biotite syenogranite in its transitional zone, and fine-grained muscovitic alkali-feldspar granite and porphyritic muscovitic biotite–alkali-feldspar granite together with monzogranite porphyry intrusions in its marginal zone. The REE minerals include titanite, allanite, monazite, bastnasite, and thorite-(Y) in the central zone, allanite, monazite, xenotime, bastnasite, and thorite-(Y) in the transitional zone, and synchysite-(Y), thorite-(Y), and xenotime in the marginal zone. The SiO2 content increases from 62 to 77 wt% from the centre to the margin, whereas the Al2O3, TiO2, MgO, FeO, and CaO contents decrease. In addition, the size of the negative Eu anomaly and HREE content increase, accompanied by decreases in Co, Zr, Hf, Sr, and Ba and increases in Rb, Cs, Nb, and Sn. These observations indicate that the Zhaibei Granite might have been formed by crystallisation differentiation of magma. The granitic pluton was also influenced by reactions with late-magmatic F-, CO2–, and REE-rich fluids that altered magmatic minerals and crystallised as REE-fluorocarbonates and thorite. The hydrothermal REE minerals constitute ∼ 40% of the total REEs in the bedrock and are the major supplier of ion-exchangeable REEs in the ores of the Zhaibei deposit. LREE-rich ores may have been derived from the LREE-rich granitic rocks, which contain bastnasite, titanite, and allanite, whereas HREE-rich ores were sourced mainly from the HREE-rich granites, which contain synchysite-(Y) and thorite-(Y). Furthermore, REE ores with enrichment in both HREEs and LREEs were probably sourced from the monzogranite porphyry bedrock, which contains bastnasite-(Y), bastnasite, allanite, and thorite-(Y).

The Serra do Mendes granitic massif (SMGM) is located in the Goias Tin Province (GTP), which is characterized by Sn, REE-bearing A-type granites. The Serra do Mendes granite is the largest massif of the Parana Subprovince, with three main facies related to the Pedra Branca Granite Suite (PB). Previous studies on this suite have indicated ages of 1.77 to 1.74 Ga, in addition to subalkaline to alkaline signatures and high Zr, Y and REE contents. Samples of fresh rock, saprolite and alluvial sediments were collected from the most common facies, biotite monzogranite (PB1a) and leucomonzogranite (PB1c), in order to characterize the REE-bearing minerals and their abundance. The analytical techniques included petrography, scanning electron microscopy (SEM), electron probe micro analyzer (EPMA) and total rock geochemistry. The most evolved facies, PB1c contains the highest quantities of REE-bearing minerals, where fluocerite-(Ce), REE oxyfluorides, bastnaesite, monazite, allanite, thorite-zircon solid solution, fluorite and apatite are the most important constituents. REE contents in facies PB1a range from 363.8–985.9 ppm, and in its respective saprolite from 60 to 1283.9 ppm with LaN/YbN ratios between 4 and 17.7%. Facies PB1c contains REEs in concentrations between 460.9 and 958.6 ppm, and its saprolite exhibits concentrations between 495.7 and 902.1 ppm. The LaN/YbN ratio in fresh rocks and saprolite is between 2 and 12.3, respectively. Along with the REE minerals, it is noteworthy the occurrence of zircon and thorite with up to 20% REE2O3 + Y2O3. These results, in addition to other factors such as the local climate and geomorphology, make the Serra do Mendes granite massif an interesting target for prospecting and exploration of REE.

The Younger Granites of Yahmid-Um Adawi area, located in the southeastern part of Sinai Peninsula, comprise two coeval Late Neoproterozoic post-collisional alkaline (hypersolvous alkali-feldspar granites; 608–580 Ma) and calc-alkaline (transsolvous monzo- and syenogranites; 635–590 Ma) suites. The calc-alkaline suite granitoids are magnesian and peraluminous to metaluminous, whereas the alkaline ones are magnesian to ferroan alkaline to slightly metaluminous. Both granitoid suites exhibit many of the typical geochemical features of A-type granites such as enrichment in Nb (>20 ppm), Zr (>250 ppm), Zn (>100 ppm) and Ce (>100 ppm) and high 10000*Ga/Al2O3 ratios (>2.6) and Zr + Nb + Y + Ce (>350 ppm). Accessory mineral saturation thermometers demonstrated former crystallization of apatite at high temperatures prior to zircon and monazite separation from the magma for both granitoid suites. The mild zircon saturation temperatures of the studied Younger Granites (around 800 °C) imply low-temperature crustal fusion and incomplete melting of the largely refractory zircon. The two Younger Granite suites were semi-synchronously evolved during the post-collisional stage of the Arabian-Nubian Shield subsequent to the collision between the juvenile shield crust and the older pre-Neoproterozoic continental blocks of west Gondwana. Their parental magmas has been generated by melting of crustal source rocks with minor involvement from mantle, which might participated chiefly as a source of heat necessary for fusion of the crustal precursor. Extensive in-situ gamma-ray spectrometry revealed anomalously high radioactivity of some Younger Granite exposures along Wadi Um Adawi (eU; 388–746 ppm and eTh; 1857–2527 ppm) and pegmatitic pockets pertaining to the calc-alkaline suite (equivalent U and Th; 212–252 ppm and 750–1757 ppm, respectively). The radioactivity of the syngenetic pegmatites arises from the primary radioactive minerals uranothorite and thorite together with the U- and/or Th-bearing minerals zircon, columbite, samarskite and monazite. The anomalously high radioactivity of some Younger Granite exposures in Wadi Um Adawi stem from their appreciable enclosure of the epigenetic uranium minerals metatorbenite and uranophane.

The paper deals on the laterization of the Madeira deposit associated with the albite-enriched granite facies of the A-type Madeira granite (~ 1.82 Ga). The Madeira deposit is located in the Amazon rain forest, where chemical weathering is intensive and lateritization is a major process of ore deposit formation. This deposit represents a particular case, where the parent rock is an ore deposit; thus primary mineralization and lateritic mineralization occur in the same profile. The parent rock has an unusual mineral association, which includes quartz, albite, k-feldspar, zircon, cryolite (Na3AlF6), fluorite, polylithionite, Zn-rich riebeckite, Zn-F-rich annite, thorite, cassiterite, pyrochlore, columbite, xenotime, gagarinite-(Y), fluocerite-(Ce), and genthelvite. An important feature of the rock is the F richness (2 to 6 wt%) mainly in the form of cryolite or fluorspar in the matrix. We first investigated the micromorphological changes of these minerals throughout the soil profile and then focused the geochemical studies in selected profiles. The chemical data were converted into volumetric proportions to quantify the variations in element contents in samples with different degrees of lateritization, and we performed mass balance calculations with Al as the reference element. In this way, we obtain many new constraints on the processes that formed the weathering profile from the Madeira deposit. The parental rock was a clearly aluminous system with lower amounts of Fe. The total loss of alkalis and partial loss of SiO2 created kaolinitic clay minerals. The SiO2/Al2O3 molar ratio ≈ 2 was suitable for generating aluminous clay minerals with 1:1 structures, such as kaolinite. Greater losses of SiO2 occurred and gibbsite formed at the top of the weathering profiles. The leaching of alkaline elements led to relative enrichment in some economically important elements, such as Sn, Nb, and REEs, in the lateritic profiles. However, the distribution of some of the metals, such as Pb, Zn, and REEs, in the weathering profile is very unusual and may be explained by some special characteristics of the paragenesis and the richness of F in the solutions, which greatly influenced the weathering processes in two different ways. The intense corrosion of even very resistant minerals due to the presence of HF in the system and relative enrichment of HREE in the profile due to the formation of complexes with F− and the downward movement of these elements.

South China is famous for its large-scale mineralization genetically related to widespread Mesozoic granites. The Jiulongnao complex is one of the largest intrusions in southern Jiangxi Province, and is closely associated with W-dominated polymetallic mineralization. The complex comprises four intrusive phases (I-IV). Phase I consists of medium- to coarse-grained, biotite granite, whereas medium- to coarse-grained, porphyritic, biotite granite and muscovite-bearing granite comprise Phase II. Phase III is composed of medium- to fine-grained, porphyritic, biotite granite and Phase IV consists of medium- to fine-grained, garnet- and biotite-bearing granite. These intrusive phases have LA-ICP-MS zircon U-Pb ages of 160.9 ± 0.6 Ma, 158.6 ± 0.7 Ma, 157.0 ± 1.5 Ma and 154.1 ± 1.2 Ma, respectively. All of the granites are enriched in Rb, Th, U, Ta and Pb, and significantly depleted in Eu, Ba, Nb, Sr, P and Ti. They have eHf(t) and eNd(t) values ranging from −17.9 to −8.2, and −10.7 to −9.8, respectively, with two-stage Hf model ages of 1.7–2.3 Ga. They are S-type granites derived by partial melting of Paleo-Proterozoic metasedimentary rocks. The four phases have TZr of 746–760 °C, 712–802 °C, 798–810 °C, and 648–731 °C, respectively. Oxygen fugacities of Phases I to III display a decreasing trend but Phase IV has much higher oxygen fugacity in its early stage, which decreased in the late stage. The four phases have different accessory mineral assemblages: Phase I is characterized by an assemblage of zircon, apatite, fergusonite, thorite and uraninite, whereas Phase II is rich in thorite, uraninite, REE-bearing minerals (e.g., monazite, fergusonite and xenotime) and fluorite. Monazite is the main accessory mineral in Phase III, whereas Phase IV contains a wide range of minerals, including thorite, uraninite, Nb-Ta-bearing minerals (e.g., fergusonite and pyrochlore), cassiterite and rutile. These mineral assemblages, together with other geological and geochemical features, suggest that W mineralization was genetically related to Phases I, II and IV, whereas U mineralization was most extensive in Phase II. Sn, Nb and Ta mineralization was associated with the highly fractionated of magmas of Phase IV.

Field relationships, textures, compositions and U-(Th)-Pb dates for minerals from the niobium‑yttrium‑fluorine (NYF-) Stetind pegmatite in the 1.798 Ga Tysfjord granitic gneiss in Norway are described. The pegmatite has a sub-horizontal orientation and anisotropic mineral layering oriented sub-parallel to contacts with the host-rock and oblique to its foliation. Epidote-group minerals have allanite cores and interstitial REE-rich epidote. Zircon, thorite, uraninite, fergusonite and xenotime, as well as apatite, fluorite, plagioclase and orthoclase are compositionally homogenous and display relict albite twinning and ternary junctions. Feldspars lack grain boundary recrystallisation textures, and no undulatory extinction is observed in quartz. Isotope U Pb TIMS analysis of zircon, allanite, fergusonite and uraninite give dates between 400 and 410 Ma that have a high degree of concordance and no evidence of inheritance. A F-rich fluid dissolved fergusonite (YNbO4) and reacted with apatite to produce xenotime (YPO4) mantles around apatite. The reaction was dated by electron-probe micro-analysis total U-Th-Pb methods to 393 ± 12 Ma. The field and petrographic observations, coupled with mineral dates are interpreted to reflect primary emplacement and crystallisation of the Stetind NYF pegmatite after the peak of Scandian orogenesis and metamorphism during exhumation of the Tysfjord granitic gneiss. The xenotime forming event reflects a late magmato-hydrothermal reaction during the final stages of crystallisation. The compositional affinity of the Stetind pegmatite to its host rock suggests that the pegmatite-magma was produced by partial melting of the Tysfjord granitic gneiss or a rock with similar characteristics. The pegmatite is one of many rare-element pegmatites in the Tysfjord-Hamaroy pegmatite field, which may indicate a Scandian phase of pegmatite emplacement into the uppermost allochthon of the Norwegian Caledonides. The results validate models that propose the production of NYF-type pegmatites by anatexis during orogenic collapse.

The Wadi Al-Baroud area is located close to the tectonic boundary between the Northern and Central Eastern Desert of Egypt. The exposed rocks include younger (post-tectonic) and older (syn-tectonic) granitoids and rare metal pegmatites (plugs and dikes). The rare metal pegmatites are comprised of feldspars, quartz, and mica, and occur chiefly within the barren younger granites and at their contact with the older granitoids. Strategic rare metal mineralization related to pegmatites includes mangano- to ferro-columbite, zircon, monazite-(Ce), yttrocolumbite, thorite, U-thorite, xenotime, euxenite-(Y), samarskite-(Y), and fergusonite-(Y) minerals that are frequently associated with mica and iron oxides. In this study, zircon, monazite, and thorite are used as potential monitors of the internal evolution of pegmatite and evolution of the granite-pegmatite system. In the younger A-type granite, zircon and thorite are common and form a solid solution with xenotime. In the pegmatite body, thorite forms a solid solution with coffinite, while zircon is Hf-rich pegmatitic type and forms two phases in the same grain - one is highly enriched in non-formula (Ca, Fe, Al, and Mn) and incompatible (Th, U, and Y) elements and the other is a chemically near-end member. In the pegmatite dike , zircon has the highest Hf and near-end-member stoichiometric compositions, while thorite is Y-rich uranothorite. Furthermore, monazite is a primary magmatic phase in the younger granites, but in pegmatite is sulfur-rich REE altered phase. Textural and chemical results show that these phases formed sequentially and intermittently through multi-genetic processes during the evolution from the granite to rare metal pegmatite and define two main chemical trends: 1) a continuous fractionation from the melt to pure exsolving hydrothermal fluid , and 2) a dissolution–recrystallization during fluid-saturated late-magmatic stages. Zircon displays a continuous Zr/Hf fractionation trend, indicating evolution from a silicate melt to an aqueous fluid. Besides, all pegmatite zircons form a solid solution with xenotime and this is a chemical fingerprint inherited from the granite zircon. Together, these suggest that the pegmatite was formed from a hydrous aluminosilicate melt and that high field strength elements (such as Nb, Ta, Y, Zr, U, and Th) can be mobilized during the magmatic to hydrothermal evolution of the alkaline granite-pegmatite system. Even in ore-barren granitic rocks, the high charge-to-ionic-radius ratios of these elements and generally incompatible nature during magmatic fractionation facilitate their extreme enrichment, even to ore-forming levels. Zircon, monazite, and thorite can provide effective exploration tools for identifying and characterizing rare metal-bearing pegmatites and insights into the mineralizing processes.

The Olympic Dam iron oxide copper-gold (IOCG)-uranium-silver deposit (South Australia) is hosted in the large Olympic Dam breccia complex within the ~1.59 Ga Roxby Downs Granite. This breccia complex formed through multiple stages of hydrothermal activity and texturally destructive brecciation that affected the granite. The deepest diamond drill hole to date (RD2773, end at ~2,329 m) intersected weakly altered, in situbrecciated granite (~370–2,329 m) and a quartz-phyric felsic unit (~2,010–2,265 m). These two rock units host coarse-grained hydrothermal minerals, from ~2,150 m to the end of the drill hole. The main minerals in this assemblage are magnetite (± hematite), pyrite, fluorapatite, and quartz, with minor disseminated chalcopyrite, sericite, chlorite, rare earth element (REE)-fluorcarbonates, monazite, uraninite, thorite, galena, sphalerite, anhydrite, schorl, rutile, and pyrrhotite. The assemblage is cut by abundant multiphase veinlets and calcite (± fluorite ± barite) veins. A zircon U-Pb age for the felsic unit (1591 ± 11 Ma) implies that this unit is broadly coeval with the granite, whereas U-Pb ages for hydrothermal uraninite (1593.5 ± 5.1 Ma), fluorapatite (1583.3 ± 6.5 Ma), and hematite (1592 ± 15 Ma) indicate that deposition of the U-REE–rich hydrothermal magnetite-fluorapatite-pyrite-quartz assemblage and replacement of magnetite by hematite occurred soon after emplacement of the granitic host rocks. Sm-Nd dating of ubiquitous calcite veins suggests formation at ~1.54 Ga. The deep ~1.59 Ga magnetite-fluorapatite-pyrite-quartz assemblage at Olympic Dam resembles those characteristic of iron oxide-apatite deposits and many other sensu stricto IOCG deposits. This study confirms that the ~1.59 Ga event involved significant and widespread IOCG mineralization in the Olympic Cu-Au province.

The paper discusses the mineralogy and geochemistry of altered rocks associated with calcite and dolomite–ankerite carbonatites of the Onguren dyke–vein complex in the Western Transbaikal Region. The alteration processes in the Early Proterozoic metamorphic complex and synmetamorphic granite hosting carbonatite are areal microclinization and riebeckitization; carbonates, phlogopite, apatite, and aegirine occur in the near-contact zones of the dolomite–ankerite carbonatite veins; and silicification is displayed within separated zones adjacent to the veins. In aluminosilicate rocks, microclinization was accompanied by an increasing content of K, Fe3+, Ti, Nb (up to 460 ppm), Th, Cu, and REE; Na, Ti, Fe3+, Mg, Nb (up to 1500 ppm), Zr (up to 2800 ppm), Ta, Th, Hf, and REE accumulated in the inner zone of the riebeckitization column. High contents of Ln Ce (up to 11200 ppm), U (23 ppm), Sr (up to 7000 ppm), Li (up to 400 ppm), Zn (up to 600 ppm), and Th (up to 700 ppm) are typical of apatite–phlogopite–riebeckite altered rock; silicified rock contains up to (ppm): 2000 Th, 20 U, 13000 Ln Ce, and 5000 Ва. Ilmenite and later rutile are the major Nb carriers in alkali altered rocks. These minerals contain up to 2 and 7 wt % Nb2O5, respectively. In addition, ferrocolumbite and aeschynite-(Ce) occur in microcline and riebeckite altered rocks. Fluorapatite containing up to 2.7 wt % (Ln Ce)2O3, monazite-(Ce), cerite-(Ce), ferriallanite-(Ce), and aeschynite-(Ce) are the REE carriers in riebeckite altered rock. Bastnasite-(Ce), rhabdophane-group minerals, and xenotime-(Y) are typical of silicified rock. Thorite, monazite-(Ce), and rhabdophane-group minerals are the Th carriers.

Mianningite (IMA 2014-072), ideally (□,Pb,Ce,Na)(U4+,Mn,U6+)Fe3+2(Ti,Fe3+)18O38, is a new member of the crichtonite group from the Maoniuping REE deposit, Mianning county, Sichuan province, China. It was found in fractures of lamprophyre veins and in the contact between lamprophyre and a later quartz–alkali feldspar syenite dyke with REE mineralization, and is named after its type locality. Associated minerals are microcline, albite, quartz, iron-rich phlogopite, augite, muscovite, calcite, baryte, fluorite, epidote, pyrite, magnetite, hematite, galena, hydroxylapatite, titanite, ilmenite, rutile, garnet-group minerals, zircon, allanite-(Ce), monazite-(Ce), bastnasite-(Ce), parisite-(Ce), maoniupingite-(Ce), thorite, pyrochlore-group minerals and chlorite. Mianningite occurs as opaque subhedral to euhedral tabular crystals, up to 1–2 mm in size, black in color and streak, and with a submetallic luster. Mianningite is brittle, with a conchoidal fracture. Its average micro-indentation hardness is 83.8 kg/mm2 (load 0.2 kg), which is equivalent to ~6 on the Mohs hardness scale. Its measured and calculated densities are 4.62 (8) g/cm3 and 4.77 g/cm3, respectively. Under reflected light, mianningite is grayish white, with no internal reflections. It appears isotropic and exhibits neither bireflectance nor pleochroism. The empirical formula, calculated on the basis of 38 O atoms per formula unit ( apfu ), is [□0.322(Pb0.215Ba0.037Sr0.036Ca0.010)Σ0.298(Ce0.128La0.077Nd0.012)Σ0.217 (Na0.127K0.036)Σ0.163]Σ1.000(U4+0.447Mn0.293U6+0.112Y0.091Zr0.023Th0.011)Σ0.977(Fe3+1.224Fe2+0.243Mg0.023P0.008Si0.006 □0.496)Σ2.000(Ti12.464Fe3+5.292V5+0.118Nb0.083Al0.026Cr3+0.017)Σ18.000O38. Mianningite is trigonal, belongs to the space group ![Formula][1] , and has unit-cell parameters a = 10.3462(5) A, c = 20.837(2) A, V = 1931.65 (20) A3, and Z = 3. The structure was solved ( R 1 = 0.070) using reflections with I > 2σ( I ) on a heated crystal; it is isostructural with the other members of the crichtonite group. Mianningite can be considered as the analogue of mapiquiroite with the M0 site preferentially vacant. Its eight strongest X-ray powder-diffraction lines [ d in A( I / I )( hkl )] are 2.627(100) (125), 2.144 (100) (135), 3.065(75) (025), 2.254 (70) (028), 1.545(60) (336), 2.883(55) (116), 2.476 (55) (027), and 1.705 (55) (146). [1]: /embed/mml-math-1.gif

The iron oxide-apatite (IOA) deposits of the eastern Adirondack Mountains consist of intrusive sheets or dikes of magnetite, fluorapatite, augitic pyroxene, quartz, and microcline. Other trace mineral phases include ilmenite with hematite exsolution, V-rich titanite rimming magnetite, zircon, monazite-(Ce), stillwellite-(Ce), lanthanite-(Ce), allanite-(Ce), and thorite. Observations under transmitted light show polygonal and cumulate textures. The ore bodies, each with knife-edge contacts with the host gneisses, are closely associated in time with A-type leucogranites and granitic gneisses ( ca . 1070–1050 Ma). Backscattered electron (BSE) images highlight the following types of fluorapatite-monazite-(Ce) relations that formed as a result of metamorphism and fluid-rock interaction: (1) areas of relatively low BSE intensities containing tiny secondary monazite-(Ce) and thorite crystals developed within brighter apatite grains and along crystal margins and fractures; (2) areas of low BSE intensity within larger fluorapatite grains; (3) oriented rods of quartz in fluorapatite; (4) monazite-(Ce) rimming fluorapatite; and (5) multi-domain clusters of fluorapatite in unzoned fluorapatite. Fluorapatite samples from these IOA deposits were analyzed by electron microprobe and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) for major and trace elements. All grains contain high concentrations of light and heavy rare earth elements and yttrium, and samples from some deposits are exceptionally enriched in heavy rare earth elements and yttrium. The crystal structures of the fluorapatites from Cheever, Mineville, Palmer Hill, Arnold Hill, and Rutgers mine were analyzed. Rare earth elements (REE) are dominant at the Ca2 site, and in the most REE-rich sample, from Cheever, 5.7% of the Ca2 sites and 3.5% of the Ca1 sites are occupied by REEs. We consider that the most likely geological scenario for the incorporation of the REEs in fluorapatite includes high concentrations of incompatible elements in a dense iron- and phosphorus-rich melt that formed by immiscibility with the silicate melt of the Lyon Mountain granite. The high REE concentration appears to have been accommodated in the fluorapatite structure through a coupled substitution with Si 4+ . A later, low-temperature stage of fluid infiltration, probably at greenschist facies conditions, re-mobilized the REE and produced secondary minerals within the ore, including low-actinide bearing monazite-(Ce), tremolite, ferro-actinolite, chlorite, rutile, and hematite.

The Seligdar apatite deposit is located in the Aldan-Stanovoy shield of the Siberian platform in Russia. This deposit is a typical ore deposit of the Nimnyrskaya approximately N-S apatite zone, which is about 400 km long. The genesis of the apatite-dolomite ores at the Seligdar deposit is a matter of debate. This article presents new evidence of the carbonatitic genesis of the apatite-dolomite rocks at the Seligdar deposit based on modern methods of mineralogical, geochronological, melt and fluid inclusion investigations. According to our data, the age of the apatite-dolomite ores is 1880 ± 13 Ma (U-Pb SHRIMP, zircon). Study of melt inclusions indicates that the ores were formed from a carbonate melt of dolomitic composition with alkali (sulphates, chlorides and fluorides of Na and K) and silica components (1–10 wt.%) at a temperature of > 1100 °C. The dolomite carbonatites have been subsequently exposed to the intense processes of hydrothermal-metasomatic alteration and metamorphism. The evolution of mineral parageneses from the magmatic apatite-magnetite-dolomite carbonatite stage to the hydrothermal stages with quartz, calcite, monazite-Ce, xenotime-Y, haematite, thorite, thorianite, sulphates and sulphides mineralization agrees with the fluid inclusion regime evolution from the carbonate melt to the chloride brines, and the varying concentrations of the chloride solutions are also described in this article. The investigation of the apatite deposits within the Aldan shield not only allows us to take a new look at the question of their origin but also helps us to study the composition of the ancient mantle, as well as the specifics of apatite-dolomite carbonatite and related hydrothermal Fe and Th-REE mineralization in this region.

Although thermal lattice expansion is a well-documented nature of crystals, including zircon and zircon-type minerals, chemical lattice expansion of natural mineral is rarely reported. Here we present a comprehensive investigation on three types of natural zircon that records the evolution of the granitic system in Xiangshan, North China, and shows expanding crystallographic parameters induced by chemical incorporation instead of thermal expansion. Prismatic and oscillatory-zoned zircon grains (Type-1A), crystallized early in the granitic magma at high temperatures in a volatile-undersaturated environment, have the smallest lattice parameters ( a = 6.603 A, c = 5.971 A). Prismatic and altered zircon grains (Type-1B), formed under volatile-saturated conditions and in the presence of F-rich fluid with numerous thorite and xenotime inclusions, have intermediate lattice parameters ( a = 6.649 A, c = 6.020 A). Pyramidal zircon grains (Type-2), formed in a subsolvus granitic system at relatively low temperatures and coexisted with fluid inclusions, have the biggest lattice parameters ( a = 6.677 A, c = 6.010 A). Trace elements, including Hf, Th, Ti, Y, and REE, and volatiles content, increase in the structure of zircon from the early to late magmatic origin, which is consistent with the expansion of the lattice parameters. The occurrence of the three zircon types in the Xiangshan arfvedsonite granites is interpreted to reflect the progressive fractionation of granitic melt from hypersolvus to subsolvus conditions. Therefore, we conclude that the lattice expansion of zircon in this study results from chemical incorporation of trace element and volatile components during the magmatic to hydrothermal evolution of granitic magma. Besides, the textural and compositional evolution of zircon can be used as efficient indices for the fractionation and evolution of A-type granitic system.

The first data on the composition and inner structure of zircon, one of the main ore minerals of the rare-metal metasomatites of the Gremyakha–Vyrmes alkaline-ultramafic massif, are reported. Early zircon generations are enriched in Y and REE and contain numerous inclusions of rock-forming and accessory minerals of metasomatites, as well as syngenetic fluid inclusions of calcite, thorite and thorianite. Late generations differ in the elevated Hf content and contain no inclusions. The elevated concentrations of Ca and Th in the central zones of crystals are related to the presence of numerous micron-sized inclusions of calcite and thorium phases. All zircon varieties have extremely low U and Pb contents. Concentrations and distribution patterns of incompatible and rare-earth elements in zircon from the metasomatites of the Gremyakha–Vyrmes Massif are similar to those of syenite pegmatites and magmatic carbonatites around the world. Mineral from these associations shows a positive Ce anomaly and elevated HREE contents. According to the compositions of zircon and thorite inclusion in it and experimental data on the simultaneous synthesis of these minerals, the crystallization temperature of zircon was 700–750°С. Using Ti-in-zircon temperature dependence, late zurcon was formed at temperature of 700–750°С. The rare-metal metasomatites are formed at the final stages of the massif formation, presumably after foidolites. Carbonatites could initiate metasomatic reworking of foidolites and accumulation of trace metals in them. The evolution of the primary alkaline–ultramafic melt toward the enrichment in trace elements was mainly controlled by crystallization differentiation.

The Keivy peralkaline granite complex, Kola Peninsula, Russia, is the only Archaean A-type granite known in the world. It contains numerous rare-metal occurrences, formed by a complex sequence of magmatic, late magmatic and hydrothermal processes acting on several different host lithologies. During fluid-induced interaction of a peralkaline granite with basic host rocks in the El’ozero occurrence, chevkinite-(Ce), thorite, fergusonite-(Y) and zircon were formed in a rare-metal rich zone within a quartz–epidote metasomatite. These minerals were then altered by lower-temperature fluids to complex assemblages containing ferriallanite–allanite-(Ce), gadolinite-group minerals, titanite, ilmenite, thorite and Nb,Y-oxides. The sequence of alteration events is used to comment on the nature and composition of the fluids involved in the low-temperature alteration of the host metasomatite. It is inferred that the hydrothermal fluids were alkaline, with significant, but varying, amounts of F, CO2 and S.

We present the first chemical age determination of monazite from a geochemically-specialized rare metal granite of the Central Eastern Desert (CED), Egypt. The Abu Diab composite A-type granite of the CED divides into three co-magmatic phases: two mica granite (TG), garnet-bearing muscovite granite (GMG), and muscovite granite (MG). The GMG granitic phase is a typical example of a rare metal, volatile-rich aqueous silicate magma. Its zircon has extremely high U-concentration (up to 45,000 ppm) and intense metamictization, resulting in significant radiogenic Pb-loss, as well as common Pb contamination, along fractures and other imperfections. Laser ablation (LA-ICP-MS) zircon U-Pb results yield imprecise to meaningless dates. On the other hand, the GMG exhibits two texturally and chemically distinct varieties of monazite, pristine (Mnz1) and altered (Mnz2), that yield similar electron microprobe (EMP) chemical ages of 587 ± 8 Ma (2σ) for Mnz1 and 587 ± 9 Ma (2σ) for Mnz2. These ages, combined with the inferred alteration temperature (T > 400 °C), indicate monazite alteration/replacement occurred during or soon after crystallization of the pluton, in response to expelled magmatic-hydrothermal fluids inferred to be F-rich, late-staged deuteric fluids. The alteration and elemental substitution of zircon and monazite reflect coupled dissolution-recrystallization processes during late-staged deuteric alteration when zircon and thorite were relatively vulnerable to post-magmatic hydrothermal effects because of their extremely metamict state. The ca. 587 Ma age is typical of A-type granite intrusion across the CED and the post-collisional stage of the Arabian Nubian Shield (ANS; 610 – 560 Ma), and is within analytical error of associated magmatic thorite (592 ± 8 Ma). These two ages agree with the timing of rare metal-rich intrusions (0.6−0.4 Ga) related to the Pan-African orogeny. Future research using the monazite chronometer may better constrain the timing of rare metal granitic magmatism of the ANS.

In this study, we investigate zircons with high U and Th contents of 12,000–24,000 and 11,000–40,000 ppm, respectively, from leucocratic granite in the Weondong region of South Korea. Hydrothermally epitaxial growth textures are observed in addition to four distinct textures with different backscattered electron (BSE) intensities within single zircon crystals . We describe the internal textures of the zircon crystals and define the chemical characteristics of each textural domain. The zircon crystals show internally recrystallized and externally crystallized textures, supporting the concept of post-magmatic fluid control. After crystallization of the primary zircon by late magmatism, four types of secondary textures were developed. The type-I domain shows patchy forms within the primary domain due to the structural and chemical recrystallization of self-irradiated zircon by a fluid-dominated diffusion reaction process. The type-II domain is characterized by a pure zircon composition, mineral inclusions (mainly thorite), and micropores due to chemical recrystallization by a coupled dissolution–reprecipitation process during interaction with aqueous fluids. The type-III domain is the purest zircon, is interconnected with type-II, and formed by a second coupled dissolution–reprecipitation process. The type-IV domain is the hydrothermal recrystallization/overgrowth texture formed by the direct crystallization process from fluorine-enriched, zircon-saturated aqueous fluid. These results indicate that the zircon crystals were formed sequentially or intermittently through multi-genetic processes by post-magmatic fluids. Furthermore, we conclude that F-enriched post-magmatic fluid migrated large amounts of zirconium, resulting in the typical overgrowth texture of zircon.

The relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios in A-type felsic rocks from the Ediacaran Katerina Ring Complex, northernmost Arabian-Nubian Shield (ANS; S. Sinai, Egypt), are investigated in this work to understand their behavior during generation of highly evolved granitic magmas and to explore the nature of magma sources. Textural and compositional relationships of cognate Th-REE- and Nb-Ta-accessory minerals in Katerina felsic rocks show that chevkinite-group minerals (CGM), monazite, thorite, allanite and xenotime formed from residual liquids in quartz syenite porphyries, quartz monzonites and peralkaline granites, whereas in aluminous granites, allanite and monazite crystallized early, and thorite and columbite formed from residual liquids. Relationships of Y/Nb, Th/Nb, La/Nb and Ce/Pb ratios with Zr/Hf ratios in the aluminous granites and with Be abundances in the peralkaline granites suggest a decrease in La/Nb and Ce/Pb ratios in the former, and in Y/Nb and La/Nb ratios in the latter with crystallization progress. This contrasts with absence of systematic variations of Th/Nb and Ce/Pb ratios in the peralkaline compositions and of Y/Nb ratio in the aluminous ones. In this latter, Th/Nb ratio can present a significant decrease only in highly evolved compositions. An analysis of Y/Nb, Th/Nb, La/Nb and Ce/Pb relationships in worldwide OIB and subduction-related magmatic suites reveals that A-type felsic rocks with (Th/Nb)N 1 may have A1-type affinity, and those with (Th/Nb)N > 2, (La/Nb)N > 2, and (Ce/Pb)N < 1 tend to present A2-type affinity. The crystal fractionation of Th-LREE- and Nb-Ta-accessory minerals and mixing of components derived from the two granite groups may cause deviations from these compositional limits that can be evaluated using constraints imposed by Th/Nb-La/Nb, Ce/Pb-Th/Nb and Ce/Pb-La/Nb relationships in OIB and subduction-related magmatic suites. Three mantle sources might have been involved in the Ediacaran alkaline magmatism from northernmost ANS that are chemically similar to those of (1) OIB suites, (2) subduction-related magmatic suites, and (3) carbonatite-metasomatized peridotites. In addition, compositions characterized by (Y/Nb)N > 0.18, (Th/Nb)N > 2, (La/Nb)N > 2, (Ce/Pb)N < 1, and crustal-like Nb/Ta ratios may point to a significant contribution of crustal sources.

Monazite-(Ce) and xenotime-(Y) from tertiary pegmatites of the central Alps (Italy and Switzerland) were studied by EMPA and SCXRD analytical methods. The REE-phosphate minerals analyzed are from LCT and NYF pegmatite dikes of the Central Alps, which includes three main areas: Vigezzo (LCT and NYF from the Vigezzo valley), Bodengo (NYF from the Leggia valley and LCT from the Cama valley), and Codera (LCT from Codera and Chiavenna valleys and Alpe Rossaccio). SEM-BSE images of monazite-(Ce) show primary growth zoning, sector zoning, and patchy zoning. SEM-BSE images of xenotime-(Y) show faint patchy-type zoning and spongiform texture. Both REE-phosphates evidence secondary mineral replacements that include thorianite, thorite, and uraninite. EMPA compositions show that the monazite-(Ce) is characterized by variable amounts of huttonite (ThSiO 4 ) and cheralite [Ca(Th,U)(PO 4 )] molecules. SCXRD analyses shows that the unit-cell volume of monazite-(Ce) correlates with its chemical composition; the b cell parameter shows an evident relationship with the huttonite molecule. The unit-cell volume of xenotime-(Y) is well correlated to its chemical composition. Xenotime-(Y) related to the NYF family shows a significant increase in yttrium and a lower U + HREE content. The Tertiary pegmatite field of the central Alps is related to the Masino-Bregaglia intrusion, the San Fedelino granite, and younger magmatic pulses generated by the migration of the metamorphic thermal Lepontine Dome towards the west. The presence of poikiloblastic thorite, thorianite, and uraninite in monazite and xenotime can be induced to form from alkali-bearing fluids via coupled dissolution–reprecipitation, under moderate to high-grade and post-peak Alpine metamorphic conditions.

The highly evolved Kuradawe granitic pegmatite dike is hosted in a harzburgite-dunite succession of the Mawat ophiolite in northeastern Iraq. It consists mainly of quartz, orthoclase, albite, tourmaline, and muscovite. Accessory minerals include cordierite, andalusite, monazite-(Ce), biotite, zircon, Nb-rich rutile, chlorapatite, chlorite, Sc-bearing columbite-(Fe), uraninite, U-rich thorite, and xenotime-(Y). The internal structure of the pegmatite consists of border, wall, intermediate, and core zones. Plagioclase composition increases from Ab 92 to Ab 97 towards the core. Whole rock major oxides such as MgO, Al 2 O 3 , and CaO decrease and SiO 2 increases toward the core. Na 2 O, K 2 O, and total FeO are enriched in specific zones. Among the trace elements, incompatible elements such as Sr, Ba, and Zr decrease and the compatible elements Ni and Cr slightly increase toward the core. The pegmatite is characterized by the dominance of tourmaline; muscovite as the dominant mica; normative corundum; high contents of SiO 2 , Al 2 O 3 , A/CNK, and Rb; low contents of CaO and Sr; and a high total FeO/MgO ratio in biotite. These features suggest an affinity with calc-alkaline peraluminous S-type granite in a subduction-related, syncollisional setting. The pegmatite is classified as beryl-columbite subtype of the LCT family. The restricted occurrence of high-temperature cordierite in the border zone may suggest that the pegmatite was overprinted by modal metasomatism during intrusion into the mantle rocks. Zircon saturation geothermometry indicates inward crystallization at temperatures of 782 °C in the border zone, 717 °C in the wall zone, and 550 °C in the intermediate zones. Geochemical data suggest that inward crystallization typified the formation of the pegmatite.

This New Mineral Names has entries for 10 new minerals, including bulgakite, dyrnaesite-(La), eleonorite, gatewayite, joanneumite, mendeleevite-(Nd), morrisonite, nolzeite, packratite, vanarsite and a new data on nalivkinite. # Bulgakite* and New Data on Nalivkinite {#article-title-2} A.A. Agakhanov, L.A. Pautov, E. Sokolova, Y.A. Abdu and V.Y. Karpenko (2016) Two astrophyllite-supergroup minerals: bulgakite, a new mineral from the Darai-Pioz alkaline massif, Tajikistan and revision of the crystal structure and chemical formula of nalivkinite. Canadian Mineralogist, 54(1), 33–48. Bulgakite, (IMA 2014-041), ideally ![Formula][1] , is a new astrophyllite-supergroup mineral. It occurs in the moraine of the Darai-Pioz glacier (39°30′N 70°40′E) in the upper Darai-Pioz alkaline massif in the upper reaches of the Darai-Pioz river, in the area of the joint Turkestan, Zeravshan, and Alay Ranges, Tajikistan. The Darai-Pioz massif is a multiphase intrusion and occupies the core of a large synclinal fold of Carboniferous (Pennsylvanian series) slates. Rocks of the massif have been intruded by fine-grained dikes of biotite tourmaline granites and veins of calcite carbonatites and fenites. Bulgakite was found in a naturally tumbled amphibole–quartz–feldspar boulder of spotty texture, as individual crystals and intergrowths in small cavities (up to 0.5 cm) and as intergrowths (up to 1 cm) of platy crystals and aggregates of poorly crystallized grains. Associated minerals are alkali amphibole, quartz, microcline, bafertisite, aegirine, calcybeborosilite-(Y) , thorite, fluorite, and later crystallized brannockite and sogdianite. Bulgakite is brownish orange with a pale brown streak and a vitreous luster. Cleavage is perfect parallel to {001} and moderate parallel to {010}. The indentation hardness of bulgakite is VHN50 = … [1]: /embed/mml-math-1.gif

The paper considers for the first time the morphology, composition, and conditions of formation of the greisens of the Solnechnoe deposit (Komsomol’sk ore district), a typical cassiterite–silicate assemblage. The greisens are localized in the root parts of the deposit and represent a system of veins and veinlets formed in the contraction fractures of the metasomatically altered roof of the monzogranite intrusion (age of 94–92 Ma). The cassiterite–chlorite–carbonate–muscovite–quartz composition of the greisens with admixture of topaz, fluorite, and apatite reflects the composition of the monzogranites. The greisens are close in age (85.3 Ma on muscovite) to the granitic aplites (80–85 Ma on the whole-rock and biotite) of the final phase of the intrusive magmatism. The fluid regime of their formation differs from that of the economic ores in higher temperature, pressure, and salinity. One distinguishing feature of the greisens is elevated contents of LREE, U, and Th, which are incorporated in the REE fluorcarbonates, thorite, and uranothorite crystallizing together with cassiterite.

The Wicheeda carbonatite is a deformed plug or sill that hosts relatively high grade light rare earth elements (LREE) mineralization in the British Columbia alkaline province. It was emplaced within metasedimentary rocks belonging to the Kechika Group, which have been altered to potassic fenite near the intrusion and sodic fenite at greater distances from it. The intrusion comprises a ferroan dolomite carbonatite core, which passes gradationally outward into calcite carbonatite. The potentially economic REE mineralization is hosted by the dolomite carbonatite. Three types of dolomite have been recognized. Dolomite 1 constitutes the bulk of the dolomite carbonatite, dolomite 2 replaced dolomite 1 near veins and vugs, and dolomite 3 occurs in veins and vugs together with the REE mineralization. Carbon and oxygen isotope ratios indicate that the calcite carbonatite crystallized from a magma of mantle origin, that dolomite 1 is of primary igneous origin, that dolomite 2 has a largely igneous signature with a small hydrothermal component, and that dolomite 3 is of hydrothermal origin. The REE minerals comprise REE fluorocarbonates, ancylite-(Ce), and monazite-(Ce). In addition to dolomite 3, they occur with barite, molybdenite, pyrite, and thorite. Minor concentrations of niobium are present as magmatic pyrochlore in the calcite carbonatite. A model is proposed in which crystallization of calcite carbonatite preceded that of dolomite carbonatite. During crystallization of the latter, an aqueous-carbonic fluid was exsolved, which mobilized the REE as chloride complexes into vugs and fractures in the dolomite carbonatite, where they precipitated mainly in response to the increase in pH that accompanied fluid-rock interaction and, in the case of the REE fluorocarbonates, decreasing temperature. These fluids altered the host metasedimentary rock to potassic fenite adjacent to the carbonatite and, distal to it, they mixed with formational waters to produce sodic fenite.

The Goias Tin Province (GTP) in Brazil has great potential for rare earth elements (REE) deposits associated with A-type granites, such as the Pedra Branca Massif, which contains several Sn deposits and REE anomalies, hosted in its cupola and fracture greisens. The Faixa Placha is the most important tin deposit in the Pedra Branca Massif and has high REE-Y concentrations, both in the Sn ore and parent biotite granite, as well as greisenized granites and greisens, with the potential to be economically used as a byproduct of tin. The values exceed 1000 ppm in light rare earth elements (LREEs) and 500 ppm in heavy rare earth elements (HREEs) + Y in the parent granite. REE concentrations in greisenized granites and greisens are similar to that of the parent granite, indicating that the enrichment in REE is due to the presence of REE-bearing primary minerals and that greisenization did not affect the original magmatic primary REE content. The REE-bearing minerals in the parent granite are allanite, monazite, xenotime, thorite, apatite, and zircon. These minerals, except zircon, are altered to secondary monazite, silicates, fluorcarbonates, and oxyfluorides, which are responsible for the concentration of REE in greisenized granites and greisens and the availability of these metals for the clay fraction of saprolites and soils. Ion exchange analyses in the saprolites and soils of a Faixa Placha profile show that the extractions in the clay fraction are more enriched in REE-Y compared to the whole soil extractions, with values between 3425 and 36,762 ppm and between 2804 and 21,689 ppm, respectively. The REEs are more enriched in the basal part of the profile, especially the LREEs. These exchangeable REE-Y concentrations indicate the potential of the Faixa Placha and nearby areas to constitute an important REE-Y deposit of the ion-adsorption-type.

Metamict minerals contain uranium and thorium, which contribute to physical degradation or metamictization of their crystal structures over geologic time. The damage occurs primarily through progressive overlapping recoil nuclei collision cascades from α-decay of 238U, 232Th, 235U, and their daughter products. We measured 222Rn and 220Rn emanations from metamict samples of nine oxides (brannerite, davidite, fergusonites, pyrochlores, samarskites, and uraninite), two phosphates (monazites), and eight silicates (cerite, gadolinites, perrierite, rinkite, thorite, turkestanite, and vesuvianite). The total absorbed α-doses ranged from 1.4 × 1015 to 6.1 × 1018 α-decay mg−1 for cerite and uraninite, respectively. The 222Rn emanation coefficients varied from 5 × 10−5% (uraninite) to 2.5% (turkestanite). The 220Rn emanation coefficients varied from 7 × 10−3% (gadolinite Ytterby) to 6.2% (gadolinite Marysin). The lowest 222Rn emanation coefficients occurred among metamict minerals containing the highest concentrations of 238U (i.e., uraninite, samarskites, and brannerite). Overall, the 222Rn and 220Rn emanation coefficients observed in this study fall significantly below previously reported values.

The paper presents a study of zircon from the Middle Paleoproterozoic Elet’ozero high-Ti layered ultramafic-mafic-alkaline intrusive complex with carbonatites and Sm-Nd isotope system of rock-forming minerals in ferrogabbro sample from this complex. Zircons extracted from syenite and ferrogabbro samples have similar pattern and experienced two main independent episodes of secondary transformation. The first episode was accompanied by the partial or complete replacement of the magmatic zircon with oscillatory zoning by porous zircon with a complex irregular inner structure, while a rim of CL-homogenous zircon around primary and porous zircons was produced during the second episode. The primary magmatic zircon is characterized by the elevated HREE, lowered LREE contents and positive Ce anomaly. The porous zircon is enriched in LREE, Ca, Ti, and frequently, in Th. While both varieties are mainly depleted in U. The REE distribution pattern in a homogenous zircon shell is similar to that of the magmatic zircon, but differs in much lower REE, especially HREE and MREE contents. The porous zircon contains microinclusions of thorite, barite, yttrialite, as well as other rare-metal and rare-earth minerals (calciosamarskite, pyrochlore, and hatchettolite), which indicates it was reworked by fluids containing not only F and Th, but also Y, U, Nb, Ta, Ba, Fe, Ti, and Ca. These components were presumably released during metamorphism-related replacement of magmatic minerals by metamorphic assemblages with fairly limited isomorphic capacity. U-Pb SHRIMP-II geochronological study of zircon showed its age varies within a wide range and correlates with peculiarities of its inner structure, which is explained by a style of superimposed processes. However, age estimations, especially for the domains dispersed alongside with porous zircon or “penetration” of shell material, often have younger values. The oldest ages (2086 ± 53 and 2086 ± 30 Ma for syenites and 2070 ± 24 Ma for ferrogabbroids) are presumably closest to the crystallization age of the intrusion. According to geological data, syenites intrude gabbroids. Therefore, the age obtained for syenites (2086 ± 30 Ma) seems to be the more preferable for the real formation age of the intrusion. Age values of porous zircon also widely vary, which is explained by the presence of relics (domains) of primary zircon in a porous matrix. We suggest that the minimum obtained dates (1.8–1.9 Ga) are the closest to the crystallization age of porous zircon. This age coincides with the Svecofennian tectonometamorphic processes, which presumably spanned the rocks of the Elet’ozero Complex, caused the metamorphism of all kind of rocks under the epidote-amphibolite facies conditions and formation of porous zircon. CL-light zircon shells were presumably formed later by interaction of zircon with a crustal fluid during the Meso- and Neoproterozoic, and even Caledonian events. The age of ferrogabbroids determined by Sm-Nd isochron method (1988 ± 63 Ma) is comparable within error with results of U-Pb dating of porous zircon, thus confirming that magmatic rocks of the complex underwent intense secondary transformations during the Svecofennian orogeny. The Middle Paleoproterozoic Elet’ozero Complex is the oldest manifestation of the high-Ti moderately alkaline magmatism at the Karelian Craton.

The Cobequid Highlands in Nova Scotia comprise a series of 365–360 Ma, REE-enriched, A-type granite plutons emplaced along an active shear zone. The purpose of this paper is to identify the sequence of REE minerals produced during long-lived, regional, hydrothermal circulation and its evolution through time. The fractures hosted in these granites were investigated using petrographic and scanning electron microscopes and the electron microprobe. Epidote-rich, biotite-rich, chlorite-rich, and Fe-oxide-rich fracture fillings have been observed. Mineral analyses revealed a variety of REE minerals in the fractures, including hydroxylbastnasite-(Ce), parisite-(Ce), synchysite-(Ce), cerianite, thorite, Nb-bearing minerals, hingganite-(Y), and chernovite-(Y). Cross-cutting relationships and mineral associations indicate that the REE minerals precipitated at different times and are associated with specific styles of hydrothermal alteration. Epidote was one of the earliest minerals to precipitate in the fractures, associated only with minor precipitation of thorite and hydroxylbastnasite-(Ce) and removal of As from sedimentary rocks, under low temperatures and reducing conditions. Biotite and chlorite precipitated shortly after epidote under more oxidizing conditions during which comparatively larger amounts of hydroxylbastnasite-(Ce), thorite, hingganite-(Y), and cerianite formed. The Fe-oxide-filled fractures formed in the latest stages of hydrothermal circulation and are associated with the largest variety and highest amounts of hydrothermal REE minerals, such as parisite-(Ce), synchysite-(Y), thorite, Nb-bearing minerals, and chernovite-(Y). The oxidizing conditions led to the precipitation of As and the formation of chernovite-(Y) after the alteration of hingganite-(Y). Thus the greatest remobilization and concentration of REE minerals took place during late, high-temperature, oxidizing hydrothermal circulation, apparently driven by minor late mafic intrusions.

Investigation of the morphology, anatomy, and chemical composition of fluorbritholite-(Y) and yttrialite-(Y) from silexites of the Keivy alkali granites in Kola Peninsula has shown that these minerals are the main REE concentrators in this area and that their content reaches 10–15 vol %. Britholite and yttrialite are associated with zircon, aeschynite-(Y), chevkinite-(Ce), fergusonite-(Y), thorite, monazite-(Ce), xenotime-(Y) and bastnaesite-(Ce). Three morphological types of fluorbritholite-(Y) have been identified: (I) subhedral crystals and grains, (II) anhedral grains intergrown with yttrialite-(Y), and (III) poikilitic crystals and skeletal aggregates. These morphological types of fluorbritholite-(Y) are characterized by successive (I to III type) decreases in P content down to the pure silicate fluorbritholite-(Y). Crystals of the first type are heterogenous: the P content decreases and the HREE content increases from core to rim. The total REE content increases insignificantly from types I to II and drastically decreases in fluorbritholite-(Y) of type III. The successive prevalence of HREE over LREE indicates the hydrothermal conditions of mineral crystallization. The chemical composition of yttrialite-(Y) is distinguished by the relatively high Th content and depletion in Al. The compositional trend (from core to rim) in heterogeneous grains of yttrialite-(Y) testifies that their heterogeneity was caused by metasomatic alteration of the mineral. The interrelation of fluorbritholite-(Y) and yttrialite-(Y) indicate that fluorbritholite-(Y) of types II and III were formed later than yttrialite-(Y). Evidence for fluorbritholite-(Y) and yttrialite-(Y) formation suggests the significant role of hydrothermal processes in the genesis of silexites.

A laser-ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICPMS) study of seven thorite and uranothorite [(Th,U)SiO 4 ] samples ranging in age from ~13 to ~500 Ma provides new insights into the U-Th/Pb isotope systematics of these geologically significant, high-Th mineral species. Despite extreme actinide enrichment and complex intra-crystal zonation in actinides and rare earth elements, this study demonstrates that radiogenic-lead loss and/or metamictization is minimal and restricted to domains that have undergone significant hydration. Dating of four igneous uranothorites yields ages that are concordant in U/Pb and Th/Pb space, consistent with other high-temperature chronometers, and are inferred to accurately reflect the timing of crystallization of each rock. Similarly, Th/Pb ages of three thorite and/or huttonite-bearing samples yield geologically plausible dates consistent with other mineral chronometers. No evidence of isotopic inheritance was observed in any of the samples. Data presented here demonstrate for the first time the feasibility of extracting accurate and precise U/Pb and Th/Pb ages from Phanerozoic thorite, uranothorite and huttonite using LA-MC-ICPMS at the 5 μm spatial resolution. These phases have the potential to be robust chronometers in igneous and metamorphic rocks as well as to provide important provenance information complementary to more widely used minerals such as detrital zircon.

Thorogummite has been discredited as a valid mineral species. No type material from the original study was available for analysis. An extensive review of the literature, both recent and historic, reveals the use of the name “thorogummite” for any hydrated, metamict thorite or unidentified alteration product of a Th-bearing mineral. All early studies on “thorogummite” and other alteration products of thorite were performed on heterogeneous mixtures of mostly secondary and metamict materials and must be considered suspect. The validity of Frondel’s (1953) proposed (SiO 4 ) 4– ↔ (OH) 4 4– substitution between thorite and thorogummite was examined and shown to be an incomplete solid solution. All compositions in the literature to date are Th- and Si-dominant and must be considered thorite. Furthermore, the majority of the compositions in the literature are outdated and likely do not represent those from crystalline, single-phases. More likely, all so-called “thorogummite” are simply metastable hydrated or metamict thorite with varying volumes of other alteration products. The discreditation has been approved by the IMA Commission on New Minerals, Nomenclature and Classification (Nomenclature Voting proposal 14-B).

Allanite has the potential to be a useful chronometer of crustal evolution, forming in response to a wide spectrum of metamorphic and magmatic conditions and incorporating weight-percent concentrations of LREE, Th and U. Despite its growing use in in situ U–Th–Pb geochronology, allanite reference materials lack sufficient U–Th–Pb isotopic characterisation and little is known concerning the response of U–Th–Pb systematics of allanite to hydrothermal alteration and self-irradiation. This contribution presents the results of a combined ID-TIMS and LA-ICPMS U–Th–Pb study on a suite of five allanite crystals, spanning ∼2.6 Ga and including three commonly-used allanite reference materials: the Siss, Bona and Tara allanites. Siss and Bona allanites preserve an inherited ca. 1 Ga Pb component, consistent with the presence of xenocrystic allanite cores or the presence of zircon micro-inclusions. Tara allanite yields concordant U–Pb ages (407–430 Ma), but is affected by Th/U fractionation, likely caused by hydrothermal alteration. Additionally, the tendency for Th to become mobilised post-crystallisation is further evidenced by two Precambrian allanite megacrysts, LE40010 (ca. 2.8 Ga) and LE2808 (ca. 1.1 Ga), that both exhibit discordant Th/Pb analyses, linked to the formation of thorite micro-inclusions along hydration pathways. Self-irradiation dose versus discordance relationships show that a percolation threshold is present in allanite at cumulative dose values close to 3 × 10 17 α-decay g −1 , an order of magnitude smaller than zircon. Collectively, the presence of common-Pb and excess- 206 Pb, its susceptibility to incur Th/U fractionation and hydrothermal Pb-loss complicates the use of allanite as a geochronometer. These factors explain dispersion of ∼4% in the isotopic compositions of Siss and Tara allanites measured by LA-ICPMS, providing a fundamental limit on the accuracy of the allanite chronometer using these reference materials.

We present the first quantitative compositional analysis of thorite in a lunar sample. The sample, a granitic assemblage, also contains monazite and yttrobetafite grains, all with concentrations of U, Th, and Pb sufficiently high to determine reliably with the electron microprobe. The assemblage represents the first documented occurrence of these three minerals together and only the second reported occurrence of thorite in a lunar rock. Sample 12023,147-10 is a small, monomict rock fragment recovered from an Apollo 12 regolith sample. It comprises graphic intergrowths of K-feldspar and quartz, and plagioclase and quartz, along with minor or accessory hedenbergite, fayalite, ilmenite, zircon, yttrobetafite, thorite, monazite, and Fe metal. Thorite, ideally ThSiO4, occurs in the assemblage adjacent to quartz and plagioclase, and includes a 12% xenotime ([Y,HREE]PO4) component. From quantitative electron-probe microanalysis (EPMA) of Th, U, and Pb in thorite, assuming that all of the measured Pb is radiogenic, we calculate an age of 3.87 ± 0.03 Ga. Yttrobetafite and monazite, which contain lesser concentrations of U, Th, and Pb than the thorite, yield ages of 3.78 ± 0.06 Ga and 3.9 ± 0.3 Ga, respectively. These dates are consistent with formation of the granitic material around 3.8–3.9 Ga, possibly associated with, or after, the formation of the Imbrium basin. This age falls within a group of younger ages for granitic samples, measured mainly by ion microprobe analysis of zircon, compared to a suite of older ages, ca. 4.20–4.32 Ga, also from zircons ( Meyer et al., 1996 ). A 3.8–3.9 Ga age may reflect an origin following the Imbrium event whereby granitic melt formed as a result of heating and melting, and was mobilized and emplaced along an Imbrium-related ring-fracture system. Silicic volcanic or exposed intrusive materials occur in several circum-Imbrium locations such as the Mairan and Gruithuisen Domes and in ejecta excavated by Aristarchus crater. Perhaps sample 12023,147-10 and some of the other granitic materials sampled at the Apollo 12 site represent rocks similar to the rocks that make up these large silicic rock occurrences.

The present work aims to study the link between mineralogy and process characteristics of North Ras Mohamed ore materials. The chemical nature of the latter was also studied to determine the type of treatment employed from one hand and the preferred lixiviate option from the other hand. For this purpose, three technological samples representing three different deposit types were examined for their potential processing options. These include basal sandstone, aplite dyke and pegmatitic bodies which were found to assay 0.05, 0.04 and 0.06% U, 0.13, 0.10 and 0.07% Th and 0.14, 0.13 and 0.09% REEs respectively, while Nb assays 1.3% and Ta 0.5%, in the pegmatitic ore sample. The corresponding minerals of these elements of interest include thorite and uranothorite in the basal sandstone ore material. On the other hand, the multiple-oxide minerals samarskite, fergusonite and allanite are found in both the aplite and the pegmatite bodies. However, the zircon, fluorite, apatite, titanite and brookite are considered as the main accessory minerals in the three study ore materials Based on the available chemical and mineralogical data on the three different ore material types of Ras Mohamed area, a physical upgrading process would be required as a major recommendation for future prolific metallurgical work.