Explore the vast range of titles available.

Thorite, as a principally thorium (Th)-bearing mineral, is an important indicator for Th mineralization. However, its occurrence and enrichment processes are still discussed and debated. Here, a unique occurrence of thorite, discovered in Nubian granodiorite rather than in highly evolved granites from southwestern Egypt, is reported. This report presents data derived from optical and backscattered electron (BSE) microscopy and energy-dispersive X- ray spectrometry (EDS) analyses conducted on the thorite and its host rock. The Nubian granodiorite thorites are viewed as secondary, not primary products. Two distinct types of secondary thorites are identified that are referred to as type A thorite and type B thorite herein. Type A thorite occurs as small grains that are enclaved in a fine-grained matrix of altered oligoclase and ferrohornblende, and clinochlore. Thorite grains, up to 100 μm in size are characterized by corona-type structures comprising of clinochlore and hematite with some barite. Their sources are most likely hydrothermal solutions occurring during an alteration stage and having relatively high conditions of sulfate activity. Type B thorite, on the other hand, forms crystallites in altered domains of magmatic allanite-(Ce), ranging in size from ~ 0.1 to ~ 10 μm. Formation of Type B thorite is a direct result of fluid-driven alteration processes, since it requires the in situ-redistribution of elements, particularly thorium, silicon, and uranium. Thorite types A and B are composed mainly of thorium uranium silicate, with variable minor amounts of Y, Al, Ce, Nd, Fe, Ca, Na, Mg, P, and Cl. Thorite compositions are within the range reported for uranothorites from other occurrences.

The current study investigates the geology and mineralogy of uraniferous microgranites from Ras Abda area, northeastern Desert, Egypt. The Precambrian basement suites of the studied area comprise older granitoids, microgranite dykes, and post granitic dykes and veins. The microgranite dykes occur as swarms and vary in color from buff and pink to dark red and brown. They are confined to a highly deformed, faulted, and sheared narrow zone, that is more than 1500m long in NE to NNE direction and up to 300 m in width. Several hydrothermal alteration processes, including hematitization, silicification and kaolinitization have varying degrees of impact on the rock. The radioactive mineralizations in the studied area are: (a) uranium minerals (kasolite and uranophane), and b) thorium minerals (thorite, uranothorite and orangite). Occasionally, secondary uranium minerals are found filling micro-fractures or coating joint surfaces.

Monazite [(Ce,LREE,Th,U,Ca)(P,Si)O 4 ], with complex zoning in Th and other elements, is commonly observed in metamorphic and igneous rocks. The hypothesis that this alteration is a product of fluid-mediated element mass transfer has been tested in the piston-cylinder press (CaF 2 assembly, cylindrical graphite oven) at 1,000 MPa and 900°C and in cold seal autoclaves on a hydrothermal line at 500 MPa and 600°C. Experiments included a relatively homogeneous monazite-(Ce) (7–8 wt% ThO 2 ) from a heavy mineral sand plus a series of alkali-bearing fluids including 2N NaOH, 2N KOH, and Na 2 Si 2 O 5  + H 2 O. Experiments were conducted using BSE imaging, EMP analysis, and both TEM and HRTEM. A subset of monazite grains from each experiment show evidence of partial alteration in the form of areas enriched in Th + Si with sharp curvilinear compositional boundaries extending from the grain rim into the monazite interior. These ThSiO 4 -enriched textures are similar to those commonly seen in natural examples of metasomatised monazite in both magmatic and metamorphic rocks. In the Na 2 Si 2 O 5  + H 2 O experiments, scarce inclusions of britholite formed in the altered monazite. The altered monazite is also characterised by strong depletion in Pb, Ca, and Y. Thorium and Si mobility, coupled with the formation of britholite inclusions, during partial alteration in the monazite grain is considered to be the product of fluid-aided coupled dissolution–reprecipitation as opposed to solid-state diffusion. Since other fluids, including NaCl and KCl brines, do not result in the formation of these textures, the experimental replication of ThSiO 4 -enriched areas in the monazite strongly suggests that similar textures in monazite observed in nature are fluid induced, specifically by alkali-bearing fluids. If true, complex metasomatically induced textures in monazite could yield information concerning the nature of the fluid responsible for their formation as well as allow for the dating of the metasomatic event, presuming that all the original radiogenic Pb has been removed.

Thorium‐rich (Th‐rich) geological units have been detected by remote sensing in the Martian crust. However, there is still a lack of mineralogical evidence to constrain the magmatic processes responsible for these anomalies. In this study, we report the first discovery of thorite (ThSiO4) grains within a zircon fragment from Martian regolith breccia meteorite NWA 11220. These zircon‐hosted thorite grains are micron‐sized (<5 μm) individual particles and are associated with magnetite and ilmenite inclusions. Transmission Electron Microscopy analysis shows that the thorite and zircon have become metamict due to radioactive decay, whereas magnetite and ilmenite remain crystalline. This metamict thorite provides mineralogical evidence for a highly evolved, Th‐saturated, and oxidized magmatism on Mars. Furthermore, our findings offer a critical ground‐truth for orbital Th anomalies and provide new insights into thorium reservoirs in the Martian crust.

Serpentinization along subducting plates induces mechanical mixing of diverse rocks and interaction with compositionally distinct fluids, which is often accompanied by the formation of rare mineral species. In this study, newly discovered baddeleyites in the Higuchi serpentinite body (HSB), Japan, are described. The HSB occurs as a 15 × 8 m outcrop surrounded by high-P/T metapelite, and baddeleyite was collected from only one serpentinite block. The baddeleyite appear as aggregates exhibiting angular or subrounded shapes with sizes of up to 2 mm in length. The aggregates are composed of acicular baddeleyite surrounded by porous zircon rims. Both the baddeleyite and the zircon yielded U–Pb ages of ca. 96 Ma, corresponding to the peak metamorphic age of the region. Within the aggregates, Th-enriched areas with sizes of less than 20 μm were observed. The baddeleyite aggregates show enrichment of light rare earth elements with positive Eu anomalies. Based on thermodynamic stability relationships, the baddeleyite aggregates are inferred to have originated as zircon megacrysts, which were mechanically incorporated into the ultramafic rock and subsequently metamorphosed during serpentinization. Subsequent metasomatism associated with carbonation and pervasive silicification led to the formation of the zircon rim and trace-elemental maldistribution. This study demonstrates significant high field strength elements (HFSE) heterogeneity on scales ranging from millimeters to micrometers within serpentinite along subduction zones.

This study aims to define the mineralogical controls on natural radioactivity and its associated hazards in the El Fereyid monzogranite, Egypt. Integrated petrographic, microchemical, and radiometric analyses identify thorite (containing ≤ 66.1 wt% ThO 2 ), monazite-(Ce) (≤ 10.0 wt% ThO 2 ), and zircon (≤ 1.4 wt% UO 2 ) as the primary carriers of radioactivity. These minerals are responsible for 232 Th and 238 U activities that significantly exceed global averages. Multivariate statistics confirm strong correlations (r > 0.8) between these Th-bearing phases and elevated gamma dose rates. We conclude that the primary magmatic crystallization and subsequent hydrothermal alteration of these accessory minerals create substantial radiological heterogeneity. Although mean radiological hazard indices remain within international safety limits, localized concentrations generate annual effective doses up to 0.7 mSv and annual gonadal dose equivalents of up to 0.9 mSv, necessitating targeted occupational precautions. This work establishes a direct petrogenetic link between rare-metal enrichment and radioactivity, providing a crucial model for resource potential and radiological risk assessment in analogous granitic terrains worldwide.

Neoproterozoic mineralized granites from the Umm Naggat and Homrit Waggat areas in the Central Eastern Desert (CED) of Egypt, are parts of the Neoproterozoic Nubian Shield. On the basis of textural and chemical characteristics, they resemble highly fractionated ferroan peraluminous A-type granites. Decorrelation stretch (DS) and band ratio (BR) techniques of Sentinel-2 and Landsat-9 data were used for the spectral identification of lithological units, alteration and mineralized zones in A-type granites. Spatial and spectral extent of the hydrothermal mineralized alteration zones (e.g., sericitization, carbonatization, kaolinitization, ferrous silicates and hydroxyl) related to the rare metal-bearing granitic plutons can be discriminated by processed ASTER data. Some structural features have been identified by Sentinel-1enhanced Soble directional filter images. The NW–SE Najd fault system is conjugated with N–S and NE–SW faults, which structurally control the distribution of both mineralized alteration zones and rare metal-bearing granites in the CED of Egypt. The studied mineralized granites comprise syenogranite and alkali feldspar granite. Essential minerals are quartz, K-feldspar (Or 94-99 ), plagioclase (An 0-7 ) and biotite, with subordinate amounts of chlorite, muscovite and fluorite. Zircon, Fe-Ti oxides, rutile, apatite, epidote, titanite, columbite and thorite are main accessory phases. Average zircon saturation temperature (T Zr ) of the studied granites ranges from 780 °C to 880 °C at pressures of 0.7–3.0 kbars and depth < 8 km. These granites are highly evolved (SiO 2  = 73–78 wt. %), and show characteristics of high-K calc-alkaline peraluminous rocks (A/CNK = 1–1.13). They are enriched in Rb, Nb, Y, Ta, Hf, Ga, Zr and rare-earth elements (ΣREEs: up to 558 ppm) and show pronounced negative Eu anomalies (Eu/Eu* = 0.01–0.29), similar to post-collisional rare metal-bearing A-type granites either in Egypt or elsewhere in the world. These A-type granites more likely crystallized from highly fractionated I-type tonalite-granodiorite magmas, followed by extensive fractional crystallization in the upper crust during and just after lithospheric delamination. Rare-metal minerals such as zircon, rutile, xenotime, thorite, cerite-(Ce), apatite, parisite, uranothorite, columbite, ishikawaite and bastnaesite crystallized under both magmatic and hydrothermal conditions. Remote sensing and geochemical data enabled us to characterize mineralized zones in A-type granites and indicated that albitization is accompanied by higher concentrations of REEs (544 ppm), Zr (up to 378 ppm), Y (142 ppm), Nb (127 ppm) and Th (26 ppm) than other alteration types, suggesting stabilization of these elements by Na-, F- and Cl-rich fluids during Na-metasomatism.

The present study was carried out on promising lamprophyre dykes at Wadi Sikait, through the mineralogical and petrography studies with emphasis on the radiological hazard’s indices along Wadi Sikait. So, the radioelement contents in the studied rocks were measured radiometrically by using gamma-spectrometry (NaI-detector). The psammitic gneisses formed an elongated zone striking NNE-SSW and are silicified, banded, jointed, sheared, mylonitized, and hematized. The lamprophyre dykes strike NNW-SSE varies in thickness from 0.5 m to 1.5 m, and extend more than one kilometer. The averages of the eU/eTh ratio are 2.02, indicating uranium accumulation, which confirmed positive disequilibrium (P-factor). Many of the radiological hazard parameters in both psammitic gneisses and lamprophyre dykes are higher than the international limits, suggesting probable hazard. 40 K plays the main and most important role in dose rate contribution. The high activity and the elevated radiological hazard parameters in the lamprophyre are related to the presence of radioactive and radioelements bearing minerals like kasolite, thorite, uranothorite, xenotime, cheralite and baddeleyite. Other mineralization was also recorded as gold and base metal minerals.

This study investigated the radioactivity of granite and its altered varieties using an airborne gamma-ray spectrometer, revealing significantly elevated levels of uranium, thorium, and potassium within specific granitic formations. Higher concentrations were identified in syenogranite, alkali feldspar granite and quartz syenite, while lower levels were observed in metavolcanics, Tonalite-granodiorite and Nubian sandstone. The average activity concentration of 238 U (74 ± 16 Bq kg −1 ), 232 Th (80 ± 15 Bq kg −1 ), and 40 K (893 ± 122 Bq kg −1 ) exceeded worldwide averages. The presence of rare metal granites diverges from international standards, due to the presence of minerals harboring radioelements as thorite, monazite, zircon and ferrocolumbite suggests these granites are unsuitable for construction.

Two magmatic REE-rich occurrences, located near Jamestown, Colorado, and hosted in the Precambrian Longs Peak granite batholith, exhibit unusual textures that suggest formation by fluoride-silicate melt immiscibility. Both contain small (<2 mm diameter) globular F-, P-, and REE-rich segregations of fluorite and monazite-(Ce). In addition, the northern of the two localities preserves evidence of a second melt immiscibility event in the form of larger (up to several cm diameter) aplite-hosted globular segregations of fluorite and the REE minerals allanite-(Ce), monazite-(Ce), fluorbritholite-(Ce), törnebohmite-(Ce), and cerite-(Ce). The southern of the two localities lacks these cm-scale globular textures, but instead contains much larger aggregates of these same REE minerals, with up to >57 wt. % ΣREE2O3, yet no fluorite, as well as large aggregates of allanite-(Ce) and quartz, and an amphibole-bearing REE-rich rock containing allanite-(Ce), other REE minerals, quartz and minor apatite. A new Nd-Sm laser ablation age of 1.422(24) Ga on monazite-(Ce) and allanite-(Ce) from the southern locality implies the same age of formation of 1.420(25) Ga as for the northern locality, with equally similar initial εNd1.42Ga values of these REE minerals. A newly discovered third locality, containing primarily allanite-(Ce), minor monazite-(Ce), and thorite, without fluorite, extends the number, spatial distribution and total volume of these mineralogically unusual magmatic REE occurrences. We suggest that the REE were concentrated in these three localities by multiple stages of fluoride-silicate melt immiscibility. For the southern locality, slower cooling of a possibly larger magma volume, or in a deeper environment, allowed greater aggregation of the immiscibly separated REE-rich phases, as well as loss of the volatile element F, resulting in a greater availability of Ca accommodated by the crystallization of amphibole and minor apatite.