Rare-metal Granites Research Articles

LATE MESOZOIC RARE-METAL GRANITES, PEGMATITES, AND GREISENS OF MONGOLIA: AGE, MINERALOGY, GEOCHEMISTRY, ORE POTENTIAL, AND PETROGENESIS

Comparative analysis of the earlier obtained and new geological data, age, mineral, petrological, and geochemical compositions of plutons of calc-alkalic granitoids and rare-metal Li–F granites shows their evolution in a wide time interval during the formation of Mesozoic areas of granitoid magmatism. Mineralogical and geochemical analysis of the evolution of plutons of palingenetic calc-alkalic granitoids (Baga Hentiyn (MZ1) and Ikh Narotiin = Hiid (MZ2)) and intrusions of rare-metal Li–F granites of Central and Eastern Mongolia revealed their petrological and geochemical differences. The closure of the Mongol–Okhotsk Basin with the formation of large plutons of calc-alkaliс granitoids, obviously related to collisional processes, did not cause significant enrichment of the late granite phases with lithophile and ore elements. Within the peripheral zones of еру MZ1 and MZ2 magmatic areas, mineralization is often associated with Mongolian multiphase plutons and small intrusions of rare-metal Li–F granites. The rare-metal granites are characterized by a decrease in indicative K/Rb, Nb/Ta, and Zr/Hf values and a regular increase in F, Li, Rb, Cs, Sn, W, Be, Ta, and Nb contents during the evolution of Li–F magmas. Igneous and, particularly, metasomatic rocks in most intrusions of ore-bearing rare-metal Li–F granites are characterized by significant variations in Sn and W contents. At the magmatic stage, the pegmatoid varieties of amazonite–albite granites and pegmatites of the zonal Baga Gazriin (MZ1) and Barun Tsogto (MZ2) plutons are significantly enriched in both Sn and W. Maximum Sn and W enrichment has been established in greisenized granites and zoned greisen bodies (zwitters), which is due to the percolation of ore-bearing solutions into the upper horizons and the mineralization of ore elements in the late phases of intrusions and in metasomatites. The wide variations in the age (321–126 Ma) and trace element and isotope compositions of Mongolian rare-metal Li–F granites within various zones of large magmatic areas suggest the influence of mantle plume sources on the composition of rare-metal granitic magmas and on their ore potential in intermediate chambers in the continental crust.

Role of Liquid Immiscibility in the Formation of the Rare Metal Granites of the Katugin Massif, Aldan Shield

Role of Liquid Immiscibility in the Formation of the Rare Metal Granites of the Katugin Massif, Aldan Shield

Magmatic-hydrothermal evolution and rare metal enrichment of the Huoshibulake B-rich rare metal granite in the Southern Tianshan: Insights from texture, geochemistry, and Hf[sbnd]O isotopes of zircon

Deciphering magmatic-hydrothermal evolution and rare metal mineralization mechanisms in granitic systems is always challenging, particularly when elucidating the intricate details of magmatic-hydrothermal transition, the critical stage when the system changes from melt-driven to fluid-driven with associated metal extraction. Here we present a case study of the Huoshibulake Nb-REE-mineralized alkali pluton in the north margin of the Tarim Carton, China. The pluton exhibits abundant tourmaline-quartz orbicules and tourmaline-quartz veins, which are the products of immiscible B-rich melt exsolved during the magmatic-hydrothermal transition. Three types of zircon crystals with different morphology have been recognized in the pluton: antecrystic, autocrystic and hydrothermal zircons, the latter two representing the melt and fluid parts of the system. LA-ICP-MS UPb dating of autocrystic zircon from granite and orbicule samples (206Pb/238U ages of 274.8 ± 1.5 and 273.6 ± 2.0 Ma, respectively) and cassiterite from the vein sample (lower 206Pb/238U intercept age of 271.4 ± 4.1 Ma) overlap within error. The similar trace-element patterns and near-identical O-isotopic compositions between hydrothermal and autocrystic zircons indicate that the hydrothermal zircons were crystallized from magmatic fluids. Zircon HfO isotopic systematics suggests that the coeval A1-type granites in the Halajun area evolved from a single parental magma chamber which originated from ∼30% of the upper crustal material mixed with ∼70% mantle-derived mafic magma. Whole-rock compositional trends reveal that fractional crystallization of felsic minerals contributed to the rare metal enrichment. The rare metal mineralization in the veins and the close association of rare metal mineralization with fluorite indicate the critical role of F-rich hydrosilicate liquids in rare metal mineralization, which is also recorded by the significant increase of rare metal concentrations from the autocrystic to the hydrothermal zircon grains.

Genesis of Rare Metal Granites in the Nubian Shield: Tectonic Control and Magmatic and Metasomatic Processes

The Igla Ahmr region in the Central Eastern Desert (CED) of Egypt comprises mainly syenogranites and alkali feldspar granites, with a few tonalite xenoliths. The mineral potential maps were presented in order to convert the concentrations of total rare earth elements (REEs) and associated elements such as Zr, Nb, Ga, Y, Sc, Ta, Mo, U, and Th into mappable exploration criteria based on the line density, five alteration indices, random forest (RF) machine learning, and the weighted sum model (WSM). According to petrography and geochemical analysis, random forest (RF) gives the best result and represents new locations for rare metal mineralization compared with the WSM. The studied tonalites resemble I-type granites and were crystallized from mantle-derived magmas that were contaminated by crustal materials via assimilation, while the alkali feldspar granites and syenogranites are peraluminous A-type granites. The tonalites are the old phase and are considered a transitional stage from I-type to A-type, whereas the A-type granites have evolved from the I-type ones. Their calculated zircon saturation temperature TZr ranges from 717 °C to 820 °C at pressure < 4 kbar and depth < 14 km in relatively oxidized conditions. The A-type granites have high SiO2 (71.46–77.22 wt.%), high total alkali (up to 9 wt.%), Zr (up to 482 ppm), FeOt/(FeOt + MgO) ratios > 0.86, A/CNK ratios > 1, Al2O3 + CaO < 15 wt.%, and high ΣREEs (230 ppm), but low CaO and MgO and negative Eu anomalies (Eu/Eu* = 0.24–0.43). These chemical features resemble those of post-collisional rare metal A-type granites in the Arabian-Nubian Shield (ANS). The parent magma of these A-type granites was possibly derived from the partial melting of the I-type tonalitic protolith during lithospheric delamination, followed by severe fractional crystallization in the upper crust in the post-collisional setting. Their rare metal-bearing minerals, including zircon, apatite, titanite, and rutile, are of magmatic origin, while allanite, xenotime, parisite, and betafite are hydrothermal in origin. The rare metal mineralization in the Igla Ahmr granites is possibly attributed to: (1) essential components of both parental peraluminous melts and magmatic-emanated fluids that have caused metasomatism, leading to rare metal enrichment in the Igla Ahmr granites during the interaction between rocks and fluids, and (2) structural control of rare metals by the major NW–SE structures (Najd trend) and conjugate N–S and NE–SW faults, which all are channels for hydrothermal fluids that in turn have led to hydrothermal alteration. This explains why rare metal mineralization in granites is affected by hydrothermal alteration, including silicification, phyllic alteration, sericitization, kaolinitization, and chloritization.

Magmatic–hydrothermal stage recorded by mica zonation and Nb–Ta–W–Sn mineralization: New insight into the genesis of highly evolved Songshugang Nb–Ta deposit (Jiangxi, SE China)

The role of magmatic and hydrothermal processes in niobium-tantalum mineralization is still controversial and has been limited by a lack of mineralogical records in the evolving magmatic–hydrothermal system. Micas as essential rock-forming minerals and comprise the amount of elements (especially rare-metal elements), become one of the ideal indicator. The Songshugang rare-metal granite (RMG) located in the southern part of Jiangxi Province, China, is renowned as the largest tantalum reservoir in South China. The albite–topaz–K-feldspar granite is the major granite, with layers of pegmatite, topaz-K-feldspar granite, and greisen overlay on it. It is the typical highly evolved peraluminous with low phosphorous RMGs (PLP-type) according to geochemistry. The Songshugang pluton preserves analogical characters in topaz-albite-K feldspar granites and topaz-K feldspar granite, and partly reserves in greisen. Detailed petrographic, mineralogy, and chemical composition study of zoned mica and accessory Nb–Ta minerals suggest that zinnwaldite and Nb-Ta oxides have experienced magmatic fractionation with gradually decrease of K/Rb and Nb/Ta ratio in prismatic zinnwaldite and columbite-(Fe). The leap of Rb (Rb2O up to 4.08 wt%) and Ta (Ta# up to 0.29) at the rim of zinnwaldite and columbite is likely attributed to supersaturation. Afterwards the overgrowth of Rb-deficit zinnwaldite (0.56–0.72 wt% Rb2O) is coeval with the Ta-highest wodginite, taking place during the magmatic-hydrothermal transition associated with a fluid-melt interaction in hydrosaline melt. The ascent of fluxing elements contributes to the formation of hydrothermal zinnwaldite and cassiterite through greisenization. The systemic coupling mineralization of zinnwaldite and Nb–Ta oxides altogether record the both the melt-driven and fluid-driven processes in highly evolved Songshugang deposit that is critical for rare-metal mineralization. The Songshugang displays a great similarity to the typical PLP RMGs Cínovec cupola in geochemistry, which are metaluminous to peraluminous, containing low phosphorous, intermediate REE, Zr, Hf, and Th content. But Songshugang has experienced strong supersaturation; the latter is more akin to highly evolved melts alike Yichun or Beauvoir. The strong supersaturation and crystallization demonstrate its discrepant mineralization mechanism in Songshugang RMGs.

Multiple-pulse magmatic intrusion and fluid metasomatism in Mesozoic Qianlishan rare metal granite, South China: Records from apatite geochemistry

South China block contains abundant rare metal resources that have widely been considered to be associated with highly evolved granitic magmatism and related fluid metasomatism. Here we perform detailed geochemical analyses on apatite and bulk rock from the ore-bearing granites (equigranular zinnwaldite granite) and ore-barren granites (porphyritic biotite granite and granitic dyke) at Qianlishan pluton, South China, to decipher the respective roles of magmatic and fluid processes and further understand the petrogenesis of rare metal granite (RMG). Apatites from both granite types are F-rich, displaying heterogeneous textures and large compositional variations in Cl, Sr, rare earth elements (REEs), Ga, Th, and U. Relative to the ore-barren granite, the apatites from ore-bearing granite contain lower Sr but higher ∑REE, Th + U and Ga, reflecting more evolved features. The oscillatory compositional zonation and bimodal O-Nd isotopic compositions in apatite from the ore-barren granite indicate multiple-pulse intrusion instead of other open-system processes such as magma mixing and/or crustal assimilation during magmatic evolution, while the additional occurrence of monazite and lower δ18O (< 8‰) in half of the apatite crystals from the ore-bearing granite require further influence of hydrothermal metasomatism. In combination with their high W + Sn concentrations and La tetrad effect in chondrite-normalized REE patterns, the ore-bearing granite experienced extensive metasomatism, during which the fluids in equilibrium with the metasomatic apatite were likely magmatic in origin. We therefore suggest that multiple-pulse magmatic intrusion and fluid metasomatism are two predominant factors during the formation of highly evolved RMG, such as the Qianlishan pluton in South China. Our results demonstrates that apatite geochemistry can be a potential approach to monitoring the magmatic evolution and fluid metasomatism during rare metal mineralization.

Peraluminous Rare Metal Granites in Iberia: Geochemical, Mineralogical, Geothermobarometric, and Petrogenetic Constraints

The intensive variables, geochemical, mineralogical, and petrogenetic constraints of the Iberian peraluminous rare metal granites (RMGs), many of them unknown, are presented. The mineral chemistry of ore and gangue minerals, whole rock analyses, geothermobarometry, melt water and phosphorus contents, mass balance, and Rayleigh modeling were performed to achieve these objectives. These procedures allow us to distinguish two main contrasting granitic types: Nb-Ta-rich and Nb-Ta-poor granites. The former have lower crystallization temperatures, higher water contents, and lower emplacement pressures than Nb-Ta-poor granites. Nb-Ta-rich granites also have higher fluoride contents, strong fractionation into geochemical twins, higher Na contents, and different evolutionary trends. At the deposit scale, the fractional crystallization of micas properly explains the variation in the Ta/Nb ratio in both Nb-Ta-poor and Nb-Ta-rich RMGs, although in higher-grade granites, the variation is not as clear due to the action of fluids. Fluid phase separation processes especially occurred in the Nb-Ta rich granites, thus transporting halogens and metals that increased the grades in the top and sometimes in the core of granites. Gas-driven filter pressing processes facilitated the migration of fluid and melt near solidus melt in Nb-Ta-rich granites. The geochemical signature of the Iberian rare metal granites mainly follows the trends of two-mica granites and P-rich cordierite granites, but also of granodiorites.

Influence of magmatic and magmatic-hydrothermal processes on the lithium endowment of micas in the Cornubian Batholith (SW England)

The Cornubian Batholith (SW England) is an archetypal Variscan rare metal granite with potential for Li-mica mineralization. We present a petrographic, trace element and multivariate statistical study of micas from the Cornubian Batholith granite series and related hydrothermally altered units to assess the role of magmatic vs subsolidus processes and of fluxing elements (F and B) on the Li cycle during the evolution of the system. The mica types are as follows: (1) magmatic, which include Fe-biotite, protolithionite I and phengite-muscovite from the most primitive granites, and zinnwaldite I from more fractionated lithologies; (2) subsolidus, which encompass high-temperature autometasomatic Li-micas and low-temperature hydrothermal muscovite-phengite. Autometasomatic species include protolithionite II, zinnwaldite II and lepidolite, which were observed in the most fractionated and hydrothermally altered units, and occur as replacements of magmatic micas. Low-temperature hydrothermal Li-poor micas formed via alteration of magmatic and autometasomatic micas or as replacement of feldspars, and albeit occur in all studied lithologies they are best represented by the granite facies enriched in metasomatic tourmaline. The evolution of micas follows two major trends underlining a coupling and decoupling between the Li(F) and B fluxes. These include as follows: (1) a Li(F)-progressive trend explaining the formation of protolithionite I and zinnwaldite I, which fractionate Li along with Cs, Nb and Sn during the late-magmatic stages of crystallization, and of zinnwaldite II and lepidolite forming from the re-equilibration of primary micas with high-temperature Li-B-W-Tl-Cs-Mn-W-rich autometasomatic fluids; (2) a Li(F)-retrogressive trend explaining the low-temperature hydrothermal muscovitization, which represents the main Li depletion process. Trace element geochemistry and paragenesis of late muscovite-phengite support that muscovitization is a district-scale process that affected the upper parts of the granite cupolas through acidic and B(Fe-Sn)-saturated hydrothermal fluids associated with metasomatic tourmalinization, which were mixed with a low Eh meteoric component.

Age and geochemical evolution of granite magmatism in Olkhon region from Caledonian syncollisional ore-free granite to the rare metal granite and pegmatite of Middle Paleozoic intraplate setting

The detailed description of two granite complexes in the Olkhon subterrane is given. The Early Paleozoic Sharanur complex was formed by granitization of gneisses of the Olkhon series. It includes migmatites, granite-gneisses, granites and pegmatites of normal alkalinity; they belong to the type of syncollisional granites. The Middle Paleozoic Aya granite complex includes mother Aya massif of amazonite-bearing granites and several types of rare-metal pegmatites. They have elevated alkalinity, low of Ba, Sr, and high LILE and HFSE elements contents. The Aya pegmatites lie in northwest cracks of stretching and associated with the rise of the territory under the influence of the North Asian plume. These cracks and pegmatites mark the beginning of a new intraplate geodynamic setting. Two geochemical types are distinguished among the pegmatites of this complex. These are amazonite pegmatites of Li-F type with Ta mineralization and complex type pegmatite with Be-Rb-Nb-Ta and Li-F mineralization (the Ilixin vein). The Tashkiney pegmatite vein is similar to Ilixin, but lies in the gneisses of the Olkhon series. It shows high concentrations of Be, Nb, Ta, as well as W, Sn, but lacks Li and F, due to a greater depth and higher temperature of the melt crystallization of this pegmatite.©2024 China Geology Editorial Office.

Late Cryogenian and early Ediacaran rare-metal rich granites in the Eastern Desert of Egypt: constraints from zircon ages and whole-rock Sr- and Nd- and feldspar Pb-isotopic compositions

Rare metals (Nb, Ta, Y, Zr, Sn, U, W and REE) are economically important and new supplies need to be found. In order to understand Neoproterozoic rare metal granites of the Arabian–Nubian Shield (ANS), six samples from five rare-metal mineralized alkali feldspar granites, syenogranites and granodiorite from the Central and SE Desert of Egypt were studied for zircon U–Pb ages and O-isotopic compositions as well as whole-rock Sr- and Nd- and alkali feldspar Pb-isotopic compositions. These are transitional between I-type and A-type granites, mostly high-K calc-alkaline, peraluminous granites with gullwing-shaped REE patterns and strongly negative Eu anomalies. Four granites gave mantle-like zircon δ 18 O V-SMOW between 4.2 and 5.96‰ and yielded ages of 628–633 Ma. This is about when subduction-related magmatism began to be replaced by collision-related magmatism. Igla Ahmr granites are older, formed at 691.7–678.9 Ma with δ 18 O V-SMOW c . 5.95‰. All have positive initial ε Nd values (+3.3 to +6.9) typical for mantle and juvenile crust. Pb isotopic compositions are unusually radiogenic compared with unmineralized ANS granitic rocks. The data indicate similar magmatic sources for ANS mineralized and unmineralized granites. Exploration for other rare-metal mineralized granites in the ANS should focus on bodies with similar characteristics. Supplementary material : Details of analytical details and supplementary tables and figures are available at https://doi.org/10.6084/m9.figshare.c.6949402

Fractal-Based Pattern Quantification of Mineral Grains: A Case Study of Yichun Rare-Metal Granite

The quantification of the irregular morphology and distribution pattern of mineral grains is an essential but challenging task in ore-related mineralogical research, allowing for tracing the footprints of pattern-forming geological processes that are crucial to understanding mineralization and/or diagenetic systems. In this study, a large model, namely, the Segmenting Anything Model (SAM), was employed to automatically segment and annotate quartz, lepidolite and albite grains derived from Yichun rare-metal granite (YCRMG), based on which a series of fractal and multifractal methods, including box-counting calculation, perimeter–area analysis and multifractal spectra, were implemented. The results indicate that the mineral grains from YCRMG show great scaling invariance within the range of 1.04~52,300 μm. The automatic annotation of mineral grains from photomicrographs yields accurate fractal dimensions with an error of only 0.6% and thus can be utilized for efficient fractal-based grain quantification. The resultant fractal dimensions display a distinct distribution pattern in the diagram of box-counting fractal dimension (Db) versus perimeter–area fractal dimension (DPA), in which lepidolites are sandwiched between greater-valued quartz and lower-valued albites. Snowball-textured albites, i.e., concentrically arranged albite laths in quartz and K-feldspar, exhibit characteristic Db values ranging from 1.6 to 1.7, which coincide with the fractal indices derived from the fractal growth model. The zonal albites exhibit a strictly increasing trend regarding the values of fractal and multifractal exponents from core to rim, forming a featured “fractal-index banding” in the radar diagram. This pattern suggests that the snowball texture gradually evolved from rim to core, thus leading to greater fractal indices of outer zones, which represent higher complexity and maturity of the evolving system, which supports a metasomatic origin of the snowball texture. Our study demonstrates that fractal analyses with the aid of a large model are effective and efficient in characterizing and understanding complex patterns of mineral grains.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 7. Genesis of lithium-bearing objects: rare-metal granites of the Ukrainian Shield

In the genetic sense, the following lithium-bearing objects have been characterized: vein Li-F granites and areal Liznykivsky granites of the Korosten pluton, rare-metal granites of the Kamianomohylsky complex, and ongonites of the Azov region. Most researchers consider Li-F granites as the final phase of magmatism of the Korostensky complex. Our conclusion differs from the mainstream view: vein Li-F granites of the pluton are products of crystallization of deep fluid flows that penetrated into the fissure cavities of the pluton rocks after the formation of magmatic massifs. In our opinion, the Liznykivsky granites are metasomatic formations that have developed on different-age rapakivi-like biotite-amphibole granites under the influence of deep fluid flows. The rare-metal granites of the Kamianomohylsky complex form three massifs in the Azov region: Kamiana Mohyla, Katerynivsky and Starodubivsky. Initially, all granite massifs were formed in the process of crystallization of magmatic melt, which later changed to metasomatic alteration of granites. Post-magmatic changes in granites that contributed to the development of rare metal mineralization include: 1) biotitization; 2) microclinization; 3) early albitization; 4) greisenization; 5) late albitization. According to the data of thermobarogeochemical studies, the stage-by-stage development of the post-magmatic alteration of the Kamiana Mohyla granitoids was substantiated and physicochemically characterized: microclinization (500-600 °С), albitization (430 °С), topazization (430 °С), silicification (430-440 °С), sulfidization (320 °С), late albitization (290-420 °С), crystallization of xenotime (200-210 °С), vein fluoritization and the growth of fluorite crystals (125-155 °С). The crystallization of ongonites took place at high temperature, which was 1140 °C at the final stage of quartz phenocrysts growth.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 7. Genesis of lithium-bearing objects: rare-metal granites of the Ukrainian Shield

In the genetic sense, the following lithium-bearing objects have been characterized: vein Li-F granites and areal Liznykivsky granites of the Korosten pluton, rare-metal granites of the Kamianomohylsky complex, and ongonites of the Azov region. Most researchers consider Li-F granites as the final phase of magmatism of the Korostensky complex. Our conclusion differs from the mainstream view: vein Li-F granites of the pluton are products of crystallization of deep fluid flows that penetrated into the fissure cavities of the pluton rocks after the formation of magmatic massifs. In our opinion, the Liznykivsky granites are metasomatic formations that have developed on different-age rapakivi-like biotite-amphibole granites under the influence of deep fluid flows. The rare-metal granites of the Kamianomohylsky complex form three massifs in the Azov region: Kamiana Mohyla, Katerynivsky and Starodubivsky. Initially, all granite massifs were formed in the process of crystallization of magmatic melt, which later changed to metasomatic alteration of granites. Post-magmatic changes in granites that contributed to the development of rare metal mineralization include: 1) biotitization; 2) microclinization; 3) early albitization; 4) greisenization; 5) late albitization. According to the data of thermobarogeochemical studies, the stage-by-stage development of the post-magmatic alteration of the Kamiana Mohyla granitoids was substantiated and physicochemically characterized: microclinization (500-600 °С), albitization (430 °С), topazization (430 °С), silicification (430-440 °С), sulfidization (320 °С), late albitization (290-420 °С), crystallization of xenotime (200-210 °С), vein fluoritization and the growth of fluorite crystals (125-155 °С). The crystallization of ongonites took place at high temperature, which was 1140 °C at the final stage of quartz phenocrysts growth.

Geochemical Evidence for Genesis of Nb–Ta–Be Rare Metal Mineralization in Highly Fractionated Leucogranites at the Lalong Dome, Tethyan Himalaya, China

Leucogranites in the Lalong Dome are composed of two-mica granite, muscovite granite, albite granite, and pegmatite from core to rim. Albite granite-type Be–Nb–Ta rare metal ore bodies are hosted by albite granite and pegmatite. Based on field and petrographic observations and whole-rock geochemical data, highly differentiated leucogranites have been identified in the Lalong Dome. Two-mica granites, albite granites, and pegmatites yielded monazite ages of 23.6 Ma, 21.9 Ma, and 20.6 Ma, respectively. The timing of rare metal mineralization is 20.9 Ma using U–Pb columbite dating. Leucogranites have the following characteristics: high SiO2 content (&gt;73 wt.%); peraluminosity with high Al2O3 content (13.6–15.2 wt.%) and A/CNK (mostly &gt; 1.1); low TiO2, CaO, and MgO content; enrichment of Rb, Th, and U; depletion of Ba, Nb, Zr, Sr, and Ti; strong negative Eu anomalies; low εNd(t) values ranging from −12.7 to −9.77. These features show that the leucogranites are crust-derived high-potassium calc-alkaline and peraluminous S-type granites derived from muscovite dehydration melting under the water-absent condition, which possibly resulted from structural decompression responding to the activity of the South Tibetan detachment system (STDS). Geochemical data imply a continuous magma fractional crystallization process from two-mica granites through muscovite granites to albite granites and pegmatites. The differentiation index (Di) gradually strengthens from two-mica granite, muscovite granite, and albite granite to pegmatite, in which albite granite and pegmatite are highest (Di = 94). The Nb/Ta and Zr/Hf ratios of albite granite and pegmatite were less than 5 and 18, respectively, which suggests that albite granite and pegmatite belong to rare metal granites and have excellent potential for rare metal mineralization.

The Presence of Wodginite in Lithium–Fluorine Granites as an Indicator of Tantalum and Tin Mineralization: A Study of Abu Dabbab and Nuweibi Massifs (Egypt)

This study examines the accessory wodginite and the discovery of titanium-bearing wodginite and Fe and Ti-bearing wodginite in lithium-fluorine granites from the Abu Dabbab and Nuweibi massifs in Eastern Egypt. The wodginite group’s mineral association includes tantalum-bearing cassiterite and tin-bearing tantalum–niobate minerals: tantalite-(Mn), columbite-(Mn), and microlite. Three forms of wodginite crystallization were identified: (1) rims around columbite-(Mn) and tantalite-(Mn) varying from 1.5 to 21.9 μm in thickness, (2) micro-inclusions in cassiterite ranging from 5.4 to 27.0 μm in size, and (3) autonomous crystals measuring 3–124 μm in length. Wodginite in the Nuweibi massif is mainly found in porphyritic granite of late-stage porphyry intrusion. It has a similar composition to the worldwide wodginite of rare-metal granites, but exhibits a lower content of TiO2 (average 0.54%) and is a mineral indicator of rich tantalum ore deposits. In contrast, wodginite in the Abu Dabbab massif is replaced by titanium-bearing wodginite (Ti/(Sn + BTa + Ti + Fe3+) = 0.23) and is associated with Fe and Ti-bearing wodginite. Wodginite and Ti-bearing wodginite are maximally enriched in manganese (Mn/(Mn + Fe2+ +Ca) = 0.95), expressed in all intrusive phases of the massif, and are mineral indicators of tantalum-bearing granites with associated cassiterite-quartz mineralization.

Trace element compositions and geochronology of cassiterite from the Bushveld Large Igneous Province, South Africa

This study presents trace element compositions and ages of four representative cassiterite samples from the Zaaiplaats, Union and Rooiberg Sn fields, all spatially associated with the Bushveld Large Igneous Province (LIP), South Africa. The Zaaiplaats Sn field is endogranitic and entirely hosted within the variably-altered Bobbejaankop and Lease granites of the Lebowa Granite Suite. In contrast, the exogranitic Union and Rooiberg Sn fields occur within the Union Tin Member of the Rooiberg Group, and the Pretoria Group of the Transvaal Supergroup, respectively. Collectively, all the cassiterite samples display quasi-parallel chondrite-normalised rare earth element (REE) patterns characterised by relative enrichments in the heavy REE, and yielded ages varying within a relatively restricted interval between 2061 ± 40 Ma and 2054 ± 3 Ma. This age range compares well with those reported from the Bushveld LIP and, when combined with mineral compositions, suggests a common granitic source for cassiterites from all the Sn fields. The exogranitic Rooiberg and Union Sn fields are identified by cassiterites with Zr/Hf of ∼40, whereas the endogranitic Zaaiplaats Sn field is characterised by cassiterites enriched in most incompatible elements (e.g., Nb, Ta, Zr, Hf, In, F and B) and Zr/Hf of ∼10. These Zr/Hf ratios agree with the endogranitic and exogranitic Sn ores from other localities, but are different from the very low Zr/Hf ratios of ∼3 reported for endogranitic cassiterites associated with rare-metal granites. The Zr versus Hf discrimination diagram may therefore be useful for distinguishing the endogranitic and exogranitic origins of cassiterites and for identifying the extent of fractionation of the causative source.

Origin, dynamics, and chemical evolution of garnet-bearing leucogranitic magma, Eastern Desert of Egypt: Controls on the rare-metal enrichment in the A-type magmatism

Egypt hosts numerous rare-metal granites, i.e., highly evolved granites enriched in rare metals (Ta, Nb, Be, Sn, Zr, Th, and REE). However, the processes involved in the rare-metal enrichment are not fully understood. We present new data on the textural characteristics and chemical composition of rare-metal mineralization associated with microgranite dikes in the Ras Abdah area of the Egyptian Eastern Desert. These dikes are garnet-bearing leucogranites (GLG) composed of perthitic alkali-feldspars and quartz. When compared to other Egyptian A-type granites, microgranite dikes are alkaline rocks with particularly higher HREE contents. Zircon, huttonite, fergusonite (Y), and Fe-Ti-Zn oxides (magnetite, Zn-bearing ilmenite and pyrophanite) are largely associated with the altered domains, which are also enriched in Nb, Zr, Y, Ta, Th, and REE. However, similarities between the chondrite-normalized REE patterns of the altered and unaltered domains of the GLG dikes favor the hypothesis of a unique magmatic signature. Moreover, the chemical and textural features of rare-metal minerals indicate that the alteration of primary minerals was caused by deuteric fluids or aqueous residual melt exsolved from the parental granitic magma (autometasomatism). Garnet compositions are rich in the spessartine component (up to 84 %), which is typical of garnet in highly evolved pegmatitic rocks. Furthermore, garnet exhibits no major element zoning but shows chemical fluctuations in trace element concentrations, suggesting correspondingly abrupt changes in melt composition due to sequential magma pulsing. This magma emplacement may cause crystal nucleation and oscillatory crystallization followed by magmatic segregation. Overall, parental magma type, dike injection, and magmatic-hydrothermal processes all play a role in the unusual enrichments of rare metals.

Age and Isotope-Geochemical Characteristics of Ta, Nb, W, Sn Mineralization Associated with Rare-Metal Granites (Khangilay Ore District, Eastern Transbaikalia)

The age relations between the formation of the parent massif and the crystallization time of the associated ore mineralization were established based on isotope-geochronological study of the massif-deposits of the Khangilay ore cluster with various metallogenic specialization in Eastern Transbaikalia. In the Orlovka Li–F granite massif, the crystallization time of columbite–tantalite (145 ± 1 Ma) and cassiterite (144.2 ± 0.3 Ma) (U-Pb, ID-TIMS) is almost identical to the crystallization time of zircon (140.6 ± 2.9 Ма (U-Pb, SHRIMP) and 145 ± 1 Ma (U-Pb, CA-ID-TIMS)), which is an age marker of the formation of massifs. This fact testifies to the magmatogenic nature of rare-metal mineralization. In the Spokojnoye massif – the “standard type” of rare-metal peraluminous granites—a 0.6–3.8 Ma time gap was revealed between the time of massif formation (141.3 ± 1.8 Ма, U-Pb, SHRIMP, 146.9 ± 0.7 Ма, Rb-Sr isotopic system) and crystallization of wolframite (141.8 ± 0.6, Rb-Sr isotopic system and 140.1 ± 1.4 Ма, Sm-Nd isotopic system). This interval likely corresponds to the life time of the hydrothermal system, which produced tungsten mineralization.

Characterization and Liberation Study of the Beauvoir Granite for Lithium Mica Recovery

A significant proportion of Europe’s lithium endowment is hosted by unconventional lithium resources such as rare-metal granites (RMG) of which the Beauvoir granite in France is a prime example. In such hard-rock deposits, where lithium is mostly hosted in micas (lepidolite, zinnwaldite), the ability to assess whether lithium can be extracted economically from the ore is essential and requires a comprehensive understanding of mineralogical properties and lithium deportment. Using three exploratory drill cores distributed along the North–South axis, a preliminary geometallurgical assessment of the granite has been conducted based on a combination of techniques including Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES), Atomic Adsorption Spectroscopy (AAS), Electron Probe Microanalysis (EPMA), Scanning Electron Microscope (SEM) coupled with automated mineralogy software, X-Ray Diffraction (XRD), optical microscope and sieving. Lithium distribution appears to be variable, reflecting the evolution of the granite, with higher mica content in the southern area and higher Li grade towards the center of the orebody. The size of micas in the assessed sample does not vary significantly. The grindability and liberation size of micas varies in the different zones investigated, PERC S being the most difficult to grind. There is always more than 50 wt% of the micas that are liberated in the samples when crushed to 1 mm. Indirect estimation of Li content based on EPMA and SEM analysis suggests that the content of lithium inside mica crystals could vary. If this estimation is confirmed by direct Li measurement, it for sure makes the calculations of the Li deportment more challenging.

Key Factors Controlling Biotite–Silicate Melt Nb and Ta Partitioning: Implications for Nb−Ta Enrichment and Fractionation in Granites

AbstractBiotite–melt Nb and Ta partition coefficients (DNb and DTa) are crucial for understanding Nb−Ta enrichment and fractionation in rare metal granites (RMGs). However, the key factor(s) affecting biotite–melt DNb, DTa, and DNb/DTa values remain unclear. To elucidate the physicochemical factors that control the partition coefficients, we performed piston−cylinder experiments at 0.5−1.0 GPa and 850−1000°C with H2O‐added (4−10 wt.%) mixtures of granitic and biotitic glasses as starting materials. Two series of experiments (graphite‐buffered and unbuffered fO2 conditions) were conducted with calculated fO2 values ranging from ∼FMQ–1.5 to ∼FMQ+4. Under these experimental conditions, biotite–melt DNb, DTa, and DNb/DTa values are 0.30–2.63, 0.24−1.02, and 1.01−2.15, respectively. Biotite–melt DNb, DTa, and DNb/DTa values increase with decreasing melt NBO/T value (non‐bridging oxygens per tetrahedron), melt H2O content, and biotite Mg#T value [molar 100 × MgO/(MgO + FeOT)]. In addition, DNb and DTa exhibit good correlations with DTi, suggesting that DNb and DTa are predictable via DTi values. With our and literature data, we used multiple linear regressions to obtain empirical expressions of DNb and DTa as functions of the three parameters. By applying the empirical models to granite differentiation process, we found that ∼99% crystallization of biotite ± muscovite‐bearing assemblages results in an enrichment in magma Ta contents by &gt;10 times with a decrease in Nb/Ta values from 10−13 to ∼1, which reproduces the Ta–Nb/Ta features of most RMGs. However, additional processes, such as columbite‐group mineral precipitation, may be required to account for the extremely low Nb/Ta values (&lt;1) of some RMGs.