Rare-metal Pegmatites Research Articles

Genetic linkage between parent granite and zoned rare metal pegmatite in the Renli-Chuanziyuan granite-pegmatite system, South China

Elucidating the causal relationship between parent granite and pegmatite and tracing the magmatic-hydrothermal evolution and rare metal mineralization are intriguing scientific issues that remain unsolved. The Renli-Chuanziyuan granite-pegmatite field, hosted in and adjacent to the Mufushan batholith, represents a significant rare metal ore district in southern China. The field reveals well-defined regional zonation, encompassing biotite, two-mica, and muscovite monzogranites at the core, which transition outward to microcline (K-pegmatite), microcline-albite (K-Na-pegmatite), albite (Na-pegmatite), and albite-spodumene pegmatites (Na-Li-pegmatite) at the southwestern margin of the Mufushan batholith. The U-Pb ages of the columbite-tantalite (coltan) grains from the Na-Li-pegmatite samples from the Chuanziyuan deposits are 139.1 ± 1.2 Ma and 138.6 ± 1.1 Ma, which are consistent with the ages of the coltan grains from the Renli deposit, indicating contemporaneous mineralization. Chemical analyses of muscovite, garnet, and coltan from various pegmatite zones reveal a gradual increase in the degree of differentiation and volatile components of the Early Cretaceous magmatic system from north to south. Particularly noteworthy is the significant increase in the abundance of Na-Li-pegmatites to the south, signifying the transition from an early melt stage with a minor fluid component to a melt-fluid stage with a substantial volume of unmixed fluid. This evolution led to the enrichment and precipitation of Nb and Ta in the Renli deposit and of Li in the Chuanziyuan deposit, which were facilitated by the separation and exsolution of flux-rich (e.g., F, H2O) fluid. The highly evolved ca. 140 Ma muscovite monzogranite exhibits a well-defined spatial and temporal relationship with rare metal pegmatites, providing strong evidence of genetic associations. Furthermore, the geochemical characteristics of muscovite and garnet from the muscovite monzogranite overlap with those of mineralized pegmatites, further suggesting (together with the simulation study) that the muscovite monzogranite served as the parental granite of the mineralized pegmatites. These findings underscore the importance of understanding the evolution of the granite-pegmatite system, particularly in the context of rare metal exploration, and contribute to a deeper understanding of the ore-forming mechanisms of zoned rare metal pegmatites.

Using tourmaline to trace Li mineralization in the Mufushan granitic batholith, South China

Granites and rare metal pegmatites of the Mufushan granitic batholith form a continuous magmatic sequence linked by fractional crystallization. Tourmaline is present in muscovite leucogranites and all types of pegmatites, including highly evolved Li-rich pegmatites. We utilized major element, trace element and in-situ B isotope analyses of tourmaline to investigate the effects of magmatic fractional crystallization and magmatic volatile phase (MVP) exsolution on Li migration and exceptional Li enrichment. Eight types of tourmaline are identified across three rock units: (i) Isolated (Tur Ia) and nodular (Tur Ib) tourmaline within muscovite leucogranites; (ii) black tourmaline in veins and/or clusters (Tur IIa), as isolated crystals (Tur IIb) and in tourmaline-quartz segregations (Tur IIc) within Li-poor pegmatites; and (iii) tourmaline as isolated pink crystals with zoning patterns (Tur IIIa), as isolated pink crystals and/or radiating clusters (Tur IIIb), and as isolated crystals enclosed in quartz block (Tur IIIc) within Li-rich pegmatites. Tourmaline in Mufushan muscovite leucogranites and Li-poor pegmatites belongs to the alkali-group and schorl series with Mg/(Mg + Fe) ratios of 0.10–0.31 and 0.12–0.48, respectively, containing almost no Li* and F. In contrast, tourmaline in Li-rich pegmatites exhibits schorl-elbaite and elbaite-rossmanite compositions with low Mg/(Mg + Fe) ratio (avg. = 0.01), and evolved Li* (0.01–0.90 apfu, avg. = 0.41 apfu) and F (0.00–0.91 apfu, avg. = 0.36 apfu) contents. A pronounced increase in YAl, (Li* + Mn) contents, and Y[Al/(Al + Fe)] ratio is observed across the transition from Li-poor to Li-rich pegmatites, consistent with the anticipated pattern of fractional crystallization. The concentration of Li exhibits a sharp increase in Li-rich pegmatites (avg. Li = 6786 ppm) compared to Li-poor pegmatites (avg. Li = 114 ppm) and leucogranites (avg. Li = 469 ppm). Lithium contents increase and reach a peak during the crystallization of Tur IIIb (6686–11,667 ppm), and have lower peak contents during the precipitation of Tur IIIc (8261–9160 ppm), indicating that the incorporation of Li is influenced by MVP accumulation and exsolution. MVP exsolution significantly reduces the solubility of Nb, Ta, and Be in the residual melt, promoting the precipitation of beryl and columbite group minerals and facilitating the migration of fluid-mobile elements such as Li, Rb, Cs, and Ga to form lepidolite. The B isotope compositions of tourmaline range from −14.8 ‰ ~ −12.6 ‰ in Li-poor pegmatites to −17.1 ‰ ~ −14.0 ‰ in Li-rich pegmatites. Rayleigh fractionation modeling reveals that MVP saturation occurs after approximately 60 % B was removed from the pegmatite melt. The compositional variation of tourmaline demonstrates that Li enrichment is not only governed by continuous fractional crystallization, but also by MVP-related accumulation and exsolution mechanism.

Sediment-derived granites as the precursor of rare-metal pegmatites in the Paleo-Tethys tectonic zone – evidence from the Bailongshan Li-Rb-Be pegmatite ore field and factors controlling mineralization

Sediment-derived granites as the precursor of rare-metal pegmatites in the Paleo-Tethys tectonic zone – evidence from the Bailongshan Li-Rb-Be pegmatite ore field and factors controlling mineralization

Internal structure and patterns of distribution of mineral types of rare metal pegmatites in the Darai Pech valley (Kunar province, Afghanistan)

Internal structure and patterns of distribution of mineral types of rare metal pegmatites in the Darai Pech valley (Kunar province, Afghanistan)

Evolution of the rare-metal mineralization system associated with collision-related pegmatites in the western Altyn Tagh Orogen, Tugeman, NW China

On a regional scale, rare-metal pegmatite groups (pegmatites of common origin) display a zonal distribution with different chemical compositions. Whether the regional distribution of such pegmatites dike in a convergent zone is related to dehydration melting of different micas remains unclear. In recent years, the Altyn Tagh Orogen (ATO) in the northwest China has gained attention due to economically significant rare-metal mineralization. Our study focuses on the geochronology of columbite-group minerals (CGMs) and geochemistry of tourmaline from the Be-mineralized pegmatites in the Tugeman and Ayage Be deposits. CGM dating shows that these Be-mineralized pegmatites formed between 485 and 484 Ma. Subsequent hydrothermal activity, occurring around 453–450 Ma, is related to the development of a ductile shear zone. Evidence from tourmaline mineralogy and major elements reveals that the evolution of the Be-mineralized pegmatite is influenced by crystallization differentiation and subsequent fluid exsolution. Tourmalines from these pegmatites exhibit B isotope compositions ranging from –12.2 ‰ to –14.8 ‰, indicating a crustal metasediment source. Based on these findings, we propose a model for the rare-metal mineralization system in the Tugeman area: the sequential formation of Be to Li-mineralized pegmatites likely results from dehydration melting of muscovite and biotite during prolonged subduction and collision between the South Altyn Subduction–Collision Belt (SAB) and Central Altyn Block (CAB).

Neoarchaean and Palaeoproterozoic tectono-metamorphic events along the southern margin of the Zimbabwe craton: Insights from muscovite 40Ar/39Ar geochronology from rare-metal pegmatites, Zimbabwe

Muscovite 40Ar/39Ar geochronology on ten samples from complex-type, rare-metal (e.g., Li, Cs, Ta, Rb, Be, Nb, Sn and W) pegmatites from the Bikita and Mweza pegmatite fields in Zimbabwe yield ages that range from ca. 2622–1940 Ma. One pegmatite from the Bikita field yield a relict age of ca. 2622 Ma which is similar to the ca. 2.62 Ga emplacement age of the Main Bikita Pegmatite previously determined by laser ablation analyses of Ta–Nb–Sn oxides. Younger muscovite 40Ar/39Ar ages of ca. 2580–2539 Ma in the Bikita field may reflect post-pegmatite emplacement tectono-thermal events under fluid-mediated conditions. Data from the Mweza pegmatite district yield dates of ca. 2027–1940 Ma which reflect a Palaeoproterozoic overprint. Palaeoproterozoic 40Ar/39Ar ages are spatially restricted to near the Northern Marginal Zone–Zimbabwe Craton boundary and are absent towards the interior of the craton in the Bikita pegmatite field.

Li-mineralized pegmatite of anatectic origin: Constraints from Li[sbnd]Hf isotopes and geochemical modeling

Pegmatites are important reservoirs of lithium resources. There is an ongoing debate as to whether Li-mineralized pegmatites were generated from evolved granitic systems via extreme differentiation or by direct melting of metasedimentary rocks. The Chinese Altay is one of the largest pegmatite provinces in the world, and includes many rare-metal pegmatites (e.g., Koktokay, Kelumute, Kaluan and Azubai). However, they display significant differences in formation ages and isotopic compositions compared with the neighbouring or potential parental granites. In this contribution, we present a case study of the Kaluan Li ore deposit in the Chinese Altay, elucidating the origins of pegmatites and related Li mineralization. The Kaluan Li-mineralized pegmatites are characterized by high SiO2, K2O, Na2O, Li, Cs, Ta, and Rb contents; low Fe2O3T, MgO, Ba, and Sr contents; and peraluminous signatures. They have homogeneous HfLi isotopic compositions (εHf (t) = −0.6 to +2.5; δ7Li = +1.6 to +5.8‰) that are within the range of HfLi isotopic compositions of the Kulumuti Group schists (εHf (t) = −2.8 to +7.5; δ7Li = −8.6 to +10.8‰). In addition, the chemical compositions of the melt derived from the partial melting of the Kulumuti Group by phase equilibrium modeling are compatible with our analyses of the Kaluan Li-mineralized pegmatites. These similarities suggest that the Kaluan Li-mineralized pegmatites were derived from the partial melting of the Kulumuti Group schists at depths during the Triassic, in a post-orogenic and extensional setting. The generation of these pegmatites was mostly controlled by biotite dehydration melting at relatively high temperatures, rather than by the low-temperature melting of muscovite. Trace elements modeling results show that approximately 33–36% partial melting of the average Kulumuti Group schist may produce melts with maximum Li concentrations ranging from 664 to 751 ppm. Subsequently, a high degree of fractionation exceeding 85%, was required for the Li concentration of the residual melt to reach concentrations suitable for crystallization into albite-spodumene pegmatites. Based on our research, an anatectic origin model may have general applicability in explaining the genesis and mineralization of rare-metal pegmatites in the Chinese Altay.

Geological and geochemical analyses of pegmatites in Egbe, Isanlu (sheet 225), Southwestern Nigeria

The hitherto pegmatite of the Egbe area has been known to bear valuable economic minerals. They are associated with other rock types including banded gneiss, schist, amphibolite, and granites. These pegmatites and the host rocks were studied in detail to elucidate their petrochemical and geochemical features and also to assess the mineralization of Tantalum- iobium and other minerals. Geological field mapping was done, thin section-petrographic analysis of ten representative rock samples was performed and nineteen whole-rock samples were analyzed for major and trace elements including REES aided by Inductively Coupled Plasma Mass Spectrometry (ICP-MS), Boron- Fusion-Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES), and Ion-Selective Electrode (ISE) for Fluorine at Acme Laboratory, Vancouver, Canada. The general structural trend of the area under study is WNW-ESE and foliations of N-S strike were observed in the banded gneiss and schist which also exhibit asymmetric and isoclinals folding respectively. The tantalite-columbite mineralization is associated with the NE-SW trending pegmatite dykes. The mineralized pegmatites are genetically related to the peraluminous S-type granite. The minerals (i.e., Albite, lepidolite and muscovite) extracted from the pegmatites are well enriched in Li, Rb, Cs, Nb and Ta compared to the host rocks. The rare-metal pegmatites exhibit pronounced negative Ce and Eu anomalies and also show weak negative Yb anomalies while the barren pegmatites have positive Ce and weak negative Eu anomalies and exhibit weak positive Yb anomalies. The pegmatites are moderately evolved compared with other highly mineralized pegmatites. The pegmatites from Igbaruku and one from the Okere area are of the rare-metal pegmatite and they are moderately fractionated while the barren pegmatite from Egbe and one from Okere are unfractionated. The economic mineral within the Egbe area is tantalite, with every possibility that the tantalite-columbite enrichment is ferrotantalite-columbite and manganotantalite columbite.

Petrogenesis of the Late Triassic Habake granitic pluton, the West Kunlun Orogen, Western China: Tectonic implications for the evolution of the Paleo-Tethys

Recent discoveries of rare metal pegmatite deposits in the West Kunlun region are believed to be related to Triassic granites. However, the tectonic background of the mineralization in this region is currently unclear. Additionally, the mineralization potential of the granite must be determined to assess whether further exploration is warranted. This paper reports whole-rock elemental and Sr-Nd isotopic compositions, and zircon U-Pb ages and Lu-Hf isotopic compositions for the Habake granitic pluton. The zircon U–Pb dating revealed that these rocks formed in the Late Triassic (210–205 Ma). The two-mica granites are strongly peraluminous high-K calc-alkaline series rocks, with initial 87Sr/86Sr ratios of 0.71294 ∼ 0.71428, εNd(t) values of −7.79 ∼ -8.15, and εHf(t) values of −1.77 ∼ −32.22; these values are similar to those of Triassic BaryanHar Group graywacke rocks. The other granites are weakly peraluminous high-K calc-alkaline series rocks, with initial 87Sr/86Sr ratios of 0.70820 ∼ 0.70823 and 0.70942 ∼ 0.71041, εNd(t) of −3.81 ∼ -4.11 and −5.33 ∼ -5.40, and εHf(t) of −0.90 to +7.02 and −1.39 to −7.68, indicating that the granodiorite and biotite granite were respectively derived from partial melting of the juvenile crust and older lower crust in continental collision stage. Our new data show that the end of the continental collision between the South Kunlun Terrane (SKT) and Tianshuihai terrane (TST) likely occurred after 209 Ma. After analysis of the ore-forming parent rocks of the rare metal pegmatites, the graywacke-derived Habake two-mica granites, has lower Li contents that too low(<150 ppm), indicating that they did not form the rare metal pegmatites.

Mechanism of beryllium mineralization in a granite-pegmatite system: Constraints from ore geology and beryl mineralogy of the large Arskartor Be-Nb-Mo deposit, southern Chinese Altai

The Arskartor Be-Nb-Mo deposit is the second largest Be deposit in the Chinese Altai, NW China, which hosts over 11,000 tons of BeO resource. The muscovite-albite granite and rare-metal pegmatite in the ore district are spatially and temporally coexisted and both are beryllium mineralized. The muscovite-albite granitic stock can be divided into a barren zone and a Be-mineralized zone. The pegmatite shows an well-developed internal zone including the layered muscovite-quartz-albite zone, (lower) beryl-muscovite-quartz zone, quartz core, (hanging) beryl-muscovite-quartz zone, and muscovite-quartz-microcline zone. Beryl is the dominant Be-bearing mineral and mainly occurs in the Be-mineralized granite, the layered muscovite-quartz-albite and the beryl-muscovite-quartz zones of the pegmatite. Subhedral to euhedral beryl in the Be-mineralized granite is interstitial to or intergrown with rock-forming minerals. In contrast, beryl crystals in the pegmatite are coarser in grain size and more euhedral in shape, and mainly coexist with coarse “booked” muscovite and blocky quartz. Concentrations of Li, Cs and Na/Li ratios of beryl are 184–760 ppm, 218–1996 ppm, and 2.13–21.3, respectively. The progressive variations of incompatible elements compositions and Na/Li ratios are consistent with the fractional crystallization mechanism of the granite-pegmatite system. Paragenesis and internal structure of beryl suggest nonequilibrium crystallization of a relatively incompatible elements and fluxes-enriched late granitic melt, generated the coarse-grained Be-mineralized granite. With the progressive enrichment of incompatible and fluxing elements and decreasing temperature, liquidus overcooling was achieved and generated the aplite and immediate zoned pegmatite that hosts abundant beryl. Moreover, the differentiating pegmatitic melt with varying amounts of aqueous fluids at different melt fractions, likely resulted in heterogeneous distribution of beryllium and subsequent variable amounts of beryl crystallization in different internal zones. The exsolution of aqueous fluids from the residual pegmatitic melt resulted in Mo-mineralization and related hydrothermal alteration. Consequently, both protracted fractional crystallization and subsolidus processes contributed the formation of the Arskartor granite-pegmatite system with Be-polymetallic mineralization.

Characteristics and formation of rare-metal pegmatites and granites in the Duanfengshan-Guanyuan district of the northern Mufushan granite complex in South China

The Mufushan area, which has abundant rare-metal pegmatites within and around the Mufushan Granite Complex, has become a major target for Ta-Nb-(Li-Be) exploration in South China. The age and origin of the pegmatites and associated rare-metal mineralization are still under debate. Here, we report the in situ U-Pb ages and geochemical characteristics of granites and pegmatites in the Guanyuan and Duanfengshan districts, which are located in the central and northern parts of the Mufushan Complex. Combined zircon, apatite and monazite U-(Th)-Pb dating revealed that biotite, two-mica, and muscovite granites from the Guanyuan and Duanfengshan districts were emplaced at 143–139 Ma, which overlaps with the U-Pb ages of columbite-group minerals (CGM) from different internal zones of the Duanfengshan pegmatites (142–140 Ma). Whole-rock major and trace element compositions and Sr-Nd-Hf isotope data reveal that the granites and pegmatites experienced continuous evolution from biotite, two-mica, and muscovite granites to pegmatite and that the magma originated from the partial melting of mica schists that are abundant in the Mufushan area. Temporal, chemical and mineralogical evidence indicates a genetic link between muscovite granite and Ta-Nb pegmatites. The textures and chemical compositions of CGM from different pegmatites exhibit features typical of magmatic CGM, indicating that fractional crystallization was the driving force that promoted Ta-Nb enrichment. The increasing alumina saturation index [ASI: molar Al/(Ca–1.67P + Na + K)] of pegmatitic melt due to albite crystallization may have been the main factor controlling CGM deposition, explaining why major Ta-Nb mineralization is bound to albite pegmatites. The Duanfengshan and other rare-metal pegmatites in the Mufushan area are derivatives of the most evolved granitic facies (i.e., muscovite granite) of the Mufushan Complex. The Duanfengshan and Renli pegmatite fields indicate that the Early Cretaceous (∼140 Ma) may have been an important, underappreciated epoch for the formation of pegmatite-related rare-metal resources in the Mufushan area and beyond in South China.

Tourmaline geochemical and boron isotopic compositions of the Bailongshan rare-metal pegmatite deposit: Implications for magmatic-hydrothermal evolution of the West Kunlun Orogen (NW China)

The Bailongshan in the West Kunlun Orogen (northern Tibet) is a newly-discovered super-large rare-metal (Li-Rb(-Be-Ta-Nb)) pegmatite deposit. Tourmaline occurs widely in muscovite granites and pegmatites at Bailongshan, but comprehensive study is yet to be done on the geochemical evolution of tourmaline from the magmatic to the hydrothermal stages. Here, we present a systematic study of in-situ major, trace elemental and boron isotopic variations of tourmaline from Bailongshan deposit, and discuss the tourmaline genesis and how boron isotopes change during the magmatic to hydrothermal stage. Three types of tourmaline have been identified at Bailongshan deposit, including disseminated tourmaline in the muscovite granite, medium-coarse-grained euhedral tourmaline in the barren pegmatite, and multicolored medium-coarse-grained tourmaline in the ore-bearing pegmatite. EPMA and LA-ICP-MS geochemical analyses reveal that the tourmaline samples belong mainly to alkali group, with the tourmalines from the muscovite granite and the barren pegmatite falling into the schorl solid-solution series and the ore-bearing pegmatite falling into elbaite. There is a major chemical change from Fe-rich compositions with moderate Al in the Y-sites (muscovite granite and barren pegmatite) to Li-rich compositions with high YAl and relatively high F (ore-bearing pegmatite). Most trace element contents vary over several orders of magnitude with median concentrations of 0.1–10 μg/g. High concentrations are found for Ga, Zn, Be, Sc, Sn and Li (several tens to thousands of μg/g), whereas low concentrations (<0.1 μg/g) are found for V, Rb, U, Th, W, and Hf. The tourmalines from muscovite granite and barren pegmatite yielded δ11B = -8.9 to −7.5 ‰ and −8.7 to −6.0 ‰, respectively, whilst the tourmaline in the ore-bearing pegmatite show a wider δ11B range (-8.8 to −5.2 ‰). The B isotopic values indicate a source of the continental crust in a post-collisional setting. The estimated δ11B value of parental granitic magma is −10.0 ‰. The overlap in δ11B values between muscovite granite and barren pegmatite indicates a little isotopic fractionation between tourmaline and melt. Rayleigh fractionation results in the observed δ11B decrease from zone I (-6.9 ‰) to zone V (-8.0 ‰). After the barren-pegmatite-hosted tourmaline formation, the δ11B value of boron-rich magma would have been about −11.5 ‰. The intragrain δ11B variation of tourmaline in the ore-bearing pegmatite is 2.7 ‰, much larger than that from the other zones, indicating the rim of the tourmaline crystallized from fluid exsolved. We calculated the boron-isotope fractionation (between fluid and melt) to be 4.2–5.7 ‰ at 600–450 °C. Chemical variations in tourmaline are continuous in the muscovite granite and barren pegmatite, consistent with fractional crystallization, whereas the tourmaline from the ore-bearing pegmatite may have formed during the magmatic-hydrothermal transition. The boron isotopic variations could be attributed to fractionation between melt-tourmaline, melt-fluid and tourmaline-fluid and Rayleigh fractionation.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 5. Mineralogy of lithium-bearing objects: lithium minerals

The fifth part of the publication "Lithium in the depths of Ukraine" is devoted to the mineralogy of lithium — silicates and phosphates, but without lithium micas, which, together with other micas, are described in Part 4. Here, the following lithium minerals are characterized in varying detail (the Li2O content of the mineral (mas. %) is given in parentheses after the formula): eucryptite — LiAl[SiO4] (11.80), elbaite Na(Al,Li)3Al6(BO3)3(F,OH)4[Si6O18] (1.1—1.4); spodumene — LiAl[Si2O6] (5.9—7.6); holmquistite Li3Mg3Al2(OH)2[Si8O22] (2.1—3.5); petalite — Li[AlSi4O10] (2.0—4.1); margarite — CaAl2(OH)2[Si2Al2O10]-(Li,Be) (1.82); donbasite — Al2[(Si3Al)O10](OH)2·Al2.33(OH)6 (0.1—3.0); cukeite (Al,Li)3Al2[(Si,,Al)4O10](OH)8 (0.8—4.3); triphillite — Li(Fe2+,Mn2+)[PO4] (5.51—8.62); lithiophyllite — Li(Mn2+,Fe2+)[PO4] (5.50—8.60); amblygonite LiAl(F)[PO4] (6.4—9.0); montebrasite — LiAl(OH)[PO4] (10.7—11.1); simferite — Li(Mg,Fe3+,Mn3+)2.0[PO4] (5.35—5.45). The description of these minerals is supplemented by a summary table of the mineral composition of rare metal pegmatites, selected according to the quantitative ratio of the main ore minerals — spodumene and petalite. The latter are not the first phases of crystallization of the pegmatite melt, so their distribution in space is close to the following pattern: the highest content of ore minerals is concentrated between the peripheral zones and cores of pegmatites. Spodumene and petalite of Ukrainian pegmatites, in comparison with similar minerals of large global lithium deposits, differ in the following features: 1) smaller sizes of mineral individuals; 2) greater xenomorphism of mineral individuals; 3) a weaker manifestation of isomorphic substitutions of atoms.

Chemical and boron isotope composition of tourmaline from Koktokay pegmatite, Altay Orogenic Belt, Northwest China: Implications for metallogenic mechanism and prospecting indicator for rare-metal pegmatites

The metallogenesis of Li-rich pegmatites remains contentious and an innovative approach for exploring such deposits is needed. The well-known Koktokay pegmatites in the Altay Orogenic Belt exhibit various mineralization degrees and patterns. In this study, we conducted systematic elemental and boron isotope analyses on five tourmaline samples to decipher the metallogenic mechanism and prospecting indicators of rare metal pegmatites. KKTH2 and KKTH3 were collected directly from the magmatic stage and magmatic–hydrothermal stage of the No. 3 pegmatite, KKTH1 was collected from the Aikoz mine pit, and KKTH4 and KKTH5 were collected from a small operational mine near the No. 3 pegmatite. Unlike the No. 3 pegmatite, this mine produces gem crystals but lacks Li mineralization. All tourmalines belong to the alkali group, whereby KKTH1 and KKTH2 are classified as fluor-elbaite, whereas KKTH3 and KKTH4 are schorl. The tourmaline in KKTH5 shows high Al content (up to 45.30 wt%), classifying as mostly rossmanite–elbaite series, with minor amounts of olenite and liddicoatite.A Rayleigh fractionation model yields a shift in △11B value of 4.8‰ between Zone IV and VI involved more than just magma, as B-isotope fractionation between tourmaline and melt would be <1‰ when temperature drop from 650 °C to 500 °C. It further indicates that different parts of No. 3 pegmatite may have originated from diverse sources.After comparing the δ11B values of tourmaline in this study with other fertile and barren pegmatite globally, we suggest that δ11B values of tourmaline higher than −10‰ is a potentially useful indicator for Li-rich pegmatites because of the likely relationship with marine evaporite or carbonate rocks in the source. Furthermore, we propose that tourmaline with a V/Sc value lower than 1 and a Li/Sr value higher than 100 can be used as indicators for Li exploration. The extent of Li migration from magma into the hydrothermal stage and mineralized in the residual melt correlates with the salinity of magma, which may reasonably explain the less intense wallrock alteration near the No.3 pegmatite. This finding provides new insight into the use of trace elements and boron isotope composition as a guide for exploring Li-rich pegmatites.

Zircon and cassiterite U-Pb geochronology and petrochemical characteristics of early Tertiary tin mineralization at Mayo Darlé, Cameroon Volcanic Line

Tin mineralization at Mayo-Darlé in the Cameroon Volcanic Line is associated with highly evolved anorogenic ferroan granite magmatism with a pervasive hydrothermal overprint. Mineralization occurs as cassiterite-quartz-muscovite stockwork and disseminated in quartz-mica and quartz-topaz greisen in low-Ca alkali feldspar granite with a composition near the 1 kbar haplogranitic thermal minimum. The trace element composition of zircon indicates elevated temperature (880 ± 55 °C) and very low oxidation state below the quartz-fayalite-magnetite buffer. Laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) identifies a partly disturbed U-Pb system for igneous zircon (U and Th contents >1000 ppm) but defines Tera-Wasserburg concordia ages and common-lead-corrected weighted 206Pb/238U ages of about 54 Ma, similar to a previous 87Rb/86Sr vs 87Sr/86Sr regression with a date of 56.1 ± 1.7 Ma (MSWD = 58; n = 9) and an initial 87Sr/86Sr ratio of 0.7085 ± 0.0035 (2 s). Hydrothermal cassiterite gives a pooled LA-ICPMS Tera-Wasserburg concordia age of 56.7 ± 0.6 Ma on two samples (each about 20 points, MSWD = 0.54 and 1.3). These new age data define a period of early Cenozoic intraplate calc-alkalic felsic magmatism as a precursor to abundant Oligocene to Recent alkali basalt volcanism along the Cameroon Volcanic Line. Geochemical and Sr–Nd–Hf isotopic data suggest that the granitic rocks from Mayo Darlé were largely derived by partial melting of Mesoproterozoic basement and modified by strong differentiation, all likely powered by heat (and possibly fluids) from the mantle. The Tertiary age of the rare-metal magmatism sets this system apart from the widespread Late Neoproterozoic to Early Paleozoic rare-metal pegmatites and granites in the Pan-African collisional belts of Africa, and also from the anorogenic Mesozoic ring complexes in Central Nigeria.

The origin of Xuefengling rare metal pegmatites and implications for ore prospecting in West Kunlun Orogen, China

The Xuefengling rare metal pegmatite deposit is located in the West Kunlun orogenic belt, Northwest China. It is one part of the Bailongshan orefield, which is located 5 km southeast of the Bailongshan deposit, and it is composed of the Xuefengling, Xuepen, Longmenshan and Shuangya ore segments. The Xuefengling pegmatite and the Bailongshan pegmatite have similar zoning characteristics, and the pegmatite-hosted rare metal mineralization is approximately 206–213 Ma. On the basis of detailed observations and characterization of the textures and mineral assemblages of pegmatites in the Xuefengling deposit, four zones are identified: a quartz–spodumene (QS) zone, quartz–albite–muscovite (QAM) zone, quartz–albite–tourmaline (QAT) zone, and block albite–quartz pegmatite (BAQ) zone. We use the textures and major and trace element compositions of muscovite and columbite-group minerals from the Xuefengling pegmatite to illustrate both the existing state of rare elements and the origin of the Xuefengling pegmatite. Our results show that from Li-poor (QAM and QAT zones) to Li-rich pegmatites (QS zone), the K/Rb and K/Cs ratios of muscovite gradually decrease from 41.6 to 10.9 and 2276 to 208, respectively, and the Mn# values of columbite-group minerals increase from 0.35 to 0.49, which are similar to the progressive evolution trend identified in Bailongshan pegmatites. However, the lower K/Rb and K/Cs ratios of muscovite from the Xuefengling pegmatites than those from the Bailongshan pegmatites indicate that the Xuefengling pegmatites may have formed from the lower degrees of fractional crystallization of the same parental magma chamber, leading to the Bailongshan ore-field pegmatites gradually strengthening their evolution from east to west.

Magmatic-hydrothermal evolution of the aquamarine-bearing Yamrang Pegmatite, Eastern Nepal: Insights from beryl, garnet, and tourmaline mineral chemistry

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

Lithium-Rich Pegmatite Detection Integrating High-Resolution and Hyperspectral Satellite Data in Zhawulong Area, Western Sichuan, China

Lithium (Li) has grown to be a strategic key metal due to the enormous demand for the development of new energy industries over the world. As one of the most significant sources of Li resources, pegmatite-type Li deposits hold a large share of the mining market. In recent years, several large and super-large spodumene (Spd)-rich pegmatite deposits have been discovered successively in the Hoh-Xil–Songpan-Garzê (HXSG) orogenic belt of the northern Tibetan Plateau, indicative of the great Li prospecting potential of this belt. Hyperspectral remote sensing (HRS), as a rapidly developing exploration technology, is especially sensitive to the identification of alteration minerals, and has made important breakthroughs in porphyry copper deposit exploration. However, due to the small width of the pegmatite dykes and the lack of typical alteration zones, the ability of HRS in the exploration of Li-rich pegmatite deposits remains to be explored. In this study, Li-rich pegmatite anomalies were directly extracted from ZY1-02D hyperspectral imagery in the Zhawulong (ZWL) area of western Sichuan, China, using target detection techniques including Adaptive Cosine Estimator (ACE), Constrained Energy Minimization (CEM), Spectral Angle Mapper (SAM), and SAM with BandMax (SAMBM). Further, the Li-rich anomalies were superimposed with the distribution of pegmatite dykes delineated based on GF-2 high-resolution imagery. Our final results accurately identified the known range of Spd pegmatite dykes and further predicted two new exploration target areas. The approaches used in this study could be easily extended to other potential mineralization areas to discover new rare metal pegmatite deposits on the Tibetan Plateau.

FEATURES OF FORMATION, MATERIAL COMPOSITION AND GEOLOGICAL STRUCTURE OF RARE METAL AND PEGMATITE DEPOSITS OF THE KALBA REGION ON THE EXAMPLE OF THE YUBILEINOE DEPOSIT

Link for citation: Oitseva T.A., Dyachkov B.A., Bissatova A.Ye., Orazbekova G.B., Zinyakin S.S. Features of formation, material composition and geological structure of rare metal and pegmatite deposits of the Kalba region on the example of the Yubileinoe deposit. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 7, рр. 164-176. In Rus. The relevance of the research is caused by the lack of knowledge on the behavior of rare metal in pegmatite ore formation in the Kalba region and the need to expand the rare-metal mineral resource base of the region and to establish geological and mineragenic mapping. The main aims of the research are identification of features of geotectonic development, geological structure and material composition of the rare-metal deposit Yubileynoe (Kalba region). Study area: large industrial rare metal deposit Yubileynoe and its mineral complexes. Methods: detailed geological-geochemical and mineralogical study of the region of work, use of materials from works of previous years, stock literature, as well as laboratory studies (mass spectrometric, microprobe, geochronological and other studies). The structural relationships of minerals with each other, as well as the geochemical interpretation of the results of laboratory studies, were taken into account during diagnosing mineral complexes. Results. Spatial and genetic relationship of rare-metal pegmatite deposit (Nb, Ta, Be, Cs, Li, Sn) with granites of the I phase of the Kalba complex P1 (285 Ma), is distinguished. In the location of the Yubileinoe deposit, the leading ore-controlling role is given to the system of deep latitudinal faults of ancient origin, renewed in the Hercynian cycle. A geological and genetic model of rhythmically pulsating rare-metal pegmatite formation of the Yubileinoe deposit is presented, which reflects the zonal development of mineral complexes from oligoclase-microcline (barren) to albite, greisen, spodumene-containing and pollucite-bearing (ore) with an increasing concentration of mineralization. Information was obtained on the composition of pegmatite ores with the release of typomorphic minerals (clevelandite, lepidolite, colored tourmalines, spodumene, pollucite, ixiolite, etc.) and the main geochemical elements of rare metal ore formation (Nb, Ta, Be, Cs, Li, F, P, etc.).

Large-scale rare-metal pegmatite deposit formation driven by supercontinent assembly

Abstract Triassic rare-metal pegmatite deposits are widespread in East Asia; e.g., the western Kunlun and Songpan-Ganze belt in northern Tibet and the Altai belt in the heart of the Central Asian Orogenic Belt. However, rare-metal enrichment processes and deposit formation mechanisms are enigmatic. Most rare-metal pegmatites in East Asia formed at ca. 220–200 Ma in the Late Triassic and are genetically related to S-type granites. Whole-rock and zircon Li and Cs contents indicate that sedimentary rocks represent a fertile rare-metal source for the pegmatite deposits and that long-term chemical weathering plays a key role in the enrichment of rare metals. The formation of these widespread deposits in East Asia was associated with lithospheric extension induced by slab retreat along the periphery of the supercontinent during Pangea assembly.