Rare-metal Pegmatites Research Articles

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.

Rare-metal Be–Nb–Ta mineralisation by pegmatite remelting: Insights from Dakalasu deposit in the Chinese Altai orogenic belt

The rare metals Li, Be, Cs, Nb and Ta are mainly extracted from pegmatite deposits that may have formed through extensive fractional crystallisation or local partial melting of crustal rocks. There are a large number of rare-metal pegmatites that formed through crustal melting in the Chinese Altai, but what controls rare-metal enrichment remains enigmatic. Here, a new columbite UPb age of pegmatite mineralisation (247 ± 1 Ma) that is distinct from the ages of surrounding biotite granites (290–270 Ma) in the Dakalasu Be–Nb–Ta deposit in the Altai is reported. Zircon from the border zone with a medium to coarse-grained graphic texture of pegmatite yields two age groups: 290–270 Ma and 249 ± 7 Ma, corresponding to the age of biotite granite and the mineralisation age of pegmatite, respectively. The consistent age of the older group and biotite granite (290–270 Ma) and the elevated εHf(t) ratios and lower Nb/Ta ratios of pegmatite suggest that pegmatite is the end member of biotite granite after fractional crystallisation. The similar age of the younger group and mineralisation, the myrmekitic texture and albite trace elements of pegmatite imply pegmatite remelting and mineralisation occurred at ∼250 Ma. Our modelling agrees with geochronology, petrology and geochemistry that Be–Nb–Ta pegmatite mineralisation requires two melting events. The first step with anatexis of metasedimentary rocks generated biotite granitic melts whose extensive fractional crystallisation generated pegmatite with preliminary Be–Nb–Ta enrichment. The second step with pegmatite remelting (<5% degree) generated the significant enrichments of Be, Nb and Ta, which are sufficient for beryl and columbite crystallisation. The Be–Nb–Ta mineralisation mechanism through pegmatite remelting is likely common in orogenic belts with high-grade metamorphism and, therefore, should be considered in future explorations.

Characteristics and Geological Significance of CO2-Rich Fluid Inclusions in Dakalasu No. 1 Pegmatite Dyke, Altay

The fluids in of pegmatite rare metal deposits are generally rich in rare metal elements and volatiles (B, P, F, H2O, CO2, etc.), and they have a high capacity for dissolving and migrating rare metals. The Dakalasu No. 1 rare metal pegmatite vein is located in northwest China’s Altay orogenic belt. Previous studies have indicated that it is a small- to medium-sized beryllium-niobium-tantalum deposit. It showed significant mineral assemblage zonations from the rim to the core, and the mineralizing fluids define a volatile-rich NaCl-H2O-CO2 ± CH4 system. In this contribution, beryl and quartz, which are widely developed in each mineral association and textural zone, were selected for fluid inclusion research through detailed petrographic investigation, microthermometry, and LA-ICP-MS analysis. Petrographic results show that at least three types of fluid inclusions are developed in each mineral textural zone. They are CO2-rich inclusions (type I), gas-liquid two-phase inclusions (type II), and daughter mineral-bearing inclusions (type III), respectively. Additionally, minor melt inclusions (type IV) are visible in the beryl from the rim zone. Microthermometric measurements showed that the homogenization temperature of fluid inclusions in the rim zone was concentrated between 242 °C and 293 °C, with an average of 267 °C, and the salinity was between 7.2–10.3 wt% NaCleqv, with an average of 8.6 wt% NaCleqv. In comparison, the temperature of the core zone was in the range of 225–278 °C, with an average of 246 °C, and the salinity focused between 6.0–7.7 wt% NaCleqv, with an average of 7.1 wt% NaCleqv. The quantitative analysis of individual inclusions by LA-ICP-MS revealed that Li, B, K, Zn, Rb, Sb, Cs, and As were relatively enriched in the rim zone. In contrast, the core zone showed a decreasing trend in trace elements such as Li, B, K, Rb, and Cs. The CO2 content in the fluid exhibited the same decreasing trend from the rim to the core zone, indicating that volatile components such as CO2 played an essential role in the migration and enrichment of rare metal elements. The melt-fluid immiscibility is likely to be a necessary mechanism for significantly enriching rare metals in the Dakalasu No. 1 pegmatite dyke.

Magmatic-hydrothermal evolution of long-lived Nb-Ta-(Sn) mineralization in Lianyunshan, NE Hunan, South China

The Lianyunshan Complex (LYSC) is a Nb-Ta-Li-Be rare metals mining area in northeastern Hunan, South China. The deposit is composed of a granite-type rare-metal pegmatite mineralization that occurs as dikes around the LYSC. The present study examines the genetic relationship, fluid evolution, and metallogeny of the co-developed ore-free pegmatite (OFP) and ore-bearing pegmatite (OBP) in granite-related pegmatite-type Nb-Ta rare-metal deposits in the LYSC. Four minerals: columbite-tantalite (coltan), zircon, cassiterite, and monazite were investigated for their chemical and isotopic compositions. The coltan grains range from homogeneous crystals to zoned varieties with growth rims that result from equilibrium and disequilibrium reactions due to local changes in the physical and chemical conditions. These structures were altered by later metasomatic replacement processes related to the hydrothermal fluid activity and produced structures such as alteration rims, patches, irregular zonations, and complex zonations, with a corresponding increase in Ta. Coltan in OBP yielded two weighted mean 206Pb/238U ages of 135.9 ± 2.1 Ma and 120.5 ± 1.2 Ma, corresponding to magmatic (early-stage) and hydrothermal (late-stage) Nb-Ta mineralization ages, respectively. The cassiterite gives a weighted mean U-Pb mineralization age of 130.5 ± 3.9 Ma, which is interpreted as the magmatic-hydrothermal age (transitional stage). Zircon grains in OBP give a lower weighted mean U-Pb age of 121.5 ± 0.8 Ma, resulting from metamictization by the later fluid-assisted alteration and recrystallization in the late-stage hydrothermal event. Monazite grains from OFP yielded a weighted mean 206Pb/238U age of 137.1 ± 0.5 Ma, while zircon gives a mean U-Pb age of 130.3 ± 0.6 Ma. The ages of 137 and 130 Ma obtained for the OFP represent the magmatic (early-stage) and magmatic-hydrothermal stage (transitional) of OFP crystallization in the LYSC. Calculated zircon εHf (t) values and TDM2 ages from OFP (−7.6 to −5.4 and 1663−1532 Ma, respectively) and OBP (−8.7 to −8.2 and 1735−1704 Ma, respectively) are akin to those of the schist and metasandstone strata of the metasedimentary Lengjiaxi metasedimentary group—a melt source material to the LYSC composite batholith. We propose a long-lived ∼15 m.y. Nb-Ta-(Sn) mineralization model for the Lianyunshan complex.

Age and Composition of Columbite-Tantalite Group Minerals in the Spodumene Pegmatite from the Chakabeishan Deposit, Northern Tibetan Plateau and Their Implications

The Chakabeishan (CKBS) deposit is the first pegmatite-type Li-Be deposit discovered in the eastern North Qaidam Tectonic Belt (NQTB) of Tibetan Plateau. The correct understanding of its petrogenesis and the precise determination of its formation age are of great significance for further regional prospecting and the discovery of new economically valuable rare-metal deposits. Therefore, a systematic study of texture, major-element composition, and U-Pb dating of columbite-tantalite group minerals (CGMs) in the spodumene pegmatite dyke from the CKBS deposit was undertaken. Three types of CGMs were identified, including concentric oscillatory ferrocolumbite (CGMs-1), homogeneous ferrocolumbite (CGMs-2), and irregular ferrotantalite (minor manganocolumbite) with abundant early ferrocolumbite replacement remnants (CGMs-3). The zoning patterns and chemical compositions in the CGMs record the complex evolutionary history of their host pegmatite from the magmatic stage (CGMs-1, disequilibrium crystallization) to the magmatic-hydrothermal transition stage (CGMs-2, equilibrium crystallization) and then to the late metasomatic stage (CGMs-3, replacement/re-equilibrium). CGMs U-Pb dating results suggest that the spodumene pegmatite dyke (No.15) emplaced at 230.1 ± 2.6 Ma. Subsequently, it experienced fluid metasomatism at 221 ± 5.3 Ma. Based on the new age data and published geochronological data, it can be concluded that the spodumene pegmatite dykes in the CKBS deposit formed in an oceanic subduction-related setting, representing a new metallogenic event in western China. Except for the CKBS deposit, a large number of rare-metal pegmatite dykes have also been discovered in the eastern NQTB, indicating that the eastern NQTB may be an important potential rare-metal metallogenic belt that should be explored in detail and arouse painstaking attention.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 4. Mineralogy of lithium-bearing objects: micas

Part 4 of the publication "Lithium in the subsoil of Ukraine" provides a description, mostly typomorphic, of layered silicates of lithium-bearing objects — muscovite, micas of the isomorphic series of annite — trilithionite (formerly known as annite (lepidomelane) — protolithionite — zinnwaldite — cryophyllite — lepidolite), and micas from the biotite group. The mineralogy of mica are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — Kamyanomohyla (stone grave) complex of Azov region — rare metal pegmatites of the Azov region and the Inhul megablock. Muscovite is a secondary low-temperature mineral of the chamber pegmatites of Volyn which grew after the crystallization of micas from the isomorphic series of annite-trilithionite. It is represented by the polytypes 2M1 and 3T. Muscovite is common mica in the Perga ore district; in greisens and some metasomatites, it is the main mineral. It contains an elevated amount of iron and belongs to the 1M polytype modification: muscovite (Fe)-1M. Muscovite is also found in the Kamyanomohylskyi complex of the Azov region, primarily in altered granites and greisens formed on them. Its characteristic feature is the elevated iron content and the 2M1 structure. Fuchsite, fibrous muscovite and sericite-1Md are also found here. Muscovite in rare-metal pegmatites is mostly a secondary mineral. Rare pink muscovite, fuchsite and lithium muscovite have been found in the Azov pegmatites. Muscovite is present in relatively small amounts in the Shevchenkivske deposit and is represented by two generations. Muscovite (Li, Fe)-1M is rarely found. The X-ray luminescent properties of muscovite from spodumene pegmatites are of great importance as they are the main typomorphic features of the development of the pegmatitic process. Muscovite is rarely found in petalite pegmatites of the Inhul megablock and is represented by two generations. Its constitution is not fully understood and is controversial. Li-Fe мicas in granites and pegmatites of Volyn are important type-minerals indicating the crystallization of granites and pegmatites from magma with high content of rare elements and volatile components, the degree of differentiation of chamber pegmatites, and the extent of post-magmatic processes. The distribution of octahedral cations in the crystal structure of micas also has typomorphic significance, reflecting the activity of volatile components, the rate of crystallization, and the degree of differentiation of chamber pegmatites. The processes of forming fully differentiated pegmatites are accompanied by a polytypic transformation: 1M → 3T → 1M. Lithium-iron micas in greisens and metasomatites have similar but somewhat different typomorphic significance of the Perzhansky ore district (in which the polytype 2O was discovered) as well as in the Kamyanomohylskyi complex of the Azov region. The article concludes with a discussion of the results of research on rare alkalies in iron-magnesium micas from various types of metasomatic rocks surrounding pegmatites in Polohivske and Stankuvatsko-Lypnyazhske ore fields.

LITHIUM IN THE SUBSOIL OF UKRAINE Part 3. Mineralogy of lithium-bearing objects: feldspars

Traditionally, feldspars are characterized in the following order: Volyn chamber pegmatites — Perzhansky ore node — kamyano-mohyla (stone grave) complex of Azov region — Kruta Balka rare-metal deposit — Shevchenkivske rare-metal deposit — rare-metal pegmatites of Inhulsky megablock. Feldspars in the chamber pegmatites of the Volyn are represented by maximum microcline-perthite, rarely by intermediate orthoclase and albite. Widely developed feldspars with close regularity, but different symmetry. The form of discharge is granular aggregates and polyhedral crystals. The outline of potassium feldspar crystals is varied. Crystals of only two morphological types have a clear arrangement: I — early high-temperature bar-like individuals, concentrated in the cavities of the graphic zone; II — columnar pseudohexagonal crystals in sinkholes. Among albite crystals, three morphological types are distinguished, depending on acidity-alkalinity and crystallization temperature. Feldspars of chamber pegmatites are well studied by radio spectroscopic, luminescent and genetic methods. Within the boundaries of the Perzhansky ore complex, multi-grained polygenic microcline-perthite dominates, the structural state of its potassium phase corresponds to a high degree of ordered distribution of Si and Al (maximum microcline). The evolution of the twin structure of potassium feldspars is briefly covered and illustrated. Pure microcline and amazonite (probably the purest on the Ukrainian Shield) were found in the perzhansky metasomatites. Feldspars are the leading minerals of the stone-burial complex of the Azov region, represented by microcline and microcline-perthite. A characteristic feature of the microcline rocks of the complex is the unique giant dendritic crystals of pink microcline. Feldspars in the Kruta Balka rare metal deposit are represented by albite, albite-oligoclase and microcline. Two feldspars — microcline and albite (in the form of perthites in microcline and independent aggregates) were diagnosed in the Shevchenkivske deposit. Microcline makes up 15-20% of the volume of pegmatites and represented by three generations. The mineralogy of feldspars in the pegmatites of the Inhulsky megablock is different. They are represented by monoclinic orthoclase, microcline and plagioclase (mostly albite, occasionally oligoclase). Their content in rocks is mostly &gt;50%, but albite &gt;potassium feldspar. In general, these feldspars have features uncharacteristic of rare-metal pegmatites: 1) high symmetry (monoclinic) and low order (t1 &gt;0,7); 2) microperthite decay structure; 3) the initial and middle stages of monodomainization are manifested. These and other features of minerals are a consequence of the specific origin of pegmatites, which represent a new genetic type of deposits of rare elements — metapegmatites.

Lithium in the Subsoil of Ukraine. Part 2. Mineralogy of Lithium-Bearing Objects: Quartz

The second part of the publication "Lithium in the subsoil of Ukraine" highlights the mineralogy of rock-forming quartz from lithium-bearing objects of Ukraine: chamber pegmatites of the Korosten pluton, Perzhansky ore district, rare-metal granites and pegmatites of the Azov region, rare-metal pegmatites of the Inhulsky megablock, hydrothermalites of the Nagolny Ridge (Donetsk basin). In all these objects, quartz is characterized mostly from the point of view of its typomorphic value. The conclusion was as follows: the habit of quartz crystals has a typomorphic value, but cannot be described for all genetic situations by one simple scheme of the evolution of simple forms; so the main typomorphic information is "hidden" in the middle of quartz crystals. Point defects of its crystal structure are of greatest importance, primarily Al-O– centers and hydrogen defects, which are the most common in the mineral. They are best studied in crystals of chambered pegmatites and hydrothermal veins of the Nagolny ridge. The dependence of these defects on the action of external factors has been clarified. In particular, in chambered pegmatites, in contrast to crystal-bearing veins, a paradox occurs: with a decrease in the temperature of quartz growth, which is accompanied by an increase in the concentration (activity) of Li in the environment of mineralization, the number of lithium-hydrogen defects in the late zones of quartz decreases. It is assumed that in productive pegmatites this is due to the competing action of lithium micas — the main Li absorbers, the role of which increased with a decrease in the temperature of the solutions and an increase in their pH. In the quartz of rare-metal pegmatites, a high concentration of Al-Li centers has been established, which reaches a maximum in the quartz of the central zones and is therefore a criterion for the degree of differentiation of pegmatites. The luminescent properties of quartz from the petalite pegmatites of the Inhulsky megablock, caused by superimposed metasomatic processes and metamorphism, are unusual.

Indicative significance of the Qitaidaban monzogranite and mafic microgranular enclaves to the formation of rare metal pegmatites in West Kunlun

Indicative significance of the Qitaidaban monzogranite and mafic microgranular enclaves to the formation of rare metal pegmatites in West Kunlun

LITHIUM IN THE SUBSOIL OF UKRAINE Part 1. Distribution and forms of finding lithium in mineral complexes of Ukraine

In order to consistently highlight the distribution and forms of finding lithium in the subsoil of Ukraine, its geochemistry and mineralogy, genetic types of deposits and ore occurrences, mineralogical criteria and methods of their search and evaluation, the authors have planned a series of articles. The first part quantitatively and qualitatively analyzed the distribution and forms of Li occurrence in existing and prospective objects — the Volyn deposit, the Perzhansky ore district, rare-metal granites of the Azov region and the Korosten pluton, rare-metal pegmatites of the Azov region and the Shpolyansk-Tashlytsky ore region (Inguletsky megablock), hydrothermal of the Nagolny ridge (Donbas). The lithium-concentrating minerals in these objects, according to our data, are the following: spodumene, petalite, evcryptite, tourmaline, holmquistite, Li-Al micas of the isomorfic series (muscovite-lepidolite), Li-Fe micas of the isomorphic series (anite (lepidomelan) or siderophyllite, protolithionite, zinnwaldite, cryophyllite, lepidolite), margarite, donbasite, kukeite, polylithionite (?), tainiolite, tryphyllite, amblygonite, simferite.

The geochronology of the rare metal pegmatite deposits: A case study in Nanping No. 31 pegmatite vein in northeastern Cathaysian block, China

Accurate dating of the pegmatite is a challenge due to the uncertainty and controversy of crystallization temperature, fractionation model, and cooling mechanism. In this study, the sizable Nanping No.31 pegmatite vein (southeast China) contain five structural zones that is considered as an ideal example for assessing credible dating method on rare metals pegmatite deposit. The CMS (Chemical composition-Mineral assemblage-Structural geology) classification is applied on the Nanping pegmatite. The No. 31 vein is identified as pegmatite by CMS features. New U–Pb dating CGMs (columbite-tantalite group minerals) in five zones have a consistent age (380 ± 10 Ma). Whilst U–Pb dating of apatite and cassiterite from different structural zones show remarkable two group isotopic ages (370–390 Ma and 145–160 Ma). The much younger age indicated the pegmatite vein has experienced a severe Yanshanian tectono-thermal event at Eastern China. By comparison with apatite, cassiterite and zircon, CGMs is the most suitable mineral for accurate dating of the pegmatite because the dating results of the minerals are much stable, even having metamictization caused by high U content or overprinting by late hydrothermal activity. This study provided new insight into the dating methods for rare metals pegmatites to accurate restrict its metallogenetic geodynamical setting.

Geology, Mineralogy, and Age of Li-Bearing Pegmatites: Case Study of Tochka Deposit (East Kazakhstan)

New geological, mineralogical, geochemical, and geochronological data have been obtained for Li-bearing pegmatites from the Tochka deposit located within the Karagoin–Saryozek zone in East Kazakhstan. Earlier, the exploration works in this zone were carried out to detect only Ta and Sn mineralization, but other ores (including Li) were not considered. The estimation of lithium resources in pegmatites from the area was methodologically imperfect. Previously, it was believed that the formation of rare-metal pegmatite veins was associated with Late Carboniferous Na-granites. The obtained geological observation confirms that the ore-bearing rare-metal pegmatites at the Tochka deposits cut the Late Carboniferous Na-granites and do not cut the Early Permian Kalba granites. The associations of the accessory minerals in host hornfels, Na-granites, and rare-metal pegmatites are different and the accessory minerals in pegmatites are similar to the accessory minerals in the Kalba granites. Geochemical data show that the behavior of rare elements (Ba, Th, HFSE, and REE) and the levels of accumulation of rare metals prove that pegmatites are similar to the product of the differentiation of the granitic magmas of the Kalba complex. The 40Ar/39Ar muscovite age of the Tochka pegmatites (~292 Ma) fits the age range of the Kalba granite complex. Based on the main principles of the generation of rare-metal pegmatites, the Tochka pegmatites formed during the fluid–magmatic fractionation of magma in large granitic reservoirs of the Kalba complex. The Karagoin–Saryozek zone—located between several large granite massifs of the Kalba complex where host rocks play a role as a roof—may be very promising for rare-metal pegmatite mineralization.

Internal Structure, Petrography and Mineralogy of Beryl in Bahr-e-Abad Area, East of Afghanistan

This paper deals with the study of beryl, its variety, petrographic, and gemological specifications in the Bahr-e-Abad area of Jalalabad city. Beryl is a relatively rare silicate mineral, cyclo-silicate, with a chemical composition of Be3Al2 (Si6O18) and a hexagonal crystal shape. It is found in igneous and metamorphic rocks in many parts of the world. In order to achieve the aim of this paper, three methods, namely; library work, fieldwork, and lab work, were conducted, and about 20 specimens were collected from the above-mentioned area and taken to the Afghanistan Geological Survey (AGS) for making the thin sections and spectrometry analysis. Bahr-e-Abad area is related to the tectonic zone of Jalalabad. Jalalabad zone is located in the eastern part of Afghanistan and southeast of the Nuristan zone. Correspondingly, this zone is related to the upper Cambrian or younger Cambrian. In this area, the age of rocks is related to Archean- Middle Proterozoic AR-PR2. Beryl mineral is mostly found in Europe, Norway, Austria, Germany, Sweden, Ireland, Russia, Brazil, the US, Colombia, and Pakistan. Afghanistan is counted as one of the world’s leading countries in having rare-metal pegmatites, which are present in Afghanistan’s pegmatite belts in Afghanistan. This mineral is widely available in the pegmatite veins of Nuristan, Sistan, Panjshir, and Laghman. All pegmatite groups of Afghanistan are related to intrusive rocks. This study found that the rocks which are situated within pegmatite veins, besides beryl mineral, generally have the same composition and contain plagioclase, feldspar alkali (sodium-potassium), and mica (phlogopite and biotite) minerals. This is a microcline – albite type.

&lt;sup&gt;40&lt;/sup&gt;Ar-&lt;sup&gt;39&lt;/sup&gt;Ar dating of pegmatites from Murzinka-Adui region (Middle Urals): Results and their geological interpretation

Research subject. The pegmatites of Murzinka-Adui region (Ethtern sector of the Middle Urals), represented by three types of veins miarolitic pegmatites with topaz and beryl (mines Mokrusha, Kazennitsa, Semenovskaia), miarolitic rubillite-lepidolite pegmatites (Lipovka veins field) and rare metal pegmatites with Ta-Nb-Be mineralization (deposits Kvartal’noe and Lipovyi Log).Materials and methods. Isotope dating was carried out via the 40Ar-39Ar method by a mass spectrometer Micromass 5400 at the Institute of Geology and Mineralogy SB RAS for mica of different composition (muscovites, biotites and lepidolites).Results. 40Ar/39Ar ages for mica from dated pegmatite veins of the topaz-beryl type coincide within the measurement accuracy: mine Kazennitsa – 252.3 Ma, Mokrusha – 253.7 and Semenovskaia – 250.3 Ma. The average age of the two series of mica from rubillite-lepidolite pegmatites was found to be 254.1 Ma. The average age of four samples of muscovites from rare metal Ta-Nb-Be pegmatites equals 252.6 Ma.Conclusions. The closure of the isotope system of micas in pegmatites of all three studied types (topaz-beryllium, rubillite-lepidolite and rare-metal with Ta-Nb-Be mineralization) occurred almost simultaneously during the timeframe of 254 to 250 Ma years ago. The obtained age values, however, cannot be identified with the time of formation of pegmatites. The analysis of the available data suggests that the closure of the micas K-Ar isotope system of the studied pegmatites as well as previously dated schists and blastomylonites of the Bazhenovo suture zone and granites of the Murzinka-Adui block marks an important episode in the geological history of the eastern margin of the Urals and the basement of the adjacent part of the West Siberian plate: the change of the transpression regime prevailing during the collision stage of the region’s development to the regime of limited postcollision extension.

THE ARCHEAN STAGE OF RARE METAL (Li, Cs) PEGMATITE FORMATION IN THE NORTH-EASTERN PART OF THE FENNOSCANDIAN SHIELD

The results of isotope geochronological study of zircons from rare metal pegmatite deposits Okhmyl’k and Vasin-Myl’k are presented. Up to date no reliable data on the age of pollucite-spodumene-lepidolite pegmatite veins in the Archean greenstone belt Kolmozero-Voron’ya were available, the age estimations varied within a long time interval from 2.7 to 1.7 Ga. New U-Pb (SHRIMP-RG) data for zircons indicate crystallization of pegmatite at 2607±9 Ma in the Okhmyl’k and 2619±29 in the Vasin-Myl’k. This age corresponds to the global Archean stage of rare metal pegmatite formation at 2.65 – 2.60 Ga. Isotope data for ~1.7 – 1.6 Ga indicate the age of the late hydrothermal-metasomatic processes in pegmatite veins.

U-Pb (SHRIMP-RG) age of zircon from rare-metal (Li, Cs) pegmatites of the Okhmylk deposit of the Kolmozero-Voron’ya greenstone belt (northeast of the Fennoscandian shield)

The results of isotopic and geochronological study of zircon from rare-metal pegmatites of the Okhmylk deposit are presented. There were no reliable data on the age of lepidolite-spodumene-pollucite pegmatites of this and the other deposits spatially located within the Archean Kolmozero-Voron’ya greenstone belt. The earlier estimates of the pegmatite age indicate a broad time range from 2.7 to 1.8 Ga. Zircon in the studied pegmatites is characterized by inner heterogeneity, where core and rim zones are distinguished. Minor changes are observed in the core zones, they have a spotted structure and contain numerous uranium oxide inclusions. According to X-ray diffraction analysis, zircon crystallinity is preserved completely in these areas. Complete recrystallization with modification of the original U-Pb isotopic system occurred in the zircon rims. New U-Pb (zircon) isotopic and geochronological data of 2607±9 Ma reflect the time of crystallization of pegmatite veins in the Okhmylk deposit. Isotopic data with ages of ~1.7-1.6 Ga indicate later hydrothermal alteration. The obtained results testify to the Neo-Archean age of the formation of the Okhmylk deposit 2.65-2.60 Ga, reflecting the global age of pegmatite formation and associated the world's largest rare-metal pegmatite deposits.

Detecting Li-bearing pegmatites using geospatial technology: the case of SW Konar Province, Eastern Afghanistan

Lithium-cesium-tantalum (LCT) pegmatites are widely distributed in northeastern, eastern, and central Afghanistan. The largest rare-metal pegmatites having Lithium (Li)-bearing minerals occur in the Nuristan pegmatite belt in Eastern Afghanistan. The main aim of this study is to detect and highlight the Li-bearing pegmatites using spectral analysis within the Southwest Konar province in the east of Afghanistan and to establish self-proposed spectral indices for the detection of Li-rich minerals. To achieve the study’s objective, we apply several algorithms, for example, false color composite, band ratio, and spectral angle mapper on ASTER, Landsat 8 OLI/TIRS, and Sentinel-2MSI data. Considering the spectral characteristics of key mineral spodumene and other diagnostic minerals, for example, lepidolite, amblygonite, and cookeite, which are considered diagnostic minerals of LCT pegmatites, particularly lithium, we utilize the ECOSTRESS Spectral Library-Version 1.0 for the interpretation of reflectance and absorption determinants of these minerals. Based on the diagnostic characteristics of the selected Li-bearing minerals, we examine several BRs and thresholding and consequently, propose new spectral indices which show a high concentration of spodumene, cookeite, and lepidolite over the northern regions of the study area. According to the obtained results, ASTER data and thresholded BRs present effective results compared to Landsat 8 OLI/TIRS. Based on the final outputs, we define nine zones having Li-bearing pegmatites, particularly over the Chapa Dara and Dara-e-Pech districts of southwestern Konar province, which could be promising areas of interest for further detailed exploration. Lastly, we compare the 118 known Li-bearing points collected from previous studies and field observations with the newly-defined zones to validate accuracy. The study’s overall accuracy is 71.1%, indicating a good match between our findings and the reference points.

Peculiarities of rare-metal mineralization and genetic relationship of mineral associations in the eastern rim of Murzinsko-Aduysky anticlinorium (the Ural Emerald Belt)

The paper presents features of the location and composition, as well as a generalization of data on the age of rare-metal mineralization developed at the deposits and occurrences of rare metals and gemstones in the eastern rim of Murzinsko-Aduysky anticlinorium, within the Ural Emerald Belt, which is a classic ore and mineralogical object and has been studied for almost two hundred years. With a significant number and variety of prospecting, research and scientific works devoted mainly to emerald-bearing mica complexes and beryl mineralization, as well as rare-metal pegmatites, scientific literature has so far lacked generalizations on the formation of numerous mineral associations and ore formations that represents a uniform genetic process in this ore district. The aim of the work is a comprehensive geological-mineralogical analysis of mineral associations of the eastern rim of Murzinsko-Aduysky anticlinorium and studying their age, formation conditions and characteristic features to determine the possibility of expanding and using the mineral resource base of the Urals through developing new prognostic and prospecting criteria for rare-metal and gemstone ore formations and creating the new devices for promising objects prospecting

Chemical evolution of micas and Nb-Ta oxides from the Koktokay pegmatites, Altay, NW China: Insights into rare-metal mineralization and genetic relationships

This study focuses on the differences in the mineralization potentials and genetic relationships between representative rare-metal pegmatites and the muscovite granite in the Koktokay field in Altay, China, as well as the possible roles that magmatic and/or hydrothermal activities played in enriching the related rare metals. To this end, the major- and trace- element compositions of micas, the major- element compositions of Nb-Ta oxides, and the Li isotopic compositions of Li-rich muscovite, lepidolite, and spodumene were systematically analyzed. The major element compositions of the micas in the No. 1 and No. 2 pegmatites are quite similar. However, the MgO (0.89–2.18 wt%) and F (0.66–2.01 wt%) contents of the micas in the contact zone of the No.3 pegmatite are higher than those of the micas in the No. 1 and No. 2 pegmatites. In addition, the MnO (0.37–0.46 wt%) and MgO (0.39–0.59 wt%) contents of the micas in the muscovite granite are distinctly higher than those of the micas in the studied pegmatites. The trace-element compositions reveal that the primary micas from the small No. 1 and No. 2 pegmatites have significantly lower Li, Be, Ta, and Cs contents and a narrower range of fractionation relative to those in the large No. 3 pegmatite, indicating a significant difference in the rare-metal mineralization potentials of these pegmatites. Moreover, there is a large difference in the δ7Li values of the Li-rich minerals in the muscovite granites (−4.37–0.07‰), No. 3 (4.3–6.81‰) and No. 1 (7.44–14.65‰) pegmatites. These results support the hypothesis that the muscovite granite and pegmatite dikes may have formed independent of each other, and that their formations were a consequence of multi-stage magmatic activities. In addition, the Nb-Ta oxides in the outer zones are mainly columbite-(Mn). The large differences in the Nb/Ta ratios of the columbite-(Mn) (1.83–14.91) and primary micas (2.22–10.41) in the outer zones could be the result of silicate-silicate melt immiscibility. Furthermore, the low Nb/Ta ratios (commonly < 5) of the bright overgrowths of the columbite-(Mn) may have crystallized directly from a hydrous alkali-halogen-rich melt rather than from a hydrothermal fluid. The distinctly higher Ta (39–167 ppm), Cs (275–579 ppm), and B (213–245 ppm) contents; considerable Li contents (400–554 ppm), and lower Nb/Ta ratios (0.5–3.2) of the hydrothermal micas suggest that hydrothermal processes played an important role in the additional enrichment of the related rare metals (e.g., Ta, Cs, Li, and B).

Geology and Petrogeochemistry of Lijiapuzi Nb-Ta Granitic Pegmatite Deposit: Implications for Ore Genesis and Prospecting

Most of the rare metal pegmatite deposits in China lie in West, Central and South China, and the Lijiapuzi Nb-Ta deposit is the only pegmatite-type Nb-Ta deposit in Northeast China, therefore a detailed study of the Lijiapuzi deposit is of great importance to the metallogeny and exploration of rare metal deposits in Northeast China. The Nb-Ta bearing pegmatites in Lijiapuzi district are composed of a microcline wall zone, a muscovite (lepidolite)-albite intermediate zone and a quartz core, and the rare metal mineralization mainly occurs in the intermediate zone and is intimately related to the albitization. The lithogeochemical features indicate that Lijiapuzi pegmatoids are rich in silicon and alkaline, poor in calcium, magnesium, titanium and phosphorus, and belong to peraluminous granitoid rocks. The enrichment of large ion lithophile elements (LILEs) and depletion of high field-strength elements (HFSEs), the distinct right-inclined REE pattern with obvious Eu negative anomaly, lower ratio of Nb/Ta and higher ratio of La/Nb and Rb/Sr indicate that the pegmatite was of a crustal origin and formed in relatively extensional tectonic setting of post-orogenesis. The pegmatites in Lijiapuzi area can be divided into two categories, i.e., the NW-trending pegmatites are shorter and thicker, with obvious zoning and localized in the upper part of the near-surface, while the NE-trending pegmatites are longer, thinner, devoid of zoning and localized in the lower part of the district. This probably means that excellent ore prospecting potential exists in the lower part of the Lijiapuzi district.