Rare-metal Mineralization Research Articles

Apatite geochemical composition of Mesozoic granitoids in the eastern Jiangnan Orogen, S. China: insights into petrogenesis and intrinsic magmatic variables

ABSTRACT The geochemical compositions of apatite are commonly used to provide reliable constraints on the intrinsic magmatic variables of the parental magma. There is a widespread distribution of Mesozoic granitic rocks in the eastern Jiangnan Orogen (EJNO), which include I-type and A-type granitoids. This study aims to investigate the geochemical composition of apatite in 11 representative I-type and A-type granitic intrusions from the EJNO to understand their petrogenesis, intrinsic magmatic variables, and polymetallic mineralization potential. The results show that apatites in these granitoids were characterized by oscillatory zonation and homogeneous texture, and exhibited high F, and low Cl contents, as well as high REE, Y, and Th contents, indicating magmatic origin. These apatites were divided into two groups depending on their geochemical characteristics and original rock types. In Group I apatites (in the I-type granitoids), the absence of an abrupt change in major and trace element concentrations from the core to the rim of the apatite crystals, combined with their low levels of MgO, Sr, and HREY (HREE+Y), serves as evidence to classify the I-type granitoids as low Sr-Y adakitic granitoids with a low Mg#, which can be attributed to the partial melting of the thickened lower crust. In Group A apatites (in the A-type granites), the normal increase in incompatible elements from the core to the rim, as well as the presence of a flat REE pattern with pronounced Eu anomalies, can be attributed to crystal fractionation of plagioclase, allanite, and zircon. Furthermore, Group I apatites have higher SO3, Cl, and molar OH/F and Cl/F ratios compared to Group A apatites. Quantitative calculation by apatite-melt partitioning and modelling suggests that the I-type granitic magmas were more volatile-rich and more oxidized than A-type granitic magmas. Taken together, based on the relationship between the intrinsic magmatic variables and the behaviour of ore-forming elements, our study demonstrates that early I-type granitoids of the EJNO have a strong W-Mo-Cu polymetallic mineralization potential, while late A-type granites may possess rare metal mineralization potential.

Petrogenesis and rare-metal mineralization of the Ririwai alkaline granitoids, north-central Nigeria: mineralogical and geochemical constraints

ABSTRACT The Ririwai anorogenic alkaline complex harbours extensive rare metal (Nb-Zr-Sn-Zn) mineralization. However, uncertainty still surrounds their origin and magmatic-hydrothermal processes responsible for their rare metal mineralization. The complex is composed of peralkaline arfvedsonite ± albite-bearing granites, mildly peralkaline fayalite-bearing granite porphyries, and weakly peraluminous biotite-bearing granites, all of which show diagnostic A1-type characteristics. Zircon U-Pb dating reveals emplacement ages between 181.4 ± 0.81 and 188.6 ± 7 Ma for the three rock units. Sm-Nd and Pb isotopes (εNd (t) = –0.6 to −5.4, 206Pb/204Pb = 17.68–17.93) constrained the Ririwai A-type granites to represent highly fractionated products of enriched mantle-derived magmas. Mass-balance modelling suggests that magma evolution was fuelled by extensive fractional crystallization of 50 ~ 60 vol.% K-feldspar, 30 ~ 35 vol% fayalite, 5 ~ 10 vol.% amphibole, and ~ 5 vol.% apatite under reduced and water-undersaturated (ΔFMQ = –1.55; logfo2 = –18.63; H2O = <2.0 wt.%) conditions and assimilation of ~ 50 vol.% crust. Whole rock and amphibole compositions revealed an increasing degree of fractionation from the fayalite-bearing granite porphyries through biotite-bearing granites to the arfvedsonite ± albite-bearing granites. This extended fractionation at the late stage of magma differentiation, facilitated by fluorine dissolution and concentration of excess HFSE and REE as alkali-fluorocomplexes in the fluorine-rich silicate melt, allowed the accumulation of economic rare metal pyrochlore and columbite mineralizations in the highly fractionated arfvedsonite± albite- and biotite-bearing granites, respectively. Nonetheless, the metasomatic reaction rim textures around the magmatic pyrochlore, coupled with the M-type lanthanide tetrad effect (TE1,3 >1.10) indicate the subsequent effect of hydrothermal processes. Tectonically, reactivated shear fractures and transcurrent faults following lithospheric stresses in a transtensional regime allowed magma uprising and emplacement of A-type granites in the Ririwai complex.

Distribution and enrichment of rare metal elements in the basement rocks of South China: Controls on rare-metal mineralization

The southeastern part of the South China Block (SCB) is composed of the Nanling-Yunkai and Wuyi terranes and the Jiangnan Orogenic Belt (JOB), of which the Nanling and the JOB are two world-famous rare-metal metallogenic belts. Rare-metal deposits in both areas are closely associated with crustally-derived granites. However, rare-metal abundances and enrichment mechanisms in Precambrian basement rocks, which probably are sources of the ore-forming granites in the SCB, have not been well understood. Bulk compositions of more than 800 basement rock samples are used to unravel the abundances, variation and enrichment mechanism of the rare-metal elements in Precambrian basement rocks of the SCB and their genetic links with rare-metal mineralization. The basement meta-sedimentary rocks of the westernmost section of the JOB have the highest Sn (10.2 ppm), W (7.7 ppm), Be (3.46 ppm) and Cs (17.1 ppm) abundances, whereas those of the eastern JOB have low Sn (2.4–3.2 ppm), W (1.2–2.1 ppm), Nb (12.9–13.9 ppm) and Be (2.22–2.34 ppm), but relatively high Li (53.3–57.0 ppm) contents. The eastern Nanling basement rocks show high Sn (4.5 ppm), W (3.0 ppm) and U (3.67 ppm) relative to upper continental crust (UCC), similar to the western Nanling basements (4.2 ppm, 3.0 ppm and 4.03 ppm, respectively), but have significantly higher Rb/Sr, Li, Be, Cs and lower CaO/Na2O and Ba than the western Nanling basements, implying the presence of more meta-pelitic rocks in the eastern Nanling basements. The Wuyi terrane is characterized by low rare-metal abundances, e.g Sn (2.1 ppm), W (1.3 ppm), Cs (5.7 ppm) and Li (36.4 ppm). Rare-metal enrichment mechanisms are also distinct in the basement rocks of different terranes of the SCB. Four types of enrichment mechanism are identified: magmatic recycling, chemical weathering, source enrichment and alternative redox depositional environments. The enrichment of Sn, W, Cs and Be in the westernmost basement of the JOB is attributed to a higher proportion of old and multi-cycled materials and alternating depositional environments, and the enrichment of Sn, W, REE and U in the Nanling basement is ascribed to the higher proportion of recycled detritus and an enriched source. Chemical weathering (clay adsorption) is an important initial enrichment mechanism in the eastern JOB basement. Comparisons of rare-metal mineralization in the SCB with the basement compositions suggest that rare-metal mineralization of the granites is not only related to the rare-metal contents of the source, but also is closely related to the lithology of the source. Stronger W mineralization in the eastern JOB and eastern Nanling than in their western parts is probably related to their more pelite-rich basements.

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.

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.

Enrichment characteristics and metallogenic significance of rare elements in Zambia: Based on 1:1,000,000 geochemical mapping

The Sino–Zambian Cooperation Project has filled the gap in Zambia national‐scale geochemical mapping, providing basic geochemical guarantees for Zambia's basic geology, mineral development, environmental protection, agricultural production and other aspects. This article aims to reveal the distribution characteristics of its rare elements (Li, Be, Nb, Rb, Sr). The median value of Li, Be, Nb, Rb and Sr is 4.94 × 10−6, 0.65 × 10−6, 7.50 × 10−6, 33.00 × 10−6 and 21.90 × 10−6, respectively. The median and average values of the Irumide Belt, Zambezi Belt, Choma‐Kalomo Block and Hook Granite Complex are higher than other tectonic belts, showing that rare elements are enriched in those areas. The distribution of element anomaly areas is mainly related to the distribution characteristics of granite type rare metal mineralization occurrences, and a small number of anomaly areas are controlled by salt lake brine‐type mineralization occurrences. A total of five rare metal geochemical anomalies have been delineated respectively based on the 85% cumulative percentage of rare elements (Li, Be, Nb, Rb, Sr). The metallogenic prospective area delineated based on the comprehensive anomaly area of rare elements will provide an important reference for searching for rare metal deposits in this area.

Unravelling the genetic relationship between pegmatites and granites in the Jiajika Li-Be polymetallic district, Songpan-Ganze Orogenic Belt, Southwestern China: Insights from monazite U-Pb geochronology and trace element geochemistry

The Jiajika Li-Be Polymetallic District is located in the Songpan-Ganze Orogenic Belt, Southwestern China. The Li-Be mineralization is genetically, temporally, and spatially, related to pegmatites in the Jiajika District. Hundreds of pegmatite dikes were emplaced surrounding the adjacent Majingzi granite pluton. Drill core samples from the 3,200 m deep Jiajika Scientific Drilling project (JSD-1) were acquired to determine the vertical extent and the petrogenesis and metallogeny of the granites, and the pegmatites, respectively, and to obtain a better understanding of their genetic relationship. The vertical zonation of the pegmatites from shallow to deep is as follows: shallow albite pegmatites; albite-microcline pegmatites; microcline pegmatites; and deeper more albite pegmatite. Spodumene occurs mainly in the shallow albite pegmatites (55–105 m depth), and disseminated beryl, columbite-tantalite, and cassiterite, mainly occur in pegmatites at depths less than 700 m. Eight samples were selected for monazite U-Pb geochronology and trace element geochemistry analyses from pegmatites and granites at different depths. LA-ICPMS monazite U-Pb geochronology for the pegmatites indicates two episodes of magmatic activity; one at 211–205 Ma (2σ, 523–2,494 m depth) and another at 193–192 Ma (2σ, 3,170–3,211 m depth). The crystallization age of the older pegmatites is in good agreement with the monazite U-Pb geochronology of the adjacent Majingzi granite (208–205 Ma, 2σ, 1,265–2,568 m depth) within analytical uncertainty, indicating their close temporal relationship. The younger albite pegmatite (193–192 Ma) is associated with the columbite-tantalite Nb-Ta rare-metal mineralization. Compared to those in the deep pegmatites (excluding the younger albite pegmatite in 3,170–3,211 m depth), and the adjacent granites, monazites in the shallow pegmatites and the adjacent granites are relatively enriched in Li, Th, and U, indicating the continuous evolution of a felsic magmatic system; with the residual melt more enriched in various incompatible rare-metal elements. Hence, the monazite U-Pb geochronology and trace element geochemistry indicate that a highly evolved felsic magma plays an important role in the petrogenesis of the Jiajika Li-Be pegmatites.

Risk assessment and rare metals mineralization associated with alteration aspects of Rhyolite flow tuffs, Egypt

Argillic alteration and hematitization are the two extensive alterations that affected Um Safi rhyolite flow tuffs. Rare metal mineralization including radioactive minerals (thorite, uranothorite), Nb-bearing minerals (columbite, yettrocolumbite, Nb-rutile), zircon, REE-minerals (LREE-carbonate, xenotime) as well as molybdite, pyrite, fluorite, hematite and ilmenite have been identified by using Energy Dispersive Spectrometer (EDS) and are well recorded in argillic and hematitized samples. The investigated rhyolite flow tuffs show that the activity concentration of radionuclides changed from 1.2 to 453.2 Bq kg−1 for 238U, from 3.2 to 489.6 Bq kg−1 for 232Th, and from 31.3 to 88954.6 Bq kg−1 for 40K. The mean values of 238U, 232Th, and 40K activity concentrations are 90.8 ± 84.5, 122.9 ± 90.5 and 6286.7 ± 1562.2 Bq kg−1, respectively. The hazard factors are estimated. Their results exceeded the recommended limit. Thus, the investigated rhyolite flow tuffs are not safe to use in building materials and other construction industries. A multi-statistical approach is performed to show the correlation between the radioactive concentration and radiological hazard factors. This approach illustrates the positive correlation between uranium and thorium due to their contribution from the natural radioactive series—moreover, a strong correlation was obtained between potassium and all radiological parameters. Thus, the radioactive hazards impact in the present study is related to the presence of radioactive minerals such as thorite and uranothorite in addition to other accessory minerals.

Magmatic–hydrothermal evolution of the Koktokay No. 3 pegmatite, Altai, northwestern China: Constraints from in situ boron isotope and chemical compositions of tourmaline

Lithium–Cs–Ta-enriched (LCT-type) pegmatites are characterized by zoning texture and extreme enrichment of rare-metals. The role of fluids in zonation development and rare-metal mineralization remains a topic of debate. The Koktokay No. 3 pegmatite in northwestern China represents a typical LCT-type pegmatite characterized by economically significant Li–Be–Nb–Ta–Cs mineralization. This pegmatite exhibits a complete evolutionary sequence from outer to inner zones, with diverse rare-metal mineralization. Tourmaline is ubiquitously present in all textural zones of LCT-type pegmatites. In the Koktokay No. 3 pegmatite, the tourmalines exhibit a range of compositions from dravite and schorl to elbaite and rossmanite. The tourmalines in this pegmatite are characterized by significantly enriched light B isotope compositions (δ11B = −14.8‰ to −8.1‰), similar to those typically observed in most pegmatites derived from continental crust sources. The tourmalines in the outer zones have less variable δ11B values (−13.8‰ to −11.5‰) and are interpreted to have crystallized in a viscous magma. The tourmalines in the inner zones exhibit larger variations in δ11B values (−14.8‰ to −8.1‰) than those from the outer zones. The decreasing δ11B values of tourmalines from the outer to inner zones are attributed to the separation of an immiscible fluid phase that preferentially incorporated heavy B isotopes. The occurrence of hydrothermal tourmaline as veinlets indicates the exsolution of fluids in inner zones, with high δ11B values ranging from −10.2‰ to −9.3‰. Therefore, the hydrothermal fluid can be saturated when the magma has been strongly evolved. In addition to fractional crystallization, exsolved fluids play a significant role in the formation of internal zones and rare-metal mineralization in LCT-type pegmatites. The rare-metals are gradually enriched through fractional crystallization of magma, and the fluid contains mobile elements such as Cs that facilitate precipitation of rare-metal minerals.

Predicted resource assessment of Central Kazakhsta ore districts based on airborne geophysical methods

Purpose. The research is aimed at creating a high-quality geophysical basis for the additional geological study of Central Kazakhstan in determining the geological structure of the study area, identifying promising areas for further geological exploration, as well as analyzing the anomalous distribution of various minerals. Methodology. The research uses the methods of aeromagnetic, airborne gamma-ray spectrometry and gravimetric (ground) surveys. The obtained new airborne geophysical data are used for additional study of the geological structure of the district and the creation of a model of the geological structure of the study area. Gamma-ray spectrometry data analysis is conducted for detailed mapping of intrusive complexes and study of their lithological heterogeneity. Findings. The processing and interpretation of the materials of the conducted field studies in combination with the results of the geological-geophysical data analysis made it possible to refine the geological structure and to present a model of ore-prospecting complexes in the study area. Areas with an anomalous distribution of potassium, uranium, and thorium have been identified, which make it possible to assess the structural heterogeneity of hidden magmatic massifs and to reveal a connection with gold, copper-polymetallic and rare-metal mineralization. Recommendations for further detailed geological exploration, including prospecting-exploration drilling, are given. Originality. Research has shown the high efficiency of airborne geophysical methods, such as aeromagnetic and airborne gamma-ray spectrometry surveys to study the geological structure of ore areas, and in combination with detailed gravimetric exploration to identify lithological heterogeneity of igneous and sedimentary rocks in the study area. New scientific-methodological techniques and the geological structure model based on them gave an opportunity to assess the prospect of the study area for ore mineralization. Practical value. The identified promising areas for mining of minerals are of interest for further research and exploration. The integrated use of geological-geophysical data will make it possible to determine more precisely the nature of radioactive anomalies and to reveal their relationship with ore-prospecting horizons. In general, the research results contribute to increasing the efficiency and reducing the geological survey costs.

Lithium isotopic systematics and numerical simulation for highly-fractionated granite-pegmatite system: Implications for the pegmatite-type rare-metal mineralization

Lithium (Li) isotope behavior during fractionation of highly-evolved granitic pegmatites and associated rare metal mineralization remains unclear, especially concerning the relative importance of magmatic versus metasomatic processes. In this study, we investigated the geochemistry and Li isotopes of the giant Renli-Chuanziyuan lithium-niobium-tantalum (Li-Nb-Ta) deposit in the Mufushan batholith (South China). We found that muscovite granite in the Mufushan complex can be divided into two groups (high-Li and low-Li). δ7Li value of the high-Li and low-Li group increases and decreases, respectively, with increasing Li content, which is likely resulted from fractional crystallization and/or magmatic volatile phase (MVP) exsolution. The MVP exsolution began with the solidification of muscovite granite, as evidenced by the zoned micas. The Li isotope fractionation, modeled by Rayleigh distillation during MVP exsolution, is consistent with the δ7Li value of Li-poor pegmatite, indicating that MVP exsolution is related to the pegmatite formation.The Mufushan Li-poor and Li-rich pegmatites have very high and low δ7Li value, respectively. Based on the Δ7Li(bulk-mica) value and numerical simulation, we suggest that the pegmatite formation at Mufushan could be linked to extensive MVP accumulation, while the different Li elemental and isotopic compositions of the two types of pegmatite are probably caused by MVP migration. In fact, published granite-pegmatite data worldwide also show negative Li vs. δ7Li correlation, indicating that such MVP exsolution, accumulation and migration are probably a common phenomenon for evolution of granitic pegmatite. Therefore, the different Li isotopes and Li-Rb-Cs proportion of Li-poor and Li-rich pegmatites indicate that MVP exsolution, migration and accumulation are key to rare metals enrichment and distinguish various types of rare-metal mineralization (Li and Nb-Ta).

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.

Geochemistry and U–Pb zircon geochronology of S-type granites in the Karagwe Ankolean Belt, northwestern Tanzania: Implications for rare-metals mineralization

The Mesoproterozoic Karagwe Ankolean Belt in the Central Eastern Africa region hosts suites of granites that intruded supracrustal rocks and are associated with Sn–W mineralization. In northwestern Tanzania, the granites are S-type, peraluminous and calc-alkalic to alkalic-calcic in composition. Geochemical analyses of the granites reveal the following concentrations: SiO2 (71–77 wt%), Al2O3 (11–15 wt%), K2O (3–7 wt%), MgO (0.06–0.86 wt%), TiO2 (0.07–0.36 wt%) and Fe2O3T (0.71–2.40 wt%). The SiO2 contents correlate negatively with MgO, CaO and K2O and positively correlate with Nb, Ta, Zr, Sr, Ba, Hf, Th and the REE (Eu, Ce and Sm). Primitive mantle normalized spider plots show elevated LILE against depletions in Ba, Nb, Ti and La, suggesting inherited arc-magmatic signatures from the protolith. Chondrite-normalized REE spider plots show elevated LREE and relatively flat MREE and HREE as indicated by (La/Yb)cn = 2–9 and negative Eu* anomalies (0.05–0.24). Modelling of nearby Uha group sedimentary rocks partial melts, supports fractional crystallization and upper crustal contamination for generation of the KAB granites. Trace elemental ratios of Y/Nb, Nb/Ta, Zr/Hf and P205 suggest the granites are weakly mineralized to barren in Sn–W.The U–Pb zircon ages point to two successive and overlapping periods: from 1418 ± 15 Ma to 1395 ± 6 Ma (mean = 1406 Ma) and from 1385 ± 8 Ma to 1376 ± 11 Ma (mean = 1381 Ma). Inheritance U–Pb dates of xenocryst zircons, comprise early to late Paleoproterozoic ages ranging from 2376 ± 30 Ma, 2000 ± 27 Ma to 1901 ± 39 Ma, and from 1795 ± 7 Ma to 1738 ± 7 Ma, implying the participation of the Paleoproterozoic sedimentary rocks in the petrogenesis of the granites. A zircon rim overgrowth age of 1015 ± 26 Ma is interpreted to date a metamorphic/anatexis event that coincided with the c.1000 Ma amalgamation of the supercontinent Rodinia and the emplacement of Sn–W enriched granites. The ages of S-type granite magmatism (1418–1376 Ma) obtained from this study are restricted to the Mesoproterozoic within the widespread bimodal magmatism event c.1375 Ma.

Characterisation and rare-metal potential of the Winneba-Mankoadze pegmatites, Southern Ghana: Evidence of two pegmatite fields

In southern Ghana, the region along the coast between Accra and Cape Coast hosts a large number of pegmatites mineralized in lithium, niobium-tantalum and tin. The pegmatites occur in many distinct groups, each extending over several kilometers. They intrude metasedimentary units of the Birimian Supergroup, and are associated with early to late orogenic granite intrusions which are metaluminous, sterile, and too old to be potential parental granites for the pegmatites. In this study, we characterized the Winneba-Mankoadze group of geographically coeval pegmatites, using field description, petrography, rare-metal mineralogy and accessory mineral geochemistry on micas, garnet and Nb–Ta–Sn minerals, in order to determine its rare-metal potential and to investigate its origin. The results indicate that the pegmatites are part of the albite-spodumene type of the Lithium–Cesium–Tantalum (LCT) family. The rare metal mineral assemblages are particularly complex and display relevant oxide species such as columbite- and wodginite-group minerals, tapiolite, microlite, cassiterite and rutile, which are evidences of an extremely evolved magmatic system. Based on mineral assemblages, whole-rock geochemistry, and mineral geochemistry on garnet, micas and the CGM, two pegmatite fields are distinguished in the Winneba-Mankoadze group, and an anatectic origin is proposed. For the first time in West Africa, we fully describe a highly fractionated LCT-family pegmatite field comparable to the most evolved pegmatite bodies in the world.

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.

Magmatic Evolution and Rare Metal Mineralization in Mount El-Sibai Peralkaline Granites, Central Eastern Desert, Egypt: Insights from Whole-Rock Geochemistry and Mineral Chemistry Data

The Ediacaran peralkaline granites, which were emplaced during the post-collisional tectonic extensional stage, have a limited occurrence in the northern tip of the Nubian Shield. In this contribution, we present new mineralogical and geochemical data of Mount El-Sibai granites from the Central Eastern Desert of Egypt. The aim is to discuss their crystallization condition, tectonic setting, and petrogenesis as well as the magmatic evolution of their associated mineralization. Mount El-Sibai consists of alkali-feldspar granites (AFGs) as a main rock unit with scattered and small occurrences of alkali-amphibole granites (AAGs) at the periphery. The AAG contain columbite, nioboaeschynite, zircon and thorite as important rare metal-bearing minerals. Geochemically, both of AFG and AAG exhibit a highly evolved nature with a typical peralkaline composition (A/CNK = 0.82–0.97) and formed in within-plate anorogenic setting associated with crustal extension and/or rifting. They are enriched in some LILEs (Rb, K, and Th) and HFSEs (Ta, Pb, Zr, and Y), but strongly depleted in Ba, Sr, P and Ti with pronounced negative Eu anomalies (Eu/Eu* = 0.07–0.34), consistent with an A-type granite geochemical signature. The calculated TZrn (774–878 °C) temperatures indicate that the magma was significantly hot, promoting the saturation of zircon. The texture and chemistry of minerals suggest that they were crystallized directly from a granitic magma and were later subject to late- to post-magmatic fluids. Both granitic types were most likely generated through partial melting of a juvenile crustal source followed by magmatic fractionation. The lithospheric delamination is the main mechanism which causes uplifting of the asthenospheric melts and hence provides enough heat for crustal melting. The produced parent magma was subjected to prolonged fractional crystallization to produce the different types of Mount El-Sibai granites at different shallow crustal levels. During magma fractionation, the post-magmatic fluids (especially fluorine) contribute significantly to the formation of rare metal mineralization within Mount El-Sibai granites.

Jurassic Uranium-Thorium Deposit of Peralkaline Granitic Rocks, Bokan Mountain, Prince of Wales Island, Southeastern Alaska

The Lower Jurassic (ca. 177 Ma) Bokan Mountain granitic complex, located on southern Prince of Wales Island, southernmost Alaska hosts a high-grade uranium-thorium deposit with past production. The complex is a circular body (~3 km in diameter) which intruded Paleozoic granitoids as well as metasedimentary and metavolcanic rocks of the Alexander Terrane of the North American Cordillera. This shallow seated intrusion, which is composed of fractionated peralkaline granites, is a zoned body with a dominant core of arfvedsonite granite and a rim of aegirine granite. All the rock-forming minerals typically record a two-stage growth history and aegirine and arfvedsonite were the last major phases to crystallize from the magma. Both arfvedsonite and aegirine granites have overlapping compositions. The rocks have high contents of rare earth elements, Th, U and high field strength elements (Zr, Nb, Hf and Ta) and low contents of Sr, Ba, Eu and Ti, typical of peralkaline granites. The complex hosts structurally controlled rare metal mineralization, which is associated with the late-stage of magma evolution and hydrothermal fluids. Fluorine complexing played a role during the transportation of rare metals in hydrothermal fluids. The U-Th deposit, which occurs at the margin of the aegirine granite zone, includes structurally controlled shear zone-hosted lenses and irregularly shaped pipe-like orebodies. U-Th mineralization is associated with desilicified and albitized granitic rocks and includes mainly uranothorite and uraninite. These minerals mostly form small ovoids in veinlets typically 0.1 to 1 mm wide. The mine produced about 77,000 t of ore at a grade of ~0.76% U3O8 and 3% of ThO2. The parent magma of the pluton was likely derived from a metasomatized lithospheric source (mantle or lower crust), which was enriched by subduction related processes during Paleozoic time.

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.).

The deep rare metal metallogenic characteristics of the Jiajika lithium polymetallic deposit in Sichuan Province, China: Revealed by the Jiajika Scientific Drilling

Jiajika, located in the Songpan–Ganzi orogenic belt in western Sichuan Province, is the largest pegmatite-type lithium polymetallic deposit in China. Nanjing University has completed a 3211.21 m scientific drilling (JSD-1) in the Jiajika lithium polymetallic deposit. Pegmatite samples from core of this hole were investigated with the aim of decreasing the bottleneck of upstream exploration and development of lithium resources. Base on the JSD-1 drill core, the pegmatite is poorly zoned, but mineral assemblages reflect a gradual evolution from bottom to top. The dominant feldspar in pegmatites evolve from microcline to albite, and the content of biotite decreases. Muscovite and tourmaline are present in the pegmatite at various depths. Spodumene is the only primary lithium mineral observed in the drill core samples, and is present at 1123 m to 56 m, especially near the surface in albite-spodumene pegmatites. U–Pb dating of columbite in pegmatites, indicate that the main ore-forming age of Jiajika pegmatites is 213.0 ± 1.6 Ma. In addition to lithium, beryllium, niobium and tantalum elements are also enriched in the drill core. Beryllium is dominantly contained in beryl and occurs mainly in pegmatites at depths of 863 m to 56 m. Niobium and tantalum are mainly enriched in columbite-group minerals, and can also occur in Nb–Ta-rich rutile associated biotite. Columbite-group minerals were observed at depths of 1728 m to 56 m. An addition intersection of columbite-group minerals mineralization occurred at a depth of 3186 m. U–Pb dating of the deeper occurrence of columbite minerals yielded a mineralization age of 190.6 ± 2.5 Ma. There are variable concentrations of lithium in muscovite, tourmaline and beryl in the drill core. However, there is a clear negative correlation of lithium concentrations with the depth, indicating the progressive lithium enrichment in the granitic magma. Although the main rare metal mineralization of Jiajika occurred at 213.0 ± 1.6 Ma, another niobium and tantalum mineralization event (190.6 ± 2.5 Ma) in-depth, which is discovered for the first time in this area, deserves also further attention.

Mineralogy, petrology and P-T conditions of the spodumene pegmatites and surrounding meta-sediments in Lhozhag, eastern Himalaya

Several giant industrial-grade rare-metal deposits have been discovered in the Himalaya most recently. However, the mechanism of how rare-metals mineralization formed in the prototype of the collisional belt is poorly understood, mainly due to insufficient studies on mineralogy, petrology and emplacement conditions. In this study, we have reported the whole-rock and mineral compositions of spodumene pegmatites, leucogranite, skarns and P-T paths of metapelites from Lhozhag, eastern Himalaya. Four spodumene pegmatite veins were studied that are enriched in lithium, beryllium, cesium and tantalite (Li-Cs-Ta subtype), mainly hosted by minerals of spodumene, petalite, elbaite, lepidolite, zinnwaldite, and margarite. Li-Be margarite is first reported from the Himalaya, and its lithium and beryllium come from the breakdown of spodumene and beryl. The surrounding skarns are enriched in lithium, beryllium, and tin, mainly hosted by minerals of vesuvianite, scapolite and garnet. Petrography and P-T estimates from the andalusite-staurolite phyllites suggest two stages of metamorphism that earlier Barrovian metamorphism was superimposed by Buchan metamorphism at conditions of 3.1 ± 0.3 kbar and 535°C or 580°C (52–56°C/km) during leucogranite emplacement. Combined with zircon and monazite saturation temperatures and conditions of Buchan metamorphism, the leucogranites should have undergone a first-stage isothermal decompression to crystallization conditions at ∼3.1 kbar and 650–720°C and a second-stage isobaric cooling at ∼3.1 kbar. The pegmatite probably underwent a similar P-T evolution supported by the appearance of two-stage growth of spodumene (Spd-1 and Spd-2 + Qz), petalite corona around spodumene, and cymatolite. The leucogranites/pegmatites have emplaced into the surficial Tethyan Himalayan Sequence simultaneously, causing contact metamorphism, skarnization and undercooling, which may have facilitated rare-metals mineralization in the pegmatites and skarns during the emplacement stage. We suggest that the pegmatites and skarns in Lhozhag, eastern Himalaya have enormous potential for rare-metals exploration.