The magmatic-hydrothermal transition in rare-metal pegmatites is crucial for understanding mineralizing processes, particularly for strategic resources like lithium and beryllium. Tourmaline, a common mineral in pegmatites, serves as an excellent geochemical tracer for this transition. This study examines the Bailongshan Li pegmatite deposit in the western Kunlun Orogen, northwestern China, through detailed textural and geochemical analyses of elbaite (Elb). By integrating data for major and trace elements and Li–B isotope compositions of Elb, the present study delineates the magmatic-hydrothermal transition and its role in ore formation. Elbaite in the Bailongshan Li pegmatite deposit crystallized progressively from Elb-1 (core, magmatic origin, dark green), through Elb-2 (mantle, late magmatic origin, dark green), to Elb-3 (rim, magmatic-hydrothermal transition origin, light green). Li and B isotopes of Elb show different evolutionary trends from Elb-1 to Elb-3: δ11B increases from Elb-1 to Elb-2, whereas no statistically significant variation is observed from Elb-2 to Elb-3.This pattern is interpreted to reflect fractional crystallization (the resolvable core-to-mantle increase) followed by the re-involvement of an early-exsolved, weakly fractionated hydrothermal fluid that imparts no resolvable δ11B change to Elb-3. In contrast, δ7Li remains stable from Elb-1 to Elb-2 but shows a “V”-shaped variation from the late-crystallized range of Elb-2 to Elb-3. This “V”-shaped δ7Li trend likely records a combination of fractional crystallization, melt-fluid separation, and Li diffusion. Boron isotope modeling indicates ≥80% fractional crystallization during Elb-1 and Elb-2 deposition, while Elb-3 formed from exsolved hydrothermal fluids derived from early melt-fluid separation that are re-involved in the crystallization of lithium-bearing minerals (elbaite) during the magmatic-hydrothermal transition with ∼25% fractional crystallization. Elevated δ7Li values (avg. + 14.1 ‰ to + 14.6 ‰) and an increase in mean Li content of ∼1800 ppm between Elb-2 (avg. 5723 ppm) and Elb-3 (avg. 7513 ppm) might reflect Li isotope diffusion driven by concentration gradients. Reintroduced, weakly fractionated exsolved fluids govern Li mineralization (increasing concentrations of Be, Sn, Ta, and Nb) in elbaite during the magmatic-hydrothermal transition at the Bailongshan Li pegmatite deposit. This study identifies that early-exsolved hydrothermal fluids are re-injected into pegmatitic magmas during pegmatite evolution, a phenomenon conducive to rare metal mineralization. Our work enhances understanding of pegmatite evolution and provides a new mechanistic explanation for pegmatite-hosted rare metal mineralization.

The role of ore metals in magmatic fluids during the magmatic-hydrothermal transition in porphyry systems remains unclear, and their contributions to porphyry ore genesis are unclear. This study offers fresh perspectives on the ore-forming process during this critical transition, focusing on the Hongyuan porphyry Mo (Cu) deposit (PMCD) in West Junggar, China. We find that sulfide-quartz-rich miarolitic cavities (MCs), characterized by micrographic quartz and feldspar, indicate the formation of initial mineralizing fluids from magmatic fluids. This conclusion is supported by three key observations: the simultaneous formation of feldspar and sulfides in the micrographic zones of MCs, the high formation temperatures (approaching 750 °C) suggested by the sector-zoned bright CL cores of quartz phenocrysts, and the magmatic sulfur source indicated by the narrow sulfur isotopic composition ranges (+0.18‰ to +4.63‰). LA-ICP-MS analyses reveal distinct trace element distribution patterns between the early magmatic and transition stages and the later hydrothermal stage. Chalcopyrite from the early stages has higher Cd and lower Zn contents, while molybdenite has higher Re contents, and pyrite has higher Co and Ni contents than its counterparts in the hydrothermal stage. The decrease in sulfur concentrations at sulfide saturation from granite porphyry to micrographic quartz-feldspar melts (from 200 ppm to 100 ppm) suggests that nearly half of the sulfur was exsolved during the formation of feldspar and quartz intergrowths from fractionated granitic magma. These findings indicate that the initial mineralizing fluids of the porphyry deposit were high-temperature, melt-bearing, and ore-rich and originated from magma. The transition from initial melt-bearing, metal-rich fluids to hydrothermal ore-forming fluids is marked by decreasing temperatures and logfS2 values, underscoring the critical role of sulfide formation during the magmatic-hydrothermal transition in the development of porphyry deposits.

Miarolitic cavities (MCs) serve as key indicators of volatile phase exsolution during magmatic differentiation, providing critical insights into the transition between igneous and hydrothermal regimes. Despite their metallogenic significance, the mechanisms controlling the selective extraction of metal-bearing fluids remain poorly understood. This study investigates the microstructural and geochemical characteristics of chalcopyrite- and molybdenite-dominated MCs in the Hongyuan porphyry Mo-Cu deposit (NW China). The cavities exhibit sulfide cores surrounded by graphic quartz-feldspar, aplitic, and K-alteration halos. Mass balance calculations reveal enrichments in Cu, Fe, Na, and Si during the magmatic-hydrothermal transition. The term "sulfide-silicate bulb" refers to silica-saturated fluid pockets or bubbles that develop during hypogene copper mineralization in porphyry deposits. The central sulfide-silicate bulbs represent hypersolidus mineral assemblages, with differential Cu-Mo precipitation linked to quartz growth rates. Late-stage meteoric water alteration further influences metal precipitation. We propose a genetic model wherein sulfide-silicate bulbs act as the primary vehicles for the extraction, transport, and focused precipitation of Cu- and Mo-rich fluids. Our results highlight the critical role of quartz growth rates and meteoric fluid influx in controlling metal segregation, providing a new framework for understanding the spatial zonation in porphyry Cu-Mo systems.

Pegmatite-aplite systems are critical hosts for Li, Nb, and Ta mineralization, yet the role of their spatial distribution and overprinting enrichment processes remains poorly constrained. The world-class Bailongshan Li pegmatite deposit (Li2O resource >5 Mt), situated in the Western Kunlun Orogenic Belt of Northwest China, hosts Li-Nb-Ta mineralization primarily in coarse-grained spodumene pegmatites (Spd-1; >3 cm wide; pegmatite layer). These Spd-1 pegmatites are crosscut by fine-grained, spodumene-bearing pegmatites (Spd-2; <3 cm wide; aplite layer) that also exhibit distinct Nb-Ta-Sn enrichment. Two types of aplite are distinguished in the Bailongshan deposit: (1) aplite associated with and parallel to pegmatite zones, which is mostly spodumene-free, and (2) aplite layers that crosscut pegmatite zones at a small angle, exhibit a fine-grained texture, host fine-grained spodumene, and are characterized by typical hydrothermal alteration. Geochronology of columbite-group minerals (CGMs) in the coarse-grained pegmatite and fine-grained aplite layers reveals primary magmatic crystallization at ca. 210 Ma and a later metasomatic alteration at ca. 190 Ma (191.8 +/- 1.5 Ma to ca. 191.0 +/- 1.4 Ma), recorded by CGMs with higher Sn, Hf, Zr, and total rare earth elements (Sigma REEs) with dissolution-precipitation textures. Spd-2 crystals in the fine-grained spodumene pegmatite primarily xenocrystic, as the structural data obtained from single-crystal X-ray diffraction of both coarse-grained and fine-grained spodumene exhibits comparable structural characteristics. The electron backscatter diffraction (EBSD) data indicated a slight orientation difference (0 degrees to 2 degrees) between Spd-2 grains and the larger Spd-1 crystals. Coarse-grained Spd-1 was incorporated the fine-grained aplite layer to form the xenocrystic Spd-2; this is evidenced by their comparable crystallographic structures despite the elevated Na, Mn, Fe, Ga, and Sn concentrations in Spd-2. The "bookshelf" structures in the aplite layer further suggest that ductile deformation facilitated the mechanical disaggregation of spodumene; this, combined with metasomatic alteration, contributed to localized Nb-Ta-Sn enrichment.

Lithium-rich granitic pegmatites supply approximately 50–60% of global Li production, yet the physicochemical mechanisms driving their exceptional Li enrichment remain contested. Here, we integrate cathodoluminescence (CL) imaging and LA-ICP-MS trace element mapping of quartz crystals from miarolitic cavities at the world-class Bailongshan Li deposit (Western Kunlun Orogenic Belt, NW China) to decipher crystallization dynamics during the magmatic–hydrothermal transition. We identify three growth zones composed of a serrated core (Q1) and oscillatory rims (Q2/Q3) recording up to ≥5 discrete fluid-pulse events, with Al and Li concentrations spanning two orders of magnitude and co-varying with CL brightness. We demonstrate that episodic fluid pressure drops transiently accelerate crystal growth and thin the chemical boundary layer at the crystal–fluid interface. We interpret this thinning as suppressing diffusive re-equilibration and enabling the kinetic incorporation of coupled Al-Li substitutions into quartz, whereas under steady-state pressure near-equilibrium partitioning inhibits Li uptake. Diffusion modeling supports systematically increasing growth rates from core to rim, consistent with progressive fluid exsolution. Crucially, we show that miarolitic quartz exhibiting ≥5 high-frequency Al-Li oscillation cycles is a robust indicator of rare-metal fertility and enhanced Li-transport capacity, providing an exploration criterion applicable across the world’s major Li pegmatite provinces. Episodic drops in fluid pressure within granitic pegmatite systems transiently accelerate crystal growth and enable the incorporation of Al and Li substitution within quartz, according to analysis of quartz in miarolitic cavities from the Bailongshan deposit.

Recent advances have significantly enhanced our understanding of the magma source, magma evolution, and sulfur saturation mechanisms of the Kalatongke Cu-Ni sulfide deposit in the Central Asian Orogenic Belt. However, limited systematic research has explored the structures that are critical to magma emplacement and sulfide accumulation. In this study, we perform a systematic multiscale analysis of the lithofacies distribution, morphology, and structural relationships between the northern and southern belts of the Kalatongke deposit. We propose that the emplacement and distribution of mafic intrusions and associated sulfide orebodies were controlled by fractures through syn-dextral shear deformation. The geometry of the Y1 and western Y2 intrusions and their mineralization were predominantly controlled by extensional T-fractures resulting from syn-shear deformation, whereas the eastern Y2 and Y3 intrusions were primarily governed by horizontal compressive-slip C-fractures, along with Riedel R and R' fractures. In the northern belt, the Y7 intrusion and its mineralization were influenced by shear between two sets of horizontal fractures trending northeast, which are nearly perpendicular to the main fault orientation of the southern and northern belts. Based on the characteristics of the fractures and the distribution of orebodies across the northern and southern belts, we propose that the Kalatongke deposit was controlled by a negative flower structure, suggesting the presence of deep structural connectivity between the northern and southern belts. Moreover, the distribution pattern of the sulfide orebodies in the Kalatongke deposit was governed primarily by the structures and their associated stress regimes.

Understanding the formation of lithium-rich pegmatites is critical for meeting global lithium demand. The 509 Daobanxi Li pegmatite deposit, located in the West Kunlun orogenic belt of northwestern China, represents a significant example of an LCT-type (Li-Cs-Ta) pegmatite system. This study investigates the paragenetic sequence of lithium (Li) minerals and the factors controlling their crystallization, providing new insights into the magmatic-hydrothermal evolution of rare-element pegmatites. Pegmatite dikes exhibit distinct zonation, comprising a wall rock zone, a border zone (aplitic layer), and a core zone (pegmatitic layer), with Li mineralization concentrated in the pegmatitic and aplitic layers. The primary Li minerals include spodumene (Spd), montebrasite (Mbs), eucryptite (Ecr), elbaite (Elb), and lepidolite (Lpd), which crystallize in the order of spodumene → montebrasite → elbaite → lepidolite. Spodumene, the dominant Li-bearing mineral, crystallizes from a Li-saturated melt during the magmatic stage. Montebrasite, a Li-phosphate mineral, forms in P-rich environments, coexisting with spodumene and columbite-group minerals (CGM). During the magmatic-hydrothermal transition, elbaite crystallizes from a B-rich melt, exhibiting skeletal and patchy zoning due to undercooling and disequilibrium crystallization. Hydrothermal alteration leads to the breakdown of spodumene and the formation of secondary minerals such as eucryptite and lepidolite, with lepidolite being the final Li-bearing phase, enriched in fluorine. The coupled dissolution-precipitation processes during the magmatic-hydrothermal transition play a critical role in the remobilization and enrichment of rare elements such as Li, Nb, Ta, and Sn. This deposit, characterized by spodumene crystallization in the Spd + Quartz stability field (⩾300 MPa, ⩽725 °C) and subsequent alteration to Ecr + quartz assemblages (<270 °C, <160 MPa), exhibits broader temperature-pressure conditions exceeding typical global pegmatites like Tanco, with no petalite formation observed due to its persistent exclusion from petalite stability fields throughout mineralization. The shear zone controls the pegmatite emplacement and lithium enrichment in the 509 Daobanxi lithium deposit, and its deformation-fluid coupling mechanism provides new insights for the exploration of LCT pegmatite deposits. The present study highlights the importance of understanding both magmatic and hydrothermal processes in the formation of LCT-type pegmatites and provides valuable insights for the exploration of critical metal resources in similar geological settings.

The Northwest Tibet region is defined by several terranes, magmatic belts, basins and sutures, which were primarily shaped by the tectonic activities associated with Proto-, Palaeo- and Neo-Tethys Oceans. However, the basement nature and Precambrian tectonic evolution of the Northwest Tibet region, particularly within the Tashikuergan-Tianshuihai terrane, remain largely unknown. The Hongliutan area, located in the northeastern part of the Tashikuergan-Tianshuihai terrane, contains a critical sequence of Precambrian metamorphic rock strata. Detailed petrological, geochronological, and geochemical analyses of these metamorphic rocks - including plagioclase schist, quartz schist, amphibolite and nearby leucogranite - reveal the intricate processes of tectonic evolution within the Tianshuihai unit. Combining these findings with previous geochronological results is crucial for re-evaluating the nature of the Tashikuergan-Tianshuihai basement and its Precambrian tectonic evolution of the Tashikuergan-Tianshuihai basement. Our results reveal the following: (1) the leucogranite and amphibolite, identified as Cambrian igneous rocks, display distinct geochemical signatures indicative of a continental arc origin. These include calc-alkaline characteristics, enrichment in Th, U, Pb, Zr and Hf and depletion in Ba, Nb, Sr and Ti. Their epsilon Nd(t) values, close to zero, further support this tectonic setting, with the leucogranite and amphibolite formed at 506 and 522 Ma, respectively. (2) The plagioclase schist and quartz schist are interpreted to be Neoproterozoic volcaniclastic rocks that formed in a rifted (passive) continental margin setting. The quartz schist is particularly rich in detrital zircons, displaying a broad spectrum of 207Pb/206Pb ages, ranging from 901 to 3364 Ma. (3) A significant subset of detrital zircons within the quartz schist exhibits oscillatory zoning, high Th/U ratios and sharp-edged, anhedral-to-subhedral crystal forms, suggesting a derivation from proximal or deep-seated terranes. The concordant U-Pb zircon ages of 2468 and 974 Ma from the quartz schist, along with the 978 Ma age from the inherited zircons in the amphibolite, and the 1.2-2.1 Ga T2DM(Nd) from leucogranite and metamorphic rocks, collectively suggest that the Tianshuihai unit is likely underpinned by a Palaeoproterozoic basement that indicates Neoproterozoic reworking.Therefore, our findings suggest the presence of a continuous, northwest-southeast trending Palaeoproterozoic basement underlying the entire Tashikuergan-Tianshuihai terrane. An alternative scenario posits that the ancient basement, currently beneath the Tashikuergan terrane, could extend into the Tianshuihai region, potentially indicating a Cambrian continental margin arc interspersed with remnants of older terranes.

The Late Triassic to Early Jurassic (ca. 220 to 190 Ma) Dahongliutan pegmatite belt, located in the Western Kunlun orogenic belt, NW China, is a newly discovered, large Li-Be ore district comprising > 320 individual rare-metal pegmatites. The pegmatite belt was emplaced in a post-orogenic setting in relation with a ductile shear zone related to the Dahongliutan detachment fault, which is spatially and temporally related to post-orogenic exhumation. Deformed spodumene pegmatites, mostly striking NW with dip angle of 50 80°, occur within or adjacent to the NW-striking detachment fault. We present new field observations, mineralogical, geochemical and geochronological results from the Dahongliutan pegmatite belt, which lead to the following conclusions: 1) High-medium temperature/middle-to-low pressure metamorphic rocks and granitoids were intruded by ductile-deformed spodumene-bearing pegmatites during development of the gneissic domes; 2) Spodumene pegmatites from the Aktas, Kalaka, Bailongshan and Longmenshan deposits record two age groups, a first one during the Upper Triassic at ca. 212–205 Ma, and a second one during the Lower Jurassic at ca. 195–193 Ma, as revealed by in-situ Rb–Sr dating of micas and U–Pb dating of columbite-group minerals; 3) Textural observations and geochemical analyses of coexisting quartz and spodumene further indicate that ductile deformation provided favorable conditions for enrichment of Li and Be in pegmatites. The Western Kunlun-Songpan Ganzi rare-metal pegmatite belt shows a close spatial and genetic relationship with ductile shear zones induced by detachment faulting, making it a potential proxy for exploration targeting of Li-Be-mineralized occurrences at the regional scale as well as in other metallogenic provinces worldwide.

The Bayan Obo ore deposit is the largest rare earth element (REE) deposit in the world and has been assumed to be hosted in dolomite that was folded in a syncline. This has been challenged by results from drill holes and low-resistivity, controlled-source audio-frequency magnetotellurics (CSAMT) survey. In this paper, we present structural analysis of clastic sedimentary rocks from around the deposit, their relationship with carbonatite, and the orientations of the carbonatite bodies and dikes to constrain the possible configuration of carbonatite. Clastic sedimentary rocks underwent mylonitic deformation to slate, metasandstone, and metaconglomerate, displaying dramatic changes of thickness along strike. Slates locally preserve intrafolial folds and hook folds bounded by foliations; metasandstones have parallel layers of recrystallized and preferred-orientated quartz aggregations; metaconglomerates contain flattened pebbles with Flinn k values of 0.01 to 0.05 and 0. The above structures and foliations were crosscut and intruded by carbonatite and associated fenite, demonstrating preintrusion transposition of original bedding to steep foliation. Preintrusion foliation provides zones of weakness that were exploited by upwelling of carbonatite magma. Northeast-SW-striking left-stepping en echelon carbonatite dikes and E-W-striking carbonatite bodies indicate that the carbonatite was emplaced in a sinistral transtensional zone. The northern and southern segments of the carbonatite bodies are parallel to the steep foliation at shallow depths and merge together at depth, constraining a Y-shaped configuration, consistent with the low resistivity result of the CSAMT survey. The newly recognized Y-shaped morphology indicates that the carbonatite extends deeper than 1,775.4 m, more than twice the previously inferred maximum depth of the syncline model, and contributes to a significant >1.78 times increase in global potential RE2O3 resources than previously estimated in 2021.

Bayan Obo ore deposit is the world’s largest rare-earth element (REE) resource, the second largest niobium (Nb) resource, and also a significant iron (Fe) resource in China. Evaluating resource potential for the deposit has become a focus of global interest. Rock-physical properties bridge geophysical exploration and geologic modeling; variation in these parameters is necessary for successful geophysical application. REE, Nb, iron, and potassium are mainly hosted in dolomite and slate of the Bayan Obo Group, and REE mineralization is genetically associated with carbonatite. Three physical properties (resistivity, polarizability, and magnetic susceptibility [MS]) of iron ore, slate, dolomite, and carbonatite dike outcrop samples at Bayan Obo are measured and statistically analyzed using 3D reconstruction, 1D/2D/3D kernel density estimation, scatterplot matrix, 3D histogram, and Pearson- and maximum information coefficient-based correlation analysis. It is evident that iron ore, iron-mineralized fine-grained dolomite, and iron-mineralized slate are mainly of low resistivity, and iron ore and iron-mineralized fine-grained dolomite have high MS. MS favorably distinguishes iron ore from slate; MS and resistivity distinguish between iron-mineralized fine-grained dolomite and carbonatite dikes. The physical properties and whole-rock geochemistry (major and trace elements) jointly demonstrate that MS of iron ore, slate, and dolomite is positively correlated with TFe 2 O 3 content, polarizability is correlated with TFe 2 O 3 , SiO 2 content is correlated with K 2 O, and resistivity is correlated with MS and polarizability, respectively. Resistivity of iron ore and dolomite is negatively correlated with TFe 2 O 3 content. Resistivity of iron ore is negatively correlated with TFe 2 O 3 , total REE ([Formula: see text]), and Nb, respectively, and correlated with thorium. The methods used have intuitive visual expression and reflect the characteristics of the physical properties and their correlation with the mineralogical composition. The results will be beneficial for determining the geometry of ore-hosting rock masses and providing crucial evidence for the resource evaluation.

The Central Altun orogenic system is a result of the amalgamation of multiple micro-continental blocks and island arcs. This complex system originated from subduction–accretion–collision processes in the Proto-Tethys Ocean during the Early Paleozoic. Research has reported the discovery of several Li-Be granitic pegmatite deposits in the Central Altun Block, including the North Tugeman granitic pegmatite Li-Be deposit, Tugeman granitic pegmatite Be deposit, Tashisayi granitic pegmatite Li deposit, South Washixia granitic pegmatite Li deposit, and Tamuqie granitic pegmatite Li deposit. The Tashidaban granitic pegmatite Li deposit has been newly discovered along the northern margin of the Central Altun Block. Field and geochemical studies of the Tashidaban granitic pegmatite Li deposit indicate: (1) Spodumene pegmatites and elbaite pegmatites, as Li-bearing granitic pegmatites that form the Tashidaban granitic pegmatite Li deposit, intrude into the two-mica schist, and marble of the Muzisayi Formation of the Tashidaban Group. (2) Columbite–tantalite group minerals and zircon U-Pb dating results indicate that the mineralization age of Tashidaban Li granitic pegmatites is 450.2 ± 2.4 Ma with a superimposed magmatic event at around 418–422 Ma later. (3) Whole-rock geochemical results indicate that the Kumudaban rock sequence belongs to the S-type high-K to calc-alkaline granites and the Tashidaban Li granitic pegmatites originated from the extreme differentiation by fractional crystallization of the Kumdaban granite pluton.

The Xilekuduke porphyry Mo-Cu deposit is located in the Altay-East Junggar region of the Central Asian Orogenic Belt, northwest China. The orebodies occurring as vein type are host within the monzogranite and granite porphyry. Ore minerals include mainly molybdenite, pyrite, and chalcopyrite, whilst the major alteration include potassic, sericite, carbonate, and silicic. Mineralization can be divided into three stages: quartz-K-feldspar-polymetallic stage (Stage I), quartz-polymetallic stage (Stage II), and quartz-calcite-pyrite (minor) stage (Stage III). Three types of fluid inclusion are present in the Mo-Cu sulfide-calcite-quartz veins: CO2-bearing (C-type), aqueous (W-type), and daughter mineral-bearing (S-type). Petrographic and microthermometric analyses of the fluid inclusions yielded homogenization temperatures for Stage I, II, and III to be 402-499 degrees C, 214-391 degrees C, and 136-254 degrees C, respectively, with corresponding salinities of 39.2-59.6, 3.7-44.9 and 4.1-14.4 wt% NaCl equivalent. The delta O-18(H2O) and delta D values of fluid inclusions in quartz are determined to be 5.3-6.0 %degrees and -76 to -60 %degrees (Stage I), 1.7-3.2 %degrees and -96 to -90 %degrees (Stage II), and -2.6 to -2.4 %degrees and -106 %degrees (Stage III), respectively. These results indicate that the primary ore-forming fluids (stages I and II) were derived from granitic magma and were mixed with meteoric water in stage III. For the sulfide and sulfate (anhydrite), their delta S-34 values are of 0.4-5.8 %degrees, 13.9-14.4 %degrees, respectively, also that suggest a magmatic source. Fluid immiscibility, meteoric water interaction, and ore fluid-wallrock interactions may have been critical for molybdenum precipitation.

Micro-continent collision and amalgamation play pivotal roles in continental convergence and contribute significantly to continental crustal growth. However, the understanding of multiple micro-continent amalgamation processes, particularly their influence on the formation of large Li-Be deposits, remains limited. The Altun orogenic system, resulting from the collision and amalgamation of three micro-continents in the Proto-Tethys Ocean, has recently revealed numerous granitic pegmatite-type Li-Be deposits, presenting an ideal opportunity to investigate the mineralization. Our research focused on two large granitic pegmatite Li deposits, South Washixia and Tamuqie in the Central Altun Tagh, Northwest China. Our findings suggest: 1) The structural and photomicrograph characteristics observed in both the Tamuqie and South Washixia granitic pegmatite Li deposits, indicate that the pegmatites emplaced in shear zone within a contractional deformation zone. 2) The age of the large granitic pegmatite Li deposit in South Washixia between 447 similar to 445 Ma, while the Tamuqie Li pegmatites formed at 448 Ma with Li-barren pegmatites formed at around 418 Ma. It is suggested that the large granitic pegmatite Li deposit in the Central Altun Block, encompassing South Washixia and Tamuqie granitic pegmatite Li deposits, originated during the final collision event of three micro-continent blocks (Qaidam, AltunQilian, and Dunhuang-Alex). We suggest that during the final collision and amalgamation event of multiple micro-continents triggering intense compression and thickening of the crust, and the thickened lower crust may undergo shear-driven dehydration melting of biotite in granulite facies to produce large-volume granitic magmas. These magmas crystallize and differentiate into lithium-rich pegmatitic magmas along shear zones, forming large lithium pegmatite deposits. Our research presents a novel mechanism for the formation of granitic pegmatite Li deposits, which emphasizes the role of shear-driven dehydration melting during the final collision and amalgamation events of three micro-continents.

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 Bemineralized 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 %o to -14.8 %o, 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).

The Bayan Obo deposit in China hosts the world's largest rare earth element (REE) resource. Age dating results for Bayan Obo range across approximately one billion years (from similar to 1.4 to 0.3 Ga), with three age groups (similar to 1.3 Ga, similar to 0.45-0.40 Ga, and 0.28-0.26 Ga). Carbonatite dated to around 1.3 Ga and granitoids to approximately 270 Ma have been identified. The Early Paleozoic vein-type mineralization is widespread in the deposit. However, magmatic activity related to the highest age peak at similar to 0.4 Ga has not well been identified in the deposit, complicating the interpretation of the ore genesis. In this study, we report a zircon Th-232-Pb-208 age of 435.2 +/- 4.6 Ma (MSWD = 1.9, N = 26) from carbonatite in Bayan Obo. The zircon morphology, characterized by bipyramidal crystal forms, low U concentrations (mostly < 1 ppm), high Th/U ratio, and carbonatite-like oxygen isotopes (5.92 +/- 0.31 parts per thousand), demonstrates that the zircon crystallized from carbonatitic magmas, thus their ages represent the timing of magmatic activity. Although remelting of the Mesoproterozoic carbonatite during Paleozoic carbonatite has been previously documented, the newly identified Early Paleozoic carbonatite derives from a different mantle source, as indicated by their more radiogenic Hf isotope compositions. This suggests that the Bayan Obo deposit experienced multiple carbonatitic activities. The Early Paleozoic carbonatitic activity may have facilitated element mobilization and mineral recrystallization, improving the exploitable levels of the world's largest REE deposit.

The Altyn Tagh region, as a belt of the Proto-Tethys tectonic belts, has not been paid attentions to the exploration and study of lithium (Li) and beryllium (Be) deposits for long time. After detailed analyses of geological data, we found that the Altyn Tagh region has potential for Li and Be mineralization. Then, we firstly enter the Altyn Tagh region to survey and search Li and Be deposits in 2018, and discovered many pegmatite-type Li-Be deposits. In this contribution, we summarized characteristics and metallogeny of these deposits in the Central Altyn Tagh as follows: (1) the pegmatites exhibit a diversity of types, reflecting regional zonation, with some displaying complex internal zonation; (2) the Li-Be pegmatites are the result of the granitic evolution in the area, with a regional zonation from biotite granite to two-mica granite, muscovite granite, albite granite, tourmaline granite, and various types of pegmatites including beryl, cassiterite, spodumene, lepidolite, and pollucite pegmatite; (3) these granites and pegmatites were products of the fractional crystallization of granitic magma, originating from biotite dehydration melting of meta-argillaceous sandstones under granulite facies conditions; this process is influenced by the regionally tectonic evolution. The pegmatite-type Li-Be deposits in the Tugeman region of Altyn Tagh are attributed to the convergence and collision between the Central Altyn and South Altyn blocks, while the deposits in the Tamuqie and Southern Washixia region adjacent to the Tatebulake batholith resulted from the ultimate collision of three continental blocks. With abundant Early Paleozoic granitic intrusions and favorable geological settings, the Central Altyn Tagh is anticipated to be a significant lithium resource for China.

The Tashisayi Li deposit was newly discovered in the eastern part of the Tashisayi batholith, located in the Altyn Tagh region of Northwest China. A Li-rich composite pegmatite-aplite dyke (γ02) displays superimposed relationships among different Li-bearing phases, including lepidolite-albite-quartz pegmatite (LAQ), spodumene-albite-quartz pegmatite (SAQ), and aplite. The timing and conditions of magmatism and Li mineralization in the Tashisayi remain enigmatic. The study involved field observations, U–(Th)–Pb dating of columbite-group minerals (CGM), zircon, and monazite, and geochemical analyses of CGM and quartz. U–Pb dating of CGM of the γ02 dyke revealed formation ages of 471.6±3.5 Ma (LAQ), 439.6±5.0 Ma (SAQ), and 416.3±4.8 Ma (aplite). Zircon U-Pb and monazite U-(Th)-Pb dating of biotite granite, pegmatitic aplite, and muscovite granite yielded ages of ca. 473 Ma, 439 Ma, and 425 Ma, respectively. The dating results indicate that the rare-metal pegmatites and granites in the Tashisayi area were emplaced during various periods from the Early Ordovician to Early Devonian, consistent with other rare-metal deposits in the Tugeman region. The textural and geochemical analyses on the CGM and quartz reveal that the LAQ, SAQ and aplite crystallized from highly evolved magmas under water-poor and relatively low temperature conditions, experiencing distinct evolution trend and forming processes. Additionally, both LAQ and SAQ were influenced by fluid or magma activities and the pegmatitic melt forming LAQ could enrich both Li and Sn. Extensive tectonic events in the Altyn Tagh Orogen, including ocean basin closure and continental collisions, promote the development of Li-rich granitic magmas. Thus, we argue that the multiple magmatic and Li mineralization events in the Tashisayi area are most likely originated from the melting of Proterozoic crustal materials, and the process was controlled by tectonic interactions between the Central Altyn, Southern Altyn, Northern Altyn, and Eastern Kunlun blocks.

伟晶岩型锂铍矿床是国家紧缺的战略性金属锂铍的重要供给矿床类型.但伟晶岩成因中深熔作用产生熔体量少、萃取锂铍效率低;岩浆结晶分异能否高度富集和高效萃取锂铍也存在争议;随着富锂铍的硅酸盐熔体、熔体-热液不混溶作用的发现,岩浆不混溶作用可能也是新的成因机制.近年来,针对伟晶岩型锂铍矿床的熔体至热液阶段成矿过程的研究主要集中在:花岗伟晶岩全岩地球化学特征解析;造岩矿物(云母、石英、长石等)与矿石矿物(绿柱石等)的精细微区元素地球化学变化规律的总结;造岩矿物、矿石矿物及副矿物(石榴石等)中熔体-热液包裹体矿物学-地球化学特征解析.但伟晶岩矿床中熔体、流体包裹体类型复杂,且与矿床形成时代也没有明显关联性. 锂铍在熔体-热液相间的分配行为和分配过程,以及运移锂铍的络合物稳定性差异是深入认识锂铍超常富集机制的关键.然而,对锂铍在熔体-热液相间分配行为的研究仍然相对薄弱,针对运移锂铍的络合物的稳定性也未开展研究.我们设计了不同矿化溶液的pH值、不同钙和铝含量影响下锂铍络合物结晶锂铍的实验,发现锂铍元素在以上3种不同条件下存在明显的差异性结晶沉淀行为:(1)pH对铍络合物的稳定性控制比锂络合物更明显;(2)在pH值不变的条件下,铝的加入促进了铍的沉淀,却影响锂的沉淀;(3)钙的加入对锂沉淀的影响没有对铍沉淀的影响大.后续将从实验地球化学角度(高温高压实验模拟)剖析锂铍各自络合物的类型、稳定性受控因素,以期建立"锂、铍络合物失稳-成矿"新机制.