Magmatic-hydrothermal Evolution Research Articles

Zircon and cassiterite geochronology of Sn-polymetallic pegmatite from the Xianghualing ore field, South China: Implications for multi-stage magmatic-hydrothermal events

The Nanling metallogenic belt (South China) is one of the largest W-Sn polymetallic provinces in the world. The ore bodies are mainly hosted in Triassic-Jurassic granitoids which formed during a complex history of magmatic evolution. Among them, the Laiziling pluton, which forms the northern part of the Xianghualing district, is an example of Sn-polymetallic deposits that underwent multiple Mesozoic episodes. In this study, the first in-situ U-Pb age dating of zircon and cassiterite minerals, trace element, and Lu-Hf isotopic data are reported for Laiziling NYF-type pegmatites. Four types of pegmatites are identified: stock-like pegmatite, vein-type pegmatite, peripheral vein-type pegmatite, and cap/sill-like pegmatite. Zircon LA-ICP-MS U-Pb geochronology of pegmatites yields an age of ~150 Ma, which is consistent with the age of the associated mineralized granitic pluton. Results of cassiterite age dating indicate that the W-Sn mineralization took place at ca. 150 Ma coeval with pegmatite emplacement. Combined with structure and trace element composition, two young ages (i.e., ~130 and 90 Ma) can be identified from pegmatite veins, suggesting that the studied zircon crystals experienced two distinct periods of magmatic-hydrothermal evolution during the Cretaceous (related to Late Yanshanian magmatism). In addition, some zircon grains are obviously enriched in LREE, which is associated with hydrothermal metasomatism. Compared to the narrow range of magmatic zircons, a wide range of inherited zircons (Proterozoic to Paleozoic) are observed in the studied Late Jurassic pegmatite (Pg1 and Pg2b), suggesting that they were incorporated from pre-existing basement rocks during magma ascent and/or emplacement. Furthermore, U-Pb data for 14 disseminated cassiterite grains yield a 206Pb/238U age of 221.5 ± 4.2 Ma, documenting evidence of cassiterite inheritance during melt ascension from country rocks or representing the initial stage of Sn enrichment. The εHf values of magmatic zircons show negative εHf values from −4.4 to −16.6 and their crustal model ages (TDM2) vary between 1328 Ma to 2200 Ma, suggesting the parent magma of the Laiziling pegmatites were derived from partial melting of older crustal components (Proterozoic basement in the Cathaysian Block of South China) and the mixing of mantle materials. This study proposes that multi-stage magmatic-hydrothermal events may have occurred not only in the Xianghualing area but also in the whole Nanling Range, and provides fresh insights into the formation processes of rare metal-bearing pegmatites in South China.

Tracing the magmatic-hydrothermal evolution of the Xianghualing tin-polymetallic skarn deposit, South China: Insights from LA-ICP-MS analysis of fluid inclusions

Tracing the magmatic-hydrothermal evolution of the Xianghualing tin-polymetallic skarn deposit, South China: Insights from LA-ICP-MS analysis of fluid inclusions

Quartz fluid inclusions and trace elements in the Lailisigaoer porphyry Mo deposit, Western Tianshan, Xinjiang: Fluid evolution and metallogenic mechanism in magmatic-hydrothermal system

The Lailisigaoer deposit is a typical porphyry Mo deposit located in the late Paleozoic Boluokenu metallogenic belt of Western Tianshan, NW China. This study aims to understand molybdenum mineralization and the dynamics of magmatic-hydrothermal fluid within the porphyry system, focusing on fluid inclusion, cathodoluminescence textures, and trace elemental composition in various generations of quartz. Six vein types in the Lailisigaoer deposit are classified as comb quartz veins with unidirectional solidification texture (UST, QI), actinolite/biotite ± quartz veinlets (M-type, QII), quartz-chalcopyrite vein (A-type, QIII), quartz-molybdenite vein (B-type, QIV), quartz-pyrite vein (D-type, QV) and quartz-carbonate vein (E-type, QVI). Micro thermometry data indicate decreasing homogenization temperatures in primary fluid inclusions from UST to E-type veins. The magmatic-hydrothermal fluids associated with UST and M-, A-, B-, D-, E-type veins underwent a transition from high temperature (342–495℃), high-pressure (∼1.25 kb), and variable salinity (6.7–41.1 wt%NaCl) in the H2O-CO2-NaCl system to low-temperature (142–238℃), low-pressure (∼0.25 kb), and low-salinity (1.6–5.1 wt%NaCl) in the H2O-NaCl system. This evolution is reflected in the proportion of quartz with oscillatory zones decreasing and irregular quartz increasing, indicating a shift from turbulent to stable fluid conditions. Furthermore, a gradual reduction in Ti concentration (from 79 ppm in UST to 1.4 ppm in E-type quartz) suggests a decrease in fluid temperature during the magmatic-hydrothermal evolution. Mineralization primarily occurs in A- and B-type veins, with molybdenum precipitation attributed to fluid immiscibility in a medium–high temperature (240–368 ℃) and high pressure (∼0.95 kb) environment. The A-type veins (mean 31 ppm in Ti concentrations) consist of equigranular (dark-core) (QIII-1) and patchy inhomogeneous CL-gray quartz (QIII-2). The B-type veins (mean 24 ppm in Ti concentrations) are characterized by equigranular (bright-core) inhomogeneous quartz (QIV-1) with growth zones that are cemented by later mosaic homogeneous CL-gray quartz (QIV-2). Based on the quartz-Ti thermometer, the mineralized veins (A- and B-type) were confined to be formed at depths of 2.8–3.6 km, with molybdenum mineralization occurring at 3.4–3.6 km. Molybdenum mineralization initiates during the QIV-1 crystallization period in magmatic-hydrothermal fluids and terminates in the QV-2 generation.

Magmatic–Hydrothermal Evolution at the Barren Wushan Pluton, Southeast China: Insight into Controls on Mineralization Potential

Abstract A-type granites typically exhibit enrichment and mineralization of critical metals such as molybdenum and tin, essential for emerging technologies. However, the key factors influencing their mineralization potential remain elusive. The scarcity of studies on barren systems impedes the understanding of this question. Here, a detailed melt and fluid inclusion study was conducted on the barren Wushan pluton to reconstruct its magmatic evolution and magmatic–hydrothermal transition and explore the factors controlling the metallogenic potential of Mo and Sn in A-type granites. The Wushan pluton displays apparent lithological zoning consisting of two major phases, i.e., medium-grained seriate to porphyritic alkali feldspar granite and fine-grained porphyritic granite. Miarolitic cavities are widely developed in each lithofacies. The silicate melt inclusions from two granitic phases are rhyolitic, with moderate F contents (0.06–0.53 wt %) and depleted H2O contents (2.0–3.5 wt %). Melt inclusions show a wide range of incompatible element contents, such as Cs (9–1977 μg/g) and Rb (268–2601 μg/g), suggesting that Wushan has undergone a high degree of magma evolution. Mo behaves incompatibly in the magmatic evolution, and its content is enriched with the increasing degree of fractional crystallization, but remains constant after the Cs content exceeds 50 μg/g. Rayleigh fractionation model suggests that a large amount of Mo is extracted from fluid exsolution, which restrains Mo from further enrichment. In contrast, Sn behaves as a mildly incompatible element during the entire magmatic evolution history. The contents of Sn increase slowly compared to the trend of Mo, and the maximum contents reach ~30 μg/g in the highly evolved melts. The separation and crystallization of Sn-bearing minerals such as biotite, magnetite, and titanite inhibit the enrichment of Sn. Intermediate-density (ID-type) fluid inclusions hosted in the miarolitic quartz, representing the initial fluid exsolving from magma, display high Mo but low Sn concentrations. Constrained from two assemblages of coexisting ID-type fluid and melt inclusions, the fluid/melt partition coefficients of metals are obtained, with DMo, fluid/melt at 16–19, while DSn, fluid/melt is only about 1. The comparison between Mo-mineralized and barren intrusions worldwide shows that the metal contents in melts and fluids are not fundamentally different. The mineralized intrusions are characterized by the lower melt viscosity and the development of apophyses, both of which facilitate the extraction of metals and fluids from large magma chambers, followed by their concentration into a small rock volume. Consequently, it appears that physical and structural conditions rather than chemical compositions play a crucial role in the Mo mineralization process. Enrichment of Sn in melts is necessary but not decisive for Sn mineralization, whereas Sn enrichment in the initial exsolving fluid determines the Sn mineralization potential of a given granitic system. Compared to Sn enrichment in source melting and fractional crystallization which commonly enhance final Sn fertility in the highly evolved melts, the efficiency of Sn partitioning between melt and fluid plays a fundamental role in converting melt fertility into Sn-enriched fluids and thereby high mineralization potential of the magmatic–hydrothermal system. Our findings suggest a prospect for Mo exploration in the coastal A-type granite belt in South China, while the potential for Sn mineralization is expected to be limited.

Geochronology and geochemistry of zircon and columbite–tantalite group minerals from the Weilasituo Sn–polymetallic deposit, northeastern China: Implications for the relationship between mineralization and the magmatic–hydrothermal transition

The Weilasituo Sn–polymetallic deposit, located in the southern portion of the Great Xing'an Range of Inner Mongolia, China, is a super-large Sn deposit associated with abundant Li, Rb, Nb, Ta, Zn, and Cu resources. Despite that previous studies have characterized the age, hydrothermal evolution, and genetic relationship between the alkali feldspar granite porphyry and associated Sn–polymetallic mineralization, the magmatic–hydrothermal evolution and ore–forming processes remain ambiguous. To address these ambiguities and bridge this knowledge gap, this contribution characterizes the texture, geochemistry, and U–Pb isotope composition of zircon and columbite–tantalite group minerals (CGMs) from amazonitized alkali feldspar granite (AMG) and albitized alkali feldspar granite (ABG) in the Weilasituo deposit. Type-I zircon (Zr1) is inclusion-poor, translucent, and is characterized by low light rare earth element (LREE) contents, high (Sm/La)N ratios (mean = 655.7), and low Th/U (mean = 0.21 < 0.3), Zr/Hf (mean = 5.46), and Y/Ho ratios (mean = 4.42), indicating that it formed during the magmatic–hydrothermal transition. Type-II zircon (Zr2) is inclusion-rich, porous, has a low CL response, and is characterized by low Th/U ratios (0.08–0.32, mean = 0.17), high LREE contents, weakly positive Ce anomalies, and low (Sm/La)N ratios (mean = 20.7), indicating that it formed via hydrothermal alteration of Zr1 (i.e., magmatic–hydrothermal zircon). Type-I CGM (CGM1) generally lacks oscillatory zoning, and has similar and positively correlated Ta/(Nb + Ta) and Mn/(Mn + Fe) values (AMG: R2 = 0.93; ABG: R2 = 0.75), indicative of a magmatic origin. Type-II CGMs (CGM2) occur as rims on CGM1 and are characterized by higher Ta/(Nb + Ta) and lower Nb/Ta ratios than CGM1, indicative of precipitation from a hydrosilicate liquid during the magmatic–hydrothermal transition. Based on the characteristics of CGMs, two stages are evident in the evolution of the Weilasituo granite porphyry: an earlier magmatic differentiation stage and a later magmatic–hydrothermal transition stage. Furthermore, the magmatic–hydrothermal transition stage can be subdivided into the AMG and ABG substages within the porphyry system based on petrological and mineralogical characteristics. The U–Pb ages for zircons and CGMs from the alkali feldspar granite porphyry range from 137.2 ± 2.0 Ma to 129.8 ± 1.4 Ma, without a notable age gap. The similarity in U–Pb ages between CGM1–CGM2 and Zr1–Zr2 indicates that the magmatic stage and the magmatic–hydrothermal transition at Weilasituo were continuous processes that occurred during the Early Cretaceous.

Mineralizations of Nb-Ta-Rb-Zr and rare-earth elements in Boziguoer, South Tianshan, NW China: Geochronology and geochemistry of monazite and bastnäsite

The Boziguoer alkaline intrusion is located in the South Tianshan Orogenic Belt on the northern margin of the Tarim Craton. The intrusion is entirely mineralized and forms a super-large rare metal (RM) and rare-earth element (REE) deposit dominated by Nb-Ta-Rb, accompanied by Zr-REE. The primary RM minerals include pyrochlore, astrophyllite, and zircon, while the main REE minerals consist of fluocerite, monazite, xenotime, and bastnäsite, which are commonly present as granular aggregates or singularly filling the interstices between gangue minerals. Through a combination of geochronological and geochemical analyses of different types of monazite and bastnäsite in the mineralized alkaline rocks, this study elucidates the role of magmatic-hydrothermal evolution on the Boziguoer RM-REE mineralization and reconstructs the geochronological framework of alkalic magmatic-hydrothermal evolution and mineralization processes, as well as establishing mechanisms responsible for RM-REE enrichment. Petrographic observations and back-scattered electron (BSE) imaging revealed several types of monazite and bastnäsite with different characteristics as follows: (1) type Ia monazite (Mnz-Ia) experienced intense hydrothermal alteration, forming residual cores of monazite mantled by apatite and allanite coronas; (2) type Ib monazite (Mnz-Ib) was partially eroded, forming concentric zoning patterns with a core of monazite, a mantle of apatite, and an outer rim of allanite coronas; (3) type II monazite (Mnz-II) is slightly modified, and commonly associated with fluorite; (4) bastnäsite and fluocerite exhibit a core-rim structure, with the core of fluocerite being brighter than the rim of bastnäsite in BSE images. According to the paragenetic relationships and compositional variations, all two types of monazite are of primary magmatic origin, while bastnäsite is of hydrothermal origin. In addition, principal component analysis (PCA) and partial least squares-discriminant analysis (PLS-DA) results indicate that Mnz-Ia and Mnz-Ib belong to the same group, different from Mnz-II. The latter has higher (Ce/Gd)N and (Th/U)N ratios, indicating relatively low-temperature crystallization of Mnz-II at late stages. In-situ LA-ICP-MS U-Th-Pb dating of monazite and bastnäsite show that Mnz-Ia and Mnz-Ib have ages of ca. 290 Ma, consistent with the zircon age of the intrusion, whereas the Mnz-II and bastnäsite have younger ages of ca. 280 Ma, representing a post-magmatic hydrothermal mineralization event at Boziguoer. These new ages indicate that both magmatic and subsequent hydrothermal processes played critical roles in the RM-REE mineralization in this deposit. The latest findings also support the model that the formation of the alkaline belt where the Boziguoer ore-bearing intrusion was temporally and spatially linked to the Tarim Large Igneous Province that is genetically related to a mantle plume.

Mineralogical evidence for the role of deep magmatic fluids in beryllium enrichment in magmatic-hydrothermal systems

Vein-type and greisen-type beryllium (Be) mineralization is closely associated with the magmatic-hydrothermal evolution in highly fractionated granites. However, the source of ore-forming fluids and their role in the migration and enrichment of Be is poorly understood. Although whole rock Ba-Rb isotope researches highlight that even deep magmatic fluids beneath the shallow magmatic-hydrothermal systems could provide rare metals and promote mineralization, it is still challenging to determine the influences of such fluids via using conventional geochemical indicators. Here we present zircon-monazite-xenotime-wolframite U-Pb ages, whole-rock geochemistry, monazite Nd isotopes, as well as muscovite and beryl geochemistry for the Zhujiayingzi quartz vein-type Be mineralization in the southern Great Xing’an Range (SGXR), Northeast (NE) China, and introduce the neighboring Nasigatu gresien-type Be mineralization for comparison. Geochronological results reveal that the Zhujiayingzi beryl-wolframite-bearing quartz veins formed in the Early Cretaceous (149–147 Ma), much younger than the host Permian (270–267 Ma) crystal tuffs, but coeval with the Nasigatu highly fractionated alkali-feldspar granite (144–139 Ma). Similar muscovite-beryl compositions and monazite Nd isotopes, combining with their close temporal-spatial relationships indicate that the Zhujiayingzi and Nasigatu Be mineralization have consistent hydrothermal assemblages and enrichment processes. Higher silica, K, and lower Al contents of muscovites from Be-rich veins (M2) and greisens (M4) than those recorded in barren crystal tuffs (M1) and alkali-feldspar granite samples (M3) at both Zhujiayingzi and Nasigatu are consistent with the evolution of the Early Cretaceous granitic magma, proving the involvement of shallow magmatic fluids exsolved from the Nasigatu-like highly evolved granitic melts. However, ore-related M2 and M4 samples have higher Mg (>1 wt%) and Ti contents than those of M1 and M3 samples, which violates the conventional hydrothermal evolution trend. Trace element compositions as well as K/Rb, K/Cs, and Rb/Sr ratios of four-type muscovites, together with the core-rim geochemical variations of muscovites at Zhujiayingzi and beryls at Nasigatu, indicate the existence of deep magmatic fluids rather than fluid-rock interaction to account for the anomalous mineralogical evidence. Such deep magmatic fluids were exsolved from large silicic magmatic reservoirs beneath the shallow magmatic-hydrothermal system, and thus likely display low evolution degrees and high Mg-Ti contents. They can not only provide heat and promote fluid-mineral interactions, but also can efficiently extract and transport Be enriched in deep crystal mushes at different depths. Thus we invoke that the Early Cretaceous Be mineralization in the SGXR was achieved under the combined action of both shallow and deep magmatic fluids derived from the crystal mush-dominated transcrustal magmatic system.

Apatite as a Record of Magmatic–Hydrothermal Evolution and Metallogenic Processes: The Case of the Hongshan Porphyry–Skarn Cu–Mo Deposit, SW China

Apatite, as a common accessory mineral found in magmatic–hydrothermal deposits, effectively yields geochemical insights that facilitate our understanding of the mineralization process. In this research, multiple generations of magmatic and hydrothermal apatite were observed in the Hongshan porphyry–skarn Cu–Mo deposit in the Yidun Terrane in SW China. The geochemical compositions of the apatite were studied using in situ laser ablation–inductively coupled plasma mass spectrometry and an electron probe microanalysis to understand the magmatic–hydrothermal processes leading to ore formation. The apatite (Ap1a) occurs as subhedral to euhedral inclusions hosted in the phenocrysts of the granite porphyry. The Ap1b occurs later than Ap1a in a fine-grained matrix that intersects the earlier phenocrysts. Increases in F/Cl, F/OH, and F/S and decreases in ΣREE and (La/Yb)N from Ap1a to Ap1b suggest the exsolution of a volatile-rich phase from the magma. The skarn hosts three types of hydrothermal apatite (Ap2a, Ap2b, and Ap3), marking the prograde, retrograde, and quartz–sulfide stages of mineralization, respectively. The elemental behaviors of hydrothermal apatite, including the changes in Cl, Eu, As, and REE, were utilized to reflect evolutions in salinity, pH, oxygen fugacity, and fluid compositions. The composition of Ap2a, which occurs as inclusions within garnet, indicates the presence of an early acidic magmatic fluid with high salinity and oxygen fugacity at the prograde skarn stage. The composition of Ap2b, formed by the coupled dissolution-reprecipitation of Ap2a, indicates the presence of a retrograde fluid that is characterized by lower salinity, higher pH, and a significant decrease in oxygen fugacity compared to the prograde fluid. The Ap3 coexists with quartz and sulfide minerals. Based on studies of Ap3, the fluids in the quartz–sulfide stage exhibit relatively reducing conditions, thereby accelerating the precipitation of copper and iron sulfides. This research highlights the potential of apatite geochemistry for tracing magmatic–hydrothermal evolution processes and identifying mineral exploration targets.

Tracing fluid exsolution and hydrothermal alteration signature of the Mufushan Nb–Ta–(Li–Be–Cs) deposit, South China: an apatite perspective

The appearance of hydrous magmas and the following separation of volatile-rich fluids through hydrothermal alteration are intricately linked to the formation of granitic rare-metal deposits, the principal source of worldwide Li, Be, Nb, Ta and Cs production. The lack of mineralogical information from the developing magmatic–hydrothermal system has, however, prevented a thorough comprehension of these processes. Apatite occurs as an accessory mineral in the metasedimentary (schist)–magmatic (muscovite monzogranite)–pegmatite (ore-free or ore-bearing pegmatite) rocks in the Mufushan Complex (MFSC) rare-metal ore field of northeastern Hunan, South China, potentially providing insights into Nb–Ta–(Li–Be–Cs) mineralization. To demonstrate that apatite can potentially record the magmatic–hydrothermal evolution of metasedimentary–magmatic–pegmatite systems, this study presents a combined textural and geochemical study of apatite from the MFSC granitic pegmatite-type rare-metal mineralization. The MFSC apatite textures and compositions have changed since it first crystallized (i.e. post-crystallization alteration). Apatite from the schist shows a homogeneous rim or homogeneous textures with cracks or inclusions (S-ap1) and a patchy core (S-ap2), indicative of a magmatic–hydrothermal origin. Apatite from the muscovite monzogranite (G-ap) displays altered and distinctive core–rim textures, with visible voids, mineral inclusions and cracks, suggestive of overprinting of early magmatism texture by hydrothermal fluid. However, compared with S-ap1, S-ap2 and G-ap, the pegmatite apatite shows more complicated textures; that is, P-ap1 (homogeneous bright and dark areas) and P-ap2 (replacement texture involving alteration rim, growth zonation, patchy and complex zoning patterns). P-ap1 underwent early magmatism and weaker post-hydrothermal overprinting, and P-ap2 reflects a magmatic–hydrothermal product. S-ap1 and S-ap2 yield lower intercept ages of 130.6 ± 1.8 and 128.4 ± 3.8 Ma, respectively, which are consistent with the transitional age of the magmatic–hydrothermal metallogenic environment in northeastern Hunan. G-ap and P-ap1 yield older ages of 136.3 ± 2.8 and 141.3 ± 6.7 Ma, respectively, which correspond to the age of magmatic early stage (Nb–Ta)-mineralization within uncertainty in northeastern Hunan. The Sr isotopic composition of apatite provides evidence for the provenance of the MFSC batholith in the rare-metal metallogenesis of the Lengjiaxi Group. Therefore, we hypothesize that apatite in granitic rare-metal deposits within metasedimentary–magmatic–pegmatite systems might be employed as a viable proxy to explore the textures and geochemical fingerprints of fluid exsolution and hydrothermal alteration. Supplementary material: Analytical techniques and the results for apatite grains in this investigation are available at https://doi.org/10.6084/m9.figshare.c.7038699

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

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

The role of magmatic versus metasomatic processes in Ta-Nb mineralization at the Jiabusi Deposit, Inner Mongolia: Evidence from textural and chemical features of rare metal minerals and mica

The exact role magmatic versus metasomatic processes play in Ta-Nb mineralization is a question that has been debatable for several decades. The Jiabusi deposit is chosen to address this question, for its ample endowments of a variety of Ta-Nb oxides and mica in the various rock types that could provide insights into the whole evolutional history of ore-forming processes during magmatic-hydrothermal evolution. Textural and chemical evidence suggests that Fe-mica in the Fe-mica granite and pegmatitic portion is magmatic, indicating that the co-precipitated columbite-group minerals (CGM) and pyrochlore-supergroup minerals (PSM) are also magmatic. In the lepidolite granite and aplite, on the other hand, two stages of mineralization occured, represented by unzoned CGM that are in equilibrium with lepidolite, snowball quartz, and fluorite that all have a metasomatic origin and subsequent CGM/PSM overgrowths that co-precipitated with metasomatic Cs-lepidolite and saccharoidal albite. These CGM overgrowths have 1–2 time(s) higher Ta/(Nb + Ta) values than the preceded CGM, generating a clear compositional gap between them. Both stages of CGM and CGM/PSM precipitated from a hydrosilicate liquid (HSL), the partial migration of which results in the disequilibrium textures observed. The lepidolite granite is largely a metasomatic rock, the protolith of which has been obscured by intense metasomatism governed by the HSL. This HSL, however, is mainly constrained to the lepidolite granite but a few migrated into the Fe-mica granite. This is the main reason for the different mineralizing styles and intensities between the two rock types.

Whole-Rock Geochemistry and Mica Compositions in Lijiagou Pegmatite Spodumene Deposit, Western Sichuan, China

The Lijiagou pegmatite spodumene deposit, located in the middle of the Songpan–Garze Fold Belt and southeast of the Ke’eryin ore field, is a newly discovered super-large deposit. In order to reveal the metallogenic tectonic environment and evolution process of pegmatite, based on the study of the geological characteristics of pegmatite, we carried out a whole-rock geochemical analysis of Ke’eryin two-mica granite and Lijiagou pegmatite and carried out a detailed electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) analysis of mica minerals in each zonal pegmatite. The results show that the Ke’eryin two-mica granite is mainly formed in the transition period from syn-collision to post-collision. After the end of the continental collision, the crust is squeezed and thickened in the post-collision extensional transition tectonic environment. Mica from the microcline pegmatite zone (MP) to the albite spodumene pegmatite zone (ASP) in pegmatite show different compositions and structural characteristics, with the evolution trend in the direction from muscovite to Li-bearing mica. The type of mica from MP to AP is mainly muscovite, and Li-bearing mica appears in ASP, which is secondary and metasomatic at the edge of primary muscovite. From MP to ASP, there was a negative correlation between Nb/Ta, K/Rb and the Li, Rb, and Cs contents of mica, while the contents of Li, Rb, Cs, and F in the Li-bearing mica of ASP increased sharply. This evidence illustrates that the favorable tectonic environment contributed to the formation of the Lijiagou pegmatitic spodumene deposit. Lijiagou pegmatite experienced the magmatic–hydrothermal evolution process and has a high degree of differentiation and evolution from MP to ASP, which gradually increased. Combined with the change in mica type, it is considered that ASP formed from the stage of magmatic transition to hydrothermal and was a hydrothermal environment, and Li, Rb, and Cs mainly began to enrich at the stage of magmatic–hydrothermal transition.

Silver Behavior During Magmatic and Magmatic-Hydrothermal Evolution of a Highly Evolved Reduced Granitic System Related to the Giant Shuangjianzishan Ag-Pb-Zn-(Sn) Epithermal Deposit, Northeast China

Abstract Magmatic-related epithermal silver-rich polymetallic deposits are among the most important sources of Ag in the world, and they are found associated with magmatic systems with striking differences. Most of the time, they are associated either with I-type oxidized (magnetite-series granite) intermediate to evolved intrusions or with S-type/A-type reduced (ilmenite-series granite) highly evolved intrusions. To better understand these associations, the Ag evolution has been tracked during the magmatic differentiation and the magmatic-hydrothermal transition stage of A-type highly evolved porphyritic granites associated with the giant Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, the largest known Ag deposit of Asia (145 million tonnes at 128.5 g/t Ag and 2.2 wt % Pb + Zn) located in the largest known metallogenic province for Ag in China (the southern Great Xing’an Range). At the Shuangjianzishan deposit, the porphyritic granite complex consists of three temporally distinct intrusions—a coarse-grained monzogranite porphyry, a fine-grained syenogranite porphyry, and a fine-grained syenogranite—having crystallized at ~2 kbar and ~750°C and recording a continuous magmatic differentiation trend. The silicate melt that generated the last highly differentiated intrusion (fine-grained syenogranite) is interpreted as the source of the mineralizing fluids forming the Shuangjianzishan Ag-Pb-Zn-(Sn) epithermal deposit, as it is the only intrusive unit that reached fluid saturation, as indicated by cotrapped fluid and melt inclusions in quartz phenocrysts and by the occurrences of unidirectional solidification textures (USTs). Silver evolution in the different porphyritic granite facies was reconstructed with laser ablation-inductively coupled plasma-mass spectrometry analyses of quartz-hosted silicate melt inclusions, amphibole-hosted magmatic sulfide inclusions, and chemical modeling. The silicate melt forming the porphyritic granite complex was sulfide saturated during the first crystallization stage, as shown by the occurrence of Ag-rich monosulfide solid solution (MSS) inclusions hosted in amphibole phenocrysts from the coarse-grained monzogranite porphyry and from mafic microgranular enclaves hosted in the coarse-grained monzogranite porphyry. However, these Ag-rich MSSs had only a minimal impact on the Ag budget of the magmatic system, as shown by the increase of the Ag concentration (~100–1,000 ppb) in quartz-hosted silicate melt inclusions during the further evolution of the system until fluid exsolution was reached. These results combined with mass balance modeling suggest that Ag and Sn are efficiently transferred to the evolving residual melt during crystallization and crystal-melt segregation. The results of this study indicate that highly Ag endowed epithermal polymetallic deposits can be formed from the exsolution of Ag-rich mineralizing fluids from relatively low volume, highly evolved, reduced melts, similar to those responsible for the formation of Sn-rich greisen deposits.

Mineral Chemistry of Pyrochlore Supergroup Minerals as Records of Nb Mineralization Processes in NYF-Type Pegmatites: A Case Study of the Emeishan Large Igneous Province, SW China

Alkaline igneous rocks have become a potentially important source of Nb, except for the carbonatites. The metallogenetic mechanism of Nb during the magmatic-hydrothermal evolution of alkaline rocks remains ambiguous. From the perspective of Nb minerals, the mineral chemistry of pyrochlore supergroup minerals provides the mineralogical evidence for indicating the respective contributions of magma and hydrothermal fluids to Nb mineralization. In the Miyi County of the Panzhihua-Xichang (Pan-Xi) area, the central zone of the Permian Emeishan large igneous province (ELIP) in SW China, hundreds of Nb-Y-F mineralized pegmatites (NYF-type) are exposed. This study conducted in situ mineral chemistry analyses on four types of pyrochlores to elucidate the Nb mineralization process. Both Pcl-I and Pcl-II exhibit well-developed oscillatory zoning (OZ), representing magmatic pyrochlore formed through disequilibrium crystallization in an oscillatory environment. Pcl-III, with a homogeneous and less variable composition, is also considered of magmatic origin due to its coherent chemical evolution with Pcl-II. Pcl-IV is considered of hydrothermal origin based on its irregular zoning texture, extremely high Na2O contents, and compositional gap compared with magmatic types. The decrease in TiO2 contents, coupled with the increase in Na2O, F, and Nb2O5 contents from Pcl-I to Pcl-III and from the core to the rim of zoned Pcl-II, indicates that fractional crystallization facilitates the crystallization of albite and the enrichment of volatiles, as well as the precipitation of Nb from the early to late stages. During the magmatic-hydrothermal transition stage, the reductive, Na- and F-enriched fluid transports Nb more effectively, leading to further Nb enrichment in pyrochlore. Consequently, there are two-stage Nb mineralization processes associated with the magmatic-hydrothermal evolution in the Miyi pegmatite, with the primary magmatic ore assemblages being the dominant Nb mineralization, which may be a general model for the mineralization of NYF-type pegmatites.

Tectono-magmatic factors for porphyry Cu-(Mo-Au) deposits formation: A case study from Pishtene ore deposit, Western Srednogorie, Bulgaria

Porphyry ore deposits are the source of much of the copper, molybdenum, gold and silver. Porphyry hydrothermal systems typically form in magmatic arcs above subduction zones. In this article, some key factors that may be involved in the formation of the Pishtene porphyry deposit in Western Srednogorie are outlined. The first process is the generation of magma in sub-arc mantle and enrichment of metals, water and other fluids. Next stage is а cyclic crystal fractionation in deep crustal magma chamber. There are a lot of other factors, such as a sulphide saturation, metal partitioning, precipitation of ore minerals, magmatic-hydrothermal evolution, erosional and weathering processes, but they are not discussed in this study.

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.

Zircons in NYF-type pegmatites in the Emeishan large igneous province, SW China: A record of Nb and REE mineralization processes

The metallogenic mechanism of Nb and rare earth elements (REEs) during the magmatic-hydrothermal evolution of alkaline rocks remains ambiguous. Zircon is a common accessory mineral occurring in both barren aplite and the Nb-Y-F mineralized pegmatite (NFY-type) in Miyi County of the Pan-Xi area, the central zone of the Permian Emeishan large igneous province (ELIP) in SW China. Here, we present in situ geochemical analyses on these zircons to reveal the Nb-REE mineralization processes during magmatic-hydrothermal evolution, as well as the prospecting potential of plume-related NYF-type pegmatites. Four types of zircons are identified in the Miyi aplite and pegmatite. Zrn-I with well-developed oscillatory zoning (OZ) represents magmatic zircons in the aplite. Zrn-II and Zrn-III are magmatic zircons in the pegmatite. Zrn-II is closely associated with albite and is restricted to the center of an individual crystal, indicating early crystallization. There are abundant nanoscale britholite and thorite inclusions in Zrn-II, indicating that the primary melt is enriched in Ca, Y, REEs, Nb, Th, and F. Zrn-III presents as the rim of Zrn-II, with a sharp boundary between them. Zrn-IV is a metamict zircon formed through hydrothermal alteration after its structure was destroyed due to high Th and/or U contents. In situ zircon U-Pb dating of both Zrn-I and Zrn-III yields concordant ages of ca. 258 Ma, coeval with the felsic magmatism in the ELIP. For positive εHf(t) values of Zrn-I and Zrn-III (1.8–5.8 and 1.5–9.1, respectively), the Miyi pegmatite is also plume-related and might be derived from magma resembling A-type granite in the ELIP. Both Zrn-I and Zrn-III show negative Eu anomalies, and there is a decrease in Sc contents from Zrn-I to Zrn-III, indicating that the Miyi pegmatite formed from a highly evolved magma. Furthermore, the synchronous increases in Na, Nb, Y and total REEs from Zrn-I to Zrn-III indicate that excess Na in the melt plays an essential role in the further enrichment of Nb, Y, and REEs. In addition, a dramatic decrease in Nb, Y and total REE contents and LREE (light REE)/HREE (heavy REE) ratios from Zrn-III to Zrn-IV illustrates that Na- and F-rich hydrothermal fluids can leach and facilitate the precipitation of these elements, particularly LREEs. Therefore, there are two-stage Nb and REE mineralization processes related to magmatic-hydrothermal evolution in the Miyi pegmatite, which may be a general model for the mineralization of plume-related NFY-type pegmatites.

Origin and mineralization processes of REE during magmatic-hydrothermal evolution: Insights from in-situ geochemistry of calcite from the Weishan REE deposit, eastern North China Craton

The Weishan REE deposit, hosting more than one million tons of light REE oxides (LREE2O3), is one of the largest LREE deposits in China. It has been considered to be a carbonatite-related REE deposit, but whether carbonatites occurred or not is still controversial, leading to the confusions of how the LREE originated and mineralized. Here, we conducted in-situ elemental and Sr-Nd isotopic analyses on different stages of calcite from the Weishan REE deposit, combined with petrographic and bulk C-O isotopic studies, with the aim to unravel the origin and mineralization processes of REE. Four stages of calcite (Cal-1, Cal-2, Cal-3 and Cal-4) were identified, of which the Cal-1 typically coexists with K-feldspar and quartz while the Cal-2 and Cal-3 coexist with sulfates and REE minerals (e.g., bastnäsite and parisite), respectively. The Cal-4 occurs in the post-ore veinlets and coexists with sulfides. The Cal-1 is characterized by exsolution of carbocernaite along its cleavage planes with highest Na, K, Sr, Ba and LREE contents. The other stages of calcite show continuous decrease of the above elements. Combined with petrographic features and elemental discrimination diagrams, it is concluded that the Cal-1 is magmatic while the others are hydrothermal. These calcites thus indicate a continuous magmatic-hydrothermal evolution. The four stages of calcite show similar isotopic compositions, which are consistent with those of the alkaline silicate rocks in the ore district, suggesting an uniform source or magma chamber for their derivation. Considering the magmatic features of Cal-1, it is inferred that carbonate melts coupled with abundant alkaline fluids were exsolved from the alkaline magmas. Alkalis (e. g., K and Na) were enriched in the magmatic-hydrothermal system with potassic metasomatism being more prevalent, which might play an important role in REE exsolution and transportation. Focused REE deposition occurred shortly after massive deposition of sulfates, indicating that REE-sulfate complexes might be the dominant transporting ligands of REE. The deposition of REE was mainly induced by fluid boiling, as indicated by the boiling/unmixing features of fluid inclusions. The Sr-Nd isotopic compositions of ores and associated alkaline rocks show affinities to the enriched lithospheric mantle (EM) beneath the study region, but are more depleted. Because subduction of the Paleo-Pacific oceanic plate beneath the eastern Asian occurred since the Jurassic, it is inferred that CO2- and REE-rich melts/fluids released from the subducted oceanic slab metasomatized the EM, leading to a REE-rich carbonated mantle. Rollback of the subducted slab occurred during the early Cretaceous, resulting in partial melting of the EM and thus generating the CO2- and REE-rich alkaline magmas. This deposit shows significant hydrothermal features with poorly-developed carbonatites, distinct from the typical carbonatite-related REE deposits in the other places. The REE mineralization is thus considered to be basically controlled by the alkaline magmas rather than the carbonatites.

Genesis of the Lamasu large skarn Cu deposit, northern Xinjiang: Constraints from garnet U–Pb dating, micro‐textural and geochemical analyses

The Lamasu deposit is the first large copper (Cu) deposit with ~0.6 Mt Cu reserve in the Chinese Western Tianshan Orogen (NW China). The Cu orebodies are mainly hosted in the exoskarn of the Proterozoic Kusongmuqieke Group. Now, the metallogenic mechanism of newly discovered skarn Cu orebodies (0.5 Mt Cu) remains poorly constrained. In this study, we conducted LA‐ICP‐MS U–Pb isotope dating, EPMA and LA‐ICP‐MS geochemical analyses on different generations of garnet from Lamasu to elucidate the magmatic hydrothermal evolution and its timing. Garnets from the Lamasu exoskarn can be divided into three types: reddish‐brown coarse‐grained Grt‐I, light brown fine‐grained Grt‐II and yellowish‐green heterogranular Grt‐III, with U–Pb age of 389.1 ± 2.0 Ma, 387.1 ± 1.8 Ma and 387.0 ± 2.3 Ma, respectively. These dates represent the oldest Cu mineralization age in the Chinese Western Tianshan, coeval with the Middle Devonian subduction of the North Tianshan oceanic plate. Grt‐I to Grt‐III particles are mainly andradite with minor grossularite, and they have different REE compositions. The Grt‐I has total REE contents (∑REE) of 101.47 to 262.87 ppm, with steeply right‐inclining REE distribution patterns (LREE/HREE of 3.81 to 68.50) and positive Eu anomaly. The Grt‐II core has ∑REE of 163.49–249.52 ppm, LREE/HREE of 2.00–4.71, and negative Eu anomaly. The Grt‐II rim has ∑REE of 46.34–99.99 ppm, with LREE/HREE of 18.06–177.23, and positive Eu anomaly. The ∑REE of Grt‐III range from 31.71 to 219.02 ppm, with flat REE distribution pattern and positive Eu anomaly, and the LREE/HREE ranges from 2.16 to 9.07. These garnets have similar trace element compositions, featured by LILE‐depletions (e.g., Rb, Ba and Sr) and HFSE enrichments (e.g., Th, U, Nb and Ce). Micro‐texture and geochemical composition of garnets indicate that the Lamasu magmatic hydrothermal system could have changed from an open to a closed environment, and from infiltration metasomatism to diffusive metasomatism, which formed Grt‐I, Grt‐II and Grt‐III successively. These garnets generally formed in a relatively oxidized fluid environment, which inhibited early sulphide precipitation and favoured for Cu enrichment during the ore fluid evolution.

The interplay between magma source and geodynamic evolution in porphyry Cu-Au fertility of the Farallon Negro Volcanic Complex, Argentina

Zircon U-Pb, O, Lu-Hf and trace element systematics are used to track the magmatic-hydrothermal evolution and metallogenic potential of porphyry intrusions and associated Cu-Au deposits. We apply this analytical approach to unveil the poorly constrained geological history of the Farallon Negro Volcanic Complex in the Central Andes of northwest Argentina. This complex contains the world-class Au-rich Cu-Au Bajo de la Alumbrera deposit (here dated at 6.9 ± 0.1 to 6.8 ± 0.2 Ma; U-Pb SHRIMP) and a series of barren to weakly mineralized satellite porphyry intrusions, including El Durazno (8.0 ± 0.3 Ma; U-Pb SHRIMP), San Lucas (7.4 ± 0.1 to 7.3 ± 0.1 Ma; U-Pb SHRIMP) and Las Pampitas (7.2 ± 0.2 to 7.0 ± 0.1 Ma, U-Pb SHRIMP). Zircon Hf and O isotope data record a change in magma source from El Durazno (δ18O = 5.7 ± 0.3‰; εHf = −0.3 ± 1.8) to San Lucas, Las Pampitas and Bajo de la Alumbrera (δ18O > 6.7‰, εHf = − 4.0 ± 0.5 to −2.2 ± 1.0). This reflects a switch from a predominantly mantle-derived magma source to a mixed mantle-derived and supracrustal source that homogenized in a lower-crustal magma assimilation, segregation and homogenization (MASH) zone. All intrusions have a hydrous (Eu/Eu* > 0.5, Dy/Yb < 0.3), oxidized (ΔFMQ >1.0, Ce/Ce* > 100) and, therefore, ‘fertile’ zircon trace element signature, despite having variable Cu and Au grades. Likewise, ore-barren extrusive units in the FNVC have an overlapping ‘fertile’ zircon signature, reinforcing the view that zircon-based proxies for fertility may not be useful for mineralization targeting at a district scale. The magmatic evolution of the FNVC was significantly influenced by the tectonic setting, as the onset of regional transpression at ∼8 Ma after a period of localized extension caused pooling of mantle-derived magmas in a lower-crustal MASH zone and build-up of volatiles and metals. The petrogenetic model proposed for the FNVC emphasizes the role of the geodynamic environment and magma evolution in the Cu-Au endowment of Bajo de la Alumbrera