Two-mica Monzogranite Research Articles

Genesis of the Ke’eryin Two-Mica Monzogranite in the Ke’eryin Pegmatite-Type Lithium Ore Field, Songpan–Garze Orogenic Belt: Evidence from Lithium Isotopes

Previous studies on the Ke’eryin pegmatite-type lithium ore field in the Songpan–Ganzi Orogenic Belt have explored the characteristics of the parent rock but have not precisely determined its magma source area. This uncertainty limits our understanding of the regularity of lithium ore formation in this region. In this study, to address the issue of the precise source area of the parent rock of lithium mineralization, a detailed analysis of the Li isotope composition of the ore-forming parent rock (Ke’eryin two-mica monzogranite) and its potential source rocks (Triassic Xikang Group metamorphic rocks) was conducted. The δ7Li values of the Ke’eryin two-mica monzogranite, Xikang Group metasandstone, and Xikang Group mica schist are −3.3–−0.7‰ (average: −1.43‰), +0.1–+6.9‰ (average: +3.83‰), and −9.1–0‰ (average: −5.00‰), respectively. The Li isotopic composition of the Ke’eryin two-mica monzogranite is notably different from the metasandstone and aligns more closely with the mica schist, suggesting that the mica schist is its primary source rock. The heavy Li isotopic composition of the two-mica monzogranite compared to the mica schist may have resulted from the separation of the peritectic garnet into the residual phase during the biotite dehydration melting process. Moreover, the low-temperature weathering of the source rocks may have been the main factor leading to the lighter lithium isotope composition of the Xikang Group mica schist compared to the metasandstone. Further analysis suggests that continental crust weathering and crustal folding and thickening play crucial roles in the enrichment of lithium during multi-cycle orogenies.

Late Jurassic granitoids in Mufushan complex and their significance for the Mesozoic tectonic evolution of eastern South China

The Mesozoic tectono-thermal evolution of eastern South China plays an important role in forming the abundant magmatic rocks and associated giant polymetallic deposits. The middle-late Mesozoic granitoids in Mufushan and adjacent regions (e.g., Lianyunshan, Wangxiang, Taohuahsan, etc.) represent the western front of the southeast China magmatic province. However, the tectonic regimes and petrogenesis of the magmatic rocks are still elusive. Here, we report zircon UPb ages, geochemistry, and Sr-Nd-Hf-Pb isotopic data for the granitic rocks in the Mufushan region, in combination with data available from the literatures, to discriminate the middle-late Mesozoic tectono–magmatic history of the Mufushan complex in north-central South China Block. New zircon UPb dating suggests that the Mufushan two-mica monzogranites were emplaced at 149–144 Ma, a short time after the 153–151 Ma granodiorites. These late Jurassic felsic magmas share broad similarities in geochemical-isotopic characteristics, with significant enrichment in LREEs and LILEs (e.g., Ba, Rb, Th, and K), depletion in some HFSEs (e.g., Nb, Ta, Ti, and P) and positive Pb anomalies, similar to those of arc-type rocks. The common existence of Neoproterozoic zircons within the magmatic rocks indicates a certain amount of ancient material involved in the genesis of the magma. The two-mica monzogranites have εHf(t) values ranging from −13.4 to +3.5, overlapping with those of the granodiorites (−11.3 to +6.6), but both are lower than contemporaneous diorites (−2.4 to +0.59), suggesting a greater incorporation of enriched materials into the source for the granitoids. The two-mica monzogranites and granodiorites have εNd(t) values ranging from −7.9 to −8.8 and − 10 to −7.9, with corresponding two-stage Nd model ages of 1.7–1.6 Ga and 1.6 Ga, respectively, falling within their two-stage Hf model ages of 2.0–1.4 Ga and 1.8–1.4 Ga, respectively. Compared with the geochemical and isotopic compositions of the coeval magmatic rocks in eastern South China, we favor that the late Jurassic Mufushan granodiorites evolved from variable mixing and differentiation of the diorites and granitoids, accompanied by a continuous magma assimilation. The presence of late Jurassic highly fractionated granites suggests an extensive magma differentiation in eastern South China and the well-developed early Cretaceous A-type granites in eastern South China reflect a dominant extensional tectonic regime induced by slab roll-back of the Izanagi plate. The involvement of subduction-related melts facilitated the underplating of mantle-derived magma and crustal heating, triggering intensive partial melting of the lithosphere and magma enrichment, as well as the polymetallic deposits in eastern South China.

Genesis of the Jiada pegmatite lithium deposit in the Ke’eryin ore field, western Sichuan, China: Evidence from whole-rock trace element and Li isotope

The origin and petrogenesis of pegmatite-type lithium deposits within the Songpan-Garze Fold Belt (SGFB) of western China remain subjects of debate. To provide further insight on this subject, this study investigated the whole-rock trace elements and whole-rock Li isotopic compositions of the two-mica monzogranite (TMG) from the Ke’eryin composite pluton, the Jiada albite pegmatite (AP) and albite-spodumene pegmatite (ASP) and their metasedimentary wall rocks within the Ke’eryin ore field in the eastern SGFB. Modeling of muscovite-dehydration melting based on the whole-rock trace elements (e.g., Li, Rb, and Sr) and Rayleigh dehydration modeling related to the whole-rock Li isotopes suggest that the Jiada pegmatites are unlikely to have originated from the low-degree partial melting of metasandstone (MS) of the Zhuwo Formation. Variations in the whole-rock trace elements and Li isotope between the TMG and the Jiada pegmatites are consistent with the evolution trend of magmatic fractionation. However, the whole-rock Li isotopic compositions of the AP and ASP display inverse variation characteristics with the muscovite Li isotopic compositions, with the AP exhibiting lower Li concentrations and higher whole-rock δ7Li values than ASP. Furthermore, the variation patterns of whole-rock trace elements do not align perfectly with the Rayleigh-type fractional crystallization processes, implying other geological processes would be also involved in the formation of the Jiada pegmatites. Collectively considering the Li isotope behavior during various geological processes, the observed variations in whole-rock Li isotopic compositions between AP and ASP can be explained by aqueous fluid enrichment during the pegmatitic melt evolution. This suggests that fractional crystallization and fluid exsolution jointly contributed to pegmatite formation and Li mineralization in the Jiada deposit. Moreover, the whole-rock δ7Li values of the wall rock of ASP (MS2) are lower than those of MS and the wall rock of ASP (MS1), primarily due to metasomatism by 6Li-enriched fluids expelled from ASP and the kinetic diffusion of Li isotopes. The high concentrations of highly mobile elements, especially Li and Cs, combined with the low whole-rock δ7Li value of the metasandstone, could serve as effective tracers for locating concealed orebodies and evaluating the metallogenic potential of Li mineralization.

Metallogenetic epoch and material source of Be-pegmatite differentiated from biotite granite in Mufushan complex

The Mufushan Complex (MFSC) is a significant rare metal mineralized in the central China district and is renowned for its marked economic value of rare metal deposits. While the main rare metal mineralization (RMM) stage in the MFSC relates to the magmatic event of two-mica monzogranite, the mineralization event related to biotite monzogranite remains unknown. To fill this gap, this study focuses on porphyritic biotite monzogranite and adjacent Be-rich pegmatite samples obtained from Changqing Pegmatite No. 1, which is situated in the southeastern part of the MFSC. We subjected these samples to zircon U–Pb dating and Hf isotope analysis using laser ablation inductively coupled plasma mass spectrometry (LA–ICP–MS) and utilized an electron probe X-ray microanalyzer (EPMA) and LA–ICP–MS to examine the major and trace elements present in the muscovite samples. Our findings revealed precise chronological data for the geological history of Changqing, pinpointing the intrusion age of biotite monzogranite to 145.8 ± 1.1 Ma and the crystallization age of Be-rich pegmatite to 144.9 ± 1.1 Ma, firmly situating these events within the Late Jurassic to Early Cretaceous epoch. Regarding isotopic composition, zircon εHf (t) for granite ranged from −9.29 to −5.09, and their corresponding TDM2 ranged from 1788 to 1520 Ma. Similarly, zircon εHf (t) for pegmatite ranged from −7.89 to −5.47, and their corresponding TDM2 ranged from 1699 to 1544 Ma. These isotopic signatures strongly indicate a shared origin for the initial magma of granite and pegmatite. The partial melting of the thick Lengjiaxi Group tasedimentary strata serves as a material source for RMM. The transition from granite to pegmatite exhibits remarkable constancy in the primary components of muscovite. By examining its geochemical attributes, we observed synchronous decreases in FeO, MgO, SiO2, MnO, Be, Rb, and Cs, coupled with synchronous increases in Nb and Ta contents, along with Ta/Nb values. These findings strongly imply that the Changqing biotite monzogranite and Be-rich pegmatite originate from the continuous differentiation and evolution of a common magmatic source, establishing a clear genetic relationship between them. The MFSC has its origins in three distinct stages of magmatic activity and RMM spanning from 160 Ma to 120 Ma. Considering the distribution patterns of similar pegmatite veins, the metallogenic potential observed during the biotite granite stage may serve as an external indicator of marked mineralization within large batholiths.

Petrogenesis of early Cretaceous granites in Mufushan complex, northeastern Hunan Province: Insights on middle-late Mesozoic tectonic evolution of eastern South China

We present new field observations, whole-rock major and trace elements, Sr-Nd-Pb-Hf isotopes and zircon UPb ages for the Mesozoic granites in the Mufushan complex, eastern South China. The age determinations by LA-ICP-MS UPb dating of zircons indicate that the porphyritic biotite granites and two-mica monzogranites have ages of ∼136 Ma and ∼ 130 Ma, respectively. These granites display highly evolved S-type granite geochemical characteristics, with high SiO2 (70–74 wt%) contents, high 10000*Ga/Al ratios (2.3–3.2, average of 2.8) and weakly peraluminous (A/CNK > 1.1). Both types of granites are enriched in large ion lithophile elements (LILEs, e.g., Rb, K, Ba, Sr) and depleted in high field strength elements (HFSEs, e.g., Nb, Ta, Ti), with negative anomalies of Eu and positive anomalies of Pb, which are akin to continental arc rocks. The two-mica monzogranites have high 87Sr/86Sr(i) (0.71355–0.71535), 206Pb/204Pb(i) (18.105–18.157), low εNd(t) (−9.1 to −9.6) and εHf(t) (−4.1 to −10.4), similar to those of the porphyritic biotite granites which are characterized by high 87Sr/86Sr(i) (0.717337–0.71692), 206Pb/204Pb(i) (18.134–18.580), low εNd(t) (−9.1 to −9.7) and zircon εHf(t) (−6.8 to −3.3). The similar emplacement ages and mineral assemblages as well as Sr-Nd-Hf isotopic signatures indicate their derivations were likely derived from a common magma source. These early Cretaceous granites yield two-stage Nd model ages of 1.6–1.7 Ga, similar to the two-stage Hf model ages of 1.3–1.8 Ga. The presence of Neoproterozoic and subordinate Mesoproterozoic zircons within the granitic rocks suggest a significant contribution of ancient crustal materials involved in the genesis of the magmas. In combination with comprehensive studies on the magmatic rocks, the early Cretaceous Mufushan granitic rocks may have experienced an extensive enrichment process, contemporaneously with partial melting of the Neoproterozoic volcanic-sedimentary sequences that produced the arc-like rocks. Almost simultaneously, an extensional event caused by the subduction and slab roll-back of the Paleo-Pacific plate (Izanagi plate) dominates the middle-late Mesozoic tectonics in eastern South China. This extensional regime was accompanied by the underplating of mantle-derived magma and crustal melting, producing the widespread early Cretaceous granites in adjacent regions. The development of coeval basin-and-range structures with the production of contemporaneous magmatic rocks and related polymetallic deposits in eastern South China are all related to slab roll-back tectonics.

Petrogenesis of Mesozoic Li-, Cs-, and Ta-rich (LCT) pegmatites from the Neoproterozoic Jiangnan Orogenic Belt, South China: An alternative origin model for the LCT type pegmatite

According to the classical petrogenesis model, Li-, Cs-, and Ta-rich (LCT) pegmatites juxtaposed in the same regional zonation are generally formed by unidirectional successive crystallization differentiation of the common parental granitic melt. However, this model cannot explain the origin of the Mesozoic LCT pegmatites from the East Jiangnan Orogenic Belt (JOB), South China. Herein, we studied the geology, zircon U–Pb ages, Hf isotope compositions, monazite U–Th–Pb ages, and Nd isotope compositions of three types of pegmatites in Renli, East JOB, South China to reveal their petrogenesis. The Renli pegmatites distributed in or around the Mufushan batholith, show mineralization zoning with distance from the batholith. The studied pegmatites were formed at the Early Cretaceous, with a decreasing trend from ca. 141 Ma for two-mica microcline pegmatite (type I) to 134 Ma for muscovite–albite–spodumene pegmatite (type III). The Renli pegmatites have coupled Hf–Nd isotope compositions and consistent Hf isotope compositions with the Mufushan granites. From the spatial–temporal, source and differentiation relationships between the Renli pegmatites and the Mufushan granites, we propose that type I pegmatites originates from biotite monzogranite while type II (muscovite–microcline–albite pegmatite) and type III pegmatites originate from the two-mica monzogranite and muscovite monzogranite, respectively, indicating a new model of parallel differentiations of triple granitic melts for the origin of LCT pegmatites in South China. The Renli pegmatites have a similar Hf isotope composition to the Neoproterozoic granitoids and the backarc sedimentary rocks of the Lengjiaxi Group formed during the Jiangnan orogeny. Combining with previous studies, we suggest that the Mesozoic Renli LCT pegmatites originated from reworking materials of the Neoproterozoic JOB caused by slab roll back of the paleo-Pacific Ocean plate during subduction.

Zircon U-Pb and muscovite 40Ar/39Ar dating of Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province, Jiangnan Orogen: Evidence for large-scale mineralization in South China at ca. 150–120 Ma

The Jiangnan Orogen is located between the Yangtze and Cathaysia blocks, and hosts abundant Au, Sb, W, Cu, Pb, Zn, Ag, and Ta-Nb-(Li-Be) deposits. Among these, both the Taolin and Lishan Pb-Zn-(Cu) polymetallic deposits in northeastern Hunan Province are large Pb-Zn deposits, which are located at the northwestern and southern margins of the Late Jurassic to Early Cretaceous Dayunshan-Mufushan composite pluton, respectively. However, the mineralization ages of these deposits remain controversial and poorly constrained. In this study, muscovite 40Ar/39Ar dating of the Taolin and Lishan deposits along with zircon U-Pb dating and geochemical analysis of the Dayunshan-Mufushan composite pluton were undertaken to constrain the age and nature of the Late Jurassic to Early Cretaceous magmatism and related mineralization in South China. Zircon U-Pb dating of the biotite monzogranite and two-mica monzogranite yielded emplacement ages of ca. 149 and 145–136 Ma, respectively. Muscovite from the ore-bearing granitic pegmatites in both the Taolin and Lishan deposits yielded well-defined 40Ar/39Ar ages of ca. 121 and 129 Ma, respectively. These results and previously published data indicate that the Dayunshan-Mufushan composite pluton was emplaced in several stages at ca. 154–148, 146–137, and 136–127 Ma, and experienced associated, multi-stage, granitic pegmatite magmatism at ca. 142, 131, and 125–120 Ma. Two mineralization events occurred at ca. 141–136 and 133–120 Ma in the Pb-Zn-(Cu-Co-Mo), Ta-Nb-Li-Be, and Au deposits in northeastern Hunan Province, including the Dayunshan-Mufushan region. Zircons from the Dayunshan-Mufushan composite pluton record low oxygen fugacity (ƒO2) conditions, indicating the pluton was likely responsible for the large-scale Pb-Zn mineralization.In addition to the 170–160, 160–150, and 120–80 Ma mineralization events, the Late Jurassic to Early Cretaceous (ca. 150–120 Ma) was also an important period of mineralization in South China. This mineralization was likely initiated by Middle Jurassic to Early Cretaceous extension associated with subduction, subsequent slab rollback, and possible break-off of the Paleo-Pacific plate, which led to lithospheric collapse and thinning.

Geochronological and geochemical constraints on magmatic evolution and mineralization of the northeast Ke’eryin pluton and the newly discovered Jiada pegmatite-type lithium deposit, Western China

The Ke’eryin ore field in the Songpan-Garze Fold Belt (SGFB), western China, is an important area of pegmatite-type lithium accumulation. However, the petrogenesis of the pegmatites and their genetic relationships with the neighboring granitic pluton are still a topic of debate. In this work, LA-MC-ICP-MS zircon and columbite-tantalite U-Pb dating, whole-rock and mica geochemical analysis, and lithium isotopic analysis of the Ke’eryin pluton and pegmatites in the newly discovered Jiada deposit were performed. Zircon U-Pb dating of biotite K-feldspar granite (BG), fine-grained two-mica monzogranite (FTG), and medium-grained two-mica monzogranite (MTG) of the Ke’eryin composite pluton yielded crystallization ages of 219.5 ± 0.7 Ma, 212.8 ± 1.1 Ma, and 209.1 ± 0.7 Ma, respectively. Columbite-tantalite U-Pb dating of albite-spodumene type pegmatite (ASP) from the Jiada deposit yielded crystallization ages of 204.7 ± 1.0 Ma. The results show that the lithium mineralization in the Jiada deposit was temporally closest to the MTG emplacement. Combined with the regional magmatic evolution sequence, it is suggested that the Ke’eryin composite pluton and the Jiada deposit were emplaced during the period of transition from tectonic compression to extension under the effect of lithospheric delamination during post-collision. Geochemically, the compositional variation in the major elements of mica minerals indicate that BG, FTG, and MTG of the Ke’eryin composite pluton and the AP (albite type pegmatite) and ASP in the Jiada deposit were formed via the same continuous magmatic evolution process. The increasing Li, Rb, Cs, Nb, Ta concentrations and decreasing K/Rb, K/Cs, Nb/Ta ratios in mica minerals show that the degree of magmatic differentiation increased in the order BG-FTG-MTG-AP-ASP, indicating that MTG could be the parent rock of the Jiada pegmatites. The increase in the δ7Li values in muscovites from MTG through AP to ASP provides new evidence to support the fact that the fractional crystallization played a significant role in the formation of pegmatites in the Jiada deposit. Alkali metal elements (e.g., K, Rb, Cs) in the muscovites of MTG, AP, and ASP followed the Rayleigh fractionation law, indicating that a Rayleigh-type fractionation process occurred. Rayleigh fractional crystallization modelling of these alkali metal elements showed that the MTG could produce a magma melt of ASP through extreme fractional crystallization (∼98–99 % fractionation). Taken together with associated geological evidence, the aforementioned features indicate that the favorable tectonic setting and the prolonged and extreme fractional crystallization of the granitic melt jointly contributed to the formation of the Jiada pegmatite-type lithium deposit.

Geochronology, geochemistry, and Sr-Nd-Hf isotopic compositions of Permian granitoids from the South Altay, NW China: Implications for tungsten-copper skarn mineralization

The Bastielieke deposit is a W polymetallic skarn deposit discovered in the South Altay, Northwest China. W polymetallic mineralization mainly occurs within the contact zone between the Permian intrusions and the Kangbutiebao Formation (Fm.) metamorphic volcanic-sedimentary rocks. Permian granitoids associated with W (Cu) mineralization include several phases of granite: biotite granite (G1), monzogranite (G2) and two-mica monzogranite (G3) in L2 ore block, biotite monzogranite (G4) in L3 ore block. We obtained zircon U-Pb ages of G3, G4, and barren porphyritic monzogranite (G5) from Lamazhao granite of 275.0 Ma, 275.4 Ma, and 277.0 Ma, respectively. All samples from G3, G4, G5 show enrichment of SiO2, weakly peraluminous, enriched in light rare earth elements (LREE), and depleted in high field strength elements (HFSE). These Permian granitoids were mainly derived from mantle magma, and mixed with some lower crust components, although the Sr-Nb-Hf characteristics are slightly differences. G1, G2, and G4 were involvement of more mantle components than G3 and G5. G1 and G5 have experienced more obviously fractional crystallization than G2, G3, and G4, and G5 displays the highest fractionated degree. Moreover, G5 has the highest magmatic oxygen fugacity compared with G1, G2, G,3 and G4 according to variable △FMQ values (G1: −2.75 to 1.42, G2: −3.14 to 2.23, G3: −3.15 to 0.70, G4: −2.92 to 1.36, and G5: −1.63 to 2.82, respectively), as well as δEu values, δCe values, and Ce/Nd ratios. Thus, we proposed that tungsten skarn mineralization in the Bastielieke deposit area is mainly controlled by high fractional crystallization, and the contribution of magma source and oxidation state cannot be neglected. In addition, the copper could be offered by oxidized fluids exsolved from mafic magmas or Cu-bearing immiscible magmatic sulfides in copper-rich tungsten skarn system.

Batholith recorded mesozoic multistage tectonic evolution of the South china block: A case study of the guandimiao intrusions

South China is a well-known grand felsic igneous rocks province. However, it is still controversial and not well understood whether the Mesozoic tectono-magmatic pattern is dominated by the subduction of the paleo-Pacific oceanic plate. In this study, we address this question by concentrating on the long-term evolutionary Guandimiao batholith, which has complex lithofacies with different formation ages and can be a superb record of the Mesozoic tectonic evolution in South China. Geochronologically, four stages of magmatism can be identified combined with previous reports: granodiorite (G1, 239 Ma), biotite monzogranite (G2-1) and two-mica monzogranite (G2-2) (230–203 Ma), granite porphyry (G3, 211–190 Ma), and lamprophyre (L4, 121 Ma). G1 and G2-1 have an affinity with I-type granite and were derived from metabasaltic to metatonalitic sources, whereas G2 and G3 show S-type granite characteristics and were derived from the para-metamorphic basement of the Cathaysia block. The L4 was derived from partial melting of garnet and spinel lherzolite and underwent mixing between Mesoproterozoic pelagic and/or terrigenous sediments and the subcontinental lithosphere mantle (SCLM) of South China. The granitoids of the Guandimiao batholith underwent intensely fractional crystallization of feldspar, Ti-bearing minerals, allanite and monazite. The zircon U–Pb dating of L4 in the Guandimiao batholith completely records the six stages of pre-Mesozoic tectonic events in the SCB. During the Mesozoic, the main body of the Guandimiao batholith (G1, G2-1 and G2-2) recorded the closure of the paleo-Tethys Ocean in the Triassic and the subsequent regional extension of the postcollision. G-3 and L4 of the Guandimiao batholith documented the transition of tectonic and dynamic regimes in the early Yanshanian and the rollback and steep subduction of the paleo-Pacific Ocean in the late Yanshanian.

Interaction of B-rich supercritical magmatic fluids with granite: first report of dumortierite in a geothermal field, Larderello, Italy

In a peraluminous two-mica monzogranite cored at 4.5 km depth in well Radicondoli 29, dumortierite occurs together with andalusite, Li-rich tourmaline, fluorite and fluorapatite. The average composition is SiO2: 30.9, Al2O3: 58.6, FeO: 0.44, MgO: 0.47, CaO: 0.02, F: 0.15. Dumortierite crystallized from supercritical magmatic fluids at T =520-620°C, P = 100 ± 30 MPa. Synthetic fluid inclusions yielded T = 510 ± 10 MPa, P = 42 ± 3 MPa at 2.9 km depth in well Venelle 2. Al data suggest present day T = 450-550°C, P = 40-80 MPa. The supercritical magmatic fluids were hypersaline brines with ~ 30 wt % LiCl and up to 2.4 wt % F, extreme contents that can be found only in pegmatites, aplites and leucogranites. Larderello granites derived from partial melting of a lower crust made up of interlayered metasediments and amphibolites. Extensive melting took place in the lower crust during the last 10 Ma owing to extensional tectonics, lithosphere thinning, roll back or break down of the west merging Adria plate and swelling of the asthenosphere below the western side of the Apennines.

Apatite U-Pb Dating and Composition Constraints for Magmatic–Hydrothermal Evolution in the Giant Renli Nb-Ta Deposit, South China

Apatite is a nearly ubiquitous accessory phase in igneous rocks that crystallizes during the entire magma evolution process and has great implications for geochronology and petrogenesis. Previous studies suggested that Nb-Ta mineralization in the giant Renli deposit was genetically related to Late Jurassic two-mica monzogranite or Early Cretaceous muscovite monzogranite. Moreover, the magmatic–hydrothermal evolution of these two stages is poorly understood. In our study, we confirm that the muscovite monzogranite, biotite monzogranite, and two-mica monzogranite are all spatially associated with Nb-Ta pegmatites. We present new apatite U-Pb ages to constrain the timing of Nb-Ta mineralization and related magmatism. The results show that apatite from the two-mica pegmatite yield a lower intercept age of 130 ± 2 Ma (2σ), and apatite grains from two two-mica pegmatite samples yield a lower intercept age of 135 ± 8 Ma (2σ) and 134 ± 3 Ma (2σ), respectively. Apatite and whole-rock geochemistry suggest the oxidation degree of the Nb-Ta mineralization increases from north (RL-6) to south (RL-16) in the giant Renli deposit. This study demonstrates that a combination of apatite composition and U-Pb ages can be used to constrain the magmatic–hydrothermal evolution of granite and pegmatite-type Nb-Ta deposits.

Tin enrichment in a highly fractionated A-type granite: Origin and mineralization potential of the Dayishan granite batholith in the Shi–Hang magmatic zone, South China

A-type granite intrusions in the southern Shi–Hang magmatic zone, South China, contain several world-class W–Sn deposits. The Dayishan granite batholith is located in the north of the southern Shi–Hang magmatic zone, and contains potential Sn mineralization. The batholith contains three intrusive phases, which are the Guankou, Tangshipu, and Nibantian phases. The Guankou phase consists mainly of biotite–K-feldspar granite (G1). The Tangshipu phase consists of three secondary units, which are coarse-grained biotite monzogranite (G2) that cut monzogranite (G3) and fine-grained two-mica monzogranite (G4). The Nibantian phase consists of coarse-grained two-mica monzogranite (G5). Zircon U–Pb dating indicates that the G1 to G4 granites were emplaced at ca. 160 Ma and the G5 granites formed at ca. 144 Ma. All the granites are silica-rich (SiO2 = 69.24–77.02 wt%) A2 sub-type granites, among which G1 granites are metaluminous and G2 to G5 granites are peraluminous. High εNd(t) (−6.9 to − 5.2) and zircon εHf(t) (−6.2 to − 1.9) values suggest that the parental magma was probably derived by partial melting of lower crust, which was induced by input of mantle-derived basaltic magmas. Oxygen fugacity determinations show that the G2 to G5 granitic magmas were reduced, but the G1 granitic magmas were relatively oxidized.From the G1 to G4 granites, Ba, Th, Nd, Zr, Hf, and rare earth element contents decrease, while Rb and Ta contents increase, indicative of extensive fractional crystallization of K-feldspar, plagioclase, and accessory minerals. This suggests that the G1 granites represent the least fractionated magmas, while the G2 to G4 granites are the highly fractionated products of the G1 granitic magma, with the G4 granites being the most fractionated. The G5 granites were formed during a later magmatic activity, though they show similar geochemical features with the G2 and G3 granites.Due to this continuous fractionation process, Sn was efficiently and progressively enriched in the G2 to G4 granites, as indicated by the good correlations between Sn contents and TiO2 contents, Eu/Eu*, Rb/Sr, Rb/Ba, K/Rb, Zr/Hf, Nb/Ta, and Y/Ho ratios, and TE1,3 values. Furthermore, the G2 to G4 granites crystallized at the magmatic–hydrothermal transition. These data indicate that the G2 to G4 granites underwent Sn mineralization, but the G4 granites are the best target for exploration. The G5 granites might also have Sn mineralization potential considering the similar geochemical features with G2 and G3 granites. Given the reduced nature of the magmas, the potential economic mineralization types are greisen and skarn.

Compositional evolution of the muscovite of Renli pegmatite-type rare-metal deposit, northeast Hunan, China: Implications for its petrogenesis and mineralization potential

The Renli deposit is the largest known pegmatite-type Ta–Nb deposit in south China. Its rare-metal pegmatites show regular zoning of pegmatite types and rare-metal mineralization assemblages from northeast to southwest. One hundred and forty major outcropping pegmatite dikes throughout the deposit can be approximately divided into four zones outward from the Mufushan batholith: microcline pegmatite zone (P1); microcline–albite pegmatite zone (P2); albite pegmatite zone (P3); and albite–spodumene pegmatite zone (P4). The sizes of the dikes decrease with distance from the batholith, and their rare-metal mineralization type changes as follows: Be → Nb–Ta (–Be) → Li (–Nb–Ta). Field geological characteristics, chronological and Lu–Hf and Sr–Nb–Pb isotopic studies indicate that these rare-metal pegmatites have a close petrogenetic relationship with the Mufushan complex granitic intrusions. However, because of the similarities in geochemical characteristics, magma source properties, and emplacement ages of these different granitic intrusions, identifying the parental rock of rare-metal pegmatites is challenging.Muscovites are common throughout the granitic intrusions and four types of pegmatites in the Renli deposit, and are intimately associated with rare-metal mineralization. The geochemistry of muscovite obtained from granites and pegmatites can be used to demonstrate the parental relationships of rare-metal pegmatites and Mufushan granites, allowing pegmatite evolution trends and the mineralization potential of the Renli deposit to be evaluated. The K/Rb versus Cs, Rb, Li, Nb, and Ta ratios and Ta/Nb versus Li, Ta, and TiO2 ratios in muscovites from the granites and pegmatites show that they form an association with the following sequence of evolution: biotite monzogranite → two-mica monzogranite → microcline pegmatite → microcline–albite pegmatite → albite pegmatite → albite–spodumene pegmatite. The above complete evolution sequence represents the magmatic stage of the deposit and the lepidolite-quartz core in pegmatite with well internal zoning represents the fluid-rich stage of the deposit. The Al4Si–3□–1 exchange vector (where □ represents a vacancy) is shown to have played an important role in the first magmatic stage of the Renli deposit when compositional changes in Li-poor muscovite formed in the magmatic stage involved this substitution. During the late fluid-rich stage formed by highly differentiated magma at the end of the magmatic evolution of the deposit, Li was incorporated into micas by Li3Al–1□–2. Many pegmatite dikes with transitional boundaries can be observed in the outcrops of two-mica monzogranite (RLG2), and geochemical characteristics of muscovite suggest that this monzogranite show the highest differentiation degree in Renli granites, whose average K/Rb and Ta/Nb ratios are close to those of the Renli pegmatites. This indicates that the two-mica monzogranite (RLG2) has the closest petrogenetic relationship with the Renli rare-metal pegmatites. Combined with the data from this and previous studies, the K/Rb ratio, Li and Cs contents of muscovite can be used to distinguish the barren pegmatite and different types (Be, Nb–Ta, or Li type) of rare-metal pegmatites to a certain degree. Therefore, muscovite can indicate the metallogenic type and economic potential in a pegmatite-type rare-metal deposit.

Petrogenesis of Jurassic Granitoids on Liaodong Peninsula, Northeast China: Constraints on the Evolution of the Mongol-Okhotsk and Pacific Tectonic Regimes

The tectonic setting of Jurassic magmatism in the Northeast China (NE China) is unclear. Here, we present new petrological, whole-rock geochemical, zircon U-Pb geochronological, and zircon Lu-Hf isotope data for Jurassic granitoids of the Wulong region, Liaodong Peninsula, NE China. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) zircon U-Pb data indicate that these granitoids were emplaced at 165–156 Ma. The biotite monzogranite, two-mica monzogranite, monzogranite, granodiorite, biotite granodiorite, and syenogranite are strongly peraluminous (A/CNK=1.09–1.29), contain peraluminous minerals such as muscovite, have high normative corundum abundances (1.26 wt.%–3.28 wt.%), and have high K2O/Na2O ratios (0.76–1.48), all of which indicate an S-type granite affinity. However, the biotite granodiorite and syenogranite have high Sr (391 ppm–570 ppm) and low Y (3.06 ppm–5.94 ppm) contents, with high Sr/Y (65.8–185.9) ratios, and the two-mica monzogranite, monzogranite, and granodiorite have relatively high Sr (138 ppm–379 ppm) and low Y (3.38 ppm–8.71 ppm) contents, with high Sr/Y ratios (19.1–77.9). All of the analyzed samples have negative zircon eHf(t) values (−41.4 to −20.6) with old two-stage Hf model ages (TDM2(Hf)=2.50–3.76 Ga). Therefore, we infer that the biotite monzogranite is the typical feature of S-type granite that was derived by partial melting of metagraywacke. The monzogranite, two-mica monzogranite, granodiorite, biotite granodiorite, and syenogranite exhibit geochemical characteristics of S-type granite with K-rich adakitic features, and were possibly derived by mixing of melts from clastic crustal materials and adakitic magmas. There are voluminous Jurassic igneous rocks in the NE China. By combining our study with the previous researches, this paper infers that the Jurassic magmatism within the Erguna-Xing’an Massif was related to the southward subduction and closure of the Mongol-Okhotsk Ocean; the Early Jurassic magmatism to the east of the Songliao Basin and in the northern North China Craton (NCC) was related to the subduction of the Pacific Plate; however, the Middle-Late Jurassic igneous rocks to the west of the Songliao Basin were related to the closure of the Mongol-Okhotsk Ocean and, in the northern NCC, were related to closure of the Mongol-Okhotsk Ocean with an influence from flat-slab subduction of the Pacific Plate.

Geological characteristics and metallogenic age of Tengshan'ao Sn deposit in Dayishan of South Hunan and its prospecting significance

The Tengshan'ao Sn deposit, located at the Dayishan ore field, Nanling Range, is one of the recently explored deposits in this region. In this study, LA-MC-ICP-MS cassiterite U–Pb and muscovite 40Ar-39Ar isotopic dating analyses for altered granite-type Sn ores yielded ages of 156.7 ± 4.3 Ma and 151.1 ± 1.5 Ma, respectively. These ages are consistent to the LA-MC-ICP-MS zircon U–Pb age of the fine-grained two-mica monzogranite (158.2 ± 1.6 Ma), indicating a coeval magmatism and mineralization for the Late Jurassic Tengshan'ao Sn deposit. It is further demonstrated that the formation of this deposit is related to the Early Yanshanian (160-150 Ma) large-scale diagenesis and mineralization in Nanling Range. It is suggested that the late-stage fine-grained two-mica (muscovite) granite has an indicative significance for searching the altered granite type Sn polymetallic mineralization.

Ore genesis of the Baishawo Be-Li-Nb-Ta deposit in the northeast Hunan Province, south China: Evidence from geological, geochemical, and U-Pb and Re-Os geochronologic data

The Baishawo deposit is a newly discovered large pegmatite type Be-Li-Nb-Ta deposit that located at the NE Hunan province, South China, with estimated reserves of 16,160 t BeO @ 0.084%, 11,280 t Li2O @ 0.85%, and 3450 t (Ta2O5 + Nb2O5) @ 0.201%. The mineralized pegmatites are mainly hosted in the two-mica monzogranite, suggesting a possibly genetic relationship. Mineral assemblages and textures of pegmatites indicate the Baishawo deposit likely belong to LCT-type. The ore-related two-mica monzogranites have high contents of SiO2 and K2O, belong to strongly peraluminous rocks with A/CNK values of 1.13–1.24, and show S-type and highly evolved features. Zircons from the two-mica monzogranite show a εHf(t) range from −14.1 to −8.0 (average −10.1) and molybdenites from pegmatites show Re contents of 7.06–8.98 μg/g, both indicating that these rocks were likely sourced from the crust materials. The Baishawo two-mica monzogranite yields a LA-ICP-MS zircon U-Pb age of 147.5 ± 1.6 Ma, and the molybdenite from the mineralized pegmatites yields an Re-Os isochron age of 140.2 ± 3.3 Ma, which is in consistent with the coltan U-Pb age of 140.7 ± 1.5 Ma, indicating an Early Cretaceous mineralization age. The obtained ages combined with previous studies in the region indicate that the Early Cretaceous (~140 Ma) is an important rare metal mineralization period in South China.

Multi-stage Jurassic magmatism in the Liaodong Peninsula: Constraints on crustal evolution beneath the eastern North China Craton

Whole-rock geochemical and in situ zircon UPb and HfO isotope compositions have been measured for the Jurassic granitoids in the Liaodong Peninsula, in order to investigate their genesis and reveal the Jurassic crustal evolution of the eastern North China Craton. Our new data, combined with field and petrological observations, indicate multi-stage Jurassic magmatism, now represented by Early to Middle Jurassic biotite granites and monzogranites, and Late Jurassic two-mica monzogranites. The Early to Middle Jurassic granitoids have relatively low SiO2 contents (64.4–69.6 wt%) and K2O/Na2O ratios (0.4–1.0), adakitic characteristics with enriched LREE and depleted HREE contents, high Sr/Y ratios (52–189), positive Eu and Ba anomalies, and negative Nb and Ta anomalies. Together with their highly negative zircon ɛHf(t) (−26.6 to −16.1) and mantle-like δ18O (4.6‰ to 6.3‰) values, partial melting of a basaltic lower crust, which formed at ca. 2.5 Ga, can be proposed for the magma source of the Early to Middle Jurassic granitoids. These source rocks have not experienced significant water–rock alteration after formation. In contrary, the Late Jurassic two-mica granitoids exhibit relatively differentiated geochemical characteristics, with high SiO2 contents (>72 wt%) and K2O/Na2O ratios and variable Eu anomalies. Their parental magma was also enriched in LREEs and depleted in HREEs, with high Sr/Y (49.8–134) and (La/Yb)N (22.6–38.0) ratios. The magmatic zircons have extremely negative ɛHf(t) (−37.5 to −19.6) and relatively high δ18O (6.9‰ to 9.6‰) values, indicating the involvement of an ancient crustal component with high δ18O values, such as metasedimentary rocks. We propose, therefore, that the Late Jurassic two-mica monzogranites originated from partial melting of reworked ancient crustal materials at the depth of lower crust, and with the magma subsequently evolving as a result of plagioclase-dominated fractional crystallization. During Early to Middle Jurassic, westward subduction of the Paleo-Pacific plate, resulted in the partial melting of the mafic lower crust and the burial of ancient crustal materials in to deep crust, while crustal stretching in Late Jurassic might account for the decompression melting of the ancient crustal source. Thus, multi-stage Jurassic magmatism in the Liaodong Peninsula recorded a complex crustal evolution history, which closely related to the westward subduction of the Paleo-Pacific plate.

Petrogenesis of the Late Triassic Mengsong strongly peraluminous granites in the southeastern Tibetan Plateau: highly fractionated from crystal mush

ABSTRACT The Triassic Lincang granites make up the largest peraluminous granitic batholith in the Changning-Menglian Paleo-Tethys orogenic belt, southeastern Tibetan Plateau. It is undoubtedly very important to investigate the role of crustal magmatism in the evolution of the Changning-Menglian Paleo-Tethys orogenic belt. The Late Triassic Mengsong pluton is composed of strongly peraluminous two-mica monzogranites, and is located in the southernmost part of the Lincang batholith. Despite all being peraluminous granites, they differ markedly in dimensions, petrographic and geochemical characteristics. Mengsong two-mica monzogranites have low contents of TiO2, FeOtot, MgO, and CaO, but high values of SiO2 and Na2O, compared to biotite monzogranites of the Lincang batholith. The Lincang biotite monzogranites show an enrichment in light rare earth elements (LREE) and weak Eu anomalies (δEu = 0.3–0.8). However, the Mengsong two-mica monzogranites show a clear tetrad effect and contain pronounced negative Eu anomalies (δEu = 0.1–0.3). Geochemical compositions and mineral textures of two-mica monzogranites indicate that they are of highly fractionated type affinity. The two-mica monzogranites are characterized by negative εHf (t) values (−9.3 to −1.7) and εNd (t) values (−9.6 to −7.9), while the biotite monzogranites have lower εHf (t) values (−15.5 to −6.1) and εNd (t) values (−14.5 to −11.5). Isotopic compositions suggest that they were cogenetic and derived from partial melting of the lower crust. Our petrogenetic and zircon U–Pb age data support models that relate the Lincang and Mengsong granites to post-collisional magmatism in the Changning-Menglian Paleo-Tethys orogenic belt during the Middle to Late Triassic. We interpret the Mengsong pluton to represent highly fractionated melts from crystal mush reservoirs and the Lincang granites to be complementary residual.

Geochemical Contrasts between Late Triassic Rb-Rich and Barren Pegmatites from Ningshan Pegmatite District, South Qinling Orogen, China: Implications for Petrogenesis and Rare Metal Exploration

The Ningshan pegmatite district in the South Qinling Orogen hosts numerous Rb-(Be) mineralized pegmatites. In this study, whole-rock geochemistry, mineral geochemistry, and zircon U–Pb isotopes of the Rb-rich and barren pegmatites were determined. The barren pegmatites consist mainly of muscovite, microcline, albite, quartz, and garnet, whereas the Rb-rich pegmatites are mainly composed of muscovite, albite, quartz, and beryl, with minor chrysoberyl, cassiterite and columbite-group mineral. The muscovite and albite are the main Rb-bearing minerals. The U–Pb zircon dating of the Rb-rich and barren pegmatites yielding an age of 212–203 Ma, which is similar to that of the neighboring two-mica monzogranites distributed in the Ningshan area. Compared with the two-mica monzogranites, geochemical features, such as the Zr/Hf, Rb/Sr and Nb/Ta ratios and trace element contents indicated that the Rb-rich and barren pegmatites derived from fractionation of the two-mica monzogranites. In combination, the current and previous results suggest that the fractionation of the two-mica monzogranites caused the generation of the affinitive residual melts that, finally, crystallized to form the pegmatites. Compared to those from the barren pegmatites, the apatite from the Rb-rich pegmatites have higher MnO (14.51–19.12 wt.%) and Cl (0.12–0.16 wt.%) contents and lower F/Cl rartios (20–29). We conclude that these differences reflect unique geochemical signatures, and the geochemical composition of the apatite can be used as exploration guidance for rare metal-rich pegmatites.