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Li-Cs-Ta (LCT) rare-element pegmatites occur as late-stage and highly fractionated bodies at the margins of regionally zoned granite pegmatite fields. The evolution of the granitic pegmatite system, including its rare-metal metallogeny, is often difficult to determine due to complex textures involving variable crystal size and a heterogeneous chemical composition. The Renli-Chuanziyuan pegmatite field (South China) displays a well-developed regional zonation sequence, involving a core of biotite-, two-mica- and muscovite monzogranites (MMs) that grades outward into microcline (K-zone), microcline-albite (K-Na-zone), albite (Na-zone) and albite-spodumene (Na-Li-zone) pegmatites. Monazite and the Th, Ca–end-member (i.e. cheralite) provide valuable age, rare earth element (REE) geochemical and Sm-Nd isotopic data for understanding the regional zoning process within the Renli-Chuanziyuan pegmatite. Monazite (from the MM and the K-, K-Na- and Na-zone pegmatites) and cheralite (from the Na-Li-zone pegmatite) have variable compositions and complex internal microtextures. The monazite and cheralite grains contain irregular areas with subtle heterogeneous BSE response along cracks and grain margins, suggesting that they have experienced alkali-bearing fluid-aided modification. However, these features are rarely seen in monazite from the K-zone pegmatite. Common Pb contamination and/or Pb loss during fluid-aided modification may have disturbed the monazite and cheralite U-Th-Pb isotopic system, due to the differential mobility of U, Th and Pb. The unaltered Na-zone monazite and Na-Li-zone cheralite yielded Th-Pb ages of 140.42 ± 2.30 Ma (2 σ, mean standard weighted deviation (MSWD) = 2.4, n = 14) and 139.58 ± 2.15 Ma (2 σ, MSWD = 2.9, n = 21), respectively. The unaltered MM, K-zone and K-Na-zone monazite yielded 206Pb-238U ages of 138.03 ± 2.18 (2 σ, MSWD = 2.5, n = 18), 140.39 ± 2.18 (2 σ, MSWD = 3.0, n = 20) and 140.58 ± 2.14 Ma (2 σ, MSWD = 2.0, n = 52), respectively. These ages for the four pegmatite zones are temporally consistent with a syngenetic origin for the magmatic sequence of biotite-, two-mica- and MM and the pegmatite system and rare-metal (Li-Nb-Ta-Rb-(Cs)-(Be)) mineralization. The Sm-Nd isotopic analyses of the unaltered monazite and cheralite from the MM and four pegmatite zones yield similar initial Nd isotopic composition with εNd(t) = −9.9 to −7.9, indicating an identical single-source region (i.e. the Neoproterozoic South China lower crust). The Sm/Nd ratios display a gradual decrease across the four pegmatite zones from the unaltered K-zone monazite to Na-Li-zone cheralite, i.e. 0.39–0.63 (avg. = 0.43) for K-zone, 0.29–0.35 (avg. = 0.31) for K-Na-zone, 0.26–0.30 (avg. = 0.28) for Na-zone and 0.21–0.27 (avg. = 0.24) for Na-Li-zone. Such progressive variations suggest their derivation from the same parental magma, which experienced varying degrees of fractionation before the extraction of pegmatitic melts. Comprehensive monazite and cheralite geochemistry, as well as in situ U-Th-Pb and Sm-Nd isotopic results indicate that Rayleigh-type fractional crystallization controls the mineralogical and geochemical evolution from a chemically zoned granite source. [ABSTRACT FROM AUTHOR]

[Display omitted] • Discrete structural styles and mineral assemblages from auriferous quartz-ankerite-pyrite-arsenopyrite veins (Q2 and Q3) suggest superimposing gold mineralization at Tuanshanbei. • Comprehensive geological and H-O-Nd isotopic composition evidences are features that better adhere to metamorphic devolatilization models, indicating that the two-staged gold mineralization events both formed from metamorphic hydrothermal fluids originated from Cangxiyan Group metamorphic rocks. The Jiangnan Orogen is China's third largest gold province, and has undergone complex orogenic processes and tectonic overprinting, forming multistage magmatism, deformation, metamorphism, and gold mineralization. Our field studies indicate that the Tuanshanbei gold ores (central Jiangnan Orogen) have two generations of auriferous quartz-ankerite-pyrite-arsenopyrite veins (Q2 and Q3), with the latter containing abundant ankerite and base metal sulfides. Both Q2 and Q3 veins are younger than the emplacement of the Tuanshanbei granodiorite vein-ore host, and cut by post-ore diabase dikes. Q2 veins were likely associated with the Early Devonian near N-S-directed shortening, along sub-horizontal EW-/WNW-striking transpressive faults, whereas Q3 veins (hosting ∼ 70% of the total Au resource), were primarily hosted in the Early Triassic moderately-/steeply-dipping NW-striking tensional/transtensional faults and moderately-dipping NE-/NNE-striking transpressive faults, associated with NW-SE-directed shortening. Discrete structural styles and mineral assemblages from Q2 and Q3 suggest superimposing gold mineralization at Tuanshanbei. To determine the source(s) of the ore-forming aqueous-carbonic fluids, we conducted mineralogical and in-situ LA-(MC)-ICP-MS Nd-isotope analyses on two generations of hydrothermal monazite, and H-O isotope analyses on the quartz from Q2 and Q3 veins. The results suggest that the Tuanshanbei ore fluids have δD = −66.7 to −57.6‰ (Q2) and −66.8 to −66.2‰ (Q3), and calculated δ18O H2O = 4.5–9.7‰ (Q2) and 6.1–7.8‰ (Q3). The H-O isotopic data suggest a metamorphic and/or magmatic water source for the ore fluids. Hydrothermal monazite (coexists with native gold and auriferous sulfides) from Q2 and Q3 veins displays subtle heterogeneous BSE response along cracks and grain margin, suggesting alteration there. The 147Sm/144Nd and 143Nd/144Nd ratios of altered parts of Q2 and Q3 monazite grain are significantly perturbed via dissolution–recrystallization by the hydrothermal fluids, whereas their initial Nd isotope compositions seem to be less affected. The unaltered Q2 and Q3 monazite samples have similar initial εNd values (Q2: −8.07 to −7.36, Q3: −10.87 to −9.99) to the Neoproterozoic Cangxiyan Group greenschist–amphibolite-facies metamorphic rocks. Geological and structural evidence suggest both Q2 and Q3 ore-forming events were related to metamorphism, typical of orogenic gold deposits. We interpreted that various parts of the basement were metamorphosed (to near the greenschist-amphibolite-facies boundary) at different times, during which the gold-bearing metamorphic fluids produced migrated into the same structural conduits and deposited the ores there in two ore-forming episodes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Multiple stage of cassiterite can be identified via BSE, CL images, elemental mapping and in situ geochronology. • Two types cassiterite yield mineralization ages of 150.0 ± 2.6 Ma and 136.3 ± 5.5 Ma, respectively. • The physicochemical conditions of the two mineralization events are revealed. Numerous large deposits are formed by multiple mineralization events, however, how to identify superimposed mineralization events is poorly understood. The Xiangdong deposit is a large quartz vein-hosted W–Sn deposit within the Dengfuxian composite granite in South China. Previous studies have suggested that there are two discrete W–Sn mineralization events in the deposit, whereas the ore-forming conditions and processes of the two mineralization events are still unclear. To address these ambiguities, this contribution characterized the microtextures, trace-element chemistry, and geochronology of cassiterite assemblages within W–Sn-rich quartz veins. Based on cathodoluminescence (CL) images, cassiterite crystals were classified into two types with textural differences — Cst 1 and Cst 2. Cassiterite 1 is subhedral to irregular and exhibits complex zonation, whereas Cst 2 is euhedral and exhibits oscillatory zonation. Trace-element concentrations and maps of cassiterite obtained via LA–ICP–MS indicate that Cst 1 has high Fe, W, U, and Sb, but low Nb, Ta, and Zr concentrations, whereas Cst 2 has high Nb, Ta, and Zr, but low Fe, W, U, and Sb concentrations. This indicates that Cst 2 formed from higher temperature and more oxidizing hydrothermal fluids than Cst 1. Laser ablation ICP–MS U–Pb geochronological results of Cst 1 and Cst 2 demonstrate they precipitated at 150.0 ± 2.6 Ma and 136.3 ± 5.5 Ma, respectively. This contribution demonstrates that integrated textural and compositional studies of cassiterite assemblages are critical to identifying hydrothermal events that superimposed W–Sn mineralization, and to constrain ore-forming mechanisms and the physicochemical conditions of the environment. [ABSTRACT FROM AUTHOR]

• Baishawo two-mica monzogranite was emplaced at 147.5 ± 1.6 Ma with features of highly fractionated and strongly peraluminous. • Baishawo Granite and mineralized pegmatites have similar origin and are both derived from crust material. • The rare metal mineralization is genetically related to the Baishawo Granite and formed during ~140 Ma. 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 Li 2 O @ 0.85%, and 3450 t (Ta 2 O 5 + Nb 2 O 5) @ 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 SiO 2 and K 2 O, 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 ε Hf (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. [ABSTRACT FROM AUTHOR]

• Key features of the Wushan skarn copper deposit are studied. • Copper mineralization involved fluid immiscibility and fluid mixing. • Magmatic and meteoric hydrothermal fluid sources are indicated for the deposit. The Wushan copper skarn deposit (1.37 Mt at 1.17% Cu) is located in the Middle-Lower Yangtze River polymetallic belt. Skarn orebodies mainly occur in the Carboniferous and Permian carbonates adjacent to Early Cretaceous granodiorite porphyries (148–138 Ma). Ore deposition underwent two episodes of metallogenic events, involving hydrothermal evolution followed by skarn formation and porphyry-related mineralization. The skarn episode formed massive, disseminated, veinlet- and breccia-style mineralization at the contact zone, whereas porphyry mineralization is characterized as disseminated and veinlet-style only. Various types of fluid inclusions (daughter mineral-bearing, CO 2 -bearing, vapor and aqueous–vapor) are classified based on their fluid composition and phase assemblages. The hydrothermal fluids are mainly derived from a magmatic origin, which exsolves during the melt-fluid differentiation. Primary fluid in endoskarn is interpreted as representing two immiscible phases evolving from a low-salinity initial fluid. The initial supersaturated fluid has a relative low salinity and the wide range of T h values (433–626 °C) implies heterogeneous trapping, corresponding to pressures of 371–646 bars and hydrostatic depth of 3.7–6.5 km. Primary fluid inclusions trapped in syn-ore quartz show the coexistence of S-type inclusions (~30.0 wt% NaCl equiv) with vapor-rich and liquid-rich inclusions, indicating fluid immiscibility and phase separation from heterogeneous trapping. The homogenization temperatures (347–434 °C) of primary vapor-rich inclusions represent the trapping temperatures, corresponding the trapped pressures range from 152 to 374 bars and a hydrostatic depth of 1.5–3.7 km. Copper mineralization in episode porphyry occurs on a very small scale and have a clear trend of decreasing temperatures and salinities during fluid evolution. A similar scenario occurred during the porphyry episode in which fluid immiscibility led to copper mineralization. Significant trends of decreasing temperatures and salinities for both mineralization episodes reflect the change from a magmatic fluid-dominated system to a mixed source fluid that incorporated formation water from the country rocks and/or meteoric water. Controlled by the chemical transition of the fluid, this mixing process produced a relatively cool fluid system with lower salinities, which enhanced the precipitation of Cu–Fe sulfides. H–O–C isotope signatures further indicate that both the fluid and metal are predominantly derived from magmatic sources, and that multiple fluid pulses contributed to form skarn minerals and sulfides in the Wushan deposit. [ABSTRACT FROM AUTHOR]