Isotope geochemistry (O, C, S, Sr) and Rb-Sr age of carbonatites in central Tuva

The Rb-Sr isochron age of igneous ankerite-calcite and siderite carbonatites in central Tuva is estimated at 118 ± 9 Ma. The following ranges of initial values of O, C, Sr, and sulfide and S isotopic compositions were established: δ¹⁸O_carb = +(8.8?14.7)‰, δ¹³C_carb = ?(3.6?4.9)‰, δ¹⁸O_quartz = +(11.6?13.7)‰, δ³⁴S_pyrite = +(0.3?1.1)‰, and (⁸⁷Sr/⁸⁶Sr)_i =0.7042?0.7048 for ankerite-calcite carbonatite and δ¹⁸O_sid = +(9.2?12.4)‰, δ¹³C_sid = ?(3.9?5.9)‰, δ¹⁸O_quartz = +(11.2?11.4)‰, δ³⁴S_pyrite = ?(4.4–1.8)‰, δ³⁴S_sulfate = +(8.6?14.5)‰, and (⁸⁷Sr/⁸⁶Sr)_i = 0.7042?0.7045 for siderite carbonatite. The obtained isotopic characteristics indicate that both varieties of carbonatites are cognate and their mantle source is comparable with the sources of Late Mesozoic carbonatites in the western Transbaikal region and Mongolia. The revealed heterogeneity of isotopic compositions of carbonatites is caused by their contamination with country rocks, replacement with hydrothermal celestine, and supergene alteration.     

Deducing the source and composition of rare earth mineralising fluids in carbonatites: insights from isotopic (C,O, <Superscript>87</Superscript>Sr/<Superscript>86</Superscript>Sr) data from Kangankunde,Malawi

Carbonatites host some of the largest and highest grade rare earth element (REE) deposits but the composition and source of their REE-mineralising fluids remains enigmatic. Using C, O and ⁸⁷Sr/⁸⁶Sr isotope data together with major and trace element compositions for the REE-rich Kangankunde carbonatite (Malawi), we show that the commonly observed, dark brown, Fe-rich carbonatite that hosts REE minerals in many carbonatites is decoupled from the REE mineral assemblage. REE-rich ferroan dolomite carbonatites, containing 8–15 wt% REE₂O₃, comprise assemblages of monazite-(Ce), strontianite and baryte forming hexagonal pseudomorphs after probable burbankite. The ⁸⁷Sr/⁸⁶Sr values (0.70302–0.70307) affirm a carbonatitic origin for these pseudomorph-forming fluids. Carbon and oxygen isotope ratios of strontianite, representing the REE mineral assemblage, indicate equilibrium between these assemblages and a carbonatite-derived, deuteric fluid between 250 and 400 °C (δ¹⁸O + 3 to + 5‰_VSMOW and δ¹³C ? 3.5 to ? 3.2‰_VPDB). In contrast, dolomite in the same samples has similar δ¹³C values but much higher δ¹⁸O, corresponding to increasing degrees of exchange with low-temperature fluids (< 125 °C), causing exsolution of Fe oxides resulting in the dark colour of these rocks. REE-rich quartz rocks, which occur outside of the intrusion, have similar δ¹⁸O and ⁸⁷Sr/⁸⁶Sr to those of the main complex, indicating both are carbonatite-derived and, locally, REE mineralisation can extend up to 1.5 km away from the intrusion. Early, REE-poor apatite-bearing dolomite carbonatite (beforsite: δ¹⁸O + 7.7 to + 10.3‰ and δ¹³C ?5.2 to ?6.0‰; ⁸⁷Sr/⁸⁶Sr 0.70296–0.70298) is not directly linked with the REE mineralisation.     

Genesis of Pb–Zn Mineralization Beneath the Xiangshan Uranium Orefield,South China: Constraints from H–O–S–Pb Isotopes and Rb–Sr Dating

The volcanic‐hosted Xiangshan uranium orefield is the largest uranium deposit in South China. Recent exploration has discovered extensive Pb–Zn mineralization beneath the uranium orebodies. Detailed geological investigation reveals that the major metallic minerals include pyrite, sphalerite, galena, and chalcopyrite, whilst the major non‐metallic minerals include quartz, sericite, and calcite. New δ¹⁸O_fluid and δD_fluid data indicate that the ore‐forming fluids were mainly derived from magmatic, and the sulfide δ³⁴S values (2.2–6.9‰) suggest a dominantly magmatic sulfur source. The Pb isotope compositions are homogeneous (²⁰⁶Pb/²⁰⁴Pb = 18.120–18.233, ²⁰⁷Pb/²⁰⁴Pb = 15.575–15.698, and ²⁰⁸Pb/²⁰⁴Pb = 37.047–38.446). The ⁸⁷Sr/⁸⁶Sr ratios of sulfide minerals range from 0.7197 to 0.7204, which is much higher than volcanic rocks and fall into the range of metamorphic basement. Lead and strontium isotopic compositions indicate that the metallogenic materials probably were derived from metamorphic basement. Pyrite Rb–Sr dating of the ores yielded 131.3 ± 4.0 Ma, indicating that the Pb–Zn mineralization occurred in the Early Cretaceous.     

Magnesium isotopic behaviors between metamorphic rocks and their associated leucogranites,and implications for Himalayan orogenesis

Magnesium isotopic compositions, along with new Sr–Nd–Pb isotopic data and elemental analyses, are reported for 12 Miocene tourmaline-bearing leucogranites, 15 Eocene two-mica granites and 40 metamorphic rocks to investigate magnesium isotopic behaviors during metamorphic processes and associated magmatism and constrain the tectonic-magmatic-metamorphic evolution of the Himalayan orogeny. The gneisses, granulites and amphibolites represent samples of the Indian lower crust and display large range in δ²⁶Mg from −0.44‰ to −0.09‰ in mafic granulites, −0.44‰ to −0.10‰ in amphibolites, and −0.70‰ to −0.03‰ in granitic gneisses. The average Mg isotopic compositions of the granitic gneisses (−0.19 ± 0.34‰), mafic granulites (−0.22 ± 0.17‰) and amphibolites (−0.25 ± 0.24‰) are similar, indicating the limited Mg isotope fractionation during prograde metamorphism from granitic gneisses to mafic granulites and retrograde metamorphism from mafic granulites to amphibolites. The Eocene two-mica granites and Miocene leucogranites are characterized by large variations in elemental and Sr–Nd–Pb isotopic compositions. The leucogranites and two-mica granites have their corresponding (⁸⁷Sr/⁸⁶Sr)_i varying from 0.7282 to 0.7860 and 0.7163 to 0.7191, (¹⁴³Nd/¹⁴⁴Nd)_i from 0.511888 to 0.512040 and 0.511953 to 0.512076, ²⁰⁷Pb/²⁰⁴Pb from 15.7215 to 15.7891 and 15.7031 to 15.7317, ²⁰⁸Pb/²⁰⁴Pb from 38.8521 to 39.5286 and 39.2710 to 39.4035, and ²⁰⁶Pb/²⁰⁴Pb from 18.4748 to 19.0139 and 18.7834 to 18.9339. However, they have similar Mg isotopic compositions (−0.21‰ to +0.06‰ versus −0.24‰ to +0.09‰), which did not originate from fractional crystallization nor source heterogeneity. Based on hornblende/biotite/muscovite dehydration melting reaction and Mg isotopic variations in two-mica granites and leucogranites with the proceeding metamorphism, along with elemental discrimination diagrams, Eocene two-mica granites and Miocene leucogranites could be related to hornblende dehydration melting and muscovite dehydration melting, respectively. Mg isotopic compositions of Eocene two-mica granites become heavier compared to the source because of residues of isotopically light garnet in the source; while those of Miocene leucogranites become lighter because of entrainment of isotopically light garnet from the source region. Thus, a new model for crustal anatexis and Himalayan orogenesis was proposed based on the Mg isotope fractionation in the leucogranites and metamorphic rocks. This model emphasizes a successive process from Indian continental subduction to rapid exhumation of the Higher Himalayan Crystalline Series (HHCS). The former underwent high-temperature (HT) and high-pressure (HP) granulite-facies prograde metamorphism, which resulted in the hornblende dehydration melting and the formation of Eocene two-mica granites; while the latter experienced amphibolite-facies retrogression and decompression, which resulted in the muscovite dehydration melting and the formation of Miocene leucogranites.     

Genesis of the stratiform Zhenzigou PbZn deposit in the North China Craton: RbSr and COSPb isotope constraints

Isotopes (RbSr, C, O, S, and Pb) were investigated from the Zhenzigou PbZn deposit in the Qingchengzi mineral field (QMF) of the North China Craton as an aid to determine the genesis of stratiform PbZn deposits in the Liao-Ji Rift. A step-dissolution RbSr age of 1798 ± 8 Ma with 206Pb/204Pb ratios of 17.7477–17.8527 were obtained from sphalerite. Sulfur isotopic ratios for pyrite (5–14.4‰), sphalerite (2.4–8.6‰), and galena (− 0.3–8.6‰) from Zhenzigou have a narrower range than those from the host Paleoproterozoic Dashiqiao Formation, and granite in the area. Calcite and limestone from ore and wallrocks at the deposit have similar C and O isotope compositions, with δ¹³C_PDB ranging from − 6.0 to − 2.3‰ and δ¹⁸O_SMOW from 9.8 to 13.7‰, which are similar to those of carbonatite and the mantle.Comprehensive analysis of the Pb isotopic composition of the sulfide from the Zhenzigou deposit and PbZn deposits in adjacent area show that the Pb originated from the upper crust and mixed with Pb from the mantle. Sulfur isotopes from Zhenzigou deposit indicate that the mineralization has a volcanic eruption source. The δ¹³C_PDB and δ¹⁸O_SMOW values indicate that the CO₂ originated from a mixed mantle, marine carbonate and organic source.Combined with the study of regional metallogenic background, this paper proposes that deposition of stratiform PbZn mineralization in the QMF began ca. 2052 Ma during development of the Liaoji Rift. The mineralization extended to ca. 1798 Ma prior to deformation associated with the Lvliang Movement, which dismembered the stratiform PbZn mineralization. The veined mineralization in the region cross-cuts the stratiform deposits and represents remobilized and redeposited deposits associated with the emplacement of Triassic plutons such as the Xinling and Shuangdinggou granites.     

Petrogenesis and tectonic implications of early Silurian high-K calc-alkaline granites and their potassic microgranular enclaves,western Kunlun orogen,NW Tibetan Plateau

The western Kunlun orogen occupies a key position along the tectonic junction between the Pan-Asian and Tethyan domains, reflecting Proto- and Palaeo-Tethys subduction and terrane collision during early Palaeozoic to early Mesozoic time. We present the first detailed zircon U–Pb chronology, major and trace element, and Sr–Nd–O–Hf isotope geochemistry of the Qiukesu pluton and its microgranular enclaves from this multiple orogenic belt. SHRIMP zircon U–Pb dating shows that the Qiukesu pluton was emplaced in the early Silurian (ca. 435 Ma). It consists of weakly peraluminous high-K calc-alkaline monzogranite and syenogranite, with initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7131–0.7229, ?_Nd(T) of –4.1 to –5.7, δ¹⁸O of 8.0–10.8‰, and ?_Hf(T) (in situ zircon) of –4.9. Elemental and isotopic data suggest that the granites formed by partial melting of lower-crustal granulitized metasedimentary-igneous Precambrian basement triggered by underplating of coeval mantle-derived enclave-forming intermediate magmas. Fractional crystallization of these purely crustal melts may explain the more felsic end-member granitic rocks, whereas such crustal melts plus additional input from coeval enclave-forming intermediate magma could account for the less felsic granites. The enclaves are intermediate (SiO₂ 57.6–62.2 wt.%) with high K₂O (1.8–3.6 wt.%). They have initial ⁸⁷Sr/⁸⁶Sr ratios of 0.7132–0.7226, ?_Nd(T) of –5.0 to –6.0, δ¹⁸O of 6.9–9.9‰, and ?_Hf(T) (in situ zircon) of –8.1. We interpret the enclave magmas as having been derived by partial melting of subduction-modified mantle in the P–T transition zone between the spinel and spinel-garnet stability fields. Our new data suggest that subduction of the Proto-Tethyan oceanic crust was continuous to the early Silurian (ca. 435 Ma); the final closure of the Proto-Tethys occurred in the middle Silurian.     

Study on the Sr,Nd,Pb and O Isotopes of Basic Dyke Swarms in the Wudang Block and Basic Volcanics of the Yaolinghe Group

The Sr,Nd and Pb isotopic characteristics of the Wudang basic dyke swarms and basic volcanics of the Yaolinghe Group show that they were derived from the same multi-component mixing source in the mantle.The Wudang basic dyke swarms have(^87Sr/^86Sr)i=0.6905-0.7061,εNd(t)=-1.9-5.0,△^208Pb/^204Pb=35.49-190.26,△^207Pb/^204Pb=Th/Ta and a wide range of La/Yb ratios;and the basic volcanics of the Yaolinghe Group have(^87Sr/^86Sr)i=0.6487-0.7075,εNd(t)=0.11-3.94，△^208Pb/^204Pb=-81.58-219.95,△^207Pb/^204Pb=4.44-16.68and higher Th/Ta and La/Yb ratios,indicating that their source is a mixture of DM and EMⅡ,and the basic volcanics of the Yaolinghe Group were contaminated by crust materials en rout to the surface.Based on the geochemical features of continental tholeiitic basalts and being products of differen tacies derived from the same source,it can be concluded that an important rifting event in the South Qinling basement block occurred during Neoproterozoic,followed by a setting of oceanic basic in the Early Paleozoic.     

Constraints of C–O–S–Pb isotope compositions and Rb–Sr isotopic age on the origin of the Tianqiao carbonate-hosted Pb–Zn deposit,SW China

The Tianqiao Pb–Zn deposit in the western Yangtze Block, southwest China, is part of the Sichuan–Yunnan–Guizhou (SYG) Pb–Zn metallogenic province. Ore bodies are hosted in Devonian and Carboniferous carbonate rocks, structurally controlled by a thrust fault and anticline, and carried about 0.38 million tons Pb and Zn metals grading > 15% Pb + Zn. Both massive and disseminated Pb–Zn ores occur either as veinlets or disseminations in dolomitic rocks. They are composed of ore minerals, pyrite, sphalerite and galena, and gangue minerals, calcite and dolomite. δ³⁴S values of sulfide minerals range from + 8.4 to + 14.4‰ and display a decreasing trend from pyrite, sphalerite to galena (δ³⁴S_pyrite > δ³⁴S_sphalerite > δ³⁴S_galena). We interpret that reduced sulfur derived from sedimentary sulfate (gypsum and barite) of the host Devonian to Carboniferous carbonate rocks by thermal–chemical sulfate reduction (TSR). δ¹³C_PDB and δ¹⁸O_SMOW values of hydrothermal calcite range from –5.3 to –3.4‰ and + 14.9 to + 19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO₂ in the hydrothermal fluid was a mixture origin of mantle, marine carbonate rocks and sedimentary organic matter. Sulfide minerals have homogeneous and low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.378 to 18.601, ²⁰⁷Pb/²⁰⁴Pb = 15.519 to 15.811 and ²⁰⁸Pb/²⁰⁴Pb = 38.666 to 39.571) that are plotted in the upper crust Pb evolution curve and overlap with that of Devonian to Carboniferous carbonate rocks and Proterozoic basement rocks in the SYG province. Pb isotope compositions suggest derivation of Pb metal from mixed sources. Sulfide minerals have ⁸⁷Sr/⁸⁶Sr ratios ranging from 0.7125 to 0.7167, higher than Sinian to Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than basement rocks. Again, Sr isotope compositions are supportive of a mixture origin of Sr. They have an Rb–Sr isotopic age of 191.9 ± 6.9Ma, possibly reflecting the timing of Pb–Zn mineralization. C–O–S–Pb–Sr isotope compositions of the Tianqiao Pb–Zn deposit indicate a mixed origin of ore-forming fluids, which have Pb–Sr isotope homogenized before the mineralization. The Permian flood basalts acted as an impermeable layer for the Pb–Zn mineralization hosted in the Devonian–Carboniferous carbonate rocks.     

Late Mesozoic magmatism and metallogeny in NE China: The Sandaowanzi–Beidagou example

The Sandaowanzi (>22t Au) and Beidagou (>5t Au) tellurium–gold deposits are located in the northeastern Central Asian Orogenic Belt (Heilongjiang Province, NE China). The ore-hosting volcanic rocks unconformably overly monzogranite and were intruded by adakitic granodiorite. In this study, we report new-age, geochemical, and Sr–Nd–Pb isotopic data to elucidate the genetic link between the igneous rocks and the Te–Au mineralization. New-age data indicate that local magmatism occurred in the Early Jurassic (ca. 177.2 Ma) and Early Cretaceous (ca. 118.7 ? 122.0 Ma). Geochemically, the igneous rocks are enriched in LREEs, Pb, K, and U, and depleted in Nb, P, and Ti, showing calc-alkaline affinity. The Early Jurassic monzogranite rocks are featured by ⁸⁷Sr/⁸⁶Sr = 0.7111?0.7118; ε_Nd(t) = ?4.6 to ?4.7; ²⁰⁶Pb/²⁰⁴Pb = 18.098?18.102, ²⁰⁷Pb/²⁰⁴Pb = 15.558?15.580, and ²⁰⁸Pb/²⁰⁴Pb = 37.781?37.928, whereas the Early Cretaceous adakitic granodiorite contains: ⁸⁷Sr/⁸⁶Sr = 0.7071?0.7073; ε_Nd(t) = ? 3.4 to ?3.2; ²⁰⁶Pb/²⁰⁴Pb = 17.991?18.080, ²⁰⁷Pb/²⁰⁴Pb = 15.483?15.508, and ²⁰⁸Pb/²⁰⁴Pb = 37.938?37.985. Initial isotopic ratios for the Early Cretaceous volcanic rocks: ⁸⁷Sr/⁸⁶Sr = 0.7061?0.7087; ε_Nd(t) = ? 3.6 to ?2.9; ²⁰⁶Pb/²⁰⁴Pb = 18.136?18.199, ²⁰⁷Pb/²⁰⁴Pb = 15.512?15.628, and ²⁰⁸Pb/²⁰⁴Pb = 38.064?38.155. The pyrite, chalcopyrite, and telluride grains yielded δ³⁴S of ?6.52 ‰ to 2.13 ‰ (mean = ? 0.82 ‰) and δ¹³C_PDB of the calcite samples are in the range of ?6.64 ‰ to ?5.24 ‰, implying the ore materials were derived from mantle. The geochemical and isotopic results indicate that primary melts of Late Mesozoic magmatic rocks have features by partial melting of the continental crust. The adakitic rocks may have been the products of the thickened lower crustal delamination and the subsequent asthenospheric upwelling during the intra-continental extension in NE China. Regionally, intrusive activity and molybdenum mineralization during the Jurassic was affected by subduction setting, whereas gold mineralization was controlled by the Early Cretaceous tectonothermal events associated with a superposition extension.     

Genesis of the Huangshaping W–Mo–Cu–Pb–Zn polymetallic deposit in Southeastern Hunan Province,China: Constraints from fluid inclusions,trace elements,and isotopes

The Huangshaping polymetallic deposit is located in southeastern Hunan Province, China. It is a world-class W–Mo–Pb–Zn–Cu skarn deposit in the Nanling Range Metallogenic Belt, with estimated reserves of 74.31 Mt of W–Mo ore at 0.28% WO₃ and 0.07% Mo, 22.43 Mt of Pb–Zn ore at 3.6% Pb and 8.00% Zn, and 20.35 Mt of Cu ore at 1.12% Cu. The ore district is predominantly underlained by carbonate formations of the Lower Carboniferous period, with stocks of quartz porphyry, granite porphyry, and granophyre. Skarns occurred in contact zones between stocks and their carbonate wall rocks, which are spatially associated with the above-mentioned three types of ores (i.e., W–Mo, Pb–Zn, and Cu ores).Three types of fluid inclusions have been identified in the ores of the Huangshaping deposit: aqueous liquid–vapor inclusions (Type I), daughter-mineral-bearing aqueous inclusions (Type II), and H₂O–CO₂ inclusions (Type III). Systematic microthermometrical, laser Raman spectroscopic, and salinity analyses indicate that high-temperature and high-salinity immiscible magmatic fluid is responsible for the W–Mo mineralization, whereas low-temperature and low-salinity magmatic-meteoric mixed fluid is responsible for the subsequent Pb–Zn mineralization. Another magmatic fluid derived from deep-rooted magma is responsible for Cu mineralization.Chondrite-normalized rare earth element patterns and trace element features of calcites from W–Mo, Pb–Zn, and Cu ores are different from one another. Calcite from Cu ores is rich in heavy rare earth elements (187.4–190.5 ppm), Na (0.17%–0.19%), Bi (1.96–64.60 ppm), Y (113–135 ppm), and As (9.1–29.7 ppm), whereas calcite from W–Mo and Pb–Zn ores is rich in Mn (> 10.000 ppm) and Sr (178–248 ppm) with higher Sr/Y ratios (53.94–72.94). δ¹⁸O values also differ between W–Mo/Pb–Zn ores (δ¹⁸O = 8.10‰–8.41‰) and Cu ores (δ¹⁸O = 4.34‰–4.96‰), indicating that two sources of fluids were, respectively, involved in the W–Mo, Pb–Zn, and Cu mineralization.Sulfur isotopes from sulfides also reveal that the large variation (4‰–19‰) within the Huangshaping deposit is likely due to a magmatic sulfur source with a contribution of reduced sulfate sulfur host in the Carboniferous limestone/dolomite and more magmatic sulfur involved in the Cu mineralization than that in W–Mo and Pb–Zn mineralization. The lead isotopic data for sulfide (galena: ²⁰⁶Pb/²⁰⁴Pb = 18.48–19.19, ²⁰⁷/²⁰⁴Pb = 15.45–15.91, ²⁰⁸/²⁰⁴Pb = 38.95–39.78; sphalerite: ²⁰⁶Pb/²⁰⁴Pb = 18.54–19.03, ²⁰⁷/²⁰⁴Pb = 15.60–16.28, ²⁰⁸/²⁰⁴Pb = 38.62–40.27; molybdenite: ²⁰⁶Pb/²⁰⁴Pb = 18.45–19.21, ²⁰⁷/²⁰⁴Pb = 15.53–15.95, ²⁰⁸/²⁰⁴Pb = 38.77–39.58 chalcopyrite: ²⁰⁶Pb/²⁰⁴Pb = 18.67–19.38, ²⁰⁷/²⁰⁴Pb = 15.76–19.90, and ²⁰⁸/²⁰⁴Pb = 39.13–39.56) and oxide (scheelite: ²⁰⁶Pb/²⁰⁴Pb = 18.57–19.46, ²⁰⁷/²⁰⁴Pb = 15.71–15.77, ²⁰⁸/²⁰⁴Pb = 38.95–39.13) are different from those of the wall rock limestone (²⁰⁶Pb/²⁰⁴Pb = 18.34–18.60, ²⁰⁷/²⁰⁴Pb = 15.49–15.69, ²⁰⁸/²⁰⁴Pb = 38.57–38.88) and porphyries (²⁰⁶Pb/²⁰⁴Pb = 17.88–18.66, ²⁰⁷/²⁰⁴Pb = 15.59–15.69, ²⁰⁸/²⁰⁴Pb = 38.22–38.83), suggesting Pb²⁰⁶-, U²³⁸-, and Th ²³²-rich material are involved in the mineralization. The Sm–Nd isotopes of scheelite (ε_Nd(t) = − 6.1 to − 2.9), garnet (ε_Nd(t) = − 6.8 to − 6.1), and calcite (ε_Nd(t) = − 6.3) from W–Mo ores as well as calcite (ε_Nd(t) = − 5.4 to − 5.3) and scheelite (ε_Nd(t) = − 2.9) from the Cu ores demonstrate suggest more mantle-derived materials involved in the Cu mineralization.In the present study we conclude that two sources of ore-forming fluids were involved in production of the Huangshaping W–Mo–Pb–Zn–Cu deposit. One is associated with the granite porphyry magmas responsible for the W–Mo and then Pb–Zn mineralization during which its fluid evolved from magmatic immiscible to a magmatic–meteoritic mixing, and the other is derived from deep-rooted magma, which is related to Cu-related mineralization.     

Geochemistry and C–O and Nd–Sr isotope characteristics of the 2.4 Ga Hogenakkal carbonatites from the South Indian Granulite Terrane: evidence for an end-Archaean depleted component and mantle heterogeneity

ABSTRACT

The South Indian Granulite Terrane (SGT) is a collage of Archaean to Neoproterozoic age granulite facies blocks that are sutured by an anastomosing network of large-scale shear systems. Besides several Neoproterozoic carbonatite complexes emplaced within the Archaean granulites, there are also smaller Paleoproterozoic (2.4 Ga, Hogenakkal) carbonatite intrusions within two NE-trending pyroxenite dikes. The Hogenakkal carbonatites, further discriminated into sövite and silicate sövite, have high Sr and Ba contents and extreme light rare earth element (LREE) enrichment with steep slopes typical of carbonatites. The C- and O-isotopic ratios [δ¹³C_VPDB = ?6.7 to ?5.8‰ and δ¹⁸O_VSMOW = 7.5–8.7‰ except a single ¹⁸O-enriched sample (δ¹⁸O = 20.0‰)] represent unmodified mantle compositions. The εNd values indicate two groupings for the Hogenakkal carbonatites; most samples show positive εNd values, close to CHUR (εNd = ?0.35 to 2.94) and named high-εNd group while the low-εNd group samples show negative values (?5.69 to ?8.86), corresponding to depleted and enriched source components, respectively. The ⁸⁷Sr/⁸⁶Sr_i ratios of the two groups also can be distinguished: the high-εNd ones have low ⁸⁷Sr/⁸⁶Sr_i ratios (0.70161–0.70244) while the low-εNd group shows higher ratios (0.70247–0.70319). We consider the Nd–Sr ratios as primary and infer derivation from a heterogeneous mantle source. The emplacement of the Hogenakkal carbonatites may be related to Paleoproterozoic plume induced large-scale rifting and fracturing related to initiation of break-up of the Neoarchean supercontinent Kenorland.     

Geological and C–O–S–Pb–Sr isotopic constraints on the origin of the Qingshan carbonate-hosted Pb–Zn deposit,Southwest China

Located in the western Yangtze Block, the Qingshan Pb–Zn deposit, part of the Sichuan–Yunnan–Guizhou Pb–Zn metallogenic province, contains 0.3 million tonnes of 9.86 wt.% Pb and 22.27 wt.% Zn. Ore bodies are hosted in Carboniferous and Permian carbonate rocks, structurally controlled by the Weining–Shuicheng anticline and its intraformational faults. Ores composed of sphalerite, galena, pyrite, dolomite, and calcite occur as massive, brecciated, veinlets, and disseminations in dolomitic limestones.

The C–O isotope compositions of hydrothermal calcite and S–Pb–Sr isotope compositions of Qingshan sulphide minerals were analysed in order to trace the sources of reduced sulphur and metals for the Pb–Zn deposit. δ¹³C_PDB and δ¹⁸O_SMOW values of calcite range from –5.0‰ to –3.4‰ and +18.9‰ to +19.6‰, respectively, and fall in the field between mantle and marine carbonate rocks. They display a negative correlation, suggesting that CO₂ in the hydrothermal fluid had a mixed origin of mantle, marine carbonate rocks, and sedimentary organic matter. δ³⁴S values of sulphide minerals range from +10.7‰ to +19.6‰, similar to Devonian-to-Permian seawater sulphate (+20‰ to +35‰) and evaporite rocks (+23‰ to +28‰) in Carboniferous-to-Permian strata, suggesting that the reduced sulphur in hydrothermal fluids was derived from host-strata evaporites. Ores and sulphide minerals have homogeneous and low radiogenic Pb isotope compositions (²⁰⁶Pb/²⁰⁴Pb = 18.561 to 18.768, ²⁰⁷Pb/²⁰⁴Pb = 15.701 to 15.920, and ²⁰⁸Pb/²⁰⁴Pb = 38.831 to 39.641) that plot in the upper crust Pb evolution curve, and are similar to those of Devonian-to-Permian carbonate rocks. Pb isotope compositions suggest derivation of Pb metal from the host rocks. ⁸⁷Sr/⁸⁶Sr ratios of sphalerite range from 0.7107 to 0.7136 and (⁸⁷Sr/⁸⁶Sr)_200Ma ratios range from 0.7099 to 0.7126, higher than Sinian-to-Permian sedimentary rocks and Permian Emeishan flood basalts, but lower than Proterozoic basement rocks. This indicates that the ore strontium has a mixture source of the older basement rocks and the younger cover sequence. C–O–S–Pb–Sr isotope compositions of the Qingshan Pb–Zn deposit indicate a mixed origin of the ore-forming fluids and metals.     

Zircon LA-ICP MS U-Pb Age, Sr-Nd-Pb Isotopic Compositions and Geochemistry of the Triassic Post-collisional Wulong Adakitic Granodiorite in the South Qinling, Central China, and Its Petrogenesis

The Indosinian post-collisional Wulong pluton intruded into the Mesoproterozoic Fuping Group, South Qinling, central China. In the southern part of the pluton, some mafic enclaves have sharp or gradational contact relationships with the host biotite granodiorite. Geochemistry, zircon LA-ICP MS （laser ablation inductively-coupled plasma mass spectrometry） U-Pb chronology and Sr- Nd-Pb isotope geochemistry of the pluton are reported in this paper. The biotite granodiorite shows close compositional similarities to high-silica adakite. Its chondrite-normalized REE patterns are characterized by strong HREE depletion （Yb = 0.33--0.96 10-6 and Y = 4.77-11.19 ×10^-6）, enrichment of Ba （775-1386 x 10-6） and Sr （643-1115 × 10^-6） and high Sr/Y （57.83-159.99） and Y/Yb （10.99-14.32） ratios, as well as insignificant Eu anomalies （6Eu = 0.70-0.83）, suggesting a feldspar-poor, garnet±amphibole-rich residual mineral assemblage. The mafic enclaves have higher MgO （4.15- 8.13%）, Cr （14.79-371.31 × 10-6）, Ni （20.00-224.24× 10^-6） and Nb/Ta （15.42-21.91） than the host granodiorite, implying that they are mantle-derived and might represent underplated mafic magma. Zircon LA-ICP MS dating of the granodiorite yields a ^206pb/^238U weighted mean age of 208±2 Ma （MSWD=0.50, 1σ）, which is the age of emplacement of the host biotite granodiorite. This age indicates that the Wulong pluton formed during the late-orogenic or post-collisional stage （〈242±21 Ma） of the South Qinling belt. The host biotite granodiorite displays ^87Sr/^86Sr = 0.7059-0.7062, Isr = 0.7044-- 0.7050,^143Nd/^144Nd = 0.51236-0.51238, εNd（t）= -2.26 to -2.66 to ^206Pb/^204pb = 18.099-18.209, ^207pb/^204pb = 15.873-15.979 and ^208pb/^204pb = 38.973-39.430. Those ratios are similar to those of the Mesoproterozoic Yaolinghe Group in the South Qinling. Furthermore, its Nd isotopic model age （-1.02 Ga） is consistent with the age （-1.1 Ga） of the Yaolinghe Group. Based on the integrated geological and ge     

Fluid-rock interaction during progressive migration of carbonatitic fluids, derived from small-scale trace element and Sr, Pb isotope distribution in hydrothermal fluorite

Associated with the Cretaceous Okorusu carbonatite complex (Namibia) is a hydrothermal fluorite mineralization hosted in Pan-African country rock marbles, which resulted from fluid-rock reaction between the marbles and orthomagmatic, carbonatitic fluids expelled from the carbonatite. Yellow fluorite I was deposited in veins up to 5 cm away from the wallrock contact, followed by purple and colorless fluorite II, smoky quartz and barite, a Mn-rich crust on early calcite, and pure calcite. This clear-cut sequence of mineral growth allows an investigation into fluid-rock interaction processes between the marble and the migrating carbonatitic fluid, and element fractionation patterns between the fluid and subsequent hydrothermal precipitates.Fluorite I shows a progressive change in color from dark yellow to colorless with purple laminations over time of deposition. Subsequent fluorite I precipitates show an increase in Ca, and a continuous decrease in F, Sr, REE, Y, Th, U and Pb contents. The ratios (Eu/Eu*)_cn, Th/Pb and U/Pb increase whereas Y/Ho, Th/U and (La/Yb)_cn decrease. The Sr-isotopic composition remains constant at ⁸⁷Sr/⁸⁶Sr = 0.70456-0.70459, but with varying, highly radiogenic Pb (²⁰⁶Pb/²⁰⁴Pb = 32-190, ²³⁸U/²⁰⁴Pb = 7-63). Fluorite II has ⁸⁷Sr/⁸⁶Sr = 0.70454-0.70459, ²⁰⁶Pb/²⁰⁴Pb = 18.349, and ²⁰⁷Pb/²⁰⁴Pb = 15.600, and a chemical composition similar to youngest fluorite I. The Mn-rich crust on early calcite accumulated REE, Ba, Pb, Zr, Cs, Th and U, developing into pure calcite with a prominent negative Ce anomaly and successively more radiogenic Sr. The calculated degrees of fluid-rock interaction, f = weight fraction of fluid/(fluid + marble), decrease from fluorite I and most fluorite II (f = 0.5) to calcite (f = 0.2-0.3) and hydrothermal quartz (f ? 0.1). A crush-leach experiment for fluid inclusions in the hydrothermal quartz yielded a Rb-Sr isochron age of 103 ± 12 Ma. Crush-leach analysis for the carbonatitic fluid trapped in the wallrock yielded a trend from the fluid leachate to the host quartz (²⁰⁶Pb/²⁰⁴Pb = 18.224 and 18.602, ²⁰⁷Pb/²⁰⁴Pb = 15.616 and 15.636, respectively) extending from carbonatite towards crustal rocks.Calculated trace element distribution coefficients fluorite/fluid are below unity throughout, and increase from La to Yb. Elements largely excluded from fluorite (Ba, Pb, LREE relative to HREE) were incorporated later into the Mn-rich crust on calcite. The trace element patterns of the hydrothermal minerals are related to changing aCO₂ and aF⁻ in the fluid during continued fluid-marble reaction. A predominance of carbonate over fluoride complexing in the fluid as reactions proceeded controlled the Y/Ho, Th/U and REE patterns in the fluid and the crystallizing phases. Deviations from these trends indicate discontinuous processes of fluid-rock reaction.     

Zircon U-Pb ages,geochemistry, and Sr-Nd-Pb-Hf isotopic compositions of the Pinghe pluton,Southwest China: implications for the evolution of the early Palaeozoic Proto-Tethys in Southeast Asia

The geological record of the Neoproterozoic to early Palaeozoic Proto-Tethyan Ocean in Southeast Asia is not clear. To better constrain the evolution of the Proto-Tethys, we present new geochronology, geochemistry, and petrology of the late Cambrian to Ordovician Pinghe pluton monzogranite from the Baoshan block, western Yunnan, southwest China. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) analyses of four zircon samples yield ages of 482–494 and 439–445 Ma for the pluton, interpreted as two episodes within one magmatic event accompanying the whole process of subduction–collision–orogeny between buoyant blocks and oceanic crust of the Proto-Tethys. The monzogranite belongs to the strong peraluminous, high-K, calc-alkaline series and shows characteristics of both I-type and S-type granitic rocks. It is characterized by extremely high Rb/Sr and Rb/Ba but low TiO₂, MgO, FeOt, and CaO/Na₂O ratios. The monzogranite is also moderately enriched in light rare earth elements (LREEs), depleted in heavy rare earth elements (HREEs), lacks HREE fractionation, and has strongly negative Eu (Eu/Eu* = 0.06–0.49), Ba, Nb, Ta, Sr, and Ti anomalies. Whole-rock ε_Nd(t) and ε_Hf(t) values range from ?8.7 to ?11.6 and ?5.55 to ?9.58, respectively. Nd and Hf two-stage model ages range from 1.66 to 2.06 Ga and 2.14 to 3.00 Ga, respectively, with variable radiogenic ²⁰⁶Pb/²⁰⁴Pb_(t) (16.547–18.705), ²⁰⁷Pb/²⁰⁴Pb_(t) (15.645–15.765), and ²⁰⁸Pb/²⁰⁴Pb_(t) (38.273–38.830). These signatures suggest that the monzogranite magma was derived from partial melting of heterogeneous metapelite, which was generated from Neoarchean to Palaeoproterozoic materials mixed with basaltic magma. The monzogranite magma underwent crystallization differentiation of plagioclase, K-feldspar, and ilmenite. Magmatism to form the Pinghe pluton occurred in a post-collisional setting. Based on the comparison of coeval granites throughout adjacent regions (e.g. Himalayan orogen, Lhasa Terrane, and parts of Gondwana supercontinent), we propose that the Baoshan block was derived from the northern Australian Proto-Tethyan Andean-type active continental margin of Gondwana and experienced subduction of the Proto-Tethyan oceanic crust and accretion of an outboard micro-continent. The Pinghe pluton could have formed when a subducting oceanic slab broke off during collision.     

Evolution of rare-earth mineralization in the Bear Lodge carbonatite,Wyoming: Mineralogical and isotopic evidence

The Bear Lodge alkaline complex in northeastern Wyoming (USA) is host to potentially economic rare-earth mineralization in carbonatite and carbonatite-related veins and dikes that intrude heterolithic diatreme breccias in the Bull Hill area of the Bear Lodge Mountains. The deposit is zoned and consists of pervasively oxidized material at and near the surface, which passes through a thin transitional zone at a depth of ~ 120–183 m, and grades into unaltered carbonatites at depths greater than ~ 183–190 m. Carbonatites in the unoxidized zone consist of coarse and fine-grained calcite that is Sr-, Mn- and inclusion-rich and are characterized by the presence of primary burbankite, early-stage parisite and synchysite with minor bastnäsite that have high (La/Nd)cn and (La/Ce)_cn values. The early minerals are replaced with polycrystalline pseudomorphs consisting of secondary rare-earth fluorocarbonates and ancylite with minor monazite. Different secondary parageneses can be distinguished on the basis of the relative abundances and composition of individual minerals. Variations in key element ratios, such as (La/Nd)_cn, and chondrite-normalized profiles of the rare-earth minerals and calcite record multiple stages of hydrothermal deposition involving fluids of different chemistry. A single sample of primary calcite shows mantle-like δ¹⁸O_V-SMOW and δ¹³C_V-PDB values, whereas most other samples are somewhat depleted in ¹³C (δ¹³C_V-PDB ≈ − 8 to − 10‰) and show a small positive shift in δ¹⁸O_V-SMOW due to degassing and wall-rock interaction. Isotopic re-equilibration is more pronounced in the transitional and oxidized zones; large shifts in δ¹⁸O_V-SMOW (to ~ 18‰) reflect the input of meteoric water during pervasive hydrothermal reworking and supergene oxidation. The textural relations, mineral chemistry and C and O stable-isotopic variations record a polygenetic sequence of rare-earth mineralization in the deposit. With the exception of one Pb-poor sample showing an appreciable positive shift in ²⁰⁸Pb/²⁰⁴Pb value (~ 39.2), the Bear Lodge carbonatites are remarkably uniform in their Nd, Sr and Pb isotopic composition: ¹⁴³Nd/¹⁴⁴Nd_t = 0.512591–0.512608; εNd_t = 0.2–0.6; ⁸⁷Sr/⁸⁶Sr_t = 0.704555–0.704639; εSr_t = − 1.5–2.7; ²⁰⁶Pb/²⁰⁴Pb_t = 18.071–18.320; ²⁰⁷Pb/²⁰⁴Pb_t = 15.543–15.593; and ²⁰⁸Pb/²⁰⁴Pb_t = 38.045–39.165. These isotopic characteristics indicate that the source of the carbonatitic magma was in the subcontinental lithospheric mantle, and modified by subduction-related metasomatism. Carbonatites are interpreted to be generated from small degrees of partial melt that may have been produced via interaction of upwelling asthenosphere giving a small depleted MORB component, with an EM1 component likely derived from subducted Farallon crust.     

Genesis of the Bangbu Orogenic Gold Deposit,Tibet: Evidence from Fluid Inclusion,Stable Isotopes,and Ar-Ar Geochronology

The Bangbu gold deposit is a large orogenic gold deposit in Tibet formed during the AlpineHimalayan collision. Ore bodies(auriferous quartz veins) are controlled by the E-W-trending Qusong-Cuogu-Zhemulang brittle-ductile shear zone. Quartz veins at the deposit can be divided into three types: pre-metallogenic hook-like quartz veins, metallogenic auriferous quartz veins, and postmetallogenic N-S quartz veins. Four stages of mineralization in the auriferous quartz veins have been identified:(1) Stage S1 quartz+coarse-grained sulfides,(2) Stage S2 gold+fine-grained sulfides,(3) Stage S3 quartz+carbonates, and(4) Stage S4 quartz+ greigite. Fluid inclusions indicate the oreforming fluid was CO_2-N_2-CH_4 rich with homogenization temperatures of 170–261°C, salinities 4.34–7.45 wt% Na Cl equivalent. δ~(18)Ofluid(3.98‰–7.18‰) and low δDV-SMOW(-90‰ to-44‰) for auriferous quartz veins suggest ore-forming fluids were mainly metamorphic in origin, with some addition of organic matter. Quartz vein pyrite has δ~(34)SV-CDT values of 1.2‰–3.6‰(an average of 2.2‰), whereas pyrite from phyllite has δ~(34)SV-CDT 5.7‰–9.9‰(an average of 7.4‰). Quartz vein pyrites yield 206Pb/204 Pb ratios of 18.662–18.764, 207Pb/204 Pb 15.650–15.683, and ~(208)Pb/204 Pb 38.901–39.079. These isotopic data indicate Bangbu ore-forming materials were probably derived from the Langjiexue accretionary wedge. 40Ar/39 Ar ages for sericite from auriferous sulfide-quartz veins yield a plateau age of 49.52 ± 0.52 Ma, an isochron age of 50.3 ± 0.31 Ma, suggesting that auriferous veins were formed during the main collisional period of the Tibet-Himalayan orogen(~65–41 Ma).     

The long-lived partial melting of the Greater Himalayas in southern Tibet,constraints from the Miocene Gyirong anatectic pegmatite and its prospecting potential for rare element minerals

The Cenozoic Himalayan leucogranite-pegmatite belt has been a hotspot for rare metal exploration in recent years. To determine the genesis of the pegmatite in the Himalayan region and its relationship with the Greater Himalayan Crystalline Complex (GHC), the Gyirong pegmatite in southern Tibet was chosen for geochronological and geochemical studies. The dating analyses indicate that the U-Th-Pb ages of zircon, monazite, and xenotime exhibit large variations (38.6–16.1 Ma), with the weighted average value of the four youngest points is 16.5 ± 0.3 Ma, which indicates that the final stage of crystallization of the melt occurred in the Miocene. The age of the muscovite Ar-Ar inverse isochron is 15.2 ± 0.4 Ma, which is slightly later than the intrusion age, showing that a cooling process associated with rapid denudation occurred at 16–15 Ma. The ε_Hf(t) values of the Cenozoic anatectic zircons cluster between −12 and −9 with an average of −11.4. The Gyirong pegmatite shows high contents of Si, Al, and K, a high Al saturation index, and low contents of Na, Ca, Fe, Mn, P, Mg, and Ti. Overall, the Gyirong pegmatite is enriched in Rb, Cs, U, K, Th and Pb and depleted in Nb, Ta, Zr, Ti, Eu, Sr, and Ba. The samples show a high ⁸⁷Sr/⁸⁶Sr_{(16 Ma)} ratio of ca. 0.762 and a low ε_{Nd(16 Ma)} value of −16.0. The calculated average initial values of ²⁰⁸Pb/²⁰⁴Pb_{(16 Ma)}, ²⁰⁷Pb/²⁰⁴Pb_{(16 Ma)} and ²⁰⁶Pb/²⁰⁴Pb_{(16 Ma)} of the whole rock are 39.72, 15.79 and 19.56, respectively. The Sr-Nd-Pb-Hf isotopic characteristics of the Gyirong pegmatite are consistent with those of the GHC. This study concludes that the Gyirong pegmatite represents a typical crustal–derived anatectic pegmatite with low metallogenic potential for rare metals. The Gyirong pegmatite records the long–term metamorphism and partial melting process of the GHC, and reflects the crustal thickening caused by thrust compression at 39–29 Ma and the crustal thinning induced by extensional decompression during 28–15 Ma.©2023 China Geology Editorial Office.     

Phanerozoic amalgamation of the Alxa Block and North China Craton: Evidence from Paleozoic granitoids,U–Pb geochronology and Sr–Nd–Pb–Hf–O isotope geochemistry

The North China Craton (NCC) has been considered to be part of the supercontinent Columbia. The nature of the NCC western boundary, however, remains strongly disputed. A key question in this regard is whether or not the Alxa Block is a part of the NCC. It is located in the vicinity of the inferred boundary, and therefore could potentially resolve the issue of the NCC's relationship to the Columbia supercontinent. Some previous studies based on the Alxa Block's geological evolution and detrital zircon ages suggested that it is likely not a part of the NCC. The lack of evidence from key igneous rock units, however, requires further constraints on the tectonic affinity of the western NCC and Alxa Block and on the timing of their amalgamation.In this study, new zircon U–Pb age and Hf–O isotopes and whole-rock geochemical and Sr–Nd–Pb isotopic data for the Paleozoic granitoids in or near the eastern Alxa Block were used to constrain the petrogenesis of these rocks and the relationship between the Alxa Block and NCC. Secondary ion mass spectrometry (SIMS) U–Pb zircon dating indicates that the Bayanbulage, Hetun, Diebusige and South Diebusige granitoids were formed at ca. 423 Ma, 345 Ma, 345 Ma and 337 Ma, respectively. The Late Silurian (Bayanbulage) quartz diorites have variable SiO₂ (58.0–67.9 wt.%), and low Sr/Y (20–24) values, while the Early Carboniferous (Hetun, Diebusige and South Diebusige) monzogranites have high SiO₂ (71.5–76.7 wt.%) and Sr/Y (40–94) values. The Late Silurian quartz diorites display relatively homogeneous and high zircon δ¹⁸O (8.5–9.1‰) and ε_Hf(t) (− 8.6 to − 5.3) values, high whole-rock ε_Nd(t) values (− 9.2 to − 7.6) and highly radiogenic Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 18.13–18.25), whereas the Early Carboniferous monzogranites exhibit relatively low and variable zircon δ¹⁸O (5.7–7.2‰) and ε_Hf(t) (− 23.1 to − 7.4) values, low whole-rock initial ⁸⁷Sr/⁸⁶Sr (0.7043–0.7070) and ε_Nd(t) (− 19.1 to − 13.5) values and variable Pb isotopes (²⁰⁶Pb/²⁰⁴Pb = 16.06–18.22). The differences in whole rock Nd model ages and Pb isotope compositions of the Paleoproterozoic–Permian rocks in either side of the west fault of the Bayanwulashan–Diebusige complexes suggest that the Alxa Block is not a part of the NCC, and that the western boundary of the NCC is probably located on this fault. Furthermore, the linear distribution of the Early Paleozoic–Early Carboniferous granitoids, the high zircon δ¹⁸O values of the Late Silurian quartz diorites, the Early Devonian metamorphism and the foreland basin system formed during the collision between the Alxa Block and the NCC indicate that a Paleozoic cryptic suture zone likely existed in this area and records the amalgamation of the Alxa Block and North China Craton. Together with detrital zircon data, the initial collision was considered to have possibly occurred in Late Ordovician.     

Isotopic compositions of C,O, Sr,and S and problem of ages of the Katera and Uakit Groups,western Transbaikal region

The age of the Katera Group, which occupies a large area in the western North Muya Range and occurs 100–150 km east of the Uakit Group, is a debatable issue. Based on geological correlations with reference sections of the Baikal Group and Patom Complex, the Katera and Uakit groups were previously considered nearly coeval units and assigned to Late Precambrian (Khomentovskii and Postnikov, 2002; Salop, 1964). This was supported partly by the Sm–Nd model datings (Rytsk et al., 2007, 2009, 2011). Finds of the Paleozoic flora substantiated the revision of age of the Uakit Group and its assignment to the Late Devonian–Early Carboniferous (Gordienko et al., 2010; Minina, 2003, 2012, 2014). We have established that Sr and C isotopic compositions in carbonates of these groups differ drastically, as suggested by their different ages. Sediments of the Nyandoni Formation (Katera Group), which contains carbonates characterized by minimum values of ⁸⁷Sr/⁸⁶Sr = 0.7056 and maximum values of δ¹³C = 4.9‰, were accumulated in the first half of Late Riphean (800–850 Ma ago), whereas the overlying Barguzin Formation (⁸⁷Sr/⁸⁶Sr_min = 0.70715, δ¹³C_max= 10.5‰) was deposited at the end of Late Riphean (700–750 Ma). Judging from the isotope data, the Nerunda Formation (Uakit Group), which contains carbonates with characteristics matching the most rigorous criteria of fitness for the chemostratigraphic correlation (Sr content up to 4390 μg/g, Mn/Sr < 0.1, δ¹⁸O = 23.0 ± 1.8‰), was deposited at the end of Vendian ~550–540 Ma ago). The sequence includes thick typical carbonate horizons with very contrast carbon isotopic compositions: the lower unit has anomalous high δ¹³C values (5.8 ± 1.0‰); the upper unit, by anomalous low δ¹³C values (–5.2 ± 0.5‰]). Their Sr isotopic composition is relatively homogeneous (⁸⁷Sr/⁸⁶Sr = 0.7084 ± 0.0001) that is typical of the Late Vendian ocean. The S isotopic composition of pyrites from the Nyandoni Formation (Katera Group) (δ³⁴S = 14.1 ± 6.8‰) and pyrites from the Mukhtunny Formation (Uakit Group) (δ³⁴S = 0.7 ± 1.4‰) does not contradict the C and Sr isotopic stratigraphic data.