The discrepancy between Na-rich compositions of modern carbonatitic lavas (Oldoinyo Lengai volcano) and alkali-poor ancient carbonatites remains a topical problem in petrology. Although both are ...supposedly considered to originate via fractional crystallization of a "common parent" alkali-bearing Ca-carbonatitic magma, there is a significant compositional gap between the Oldoinyo Lengai carbonatites and all other natural compositions reported (including melt inclusions in carbonatitic minerals). In an attempt to resolve this, we investigate the petrogenesis of Ca-carbonatites from two occurrences (Guli, Northern Siberia and Tagna, Southern Siberia), focusing on mineral textures and alkali-rich multiphase primary inclusions hosted within apatite and magnetite. Apatite-hosted inclusions are interpreted as trapped melts at an early magmatic stage, whereas inclusions in magnetite represent proxies for the intercumulus environment. Melts obtained by heating and quenching the inclusions, show a progressive increase in alkali concentrations transitioning from moderately alkaline Ca-carbonatites through to the "calcite CaCO
+ melt = nyerereite (Na,K)
Ca
(CO
)
" peritectic, and finally towards Oldoinyo Lengai lava compositions. These results give novel empirical evidence supporting the view that Na-carbonatitic melts, similar to those of the Oldoinyo Lengai, may form via fractionation of a moderately alkaline Ca-carbonatitic melt, and therefore provide the "missing piece" in the puzzle of the Na-carbonatite's origin. In addition, we conclude that the compositions of the Guli and Tagna carbonatites had alkali-rich primary magmatic compositions, but were subsequently altered by replacement of alkaline assemblages by calcite and dolomite.
The petrogenesis of temporally and spatially associated carbonatitic and deeply derived carbonated alkaline silicate magmas provides an opportunity to gain insights into the nature of the deepest ...lithospheric mantle. The Chuktukon massif, which is part of the Chadobets alkaline ultramafic carbonatite complex (Chadobets upland, Siberian craton) is a carbonatite-melilitite-damtjernite intrusion, whose emplacement was coeval with the Siberian Traps large igneous province (LIP). In this study, the sources of the primary melts are examined, the petrogenetic evolution of the complex is reconstructed and the relationship with the Siberian LIP is also discussed. Isotopic and geochemical information indicate that the source for the Chuktukon primary melts was isotopically moderately depleted and the primary melts were formed by low degree partial melting of garnet carbonated peridotite. Hydrothermal processes caused 18O- and 13C- enrichment. The weathering process was accompanied by trace element re-distribution and enrichment of the weathering crust in Zn, Th, U, Nb, Pb and REE, relative to the Chuktukon rocks and a change in radiogenic (Sr, Nd) isotope compositions.
•The primary melts were derived from an isotopically depleted mantle source.•The primary melts were formed by low degree partial melting of carbonated peridotite.•The partial melting was under the influence of heat from the Siberian plume.
Fe-rich carbonatites with a mineral assemblage of ankerite-calcite or siderite are widespread in southern Siberia, Russia. The siderite carbonatites are associated with F-Ba-Sr-REE mineralization and ...have a
40
Ar/
39
Ar age of 117.2 ± 1.3 Ma. Melt and fluid inclusions suggest that the carbonatites formed from volatile-rich alkali- and chloride-bearing carbonate melts. Ankerite-calcite carbonatites formed from carbonatite melt at a temperature of more than 790 °C. The ferrocarbonatites (the second phase of carbonatite intrusion) formed from a sulfate-carbonate-chloride fluid phase (brine-melt) at >650 °C and ≥360 MPa. The brine-melt fluid phase had high concentrations of Fe and LREEs. A subsequent hydrothermal overprint contributed to the formation of economically important barite-Sr-fluorite-REE mineralization in polymict siderite breccia.
Petrological, whole-rock major and trace element, and Sr–Nd–Pb isotopic data are reported for the late Mesozoic Dzheltula alkaline igneous complex in the Aldan–Stanovoy Shield, Russia. The alkaline ...rocks are emplaced into the Tyrkanda mélange zone. The Dzheltula complex consists of monzonites, foid monzonites, and alkaline syenites; granite dykes intrude the complex. All alkaline rocks have high LILE contents (e.g., Ba and Sr), high light REE/HFSE ratios, strongly fractionated REE patterns, and typically lack Eu anomalies. Granite shows different major and trace-element characteristics in comparison to monzonites and syenites. The major and trace-element characteristics of the Dzheltula complex rocks and minerals are consistent with formation by combined assimilation and fractionation processes of an alkaline parental magma of lamproitic composition. The alkaline rocks have moderately radiogenic Sr (
87
Sr/
86
Sr(
t
) = 0.7057–0.7065) and unradiogenic Nd (
ɛ
Nd(
t
) = − 11.3 to − 15.2) and Pb (
206
Pb/
204
Pb = 17.17–17.26); granite has more enriched
87
Sr/
86
Sr(
t
) value (0.707408) but similar
ɛ
Nd(
t
) = − 12.93 The trace element and Sr–Nd–Pb isotopic data for the Dzheltula complex indicate its mantle source experienced ancient metasomatic enrichment, probably associated with subduction.
The Ust-Chulman apatite ore body is situated within the Nimnyrskaya apatite zone at the Aldan shield in Russia. The latest data confirm the carbonatitic origin of the Seligdar apatite deposit ...(Prokopyev et al. in Ore Geol Rev 81:296–308, 2017). The results of our investigations demonstrate that the magnetite-apatite-dolomitic rocks of the Ust-Chulman are highly similar to Seligdar-type dolomitic carbonatites in terms of the mineralogy and the fluid regime of formation. The ilmenite and spinel mineral phases occur as solid solutions with magnetite, and support the magmatic origin of the Ust-Chulman ores. The chemical composition of REE- and SO
3
-bearing apatite crystals and, specifically, monazite-(Ce) mineralisation and the formation of Nb-rutile, late hydrothermal sulphate minerals (barite, anhydrite) and haematite are typical for carbonatite complexes. The fluid inclusions study revealed similarities to the evolutionary trend of the Seligdar carbonatites that included changes of the hydrothermal solutions from highly concentrated chloride to medium–low concentrated chloride-sulphate and oxidized carbonate-ferrous.
The relevance of the work is caused by the fact that the study of speciation of lanthanide + yttrium (REE+Y) in chloride-sulfate-carbonate fluids in various weakly alkaline and weakly acidic ...conditions allows one to assess the effect of parameters of the ore-forming system on transportation and fractionation of rare-earth elements in oreogenesis within the carbonatite ore -magmatic systems. The main aim of the study is to estimate the contribution of the fluorine-, chloro-, carbarnate-bicarbonate, sulfate and phosphate complexes of REE+Y to transport and ore deposition by hydrothermal fluids in weakly alkaline and weakly acidic conditions at 500–100 °C and a pressure of 2000–125 bar. The methods: computational modeling of the effect of hydrothermal fluids on monazite and calcite using the HCh package (developed by Yu.V. Shvarov). To establish the equilibrium state in the program's algorithm, the method of determining the minimum Gibbs free energy of the system (the GIBBS program) in combination with the thermodynamic base UNITHERM, supplemented by experimental results for REE complexes and minerals, was used. The results. The paper introduces the distribution of REE+Y by forms in cooling chloride-sulfate-carbonate highly concentrated weakly acidic and weakly alkaline fluids. It was shown that under weakly alkaline conditions, the leading ones are the neutral and second hydroxocomplexes up to 200 °C. As the temperature decreases to 100 °С, REE+Y are found in the form of the carbonate and second fluorocomplex (Ln, Y)F2+. Under weakly acidic conditions, sulfate complexes of lanthanides prevail sharply in the entire studied range of fluid parameters. With an increase in the lanthanide number (especially for heavy REEs), the role of fluoride complexes grows with a decrease in contribution of sulfate complexes.
The N-S trending Central-Aldan magnesiocarbonatite province is located in the Aldan-Stanovoy shield (South Yakutia, Russia). Several apatite-dolomitic carbonatite occurrences were studied: Seligdar, ...Muostalaah, Ust-Chulman and Birikeen. Mineralogical and petrographic investigations indicate intense hydrothermal-metasomatic alteration and metamorphism, which are reflected in the evolution of the mineral parageneses. The primary minerals are fluorapatite, magnetite, ilmenite, dolomite, K-feldspar, phlogopite and accessory zircon, titanite, baddeleyite and thorite. The hydrothermal-metasomatic minerals are quartz, calcite and siderite aggregates with haematite, monazite-(Ce), xenotime-(Y), rutile-(Nb), barite-(Sr), anhydrite, ancylite-(Ce) and rare sulphide mineral phases. Alkaline rocks associated with the Muostalaah complex, were also studied. The following U-Pb ages have been obtained (Ma): 1930 ± 7 for Muostalaah alkaline basic rocks, 1906 ± 6 for Muostalaah carbonatites, and 1880 ± 13 and 1878 ± 17 for Seligdar and Ust-Chulman carbonatites, respectively.
The relevance of the research is caused by the need to determine the age and fluid regime of formation of Khaak-Sair gold-sulfide-quartz ore occurrence in listwanites, characterized by a peculiar ore ...mineral composition, expressed in the presence of mercurial gold, selenides (fichesserite, naumannite, timannite, claustallite) and tellurides (hessite, Te-bismuthite and coloradoite). The research is aimed to date and examine PT ore-bearing fluid parameters and geochemical peculiarities, and the fluid sources of Khaak-Sair gold-sulfide-quartz ore occurrence in Western Tuva. Methods. 40Ar/39Ar dating was carried out by the method of step heating. The optical studies of ores were performed on Olympus BX41 and P-213M optical microscopes. The mineral composition was detected using MIRA 3 LMU scanning electron microscope with EDU of Oxford Instruments Nanoanalysis Ltd. The temperatures, salt composition, salinities and fluid pressures were obtained from individual fluid inclusions using Linkam TMS-600 stage equipped with Olympus BX 51 optical microscope; the volatile composition of fluid inclusions was examined on Ramanor U-1000 spectrometer with the Horiba DU420E-OE-323 detector, Millennia Pro laser (Spectra-Physics); the bulk volatile composition of the fluid was determined on the Agilent 6890 gas chromatograph, the anions in the water extraction was estimated on the CVET-3000 ion chromatograph, the cation and trace elements were detected by ICP MS (Elan-6100); the sulfur isotope ratios in galena were calculated on Finnigan MAT Delta gas mass-spectrometer in double-entry mode (analysts V.N. Reutsky and M.N. Kolbasova, IGM SB RAS); δ18С and δ18О isotopic ratios in quartz and carbonates were examined on Stable Isotope Ratio Mass Spectrometer Finnigan™ MAT 253 with Finnigan GasBench II sampler and IAEA standards: NBS-18 and NBS-19 (analyst M.N. Pyryaev, IGM SB RAS) and Isoprime with AQS (Akita Quartz Standard, analysts H. Kavarai, O. Matsubaya, University of Akita), respectively. Results. The 40Ar/39Ar dating of synore listwanites is shown 379,4±4,4 million years that corresponds to the Late Devonian. We identified that the ore hosted listwanites were formed due to aqueous Na-K-chloride fluid with salinity of 3,4–6,5 wt. % NaCl eqv and temperatures at least 325–200 °C. Gold-sulfide-quartz veins were formed at P~0,5–0,75 kbar (~1,5–2,3 km) due to CO2-water chloride (Na-K±Fe) fluid containing CH4 with salinity ranged between 4,5 and 37,4 wt. % NaCl eqv. and temperatures from 320 up to 120 °C (I ore substage – 310–200 °С and II ore substage – 320–120 °С), and with fO2, fS2, fSe2 and fTe2 variations that have contributed to the diversity of Au, Ag and Hg mineral forms. The values of δ34S from galena vary from –0,6 to –0,4 ‰, and the calculated values of δ34SH2S of I ore substage fluid vary from +1,5 to +2,1 ‰ (for T=280–210 °C), and II ore substage fluid – +1,6...+2,6 ‰ (for T=290–190 °C), which indicates the magmatic origin of sulfur. Values of δ18О in quartz from ore veins vary from 17,0 to 17,4 ‰, dolomite – +17,4...+17,8 ‰, calcite – +16,5 ‰, and calculated values of δ18ОH2S of I ore substage fluid vary from +8,1 to +5,7 ‰ (for T=250–210 °C), and II ore substage – +6,7 ‰. ...–2,2 ‰ (for T=230–120 °C) suggested that in the early stages of the ore-forming process fluid was of magmatic origin, and in later stages it was mixed with meteoric waters. The values of δ13C in dolomite of I ore substage vary from –0,4 to –0,7 ‰; calcite of II ore substage – –0,3 ‰, and the calculated values of δ13C in the fluid vary from –1,2 to +0,1 ‰ (for T=250–210 °C) and from –3,3 to +0,5 ‰ (for T=230–120 °C), respectively. This presupposes carbon inflow from granitoid magmas and/or its borrowing from host rocks. The composition of the fluid was transformed from early to late substages from carbon dioxide to water chloride with a decrease in chloride amounts of alkali and alkali-earth metals (from 37,4 to 4 wt. % NaCl eqv).
The Seligdar apatite deposit is located in the Aldan-Stanovoy shield of the Siberian platform in Russia. This deposit is a typical ore deposit of the Nimnyrskaya approximately N-S apatite zone, which ...is about 400km long. The genesis of the apatite-dolomite ores at the Seligdar deposit is a matter of debate. This article presents new evidence of the carbonatitic genesis of the apatite-dolomite rocks at the Seligdar deposit based on modern methods of mineralogical, geochronological, melt and fluid inclusion investigations. According to our data, the age of the apatite-dolomite ores is 1880±13Ma (U-Pb SHRIMP, zircon). Study of melt inclusions indicates that the ores were formed from a carbonate melt of dolomitic composition with alkali (sulphates, chlorides and fluorides of Na and K) and silica components (1–10wt.%) at a temperature of >1100°C. The dolomite carbonatites have been subsequently exposed to the intense processes of hydrothermal-metasomatic alteration and metamorphism. The evolution of mineral parageneses from the magmatic apatite-magnetite-dolomite carbonatite stage to the hydrothermal stages with quartz, calcite, monazite-Ce, xenotime-Y, haematite, thorite, thorianite, sulphates and sulphides mineralization agrees with the fluid inclusion regime evolution from the carbonate melt to the chloride brines, and the varying concentrations of the chloride solutions are also described in this article. The investigation of the apatite deposits within the Aldan shield not only allows us to take a new look at the question of their origin but also helps us to study the composition of the ancient mantle, as well as the specifics of apatite-dolomite carbonatite and related hydrothermal Fe and Th-REE mineralization in this region.
•The apatite-dolomite ores of the Seligdar deposit were formed from a fluid-rich carbonatite melt of dolomitic composition.•The age of the dolomite carbonatites is 1880±13Ma.•The rocks were exposed to the intense processes of hydrothermal-metasomatic alteration and metamorphism.
Gold ore objects in skarns are widespread in geological structures of the Eastern Tuva, but their estimation is considerable difficult due to poor information about mineralogical, geochemical and ...petrographic peculiarities of ores. The study of the genesis and conditions of gold deposits formation, which are located in skarns, is one of the fundamental scientific disciplines in geological science. The aim of the study is to examine the mineralogical and geochemical peculiarities and conditions of ore formation of the Barsuchy deposit in North-Eastern Tuva. Methods: field work, detailed mineralogical study of ore mineralization using Tescan Vega 3 SBU scanning electron microscope with EMF Oxford Instruments X-act. PT conditions of mineral associations’ formation are determined by fluid inclusion study as well as using geofugometers and mineral paragenesis. Results. The authors have manifested that the gold mineralization of the Barsuchy deposit is post-skarned and has a hydrothermal genesis forming a vein-disseminated mineralization of stockwork-type in quartz-diorites, contact (hornfels, skarns) and hydrothermal-metasomatic formations. Near-ore processes are expressed in beresitization and listwanitization of quartz-diorites, skarns and carbonate rocks. The native gold was formed during two stages. According to the composition of the productive mineral associations, Barsuchy deposit is related to a gold-pyrrhotite-pyrite-chalcopyrite type with the AuTe2 calaverite, petzite, hessite and minerals of the tellurobismuthite-tellurantimony series. The gold-quartz-sulfide mineralization is formed due to aqueous fluids with Na and K chlorides containing CO2 and CH4 with a salinity of 1–10,5 wt. % NaCl-eq. accompanied with Redox-potential changes and the variations of f S2, f Se2, f Te2 and temperature fall of the ore-bearing fluid (the first productive stage is 360–280 °C, the second one – 320–240 °C). According to mineralogical and geochemical features, Barsuchy deposit belongs to gold-sulfide-quartz formation (with less than 5 % sulfides) and is close to Au-Bi geochemical type of deposits.
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