Stable (C, O) and radiogenic (Sr, Nd) isotopic evidence for REE-carbonatite formation processes in Petyayan-Vara (Vuoriyarvi massif, NW Russia)

Fomina, Ekaterina; Kozlov, Evgeniy

doi:10.1016/j.lithos.2021.106282

Cited by 6 publications

(7 citation statements)

References 66 publications

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“…The main contribution to the mass change during the formation of bastnäsite carbonatites is made by the non-carbonatite SiO 2 component (see Table 2 ), which indicates a significant input from the host aluminosilicate rocks. These interpretations fully agree with the available geological data [16] .…”

Section: Methods Detailssupporting

confidence: 90%

“…However, a numerical experiment showed that the use of one (common) protolith has almost no effect on the final result. We emphasize strong evidence that the primary fluids altering the source rocks contained very few x and y components under consideration [ 12 , 15 , 16 ]. We note that the considered components (Sr, Ba, and REEs) are abundant in carbonatites and very few in the host rocks.…”

Section: Methods Detailsmentioning

confidence: 99%

“…We note that the considered components (Sr, Ba, and REEs) are abundant in carbonatites and very few in the host rocks. Thus, their introduction from an external source is unlikely, while their redistribution between the indicated types of carbonatites is confirmed by geological methods [ 12 , 15 , 16 ]. The proposed methodology is applicable to the specified geological profile of the processes.…”

Section: Methods Detailsmentioning

confidence: 99%

“…Therefore, the volume change is less significant (+13%, see Table 2 ). Baryte carbonatites were formed due to pseudomorphic replacement and filling of cavities [ 12 , 16 ]. The isocon analysis was carried out for the volume constancy case for these rocks.…”

Section: Methods Detailsmentioning

confidence: 99%

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Mass balance of complementary metasomatic processes using isocon analysis

Kozlov

Fomina

2022

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This study develops a method to estimate the redistribution of elements during several associated metasomatic processes simultaneously involved in the formation of a geological complex . The method is based on classical mass balancing using isocon analysis. The proposed approach is applicable if geological prerequisites indicate that (a) the metasomatic rocks inherited some components ( x, y , etc.) from one of the earlier rocks of the studied complex; (b) these components have been transported by a fluid; and (c) this saturated fluid has produced several varieties of metasomatic rocks rich in components x, y , etc. In the case of the specified background, the proposed method estimates the mass proportions between the source rock and the varieties of the resulting metasomatic rocks. We present the geological profile of the processes to which the proposed method is applicable, the mathematical model of the method, examples of the application and interpretation of the results, and geological criteria to verify the obtained model results. In brief, This study introduces a method for calculating the mass proportions between the source rock and metasomatic rocks formed from the material remobilized from the source rock; The paper considers the applicability limits of the method, exemplifies the interpretation of the results, and shows the methods for monitoring the correctness of these results.

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Section: Methods Detailssupporting

confidence: 90%

Section: Methods Detailsmentioning

confidence: 99%

Section: Methods Detailsmentioning

confidence: 99%

Section: Methods Detailsmentioning

confidence: 99%

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Mass balance of complementary metasomatic processes using isocon analysis

Kozlov

Fomina

2022

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“…The study of these processes is hindered by the fact that carbonatites are easily modified by hydrothermal reworking, structural events or multiple overlapping processes, resulting in difficulty in recognizing the effects of magmatic processes (Chakhmouradian et al, 2016b;Yaxley et al, 2022). Magmatic evolution processes responsible for REE enrichment are commonly complicated and in many systems may be unique due to extensive crystallization and contamination in carbonatite systems (Bühn et al, 2001;Chen & Simonetti, 2013;Giebel et al, 2019a, b;Anenburg et al, 2020a, b;Fomina & Kozlov, 2021;Bouabdellan et al, 2022;Chmyz et al, 2022;Walter et al, 2022Walter et al, , 2023. For instance, REE accumulation in the world's largest REE deposit at Bayan Obo has been inferred to be controlled by an unusual magmatic evolution history from ferroan-, followed by magnesian-and finally calcio-carbonatite varieties (Yang et al, 2011(Yang et al, , 2019.…”

Section: Introductionmentioning

confidence: 99%

Carbonatitic Magma Fractionation and Contamination Generate Rare Earth Element Enrichment and Mineralization in the Maoniuping Giant REE Deposit, SW China

Liu

Smith

et al. 2023

Journal of Petrology

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Carbonatite intrusions host the world’s most important light rare earth element (LREE) deposits, and their formation generally requires extraordinary fertile sources, magmatic evolution, and hydrothermal events. However, carbonatitic magma evolution, particularly the role of fractional crystallization and contamination from silicate rocks in REE enrichment, remains enigmatic. The Maoniuping world-class REE deposit in southwestern China, is an ideal target to decipher magmatic evolution and related REE enrichment as it shows continuous textual evolution from medium- to coarse-grained calcite carbonatite (carbonatite I) at depth, to progressively pegmatoidal calcite carbonatite (carbonatite II) at shallow levels. In both types of calcite carbonatites, four generations of calcite can be classified according to petrographic and geochemical characteristics. Early-crystalizing calcite (Cal-I and Cal-II) are found in carbonatite I and exhibit equigranular and a polygonal mosaic textures, while late calcites (Cal-III and Cal-IV) in carbonatite II are large-size oikocrysts (>0.5 mm in length) with strain-induced undulatory extinction and bent twinning lamellae. All these generations of calcite yield similar, near-chondritic, Y/Ho ratios (26.6−28.1) and are inferred to be of magmatic origin. Remarkably, gradual enrichment of MgO, FeO and MnO from Cal-I to Cal-IV is coupled with a significant increase in REE contents (~800 to 2000 ppm), with LREE-rich and gentle-to-steep chondrite-normalized REE patterns ((La/Yb)N = 3.1–26.8 and (La/Sm)N = 0.9–3.9, respectively). Such significant REE enrichment is ascribed to protracted magma fractional crystallization with initial low degree of fractional crystallization (fraction of melt remining (F) = ~0.95) evolving to late stage (F = 0.5–0.6) by formation of abundant calcite cumulates. Differential LREE and HREE behavior during magma evolution largely depend on separation of phlogopite, amphibole, and clinopyroxene from the carbonatitic melt, which is indicated by progressively elevated (La/Yb)N ratios ranging from 3.1 to 26.8. The four generations of calcite have significantly different C and Sr isotopic compositions with δ13CV-PDB decreasing from –3.28 to –9.97 ‰ and 87Sr/86Sr increasing from 0.70613 to 0.70670. According to spatial relations and petrographic observations, the relative enrichment of δ13C and depletion in 87Sr/86Sr ratios of Cal-I and Cal-II show primary isotopic characteristics inherited from initial carbonatitic magma. By contrast, the variable Sr and C isotopic compositions of Cal-III and Cal-IV are interpreted as the results of contamination by components derived from silicate wall rocks and loss of CO2 by decarbonation reactions. To model such contamination processes, Raleigh volatilization and Monte Carlo simulation have been invoked and the model results reveal that carbonatitic melt-wall rock interaction requires 40% radiogenic Sr contamination from silicate rocks and 35% CO2 degassing from carbonatitic melt. Moreover, positive correlations between decreasing δ13C values and increasing REE contents, together with bastnäsite-(Ce) precipitation, indicate further REE accumulation during the contamination processes. In summary, alongside REE-rich magma sources, the extent of fractional crystallization and contamination during carbonatitic magma evolution are inferred to be important mechanisms in terms of REE enrichment and mineralization in carbonatite-related REE deposits worldwide.

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