TY - JOUR

T1 - Ti-Nb Mineralization of Late Carbonatites and Role of Fluids in Its Formation: Petyayan-Vara Rare-Earth Carbonatites (Vuoriyarvi Massif, Russia)

AU - Козлов, Евгений Николаевич

AU - Фомина, Екатерина Николаевна

AU - Сидоров, Михаил

AU - Шиловских, Владимир Владимирович

N1 - Funding Information: Funding: This research was funded by the Russian Foundation for Basic Research grant number 16-35-00132]. Funding Information: Acknowledgments: This work was carried out in the Geological Institute KSC RAS under the state order No. 0231-2015-0009. The authors express their sincere appreciation to T.A. Miroshnichenko for help with translation. We also thank A.V. Chernyavskiy (GI KSC RAS) for his help in the field works, as well as V.N. Bocharov (RC “Geomodel” SPbSU) and A.V. Bazai (GI KSC RAS) for their assistance in studying the structure and composition of the minerals. The authors express their sincere gratitude to two anonymous reviewers.

PY - 2018/8

Y1 - 2018/8

N2 - This article is devoted to the geology of titanium-rich varieties of the Petyayan-Vara rare-earth dolomitic carbonatites in Vuoriyarvi, Northwest Russia. Analogues of these varieties are present in many carbonatite complexes. The aim of this study was to investigate the behavior of high field strength elements during the late stages of carbonatite formation. We conducted a multilateral study of titanium- and niobium-bearing minerals, including a petrographic study, Raman spectroscopy, microprobe determination of chemical composition, and electron backscatter diffraction. Three TiO 2-polymorphs (anatase, brookite and rutile) and three pyrochlore group members (hydroxycalcio-, fluorcalcio-, and kenoplumbopyrochlore) were found to coexist in the studied rocks. The formation of these minerals occurred in several stages. First, Nb-poor Ti-oxides were formed in the fluid-permeable zones. The overprinting of this assemblage by residual fluids led to the generation of Nb-rich brookite (the main niobium concentrator in the Petyayan-Vara) and minerals of the pyrochlore group. This process also caused niobium enrichment with of early generations of Ti oxides. Our results indicate abrupt changes in the physicochemical parameters at the late hydro (carbo) thermal stage of the carbonatite formation and high migration capacity of Ti and Nb under these conditions. The metasomatism was accompanied by the separation of these elements.

AB - This article is devoted to the geology of titanium-rich varieties of the Petyayan-Vara rare-earth dolomitic carbonatites in Vuoriyarvi, Northwest Russia. Analogues of these varieties are present in many carbonatite complexes. The aim of this study was to investigate the behavior of high field strength elements during the late stages of carbonatite formation. We conducted a multilateral study of titanium- and niobium-bearing minerals, including a petrographic study, Raman spectroscopy, microprobe determination of chemical composition, and electron backscatter diffraction. Three TiO 2-polymorphs (anatase, brookite and rutile) and three pyrochlore group members (hydroxycalcio-, fluorcalcio-, and kenoplumbopyrochlore) were found to coexist in the studied rocks. The formation of these minerals occurred in several stages. First, Nb-poor Ti-oxides were formed in the fluid-permeable zones. The overprinting of this assemblage by residual fluids led to the generation of Nb-rich brookite (the main niobium concentrator in the Petyayan-Vara) and minerals of the pyrochlore group. This process also caused niobium enrichment with of early generations of Ti oxides. Our results indicate abrupt changes in the physicochemical parameters at the late hydro (carbo) thermal stage of the carbonatite formation and high migration capacity of Ti and Nb under these conditions. The metasomatism was accompanied by the separation of these elements.

KW - метасоматизм

KW - брукит

KW - анатаз

KW - пирохлор

KW - ниобий

KW - карбонатиты

KW - массив Вуориярви

KW - Anatase

KW - Brookite

KW - Carbonatites

KW - Metasomatism

KW - Niobium

KW - Pyrochlore

KW - Vuoriyarvi massif

UR - http://www.scopus.com/inward/record.url?scp=85051010666&partnerID=8YFLogxK

U2 - 10.3390/geosciences8080281

DO - 10.3390/geosciences8080281

M3 - Article

VL - 8

JO - Geosciences (Switzerland)

JF - Geosciences (Switzerland)

SN - 2076-3263

IS - 8

M1 - 281

ER -