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

Abstract

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.

The Petyayan-Vara Carbonatite-Hosted Rare Earth Deposit (Vuoriyarvi, NW Russia): Mineralogy and Geochemistry

“…Typically, these grains' compositions are Ca 1.1 Na 0.9 Fe 0.1 Nb 1.8 Ti 0.2 O 6 F, which corresponds to fluorcalciopyrochlore [89]. Hydroxycalciopyrochlore and kenoplumbopyrochlore are less abundant [90]. Magnesiocarbonatites were overprinted by Ti-rich carbonatitic fluids as evidenced by fine veinlets.…”

Study of diffraction data sets using factor analysis: a new technique for comparing mineralogical and geochemical data and rapid diagnostics of the mineral composition of large collections of rock samples

“…Of no less interest is the appearance of significant factor loadings of Ti, Nb and Ta on microcline and (less) phlogopite factors (see Tables I and II). As was discovered, these HFSE are concentrated mainly in Nb-rich titanium oxides represented by three polymorphic modifications (Kozlov et al ., 2018). Nevertheless, titanium or niobium minerals are not expressed by their own factors with high loadings on Ti, although they are rock-forming in some of the samples.…”

“…We investigated sample collections of two geological objects of the Kola region (northwest Russia): 43 samples of rare-earth carbonatites of the Petyayan–Vara field (the Vuoriyarvi Devonian alkaline-ultrabasic carbonatite massif) and 19 samples of the sillimanite schists of the Makzabak mountain (contact rocks of the Keivy Precambrian supracrustal complex near alkaline granites of the Western Keivy massif). With all the differences, all these rocks have a pronounced taxitic structure and formation during several superimposed metasomatic events (Kozlov et al ., 2018; Fomina et al ., 2019). In this regard, the identification of the relationship of a chemical element distribution with a specific mineral association is an important task.…”

Использование Факторного Анализа Для Экспресс-Диагностики Минерального Состава Геологически Сложных Объектов По Рентгенодифракционным Данным

“…В основу исследования легла коллекция из 43 образцов редкоземельных карбонатитов поля Петяйян-Вара (девонский щелочно-ультраосновный карбонатитовый массив Вуориярви). Эти породы, образовавшиеся в ходе нескольких наложенных метасоматических событий [5], характеризуются структурно-конституционной такситовой текстурой и чрезвычайно сложны для петрографического изучения.…”

“…1 и 2) при отсутствии факторов собственно титановых минералов. Как было установлено, титан, ниобий и тантал в карбонатитах Петяйян-Вары сконцентрированы главным образом в богатом Nb бруките, тесно ассоциирующем с микроклином [5]. Наиболее интенсивные пики дифрактограммы брукита совпадают с пиками микроклина, что, по всей видимости, и не позволяет различить на факторе последнего «пиков-паразитов» брукита.…”