Hydrothermal alteration of chevkinite-group minerals. Part 2. Metasomatite from the Keivy massif, Kola Peninsula, Russia

Abstract

Chevkinite-(Ce) in a mineralized quartz-epidote metasomatite from the Keivy massif, Kola Peninsula, Russia, underwent at least two stages of low-temperature alteration. In the first, it interacted with hydrothermal fluids, with loss of Ca, Fe, LREE and Si and strong enrichment in Ti. The altered chevkinite was then rimmed and partially replaced by a zone of ferriallanite-(Ce) and davidite-(La), in turn rimmed by a zone of allanite-(Ce) richer in the epidote component. The allanite zone was in turn partially replaced by rutile-titanite-quartz assemblages, the formation of titanite postdating that of rutile. Aeschynite-(Y), aeschynite-(Ce) and REE-carbonates are accessory phases in all zones. The hydrothermal fluids were alkaline, with significant proportions of CO2 and F. At various alteration stages, the Ca, Si ± Al activities in the fluid were high. Formation of the aeschynite is discussed in relation to its stability in broadly similar parageneses; it was a primary phase in the unaltered chevkinite zone whereas in other zones it formed from Nb, Ti, REE and Th released from the major phases.

Hydrothermal alteration of chevkinite-group minerals: products and mechanisms. Part 1. Hydration of chevkinite-(Ce)

“…In our studies of the CGM, we have divided alteration schemes into two types; (1) those which started with compositional modification of the CGM and the production of a zone of 'altered chevkinite', the term employed by Jiang (2006), Vlach and Gualda (2007) and Papoutsa and Pe-Piper (2013); and (2) those where formation of this zone was accompanied or followed by the formation of a new mineral assemblage. This paper describes examples of type 1; a companion paper (Macdonald et al, 2015) focuses on type 2 alteration.…”

Hydrothermal alteration of a chevkinite-group mineral to a bastnäsite-(Ce)-ilmenite- columbite-(Fe) assemblage: interaction with a F-, CO2-rich fluid

“…In a study of A-type granites and syenites of the Graciosa Province, southern Brazil, Vlach and Gualda (2007) documented increases in Ti and reductions in REE and Fe resulting from interaction between chevkinite-(Ce) and post-magmatic hydrous fluids. Bagiński et al (2015) and Macdonald et al (2015) documented the alteration of chevkinite-(Ce) to a phase strongly enriched in Ti (and to a lesser degree in Nb and Th) and depleted in Si, REE and Fe compared to the unaltered phase.…”

The Effect of X-ray Energy Overlaps on the Microanalysis of Chevkinite (Ce, La, Ca, Th)4(Fe2+, Mg)2(Ti, Fe3+)3Si4O22 Using SEM EDS-WDS

“…The challenges include analysing La and Ce using EDS or WDS, and detection of Ba with different processing scenarios (Table 3). It is noted that Ba, which can be present in chevkinite, especially in the altered crystals [33] was identified during automatic peak search by the EDS part of INCA software (at 0.9 wt % BaO) but was not detected by WDS during separate checks. However, it was added here as an EDS-detected element to illustrate the associated errors possible, when prior knowledge of mineral chemistry is unavailable.…”