Allanite-(Ce) — the character mineral of metakimberlites from the lake Kimozero, Karelia

Putintseva E. V., Spiridonov E. M.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2016. V. 145. N 4. P. 79-91

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Language: Russian

Abstract

Paleoproterozoic kimberlites of Kimozero area (in Karelia) are the oldest ones in Russia. They are strongly tectonized and metamorphosed, thus converted into metakimberlite rocks of the prehnite-pumpelliite facies. There are relatively widely developed metamorphogenic minerals of lanthanides in them: allanite-(Ce), bastnaesite-(Ce), bastnaesite-(La), parisite-(Ce), monazite-(Ce). Boundaries between their crystals and other metamorphogenic minerals: titanite, antigorite, tremolite represent the induction surfaces of concerted growth. Thus, they may be considered as a new genetic type of rare earth minerals. Among minerals of lanthanides, allanite-(Ce) is the most common one, it occurs among pseudomorphs of clinochlore after phlogopite, or in intergrowths with titanite in aggregates of tremolite-actinolite, calcite and dolomite. The Kimozero allanite has a specificity - its crystals are not zoned, but differing with significant variability of contents and composition of lanthanides and the Fe³⁺/Fe²⁺ ratio in its grains distant not more than dozens of microns. The Kimozero allanite belongs mostly to the allanite-ferriallanite series (up to 30 % of the ferriallanite end member); the lesser part corresponds to the series «allanite—chromium-bearing allanite». During the metamorphic later processes allanite was partly replaced by parisite and bastnaesite, or monazite.

Key words: allanite-(Ce), metakimberlites, prehnite-pumpelliite facies, Kimozero, Karelia.