Сhevkinite-(Се) and perrierite-(Се) in the island arc quartz gabbro-norite-dolerites of the Aju-Dag intrusion, Rocky Crimea

Spiridonov E. M., Filimonov S. V., Semikolennykh E. S., Korotayeva N. N., Krivitskaya N. N.

Zapiski RMO (Proceedings of the Russian Mineralogical Society). 2019. V. 148. N 4. P. 61-79


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Language: Russian 


Сhevkinite-(Се) and perrierite-(Се) are minerals characteristic for alkaline magmatic rocks and high-temperature alkaline metasomatites, and yet they are typical accessory minerals in Mesozoic island-arc gabbroids of the Rocky Crimea. Early magmatic mineral associations in these low-alkaline rocks of Ayu-Dag intrusion include accessory Ti—Zr—LREE minerals under-saturated in silica: chevkinite-(Се), perrierite-(Се), zirconolite, baddeleyite. Сhevkinite and perrierite occur as isolated shortly prismatic crystals up to 0.1 mm in size and strongly corroded inclusions in center of late-magmatic allanite-(Ce) crystals. Both minerals are the main concentrators of lanthanides in Aju-Dag gabbroids. Distribution of lanthanides in them is as following: Ce ˃> La >> Nd >> Pr > Gd, Sm, Tb, Dy. Contents of lanthanides in chevkinite and perrierite are identical: Ce (54—58 % REE) — La (25—31 %) — Nd (12—20 %). Contents of Zr, Th, Y, Sc in both polymorphs are identical also. Сhevkinite-(Ce) of isolated crystals is magnesium-dominant; its composition is: [Cе1.5La0.8—0.9Nd0.3—0.4Pr0.1(Gd+Sm+Tb+Dy)0.1Y0.2Sc0.1Ca0.7—0.8Na0.1]4(Mg0.5Fe3+0.5)1 (Fe3+1.1—1.2Ti0.4—0.7Zr0.1—0.2Al0.1—0.2)2Ti2[(Si3.7—4Al0.3—0)4O22]. Сhevkinite-(Ce) from inclusions in allanite is poor in Mg, its formula is: [Cе1.5—1.7La0.6—0.9Nd0.5—0.6Pr0.1(Gd+Sm)0.1Y0.1—0.2Sc0.1Ca0.6—0.8Na0.1]4 (Fe2+0.6—1Mg0—0.1Fe3+0—0.4)1(Ti0.8—0.9Fe3+0.3—0.7Al0.2—0.4Zr0—0.2)2Ti2[(Si3.9—4Al0.1—0)4O22]. Perrierite-(Ce) composing idiomorphic crystals is magnesium-dominant, its composition is: [Cе1.2—1.6La0.6—0.8Nd0.3—0.4Pr0.1 (Gd+Sm+Tb+Dy)0.1Y0.1Sc0.1Ca1.0—1.1Sr0—0.1Na0.1]4(Mg0.9—1Fe3+0.1—0)1(Fe3+1.0—1.2Al0.2—0.7Ti0.3—0.5Zr0—0.2)2Ti2 [(Si3.9—4Al0.1—0)4(O21.3—21.5OH0.7—0.5)22]. Perrierite-(Ce) occurring inside allanite is poor in Mg, with the formula: [Cе1.3—1.5La0.7—0.8Nd0.3—0.5Pr0.1(Gd+Sm)0.1Y0.1Sc0.1Ca1.1—1.3Na0.1]4(Fe2+0.4—0.5Fe3+0.2—0.4Mg0.2)1 (Al0.5—0.7Ti0.3—0.8Fe3+0.3—0.9Zr0.1—0.3)2Ti2[(Si3.9—4Al0.1—0)4(O21.4—22OH0.6—0)22]. Presence of chevkinite, perrierite and zirconolite in unusual geochemical settings may be explained perhaps by poor development of late-magmatic processes in near-surface intrusions of Crimeaʼs Mesozoids.

Key words: chevkinite-(Ce), perrierite-(Ce), gabbro-norite-dolerite, Ayu-Dag, Rocky Crimea