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

https://doi.org/10.30695/zrmo/2019.1484.05

Full text is available on Journals.eco-vector.com

Language: Russian

Abstract

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: [Cе_1.5La_0.8—0.9Nd_0.3—0.4Pr_0.1(Gd+Sm+Tb+Dy)_0.1Y_0.2Sc_0.1Ca_0.7—0.8Na_0.1]₄(Mg_0.5Fe³⁺_0.5)₁ (Fe³⁺_1.1—1.2Ti_0.4—0.7Zr_0.1—0.2Al_0.1—0.2)₂Ti₂[(Si_3.7—4Al_0.3—0)₄O₂₂]. Сhevkinite-(Ce) from inclusions in allanite is poor in Mg, its formula is: [Cе_1.5—1.7La_0.6—0.9Nd_0.5—0.6Pr_0.1(Gd+Sm)_0.1Y_0.1—0.2Sc_0.1Ca_0.6—0.8Na_0.1]₄ (Fe²⁺_0.6—1Mg_0—0.1Fe³⁺_0—0.4)₁(Ti_0.8—0.9Fe³⁺_0.3—0.7Al_0.2—0.4Zr_0—0.2)₂Ti₂[(Si_3.9—4Al_0.1—0)₄O₂₂]. Perrierite-(Ce) composing idiomorphic crystals is magnesium-dominant, its composition is: [Cе_1.2—1.6La_0.6—0.8Nd_0.3—0.4Pr_0.1 (Gd+Sm+Tb+Dy)_0.1Y_0.1Sc_0.1Ca_1.0—1.1Sr_0—0.1Na_0.1]₄(Mg_0.9—1Fe³⁺_0.1—0)₁(Fe³⁺_1.0—1.2Al_0.2—0.7Ti_0.3—0.5Zr_0—0.2)₂Ti₂ [(Si_3.9—4Al_0.1—0)₄(O_21.3—21.5OH_0.7—0.5)₂₂]. Perrierite-(Ce) occurring inside allanite is poor in Mg, with the formula: [Cе_1.3—1.5La_0.7—0.8Nd_0.3—0.5Pr_0.1(Gd+Sm)_0.1Y_0.1Sc_0.1Ca_1.1—1.3Na_0.1]₄(Fe²⁺_0.4—0.5Fe³⁺_0.2—0.4Mg_0.2)₁ (Al_0.5—0.7Ti_0.3—0.8Fe³⁺_0.3—0.9Zr_0.1—0.3)₂Ti₂[(Si_3.9—4Al_0.1—0)₄(O_21.4—22OH_0.6—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