Chevkinite-(Се) and Perrierite-(Се) from the Island Arc Quartz Gabbronorite–Dolerite of the Ayu-Dag Intrusion, Crimean Mountains

• Published in: Geology of ore deposits Vol. 62; no. 7; pp. 638 - 651
• Main Authors: Spiridonov, E. M., Filimonov, S. V., Semikolennykh, E. S., Korotaeva, N. N., Krivitskaya, N. N.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2020; Springer Nature B.V
• Subjects: Cerium; Composition; Concentrators; Crystals; Depletion; Dysprosium; Earth and Environmental Science; Earth Sciences; Fluids; Gabbro; Gabbros; Gadolinium; High temperature; Igneous rocks; Inclusions; Intrusion; Island arcs; Lanthanides; Lanthanum; Mesozoic; Mineral assemblages; Mineral Resources; Minerals; Minerals and Mineral Parageneses; Mountains; Samarium; Silica; Silicon dioxide; Terbium; Titanium; Zirconium; Crimean Mountains; Rocky Crimea; perrierite-(Ce); chevkinite-(Ce); gabbro-norite-dolerite; Ayu-Dag
• ISSN: 1075-7015; 1555-6476
• DOI: 10.1134/S1075701520070119

Chevkinite-(Се) and perrierite-(Се), which are characteristic minerals of alkaline igneous rocks and high-temperature alkaline alterations, are typical accessory minerals in the Mesozoic island-arc gabbros of the Crimean Mountains. The early magmatic mineral assemblages from these low-alkali gabbros of the Ayu-Dag intrusion contain accessory Ti–Zr–LREE minerals depleted in SiO 2 : chevkinite-(Се), perrierite-(Се), zirconolite, and baddeleyite. Chevkinite and perrierite occur as isolated short prismatic crystals of up to 0.1 mm and strong corroded inclusions in the cores of the late-magmatic allanite-(Ce) crystals. Both minerals are one of the major concentrators of lanthanides in the Aju-Dag gabbros. Lanthanides are distributed in chevkinite and perrierite as follows: Ce La > Nd Pr > Gd, Sm, Tb, and Dy. The lanthanide ratios in chevkinite and perrierite are similar, % REE: 54–58 Ce, 25–31 La, and 12–20 Nd. The Zr, Th, Y, and Sc concentrations in both polymorphic modifications from the Ayu-Dag gabbros are identical. Chevkinite-(Ce) that occurs as isolated crystals is Mg-dominant; its composition is [Cе 1.5 La 0.8–0.9 Nd 0.3–0.4 Pr 0.1 (Gd + Sm + Tb + Dy) 0.1 Y 0.2 Sc 0.1 Ca 0.7–0.8 Na 0.1 ] 4 (Mg 0.5 ) 1 ( Ti 0.4–0.7 Zr 0.1–0.2 Al 0.1–0.2 ) 2 Ti 2 [(Si 3.7–4 Al 0.3–0 ) 4 O 22 ]. Chevkinite-(Ce) enclosed in allanite is depleted in Mg; its composition is [Cе 1.5–1.7 La 0.6–0.9 Nd 0.5–0.6 Pr 0.1 (Gd + Sm) 0.1 Y 0.1–0.2 Sc 0.1 Ca 0.6–0.8 Na 0.1 ] 4 ( Mg 0–0.1 ) 1 (Ti 0.8–0.9 Al 0.2–0.4 Zr 0–0.2 ) 2 Ti 2 [(Si 3.9–4 Al 0.1–0 ) 4 O 22 ]. Perrierite-(Ce) that forms euhedral crystals is Mg-dominant; its composition is [Cе 1.2–1.6 La 0.6–0.8 Nd 0.3–0.4 Pr 0.1 (Gd + Sm + Tb + Dy) 0.1 Y 0.1 Sc 0.1 Ca 1.0–1.1 Sr 0–0.1 Na 0.1 ] 4 (Mg 0.9–1 ) 1 ( Al 0.2–0.7 Ti 0.3–0.5 Zr 0–0.2 ) 2 Ti 2 [(Si 3.9–4 Al 0.1–0 ) 4 (O 21.3–21.5 OH 0.7–0.5 ) 22 ]. Perrierite-(Cе) enclosed in allanite is depleted in Mg; its composition is [Cе 1.3–1.5 La 0.7–0.8 Nd 0.3–0.5 Pr 0.1 (Gd + Sm) 0.1 Y 0.1 Sc 0.1 Ca 1.1–1.3 Na 0.1 ] 4 ( Mg 0.2 ) 1 (Al 0.5–0.7 Ti 0.3–0.8 Zr 0.1–0.3 ) 2 Ti 2 [(Si 3.9–4 Al 0.1–0 ) 4 (O 21.4–22 OH 0.6–0 ) 22 ]. The presence of chevkinite, perrierite, and zirconolite in an unusual geochemical environment is possibly caused by weak late-magmatic processes in the shallow gabbro intrusions, which are depleted in fluids, of the Crimea Mesozoides.