Sc- and REE-rich tourmaline replaced by Sc-rich REE-bearing epidote-group mineral from the mixed (NYF+LCT) Kracovice pegmatite (Moldanubian Zone, Czech Republic)

Abstract

Primary black thick-prismatic Al-rich schorl to rare fluor-schorl (TurP1), locally overgrown by brownish-green Li-rich fluor-schorl to fluor-elbaite (TurP2) from the Kracovice pegmatite (mixed NYF+LCT signature), was partly replaced by secondary Li-rich fluor-schorl to fluor-elbaite (TurS) plus the assemblage REE-bearing epidote-group mineral + chamosite. Primary Al-rich schorl (TurP1) shows high and variable contents of Sc (33-364 ppm) and Y+REE (40-458 ppm) with steep, LREEenriched REE pattern. Overgrowing (TurP2) and replacing (TurS) Li-rich fluor-schorl to fluor-elbaite is typically depleted in Sc (21-60 ppm) and Y+REE (3-47 ppm) with well-developed tetrad effect in the first (La-Nd) and the second (Sm-Gd) tetrads. Scandium-and REE-rich black tourmaline (TurP1) crystallized earlier from the melt, whereas crystallization of primary Li-rich fluor-schorl to fluor-elbaite (TurP2) most likely took place during late magmatic to early hydrothermal conditions. Both the secondary Li-rich fluor-schorl to fluor-elbaite (TurS) and the unusual assemblage of REE-bearing epidotegroup mineral + chamosite are likely coeval products of subsolidus reactions of the magmatic Al-rich schorl (TurP1) with evolved REE-poor, Li,F-rich, alkaline pegmatite-derived fluids. Well-crystalline REE-bearing epidote-group mineral (Y+REE = 0.42-0.60 apfu) confirmed by Raman spectroscopy has a steep, LREE-rich chondrite-normalized REE pattern with significant negative Eu anomaly and shows variable and high contents of Sc (≤3.3 wt% Sc 2 O 3 ) and Sn (≤1.0 wt% SnO 2 ). Substitution ScAl -1 and minor vacancy in the octahedral sites are suggested in the REE-bearing epidote-group mineral.

The mineralogy of the historical Mochalin Log REE deposit, South Urals, Russia. Part I. New gatelite-group minerals ferriperbøeite-(La), (CaLa3)(Fe3+Al2Fe2+)[Si2O7][SiO4]3O(OH)2 and perbøeite-(La), (CaLa3)(Al3Fe2+)[Si2O7][SiO4]3O(OH)2

“…The bands at 971, 692 and 413 cm –1 in the Raman spectrum of ferriperbøeite-(La) and those at 969, 690 and 415 cm –1 in the Raman spectrum of perbøeite-(La) are close to strong bands in the Raman spectrum of allanite-(Ce) observed at 972, 689 and 421 cm –1 (Andò and Garzanti, 2014; Čopjaková et al , 2015) and can be assigned tentatively to the epidote-type module (see below).…”

“…The Raman spectra of ferriperbøeite-(La) and perbøeite-(La) are similar to that of västmanlandite-(Ce) (Holtstam et al, 2005) in the range of 300-1100 cm -1 but significantly differ from the latter in the regions of O-H stretching vibrations (above 3200 cm -1 ) and stretching vibrations involving REE and divalent cations forming low-force-strength bonds (below 300 cm -1 ). The bands at 971, 692 and 413 cm -1 in the Raman spectrum of ferriperbøeite-(La) and those at 969, 690 and 415 cm -1 in the Raman spectrum of perbøeite-(La) are close to strong bands in the Raman spectrum of allanite-(Ce) observed at 972, 689 and 421 cm -1 (Andò and Garzanti, 2014;Čopjaková et al, 2015) and can be assigned tentatively to the epidote-type module (see below).…”

Beryllium minerals as monitors of geochemical evolution from magmatic to hydrothermal stage; examples from NYF pegmatites of the Třebíč Pluton, Czech Republic

“…The first two pegmatite types relate to the REL-REE subclass, a rareelements class of the NYF family (Černý and Ercit 2005). Nevertheless, they are F-poor and do not entirely fit the definition of NYF family (Simmons et al 2012), whereas the (iii) Kracovice represents mixed NYF-LCT pegmatite (Novák et al 1999;Černý and Ercit 2005;Novák et al 2012;Čopjaková et al 2015). Martin and De Vito (2005) considered pegmatites of Třebíč Pluton to be NYFrelated, and to a specific type of pegmatite derived from ultrapotassic orogenic pluton belonging to a shoshonitic association (see Žák et al 2005).…”

Non-Metamict Aeschynite-(Y), Polycrase-(Y), and Samarskite-(Y) in NYF Pegmatites from Arvogno, Vigezzo Valley (Central Alps, Italy)

“…The tetrad effect is usually best developed in the first and third tetrad T 1,3 [49], but some HREE-enriched systems can develop evolved tetrad effects on T 3 and T 4 as described by Škoda et al [44]. The M-type tetrad effect was reported for evolved Li-F granites, fractionated pegmatites, and their associated minerals [49][50][51][52][53][54][55], as well as minerals crystallized from felsic magma-derived fluids [54][55][56][57] and is attributed to a distribution of REE among magmatic/solid and fluid phases. It is also frequently linked to the F-rich environment, but the sole role of F is questioned by Škoda et al [44].…”