Textural relationships and compositional variations of (Fe,Mn)-(Ti,Sn)-(Nb,Ta) oxides and associated minerals from low-to moderately fractionated, mixed (NYF + LCT) anatectic pegmatites, which belong to the Julianna pegmatitic system, exposed at Piława Górna, Lower Silesia, Poland, were studied to elucidate the geochemical evolution of the pegmatite-forming melt. The primary Nb-Ta oxides crystallized in the following sequence: (1) columbite-(Fe) evolving to columbite-(Mn), associated with Nb-and Ta-bearing ilmenite-pyrophanite + almandine-spessartine garnet + Ti-poor schorl, (2) columbite-(Fe), (3) tantalite-(Fe), (4) Ti-and Sn-bearing ixiolite ± ferrowodginite ± Nb-and Ta-bearing cassiterite ± columbite-(Fe), all crystallizing along with Ti-enriched schorl evolving to dravite. The most characteristic features of the mineral assemblages are the reversed Mn-Fe fractionation trends and increasing Ca concentrations at the final stage of crystallization. These compositional variations are explained by a possible pre-emplacement contamination of the pegmatite-forming melt and re-equilibration of biotite and plagioclase from the early-crystallized outer zones of the pegmatites with rapidly cooling pegmatitic melt. Local changes in melt composition were of minor importance. Late alterations, such as chloritization and muscovitization of biotite or albitization of Ca-rich plagioclase were significant only at the hydrothermal stage.
The newly dis cov ered Julianna peg ma titic sys tem from the Pi³awa Górna Quarry (the Góry Sowie Block, Sudetes, NE mar gin of the Bo he mian Mas sif) is de scribed in terms of geo log i cal set ting, pe trog ra phy and de scrip tive min er al ogy. The sys tem repre sents the larg est peg ma titic oc cur rence in the Pol ish Sudetes and con sists of a com plex net work of cogenetic rare-el e ment gra nitic pegmatites that in truded into tectonized am phi bo lite as dis cor dant dikes. The pegmatites range from bar ren and weakly zoned to tex tur ally well-dif fer en ti ated ones that are com posed of a fine-grained bor der zone, coarse-grained wall zone, graphic and blocky feld spar in ter me di ate zones and a quartz core. Uni di rec tional and skel e tal so lid i fi ca tion tex tures are well-de vel oped. The Julianna pegmatites con sist of rock-form ing plagioclase (£An 39 ), microcline, quartz and bi o tite accom pa nied mostly by ac ces sory to mi nor mus co vite, tour ma line, gar net and beryl. They crys tal lised from anatectic melt of hy brid NYF (ni o bium-yt trium-flu o rine) + LCT (lith ium-ce sium-tan ta lum) geo chem i cal char ac ter is tics. Pegmatites with a low to mod er ate de gree of frac tion ation, that dom i nate in the Julianna sys tem, bear NYF-sig na ture ac ces sory min er als, such as al la nite-(Ce), colum bite-, euxenite-and samarskite-group min er als, fergusonite-(Y) and gadolinite-(Y). How ever, rare dikes that at tained a very high de gree of frac tion ation con tain typ i cal min er als of LCT-sig na ture in clud ing tour ma lines of the elbaite-olenite-rossmanite se ries, le pido lite, lithiophilite, spodumene, Cs-rich beryl and pollucite.
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