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MONAZITE AND ALLANITE FROM THE DITRAU ALKALINE MASSIF, EAST CARPATHIANS, ROMANIA (CROSBI ID 92159)

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Hirtopanu, Paulina ; Bermanec, Vladimir ; Udubasa, Gheorghe ; Melgarejo, Joan Carles MONAZITE AND ALLANITE FROM THE DITRAU ALKALINE MASSIF, EAST CARPATHIANS, ROMANIA // Anuarul Institutului Geologic al Romaniei (1996), 72 (2000), 41-x

Podaci o odgovornosti

Hirtopanu, Paulina ; Bermanec, Vladimir ; Udubasa, Gheorghe ; Melgarejo, Joan Carles

engleski

MONAZITE AND ALLANITE FROM THE DITRAU ALKALINE MASSIF, EAST CARPATHIANS, ROMANIA

The Ditrau alkaline intrusive complex occurs in the pre-Alpine metamorphic rocks of the Bucovinian Nappe in the Carpathians, in wich it produced a marked thermal aureole. It is like dome of elliptical shape (14x19 km diameter) with un imperfect ring structure. The petragraphic complexity involves large series of ultrabasic to acid, silica saturated and silica undersaturated alkali rocks: granites, syenites, nepheline syenites, diorites, tinguaites, lamprophyres, camptonite, spessartites, microdiorites and microsyenietes, nepheline syenite aplites, carbonatites. Also, at the immediate contact there appear beautiful hornfelses with biotite, cordierite, analusite, wollastonite, corundum, spinel, alkali amphibole and chloritoid. The large variety and the complexity of the mineralogy of Ditrau massif are reflected by the existence of about 200 minerals; native elements, sulphides, oxides phosphates, sulphates, wolframates, arsenates, flurides and different silicates (olivines,pyroxenes, pyroxenoides, amphiboles, epidotes, micas, alkali feldspras, plagioclases, feldspatoides, Ba-feldspars, chlorites and zeolites. Some rare minerals, like eudialyte, astrophyllite, columbite etc or accessory minerals like zircon, sphene, apatite, monazite, allanite etc are present as rock forming minerals of the nepheline syenite or of the carbonatites. The vein mineralisation develops in the diorite hornblendite complex in NV part of the massif. Two parangenesses are quite distinct; monazite-pyrite-carbonates-allanite and molybdenite-sphalerite-galena. Monazite display big cm-sized crystals with a brown-red colour and a radiated structure. Allanite has a black colour and is closely associated with monazite and carbonates (bastnaesite, hydroxylbastnaesite, calcite, rhodochrosite). In thin section monazite-(Ce), the commonest one has yellow light colour and high relief and birefringence. Monazite-(Nd) is rare in Ditrau massif and has a distinct colour bright rose. Monazite- (Ce) appears associated with ankerite, calcite,bastnaesite, hydrxylbastnaesite, allanite, pyrite, stannite, sphalerite, wurtzite, pyrochlore, willemseite, uraninite, durangite and borovskite (?). The calcium bearing thorium rich member of the monazite group, cheralite, isostructural with monazite was determined by the aim of XRDA. The samples analysed where collected on the waste dump of the Adit No 25 of Jolotca vein field. Microprobe analyses gave for monazite (%wt): SiO2 0.314, CaO 0.156, P2O5 29.503 ThO2 3.085, La2O3 19.036 Ce2O3 34.391, Pr2O3 2.606, PbO 0.264, Yb2O3 0.122, Er2O3 0.034, Gd2O3 0.671, Sm2O3 1.107, Nd2O3 9.024. Total 100.313. For allanite (%wt): Sio2 28.289, CaO 7.497, Al2O3 9.938, MgO 0.905, P2O5 0.139, Fe2O3 20.094, ThO2 0.155, La2O3 8.356, Ce2O3 14.685, Pr2O3 1.027, PbO 0.035, mnO 2.125, Y2O3 0.126, Er2O3 0.034, Gd2O3 0.304, Sm2O3 0.481, Nd2O3 3.626. Total 97.817. The intergrowths of monazite with allanite occur elsewhere in the world in carbonatites or in barite carbonate rock near alkali syenite. The Ditrau alkaline massif contains thus a significant carbonatite or carbonatite - like component with significant monazite allanite as quite, intergrowths.

Monazite; allanite; alkaline rocks; Ditrau massif

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Podaci o izdanju

72

2000.

41-x

objavljeno

1453-357X

Povezanost rada

Geologija