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The Mines and Minerals of Lavrion - Allanite-(Ce)

Last Updated: 14th Nov 2019

By Branko Rieck

ALLANITE-(Ce), {CaCe}{Al2Fe2+}(Si2O7)(SiO4)O(OH), monoclinic


Allanite-(Ce) is one of the minerals that do not occur in beautiful crystals at Lavrion. Usually advanced methods of analysis are necessary to confirm its presence.

General Appearance
At all localities in the Lavrion Mining District, allanite-(Ce) occurs as tiny inclusions of reddish-brown grains in the host rock. So far (2019) these grains have never appeared in sizes that make them visible to the naked eye. Even with a good stereomicroscope allanite-(Ce) is very difficult to discern. It is usually only seen in polished sections or in thin sections with highly magnifying microscopes or electron microscopes.

Paragenesis
Depending on the rock-type the paragenesis is slightly different.
In the highly metamorphic ores in Plaka we find REE-bearing epidote, hedenbergite (that is often zoned), anorthite and minor albite.
The skarn samples usually have epidote, fluorapatite, chamosite, muscovite, pyrrhotite, pyrite in a quartz-matrix. Accessory minerals are often monazite-(Ce) and xenotime-(Y).
Finally, the altered porphyry system contains quartz, biotite, plagioclase (oligoclaseandesine), actinolite, clinopyroxene (diopside), titanite and fluorapatite.

Localities
Allanite-(Ce) was first reported by Galanos (2009) from thin sections of samples of a granodioritic dyke from the Hilarion area. Later it was discovered by Kolitsch in a polished section from as skarn specimen originating from the Adami 2 adit (Kolitsch et al., 2015). In this sample allanite-(Ce) forms tiny grains with a marked zonal growth. From the Plaka area, too, but without a detailed locality is a piece of pyrrhotite-rich drill-core that also contains allanite-(Ce), also published by Kolitsch. Another discovery is reported by Voudouris (Voudouris et al., 2018) from a contact seam between an acid dyke and marble from the second level of the Hilarion area. Here a wide variety of compositions can be observed from REE-bearing and REE-rich epidote to allanite-(Ce). In this case it is a secondary product of the hydrothermal alteration of monazite-(Ce). Finally, this mineral is also described from the potassic-sodic-calcic alteration of the porphyry system in Plaka (Mélfou, 2018).




08869390015736396972062.jpg
Fig. 1: SEM micrograph (BSE mode) of subhedral monazite-(Ce) (white) next to members of the solid-solution series between REE-bearing epidote and allanite-(Ce) (up to straddling the boundary between both) (bright grey, zoned), and in association with fluorapatite (grey), chamosite (dark grey), muscovite (dark, bottom) and a tiny pyrrhotite grain (bottom left), all in matrix of quartz from a contact seam between an acid dyke and marble from the second level of the Hilarion area.



06825150015736396992161.jpg
Fig. 2: SEM micrograph (BSE mode) of bastnäsite-(Ce) (bright lamellae) syntactically intergrown with synchysite-(Ce) (grey lamellae), intergrown with allanite-(Ce) (grey, zoned; in central area), with muscovite laths (dark, top left), chamosite (dark grey, left) and pyrite (right, grey). The two REE carbonates seemingly originated due to hydrothermal alteration of allanite-(Ce). This sample is from a contact seam between an acid dyke and marble from the second level of the Hilarion area.



03162440015736397016792.jpg
Fig. 3: SEM micrograph (BSE mode) of a polished section of a grey-green, fine-grained, pyrrhotite- and galena-bearing (in narrow calcite veins) skarn sample found near the parking area close to the hydrosulphate adit. This sample was rich in epidote, chamosite, ferroactinolite and contained violarite and siegenite as rare accessories. Allanite-(Ce) forms a bright grey, thin rim around zoned REE-bearing epidote. The matrix is composed of quartz (dark), clinochlore (dark grey) and minor galena (white).



09724430015736397012742.jpg
Fig. 4: SEM micrograph (BSE mode) showing allanite-(Ce) (bright grey) grading into more or less REE-bearing epidote (more or less medium grey), in zoned hedenbergite (grey to dark grey); the dark grey phase on the left is anorthite; very dark (top right) is minor albite. Polished section of the pyrrhotite-rich region in a pyrrhotite-bearing drill core found in the Plaka region.





References
Galanos, E. (2009) Νεα εμφανιση σκαρν και γρανοδιοριτικων φλεβων στην καμαριζα λαυριου και η πιθανη τησ σχεση με τισ παραγενεσεισ Ni-ουχων ορυκτων τησ περιοχησ. Diploma Thesis, University of Athens, Greece, 68 pp. (in Greek).
Kolitsch, U., Rieck, B., and Voudouris, P. (2015) Mineralogy and genesis of the Lavrion ore deposit: new insights from the study of ore and accessory minerals. MinPet 2015, Leoben, Austria, September 10-13; abstract in Mitteilungen der Österreichischen Mineralogischen Gesellschaft, 161, 66.
Mélfou, M.V. (2018) Ορυκτολογία ποτασσικών και νατριοασβεστούχων ζωνών εξαλλοίωση από πορφυριτικά κοιτάσματα της Ελλάδας (Μαρώνεια και Λαύριο). Mineralogy of potassic-sodic-calcic zones of porphyry systems in Greece (Maronia and Lavrion). MSc thesis (unpubl.) Aristotle University of Thessaloniki, Department of Mineralogy, Petrology and Economic Geology. (in Greek with a short English abstract).
Rieck, B., Kolitsch, U., Voudouris, P., Giester, G., and Tzeferis, P. (2018) Weitere Neufunde aus Lavrion, Griechenland. Mineralien-Welt, 29(5), 32-77 (in German).
Voudouris, P., Mavrogonatos, C., Rieck, B., Kolitsch, U., Spry, P.G., Scheffer, C., Tarantola, A., Vanderhaeghe, O., Galanos, E., Melfos, V., Zaimis, S., Soukis, K., and Photiades, A. (2018) The gersdorffite-bismuthinite-native gold association and the skarn-porphyry mineralization in the Kamariza mining district, Lavrion, Greece. Minerals, 8, 531.

Acknowledgements
Thanks go to Dr. Uwe Kolitsch for constructive comments and diligent proofreading to improve this article.




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