Prabornaz Mine (ex Praborna Mine), Saint-Marcel, Aosta Valley, Italy

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Miniera di Prabornaz, Saint-Marcel, Valle d'Aosta, Italia

The manganese concentrations of Prabornaz are restricted to a 4x8 m thick quartzite unit of diverse lithologies which represent the basal part of the sedimentary cover of an ophiolite suite. Together they constituted the Piedmont Nappe which was metamorphosed up to the eclogite facies in Cretaceous times and was retrogressed in the early Tertiary.

The quartzite unit is composed of a succession of siliceous levels characterized by Mn-bearing minerals reflecting differences in chemical composition and oxygen fugacity inherited from the original sediments. The parageneses evolved during the polyphasic Alpine metamorphism passing through a pre-eclogite blue-schist facies event, the main eclogite facies event, and the several post-eclogite stages terminating in the greenschist facies.

These Mn concentrations were subsequently penetrated by several networks of cross-cutting veins and late fractures which were responsible for the mobilization of certain elements, in particular K, Sr and Ba.

References

- Rondolino R. (1934) Sopra alcuni minerali di S. Marcel (Valle d'Aosta). Periodico di Mineralogia – Roma 123-139.
- Rondolino R. (1936) Sopra alcuni anfiboli manganesiferi di Praborna (San Marcel, Valle d'Aosta). Periodico di Mineralogia – Roma pp. 109-121.
- Palache, C., Berman, H., & Frondel, C. (1951), The System of Mineralogy of James Dwight Dana and Edward Salisbury Dana, Yale University 1837-1892, Volume II: 1021.
- Bondi, M., Mottana, A., Kurat, G. & Rossi, G. (1978): Cristallochimica del violano e della schefferite di St. Marcel (Valle d'Aosta). Rendiconti della Società Italiana di Mineralogia e Petrologia, 34, 15-25.
- Brown, P., Essene, E. J. & Peacor, D. R. (1978): The mineralogy and petrology of manganese-rich rocks from St. Marcel, Piedmont, Italy. Contrib. Mineral. Petrol. 67, 227-232.
- Mottana, A., Rossi, G., Kracher, A., & Kurat, G. (1979). Violan revised: Mn bearing Omphacite and Diopside. Tschermaks Min. Petr. Mitt., 26, 187-210.
- Martin, S. (1983): La mine de Praborna, Val d'Aoste (Italie): une série manganesifère metamorphoisée das la facies éclogite. These 3me cycle, Univ. Paris VI, xx pp.
- Martin-Vernizzi, S. (1984) La mine de Praborna (Val d'Aoste, Italie: une série manganésifère métamorphisée dans le faciès éclogite. Thèse de doctorat, Université Pierre et Marie Curie, Paris, France.
- Perseil, E. A. (1985): Some characteristics of manganese oxide facies in the deposit at St. Marcel-Praborna-Val d'Aosta, Italy. Miner. Deposita 20, 271-276. (in French)
- Preite, D. (1985): La pagina dei Micromounts – Omfacite di Quincinetto e Praborna. Rivista Mineralogica Italiana, 9(2), 88.
- Perseil E. A. & Smith D. C. (1995) Sb-rich titanite in the manganese concentrations at St. Marcel-Praborna, Aosta Valley, Italy: petrography and crystal chemistry. Mineralogical Magazine: 59: 717-734.
- Smith, D.C. and Perseil, E.-A. (1997) Sb-rich rutile in the manganese concentrations at St. Marcel-Praborna, Aosta Valley, Italy: petrology and crystal-chemistry. Mineralogical Magazine: 61: 655-669.
- Perseil, E. A. (1998) Evolution cristallochimique des oxydes de manganèse dans le gisement de St. Marcel Praborna (V. Aoste, Italie) - Rend. Fis. Acc. Lincei, s. 9, v. 9 (1998) 4, pp. 315 - 336
- Piccoli, G.C., Maletto, G., Bosio, P., Lombardo, B. (2007): Minerali del Piemonte e della Valle d'Aosta. Associazione Amici del Museo "F. Eusebio" Alba, Ed., Alba (Cuneo) 607 pp.
- Tumiati, S., Martin, S., Godard, G. (2010): Hydrothermal origin of manganese in the high-pressure ophiolite metasediments of Praborna ore deposit (Aosta Valley, Western Alps). European Journal of Mineralogy 22, 577-594.

Mineral List

Actinolite Aegirine Aegirine-augite Albite Aluminoceladonite Anatase 'Ardennite' Birnessite Braunite (TL) Calcite Calderite Celadonite 'Chlorite Group' Clinochlore Clinozoisite Cryptomelane Diopside

Diopside var: Schefferite var: Violane Edenite Epidote Fluorapatite Gold Hausmannite Hematite Hollandite Ilmenite Jacobsite Jadeite Kutnohorite Magnesiochloritoid Magnetite Manganiandrosite-(Ce) (TL) Manganite

Microcline Muscovite var: Alurgite Neotocite Omphacite Parvowinchite Pentlandite Phengite Phlogopite Piemontite (TL) Piemontite-(Sr) Priderite Pyrolusite Pyrophanite Pyroxmangite Quartz Rhodochrosite

Rhodonite Richterite Roméite Group (TL) Rutile Spessartine Strontiomelane (TL) Talc Tephroite Tiragalloite Titanite var: Greenovite Todorokite Tremolite Uvarovite Violarite Winchite

67 entries listed. 59 valid minerals. 4 type localities (valid minerals). 1 type locality (other).