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Poggio Mortaio (Poggio Mortaio Mine; Monte Argentario Mine; Poggio delle Polveriere; Terra Rossa; Il Passo), Monte Argentario, Grosseto Province, Tuscany, Italy

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Location is approximate, estimate based on other nearby localities.
Latitude & Longitude (WGS84): 42° North , 11° East (est.)
Margin of Error:~47km
Name(s) in local language(s):Poggio Mortaio (Miniera di Poggio Mortaio; Miniera di Monte Argentario; Poggio delle Polveriere; Terra Rossa; Il Passo), Monte Argentario, Provincia di Grosseto, Toscana, Italia

Old mining area for Fe-Mn ores at Poggio Mortaio (the locality of the Fe-Mn deposit is also known as Poggio delle Polveriere; Terra Rossa; Il Passo), on the NE slope of Monte Argentario, near Orbetello.

Ore mineralisations occur at the contact between Calcare Cavernoso and phyllitic rocks of the Monticiano-Roccastrada unit (Tuscan Verrucano). The Fe-Mn deposit (consisting of limonite, hematite, and manganese oxides), exploited in the period 1874-1958, occurs in the upper part of the Calcare Cavernoso formation, while large unexploited ore deposits occur at deeper levels: a Zn-Pb-Fe mineralised horizon, at a depth of 100-120 m below sea level, in the middle and lower part of the Calcare Cavernoso formation and a pyrite-magnatite body, between 192 and 400 m below sea level, at the contact with the schists.

The Fe-Mn deposit, discovered at Terra Rossa (Terrarossa) in 1873, was initially exploited during the period from 1874 to 1911 by the company Fratelli Rae of Livorno. Operations ceased when the groundwater table was reached, due to difficulty in draining the underground works. Mining was restarted in 1916 by the siderurgical enterprise Ilva, which exploited four main ore masses (named Elena, Guglielmo, Enrico, and Massa No. 1) embedded in limestone. In 1939 the mining concession was transferred to the company Ferromin, which continued operations until 1944, when heavy bombings on Porto Santo Stefano seriously damaged the mining infrastructure. The post-war period saw a new development of the mine and the maximum annual production (40,000 tons of ore) was reached in 1952. Two shafts and various gallery were excavated in this period. Furthermore, geological and mining investigations performed in the 1950s revealed the presence of deeper ore bodies, consisting of mixed sulfides and pyrite-magnetite. In 1958 operations at the mine ceased, mainly because of a significant impairment of the Fe-Mn ore quality (due to the presence of Zn and fine-grained clay). Further exploration works on the Zn-Pb-Fe and pyrite-magnetite deposits were performed during the 1960s by the companies Società Mineraria dell'Argentario and Società Monte Amiata.

Thirteen mineral species have been recently identified from specimens of the Fe-Mn mineralisation (Biagioni et al., 2016). These specimens were collected at the beginning of the 1990s on a dump, located in the area where a luxury residence now stands.

Mineral List

20 valid minerals.

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- Jervis G. (1874): I tesori sotterranei dell'Italia. Vol. 2: Regione dell’Appennino e vulcani attivi e spenti dipendentivi. Ed. Loescher, Torino, 624 pp.
- D'Achiardi A. (1883): I metalli. Loro minerali e miniere. Ulrico Hoepli Editore, Milano, Tipogr. T. Nistri e C., Pisa, 2 vol., 403 and 634 pp.
- Millosevich F. (1919): Giacimenti italiani di minerali accessori per la siderurgia. Atti della Società Italiana per il Progresso delle Scienze, 10, 335-352.
- Eldmann L. (1921): Il giacimento manganesifero e la "manganite" del Monte Argentario. Rassegna Mineraria Metallurgica e Chimica, 55, 1-3.
- Pompei A. (1924): Brevi notizie tecniche sui principali giacimenti minerari della Toscana. Annali dell'Agricolutura, 4, 635-636.
- Lotti B. (1928): I depositi dei minerali metalliferi. Guida allo studio e alla ricerca dei giacimenti metalliferi con speciali esemplificazioni di giacimenti italiani. Seconda Edizione. Edizioni de “L’Industria Mineraria”, Stab. Tipografico A. Porcile, Genova, 236 pp.
- Burckhardt C.E., Falini F. (1956): Memoria sui giacimenti italiani di manganese. In: Gonzales Reyna J. (ed.), XX Congreso Geologico International. Symposium sobre yacimientos de manganeso. V. Europa, Mexico, 221-272.
- Melchiorri G. (1958): La scoperta del giacimento di polisolfuri del Monte Argentario. L'Industria Mineraria, 9, 521-524.
- Burtet Fabris B., Omenetto P. (1975): Osservazioni sulla mineralizzazione ad ossidi e solfuri del M. Argentario (Grosseto). Rend. Soc. Ital. Mineral. Petrol., 30, 3, 963-967.
- Del Caldo A., Moro C., Gramaccioli C.M., Boscardin M. (1973): Guida ai minerali. Fratelli Fabbri Editori, Milano, 208 pp.
- Pipino G. (1985): Eccezionali cristalli di calcantite a Monte Argentario. Riv. Mineral. Ital., 8, 2 (2-1985), 80.
- Biagioni C., Cerri M., Bernocchi M., Betti C., Del Chiaro L., Mangoni G., Bazzoni C. (2016): Monte Argentario. I minerali del giacimento ferro-manganesifero. Riv. Mineral. Ital., 40, 1 (1-2016), 8-20.

External Links

Nannoni R. (2007): Monte Argentario: geologia e attività minerarie. In: Almanacco del Monte Argentario - http://www.argentario-almanacco.it/201_Geologia/201_it.html

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