(Mines of Sulcis)
The Rosas Ore
The Rosas ore includes galena, blende, chalcopyrite and mixed sulfides. It is found in a metamorphic area, between limestones and schists. The ore is very complex from a geological and mining point of view. It is closely related to the nearby Sa Marchesa ore, and lies along the high rounded folds and fractures of the ground.
The ore is a result of the deposition of sulfides during a sedimentary phase probably divided in three stages:
During the first phase of the Caledonian orogeny the ore doesn't seem to have changed its position or conformation. Subsequently the orogenic activity increased, and the ore was moved and fractured.
According to the most reliable theory, the movement related to the Hercynian Orogeny, along with the metamorphism caused by the granite's push, caused other migrations of minerals and their new crystallization. A typical example of this phase is the transformation of pyrite in pyrrhotite and haematite-magnetite. Contemporarily the barite and galena were considerably moved and concentrated in far away sites. It does not seem that the other sulfides suffered attacks and noticeable oxidations.
History of the mine
The first information on mining activity in the area of the Rosas mine goes back to the first decades of the XIX century. At that time all the mining activity in Sardinia was directly managed by the State Administration. The first papers attesting to a mining prospect south of Monte Orri date from these years.
In 1832 the State Administration granted three local enterpreneurs with some prospect permits. A few years later they founded the Società Anonima dell'Unione per la Coltivazione delle Miniere del Sulcis e del Sarrabus in Sardegna. In 1851, this company was granted with the mining license of Rosas, and began to exploit a galena ore.
The first years of the mine were difficult, and were spent among civil lawsuits and frequent changes of ownership. Only in 1883, the energy and competence of the mining engineer Giorgio Asproni brought the mine out of difficulties.
At the beginning mainly lead, zinc and iron were extracted. At the end of the XIX century, within a few decades, more than 60.000 tons of blende, calamine, cerussite and galena were extracted.
The first works were concentrated in the west sector of the mine. When the ore started to run out, they were moved to the eastern sector, in the area named Trubba Niedda.
At the beginning, the Rosas mine was very productive, and until 1911 the obtained yield was 23%, that is to say 23 kilogrammes of lead for every quintal (= 100 kilos) of mineral dressed. During the First World War the yield went down to 11%, and then to 8% from 1919 to 1924. Nevertheless, a search in 1922 estimated that there were still 95.000 tons of mineral to be extracted.
During these years the previous claimants agreed with other capitalists and founded the company named Società Miniere di Rosas. The nearby mines of Mitza Sarmentus, Sa Marchesa and Bega Trotta were closed.
In 1938 the flotation plant was finished. It could dress 50 tons of minerals in a day, but became operative only at the end of the Second World War.
At the end of the war, the mine was in perfect condition. It had a comfortable village, a functional managing centre, modern plants and a large variety of extractable minerals. In 1951 about 152 people lived in the village.
In the 1950's the AMMI (Azienda Minerali Metallici Italiani = Metallic Minerals Italian Company) made some investiments that kept hope alive for the future of the mine. The minerals dressed by the flotation plant were very rich. The average grades, in fact, were up a little to 5% for zinc and 0,63% for copper.
The crisis became irreversibile in the 1970's, for this mine and for all the Sardinian mining activity. The mine was closed once and for all in the 1980's.
The minerals of the mine of Rosas
Allophane, Arsenopyrite, Aurichalcite, Azurite, Bismuth, Brochantite, Calcantite, Calcite, Calcopirite, Cerussite, Clinozoisite, Cordierite, Cuprite, Diopside, Ematite, Epidote, Fluorite, Argentiferous Galena, Greenockite, Limonite, Linarite, Malachite, Manganite, Orneblenda, Parauricalcite, Pyrite, Pyrohisite, Pyromorphite, Plumboallophane, Quartz, Copper, Rosasite, Siderite, sphalerite, Uralolite.
You can find information on the mine in ANTONIO FRANCESCO FADDA - Siti minerari in Sardegna - Coedisar, Cagliari 1997, and in SANDRO MEZZOLANI, ANDREA SIMONCINI - Sardegna da salvare. Paesaggi e Architetture delle Miniere - Editrice Archivio Fotografico Sardo, Nuoro 1993
IGM map: 556-III
Questa pagina è stata visitata 8645 volte