Snake-shaped carbonate folds replaced by skarn (Campiglia Marittima, Italy)
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GEOSITES
Snake‑shaped carbonate folds replaced by skarn (Campiglia Marittima, Italy)
Skarn is a metasomatic rock usually produced by interaction of carbonate rocks with hydrothermal fluids, commonly related to igneous intrusive bodies (Meinert et al. 2005). Skarn ore deposits are among the world’s major source of Cu, Pb, Zn, Ag, and Au (Baker et al. 2004). For this reason, the knowledge of ore-forming processes in these magmatichydrothermal systems has a prominent scientific and industrial relevance. Since the nineteenth century, the Campiglia Marittima system played a pivotal role in the construction of skarn formation models (Da Mommio et al. 2010). This supported the birth of Archaeological Mines Park of San Silvestro in 1996. The Park is fostering the extraordinary geological and archaeological “open-air archive” where scientific research enhanced the traces of a mining activity that began in the seventh century B.C. At Campiglia Marittima, a granitic pluton intruded a Mesozoic sedimentary carbonate sequence around 5.4 Ma (Paoli et al. 2019 and reference therein). The intrusion triggered thermal metamorphism and deformation in the host rocks. Deformation is progressively more intense towards the granite contact, with the development of disharmonic non-cylindrical isoclinal folds (Vezzoni et al. 2017; Fig. 1). Hydrothermal fluids selectively exploited anisotropies in the meta-carbonate rocks. This process produced an exoskarn paraconcordant with the marble foliation, also partially replacing former disharmonic folds developed in the marble (Vezzoni et al. 2016; Fig. 1a, b). The metasomatic
minerals are mainly represented by phlogopite, titanite, plagioclase, diopside with minor amphibole and apatite. Phlogopite abundance increases significantly in specific layers, thus indicating that the original limestone layering may have been one of the governing factors in its origin (Paoli et al. 2019). Nevertheless, the overall skarn texture is isotropic, highlighting that mineral paragenesis formed after the main deformation process (Vezzoni et al. 2017; Paoli et al. 2019). The presence of these special features makes this outcrop one of the key geosites for studying skarn formation. This geosite is located in an active mining area (Lat. 43°04′17.29ʺ N; Long. 10°35′22.09ʺ E) and it was exposed by the exploitation activity at the beginning of the 2000s. In the following years, the developing shape of the outcrop was the subject of research, field workshops and teaching activities. At present, the geosite is covered by mine waste precluding direct observation. Thus, mining activity is sometimes resulting in exposure of special, relevant outcrops but, on the other hand, it can have an impact on the long-term conservation of geosites. Over the latest years, there has been a growing interest in the topics related to geoheritage (Reynard and Brilha 2018). In consequence, conservation could be achieved by a fruitful collaboration between mining companies, research institutions and geoparks, aimed to select the special geosit
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