Two days in intimate contact with the oldest Italian rocks. The Cambrian-Ordovician beds (520-480 Ma), the Mining activities and the caves /Seddas Moddizzis-Monte San Giovanni-Grotta di Santa Barbara-Miniera di Monteponi, Iglesiente, Sardinia).

We present a synthetic outline of a geological field excursion at the Iglesiente area, one of five prototype locations proposed by the “Edugeo” Project of the FIST. Like the other didactic excursions suggested by “Edugeo”, this Iglesiente excursion focuses on mature high-school students (17-19 years old) and on their teachers, with the aim of fostering an early and broad interest on the Earth Sciences and raise enrolment in the Geology university courses. The “Edugeo” excursions are committed to a high scientific content and, at the same time, to a highly educational approach, in order to make high-school students aware of the geological meaning of rocks and landforms through the typical scientific method based on objective observations of field data. The objective of this excursion, spread over two days, is the stratigraphy of the oldest Italian sediments (Cambrian-Ordovician), their paleogeographic meaning, the development of the karst features, and the generation of the extensive Pb-Zn deposits hosted by carbonate rocks. The entire excursion is located within the Iglesias syncline, through the mine villages of Seddas Moddizzis, San Giovanni and Monteponi (Iglesias and Gonnesa). In tandem with this field activity, we prepared an introductory lecture (one hour long) and a two-hour workshop to provide the fundamental cultural background to the geological processes that occurred in the area. Both lecture and workshop will be held in a lecture hall of the University of Sulcis-Iglesiente, in the Monteponi mine buildings. The first day focuses on the geology and stratigraphy of the Cambrian-Ordovician sequences of Mount San Giovanni (Gonnesa-Iglesias). The many outcrops along the walking trails (over a distance of about 4 km and with a vertical interval of about 150 m) are an ideal “school-book” introduction to the geological environment in which these rocks formed, as well as to the changes they underwent during geological times. Outcrops are represented by siltstones, fine sandstones, oolithic limestones, limestones, dolostones and phyllites mostly deposited in a shallow sea that touched the Southern European continent between 520 and 480 Million years ago, as determined by their fossil content (trilobites, archaeocyathites, etc.). Especially the carbonate members are rich in Pb and Zn sulphides and their oxidation products, which are now visible in the abandoned mine plants and villages. The second day will be spent within the mine environment. We will first visit the San Giovanni mine complex with the Galleria Lheraud, then the deep Carolina shaft and the mineralised voids nearby, the Santa Barbara cave, and the natural karst cavities intercepted by the mine workings. This part of the trip will explain the genesis of these ore bodies, mine engineering problems, and underground karst geomorphology. The Santa Barbara cave, in particular, is a typical example of hypogene cavern with a high variety of speleothems, including the famous barite crystals. Its genesis, still under debate, will bring visitors back up to the Triassic time or even earlier, being the cave a unique repository of sedimentological and geochemical evidence of profound changes in the surface landscape. After lunch the excursion will visit the Monteponi mine, with the Compressor’s room, the mining tunnel of Villamarina with its machineries, and, finally, the red tailings that so much characterise the landscape of this area. In this last part of the trip, students will have further insight into the capacity of Man to exploit metal deposits and impact on the natural environment. The possible ways of remediation will also be introduced. Because of the complex interplay between distinct geological processes and late human activities, we consider this Iglesiente excursion an excellent tool for introducing Geology to high-school students, which makes this attractive geological site important for both science and outreach programs.