Valsassina, Lecco Province, Lombardy, Italyi

Regional Level Types
Valsassina	Valley
Lecco Province	Province
Lombardy	Region
Italy	Country

The Valsassina mining district, from a geological point of view, can be divided into four distinct areas based on the type of mineralization.

1) The first area, that comprises the territory of Valsassina to the south of Introbio village, is characterized by the presence of various mineralization hosted within limestone and dolomite rocks of the Mesozoic sedimentary succession.

Small lentiform/vein iron deposits, usually hosted by the Esino Limestone, are widely spread in the area of Ballabio, Barzio, Pasturo, Cremeno, Baiedo and Moggio. These deposits, composed by limonite with also relicts of pyrite and other strongly oxidized iron sulpides at the core of the deposits, were mainly exploited in ancient times for iron ore extraction. Ancient mines and small excavations for the extraction of iron, linked to this type of deposit, are present at Pizzo d'Erna, Monte Melma, Val Calolden, Culmine San Pietro, Colle di Balisio, Campo del Ferro, Prato dell'Orso, Zucco Angelone and near Pasturo.

In the area between Monte Coltiglione, Val Calolden and Piani dei Resinelli, there are some extensive and historically important lead and zinc MVT (Mississippi Valley Type) deposits hosted at the contact between Esino and Breno formations, associated with breccias and karst structures, or inside the Calcare Metallifero Bergamasco formation. These ore bodies are constituted, in proportions that are strongly variables according to the mining site, by galena, with sometimes a small amount of silver, sphalerite, Pb-Zn secondary minerals (calamines), calcite, dolomite, fluorite and baryte (Rodeghiero et al., 1986).

2) The second area, located between Val Biandino and Val Varrone, is characterized by the presence of a large number of discordant vein bodies, composed by siderites (with also hematite, quartz and baryte), hosted mainly within the Servino and Verrucano Lombardo formations.

3) The third area, which is largely included between the villages of Introbio and Cortenova, is characterized by the presence of polymetallic NNW-SSE trending and base-metal NE-SW trending veins, part of the Valsassina five-elements hydrothermal system (Vergani, 2019). These ore bodies appear as sub-vertical vein systems, hosted along faults that cut the rocks of the metamorphic basement and the overlying Permian volcano-clastic cover, with a thickness that can varying from few centimeters to several meters.

4) In the area between Margno and Casargo there are some mineralization different from the others described above. In the whole area, and in particular near Indovero village, are observable more or less diffused veins or concordant lenticular bodies composed by hematite and/or siderite, associated with quartz, hosted by gneiss and schist. In the Margno village area, at Alpe Grasso locality, there are some old cinnabar mines. Here cinnabar occurs in quartz veins and disseminated within the gneiss or, as described by Cadisch (1942) and Arieni (1996), inside the Servino Formation.

Fossils

There are 3 fossil localities from the PaleoBioDB database within this region.

These data are provided on an experimental basis and are taken from external databases. Mindat.org has no control currently over the accuracy of these data.

Occurrences	12
Youngest Fossil Listed	237 Ma (Middle Triassic)
Oldest Fossil Listed	252 Ma (Permian)
Stratigraphic Units	Unit No. Occurrences Age Servino - Middle 6 252.17 - 251.2 Ma (Phanerozoic)
Fossils from Region	Click here to show the list.
Accepted Name Hierarchy Age Claraia genus Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia 252.17 - 251.2 Ma Phanerozoic Decurtella decurtata species Animalia : Brachiopoda : Rhynchonellata : Rhynchonellida : Austrirhynchidae : Decurtella : Decurtella decurtata 247.2 - 242 Ma Triassic Tetractinella trigonella species Animalia : Brachiopoda : Rhynchonellata : Athyridida : Diplospirellidae : Tetractinella : Tetractinella trigonella 247.2 - 242 Ma Triassic Claraia aurita species Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia : Claraia aurita 252.17 - 251.2 Ma Phanerozoic Claraia clarai species Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia : Claraia clarai 252.17 - 251.2 Ma Phanerozoic Nudirostralina trinodosi species Animalia : Brachiopoda : Rhynchonellata : Rhynchonellida : Norellidae : Nudirostralina : Nudirostralina trinodosi 247.2 - 242 Ma Triassic Koeveskallina koeveskalyensis species Animalia : Brachiopoda : Rhynchonellata : Spiriferinida : Mentzeliidae : Koeveskallina : Koeveskallina koeveskalyensis 247.2 - 242 Ma Triassic Silesiathyris angusta species Animalia : Brachiopoda : Rhynchonellata : Terebratulida : Zeilleriidae : Silesiathyris : Silesiathyris angusta 247.2 - 242 Ma Triassic Claraia intermedia species Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia : Claraia intermedia 252.17 - 251.2 Ma Phanerozoic Claraia radialis species Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia : Claraia radialis 252.17 - 251.2 Ma Phanerozoic Claraia bittneri species Animalia : Mollusca : Bivalvia : Pectinida : Pterinopectinidae : Claraia : Claraia bittneri 252.17 - 251.2 Ma Phanerozoic Daonella esinensis species Animalia : Mollusca : Bivalvia : Ostreida : Halobiidae : Daonella : Daonella esinensis 247.2 - 237 Ma Triassic
Fossil Localities	Click to show 3 fossil localities

Localities in this Region

Other Regions, Features and Areas that Intersect

References