Gran Lago (Grand Lac), Champdepraz, Aosta Valley, Italyi

Regional Level Types
Gran Lago (Grand Lac)	Lake
Champdepraz	Commune
Aosta Valley	Autonomous Region
Italy	Country

Rodingite outcrops and loose blocks in the area around Gran Lago/Grand Lac, the largest natural lake in Valle d'Aosta, and the small lakes to the NW of Col de Gran-Rossa.

Rodingite dykes, pink to reddish to brown in colour, embedded in serpentinite crop out near Grand Lac. They mainly consist of garnet (up to 80%) and chlorite (20-50 %) with a variable amount of vesuvianite (0-50%), diopside (0-30%), spinel group minerals (prevalent magnetite, chromite, chromite-hercynite series) and rare titanite, epidote, clinozoisite, allanite-(Ce), and ilmenite; the chlorite rim consists of clorite (90-95%) ± garnet, and magnetite. Garnet is mainly grossular; a Cr-rich garnet on the rims of chromite, chromite-hercynite, and Ca-Fe garnet is locally observed. Some rodingites are particularly rich in diopside (up to 65%), with associated chlorite (5-25%), and garnet (10-40%).

Foliated rodingites with diopside (65-90%), chlorite (10-25%), and garnet (up to 10%) occur at the contact between rodingite dykes and serpentinite; foliated rodingites with chlorite (40%), clinozoisite-zoisite (~30%), epidote (20%,) and diopside (fino a 10%) crop out to the east of Grand Lac.

An outstanding finding of zircon was made in some garnet-chlorite rodingite blocks near the small lakes to the NW of Col de Gran-Rossa (Bertoldi, 1991; Piccoli et al., 2007; Castello & Paganone, 2016). The small pseudo-parallel fissures frequently occurred in such rodingitic blocks yielded about 300 zircon crystals, ranging from 1 to 3.8 mm in length and showing a very elongated prism and the four faces of the tetragonal pyramid. Most of these crystals are transparent and amber to brown in colour; colourless crystals are very rare.

Fossils

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References