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

Regional Level Types
Gran Lago (Grand Lac)	Lake
Champdepraz	Commune
Aosta Valley	Autonomous Region
Italy	- not defined -

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