Schmorrasgrat-South, Ausserferrera, Ferrera, Viamala Region, Grisons, Switzerlandi

Regional Level Types
Schmorrasgrat-South	- not defined -
Ausserferrera	Village
Ferrera	Municipality
Viamala Region	Region
Grisons	Canton
Switzerland	Country

Schmorrasgrat is the name given to the ridge separating the Mulegn Valley (Mulin valley), a right side-valley of the main Ferrera Valley, from the Schmorras Valley (Val Schmorras), a minor southwestern branch of the Oberhalbstein (Surses), between Piz Settember to the north and Piz Alv to the south. The southern segment of the ridge, between Fuorcla Cotschna and Piz Alv, is called Schmorrasgrat-South.

Outcrops of silicate-rich Fe-Mn ores in Triassic dolomite marbles of the Middle Penninic Schams cover nappes. Traces of old exploitation. Swiss coordinates: 757.950/155.100 and 758.075/155.200.

Johninnesite is a locally abundant mineral which occurs in a restricted area (about 10 m) of the deposit. The host ore consists of hematite, jacobsite, quartz, dolomite, kutnohorite, and amphibole (magnesio-riebeckite), which is often brecciated so that quartz and dolomite grains up to 2 cm are embedded in a black matrix of the ore minerals. Johninnesite, that originally was thought to be a yellow amphibole, may be the main component, with minor quartz and carbonate, in discordant veins up to 5 cm in width, or it may occur as an accessory in quartz, carbonate, manganberzeliite-palenzonaite veins. Rare associated minerals in both kinds of veins are wallkilldellite, pink manganoan biotite and fluorcalcioroméite. Three johninnesite morphologies can be distinguished: fibrous crystals up to 4 cm in length, elongated perpendicular to the vein walls, which with quartz + carbonate grow synchronously to the opening of the fracture; rarely, similar veinlets containing prismatic crystals; small micaceous crystals (< 1 mm) which fill thin fractures over several square centimetres (Brugger et al., 1997).

Mn-rich garnet metasomatite mainly consists of garnet (although calderite has been reported, it seemes that garnet is more often a Mn-rich andradite significantly enriched in calderite component), Mn-rich aegirine augite, calcite-rhodochrosite, baryte and hematite.

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References