In the Italian Western Alps four main types of deposits can be identified, which were exploited for iron in the past. Metasediment-hosted iron ore deposits occur within sequences of pre-carboniferous to triassic age, in tectonic units of continental affinity. Main ore minerals are represented by hematite and/or siderite. Based on the association with metasedimentary units and the stratiform morphology, they are generally considered as pre-alpine, synsedimentary mineralizations. Ultramafic-hosted magnetite deposits within the metaophiolitic Piemonte Zone consist of two different sub-types. A first one comprises most of (possibly all) the Aosta Valley deposits, deriving from podiform chromitites bodies. A second sub-type is represented by the Alpe Radis mineralization (Lanzo Valleys), which appears to derive from stratiform chromitite bodies. For all these ultramafic-hosted magnetite deposits, alpine metamorphism has been a critical factor in the chromite - magnetite transformation. Skarn-related deposits are connected with the Traversella plutonic body, emplaced into the Sesia-Lanzo continental unit during a magmatic event of late-alpine age. Iron mineralizations consist of magnetite and hematite magnetite skarns, as replacement products of dolomite marble horizons. The skarns record a polyphase evolution, the iron mineralization being related to alteration of previously formed skarn assemblages. Metamorphic-hosted hydrothermal siderite deposits were also exploited for iron in the past. Preliminary data on the Lago dietro la Torre siderite mineralization show that the siderite deposit is part of a composite mesothermal system developed within the Piemonte Zone, after the mesoalpine metamorphism. The wide spectrum of iron deposits typologies in the Western Alps reflects the complex iron mobilization - remobilization processes in the crust, connected with the evolution of this sector of the alpine belt.
The Iron Ore Deposits of the Italian Western Alps
ROSSETTI, Piergiorgio
2000-01-01
Abstract
In the Italian Western Alps four main types of deposits can be identified, which were exploited for iron in the past. Metasediment-hosted iron ore deposits occur within sequences of pre-carboniferous to triassic age, in tectonic units of continental affinity. Main ore minerals are represented by hematite and/or siderite. Based on the association with metasedimentary units and the stratiform morphology, they are generally considered as pre-alpine, synsedimentary mineralizations. Ultramafic-hosted magnetite deposits within the metaophiolitic Piemonte Zone consist of two different sub-types. A first one comprises most of (possibly all) the Aosta Valley deposits, deriving from podiform chromitites bodies. A second sub-type is represented by the Alpe Radis mineralization (Lanzo Valleys), which appears to derive from stratiform chromitite bodies. For all these ultramafic-hosted magnetite deposits, alpine metamorphism has been a critical factor in the chromite - magnetite transformation. Skarn-related deposits are connected with the Traversella plutonic body, emplaced into the Sesia-Lanzo continental unit during a magmatic event of late-alpine age. Iron mineralizations consist of magnetite and hematite magnetite skarns, as replacement products of dolomite marble horizons. The skarns record a polyphase evolution, the iron mineralization being related to alteration of previously formed skarn assemblages. Metamorphic-hosted hydrothermal siderite deposits were also exploited for iron in the past. Preliminary data on the Lago dietro la Torre siderite mineralization show that the siderite deposit is part of a composite mesothermal system developed within the Piemonte Zone, after the mesoalpine metamorphism. The wide spectrum of iron deposits typologies in the Western Alps reflects the complex iron mobilization - remobilization processes in the crust, connected with the evolution of this sector of the alpine belt.
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