Genesis of siderite ore bodies of the Gaffiona and Spiazzo mines (Scalve Valley, Southern Alps) constrained by a multi-analytical dataset.

The Gaffiona and Schilpario mines, located 4 kilometres from the city of Schilpario (Bg), are a historical siderite-hematite mines of the Scalve Valley (Italian Southern Alps). These mines are located within the so-called Barisella mine district, which was an ore district made of at least dozen siderite mines that were exploited by >60 km of galleries. The objects of this study are two galleries of the Gaffiona and Spiazzo mines, along which massive stratabound/stratiform siderite-hematite ore bodies are still outcropping hosted by the main lithologies of the mine, i.e., the clays, sandstones, and marls of the Lower Triassic Servino Formation. The main purpose of this study is constraining the fluid-rock interaction process(es) that formed the Gaffiona and Spiazzo ore bodies at the probable mineralization age. To this end, I combined field documentation and sampling of the mine lithologies with microtextural analysis (transmitted and reflected light petrography), X-ray diffraction (XRD) analyses, and geothermometric constraints determined via semi-quantitative analyses carried out with scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) of the chlorites associated with quartz from the Gaffiona wallrocks.