Unravelling the root zone of ultramafic-hosted black smokers-like hydrothermalism from an alpine analogue

Hydrothermal processes are important processes at Mid-Oceanic Ridges (MOR). However, limited exposure on the seafloor often restricts complete understanding of these complex systems at depth. Fossil hydrothermal systems, such as the Marmorera/Cotschen system preserved in the Platta nappe, SE Swiss Alps, offer insights to decipher the hydrothermal architecture and processes. The serpentinite-hosted Cu-Fe-Ni-Co-Zn mineralization at Marmorera/Cotschen (MCHS) displays a close association with mafic intrusions. Mineralogical and geochemical investigation allowed to highlight an evolution from the fresh serpentinite to Fe-Ca-rich silicates to semi-massive sulphides and then to Cu-rich massive sulphide. Even if the geometry, mineralogy and sulphide geochemistry of the MCHS are close to those of ultramafic-hosted black-smokers (e.g., Rainbow) at the MOR, the lack of chimneys and the systematic association between mineralization and mafic dykes suggests that the MCHS likely corresponds to the root zone of an ultramafic-hosted black-smoker system