Mid-Ocean Ridges host various types of hydrothermal systems including high-T black-smokers found in ultramafic rocks exhumed along slow spreading ridges. These systems are mostly described in two dimensions as their exposure on the present-day seafloor lacks the vertical dimension. One way to understand these systems at depth is to study their fossilized equivalents preserved on-land. Such observation can be done in the Platta nappe, Switzerland, where a Accepted Article This article is protected by copyright. All rights reserved Jurassic-aged mineralized system is exposed in 3D. Serpentinites host a Cu-Fe-Ni-Co-Zn-rich mineralization made of sulfides, magnetite and Fe-Ca-silicates either replacing serpentinites or within stockwork. Fe-Ca-silicates, abundant at the deepest levels, vanish in the mineralization close to the paleo-detachment. Fluids were channelized along mafic dykes and sills acting as preferential drains. Warm carbonation (~130°C) is the latest hydrothermal record. We propose that this system is an analog to the root zone of present-day serpentinite-hosted hydrothermal systems such as those found along the Mid-Atlantic Ridge.