**4. Results**

#### *4.1. Serpentinite Substratum*

Serpentinized harzburgites are composed mainly by lizardite (>95%), chlorite, magnetite, and only minor relicts of Mg-Al chromite (Figure 4a). Serpentine is present as mesh-textured matrix embedding bastite porphyroclasts with local chrysotile veins and can be intergrown with clinochlore. Primary Mg-Al chromites range in size from few microns up to ~1 mm. They show the typical lobate habit of spinels in mantle rocks and are characterized by rims of Fe-chromite. Along the Isabella adit, several cataclastic zones, plunging at a subvertical to medium angle and oriented like the main mineralized cataclastic zone, produced pervasive brecciation of serpentinized harzburgites (Figure 4b). Breccias are clast supported, with angular and subangular clasts ranging in size from submillimetric to pluri-decimetric. The matrix is constituted of fine-grained serpentine and andraditic garnet (identified by XRD). Small crystals of andradite (~2 to 3 μm in diameter) are observed both in matrix and clasts. They are anhedral and form interstitial aggregates (Figure 5).

The studied samples do not show evidence of pervasive Mg carbonation at the microscopic scale or carbonate precipitation. Coatings and crusts of hydrous Mg carbonates and Mg-clay have only been observed on the exposed rock surfaces in the mine adits.

**Figure 4.** Thin sections of serpentinite sampled along the mine adits: (**a**) Serpentinized harzburgites and (**b**) serpentinite breccias.

**Figure 5.** SEM-EDS image of interstitial andradite garnet in the matrix of serpentinite breccia.
