The Formation of Magnesite Ores by Reactivation of Dunite Channels as a Key to Their Spatial Association to Chromite Ores in Ophiolites: An Example from Northern Evia, Greece

Ophiolite magnesite deposits are among the main sources of magnesite, a raw material critical for EU. The present work focuses on occurrences at Kymasi (Evia Island, Greece), in close spatial association with chromitite within same peridotite massif, and relationship between ultramafic rocks late veins. Chromitite lenses hosted dunite, contact partially serpentinized cut by Close to veins, shows evidence carbonation (forming dolomitized peridotite) brecciation serpentinite–magnesite hydraulic breccia, veins). Spinel mineral chemistry proved be crucial understanding relationships different lithologies. Spinels (Cr# 0.55–0.62) similar spinels 0.58–0.66). breccia 0.83–0.86) comparable dunite 0.79–0.84). This suggests that older weak zones, such as channels, were reactivated fluid pathways precipitation magnesite. Magnesite stable isotope composition, moreover, points towards meteoric origin oxygen, an organic source carbon. acquired data suggest following evolution rocks: (i) percolation Cr-bearing melts supra-subduction mantle wedge channels; (ii) obduction ophiolitic sequence serpentinization; (iii) uplift erosion shallow crustal level; (iv) carbon-rich waters rich depth, reactivating channels preferential zones; (v) veins partial host rock.