Epidosites of the Troodos Ophiolite: A direct link between alteration of dykes and release of base metals into ore-forming hydrothermal systems?

The role of source rocks in the formation of Cyprus-type Volcanogenic Massive Sulphide (VMS) deposits is not fully understood. In this paper we suggest that the formation of epidosites – episode + quartz ± chlorite ± titanite rocks commonly found at the base of ophiolitic sheeted dyke complexes – has the potential to release cobalt and zinc into active hydrothermal ore forming systems. New geochemical and mineralogical data from the sheeted dyke complex of the Troodos ophiolite indicates that progressive alteration of greenschist facies altered metabasalts to end-member epidosites results in decreasing base metal concentrations (Zn, Co) in individual dyke units. We believe this relationship provides the clearest evidence that epidosites act as source rocks for VMS deposits, and, moreover, the process of epidositisation provides a method of mobilizing metals such as Co and Ni that are considered generally immobile under typical greenschist grade alteration.