South Mathiatis: An unusual volcanogenic sulphide deposit in the Troodos ophiolite of Cyprus

Abstract

The South Mathiatis deposit in the Troodos ophiolite of Cyprus is located within Lower Pillow Lavas in the central part of the Mitsero (Ayios Epiphanios) graben, and is characterised by elevated Zn contents, and a hydrothermal mineral assemblage in which galena is locally an important component and barite is a common gangue mineral, features which place it apart from other Cyprus-type deposits. The mineralisation is hosted within a gently dipping sheet flow-dominated sequence of lavas with common autobrecciation textures and associated hyaloclastites, and is stratigraphically controlled between lava flows, locally floored by unmineralised hyaloclastites. The environment of extrusion is interpreted as a ponded sequence, similar to the adjacent Agrokipia deposit. The Zn-rich mineralisation appears to be controlled by local structures which allowed access to the hydrothermal fluids, which then migrated laterally along lithologically favourable concordant zones. The sulphide assemblage is dominated by sphalerite together with ubiquitous pyrite; however, both chalcopyrite and galena are locally important; quartz and barite comprise the gangue-mineral assemblage. Red jasper is spatially associated with the sulphide mineralisation and displays abundant filamentous structures similar to forms identified in other VMS environments. Wall rock alteration associated with the mineralisation is weak, and this is reflected in the absence of a magnetic signature, in contrast to typical Cyprus deposits. The Zn mineralisation is also transparent to electrical methods suggesting that other similar deposits may be present in the ophiolite but remain as yet undetected.