‘T’-type mineralisation : a pseudo-epithermal style of VHMS associated gold mineralisation, Cyprus

A recent investigation of five VHMS prospects located in the Troodos ophiolite, Cyprus (Tourounjia, Alestos, Papoutsi, Kokkinovounaros and Agrokipia B), has indicated the possible presence of a pseudo-epithermal style of mineralisation. This is based on the presence of anomalous Au concentrations and hydrothermal brecciation. Short wavelength infrared (SWIR) analysis using a portable infrared mineral analyser (PIMA) was carried out to investigate the alteration mineralogy of these deposits and compare them with Cyprus-type mineralisation. Three distinct styles of alteration are present, two represent typical Cyprus-type VHMS alteration, with acidic alteration, not previously documented in Cyprus-type VHMS deposits, being the third. A process of sub-seafloor boiling, as inferred to be occurring presently in the Lau basin, most easily explains the formation and spatial link between acidic alteration and the zones of explosive hydrothermal brecciation present in the Tourounjia and Alestos deposits. It also provides a model to account for the high Au content found in the boreholes from Tourounjia.