Quantifying the release of base metals from source rocks for volcanogenic massive sulfide deposits: effects of protolith composition and alteration mineralogy

This detailed study of the release of base metals during hydrothermal alteration from the sheeted dike complex of the Troodos ophiolite, Cyprus, aims to better understand the source of these elements in ore-forming hydrothermal fluids. The study area, similar to 10 km(2) between the villages of Spilia and Kannavia, has previously been recognized as a region in which the abundance of epidote in the altered sheeted dikes is higher than average - a so-called epidosite zone. The originally basaltic to andesitic sheeted dikes have been variably altered, but the secondary mineralogy is independent of the protolith composition. Four alteration fades have been identified in the epidosite zone. With progressively increasing modal epidote, decreasing modal amphibole, and decreasing bulk-rock Mg these are: (i) diabase, which is composed of amphibole + chlorite + albitic plagioclase +/- epidote +/- quartz, (ii) transitional diabase-epidosite, (iii) intermediate epidosite, and (iv) rare (