Postmagmatic evolution of platinum-group and base-metal mineral assemblages in Palaeozoic ophiolitic chromitites from the Dobromirtsi massif, Rhodope Mountains (SE Bulgaria)

The distribution of platinum-group and base-metal minerals in the metamorphosed ophiolitic chromitites of the Dobromirtsi ultramafic massif (Rhodope Mountains, SE Bulgaria) show that in the altered zones of chromites and in the silicate matrix between chromite grains, there is an increase in the proportion of Ni-rich, S-poor sulphides and As-rich minerals, relative to the unaltered zones of the chromite. This distribution is interpreted in terms of postmagmatic evolution of the chromitites: Ocean-floor metamorphism followed by hydrothermal alteration, associated with greenschist-amphibolite facies regional metamorphism causing S leaching followed by supply of additional S, As and minor Sb and Sn.