On the origin of the PGE mineralization in the Eatsite porphyry Cu Au deposit, Bulgaria: comparison with the Baula Nuasahi complex, India, and other alkaline PGE-rich porphyries

International audienceThe Elatsite porphyry-copper deposit contains platinum-group minerals associated with base-metal sulfides, i.e., merenskyite, moncheite, palladoarsenide and an undetermined Pd–Ag–Te–Bi mineral, all in a magnetite – bornite – chalcopyrite assemblage. Other minerals such as linnaeite, carrollite, siegenite, rammelsbergite, which are uncommon in typical porphyry-copper deposits, indicate a mantle derivation for the specific PGE–Co–Ni episode of mineralization. The Pt–Pd-rich facies is characterized by extremely low Os, Ir and Ru contents (respectively <3.0, <0.6 and <1.0 ppb), with up to 349 ppb Pt and 3440 ppb Pd. Mineralization results either from (1) multi-stage events involving a preconcentration of the PGE in magmatic disseminated (Ni–Cu–Co) sulfides related to a mantle-derived magmatic event, with subsequent selective hydrothermal remobilization, or (more probably) from (2) particular conditions in the partial melting of the mantle and magmatic evolution that rendered the precious metals available in the magma, along with a specific evolution that prevented the early formation of the sulfides whilst the PGE (mainly Pd) were concentrated in the hydrothermal fluids. This PGE–Co–Ni episode is a very specific event in the main mineralizing process giving rise to the massive deposition of the Cu-porphyry system. The characteristics of the PGE mineralization deviate from those of a purely hydrothermal PGE mineralization in a mafic environment, as exemplified by the Baula–Nuasahi mineralization (India), in that they tend to converge toward (and present striking similarities with) the PGE mineralization in alkaline porphyry deposits, such as are found in British ColumbiaLe porphyre cuprifère d’Elatsite, en Bulgarie, renferme une minéralisation en éléments du groupe du platine (EGP) associée à une paragenèse à magnétite – bornite – chalcopyrite. Les EPG sont sous la forme de merenskyite, monchéite, palladoarsenide et d’un minéral indéterminé de Pd–Ag–Te–Bi. D’autres espèces, telles linnéite, carrollite, siegenite, rammelsbergite, inhabituelles dans les porphyres cuprifères, indiquent une source mantellique pour cet épisode spécifique à EGP–Co–Ni. La minéralisation se caractérise par des teneurs très basses en Os, Ir et Ru (respectivement <3.0, <0.6 et