ON THE ORIGIN OF THE PGE MINERALIZATION IN THE ELATSITE PORPHYRY Cu Au DEPOSIT, BULGARIA: COMPARISON WITH THE BAULA NUASAHI COMPLEX, INDIA, AND OTHER ALKALINE PGE-RICH PORPHYRIES

Abstract

The 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 Columbia. sOmmAire Le 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 <1.0 ppb) dans les faciès riches en Pt et Pd, avec jusqu'à 349 ppb Pt et 3440 ppb Pd. Elle résulte soit (1) d'un événement polyphasé impliquant une préconcentration des EGP dans des sulfures de Ni-Cu-Co disséminés, liés à un épisode magmatique d'origine mantellique, suivi d'une remobilisation hydrothermale sélective, ou, plus probablement, (2) de conditions particulières de fusion partielle du manteau et dans l'évolution magmatique, qui font que les métaux précieux restent disponibles dans le magma, et qui empêchent la cristallisation précoce des sulfures, alors que les EGP (principalement Pd) vont se concentrer dans les fluides hydrothermaux. Cet épisode à EGP-Co-Ni correspond à un événement très spécifique dans le processus de minéralisation qui mène au dépôt mas...

Critical Factors Controlling Pd and Pt Potential in Porphyry Cu–Au Deposits: Evidence from the Balkan Peninsula

“…A salient feature is the unusually high precious metal content, recorded in high Cu-grade ores (magnetite-chalcopyrite-bornite) from the level 1310 South, which are similar to those analyzed by previous authors [18,19]; Table 3. In addition, the elevated Ag (up to 220 ppm), Bi (up to 290 ppm), Se (up to 800 ppm) contents, and the common occurrence of Au-Ag-Te-Se minerals in the magnetite-bornite-chalcopyrite ore assemblage [18,19] may be of genetic significance.…”

“…Palladium, Pt and Au dominate in the mt-bn-cp assemblage, which is associated with potassic-propylitic alteration, while the pyrite-chalcopyrite assemblage is linked to phyllic and argillic alteration [18,19]. The average 890 ppb Au, 40 ppb Pd and 16 ppb Pt contents are higher in ore samples dominated by magnetite, bornite and chalcopyrite, compared to 460 ppb Au, 14 ppb Pd and 4 ppb Pt in samples consisting mainly of chalcopyrite and pyrite [16][17][18][19].…”

“…The average 890 ppb Au, 40 ppb Pd and 16 ppb Pt contents are higher in ore samples dominated by magnetite, bornite and chalcopyrite, compared to 460 ppb Au, 14 ppb Pd and 4 ppb Pt in samples consisting mainly of chalcopyrite and pyrite [16][17][18][19].…”

“…In addition, the elevated Ag (up to 220 ppm), Bi (up to 290 ppm), Se (up to 800 ppm) contents, and the common occurrence of Au-Ag-Te-Se minerals in the magnetite-bornite-chalcopyrite ore assemblage [18,19] may be of genetic significance.…”

“…These precious metals belong to the platinum-group elements (Os, Ir, Ru, Rh, Pd and Pt or platinum-group elements (PGEs)), which are the most valuable elements, of strategic importance, due to their growing use in advanced technologies (medicine, electronics) and automobile catalyst converters. Although they are traditionally associated with mafic-ultramafic complexes, significant Pd and Pt contents were described in certain alkaline porphyry deposits, such as the Cordillera of British Columbia (Copper Mountain, Galore Creek), Allard Stock, La Plana Mountains and Copper King Mine in USA [12,13], Skouries porphyry deposit, Greece [14,15], Elatsite, Bulgaria [16][17][18][19], Santo Tomas II in the Philippines [20,21] and elsewhere ( Figure 1). …”