Occurrence of the rare minerals in porphyry Cu deposits: Evidences from the potassic alteration of Sarkuh porphyry deposit

The Sarkuh porphyry Cu deposit located in the Urumieh – Dokhtar Magmatic Belt (UDMB), is associated with the emplacement of Miocene intrusions mainly containing granite – granodiorite within Eocene units including tuff, andesite, basaltic andesite, and pyroclastic breccia. Potassic alteration of the deposit (dominated by magnetite, secondary and re-equilibrated biotites as well as anhydrite) is well extended. In this study EDX spectra of accessory minerals within potassic alteration was assessed to trace the occurrence of rare minerals. Additionally, EMPA results of magnetite paragenesis were linked to physicochemical attributes of rare minerals occurrences. Results indicate that unusual occurrence of Ce-La rich epidotes with REE-enriched monazites and Ce-bearing titanites are accompanied with apatite, anhydrite, hydrothermal biotite, quartz, and magnetite assemblages in the potassic alteration. Magnetite composition implies that early-stages high temperature magmatic – hydrothermal fluids (>500 °C) with low rates of fluid – rock interaction were contributed in the magnetite crystallization. Commonly, these magnetites are accompanied by hematite and anhydrite providing insights into the very high oxygen fugacity conditions (near magnetite - hematite buffers ~ ΔFMQ+4). Considering the chemistry of magnetite paragenesis, it seems that the occurrence of rare minerals are mainly associated pre-ore stages in the potassic alteration