Impact of sulfide saturation events on the fertility of porphyry-related magmatic system

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Porphyry Cu-(Au-Mo) deposits are fossils magmatic-hydrothermal systems that provide 75% of the copper vital to our society and a significant portion of key other metals (e.g., Mo, Au, Re). Previous studies have demonstrated that porphyry Cu-(Au-Mo) deposits are formed by large volume of hydrothermal fluids outgassed from a cyclically rejuvenated upper crustal magma reservoir composed of intermediate to felsic magmas derived from the differentiation of primitive arc basalts in the lower crust. Processes affecting ore ingredients (i.e., Metals, H2O, S, Cl) during the entire transcrustal evolution of a magmatic system strongly influence its capacity to form an economic deposit and control the metal signatures of the mineralized rocks (i.e., Cu/Au ratio). Magmatic sulfide saturation events occurring during the transcrustal evolution of a magmatic system have been suggested to be one of the most important factors controlling the fertility of a magmatic system (i.e., capacity to form an economic porphyry Cu-(Au-Mo) deposits). Crystallization of magmatic sulfides rich in chalcophile metals (Cu, Au, PGEs) and sulfur strongly depletes the residual melt in these elements. Magmatic sulfides can be either fractionated out of the system and in this way reducing the fertility of the magmatic system or they can act as a temporary storage medium and be latter remobilized by hydrothermal magmatic fluids. Therefore, magmatic sulfide saturation events are currently either view as a detrimental, as a neutral, or as a positive process on the fertility of a magmatic system. This lack of consensus hampered the development of new efficient exploration methods for porphyry Cu-(Au-Mo) deposits. This debate is sourced from the difficulty to time sulfide and fluid saturation events during the transcrustal evolution of a magmatic system. The current project will address this knowledge gap by the study of two different magmatic-hydrothermal systems belonging to the Menderes Massif (western Turkey) and to the Stikinia Terrane (British Columbia, Canada). In these two magmatic systems, magmatic sulfide saturation events will be identified and characterized by the study of magmatic sulfide inclusions. These inclusions will be chemically characterized by LA-ICP-MS and sulfide saturation events will be timed using the chemical composition (i) of the phenocrysts hosting these inclusions and (ii) that of co-trapped silicate melt inclusions. Fluid saturation events will be tracked using the sulfur isotopic composition of the magmatic sulfide inclusions, as their sulfur isotopic signature is directly linked to the quantity of fluid exsolved from the magmatic system. This approach never applied to magmatic systems related to porphyry Cu-(Au-Mo) deposits will allow the unambiguous evaluation of the impact of sulfide saturation events on the fertility of magmatic systems and on the metal signatures of formed porphyry Cu-(Au-Mo) deposits.