Magmatic sulfides in high-potassium calc-alkaline to shoshonitic and alkaline rocks

摘要

We investigate the occurrence and chemistry of magmaticsulfides and their chalcophile metal cargo behaviour during the evolution ofcompositionally different magmas from diverse geodynamic settings both inmineralised and barren systems. The investigated areas are the following: (a)?the MioceneKonya magmatic province (hosting the Do?anbey Cu–Mo porphyry and InliceAu epithermal deposits, representing post-subduction) and (b)?the Miocene Usak basin(Elmadag, Itecektepe, and Beydagi volcanoes, the latter associated with theKi?lada? Au porphyry in western Turkey, representing post-subduction). For comparison wealso investigate (c)?the barren intraplate Plio-Quaternary Kula volcanicfield west of Usak. Finally, we discuss and compare all the above areaswith the already studied (d)?Quaternary Ecuadorian volcanic arc (host to theMiocene Llurimagua Cu–Mo and Cascabel Cu–Au porphyry deposits, representing subduction).The volcanism of the newly studied areas ranges from basalts toandesites–dacites and from high-K calc-alkaline to shoshonitic series.Multiphase magmatic sulfides occur in different amounts in rocks of allinvestigated areas, and, based on textural and compositional differences,they can be classified into different types according to theircrystallisation at different stages of magma evolution (early versus latesaturation). Our results suggest that independently of the magmacomposition, geodynamic setting, and association with an ore deposit, sulfidesaturation occurred in all investigated magmatic systems. Those systemspresent similar initial metal contents of the magmas. However, not allstudied areas present all sulfide types, and the sulfide composition dependson the nature of the host mineral. A decrease in the sulfide Ni∕Cu (a proxyfor the monosulfide solid solution (mss) to intermediate solid solution (iss) ratio) isnoted with magmatic evolution. At an early stage, Ni-richer, Cu-poorersulfides are hosted by early crystallising minerals, e.g. olivine–pyroxene,whereas, at a later stage, Cu-rich sulfides are hosted by magnetite. Themost common sulfide type in the early saturation stage is composed of aCu-poor, Ni-rich (pyrrhotite mss) phase and one to two Cu-rich (cubanite,chalcopyrite iss) phases, making up ～84 and ～16?area % of the sulfide, respectively. Sulfides resulting from the latestage, consisting of Cu-rich phases (chalcopyrite, bornite, digenite iss),are hosted exclusively by magnetite and are found only in evolved rocks(andesites and dacites) of magmatic provinces associated with porphyry Cu(Konya and Ecuador) and porphyry Au (Beydagi) deposits.