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

Published in Solid earth. 2020, vol. 11, no. 1, p. 1-21
Abstract We investigate the occurrence and chemistry of magmatic sulfides and their chalcophile metal cargo behaviour during the evolution of compositionally different magmas from diverse geodynamic settings both in mineralised and barren systems. The investigated areas are the fol- lowing: (a) the Miocene Konya magmatic province (hosting the Dog ̆anbey Cu–Mo porphyry and Inlice Au epithermal deposits, representing post-subduction) and (b) the Miocene Usak basin (Elmadag, Itecektepe, and Beydagi volcanoes, the latter associated with the Kisladag ̆ Au porphyry in western Turkey, representing post-subduction). For com- parison we also investigate (c) the barren intraplate Plio-Quaternary Kula volcanic field west of Usak. Finally, we discuss and compare all the above areas with the already studied (d) Quaternary Ecuadorian volcanic arc (host to the Miocene Llurimagua Cu–Mo and Cascabel Cu–Au porphyry deposits, representing subduction). The volcanism of the newly studied areas ranges from basalts to andesites–dacites and from high-K calc-alkaline to shoshonitic series. Multiphase magmatic sulfides occur in different amounts in rocks of all investigated areas, and, based on textural and compositional differences, they can be classified into different types according to their crystallisation at different stages of magma evolution (early versus late saturation). Our results suggest that independently of the magma composition, geodynamic set- ting, and association with an ore deposit, sulfide saturation occurred in all investigated magmatic systems. Those systems present similar initial metal contents of the magmas. However, not all studied areas present all sulfide types, and the sulfide composition depends on the nature of the host mineral. A decrease in the sulfide Ni/Cu (a proxy for the monosulfide solid solution (mss) to intermediate solid solution (iss) ratio) is noted with magmatic evolution. At an early stage, Ni-richer, Cu-poorer sulfides are hosted by early crys- tallising minerals, e.g. olivine–pyroxene, whereas, at a later stage, Cu-rich sulfides are hosted by magnetite. The most common sulfide type in the early saturation stage is com- posed of a Cu-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 late stage, 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.
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Research groups Isotope Geochemistry, Geochronology and Thermochronology
Mineral Resources and Geofluids
(ISO format)
GEORGATOU, Ariadni Afroditi, CHIARADIA, Massimo. Magmatic sulfides in high-potassium calc-alkaline to shoshonitic and alkaline rocks. In: Solid Earth, 2020, vol. 11, n° 1, p. 1-21. doi: 10.5194/se-11-1-2020 https://archive-ouverte.unige.ch/unige:128310

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Deposited on : 2020-01-07

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