Magmatic evolution of the mineralized Stiavnica volcano (Central Slovakia): Evidence from thermobarometry, melt inclusions, and sulfide inclusions

摘要

The factors that control the fertility (e.g. capacity to form an ore deposits) of a magmatic system are still a matter of debate, requiring more studies on the evolution of ore-related magmas. This study presents a detailed reconstruction of the magmatic system forming the Stiavnica volcano, the biggest mineralized center of the Western Carpathians (Central Slovakia). The Stiavnica volcano represents an interesting study object because the magmatic system was sulfide-saturated during its entire evolution, and porphyry systems with contrasting Cu/Au ratio are present in the same volcano. This situation allows to study the impact of magmatic sulfide saturation on the Cu/Au ratio of porphyry deposits. Pressure, temperature, and the compositional evolution of pre-, syn-, and post-mineralization magmas were reconstructed based on the chemical composition of phenocrysts and hosted silicate melt inclusions and sulfide inclusions. Dominantly andesitic magmas forming the volcanic and intrusive rocks of the volcano were sourced from an upper crustal (similar to 1 to similar to 3 kbar) reservoir in which most phenoaysts grew from a sulfide-saturated dacitic to rhyolitic melt. This upper crustal magmatic reservoir was active during 3 My, and most ore-deposits, including Cu-Au porphyries, formed during cooling periods where the residual melt reached fluid saturation. In contrast, the Au-only porphyry deposit formed alter shallow emplacement (1 km) of a hot magma that was produced by mixing between a magma derived from a lower crustal (8 kbar) reservoir and one from the upper crustal reservoir. Inclusions of monosulfide solid solution were found in phenoaysts crystallizing over a large range of temperature and pressure in ore-related and barren magmas suggesting that sulfide saturation doesn't play a critical role on the fertility of the magmatic system. Finally, this study reveals that composition of the magmatic sulfides does not play a direct role in the Cu/Au ratio of the formed porphyry deposits. (C) 2020 Elsevier B.V. All rights reserved.