Isotopic composition of sulfur in the Borov Dol deposit, North Macedonia

The study of the isotopic composition of sulfur is essential for the development of genetic models of porphyry copper deposits. In order to determine the origin of metals and sulfur in the Borov Dol porphyry copper deposit, a series of research and analyses of sulfur isotopes (32S, 34S) and their isotopic ratio (δ³⁴S) were conducted. Samples were taken at the Borov Dol deposit, mainly of pyrite (from the hydrothermal temperature range of 250–350ºC), then chalcopyrite, galena, sphalerite, and chalcocite. At the Borov Dol deposit, the values show a wide range starting from –7.25‰ to +5.40‰ δ³⁴S, with an average of –0.38‰ δ³⁴S. Accordingly, the source of the sulfur is magmatic, associated with the deep parts of the Earth's crust or with the boundary zone between the continental crust and the upper mantle, with intrusive fractionation and partial enrichment with the light sulfur isotope, which is reflected in the negative value in the higher levels of the deposit, or in the slight enrichment of the heavy sulfur isotope, which is reflected in the positive value in the lower levels of the deposit. The sulfide parageneses in the Borov Dol porphyry system were most likely deposited from oxidized hydrothermal ore-bearing solutions, whereby there is no equilibrium in the system during the crystallization of the early-stage paragenesis. The equilibrium in the system is established during the crystallization of the paragenesis in the middle and late stages.