The Sb–As Lojane Deposit (Republic of North Macedonia): Types of Ores and Conditions of Their Occurrence and Geochemical Features

This article presents the results of comprehensive studies of Sb–As ores from the Lojane deposit, located in the northeastern part of the Republic of North Macedonia, near the border with Serbia. Five types of Sb–As ores are distinguished in the deposit: brecciated realgar orpiment ores; realgar breccias; brecciated antimonite ores; massive, almost monomineral realgar ores; and realgar–antimonite nested ores. The ores are characterized not only by the unusual paragenesis of minerals of nickel, arsenic, and antimony, but also by a very close fusion of antimonite, realgar, and collomorphic quartz. A wide range of elements in ores (As, Sb, Cr, Ti, Mn, Ni, Mo, Co, Ag, Tl, U, etc.) is likely due to the combination of mineralization from multiple distinct parageneses that occurred at different times. Thermometric studies of fluid inclusions in quartz indicate a temperature range of T_hom varying from 180 to 220°C, with an average value of 201°C. Studies of the isotopic composition of sulfur in antimonite and realgar showed fairly narrow intervals of δ³⁴S values from –5.19 to –0.26‰ and from –4.80 to 1.92, respectively, indicating an endogenous sulfur source. Based on these findings, the Lojane deposit can be attributed to the epithermal class.