Magnesian Skarns from the Djurkovo Pb-Zn Deposit: Mineral Composition and Retrograde Alteration

Abstract

The studied diopside-forsterite skarn from the Djurkovo base metal deposit formed through high-temperature metasomatic processes between dolomitic marble and fluids associated with a thin pegmatite dyke. Early prograde stages involved decarbonation reactions and SiO₂ addition, resulting in diopside and forsterite deposition, followed by phlogopite crystallization. Subsequent retrograde alteration replaced primary minerals with tremolite, serpentine, talc, and chlorite, the latter indicating precipitation temperatures at ~260 °C. Mineral assemblages and textures reflect a multistage evolution involving progressive hydration and oxidation (evidenced by troilite/magnetite transformation). Trace element geochemistry reveals incorporation of Li, B, Zn, Ga, V, Cr, Cs, Y, and Nb, generally concentrated in retrograde phases. Despite the lack of economic mineralization, the geochemical signatures of the studied skarn provide insights into fluid evolution and mineral-forming processes and may assist in broader exploration within the Central Rhodopean metallogenic province.