Geochemistry of skarn and porphyry deposits in relation to epithermal mineralization in the Arasbaran metallogenic zone, NE Tabriz, Iran

Abstract

The Arasbaran metallogenic zone in northern Iran is part of the Alborz–Azerbaijan magmatic zone, which developed along the southern margin of Eurasia during the Early Mesozoic–Late Cenozoic. This region hosts precious and base metal mineralization, including porphyry, skarn, and epithermal copper, molybdenum, and gold deposits. Rare earth element variations across all the deposits are similar, indicating a similar source for these elements. The north-west trending belt comprising the Nabijan to the Sonajil deposits consistently shows chiefly alkaline conditions of formation. Fluid inclusion studies indicate that both high and low temperature hydrothermal fluids participated in the formation of all of the deposits. The mineralization age decreases from north to south and east to west and, although metal zonation is complex, the Cu–Au association post-dated the Cu–Mo mineralization reflecting that the ore fluid evolved in terms of both cooling and chemical changes due to fluid–fluid and fluid–rock interactions. In this region most deposits record a concentric zonation, with the centres preserving porphyry and skarn deposits and deposits becoming progressively epithermal toward the outer parts of the mineralizing system. According to this, the mineralization age decreases from the porphyry and skarn deposits to the epithermal deposits. The homogenization temperature and salinity both decrease from the centre to the outer zone. The pattern of homogenization temperature zonation, which is concordant with salinity zonation, suggests that fluids migrated up-dip and towards the margins of the zonation system.