Mineralogy, geochemistry and genesis of carbonate - silica serpentines (listwaenite) in north of Nain ophiolite (west of central Iran)

The mantle sequence serpentinized peridotites of north of Nain have been converted to carbonate- silica assemblage known as listwaenite at various temperature and pH in response to CO2 and SiO2 bearing fluids. On the basis of carbonate and silica minerals content, three types of listwaenite have been recognized: carbonate, carbonate- silica and silica listwaenites. Generaly carbonate minerals are magnesite, dolomite, ferrite-dolomite and ankerite. Calcite and other carbonate minerals are rare. Silica minerals (including quartz, chalcedony and chert) accompanied by accessory Cr-spinel, chlorite, sulfide minerals also occur in listwaenites. Silica matrix in silica listwaenite containing high amounts of Hg, Ag and As elements and shows that these elements have transported by SiO2 bearing hydrothermal fluids as arsenide complexes.