Fluid inclusions in sphalerite at Laisvall, Sweden

Abstract

Sphalerite from the upper sandstone ore of the Laisvall sandstone lead–zinc deposit contains two-phase, primary, pseudosecondary and secondary inclusions. The inclusions homogenize at a modal value of 155°C and melt at −22°C. The secondary inclusions, which include necked-down types, tend to homogenize at +200°C and melt at −27°C. A fourth type of inclusion has been observed which contains a single dark phase, probably hydrocarbons. The melting temperatures of the primary inclusions indicate a strong Na-Cl brine with 24 equivalent wt.-% NaCl. The freezing temperatures of −60 to −90°C indicate that the trapped fluid contained calcium. These preliminary fluid-inclusion data suggest that the Laisvall sphalerite was precipitated at around 155°C from a concentrated Na-Ca-Cl brine.