THE 79 AD VESUVIUS MAGMA CHAMBER - A SEM-EDS STUDY OF DAUGHTER MINERALS IN HYPERSALINE FLUID INCLUSIONS FROM COGNATE SYENITES

Daughter minerals in multiphase hypersaline fluid inclusions in sanidi ne crystals were investigated through SEM-EDS analyses. The samples st udied are cognate xenoliths of feldspatoid-bearing syenites ejected in 79AD eruption of Vesuvius, representing the magmatic mush crystallize d at the wall of the magma chamber. The hypersaline fluid inclusions i ndicate that an immiscible fluid phase exsolved from the melt. This st udy allowed to identify two daughter mineral associations: a chlorides -bearing association and a fluorite-bearing association. It is propose d that the two associations reflect the chemical variations of the flu id phase during exsolution, in response to the different melt/fluid pa rtition coefficients for chlorine and fluorine. The presence of tungst en in chlorides-bearing fluid inclusions stresses the importance of ch lorides-bearing brines in the transport of ore metals.