LAMPROPHYLLITE AND BARYTOLAMPROPHYLLITE FROM THE TERTIARY GARDINER COMPLEX, EAST GREENLAND

Lamprophyllite and barytolamprophyllite have been found in the Tertiar y Gardiner Complex, East Greenland, a circular complex dominated by ul tramafic cumulates with strongly alkaline rocks such as melilite rocks , carbonatites and phonolites, emplaced as two generations of radial d ykes and ring dykes. Lamprophyllite and barytolamprophyllite are late phases in pegmatitic, natrolite-rich vugs in ijolites belonging to the second dyke generation and in related peralkaline veins and dykelets. In addition to natrolite the lamprophyllites are typically found in a ssociation with titanian andradite (melanite), titanite, lorenzenite a nd pectolite. Microprobe analyses of lamprophyllite and barytolamproph yllite from Gardiner Complex show significant variations in the Sr/Ba ratios ranging from 4.40 to 0.26, the latter representing a barytolamp rophyllite sample with 20.06 wt % BaO, to the authors' knowledge the h ighest value so far recorded. The variation in the chemical compositio n is concentrated in the M1 site accomodating the large ions Sr, Ba, K and Na. Refined X-ray powder diffraction data is presented and a lini ar correlation between Ba content and the asinbeta distance in the uni t cell demonstrated.