Lamprophyllite and barytolamprophyllite from the Tertiary Gardiner Complex, East Greenland

Lamprophyllite and barytolamprophyllite have been found in the Tertiary Gardiner Complex, East Greenland, a circular complex dominated by ultramafic cumulates with strongly alkaline rocks such as melilite rocks, carbonatites and phonolites, emplaced as two generations of radial dykes 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 association with titanian andradite (melanite), titanite, lorenzenite and pectolite. Microprobe analyses of lamprophyllite and barytolamprophyllite from Gardiner Complex show significant variations in the Sr/Ba ratios ranging from 4.40 to 0.26, the latter representing a barytolamprophyllite sample with 20.06 wt % BaO, to the authors’ knowledge the highest value so far recorded. The variation in the chemical composition 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 liniar correlation between Ba content and the asinß distance in the unit cell demonstrated.