Different Localities of Potassium-Rich Silica-Undersaturated Igneous Rocks and Their Silica-Rich Variants - Origin of Potassium-rich Silica-deficient Igneous Rocks - page 188

Fig. 4.29 Localities of Kimberlite and Lamproites Dykes in the Holesteinborg District, CentraWest
Greenland also shown are additional, and probably related, dykes (Escher and Watterson 1973)

The lamproite dykes are usually less than 1 m wide, sometimes zoned and are
usually intruded in an en echelon manner. The lamproites often include country
rocks xenoliths, which exhibit minor reaction rims. Modal analysis of some
pseudoleucite-bearing lamproites are given in Table 4.18 .
The olivines have Fo content varying between 75 and 93 %. Leucite are
sometimes 5 mm across and are basically pseudoleucites (K-feldspar-nephiline
intergrowth) clinopyroxenes are usually diopsidic, whereas amphiboles are K-
richterites (x = dark greenish brown or pale green, z = darkish green). Pholophites
are TiO 2 rich. The TiO 2 contents varies between 6 and 8 wt%. The pleochroic
scheme is as follows: X = pale yellowish brown, Y = Z = orange brown.
Alkali feldspar occurring in the groundmass are K-feldspar with up to 3.84 wt%
FeO. Holesteinberg lamproites sometimes contain priderites. Chemical analyses of
the lamproites are given in Table 4.19 .
The Rb-Sr isotopic age determination of phlogophite concentrates suggest an
age of 1227 ± 12 Ma. The age of dyes is 587 ± 24 Ma this suggest that lamproites