Rb-Sr isotope data arc presented for nine whole-rock samples of perthite granite from Masugnsbyn - and six whole-rock samples of Sjaunjatuottar syenite. The ages and initial Sr87/Sr86ratios of. 1535 ± 30 m.y. and 0.713 ± 0.004 for the perthite granite, and 1565 ± 25 m.y. and 0.710 ± 0.002 for the syenites compare favourably with the “younger” Lina-granite age of 1565 ± 35. m.y. and initial ratio of 0.712 ± 0.003 (Welin et al. 1971). The ages are indistinguishable within the limits of precision of the age measurements. A discussion of the relationship between the various granitic rocks and their connection with the skarn iron ores is given. Analyses of the interlaboratory standards NBS K-feldspar 70 a and GSP-1 are presented in the Appendix.