The Precambrian geochronology of granitic rocks from northern Sweden

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/Sr⁸⁶ ratios.of, 1535 + 30 m.y. and O.713±0.004 for the perthite granite, and 1565f:25 m.y. and 0.710±0.002 for the syenites compare favourably with the “younger” Lina-granitc 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.