Occurrence of epidote, pumpellyite and prehnite in Proterozoic clastics, dolerites and basalt from central Sweden.

Dolerite intrusions near the Norwegian border have produced alteration zones in contact with clastic sediments and basalt. In the clastic rocks, mainly sandstones, the assemblage is epidote + chlorite + phengite + calcite + sphene, whereas in the basic igneous rocks it is epidote + pumpellyite + quartz + or - calcite + or - prehnite + or - actinolite. The epidote is Fe-rich with Fe/(Fe + Al) = or <0.43; pumpellyite ranges from the Al-rich to the Fe-rich variety. The occasional prehnite has relatively low Fe (FeO = or <1.9%) and high Mg(MgO = or <2.3%). An allanite is also reported (Ce₂O₃ 13.7%). The formation of epidote in the sandstones is mainly related to the reaction of Ca-Fe-rich hydrothermal fluids with interstitial illite and detrital feldspars under conditions of high fO₂ and 250-300oC.-R.A.H.