The Skellefte district in northern Sweden is a 1.9 Ga, extensively mineralized, mainly felsic, submarine volcanic belt. The geological evolution of the district includes the formation of numerous shear zones truncating the area. In the Renström and Petiknäs North mines, located in the central part of the Skellefte district, shearing has resulted in the development of geological deformation structures that are commonly used as shear-sense indicators. Indicators are few and ambiguous in the Petiknäs North mine, but in the Renström mine they are distinct and indicate opposite movements on the two observed shear zones. A west side up movement in the western shear zone and an east side up movement in the eastern shear zone may indicate the formation of a depressed block on a branching dip-slip system. Subvertical movement indicated by steep lineations confirms this model, and reverse movements of the shear zones, indicated by s-c fabric, suggest that this formation formed during local transpression. Metamorphic and deformational events, as well as intense alteration, have influenced the mineralogical composition of rocks in these areas. Geochemical analyses and several thin sections of samples from the mines indicate rock compositions ranging from rhyolite to basalt, with retrograde mineral assemblages corresponding with low-pressure, greenschist to lower amphibolite facies metamorphism. The mineral assemblages observed, together with structural observations, indicate retrograde conditions during shearing. This suggest that shearing took place after the peak metamorphism. A crenulation cleavage produced by a second deformation phase in the areas, overprints the shear foliation in the Petiknäs North mine, indicating that shearing took place before the second deformation phase. In the Renström mine, the shear foliation is not overprinted by a crenulation cleavage, indicating that shearing in this area took place after the second deformation phase.
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