The iron formation in Stynsbo is a stratabound skarn banded magnetite ore hosted by felsic metavolcanics and amphibole-chlorite shist. The skarn assemblage consists of hedenbergite and actinolite with the pyroxene dominating in association with the massive ore. Traces of calcite can be found locally indicating almost complete skarn alteration. The mineralogical textures and petrology of Stynsbo indicate an epithermal origin.
The Silvergruvan iron formation is also a stratabound skarnbanded magnetite ore and hosted by altered felsic volcanics. The skarn assemblage is dominated by hedenbergite and actinolite. Traces of calcite are associated with magnetite and massive sulphides. The mineralogical textures and petrology of Silvergruvan indicate an epithermal origin.
Any geochemical difference between Silvergruvan and Stynsbo is best noted between the sulphide mineral assemblages. The Silvergruvan sulphide association is comprised of sphalerite, galena, pyrrhotite and pyrite together with arsenopyrite as an accessory mineral. Stynsbo is dominated by pyrrhotite and chalcopyrite, with Galenobismuthinite, native bismuth, molybdenite and electrum as accessory minerals.
The host rocks of the deposits (at both Stynsbo and Silvergruvan) show strong recrystallisation, and profound effects of retrograde metamorphism are recorded as a widespread chloritisation. Prograde and retrograde metamorphism is recorded in garnets, although thermobaromethry is impossible due to the intense chloritisation.
Arkivexemplar i Uppsala universitets arkiv