Volcanic stratigraphy, chemical stratigraphy and alteration system of the Storliden massive sulphide deposit, Skellefte district, northern Sweden

Abstract

The Storliden massive sulphide deposits is hosted by a thick tholeiitic volcanic succession that mainly comprises andesitic and rhyolitic volcaniclastic rocks and felsic synvolcanic sills. Metamorphic recrystallization of hydrothermally altered rocks associated with the massive sulphides has produced a distinct coarse grained “spotty” mineralogy, composed of muscovite-biotite, cordierite-phlogopite, and spinel-orthoamphibole-humite assemblages, which obscures the original stratigraphy. Using a combination of physical facies mapping and immobile-element-based litho-geochemical methods, the stratigraphy in the alteration zone has been identified and correlated with the more distal least altered areas. The application of this lithogeochemical approach to several cross sections has enable interpretation of synvolcanic structures and cross cutting relationships between alteration and stratigraphy. Quantification of the alteration effects is based on the calculation of mass changes, which indicates that significant amounts of Mg, Si and Fe have been added near the orebody.