Determining host rock protolith in an altered VMS deposit in the Rävliden area, North Sweden

Abstract: The Rävliden mine is located in the Skellefte district in northern Sweden. In close proximity lays the Kristineberg deposit containing zinc, copper and lead ore which has been mined since the 1940’s. The district is rich in massive sulphide deposits and the mining history can be dated back to the 1920’s. New deposits are still being discovered and understanding the origin of the ores and their formation processes are more and more important when looking for new orebodies. The area itself is ca 1.8 Ga and most rocks have undergone hydrothermal alteration and been metamorphosed. The main purpose of this study was to determine the host rock protolith and the method chosen was developed by MacLean and Barrett (2005) in which immobile element ratios are used for determining the chemostratigraphy.     Two main alteration types are recognized and two minor ones. The dominant ones being sericite and chlorite alteration. The boreholes also display some silicification and carbonate alteration. While the TAS-diagram shows that most samples are either dacitic or rhyolitic with a small group of andesitic rocks. Further usage of both the Alteration box plot and various immobile element plots show that the amount of dacitic samples are low. Instead rhyolite is the predominant rock type with four subgroups, there is also one dacite group and one probable andesitic intrusion. The mineralisation is low so it was not possible to correlate alteration type to ore occurrence, nor was it possible to see any correlation between protolith and mineralisation. The study did determine the protolith for the boreholes and the data and therefore the method can be used for exploration in other areas.