The alteration mineralogy of Svartliden, Sweden

Abstract: The alteration mineralogy of Svartliden, Sweden Svartliden mine is an open pit in northern Sweden close to the Skellefte field in the “Gold Line”, which is a zone associated with gold mineralization. Svartliden gold mine was discovered by amateur geologists who were prospecting after boulders that contained low sulphide contented. This was unusual for the Skellefte field. The main rocks are meta-greywacke, metavolcanite, Revsund granite and Härnö granite. The region is subjected to several different metamorphic events. Metamorphism is when rocks are subjected to change in pressure and temperature. The aim of the study is to find out what the typical mineralogy for this area and if there is any changes of the minerals composition and chemistry. 19 samples have been collected to be studied using both optical microscopy and scanning electron microscopy from one drill core labelled SV09175. The mineralization and granite at Svartliden are both younger than the host rock. Granit intrusions at Svartliden are approximately 1.80 and 1.77Ga. The ore was formed in a high pressure and temperature deformation zone. The results from the 19 samples were interpreted to belong to three alterations zones. These are proximal, mineralized and distal. The proximal zone is a zone that is relatively close to the ore and containing the following minerals: amphibole, pyrrhotite, quartz and pyroxene. The mineralized zone is the zone where gold may be found and this contains the following minerals: amphibole, pyroxene, pyrrhotite, arsenopyrite, quartz and löllingite. The distal zone is a zone that is a bit farther away from the ore and the minerals found in this zone are: biotite, amphibole, pyroxene and biotite alteration. As mentioned the mineralization and granite intrusion are interpreted as secondary and evidence supporting the mineralization for being secondary are the presence of prehnite, diopside, chloritization of biotite and löllingite. These minerals are associated with retrograde metamorphism. Retrograde metamorphism is when rocks are subjected to decrease in pressure and temperature after have reached the highest metamorphism.