Skarnoid rocks in the western part of Pitkäranta area, on the coast of Sumerianlahti gulf, and their metallogenic potential
The aim of this thesis was to study the small area on the northern shore of the lake Ladoga, in the Pitkäranta district, on the eastern shore of the gulf Sumerianlahti. The study had two main purposes: firstly to get a theral geological and mineralogical overview of the area, and secondly, to investigate the possible metallogenesis there. A central hypothesis was formed that a skarn forming process has occurred in the area and connected to this, ore mineralisation is present. Field work was conducted in the area, during which the area was mapped and rock samples were collected. The samples were later investigated: both thin sections and polished sections were made and analysed, using the polarized light microscope, reflected light microscope and scanning electronic microscope. The mapping showed that the area has undergone to serious tectonics comprising both Archean and Proterozoic rocks. The tectonics has resulted in several faults, directed either from south-west to north-east or south-east to north-west. The mineralogical study showed that the rocks from Archean in the area are granite-gneisses, from the mantle granite-gneiss domes, and intrusive amphibolites inside the domes. The rocks from Proterozoic are mostly mica- and amphibole-schists in the lower substage of Pitkäranta suite, and amphibole-bearing quartzites and amphibolites in the upper substage of Pitkäranta suite. During the mapping process, several skarn-like lenses were discovered in the area, but the mineralogical composition of those lenses indicated, that they are skarnoids of uncertain origin, rather than actual skarns. They did consist of pyroxen, amphibole and carbonates, but lacked garnets. 51 The study of polished sections showed all together four ore minerals (pyrite, chalcopyrite, Fe-Ti oxide, titanite) and graphite. Both Fe-Ti oxide and titanite follow the rock’s own texture, and therefore are origining from the preliminary sedimentary rock. The amount of chalcopyrite was moderate and did not indicate an ore deposite either. From the results it can be concluded that the original hypothesis of skarn forming process and ore mineralisation was disproven by it, as no actual skarn was identified and no evidence of significant ore mineralisation was found.