Geology, alteration and lithogeochemistry of the Paleoproterozoic Korpela VMS occurrence in Eastern Finland

AbstractKorpela is a Cu-Zn-Au VMS occurrence hosted by bimodal, sub-alkaline, volcanic and volcaniclastic rocks. It is part of a Svecofennian supracrustal sequence 1.93–1.91 Ga in age. In this study, lithogeochemical evidence is used to assess the VMS-prospectivity in the Korpela area to serve regional-scale exploration and provide detailed information on chemostratigraphy and hydrothermal alteration within the Korpela succession. Korpela is understood to have been formed in an evolved arc rift, possibly in a continental back-arc environment. The felsic rocks of the sequence are FII-FIIIa, HFSE-enriched (A-type) rhyolites overlain and, locally cross-cut, by mafic rocks with MORB/BABB signatures and felsic synvolcanic porphyry dykes. In the vicinity of Korpela, tonalitic subvolcanic intrusions intrude the supracrustal rocks which share textures common with local shallow VMS-related intrusion complexes. The Korpela area comprises a volcanic succession where primary volcanic textures are completely destroyed by multiple deformation, metamorphism and alteration. Using detailed volcanic chemostratigraphy established from downhole geochemical profiles, 12 chemostratigraphic units and 21 chemical rock types could be identified ranging from basalt to rhyolite. Several metamorphic mineral assemblages were identified which were further classified into six alteration types, i.e. Mg-Fe-S, K-Al-Fe-(± S), K-Al-Mg-Fe-S, K, Si-K-Ca-(± S) and Ca-(± Na), using a combination of mineralogy and geochemistry. The chemostratigraphy and alteration studies help in understanding the volcanic stratigraphy and in recognising a potential VMS-related alteration.