In the Pampalo mine, Hattu schist belt, the disseminated and vein type ore is hosted by a NNE-oriented sinistral shear zone located in the eastern limb of a multiple folded NNW-oriented antiform. The metabasalt in the footwall of the mineralized zone shows amphibole-chlorite-carbonate alteration.
The major mineralized zone consits of an up to 30-50 m wide intermediate meta-pyroclastic rock unit (mafic schist) with up to a few meters thick boudins of felsic feldspar-prorphyry dikes. These rocks are characterised by intense albite-potassium feldspar-biotite alteration with local patches and veinlets of quartz-tourmaline-sericite. The largely barren talc-chlorite schist (meta-komatiite) in the hanging wall also contains altered blocks of feldspar porphyry with gold mineralization and weakly altered blocks of tonalite. The talc-chlorite schist is also characterised by carbonate alteration.
Along the contacts with talc-chlorite schist, up to 10-15 cm thick amphibole rich reaction zones rim the feldspar-porphyry and tonalite blocks. Significant (>1 g/t) gold grades are restricted to the mafic schist and felspar-porphyry units indicating that albitization, Potassium feldspar alteration and biotitization are the major alteration types associated with gold deposition.