Hydrogen sulfur (H2S) emitted upon high-temperature geothermal exploitation, contributes to air pollution, due to its corrosive nature, odor and toxicity at high concentration. The best solution to mitigate H2S pollution is considered to be the sequestration of H2S back into geothermal reservoirs, through mineralization into pyrite. Laboratory experiments and on-site geo-chemical monitoring indicate that this solution is effective but there lacks physical evidence, as well as information about the spatial distribution and speed of pyrite formation. Thanks in particular to the high electrical conduction and polarization associated to pyrite in volcanic rocks, repeated geophysical measurements before and after H2S injection have the potential of providing a dynamic view of changes associated to H2S mineralization. At Nesjavellir geothermal site, H2S injection is planned for September 2020 at 200-500 m depth. Four complementary geo-electrical and electromagnetic methods are combined and repeated before and after injection: surface DCIP, WalkTEM, self-potential and borehole logging.