Markku Hagström

Deep groundwaters in the very old (Archean and Paleoproterozoic) bedrock of Finland have been under extensive studies over the past few decades. The studies have mainly been driven by the need to understand groundwater circulation related to deep geological disposal of radioactive waste. Sampling and analysis of groundwater chemistry and dissolved natural gases (e.g. methane, hydrogen, helium, nitrogen, argon) has been performed at variable depths (0 - 2500 m) from diamond drillholes by several operators. The data from various drillholes has been collected by GTK into a deep groundwater database of Finland. Only a single sampling and analysis has been made in most of the sampling locations, but on few occasions time series samples have also been taken. Certain geological formations within Finland are known to include rock types such as serpentinized ultramafic bodies and U-, Th-, and K-bearing granitic rocks, that in theory are prospective for natural hydrogen, due to associated hydrothermal alteration and radioactive decay. Various ultramafic rock successions around the country such as hydrothermally modified Outokumpu-type ophiolites, serpentinized komatiites in Archean and Paleoproterozoic greenstone belts and 2.44 Ga layered intrusion magmatism related mafic-ultramafic bodies form potential targets for the occurrence of natural  gases. Additionally, potential of iron-rich lithologies such as IOCG deposits, oxide gabbros and carbonatites have also been discussed.  In this presentation, we attempt to interpret the existing gas data, and correlate it to the geology of the sampling sites, using drill core data, hydrogeochemical and other methods. In addition, we initiate layered natural hydrogen prospectivity mapping of Finland, based on existing gas and drill core data, rock type maps, geophysical data, and new measurements, if time allows. Existing drillholes within interesting formations, previously used for mineral exploration and geological research, will be used to gain access to the subsurface.   We also assess the overall data quality and provide first insights on the overall occurrence of natural gases in the Finnish bedrock and showcase further implications on the research needed to meet the full potential of the natural and/or enhanced gas utilization in Finland.