Exploration for geologically occurring hydrogen is taking off worldwide.
In May, FDE announced a serendipitous discovery of hydrogen whilst drilling for coalbed methane in the Lorraine region in France. In Nebraska, USA, Hyterra Ltd drilled the world’s first wildcat well specifically targeting H2 and is currently flow testing. The company also obtained an exploration licence in neighbouring Kansas.
Other locations of interest are in Australia and Mali among others. What all these localities have in common is that hydrogen occurs as a free gas in the subsurface, similar to a hydrocarbon reservoir. The H2 is thought to result from water-rock interactions such as serpentinisation of iron-rich rocks, or otherwise mantle degassing.
However, a completely different hydrogen play has been discovered in the Sasketchawan province of Canada, in association with the Cigar Lake Uranium deposit. The 1.4 Gyr orebody is situated in the Athabasca Basin, on the boundary between the Aphebian basement and unconformable overlying Paleoproterozoic sandstones.
Hydrogen formed via radiolysis of pore water: Uranium decay emits radiation that breaks water molecules apart which results in H2 as one of the end members. The H2 subsequently became trapped in the hydrothermal alteration halo that is present around the orebody. The alteration zone is made up of clay, extending up to 30m away from the ore surface. Different clay minerals formed in the sandstone above the ore, mainly kaolinite and illite, while the argilitized basement has a high concentration of chlorite.
Research from Laurent Truche and co-workers showed H2 is preferentially adsorbed to chlorite and therefore concentrated in both the ore zone itself as well as the clay halo below the orebody. Chlorite adsorption is an efficient H2 trapping mechanism, an estimated 476 tons of H2 is believed to be trapped within the deposit. The hydrogen can be released from the clay surfaces via thermal desorption, starting at temperatures of 80°C.
However, for now the sole focus at Cigar Lake is mining of uranium.
