Thank you Gerda! This stamp is from the 2009 5v issue of UNESCO sites showing the Spiennes Neolithic flint mines. Were the blades at top found there?
She also sent this postcard view of inside the mines, and writes that they are, 'closed to the public until 2013' as they are 'building a totally new visitors center'. Gerda plans to visit next year, very jealous!
Thank you Cees! The left stamp on this 1968 FDC shows the mines, a flint tool, and a deer antler pick? These stamps are from a 4v 'Historical Events' set.