Open this photo in gallery: Giant pillars that hold up the roof of the Tanco underground mine in Manitoba contain one of the world’s last remaining minable deposits of cesium. Beijing-based Sinomine Resource Group is proposing partially draining a lake above, and building an open pit mine to extract the resource.Handout About 180 kilometres from Winnipeg, below Bernic Lake in eastern Manitoba, sits one of the world’s last remaining minable deposits of cesium. The soft silvery gold-coloured metal is housed in otherworldly giant pillars that hold up the roof of the Tanco underground mine. For stability reasons, it can’t be…