Not the first time that has happened. In 1971 myself and another geologist were in the top adit examining post-emplacement shearing in a quartz vein. The floor appeared solid. I tossed a small piece of quartz towards the side of the adit. The was a single noise as it hit the wall or floor, then silence for a couple of seconds, then a distant splash. It dispelled my delusion that I could recognise false floors by sight.I remember the tales from when they were developing Sygyun.
They investigated the top adit and it looked great, then they went into the lower adit and realised they had been walking on rotting timber high above the stopes!