We have been mining for more than 5months now somewhere in Nigeria. The pit was known to be producing Siberian type of amethyst and was left since 1992,due to thesame problem we are facing now. We are mining manually,and anytime we are about to reach VUGHS, we always experiencing collapsing of wall along the terrain of the main pit. The collapsing area is now forming a shape of "gutter" of about 4meter wide and 8meter long from where Vughs are.
Please,i need your advice on and probably what may likely caused this problem.