sep 30, 2021 at just over $1.3 trillion, the mining.com top 50 most valuable mining companies lost a combined $158.5 billion in market capitalization over the three months to end september, as iron ores,underground mining methods,slice. mining continues upwards towards the surface until the ore body is depleted. sublevel caving sublevel caving is usually carried out when mining of the ore body through an open pit method is no longer economically feasible. mining now proceeds underground, underneath the open pit. at first, both a raise and a network of tunnels are made.