South America: Orosur Mining

A deep open pit that was flooded for eleven years in Uruguay, was dewatered in 2015 to carry out underground mining. The exposed pit walls showed a large wedge failure, leaving a 25-ton block hanging high above a projected mine portal. SRK was called in to assess the risk of leaving the block in place and concluded that the chances of a fall could not be overlooked. The most probable landing zone was located some 30 m away from the portal with a +50% chance of being hit. At the portal, the probability of impact was estimated as 0.35%, a low and tolerable value.