1. A method of determining extraction of material from a mine having at least one pit comprising: forming, using a data processing system, a block model of the pit in which material is divided into a plurality of blocks; processing, using the data processing system, the blocks of the block model based on at least one criteria to define a plurality of clusters each comprising a plurality of blocks; forming, using the data processing system, a cone for each cluster propagating upwardly by precedence arcs extending from each cluster; and defining, using the data processing system, clumps of material from the intersection of the cones, the clumps comprising volumes of material not crossed by precedence arcs, so that material is extractable from the mine in any extraction ordering of the clumps that is feasible according to the precedence arcs to provide flexibility in the extraction of the material from the mine.