1. A method for assigning a cost-directed spacing to a borehole of predetermined diameter on a drill line along a bench of rock having a known density and a rock face, each location and borehole being subject to blast design criteria including a minimum spacing criterion, a maximum spacing criterion, and a minimum energy factor criterion, the method comprising: (i) proposing, by a processor, a compliant spacing for a borehole on the drill line with reference to at least one associated burden boundary; (ii) associating, by the processor, with the borehole a rock burden determined in part relative to the at least one burden boundary; (iii) determining, by the processor, a cost-based loading configuration for the borehole according to a method for determining a priority-directed loading configuration for the borehole subject to blast design criteria, the method comprising: (a) selecting a segment of the explosive column portion of the borehole to be filled with explosive material, wherein the explosive materials are evaluated in order of cost to generate a cost-directed loading configuration; (b) determining the rock burden associated with the identified segment; (c) evaluating candidate explosive materials for use in the identified segment in order of priority until one is found that meets the blast design criteria, wherein the explosive materials are evaluated in order of cost to generate a cost-directed loading configuration, and assigning the first complaint material to the selected segment, assigning stemming to the segment when all the candidate explosive materials fail to meet the minimum energy factor criterion and indicating whether all the candidate explosive materials exceed the maximum energy factor criterion; and (d) repeating steps (a), (b) and (c) for each segment of the explosive column, and recording the resulting compliant configuration and determining its associated cost; (iv) proposing, by the processor, a different compliant spacing with a corresponding borehole-boundary distance; (v) repeating step (ii), (iii) and (iv) for each different compliant spacing; and (vi) identifying, by the processor, the compliant spacing with the lowest cost compliant loading configuration.