Employee was standing a concrete equipment pad performing maintenance on the P-2 ball mill lube system. When he stepped down to the catwalk approx. 24"" below, he felt pain in his foot. An X-ray was inconclusive so he was treated for a sprain & this incident was classified as first aid. On October 17, a new X-ray revelaed a fracture in the 4th metatarsal so now reportable.