I was in the process of routine maintenence. I was began greasing the bearings on the conveyor tail pulley's when I slipped in a puddle of mud. I lost my balance and landed on my right foot. I heard a pop sound and a sharp pain shot thru my ankle. As I tried to stand up the pain became unbearable. I fell back to the ground and asked for help. 2 men came & put me into control room.