The pilot commenced mustering at about 0500 hours, flew for three hours, then carried out routine station duties until it was time to muster another paddock. After approximately 20 minutes airborne he decided to land for a drink of water, which he carried in the helicopter. As the helicopter passed through 10-15 feet on approach, the pilot heard a loud noise, which only lasted for a moment, then the helicopter began to rotate. He lowered the collective and landed the machine upright after two revolutions. Investigation revealed that the tail rotor assembly had hit a small mulga sapling, causing the tail rotor and gearbox to separate from the helicopter. The pilot could not recall having sighted the sapling as he approached to land. Outside air temperature at the time of the accident was plus 38`C.