The loaded haul truck was travelling down a ramp towards a bend.
The empty haul truck was travelling towards the bend to continue up the ramp. It then entered the corner at an excessive speed, lost traction and started to slide.
The rear of the truck slid, the dovetail struck the side of the loaded truck and spun through 180 degrees with the empty truck came to a stop behind the loaded truck.
The NSW Resources Regulator said both workers were uninjured.
"Workers must operate vehicles and equipment at a speed that is appropriate to the prevailing conditions," it said.
"Workers must remain vigilant in monitoring changes in conditions in operating environments. Engineering controls that minimise the risk of loss of control should be considered, including the use of centre bunding, speed monitoring systems and alarms."