I think this train number is the service from Broken Hill to Port Pirie but can someone please confirm.
The numerical area codes are defined in the ARTC TOC manual...
So any train from Broken Hill to Port Pirie will be 54xx, the reverse 45xx
On 12 January (if I recall correctly) I photographed 4500S which was the empty concentrate train from Pirie to Broken Hill
The suffix "S" is said to refer to trains that don't leave South Australia, which is patently incorrect for any train between Broken Hill and Port Pirie. It might refer to trains running on former SAR tracks, which did reach Broken Hill.
The Master Train Plan should show that train and who operates it.