Don't know what it is now but #100 was always the Broken Hill to Port Pirie ore train back in the days.
Could be anything now for all I know so open to correction.
5100 ran todday
Without trying to contradict you, from my memory of working on the Peterborough Division in 75/76 100/101 was a general goods, 500/501 was the ore train, 700/701 was also a goods train while 250/251, 550/551 and 650/651 were the reverse movements of these trains. These ran 6 days a week apart from 500/501 550/551 which were 7 day operations. There were a number of other trains depending on traffic which were run or cancelled as traffic demanded.
101 usually left Peterborough about 2 in the afternoon, 501 was about 9:30pm and 701 about 1:30am as I recall.
250 would arrive between 12:30 and 2:30 and leave about 4
m after a loco change, 550 about 8:30pm and 650 about 11pm
Indian Pacific locos 256/257 and 456/457 would also go through between Pt Pirie and Broken Hill.