My grandfather made this, he was a foundryman on Cockatoo Island shipyards, Sydney.
The centre is a threepence with the head of King George V inlaid in a cut out halfpenny reading Commonwealth of Australia 1913, then that was inlaid in what looks to be a round disc (not sure which metal) and a brass star pattern.
The writing around the disc reads
"HMAS Brisbane, keel laid January 25th 1913"
Grandpa had his own little hobby foundry in our backyard and I have a lot of brass work that he made.