Green’s Dictionary of Slang

1. (UK Und.) jewellery of low value.

1859		Matsell Vocabulum.
1895		C. Crowe Aus. Sl. Dict. 57: Pennyweights, gold and silver trinkets.
1897		Eldridge & Watts Our Rival, the Rascal 29: Two men enter a [jewelry] store together and one engages the attention of a salesman while the other steals anything within reach. These pilferers are distinguished as ‘pennyweight’ thieves.

2. (Aus.) small gold pieces, in terms of prospecting.

1924

E.G. Murphy ‘Out Back’ Dryblower’s Verses 23: We’ve lifted the dirt where the pennyweight gleams.