Entry from British & World English dictionary
[mass noun] dialect
1Worthless material; rubbish. 1.1Australian
/NZ Rock which contains no gold or from which gold has been extracted.
/NZ Worthless information; nonsense.
late Middle English: diminutive of earlier mul 'dust, rubbish', from Middle Dutch.
poke mullock at
/NZ informal Ridicule (someone).
Definition of mullock in: