Definition of mullock:
(n) :
(now UK dialect) Rubbish, waste matter.
(n) :
Nonsense, rubbish.
(n) :
(UK, Yorkshire, dialect) A mess; the result of a blunder.
(n) :
(Australia, New Zealand, mining) Mining waste or ore processing waste:
(n) :
(Australia, New Zealand, mining) Overburden: waste material generated while searching for minerals or while mining, such as when sinking a shaft.
(n) :
(Australia, New Zealand, mining) Tailings: waste rock from which the wanted gold, minerals, opal, etc., has been extracted.