Do a cleaning job for gold, perhaps (4)

I believe the answer is:

dust

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'do' is the definition.
Although both the answer and definition are singular nouns, I can't see how they can define each other.

I can't explain the remainder of the clue.

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(Other definitions for dust that I've seen before include "Powdery matter" , "Fine dry powder" , "Clean - dirt" , "Hopes to turn to this" , "Sprinkle -- powder" .)

I've seen this clue in the Evening Standard.

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