A stone mine? (3)

I believe the answer is:

pit

I believe this is a double definition.

'a stone' is the first definition.
('pit' can be a synonym of 'stone')

'mine?' is the second definition.
(down the pit)

(Other definitions for pit that I've seen before include "Coalmine" , "Tip into crater" , "Sizeable hole in the ground" , "Hollow" , "Cherry stone" .)

I've seen this clue in the Evening Standard.

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