If you want it mined, ring the engineers! (3)
I believe the answer is:
ore
'if you want it mined' is the definition.
I can't tell whether this defines the answer.
'ring the engineers' is the wordplay.
'ring' becomes 'o' (letter resembling a ring).
'the engineers' becomes 're' (Royal Engineers).
'o'+'re'='ORE'
Can you help me to learn more?
(Other definitions for ore that I've seen before include "Raw mineral" , "Raw material" , "Mineral - Scandinavian monetary unit" , "Mineral - Scandinavian money" , "Solid rock containing metal" .)