Firm by mountain — it is in place of mineral extraction (7)
I believe the answer is:
coalpit
'place of mineral extraction' is the definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'firm by mountain it' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'by' is a charade indicator (letters next to each other).
'mountain' becomes 'alp' (the Alps are a mountain range).
'co'+'alp'+'it'='COALPIT'
'is in' acts as a link.
Can you help me to learn more?
(Another definition for coalpit that I've seen is " mine".)