Opening ground, authorise ore to be extracted (6)
I believe the answer is:
hiatus
'opening' is the definition.
(I know that hiatus is a type of opening)
'ground authorise ore to be extracted' is the wordplay.
'ground' indicates an anagram ('grind' the letters into a new form).
'to be extracted' suggests deleting specific letters.
'authorise' with 'ore' removed is 'authis'.
'authis' anagrammed gives 'HIATUS'.
(Other definitions for hiatus that I've seen before include "Pause or break in continuity" , "A lacuna or interruption" , "Interval" , "Opening" , "Break -- respite" .)