Meanwhile their tin mine collapses (2,3,7)

I believe the answer is:

in the interim

'meanwhile' is the definition.
(thesaurus)

'their tin mine collapses' is the wordplay.
'collapses' indicates an anagram.
'their'+'tin'+'mine'='theirtinmine'
'theirtinmine' with letters rearranged gives 'IN THE INTERIM'.

I've seen this clue in The Globe and Mail.

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