Valuable memoranda from the finance department? (8,5)

I believe the answer is:

treasury notes

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'from the finance department?' is the definition.
I can't tell whether this definition defines the answer.

'valuable memoranda' is the wordplay.
'valuable' becomes 'treasury' (I can't explain this - if you can you should believe this answer much more).
'memoranda' becomes 'notes' (I've seen this in another clue).
'treasury'+'notes'='TREASURY NOTES'

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I've seen this clue in The Irish Independent.

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