Crossword Genius

Around opening, one hammered sheet for platinum? (10)

Ross

I believe the answer is:

seventieth

I'm a little stuck... Click here to teach me more about this clue!

'around' is the definition.
Both the definition and answer are adjectives. Perhaps there's a link between them I don't understand?

'opening one hammered sheet for platinum?' is the wordplay.
I cannot quite see how this works, but
'opening' could be 'vent' (vent is a kind of opening) and 'vent' is found in the answer.
'one' could be 'i' (Roman numeral) and 'i' is located in the answer.
an anagram of 'sheet' is 'seeth' which is within the remaining letters.
This accounts for all the letters.
This explanation may well be incorrect...

Can you help me to learn more?

(Other definitions for seventieth that I've seen before include "small fraction of whole" , "platinum to celebrate" , "Ordinal number" , "person's birthday" .)

I've seen this clue in The Guardian.
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