Where you could find a mass of tea (5)

I believe the answer is:

assam

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'tea' is the definition.
(I've seen this before)

'where you could find a mass' is the wordplay.
'a mass' anagrams to 'ASSAM'.
Though, I am not sure how this is indicated.

'of' acts as a link.

Can you help me to learn more?

(Other definitions for assam that I've seen before include "region out east" , "Indian province" , "India tea-producing state" , "State of NE India" , "N East Indian state?" .)

I've seen this clue in the Evening Standard.

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