A measure of the gold ale from ? la carte (5)

I believe the answer is:

carat

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'a measure' is the definition.
(carat is a kind of measure)

I can't explain the remainder of the clue.

(Other definitions for carat that I've seen before include "Unit of weight used for gems" , "weight of rocks" , "Gemstone weight unit" , "Weight of ice" , "Unit of weight for gems and pearls" .)

I've seen this clue in the Irish Times and the Irish Times (Crosaire).

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