Caribbean island amalgamated metals (4)

I believe the answer is:

cuba

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

'caribbean island' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for cuba that I've seen before include "Castro's country" , "West Indian island" , "Island N. of Jamaica" , "detached area" , "Guantanamo Bay location" .)

I've seen this clue in the Sydney Morning Herald.

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