Old rare metal detected in animals (7)

I believe the answer is:

wolfram

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'old rare metal' is the definition.
(historic name for tungsten)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for wolfram that I've seen before include "Tungsten" , "greyish-white metal" , "Heavy metal" , "elemental" , "Element by another name" .)

I've seen this clue in The Telegraph.

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