After this picnic ends he gets top class tungsten source (9)

I believe the answer is:

scheelite

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'tungsten source' is the definition.
The definition suggests a singular noun which matches the answer.

'after this picnic ends he gets top class' is the wordplay.
'after' means one lot of letters go next to another.
'ends' suggests the final letters.
'gets' means one lot of letters go next to another.
'top class' becomes 'elite' (I've seen this in another clue).
The last letters of 'this picnic' are 'sc'.
'sc' next to 'he' is 'sche'.
'sche'+'elite'='SCHEELITE'

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

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