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Stuck on r/h corner
6d Continental bloc area is shifting around Uruguay (7) E?R????
16a What you might find during 29 in polar Canada (6) ?R???A
for 29 I have mystery tours
12a A modest grey (4) ???Y

the first could be Eurasia, I think.

12A - Ashy?

arcana

Grateful thanks Kemlo and ixion

What about Arcana for the second one.
I don't have a Chambers Dictionary but know that "arcane" means something like 'hidden'. Maybe Arcana are 'hidden things' such as you might find on a mystery tour. The letters are hidden in the words of the clue?

Eurasia is an anagram of areais and U - Uraguay

orry - typo