Structure generates like this on seed:
-4161746037064873748
Co-ordinates: 3618,92,3336
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duplicates 1
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Comments 5
That mineshaft started in a mesa/badlands biome, where mineshafts can generate anywhere on the surface.
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We're tracking this issue in MC-238833, so this ticket is being resolved and linked as a duplicate.
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Pillager outposts generating with too many substructures is tracked at MC-228463. As for the "perfect circle", that is normal generation.
Also, exploring will find a cursed pillager outpost with 5 cages.