Mysterious Stain

Found out after cutting an oak log that it reacts to being in contact with metal. Maybe you experienced sawmill guys can tell me in the comment section what this discoloration is all about? It's a mystery to me, my guess is it's the tannic acid or something else in the oak that reacts with metal. It was a dark bluish purple color stained in the wood every place it touched the sawmill deck or up against the back stops. The back stops rusted over night from me leaving the log on the deck.

https://www.vrbo.com/338940
https://logcabinhomestead.com/
https://www.facebook.com/profile.php?id=100064706347381
https://www.brighteon.com/channels/logcabinhomestead
https://www.youtube.com/channel/UCrsobbFCr9QE88TLcwEFVPA