I found the valuable blue metal and carefully dug out some of it.
I built a craftsdwarf workshop, set its profile to strand extraction only, and checked that I had a dwarf with strand extraction activated.
I queued "Extract Metal Strands" on repeat in the workshop.
Then I noticed this cancellation spam:
Ingish Giginzasit, Engineer cancels Extract Metal Strands: Needs rhyolite.WTF!?
No blue metal has been moved from the mining site yet. The job disappeared from the workshop.
Should I try to find rhyolite somewhere to see what happens?
I don't play a heavily modded version of the game. I think I only have one variant of modest mod, that I didn't tweak.
If you are curious, here's a save of the game some time before the blue metal has been dug out here:
https://dffd.bay12games.com/file.php?id=15206I uploaded this save because of a crash. Since then, I think I managed to avoid the crash by setting fire to the stuck goblin siegers using df-hack's "liquids-here" command.
The blue metal will be dug out in an already designed extension of the bridge-protected tunnel at level 14 (one level above where hotkey F8 leads to). However, to get to that point, the crash must first be avoided (for instance by calling all the dwarves back inside and using the appropriate burrow before they spot the invaders and playing with cheat-lava as explained above to remove the apparent crash-trigger).