I’m still a Noita novice, but in my few runs I stumbled on this seed 1832853566 which I feel might be quite special. Part of the ground easily turns into gold. I don’t know how common this is, but I am sharing here for future reference.
It looks like the recipe for the gold creating substance Draught of Midas is somewhat simple but unstable in this seed.
Tap for details on the seed's hidden alchemy recipe
It’s supposedly water, grass, and toxic sludge to make the precusor. Any precusor will turn into Midas when meat is added to it.
I imagine that spot you found the gold appearing was were you killed a toxic slime and it bled on to grass that was touching water. Once Draught of Midas is created, it can transform an infinite amount of material to gold with as little as a drop.
Since water turns toxic sludge into water, the recipe won’t easily produce a lot of it, but any amount is enough to use. Water also dilutes draught of Midas, causing its reaction to happen less.
It’s not incredibly rare, but rare enough to not see it often without looking up the alchemy recipe.