A short and to-the-point idea.
Some swamps would, like clay, generate iron/ore nodules. They'd get quality in the same way as clay, and "regenerate" over time, like clay. Ten nodules add up to one nugget, or they could be smelted like ore, with a low-burn-time, to *possibly* generate a nugget.
Just something to cope with the lack of mines that seems to be all the rage these days. If anyone wants me to flesh the idea out more, I will.