Iron nodes

[Kharris]

I have found 4 iron nodes using dowsing rod, all four are (now) on completely flat ground. When I try to build a mine entrance on any of them, all I get is 'You cannot build that there' message. Any ideas?

[Procne]

Mine entrance can only be built on dirt or paved ground. So you either have to pave the area or turn it into dirt

[Kharris]

Paving the node worked

Thanks for the help.