server/res/core/resources/laen.xml

<?xml version="1.0"?>
<resource name="laen" limited="yes" material="rm_laen">
  <item weight="200" score="100">
    <construction skill="mining" minskill="7"/>
  </item>
  <resourcelimit>
    <modifier type="require" building="mine"/>
  </resourcelimit>
</resource>