Severed minerals and sold minerals are not exactly the same thing, but that is a technicality that really does not need to be expanded on. Being severed just means the rights to the surface and the rights to the minerals are no longer one in the same. You can sell the minerals, which in turn severs them from the surface. However there are other ways to sever minerals than just selling them.
The only way there is a contract (lease) involving the landowner is if the landowner owned the minerals at the time of the lease. If the minerals were severed in full prior to a lease being signed on the minerals, then the landowner would have no part in negotiating a lease on the minerals. In cases where the minerals were severed years ago, you will need to have a full mineral title ran on the property in order to find out who signed to the lease and who has the rights to the lease today.
If there are existing operations on the property, then you can look on the tanks/pump jacks for any identifying information regarding who operates those facilities. You can also try using the
DNR's Emergency Well Locator in an effort to identify who owns the existing wells.
If that is unsuccessful, then you will need to spend some time in the courthouse. I can type a novel on how to run title, but it will bore you to death and ultimately, I'll confuse you also. A competent realtor should be able to help you track down the current operator, but that is not always the case. With some of these older leases, the ma and pa operators can be hard to identify. Like I mentioned in my last PM, I'll help you however I can. Start with the well locator and see if that helps you and we can go from there.