All leases and conveyances granting the right to explore or prospect for minerals or oil and gas and for the mining and removal of the same on or from county-owned lands, executed and delivered by the governing body of a county prior to August 3, 1955, and which might be invalid only because the governing body of the county was not expressly authorized by statute to execute and deliver such leases or conveyances, hereby are validated and declared to be legal and enforceable.
ORS 275.296