Oil and gas leases shall not be issued on unleased lands which have been classified by the department as being within a known geologic structure of a producing oil or gas field, except as follows: Upon application of any person, the department shall lease in areas not exceeding six hundred forty acres, at public auction, any or all unleased lands within such geologic structure to the person offering the greatest cash bonus therefor at such auction. Notice of the offer of such lands for lease will be given by publication in a newspaper of general circulation in Olympia, Washington, and in such other publications as the department may authorize. The first publication shall be at least thirty days prior to the date of sale.