Every court-appointed conservator, administrator, executor or guardian of an estate shall have authority to execute all instruments of conveyance of an oil and gas lease on property of the estate in his trust without notice or court proceedings other than approval of the conveyance by the judge of the court having jurisdiction of the proceeding endorsed on the instrument of conveyance with a finding by the court that the bonus value of the lease does not exceed Five Hundred Dollars ($500.00).