and 142 of this title for the purpose of exploratory drilling to discover water supplies for irrigation or other purposes, and which have had wells or other permanent improvements placed thereon by and at the expense of the United States are no longer needed for the purpose for which they were withdrawn and improved, the Secretary of the Interior may appraise the lands, together with the improvements thereon, and thereafter sell the same to a citizen of the United States for not less than the appraised value at public auction to the highest bidder, after giving public notice of the time and place of sale by posting upon the land and publication for not less than thirty days in a newspaper of general circulation in the vicinity of the land.