Within thirty (30) days after the close of the year for which the permit was issued, and likewise after the close of each subsequent year, the operator, if he continues to engage in strip mining, shall file with the Department of Mines and Mineral Industries¹ a new bond covering such new acres as he may estimate will be affected during the following year. The bond shall be at the rate of five hundred dollars ($500) per acre, unless it has been determined by the secretary that a bond in excess of five hundred dollars ($500) per acre is required. The bond shall not be less than five thousand dollars ($5,000) and shall be accompanied by an annual report, upon a form furnished by the department, setting forth the number of acres of land affected during the preceding year and the number of acres of land that will be affected during the ensuing year at each operation: Provided, however, That any portion of a bond covering an operation which may remain unencumbered at the end of an operational year may be applied to acres of land which the operator anticipates will be affected during the following year.