The maximum amount of payments which may be made pursuant to this Act on account of sales of newly mined ores or concentrates produced therefrom made during the calendar year 1962 shall not exceed $ 4500000; the maximum amount of such payments which may be made on account of such sales made during the calendar year 1963 shall not exceed $ 4500000; the maximum amount of such payments which may be made on account of such sales made during the calendar year 1964 shall not exceed $ 4000000; and the maximum amount of such payments which may be made on account of such sales made during the calendar year 1965 shall not exceed $ 3500000.