The study together with specific legislative recommendations shall be submitted to the President and the Congress no later than eighteen months after August 3, 1977: Provided, That, with respect to surface or open pit mining for sand and gravel the study shall be submitted no later than twelve months after August 3, 1977: Provided further, That with respect to mining for oil shale and tar sands that a preliminary report shall be submitted no later than twelve months after August 3, 1977.