I think exerting has no limit of how many times it can be done if "as it becomes tapped/when you tap it" is not specified so emberpeak citadel produces infinite mana.
even if you could only do it once, tapping AND exerting this land produces 3 mana.
			
			even if you could only do it once, tapping AND exerting this land produces 3 mana.
 
				 
 
		 
 
		 
 
		 
 
		 
 
		 
 
		



 
 
		 
 
		



