My first take was throwing knife, too, especially with the way it's sharpened and the fact that the balance is near the middle.  
 
Most spears either seem to have a rat-tail tang or (more commonly) a socketed base.  That wide base with two rivet holes really suggests a knife handle to me. 
 
As for the leaf shape--that goes back to the bronze age, so it's not a great clue unfortunately. 
 
Best, 
 
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