You are presented with the quiz "When do vein deposits of gold and silver form?" 

But you don't know the answer, so you turn to your teacher to ask for hints. He says that "vein deposits of gold and silver are formed by igneous intrusion" and "magma that cools slowly deep below the surface produces coarse-grained intrusive igneous rocks". 

So, what's the best answer to the question?


 

     When magma cools      