You are presented with the quiz "What geological formation must occur for the availability of material for silver jewelry to occur?" 

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 "jewelry is made of silver, gold or platinum and is usually set with precious stones". 

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


 

 Igneous intrusion          