Fact 1: Vein deposits of gold and silver are formed by igneous intrusion.

Fact 2: Granite, on the other hand, is an intrusive igneous rock.

Given the two facts above, answer the question "what are vein deposits of gold and silver formed by?" with the following options: 
- mines
 - tube
 - calcite
 - cracking
 - rocks
 - wind
 - granite
 - streams


 

       granite  