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

Fact 2: Intrusive igneous rocks form underground.

Given the two facts above, answer the question "where are vein deposits of gold and silver formed?" with the following options: 
- clouds
 - graptolites
 - underground
 - patch reefs
 - plants
 - calcite
 - platinum
 - soft soil


 

   underground      