open-pit mine vs ore

open-pit mine

noun
  • A type of mine where rock or minerals are extracted from the earth by their removal from an open pit or borrow. 

ore

noun
  • Rock or other material that contains valuable or utilitarian materials; primarily a rock containing metals or gems for which it is typically mined and processed. 

How often have the words open-pit mine and ore occurred in a corpus of books? (source: Google Ngram Viewer )