The process is describe here.  Explains tailing pond.

Gold cyanidation

From Wikipedia, the free encyclopedia

Gold cyanidation (also known as the cyanide process or the MacArthur-Forrest process) is a metallurgical technique for extracting gold from low-grade ore by converting the gold to a water soluble coordination complex. It is the most commonly used process for gold extraction. Production of reagents for mineral processing to recover gold, copper, zinc and silver represents approximately 13% of cyanide consumption globally, with the remaining 87% of cyanide used in other  industrial processes such as plastics, adhesives, and pesticides. Due to the highly poisonous nature of cyanide, the  process is controversial and its usage is banned in a number of countries and territories.