How did pre-Columbian societies extract gold?

ScienceNOW : When Spanish conquistadors seized the Inca emperor Atawalpa in 1532, they demanded an enormous ransom of silver and gold that took weeks to collect.Such an enormous stash suggests that the Andean people knew sophisticated metallurgy, but there has been little evidence to support this.Now a team of geologists and archaeologists have found clues that may indicate that these indigenous people refined gold with mercury amalgamation , an important metallurgical technique that is still in use today.