I was watching a HowItsMade video on gold bars and it looks like it's a very complex process to make pure gold and basically requires us to dig a crater in the earth just to get one bar of gold. Were the Aztecs able to make pure 24 karat gold or was it mostly alloys containing low levels of gold?
Native gold is quite rare in Mexico. Most of the time, the gold being used was some sort of alloy mixed with silver and/or copper to reduce the amount of actual gold needed. Goldsmiths would then head the alloy to different temperatures and then hammer away impurities (the silver or copper) to bring out the gold in the alloy.
I have a previously answered question on Aztec gold working if you are interested.