Of course you are right about the grade. Cyanide would be absolutely useless without proper crushing, preliminary ore separation and concentration, on ore of that grade.

It cannot be used without the rest of a modern mill, which is why most of the illegal miners use mercury not cyanide for their purpose and few of them ever worked at Brisas due to the low grade. It would take over 50 tonnes of ore to get an ounce of metal even with a fully operating modern mill.

There wouldn't be many mines in Venezuela using cyanide, and almost all the ones that do are run by the government.