Investors cheered when Venezuela opened its vast mineral reserves to private capital in April but gang control over many mines could prove a powerful obstacle.

The South American country, which is undergoing a profound transformation following the U.S. overthrow of leftist strongman Nicolas Maduro in January, has the world¡¯s largest proven oil reserves.

But it is also rich in gold, diamonds, bauxite and coltan, a mineral essential for technology and defense that is classified as critical by Western powers, as well as rare earths.