SAN JOAQUIN, Mexico (AP) — A drill echoes through narrow tunnels deep within the mountain where miner Hugo Flores bores into rock in search of one of Earth’s most toxic elements. Buried in red stripes of minerals illuminated by his headlamp is mercury .

A boom in mercury mining is underway in Mexico's pine-covered mountains known as the Sierra Gorda – one of the most biodiverse stretches of the country.

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