A small brown line snakes its way through the rainforest in northern Sumatra, carving 300 metres through dense patches of meranti trees, oak and mahua. Picked up by satellites, the access road – though modest now – will soon extend 2km to connect with the Tor Ulu Ala pit, an expansion site of Indonesia’s Martabe mine. The road will help to unlock valuable deposits of gold, worth billions of dollars in today’s booming market. But such wealth could come at a steep cost to wildlife and biodiversity: the extinction of the world’s rarest ape, the Tapanuli orangutan.

The network of access roads planned for this swath of tropical rainforest will cut through habitat critical to the survival of the orangutans, scientists say. The Tapanuli (Pongo tapanuliensis), unique to Indonesia, was only discovered by scientists to be a separate species in 2017 – distinct from the Sumatran and Bornean apes. Today, there are fewer than 800 Tapanulis left in an area that covers as little as 2.5% of their historical range. All are found in Sumatra’s fragile Batang Toru ecosystem, bordered on its south-west flank by the Martabe mine, which began operations in 2012.

“This is absolutely the wrong place to be digging for gold,” says Amanda Hurowitz, who coordinates the forest commodities team at Mighty Earth, a conservation nonprofit monitoring developments at the open-pit mine. “And for what? So mountains of gold bullion bars can sit in the vaults of the world’s richest countries.”