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.”

Martabe goldmine in the Batang Toru rainforest, the only known habitat of the Tapanuli orangutan, on Sumatra island. Photograph: Nanang Sujana/AFP/Getty Images

Dozens of orangutan nests lie in the vicinity of the mine’s planned expansion, according to Mighty Earth. In late September, construction began on new access roads through the forest around Martabe mine, according to PT Agincourt Resources, a subsidiary of the British multinational Jardine Matheson, which operates the mine. One of the new roads running through secondary forest has already come within 70 metres of a cluster of orangutan nests, Mighty Earth says.

For Jardine Matheson, which acquired the mine in 2018, expansion is critical to their bottom line. In 2020, the company said it would open up a new pit and build the supporting infrastructure to reach at least 460,000 additional ounces of gold hidden within Tor Ulu Ala. Gold mining is intensifying across the world as companies race to capitalise on near-record prices. At today’s rate of more than $4,000 (£3,000) an ounce, Tor Ulu Ala could generate nearly $2bn.

“While we understand the concerns of some critics, without the mine, which is now the income for approximately 3,500 employees – 70% of which are locals that rely on the mine operation – the alternative will be worse,” says Ruli Tanio, the vice-president director of PT Agincourt. “Being responsible miners, we can provide some opportunity for the orangutan in terms of funding.”

But many scientists disagree, saying the expansion of the mine could push the critically endangered Tapanuli orangutans to extinction in a few generations. Even removing just 1% of the population a year would ultimately end in extinction, they say, as orangutans only reproduce every six to nine years.

“It doesn’t take much – especially if you start killing orangutan females – for the population to go extinct,” says the biological anthropologist Erik Meijaard, director of the scientific consultancy Borneo Futures and one of the first experts to describe the species.

A dominant male Tapanuli orangutan in Batang Toru forest. The animals only reproduce every six to nine years. Photograph: Maxime Aliaga/NPL

Concerns about Jardine Matheson’s decision to move ahead with expanding the mine – without an agreed plan in place to reduce impacts to the Tapanulis – have spread beyond the scientific community. Last year, Norway’s $1.6tn sovereign wealth fund sold its holdings in three Jardines firms, citing concerns about the company being responsible for “severe environmental damage”.

Tapanulis, with their frizzy, cinnamon hair and wide faces, are not only the rarest orangutan, but represent the oldest lineage of all orangutan species – descendants of the first ancestral orangutans that arrived in Sumatra from mainland Asia more than 3m years ago.

In Batang Toru, the final holdouts of the species dwell in just three populations – the west block, east block and Sibual-buali reserve – spread across a patch of mountainous forest roughly the size of Rio de Janeiro. (Earlier this year, scientists confirmed they had found a small, isolated cluster of Tapanulis living in a peat swamp about 32km (20 miles) outside Batang Toru.)

“We assume [the Tapanuli] was really widespread a couple of hundred years ago,” says Meijaard. But unsustainable hunting and fragmenting of the forest drove the last of the species to seek refuge in the higher elevations of Batang Toru.

Even before the proposed mine expansion, the Tapanuli was threatened by development. A Chinese-owned hydroelectric project is being built on the Batang Toru River, which flows north-south along the eastern side of the ecosystem. The dam would affect an area that contains the highest density of Tapanuli orangutans – about 42 individuals – according to one 2019 assessment in the journal of the Society for Conservation Biology.

Land cleared ahead of the building of a hydroelectric dam in the Batang Toru rainforest, August 2018. Photograph: Nanang Sujana/AFP/Getty Images

The expansion of the Martabe mine represents another blow, squeezing the apes from another side. “The Tapanuli orangutan really cannot afford any losses,” Meijaard says.

The Martabe mine was established in 2008, near the western block of Batang Toru where an estimated 533 Tapanulis are thought to live. The mine’s footprint spans about 650 hectares (1,600 acres), with 2 hectares falling within the Batang Toru ecosystem’s “key biodiversity area”, as designated by conservation NGOs in the Alliance for Zero Extinction.

PT Agincourt says it will expand the mine by about 250 hectares (617 acres) by the end of Martabe’s operational lifespan in 2034, building not only the new pit and access roads, but a large tailings-management facility. This growth includes clearing another 48 hectares of mostly primary forest in the key biodiversity area. But the company says it is also setting aside a 2,000-hectare conservation zone within its concession, as well as creating another “offset” protected area about 40km from the mine site.

“Without the [mining] revenue from this small area, it will be very hard to carry out the conservation work and the restoration work that is planned,” says Christopher Broadbent, a UK-based sustainability consultant to PT Agincourt. “If the mine were to walk away, the unintended consequences would be almost certainly disastrous for the orangutan.”

PT Agincourt estimates its mine’s expansion will directly or indirectly affect between six and 12 orangutans. Tanio says: “Throughout our 13 years of operation, there have been no cases of fatality of orangutan directly from the mining activities.

“The notion the mine can kill an orangutan directly has proven to be quite false.”

But studies show that even indirect effects can take a toll. Female orangutans are particularly sensitive to habitat loss, as they tend not to move when they lose parts of their home range, leaving them at risk of starvation. PT Agincourt says land clearing will proceed slowly, allowing time for the orangutans to move out of the way.

The mine expansion will involve clearing an additional 48 hectares of mostly primary forest in the key biodiversity area by 2034. Photograph: SOCP/Andrew Walmsley/EPA

“We don’t know enough to be able to say that every orangutan that moves will find some new forest to call home,” says Phil Aikman, a campaign director at Mighty Earth. Some studies suggest that pushing orangutan groups closer together will lead to social tensions and conflicts. “The big concern here is that mitigation may or may not work.”

For the past five years, environmental advocates as well as the International Union for Conservation of Nature (IUCN), have pushed to delay new construction until a mutually agreed plan is in place to protect the Tapanuli. For a time, Jardine Matheson voluntarily agreed to a moratorium on construction, engaging with the IUCN’s Avoid, Reduce, Restore and Conserve (ARRC) taskforce, which advises companies on how to avoid ape habitats and reduce impacts. But that agreement expired in December 2022.

The primatologist Genevieve Campbell, who leads the taskforce, says Jardine Matheson had made it impossible to proceed as they were unable to share raw data, including orangutan survey data within the mining permit. Jardines says the Indonesian government prevented the company from sharing that information.

But that relationship has improved in recent weeks. In November, PT Agincourt Resources signed a new conditional memorandum of understanding with the ARRC taskforce, allowing their scientists to provide independent input on the mine’s development plans and mitigation strategy.

PT Agincourt told the Guardian it would temporarily pause road construction for three weeks to allow the IUCN to complete its review. The planned protection zones, as well as a new orangutan research centre funded by the mine mean the “Tapanuli will be better off with the mine”, Tanio says.

A female Tapanuli orangutan with twins in Batang Toru forest. Females are particularly sensitive to habitat loss. Photograph: Courtesy of SOCP

Campbell disagrees that the mine’s overall impact will be positive for the Tapanuli. “You cannot say that any great ape species is better with mining than without.”

For Meijaard, little can truly compensate for the mine’s effects on the orangutans.

“You can plant 10,000 hectares of forest with lots of fruiting trees … so the orangutans potentially have somewhere to go. You can push them fast or you can push them slow. But you’re still pushing them into competition with other orangutans in an area that is, ecologically, quite restrained for the species.”

“If we really want to protect the species, we have to aim for zero losses,” he says.

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