Environmentalists are calling for mining giant BHP Billiton to abandon coal mining in Indonesia's central Kalimantan province, also known as Borneo.

At issue is the IndoMet coal project, a joint venture between BHP Billiton and Adaro Energy, Indonesia's second largest producer of thermal coal. BHP Billiton owns 75 percent of the project, with the remaining 25 percent held by Adaro.

IndoMet covers 865,000 acres in the Borneo rainforest and is believed to have coal reserves of more than 774 million tons, reports The Guardian newspaper. The first stage of IndoMet's development is a small operation called Haju.

Environmental group Friends of the Earth says IndoMet will cause mass deforestation and damage the rivers of the upper Barito basin.

"These are sensitive forests full of biodiversity," Nick McClean, the group's climate justice spokesman told The Guardian. "There has been some logging of the lowland areas in the past but much of the area hasn't been scientifically surveyed. We could lose species we don't know anything about," he said.

The region is inhabited by remote communities and the endangered orangutan.

"We do know that river systems absolutely will be impacted. It's alarming to think that BHP will be clearing an area simply to export coal that may not have a future."

Hendrik Siregar, Coordinator of The Indonesian Mining Advocacy Network, known as JATAM, in a news release last month said, "BHP Billiton, backed by UK shareholders and investors, tells the world that it is 'resourcing the future.' Local communities in Central Kalimantan are telling us that coal mining is destroying their future."

In a July blog post entitled "What is BHP up to in Indonesia?" Bob Burton, director of Australian environmental organization The Sunrise Group wrote that the mining giant "is keeping very quiet" about its involvement in IndoMet.

Little information on the project was disclosed in the company's presentation to analysts in June, he noted.

In response to an email inquiry, BHP Billiton told Burton that the Haju mine project would cost the company $80 million and would produce one million tons of coal a year from early 2014. However, the company did not respond when asked whether an environmental impact assessment had been undertaken.

A spokeswoman for BHP told the Guardian that the environmental impact of further mining would be fully assessed.

"Our plans do not include mining in any protection forest areas in central Kalimantan, and any development in central and east Kalimantan will be subject to detailed environmental and social impact assessments, feasibility studies and will require all appropriate permits to be in place before activities commence," the spokeswoman said.