Two years ago, Jabir Idrissa was one of Tanzania’s leading investigative journalists, breaking stories on alleged corruption, the environment and human rights abuses for two of the most respected publications in Dar es Salaam.

Today, he is out of work, his former employer cannot print, and he is struggling to provide for his family.

What ruined his life, he says, was a story about the North Mara goldmine that infuriated the government and led to a two-year publication ban.

The company that runs the mine, London-listed Acacia Mining, is not implicated in the crackdown, which is part of increased restrictions on press freedom in Tanzania under the presidency of John Magufuli, who came to power in 2015. Since then at least four publications have been banned.

The Guardian is part of a coalition led by Forbidden Stories that has talked to 12 reporters who say they have been harassed, threatened or censored by the authorities while trying to cover alleged human rights violations, environmental damage or corruption at the mine.

From 2005, Idrissa worked as an investigative reporter on two sister newspapers, MwanaHalisi and Mawio.

He says he loved his job because it played an important role in holding governments to account.

He and his colleagues started reporting on the North Mara goldmine about 10 years ago. After the tailings dam was flooded in 2009, they covered the impacts resulting from contamination of rivers and other water supplies.

They also published reports about allegations of killings and beatings of intruders by police and security guards. He said he felt the problems could be solved if journalists raised the concerns with a wider audience and gave “investors the correct information”.

Investigating the root of the problems, he and his colleagues scrutinised the mining contracts with the government, which appeared to them to lack transparency and accountability.

“The top big shots did not want the public to know about it, what was inside the contracts between Acacia and the government,” he said. “People didn’t like that. It was as if we were opening the graves, hence ending us in trouble with the government.”

The editorial staff of Mawio knew the subject was sensitive but decided to go ahead because they felt transparency was in the public interest.

“We stuck to the idea that, yes, it is risky, but we have to do it because people are complaining and we have to listen to their voices.”

Soon after, colleagues of Idrissa were summoned to the newspaper registrar and handed a two-year banning order from the information ministry.

“We were told that Mawio is inciting hate and has disrespected retired presidents,” he recalls.

Later they found their computer systems had been hacked and all the documents relating to the mining company were missing. Police later came to the office and took more materials.

“We were shocked to see what the government did. We also realised that really the government wanted to keep us quiet and the only way was by banning those newspapers.”

A court later said the paper had done nothing wrong and overturned the ban, but by then the damage was done. The government has refused to issue a publication licence.

Media laws introduced recently say journalists can be imprisoned for up to three years for knowingly publishing information or data deemed “false, deceptive, misleading, or inaccurate”.

From 2016-17, four publications were banned for between three months and three years. Tanzania has slipped 25 places on the Reporters Without Borders World Press Freedom Index, where it ranks 118th out of 179 countries.

Reporting on the North Mara mine has often resulted in problems with government authorities. In 2011, four reporters – Berdina Nyakeke (the Citizen), Anthony Mayunga (Mwananchi), Mabere Makubi (Channel Ten) and Anna Mrosso (Nipashe) – were arrested on their way to investigate claims that the bodies of people shot by police had been dumped at Kewanja village.

Nyakeke was also told by the regional commissioner that she should not write about the villagers’ point of view on water pollution.

The same year, the Canadian journalist Jocelyn Edwards was detained for eight hours and deported for trying to report on the alleged killing of five villagers by security guards. Her notes were confiscated as a potential danger for the “security and stability of the country”.

Acacia told the Guardian it was unaware of such reports, but would be prepared to investigate if allegations were brought to its attention. The company said it promoted transparency. “The mine goes to considerable effort to engage with members of the local community and actively promote community cohesion.”

Idrissa cannot find a new journalism job. He says other media organisations are afraid to hire him because they fear repercussions from the government. He has moved to Zanzibar to try to find work. Relatives help. He runs a small shop but says he is struggling to support his wife and children.

“It is hand-to-mouth, which is hard,” he says. “All of them look at me and it is my duty to take care of them, so I am really hurt deep inside. I feel I was treated unfairly and what can I do? We are all stressed out to the point that our physical health is suffering and yeah, it’s bad. It’s bad.”