The international group says sales of polished diamonds below 0.50 carats are slow due to excess supply, weak Chinese demand and tight Indian liquidity.
Prime Minister James Marape doubled down on his plans to earn more taxes from the gas-and-gold-rich country's natural resources sector on Wednesday, but said major reform would not take effect for years.
James Marape, a former finance minister who became leader after winning a vote in parliament, put some of the world's biggest resources companies on notice over a perceived lack of wealth flowing from their projects back to communities.
Lynas' status as a non-Chinese producer came into sharper focus this week after major Chinese newspapers reported Beijing was ready to use rare earths to strike back in its trade war with the US.
The 216 million tonne Jongju deposit 150km north of Pyongjang, theoretically worth trillions of dollars, would more than double the current global known resource of REE oxides.