Gold futures in India, the world's second-biggest bullion consumer after China, hit their highest level since March 1, at 32,834 rupees per 10 grams, earlier this week.
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.