It's a progressive royalty rate. As gold rises, the % of...

It's a progressive royalty rate. As gold rises, the % of royalties rise too. The company released a chart previously.

So every year, say gold rose 4%, and costs rose 4% due to inflation, your profit is roughly stable. But problem: the royalty rate changes from 10 to 10.5%, taking an extra 0.5% of your revenue, reducing the profit significantly.

It's a horrible royalty system in the long term. It's very similar to the Australian system of income tax rates, where inflation pushes more people into the upper tax brackets every year (but this may be offset, if the government raises the tax brackets). But that means it depends on the Thai government raising the royalty brackets - doubtful?