So ... I don't know what's going on in Tanzania, it's hard to know who to believe; Acacia Mining or the government, and now, Petra Diamonds or the government.
Take a look at Petra Diamonds'
announcement regarding the matter and note their claim:
"
...Petra confirms that all operations related to the mine are conducted in a transparent manner and in full compliance with legislation in Tanzania and the Kimberley Process."
If Petra was misbehaving then your conclusion that the mining industry in Tanzania is being "cleaned up" could be valid. If Petra was not misbehaving, that would be alarming for private investors in Tanzania.
I don't know what's really going on there and I don't think anyone on this forum does either.
