A presidential commission says Tanzania has lost 188 trillion Tanzanian shillings ($84bn) over 19 years due to mining companies under-reporting the amount of minerals they have been exporting.
This is denied by mining companies.
In a live televised ceremony at state house in Dar es Salaam, President John Magufuli ordered the minister for legal affairs to review all mining laws.
The commission also says Canadian mining firm Acacia Mining – the largest gold miner in the country – never registered in Tanzania and therefore is operating illegally.
The comes a few days after another government report which said containers at the port were carrying up to 15.5 tonnes of gold instead of the 1.1 tonnes which was declared by Acacia mines.
Acacia Mining denied this, saying the findings contained “significant discrepancies”.
The previous report led to the sacking of the minerals minister and other top officials in the mineral sector.