Officials from Ghana’s immigration service have announced the arrest of 125 Chinese nationals for small scale mining in the Central, Western and Ashanti regions. Assistant Commissioner of Immigration and Head of Public Affairs Francis Palmdeti said 61 of them were arrested during security sweeps in the Western and Central regions while 64 were detained during another operation in Ashanti.

“The invasion of the small scale mining industry by foreigners has reached alarming proportions,” he said in a statement. “This operation is the first of a series that will be carried out across the nation.”

Ghanian authorities, he added, have been coordinating efforts to intercept illegal miners by intensifying the screening of false passports and forged visas. Along with South Africa and Mali, Ghana has some of Africa’s biggest gold reserves.