Ghanaian police have arrested 46 foreign nationals from China and India accused of illegally mining gold.
They were detained in overnight raids in the country's Central region where they were operating small barges to dredge the bed of the River Offin.
More than 4,500 Chinese nationals have been repatriated this year after a series of swoops on illegal goldmines.
Officials says since the clampdown began, some illegal miners have been going out at night to avoid detection.
Ghana is Africa's biggest gold producer after South Africa.
Ghanaian law prevents foreigners from working in small-scale gold mines.
The authorities say the illegal mining pollutes the rivers and destroys the environment.
Illegal miners use makeshift barges to dredge mud from river beds which is then sifted for gold.
The BBC's Sammy Darko in the capital, Accra, says illegal miners also mine in the forest leaving behind huge holes and cutting down trees.
The holes collect with water and chemicals like mercury used to sieve through the mud for gold drain into rivers.