Did you know that Brazil imported nearly 5x as many slaves from Africa as compared to the American Colonies. When Brazil was first colonized by Portugal it had nearly 8 million native inhabitants. (Today there is less than 870,000) Many of these people died while cultivating sugar for Portugal in abhorrent conditions. Others fled. So Portugal brought African slaves to take their place. Sugar was the largest commodity brought back to Europe from Brazil for more than 150 years. At the turn of the 18th century there was another commodity that brought another 2 million slaves from Africa. It was gold. Nearly 30,000 explorers headed to Brazil after the discovery of gold at Minas Gerais. The gold rush of Brazil was short lived, and ended around the 1750s. 
This 4000 Reis made of Brazilian gold was made during the height of the gold rush and most certainly mined by slaves brought from Africa during this time period. Minted in the State of Bahia.