Guyanese gold marketed as pure gold may actually have been laced with silver alloy before being shipped to overseas markets, reported the Associated Press.

Authorities in the South American nation of Guyana are currently conducting a probe to determine if locally mined gold has indeed been tampered. Police have shuttered the Guyana Gold Board's buying office in Bartica, a remote Guyanese mining town situated at the confluence of the Essequibo and Cuyuni rivers, 50 miles upstream of the Atlantic. The office was responsible for regulating the sale of raw gold.

Officials in the Natural Resources Ministry said that government officials in the Bartica would mix silver with gold bullion and then gold plate the mix, presenting their output as pure gold bullion.

Investigators allege that these individuals from the gold board’s office knowingly mixed silver alloy with mined gold, and misrepresented it when they shipped it to Georgetown, the capital city of Guyana, where it was then exported to other nations. Authorities believe that millions of dollars worth of gold laced with silver has been shipped.

Four people involved in Guyana’s gold trade have been arrested to date.

On Sunday, Guyana’s Mining Minister Robert Persaud said that investigators are looking into the extent of the fraud and are working with overseas law enforcement agencies to determine if there is a "foreign element in this racket."

Gold is the country’s main export and is sold to several international markets, including the U.S. and the U.K.

Bartica has a population between 15,000 and 20,000 residents, many who work in the Guyanese bush mining raw gold and diamonds.

Guyana is situated along the Atlantic Ocean on the northern coast of South America, southeast of Venezuela and northwest of Suriname. It also shares its southern, and part of its western, border with Brazil.