The value of the gold bars in central bank vaults fell to $4.62 billion, down 18.5% from $5.67 billion dollars at the end of 2018 - the lowest in 75 years.
Laid off miners are blocking trains in protest against Blackjewel, which halted operations in July without settling its final salary obligations to more than 1,800 workers across the country.
The upgrade is expected to increase average annual gold production at Ahafo by between 75,000 and 100,000 ounces for the first five years, starting in 2020.