The new resource, the first upgrade since the mine was suspended 20 years ago, was increased by 114.5% to 1.064Bt.
More than 9 million ounces of gold and 3 million tonnes of copper were mined from the Paguna deposit throughout the 1970s and 1980s, however militant action led to the mine's suspension in 1989.
When the mine closed Paguna had an ore reserve of 496Mt at 0.42% copper and 0.55 grams per tonne of gold.
The upgraded findings were based on the study of archived data and took the Paguna mineral resource to 1.064Bt at 0.33% copper and 0.37gpt of gold, with
1Bt categorised as indicated while the remaining 64Mt fell in the inferred category.
Bougainville Copper is 53.58%-owned by Rio Tinto. The Papua New Guinean government holds a 19.06% stake and the remaining 27.36% is publicly held.
Shares in Bougainville Copper were unchanged at 67c.