Return to Bougainville – Reassessing the Mineral Potential of a Long-Forgotten Island

Apr 10, 2018

Michael Agnew, Society of Economic Geologists April 2018

“In June 2019, the population of Bougainville, a southwest Pacific island of 9,380 km2, will vote on whether to remain an autonomous region of Papua New Guinea or become the world’s newest nation.”
Agnew, M,. 2018, Return to Bougainville-Reassessing the Mineral Potential of a Long-Forgotten Island: Society of Economic Geologists, v. 113, p. 1, 18-24.

Introduction – 

In June 2019, the population of Bougainville, a southwest Pacific island of 9,380 km2, will vote on whether to remain an autonomous region of Papua New Guinea or become the world’s newest nation. Proponents of an independent Bougainville are looking for sources of revenue to kick-start the island’s economic development, including reopening the mothballed Panguna copper-gold mine (Barrett, 2017). However, significant local opposition to such a step remains (e.g., Davidson, 2018), so the future exploration prospects for the island are uncertain.

Panguna commenced production in 1972, as the world’s largest copper mine, with total metal endowment of 18 billion pounds of copper and 30 million ounces of gold (historic production and remaining JORC-compliant resource; Collier et al., 2011; Bougainville Copper Limited, 2016). The operation closed 17 years later amid a prolonged campaign of sabotage by the Bougainville Revolutionary Army, stemming from social, environmental, and economic issues catalyzed by the mine (Denoon, 2000; Barrett, 2017). The Autonomous Bougainville Government and Papua New Guinea Government currently each own 36.4% of Bougainville Copper Limited, the publicly listed administrator of the mine after Rio Tinto divested their stake in the company during 2016.

Bougainville has 17 post-Miocene volcanoes, including the active or dormant Bagana, Balbi, and Loloru volcanoes (Blake, 1967). There are more than 60 volcanic vents and intrusive centers and numerous active or extinct fumarolic, acid sulfate-altered areas (Blake and Miezitis, 1967; Rogerson et al., 1989). Small-scale gold mines operated intermittently in the Kupei and Panguna areas from 1930 to 1960 (Blake and Miezitis, 1967). Apart from a geologic survey mapping and sampling program during the 1980s, little or no mineral exploration has occurred outside the Panguna mine lease since 1971. A decades-long moratorium on exploration and mining was lifted in October 2015. The Autonomous Bougainville Government’s Mining Act 2015 paves the way for a new generation of mineral exploration on the island, which remains highly prospective for porphyry, epithermal, and skarn deposits.

This article provides an overview of the tectonic and structural setting, stratigraphy, magmatic history, and geochemistry of Bougainville. Magmatic fertility indicators and whole-rock and stream sediment geochemical data were combined with the interpreted geology to delineate areas that are prospective for magmatic-related copper and gold deposits. A database of 269 X-ray fluorescence and instrumental neutron activation analyses was compiled from published papers and unpublished Ph.D. theses. Sample coordinates from the Panguna mine grid were transformed into latitude/longitude using a registered Google Earth image, color plate 2 from Clark (1990), and the original grid orientation (J. Lew, pers. commun., 2017). Linear topographic features, extracted from an ASTER digital elevation model, were combined with published interpreted structures over the island.

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SEG Newsletter 113 – April 2018.
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FIGURE 1. Tectonic setting of Bougainville and neighboring islands of Papua New Guinea and the Solomon Islands. Metal endowment of major deposits was calculated from resource and/or production data. Modified from figure 2 of Holm et al. (2016). Shaded areas occur above the 2,000-m bathymetric contour and show major oceanic crustal features.