The mountains include a number of volcanoes. Seventeen post-Miocene strato volcanoes have been identified on Bougainville, the largest island of the Solomon Group. From north-west to south-east, these are the Tore, Balbi, Numa Numa, Billy Mitchell, Bagana, Reini, and Bakanovi volcanoes and the Takuan and Toroka groups of volcanoes. There are several other post-Miocene volcanoes in northern Bougainville which have not been accurately delineated.
Three of the volcanoes are active or potentially active; these are Bagana, the most active volcano in the Territory of New Guinea, and the dormant Balbi and Loloru volcanoes.
The Keriaka limestone plateau south of Mt Balbi contains Benua Cave, one of the largest underground caverns in the world.
The volcanoes are built up of lavas and pyroclastic deposits mostly of andesitic composition, although some dacitic rocks are also present.
EL03 and EL04 cover a combined 1704 square kilometres of highly prospective, Mineral Resources Authority (MRA) mapped Emperor Range Volcanics – andesite, basalt, agglomerate, tuff and associated fan deposits, intruded by a mapped 150 square kilometres of Oligocene to Pleistocene diorite, microdiorite, monzonite, granodiorite, syenite and granophyre. Similar intrusives host the giant Panguna deposit (1,838Mt @ 0.30%Cu and 0.34g/tAu, as published by Bougainville Copper Limited – ASX: BOC in the 2016 Annual Report published 31 March 2017)