The lower two members of the Jurassic to Triassic Kunga Group, the Sadler and Peril formations, represent the main limestone resource of the Queen Charlotte Islands, particularly the basal Sadler limestone. Its thickness varies from less than 30 metres to more than 200 metres.

A bed of massive grey limestone of the Upper Triassic Sadler Formation strikes north across Kunga Island for 3 kilometres and dips 40 to 60 degrees to the east. The bed is bounded to the west by underlying volcanics of the Upper Triassic Karmutsen Formation and to the east by thinnly bedded black limestone of the overlying Upper Triassic Peril Formation. On the north shore of the island the bed is 180 metres thick, where it is intercalated with a mafic flow or sill 23 metres thick.

A chip sample taken across a stratigraphic thickness of 152 metres at the south shore of Kunga Island assayed 53.2 per cent CaO, 0.11 per cent MgO and 42.03 per cent loss on ignition (EMPR Open 1992-18, page 45)