This area of about 320 km2 is located south of Marrawah, and includes the townships of Arthur River and Nelson Bay. The Sundown sheet also covers the Nelson Bay River iron ore deposit currently being developed by Shree Minerals, and one aim of the project is to place this deposit in a regional context. Other commodities recorded in the area include copper, silica, chromite and heavy minerals. Forestry, grazing, bee-keeping, tourism, off road recreation and conservation (including Aboriginal sites) are other land uses in the area.
The geology of the area was previously poorly known, particularly away from the coast. It consists of a mostly northeast-dipping and facing siliciclastic sequence, part of the Mesoproterozoic to early Neoproterozoic Rocky Cape Group, which is overlain in the Salmon River area by the late Neoproterozoic volcanosedimentary Togari Group. The new mapping has refined the local stratigraphy and structure, delineated several discordant mafic dykes, and defined the limits of extensive windblown sand cover.
Fieldwork for the Sundown sheet was based from accommodation at Balfour, and required three geologists for about 65 field days in 2012/13. The Bluff sheet was mapped from Marrawah by two geologists over a similar period in late 2013. The lower reaches of the Arthur, Frankland and Nelson Bay Rivers were completely traversed, as well as an extensive network of mainly logging roads, the coast, and numerous smaller streams. Orthophotos and magnetic and radiometric images derived from the airborne geophysical survey, flown in 1996 for MRT, facilitated mapping, particularly in areas of relatively poor outcrop inland. Both maps are currently being compiled and publication is expected in late 2014. Explanatory notes will also be provided.