Roder, G.H.; Suggate, R.P. 1990 Geological map of New Zealand 1:50,000 Sheet L29 BD Upper Buller Gorge. Lower Hutt: New Zealand Geological Survey. Geological map of New Zealand 1:50,000 L29 1 fold. map + 1 booklet
Abstract: Plutonic rocks of the Karamea Batholith intruding lower Paleozoic sedimentary rocks form ranges between the Tertiary rocks of the western margin of the Murchison depression to the east and of the northeast limit of the Grey-Inangahua depression to the west. Greenland Group greywacke and argillite are regionally metamorphosed to chlorite zone of the greenschist facies, on which is superimposed contact metamorphism of the hornblende hornfels facies. ... Rb/Sr dating indicates that the initial cooling age of granites are all over 300 Ma, less than the 450 Ma age of the Greenland Group rocks; a late Devonian-earliest Carboniferous (Tuhua Orogeny) age is inferred. K/Ar ages appear to indicate Early Cretaceous (Rangitata Orogeny) uplift or reheating. In the east the Tertiary sequence begins with the Upper Eocene Maruia Formation. ... The Maruia Formation overlaps westwards and southwards onto pre-Tertiary rocks, with basal shallow marine formations. ... The youngest Tertiary rocks are the lower Miocene Inangahua Formation (mudstone) in the west and central northern areas and the Mangles Formation (Tutaki Member; sandstone/mudstone) in the east. The Tertiary units thicken eastwards, the Maruia Formation up to 1000m and the Matiri Formation from 10m to over 400m. Quaternary terrace deposits are up to 300 m above the rivers, the highest terraces being strongly warped in keeping with the pattern of deformation of the Tertiary rocks. Gold in quartz reefs in the Greenland Group and alluvial gold principally along the Buller River, were formerly important. Some molybenite mineralization is known. Coal resources are small and inaccessible; the bituminous coal is very high in sulphur. Very pure algal limestone is quarried for industrial and agricultural use, but economic access is becoming difficult. The area is one of high earthquake risk, with major active faults.