Francis, D.A.; Webby, D.C.; Christie, A.B.; Brown, L.J. 1991 Geological resource map of New Zealand 1:250 000 : sheet QM 303 Raukumara. Lower Hutt: DSIR Geology & Geophysics. New Zealand Geological Survey report M 180. 57 p.
Abstract
Aggregate is the only rock commodity produced in significant quantity in the Ruakumara sheet. Northwest of the main divide the bedrock is hard, indurated sandstone and mudstone (greywacke and argillite), and good quality aggregate is comparatively plentiful. In contrast, in the populated region from Gisborne to Ruatoria, to the east and southeast of the main divide, the bedrock is mostly softer mudstone-dominant sedimentary rock, and suitable hard rock resources are less abundant. In this region hard limestone is quarried as the main aggregate source. Sand suitable for concrete is worked from Holocene coastal deposits at Whangara and Pouawa. Bentonite is extracted intermittently from a deposit at Paraheka Station, has been worked north of Whatatutu, and is present in economic grades in many other localities. Lime for agricultural use is at present transported into the Gisborne area from quarries in areas south of the Raukumara sheet. Although limestone of agricultural grade is present within the sheet, this is currently used only as aggregate. Other minor mineral commodities include barite, clay for locally produced earthenware pottery, and ditomite (not confirmed). Copper and manganese mineralisations occurs associated with submarine basic volcanics of the Matakoa Volcanic Complex (Cretaceous to Eocene). The main prospects are at Lottin Point and Te Kumi, although mineralised boulders have been recorded elsewhere in the north of the Raukumara Sheet. Several oil seeps and numerous gas seeps provided the stimulus for oil exploration since 1884. Twenty nine wells have been drilled onshore, but none has produced payable quantities of oil or gas. The area has generally good indications for petroleum, especially southeast of the main divide, and is virtually unexplored. Petroleum is the most significant long-term resource prospect for the area. Groundwater is a resource of major importance in the cultivated and populated areas. Hot springs at Te Puia have significant potential for further development, and cold brine springs are widespread in the eastern and southeastern parts of the area.
