Oldest N.Z. Fossils In West Nelson

Press, Volume CI, Issue 29744, 10 February 1962, Page 14

Oldest N.Z. Fossils In West Nelson

The oldest fossils in New Zealand are small marine crustaceans called trilobites, found in Cambrian limestone in the Cobb Valley. They are probably more than 500 million years old. The Cobb Valley is one of the areas included in the latest of the series of 28 coloured geological maps of New Zealand, being issued by the Geological Survey, Department ot Scientific and Industrial Research. The latest map is sheet 13 and is entitled Golden Bay. It shows the distribution of the rocks of different types and ages that make up the mountainous west Nelson region, one of the most geologically complex parts of New Zealand. The maps are produced on the scale of four miles to the inch.

Nelson’s younger rocks, although of smaller extent, have considerable emonomic importance. Half a million

tons Of coal has been extract- ! ed from them in the Collmg- , wood-Puponga districts, and ' they include the limestone i used at Golden Bay for the manufacture of most of the cement used in the central ■ part of New Zealand. The . proposed oil search in the ; Farewell Spit area will be > directed at the thick mass of '■ these younger strata that are . partly submerged beneath Golden Bay. Field Work To produce the new map, , Geological Survey geologists carried out many months of 1 strenuous field work. Their ' task was made difficult by the roughness of the moun- ; tain country, the heavy bush cover, and the complex manner in which the rock masses of west Nelson have been contorted and broken. , Much of the region con- , aists of some of the most : ancient rocks in New Zea- , land. indudlng granite, schist, marble, state and otter rocks, some of them dating back to the Cambrian and Ordovician periods'about 500 million years ago. In the past many mineral occurrences have been reported in west Nelson, mainly in these ancient rocks, but most of them have proved disappointing. The new map forms a basis for more scientific prospecting in the future. It embodies a new interpretation of the struture of the outer part of lhe crust in this part of New Zealand arising from recent exploration there, mainly by Mr G. W. Grindley of the survey’s Wellington district office, ; who compiled the map. The new knowledge of the geological structure may help . explain the erratic distribution and disappointing size of the known mineral occurrences, and help direct search to more promising areas. Gold Reefs The old rocks contained the gold reefs of the Aorere and Golden Ridge districts near Collingwood. Old alluvial gravel from, them caused a gold rush 100 years ago. Lead, silver, and zinc are other metals that have been ’ worthy of attention in these rocks in the past. They also contain many non-metallic minerals at present being mined such as dolomite at Collingwood and talc-magnesiite and asbestos in the Cobb Valley. Marble quarried on Takaka Hill, mainly fdr the chemical industry, is one of tihe ancient rocks also. It was used in polished form for the interior of Parliament Buildings. and much is still used in the rough for decorative stonework.