Dun Mountain, rising to 3,703 ft, is the highest mountain in the vicinity of Nelson City. It lies on the dividing ridge between the Pelorus River and Tasman Bay and its western slopes are drained by the Maitai and Roding Rivers, discharging into Tasman Bay and the Waimea Plains. From Nelson, Dun Mountain is conspicuous because of its lack of forest, and because of the reddish soil on the summit and upper slopes. The mountain was named by early residents of Nelson for its dun colour. In 1859 the Austrian geologist Ferdinand von Hochstetter discovered that the mountain was made of dense igneous rock, composed chiefly of two minerals—olivine (magnesium—iron silicate) and chromite (chromium—iron oxide). This unusual rock he named dunite, a name since applied to rocks of this type throughout the world. Because of the peculiar rock composition, the soils lack plant nutrients and so are devoid of vegetation, apart from stunted shrubs and grasses.
Dun Mountain was the scene of sporadic mining activity between 1850 and 1865, when small deposits of chromite and copper ore attracted some attention. The Dun Mountain tramway, now disused, was constructed to carry the ores to Nelson. The mountain has always been attractive to mineral prospectors and collectors; recently a survey was carried out to investigate the possibility of mining the dunite for use as a basic ingredient in the manufacture of superphosphate, but the project fell through on economic grounds. A proposal to dam the Maitai River for the Nelson water supply will add a lake to the mountain's natural beauty and further increase its scenic and recreational value.
by George William Grindley, M.SC., New Zealand Geological Survey, Lower Hutt.