Story: Iron and steel
Page 1 – Iron – an abundant resource
Iron, especially in the form of steel, is the dominant metal used in all modern societies and a key factor in their industrial development. It is the fourth most abundant element in the earth’s crust and, after aluminium, the second most abundant metal.
Most of these metals are smelted from naturally occurring material known as ore. Iron is extracted from iron ores, commonly found in rock. The main purpose for extracting iron is to make steel.
New Zealand has only a small amount of one frequently used iron ore – limonite, which is found at Onekakā in north-west Nelson. However, it does have another, unique source of iron: beach sand composed of a type of iron oxide called titanomagnetite.
The North Island ironsands
During his first voyage around New Zealand in 1769–70, Captain James Cook recorded ‘a black sandy bottom’ in his journal, as the Endeavour sailed southward along the coast near Raglan. In 1839 Ernst Dieffenbach, hired by the New Zealand Company to describe New Zealand’s natural resources, noted the ‘black titanic iron-sand’ on beaches along the Taranaki coast. In fact these sands stretch for 480 kilometres, from Kaipara Harbour down to Whanganui.
Beach sands containing iron minerals are common around the world. Many have been studied as potential sources of iron, but few are of commercial value. New Zealand’s ironsand deposits, among the largest in the world, are rich in the mineral titanomagnetite. This is a black, heavy, magnetic iron ore which originates as crystals within volcanic rocks. In New Zealand, it occurs in the darker rocks of the Taranaki volcanoes and the lighter-coloured rocks of the Taupō Volcanic Zone. As the rock is slowly eroded, rivers carry the grains of titanomagnetite to the coast. Ocean currents then move the minerals along the coastline, and the action of wind and waves concentrates them in dark-coloured sands on the sea floor, on beaches and in dunes.
These ironsands form the country’s greatest reserves of metal ore.
The British colonists who first arrived in New Zealand expected to find mineral wealth, and hoped that the country could become a manufacturing hub – a ‘Britain of the South’. In 1865, promotional material referred to a future in which ‘the forests and fertile plains of New Zealand will resound with the clang of the forge and the hum of the factory, and the midnight glare of the furnace illumine the surface of her lakes and rivers.’ 1
Extracting iron for steel
European settlers soon discovered this abundant resource, but the sands defied efforts to extract the valuable iron. It would take more than a century of perseverance and ingenuity for New Zealanders to develop a specialised technology to make steel from sand.