If you are unwilling/unable to access the given co-ordinates, please see Q2 below which will give you an alternative. (Thanks to XboomstickX for this info).
An EarthCache featuring the Ironsands at Waipipi Beach. Ironsand was mined here from 1971 – 1987. This cache will take you to the proximity of the old ironsand mine and will teach you a little about ironsand and how it was formed and how it was mined.
There are questions to answer, a photo to be taken and an experiment you will have to complete to claim this EarthCache and you will need to bring along a magnet. Further information below.
Waipipi Beach
Formation of Ironsand
In the North Island ironsand occurs along the west coast between Wanganui and Auckland.
About one and a half million years ago the volcano of Karioi, south of Raglan, erupted and other volcanoes became active between Raglan and the Waikato Heads. These eruptions continued until about a quarter of a million years ago when volcanic activity started in Auckland and at Mount Taranaki. Volcanic rocks were deposited both inland and along the coast. The erosion of this rock has provided the major raw material for the ironsand deposits. Measurement of the sediments carried by the Waikato River indicate that the major source of the Waikato North Head deposit is coastal erosion of the Taranaki volcanics rather than sand carried by the river from Ruapehu. Erosion of these volcanoes over several hundred thousand years, and the action of sea currents, waves and wind has concentrated the heavy minerals along the coast.
These 'blacksands' were noted by Captain James Cook during his first voyage in 1769. He called the area 'The Desert Coast'.
Many attempts have been made to work the ironsand deposits, the first in 1849. The main iron mineral in the sand is titanomagnetite, a compound of the elements titanium, iron, and oxygen. It was the presence of titanium which caused the usual iron making process to fail. The titanium oxide in the ore has a very high melting point and the slag blocks conventional blast furnaces. In addition the fine sand fell through the furnace and choked the hearth. Over the next 100 years at least six experiments to produce iron from ironsand were unsuccessful.
In the late 1960s steel producers in Japan were looking for new suppliers of titanomagnetite. The same material which was known to block blast furnaces could now be used to preserve furnace linings and aid the steel making process. Extensive trials by the government using North Island ironsand, coal, and limestone led to New Zealand Steel being set up to develop an ironsand mining operation near the coast, north of the Waikato River and build a steel mill at Glenbrook, south of Auckland. Steel production started in 1970 with the Glenbrook mill pioneering the direct reduction of ironsand and coal to make iron and steel. The Glenbrook process is unique. No other steelmaking operation in the world makes steel in the same way.
As well as the ironsand mining operation at North Head, two similar ironsand mining operations were developed on the west coast of the North Island here at Waipipi near Wanganui in 1971 and further north at Taharoa in 1972.Gravity and magnetic separation are used to produce concentrate which was pumped through pipelines to an offshore buoy for loading into specially designed ships. The Waipipi plant closed in 1987 having produced about 15.7 million tonnes of concentrate.
The ironsand resources of the North Island are very large. Detailed investigations of only parts of the coast have given resource estimates of 1444 million tonnes of titanomagnetite and 8.4 million tonnes of ilmenite. These resources would keep the existing scale of operation going for several hundred years.
Mining
First the sand has to be mined. Bucketwheel excavators place the sand on shiftable conveyors. The conveyors discharge onto a main trunk conveyor which feeds a stockpile from which the sand is fed into the concentration plant.
In the plant the titanomagnetite is separated from the other sand and unwanted materials. Titanomagnetite is magnetic and heavier than other minerals in the sand, so magnetic and gravity methods are used to separate it from other minerals. Mined sand firstly passes through revolving screens called trommels to remove stones and other impurities. Oversize material like stones, roots, and lumps of clay are sized out and discarded. Water is added to the sand to produce a slurry. Magnetic separators remove the titanomagnetite which accounts for about 20% of the sand, but some low grade sand is also trapped. This is removed by gravity in cone concentrators and spiral separators. Sand and water flow over the surface of the cone and the heavier iron minerals sink to the bottom and pass through the slots in the cone. A series of cones and spiral separators remove nearly all the light minerals. The final stage uses finely adjusted magnetic separators . Water is added to the ironsand concentrate so that it can be pumped through pipelines. The nonmagnetic sands which are not required are returned to the mining area.
Once you complete the following EarthCache requirements you can post your find without delay, as per the EarthCache guidelines. You will also need to verify your find by sending us a message with your answers to these questions and we will answer in due course:
1. Use the text "Waipipi Ironsands - GC22NH3" in your email.
2. The published co-ords will take you to a monument featuring one of the ships used during Waipipi’s mining operations. What was the name of the ship and where were the ironsands shipped to? If you are unable to access this area easily, then please go to these co-ordinates: S 39 50.026 E 174 38.182 and let us know what you see here.
3. (Optional) Take a photo of you and/or your GPS with the monument in the background – don’t include the plaque with the answers on please. Post the photo with your log. As (1) above, alternative is take a photo of what you see here.
4. As you will have read in the educational material provided on this cache page, titanomagnetite (the main mineral in ironsand) needed to be separated from foreign matter and other sands/impurities. We would like you to conduct a simple experiment which attempts to copy this process.
You will need to bring with you a magnet of some kind. (The bigger the magnet the quicker you will complete the experiment). Proceed to the beach below the monument (or nearby the alternative co-ordinates) and place a quantity of dry ironsand in the palm of your hand or a small container if you prefer. Using the magnet extract the titanomagnetite from your sample. Continue to pass the magnet over the sample until you have extracted all of the titanomagnetite. You are required to assess the percentage of sand/impurities that remain once all of the titanomagnetite has been removed. (If the sand is wet you will have to take some home to dry out). Send us the result of your experiment along with the answers to Q2 above. Please do not post answers with your log or it will be deleted.
Please DO NOT post answers with your log. Just post your photo.