New Zealand rock hunting
Heather Wilson (New Zealand)
I am involved in a rock and mineral club at Dunedin, which is situated about a third of the way up the east coast of New Zealand’s South Island. Given the possibility of flying from one end of the country to the other in three hours, we receive many tourists who come to see the superb range of scenery we have here. For rock hunters, there is also the benefit of there being no wild animals (other than the occasional redback spider) to attack you. However, if you venture onto farmland without permission, there may be the odd wild farmer or two to fend off. It is generally considered polite to ask before you fossick.
Because New Zealand is so far from Europe, many of its rocks and fossils are very different. The rocks here are recognised and defined by fossils particular to New Zealand, and are given local names, which are known collectively as the ‘NZ series’. As geologists have found good examples of New Zealand rocks representing the geological ages, they have built up a sequence of type sections with fossils and sediments, that have become a standard reference for comparison with all other rocks of that age in the country. This series is used on the one-inch-to-the-mile geological maps that are indispensable for anyone seriously looking at the geology and physical geography of the country.
New Zealand’s oldest rocks are thought to be around 600-800 million years old and date from the time when the formation of the western block of the country occurred. About 300-150 million years ago the eastern block of NZ was formed, and around 85 million years ago the country broke away from the Australian edge of Gondwana to become established as a small continental area, through which a plate boundary passed. Sixty million years later, around 25 million years ago, NZ was mainly under the sea and soft sediments were deposited over the older rocks. In the last 20 million years the country has emerged from the sea again and terrestrial flora and fauna have colonized the land.
One reason to come to New Zealand is having so many fun places to visit and things to do. For example, we have bungee jumping in the Kawara Gorge (Fig. 3), in Central Otago.
On the way down, you can look at the schist rock to see if you can find any gold in it. The river below is full of gold and, in the early days, there were many prospectors who made their fortune here, and many pounds of gold were removed. Nowadays, you can pan for gold and still find nuggets if you are lucky.
The vanished world fossil trail
Anyone who likes geology will be interested in the Vanished World Fossil Trail in the Waitaki Valley area. Some 24 million years ago, the Waitaki region was under the sea. Creatures from this sea became incorporated into the seafloor material. As this was slowly buried deep beneath the seabed through the process of sedimentation, it became compressed and cemented to form limestone.
Uplifted to the surface in the last few million years, the rocks have subsequently been eroded into a range of shapes. Study of these limestones has helped scientists unravel the mysteries of this area’s geological past and the evolution of the creatures that have left their fossil presence in these rocks. Waitaki rocks contain records of ancient creatures ranging from intricately-patterned and microscopic diatoms to the whales that swam in the ancient seas.
The trail allows public access to geological localities that reveal this ancient history, including fossiliferous sites, extinct volcanoes, mineral-rich localities and major landforms. The Vanished World localities are found along the Otago coast, from Waianakarua to Oamaru, and inland to the Vanished World Centre, a museum based at Duntoon, that exhibits fossils and information on how the area was formed. The trail has been designed to provide a glimpse of, and an introduction to, a particular stretch of geological time when the New Zealand region was witness to the development of animals such as the cetaceans (whales, dolphins and porpoises) and penguins.
The trail complements Waitaki’s other well known tourist attractions, which include the Moeraki Boulders, the Oamaru Blue Penguin colony and the clay cliffs at Omarama. It is self-guided – you simply drive from place to place, starting from, or stopping at, any point.
Notable features to see along the trail include the so-called ‘Elephant Rocks’ at North Otago, near Duntroon. Weathering processes have worn away surrounding, softer rock layers, leaving harder rock cores. Some of these limestone rocks have been weathered by wind and rain into weird and wonderful shapes. If a little imagination is used, some are definitely elephant shaped.
Another of the sites on the tour is Boatman’s Harbor, Oamaru, where unusual volcanic structures known as ‘pillow lava’ are visible. These spherical and pillow-shaped masses are the result of fingers of lava flowing onto an ancient seafloor from the Oamaru volcano some 40 to 50 million years ago. Erosion by the present day sea has cut across parts of the flow, enabling the glassy surface of the pillows to be seen, along with fossil-bearing marine sediments that fill the gaps in between the hardened lava.
Macrae’s Gold Mine
Another place to visit in Otago is Macrae’s Gold Mine. Here there is a two-hour long tour that takes you to see enormous trucks and excavators in action. You can visit heritage mining sites, one of which includes a complete battery stamper. There is also the gigantic Fraser’s open cast pit and the Otago Fish and Game Hatchery, where you can see the rainbow salmon breeding ponds, followed by a stop at the gold-processing plant. Tours start at 10.30am and 1.30pm on most days. You can’t fossick for gold yourself here, but there is a little stream near Palmerston where you can pan for your own gold.
New Zealand weather
The weather in New Zealand varies from place to place. The climate is more tropical and has a higher humidity at the top of the North Island. On the South Island, it can be cooler, especially in winter, when you can get –10oC frosts and snow. The country very rarely experiences extreme weather such as tornadoes or hurricanes, but we do get the odd thunderstorm. Inland areas can get very cold in winter and hot in summer.
It pays to do your fossicking in the warmer months as, at times in the winter, it freezes here and it is very hard trying to pry one frozen rock off another. In addition, as New Zealand has a lot of coastline, you can experience four seasons in one day at some times of the year, especially in spring. From August through to May is probably our main season for hunting specimens, due to the milder weather during these months. Even so, it always pays to take a warm change of clothes and a jacket with you, no matter what time of year it is. Some sites also need hard hats, protective goggles and gloves.
Around Dunedin (local to, and therefore popular with, the Otago Rock and Mineral Club), there are several quarries. One is Blackhead Quarry where there are vesicles that contain calcium and sodium-rich zeolites, as well asabundant calcite and rare pyrite. If you are lucky, you can find beautiful specimens of natrolite, phillipsite and calcite. The trouble with this quarry is that a large sledgehammer is required, along with hard hats and other protective gear. You also need a certain amount of energy, as breaking the quarry’s basalt rocks for crystals is hard, backbreaking work.
Another good site is Waltam Park Quarry (Fig. 7) at Fairfield, just outside of Dunedin, where the KT boundary can be seen.
Ammonites, shells and other fossils are found below the KT line. You will need gumboots and some sort of digging implement here. Please watch where you dig though, or you may end up with half a cliff falling down on you (Fig. 8).
