Ngā Tohuwhenua Mai Te Rangi: A New Zealand Archeology in Aerial Photographs
17 — Gold-Mining
Gold-mining sites and contemporary wild-flooding at Northburn, near Cromwell, 1968
From left to right across the photograph are the modern bed of the Clutha River, the rise to the high terrace, and then the hill country. The wild-flooding is marked by the darker water-soaked ground on the high terrace. The water is flooding out of a supply race and storage ponds originally designed in the 1860s by gold-miners for sluicing the high terrace. Head races from the ponds to the gold-sluicing area (marked by 'herring-bone' tailings) show clearly. The wild-flooding water from the supply race has flowed into and gathered in the original head races and the storage ponds, and is beginning to flow down the terrace face, mimicking the flow pattern of the older miners' ground-sluicing.
Several eras and systems of alluvial gold-mining are represented here. On the high terrace 60 m above river level, supply races feed into a number of small holding dams created by an earth embankment constructed on the slightly sloping surface of the high terrace; these show as dark patches at bottom right. During working hours the water from these dams was fed into the head races and then across slight slopes down to the work faces, marked here by fainter linear traces of tailings upslope from the herringbone tailings. The final work faces were at the edges of the herring-bone tailings. Tail races carried water away from the tailings area. In the bed of the Clutha River which runs from top to bottom are the tailings of dredges, dating from about the turn of the century.
Gold-mining, a major theme of New Zealand folk history, has had a great impact on the New Zealand landscape. The principal areas of mining were Central Otago (gold discovered in 1861), the West Coast (1864), Nelson/Marlborough (1857) and the Coromandel (1852). Mining in the Cook Strait area was attempted but was largely unsuccessful. 1 In preparing this book, I found that the most visually interesting remains were in Central Otago, particularly near Cromwell in the Clutha River valley. On the West Coast and the Coromandel ranges, areas of high rainfall with a high proportion of land managed for nature conservation, forest has covered over many interesting sites.
Gold-mining took two main forms: quartz bedrock and alluvial gravels (river plains and terraces). The quartz bedrock mining featured mainly on the northern West Coast, in the Reefton area and the Paparoa Ranges, and in the Coromandel; some hard-rock mining also was conducted in Central Otago. This was a capital-intensive industry. The rock had to be mined, crushed and chemically treated, requiring large plants and buildings, some of which still survive. There were also major associated works which generated the energy necessary to crush the rock: either direct water power or, later, hydro-electric generation. Generally this capital-intensive exploitation of hard-rock resources came later in the gold-mining era, peaking in production over the decades 1890-1920, 2 and with developments still continuing today. A characteristic landscape effect from hard-rock mining is the debris from the exploratory tunnels (adits). This was cast out down the slope from the tunnel entrance in cone-shaped screes or piled around the head of shafts, as at Bendigo illustrated here.
Opposite. The Bendigo goldfield, near Cromwell, which operated from 1865 to the 1930s
The view is to the east along the North and South Lodes of the Cromwell Reef. In the foreground are the Main Shaft, battery, office and smithy foundations of the South Lode, with talus (debris) heaps from other shafts further to the east on the line of the same lode. At upper left is the talus heap of the Engine House Shaft on the North Lode.
Below. A near-vertical view to the south of the Engine House Shaft (fenced, at middle) which was about 180 m deep. Adjacent are the foundations of the stamper for crushing the quartz (showing as a prominent rectangular block) and other machinery buildings.
Settlement on the Bendigo field
The walls and foundations of the buildings of Welshtown, one of the principal mining settlements of the Bendigo field. A water race terminates at left, and at upper right, by the road, is a section of worked lode. The buildings have been cleared of shrubs and architecturally stabilised in recent years. The view is to the north. The huts are about 8 by 4 m in plan.
Alluvial mining is for gold taken from secondary sources of deposition, i.e., where geological processes had removed gold particles from the quartz rock. Gla-ciation transported enormous quantities in earlier eras and also created high terraces, lying up to 100 m above the modern valley floor. The mining concentrated on areas where the original gold-bearing ore had been transported down river and deposited on these terraces. Within the bulk of a terrace, alluvial miners would quickly recognise layers that held the promise of concentrations of gold, and capital equipment and facilities were constructed to exploit them.
Alluvial mining occupied two main phases in Central Otago and the West Coast, the principal areas for this type of mining. 6 The earliest phase was when small groups of men rushed to the easily accessible alluvial deposits and mined them by hand using simple equipment. Very little evidence of this phase of activity remains. It was inefficient, only partially working the deposit, and has been destroyed by later activity. The second phase was capital-intensive and has produced massive change in the landscape, much of which survives today. Large investments were made in either dredges, which worked the river bottoms, or hydraulic systems which worked the higher terraces and the valley floors. Because of the size of the investment, or the fact that the individualistic methods of the miners needed regulation, the government became involved in surveying, building and controlling both head and tail races.
In Central Otago, dredges worked through to the 1930s; on the West Coast, dredges are still working at the present day. This process left a raised valley floor, comprising ridge after ridge of the heavier gravels or boulders, placed by the tail-arm of the dredge. The sand and finer gravels were passed back into the river or a pond after the gold had been extracted. Modern dredges, and the hydraulic backhoes that have largely replaced them, normally have stricter standards of rehabilitation in which the gravels are replaced and covered with top-soil so that plants will grow. This partly obscures the direct mining effects. Where the earlier deposits are reworked, as often happens, they are destroyed.
Hydraulic sluicing produced an even more fascinating landscape. The process worked in three separate parts: headwaters collection and reticulation to the work face; the sluicing face itself; and methods for disposing of the sluiced water, the gravels it contained and the boulders that the sluice water could not shift. Before an investment was made, the extent, quantity and depth of the gold was checked by digging shafts down into the terraces. The areas that could be worked by this method required gravity-feed of the water both to and from the sluicing locality.
The work face itself changed over time. The earliest was ground-sluicing: water was simply flooded over the surface of a terrace, the surface broken up by pick and shovel, and the silt and gold particles transported by the water to simple races and riffle boxes where the gold settled. 7 A development of this technique, apparently unique to Central Otago, was 'blowing down'. This again involved simple races to the head of the claim, but involved more elaborate stacking of tailings to rid the worked areas of large stones that could not be carried away by the water. A phase of such techniques can be seen at Northburn, near Cromwell, dating from about 1863. 8
These techniques depended on relatively simple access to the gold, with the slope of the gold-bearing de- page 262 posit dipping down towards the potential tail races. Such techniques were obsolete by the 1880s when only much deeper deposits remained to be worked. Access required digging into the face to a greater depth and elaborate methods for ridding the site of water. A large stream of water from a pipe under high pressure was directed, using a California sluice-monitor, on to a vertical gravel workface. The gravels were washed away and down into a central race where the gold was collected. Stones too large to be moved by the water were placed in regular patterns of tailings to remove them from the work face and to guide the water away from the face. 9 The tailings and the remnants of the very last face to be worked are all that survive today.
Hydraulic headworks are one of the enduring historic elements of the Central Otago landscape. These consist of dams and supply races, the latter tracing a near-horizontal level around the sides of hills. Often of course the water would be piped, in which case no trace of a race survives. The bridges and fluming that might be needed to cross a gully also leave little trace. Some of these headworks systems still survive today, in use for irrigation or town water supply. Few water races, unfortunately, survive in reserve areas. They are simply too extensive to make it worth placing a complete system of them in reserve areas.
Ground-sluicing and the sluice-monitors needed a considerable volume of water to be effective in removing the dirt. However, the streams that could be brought to a particular area sometimes had limited volume, especially in summer. In Central Otago, much effort went into conserving this water and using it to good effect. Water was ponded in earth-walled paddocks (i.e., holding dams) on broad ridges or terraces adjacent to and slightly above the sluicing area. It would accumulate overnight and then be released in the desired volume through head races into the sluice area during the day, although some took 'night water' at cheaper rates. On the high terraces of Central Otago, such as Northburn, these paddocks could be as much as 10 ha in extent, and the water stored in them seldom more than 1 m deep. On the West Coast, more conventional dams might be constructed.
In the sluice area, the most efficient way to deal with the gold-bearing deposits was chosen. This involved opening up an area of the terrace in a sequence determined by good engineering practice, with the boulders and coarse gravel stacked in tailings, while the balance of gravel and sand ran down to a central race. In the 'herring-bone' pattern of tailings, for example at North-burn, rows of placed stones radiate out in a distinctive pattern from the central race. In the central race towards the working face a long wooden box with riffles settled gold particles out of the sluiced gravel and sand.
Once the water had been used, it had to be got rid of. With a gravity-feed system, there was no prospect of recycling the water. Removing it was easy if the terrace was the highest one in the valley. Tail races were constructed to take it away into the river. Occasionally, it was necessary to run an artificial channel or fluming along the top of the gravel tailings to prevent them building up and impeding the placement of further gravel tailings. If it was not possible to run the tail races directly downhill, then elaborate races and tunnels had to be constructed. This was essential to rid the lower sluicing sites of the water. On the Kūmara goldfield, West Coast, residential sections stood in the way, and these were tunnelled under. A late development of the process was venturi-siphoning of the water from the work face. This opened up deep deposits of gold-bearing gravel from below the natural level of the river waters.page break
Herring-bone tailings on the high terrace at Northburn
The area of 'blowing down' is on the slope just uphill of the prominent herring-bone tailings. The head races for this activity are obscured by the later herring-bone tailings and the modern border-diking at far right. The view is to the north-east.
Kumara township and goldfield on the Taramakau River, West Coast
The full extent of the field is marked by the great field of tailings, with the last working face on the left of the photo. The extent of the gold deposits would originally have been tested by shafts, and the major supply races and head dams constructed by the government of the day. The dam at left has been breached and is smaller than its original area. The water in the dam is about 200 by 80 m in extent. It fed a great many head races, one of which can be seen still lying on 'virgin' ground out in the general area of the tailings. Not only did the government construct the supply races, it also had to construct tail races, the spirit of cooperation being sometimes lacking among the miners.
The north-eastern (top right) corner of the photograph shows the freehold land on either side of the prominent road which had to be tunnelled under to remove water from the claims. Finer tailings (able to be carried in water) from the races show as elongated fans adjacent to the river. The heavy tailings (stones and boulders) are stacked in the various claims, left of the road.
1 G.J. Williams (1974: 5-7).
2 G.J. Williams (1974: 6).
3 Fraser (1907: 133).
4 Park (1908:48-52); G.J. Williams (1974:53). The gold would be worth $18 million at today's prices.
5 Plans in Park (1908: 49-51).
6 G.J. Williams (1974: 5-7).
7 Hooker (1991, pers. comm.).
8 Park (1908: 47-48); Higham et al (1976: 171).
9 Ritchie (1981).