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New Zealand Goldmining 2
Travels in the Coromandel Goldfields
The Broken Hills DOC (Department of Conservation) campsite is one of our favourites and I have lost count of the number of times we have been there. It is in the South East of the Coromandel on a site beside the banks of the Tairua river with stunning scenery amongst spectacular towering hillsides. It is right in the middle of the old Broken Hills and Golden Hill Goldfields and has and a considerable number of goldfield walks, taking from minutes on well formed paths to hours involving energetic climbs and passages through old tunnels. There are still remains from most of the activities in goldmining, stamper batteries, power houses, cyanide vats, adits (tunnels), water races, tramways and aerial ropeways to name a few making it an excellent starting place for learning about goldmining in the Coromandel. It, as much as anywhere, initiated our interest in the goldmining heritage in New Zealand.
Gold was found relatively late at Broken Hills in 1893 and major development did not start until 1907 and processing in 1910 with most of the extraction depending on use of Cyanide. Around the turn of the 20th century, a bustling gold-mining settlement named Puketui was established in the Broken Hills Gorge. By 1912 a settlement of 200 people had sprung up along the river. It had a post office, hall and several shops. Plans were prepared for a permanent township on the site now occupied by the Broken Hills Campsite. The goldfields round Broken Hills were however largely exhausted by 1913 by which time only 55,000 oz of gold had been recovered. The size of the settlement diminished rapidly although some small-scale mining continued in the area until 1923. Because the field was fairly recent it is better document than many and the DOC information (and our books) have some good photographs of the various batteries, aerial ropeways etc taken when they were in use.
There were two main areas, the Golden Hills Mines and the Broken Hills mines which were opposite sides of the river. The Golden Hills mines started large scale production in 1908 and most of the longer walks are on the Golden Hills Mines side of the river including walks along the old water races complete with a series of short tunnels used to supply water to the Pelton wheels (turbines) used to power the Government Stamper Battery just below. Unfortunately virtually nothing remains of that battery although the site is easily accessible. By 1910 the production was thought to merit the building of a new stamper battery on the opposite side of the rive and connected by an aerial ropeway. The new battery however used an expensive but unreliable coke-powered suction gas engine and the battery was too large for the size of the reef being worked so production only continued for 3 years. One can however still see many remains of the battery including the foundations of the Stamper Batteries and parts of the 4m diameter cyanide vats at the end of a short (20 Min) walk.
Broken Hills Historic Mine: The Broken Hills Mines are of more interest to us because they continued longer with small scale production continuing until 1923 and parts have recently been open. The current mining is using purely historic methods and you are unlikely to notice it is taking place as there is no publicity and the external impact is very small. The area which was reopened as a historic mine was originally worked from 1899 to 1912, producing about 30,000 oz of gold from over 30 000 tonnes of ore during that time. It is a typical narrow-vein hard rock underground metalliferous mine, and was worked by shrinkage stoping methods. It is characterised among other things by good ground conditions. A family group led by Stuart and Miranda Rabone applied for a mineral exploration permit over the area in 1991 and in 2000 was granted a Special Purpose Mining Permit over the historic mine workings allowing mining to be carried out on a small scale using historical and traditional (essentially hand-held) techniques.
Over the last 15 years, the old section of the mine has been restored and made safe, and the vein system has been further developed. The mining utilises hand-held airleg drills and haulage by 24” gauge rail network in tunnels generally 1-1.5 metres wide and 2 metres high. The number of staff varies but is typically four and on occasion rises to a total of six persons. This is a an unusual and exceptional operation - there are currently only three underground hard rock metalliferous mining operations in New Zealand, namely Oceana at Macraes, Newmont at Waihi (Favona – Trio) and this historic mine at Broken Hills at Tairua. The first two are large scale highly mechanised modern operations. The Broken Hills Mine is unique in New Zealand as a small scale hard–rock underground mine utilising traditional, but nevertheless efficient, methods of extraction. The following pictures were taken the day before a visit underground and show how small the impact is. There is virtually nothing different from any other old adit entrances except for the few minutes when the train is unloading.
The success of the operation has been very dependent on the experience (and qualifications) of the family team led by Stuart Rabone, the General Manager. His qualifications and experience are to me exemplary and include an MSc and PhD in Geology and tertiary qualifications in Engineering Geology as well as membership of the appropriate professional bodies such as FAusIMM and T.IPENZ. I can safely say as I have plenty of alphabet soup of my own that paper qualifications count less to me than relevant practical experience and Stuart has 45 years’ experience in metalliferous mineral exploration and development, including Golden Cross, Waihi (Martha – Correnso and Favona – Moonlight) in addition to the 14 years’ experience restoring and operating Broken Hills Mine itself - it shows as soon as one talks to him.
At the time the mine was not in full operation as its licence is suspended until a second method of egress has been created. The mining regulations and how they are applied in practice has been changed recently and even a small mine is required to comply with the new regulations.
To understand the major changes in regulatory environment one has to know a little about the recent Pike River Mine disaster which was a major coal mining accident caused by a series of methane explosions in 2010. This accident killed 29 of the 32 miners underground at the time. It ranks as the worst mining disaster in New Zealand in a century. The resulting Royal commission concluded two years latter that the regulation and inspection of mining by the Department of Labour had failed to prevent the accident and shortly afterwards Prime Minister John Key said he would apologise in person to the families of the deceased, for the Government's weak regulations and inadequate inspection regime. Efforts were made to prosecute various directors with only minor success and little money reached the families. I do not want to go into many details of the disaster which contained a catalogue of short cuts and poor infrastructure but shortfalls identified included a lack of secondary egress and poor ventilation in an area known for methane problems, a classic risk in Coal mines but almost unknown in hard rock mines. The Pike River Mine was using a very new method of extraction (hydro-mining) over 4000 feet underground arguably without the owners having sound appreciation of the particular risks associated with technique and and how those risks differed from other forms of mechanical mining and there were a number of previous incidents with methane.
It is easy to understand why change is required in such a politically charged environment but to me it is less clear why regulations relevant to Coal Mining and need to be applied to Hard Rock mining where for example methane gas build up is almost unknown. But the new regulations are a fact and will undoubtedly avert some disasters in the future. To me regulations alone are not a total solution but it also depends on the regulators and they must have more experience available than those they are regulating and must be all seeing. I ran many projects and always insisted that most of the project meetings were on site so I could get a feel for what was going on rather than depend on presentations and regarded the ongoing quality and experience of staff to be extremely important - big firms tend to put an impressive team into project proposals which evaporates once work starts! Enough of my own biases and back to our underground visit other than to say that after talking to Stuart and Miranda I felt very safe in going into the old workings and very privileged to have the opportunity.
The Broken Hills Mine was worked on a number of levels and a number of maps of the old workings which extend for nearly a kilometre from the entry portal still exist. I only managed to get a picture of the level we were visiting but the coloured multiple level one made the complexity more obvious. We only went into the workings on the entry level and that has been largely cleared of any old spoil and falls from the stopes. The mine adits are entirely in hard rock apart from the entries which have a massive timber support frames - the rest of the tunnels need very little support and I only noticed a single area with rock bolts in the adits. The tunnels are all high enough to easily walk through although we obviously had hard hats (and all the proper kit including helmet lamps and big power packs and were fully briefed). Most of the adits have narrow track (24 inch) rails laid for the trucks which remove the ore (rock with gold for processing) and tailings (the rock not containing any gold or too little to be worth processing). Ventilation was good and there was an obvious and very cold flow of air in our faces. As we went further there were big plastic tubes hanging to give forced ventilation into areas where there was work going on and to clear fumes from the workings, the train engine and other equipment. The compressed air and power cables were also hanging above us. The was little problem with drainage with a very small channel beside the rails carrying it out. We were fascinated to see there were some small fish which has adapted to the underground existence and even a small eel sometimes appears.
The mine was worked as adits which were searching for or following the veins of quartz which contained the gold. We saw the veins which were only quite narrow in the roof - they appeared to be 5-10cms wide. The veins were near vertical and the richer areas were mined as a series of near vertical stopes. Stoping is the mining term for extracting the ore, leaving behind an open space known as a stope. Stoping is used when the local rock is sufficiently strong not to cave into the stope, although in most cases artificial support is also provided. In the case of the Broken Hills mine a large number of timber supports known as stulls have been placed between the hanging wall of the vein and footwall. These 6 inch or so square timbers stabilised the stope and supported a number of working platforms for the miners to work from and drop the ore onto before it was lowered down to the adit level for removal. They had a small square cut out in the rock at one end and were angled and jammed so they would only get stronger as loads were applied on the platforms they supported. These structures have been renewed in in places but most are still in perfect condition after best part of a century. Good timber was one of the major requirements for historic methods of mining.
We could look up into several of the stopes from below and also down into one which probably extended to a lower level. They were very difficult to photograph in a way which makes they easy to understand as flash obviously only penetrated a short distance. The video using an LED torch gives a better impression and I have taken a few stills from it. In the life they were extremely impressive rising or falling some 50 ft or more and extending similar distances horizontally. They were however the minimum width to allow the miners access, around 2 feet with the massive stulls crossing and supporting various platforms. Some of the old iron and wooden access ladders were still visible with the wooden ones looking in much better condition. As I said earlier there was a very strong flow of cold air through much of the workings and enquires elicited the information that some of the stopes on the upper levels had shafts up to the surface which still provide some of this ventilation but have been covered to prevent anything falling down through to the working levels. In a dire emergency it seems to me that they could be an additional escape or entry route.
As said earlier the majority of the old workings had been cleared and made safe before the new adits have been driven for mining and we went into some of the new areas and saw one of the small stopes they had been working. We could not go into the area where a new adit is being driven to link to an existing adit with a portal further the track to provide the secondary egress route. This required a drive of 70 metres at about 2 metres a day and there was to be no production until that was completed. It was apparently quite a task to find the old adit entry as there had been a rock fall and the combination of convention metrology from the old drawings, modern satellite GPS measurements and real photographs before and after the slip were utilised. The extra entry is about 220 metres from the portal used for working. We had seen the train with its tipper trucks outside the previous day and we passed it on our way through the workings. The loading at the workface is by a bogger which is a special design of front loader for mines which loads in front and deposits the load behind it into the tipper trucks. We saw one during a previous visit into an Australian Mine. There have been a number of television programs covering the mine and there is a video of the train and blogger working by TVNZ at http://tvnz.co.nz/national-news/file-video-inside-broken-hills-gold-mine-4728919
Some of the other old equipment is still in place including an original winch used compressed air rather than steam. It looks in surprisingly good condition although dry rot had got into the woodwork. The ore is taken out by train and tipped into a small lorry and stored until there is sufficient for processing. It is not processed by Broken Hills Historic Mine themselves as that would not be economic.
Overall we spent a fascinating hour and a bit underground. They are remaking history in a way that static displays and written text can never do. The underground working we have seen previously were sanitised and artificial and the difference was even more noticeable than we expected. There is obviously some new equipment used such as modern compressors but they are not of the essence and the ventilation piping is different but it still feels like history being remade. Existing readers will already know our views on museums full of videos and plastic copies of artifacts and structures however well done.It will be an opportunity for future engineers from throughout the world to feel and learn from history as well as demonstrating the opportunities for small scale activities activities to complement the large and with far less impact.
The following two write-ups sum up camping and the various walks we have done round Broken Hills so well we have left them on this page!
Broken Hills in 2001 We camped at Broken Hills, a DOC camp site in the a historic goldfields area we have been to several times before. The camp site has stunning scenery and is sited, in the middle of the old Broken Hills and Golden Hill Goldfields, on the banks of the Tairua river. It was surprisingly empty so early in the season and we had a choice of pitches and a nice area almost to ourselves.
We did a number of the shorter Goldfield walks the day we arrived which gave us a chance to look at the sites of the three main Stamper Batteries, two of them have quite a lot of remains and one can piece together a lot of the history. We also walked up to look at one of the old water races complete with a series of short tunnels used to supply water to the Pelton wheels (turbines) used to power the Government Stamper Battery just below. Unfortunately nothing remains of that battery.
The second morning we were woken at 0530 by the most incredible dawn chorus, starting with Tuis and Bellbirds and building up till it was almost deafening. The forecast was not good so we set off early on our major walk taking us up to where the mines were sited. We saw many of the old adits (mine tunnels) some still open for exploration. You can also see the site of the aerial ropeway which transported the ore right across the valley to the Golden Hills battery we looked at the previous day. The highlight of the three hour walk was going through the Collins Drive - a 500m tunnel from one side of the hill to the other. Fortunately we had a couple of torches with us. By the time we got down the mist was coming down and we took the tend down still a bit damp. At least we had not suffered the flash floods promised for the area overnight!
Broken Hills in 2002 Our next visit was in 2002 and once more the camp site was largely deserted - even at a weekend only three other pitches were occupied plus a large group from the International Rotary Caravan Federation on their annual bushcamp which had taken one of the flats by the river. We chose a well sheltered corner which caught all the afternoon and evening sun. The hills towering over the site cut off the sun in the morning and it was fascinating to lie in the tent and hear overnight the Moreporks (a type of owl) calling and the strange grunting whistling and snuffling noises of Possums - quite frightening the first time you hear heavy breathing outside the tent in the middle of the night! Then comes the start of the dawn chorus of Bellbirds, Tuis, Fantails and many others then the cicadas starting up in far distance where the sun was hitting the ground and getting closer and closer as the sun rose until one knew it was time to arise oneself.
We went on the longest of the circular tracks taking one first to a high viewpoint looking over the towering rock formations beside the site (322m) then back down to cross under the hill in a 500 metre long old mining adit, correctly called the number two level but always referred to as Collins drive. It was a bit wet and muddy in places but safe enough with a couple of torches and spare batteries. The tunnel has lots of glow-worms with their trailing sticky cords and surprisingly bright lights - some you could still see the lights even when a torch was illuminating them. Once out of the tunnel their are steep descents past more tunnels, we explored a few until they got too deep in mud.
There are remains to look at of the stations for the aerial ropeways that crossed high over the valley to the Stamper batteries used to extract the gold from the quart ore on the other side of the river. As we descended further the track made use of the old horse drawn tramways where one could still see one was walking on the remains of the sleepers. Finally we followed the route of an old water race round the side of the hill through short tunnels and over the remains of aqueducts until we reached the site of a major landslide almost opposite the Golden Hills Stamper Battery and then descended back down. It was a vigorous walk - the climb up never seemed to end - and definitely needed walking boots. With all our extensions it took close to three an a half hours, quite a bit longer than the DOC boards implied at the entry.
Note: Not all the tracks are marked on the maps and there now seems to be a shortcut down from Collins drive past the Aerial ropeway which would cut some time off at the expense of a number of interesting features such as the tramways, adits and water race. We also noticed that many of the information boards were missing - hopefully they are being refurbished but we were warned that there are pressures to play down the amount of goldmining in the past as a part of the campaigns against the restarting of some goldmining.
After a swim in the river, which has a reasonable swimming hole, we had recovered enough to do the two shorter walks the other side of the river which take one to the Broken Hills Battery and the Golden Hills Battery. We explored both a bit more than last time and found all sorts of interesting old structures buried in the bush as well as the foundations of the stampers. They were mostly tanks and other equipment concerned with the cyanide treatment of the ore as far as we could tell.
Thames - Goldmine and Stamper Battery. We spent the following morning in Thames soaking up more goldmining history. Firstly we went to the Thames Goldmine and Stamper Battery, which has a working Stamper Battery, separating table, Berdan and Mercury Distillation separator. You also a brief tour underground following the first trial adits (tunnel to non miners) which identified some Quartz reefs containing Gold. A very well spent $6 and a must to visit in the Coromandel - Gold was a major influence in the area and plays a unique part of NZ history.
Thames was the first area where gold was exploited in the Coromandel and had some exceptional rich Bonanzas, one where the Bullion (Gold and Silver) was over 50% of the Quartz reef and one blast reputedly produced 2 tons of quartz which contained 25,000 oz. of Bullion. Mostly it was only a few ounces per ton and as time went on the workings were taken as deep as 1000 ft and massive steam pump engines had to be installed. The guided tour and the comprehensive photo museum put into place a lot of what we had seen at Broken Hills in the way of abandoned batteries, adits and tramways.
Thames - Mining Museum and School of Mines. We also visited the Mining Museum and School of Mines. The School of Mines is no longer open every day out of season so we will have to return to see the most interesting part. The complex is owned by the NZ Historic Places Trust and it is worth noting that they have reciprocal arrangements with the UK National Trust so one can get in free. We now have a list of their properties and will follow up further. We bought a fascinating book "Coromandel Gold - A guide to the Historic Goldfields of the Coromandel Peninsula which has a lot of background and maps of all the major Goldfields and associated information producing a practical guide for visitors to experience something of the 'magic' of the old mining areas from the surviving features - long abandoned tunnels and shafts, crumbling foundations of Stamper batteries, rusting pieces of machinery and disused tramways and water races. We had seen many of these including Stamper Batteries in Broken Hills even on our short walks.
We returned to Thames a week or so later to revisit the Museum and School of Mines and see the bits of the School which had been closed the first time. We were just left to ourselves to wander round the School which finally closed in 1954. There is a lot of fascinating stuff and the laboratory looks as if it has never been changed - the bottles of reagents are still on the benches with their contents! There are also a lot of old photographs etc some of which showed the small Battery which was used for assays and experimental runs (one ton).
We then had a real piece of luck as I asked the person on the front desk if there was anything else left from the School and if we could see. It turned out there were a number of artifacts they hoped to restore and he took us into the old building to have a look. He was a fund of knowledge and we found out he had worked as the accountant for one of the gold firms and then had been the original curator when the museum was set up. He is now retired and only comes in as a volunteer. He is knowledge goes back a long way and, as he cycled off slowly into the distance we were told us he is now 87 - we hope we will be as fit, sharp and active at that age. He had stayed talking until well after normal closing up time.
As we were leaving I noticed on the shelves that some of the artifacts were for sale and we are now the proud owners of one of the original crucibles used for melting the Gold with a flux to purify it - even better it is from the Broken Hills area where we have camped and walked round the remains of the batteries several times.
It was a couple of years before we returned next the Museum and the School of Mines on a wet day on our way South from Coleville. It was close to three when we got to Thames and we only got into the Museum just before they closed. The gentleman in charge turned out to be the son of the gentleman who had taken a lot of time with us on our last visit three years before. We talked for quite a while past closing time and he made suggestion about where we could find some of the books we were looking for and told us about a place holding Internet auctions of the sort of books we wanted (The Crows Nest Bookshop in Hamilton). Since then we have discovered an excellent internet site for old books which we mention in our page on New Zealand Books.
Coromandel - the Government [Stamper] Battery. The Battery is actually several miles North of the town. Our first visit was in 1999 not long after the Government Battery had been restored to a working condition. The stamps were powered up briefly for one to see as were a couple of the Berdans. There was also a Ball Mill in working condition feeding a small mercury amalgamating table. This first visit was slightly disappointing as the guide was not as knowledgeable as the one at Thames but the equipment was complementary and we considered it a worthwhile visit.
Our return visit in 2002 was much more interesting and instructive as the Government battery is now in the hands of a real enthusiast (and trained geologist) and we spent much longer with Ashley than we should have done and learnt a lot more than we would have got on a standard tour of half an hour or so - we were there almost 2 hours. He was a fund of knowledge on mining, past present and future, in the area and the battery is once more active processing small batches of ore.
The Government Battery is especially interesting as it is the only Stamper Battery still working on the original site - as the name implies it was a small battery set up by the government for assay purposes and occasional small runs under contract. It was set up just after the turn of the century for crushing relatively small amounts of ore for small prospectors. This avoided their having to use the large batteries already in existence and risk their small quantity getting mixed in with larger batches. The Government Battery had a total of 6 stamps which were divided into a battery of 5 and a single stamp for testing small batches for assay. It was set up with money from the Institute of Mines at Thames, the Government and other interested parties. The gold is currently separated from the crushed ore and water on corduroy sheets as it leaves the Stamper heads ready for further processing. The gold being so much heavier sinks and collects on the corduroy.
As well as the Stamper battery there are three Berdans which grind the gold and other ore collected from the corduroy even further. This grinding is done with mercury present which dissolves the gold which can eventually be collected as an amalgam. The amalgam used to be separated using chamois leather but modern chamois leathers are oiled and do not work well so a synthetic material is currently being used. There is a big steel retort which is once more in active use for the distillation of the mercury amalgam over a wood/coke fire using an set up looking much like a forge. This 'forge' is the re-used to heat the gold/silver alloy left after the distillation in crucibles with a flux (mixture of various salts) to clean it before casting ready for assay - most bullion from the Coromandel is 70% silver and 30% gold.
There is also a Ball Mill, a technique which largely replaced Stampers as time passed. Ball Mills are large rotating drums with a number of steel balls which gradually grind the water and ore mix to a fine paste which can then be washed through fine filters and on to conventional separation mechanisms such as the corduroy sheets or mercury amalgam covered copper sheets. These days Ball Mills are used to treat ore before Cyanide treatment - a technique which was not used at the time the Government Battery was set up.
The Stamper is driven by an early Lister gas oil engine and the Berdans and other equipment by a large overshot water wheel - unfortunately not in operation on our second visit as the floods had blocked the outlet from the dam and it was far too dangerous to risk clearing it till the levels fell. The bridge over the "stream" beside the Battery was at serious risk from the raging torrent. Unfortunately the council had decided that a minor crack along one of the vast pieces of timber needed investigation and had put a flimsy prop right in the centre of the stream. Ashley said he had warned them what could happen if the stream came up and we could now hear the huge boulders being rolled down crashing against the prop. It had already been seriously distorted overnight and was now twisting the whole bridge - I suspect he is thankful it is a council bridge not his!
When we continued into Coromandel town we heard that many of the roads across the ranges and over the other side, which we had just left, were closed by floods and slips so it seemed prudent to head South for Thames after a lunch of the local specialty of Paua patty. Paua is a shellfish, similar to Abalone, living in shells with iridescent blues which are also turned into jewellery.
Colville School of Mines Museum. We also visited the Museum in the old Colville School of Mines in 1999. It not only has a number of mining artifacts but also covers something on the Kauri logging and Gum digging (for varnish) which was also carried out in the area. It is being built up, we gather, by an enthusiastic band of volunteers so it may well be more comprehensive in the future and even more worthy of a visit.
| Copyright © Peter and Pauline Curtis
Spelling corrections: 8th January, 2016