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The views from the Number 7 Level Track of the lower Waitawheta Gorge are spectacular. The wooden footbridge of the Crown Tramway Track pales to minute significance against the majestic backdrop of the sheer walls of the gorge.
Near the western end of Karangahake Gorge at the overbridge on S.H.2, turn into Crown Hill Road. Head uphill and turn left, continuing along Crown Hill Road to a parking bay on the right at the roadend.
The start of the track is signposted through the gate.
This description follows an anti-clockwise loop around the mountain.
Timings and directions given here may vary considerably from those posted on the track.
After 15 minutes a signpost shows Number 7 Level to the left. This is where you will rejoin the track having completed the loop.
Head right, along the wide rocky track on a steady gradient, ignoring the track on the left after 25 minutes. The track becomes grassier through low scrub, and after 30 minutes reaches a 5-minute-return detour to a lookout on the right.
The track is muddier, more slippery and rutted as it climbs steadily for 45 minutes to a junction. Left is the 20-minute-return along a narrow track to the antenna near the summit.
Retrace your steps to the junction and continue downhill for 20 minutes to another signposted junction.
Head left for 15 minutes until you reach the junction with the track to Mangakino Stream and Number 7 Level.
For the next 1½ hours the track descends Number 7 Level, passing the junction with the Dubbo 96 Track after 1 hour and many old mining tunnels.
The horizontal mine tunnels (adits) and vertical shafts pepper the slopes of the mountain. Stay to the marked tracks.
By the mid 1880s the Woodstock Company, New Zealand Crown Mines and Talisman Goldmining Company has acquired all the claims on Karangahake Mountain.
The Maria Reef was the main reef of Mount Karangahake, and was traced 700 metres vertically over 16 levels to 150m below sea level. Four main shoots were known as Woodstock, Talisman , Bonanza and Dubbo.
The frighteningly sheer canyon walls of the Ohinemuri and Waitawheta Rivers now form spectacular backdrops to the network of tracks accessing some of the most complete and impressive remains of Coromandel’s goldmining legacy. But to the engineers of the goldmining companies, they presented daunting constructional barriers. The Crown, Talisman and Woodstock Batteries that later occupied the slopes were the first in the world to introduce the cyanide process, a treatment method that had the effect of opening up Karangahake’s goldfields.
Following the glimmer of gold in 1875, many claims were pegged in the Karangahake area with the usual unfounded optimism. A number of companies, including the Hauraki, Maria, Hidden Treasure and Monastery were formed, but most fell into control of the three most successful companies, the New Zealand Crown Mines Ltd, the Talisman Consolidated Ltd and the Woodstock.
The main problem encountered by the early companies was the nature of the ore around Karangahake. The low grade refractory ore was unable to be treated with the metallurgical knowledge and plant available at the time. Only 45% of the gold was generally recovered (and even less of the silver). Moreover, the rugged terrain and high cost of transporting ore to the batteries made operations uneconomic.
The traditional means of treating ore in the Coromandel goldfields, such as those at Thames and Coromandel, involved crushing and processing quartz to extract the bullion. Lumps of ore were put through jaw crushers and conveyed to batteries of stamps. These pulverised the rock with repeated blows and reduced the size of the particles to sand. Ball or tube mills were later employed to further reduce the particle size and increase the efficiency of recovery.
Phil Moore and Neville Ritchie in their book Coromandel Gold, continue the description of the process. “In the early years, crushed ore from the stampers was washed over amalgamating tables covered with copper or Muntz metal (60 percent copper, 40 percent zinc alloy) plates. These had a thin film of mercury on the surface, which trapped a portion of the gold and silver, forming a putty like amalgam. Periodically the plates would be scraped and the amalgam retorted in a furnace to recover the mercury for reuse, while the remaining spongy brown bullion would be melted into bars. A good deal of the metallic mineral fraction, however, passed over the tables and was caught in riffles, or heavy felt ‘blankets’, which were regularly washed to remove the sludge. This was then transferred to berdans.”
These inclined steel bowls acted like a pestle and mortar and further reduced the particle size , freeing up smaller gold particles and allowing for greater recovery of bullion by amalgamation. Despite this process, it was a known fact that almost half of the gold (and silver) was lost in the tailings, the slurry like material of waste rock, discarded after treatment.
At Karangahake, the gold was of a very fine consistency and mixed with sulphides. The technology simply wasn’t efficient enough to extract sufficient gold from the ore to make mining profitable.
The La Monte furnace and smelting process proved unsuccessful, as procuring suitable fluxes was uneconomic. A reverberatory furnace was then designed to treat ores, but again the high cost of fluxes cased the method to loose favour. Dry crushing, occasionally in partnership with ore roasting in massive subterranean kilns, was still deemed unprofitable. Pan amalgamation on J. Railey’s plant only recovered small quantities of gold like the tradition battery process.
It was not until 1889 that advancements in the recovery process occurred. The Cassell Cyanide Company starting experimenting with methods of extracting gold by solution with potassium cyanide and then precipitating it with granulated zinc. Although there were many minor variations on the process, designed to marry with a mix of ore grades in different mines, at Karangahake the process essentially followed this description.
After roasting, the ore was dry crushed and loaded onto railed trucks leading to platforms above the vats. The hand traversing gearing allowed an operator to top the load in a desired direction, reducing the amount of handling and increasing the ability of the ore sand to percolate freely.
After depositing onto a platform, the sand was sprayed in a shower onto the base of the vat to a thickness of two feet. The vats were around 22 foot 6 inches in diameter, four feet deep with a five inch filter on the bottom. This consisted of a wooden grating and a taught hessian cloth stretched over the rounded corners.
A strong potassium or sodium cyanide solution (0.4-0.7%) was then fed from the bottom under pressure through a filter cloth until it reached two inches above the level of the sand. The ‘pregnant’ cyanide solution below the filter cloth, loaded with dissolved gold and silver, was siphoned off and the remaining mixture allowed to percolate freely for 24 hours.
After the strong solution was drained, a weaker makeup (0.25%) was added to a depth of 6.5 inches and vacuum cylinders activated for 30 hours. The final procedure was to pour 10 inches of water from the top to complete the percolation and remove the gold bearing slurry.
Sludge doors at the base of the vat opened and the slurry was sluiced out via a hose. The bullion precipitated as a black sludge and the cyanide was reused. The zinc solution was then refined with the addition of an acid, which removed the zinc, allowing the bullion to be recovered, melted and poured into bars. A later advancement in the method used compressed air to agitate the solution and a finer crushing of the ore also increased reclamation. The government later bought the rights to the process, to ensure steady production continued.
The process was particularly beneficial in the Karangahake goldfield, as the ores were of low grade. The process allowed a recovery rate of 92%. However, as the Cassell Company asked for a royalty of 7-8% of recovered gold, the process was only adopted slowly.
Despite the many claims pegged around Mount Karangahake, the Woodstock, Crown and Talisman Claims proved to be the most profitable. Most were centred on Mount Karangahake, that rises knife like from the confluence of the Waitawheta and Ohinemuri Rivers. These have incised deep gorges with sheer walls leaving little flat land on their banks. The trials of extracting ore were thus further compounded by finding suitable sites to locate the stamper batteries and other processing equipment.
By far the most productive reef system embedded within the bowels of Mount Karangahake, was the Maria quartz reef, which was eventually excavated over 700 vertical metres on 16 main levels. The system of tunnels, adits and shafts formed a labyrinth and the lowest level was nearly 150 metres below sea level. The reef averaged two-three metres wide, and possessed four distinct ore shoots within its makeup, the Woodstock, Talisman, Bonanza and Dubbo.
The three most substantial batteries were the Crown, Talisman and Woodstock, all centred on the confluence of the Waitawheta and Ohinemuri Rivers, which were dammed to provide power. The batteries were constantly remodelled to incorporate the new technologies being employed and at times possessed over 40 heads of stamps each. They contributed to a total production of 3,510,691 ounces of bullion valued at £2,958,013, derived from 687,043 tons of quartz.
North Island ▷ Bay of Plenty ▷ Waihi
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