There be gold in them there hills!!

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Leaving the rafting place, we pushed on northwards in the pouring rain lunching at Maketu, then on through Tauranga where we failed to replace our punctured tyre because it was now Saturday afternoon and everything was closed. Overnight found us 10k’s inland up in the hills near the Tuahu walkway and back out again to the main road the next morning, onto Kati Kati and then Waihi - home of the Martha Mine, one the world’s largest open pit goldmines. We wandered around the historic Cornish pumphouse, recently moved to avoid it falling into the open cast mine and learnt that we couldn’t tour the mine until the next day (Monday), but that there was an interesting area just a short drive away that could entertain us until then.

And so we drove to Karangahake Gorge that afternoon, site of the original goldrush in 1875 and did a 20km return walk alongside the Ohinemuri River from Waikino to Karangahake, including through a cool 1km tunnel. We passed Victoria Battery commissioned in 1896 to crush over 800 tonnes of ore per day to the consistency of sand. The 200 stamps formed the largest crushing battery in Australasia and the constant 24 hour pounding could be heard as far as Waihi, 5km away. Another nerdy fact (and for the record Lexa wanted me to add this in), a series of 7m tall, 4m diameter ‘agitators’ were used at the battery, being filled with crushed ore and weak cyanide solution in a process that separated out the precious metals. We walked up some of the spectacular Waitawheta Gorge to some of the other old quartz crushing batteries of Crown, Woodstock and Talisman. These had closed down by 1920, but the Victoria continued servicing the nearby Martha Mine in Waihi until 1952. We also ventured into some seriously scarey Scooby-doo tunnels held up with old fashioned looking pit-props and wished that we had better lights. We only went in about 500m, but managed to find glowworms and cave weta’s, a sort of stick insect type thing.

When the Karangahake mines closed in 1920 over 4million ounces of bullion had been extracted (about £4million). In its heyday 2000 people lived there with a post office, school, churches, shops, house hotels, croquet and bowling clubs, but like so many other goldrush towns there are now only a few foundations hidden in the undergrowth and some big lumps of metal that have survived the test of time. It was a really interesting walk with great scenery, lots of history, some fun tunnels and most importantly Lexa got to try out her walking stick for the first time with the intention of preserving her dodgy knees and it proved a great success apart from getting sore arms instead!

That night we camped at the free and rather chilly Dickey’s Flat DOC site just near the gorge and started the Monday morning with a quick walk from the campsite down to a 150m long tunnel and through to some other mine workings before heading back to Waihi to book ourselves onto the 1pm mine tour. At the mine visitors centre we met dynamic Doreen, a rather intense and enthusiastic woman that ran the place for the mining company, loved mines and had worked at this one for years. Together with free tea and coffee we were given a passionate insight into the place, shown several videos and heard numerous anecdotes about the hundreds of mines she visited around the world including of course the Cornish tin mines. So brace yourselves, Doreen wouldn’t forgive us if we didn’t spread the word and let you all into a bit of the history behind Waihi’s Martha Mine:

Waihi has had a history of gold mining that started in the mid 1870’s, when prospectors were lured in by large lumps of quartz sticking out of the scrub. The gold here isn’t like in the south island where it’s found in the form of nuggets, but as lots of mineral rich rock that needs crushing and treating with cyanide to extract the shiny stuff. Waihi started as an underground pit and was not viable until the 1890’s when a London based company took over and introduced the cyanide method of recovery. At that point Waihi became the 3rd largest inland town in New Zealand with population of 7000. This underground mine consisted of 7 vertical shafts, the deepest going 640m down with a radiating network of 175km of tunnels and was one of the most important gold/silver mines in the world, closing in 1952 having produced 5.6 Milllion ounces of gold (174,160kg), 38.4 million ounces of silver (1,193,180kg) from 11,932,000 tonnes of ore.

Now we need to do a bit of geology before we can continue… Millions of years ago volcanic eruptions deposited Andesite lava to form Waihi’s bedrock. Some millions of years later, earthquakes created near vertical cracks in the bedrock and the quartz veins of the Waihi mineral deposits formed when mineral rich hot water rose in those cracks. In fact the early Waihi area would have looked very much like Rotorua does today. So quartz veins or reefs were formed as minerals including gold and silver were deposited along with silica. Millions of years of erosion then removed hundreds of meters off the top of the volcanic rocks, eventually exposing the harder quartz veins beneath, those bits the original prospectors stubbed their toes on.

So the Martha lode is a gold-silver orebody and is giant by world standards, with the reef system at least 1.6km long, 600m deep and up to 30m wide. The majority of this and other subsidiary reefs and veins were mostly mined out by the underground operations up until 1952, however many smaller veins remained untouched. With the worldwide resurgence in gold prospecting in the 1970’s brought on by the increasing need for gold in space, electronics and photography industries, geologists looked at Waihi again and open pit operations started in 1987 digging the same area covered by the original mine shafts. From that point on the mine treated about 1.3million tones of ore annually, now totaling about 250million tones and is due to close soon having produced $600,000 of bullion.

The area is now entering a new stage in its history, going underground again with the opening of the new Favona mine nearby. With today’s more responsible attitude to the environment, this mine uses a slightly different technique whereby they will dig to the maximum depth of 300m and then work up to the surface recovering the ore, back filling the workings as they go to avoid producing the usual vast amounts of waste rock and don’t have to spend millions sorting out the mess they have made afterwards. Considering that rock with as little as 1gram of gold per tonne can be mined economically using open pit modern technology, similar reef operations are being mined at Favona as an underground operation with more like 10-15grams per tonne, so there is definitely still gold in them there hills! The bullion produced on site is a mixture of gold (10-25%) and silver (75-90%) and rather surprisingly this is then shipped to Western Australia for further processing and separation.

The mine tour itself wasn’t that spectacular; we were driven around in a minibus unable to get out for security reasons and didn’t see anything getting blown up…most disappointing. One thing I do remember is that they were keen to emphasise that whilst the waste water they returned to the rivers did contain traces of cyanide, higher levels occurred naturally in almonds… so now you know!

You might have thought that we were all mined out by now (ha ha) but no, we left Waihi heading north and then inland near Whangamata in search of more possible mine sites at a place called Wharekirauponga. We parked up for the night at the road head by a geological reserve (special rocks) and were slightly freaked out by possums scratching around outside and jumping on the van. In the morning I came across the bizarre sight of a huge pile of dead fish just lying on the grass… and we’re not talking a couple of freshwater trout, but big and reasonably fresh barracuda, rays and snapper…weird! Who would go to the effort of catching all this at sea and then dumping it 15km inland up a mountain???!!! Anyway we didn’t let that stop us enjoying a great walk up the river to some lovely waterfalls, old tramways and tunnels and in a moment of madness I decided it would be a great idea to go for a swim and to my surprise managed to persuade Lexa to join me. Bearing in mind the air temperature was about 12degC and the water about 5, we didn’t stay in for long, but still felt suitably proud of ourselves for trying!

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Comments

[Jenny]

Near the end
Well you two you're nearing the end of your amazing trip. Take care of all those weird animals in the Galapagos Islands won't you. Granny's really worried as she saw a documentary about the islands on TV recently!! She said that's one place she wouldn't like to go for sure! Have a great finale anyway and look forward to seeing you when you're back in England.