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Glaciation & Gold In The Queenstown Area Otago Nz

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Hi Guys, I am giving this its own thread as I think it deserves its own separate topic. It started with a Reply to Jim_Alaska's Query on my Continued On From My Previous Gold Finds post.

Jim_Alaska Posted yesterday at 04:24 AM

“JW, the gold in your pictures seems to be water worn. Is it glacial gold or was there once a river at the height you were working that slope?”

 

kiwijw Posted yesterday at 01:46 PM...

Hi Jim, It is a tricky one. Most definitely was a glacial valley & with more than one advance.This particular valley was just one finger of this massive glacier that buried the countryside for many thousands of feet with just the rugged mountain tops protruding above the ice. Evidenced by there jagged rugged peaks as opposed to just below them the ice grounded & smoothed styrated mountain sides. There is a river way down below. That river is believed to have not used to have been there & is fairly recent geologically speaking. The glacial lake that now flows out through that river used to flow out many many miles way further south at what is now the southern end of Lake Wakatipu. Possibly the last major advance of the glacier pushed up a terminal moraine, like a giant bulldozer blade of ice pushing material ahead of it. Effectively blocking off this glacial river draining system like a natural earth, rocks & boulders, dam. Today the main highway passes through the boulder field of massive rocks & debry that was pushed & carried many many miles & traveling on the ice. And then literally just dumped when the ice retreated & melted away never to advance again. Dropping these massive rocks to the ground. A lot of these rocks are very foreign to the local geological makeup of the surrounding mountains. Having come from a long way back. These foreign rocks are known as erratics. I know Jim that you will have an understanding of all this but I am being a bit more thorough in my description for those that don't.

After traveling this highway a bit further it climbs up & over the moraine & then drops down into, across & up the other side of this now cut off & dried up riverbed. You can see it as plain as day. Even one not up to play with what has gone on will recognize it as an old river despite that it has grass growing in it now. Well sort of among the rocks & gravels. The banks are still there & the dried up river trough "flows" & winds its way down this glacial valley, although very wide,  for miles. The road still passing through older boulder fields & moraines. About the same time as this last advance that blocked off this river, give or take a few hundred or thousand years geologically speaking, it is believed there was a major event that ripped open the ground in this valley where I have been detecting that caused this "new" river & the present day out let for the lake. This major event affected & changed many other land drainage localities in the Otago region. In some cases draining massive lakes. Along with mountain building, land upheaval, faulting & folding, subsidence & glaciation, Otago is a tortured landscape like no other. Bearing in mind that the Southern Alps, from which these glaciers flowed from, are caused by the collision zone of the pacific tectonic plate with the Indo Australian plate.  

Getting back to your initial comment. Yes the gold is very alluvial. All the Queenstown area gold & most of Otago gold is very alluvial no matter where you find it. Could be 5 thousand feet up on top of a mountain plateau or any where up & along the flanks. No present day river or water for miles. No sign of water worn rocks or debris. Glacial debris....yes....tell tale alluvial river worn material.....no not always up in the hills except in present day rivers. Maybe glacial melt water river/creek type "alluvial" material. But they aren't as rounded & water worn in a lot of cases as a lot of that material is just ruble & debri that got carried on the glacial ice & not pounded & rolled like river material does. The Glacially carried material just being dropped when the ice melted away & only subjected to the dying glaciers melt water forming a river  to give it an alluvial worn look. Until there was no melt water left & the river dried up. I am talking up in the hills & higher areas not the valley floors that carry present day rivers. I guess I am theorising in my own head trying to work it out. I know over the years I have given up but it still intrigues me. Possibly the alluvial gold that is now way up in the hills was deposited by river systems that no longer exist. That the glaciers came & wiped out the the rivers alluvial gravels & material. Leaving the gold buried down in the schist where I am finding it. The land also being pushed up to the heights it is now.

The higher sides of this valley I have been detecting in & where this"new" river now flows out from the lake has two hugely major gold bearing rivers flowing into it. The Shotover river, known in the early gold rush days as the richest river in the world, & running parallel & separated by a ridge line, the Arrow River. In turn these two rivers had hard rock gold mines developed near their heads. These loads being only a shadow of what they must have been to have released the amount of gold they did. On Lake Wakatipu, a glacial lake, all the gold deposits & loads are on this northern side going back to the lakes head. Nothing on the other side of the lake. The stamper battery & crushing plant being the glaciers which would have filled these side valleys of the gold bearing creeks & rivers of today flowing into the lake from the north & the Shotover & Arrow rivers flowing into this now "new" river that drains the present lake. The signs are there that the lake was much bigger & the water level much higher than today. Possibly held back by massive moraines until this major event happened & erosion from the lakes release cut through & washed the moraine away. Leaving pockets of lateral moraine & glacial silt deposits which are in there own right massive & obvious.

 https://www.doc.govt.nz/Documents/about-doc/concessions-and-permits/conservation-revealed/wakatipu-landscapes-lowres.pdf

I have gotten carried away again.  I may even add to this.

Good luck out there

JW

kiwijw Posted yesterday at 05:14 PM

I have included this link of the Ree's & Dart track. More so just for the photos but it is an enjoyable read nonetheless. These two rivers enter at the very head of Lake Wakatipu & there headwaters were the source of this once immense glacier. The Dart glacier just a small Remanent & one of many now smaller glacier remnants up in the mountains heads. The photos of the Dart Glacier show what I was talking about with the rock debris sitting on top of the ice & just going along for the ride & just being dropped when the ice melted away. I have also included it to show just how very similar the glacial countryside is to what Steve has been sharing with us on his Chisana & Gold Hill post. Virtually identical. Enjoy.

https://www.gang-gang.net/nomad/NZ/NZ34.htm

JW 

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Another interesting thread, I'll pull up a chair.

I live on top of a moraine, over time I've been trying to assemble a viewpoint of the historic events that shaped this area. 

If I go down on the north side of the moraine, I can find the leading edge where the limestone sits on top of the Canadian shield. This limestone is a 450 million year old shallow tropical sea. The edge left exposed by the glacier with a moraine on top.

What is interesting is the cooling glaciation events that exposed this tropical sea are the same events that consumed the water in the sea to begin with causing the second largest mass extinction event in the worlds history.

It's cool that in 2018 I can actually walk along this sea floor and look at fossils that were already 300 million year old fossils when the dinosaurs roamed.

I'm always keeping an eye out for interesting erratics because you never know. I can't tell you how man times I used to go out looking for relics, only to get skunked/sidetracked breaking open big hot-rock erratics with a hammer or looking for Kimberlite.

The video with the animations was nice.

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Great topic. Thank you for the information.  Glaciation is one thing I have been looking at for years while metal detecting for gold.

Not sure but it seems that nuggets I have found in a gold bearing terminal moraine are just like the gravels they leave. Unsorted in size and shape with no reason for their deposition. Gold is scattered except where it may be re concentrated from the melt-water streams from the ice. This leads to using VLF detectors for surface gold and a GPZ or PI for deep gold. 

         One more thing to comment on. I have not given up on the 19 inch GPZ coil. I have made finds the 14 inch coil can't recognize .On average I find nuggets from the surface to 14 inches  in depth for the 14 inch coil and surface to 24 inches with the 19 inch coil. I can say the nuggets found = the size of the coil 14 GPZ  is 14inches / 19 GPZ is 19 inches , so a 5 inch gain average  result. I may find fewer nuggets with the 19 but it has been worth the time spent trying to use it rather than let it sit. Do not give up on that coil. It takes time to learn it. These glaciated areas are great places to roam around with large coils.

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Thank you inthemountains for you added comments. Yes, glacial deposited gold is a real head scratcher if you think you are going to find the source. Even within the material it is all mixed up in there is no law & order, just randomly scattered all throughout it. Unless like you say it has been resorted & reconcentrated by the glacial melt water stream.

This is the Franz Josef Glacier on the West Coast of the South Island here in NZ. The river flowing out from under the glacier emerging from that  large Ice cave at the snout of the glacier.

PIC_0106

  The water is milky white due to extremely finely crushed rock particles, known as rock flour, caused from the powerful grinding & crushing power of the ice on the country rock as the ice flows like a very slow moving frozen river on the country bedrock. In this case mostly greywacke & some schist. The rock flour being so fine it never settles & just remains in suspension in the water. The milky white of a river is the tell tale sign of a glacial river. You will notice the rock I am standing on & the others in the foreground & elsewhere, are laced with quartz. There are old gold workings just downstream of where I am standing at the junction of this river & a side feeder creek coming into it. You will also notice the rock debri sitting on top of the ice & in the next pic also. The pile of gravel sloping up on the left from the ice, in the above pic, is a small lateral moraine, which is material that gets pushed to the sides running parallel with the tongue of ice. It becomes more pronounce as the glacier melts back leaving the material behind. This is a dying glacier, aren't they all?, so the terminal moraine, the pile of debri that is pushed ahead of the ice like a giant bulldozer blade, is not present as it is much further down "stream"  where it has been left from the last push advance of the ice but the ice has now melted way back. It does occasionally have a small advance.

PIC_0101

In the above pic there has been a small advance. You can tell by the ice being right up against the bushline on the left side. When it melts back the bushline will be higher as the ice would have ground the bush away & leave a smooth bare rock wall face, like on the right side. The glacier at this point has melted right back  to the start of this valley floor & where the valley starts to level off from the steep drop down from the mountain  heads & where the river flows to the Tasman sea not that far away. In this case from our country's tallest mountain. Mount Cook. Named after Captain James Cook who put New Zealand on the world map & claimed the country for the British Empire about 1770. There are numerous glaciers flowing off mount Cook. The Fox Glacier which is the next valley over, & also flows into the Tasman sea. Our biggest & longest Glacier, The Tasman Glacier, flows off Mount Cook on the other side of the Southern Alps main dividing range. Named after the Dutch sailing explorer Able Tasman. Who was the first recorded European credited to have discovered New Zeelandea, as he named it, in 1662. Over 100 years before Cook. He had a very bad experience with the natives who killed many of his crew. He fled the shores never to return naming the bay of his departure, Murderers Bay. Now called Golden Bay due to its golden sands. Tasman is also credited for "discovering" Australia. Calling it New Holland. Also the sea that is between Australia & NZ is called the Tasman Sea.

Here is a time laps of the flowing river of ice of the Franz Josef Glacier. Watch the whole video, not just the first 15 seconds. It is stunning & mind blowing. Enjoy.    

 

I will leave it there for now.

JW :smile: 

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Fantastic Video JW, mesmerizing indeed, it is staggering, and worrying, seeing how much of the glacial ice retreats when they play the footage in reverse.

Thanks for the info.

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