collapse


* User Info

 
 
Welcome, Guest. Please login or register.
Did you miss your activation email?

* Who's Online


Dot Guests: 158 | Dot Users
Dot Hidden: 0

* Board Stats

  • stats Total Members: 12964
  • stats Total Posts: 130008
  • stats Total Topics: 18183
  • stats Total Categories: 5
  • stats Total Boards: 48
  • stats Most Online: 814

* Advertisers

Gear Pan
The lil Gold Spinner
BC GOLD
The lil Gold Spinner
The Pocket Sluice

Author Topic: Ancient River Channel  (Read 14493 times)

0 Members and 1 Guest are viewing this topic.

Offline BC Prospector

  • PPT Invited
  • *****
  • Posts: 29
  • Province/State: Gold Creek
  • Kudos: 3
Ancient River Channel
« on: April 23, 2010, 04:32:04 PM »
Has anyone found an ancient river channel that hasn't be touch by any glaciers ?  What do they look like compared to our rivers today? After nine years of searching here in the Kootenays, I may have found one but I'm not sure.  Do to the fact that its in the headwaters where the alpine glaciers would have started and that it's protected by a narrow gorge,. I think the glacier would of slid right over top of it riding on each side of the valleys bedrock. Not all glaciers clean out valleys to bedrock.  Also the alpine glaciers which flow from west to east would have slid down the valley running into the main continental glacier causing the alpine glacier to stop or move ever so slowly  as it was sheared off. Eventually the continental glacier would have ridden high above all these lower mountains causing everything to freeze up. Of course this would have taken thousands of years and thousands more before the melt. Whats interesting about this river bed I found is that it's burried under ten feet of glacier til and all the river rock are  the size and shape of five gallon pails. The rocks are also river worn, smooth all around and they are stacked on one another as if a mason had built  this river bed. Between the boulders is a thin bed of pea gravel/sand mix which is very dry and hard to break apart. I've never seen a river bed with all large rocks and no small rocks. The oval rocks  all seem to be pointing in the same direction.  I should also mention that the river bed is high on a bench and gold has been found in the area up to five ounces in size. I  found this river bed last year just when winter was settling in and I was only able to remove the boulders down about three feet. Its hard pulling these boulders out of a ten foot pit with only hand tools. It's going to be a few more weeks until I can get back in to start mining again. I'm not certain that my theory is right but I would sure enyoy anyones input on this.  Thanks

Offline spud

  • PPT Invited
  • *****
  • Posts: 171
  • Kudos: 2
Re: Ancient River Channel
« Reply #1 on: April 23, 2010, 04:40:49 PM »
sounds very interesting BC!  I would try to get to bottom and i would pan all the way --- maybe this ground was laid before gold was coming down the river ? ive had that happen to me once  lol                                          do keep the forum informed on your progress  im sure it will make a great story!

Offline GollyMrScience

  • PPT Invited
  • *****
  • Posts: 2951
  • Province/State: Near Edmonton Alberta
  • Kudos: 160
Re: Ancient River Channel
« Reply #2 on: April 23, 2010, 06:11:07 PM »
You could be dealing with an interglacial channel. From the decription you are dealing with a water deposited bed but the energies are obviously really high. No small stuff - just large rocks laid in like brickwork.
You see these sometimes in glacial meltwater channels where there is perhaps an ice dam formed up on a meltwater lake. The dam lets go and the water flushes out of there with lots of energy and little forgiveness. It grabs the glacial till thats there and whatever local rock it can grab, Many times the meltwater channel will find an exisiting river channel and rework the materials in it.
Once the meltwater stops then you can get a couple of glacial pulses and glacial till laid down on top of everything.

Another possibility is a pre glacial channel that was driven by seasonal flood waters from alpine glacier melt but generally those will still have some layering of fines and course as the high energy ends letting course stuff settle first and then the lower energy leaves the finer stuff on top. The next year you get another flood cycle. Though the high energy tends to wash away the fine stuff but there should still be layers.

You are right that sometimes glaciers don't get everything and there could be pre glacial channle remnants.

Check the rocks for evidence of exotics - rocks that would have been transported there by glaciation. It can be a real puzzle but what you are looking for are rocks that are not from the local rock types but it is in the channel. Look for clues in the obvious till to see if you can spot rock types that are not from around there and then compare to the rocks in the channel rocks.

You can also get hybrid streams but those can get really wierd.  ;D
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline BC Prospector

  • PPT Invited
  • *****
  • Posts: 29
  • Province/State: Gold Creek
  • Kudos: 3
Re: Ancient River Channel
« Reply #3 on: April 23, 2010, 11:20:34 PM »
Hi Spud, Good to hear from you way over there in Australia. I'm keeping a watch on Jessica Watson, the 16 year old sailing solo around the world. You all must be very proud of her. I know I am. I'll be sure to keep this forum posted on my findings.  Hi Golly. I knew you would come to my rescue with some great answers. I also thought of a flash flood from a glacier dam breaking or maybe the side channels when the glacier was melting back. I've seen a valley which was formed from the side melt water of the continental glacier on the Kootenay river. About 100 yards up stream from my test pit I found stratified material which started with sand then  pea gravel and  then a Pebbly mix and so on. Another interesting thing I found upsteam on a bench is pudding stone or conglomerate. I showed a piece of it to a local geologist who couldn't identify it and he wants me to bring a larger sample to his office. I think it may have been formed under water in a volcanic vent. It's color is from a light chocolate brown to a dark chocolate brown. It has sandy white pebbles in it thesize of small hen eggs. One larger piece has what looks like hematite that was forming in it before it cooled or hardened. I'm also finding course nuggets of hematite which some are as big as a softball. Again this is up stream on a high bench. So within 1000 yards upstream of my pit I'm finding a lot of mineralization. In all my years prospecting I've never seen so many interesting showings. We hiked up the mountain above my pit about 1500 feet and found an outcrop of bedrock with smooth wave marks. Obviouly there must have been a large body of water there. Maybe even before the mountains were formed. I'm still trying to put the pieces of this puzzle together. I'll check these rocks in the pit for exotics as you mentioned. Thanks for the information.

Offline GollyMrScience

  • PPT Invited
  • *****
  • Posts: 2951
  • Province/State: Near Edmonton Alberta
  • Kudos: 160
Re: Ancient River Channel
« Reply #4 on: April 24, 2010, 08:21:00 AM »
Wow BC it looks like you are up to your eyeballs in exotics with the local geology let alone what the glacier dragged in there. Its gonna be a puzzler thats for sure!
Pudding stone and other forms of conglomerate are something to really pay attention to. They are the the next step up from cemented gravels and if they are derived from a gold bearing stream that gold is still in there. Some present day placer deposits have been tracked back to one of these ancient streambed "fossils" that a modern stream has cut through.
Sounds like fun!
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline GollyMrScience

  • PPT Invited
  • *****
  • Posts: 2951
  • Province/State: Near Edmonton Alberta
  • Kudos: 160
Re: Ancient River Channel
« Reply #5 on: April 24, 2010, 08:37:19 AM »
BC when you look at that puddingstone are the white pebbles rounded like in a stream or do they (at least some) have squareish sides or ends?
Your volcano thought could be close to the mark if those white pebbles are feldspar. You could be dealing with a volcanic conglomerate either formed as water reworked pyroclastic materials from a volcano or even more dramatic a lahars type deposit. The lahars form when there is enough water mixed with the pyroclastic material that it runs down the side of the volcano in a flood. Very bad place to be! Terrible destructive, fast moving and destroying everything in its path. That mix of pyroclastic and water flows like a thick river and will show at least some characteristics of water flow though it happens so fast that everything is over before any real good sorting can occur. Sometimes these lahars are nearly boiling rivers of mud and debris. With that sort of behaviour its no wonder natives on volcanic islands worked hard to keep the volcano god happy.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline GollyMrScience

  • PPT Invited
  • *****
  • Posts: 2951
  • Province/State: Near Edmonton Alberta
  • Kudos: 160
Re: Ancient River Channel
« Reply #6 on: April 24, 2010, 09:32:38 AM »
Another little bit on the lahar - they can be from ice and snow melting from the inside of a volcanic crater, they can be from lakes that have formed in the crater, stean from rain and local water table being shot up through the vent, heavy rain soaking the pyroclastics down so they release as a mud flow or debris flow. Varying amounts of water and energy but all kinda scary and to a large extent unpredictable though not unexepected. The vid below that shows what would happen in the US when a lahar hits a major city shoud give a good idea why people should be wary.

Some video footage of lahars.


      YouTube
            - Puyallup Lahar
   



      YouTube
            - Lahar sur le volcan Semeru, Java, Indon√©sie
   



      YouTube
            - Mt Ruapehu volcanic lahar
   



      YouTube
            - Lahar Llaima volcano, July 3, 2008
   


What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline Chuxgold

  • PPT Invited
  • *****
  • Posts: 819
  • Province/State: Naches Washington
  • Kudos: 10
  • The thinker.
Re: Ancient River Channel
« Reply #7 on: April 24, 2010, 10:02:06 AM »
As to where there has been glaciationíll till left in a stram bed. If there is no bed rock. It is hard to discern between what was left by a flow of material or is a old channel. Same size boulders usually says something about the evenness of the conditions that made them. With each having a similar hardness.
It is vary rare if not impossible for boulders to classify out in specific sizes with gravety. As it is more a mater of the bigger getting smaller. Not how they mite lodge better here or there. There is always a odd sized one in the mix  getting smaller faster.
To have rocks the size your talking about. I would think the entire area would have the same size boulders. Unless in a channel Were they would be worn more. With dents and breaks from the trauma of erosion in a stream. Not just pressure like what made all of them around there.
Also would be more gold in even more eroded material. Not because of what its releasing. But because it shows how much time it spent in a watery movement.
A movement that carries gold. And if its duration was long enough to change the stones. It carried lots more gold over that smaller space.
What your working sounds like the banks of a ancient stream. Where the smaller material has eroded out from in-between the larger. Easily escaping down a ever increasing valley bank. Sliding and shifting the larger into a single mass. Locked together by being so similar in size.
with no sulfides in till. There is no decomposition except for what it has brought with it. And will not make it far if it was formed to close to a sulfide seam.
But ones that are well traveled And lay in only till. Will do so for millions of years. Unless close to the bead rock were it could find sulfides again.
Chuck.
Give self, to gain wisdom,

Offline GioTheGreek

  • PPT Invited
  • *****
  • Posts: 162
  • Kudos: 0
Re: Ancient River Channel
« Reply #8 on: April 24, 2010, 10:53:47 AM »
The process that wipes out the villages on the Volcano hillsides, are the lahars! I thnk I remember reading about that somewhere... some crazy mudflow thats more destructive than the lava itself.

I've been looking for ancient streambeds around here, to see if I can go do some nugget shooting, but, I have no idea where to start.


Offline Sleeping Village

  • PPT Invited
  • *****
  • Posts: 74
  • Kudos: 0
Re: Ancient River Channel
« Reply #9 on: April 24, 2010, 12:25:13 PM »
Very cool, BC Prospector. I wish you the best of luck on your hunt for ancient channels.

Have you ever read the book Ancient River of Gold? Before the mountains were built... The author believes that a gold-rich, massive ancient river ran up through northern Idaho and entered Canada somewhere near Creston here then running northward toward the Big Bend area before headin' west. He also figured there were two smaller tributary type channels of of this river that ran west, one near Nelson and the other further south near the border. I'm in the process of mapping roughly where these channels may have ran based on modern deposit concentrations...The glaciation makes this tricky :P

Good luck to ya <-good_>


 


Gear Pan
Gold Rat