Ken's Journal
No. 5 - Summer 2005

Chicken, Alaska & Dawson City, Yukon
July 6-9, 2005 - Days 36-39 on the road. Part III.

So Ok, What's a gold Dredge? Early miners to the area knew that the Klondike held massive quantities of placer gold, and knew there was much more than a miner could find with his pan. So what's placer gold? Placer gold is gold that's been moved from it's original location deep underground by the action of erosion -- so where do you find it? In stream beds, creek beds, river beds and wherever the water "used to" flow. Large mining operations consolidated claims and borrowing dredge technology that was used in California and Europe, developed a gold dredge suitable for use in the Klondike.


Earlier, when I was on top of Midnight Dome, I looked behind the Dome, opposite Dawson City. This is what I saw - what the hell is that? That is the pattern of tailings left behind a large gold dredge. The tailings are the waste piles of debris left after the gold is recovered. Because of the way a dredge works, this is the pattern of debris piles that are left. On the highway next to them, you'd not know what they were unless you knew what you were looking at --


I'll use the pictures the Canadians graciously left beside "Dredge #4," the largest dredge ever used in the Klondike gold fields. The Blue outline is the basic dredge and the black outlines are the key mechanicals.

Let's see if I can explain the flow of gold as it moves from formation to your wife's finger.

First, gold was formed when the earth was formed - it's one of the heavy elements. Sometime after formation deep in the earth, the upheavals of the crust exposed veins of gold to the elements - millions of years ago. Subsequent erosion by the action of the oceans, creeks, streams and rivers, brought this precious element to the creek, stream and river beds where it's found today.

Because Gold is some 19 time heavier than water and 9 times heavier than the gravel that holds it, it sinks to the bottom of the mix. To pan gold, you take the gold bearing gravel, put a shovel-full in a pan, add water and rock the pan - the gold settles to the bottom. Rock the pan to allow the water to drain and the lighter particles of sediment, now on the top, wash out with the water. Repeat this as many times as required until only the gold is left. It's a little more difficult than it sounds - I've successfully done it and can tell you it takes a bit of practice. A more sophisticated miner would use a sluice to remove most of the debris before panning the remaining. At it's simplest, a sluice is a long, sloping box with cleats in the bottom. Gold bearing gravel is added at the top as large quantities of water wash the gravel to the bottom. The gold, again, heavier than any of the other components, sinks to the bottom and gets caught behind the cleats.

A gold dredge works essentially the same way a sluice works - quantities of gold bearing gravel are "sluiced" with larges quantities of water in multiple sluices. The sluices are much more sophisticated than the simple one used by the individual miner. The slope is optimally engineered, the "cleats" are optimally engineered, cocoa mats are used under the cleats and mercury may be used as well (Mercury is the only element that will readily combine with gold - forming an amalgam. The amalgam is later heated, boiling the mercury off before the gold boils, leaving just the gold. The vaporous mercury is condensed and recovered for use again.)

Anyhow, how does it all work? Follow along on the diagram above.

The bucket excavator (2) drags tons of gold bearing gravel (1) into the dredge and drops it in a revolving screen (3) where the smaller pieces of gravel are dropped into the gold saving sluice (4). The larger pieces of gravel remaining are washed so any gold hanging on will fall into the sluice for recovery. The washed gravel then travels to the bottom of the revolving screen and is dropped onto the tailings stacker (5), a large conveyer belt. The tailings are dropped onto a pile behind the dredge.

The dredge itself is on a floating barge (8) which floats in the self-dug dredge pond (9). So as the Dredge removes material from the front and deposits the waste in the rear, the dredge essentially moves it's pond as it works. The excavator is fixed and does not move side-to-side, only up-and-down and in this particular dredge, can remove gravel from some 35 feet down. To move side-to-side, it's necessary to move the dredge side to side. That's where the Pivot Points (6) come into play. A pivot point is lifted by a crane and dropped into the tailings. Workers have already constructed anchors on the shore for cables from each side of the dredge in the front. Soooo, to move the excavator side-to-side, the cables are worked to move the front of the dredge side-to-side while it pivots on the pivot points!! After a full side-to-side sweep has been made, the pivot point is lifted and the dredge is pulled forward using the same cables. The pivot point is dropped again, and the process starts over again. And that's how those strange tailing patterns at the top of this page were created!! In a good year, a dredge may move only a mile or two up-stream.

The whole process, as simple as it sounds, gets a bit more complex - especially in the Klondike gold fields where permafrost is common.

First off - permafrost is ice - and ice is as hard as a low grade concrete. A dredge can't touch it - just bounces off. Additionally, the gold bearing gravel may be covered by a layer of sediment sometimes hundreds of feet deep.

So first you remove the sediment to get to the gravel - that's typically done with water jets to wash it away. Then, once you've exposed the gold bearing gravel, you have to thaw it out before you can excavate it. That's done with pipes driven into the frozen gravel carrying steam - later it was found plain water worked just as well. And all of this is done in a season that's only 9 months long.

So where did the power come from to operate this stuff? Almost everything ran on electricity, the pumps, the dredge, whatever - this was the early 20th century - in the case of Dredge # 4, a hydroelectric power plant was built to power all the dredges in the valley.

All of this took a lot of manpower - mostly under pretty brutal conditions - OSHA didn't exist back then. There was a team inside the dredge - where the noise was unbearable. One, you had rocks and stones being tumbled in the screen and two, little of the mechanicals were lubricated so it was metal-on-metal. Any lubrication - oil or grease - sticking to the gold would have floated it out of the sluices - at a loss to the operators. (When you buy a pan for gold - the first thing you do is clean it really well to get rid of any oil or grease from manufacture - slightly rusty is good!) So the operators inside the dredge were subjected to a symphony of boulders bouncing inside a rotating metal tube and metal-on-metal screeches! They frequently went deaf. Others were responsible for ensuring the buckets on the excavator stayed clean of clay, tree branches or anything else that might impede the flow of good gravel. One was responsible for ensuring that nothing clogged the tailings stacker - if blocked, the tailings would spill inside the dredge, quickly sinking her. Others were on outside crews building anchors and moving and repairing the cables. More worked the stripping guns and thawing points. When steam was used for thawing the permafrost, boilers had to be maintained with a steady supply of wood for the fires. One man, the captain so to speak, manned the control room (7) and operated the entire dredge. This is also the only place that has any heat - not for the operator, but to keep the grease that lubricates the cable controls from freezing - one of the few places where lubrication was used.

The sluices were cleaned once a week or so - the mats were rolled and taken for cleaning and processing. After processing the gold was melted and formed into bars, assayed and transported.

So in a nutshell, that's how it was done - all for just a few (million) ounces of gold - - -

The business end of Dredge #4 - the excavator minus the buckets. Whenever a dredge was shut down for the season, the buckets were removed for repair. This is how the dredge was found when it was decided to restore her.


Looking down the business end from the control room.


The chain of buckets laying beside the dredge. Each of these is about three feet wide.


Gears on the main drive for the bucket chain.


And giving the whole thing a little perspective - this is the whole dredge.
My RV is in the foreground.

You'll notice the signs above are bi-lingual - English and french. Very strange in Canada. Everywhere you go all the signs are bi-lingual - except for Quebec where all the signs are in french only. I suppose the french in Canada just don't have the wherewithal to learn a second language. I think it's nice of the Canadians to look after those less gifted than the rest of them.

Next - We start for Anchorage to get Lesley to her flight back to the lower 48. We take a round-about way through Chicken, Tok, Delta Junction, Paxson and across the Denali Highway (a really charitable designation - it's 100 miles of abused dirt) to the Parks Highway and south to Anchorage.

So next will be our adventures on that little trip!

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