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Giant GOLD DREDGES make a comeback, Mongolian Dredge Fleet disproves drills
Steppegold
post Feb 15 2007, 07:07 PM
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Moving a little downvalley, here is the first of the pair of Toson Dredges - both owed by a Mongolian woman miner Garamjav.

This is the South Toson Dredge. It is slighty squatter than the sister dredges in order to enable it to twist and turn in the narrow floodplain it was designed for in Tolgoit in North Mongolia. When it had exhausted its reserves, Garamjav bought the dredge had it cut up into about 200 truckloads and had it reassembled here in the Tuul Valley.


You can see big bananas being formed by washed oversize dumped by the winterised rear stacker conveyor, and notice the 2 spuds - one up, one down - the down spud acts an anchor on which the dredge swings. Forward movement is by twisting the dredge and dropping the second spud and raising the first spud, rather like walking on stilts.

The 2 discharge chutes are discharging water and undersize tailings from the washplany aboard the dredge. The fine tailings (with fine gold the sluices cannot catch, plus coarse gold stolen by sticky clay robbers) are dumped first and then buried by the oversize bananas (with nuggets and improperly washed clay balls with gold) of the crocodile.

These dredges are designed to use mercury but do not do so - mercury usage at placer gold mines was BANNED in the Soviet Union and in Mongolia in order to protect the health of mineworkers. The design of the dredge remains the same.
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Steppegold
post Feb 15 2007, 07:19 PM
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Here is the front end of the Toson Dredge. Being owned by a woman it is the neatest of the dredges!
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Steppegold
post Feb 15 2007, 07:21 PM
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That's enough pictures for today - any comments or questions?
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Steppe
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jmann
post Feb 15 2007, 08:05 PM
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Cool very cool. Joe
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russau
post Feb 16 2007, 06:07 AM
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thats a really neat picture tour you gave us! thankyou!
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Denise
post Feb 17 2007, 10:41 AM
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Fantastic pictures and info!! smile.gif

Correct, the Snowstorm Dredge was a drag-line dredge. There were 2 dredges that worked near Fairplay Colorado.
Here is a link to a picture of the BIG bucket-line dredge that worked here.

http://history.oldcolo.com/history/research/mining_5.html

If you look at the CP webcam, you can see a small piece of the tailings it left on the right.

Denise


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gold_tutor
post Feb 24 2007, 10:36 AM
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QUOTE (Steppegold @ Feb 15 2007, 05:21 PM)
That's enough pictures for today - any comments or questions?

Steppe



Hi, Steppe,

I'm watching this thread with keen interest.

Will you please continue to post.

I'm especially intrigued by the offer you've made to discuss the qualitative error of drilling results when followed up by mining using bucketline dredges.

Hurry back.

Megan Rose
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Coalbunny
post Mar 2 2007, 05:35 AM
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I/m more interested in the efficency of a bucketline compared to that of a suction dredge.


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Steppegold
post May 29 2007, 07:55 PM
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Gold_Tutor - sorry I've been late in replying.

We all trust the churn drill (=placer drill, cable tool drill, motorised banka drill).
So did I.
But not now.
The world's largest repeat drilling by churn drill and bucket drill is in a 50km stretch of the Tuul floodplain here in Mongolia, a formerly 'Top Secret' report by Soviet placer geologists. The answer is stunning. The churn drills lost so much gold compared with the bucket drills. Wow!

Churn drills are OKish on dry terraces and for shallow holes, as shown by the Yukon drilling tests using radiotracer gold.

Churn drills on floodplains or deep enough to be in wet ground UNDERestimate the gold content by 30-60%. That is amazing.

And the Soviet churn drills are as good as or better than your North American churn drills as the diameter is 325mm giving a much bigger sample and far less noise from sidewall effects.

I am preparing an article for publication on this and will report back when its ready.

cheers

Steppe
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Steppegold
post May 29 2007, 08:11 PM
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Coalbunny - you asked a good question:
"I'm more interested in the efficency of a bucketline compared to that of a suction dredge."

Its actually a bit convoluted to give a proper answer.

A BIG bucket-line dredge should recover ALL the material provided it is small enough to fit in the bucket. My friends caught a Mammoth in one of the buckets of their bucket-line dredge.

A bucket-line dredge usually swings as it cuts, and therefore it is usual to have an onboard washplant. That's OK, but the nature of the swing and dredging limits the length of the dredge, so often the space for the onboard washplant is limited. That means a brilliant dredge is likely to have a not-as-good-as-it-should-be onboard washplant, and retrofitting a new washplant is impossible without stopping production for months.

Right, now for suction dredges.

An advantage of a BIG suction dredge is that it generates slurry that can be pumped to a floating washplant sat on a barge/pontoon nearby or even at a distance. Therefore there is no limit to the size or layout of the washplant, it can be altered easily, and retrofitting can be done without any serious delay.

The disadvantage of a suction dredge is that if the material is cobbly, as it often is, then the cobbles cannot be pumped up and so one by one accumulate on the bed of the dredge pond. That is not a good idea for eventually it means that the suction dredge cannot get at the virgin material below, or if it does then the gold is liable to be dropped in the crevices between the cobbles - the dredge pond may end up carpeted in gold! In contrast a heavyweight bucket line dredge is able to rip loose bedrock.

That said, cutter suction dredges are cheaper to buy than bucket line dredges, are much more readily available as they are civil engineering dredges for rivers and coastline, and are much easier and quicker to transport, assemble, disassemble and truck to the next location. It can be as quick as a few days, but for a bucket line dredge it is usually some months, often many months.

Cutter suction dredges are probably cheaper to operate and cheap enough to also remove the overburden. Indeed a winning combination in terms of cost, speed, recovery, freedom of movement and rehabilitation is a cutter suction dredge up front to pump away the overburden followed by a bucket-line dredge that mines (and washes) only the placer.

I hope this helps a bit

Steppe
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CP
post Jun 23 2007, 07:51 AM
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Hi Steppe,

Awesome series of photos you posted and thank you for the invite. If I can ever get to Mongolia I would love to see any of these monsters. cool.gif

I was reading through these again today and noticed you asked about the Snowstorm dredge pics in the first post. You can see the a pic of it's riffles in fact, right here on the CP forums. biggrin.gif Coolest prospecting site on the web. wink.gif
http://www.coloradoprospector.com/forums/i...php?showtopic=5
I'm not sure but these may be some of the very few pics of this dredge even on the net anymore.....possibly the only ones of the interior parts.....Enjoy.

I've also got some information on the "placer drilling" that someone sent me....I'll try to put it together in the next few weeks and get it posted.

CP


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Steppegold
post Jun 23 2007, 01:50 PM
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Hi CP - thanks for the link - tremendous information!

Mongolia's fleet of five large Siberian bucket-line dredges were originally all equipped with inclined flat bar riffles set on square-ribbed black rubber matting.

Since then, several have been upgraded by installing new sluices consisting of large expanded metal MESH, still on square backed ribbed rubber matting. Unfortunately these are not as effective as they could be, being flexible MESH prone to buckle and warp up off the matting, rigid GRATING would have been better.

Here are some unique pictures of sluices of one of these giant dredges, minutes after the new riffles were installed:

Steppe
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Steppegold
post Jun 23 2007, 01:57 PM
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What should interest you guys and gals who know the Snowstorm Dredge well, is that the Siberian Dredges have self-cleaning sluice boxes. Think of 20-30 sluice boxes in a row (in parallel), all on wheels on a track, all on an endless chain. Every few minutes, CLANG!, and the whole lot moves to the left, sending the end sluice box off the end to turn upside down, while a freshly cleaned sluicebox appears at the other end. Its a bit hard to explain. Think of the 7 dwarves in bed, lets make it 40 dwarves and a bed with room enough only for 20. One fed up dwarf climbs in the bed and all the sleeping dwarves shuffle along and so Happy is shoved out of the other side of the bed. Happy ends up upside down under the bed, and has to wait his turn until every dwarf is shoved out of bed.

Anyway here are the wheels on a sluicebox:

Steppe
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Steppegold
post Jun 23 2007, 02:07 PM
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The Siberian bucket line dredges are good at digging and washing riverl alluvials. But two of the five also have gold-rich stiff red paleoplacer clay of Neogene age to content with - laterite clay. As a test I left a chunk in my apartment and it turned quickly into a solid brick!

The buckets of the bucket line dredges scoop up the clay with no problem. However, the huge on-board trommels cannot dissaggregate the clay fully. Some go down the sluices as goo-ey gold robbers, picking up gold as they go, and report to the fine (undersize) sluice tailings.

The bigger clay balls report to the rear stacker conveyor and hey they balls are rich in gold! Here is a local stealing a clay ball:


And here are 300 local 'informal' miners doing the same:


The clay balls are washed by hand in green bowls - this is bowling, a bit different from panning!


And here are the locals running away when the security guards arrived:


So, if you are looking at dredge tailings for gold, particularly nuggets, the place to look may be the bits of the dredge tailings that are mounded up (banana-shaped ribs on the back of the crocodile of tails) yet have revegetated faster than normal. That's due to clay balls being chucked out of the rear end of the dredge. No all clay balls have gold, but when they do then 300 people make a living!

Steppe
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Coalbunny
post Jun 28 2007, 11:18 PM
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I'd like some comparative facts.
1. What size of suction dredge woul it take to equal the cubic yards moved by a cutter dredge?
2. What is the cost of operation for a cutter dredge?
3. What would be the cost of operation for a suction dredge as mentioned in #1?
4. What is the overall recovery of the cutter drdge in a 24 hour period compared to the suction dredge in #! for the same 24 hour period?
5. What are the manpower requirements for both dredges?
6. What is the actual down-time of the cutter dredge in comparison to the expected down-time for the dredge in #1?
7. Are they hiring? biggrin.gif


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If they were they'd have eaten the snake instead of the apple and we'd still be in heaven....
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