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Darrell D

Recovery Rates For Hydraulic And Ground Sluice Mines

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Darrell,

  A lot depends on what they were using in the box for a recovery medium, the type of bedrock and the character of the gold.

 

 Certainly not good by todays standards. The water surging associated with hydraulicing was a considerable factor in recovery.

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Hi Darrel,

Correct me if I am wrong but I believe the part that you are asking about is the actual washing of gold along the ground to get to the sluice. 

 

Geowizard describes a small location where he found some pay that the hydraulic miners washed along and then missed (he has a good logical explanation in his post).  He didn't state any approximate dimensions for this find so I am not sure how large an area it was.  I would guess that this happens occasionally. 

 

I have to wonder when they got down to bed rock, using high velocity water caused much random displacement of gold. In some instances maybe they used a dozer to scrape through some of the bedrock.  I would suspect there is some gold still in the bedrock, but difficult to say how much.  Lots of variables!

 

Looking at it from another perspective, I have read some of the early USGS reports for different areas in alaska.  Numerous times comments state that the old timers re-worked an area.  But it usually doesn't say much more than that.  A few times there have been comments that say the old timers went back and reworked the perimeters of the original paystreak.  I just can't find enough details to conclude that the oldtimers re-worked the "original paystreak location" or some "other location".

 

Just my 2cents

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Thanks for the answers, the reason I am asking is I have researched an area that had an old hydraulic mine on it. It ran for two seasons in 1906-07. This area had also been ground sluiced and was reported to have got 12.5 oz from 900 yards, ground sluicing. So I am wondering if this area may be more viable with better recovery methods. It has 5 feet of snow right now, so it will be a few months before I can get out to it.

 

thanks

Darrell

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So I am thinking that if they where getting $17.10 by ground sluicing then the same ground would pay more using a more efficient method. Will have to see if I can find that same ground.

I would think recovery by ground sluicing would be in the 50% range? Don't know

 

Darrell

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I am a relative newcomer to mining, and I am not a professional miner either, so my $.02 here should be taken with about that much salt. That said, I do a lot of reading, I mean a lot,  and I have done a lot of research, which a lot easier now because companies are beginning to publish old books and journals that were previously difficult, if not impossible to find.

 

The example I offer is: "The Auriferous Gravels of The Sierra Nevada of California Volume 6, No. 1", by Josiah Whitney. While the character recognition software they use to reproduce these old writings is imperfect, the information contained in these volumes is priceless for seeking answers to questions such as yours. Indeed, you can find little tidbits of information that can lead to forgotten discoveries, and long lost information. Consider the following passages in the previously mentioned volume:

 

"The distance from Scott's Ravine to Wilcox's Ravine, by the stream, is not far from four and a half miles. In the absence of any data, it is not possible to make an stimate of the amount of gold and quicksilver lying buried in these 10,000,000 cubic yards of gravelly pebbles."

 

The same passage continues:

 

"In the course of the meandering of Steep Hollw and Bear River, little of interest was found connected with the geological bearings of the gravel question. At one spot on the Bear River however, about a mile above it's junction with Steep Hollow, where the stream changes from a southerly to a westerly course, a small quantity of gravel was found at an elevation of a few feet above the present tailings, probably about 75 feet higher than the bed of the river before washing began. This must have been left where it now is, while the river bed was at or near that elevation. There was not enough of the gravel to pay for working, but the bank had been opened by some prospectors."

 

So, summarizing my point, recovery rates may have only been 50-60% efficient (in 1884, or even in 1907), but one must also consider the fact that some areas were not mined because the amount of gold found, evaluated at $35 per ounce, may not have made economic sense to process and extract.

 

Side note: Everytime I read Whitney, I want to go to the mountains right away and start prospecting! What a glorious feeling his writings create in me!

:)

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I read this morning, in "TheTertiary Gravels of the Sierra Nevada of California" (Lindgren 1911), on page 72,  Lindgren writes (referring to the Forest Hill divide in Placer County at the Morning Star and Big Dipper drift mines,), "From 6 to 7 feet of gravel was extracted, and the contents ranged from $10 to $14 a cubic yard; gravel containing less than $2 was not considered payable."

 

Can you imagine? That was at $20.67/oz in 1911, and now using $1200/oz, the equivalent value considered not considered payable would be $116/cubic yard! So much more efficient are our current methods of exrtraction, that amounts over $.10/cubic yard is considered payable if you can get to the material without spending too much in fuel and labor for the removal of overburden.

 

I guess my point is that recovery rates were inefficient, but that much of the gold placer gold in the tertiary gravels was left unextracted, in search of the better paying leads and streaks, at least as far as drift mining was concerned. Hydraulicing, of course, took much more because it was the overlying gravels too.

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Darrell,

 

My understanding is - "They" got the $17.10 (todays prices) and if they were 50 percent efficient, they left $8.50 gold. :)

 

- Geowizard

Don't put the cart after the horse. They recovered $17.10 @ 50% effeciency. That left the other 50% ($17.10 or more) still on the ground. Old school math  :D

Bob

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Here's the "New math";

 

The old timers got the "easy pay". That's the 50 percent of the gold that hangs in the box. Mining the tailings will be more difficult because the gold is smaller. Recovery will probably be 50 percent of the remainder - not 100 percent. :)  

 

A good sampling program will reveal the truth in what might be expected.

 

- Geowizard

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The "First Run" through the sluice gets the gold that hangs in the sluice.

 

The "old timers" used cocoa mat for bedding and it probably is superior to many "modern" mats used in sluice boxes.

 

You would be lucky to get 50 percent of the remaining 50 percent. It's probably $5.00 gold.

 

- Geowizard

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Nice tails indeed Harry!

 

I work my axx off busting up virgin hard pack gravel and don't see gold that size….

 

I would argue that today's technology is far superior to the days of old when hydraulic methods were used.  They got paid in volume.

 

A modern wash plant should have a much higher recovery rate than hydraulic mining if the fancy tech is used like jigs and concentrator bowls for the tiny stuff - down to say 200 mesh.

If you know the gold in the tails is all within a certain range of particle size, then you only have to engineer your recovery system to catch that range of size and nothing else.  As an added bonus, tailings are usually in a nice, accessible heap, ready to attack.  The miner doesn't have to move heaven and earth to get to it.

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Geo

Here they had no running water. They would hold runoff in holding ponds and when they had enough, they would pull the gate and shovel like crazy. I'm sure they overloaded their boxes. It's not unusual to find 1/4 oz. pieces in the tailings.

A number of years ago, I found a "sluice robber" (clay ball) that had 72 nuggets in it.

Try that on your BS meter

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Darrell,

 

I have been doing in real life, what you are asking. The process of recovering gold from low grade tailings is a challenge as anyone familiar with the subject will confirm.

 

Outside of the realm of gravity separation and concentration, things get very risky.

 

Personally, I would not expect a big pan of nuggets as has been presented by others. :)

 

- Geowizard

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