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Geowizard

Tailings Dump Processing

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There is a lot of interest these days in processing the tailings dump from past hard-rock mines.

 

This thread provides a venue for discussion of related questions and answers. :)

 

- Geowizard

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With reference to calculation of the volume of a tailings dump:

 

Going back to High School Geometry, we know the area of a right triangle is equal to 1/2 times the base times the height.

 

To be continued... :)

 

- Geowizard

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2250 tons X Assay X Recovery = actual ounces recovered

 

Sampling a dump is not easy. It is consists of layers that are hard to reach except on the outer surface. It self segregates with fines on top and coarse on the bottom. The fines tend to be highest in grade. so sampling the top surface may well give a systematic bias.

 

Recovery is hard to calculate as well. If just using gravity, it may run from just a few percent up to 90% - and that range makes a huge difference.

 

Chris

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Oh, the sampling techniques and recovery rates are so important its always a good thing to bring them up. The tons per yard is also a critical factor that should not just be assumed. Even just moisture can be an important factor as assays per ton are per ton dry weight, and most dumps have significant moisture content.

 

Dump volumes are actually even more complex than you have portrayed The top of a dump, while it appears flat is rarely so. Miners would slope their track a bit so that they had an easier time hauling out the material - better to go back up hill empty. The natural base the dump is deposited on can be complex and must be subtracted out. Sometimes dumps are placed on flats, but more often on hillsides. The problem is that there is typically little information as to what was on the ground before the dump was deposited on it. . The other thing is that dumps are often rounded in plan view - made from a series of dump lines in a radiating circle. For calculating the area of complex rounded composite dumps, in the past I would map them by survey, then divide the dump into horizontal slices, and use a planimeter to calculate the area of each horizontal slice. 

 

Its an interesting topic as there are a lot of dumps out there with values that can be interesting as the price of gold and silver move upward.

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Measurement uncertainty;

 

"All measurements are subject to uncertainty and a measured value is only complete if it is accompanied by a statement of the associated uncertainty."

 

 

- Geowizard

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In math, approximations are fuzzy and tend to reflect the intended outcome of the calculator.  Sometimes the opposite, but not as often.  Once approximations are used as a tool to predict financial outcomes, the sky is the limit. 

 

We are discussing tailing piles so fuzzy is gonna be the end result.  I think intentionally downsizing the volumes is the better of the 2 choices.

 

Also, the assay of tailing piles is more than fuzzy, it's guesswork.  Who actually can be certain of the unexposed contents?

 

When we combine fuzzy multiplied by guesswork.........

 

I recommend a cautious math that factors in a HEAVY reserve of potential pay material.

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Another factor is dilution. When you pick up the dump to do something with it - whatever the treatment method - you will leave some on the ground and pick up some soil. For equipment operators, they don't always easily see where the dump ends and the native soil begins. Some don't really care that much as it all pays the same to them.  I think geowizard has some experience with this.

I also processed a series of dumps by heap leaching in the 1980s, and faced the same issue. You almost have to put a geologist or other "ore knowledgeable" individual to supervise the pickup of the dump.

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I don't know if all of this is leaving everyone dumbfounded, confused or overwhelmed. :)

 

Simple questions can have complicated answers.

 

To be continued... :)

 

- Geowizard

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Interesting stuff on this thread.  I would like to solicit some further comment.  

Both mine dumps and tailings piles are mentioned above, so I don't think this is about mill tailings.  

So, you are talking about mine dumps or mine tailings that contain good values and are worth processing.  These dumps can contain all sorts of large waste rock and trash.

Here's a question...

Why would someone process an entire dump pile full of junk if they can sort out the waste?  I realize hand-sorting is time consuming, but if it could be done in a practical manner, then you would only be processing ore.  Many of the original high-grade mines relied on hand-sorting.  Is it not practical today?  Perhaps if it's not part of an automated/mechanized process, it's not even considered. 

Also, it seems that the iron trash mentioned could easily be stripped out with an industrial-sized magnet like they use at recycling yards.  You sure wouldn't want to run pieces of ore track or drilling rod through your crusher. 

I get a kick out of hunting mine dumps and finding ore to process in "mini-batches".  It must be free-milling and at least a couple oz/t.  That is the extent of my hard-rocking.  I realize you guys are talking about processing huge volumes, so my perspective comes from a low-volume, layman's level.

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diggingbar,

 

Excellent post! :)

 

You make several important points. If time is the only investment and your time can be spent doing something productive like hand sorting a tailings pile, it makes sense. In the case of large mining operations, hand sorting was done by men that were already being paid. So, the accuracy of sorting wasn't a priority for them unless a supervisor noted that they were not doing a good job at it.

 

Specimens;

 

There are literally tons of specimen minerals that are laying around in tailings dumps. The specimens may have little or no worth for their metal content, however, they are prized for their collectability as specimens. Local swap meets and the internet market places are great venues for selling specimen minerals.

 

I know of a few cases where old silver mines are being given a second and third look over. The mines contain chunky native silver. Metal detectors can be used to identify hidden silver and gold nuggets that were not exposed in the rock.

 

Back during the late 1970's Silver boom suspected to be caused by the Hunt brothers, a silver mine known as the Silver Dime Mine had all of the tailings loaded up and shipped to a smelter to recover the silver. It was reported that 10,000 ounces of silver was recovered. Silver had gone from $11 per troy ounce to $50 in January, 1980.

 

- Geowizard

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Micro mounts;

 

Micro mounts are small mineral specimens that are smaller than "Thumbs". These fit nicely into small "Perky" boxes. There are many micro mount collectors that pay big bucks for very small specimens.

 

Small gold attached to matrix in and around a mill site can be found by the diligent observer. Some of it is large enough to be detected with a metal detector some requires a very keen observer. Small micro mount specimens of gold may have very little value in gold. If the gold is visible - it has "nugget effect"!

 

LOOK! GOLD! :)

 

- Geowizard

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Yep, finding mineral specimens on mine dumps is fun and rewarding.  

Of course, the gold specimens are a great prize and the rarest to find.  I don't have the patience to hunt mine dumps with a metal detector.  I know that's how the whoppers are found, but usually, there is way too much trash to deal with.  Instead, as you mention above, you can be a "diligent observer" and simply use your eyes… your free metal detector.

 

Using a magnifying loupe (I like the cheap ones that are about 2 inches diameter over the tiny little jeweler's loupes) in the right location, you can sometimes find enough specimens showing "vg" to fill a bucket.  This material may not be showy enough to be specimen grade, but sure makes fine ore to process.

 

I will add that if you are able to cut your specimens with a lapidary saw, then you can sometimes get a specimen to reveal much more gold than it was originally willing to do, thereby making it marketable.

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