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Author Topic: Micro Flood Gold  (Read 83712 times)

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Offline The Fossicker

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Micro Flood Gold
« on: January 01, 2010, 08:36:39 PM »
Howdy All,
I thought I would pass along my latest kick in gold prospecting - looking for micro flood gold in rivers. What I mean by "micro" would be 100 - 200 mesh. Generally when I'm looking for the little stuff I look for fall out areas where black sand layers on the surface or deeper seems to be the place of choice for what I'm after. Lately though I have been coming upon sand and gravel bars that have built up to 6 feet or better in height near the mouth of some rivers. These bars are usually covered by small rounded cobble on top and almost pure sand below with very little black Sand at all. Cross cutting a trough through these mounds shows large amounts of micro gold in the first inch or so, then nothing. I'm still not sure why this is happening only on the top portion, but it is acting just like standard flood gold which in most places I've been does not penetrate deeper than 6 inches. Wheather I figure it out or not, I'm having fun getting the little stuff and it's starting to add up one grain at a time! How about let's hearing from others who have some experience chasing small micro gold and trying to find where it likes to hide. Any tips??

The Fossicker
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Offline J-Bear

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Re: Micro Flood Gold
« Reply #1 on: January 01, 2010, 10:20:48 PM »
Hello Fossicker
What equipment would you use to recover micro fine gold?

Offline sluicedog

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Re: Micro Flood Gold
« Reply #2 on: January 01, 2010, 10:51:36 PM »
Thats exactly what I have chosen to focus on....for now
Micro Fine Gold.
I have been working the silts of the Lower Fraser River....I'm pretty sure it's probably more like -300 to -400 mesh.
I know it is there.... but to recover it is no easy feat...there is black sand as well.... but it too is micro sized  ^#!
The time and gas I save in driving to the Fraser Canyon...well .... I hope to offset it with the time spent on the micro gold recovery...we will see  [^Crazy!#]

Offline sluicedog

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Re: Micro Flood Gold
« Reply #3 on: January 01, 2010, 11:48:57 PM »
That is great news finch68....I'd love to follow you along on this journey....I was looking for an article describing the flow rates of water at the Mission Bridge river flood guage....

It runs somewhere around 14,000 cubic metres per second   running through there on the spring Freshet....with that volume of water and force I just believe the fine gold has no chance to settle out too quickly, and it is probably scouring out the Fraser Canyon of any fine gold....only to be carried for miles down stream with thousands of yards of silt....well thats what I'm betting on...we will see  <-good_>

Offline sluicedog

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Re: Micro Flood Gold
« Reply #4 on: January 02, 2010, 12:29:39 AM »
I know what you are referring to.... I had that site Bookmarked...a couple of years ago we were asked to get ready to evacuate Fort Langley....so I would be watching the levels several times per day...even drove to the river morning and evening to watch the water rise....scarry stuff I have to say  <~ShOcK~>

Offline Blister

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Re: Micro Flood Gold
« Reply #5 on: January 02, 2010, 12:34:21 AM »
 I don't know much about miller tables. only what I've read on here. Could you classify down as far as you can, then use a miller table? or maybe leach?

Offline sluicedog

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Re: Micro Flood Gold
« Reply #6 on: January 02, 2010, 12:50:48 AM »
Blister
That is the approach I have taken ...classify as far as you can go ...then go with the Miller Table style recovery.
You can always blue bowl the -30 and -50 and -100 mesh after that I think the Miller has the best chance...just my opinion so far  <-good_>
I am resisting going to chemicals....chemistry was not one of my strong subjects....so rather than burn out a lung or two, I prefer to work with gravity and water.

Fossicker may want to add to this  <-wave->

sluicedog
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Offline GollyMrScience

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Re: Micro Flood Gold
« Reply #7 on: January 02, 2010, 09:31:20 AM »
Hi guys - I have worked quite a bit with the micro gold placers and have a few things I can share.
Firstly the reson that you only see gold in the upper layers is twofold.
The first has to do with scour zone and the second with new gold contributions.
This applies to an enduring sand deposit.
Each year the river is reworking that area but if there is not sufficient energy to flush the entire deposit then the bar will reflect the effect that the energy does have.
This will be in the form of a zone near surface that gets reworked each year. That zone will show certain characterisitcs.
There will be a courser trend to the materials. Even a layer of cobble overlaying fine sand that gets many people scratching their heads.
They can't see how the river could deposit the stones but leave the sand underneath.
In fact what is happening is that the river has enough energy to remove sand from the upper layer but not the courser materials so the lag deposit of cobble builds up and creates a new dynamic on the bar. It forms up an armor layer that further shields the materials under it and prevents the scour from cutting any deeper.
This new layer will further act to retain new micro gold that washes down and across that bar each year. Building up the gold concentration and preventing deposited gold from progressing any deeper because while gold is commonly said to head for bedrock it does not dig its own hole. Gold moves to the lowest area it can within a dilated bed. If the river isn't cutting to bedrock allowing gold moving in sands and gravels to penetrate that far then the gold will be at the bottom of the layer that was moving and that might only be the top two inches of sand on an armour layered bar.

If you were to actually go through the time and energy and money to cut a trench through a bar like this you would find micro gold throughout it but no meaningful concentrations unless in a scour zone. The gold is there but not enough to justify working all that sand.
As for recovery methods you will need to determine the best system by the range of gold you intend to recover. You then have to match that against the volumes of material to move versus the expected return versus the access and ability to mine with certain equipment including permitting and operations.
For a hand miner there is a definite consideration to be made for access.
A hand shovel operation can get into some difficult places pretty easily and since only the upper layers (in the above discussion) are being worked the need to have deep digging capability is eliminated. For bar skimming in fact a hand miner can really come into their own as they can take a very restricted section of best pay and do not need to take massive tonnages of material that bigger equipment would end up taking by default. They will also be able to keep their recovery infrastructure to a minimum as they do not have to upgrade the processing to keep up with the digging equipment or the amounts of lower grade material the bigger equipment grabs.

A well run sluice can recover pretty well down to 100 mesh. After that it becomes harder and harder to work with - demanding more mining infrastructure and more problems with recovery both at the primary stage and from the concentrate.
For sluicing, a fine gold operator needs to think about classifying better than the usual 1/2 inch minus though good recoveries can be made to 100 mesh even at 1/2 inch minus to a good sluice. A two level sluice would be simplest with major effort made to get classified materials to the sluice. A field operation would consider a fine screen trommel of perhaps 20 mesh.
20 mesh plus to the course gold sluice - so in reality that sluice would handle 1/2 minus to 20 mesh plus and then a fine gold sluice using thin laminar flow over low profile riffles or specialty matting.
Unless the operator is willing to do very frequent cleanups black sand could be an issue for the fine gold sluice. Magnetic sep of the black sands before the sluice or a switch to a system that recovers fine gold and is not bothered by black sand would be in order.
That could be a fine gold trommel with the 1/2 inch to plus 20 to a regular sluice and the minus 20 to a small jig. Since the jig can handle discharge of concentrate while running large volumes of black sand are not an issue but accomodation will have to be made when its time to recover the gold from the cons. The jig is also able to get good recovery of gold across a wider range than the sluice so the trommel could be as course as 1/4 inch and the jig would still have good recovery down to 200 mesh gold or finer. If that was the path chosen then the operator would merely run a sluice at the trommel discharge to get tailing away from the end of the trommel and to act as a nugget trap.
I can expand on this stuff later when I have a bit more time if you guys are interested.
What the heck - lets just keep mixin' stuff together till it blows up or smells REALLY bad!

Offline Blister

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Re: Micro Flood Gold
« Reply #8 on: January 02, 2010, 09:43:05 AM »
Definitely interested  <-good_>

Offline sluicedog

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Re: Micro Flood Gold
« Reply #9 on: January 02, 2010, 09:55:13 AM »
Interested...Hell yea ...GMS  <-yahoo_>

I am still trying to get my head around these Jigs you speak of, every picture I see only shows the outside and very rarely the inside  <-thinking->

Are these bad boys (jigs) something a reasonably handy fellow could build themselves ?

Does any one have any drawings or DIY information....the double sluice is a good idea...however if the gold is assumed to be -100 to begin with, would this change the strategy on equipment construction?

sluicedog
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