Orange, Rusty Cemented Gravels

[mikep691]

Over the years, we've mined the gravels in the creek, on the bedrock at our claim. These gravels can be as shallow as a few inches to a few feet thick. Some areas are cemented to the point of nearly impenitrable and most always rusty and orange in color. This layer is usually 3"-6" thick, sometimes high in the bank of the creek and sometimes right above the bedrock. The area has been extensively worked since the late 1800's, and we believe the 1 to 4 grams of gold per yard that we recover was left over from the old timers.

Since we're moving a lot of gravels, it's hard to tell how much is actually embedded in this cemented gravel. We do know that there is gold scattered throughout the gravels. This why we don't just strip the "overburden" but run everything through the box.

I guess what I'm asking is your opinions on the best way to approach these cemented gravels, and if you've experienced this in your diggings. There is likely no right or wrong approach, Just picking brains...

 

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[arizau]

The color suggests the colored gravel is due to an iron compound so it makes sense to me that gold might settle with it. Where I prospect it does anyway.

Good luck.

 

[mikep691]

The color suggests the colored gravel is due to an iron compound so it makes sense to me that gold might settle with it. Where I prospect it does anyway.

Good luck.

We've always heard it was a good problem to have LOL

 

[russau]

I've seen the same thing here in Misery ! I scooped up a sample and had it sent off to see exactly what it was............It came back as some iron oxide and it probly is leaking from a old metal barrel .

 

[Bodfish Mike]

If you soak the chunks in water for a few hours do they break down ? -- I have done that in a 5 gallon bucket and give it a stir once in awhile.
Lately I just move to easier diggings.
Cheers Mike

 

[mikep691]

If you soak the chunks in water for a few hours do they break down ? -- I have done that in a 5 gallon bucket and give it a stir once in awhile.
Lately I just move to easier diggings.
Cheers Mike

Good thought Mike, only they've been soaking in water for 100 years already. It would definitely be different is I wasn't moving these gravels from a live creek bed.

 

[Tesorodeoro]

I’d say, there is a chance it acted as a false bedrock and trapped gold on the surface of the cemented gravels...that there may be gold in the cemented gravels....and that they may cover actual bedrock that has older gold trapped on it. You are likely looking at significantly different geological ages.

If I had to throw a WAG out there...the cemented gravels probably contain the finer gold but who knows.

How are you currently mining the material? Sluice...trommel...panning?
Are you finding pickers and nuggets? If so, do they make up a large percentage of the gold you are finding weight wise?

Are the gravels made up of hard smooth rocks, or sub-angular softer rocks?

Lastly....I’ve found some great gold nuggets laying on the surface of what looks like rich black topsoil. It’s not all sorted by water flows...it just ends up where it is due to circumstances such as glacial melt and liquefaction.

If it were me, I’d try to separate the different materials...run some trials at each depth.
No sense running full depth if your gold recovery is coming from a 1/2” thick layer. That was the reason for surface mining. You could have rich recovery on the surface and not ever realize you didn’t need to process the remaining depth because even diluted it was still pretty good.

 

[Hard Prospector]

I would recommend running them through a portable cement mixer (if you can get one to the site). Works wonders breaking that nasty, crusty $h*t down and in decent volume. Then sluice or highbank the slurry.

 

[mikep691]

I'm an outlaw these days. We suck them up and spit them out. I can't say just where the gold is, but know it's scattered through 3 feet of gravel on top of the bedrock. Mostly small gold 1-4 grams per yard, but pickers and nuggets up to 1gram. The search is the fun part.

 

[mikep691]

I would recommend running them through a portable cement mixer (if you can get one to the site). Works wonders breaking that nasty, crusty $h*t down and in decent volume. Then sluice or highbank the slurry.

When we get to these cemented gravels, it's under 2-3 feet of water

 

[mikep691]

I’d say, there is a chance it acted as a false bedrock and trapped gold on the surface of the cemented gravels...that there may be gold in the cemented gravels....and that they may cover actual bedrock that has older gold trapped on it. You are likely looking at significantly different geological ages.

If I had to throw a WAG out there...the cemented gravels probably contain the finer gold but who knows.

How are you currently mining the material? Sluice...trommel...panning?
Are you finding pickers and nuggets? If so, do they make up a large percentage of the gold you are finding weight wise?

Are the gravels made up of hard smooth rocks, or sub-angular softer rocks?

Lastly....I’ve found some great gold nuggets laying on the surface of what looks like rich black topsoil. It’s not all sorted by water flows...it just ends up where it is due to circumstances such as glacial melt and liquefaction.

If it were me, I’d try to separate the different materials...run some trials at each depth.
No sense running full depth if your gold recovery is coming from a 1/2” thick layer. That was the reason for surface mining. You could have rich recovery on the surface and not ever realize you didn’t need to process the remaining depth because even diluted it was still pretty good.

Ever heard of the Jura? My spelling may be wrong, but I believe this may be related area. A west to east running year round creek, at 5000 feet elevation.

 

[RTR]

Over the years, we've mined the gravels in the creek, on the bedrock at our claim. These gravels can be as shallow as a few inches to a few feet thick. Some areas are cemented to the point of nearly impenitrable and most always rusty and orange in color. This layer is usually 3"-6" thick, sometimes high in the bank of the creek and sometimes right above the bedrock. The area has been extensively worked since the late 1800's, and we believe the 1 to 4 grams of gold per yard that we recover was left over from the old timers.

Since we're moving a lot of gravels, it's hard to tell how much is actually embedded in this cemented gravel. We do know that there is gold scattered throughout the gravels. This why we don't just strip the "overburden" but run everything through the box.

I guess what I'm asking is your opinions on the best way to approach these cemented gravels, and if you've experienced this in your diggings. There is likely no right or wrong approach, Just picking brains...

Your stuff sounds like this stuff ? After a good washing >>

 

[N-Lionberger]

We have that stuff at our spot, last time it was about 3 to 4 feet under cobble and loose flow material, it has the bigger rougher pieces in it gets better when I go down haven't hit bedrock there yet. Run a 1" pressure line from a Y on your pump to a blaster nozzle, it makes shorter work of nit picking and cleaning the cobbles from the cement.

 

[Tesorodeoro]

When we get to these cemented gravels, it's under 2-3 feet of water

Not much you can do but try to follow bedrock. Gotta move that material somehow. I’d be careful if that rusty layer is loaded with black sands. Maybe do a separate clean out? Have fun!

 

[mikep691]

We have that stuff at our spot, last time it was about 3 to 4 feet under cobble and loose flow material, it has the bigger rougher pieces in it gets better when I go down haven't hit bedrock there yet. Run a 1" pressure line from a Y on your pump to a blaster nozzle, it makes shorter work of nit picking and cleaning the cobbles from the cement.

What do you think of using a dry land nozzle?

 

[IdahoGoldGettR]

I know I’ve posted these pics before but since we are on the topic of “rusty cemented gravels,” I thought I’d share my experience. A few years back, I found a compacted gravel layer that showed rust colored similar to what you have described. The first photo illustrates this rust compacted layer I had encountered. When I say this gravel was compacted, I mean it took a 5 foot pry bar and a lot of work to loosen it up, but loosen it up I did. Just below this rusty layer was an inch or so of a clay/sand mixture then it was roughly 4-6 inches to bedrock. Obviously there was a good amount of gold in the bedrock but there was also gold in the rust area. I had came to this conclusion because I did do some actual test pans of the compacted gravels and found there to be some tarnished gold. These gold pieces did have that “iron/rust” substance on it but did not detract from its value as it was easily removed with a little mixture of a diluted nitric acid solution. Photos 2, 3, and 4 show the actual gold that was recovered that one day when this first picture was taken. A closer look will reveal the iron/rusty type pieces of gold throughout the pan. As I said earlier, this tarnished gold was later cleaned with the diluted nitric acid solution. My advice is to do what I have done and others have suggested and separate these rusty gravels with whatever means possible and find out what values they may contain (if any) and work from there. “One never knows what may lay beyond the next six inches.”

 

[N-Lionberger]

What do you think of using a dry land nozzle?

I have one I made from a regular suction nozzle, it started out as a blaster that ran parallel to the nozzle then it went in the side like on a hydroforce nozzle which worked much better for the dry land dredging ability eg self priming so you can suck up material outside of a pool of water, recover is poor as the sluice is robbed of the water it normally would having in water dredging, also has a tendency to surge. For underwater dredging a seperate blaster hose is really handy.

 

[mikep691]

I have one I made from a regular suction nozzle, it started out as a blaster that ran parallel to the nozzle then it went in the side like on a hydroforce nozzle which worked much better for the dry land dredging ability eg self priming so you can suck up material outside of a pool of water, recover is poor as the sluice is robbed of the water it normally would having in water dredging, also has a tendency to surge. For underwater dredging a seperate blaster hose is really handy.

Since this stuff is under water anyway, I was thinking just using the concentrated jet to break up the cemented, then turn it off to suction it up afterward. That way it won't affect the sluice as much.