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ManVSgold
03-17-2013, 06:18 PM
I don't know about you guys but the Overburden im seeing often pays very well.Maybe not bedrock well, but very well none the less. I know the big mines throw out feet and feet of the stuff and I even know dredgers who will remove their sluice box from their dredge,crank the motor up and blow feet and feet of overburden out until they get near the pay layer.Now,in my experience I have found most all my nuggets on, or in the overburden.Some trips didn't yield much as far as fines go but I would always get a nugget or two for my troubles, running the overburden. Of all the nuggets we took last season,more than 3/4 of them came out of the overburden.Many of them within an inch or 2 of the surface. So,my point to writing all this is to ask some questions.

Shouldn't we not be extremely careful with overburden in Glacier deposit areas since the gold distribution can be so sporadic ??

How have you guys done processing your overburden?

What do you guys do with your overburden?

Are you finding your larger nugget in or on bedrock or on overburden?

How has your overburden payed compared to the pay layer/bedrock?

A lot of you know I belong to many many gold forums and some of you belong to those as well.I will be posting this to the other forums too,to try and formulate some kind of conclusion to test this season.Overburden has treated me very well,now let us know how its treated you.

Jeff
03-17-2013, 11:57 PM
When its rich overburden in the top foot or so, its probably from rich bench gravels nearby. Heard the stories, never experienced it myself.

geowizard
03-18-2013, 06:32 AM
Possibly too much TV?

Miners have always tested overburden. If there's pay you mine it. If not, strip it.

- Geowizard

Steve Herschbach
03-18-2013, 06:36 AM
By definition if it has gold in it then it is not overburden. It is paydirt and discarding paydirt as overburden is to be avoided.

I thought you were dredging? When I dredge, everything goes through the sluice box.

dewam
03-18-2013, 08:27 AM
When dredging, I have always found that if you are in gold, you see gold. Everything goes through the box, but when running "overburden", I do tend to hog the tube and occasionally overload the box. If I see gold then I try to run a more even and careful feed.

geowizard
03-18-2013, 09:03 AM
There are many reasons for gold to be in the "overburden". I'm using the term loosely. Placer gold is an erosional product and can erode into the stream from a bank along the stream. The bank may have layers of sedimentation that carry gold and other layers that carry no gold. The deposition of the sedimentary layers vary widely from one watershed to another.

The only rule is to test everything!

- Geowizard

ManVSgold
03-18-2013, 11:25 AM
As far as me,I run everything down to bedrock then I lick the bedrock clean.But, these darned people keep saying Im waisting my time running the upper 4-6 feet of the gravel bar.(The bar im working has 4-6 feet of "overburden".)They told me to pull the sluice box off and crank the motor to 95% and just shoot that crap out in a hurry. These are some old school dredgers too.Probably 25 years on a dredge each man.Anyway,I got lots of nuggets out of it so Im thinking of re-running their 10+ years of "blown out" tailings.They have both always used a 4" so my 6 inch should clean their tailings fast since it will all go through the 6" hose pretty easy.Keep the comments coming.Im getting some very interesting responses.

geowizard
03-18-2013, 12:30 PM
yep, makes you wonder about assumptions people make! I run a six (bought from AMDS). It's a Keene mini-six with two 9 HP Hondas. I put a single piece of all-thread across the suction intake. If it sucked a boulder in, it looked like a snake that ate a big gopher!

IT's fixed.

Sounds like a good dig!

Good Luck! Please keep us posted!

Geowizard

Steve Herschbach
03-18-2013, 01:02 PM
Go figure. I have never thought pulling my box off would get me through the gravel faster and still do not. It is either hog it or not - but why pull the box off?

Old school miners are the reason why new school miners can make a living mining tailings. That gold you are finding near surface may have been put there by one of those guys.

That said, I have been on creeks where the gold is like 95% or more on bedrock. Every situation must be evaluated on its own. There is no hard and fast rule "do this or do that". Except for "process the material that has gold in it and do not waste time (money) precessing material that does not"!

Reno Chris
03-18-2013, 01:09 PM
I don't know about you guys but the Overburden im seeing often pays very well.

Would be happy to show some overburden that does not pay if you wish.

ManVSgold
03-18-2013, 04:19 PM
Thanks Chris, Ill be right over:cool:

Bill Bohan
03-24-2013, 06:06 PM
The more sub angular to angular your gravel is the possibility is that it your overburden is stacked in enrichment zones of overburden like that of an "elluvial" placer. Here in Alaska our gold does not migrate extended distances like down in the lower 48 cause our water shed is frozen perhaps 8 months out of the year
Permo-bedrock is stratified and angular. Many miners call this false bedrock even though its layers connect within proper sequence to the hardened bedrock beneath it. Within "E" luvial placers oxidation of sulfides to sulfates and the rust slime "limonite" will occur at the water table and oxisphere. Free gold and Refractory -encapsulated gold is bound up in these zones but may still maintain position within the permo bedrock until frost wedging releases and exposes the strata to an energy force that will allow migration.... ie. a steam channel. Immature placers are staked with layers of enrichment.
When you hog gravel with your dredge at the bedrock gravel interface you think your pulling all of your gold off of bedrock, but what actually happens is that before the gravel face collapses in front of you the watertable saturates the gravel and upon collapse, the upper tiers of gold dive through the gravel and land onto bedrock perhaps two feet ahead of the collapsing gravel. All you see is a cloud of murk. Gold is coming from the upper layers and enriching the bedrock.
This also happens with blasting of hardrock. The rock in this case lifts from the pit causing what is called swell factor. The blasted rock is fragmented and has air between each fragment of rock. In the course of swelling and excavating blasted rock the gold on a micron scale will shake to the floor bottom (gravity separation) and enrich the lower (foot wall) level within reason of course.

geowizard
03-26-2013, 06:44 AM
Because the possibilities are infinite, the answers are infinite.

There are infinite possible variations of sorting, resorting, erosional events and glacial events that cause the deposition of sediments. That's just in the realm of virgin ground.

Overburden can be manmade. Dredge tailings at Ganes Creek represent manmade overburden. The overburden has produced amazing gold nuggets. How many times have the dredge tailings been pushed, stacked and pushed again? New gold is exposed when the overburden is leveled and contoured for a road or to do reclamation work.

- Geowizard