Bottom wash?

[bundyjd]

Can anyone explain what "bottom wash" means in this context?

The alluvial gold was restricted to the bottom wash as no colours were obtained from gravel exposures tested or from the creek bed itself. The wash was worked from shafts up to 10m deep and some dredging and sluicing has taken place.

 

[Bazz]

Thanks

Great question, I look forward to an informed reply.

Cheers

Bazz

 

[user 1769]

In my opinion, it means that the modern course of the creek flows over deep alluvial ground, and the modern alluvial is barren. The bottom, which would sit on bedrock or clay, might be of tertiary age or older, and contained all the gold. You'd have to clear all the barren overburden (up to 10 meters?) before you'd get to gold-bearing wash.

 

[GaryO]

Lol start digging

 

[bundyjd]

Lol start digging

 

[RotGrub]

In my opinion, it means that the modern course of the creek flows over deep alluvial ground, and the modern alluvial is barren. The bottom, which would sit on bedrock or clay, might be of tertiary age or older, and contained all the gold. You'd have to clear all the barren overburden (up to 10 meters?) before you'd get to gold-bearing wash.

I'm in agreement with mfdes... its a bit beyond my pick and shovel.

 

[AtomRat]

Bottom wash to me is the last 6 inches of ancient alluvial layer before it hits the bedrock, pipeclay or floor etc. A lot of over-burden to remove if you want to get to it. I dig shallow tunnels into the hill no more than a meter in, sometimes using wooden supports ( not recommended for non-experienced or those who value life ) to hold up the overburden.

It usually contains your gold, pyrites, dark coloring such as black, brown, olive green or blue sometimes. Depending on the alluvial area, you can find sapphire, garnet and other heavies in the "bottom wash".

 

[dwt]

Can anyone explain what "bottom wash" means in this context?

The alluvial gold was restricted to the bottom wash as no colours were obtained from gravel exposures tested or from the creek bed itself. The wash was worked from shafts up to 10m deep and some dredging and sluicing has taken place.

Bottom wash could be as shallow as 1 foot, or as as deep as 900 plus feet, it all depends on the ground, in one instance, early prospectors were shaft sinking on a river bank here in the GT, they were all bottoming out on basalt at about 20 feet, not before digging through 5 feet of sandstone bedrock.
So they had a layer of top soil on top of 'sandstone bedrock' which was on top of a layer of gravels which was gold bearing, when they dug out the gravels and hit basalt they thought they had 'bottomed out' or dug out the bottom wash, one mining party pushed through the basalt 6 feet to hit another gravel wash line, it yielded gold nuggets up to 6 pound,
The 'Welcome Nugget' found down some 900 plus feet in Ballarat come from and ancient old river bed, was that 'bottom wash'?
Probarbly more questions than answers here, but keep in mind what you see the ground do on the surface, it's more than likely mirror imaged underneath and then some.
Bottom wash in one area could be 30 feet down and 20 feet away it could be 5 feet down, and this does not include 'false bottoms' created by basalt or sandstone layers that have formed over the top of older wash lines