South Oregon Black Gold

[49erjohn]

Why is some of the placer gold found in South Oregon black in color? Thanks for your help. JOHN

 

Amazon Forum Fav 👍

A Handbook of Civil War Bullets and Cartridges - Grab it through Amazon!

[IMAUDIGGER]

It’s not just Southern Oregon...Northern California as well.

If I were to throw a wild guess out there, I’d say you are finding it in some virgin ground and some of the softer rocks show signs of having a black stain in them as well when you break them open? Maybe in an area where water has routinely seeped through the material?

 

[IMAUDIGGER]

Example..


I think it's some sort of manganese oxide coating.
Someone suggested to me a couple years ago that it could be from some sort of anaerobic biooxidation process.

Maybe someone with actual knowledge will contribute.
There is evidence of ocean bottom in Southern Oregon and Northern California. That could be part of it?

 

[CoinFetcher]

I have seen 14K gold on a beach have a simialr black coating

 

[IMAUDIGGER]

I have seen 14K gold on a beach have a simialr black coating

I believe that would be from the salt water oxidizing the silver in the 14k gold.
The placer gold in Southern will generally be 95-97 pure. So not much silver content.

 

[IMAUDIGGER]

John, can you verify if my example is representative of what your referring to?

The rocks in the vicinity of where I find black gold look like this..with a similar black color visible..



Is this what your seeing nearby?

 

[galenrog]

Any coating that oxidizes black, or any dark earth tone, is possible. Manganese oxides are common as nugget coatings and are found in SW Oregon. Silver that has leached to the surface of gold nuggets over time can oxidize black before eroding off. This can be found in areas where silver percentage in native gold is relatively high. Copper, also found in native gold nuggets, will act in much the same manner as silver, but will oxidize in green, blue, and red earth tone shades, depending on local conditions.

I am certain there are other completely natural conditions that can cause a dark layer, of varying thickness, on gold nuggets, but my notes are in the attic, I think.

Time for more coffee.

 

[IMAUDIGGER]

The coating on the nuggets I pictured above is easily removed with jewelry grade cleaner and is typically only found on gold that has not moved in god only knows how long.

The coating does not survive a trommel tumble.
I once found a nice little virgin stretch of a gully and the bottom 6” (3.5 feet down) was a very thick black oily goo. All the rocks on the bottom were laying flat. The gold was all coated black in a similar fashion. Nuggets literally laying in every low spot in the bedrock. Matter of fact, the gold on my profile page was laying in one of those gentle little dips in the bedrock.
; )

However till John checks back, we won’t know if this is what he is asking about.