Would you dig here? Ancient river

[Crashcrew]

While out hiking and looking for bedrock I think I stumbled upon something special. I used a pick and tried to chip away at the cemented gravels with no luck...it's like concrete. Then I brought a hammer drill out and chipped away several pieces to bring home. I should get my rock crusher next week and then I should know for sure if there is gold. I'm in SW Colorado somewhere in the La Plata mountains in a known gold area. Its basically two huge sheets of bedrock and in between is about a foot of tertiary gravels (ancient river bed). There is also signs that it was mined back about 8 ft but it was in the late 1800's. I only say that because there is remnants of an old cabin. Also this outcropping of bedrock is about 30 ft higher than the river and about 100 ft away. Please comment and help me out before I go crazy working to get this stuff out thinking I found one of the lost mines

 

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[ecmjamsit]

Metal detect the area and see if there are clues to the mining activity. Look for pieces of high grade ore. Crush the ore with a hammer and pan it. Get a 100X microscope(Radio Shack) and see if you can see free gold in the ore.

 

[rodoconnor]

Never know till you sample. Is Radio Shack still around ?

 

[N-Lionberger]

I know of a place with material that looks like that and is as described like cement. Detecting has been difficult as its almost all iron lol, my particular spot has some color.

 

[Hoser John]

Are you finding any gold as not mentioned ? And Radio shacks just closed yet another 120+ stores...their net presence is now their mainstay as brick and mortar stores going away for them and many others. Bummer as it left only 1 place in town here to buy electronics and they jacked up prices as soon as RS closed. John

 

[dave wiseman]

Is it an old tertiary gold bearing channel or glacial moraine?

 

[Crashcrew]

So no rock crusher yet...it's coming next week.

I do believe it is tertiary gravels since all of the chunks I got off are filled with small perfectly rounded stones.

I know it was mined back until they hit solid bedrock. I can only imagine there is gold because for someone to spend that much time back in the day breaking that stuff. I have a hard time now with modern tools. So I DO think there is gold.

 

[triple d]

The green vein on lower right. I crush a material very much like it and fine gold in it. Not a lot but never the less gold. It has a lot of mica in it and some quarts. Very crumbly.

 

[93Vertang]

Make sure there isn't a claim your working. If your not the owner it could get hot if you don't have permission. Check with the county records.


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[Clay Diggins]

I would sample but I doubt it is worth digging.

In the La Plata district I would look more towards recent stream bed deposits for placer gold. The La Plata gold deposits are igneous in origin and were intruded during the Tertiary period. The placers are rather poor producers with most of the gold being still contained in the primary intrusion margins and a few small hydrothermal deposits (hardrock lode mines). It's extremely unlikely the cemented river gravels you show were deposited during the tertiary period. But they could be from a much earlier sedimentary period or an earlier or later glacial period. The odds of finding mineable gold in these type deposits in that area is pretty slim.

Pretty much all of the placer gold found in the La Plata district is much more recent than the Tertiary intrusions that created the in situ hard rock gold deposits that the district is known for. The placer deposits are all Quaternary period and came well after the Tertiary movements that created the dome and hinge features of that area as well as the gold deposits.

I suggest you study the Geological Survey Professional Paper 219 (PDF) Geology and Ore Deposits of the La Plata District Colorado. It has some nice maps of the known placer areas as well as some more detail on the gold deposit mechanisms.

A few quotes from that paper:

Although the first gold discovered in the district was in the form of placer deposits along the La Plata River, placers have never played an important part in the district's mining history, and the total production from them is negligible.

The placer gold in and near the La Plata Mountains is obviously derived from the eroded parts of the local ore deposits and has been concentrated by Quaternary streams draining the mineralized area. As it seems highly probably that much gold was present in the parts of the ore deposit that have been removed by erosion since Tertiary time, it is fair to ask why the resulting placer deposits are so few and in general so low in grade.

Much has been written of the Tertiary river deposits in some areas of California. The fact that California has some Tertiary gravels that have mineable gold has little to do with the young intrusive igneous deposits of the Colorado Rockies. The Orogenic deposits of the west coast have only a marginal relationship with the origins of the gold found in the La Plata district. Apples and Oranges.

I hope that helps?

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