Sunday, October 20, 2013

More on Eolian and "Reverse Eolian" Dry Placers


 ("Toe-may-toes" or "toe-mah-toes?"

Jack, a Bedrock Dreams reader and supporter sent this comment in on my last post about eolian placers: "I read your posts with enthusiasm regularly. However, I don't agree with you on this. An eolian placer forms when the lighter material blows off of the gold, leaving the gold concentrated in place. Anyway, keep up the posts and the attitude. We need more of you in our world right now." I replied to Jack on this point agreeing to disagree, so let's pursue this topic on eolians a bit further.

First off, I want to thank Jack for expressing his opinion on this subject whether it coincides with mine or not. I also want to thank him for his kind words and ongoing support. Next, I urge all of you to follow Jack's lead here if you find I'm in direct error or have an alternate viewpoint on any aspect of gold prospecting or mining. I'm not here to try and lord it over anyone or imply I always know more than you do...I've learned a lot about small-scale gold mining and prospecting over the course of three and a half decades but I surely don't know it all (and you can take that last to the bank). OK, that out of the way, let's proceed.

"Goodies" Would Start Appearing

Years ago I spent my gold mining off time recovering "gold" (jewelry and coins) from the beaches of Southern California during the winter months when the big Pacific storms would roll in. There were many occasions during those events when I witnessed what Jack is talking about some distance up and away from the surf line where dry beach sands were being blown off by the high winds accompanying the storms. Note that I'm talking here about those instances where no accompanying rain was falling as well.

During these high wind events you could actually stand there and watch shallowly buried coins (and the occasional piece of jewelry) being uncovered by the force of those winds. As the winds lifted and blew the lighter materials and dross off to race away further inland, the "goodies" would start appearing and all I had to do was reach down with a sand scoop, pluck them up, and then deposit them into my recovery bag. For those of you who've never witnessed anything like this it's an amazing sight to behold and gratifying in more ways than one, to say the least. Now switch the concept of this event to shallow particles of gold or very thin flakes. Would those remain in place or would some be carried away?

"Reverse Eolians"

When this concept is applied to what Jack's talking about you can easily see his point about eolian placers. Gold that's eroding out from a vein, outcrop, or ledge that's uncovered by strong winds or high-wind events is suddenly exposed to the naked eye. However, rightly or wrongly this is where I begin to diverge in terms of what I think a standard eolian is. Jack's view is that the concentrated gold remains in place but is uncovered and my view is that the lighter particles (fines, flat flakes, etc.) that are uncovered become wind borne and are carried away to form small deposits elsewhere. I even cooked up my own terminology to describe Jack's version of eolians, the "reverse eolian." Believe it or not (and I'm not trying to BS anyone here) "reverse eolians" was to be the very next topic in my series on dry washers, desert gold, and working dry ground.

(Is it reasonable to believe that very small and light "flour" gold like this could be carried away by strong winds and deposited elsewhere in a dry placer environment?)

When you examine the existing mining literature you'll find both Jack's and my view in the definition for eolian placers. A good deal of that mining literature talks about eolian deposits...in my feeble mind deposit means that something is being deposited or carried into place, not remaining in place. If we use the example of the extensive eolians at Timan Ridge in Russia, it's my understanding from the scientific paper I read on the subject that those placers were formed from wind-blown particles and flakes during ancient geologic epochs (Protozoic and Cenozoic). Once again, I've also read brief definitions of eolians that follow more closely to Jack's idea of what an eolian truly is. So is it "toe-may-toes" or "toe-mah-toes? Eolian or "reverse eolian?"

I'll have to let the geologists and earth scientists out there answer that one (and feel free if you're one of those). In the mean time, there's always room for error on my part. If I am erroneous here then you can rest assured I'll come back to you all with hat in hand and apologize for getting things wrong and passing along bum info (something I wouldn't be very proud of).

Whatever the case, I want to thank Jack again for speaking up on this topic and providing an alternate viewpoint.

Best to all of you!

(c) Jim Rocha (J.R.) 2013

Questions? E-mail me at jr872vt90@yahoo.com

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6 comments:

  1. Jim, I'd say you are both right.....but that is from the peanut gallery and a guy that really doesn't know what he's talking about! Thanks to you I'm slowly learning though!

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  2. I think you YOU may be right Gary! Either way, it's all good. Best, J.R.

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  3. Great rebuttal JR. I just wish I had more time to spend out looking for either of these. Keep up the posts as I look forward to them always. Thanks for all the effort.

    Jack M.

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    1. Well you stood tall and gave your view...as you rightly should always. Honestly, I think we're both right on this one! Best, J.R.

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  4. J.R.,
    The reverse Eolian is an interesting concept to me because I think I have an example of the effect. It also occurs to me that mine may be a cautionary tale about effective sampling and record keeping. I have been poking around in the mountains here in NM, and I've had some luck finding really small gold in one area. I was taking small samples (5 gallon buckets and less) from various locations and getting mixed results. One day I got lazy, Instead of digging a nice sample hole I just shoveled up the loose gravel from the surface of an interesting location. When I panned it later I was shocked, it was the richest of all my samples by at least 5 times. I didn't even think about how that sample was collected. I went back to the spot and got 5 buckets full. Certain that I would recover a nice little pinch from all that ore, I panned away the night. I was very disappointed in the amount I recovered. 5 buckets from that "rich location" only produced about twice as much gold as I had from the single sample bucket. Undaunted I kept sampling, eventually I did it again, I sampled just the surface. Lo and behold it was another "rich spot"! And the result was the same again, low yield from a larger sample. Thats when I sat back and thought it through, the years of wind and rain have washed away the lighter materials on the surface, concentrating the gold in the top 1-2 inches, i.e. reverse Eolian placer "deposit". I have since confirmed the "surface concentration" effect many times over. Now I have a name for it. Oh, and the cautionary part; don’t just make note of where you collect a sample, but also how you collect it. Data, Data, Data. In God we trust, all others bring data. Every little bit helps…….

    -Bo

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  5. Great commentary Bo. I had a similar experience early on in my mining career and it taught me the same lesson. Make sure you know where you get what you get! If you have to, record info in a notebook. Want to share that spot with me? (Just teasing ya..!) Thanks for commenting, J.R.

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