Monday, May 28, 2012

Gold Deposition in Dry Placers (Part 1)

 (Yours truly checking out a potential dry placer location in New Mexico.)

Main Difference Between Wet and Dry Gold Placers

Like myself, many of you living and working in the Western and Southwestern U.S. cut your mining teeth in the numerous dry placer gold areas of Arizona, New Mexico, Nevada, or southeastern California. Although many aspects of sampling and working dry gold placers are similar to those found in wet placer districts, there are distinct differences between the two.

Wolverine Boots
Dickies Work Clothes
 
One of the main differences between wet and dry gold placers is how gold gets deposited in each environment. In wet placers (streams, river, creeks) the physics of gold deposition remain fairly constant due to the steady hydraulic action of running water. In desert or dry placer environments, however, gold deposition is pretty much dependent on periodic or isolated high-water events such as flash flooding or brief downpours that cease nearly as quickly as they begin.

One Tip I Can Give You

From a gold prospecting or mining standpoint, this fact presents unique problems for dry placer miners who can't always rely on the basic deposition theories governing wet placers. One thing I learned in my many years working dry or desert placers is that gold deposition in those dry environments is, for the most part, inconsistent as hell. Yes, in dry placer areas you'll still find gold behind large obstructions, on inside bends, sitting atop or just above bedrock, and so on, but you're just as likely to find it in locations you wouldn't dream of in a wet placer locale.

Mining Equipment
Gold Concentrates
Gold Concentrators

One tip I can give you in this regard is that you really need to think outside the "normal" mining box when working dry placers. For example, in wet placers you can pretty much bet that larger gold (including nuggets) or paystreaks will be found at depth. This can also be true of dry placers, but I can't count the number of instances where I found those same nuggets and paystreaks resting in the top 6-12 inches of a dry wash and once I dug deeper...well...nada, nothing.

"Erratic" is the Key Word

By way of example, I once dug half of a 5-gallon bucket of gravel from behind a large boulder (obstruction) in a New Mexico dry wash in what would not be considered a prime location in a wet placer due to the fact that this spot was in a straight-shot chute, not a prime low-pressure deposition area.Yet, from that single half bucket of gravel I pulled a full 1/4 troy ounce of gold, including two perfectly matched nuggets!

 (Dry placer areas like this can contain nice pockets of gold.)

Now here's the real kicker...all that gold came from the top 6 inches of gravel. Once I began digging deeper (and quite feverishly I might add) behind that boulder, there was no more gold to be found. Not even a speck. This illustration is indicative of just how "erratic" (and that's the key word here) gold deposition can be most in dry placer locations.

There's more to come, so hang tough.

Good luck!

If you liked this post, you may want to read: "The Gold Claimer Brand Gold Trommel/Concentrator (Part 1)"

(c)  Jim Rocha (J.R.)  2012

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

2 comments:

  1. JR, do you ever use topos along with satellite imagery like Google Earth? The past year or so, I've learned a lot about coordinating surface colors, with known washes where I've gotten good color before. If you can remember exact spots where you got color before, and look it up on Google Earth, then look at a place where you haven't EVER gotten color, no matter how much you dug to China, you will see the coloration and 'wear' patterns I am talking about.

    I have found, at least in parts of Arizona and New Mexico, a distinct 'white-gray' color near 'pay zones', as well as 'gray-black staining' in areas that have flooded in recent history that are darker than surrounding 'high ground' (I'm still working on this theory of 'seeing hematite', and what it means in relation to reading the satellite images).

    Take care...

    Mountaindweller

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  2. I use Google Earth quite often Mountain. Another really good source are older geological surveys and bulletins...you'll be surprised at what can be found in those. In mining, anything that works...well, works! Best, J.R.

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