Sunday, May 8, 2016

"The Heavies Drop Out First" (Part 1)

(Lead fishing weights are one type of "heavy" found in streams.)

We're all familiar with common sayings based on gold mining like "It was just a flash in the pan," "Things didn't pan out," or "Gold is where you find it." In this post I'll be talking about another common saying and it's influence on (and importance to) your small-scale gold mining efforts.

Although not as common among the unwashed masses as it is with small-scale gold miners, the phrase, "The heavies drop out first" has been around for quite a while. It's one of the simplest and most descriptive sayings dealing with placer gold deposition as well as being one of the most important. So you newbies out there open your eyes and ears up, OK?

(Oxidized iron or fused clumps of iron are often indicators of the presence of gold.)

The "Pecking Order"

What are heavies? For our purposes they are gold, ferrous metals (iron), lead, black sands, and any other mineral or metal whose specific gravity is heavy enough to cause that mineral or metal to drop downward quickly once it enters water. That entrance could be via erosion, flooding or flash flooding, gravity, or just about any other force of motion you can think of. Once in a flowing stream or flooding wash, these heavies will be the first to drop out of that flow or to be caught up by obstructions, low-pressure areas, and ultimately...bedrock. Everything else...wood, blonde or "blow" sands, smaller rocks and gravels, minerals like mica flakes or pyrite crystals, thin flat flakes of placer gold, or fine or "flour" gold will be carried along until they too find a resting place in that stream or wash. However, it's important that you understand the "pecking order" of this sort of fall out pattern. The best way of illustrating that premise is via the known specific gravity (i.e., density) of those individual stream or wash materials:

Metal, Mineral, or Material                          Approximate Specific Gravity

Gold ....................................................................................19.32
Silver ...................................................................................10.49    
Lead .....................................................................................11.34
Iron.........................................................................................7.85
Aluminum (melted) ...............................................................2.56
Copper ...................................................................................8.93
Platinum ...............................................................................21.40
Brass ......................................................................................8.40
Pyrites ....................................................................................5.10
Mica .......................................................................................2.90
Mercury ...............................................................................13.59
Quartz ....................................................................................2.70
Garnet ....................................................................................4.00
Magnetite ...............................................................................5.20
Hematite .................................................................................5.30
Ilmenite ..................................................................................4.72
Monozite ................................................................................4.90
Granite ....................................................................................2.65
Gneiss .....................................................................................2.80
Wood ......................................................................................1.00
Dirt/Sand.................................................................................1.85-2.00

OK, that should help things a bit since these are common metals, minerals, materials, and rocks found in gold-bearing streams and washes.

 (Garnets are often associated with placer gold.)

Signposts

Which ones are the heavies? I'd say anything with a specific gravity of 4.00 and up. Why? Because I've found garnets mixed into my black sands in various mining locations in California and here in New Mexico as well. Platinum and gold win the specific gravity or density contest since they're both 20 times heavier than water (or nearly so in gold's case). Close behind them are mercury, lead, and silver followed in order by copper, brass, and iron. These are all considered the heaviest of "heavies." With the exception of platinum, at one time or another in my small-scale mining career I've found one or more of these heavies in my gold pan, sluice box, dry washer, or suction dredge sluice. Any time you find one or more of these heavies in your recovery process that's not gold, it may provide a signpost to gold, especially things like lead, mercury, iron or fused iron clumps, garnet, and of course...heavy  black sands.

 (Heavy black sands in a sluice box.)

Still Confused?

OK, so perhaps now some of you have a little light bulb turning on in your heads concerning the phrase, "The heavies drop out first." If you're a greenhorn to small-scale gold mining and still a bit confused by all this specific gravity stuff, it simply relates to the density or "heaviness" of certain stream or wash-borne materials in water. It doesn't matter if that water flow is constant or intermittent. These heavier minerals and metals will be the first to drop down and settle in that stream or wash. We'll talk more about this concept in the second part of this series.

Until then, keep the faith.

(c) Jim Rocha (J.R.) 2016

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

4 comments:

  1. JR, I'm a little confused.....I have heard several times now what you say here "Oxidized iron or fused clumps of iron can be an indicator of gold." Is it because they tend tend to collect in the same places being heavy, is it likely to form together, or something more? I know heavy mineralization of iron is a good sign, and I have heard the saying "Gold rides an iron horse".
    Also, I have found several clumps of mercury coated gold in this area. I read about, and tried the potato method. (cut a potato in half, cover the gold with it, and heat it to burn off the mercury....get rid of the potato!) Is there a better way? I always make sure to stand up-wind! Gary

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  2. I'll answer your question in the next post Gary.

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  3. I've come across mercury-coated alluvial gold down here in Tasmania fairly often, and over time it seems to sublimate off. I had a couple of vials of fines with a high proportion of hg-coated gold that is now all yellow, after a couple of years.

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  4. Recovered placer gold coated with mercury many times in N. Calif. when I was dredging. I'd d burn it off with nitric. Thanks for commenting and best to you.

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