Thursday, May 12, 2016

"The Heavies Drop Out First" (Part 2)

 (Gold has an interesting affinity for iron.)

I addressed the basic concept of heavies pretty well in my previous post so I won't beat that dead horse any longer. I will answer a reader question or two and either in this post and in the next I'll talk about how heavies actually drop out in a stream flow, including variances on that theme. So stick around and learn something useful instead of listening to that tinny banjo music playing "Oh Susannah!" on Ma and Pa Kettle's "Git Yerself Sum Gold" website. (I know, I know...I'm bad.)

OK, back to reality. My good friend and Idaho mining pard "Muskrat" (Gary Thomas) asked a very good question in his comments on Part 1 of this series of posts. Here's "Muskrat's" query:

J.R., 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, or 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."

Well Gary, you're right on all three counts to some degree or another.

Yes, they are both heavies but gold's specific gravity (i.e., density in water) of 19.32 far outweighs iron's 7.85 by a factor of more than two times. Remember, however, that I consider any mineral, metal, or material with a specific gravity of 4.00 or higher to be a heavy since garnets are at this density and are often recovered with gold and heavy black sands (at least in certain locales).

So to answer the first part of your question, yes, iron and gold tend to collect in the same locations.

Iron and placer gold are often found in close proximity because iron is heavy enough to often be deposited where the placer gold is. Sometimes those rusty (oxidized) iron scraps and old nails can tell you a lot about gold deposition and often they'll start showing up in your test pans or your dredge's or highbanker's sluice box heralding the presence of gold. I've seen this happen countless times in my small-scale mining career, even as recently as last summer here in New Mexico's Tusas Mineralized Zone.

I don't know what causes the clumping together of iron and gold but it does happen.

As far as clumps of oxidized iron fusing together with both silver and gold I've come across this interesting little bit of physics more times than I can count, both in beach treasure hunting (detecting) and in placer gold mining. I don't fully understand the chemical reaction/attraction thing here...perhaps a chemist or geologist could clue me in. All I know is that this fusing together of odd bits of oxidized ferrous metal is not uncommon out in the field. For example in my beach hunting days I frequently found gold jewelry and silver coins fused in with conglomerations of old oxidized iron nails, screws, scrap metal, etc. Although not as frequently, I've found placer gold (including small nuggets) fused together in similar clumps of ferrous metal. That's the long and short of it. Why it happens I can't say...I just know from experience it DOES happen.

 (I've used this pic before, but it really expresses the idea about fused iron clumps.)

Yep..."Gold rides an iron horse."

As Gary rightly points out, "Gold rides an iron horse." Gold and iron (and iron pyrites) tend to have a close connection, often from a geological standpoint as well as a chemical bonding standpoint. Iron-stained ores often contain gold as do pyritic ores. I suspect the main culprit here is some sort of chemical reaction or attraction between the two metals, but that's only supposition on my part since I'm an engineer and not a scientist. It's an intriguing mystery though. Ma Nature does all sorts of strange things when it comes to metals and minerals.

 (Sulfide gold ores like this are iron based.)

The upshot of Gary's perceptive questions is simply this. Don't worry about how gold and iron get together, just understand that they do in frequent (but not all) instances. That's the message to take away here. When you're out and about and rusty bits of iron start showing up in your sluice box, take heed and pay close attention. I also recommend that you take a VERY CLOSE LOOK at any clumps of fused ferrous metal you come across or recover in your small-scale mining and prospecting efforts. Iron won't always herald the presence of gold but it does in more instances than you might currently imagine. So be aware and look past the obvious.

There's more to come on heavies. Stay tuned and keep the faith.

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

Questions? E-mail me at


  1. JR, very interesting, thank you. I guess the next time I find a pile of rusty junk I'll hit it with a hammer a few times and break it up!

  2. Generally not a bad idea Gary!

    1. 1.5, the attraction of gold and iron is there for sure.
      I believe (it isn't 100% just a theory/idea) it may have to do with "heat" Gold does somewhat Stick/Join together when in hot water. I've done my own experiments, get a gold pan, place some fines, add hot/warm water, then watch how the fines almost magically join up/chase each other.
      So with this thought in mind, imagine a piece of metal, conducting/heating up during the day, it possibly is then naturally attracting any gold that runs past it and also it (the metal) will be in a (choice spot/location)like that of natural dropout/eddy/run would help the likelihood of it being able to then have more gold "run past it" This is why I believe iron/metals attract the gold, as such

  3. After reading part 1, I wasn't sure that there was more than the establishment that heavies drop together. But, here the question is more than that. Why is gold sometimes fused with metals that are near it? In my opinion there are different variables at work wherever this occurs. There are many minerals in water and soil (unique to a specific area). And, man-made objects are slewing off minerals as they deteriorate, especially iron objects. If a piece of gold is resting next to some iron, it's unlikely that one would be attracted to the other. But, how else do they become fused together? Let's look at water as a key provider of iron, either from underground sources or surface contamination. The iron particles tend to settle with much larger iron objects due to weight and magnetic properties. When the water is not moving, and more oxygen is present, processes of rust formation are even faster than under water. It's true that rust doesn't rust. But, any iron that attaches to rust will rust. In effect, it grows in thickness. Now, let us consider the microscopic surface of a piece of gold. Under a scope, gold has a surface that is as much air pockets and crevices as it is tiny valleys and mountains. Even, the most highly polished metals have incredible, near molecular, imperfections. When rust is in contact with gold, it doesn't combine with it, in a metallurgic sense. As rust is adding layers, it begins to fill in the tiny pockets in the gold's surface. It locks into it, but remains unmixed at a molecular level. You can experiment with this process using a high quality polished low carbon stainless steel knife blade. If you rub the blade surface (must be free of oils) with steel wool or a piece of soft iron or steel (high carbon), then wipe it with a damp paper towel, and set it aside, wrapped in another clean damp paper towel, where it will remain damp for a time, iron particles, invisible to the eye, will be embedded in the surface of the blade. This iron will rust and the color will be seen. This can be removed with chemicals and/or sandpaper. It's similar to rocks forming into a conglomerate with smaller rocks, sand, and clay, binding them together. But, conglomerates are whole different thing to deal with, unless you like chipping cement.

  4. Interesting theory...could very well be. Thanks for the info.

  5. I'm very impressed with the theories expressed in the comments. You guys are very, very me wondering now.

  6. JR, so if I understand these comments, the iron isn't attracting the gold so much as the rust is forming around the gold. So in the end, it is because being heavy, they both settle in the same place in the stream bed. If you look closely at badly rusted iron,it sort of flakes apart in layers similar to cracks in bedrock. I suppose gold could get stuck in those cracks and as the iron rusts more, be trapped inside.....very interesting stuff of the reasons I like your site. Keeps you thinking. Thanks!

  7. Well, all of this sure has me thinking, that's for sure!

    1. 1.5 Replying to "DaggerDan" comments mainly;
      Whilst reef gold makes it's way to streams/rivers, it will begin the process of having other "elements" or "impurities" leeched from it (dissolved oxygen in the water and organic acids) "any silver is usually beaten to the outer edge of the nugget" We all know silver isn't magnetic (not attracted to iron) But then again, I'm thinking that maybe during the leeching process (where the gold is increasing in purity) that this is the time when iron maybe the first to make it's way to the outer "initially" (iron first then silver) and that's the time of the attraction? (when the ironstone/blacksand type material is first to leave) I haven't said this very well, it's just to chuck the idea out their.

  8. Great comments and these come from Down Under.