Some Lesser Known Minerals Associated With Gold (Part 1)


There are a ton (figuratively speaking, of course) of minerals and metals associated with both lode and placer gold, most of which most of you are familiar with. But in this post I want to bring your attention to some lesser know minerals that Ma Nature has thrown into the gold mix. You'll undoubtedly learn something new here, so please read on.

The minerals I'm going to list here apply to both lode and placer gold locations. In many instances the lodes containing varying amounts of these minerals can be the source of associated gold placers, or they can be found in placers without immediate (or nearby) lode origins. However you come across these minerals doesn't really matter. What does matter is that they usually are (or can be) "signposts" that can scream "Gold!" Note that I say "can." Just like Ma Nature herself, I make no guarantees here, nor should you automatically assume any rocks you pick up that contain these minerals also contain gold (or silver) with 100% certainty. However, all of these minerals are highly indicative of precious metals mineralization.

1) Krennerite

This is a telluride that can contain silver as well as gold. Tellurides are minerals that are very close to, but different, than more common sulfides or iron oxides. They often form the basis for certain refractory gold ores. Anyway, Krennerite's color ranges from a whitish-gray to a brassy yellowish color not unlike that of some iron pyrites. Krennerite most often displays a crystalline structure and can have a metallic sheen.

(Whitish-grey krennerite.)

(Close up of yellowish krennerite and its crystalline structure.)

2) Weishanite

This mineral is formed of hexonal crystals that form in small irregular grains. Weishanite is typically associated with gold, silver, galena (lead ore), scheelite, and pyrite. Its color can range from a pale yellow to the oranges and reddish-oranges often seen in iron sulfide ores.


(Close up of weishanite.)
3)  Sylvanite

This mineral is very close to another we'll talk about, calaverite. Essentially sylvanite forms with both gold and silver as part of its structure. The fact that sylvanite typically contains more silver than gold is what sets it apart from calaverite. Aside from its mineral classification, sylvanite is considered a primary gold ore, so it is more commonly known than some of the minerals presented in this post. Its metallic-looking crystal structure can vary, but if you look closely at the photograph below, you can get a pretty good idea of how its crystals form and the metallic sheen they take. Sylvanite is usually steel-grey to silver-white in color, but sometimes shows itself as creamy white or even a light brown.

(Sylvanite. )

4)  Petzite

Another telluride mineral that's most often associated with hydrothermal precious metal deposits and that contains both gold and silver, and can also be part of copper and mercury (cinnabar) mineralization. Its crystals are cubic and can run in size from very large to small granules. A couple of notable regions where petzite has been found in abundance is Australia and in the California Motherlode Region. It tends to be a bright, steel grey color but can also have the look of black cast iron.

 (A nice specimen of gold with a layer of petzite crystals at the bottom.)

5) Nagyagite

This is a very rare sulfide mineral that is almost always associated with gold ores. It's composed of thin, tabular crystals that sometimes have lines or "striations" in or on them. Nagyagite displays a metallic luster that's usually blackish or lead-grey in color. This mineral has been found in many locations throughout the world, including North Carolina, California, Montana, and Colorado in the United States. It's also been found in Europe, Asia, and in the Kalgoorlie and Golden Mile districts of Australia. Along with gold, it can also contain lead, silver, and copper.

(Close up of nagyagite crystals.)

6) Calaverite 

This mineral is very well-known and was named after where it was first found in Calaveras County  during the California Gold Rush. Historically speaking, it's always been known as a mineral associated with rich gold ores. Again, it's second cousin is sylvanite and sometimes they go hand in hand in certain locations or regions. Calaverite's main constituents are gold and tellurium and it's usually found in host veins created from low-to-mid-to-high temperature mineralized deposits. This mineral is composed of uniformed-shaped crystals that can be in very large masses at times (like those found at Carson Hill in California) but are very brittle. Typical colors for calaverite are yellow or yellowish-white.

(Calaverite in quartz.)

(Calaverite gold ore from the Golden Mile District of Australia.)

8) Auricupride

This mineral is a natural combination of copper and gold. Its crystalline structure is cubic and it is usually malleable (i.e., you can bend, stretch, or work it). Auricupride often forms in grains, granules, elongated "streaks," or even larger plate-like masses that can be yellowish in color or, more frequently, that have a rosy or reddish tint to them. This rose or pinkish-orange color comes from the melding of copper and gold together, by the way. 

(Auricupride "streaks" in host rock.)

(A large plate-like mass of auricupride.)

Their Thing and Our Thing

As with all things in Ma Nature's world, there are no clearly defined rules. This is true with the minerals already mentioned here and with those to come in my next post. There are always variables, cross-overs, mixtures and meldings, and just plain weird-ass stuff. That's what makes gold mineralization so interesting to me. Sure, gold is gold, but the variety of ways and means that it's delivered to us is just plain remarkable in my book. And your task as gold prospectors and miners (no matter how experienced or inexperienced you may be at present) is to continually add to your breadth of knowledge. No, you don't need to memorize all the scientific names or structures or other inconsequential crap that academics rely on. They have their thing and we have ours. But my hope is that by presenting these sorts of things to you, I may be able to open your eyes up a bit out in the field.

Lastly...please, please, please don't send me any rock images to identify. I'm a small-scale gold miner with a smattering of geological knowledge under my belt. I'm NOT a geologist by any stretch. The reason I say this is the very minute I removed my note in the sidebar about not accepting e-mails with rock images attached for identification, guess what happened? Yep, I got an e-mail asking me to ID rocks and/or whether they contained gold. Geeze Louise! I want to be as helpful as I can be but that's a dead issue for me these days, OK?

Thanks!

(c) Jim Rocha 2019

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

Comments

  1. I've never heard of any of these. Those with the visible gold showing would sure be a thrill to find!!!

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  2. I would really appreciate you guys publishing something of what raw gold looks like meaning is there ever a Time that the gold is covered with something and you have to remove whatever build up to be able to see that it's even gold? Or the yellow will always be visible when it comes to Gold finding? Say for instance rubies or emeralds you usually have to take off the layer of black to notice that it is a ruby. Is there any examples of what gold would look like before it is that golden color?

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    Replies
    1. Who are the "guys?" It's just me writing and publishing this blog. There are a couple of instances I can think of that fall into your query. Amalgam (placer gold covered with mercury) and instances where desert "varnish" or caliche have partially or fully coated gold. But perhaps a post is in order for this topic. Methinks you haven't seen much gold in its natural state otherwise this wouldn't be an issue for discussion. But I will do what I can to target this issue in a post.

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