A List of Rock Types and the Gold They Contain (Conclusion: Quartz)
In this post I'll be wrapping things up for this series so we can move onward and upward. Hopefully, you've gained some newfound knowledge in these posts. I hope this is especially true for you less experienced small-scale gold miners and prospectors.
Here's the Fallacy
As we've already established, quartz is the second-most prevalent mineral on earth. Again, quartz is a mineral...not a rock. But it holds our interest because of its known frequency as a host for natural gold. Some of the richest gold lodes ever discovered here in the United States and elsewhere were (and are) based on quartz host veins. But here is where the fallacy arises that all quartz veins contain gold and that all quartz is suspect as a gold carrier. Yes, even the most common quartz decorative gravels contain gold...but only in the parts-per-billion (ppb) range. In a gold context, you might as well shovel horseshit. Quartz can only become a host or carrier of significant amounts of natural gold when it is formed with or near mineralized solutions that are intruded (pulled inward) or extruded (pushed outward) under certain large-scale geologic conditions whose two main components are extreme heat and pressure. Just how much gold will be hosted in quartz is based on the "richness" of these solutions and their predominance over other metals such as iron, copper, silver, and so on.
(You might as well shovel horse manure instead.)
You Guessed It
To my knowledge (intellectual and experiential) gold ores are NEVER composed solely of gold. They will also contain smaller amounts of copper, silver, or iron as well as certain minerals. Even those placer nuggets, flakes, or fines you pan out or find with your gold detector are not pure gold (i.e., 24 karat or .999 fine out of a thousand parts). Depending on where you recovered your gold it can range in purity from the low .600s to mid-.700s on upwards to the low .900s. Not far from where I live (in fact...14 miles) is an old gold lode and placer area where the gold recovered runs consistently about .917 fine. It is the prettiest yellow you'll ever see anywhere. So if placer and vein gold is never pure what are its other constituents? You guessed it. Silver, copper, iron, and so on. The purity of the gold in quartz is, once again, based on where and how it was formed millenia ago. That gold area not far from my home (and that I can see anytime I walk out the front door)? It's around 22 million years old and is part of an ancient volcanic batholith whose highly mineralized pyritic rock structure (and the quartz within that structure) metamorphosed (underwent chemical and structural alteration) over time.
(Gold in a chunk of iron-stained quartz.)
Quartz, Rocks, and Gold
So most quartz acting as a significant gold host will be mineralized. That means it has spawned or been mixed with the mineralized solution(s) that created the gold it contains under extreme heat and pressure. Again, there are many visual clues to the possible presence of gold in quartz. Heavy iron staining, rainbow coloration, the presence of iron pyrites, and so on. But these visual clues alone DO NOT MEAN THAT YOUR CHUNK OF QUARTZ CONTAINS GOLD. Unless visible gold particles, crystals (yes, there is crystalline gold), or even larger pieces of gold can be readily seen with the naked eye, or with a jeweler's loupe or magnifying glass, then chances are that your quartz chunk is barren...no matter how "mineralized" it may look. In these cases, only fire or chemical assays or crushing and panning samples will tell the true tale. Ditto for any mineralized rocks you pick up in the field. Because quartz is NOT the only host for gold or a carrier of gold. This is an important point than some of you have failed to grasp (based on your e-mail queries, that is). To confuse things even more, some gold ores are "refractory"...meaning they are extremely diffucult to process or because any gold they contain is still in a chemical state. A dump truck could unload a ton of money in refractory ores in your driveway and you wouldn't even know what all that rock was. Or its economic value. I'm generalizing here about your basic knowledge in this regard, but even with 40 years of prospecting I'd have a hard time recognizing all that money in my driveway. Perhaps you see now that gold genesis, its relationship to hosts such as quartz and other rocks, mineralization, and gold geology in general is a highly complex subject that you could spend your entire life studying. And that's no BS. The field variables are just plain crazy when it comes to quartz, rocks, and gold.
(Refractory gold ore.)
Sugar and Bull
Now I'll throw another monkey wrench into the works. Some quartz veins containing natural gold are as white as snow and display absolutely no visual clues like those I've mentioned previously. In other words the geological forces and mineralization that took place to form that gold in that pure white quartz were somehow different than the "normal" mineralization processes that leave visual clues like iron staining. I know...what the hell? But Ma Nature doesn't play by our rules, she plays by her own. I would postulate that quartz devoid of visual mineralization signs (oxidation or sulfidation by other metals) was created in an extreme gold-rich environment where "contaminants" like iron, silver, or copper did not abound. But I'm not a geologist and could be dead wrong with this assumption. The old timers called this type of gold-bearing quartz "sugar quartz" because it had often had the look of powdered or confectioner's sugar. Now here's another old-timer moniker. Barren (even if mineralized) or just plain everyday quartz was known as "bull quartz." It's this sort of "bull" that the uninitiated and less experienced often think is their ticket to wealth and is expressed in queries like, "Is there gold in my rocks?"
Why Not Educate Yourself?
Maybe now you can see what a complex topic all this is. What rocks contain gold? What rocks carry gold? Is quartz always a gold carrier? And on and on ad infinitum. If you really want to get solid answers to these questions start studying, researching, and spending some long hours out in the field prospecting. It'll take some time but you'll learn what's what. After all, no one (including myself) has all the answers. With a complex topic such as this it's almost mandatory that YOU educate yourself. Ma Nature will guide you as long as you're willing and open to the possibilities.
(Let Ma Nature guide you.)
Why not take advantage of her classroom?
(c) Jim Rocha 2018
Questions? E-mail me at firstname.lastname@example.org