A List of Rock Types and the Gold They Contain (Part 4...Quartz)
In this post I'll start wrapping up this series by devoting this post to quartz as well as the next...and final post. There's a lot of confusion about quartz out there as it concerns gold. I hope to clarify this confusion somewhat and perhaps put an end to the erroneous assumption that "generic" quartz is always a gold carrier. In point of fact...it's not. But first let me get something else out of the way.
My Clearest Intention
In my previous post I went off on one of my occasional rants. Sometimes my getting on the soapbox is a good thing and sometimes I get a little carried away. Either way my clearest intention is to give you the truth as I see it...no holds barred. As you know, I'm not one to mince words, take the "blow smoke up your ass" approach, or play the fool. It is true, however, that one can always take a more diplomatic approach to getting a message across. My rant in the previous post wasn't diplomatic at all. I was expressing a certain amount of frustration with a certain type of question that I feel I've already answered numerous times in the past. But my intent was not to scare folks off from asking questions if I can answer them. If I can't answer your questions, I'll try and send you to an information source that can. I guess the bottom line is that there are no "dumb" questions. So feel free to ask your questions but remember that your "Do my rocks contain gold?" queries are like sand in the wind. How can I answer those sorts of queries from digital photos alone? If I don't see visible, free-milling gold in your pics then I'm basically stuck just like you are. In that eventuality your best bet (as I've pointed out numerous times) is to get a chemical or fire assay done or crush those rock samples into a fine powder and pan them out or run them through a fine gold recovery system. OK, on to quartz.
(Sometimes I get onto my soapbox.)
In Other Words
The very first thing to understand about quartz is that it is NOT a rock, but a mineral. I mentioned this previously but it's worth touching on again. This may be a minor point in the grander scheme of things but quartz is not a host rock for gold...it's a "host" mineral. In other words if granite is the host rock and that granite is riddled with quartz veins or stringers, then any appreciable amounts of natural gold will be found in the quartz (a mineral), not the granite. Again, of and by itself quartz contains on average 12-100 parts-per-billion (ppb) of gold. That's not much, needless to say. Another thing to understand about quartz is that it is the second-most prolific mineral found throughout the world and is only surpassed by feldspar in its availability. In other words, quartz can be found just about anywhere, even in places like the state of Nebraska where there isn't any gold (or historical record of gold production). You could shovel ton after ton of fine gravel from the Platte River in Nebraska and never recover so much as a flyspeck of placer gold. But you will recover quartz pebbles. Getting the idea here?
(Quartz veins and stingers in host rock.)
Here's Where the Confusion Starts
Quartz is composed of silicon and oxygen atoms and its chemical formula is SiO4. It displays a range of colors in its generic state...from clear to milky white, to rose and smoky gray, to...well, you name it. Quartz crystals of certain orders can become gem minerals like amethyst, citrine, and various forms of beryl. In times past quartz was called "rock crystal," a designation that's only half correct as you now know. Quartz (quartz crystal) is a common structural component of many types of rock, including some of those we've already covered in this series of posts. The connection between quartz and gold occurs because it too tends to form as a chemical solution in super-heated hydrothermal veins before solidifying under extreme heat and pressure. But here is where the confusion and erroneous assumptions begin. Just because quartz is formed under similar geological conditions as gold DOES NOT mean that all quartz will emerge as a gold "host" material. In fact just the opposite is true. Most quartz (whatever color or consistency) will not contain any gold other than the ppb numbers I've already stated. Again, MOST quartz will NOT carry gold as a host. I can't stress this point enough, especially to those inexperienced folks out there who consistently think that quartz equals gold. This is simply not true.
(Smoky quartz...pretty to look at but not a gold host.)
The key to quartz as a host material for gold, copper, silver, iron, or other metals (and minerals) is mineralization. When quartz is formed in veins where high levels of metallic chemical solutions are also being produced then it's a pretty good bet that some of that quartz will itself be "mineralized" and end up solidifying with particles of gold, silver, copper, iron, etc. attached to it or within it. The quartz then becomes a "host" for those metals (or other minerals) and can display the visible characteristics of precious metal mineralization such as colorization (mixtures of red, crimson, brown, reddish-orange, green, bluish-green, blue, bluish-grey, yellow, yellow-orange, orange, and so on). These visible clues are the result of that quartz being exposed to or created with metals like iron, silver, copper, lead, and so on. Just as iron scrap will oxidize into a rusty reddish-orange, when iron in quartz oxidizes it will color that quartz to greater or lesser degrees. Copper oxidizes a bluish-green or green color and this will be manifested on the surface (or interior) of quartz that has been exposed to or experienced copper oxidation. Silver will oxidize a blackish or bluish-grey color and any quartz carrying silver or having been exposed to silver sulfides will display these colors as well. And so on. But here's the kicker and it's a point that only experienced miners and prospectors understand. Just because quartz is displaying the visible characteristics of metal (or mineral) mineralization doesn't mean that quartz is carrying gold. It's simply a signpost or visual clue that some sort of mineralization has happened with that quartz and the possibility of gold being present is worth further study or examination. And the context or location of where that mineralized quartz is found also tells the tale. If you find an iron-stained chunk of quartz in a state, province, or location where NO gold has been found before or there are NO historical records of gold being produced there well...chances are you're shit out of luck from a gold standpoint. In other words, if I find an interesting (mineralized) piece of quartz in the California Motherlode Region it may have significance. On the other hand, if I find a similar chunk of quartz in Kansas then my hopes of striking it rich have just been shattered. This is the clearest way I can get my point across to those of you out there with minimal gold mining or prospecting experience.
(Free-milling gold in mineralized quartz.)
We'll tie this all up in my final post on this topic.
Best to all.
(c) Jim Rocha 2018
Questions? E-mail me at firstname.lastname@example.org