The Basics of Gold Mineralization
(Howdy do comrade?)
Before I get into the heart of the matter about gold mineralization let me toot my own horn a bit. I'm now a published author in Russia! Yep, you heard right. One of my articles was recently published in a Russian mining trade magazine and the editor was kind enough to send me a copy of the mag. Here's the problem though. It's all in Russian! Anyway, I can still admire the pics of myself within the article. Anyhoo, enough of that. Let's move on to the business at hand.
Most (but not all) gold mineralization regions are produced within hydro-thermal deposit zones. The hydro-thermal thing ain't rocket science and is pretty easy to grasp..."hydro" meaning water and "thermal" meaning heat. This water is super-heated and contains minerals in a chemical state (solution) that are typically thrust vertically to funnel through channels by high pressure.
So first things first:
1) You need a source of fluids and the metals/minerals they contain.
2) Usually that gold-enriched source is found in the deepest layers of the earth's crust at depths of around 20-30 kilometers (around 65,000 to 98,000 feet!). This deep crustal layer is called the "Archean" by geologists and tends to be the "richest" in terms of mineralized fluids and metals. The crustal layers sitting above the Archean can also be mineralized but never as much as that deeper layer.
3) You need channels to funnel enriched solutions toward the earth's crust. These channels can be created through vulcanism, tectonic shifting or fracturing, or crustal "trenching" caused by other powerful natural forces.
4) Either below or above the earth's crust you need fissures (veins) to act as traps to capture enriched solutions on their way up to the surface. Oftentimes, these veins or traps are laid out in a lateral or diagonal direction as well. To emphasize this point ask any hard rock miner just how confusing following veins can be directionally and depth-wise (i.e., direction and dip).
5) Due to the heat factor already mentioned, gold is concentrated in the melted portions of crustal rock surging upward in solution. In hydro-thermal deposits this rock is typically METAMORPHIC in nature. (How many times has Old Jimbo here stressed the metamorphic connection to you guys and gals over the years? Huh? How many???)
6) Gold cannot move in mineralized solutions without the presence of other natural elements. That's why other metals or minerals can be found associated with gold and gold ores. Elements like iron, copper, silver, etc. (Did the light bulb just turn on inside your busy brain?) Believe it or not, chlorine and chloride solutions are the most common gold transporters.
7) In shear zones (also called "shear-hosted" gold deposits) gold is usually transported in solutions containing sulfides (sulfas). So when you hear me prattle on about iron sulfides, copper sulfides, silver sulfides, etc. perhaps you finally realize I'm not talking out my ass!
(Iron sulfide gold ore.)
8) As these solutions are forced upward close to the earth's outer crust they cool considerably and begin to lose the pressure gradient that forced them skyward. This is when the metallic aspect of gold's beauty begins to take place. With less heat and less pressure to hamper it, the gold can begin to form within those fissures, veins, or veinlets.
9) This lode gold deposition process can happen in just about any type of rock but more brittle rock formations tend to shatter and lose their ability to hold the gold. Certain types of mafic (silica-based or igneous) rock formations do well at hosting gold as do banded iron formations (geological formations with a high incidence of iron).
(Rocks from a banded iron formation.)
10) One of the biggest factors to finding source gold is knowing rock formation structure. I've just scratched the surface here so it's up to you to research and study everything you can about gold host structures.
That's Geology 101 concerning gold mineralization boys and girls. Now get to studying!
(c) Jim Rocha 2017
Questions? E-mail me at firstname.lastname@example.org