Interpreting Visual Prospecting Clues: a Dying Art? (Part 1)
As I've said before in Bedrock Dreams, I believe that gold prospecting is a dying art in the small-scale mining community. Moreover, many "weekender" type gold prospecting and mining enthusiasts don't even possess the most rudimentary ability to interpret the visual clues Mother Nature provides to the potential presence of gold and other precious metals.
This is in direct contrast to the old time prospectors and miners. I don't say this this as a put down or to humiliate or denigrate anyone...it's just a statement of fact. Additionally, I also understand that comparing the mining situation in past history to ours today is somewhat of an apples versus oranges thing. Yet, knowledge is knowledge, just the same.
The old timers may not have been highly educated or able to fully understand the science of gold prospecting, but they did have the ability to "read" the terrain around them and pick up on the visual clues Ma Nature provided. In fact, some of the richest gold and silver discoveries in the American West were a result of this innate ability to interpret visual prospecting clues.
With a tip of the hat to the old timers, there are any number of visual clues or tip offs that may lead you to precious metal. These include the following:
1) Sudden or abrupt changes in country rock
This sort of radical change in local geology is often a sign post to mineralization. As some of you already know, potential gold locales typically contain a prevalent or dominant host rock known in geology and mining circles as country rock. When the country rock drastically changes from one type or form into another, the specific boundary (or contact zone) where this change occurs often delineates significant geological change on a much broader scale, including possible precious metals mineralization.
This sort of country rock change or abrupt transition is most easily seen in desert or dry environments, but a sharp eye can discern its presence anywhere. The old timers may not have understood the science behind country rock shifts (geological contact zones), but they knew this could be an important visual clue to the presence of gold, copper, silver, and so on.
2) Sudden or abrupt changes in vegetation
Many aspiring gold prospectors and miners today have a hard time understanding this visual clue, although the physical principles involved are quite basic. The main thing to remember is that dramatic shifts in vegetation types in a localized area are not always the result of changes in altitude or the result of common environmental factors like rainfall, cold and heat, and the like. Sudden chemical changes in the soil itself can have a significant impact on vegetation, stunting or killing it, or denying purchase to weaker species of plants or trees while providing the same to hardier species. Where are these chemicals coming from that are impacting plant life so dramatically? Take a guess...
If you said sulfides or any other type of chemical reaction taking place in host rocks from the oxidation of irons, iron pyrites, or other constituents you are absolutely correct. So how do these chemicals adversely impact vegetation to the point that it becomes a visual clue to the possibility of precious metals mineralization.? Here's a simple test. Try soaking a bucket of rusty nails in water and then using that rusty water on a given plant. Next, use pure, untainted water on an identical plant. Would you expect to see differences between the two at some point? If we take this a step further the iron oxides in the tainted water might also prevent certain plants from growing while other, tougher species might fight their way through or even thrive.
(There's gold in this area...could you find it?)
The old timers kept an eye out for just these sorts of vegetation changes, particularly if those changes were sudden or abrupt. Along with other visual clues these sorts of changes could mean that mineralized (and potentially gold-bearing) rock was leaching oxides or sulfides into the soil of the immediate area.
Art of "Visual" Prospecting
The old timers may not have been very "sophisticated" in the snobbish sense of the term, but one thing I can guarantee you is this: they weren't stupid people. Their ability to discern even slight amounts of precious metal over broad swaths of terrain was based partly on trial-and-error, a good deal on hard-won experience, and the rest on an intuitive understanding of just what Mother Nature was telling them through her visual clues.
This ability, this "art" that the old timers were able to use freely and effectively in the past is now on the decline. There are numerous reasons why this is so and I won't bother to go into them here. Hopefully, the art of "visual" prospecting won't be lost forever at some point as I often suspect it will be.
Believe it or not, you have a choice in the matter...
(c) Jim Rocha (J.R.) 2013
Questions? E-mail me at firstname.lastname@example.org