Monday, August 19, 2013

Interpreting Visual Prospecting Clues: a Dying Art ? (Part 4)


 (Mother Nature offers up many visual clues if you know what to look for.)

Unlike their counterparts of the late 1800s and early 1900s, many aspiring gold prospectors and miners today have little knowledge or experience in interpreting Mother Nature's visual clues to the presence of precious metals. In a very slight way I'm trying my best to correct that perceived deficiency by passing along a few tips that will help you "see" what's going on out there.

Micro versus Macro?

If you've been reading this series of posts carefully you'll know that I've reiterated time and time again that regardless of the nature of the visual clues that may lead you to gold (or other precious metals or minerals), there is invariably an abrupt transition taking place geologically. This geological "abruptness" is just as relevant to smaller or localized areas or zones as it is to those of a large-scale nature. Rarely do highly mineralized zones occur in geological environments containing a single rock type or that transition very slowly from one distinct geological zone to another.

Gold Prospecting 
Gold Pans
Gold Concentrators

My son (a geologist fresh out of college) would probably take issue with that last statement. Undoubtedly there are exceptions to this rule of thumb (the California Motherlode?). I'm not here to debate all the PhDs and budding field geologists out there, including my own son. However, they're theoreticians first and foremost...not gold miners. You, I, and every other gold prospector or miner out there looks at geology from a very intimate or micro-scale standpoint while the scientists tend to look at things from a macro or large-scale view. That may be an over-simplification of sorts, but I think you get my drift.

Abrupt Transitions

Shifting gears again, I'd like to get back to this idea of the significance of abrupt geological changes. Let me give you a perfect example:

The Ortiz Mountains lie a scant 14 miles from my home outside Santa Fe, New Mexico. First discovered and "rushed" in 1829 I believe, the area possesses a singularly unique geology that's rooted in localized batholithic upthrust, metamorphism, and the presence of pyritic ore bodies (iron sulfides). This potent geological combination produced gold veins that eroded out along the north-and south-trending flanks of the Ortiz over millenia leaving behind some relatively rich dry placers (Old and New Placers Districts).

Yet, just a few miles south, southeast, and southwest of the Old Placers District there is virtually no precious metals mineralization at all...drive a few miles down Highway 14 (the famous "Turqouise Trail") and geological conditions suddenly shift to become coal-bearing and the underlying country rock changes to some degree as well. In fact, the old coal mining town of Madrid is in this locale. Drive a few miles farther south and you'll enter the southern boundaries of another placer and lode gold boom area, the New Placers District. So another abrupt change takes place in terms of gold mineralization

Jumping back north again, travel just a tiny bit north and west from the Old Placers and you'll find the old Spanish village of Los Cerrillos. Immediately north and west of Cerrillos (or adjacent to) are the Cerillos Hills and some of the oldest turquoise mines in the United States! Talk about abrupt mineralized zones...I've always marveled at these sorts of abrupt geological transitions. They always get my gold "radar" up and running.

OK, enough of that. Here's your next tip:

5) Evidence of other metals or minerals

At first glance this may seem like a no brainer. Still, there may be some of you out there who might not make the connection between copper and gold, silver and gold, garnets and gold, or any number of other combinations that lead to the presence of the gleaming yellow metal. Let me clarify things a bit here: most gold ores (and placer gold for that matter) contain small amounts of silver, copper, iron, or other such "contaminants." Conversely, most silver and copper ores contain small amounts of gold. This may also be true of iron ores but again, I'm no geologist and I'm not going to stick my neck out on that one! The percentage of gold contained in these other sources or "hosts" is a crap shoot at best...sometimes it's more and sometimes it's less (or very, very little).

 (The Ortiz Mountains of New Mexico...gold was found here in both the Old Placers and New Placers Districts.)

That's really not the issue here though. Nor is the fact that in some instances semi-precious stones or gem minerals like garnet are found with or near gold, despite the fact that both are formed from what I believe are different types of mineralization. Most gem minerals are heavy on the mica side when it comes to mineralization and as a gold prospector and miner I've never been fond of micaceous geological environments. That said, I can name at least half a dozen of these sorts of environments where I've found or mined gold, so out-of-the norm minerals need to be "seen" as a potential visual clue.

Getting back to that issue at hand I spoke of earlier...keep your eyes peeled for any and all potential connections that might link you to gold, whether that link is tin, iron, copper, silver, garnets, moon rocks, kryptonite, or whatever. Mother Nature likes to play funny little tricks on those who try to tease her treasures from her. So keep an open mind and your eyes sharp, and if in doubt...check things out.

(c)  Jim Rocha (J.R.)  2013

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


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12 comments:

  1. Wow...that's an interesting question and an intriguing theory. There's no doubt that volcanic and tectonic activity has much to do with gold mineralization. Volcanoes of and by themselves don't often produce gold per se though. But areas of ancient volcanic activity that have undergone metamorphosis (metamorphic rock) have long been good gold producers here in the Western and Southwestern USA. The other major factor is uplift, particularly with batholiths like the huge one that created California's Motherlode gold. In terms of meteorites, there are two main types: stone and nickel-iron. These don't contain gold in any appreciable amount to my knowledge. What are believed to contain precious metals in large amounts are asteroids. Great comments! Thanks, J.R.

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  2. Anonymous has left a new comment on your post "Interpreting Visual Prospecting Clues: a Dying Art...":

    Jim,
    Do you think that a majority of the gold discovered / mined on the earths surface came from the earths core? Ie volcanic movement / plate tectonic pressures? Could there be areas of "meteoric" displacement...that did not happen so long ago...that are also is gold bearing? Watching a ecent "science" oriented show brought this question to mind. Discussing meteor / astroid strikes and the possible minerals brought to the earths surface by this type of meteoric action over the millenium.

    I'm sure the mineralization you are discussing currently are very different for both of these types of areas. Any thoughts? Thanks for your input! (Note: This comment came in from Anonymous...I messed up on the publishing end here. My apologies. J.R.)

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  3. Wow! Great stuff here again JR! The ten dollar words don't fit in my 10 cent brain very well, but I think I know what you are saying. I gotta ask though, your answer to the last comment, what is the difference between an asteroid and a meteor? I thought they were the same thing. It would be amazing if it turned out that all the gold on Earth came from someplace else in that way! I bet NASA would get the space program jump started if it turned out to be true! Fair week here this week, Busy,Busy BUSY!!! Soon as it's over, I'm going prospecting dang it! Only been out twice all year! Found a little....key word is "little". Gary

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  4. Asteroids are larger, planetary type (planetoids) objects and sometimes have their own moons. If one of those hits us were essentially cooked. I read a while back one such asteroid is thought to be composed of over 75% gold!! You heard right. Meteorites are fragments of meteors (meteoroids) which are much smaller...these smaller pieces are what fall to earth. That's the best I can explain it I think. Best! J.R.

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  5. Jim,
    Your right on the money...or pretty close. One of the interesting things that happen (happened) during the making of the Milky Way Galaxy...and all other galaxies for that matter, was the extreme heat and pressure caused the molecular alignment of atoms to become so dense that most of the "heavy" metals on the periodical chart were formed at that time...and dispersed through out the universe...by meteoric / asteroid strikes. But...of course, so was the Earths core...with it's own metallic contents.

    In plain English....the higher the "atomic number" on the chart...the heavier the material is. Gold is very heavy....and dense as we all know. So is lead / platinum / silver / uranium / plutonium...etc. This was caused by the forces of nature....very long ago. So your comment about the "golden" asteroid are correct.

    If you haven't seen what they pay for small pieces of asteroids / meteors you should check it out! More rare than even gold....the fetch up to and above $4000 - 6000 an ounce. Most recently on gentlemen sold his very small piece of a meteor for over $100000 dollars! Kind of like "gold" from the sky!

    A few months ago there was a falling meteor up here in the norther motherlode. NASA and private space junkies were all trying to figure out where it landed. Why....well one small piece would pay for your years of fruitless hunting! So...as we go about the business of small scale mining...keep your eyes out for bizarre...and strange looking rocks.....they may just be from "out of this world"!!

    F.Y.I. Most of these "space rocks" are found by metal detectors...both small and large! Alright "nugget" shooters....find one of those!!! You may just quit gold prospecting altogether!! Thanks again Jim...great topic!

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  6. Thanks for providing the great info here. Highly interesting, to say the least and you know your stuff! With the prices of meteorites, maybe we're all in the wrong business. Best, J.R.

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  7. Once again, I learned something new here today. THANKS!!

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  8. Very interesting reading here, and in your other posts. Needless to say, I will be a frequent visitor.

    I was intro'd to prospecting 20+ years ago around Payson & Prescott, Az. I then left the area for Fl. and didn't take this back up until coming to Mn. last year. Supposedly, we here have no lode gold according to the DNR. Only tiny amounts of glacial gold brought down from Canada 10,000 years ago. Despite what the state tells us, I have meet many people around these parts that feel differently. I have also personally found more gold in a very short period of time, than I could believe is simply washing out of the overburden left by the glaciers. Granted, it is not large pieces, mostly very small 1/16th" or less. But quite honestly, I know in my heart, every time I go out prospecting for a few hours, even with the very basic knowledge & equipment I have, I will return with something gleaming yellow, and it's not pyrite.

    I have spent countless hours reading books, internet, and watching others on y-tube prospecting for gold.

    Getting to my point: The basic thing I'm wondering:

    The gold I'm finding is in a flowing granite creek bed with maybe 50% exposed bedrock. I have noticed some of the most basic items you have pointed out in this series of articles being present in my area, such as: Garnets, sulphides and mineralization of rocks, contact zones, what appears to be 'bull quartz' veins, other quartz veins with minor mineralization, and a wide range of coloring to the country rock - the vast majority of which is granite of some type or form. Yet unless I'm mistaken, gold is not commonly found in granite. Additionally, I have not found a likely source for gold in this area, but find it hard to believe it's all from glacial deposits.

    Any ideas you can offer would be well received. Like the (way back) 'old-timers' and your previous anonymous writer, I too believe highly in the concept of basic observation to understanding and learning from a given situation or environment. To that end, something I have personally done in the past, and will continue to do, is walk my particular creek a great distance further than I have planned to prospect it, and take/taken pictures each time I visit it, for a photo record of the changing environment. And I can already say that those photo records have come in very handy for later review of areas and clues I missed while walking. (Btw - I only started taking the pictures because of my poor memory, but they have become excellent tools for later review...)


    Sincerest Regards,
    Jim Lynch

    P.S. Please forgive the long read...

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  9. Granite has been the source of great amounts of gold. The Calif. Motherlode Region is a good example. The entire Motherlode is a gigantic granitic batholith that held numerous rich quartz veins. Granted, it wasn't the granite per se holding the gold, but many qaurtz veins, stringers, and veinlets were shot through it. There are other country rocks all about the Motherlode as well...serpentine being a common one.

    I have to confess I don't know much about Minn. gold other than its glacial characteristics. But Mother Nature likes to pull surprises. The experts may be stating there is no hard rock gold there of ECONOMIC consequence. However, that doesn't mean some small veinlets or stringers don't exist. This is only supposition on my part though...

    Thanks for the comments, J.R.

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  10. Funny.....how can the "Land of a Thousand Lakes" not have gold in it? I think your right Jim..... maybe not enough for "Economically feasible" mining.

    Officially as we get more "enviros" out there in ALL 50 states...they will bury these little facts....to keep the small miners out of "their" state. So...poop poop on the DNR....go get the gold.

    As my memory is slipping due to "sometimers" ....the pictures are a great idea...just put a GPS number on them so yo know later....where they are. Good reading Jim. Be safe out there!

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  11. Well my friend, you get out there and prove the experts wrong...they're not always right you know. Thanks for commenting and take care. J.R.

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