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Jasong's Vugs


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I subscribed to jasong's youtube channel. One of his vids is about vugs, crystals and their relations to gold.

I found it interesting that his approach to narrowing the search by locating "indicators" is the same as mine.

In a couple of earlier post I made, "dikes" and "the tunnels" I eluded to these indicators and made the statement that, "sometimes, in order to find the gold, you have look at what's under your feet". jasong's vid brings this statement to the forefront.

jasong also talks a bit about how gold is formed in the vugs - pretty interesting. He also gives brief descriptions of other indicators, those being crystals.

Maybe we could have a discussion?

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Very well said, I also have observed those indicators in areas where I have found crystalline specimens. Primarily small to medium size quartz crystals , pyrites,, heavy iron zones along veins and dyke systems. Another is the pattern the gold has formed into from its nearest host rock . like a natural mold for the gold to shape into. Thanks for sharing! Its this type of information I look for, finding the gold is one thing, but actually knowing how gold forms and how crystalline gold grows under what conditions is interesting. 

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Interesting stuff.

For the larger nuggets to fourm the reducing agent would have to be weak this way the gold would preceptate slower. A lesser number of nucleation sites will also help with larger nuggets being formed.

This means the host rock must cool quickly.Crystals have to cool slow or the atoms don't line up yet most of the gold pockets I have found have been in a vug with crystals. Or as we know minerals must leach to give room to forum large nuggets in secondary inrichments.

All that mud in a gold pocket is what is left of the minerals thar formed with the gold. At depth the below the oxidized zone the minerals are not broken down and the gold in the pockets is usually not in crystal forum.

The reason I know is because I have found them. The more gold you find the more you learn IF you slow down and pay attention.

Crazy stuff and fun to think about.

Root

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Jasong, That has blown my theory, all large gold specimens I have found have been in massive quartz, only specimens I have with crystals have had only small, flakey or wiry gold.

But you cement the old saying tis where it tis. Just love gold, probably occurs with all other mineral occurrences, I cannot think of one it doesn`t. Locally we have it with scheelite right through to coal.

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I'm happy to know this video is promoting discussion. These kinds of videos get the least amount of views but for me this is the most interesting part of prospecting - the mystery and figuring out how to solve it. Gold to me is just the final punctuation on the last page of a detective novel, the proof that a theory was right (or wrong). I live for the puzzle and adventure!

 

Norvic: I know very little about Aussie geology and I've never been there so your observations are likely correct for your conditions. Many of my videos are US-centric because this is the only place I've prospected. I've prospected all the western lower-48 except WA and ID and these are some threads I find in common no matter what state I am in. Granted, even here there are exceptions and I haven't been east of the Mississippi so even out there it may or may not apply.

 

When I talk about "big" gold I mean anything that is detectable size. Not all my subscribers are detectorists where our definition of big gold means something different. For example, in CO I only personally know of 3 nuggets found in the last 10 years larger than 1/4 ounce, but I still observe many of the same conditions producing that nuggety gold there as I do in Arizona where larger gold is more common. Often (but not always), I observe larger gold is found in the smaller veins and within pockets and not in massive quartz. Definitely are some notable exceptions to that rule as well though.

 

We really are part detective as prospectors, the more we keep our eyes open and make observations the more successful we can be I think.

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One thing which I didn't include in the video because honestly I don't understand enough about geochemistry is a bit more on iron oxides/sulfides and their association with gold.

 

I've observed time and again that nuggets very commonly have hematite inclusions but only rarely do they have magnetite inclusions. Now, both are iron oxides and pretty similar chemically speaking, so why is it so common that we find hematite included but not magnetite? Note: I'm not talking about black sand concentrations where the magnetite is associated with gold because of natural gravity separation here. Also, yes occasionally we do get those odd "magnetic" nuggets with magnetite inclusions but they are rare except in specific places.

 

A few years ago a metallurgist friend and fellow prospector ran his dredge cons through the spectrometer and a SEM (scanning electron microscope) and found the same thing, that the only black sand particles which contained gold were the hematite particles. And thus a guy could safely remove all the magnetite via a magnet before crushing and processing his cons and thereby reduce the amount of material to be processed greatly.

 

Well, after talking to NVChris earlier this year where he mentioned pseudomorphs it got me thinking about the subject further. Magnetite rarely forms a pseudomorph after pyrite but it's very common for hematite to do so. Even more common is Goethite after Pyrite though. So as the year has progressed I've been testing every nugget I find with a "blackish" material included and I've found that in fact a number of nuggets actually contain Goethite when I used to just assume it was hematite. They look very similar but Goethite will streak more yellowish than Hematite which is earthy red and pretty unmistakable.

 

So, I think one reason (among many others) we find hematite and goethite commonly included into gold nuggets themselves is their tendency to form pseudomorphs of pyrite, and in the crystalline world, the real strong association is actually with pyrite which was the original mineral and later gets altered and frees up its gold. So, this is why I stress that it's important to look for pyrite casting in your nuggets that you find and to pay attention when you start seeing large pyrite crystals or pseudomorophs of pyrite in the country rock or vein material itself.

 

Cubic cross sections can be quite deceiving so it's helpful to take a cube in hand and imagine what certain negatives (casts) would look like if the cube was cut from various angles and in different parts. The angles will not always be 90 degrees depending where you slice the cube at.

 

But again, I'm not a geochemist or a geologist, these are just observations and I'm not comfortable enough with their correctness to have included it in the video but it may be worth considering just on a theoretical basis.

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A pseudomorph? I thought that was a false fossil?  Sometimes I see speckled patterns in rocks which look like some sort of fossil, only to be told it is a pseudomorph. So, what does a pyrite pseudomorph look like exactly? 

 

And why is placer gold so often associated with blue clay in creek bottoms? I understand the clay is decomposed shale? Except I thought shale was gray ,not blue?

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Tvanwho, those three sample in my videos are all pseudomorphs of pyrite if you'd like to see an example. In specific they are Hematite after Pyrite. The black cube inclusions are what I'm talking about.

 

I don't know a lot about fossils, but when you think about it, it can be a similar process. Chert or something fills in and takes the form of a what was once a fish. Or have you seen those pyrite ammonites? I think you could call those pseudomorphs, one mineral is replacing biologic matter instead of replacing another mineral. Or whatever is happening, I honestly don't know a lot about fossils and fossiliation.

 

Phyllite can be blueish looking though its metamorphic, if you are referring to NNV? I'm guessing it probably weathers into something like clay too. But those would definitely be questions better answered by someone like Reno Chris than myself. Personally I've only found blue clay once when I was dredging. Mostly the clay I dig into when I detect is reddish from iron oxidizing. What I can say from my time in the oilfield is shale can be many colors from pale white to jet black.

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Yes I think I misunderstood your definition of large gold, in which case my experience with crystals and gold is in line with yours. eg the large rich specimen that Gerry got with the GB2, that appears to be in massive quartz. I`m very geology illiterate, thus when someone tells me to only look in say "greenstone", I wander around just looking wherever with mainly mixed results sometimes Wow results.

 

Have a few specimens of gold in limestone nearly marble where the gold appears to have replaced plant fossils. I posted a "zoomed" photo of one such specie back a few months.

Not having prospected anywhere but OZ, I`ll stick my neck out and state I doubt whether there is many differences wherever. I will endeavour to get a specie of gold in quartz/coal next season. Unfortunately the ones I`d got in the past I`d never taken a photo of, they went straight into the crusher as they had a fair bit of weight, and I did not consider they were perhaps rare.

 

But your video is very enlightening, it got the grey matter into gear. Much appreciated.

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