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Where does gold come from? with AZ Nugget Bob...


AzNuggetBob

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GeoJack, that's a good picture. I see the yellow color next to it. I wonder if that is the leftover iron pyrite which has yet to oxidize into the Limonite. Thanks for sharing.

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GeoJack if your referring to the kind of mustard yellow stuff I'd say limonite/iron oxide. The bright stuff looks like gold. Nice photo. the problem with identifying from a photo is so many minerals look similar in a photo. without having it in your hand or doing some tests even smell, its not easy on some.

Andyy
I'm a big fan of gatorade too. I drink a lot of it so I cut it about 50/50 with water. This time of year I drink it even if I'm not out hunting. before I got my camelbak hydro pack I carried frozen plastic GI canteens too. in this heat you may need both. you got to be careful out their in this heat.
Also something I forgot to mention on your San Domingo area reply is another term for that type of deposit is "epithermal". so search it and "secondary gold deposits" and you'll find a lot more info related to these gold deposits.
good luck to ya
AzNuggetBob

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So epithermal and therefore, close to the surface. I've been reading Jim Straight's book over and over again. Will dig more. Many thanks!

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post-25522-0-28027400-1434891396_thumb.jYes, it is gold.

Still learning about all the minerals associated with it and how they are part of the story. Thanks all for the help.

Grasshopper is learning.

This would explain the reason I get a tone with GB2 but nothing shows up when crushed and panned. Nice to finally see it next to some AU.

Still chasing it on the reef.

Rick

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My first impression of the photo was that I saw the gold before even looking at the other mineral, but I agree that it make sense that it would be limonite, which is a very good indicator of gold in areas known for gold deposits, in the southeastern part of the country we find lots of limonite cubes in many of the areas we find our gold.

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Wow that is a beautiful specimen. I thought it might be pyrite around the edges because I saw something similar in Alaska while visiting nugget creek near the Mendenhal glacier a week ago. I was walking along the tourist path and in the trail markers I saw the Limonite. Then you look really closely next to it and saw the yellowish cubes next to it. Yours wasn't cubic so I should have known it was more likely gold. I'm still learning too. I'm going to start taking my cell phone for pictures (just leaving it off while detecting).

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  • 2 weeks later...


My Favorite Bedrocks for Nugget Gold. ( More recent outcrops)
I'm always on the lookout for these bedrocks and float.

Granite

http://geology.com/rocks/granite.shtml

https://www.google.com/search?q=Schist&source=lnms&tbm=isch&sa=X&ei=jcuUVe_7K4GqyASRiZ8Y&ved=0CAcQ_AUoAQ&biw=1024&bih=629#tbm=isch&q=granite+rock





Gneiss

http://geology.about.com/od/rocks/ig/metrockindex/rocpicschist.htm

https://www.google.com/search?q=Gneiss&source=lnms&tbm=isch&sa=X&ei=qMyUVYHxNYuSyASszLqgCw&ved=0CAcQ_AUoAQ&biw=1024&bih=629




Schist

http://geology.com/rocks/schist.shtml

https://www.google.com/search?q=Schist&source=lnms&tbm=isch&sa=X&ei=jcuUVe_7K4GqyASRiZ8Y&ved=0CAcQ_AUoAQ&biw=1024&bih=629





Look for these bedrocks in any combination especially when intersected by Iron stained Quartz, and/or Veins,Vugs,Stringers,Dikes of oxidized Magnetite,Hematite,limonite.or float nuggets of these minerals.

http://geology.com/minerals/hematite.shtml

https://www.google.com/search?q=Hematite&source=lnms&tbm=isch&sa=X&ei=_M2UVcqeItShyATgqb3YDA&ved=0CAcQ_AUoAQ&biw=1024&bih=629

Also many of the red dirt patches of ground that gold nuggets are found in, are caused by iron/rust staining from oxidized Magnetite,Hematite.

I've found some of my best patches by following the diggings/drywashing left by the old timers. If they took the time to hand stack the wash, they where finding good gold."Follow the Drywashers" Great book by Jim Straight, and there may be a nugget patch above the wash where the old timers worked. that's why I get excited when I find old hand stacked washes.
Pay close attention to the washes your prospecting. those old stacked rocks along the edge of a wash can be hidden and almost blend back into the washes with time and weathering or be covered up with leaves, pine needles ETC.
The nice thing about drywashing and detecting is, you get more gold! the gold may be there, but too small to detect.


post-26382-0-85461400-1435814415_thumb.j

More to come.

Take care out there and good luck.
AzNuggetBob

Edited by AzNuggetBob
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Thanks for your input here GeoJack. I have not seen or read that article yet but if its in ICMJ I'll check it out. There is, a lot of small gold out there. AzNuggetBob

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Great post, AzNuggetBob. Are contacts zones of schist and granite easy to see (or any contact zone for that matter)? I have looked for pictures online for this, but usually you just get pictures of road cut-outs, which really don't represent what you see in the field and on a hill. All I can guess is that the outcroppings gradually switch over from one rock type to another, hence the use of "zone".

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AzNuggetBob, not about small gold, micro mining, less than the big boys. How to determine the actual cost to mine etc. Good stuff on sampling the vein system and how to do it right. Something I had been missing from my processes.

Hard Rock University - Expensive Hobby or Real Business by Keith Bowen.

Good read.

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GeoJack, thanks for the info. proper sampling is very important but also keep in mind that rich surface deposits can be misleading as well. Id also do research on a given area's history too. some area's have notoriously shallow deposits. surface sampling doesn't always show the full extent of the enrichment. core drilling is a good way to go but expensive.

Andy sometimes it hard to see the change between bedrock zones because of float,sand,rock,silt, even brush overlay on the surface. but the two rock types are visually very different.
AzNuggetBob

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Andy here is a little more info on schist.
This really helped me learn a lot more about geology when I first started out. besides all the books I started concentrating on geology maps of known gold areas. I looked for geologic patterns around the known gold mines. What types of minerals they were digging in or along contacts,veins,dikes,shear zones etc. most of the large "well known" areas have been mapped with pretty good detail but are great sources to learn what to look for. If you look at the map key on the bottom or on the side of these maps you will find a description of the minerals by color code and abbreviation for the mineral type and rock age. Here is one from the Lynx Creek Az. area.
http://repository.azgs.az.gov/sites/default/files/dlio/files/nid1555/dgm-103_prescottvalleysouth_0.pdf
Also this link/site above is a great place to get this type of info and maps.this link is a PDF format so it will take some time to load, but worth it.
For more info http://repository.azgs.az.gov/
As you can see one of the primary rock types along Lynx creek is a schist, or a variation of the schist belt that runs across Az. (simular to other gold area's with schist belts in the U.S.) It can change in color from light tan to dark green even black on very fine gold depending on the associated minerals where and when it Metamorphosed, or even some weathering on the surface. The generic term greenstone is sometimes used to refer to green schist, but can also refer to other types of green colored rock too,even some gemstone and that's why I prefer not to use the term.
BTW the nugget around my neck in my avatar is my favorite find so far, from Lynx creek.
It's out there. :)
AzNuggetBob

Edited by AzNuggetBob
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Bob.. You really know mineralogy... jim

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AzNuggetBob - that piece around your neck would be an awesome find. When I recently found my first nugget, I had dug so much trash, I felt like I had a unicorn in my hand. It just didn't seem real. But this was just by picking a claim with schist and getting lucky, as I know very little about identifying anything other than shallow bedrock :D

I've got all of the county geology maps of AZ but they seem to lack detail. Yours from the repository seem to be much more useful. I will have to utilize this link and start studying correlations in this way.

There does seem to be a lot of general uses of greenstone. I have been told that the volcanic basalt is one that is good for identifying contact zones. The chlorite gives them a slightly green tint, but sometimes you have to break them open to really notice it. Just collecting my clues for now.

On another note, I was going to take my wife and daughter to Lynx Creek Campground (next weekend) but during the busy season they require you to stay Friday and Saturday. You can't just stay Saturday night. So sick of the government restrictions. :grr01: Grrrrr..

Anyways, thanks again for the info and happy 4th of July!

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Bob, Melones fault system, pocket mines of El Dorado county. Got some "rich" history.

GeoJack Oh ya, that area has a lot of history and a lot of gold. you got some claims up there. I understand they have some manganese there and I have to say its common around many of the gold mines here in az. that's what causes all that black desert varnish. Land of the black gold nuggets.

This desert huntin is a whole different game. you ever prospected over here? if your goin to hunt down south in the summer here you got to bring your own shade. :D I spend most of my time over there up around Redding. lake shasta,clear creek,trinity river. that's my old stomping grounds. I was over there during the 1980's gold rush. the creeks were lined with dredges. everybody was finding gold.

Bob.. You really know mineralogy... jim

Jim,

I've learned a lot from your books over the years. the things Ive learned in them about drywashing alone,have helped me find a lot of gold nuggets the old timers missed. many Thanks.

I hope your doing well.

AzNuggetBob - that piece around your neck would be an awesome find. When I recently found my first nugget, I had dug so much trash, I felt like I had a unicorn in my hand. It just didn't seem real. But this was just by picking a claim with schist and getting lucky, as I know very little about identifying anything other than shallow bedrock :D

I've got all of the county geology maps of AZ but they seem to lack detail. Yours from the repository seem to be much more useful. I will have to utilize this link and start studying correlations in this way.

There does seem to be a lot of general uses of greenstone. I have been told that the volcanic basalt is one that is good for identifying contact zones. The chlorite gives them a slightly green tint, but sometimes you have to break them open to really notice it. Just collecting my clues for now.

On another note, I was going to take my wife and daughter to Lynx Creek Campground (next weekend) but during the busy season they require you to stay Friday and Saturday. You can't just stay Saturday night. So sick of the government restrictions. :grr01: Grrrrr..

Anyways, thanks again for the info and happy 4th of July!

Andy

I dont think I''ll be able to make it up there next weekend. It is a great place to beat the heat, get some fresh air and maybe even find some gold. I dont spend much time in the camp ground when I'm up there anyway. I'd bet its a bit crazy up there this weekend. If you spend a lot of time up in that area I may see ya up there this fall. I'm thinking about doing a road trip and I may stop by up there on my way out of town. best of luck to you and hope you find some more gold.

Happy 4th.

AzNuggetBob

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http://mrdata.usgs.gov/geology/state/sgmc-lith.php?text=greenstone

Greenstone
A field term applied to any compact, dark-green, altered or metamorphosed basic igneous rock (e.g. spilite, basalt, gabbro, diabase) that owes its color to the presence of chlorite, actinolite, or epidote.

AzNuggetBob

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Jack
Ya that's another great gold area. Ive been in and out of that area for years. crazy gold in that area. I luv those chevron gold nuggets.
I never was much into underground mining. doesn't mean I wont find a rich vein outcrop, claim it and lease it! :thumbsupanim
Im a die hard placer miner at heart though. and there's still a lot of placer gold out there too. I have done some strip mining and re-processing hard-rock tailings piles, heap leach, etc.

I've read their drift mining the old ancient placers up in El Dorado county area. sort of a cross between hard rocking and surface placer mining and finding some big old gold nuggets in there.

That's one of things I like about desert hunting verses up in the pines. you can see the geology better at a distance. its harder to trace the veins and see vein enrichment zones and contacts because of the pine needles too. but that's where the geo maps can come in handy.
AzNuggetBob

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I was lucky enough to be invited into one of the mines in Foresthill, Tertiary gravels. Tough going in that stuff.

I'm still trying to figure out if I follow the strike down or move along the surface and sample the seam. Two locations that show HG in the tailings, some to none in the surrounding vein. Both go down the strike.

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Jack
do you know the probable attitude of the vein? take a series of samples along the vein and dont forget to mark the sample sites with a numbered stake, and mark them on a map is the way we always did it.
Btw have you speci hunted under this vein yet?
AzNuggetBob

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