Gold & Basalt

[OwenT]

I just watch an old Jeff Williams video and he mentioned at one point that you'd want start panning if you find an area of basalt with green in it. Now I'm assuming he was referring to olivine but I've never heard of a gold deposit associated with basalt before and the presence of olivine wouldn't change much in that respect I don't think. Any ideas?

 

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[et1955]

Hi Owen, hope you are doing well, interesting question, could the green be copper, there are a lot of copper mines around the Sky and basalt, gold was a by product of the mines. If you don't get an answer I'll ask Scott Harn of ICMJ magazine, he comes to the WPMA gold show every year.

 

[OwenT]

Hi Owen, hope you are doing well, interesting question, could the green be copper, there are a lot of copper mines around the Sky and basalt, gold was a by product of the mines. If you don't get an answer I'll ask Scott Harn of ICMJ magazine, he comes to the WPMA gold show every year.

Thanks Ed.

Interesting, I had never heard of copper in basalt either.

One reason I bring this up is a few years ago I was talking to a friend and he said that several years earlier he had been up at a creek in central washington swimming where he saw a man doing what sounded to me from his description like dredging. He said he asked him what he was doing and the man said he getting gold and even showed him some. The puzzling thing is that it's an area of all basalt, at the exact location the bedrock is a sort of sand/mudstone and I couldn't find gold there. I did find one small piece of white quartz once but I imagine it came from glaciers that once reached down as far as this creek but that wouldn't explain how there is that much gold there either. Also Landmatters doesn't show any historic mining claims. Either I missed something or it wasn't gold.

I am doing well, just trying to find the good spots here in Utah. They're out here but I've got to look hard I think. Lucky for me the university Library is another gold mine of information. Not just books on Utah, books on lots of places. Also, not just books, but access to huge online databases of articles and reports. I've been trying to do Washington research too with it. So, If there's ever anything like that you're looking for I just might be able to help.

 

[Clay Diggins]

Jeff was probably talking about greenstone belts which are commonly found associated with highly altered and fractured basalt.

Greenstone belts have some of the richest and most concentrated gold deposits. Many of the worlds biggest gold mines are situated in greenstone belts.

Heavy Pans

 

[OwenT]

Jeff was probably talking about greenstone belts which are commonly found associated with highly altered and fractured basalt.

Greenstone belts have some of the richest and most concentrated gold deposits. Many of the worlds biggest gold mines are situated in greenstone belts.

Heavy Pans

That makes sense. I'm guessing that has mostly to do with basalt from oceanic crust? Nothing to do with Columbia River basalts.

 

[et1955]

Owen check out " Nick Zentner " Prof of geology , central Wa university. He explains alot

 

[Capt Nemo]

Keeweenaw Peninsula. Heard that there's some gold found at the tip.

 

[tonofsteel]

I think he was referring to greenstone belt gold as well. Here is an example of some basalt ore from a greenstone belt.

After reading and watching a whole bunch it sure seems like finding minerals is as much art as it is science. In each region there are the most common ore genesis that you can find by reading reports, but many times there is mineralization outliers where something unexpected will be found.

Early on in the prospecting journey I was trying to find out what ore looks like and have found examples of ore in almost every type of rock. It seems as important to look for clues like alteration (ie. the green in greenstone) as much as knowing the common ore types/genesis in a region.

 

[tonofsteel]

Now I'm assuming he was referring to olivine but I've never heard of a gold deposit associated with basalt before and the presence of olivine wouldn't change much in that respect I don't think. Any ideas?

could the green be copper

https://geomaps.wr.usgs.gov/parks/noca/nocageol2c.html

In progressive metamorphism of a basalt, the course of change is different because the original basalt reacts differently to heat and pressure. In fact, it is so stiff and resistent to the squeezing (unlike wimpy shale) that the first reincarnation as a metamorphic rock is simple recrystallization to a rock called greenstone named because it is made of many green metamorphic minerals. Further squeezing finally overcomes the basalt or greenstone resistance, forming greenschist, which has many of the same minerals as greenstone but with the flaky foliation of all schists. Rising temperature and continued squeezing causes new minerals to crystallize, and what was formerly basalt becomes amphibolite, a rock that looks like a dark gneiss and is rich in hornblende and feldspar, but with very little quartz.

Greenstones contain sodium-rich plagioclase feldspar, chlorite, and epidote, as well as quartz. The chlorite and epidote make greenstones green.

If there is copper mineralization in the greenstone then this could also contribute to the green if it is weathering out AFAIK.

 

[oldmancoyote1]

Ice Age Flood

One likely source of the gold is that it was brought in by the ice age flood responsible for central Washington's scablands.

 

[oldmancoyote1]

Greenstone is somewhat altered basalt. It's contains a number of faintly greenish minerals.

In large greenstone belts in Canada, Australia, etc., it provided a place to trap gold-bearing fluids arising from deep within subducted oceanic crust. Greenstone belts are extremely old. I don't recall exact dates but a billion or more years is approximately correct. And yes, they do contain huge gold deposits.

Greenstone in the U.S. is usually associated with belts of rocks plastered against the side of the continent called ophiolite complexes. In a simple sort of way they consist of belts of ultra-mafic rocks, followed by greenstone rocks, followed by oceanic sedimentary rocks. Again the greenstone can serve as a trap for gold-bearing fluids. The ultra-mafic rocks are usually serpentined which may have something to do with the gold-bearing fluids. There are multiple ophiolite belts along the western edge of North America. Examples include the Mother Lode of California's Sierra Nevada and the three ophiolite belts of the Klamath Mountains of California and Oregon. It usually takes something more to cause the gold to precipitate within the greenstone for example dikes.

Hope this helps.

 

[Jim in Idaho]

About 30 years ago, a company found gold in basalt hoodoos a few miles north of Gooding, in southern Idaho. They had claims in the area, but in the end decided not to pursue it. There's gold in the Big Lost River, too, and they figure it erodes out of the basalt. No greenstone in either spot.
Jim