A question about minerals (including gold) in Slate

[brianc053]

Hi everybody. I've been wondering about something and could use your help.

I've been visiting a stream in New England where there's slate bedrock exposed within a stream (technically a Brook), and the bedrock runs across the stream so it's your classic natural riffles. I've visited about 4 times so far and it always produces flour gold. It also produced a small picker that's shown in dvdtharaldson's "MA/VT/NH Panning" thread, page 33. So there's gold in this Brook.

Learning from KevinInColorado and WesternMassGold, I spent my latest trip there just prying apart the slate and since I only had a few hours on-site (before I had to attend to my day job) I collected the slate in buckets and brought it home.

I've started going through the slate and I'm finding specimens that have small (dime-sized) deposits of metals. I've attached a few pictures below; sorry for the poor quality, I'll work on that if people are interested.
Even with the fuzzy pics you'll probably notice that the metal deposits look like rust / iron. In some other samples (I haven't taken pictures yet) I'm finding a little seam of quartz here and there. This area has some large (6-12 inch wide) bands of quarts in places, also.

So here's my question, with a setup: I know there's gold in the stream, and I know there's metal deposits between the pieces of slate, so....is the gold coming from between the slate?

Thinking about it another way, if I pry apart enough of this slate will there be a decent chance of finding another little picker or a small seam of gold? Nature has been prying apart the slate for years - do you think that's what deposits the flour, flake and small picker gold in the stream?

Alternately, I'm aware that the gold in the stream and between the slate pieces could be glacial gold. But because I'm seeing these deposits of other minerals between the slate, I'm just wondering...are there more little pickers between those rocks?

I can't wait to hear your thoughts.
- Brian

Specimen #1


Closeup of #1


Specimen #2


Closeup of #2

 

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[PaDirtDigger]

100% iron pyrite... Sometimes it is in slate and shale as pyritized (bad spelling...) fossils like shells etc... Id definitely continue to collect there! Thats awesome!

 

[triple d]

I would crush the rusty looking stuff. And pan it to see if there any gold in it. If there"s pyrite in it could be gold also. Could be some of the quartz decomposing with the metals. If its not placier gold most likely coming from the rusty stuff.

 

[arizau]

Check out the youtube video in the first post here. http://www.treasurenet.com/forums/g...auk-mining-district-geology-presentation.html
Some of what you are seeing may be similar to what is explained in the video but it is more likely just a trap for glacial gold or whatever.

Good luck.

 

[Adventure_Time]

I'd focus on the quartz within the slate formation, if theres any gold concentrations it will be in and around the quartz seams.

 

[KevinInColorado]

Very observant of you Brian, hope you find some colors in those mineralized bits!

 

[Hoser John]

In some places here in Cali it's like opening the golden pages in a book. Test with acids , scrape it off with a knife, is it magnetic? If it goes crunch, cracks or crumbles usually pyrite family, which is huge-John

 

[brianc053]

Hi all, I thought I'd provide a quick update.
I went through two 5-gallon buckets of shale like the one in picture #1; notice how there's dirt stuck to the shale. I was washing them off in a big tub, and then I classified and panned/blue-bowled the various mesh sized material.
Picture #2 shows the gold recovered from 2 buckets worth of material. That material took about an hour to collect.
Picture #3 shows another of those iron pyrite deposits in the shale. I was able to crush one up and pan it; it crushed like pyrite does, and while there may have been a sub-100 mesh gold piece I wasn't sure.
Picture #4 is another specimen that had some interesting color on it; I don't think that yellow on the left side is gold, though some scientist with tests could theoretically find microscopic gold that causes it to look yellow.
I included picture #5 just because I thought the way that shale shattered and the resulting colors from the minerals along the crack was very pretty.

In summary, in 2 5-gallon buckets I didn't find any visible gold, and I only found a small amount of free gold trapped in the dirt between the shale pieces. Like most of you said, it's probably glacial flood gold.
But I'm going to keep looking for a small local deposit anyway...

------------------------------------------------
Picture #1: bucket of material pre-cleaning


Picture #2: gold from 2 buckets of collected material


Picture #3: Iron pyrite deposit


Picture #4: an interesting specimen


Picture #5: I just thought this was beautiful

 

[ohiochris]

Slate isnt typically associated with gold that I have heard of. Being in New England I think you are seeing what happens where I am a lot too. The gold is coming from another source....where I am it comes from glacial moraine , brought from up north during glaciated periods ( this is true in much of NE as well ). Once washed into the stream it gets trapped in the shale. Shale makes an excellent gold trap with all the cracks and crevices , as a bonus its usually a lot easier to pick it apart and mine than most bedrock is. The other minerals you see stuck to the shale can either be from the shale or believe it or not can actually be coming from the water flowing over and through it.

 

[LP13]

Slate is a sedimentary rock formed in large lakes or oceans. Generally sandstone is the stone created when deposits of near shore sands get compressed and buried under more and more overburden and eventually re-cement into new stone, sandstone. Farther out from shore, only finer particles make it and so finer and finer stone is created. Slate, shale and siltstones. These are usually too far from shore to have captured particles of gold and if there is gold in it it would be very microscopic. I would guess much smaller than 1 micron even.

When the deposit of sedimentary rock moves around because of plate tectonics, it might eventually get to the surface where you find it on dry land, and there, or while it moved above the surface, cracks in the sedimentary rock might capture some fine gold that might work down into it from surface water going into the ground, or if there was hot springs deeper down before it got to the surface that had some mineralization, it might then get some deposits of some kind in it in the cracks (called uplift fractures) that would be all through the rock layer.

I would be more inclined to look for gold in sandstones than I would finer sedimentary rocks. However, having said all that, I am sure that somewhere in the world there are just the right conditions to deposit gold in some slate maybe! We live in an amazing world.

 

[Hoser John]

Gold is where you find it as nature did not read any books. For every man made rule nature has millions of exceptions. Mariposa along the Merced has been mining gold from slate since General John Fremont, father of California, discovered it back in the 1800s . The Specimen Queen was a example of a multitude of gold sources from many kinds of host minerals. Here in Shasta county the Iron Mountain Mine and Tom Green same same...John

 

[brianc053]

As it has turned cold outside I've been cleaning up the samples I gathered over the Summer/Fall and I came across this one; I really liked it because it showed me how a quartz vein could run through the shale and then be further intruded by a mineral, in this case iron. (or at least that's how I interpret what I'm seeing - your expert input is always welcome if I need to be corrected).

I can't wait for the 2016 Season!

 

[ohiochris]

As it has turned cold outside I've been cleaning up the samples I gathered over the Summer/Fall and I came across this one; I really liked it because it showed me how a quartz vein could run through the shale and then be further intruded by a mineral, in this case iron. (or at least that's how I interpret what I'm seeing - your expert input is always welcome if I need to be corrected).

I can't wait for the 2016 Season!

View attachment 1244474

Im no expert but that may not be quartz , could be calcite , and from what Ive read is more commonly found in shale. One way to tell for sure is take a piece of it and put it in vinegar....if it bubbles or fizzes its calcite. Over time as water flows over or through a poreous surface like shale , minerals like calcite and iron in the water collect and build up. Does look interesting though.

 

[brianc053]

Im no expert but that may not be quartz , could be calcite , and from what Ive read is more commonly found in shale. One way to tell for sure is take a piece of it and put it in vinegar....if it bubbles or fizzes its calcite. Over time as water flows over or through a poreous surface like shale , minerals like calcite and iron in the water collect and build up. Does look interesting though.

Chris, thank you for the suggestion - I didn't know that it could have possibly been calcite.
My son (12 years old) and I followed your advice: we got out the vinegar, put it in a bowl and tossed a chip of the white rock into it. No bubbles - nothing. (pic attached).
My son then said "Dad I know what will fizz: baking soda." So, in order to ensure that the vinegar was good and not too old, I said "sure toss it in." Bubbles (pic attached).

Thanks for inspiring a little kitchen chemistry Chris!

- Brian

The rock:


Baking soda in the Vinegar:

 

[ohiochris]

Chris, thank you for the suggestion - I didn't know that it could have possibly been calcite.
My son (12 years old) and I followed your advice: we got out the vinegar, put it in a bowl and tossed a chip of the white rock into it. No bubbles - nothing. (pic attached).
My son then said "Dad I know what will fizz: baking soda." So, in order to ensure that the vinegar was good and not too old, I said "sure toss it in." Bubbles (pic attached).

Thanks for inspiring a little kitchen chemistry Chris!

- Brian

The rock:
View attachment 1246123

Baking soda in the Vinegar:
View attachment 1246124

Cool ! Glad I could help. Atleast based on what I read about it I think that may rule out calcite , not sure if any other non reactive minerals accumulate that way or not. I tend to believe the gold you are finding is from a glacial source but that dont necessarily rule out the possibility of gold associated with quartz in your finds. I would be tempted to sacrifice some of the quartz by pulverizing it as much as possible and then panning it out to see if any gold flakes show up. I do this a lot when I find quartz pieces or suspect ore in the river. I made a rock crusher for not a lot of money out of a 1 foot section of heavy steel ( 2" ? ) pipe threaded at the ends , and end cap , and a piece of heavy solid steel rod....all bought at Lowes. Takes some work but I can turn small amounts of anything that will fit into the pipe into mostly powder which pans easily.