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Author Topic: photomicrographs or other close-up pictures  (Read 76459 times)

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Offline Guest

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Re: photomicrographs or other close-up pictures
« Reply #20 on: January 27, 2010, 09:52:30 PM »
Okay got a question for ya, now I understand inches, fractions, metric, and that but in order understand your pictures finch68, could you give me an idea of what is 100um or 500 um this micron stuff sort of have a little trouble visualizing it.........Guest

could you translate it into 1/16  1/32/ 1/64 type idea for us , thanks...

Offline Blister

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Re: photomicrographs or other close-up pictures
« Reply #21 on: January 27, 2010, 10:02:52 PM »
 Ok this will sort of blow your mind.

1 micron = 0.00003937007874 inch. So pretty close to 4/100,000 inch. If I counted the zeros properly :o

Offline PlacerPal

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Re: photomicrographs or other close-up pictures
« Reply #22 on: January 27, 2010, 10:35:26 PM »


What is a micron?  A micron is another measurement of particle size. 
A micron is one-millionth of a meter or one twenty-five thousandth of an inch.

Sieve Mesh #         Inches          Microns        Typical Material

14                         .0555             1400               

28                         .028               700              Beach Sand

60                         .0098             250               Fine Sand
 
100                        .0059             150             

200                        .0029              74               Portland Cement

325                         .0017              44               Silt

400                         .0015               37              Plant Pollen




Offline finch68

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Re: photomicrographs or other close-up pictures
« Reply #23 on: January 27, 2010, 11:14:01 PM »
If it should turn out that anyone wants me to do microscope scanning of their sand, etc, I would ask that you give me a general idea of the source so it adds to my collection of pictures of material from different areas.  I don't want to know specifically someone's secret placer gold field, but terms such as lower Fraser River, or Northern Fraser River, or Western Similkameen, or similar general identity would help put some geography to the pictures.  If I get any kind of catalog set up I would be happy to share it.

Oh, and it need not be restricted to samples with gold in them.  Any generally identified sand samples would be OK.

finch68

Offline finch68

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Re: photomicrographs or other close-up pictures
« Reply #24 on: January 28, 2010, 11:48:34 AM »
Here are 2 more pics to show you a little trick to see particle colour a bit better under the microscope,  These are -20 +48 mesh Fraser River sand.

The first pic is dry sand on the microscope slide, as have been all the other pics I have posted.  The second pic is with a drop of water added to the sand and a second slide placed over the drop so that you have the sand and water sandwiched between two pieces of glass, excluding air from the view.  

In this first pic you can see the particles pretty well, but they look dusty or cloudy.  The colours are not real bright or distinct.  The quartz particles look like they are not quite clear.  By the way, after several comments, I have put the scale bar in inches, instead of microns  ;D.



In this second pic the colors are much more distinct,  the quartz looks really clear and surface detail is more apparent.  You can see 2 or three little perfectly circular bubbles of air that I did not manage to get out of the space between the slide and its cover.



When trying to do mineral identification from slides of sand grains it can be helpful to use this technique.

finch68

Offline popandsonminers

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Re: photomicrographs or other close-up pictures
« Reply #25 on: January 28, 2010, 01:33:13 PM »
Here are some pics of gold in black sand.  They came from the same adit floor as the gold in the other post about the electric sluice.  This is a hardrock mine, not a placer deposit.  Hope the pics post OK.  I think each dash mark is 20 microns.  So, five dashes is 100 microns = 150 mesh

Offline finch68

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Re: photomicrographs or other close-up pictures
« Reply #26 on: January 28, 2010, 02:27:13 PM »
Very nice pics popandsonminers

finch68

Offline finch68

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Re: photomicrographs or other close-up pictures
« Reply #27 on: January 28, 2010, 02:31:54 PM »
Great photos SeloamLakeGoldMiner.  Hope to see more.

finch68

Offline finch68

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Re: photomicrographs or other close-up pictures
« Reply #28 on: January 31, 2010, 12:18:21 AM »
In another thread someone said that "visual assay" was an important tool to use to figure out what is in your gravels if you are into placer gold.  I agree completely.  I'm sure the aame is true for hardrock, but that is outside of my current experience, so I'll stick to placer analyses.

I was out to my Fraser River claim on Wednesday and brought home some -1/4 inch gravel.  Yesterday, I panned about a handful of -14 mesh and found a few small flakes.  More importantly, I wanted to find out what is in my pan concentrate.  So I took the concentrate and dried it.  Then I took a super magnet and removed all thehighly magnetic material - the stuff that will jump up an inch or so to my magnet.  Next I removed the stuff that is much less magnetic.  This is the stuff that is attracted to my super magnet when it is basically rubbed into the sand.  This leaves the non-magnetic stuff.  So I end up with three portions: really magnetic, slightly magnetic, and non-magnetic.

In the non-magnetic fraction there is still a lot of really black material as you can see in this picture.



So my question was - What can the non-magnetic black stuff be.  Now it really helps in identifying minerals if you have some kind of idea what might be there.  So I went to the ARIS Assessment reports website and downloaded some assessment reports for mineral claims that cover the creeks and possible contributors of erosional material to my claim.  The big guys like to have detailed geology and make a big deal of identifying all the minerals they find on their ground.  This is very helpful in considering what I might be seeing in my gravel.  I made a list of all the minerals they reported that could show up on my claim.  Then I Googled each one and looked at the properties and viewed available pictures.

One real likely possibility seemed to be "hornblende".  This is a very common black rock that is not valuable, and is not an ore of anything, and is not magnetic, but occurs very frequently.  An extremely important method for identifying hornblende is based on the fact that it has a cleavage of 56 and 124 degrees.  This means that if fragments are broken along the cleavage planes it should be possible to find grains with these angles between the faces.

The following pictures show grains with just such angles (actually, I concentrated on the 124 degree angle).  My apologies that in my excitement to show the angles I forgot to put on scale bars.  Just know these are all just a bit smaller than 14 mesh.  My microscope software has the ability to show the angle between crystal faces and so that is what is shown on the pics.











Remember that the particles sit randomly on the microscope slide, so not all are going to present the 124 degree angle exactly.  However, I found dozens of particles with this orientation - much more than random chance alone could account for.  So I am convinced that a large portion of the black, non-magnetic particles that have this surface characteristic are hornblende.

It is important to understand the mineral content of the sand if one wants to understand the possible host rocks for the gold bearing source of the gold.  Also, understanding the content of the sand might play a role in understanding the best way to separate the gold from the sand.

I will discuss other minerals in my sands in future posts.

Comments?

finch68


Offline fatkat

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Re: photomicrographs or other close-up pictures
« Reply #29 on: January 31, 2010, 06:51:22 AM »
I used a shallow dish with a drop of water ...surface tension lowered ...the sample can then be agitated ...you would not believe how often a grain of gold is hiding under a larger peeble.

 


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