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Author Topic: Microscope pictures of pyrite  (Read 10248 times)
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finch68
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« on: March 15, 2011, 11:04:09 AM »

I figure I should start a new thread here for microscope pictures of minerals and ores that are not placer or sand related.

The following 2 pictures are of crushed pyrite ore from a mine in Alaska.  The material has been screened into different size fractions.  These are of the coarser fraction.  All pictures are stacks of 8 to 15 individual frames.  Then, since my stacking program makes jpg pictures that are usually more than 1,000 KB in size, I use Corel Photo Paint to re-sample the photos down to a more manageable size for this forum.

 

You can see that at this size fraction the crushing has not completely liberated the pyrite from the quartz that it is bonded to.  I took a couple of frames of single fragments to show the bonding of pyrite to quartz.




The next frame is of a smaller size fraction.  Here the liberation is really quite complete.



So, microscope work can help to tell what is needed for crushing for milling purposes if liberation is a big deal - which it usually is.

finch68
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popandsonminers
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« Reply #1 on: March 15, 2011, 12:30:39 PM »

Finch, those are spectacular pictures!  You have it down to a science.

Do you know the mesh size that each of those pictures was at?  What size was the pyrite finally liberated?

I wonder if gold acts the same as pyrite?  It probably "depends" on the character of the ore and minerals.  I will be looking during some of my future views thru my microscope.

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« Reply #2 on: March 15, 2011, 12:39:22 PM »

Omg Finch...! Hat of to you! Wow! Tomorrow i will send you some samples..! Wink Thanks for those divine pictures! It would be neat if you gather all of those pictures together and name them, pyrite, copper, gold etc... Thanks!

/Elgreba
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« Reply #3 on: March 15, 2011, 01:20:51 PM »

 [-1st-] im thinkin if finch made prints of a bunch of his pics he could do a sell out art show in a new york art gallery.  Yes  Yes  jerry
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finch68
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« Reply #4 on: March 15, 2011, 05:02:25 PM »

Reply to Popandsonminers:

I wasn't actually paying much attention to the actual sizes of the fragments when I was getting ready to post the pictures, so after your question I went back and took a closer look.  In each picture there is a double arrow-ended scale that shows the scale of the picture.  In each case for these pictures the scale marker is 0.5 mm long.  My apologies to those folks who like to work in inches or thousandths of inches - I tried going that way, but it makes me uncomfortable as I have been a metric guy for far too many years.  However,  I know a lot of people relate to Mesh Size, particularly in North America, so  the 0.5 mm scale is the equivalent of 35 mesh.

Liberation size is one of those wishy-washy terms that can mean different things depending on the application.  But for most general applications the "liberation size" is the size that ore needs to be crushed down to to separate the good stuff from the gangue.  Liberation size is extremely dependent on the character of the ore.  For example it depends on both mineral particle size and gangue particle size.  Not only that, but it depends on the particle size distribution of each.  It also depends on the location of the good stuff withing the gangue.  For example, particles of good stuff that are occluded within gangue particles will have a significantly different liberation size than the same size of good stuff that is always on the outside of the gangue particles.  To complicate the matter even more, the liberation size may depend on the type of process that is being used to recover the good stuff.  For example, the liberation size for a leaching process only requires that all teh particles of good stuff be exposed to the leaching fluid - not necessarily completely separated from the gangue.  On the other hand, flotation processes require that the good stuff and the gangue are completely separated to allow recovery of the good stuff - so a different liberation size.

OK, that got sort of long winded.

Anyway, for the pyrite pictures above, the frame showing the larger fragments clearly had lots of pyrite clinging to quartz.  The average size of particles in that sample was about 2.00 mm or 10 mesh.  So the liberation size defined as the size needed to separate pyrite from quartz was smaller than 10 mesh.  In the photo showing the smaller particles the average size was about 0.5 mm or 35 mesh.  In this case, there was almost complete separation of the pyrite from the quartz. so the liberation size was greater than 35 mesh.

So there we have a rough petrographic study telling us that for this ore sample the liberation size is somewhere between 10 and 35 mesh.  If this was ore for a new mine it would not require a lot more study to pin this liberation size down even closer for purposes of designing crushing equipment for pyrite recovery.

finch68
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tomcat
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« Reply #5 on: March 15, 2011, 06:39:40 PM »

Please explain why you would want to recover pyrites....is there some form of value in this stuff unsure
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« Reply #6 on: March 15, 2011, 08:05:26 PM »

Please explain why you would want to recover pyrites....is there some form of value in this stuff unsure

Indeed, pyrite can have all sorts of good stuff locked up in it. Gold, silver, and copper to name a few.

Great pictures thanks for sharing!
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« Reply #7 on: March 15, 2011, 09:27:48 PM »

Well, first of all astrobouncer is correct, that other really valuable stuff can be mined in conjunction with pyrite.  But on its own, pyrite is mined to convert into sulfuric acid.  Almost 7 million tonnes are mined per year to turn into sulfuric acid.  The pyrite is heated in the presence of oxygen and forms sulfur trioxide that is dissolved in water to form sulfuric acid.  Not only that, but the residual iron cinder is used in the manufacture of cement and even as an iron source in smelters.

Not bad for "fools gold".

finch68
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« Reply #8 on: March 15, 2011, 09:44:12 PM »

Great pics Finch

It is amazing how different minerals can look under magnification and how much you can learn.  The best part about a microscope is you can find one for fairly cheap (less than $100) on line and get your magnification down to x100 compared to your standard hand lens which maxes out at around x20.

Thanks for sharing and I wanted to add a few pics myself.  Okay lets see how this goes... For the three following pics each dash is 10 microns and each numbered dash is 100 microns


This first picture is gold at x50 magnification.

This pic is to show how the gold is still attached to the sulfide material.  This piece is around 150 mesh.

Here is a pic showing a ~800 mesh piece of gold attached to a sulfide grain.  

There are many cases where the sulfides will actually totally encase the gold particles making cyanidation very difficult.  Our ore gets ground to 80% passing a 280 mesh screen in the ball mill before it goes to the cyanide tanks.  With this grind and around 24 hour retention time the mill is recovering 95%.

This is why after all your "free gold" has been removed from your sulfide concentrate at a grind size of minus 100 mesh your sulfides can still contain abundant values.  

We assayed some of the concentrates off our shaker table that all passed a 200 mesh screen and all the free gold was removed.  The 200 mesh minus sulfides (mostly pyrrhotite with a little chalcopyrite) assayed .687 opt.  At those values they are definitely worth holding on to.

Thanks again and keep the pics coming.

Jason Gaber
Mt. Baker Mining and Metals
mbmmllc@gmail.com
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« Reply #9 on: March 16, 2011, 12:33:00 AM »

Great pictures Jason:

I must get one of those micrometer slides to show scale, but they are so damn 'scuse me darn expensive.  What I really want to get is a good polarizing petrographic microscope.  But at about $3,000 for a decent one with a camera some of my claims had better look promising or not going to happen LOL

finch68
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