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7 Days Of Arizona Detecting With The 6000


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2 hours ago, jasong said:

I ended up buying my own assaying equipment and teaching myself to assay because I didn't trust these lab results.

How much material is actually analyzed with an assay?  One of the problems with XRF analysis is that it is a surface measurement, not a bulk measurement.  If the sample isn't homogenous then you only get a localized reading which may not represent the entire sample.  Is that problem non-existant for an assay?

Hope I'm not getting OT here.  On the gold mining cable shows they sometimes pan one panful (or two or three), count the colors, and decide if the ground they took it from is worth putting into production.  But the more careful miners then run a much larger sample (e.g. 100 cubic yards) through a trommel+sluicebox and get a much more reliable determination of the expected yield before committing the time, labor, fuel cost, etc. to production.  I suppose sometimes the pan-only thing is just for 'show', I don't know.

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51 minutes ago, GB_Amateur said:

How much material is actually analyzed with an assay?  One of the problems with XRF analysis is that it is a surface measurement, not a bulk measurement.  If the sample isn't homogenous then you only get a localized reading which may not represent the entire sample.  Is that problem non-existant for an assay?

Hope I'm not getting OT here.  On the gold mining cable shows they sometimes pan one panful (or two or three), count the colors, and decide if the ground they took it from is worth putting into production.  But the more careful miners then run a much larger sample (e.g. 100 cubic yards) through a trommel+sluicebox and get a much more reliable determination of the expected yield before committing the time, labor, fuel cost, etc. to production.  I suppose sometimes the pan-only thing is just for 'show', I don't know.

Labs usually take between 50g to 150g of material for the actual assay. I send in about 500g-1kg samples usually. I believe they crush it all and mix it, and keep it for some time in case re-assays are ordered. Or you might use some leftover do metallic screening process on samples that assay over some threshold like 5g/ton in order to not miss high value results.

Sampling is usually of 2 types - grab samples or chip samples. 

Grab samples can assay extremely high and be unrepresentative of an ore body. This is kind of what an XRF does. Thus, it should mostly be a qualitative measurement just like XRF, even though it's an actual assay. IE - more useful just to show if something is there or not, and how high in value it could potentially run in small, selective hand picked quantities. This sampling is often just picking up some good looking pieces of ore by hand/eye. If a project is only posting flashy grab sample assays...be wary! When small scale prospectors assay material, often this is all they are doing too.

Chip sampling is different. I base my method loosely off my time with field geologists on my Gold Basin project. Basically, draw a line across an area of interest and hammer off chips semi-continuously over that entire interval into the sample bag. So, you are getting an overall representation of the gangue rock, many parts of the ore zone, and even some soil or caliche if they are in cracks and fall in the bag. You can do multiple sample intervals over the same line and get much different results - for instance if your line is 20ft wide then you could do a 3ft interval over just the vein, and two 3ft intervals over each side of the wall rock, and a 20ft interval over the whole thing. So, you can have assays that end up representing any part of your zone of interest individually, or any combination of them.

When doing this, it's important to ignore what you are hammering and just take it all in, the whole kit n kaboodle whatever it may be. No selective bias at all. 

This is important today because many projects are looking at bulk open pit mining, so if your gangue material is holding something like a consistent 0.5g/ton gold in addition to the primary vein/ore, well then it might be economically feasible today whereas it wasn't in the past. 

It's also similar to core sampling, where instead of spray painting a line to sample across, you are assaying different intervals of the core where the drill hole itself is your sample line.

My terminology here probably isn't 100% correct, but you get the idea of the process more or less. 

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