First fire assay questions

[IDAu]

I just did my first two fire assays on ore from my mine and I have some questions. The first assay worked perfectly and I recovered a small 0.002” bead. However, I added a couple grams of extra sulfides to the sample so I wanted to redo it with raw ore.

The only thing I did differently the second time is not add extra sulfides, and switched to an iron rod in the crucible instead of iron wire( wire was falling apart).

When I pulled the iron rod it had a ton of gunk stuck on it, even though it was white hot.

My lead prill was 2g less on this cons attempt, but I recovered another 0.02” bead.

Samples were 29.1g


My questions are….

1)What went wrong with the iron?
2) How can I mass such a tiny bead. Running some calculations a perfectly spherical pure gold bead that size should be over 1.3mg. But it’s not perfectly round or pure
3) How can I figure out the gold/silver ratio on such a tiny bead? I can’t imagine using AR on this small of an amount.

4) My cupellation is INSANELY slow. 4 hours total. I’m using a top load furnace so I’m sure it’s not getting great airflow but I added a fan, messed with temp, etc. and no change. Someone mentioned iron heavy samples being slow to cupel? I used an entire full 5 gal propane tank on two assays. I need to figure that out asap.

5) My cupel also seemed to form a ton of slag on the second assay. After scooping it off, it seemed to start going again. What is happening?

Really excited to figure out what grade my ore is. Appreciate the help.

 

[IDAu]

An assayer said to dip the bead in warm dilute three to one nitric acid and observe the color. I did that and it didn’t change.

I watched a video on parting that said, leave it in warm dilute acid for 10 minutes. So I made a batch of two to one and did that. The flat brown bead was in for 10 minutes and the other greenish one was in for just a couple. Did I ever have any gold to begin with??

 

[Yggdrasil]

I just did my first two fire assays on ore from my mine and I have some questions. The first assay worked perfectly and I recovered a small 0.002” bead. However, I added a couple grams of extra sulfides to the sample so I wanted to redo it with raw ore.

The only thing I did differently the second time is not add extra sulfides, and switched to an iron rod in the crucible instead of iron wire( wire was falling apart).

When I pulled the iron rod it had a ton of gunk stuck on it, even though it was white hot.

My lead prill was 2g less on this cons attempt, but I recovered another 0.02” bead.

Samples were 29.1g


My questions are….

1)What went wrong with the iron?
2) How can I mass such a tiny bead. Running some calculations a perfectly spherical pure gold bead that size should be over 1.3mg. But it’s not perfectly round or pure
3) How can I figure out the gold/silver ratio on such a tiny bead? I can’t imagine using AR on this small of an amount.

4) My cupellation is INSANELY slow. 4 hours total. I’m using a top load furnace so I’m sure it’s not getting great airflow but I added a fan, messed with temp, etc. and no change. Someone mentioned iron heavy samples being slow to cupel? I used an entire full 5 gal propane tank on two assays. I need to figure that out asap.

5) My cupel also seemed to form a ton of slag on the second assay. After scooping it off, it seemed to start going again. What is happening?

Really excited to figure out what grade my ore is. Appreciate the help.

What was your Flux mix?
It seems your slag is way to thick.
Do you have Sulfides in your ore?

 

[Yggdrasil]

An assayer said to dip the bead in warm dilute three to one nitric acid and observe the color. I did that and it didn’t change.

I watched a video on parting that said, leave it in warm dilute acid for 10 minutes. So I made a batch of two to one and did that. The flat brown bead was in for 10 minutes and the other greenish one was in for just a couple. Did I ever have any gold to begin with??

You need to read up on this, not only listen to others or some random videos off the net.
Why dip it?
To improve color?
That do not seem to be an assayer talking.
What is usually done is that after proper weighing the bead is flattened and then "parted" by Nitric.
This will remove all the Silver and all that is left is the Gold and PGMs (if they are there).
This is NOT a per minute/hour job.
Put the flattened bead into dilute hot Nitric and let it react until there is no more reaction. Then let it sit some more time.
Clean it well with water, dry it and weigh it.
Now you know how much Silver and Gold you have in your ore.
I suggest you read the Fire assaying book of Bugbee.

 

[IDAu]

What was your Flux mix?
It seems your slag is way to thick.
Do you have Sulfides in your ore?

As mentioned in that post. Yes. There are sulphides. I would say not much though. I got about 2.6g of sulfides in 22 pounds of ore.

The first batch, with far more sulfides, poured like water. The second batch was way too thick. I guess 2.6g less made it that way. My slag was green instead of black as well.

29.16g ore
40g litharge
3g silica
28g sodium carbonate
30g borax

 

[IDAu]

You need to read up on this, not only listen to others or some random videos off the net.
Why dip it?
To improve color?
That do not seem to be an assayer talking.
What is usually done is that after proper weighing the bead is flattened and then "parted" by Nitric.
This will remove all the Silver and all that is left is the Gold and PGMs (if they are there).
This is NOT a per minute/hour job.
Put the flattened bead into dilute hot Nitric and let it react until there is no more reaction. Then let it sit some more time.
Clean it well with water, dry it and weigh it.
Now you know how much Silver and Gold you have in your ore.
I suggest you read the Fire assaying book of Bugbee.

Some random video? It was a long format series called the fine art of fire assaying…As I mentioned...Parting is what I was attempting to do.




Correct. It is not a “per minute” thing but a starting point while watching the reaction. I didn’t continue because one bead all but disappeared 10 minutes in.

The dip was to look for a color to roughly assess gold concentration. Example, if yellow/gold, at least 50% etc. based on some chart in his fire assaying book. I don’t have an analytical balance capable of weighing 0.0001g accurately. All I was after was a rough estimate of gold to silver ratio.

 

[Yggdrasil]

Some random video? It was a long format series called the fine art of fire assaying…As I mentioned...Parting is what I was attempting to do.




Correct. It is not a “per minute” thing but a starting point while watching the reaction. I didn’t continue because one bead all but disappeared 10 minutes in.

The dip was to look for a color to roughly assess gold concentration. Example, if yellow/gold, at least 50% etc. based on some chart in his fire assaying book.

If it disappears, there is no Gold.

 

[Yggdrasil]

As mentioned in that post. Yes. There are sulphides. I would say not much though. I got about 2.6g of sulfides in 22 pounds of ore.

The first batch, with far more sulfides, poured like water. The second batch was way too thick. I guess 2.6g less made it that way. My slag was green instead of black as well.

29.16g ore
40g litharge
3g silica
28g sodium carbonate
30g borax

No flour or other Carbon source?
I'm not sure the CO₂ from the Carbonates are sufficient to reduce the Litharge to Lead.

 

[IDAu]

No flour or other Carbon source?
I'm not sure the CO₂ from the Carbonates are sufficient to reduce the Litharge to Lead.

Whoops. Forgot 10g of charcoal.

Lead prill was 18g on the first and 16.5g on the second.


Any idea about the 4 hour cupelling issue? I can burn half a tank on one sample. And now I’m wondering if I just had a tiny bead of lead that wouldn’t completely cupel.

 

[Yggdrasil]

Whoops. Forgot 10g of charcoal.

Lead prill was 18g on the first and 16.5g on the second.


Any idea about the 4 hour cupelling issue? I can burn half a tank on one sample. And now I’m wondering if I just had a tiny bead of lead that wouldn’t completely cupel.

What kind of cupels do you use?
It seem awful deep?

Temperature and oxygen are critical for a proper cupelling run.
Today most cupel furnaces are electric due to better temperature control and better control of the oxygen access.
In your case the temperature may be off and also there may not be enough oxygen left as the flame has consumed it already.

 

[IDAu]

What kind of cupels do you use?
It seem awful deep?

Temperature and oxygen are critical for a proper cupelling run.
Today most cupel furnaces are electric due to better temperature control and better control of the oxygen access.
In your case the temperature may be off and also there may not be enough oxygen left as the flame has consumed it already.

#8 MgO

I tried it as low as possible and as hot as possible, with the lid on and off, and with a fan blowing in the intake. I can see the surface shedding off pretty regularly like it’s working I think? It’s just so slow.

 

[Yggdrasil]

#8 MgO

I tried it as low as possible and as hot as possible, with the lid on and off, and with a fan blowing in the intake. I can see the surface shedding off pretty regularly like it’s working I think? It’s just so slow.

Did you buy them as cupels or make yourself?

 

[IDAu]

Did you buy them as cupels or make yourself?

Bought from make your own gold bars

 

[Yggdrasil]

Bought from make your own gold bars

You can make your own from Portland Cement.
How deep are they?
Images can lie a bit.

 

[IDAu]

You can make your own from Portland Cement.
How deep are they?
Images can lie a bit.

They don’t seem deep at all to me. Here’s the link

https://www.amazon.com/gp/aw/d/B0CN8MYPZ9?psc=1&ref=ppx_pop_mob_b_asin_title

 

[Yggdrasil]

They don’t seem deep at all to me. Here’s the link

https://www.amazon.com/gp/aw/d/B0CN8MYPZ9?psc=1&ref=ppx_pop_mob_b_asin_title

Looks ok.
The image might be "lying" due to coloration around the prill.

 

[goldshark]

You don't need 10 grams of flour. 1 gram will reduce 11 grams of Litharge, plus there is some Sulphur. Get a cone mold. Give a swirl and a light tap to crucible before pouring into cone mold. This helps the micro beads to coalesce in the bottom. Pouring while the slag is thin is imperative. Watch how quickly ( some good short videos on Youtube ) by big assay houses. They remove the crucible, tap, and pour within 30 seconds of being removed from the furnace, if not 15 seconds. Lolligagging is not tolerated, it can cause the assay to freeze to a degree, possibly affecting results.
The purer the Gold bead, the rounder it will solidify. The bead should only be measured with calipers after inquarting, then remelting to temperature. An accurate scale is very expensive.
Iron nails, due to the increased surface area, are better at de Sulphuring, than a bar or rod. For an assay ton of low sulfide rock, 5-6 4p non galvanized nails are adequate. Don't let the nails slide from the crucible into the cone mould upon pouring.
It will take a couple of experimental assays to get the results perfect.
A small furnace will consume less Propane. If you are only doing 1 at a time, a furnace which barely holds 1 crucible will pay for itself in no time, by savings in Propane and time alone.
A small electric furnace for cupeling, is almost imperative for accurate conditions and accuracy.

 

[IDAu]

You don't need 10 grams of flour. 1 gram will reduce 11 grams of Litharge, plus there is some Sulphur. Get a cone mold. Give a swirl and a light tap to crucible before pouring into cone mold. This helps the micro beads to coalesce in the bottom. Pouring while the slag is thin is imperative. Watch how quickly ( some good short videos on Youtube ) by big assay houses. They remove the crucible, tap, and pour within 30 seconds of being removed from the furnace, if not 15 seconds. Lolligagging is not tolerated, it can cause the assay to freeze to a degree, possibly affecting results.
The purer the Gold bead, the rounder it will solidify. The bead should only be measured with calipers after inquarting, then remelting to temperature. An accurate scale is very expensive.
Iron nails, due to the increased surface area, are better at de Sulphuring, than a bar or rod. For an assay ton of low sulfide rock, 5-6 4p non galvanized nails are adequate. Don't let the nails slide from the crucible into the cone mould upon pouring.
It will take a couple of experimental assays to get the results perfect.
A small furnace will consume less Propane. If you are only doing 1 at a time, a furnace which barely holds 1 crucible will pay for itself in no time, by savings in Propane and time alone.
A small electric furnace for cupeling, is almost imperative for accurate conditions and accuracy.

I have a cone mold. I pour within 15 seconds, probably in less than 10 actually. This second batch was super thick even when white hot as I mentioned.

Is there any way around an expensive balance? I simply cannot afford one like that. It's also not incredibly important to get super accurate results. I was thinking If I measured the bead, calculated the volume of a sphere and with the density of gold it would give me the weight. Of course that only works for pure gold. But if a simple color test could tell me the bead was at least 50% gold, I should be able to get a rough idea of what.

Example, volume of 0.002" bead X density of gold gave me 1.32mg. If 100% silver, 0.72mg. So at least 50% gold should give me somewhere in the middle around 1 oz/tn.

If I can verify I have at least 0.5oz/tn it's a go for running all the material anyway.


Thanks for the tip on the furnace. I wish I could find an electric one that was affordable.

 

[Yggdrasil]

I have a cone mold. I pour within 15 seconds, probably in less than 10 actually. This second batch was super thick even when white hot as I mentioned.

Is there any way around an expensive balance? I simply cannot afford one like that. It's also not incredibly important to get super accurate results. I was thinking If I measured the bead, calculated the volume of a sphere and with the density of gold it would give me the weight. Of course that only works for pure gold. But if a simple color test could tell me the bead was at least 50% gold, I should be able to get a rough idea of what.

Example, volume of 0.002" bead X density of gold gave me 1.32mg. If 100% silver, 0.72mg. So at least 50% gold should give me somewhere in the middle around 1 oz/tn.

If I can verify I have at least 0.5oz/tn it's a go for running all the material anyway.


Thanks for the tip on the furnace. I wish I could find an electric one that was affordable.

Any small glass fusion kiln would be hot enough for cupelling.
It only need around 900-1100 C.

I'd guess 200-600 USD or around there should be enough.
I think I payed 250 for mine a rather large one.

 

[4metals]

Usually in fire assay you add silver to at least one sample and do not add silver to at least 1 sample. The reason of inquarting is to allow parting in nitric acid. The result of the sample without Silver added is the total precious metals result and the parted sample is the gold result. The doré bead will not produce meaningful results with a caliper measurement because you cannot know the percentage of each precious metal.

Since you do not have a good analytical balance, you will need to cupel the gold from the parted sample to get it to melt into a bead so the result from the caliper will approach accuracy. I am not a big fan of the caliper to infer purity, but the price of an analytical balance does present obstacles for some.