Flux formulas

[rookieminer]

I've started assaying with an assay start up kit that included an assay flux.
The formula is:

41 gr. litharge
27 gr. soda ash
18 gr. borax anhydrous
2.5 gr. charcol
1.5 gr. silica

I have roasted all of the samples before the assay.
Since then I have purchased some more literature on fire assaying (a textbook of Fire Assaying By Edward E. Bugabee, and Fire assaying by Shepard & Dietrich).

The main ore I'm working with at this time is an altered basalt with quartz fissures, and misc sulfides. As a whole there is very little quartz, compared to the average gold in quartz ore.
After reading the section on assay fluxing in Bugbee's book, I'm wondering if the small amount of quartz in the ore I'm working with would be a problem with the flux I've been using (with the very small amount of silica added).
I'm going to try the regular flux formula in Bugbee's book, with the oxidizing addative.

Any thoughts on this?

rookieminer

 

[fireguy]

I've started assaying with an assay start up kit that included an assay flux.
The formula is:

41 gr. litharge
27 gr. soda ash
18 gr. borax anhydrous
2.5 gr. charcol
1.5 gr. silica

I have roasted all of the samples before the assay.
Since then I have purchased some more literature on fire assaying (a textbook of Fire Assaying By Edward E. Bugabee, and Fire assaying by Shepard & Dietrich).

The main ore I'm working with at this time is an altered basalt with quartz fissures, and misc sulfides. As a whole there is very little quartz, compared to the average gold in quartz ore.
After reading the section on assay fluxing in Bugbee's book, I'm wondering if the small amount of quartz in the ore I'm working with would be a problem with the flux I've been using (with the very small amount of silica added).
I'm going to try the regular flux formula in Bugbee's book, with the oxidizing addative.

Any thoughts on this?

rookieminer

That doesn't seem like an unreasonable flux mix for general samples. Have you tried firing any samples? How did they come out? 90 grams of flux would be about right for a 1/2 assay ton of sample.

That flux does have very low silica so is probably made for siliceous ores. If your ore is not contributing enough silica (acid) to the flux your slag may come out thick, and "chalky", and perhaps have swirls of color. If this is happening you will need to increase the silica (and perhaps borax). Also, having a higher litharge percentage makes for a more forgiving flux. Shepard & Dietrich includes an especially good section on fluxing.

Perhaps a better "all purpose" flux might be:
70% litharge
23.3% soda ash
4.5% borax
2.2% silica
Make additions as needed. Add reducer (flour) as required.
Don't forget to add an inquart http://www.inquarts.com

Roasting may help on the sulfide samples, but should not be necessary for other samples. All of your calculations should be based on the pre-roasted sample weight.

 

[rookieminer]

I would also like to fire assay for gold a copper ore (chrysocolla). How much flour for a reducer would you recomend?

rookieminer

 

[rookieminer]

This flux was recomended for 1a.t. with 90 grams of flux. It seemed to be working ok, but after trying it with 1/2 a.t. I did get higher results.

I also seemed to get better results by roasting in comparison to the iron nail method. Do you think roasting is the best way to deal with sulfide ores? I was curious about trying the nitre method. I've read that it can work quite well, but I wonder if it is not commonly used in assay offices because of the cost?

rookieminer