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I was looking into these specific minerals: arsenopyrite, pyrite, chalcopyrite, barite, calcite, dolomite. I investigate issues with tellurides not showing expected gold concentrations.

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  • $\begingroup$ What do you mean when you say : " I investigate issues with tellurides not showing expected gold concentrations" ? Issues ? What sort of issues ? What is an "expected gold concentration " ? Has it any relationship with the previous sentence ? Has it any relationship with the aqua regia from the title ? Explain ! $\endgroup$
    – Maurice
    Nov 16 '20 at 20:07
  • $\begingroup$ There is gold predicted at the site where these samples are. We tryed to prove the presence of gold through aqua regia tests, but the resulting gold concentrations are low. My suspicion is that the majority of the gold resides as an inclusion in these minerals, and the aqua regia test won't be able to show that because of its inability to dissolve the host. $\endgroup$
    – asdchem
    Nov 16 '20 at 20:17
  • $\begingroup$ If gold is included in inclusions, why don't you grind your minerals to a powder ? $\endgroup$
    – Maurice
    Nov 16 '20 at 20:34
  • $\begingroup$ It was ground, but the particle sizes are probably smaller then the smallest grinding size. $\endgroup$
    – asdchem
    Nov 16 '20 at 21:17
  • $\begingroup$ Osmium or iridium minerals are not soluble in aqua regia. The arsenide and sulphide of platinum are slightly soluble in aqua regia but the rate of solubility is very slow. Sperrylite(PtAs2) and Cooperite(PtS) is insoluble in aqua regia. (minsocam.org/ammin/AM22/AM22_1016) $\endgroup$ Nov 17 '20 at 9:36
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Chemical Book reports that barium sulfate (barite, or baryte) is

slightly soluble in concentrated sulfuric acid and soluble in carbonate alkali metal solution in which it is converted to barium carbonate; it is insoluble in other kinds of acid or base.

It sounds like the barite is your culprit. If you try grinding it with an eye towards physically separating the denser gold from it, the Mohs hardness of the mineral is 3-3.5, so there appears to be no issue with the physical grinding process.

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  • $\begingroup$ Thank you for your input. It is likely that the grinding sizes are insufficient as well. $\endgroup$
    – asdchem
    Nov 16 '20 at 21:20

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