Dear all,
Before writing blunders or occupying SEM for nothing, I would like some advices on this arsenopyrite. The ore from this mine (Sb) contains a significant amount of Au according to historical data (1909) : from 1-12 g/ton. Could those yellow spotsin Asp be gold? I fear to be confused with chaclopyrite. In my opinion they doesn't look to be reflective enough, but I am not used to metallographic studies... Many thanks in advance for any input.
I'm sure it's not native gold, it's pyrite in arsenopyrite. For comparison, I have attached two reflected light images, in which one shows the direct comparison between arsenopyrite and pyrite, as well as the direct comparison between pyrite and native gold which has much higher reflectivity than pyrite and arsenopyrite.
Best regards,
Guenter Grundmann
Thanks a lot Guenter. I was almost sure that it was not gold, and even at this scale "fool's gold" deserves its name.
Hi Vincent,
here, additionally attached, just for fun, an image showing arsenopyrite in direct grain boundary contact to chalcopyrite. The reflectance value (in %) of arsenopyrite (50.36 - 51.21) is clearly higher than that of chalcopyrite (38.69 - 39.80).
Best regards,
Guenter
Pyrite in arsenopyrite appears most probable. Definitely, it's not gold in your images. - It is well-known that arsenopyrite can carry huindreds of ppm Au in its crystal lattice, e.g. at the Ashanti Mine in Ghana.
If interested, there are more numbers on that in my "old" Ashanti papers (see ResearchGate).
Thomas
High-grade gold ores in the Alleghany District, California are mostly associated with arsenopyrite. When traces of chalcopyrite occurs they appear as a olive-green grains in reflective light). Cp is much less reflective than nat Au. The Next Posting HAS PICS OF Au w/asp.
It is not native gold but pyrite.Native gold has much higher reflectivity than pyrite and arsenopyrite, It will be very bright and it's color is pure yellow.
H-Y Feng
What you say is certianly true but sometimes, depending on the amount of silver, the "nat Au" is not so yellow.
Ray C
What FHY says is true, but "native gold" can be paler if it carries too much Ag.
Good day!
I think that this photo will be quite obvious as the native gold looks in assnirprite. You may note that native gold with a large admixture of silver (according to x-ray microanalysis) has a very bright yellow color against the background of arsenopyrite.
A sample of gold ore from one of the deposits in the Northern Urals. This gold deposits is located near the Krasnoturyinsk.
Pyrite is more possiable than native gold based on the reflcted light picture. Native gold is significantly bightly and you can turn up your microscrope light intensity and look the difference.
And you also can detremine the Py, Ccp, and Au minerals under transmitted light condition, such as color and anisotropism.
It is also noted that there are the clear replacement in the Fe-S-As minerals (Py likely replaced by Apy).
Looking more, and looking correctly.
Zhankun Liu
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