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GeneralRE: Paragenesis of acanthite inclusions in luzonite

20th Apr 2017 19:44 UTCKyle Beucke 🌟

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Greetings,


I apologize for re-posting this. I had a sample of copper sulfosalt (based on XRD, mostly luzonite and famatinite) that had assayed very high in silver slabbed and analyzed with a microprobe. Inclusions of acanthite were found.


Here is an electron image of one area of luzonite with two acanthite inclusions labeled:



The surrounding gray is probably luzonite and it has some silver (~1%).


These acanthite inclusions are irregular in shape and there does not appear to be any pattern to their occurrence. Any suggestions on how to interpret the paragenesis here? Am I correct in assuming the acanthite must be hypogene and not supergene? This assumption is based on: 1. No identified supergene minerals associated with the acanthite, and 2. The acanthite does not follow any obvious fracture in the copper sulfosalt, but rather is disseminated through it. Is it more likely that the acanthite was deposited at the same time as the copper sulfosalt, or did one likely precede the other?


Thanks,


Kyle

21st Apr 2017 00:19 UTCRichard Gunter Expert

Hi Kyle:


It appears the Acanthite grains occur at the grain boundaries within the Luzonite. There is data to indicate that a sulphosalt such as Luzonite can only accommodate so much silver in its structure. That is why you have some silver in the surrounding Luzonite. Too much silver will not be able to be accommodated in the Luzonite and so will be swept into the grain boundaries. This type of texture is more easily seen in pegmatites but the low-temperature environment of Luzonite will eliminate other causes such as the partial melting of incompatible elements. Are there euhedral Luzonite crystals in the paragenesis?

21st Apr 2017 00:46 UTCKyle Beucke 🌟

Thanks, Richard. Are you suggesting this might be an exsolution texture, or that the acanthite was deposited more or less simultaneously with the luzonite?


This particular sample did not have visible, euhedral crystals. An XRD of similar looking material from the same hand sample indicated major luzonite and famatinite and minor enargite and tetrahedrite.


Thanks,


Kyle
 
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