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trying to clarify location for Peruvian galena

Posted by Don Windeler  
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Don Windeler March 11, 2018 02:25AM
Folks:

As I continue with my collection cataloguing / windmill tilting, I’ve surfaced another mystery locality on which I’d like to hear opinions.

This is a galena specimen, with little octahedral crystals that appear to have overgrown a larger octahedron. There is a smattering of clear quartz crystals fencing the edge of the specimen. No matrix, only galena and quartz. The labels from Al McGuinness and Jeanne Megar, circa 1970s-80s, read “Pashcancha, Ancash Dept., Peru.”




There is no “Pashcancha” in MinDat, but there are two candidates in Ancash Department:
Pasacancha https://www.mindat.org/loc-159101.html
Pachapaqui https://www.mindat.org/loc-2306.html

Pasacancha reads pretty close to Pashcancha, but MinDat only lists bindheimite as a mineral at the locality. Other resources online indicate it was a small copper mine with some gold and lead production, but nothing on the associated minerals. Pachapaqui is a large mineral producing locality, but I didn’t see any galena specimens in the MinDat entry that look much like the octahedra on my piece.

I lean toward Pasacancha because it's only one character off, but I hesitate because it's a much less common locality and I have no other supporting evidence. Anyone out there with experience or information that could help clarify?

Thank you!
D.
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Don Windeler June 11, 2019 11:59PM
Folks:

Just went back into my old message list and figured I'd bump this one. Please let me know if anyone has any ideas -- thank you!

D.
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Frank K. Mazdab June 12, 2019 05:50AM
Are you sure those are galena? Just from the two photos here, they look a bit more like tetrahedrite.
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Don Windeler June 12, 2019 06:39AM
Hmph. I suppose that's possible -- I will go dig out the original piece and see if there's any additional things I can do to distinguish the stuff between galena and tetrahedrite. It was a piece picked up at a club auction -- albeit one that usually has good material -- and I was mostly focused on clarification of the locality rather than constituent minerals.

Of course, any kind of ID improvement is a good thing in my book!

Cheers,
D.
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Frank K. Mazdab June 12, 2019 07:27AM
If you can find the original piece, then chipping off a tiny grain on the discreet bottom of the specimen can allow you to perform a quick test between galena and tetrahedrite. Gently crushed, galena will cleave into little flat-faced cubes or rectangular chunks, whereas tetrahedrite doesn't have cleavage and its fragments will have irregular to even slightly sub-conchoidal fracture surfaces. Using a hand lens to evaluate the cleavage/fracture will let you select a very tiny original grain, minimizing any significant damage to your specimen.

edit: or there may already be some broken surfaces to evaluate, and then you might not need to break off any crystals at all.



Edited 1 time(s). Last edit at 06/12/2019 07:30AM by Frank K. Mazdab.
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