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PhotosDoes this qualify as a South Dakota gold specimen?

27th Mar 2024 12:51 UTCEd Clopton 🌟 Expert

Chlorite-biotite schist

Homestake Mine, Lead, Lead Mining District, Lawrence County, South Dakota, USA

I don't doubt that this core sample came from a gold mine, but unless there is visible or instrumentally detected gold present, I don't think this qualifies as a specimen of gold.

27th Mar 2024 13:30 UTCRolf Luetcke Expert

Ed,

I agree, unless visible gold can be seen in a photo, wouldn't put this as a gold specimen.

27th Mar 2024 14:22 UTCBeau Crockett

Yeah, I was wondering if a manager would flag that when I uploaded the photo. I do not know definitively what minerals are present in the sample, but "core sample" isn't a valid label for a specimen photo so I had to label it with some mineral or rock. Do you have a suggestion for what title (e.g. rock or mineral) could be given to that specimen so that it still shows up as a specimen photo?

27th Mar 2024 15:03 UTCKevin Conroy Manager

This is a rock. Hopefully one of the experts for this area will tell us which rock it is.

27th Mar 2024 15:54 UTCUwe Kolitsch Manager

My assumption was amphibolite, but close-up photos would be necessary.

28th Mar 2024 00:26 UTCBeau Crockett

Unfortunately, I won't be able to get any photos of this specimen until mid-May. If no regional experts are able to identify the rock type, then it can be put into user gallery. My primary reason for uploading photos is for my Mindat catalogue, so I'd rather have my images in user gallery than in public gallery with uncertain information.

27th Mar 2024 15:09 UTCHarold Moritz 🌟 Expert

It should be labeled as the rock type/formation. Take a look at the pix/captions of chunks of gold-bearing rock displayed around the visitor center there that I posted recently to see if they match your core (I don't think they do). The caption for this photo

https://www.mindat.org/photo-1299064.html

describes the various rock types visible in the open pit (summarized from a panel in the visitor center), but the core may be from underground parts of the mine not described. And the rock types vary on a small scale, so not sure you can make a certain ID on the core's rock type. Maybe it's the Poorman Formation schist, which does have some gold in it. But don't quote me on that!

27th Mar 2024 15:11 UTCKevin Conroy Manager

I added "South Dakota" to the title of this discussion to attract experts attention.

28th Mar 2024 06:16 UTCFrank K. Mazdab 🌟 Manager

it seems a variety of different phyllites and schists host the gold at Homestake, but all(?) of them seem to at least have quartz, biotite and chlorite in common. Although any particular sample might also have grunerite, siderite, garnet, ankerite and other minerals, calling this specimen a "chlorite-biotite-quartz schist" seems to at least cover the fundamentals.

https://pubs.usgs.gov/bul/1857j/report.pdf

28th Mar 2024 09:16 UTCKeith Compton 🌟 Manager

At least it qualifies as a South Dakota rock specimen !!

29th Mar 2024 16:59 UTCRolf Luetcke Expert

This was just brought to me yesterday and wanted to point out to the one who posted the "gold" core. This is also a core and in this case the core was from over 500 feet down at the SE Arizona Johnson Mine Burro Pit. It is a drilling project worked recently and in the core were a good number of copper crystals. For future posting in cases like this, the photo of copper or in the above case, gold, should be shown as in this photo and a child photo certainly can be added to show what the mineral was in.

This photo is 1 cm across and shows the mineral well.

29th Mar 2024 17:01 UTCRolf Luetcke Expert

Here is a section of the approx. 8cm core the copper is in, just to show how the "gold" may have been posted, if there was indeed gold in the core.

1st Apr 2024 16:38 UTCThomas Loomis 🌟 Expert

I agree, it should not be labelled as "gold". Is the proper Formation" known? Maybe it's the Homestake Fm or Poorman or Ellison. It's difficult unless you know Homestake geology. I think at best, post it as a "migmatite". It would certainly fit the definition.

1st Apr 2024 21:36 UTCRalph S Bottrill 🌟 Manager

I am not sure if it’s a migmatite or gneiss unless it can be shown the pale bands are feldspathic leucosomes rather than sandy layers in a highly deformed sediment; I have seen lots of the latter look like this. But I am unfamiliar with the geology there.

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