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Identity HelpTellurides? Cid mining district (Silver Hill area) NC USA

29th Jul 2014 23:37 UTCRohde Rubble

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Luster: Metallic

Color: White -- Gray --- Yellow

Streak: Varies with color but relative to

Hardness: 2.5 or lower (scratched by fingernail)

Dimensions: ~ 9cm x 9cm (main crystal structure app. 2.5 cm x 2 cm)

Locality: Cid Mining District, Davidson Co. , North Carolina, USA --- from Silver Hill Mine app. 10 miles nne as the crow flies

Optical: Highly anisotropic

These samples were found within a 20 foot zone in a metamorphic carbonate matrix that grades from predominately calcite - dolomite -- ankerite -- secondary enrichment (quartz dominated) -- oxidation zone. Substantial evidence of mineral leaching, and reconcentration.

Other minerals collected in this vein: Garnet, quartzite, silver, galena, pyrite. The small area these were collected show a regional contact zone particular to the whole structure with a layering of minerals otherwise well sorted in a typical carbonate dominated metamorphic series. Slight saddling curves of carbonate minerals most apparent in dolomite.


The focus is on the mineral in the center of the matrix which may be flattened or worn by weathering, being found at or near surface level. No reaction to HCL other than slight etching host material. Nitric acid testing was inconclusive (going from 10k to 18k). Images 1 and 2 of same sample, image 3 of another which has a looser less defined structure.

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29th Jul 2014 23:54 UTCRohde Rubble

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Here are 3 more which may show what I am trying to explain, showing the crumbly calcite dominated matrix (image 1) a piece etched with 18k nitric acid (image 2) and a boxworks type limonite gossan in the oxidized zone. May I add image 1 has been sitting outside in a bucket for 1 or 2 years hence some darkening of the minerals (almost black but very dark purple in daylight). Image 2 the area etched is in the lower right but there is a small dendritic crystal to the upper left which was not etched.


Image 1: 9cm x 4cm

Image 2: 8cm x 5cm

Image 3: 15cm x 10cm


My hope: Image 1: Calaverite with AU -------------- Image 2: Calaverite ----------- Image 3: Silver, sylvanite, pyrite, and quartz in limonite

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01384990016033830875359.jpg

30th Jul 2014 00:06 UTCRohde Rubble

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And at the risk of doing too much bandwidth I thought it might help to add closeups of #2 and #3 along with the large piece #2 was sourced from (22cm x 14cm x 10cm). The limonite piece is still being cleaned slowly and carefully since I really have a crush on it and want to treat it right but if it's not clean enough to mean anything, apologies, and thank you to anyone's inputs! Although I think I will send some out to get scanned (reccomendations are welcome if allowed as to a good lab with a decent turnaround). Best of the best!

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30th Jul 2014 00:40 UTCReiner Mielke Expert

Most of it looks like muscovite to me.

30th Jul 2014 05:15 UTCRohde Rubble

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Thank you for looking Reiner. Forgot to say in OP this mineral is opaque, it is sectile, very slightly ductile but when it gives it breaks into mostly triangular and nearly rectangular pieces. On the scale of a 5mm piece breaking into less than 1mm, the 30x loupe is my new best friend and I never thought I'd be this handy with a pair of tweezers. Next I put a light beneath the small stuff, shining upwards and they are still opaque. Dropping these particles into water they drop fast straight off the tweezer. Something about small pieces of mica I noticed they stick to the tweezers and usually require manual removal, which breaks them and float. At the risk of this sounding facetious I'm only telling you because muscovite was my initial thought too.


On a geologic note, this area I have collected has been very good to learn basic geology because I get to study this vein from the granitic outcroppings where it emerges as a talc schist about 200 meters above the oxidation zone, all the way to its oxidized state, the creek gets blood red here from all the acids draining off such a large ore zone which alters very fast, into a small slow moving creek, (serious probably undocumented AMD problem here).... anyways


As I looked at my series of samples from the top down, I noticed the micas diminished, (biotite, roscoelite, and muscovite) The weathered rocks from the large granites have large well developed micas and small poorly sorted minerals. They can break with a karate chop! As the vein becomes more developed the micas get smaller and more brittle, as the minerals series replaces and alters becoming stronger under increasing pressure, and about halfway through there is very little to no mica in the oxidized zone.


I was studying about this series of enrichment, reading some old USGS bulletins which theorized sulfuric acids may have the ability, mainly in secondary or tertiary ore enrichment zones under localized pressure, to have dissolved, altered and redeposited the . This playing a possible role in the formation of telluride compounds. Is this true? If memory serves me this was an old bulletin from the 1920's...


Also saw one of the few telluride localities in the world listed on MD DB, is right here, next to yours truly, in Montgomery Co. Who's to say though?


Sorry if that is too wordy but I just wanted to parlay my observations, not trying to softpeddle anything that isn't there to begin with:-D Learning is the big payoff, no matter what I have found some nice garnet and quartz boxworks.


Can anyone recommend a good service to get this analyzed properly? Would I have to get some concentrates analyzed by the tried and true fire assay, or can x ray scans determine this data quality.

09483230016033830875637.jpg

30th Jul 2014 14:13 UTCReiner Mielke Expert

For basic chemical analysis (EDS) I would recommend kaygeedeeminerals.com/ ( sorry can't give you the link right now server seems to be down). For more detailed work I would recommend http://attminerals.com/
 
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