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The native gold from Guelmim-Oued Noun, Morocco - (35)
  
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Cesar M. Salvan
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PostPosted: Dec 29, 2020 06:08    Post subject: The native gold from Guelmim-Oued Noun, Morocco - (35)  

Recently, my dear friend Jordi Fabre sent me a couple of samples from a new, really interesting find: native gold from a unknown deposit (as far as I know) in the region of Guelmim-Oued Noun in Morocco. The samples are small and the quality does not represent the overall quality of the specimens I've shown, but were selected as 'sacrificial' for analytical purposes. So, do not consider the pictures here as representative of the quality and beauty specimens recovered, which in most cases, shows well developed crystals.

The crystal habits and elongated, filiform shapes made some people question whether the samples were fabricated or not, and if the specimens are forgeries. Of course, with just pictures is not possible to determine any valid diagnostics. So, I was very happy when I received the samples for first hand study. They show textures from spongy to roughly crystalline, filiform and are accompanied by abundant iron oxides.

The identification of iron oxides shows both hematite and goethite, the last forming characteristic botryoidal textures. The iron oxides and gold have grown intimately and it is interesting that they are usually not mixed. Instead, they appear to be formed in two stages, one in which pulverulent hematite was deposited followed by growth of goethite layers.
Occasional quartz grains appear included in the material. The mixing of iron oxides with gold particles is so intimate that the samples showed an unusual enhancement of Raman signals of the former for the species (probably a solid state SERS effect, I will investigate that more)

The analysis of metal showed gold in the range 88.5 to 93%, with silver (3-6.4%) and traces of copper and lead. The composition is slightly variable depending on the iron oxide presence. Overall, in the studied samples there is no evidence of forgeries. No "wires", around which an unusually skilled scam artist grew gold crystals. The composition and mineralogy point clearly to native gold, at least in the analyzed samples.

Caveat: I would like to remind that inductive thinking is one of the weaker in Science. What does that mean? It means that if I analyze a sample from a deposit, I can speak only about that analyzed sample; I cannot make a general statement about all material purportedly mined in that deposit, especially considering the complete lack of geological context of the samples. That is why the concept of "representative sample" is important. In this case, the samples are only representative of a determined lot with similar characteristics and mineralogy.



oro hilo web.jpg
 Mineral: Gold
 Dimensions: 1 cm
 Description:
One of the studied gold samples. It is very thin and it weights only 140 milligrams
 Viewed:  4745 Time(s)

oro hilo web.jpg



oro detalle muestrasOK web.jpg
 Locality:
Morocco (Western Sahara)
 Dimensions: 2 mm
 Description:
Detail of the sample in the previous picture
 Viewed:  4751 Time(s)

oro detalle muestrasOK web.jpg



oro goethita web.jpg
 Mineral: Goethite and gold
 Locality:
Morocco (Western Sahara)
 Dimensions: 1.5 mm
 Description:
Detail of the goethite, forming brownish black botryoids mixed with gold.
 Viewed:  4747 Time(s)

oro goethita web.jpg



imagen web 2.jpg
 Mineral: Hematite and goethite on gold
 Dimensions: 2 mm
 Description:
Hematite (lower half) appears as red to brown, dull, pulverulent material. Goethite (upper half) appears as typical black botryoidal material.
 Viewed:  4746 Time(s)

imagen web 2.jpg



imagen web 1.jpg
 Mineral: Gold
 Dimensions: 2 mm
 Description:
Detail of the analyzed sample
 Viewed:  4748 Time(s)

imagen web 1.jpg



imagen web 4.jpg
 Mineral: Gold
 Description:
Energy dispersive X-ray spectrum of the sample shown in the pictures, showing the overall composition in an area of 400 micrometers.
 Viewed:  4753 Time(s)

imagen web 4.jpg


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Tomasz Praszkier




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PostPosted: Dec 29, 2020 06:40    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

Hi,
Thanks for the data, They confirm microscopic observations that we did.
We never sent them for more analyses as there was never doubts that they are fake for several reasons. One reason is that they are overgrown by thick Mn-Fe oxides which additionally are overgrown by calcite. What's more, quartz crystals are frequently found growing on the gold, but also some gold is growing on the quartz (multistage quartz growth). I went through about 500 crystals under the microscope and there is nothing suspicious in them, besides the quality and enormous size for gold.
There are several habits of twins from the find - from very thin (pseudo-wire habit - sic! no wires!) to quite thick. Some of them are without visible crystal faces, and others are very sharp with great luster. Bigger crystals on the edges of the twins are more or less hoppered.
The specimen in the photo (by Mark Mauthner) is 4.5 cm tall, and shows quartz growing on a cluster of spinel law twinned golds.



2020_1218_005.jpg
 Mineral: Gold
 Locality:
Aouint Ighoman, Assa-Zag Province, Guelmim-Oued Noun Region, Morocco
 Dimensions: Specimen height 4.5 cm
 Description:
Spinel law twinned gold crystals with quartz, from recent find in Guelmim area in Morocco. 4.5 cm tall. M. Mauthner photo. Spirifer Minerals specimen.
 Viewed:  4734 Time(s)

2020_1218_005.jpg



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PostPosted: Dec 29, 2020 08:18    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

Hello All, I have never had any doubts about the natural nature of the gold crystals from this locality. They are natural and I am glad to see the above detailed analytical work. However, I have seen many faked specimens. The makers make by taking loose natural crystals and affixing them to the surface of barren matrices. It appears that they coat or soak the iron oxide in a glue and sprinkle gold crystals and more iron oxides on the surface of the matrix. The specimens look very convincing at first glance but the gold crystals are only on the surface of the matrix, laying fairly flat but not protruding out of the matrix. I have also purchased perfectly natural gold specimens from this locality with gold crystals naturally protruding from the matrix. Caveat emptor!

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Tomasz Praszkier




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PostPosted: Dec 29, 2020 08:29    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

Dave, you have seen faked specimens (glued to matrix) from this particular find? That would be interesting as I did not see any, and I saw the majority of the material. There are a lot of very small crystals and grains without crystal forms, so I guess this is "perfect" material to fake some specimens ...
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PostPosted: Dec 29, 2020 08:42    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

Hi Tomek et al, I guess I’ll never know if it is the exact find but it looks the same. I examined all the specimens closely. All were specimens for sale from Moroccans, during Tucson, 2020. As I said, I did find bona fide specimens as well, but many were manufactured.
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PostPosted: Dec 29, 2020 08:50    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

If that was Tucson 2020 it can not be from this find. Most probably you are talking about golds from Bleida, They are also partly in gossan-type rocks associated with copper secondaries.
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PostPosted: Dec 29, 2020 09:04    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

I bow to your knowledge of Moroccan minerals and localities. Still those were very similar specimens (no copper secondaries that I noticed) and people should be aware of it and the possibility that such specimens could be attributed to this newer find.-
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PostPosted: Jan 11, 2021 14:00    Post subject: The native Gold from Guelmim-Oued Noun, Morocco - (35)  

The time helps to clarify things. Advancing of the right locality for these Golds, we already know the name of the closer village: Aouint Ighoman, and that some people use the name 'Aouint Ighoman Guelmim' for the labours where these wonderful Golds are collected.
There are a lot histories about it currently, telling that these labours are on an old mine. Will see in the future what real (or not ;-) are these histories.
Very few pieces with 'scorpion' crystals are on matrix there but some more on matrix with the scoriaceous type.
As a curiosity some piece have the Gold crystals on Calcite matrix.



Gold on Quartz from Aouint Ighoman.jpg
 Mineral: Gold on Quartz
 Locality:
Aouint Ighoman, Assa-Zag Province, Guelmim-Oued Noun Region, Morocco
 Dimensions: 4.5 x 4.1 x 3,3 cm
 Description:
Photo: Joaquim Callén
 Viewed:  4122 Time(s)

Gold on Quartz from Aouint Ighoman.jpg



Gold on Quartz from Aouint Ighoman detail.jpg
 Mineral: Gold on Quartz
 Locality:
Aouint Ighoman, Assa-Zag Province, Guelmim-Oued Noun Region, Morocco
 Dimensions: Crystal: 1.6 x 0.3 cm
 Description:
Photo: Joaquim Callén
 Viewed:  4122 Time(s)

Gold on Quartz from Aouint Ighoman detail.jpg



Gold on Calcite from Aouint Ighoman.jpg
 Mineral: Gold on Calcite
 Locality:
Aouint Ighoman, Assa-Zag Province, Guelmim-Oued Noun Region, Morocco
 Dimensions: Crystal: 0.5 x 0.2 cm
 Description:
Photo: Joaquim Callén
 Viewed:  4123 Time(s)

Gold on Calcite from Aouint Ighoman.jpg


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PostPosted: Feb 17, 2021 19:21    Post subject: Re: The native gold from Guelmim-Oued Noun, Morocco - (35)  

We keep studying the gold from Guelmim. The associated minerals tell us a history that, I hope, will be consistent with the geochemical context.
The gold is associated to a series of minerals, possibly related to the arid environment where the deposit is located:

-goethite/hematite. The association of gold with goethite is very common. The colloform goethite observed in the samples, mixed with gold layers is common in supergenic gold deposits. The iron oxides are also associated to aluminum hydroxides, silica and quartz grains.

- Chlorargyrite: Grains of AgCl are frequent in the sample. This could be surprising at first sight, but it is not at all. The Au is not alone in the Guelmim samples. Instead, the samples are composed with inhomogeneous gold-silver alloys, ranging from 1-5% silver to 28% silver. The richer silver regions of the samples also contains variable copper, up to 2%.
Silver, gold and lead are mostly mobilized in the form of halide complexes. as well as in the form of organic complexes. But geochemically, the halide complexes are really important. In an arid environment, fluids are very enriched in chloride. The formation of AgCl grains in the samples evidence the mobilization of silver (more reactive than gold) by the chloride-rich water.

- lead minerals: one peculiarity I found in the samples is the association of the gold with lead minerals: lead chloride (probably laurionite) and phosphohedyphane. Both are forming very small crystals associated to the goethite and the gold surfaces. Probably the origin of these minerals are related also to the arid environment, as lead is mobilized in the form of chloride complexes.

- copper-zinc alloy: In the gold surface are present exolutions, small inclusions and coatings of copper-zinc intermetallic compounds. The composition match with danbaite (CuZn2). It is interesting. I never found something similar in gold samples.



phosphohedyphane gold.jpg
 Mineral: Phosphohedyphane
 Description:
 Viewed:  2833 Time(s)

phosphohedyphane gold.jpg



sem gold pbcl2.jpg
 Mineral: Laurionite
 Description:
lead chloride crystals. Probable laurionite (not confirmed)
 Viewed:  2830 Time(s)

sem gold pbcl2.jpg



sem gold cu.jpg
 Mineral: Gold
 Description:
Inhomogeneity of the gold-silver proportion
 Viewed:  2836 Time(s)

sem gold cu.jpg


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