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gold panning
  
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Roger Warin




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PostPosted: Dec 19, 2019 15:01    Post subject: gold panning  

Hi,
What do you think of the origin of these golden sphere?
The discoverer (gold panning) interprets them as having a human origin.
This dates from the Celts who were thus the first gold smelters.
The gangue would not be quartz but slag.



86-figure 14 bille-ter_R.jpg
 Mineral: Gold
 Locality:
Ardennes Region, Belgium
 Dimensions: 0,1 mm diam.
 Description:
not on quartz
 Viewed:  1172 Time(s)

86-figure 14  bille-ter_R.jpg


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jose luis jara jara




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PostPosted: Dec 19, 2019 15:24    Post subject: Re: gold panning  

What a beautiful golden ball
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Pete Richards
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PostPosted: Dec 19, 2019 15:43    Post subject: Re: gold panning  

It should be pretty easy to tell quartz from slag (glass) optically.... Index oil ~1.5 under crossed polarizers.
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Collecting and studying crystals with interesting habits, twinning, and epitaxy
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Roger Warin




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PostPosted: Dec 19, 2019 16:01    Post subject: Re: gold panning  

Thank you, Pete.
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mmauthner




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PostPosted: Dec 21, 2019 05:06    Post subject: Re: gold panning  

Hi Roger,

I think your sphere is very possibly quite natural.

Spherical gold is very interesting and not unheard of. I mention two localities producing spherical crystals in British Columbia in our (Carl Francis is my co-author) article on BC gold in Rocks & Minerals magazine [2006 Vol. 81(1)14-22].
What is very intriguing about the Harrison Lake locality is that razor sharp octahedra, with or without equally sharp modifying forms, can accompany a quasi-to near-perfect spherical crystal in the same vug. Why one crystal has 'more common' forms and another is spherical is boggling.

I should mention that in the attached photo, the sphere was rattling around in the vug when Ty had etched the calcite out. In picking away at the sides to better view the octahedron, the sphere fell out, so Ty glued it back in place where he first saw it. It was his guess that the sphere was never attached to the quartz as it has no point of attachment on it, but rather 'floated' in the calcite. The glue can be seen at the lower left of the sphere, where it meets the quartz.

We have found other spheres as well, some attached to the quartz, some not. This specimen was one of the few where the 'normal' crystal was so close to the sphere and truly in the same vug.

Best,
Mark



Harrison Au octo-sphere.jpg
 Mineral: Gold
 Locality:
Harrison Gold Mine, Bear Mountain, Harrison Lake, Chilliwack, Regional District Fraser Valley, British Columbia, Canada
 Dimensions: sphere = 0,4 mm across
 Description:
 Viewed:  1023 Time(s)

Harrison Au octo-sphere.jpg


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Pete Richards
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PostPosted: Dec 21, 2019 09:13    Post subject: Re: gold panning  

A possible explanation for the occurrence of spheres next to well-formed octahedra is that the spheres are polycrystalline - analogous to wavellite. This, of course, is not a full answer, because then the question becomes, why did one form as a single crystal and the other form as an aggregate of many crystals. Such a question is probably unanswerable....

Testing this idea might well require special x-ray techniques, as several recent papers by John Rakovan and others have shown.

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lluis




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PostPosted: Dec 21, 2019 10:15    Post subject: Re: gold panning  

Hi, All

Some time ago, I read in Mineralogical Record, if my memory serves me well, that nuggets in the Mother Lode were seen that show a concentric structure (layers over layers), and I have also read that seems that small nuggets dissolve to make the bigger ones grow.
Chemically it is not a wonder, but maybe it could explain the balls: just concretions of gold over a nucleus, as happens with natural pearls..
Why pearls and not crystals?
I think that is just a matter of conditions .....

With best wishes

Lluís
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Roger Warin




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PostPosted: Dec 22, 2019 00:31    Post subject: Re: gold panning  

Hi Pete, Mark, LLuis,

On Christmas Eve, chance makes us think of the gold of the Three Kings ...
At the Show of Saint-Marie-aux-Mines (June 2018), there was an exceptional exhibition which showed gold and its nuggets associated with minerals of similar shape, without chemical relationship between them. Only an aesthetic comparison. This exhibition closed with the presentation of gold specimens in pseudomorphoses of pyrite, from Bodaybo, Russia.

I tried to understand the genesis of this golden octahedron in pseudomorphose of pyrite. I didn't find anything that seemed interesting to me. I was thus led to search myself and I published in the small review AGAB-Minibul - 2018 - Vol. 51 (8) pp. 208-209, my hypotheses. I submit them to your criticism, because in fact it is a question of explaining the geological origin of gold nuggets.

Such gold pseudomorphoses after pyrite are very rare. The absence of a single lattice differentiates these pseudomorphoses from an octahedral crystal of gold (another possibility but which cannot be envisaged because of the absence of a lattice here). But what are the physicochemical relationships that exist between gold, which we know the nobility of its character, and pyrite, mad gold (l’or des fous, in French), an ersatz FeS2? It is necessary to reexamine the primordial properties of these elements: Au, Fe and S.
Under certain conditions, their siderophilic character appears. Sulfur likes iron, gold likes iron. In contrast, lithophilic rocks are hungry for oxygen like in silicates or oxides.

Because of its siderophile and chalcophile (copper-like) character, sulfur extracts copper and iron (and other similar elements). These are the primary ores often made up of sulphides. Sulfur is said to be a mineralizing agent.
As for gold, it is probably mobilized by thio-bacteria which find the sulfur of their constitution in pyrite and abandon gold there by tiny increments on this compatible familiar ground. Pyrite, however, retains its tendency to crystallize in a pure state. Excess impurities foreign to the FeS2 composition will therefore be rejected. In this case, the gold-bearing thio-bacteria, that is to say gold, are found on less densely populated sites, namely the edges and especially the summits of the pyrite crystal. The consequence is that the crystal is thus shielded by a breastplate of tiny grains of gold.

During the subsequent alteration of the pyrite carrying its impurities, FeS2 disappears and there remains only this gold aggregate, tiny disordered crystals which seem to be a coherent assembly, whereas they are only the residues of an octahedron of pyrite that carried them. This formation is exceptional since it would suppose the presence of thio-bacteria which would mobilize the diffuse colloidal gold present in any pegmatite.

As for them, the gold nuggets would result from the same collection but by non-sulfur bacteria, in a lithophilic medium. This is a magnificent example of the chemical duality that exists between sulfur and oxygen, two elements produced in abundance by stellar nucleosynthesis. They are close to each other but the size of the atoms is so different that the nature of the bonds has evolved differently. The subject will eventually be taken up in a discussion on the terrestrial nucleus, far too light to be made up only of iron and nickel. Sulfur is introduced in large quantities.

This is what I wrote in 2018. In fact, the association of tiny gold grains of a sphere would be done as suggested by Pete "the spheres are polycrystalline" like the aggregation of the crystalline germs in pyrite. I would like to know your opinion, because I did not find in Belgium adherents to my thought!
By extension, I also believe that the nuggets are the fruit of this type of aggregate, possibly reheated and compressed under geological conditions.

PS: The amount of gold in the Earth's lithosphere is small, compared to the mass received during the differentiation of the planet. Almost all of the gold has been carried by sulfur to the central core. Relatively little gold remains, scattered in the silicate rocks. These latter particles would not have been able to aggregate if no other concentration process had taken place, in fact the influence of sulfur or non-sulfur bacteria. These are the basis for the formation of colloidal gold which was then set in motion by hydrothermal fluids. This is the reason why gold is often found associated with quartz, soluble under these hydrothermal conditions. Then these deposits of colloidal gold were remelted by the high temperatures, thus leaving the crystalline gold, rid of its biologic memory.

I think that the biologic memory of the grains of gold is precisely the ovoid or globular texture with flaky scales.

Thanks for reading me.
Roger.



8-Pseudo-pyrite_20490_R.jpg
 Mineral: Gold after Pyrite
 Locality:
Bodaibo, Irkutskaya Oblast', Prebaikalia, Eastern-Siberian Region, Russia
 Description:
 Viewed:  897 Time(s)

8-Pseudo-pyrite_20490_R.jpg


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