The mineral is not well displayed, but it should be pyrite. Pyrite is common in certain granitic rocks as late-stage or alteration mineral.

I am sorry in the images i dont see any shining golden mineral, a few flakes of muscovite/ biotite are visible.

the predominant dark colored may not be biotite as it is not flaky

it could be either amphibole-pyroxene or may be tourmaline?

Hakima:

The NE part of lower image certainly shows specks of Golden-yellow lustre. You need to get petrographic thin section of the rock made to readily determine different mineral components and also confirm the GRANITE nature of the rock. You need to firmly establish if you are dealing with "Fool's Gold" (Pyrite) or actual Gold grains usually found in Quartz veins of granitoid rocks. Have a look at this link:

https://www.terrapub.co.jp/journals/GJ/pdf/3705/37050567.pdf

Best

Syed

Dear all,

Many thank for your reactivity, time and interest. 

I will prepare a thin section and tell you the result.

Syed thank you so much for the link it was very interest.

Cordially,

Hakima

Dear Hakima,

The shining one  may be flaky Biotite or Pyrite. Along the river section or called alluvial Placer deposit, Its common you may get Pyrite with in Granite. Also after thin section, If its pyrite, then you may go for EPMA analysis to see the Au contents within Pyrite. 

Dear Sagar,

So my sample can contents the Au within Pyrite..! I'm so happy to read this. I hope that the thin section can identify the existence of Au.

Many thank for your reactivity, time and interest.

With all the best,

Hakima

probably this mineral ,is the alteration biotite?

Dear Reza,

It should be true, but it is golden and shining with the sun.

Many thank for your reactivity, time and interest.

Best regards

Hakima

Dear Hakima,

For the upper image (20161015_1505_29.jpg) (see the zoom),  I think that the shining mineral is a pyrite.

For the Lower image (see the zoom), I think that is just a flackes of Biotite (if not an amphibole) and muscovite. Biotite is broken here and is altered.

You can prepare a thin section to detrmine the mineral assemblages and also prepare a polished thin section if you want to be sure that shining mineral is really pyrite.

Here, I attached for you the zoom for each mineral.

Good Luck.

Best wishes.

Add your answer

In order to have gold or pyrite in a granitic rock, one should be able to see a vein cutting across. However, there is no such veins visible in this rock. Gold, if any, will be introduced by hydrothermal solutions that cut across granite soon after the rock solidifies.

Dear Hakima

In order to understand the gold mineral in your samples, it is better to prepare a thin section. As I can see in your sample there is no alteration zone or vein cutting across.  

Best regards

Mansour

Dear all,

pyrite could easily be discriminated megascopically from gold by hardness and other optical and physical properties. No thin section required for this business. Anyway, that the mineral represents gold is million times less likely than being an iron sulfide. Granite is not a common host of free gold. On the other hand, alteration of mica (biotite etc.) may readily free up iron which, in the presence of sulfur contained in the alteration fluid, may form pyrite. Not a big deal and frequently reported for granitic and other rocks.   

H.-J. Foerster:

Your statement: "pyrite could easily be discriminated megascopically from gold by hardness and other optical and physical properties", in this particular case, sounds misleading, as based on just a tiny piece of this rock such tests are not practically feasible. We have no data of field from where the rock piece was collected, and whether there was also a vein in Granite, but it must be realized that about 50% of Igneous rocks including Granite do contain Gold and require more sophisticated tests. Thin section was primarily recommended to confirm Granite. Kindly have a look at this classic link:

http://pubs.usgs.gov/circ/1969/0610/report.pdf

Best

Syed

I have nothing to add and stop discussing this issue.

 H.-J.Foerster:

Thanks for your prompt response but regret that we could not benefit from your expertise.

Vielen Dank

Syed

hii all, Its so much interesting regarding the discussion of  gold content in Pyrite.

As there are many Granite hosted gold deposits discovered so far, hence its may be a chance.

If any shear zone cut across the river, then there may be a chance of getting  small piece of granite, Which may contain gold content(ppm) with in Pyrite, which may be confirmed by EPMA analysis.

These two handpiece photos are simply not suitable for any "exact" diagnosis or determination of a small glittering spot.

If at all, a polished thick section or a polished thin section is required for that diagnosis. If this golden mineral is actually opaque, it could be not only pyrite, but also pyrrhotite and/or chalcopyrite. If this "golden shining mineral" is translucent, it could also be altered biotite or muscovite = fools gold!

Hakima did not say gold, but golden mineral; i.e. the colour is golden as I undersstood the question. Consequently, pyrite (as discussed by others above) is golden. Also, sericite (altered mica) is also golden.

Regards

Dear all,

Many thanks for your reactivity, time and interest.

Really, i'm very glad to benefit from your discussion and expertise.

When the thin section is prepared, i will post the pictures associates.

Best regards,

Hakima

I am with Günter: Looks like "fools-gold" (alterated biotite).

Regards, Udo

Hakima:

As we eagerly look forward to the results of your analysis, this link and the video therein may be of interest to you for understanding "Fool's Gold".

https://www.thermofisher.com/blog/mining/pyrite-the-real-story-behind-fools-gold/

Best

Syed

Dear Syed,

Thank you for the link it was very interesting.

So the  Pyrite is called “Fool’s Gold” because it resembles gold to the untrained eye. 

Best regards,

Hakima

While you are waiting for the lab results here is a picture of altered granite with a quartz vein and a small speck of bright and shiny gold (not fool's gold, but real gold). Notice also a bit of pink orthoclase (an alteration mineral that often accompanies gold).

The answer is reflection at  the surface of the minerals with metalic element contents

Dear Hakima,

The simplest way to identify the shining mineral is to scratch small amount of it and to analyze the powder by X-ray diffractometry.

Best regards,

Irina Marinova

Dear Irina,

Thank you so much for your sugestion. Unfourtunatly we don't have X-ray diffractometry in our university. All i can do it is to preparing a thin section.

Cordially

Hakima

What shiny golden mineral - it needs a better photo than that to ask the question :-) ? I can't see any.

I assume you do not mean biotite weathered to a golden colour - I have seen people make that mistake but of course biotite has strong basal cleavage that you can prise open with a needle or thin knife blade. Impossible to know from the photo, but I would have thought the mafics might be more amphibole, with some plates of weathered biotite (guessing). , You do not give details like hardness, streak etc  (eg pyrite has a black streak but so do other things). If you can make a flat face and polish it, often it is possible to then scratch it with a needle under the microscope and see how soft it is and its streak colour.