First heavy mineral grains must be separated form the light minerals in placers. Then try it by a diamond-tester (can also be used for other HM) and opitcal spectral devices. The last decision has to be taken by the unarmed eye.

HGD

Dear Harald G.Dill thanks for your answer. these diamond grains are not inside the placers, and are located in the structure of ultramafic ophiolite rocks. first, they must be crushed to the appropriate size and then separated, but I don't know how this should be done.

Firstly how certain are you of diamond in the (presumably primary unmetamorphosed) ophiolite recognising that diamond requires high pressures for genesis typically ~25kb and cool geotherms whereas ophiolites are typically shallow

Dear Geoff Grantham

thank you very much for your answer. in recent years, much research has been conducted on finding diamonds grains in ophiolites rocks, especially in ultramafics rocks and chromitites, for example a study by Jingsui Yang and .. called (Peridotites, chromitites and diamonds in ophiolites) in 2021.

As you said, a number of minerals can be separated by magnetic separation, but the problem is whit iso-density and non-magnetic minerals, which I do not have the equipment to separate. Anyway thank you

Even if you suspect diamonds in ophiolites you should scout the environs of your sampling sites for diamonds or diamond marker heavy minerals. It is easier to deal with them tha with microdiamondsin magmatic rocks.

See Dill (2010)

1)Magmatic deposits

1)Diamond in komatiites, lamprophyres and other ultrabasicrocks (51b A)

2)Diamond in peridotites of ophiolite sequences (51c A)

3)Diamond deposits bound to kimberlites (51a A-51a F)

4)Diamond deposits bound to lamproites (51a E)

2)Sedimentary deposits

1)Placer deposits

1)Alluvial-fluvial and nearshore-marine modern diamond placer deposits (51a I)

2)Palaeoplacer diamond deposits (51b I)

3)Alluvial-fluvial carbonado placer (51c I)

3)Metamorphic deposits

1) Microdiamonds in impact structures (51a N)

2) Microdiamonds in high-pressure zones (51b N)

3) Microdiamonds in garnet gneiss (51b J)

4) Diamond in graphiteschist (51c J)

HGD

Yes, that's absolutely true, and I've even collected some placer and crushed some of ultramafic ophiolitic rocks, but the main problem is still the lack of proper equipment to separate minerals of the same density. and I'm looking for an available separation methods.

In placers it should be a lab-combination of various heavy liquids which you can use up to 4.25 g/cm3at 20 °C (Clerici Solution toxic !!) and (electro)magnetic separation if you can avail of a Frantz isodynamic separator. The Wilcke-hand magnet is a good alternative even if it is not such a comfortable device but much cheaper. The last batch of minerals you should screen for minerals under UV lamp of different wavelengths. This is the only way to tackle the problem. Apart from experience you need a lot of patience

I wish you much success

HGD

see also:

DILL H.G. ,  KHISHIGSUREN S.,  MAJIGSUREN Yo. BULGAMAA J., HONGOR O. and  HOFMEISTER, W. (2004) The diamondiferous peridot (olivine)-garnet deposit Shavryn Tsaram, Central Mongolia, with special reference to its placer deposits.- Gemmologie, 53: 87-104. (from the RG server on request)

Dear prof.

thank you for your guidance, I will try o consider all the issues and I will inform you of the results. Of course, this may take some time because it is time-consuming and I am currently looking for a geologist who will agree to perform the necessary analyses and present a joint paper together to complete my PhD thesis on copper mineralization in the Kermanshah ophiolites in Iran. thank you again for your guidance.

I did not know what devices you can avail of but this what I recommended (heavy liquids, hand-magnet adjustable regarding to the height above sample, a UV lamp and some tools for grain sorting) should be affordable.

I wish you much success

HGD

Thanks for your suggestion, I think I can use the tool you suggested here. It should be noted that the size of diamond grains in ophiolites is usually less than half a millimeter.

I agree with Geoff Grantham. Ophiolitic rocks are too oxidised to contain abundant (if any) diamond. This mineral is only stable at high depths and at relatively high temperatures typical of ophiolitic rocks it rapidly modify its structure into graphite or it reacts with more oxidised regions in the shallow mantle to transform into CO2 and eventually reacting with silicates to form magnesite (at P >3 GPa) or dolomite (at P 2-3 GPA) or to remain CO2 (at P

See classification of primary and secondary diamond deposits (%1cA)

1)Magmatic deposits

1)Diamond in komatiites, lamprophyres and other ultrabasicrocks (51b A)

2)Diamond in peridotites of ophiolite sequences (51c A)

3)Diamond deposits bound to kimberlites (51a A-51a F)

4)Diamond deposits bound to lamproites (51a E)

2)Sedimentary deposits

1)Placer deposits

1)Alluvial-fluvial and nearshore-marine modern diamond placer deposits (51a I)

2)Palaeoplacer diamond deposits (51b I)

3)Alluvial-fluvial carbonado placer (51c I)

3)Metamorphic deposits

1) Microdiamonds in impact structures (51a N)

2) Microdiamonds in high-pressure zones (51b N)

3) Microdiamonds in garnet gneiss (51b J)

4) Diamond in graphiteschist (51c J)

HGD

Dear prof. Michele Lustrino

Thank you for your attention.In an article titled (Peridotites, chromitites and diamonds in ophiolites, 2021) Jingsui Yang said that: "the presence of ultra-high-pressure mineral inclusions, such as microdiamonds, metal alloys, Mn silicates and coesites, in podiform chromitites and other ophiolitic mantle rocks offer evidence of deep and reduced formation conditions. The composition of ultra-high-pressure minerals, and especially the light carbon isotope composition of ophiolite-hosted diamonds, indicates a contribution of recycled crustal material to the mantle portions of ophiolites".

It is likely that the ultramafic ophiolite rocks, while ascending from the suprasubduction zone, passed through an environment suitable for the formation of diamond minerals and brought some of them to the surface and embedded them in the ophiolite sequence.

I also thank Professor Harald G.Dill for his attention.

It has been found that diamonds found in several of these paragenesis is related to the cutting and polishing techniques, not to real reduced conditions (which would be very anomalous in the shallow mantle).

Michele

What does not fit cannot be true !

This is true from politics to science

HGD

Dear prof. Michele Lustrino

Below are the number of articles on the subject, I hope they will be of interest to y:

J. Yang, Z. Xu, L.F. Dobrzhinetskaya, H.W. Green, X. Pei, R. Shi, et al. Discovery of metamorphic diamonds in central China: an indication of a > 4000 km long zone of deep subduction resulting from multiple continental collisions Terra Nova, 15 (6) (2003), pp. 370-379 View in ScopusGoogle Scholar

W. Bai, M. Zhou, P.T. Robinson Possibly diamond-bearing mantle peridotites and podiform chromitites in the Luobusa and Donqiao ophiolites, Tibets Can J Earth Sci, 30 (8) (1993), pp. 1650-1659 View at publisherCrossrefGoogle Scholar

J. Yang, P.T. Robinson, Y. Dilek Diamond-bearing ophiolites and their geological occurrence Episodes, 38 (4) (2015), pp. 344-364 View at publisherCrossrefView in ScopusGoogle Scholar

D. Lian, J. Yang, D. Yildirim, W. Wu, Z. Zhang, F. Xiong, et al. Deep mantle origin and ultra-reducing conditions in podiform chromitite: diamond, moissanite, and other unusual minerals in podiform chromitites from the Pozanti–Karsanti ophiolite, southern Turkey Am Mineral, 102 (5) (2017), pp. 1101-1113 View in ScopusGoogle Scholar

Y. Chen, J. Yang, Z. Xu, Y. Tian, S. Lai Diamonds and other unusual minerals from peridotites of the Myitkyina ophiolite, Myanmar J Asian Earth Sci, 164 (2018), pp. 179-193 View PDF View articleGoogle Scholar

W. Wu, J. Yang, C. Ma, I. Milushi, D. Lian, Y. Tian Discovery and significance of diamonds and moissanites in chromitite within the Skenderbeu massif of the Mirdita zone ophiolite, West Albania Acta Geol Sin, 91 (3) (2017), pp. 882-897 View at publisherCrossrefGoogle Scholar

S. Das, A.R. Basu, B.K. Mukherjee In situ peridotitic diamond in Indus ophiolite sourced from hydrocarbon fluids in the mantle transition zone Geology, 45 (8) (2017), pp. 755-758 View in ScopusGoogle Scholar

D. Howell, W.L. Griffin, J. Yang, S. Gain, R.A. Stern, J. Huang, et al. Diamonds in ophiolites: contamination or a new diamond growth environment? Earth Planet Sci Lett, 430 (1) (2015), pp. 284-295 View PDF View articleView in ScopusGoogle Scholar

J. Yang, P.T. Robinson, Y. Dilek Diamonds in ophiolites Elements, 10 (2) (2014), pp. 127-130 View at publisherCrossrefView in ScopusGoogle Scholar

Cheers,

arsalan