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The Genesis of Blue Diamonds
Lucille Daver, Helene Bureau, Eloise Gaillou, E. Boulard, Benoît Baptiste, Oulfa Belhadj, Nicolas Guignot, Eddy Foy, Pierre Cartigny, Daniele L. Pinti
To cite this version:
Lucille Daver, Helene Bureau, Eloise Gaillou, E. Boulard, Benoît Baptiste, et al.. The Genesis of Blue Diamonds. 2019 Diamond Conference, Jul 2019, Warwick, United Kingdom. �hal-02506335�
[1] Gaillou, E., Post, J. E., Rost, D., & Butler, J. E. Boron in natural type IIb blue diamonds: Chemical and spectroscopic measurements. American Mineralogist, 97 (1), 1-18 (2012). [2] Smith, E. M., Shirey, S. B., Richardson, S. H., Nestola, F., Bullock, E. S., Wang, J., & Wang, W. Blue boron-bearing diamonds from Earth's lower mantle. Nature, 560 (7716), 84-87 (2018).
Acknowledgment:
We thank GEOTOP, FRQNT international internship scholarship and the Diamond Conference Young Researcher Award for their funding. The SEM facility of IMPMC is supported by Région Ile de France Grant SESAME 2006 NOI-07-593/R, INSU-CNRS, INP-CNRS, UPMC, and by the French National Research Agency (ANR) Grant ANR-07-BLAN-0124-01. We thank M. Guillaumet for his assistance during FTIR measurements, and Christophe Sandt and Ferenc Borondics from the SMIS beamline at SOLEIL synchrotron for their support during Raman mapping. We thank Ludovic Delbes, Philippe Rosier and the cellule projet from IMPMC for their assistance during the preparation for XRD experiments.
References
Materials
Cullinan mine in South Africa
Boron: 0.22 to 0.38 ppm B
Four diamonds:
1 x3 mm for ~0.10 ct
- Two with primary inclusions
- Two with primary and secondary inclusions
B8-1 600 µm
B16-1 1000 µm
1200 µm
B18-1
800 µm
B20-1
Boron content measurement:
- Infrared spectroscopy (FTIR)
Mineral phase identification:
- µ-raman spectroscopy (532 nm)
- Synchrotron X-Ray diffraction
Methodology: in situ investigations
C B
Boron would be inherited from slab dehydration and carried to lower mantle (>660 km) in dense hydrous silicate minerals (DHMS).
It is proposed that blue diamonds are of ultra-deep origin, from the lower mantle, and exclusively formed in subduction settings [2] .
Boron cycle in the mantle is realtively unknown and the study of these boron-bearing diamonds brings new insights on this deep cycle.
Introduction:
Blue diamonds are among the rarest type of gems : <0.1% of the extracted diamonds. Mainly from South Africa (Cullinan mine) and India (Kollur mine), ±
Central Africa, South America and Borneo.Their blue color is due to trace amounts of boron in the lattice structure and the near absence of nitrogen, thus
defined as type IIb diamonds [1].
The Genesis of Blue Diamonds
4IRAMIS
6IRAMIS
71
2
1
3
5
2
1, * 2 3 2 2
Lucille Daver , Hélène Bureau , Eloıs̈e Gaillou , Eglantine Boulard , Benoit Baptiste , Oulfa
4 5 6 7 1
Belhadj , Nicolas Guignot , Eddy Foy , Pierre Cartigny and Daniele L. Pinti
¹GEOTOP, University of Quebec in Montreal, Canada, ²IMPMC, Sorbonne Université, France, ³Mines ParisTech, PSL Research University, France, ⁴Center for Research on the Preservation of Collection, National
Natural History Museum, France, Synchrotron Soleil, France, ⁶LAPA-IRAMAT, University of Paris-Saclay, France, ⁷Stable Isotope Geochemistry Laboratory, Institut de Physique du Globe de Paris, France.
5*Correspondence: daver.lucille@uqam.ca
Discussion
Mineral assemblage: Inclusion of Ilmenite : Eclogitic paragenesis at lithospheric depth
Forming fluid: Primary and secondary inclusions may be the witness of a H 0-C
2 graphiteparent fluid
Inclusion of walstromite (retrogressed Ca-Perovskite (CaTiO3) ; >9 Gpa): Sub-lithospheric depth
Boron: inherited from sea water through the subduction zone : H 0 + C
2 organic+ boron, available in the
lithosphere after slab dehydration: Data suggest a deep recycling of marine fluids that may be the the
parents of blue diamonds
We suggest that blue diamonds are not exclusively ultra-deep and may form at any depth in the
mantle, from lithosphere (>150km) down to the lower mantle (~750 km), in subduction-related B-C-
H O-rich fluids.
23
2
1
4
Oceanic lithosphere Continental
lithosphere
410 km
660 km Transition zone
Lower mantle 2.5
3
or serpentinite to DHMS and 2.5 DHMS breakdown and realease boron [2]
4: bring to surface throught kimberlite eruption
2: Water and boron release during slab dehydration
1: Seawater (H2O + C + B) throught subduction
3: Growth of B-bearing diamond
A unique water-C- rich fluid present in both primary and secondary inclusions
Two-phase inclusions
+ Inclusions of CaSiO3-walstromite
3200 3600 3800
3000 3400 4000
2800
B8-1-inclu07-013355 2900
2967 3247 3450 B8-1-inclu-01-02
B8-1-inclu03-02
3185 3480 2930
Water area Methane
3630 3000
10µm 15µm
10 µm
2905
Inclusions II
Raman shift (cm )-1
2000
1600 1800 2200 2400 2600 2800 3000
Intensity
Graphite ref.
Diamond ref.
1580 2725
2450 2660
C=O 1840
2450 CO 2660
2190
10 µm
10 µm
Central Hexagonal Mineral Outer Colorless Halo
Inclusions I
Results
+ Ilmenite (FeTiO )
350µm B20-1-2
50µm
B18-1
Diamond ref.
2000
1500 2500 3000 3500
Raman shift (cm )
-1Intensity
Graphite ref.
Water area
1584 2727
3253 1587
3258 2733
B18-1 B20-1-2