Tomlinson, E.L. and Jones, A.P. and Milledge, J. and Beard, Andy (2003) Multiple fluids in diamond coat and their role in diamond growth. In: Eighth International Kimberlite Conference, 2003, Victoria, Canada. (Unpublished)
Abstract
This work is an assessment of the role of fluids in diamond growth using mantle fluid compositions measured in micro-inclusions in coated diamond. Coated diamonds comprise a clear octahedral core surrounded by an overgrowth of inclusion-rich octahedral diamond. Navon and Hutcheon [1] recognized that micro-inclusions contain fluids rich in H2O, CO32-, SiO2, K2O, CaO and FeO, present in bulk proportions that resemble potassic magmas. Schrauder and Navon [2] studied the composition of individual inclusions, noting that they vary linearly between a carbonatitic and a hydrous end-member. A third fluid type, a KCl brine, was identified in cloudy diamonds [3], this fluid was thought to be distinct from the two end-members described in fibrous diamonds. EMPA AND FTIR DATAElectron-microprobe and infrared spectroscopy results for coated diamonds from the Democratic Republic of Congo, indicate that all 3 fluids are present in the diamond micro-inclusions. The fluid compositions lie along two continua (figure 1): Carbonatite-Silicate Series: Span a continuum between 1) a carbonatite-like (rich in CaO, P2O5, FeO and MgO) and 2) an alkali silicate (rich in SiO2, Al2O3, K2O and TiO2) end-member with roughly K-feldspar stoicometry. SiO2 correlates with the other major elements, suggesting a mixing relationship. The presence and abundance inclusions without K-Cl indicates that these end-members mixed before the involvement of K-Cl. K-Cl fluid-Silicate Series: Span a continuum between 1) the alkali silicate end-member and 2) an end member rich in K and Cl. There is a positive correlation between Cl and K2O (also between Cl and Na2O), but the trends for the other major elements are the same as the carbonatite-silicate series. The calculated Cl end-member composition is similar to the ìbrineî identified in cloudy diamonds [3]. These inclusions are preferentially located at the core-coat boundary, suggesting that the K-Cl fluid is involved early in coat growth. A fourth fluid end-member, rich in sulfur, has also been identified (figure 1). Diamonds whose bulk inclusion compositions fall towards the silicate end-member contain more H2O than the carbonatite-like end-member. Figure 1: Individual inclusion compositions grouped into series. ♦- Carbonatite-silicate series; ! - Silicate K-Cl series; ! - S-rich. Also shown, - calculated series end-member compositions, and published data for inclusions in fibrous diamond: ♦- Zaire and Botswana [1]; " - Jwaneng, Botswana [2]; ♦- Brine in cloudy diamond, Koffiefontein, South Africa [3].
Metadata
| Item Type: | Conference or Workshop Item (Paper) |
|---|---|
| School: | Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences |
| Depositing User: | Sarah Hall |
| Date Deposited: | 10 Jun 2019 15:17 |
| Last Modified: | 02 Aug 2023 17:51 |
| URI: | https://eprints.bbk.ac.uk/id/eprint/27775 |
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