HR: 1400h
AN: V33B-03    [Abstracts]
TI: Quantitative Analysis of Trace Element Impurity Levels in Some Gem-Quality Diamonds
AU: * McNeill, J C
EM: j.c.r.mcneill@durham.ac.uk
AF: University of Durham, Dept. Earth Science, NCIET, South Rd, Durham, Durham City, DH1 3LE, United Kingdom
AU: Klein-BenDavid, O
EM: ofrak1@googlemail.com
AF: The Hebrew University, Institute of Earth Science, Jerusalem, Israel, 91904, Israel
AU: Pearson, D G
EM: d.g.pearson@durham.ac.uk
AF: University of Durham, Dept. Earth Science, NCIET, South Rd, Durham, Durham City, DH1 3LE, United Kingdom
AU: Nowell, G M
EM: g.m.nowell@durham.ac.uk
AF: University of Durham, Dept. Earth Science, NCIET, South Rd, Durham, Durham City, DH1 3LE, United Kingdom
AU: Ottley, C J
EM: c.j.ottley@durham.ac.uk
AF: University of Durham, Dept. Earth Science, NCIET, South Rd, Durham, Durham City, DH1 3LE, United Kingdom
AU: Chinn, I
EM: Ingrid.Chinn@debeersgroup.com
AF: De Beers Geoscience Centre, South Africa, South Africa
AU: Malarkey, J
EM: jacqueline.malarkey@durham.ac.uk
AF: University of Durham, Dept. Earth Science, NCIET, South Rd, Durham, Durham City, DH1 3LE, United Kingdom
AB: Perhaps the most important information required to understand the origin of diamonds is the nature of the fluid that they crystallise from. Constraining the identity of the diamond-forming fluid for high purity gem diamonds is hampered by analytical challenges because of the very low analyte levels involved. Here we use a new ultra- low blank 'off-line' laser ablation method coupled to sector-field ICPMS for the quantitative analysis of fluid-poor gem diamonds. Ten diamonds comprised of both E- and P-type parageneses, from the Premier Mine, South Africa, were analysed for trace element abundances. We assume that the elemental signatures arise from low densities of sub-microscopic fluid inclusions that are analogous to the much higher densities of fluid inclusions commonly found within fluid-rich diamonds exhibiting fibrous growth. Repeatability of multiple (>20) blanks yielded consistently low values so that using the current procedure our limits of quantitation (10-ċ blank) are <1pg for most trace elements, except for Sr, Zr, Ba, from 2-9pg and Pb ~30pg. Trace element patterns of the Premier diamond suite show enrichment of LREE over HREE. Abundances broadly decrease with increasing elemental compatibility. As a suite the chondrite normalised diamond patterns show negative Sr, Zr, Ti and Y anomalies and positive U, and Pb anomalies. All sample abundances are very depleted relative to chondrites (0.1 to 0.001X ch). HREE range from 0.1 to 1ppb as do Y, Nb, Cs. Other lighter elements vary from 2-30ppb. Pb reaches several ppb and Ti ranges from ppb values up to 2ppm. No significant difference were observed between the trace element systematics of the eclogitic and peridotitic diamonds. Overall, these initial data have inter-element fractionation patterns similar to those evident from fluid-rich fibrous diamonds and can be sued to infer that both types of diamond-forming fluids share a common origin.
DE: 3620 Mineral and crystal chemistry (1042)
DE: 3621 Mantle processes (1038)
SC: Volcanology, Geochemistry, and Petrology [V]
MN: 2009 Joint Assembly