Trace elements in sulfide inclusions from Yakutian diamonds |
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| Authors: | G P Bulanova W L Griffin C G Ryan O Y Shestakova S-J Barnes |
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| Institution: | (1) Yakutian Institute of Geosciences, Lenin St. 39, Yakutsk 677007, Russia, RU;(2) CSIRO Exploration and Mining, Box 136, North Ryde, NSW 2113, Australia, AU;(3) Key Centre for Geochemical Evolution and Metallogeny of Continents, School of Earth Sciences, Macquarie University, Sydney 2109, Australia, AU;(4) Kemerovsky Polytechnic Institute, 30 Leningradsky Avenue, Kemerovo 650003, Russia, RU;(5) Sciences de la Terre, Universite due Quebec, Chicoutimi, Canada, G7H 2B1, CA |
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| Abstract: | Sulfide inclusions in diamonds may provide the only pristine samples of mantle sulfides, and they carry important information
on the distribution and abundances of chalcophile elements in the deep lithosphere. Trace-element abundances were measured
by proton microprobe in >50 sulfide inclusions (SDI) from Yakutian diamonds; about half of these were measured in situ in polished plates of diamonds, providing information on the spatial distribution of compositional variations. Many of the
diamonds were identified as peridotitic or eclogitic from the nature of coexisting silicate or oxide inclusions. Known peridotitic
diamonds contain SDIs with Ni contents of 22–36%, consistent with equilibration between olivine, monosulfide solid solution
(MSS) and sulfide melt, whereas SDIs in eclogitic diamonds contain 0–12% Ni. A group of diamonds without silicate or oxide
inclusions has SDIs with 11–18% Ni, and may be derived from pyroxenitic parageneses. Eclogitic SDIs have lower Ni, Cu and
Te than peridotitic SDIs; the ranges of the two parageneses overlap for Se, As and Mo. The Mo and Se contents range up to
700 and 300 ppm, respectively; the highest levels are found in peridotitic diamonds. Among the in-situ SDIs, significant Zn and Pb levels are found in those connected by cracks to diamond surfaces, and these elements reflect
interaction with kimberlitic melt. Significant levels of Ru (30–1300 ppm) and Rh (10–170 ppm) are found in many peridotitic
SDIs; SDIs in one diamond with wustite and olivine inclusions and complex internal structures have high levels of other platinum-group
elements (PGEs) as well, and high chondrite-normalized Ir/Pd. Comparison with experimental data on element partitioning between
crystals of monosulfide solid solution (MSS) and sulfide melts suggests that most of the inclusions in both parageneses were
trapped as MSS, while some high-Cu SDIs with high Pd±Rh may represent fractionated sulfide melts. Spatial variations of SDI
composition within single diamonds are consistent with growth histories shown by cathodoluminescence images, in which several
stages of growth and resorption have occurred within magmatic environments that evolved during diamond formation.
Received: 5 July 1995 / Accepted: 21 February 1996 |
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