Abstract

Fluids extracted from two Type I and one Type II diamonds from the Panna mine of India have been analyzed by mass spectrometry. Two extraction methods were used. In the first, each crystal was crushed at 200°C in the high vacuum inlet of a high-sensitivity mass spectrometer. In the second, gases were released by graphitizing selected crushed fragments with a rhenium heater operated at about 3000°C under high vacuum. Gas compositions varied between the three crystals and the two methods, but they are qualitatively consistent. The compositions are also qualitatively consistent with those reported earlier for diamonds from other global locations. The range in volume percent for major constituents released by crushing are H2 (58.5–65.3), H2O (10.8–26), CO (tr–2.7), CO2 (9.9–18.3), CH4 (5.4–10), N2 (tr–1.2), and by graphitization, H2 (41.1–45.3), H2O(20.9–28.5), CO(5.5–6), CO2 (12.1–16.4), CH4 (4.4–12.7), N2 (2.7–3.7). Average H, O, C, and N atomic percents from crushing and graphitization are, respectively, 73.6, 17.4, 8.4, 0.6; and 64.5, 17.5, 16.0, and 2.0. Hydrogen was the most abundant compound found by both methods of extraction, and it was more abundant in the Type II diamond than in the Type I diamonds. A positive qualitative correlation was found between N2 and CO contents and anomalous birefringence. Variations in entrapped fluid composition with diamond crystal form and source locations are discussed in terms of diamond crystallization depth in the upper mantle, the redox state, and the age of diamond crystallization. The H2:H2O ratio found in the occluded fluid of Indian diamonds can be interpreted as supporting a molten iron–silicate equilibrium in the mantle at the time of the Earth’s core formation.

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