Isotopic Signatures of Carbon in the ‘Los Pobres’ Graphite Mine, Ronda, Spain
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Oxford University Press
Ronda peridotitesGraphite formation temperatureRaman spectroscopyCarbon isotopesFluid inclusions
Anna Neubeck, Curt Broman, Magnus Ivarsson, Nils G Holm, Martin Whitehouse, Sara Nilsson, Wolf Geppert, Fernando Gervilla, Isotopic Signatures of Carbon in the ‘Los Pobres’ Graphite Mine, Ronda, Spain, Journal of Petrology, Volume 61, Issue 4, April 2020, egaa042, [https://doi.org/10.1093/petrology/egaa042]
SponsorshipSwedish Research Council 2013-7320 2012-4364 2017-05018 2017-04129; Villum Investigator Grant 16518
Graphite formation temperatures in the ‘Los Pobres’ mine within the Ronda peridotite, Spain, previously reported to be between 770 and 820 °C, have been reinterpreted based on new temperature measurements using Raman spectroscopy. Additional in situ and bulk stable carbon isotopic measurements and fluid inclusion studies contributed to improved understanding of parts of the graphite formation process. Raman spectroscopy revealed that the formation of the ‘Los Pobres’ graphite extends to temperatures as low as 500 °C, indicating a broader temperature range than previously reported. Stable carbon isotopes and temperature estimates suggest two different crystallization events, followed by a late hydrothermal alteration of the host rock. The first event occurred at temperatures higher than ∼600°C, in which crystalline graphite was formed with a mixed 13C composition as a result of the mixing of two different carbon-bearing sources. The second graphite formation event took place below ∼600°C, within the same system, but with lower purity and crystallinity of the graphite. In the third event, the temperature decreased to less than 550 °C, and hydrothermal fluids altered the host rock, precipitating silica and iron oxides in veins penetrating both the host rock and the deposited graphite.