ORIGINAL PAPER Deformation-related spectroscopic features in natural Type Ib-IaA diamonds from Zimmi (West African craton) Karen V. Smit 1 & Ulrika F. S. D’Haenens-Johansson 1 & Daniel Howell 2,3 & Lorne C. Loudin 1 & Wuyi Wang 1 Received: 29 November 2017 /Accepted: 2 May 2018 # Springer-Verlag GmbH Austria, part of Springer Nature 2018 Abstract Zimmi diamonds (Sierra Leone) have 500 million year mantle residency times whose origin is best explained by rapid tectonic exhumation to shallower depths in the mantle, associated with continental collision but prior to kimberlite eruption. Here we present spectroscopic data for a new suite of Zimmi sulphide-bearing diamonds that allow us to evaluate the link between their spectroscopic features and their unusual geological history. Cathodoluminesence (CL) imaging of these diamonds revealed irregular patterns with abundant deformation lamellae, associated with the diamonds’ tectonic exhumation. Vacancies formed during deformation were subsequently naturally annealed to form vacancy clusters, NV 0/- centres and H3 (NVN 0 ). The brownish-yellow to greenish-yellow colours observed in Zimmi Ib-IaA diamonds result from visible absorption by a combination of isolated substitutional nitrogen (N 0 S ) and deformation-related vacancy clusters. Colour-forming centres and other spectro- scopic features can all be attributed to the unique geological history of Zimmi Ib-IaA diamonds and their rapid exhumation after formation. Keywords Zimmi diamond . Type Ib-IaA . Spectroscopy . Isolated nitrogen . West African craton . Deformation Introduction Type Ib diamonds contain abundant neutrally-charged isolat- ed substitutional nitrogen (C centre, N 0 S ) and account for less than 0.1% of natural diamonds (Harlow 1998). This rarity is because over geological time and at temperatures typical of the cratonic lithosphere, isolated nitrogen aggregates to A centres (N pairs) and B centres (4 N around a vacancy). Preservation of N 0 S in natural diamonds is normally explained through either short mantle residency times or storage at T < 700 °C (Taylor et al. 1996), whereas most cratonic diamonds are billions of years old and resided at >1000 °C (Stachel and Harris 2008; Shirey and Richardson 2011). The Zimmi alluvial locality (West African craton) is known for producing yellow Ib-IaA resorbed diamonds with abundant sulphide inclusions (Shigley and Breeding 2013; Smit et al. 2016). Rhenium-Os age constraints obtained for sulphide-bearing Zimmi diamonds (Smit et al. 2016) indi- cate that these diamonds did not have short mantle residency times and were not related to any Jurassic kimberlite activity common in this part of the West African craton (Skinner et al. 2004). Ten sulphides in three diamonds had Re-Os isotopic compositions that plot along 650 Ma age arrays (Smit et al. 2016). Since most of the known kimberlites in the Man shield erupted around 150 Ma (Skinner et al. 2004, and references therein), it implies that the Zimmi diamonds resided in the mantle for around 500 million years. At tem- peratures in the local diamond stability field (T > 850 °C; Smit et al. 2016), N 0 S would not remain unaggregated for 500 million years, so a mechanism is needed to bring the diamonds to shallower depths (i.e., cooler temperatures) in the West African lithosphere. Editorial handling: L. Nasdala Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00710-018-0587-6) contains supplementary material, which is available to authorized users. * Karen V. Smit ksmit@gia.edu 1 Gemological Institute of America, 50 West 47th Street, New York City, NY 10036, USA 2 Dipartimento di Geoscienze, Università degli Studi di Padova, Via G. Gradenigo 6, 35131 Padova, Italy 3 Diamond Durability Laboratory, 580 5th Ave, New York City, NY 10036, USA Mineralogy and Petrology https://doi.org/10.1007/s00710-018-0587-6