Revisiting the Côte d’Ivoire tektite strewn field

Abstract

The tektites of the Côte d’Ivoire strewn field, called “ivorites”, come from the Bosumtwi meteorite impact crater formed 1.07 Ma ago in Ghana. Unlike other tektite strewn fields in the world, this tektite strewn field has remained under-explored after the pioneering works of A. Lacroix in the 1930s who reported the first tektites on the African continent, followed by a few explorers in the 1960s. To date, the geochemical properties of only slightly more than 20 ivorites have been measured, while there are potentially thousands to be discovered by analogy with other strewn fields. Based on these earlier works, the ivorites strewn field is considered to form an ellipse of about 1500 km2 around the town of Ouellé and Daoukro, setting apart three isolated finds. We conducted six exploratory missions in Côte d’Ivoire between 2019 and 2023 and report 174 new finds. These discoveries are mostly within the known limits of the strewn field, but several discoveries outside these limits extend the strewn field to an area of 4100 km2. The furthest discovery considered to be part of the strewn field is more than 45 km south of its previous limits. These new ivorites present various shapes (teardrops, dumbbells, spheres, ellipsoids) with masses ranging from 1 to 96 g. A geochemical analysis of 172 of these ivorites was performed using a portable X-ray fluorescence spectrometer. In addition, 87 ivorites (unknown locations), made available by the SODEMI museum (Côte d’Ivoire's governmental mining development company in Abidjan) were also analyzed. Their geochemical composition is clearly distinct from that of tektites from other strewn fields. However, these analyses reveal a more variable chemical composition than the apparent homogeneity previously inferred from a small number of specimens. The magnetic susceptibility of these tektites, measured with the SM150 device, is homogeneous and the small variations are essentially related to the iron content. The measured density of ivorites is comparable to the pore-free densities estimated from their chemical composition, implying that the abundant vesicles commonly observed at the surface, associated with bubbles and degassing of the silicate melt, are not present in the interior.