Three-dimensional Fe speciation of an inclusion cloud within an ultradeep diamond by confocal µ-X-ray absorption near edge structure: evidence for late stage overprint.

ABSTRACT

A stream of 1-20 µm sized mineral inclusions having the negative crystal shape of its host within an "ultra-deep" diamond from Rio Soriso (Juina area, Mato Grosso State, Brazil) has been studied with confocal µ-X-ray absorption near edge structure (µXANES) at the Fe K and Mn K edges. This technique allows the three-dimensional nondestructive speciation of the Fe and Mn containing minerals within the inclusion cloud. The observed Fe-rich inclusions were identified to be ferropericlase (Fe,Mg)O, hematite and a mixture of these two minerals. Confocal µ-X-ray fluorescence (µXRF) further showed that Ca-rich inclusions were present as well, which are spatially separated from or in close contact with the Fe-rich inclusions. The inclusions are aligned along a plane, which most likely represents a primary growth zone. In the close vicinity of the inclusions, carbon coated planar features are visible. The three-dimensional distribution indicates a likely fluid overprint along an open crack. Our results imply that an imposed negative diamond shape of an inclusion alone does not exclude epigenetic formation or intense late stage overprint.