SINDIA followed a multi-step approach whereby micro-X-ray diffraction, tomographic techniques and fluorescence were combined to deeply characterize and map the spatial distribution of sulphide inclusions within the diamond host. A suite of 25 sulphide inclusions in diamonds from two Canadian Cratons were investigated in-situ to understand their mineralogy, original composition and crystallographic relationship with respect to their diamond host to assess whether the mineral inclusions formed at the same time as the diamond (syngenetic), or whether the diamonds enclosed pre-existing mineral grains (protogenetic). Single crystal X-ray diffraction analyses allowed the collection of crystallographic data on inclusions in diamonds down to 30-40 μm in size and most importantly allowed quantifying the whole inclusion without compromising it via polishing, providing a true “bulk” analysis. To this end, single-crystal data collections were converted into 2D powder patterns to perform Rietveld refinements of the diffraction pattern of the polycrystalline assemblage, offering an alternative approach to quantifying the relative amount of each sulphide phase present in the analysed volume and to derive the original composition of the Mss stable at high temperature in the mantle. These analyses have also provided, for the first-time, crystallographic evidence supporting a protogenetic origin of sulphide inclusions. The accurate bulk composition of the Mss determined here was then combined with the most recent sulphide experimental data and the formation condition (based on the available inclusion geo¬thermobarometry) of the investigated diamonds, to interpret the state of the sulphide inclusions at the time of incorporation into the diamond. Our results indicate that the sulphide inclusions were encapsulated in diamonds as solid grains and are therefore protogenetic supporting the findings from the crystallographic orientation relationships. Precisely characterized sulphide inclusions were also homogenised at high temperatures using a gas mixing furnace, and rapidly quenched to recover the original (Mss). In doing so, the major element composition of the sulphide inclusions was made uniform, by heating, while a gas was injected to avoid decomposition of the diamond. After homogenization, X-ray diffraction data confirmed a change from a polycrystalline assemblage of exsolved sulphide phases (pyrrothite, pentlandite and chalcopyrite) to single-crystal Mss. The new findings were finally coupled with a diffusion model in order to place constraints on the reliability of absolute ages derived from diamond inclusions. The results indicated that Re-Os equilibration is sufficiently fast in sulphides inclusions at mantle temperatures, confirming that even if the minerals are protogenetic, they can define true isotopic ratios and therefore provide true ages of diamond.
