Historical diamond mine waste reveals carbon sequestration resource in kimberlite residue

Mined sub-aerially stored kimberlite provided a natural laboratory in which to examine the potential for carbon sequestration in ultramafic materials. A 15 cm hand sample of similar to 50-year-old 'cemented' coarse residue deposit (CRD) collected from a cemented surface layer in the Cullinan Diamond Mine tailings in Gauteng, South Africa, demonstrated the encouraging effects of weathering on mineral carbonation of kimberlite. The examination of petrographic sections using light microscopy, X-ray fluorescence microscopy (XFM) and backscatter electron - energy dispersive spectroscopy demonstrated that weathering produced extensive, secondary Ca/Mg carbonates that acted as an inter-granular cement, increasing the competency of the CRD, i.e., producing a hand sample. Nearly every grain in the sample, including primary, un-weathered angular carbonate clasts were coated in secondary, mu m- to mm-scale carbonate layers, which are interpreted as secondary materials. DNA analysis of an internal, aseptic sample of secondary carbonate revealed that the weathered kimberlite hosts a diverse microbiome consistent with soils, metal cycling and hydrocarbon degradation that was found within the secondary carbonate, interpreted as a biomaterial. The formation of secondary carbonate demonstrates that 'waste kimberlite' from diamond mining can serve as a resource for carbon sequestration.

Automated summary

Mined sub-aerially stored kimberlite can be a valuable resource for carbon sequestration, as demonstrated by the weathering process that produces extensive secondary carbonates. The examination of the samples from the Cullinan Diamond Mine tailings in South Africa showed that the weathered kimberlite hosts a diverse microbiome consistent with soil and hydrocarbon degradation, indicating its potential for carbon sequestration.