Diamonds and their mineral inclusions from the Sloan diatremes of the Colorado-Wyoming State Line kimberlite district, North America

Doctoral Thesis


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University of Cape Town

The Sloan diamonds were investigated for their physical characteristics, inclusion mineralogy and composition, and carbon isotope composition. The relationships between these features are described and interpreted with respect to diamond genesis. The physical characteristics investigated include crystal state, crystal regularity, primary morphology, resorption morphology, primary and secondary sizejmass, colour, surface features and inclusion content. Significant relationships between these characteristics were found. The proportion of an individual crystal, lost during resorption, decreases with increasing diamond size. Larger crystals and diamonds displaying brown colours appear to have been more susceptible to breakage relative to smaller crystals and diamonds of other colours, respectively. Brown colours were more common on smaller diamonds relative to larger stones and, further, were more common on single crystal forms relative to twinned/aggregate crystals. Variation in diamond physical characteristics between the various kimberlite phases in the Sloan 1 & 2 complex has been documented. The Sloan 2 phase is characterized by larger and less resorbed diamonds relative to those in other kimberlite phases in the diatreme. In addition, corrosion sculpture is much more common on Sloan 2 diamonds.

Bibliography: v. 1, pages 157-171.