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Characterising Diamond Breakage from the Processing of
Kimberlite Ore: A Case Study
Sara Burness, Megan Becker, Aubrey Mainza
Centre for Minerals Research, Dept Chemical Engineering, University of Cape Town
Geoffrey Howarth
Department of Geological Sciences, University of Cape Town
ABSTRACT: In-situ diamond recovery requires the breaking down of kimberlite ore to liberate the precious
stones. However, during the comminution process, diamond breakage is a common occurrence and a major
concern for diamond producers as size reduction lowers critical revenue. This study focuses on small and micro-
diamonds sampled from the historical Roberts Victor Mine, South Africa, and employs non-destructive imaging
techniques (micro-CT and SE microscopy) to characterise their crystallographic morphology and natural versus
mechanical breakage patterns. The findings reveal striking similarities between small diamond and macro-
diamond breakage, suggesting micro-diamonds as reliable proxies for understanding breakage dynamics. Given
the large abundance of micro-diamonds in kimberlite-type ore and their potential role in predicting breakage
patterns in larger stones, this research highlights the importance of considering micro-diamonds in optimisation
strategies for processing methods while also preserving diamond value.
INTRODUCTION
Natural diamonds are unrivalled in their brilliance, senti-
mental value as well as strength and durability. They are the
quintessential precious stone of the jewellery industry and
are further valued for their outstanding hardness as indus-
trial diamonds (Field, 2012). Diamond is not a common
rock-forming mineral and the temperatures (900–1400°C)
and pressures (4 GPa) required to form diamonds pre-
clude them from forming at surface conditions thus con-
tributing to their scarcity. Diamond notably forms largely
within the Earth’s thick continental lithospheric mantle at
~150 km depth, but deeper forged stones also exist (Shirey
et al., 2024). Individual diamonds can be transported to the
surface of the Earth as xenocrystic cargo within kimberlite
and olivine-lamproite magmas forming primary magmatic
deposits, which may later weather into secondary placer
deposits. Understanding diamond formation mechanisms
(e.g., Stachel and Luth, 2015) and their transport to the
earth’s surface is key to being able to characterize their dis-
tinctive crystallographic morphologies and growth zones.
These are often reshaped by complex resorption reactions in
the mantle as well as in the kimberlite magma en route to
the surface culminating in secondary forms (Fedortchouk,
2019). Both primary and secondary forms are recovered
through mineral processing after which sorting and grading
is done. This is based mainly on their size, colour, shape,
and clarity (e.g., the ‘4Cs’ of diamond grading, established
by the GIA—Gemological Institute of America and sub-
sequently employed by De Beers). Diamonds recovered
from a single mine can range from near worthless ‘boart’
to gem quality, meaning that there can be no one value
placed on rough diamonds as is commonplace for other
Characterising Diamond Breakage from the Processing of
Kimberlite Ore: A Case Study
Sara Burness, Megan Becker, Aubrey Mainza
Centre for Minerals Research, Dept Chemical Engineering, University of Cape Town
Geoffrey Howarth
Department of Geological Sciences, University of Cape Town
ABSTRACT: In-situ diamond recovery requires the breaking down of kimberlite ore to liberate the precious
stones. However, during the comminution process, diamond breakage is a common occurrence and a major
concern for diamond producers as size reduction lowers critical revenue. This study focuses on small and micro-
diamonds sampled from the historical Roberts Victor Mine, South Africa, and employs non-destructive imaging
techniques (micro-CT and SE microscopy) to characterise their crystallographic morphology and natural versus
mechanical breakage patterns. The findings reveal striking similarities between small diamond and macro-
diamond breakage, suggesting micro-diamonds as reliable proxies for understanding breakage dynamics. Given
the large abundance of micro-diamonds in kimberlite-type ore and their potential role in predicting breakage
patterns in larger stones, this research highlights the importance of considering micro-diamonds in optimisation
strategies for processing methods while also preserving diamond value.
INTRODUCTION
Natural diamonds are unrivalled in their brilliance, senti-
mental value as well as strength and durability. They are the
quintessential precious stone of the jewellery industry and
are further valued for their outstanding hardness as indus-
trial diamonds (Field, 2012). Diamond is not a common
rock-forming mineral and the temperatures (900–1400°C)
and pressures (4 GPa) required to form diamonds pre-
clude them from forming at surface conditions thus con-
tributing to their scarcity. Diamond notably forms largely
within the Earth’s thick continental lithospheric mantle at
~150 km depth, but deeper forged stones also exist (Shirey
et al., 2024). Individual diamonds can be transported to the
surface of the Earth as xenocrystic cargo within kimberlite
and olivine-lamproite magmas forming primary magmatic
deposits, which may later weather into secondary placer
deposits. Understanding diamond formation mechanisms
(e.g., Stachel and Luth, 2015) and their transport to the
earth’s surface is key to being able to characterize their dis-
tinctive crystallographic morphologies and growth zones.
These are often reshaped by complex resorption reactions in
the mantle as well as in the kimberlite magma en route to
the surface culminating in secondary forms (Fedortchouk,
2019). Both primary and secondary forms are recovered
through mineral processing after which sorting and grading
is done. This is based mainly on their size, colour, shape,
and clarity (e.g., the ‘4Cs’ of diamond grading, established
by the GIA—Gemological Institute of America and sub-
sequently employed by De Beers). Diamonds recovered
from a single mine can range from near worthless ‘boart’
to gem quality, meaning that there can be no one value
placed on rough diamonds as is commonplace for other