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The Sheahan Diamond Literature Reference Compilation is compiled by Patricia Sheahan who publishes on a monthly basis a list of new scientific articles related to diamonds as well as media coverage and corporate announcements called the Sheahan Diamond Literature Service that is distributed as a free pdf to a list of followers. Pat has kindly agreed to allow her work to be made available as an online digital resource at Kaiser Research Online so that a broader community interested in diamonds and related geology can benefit. The SDLRC Blog is a guest commentary by an industry expert about articles, themes and trends in recent issues of the SDLRC.
March 2021
Comments by Brooke Clements
Brooke Clements is President and CEO of Craton Minerals Ltd., a Vancouver-based private diamond exploration company focused on discovering North America's next diamond district. He is also President of JBC Ventures Ltd., a consulting company specializing in mineral exploration and community and government relations. From 2007 to 2015 he was President of Peregrine Diamonds Ltd. where he led the team that discovered the Chidliak diamond district on Baffin Island in the Canadian Arctic. Before that, Brooke was Vice President, Exploration for Ashton Mining of Canada Inc. Under his leadership, Ashton and their partner SOQUEM discovered the Renard diamond district in Quebec where the Renard Diamond Mine commenced production in 2016. From 1982 to 1997, Brooke was an Exploration Geologist and Regional Manager for Exmin Corporation where he conducted diamond exploration programs throughout the United States. He holds a BSc in Geology from Indiana University and an MSc in Economic Geology from the University of Arizona.
Brooke Clements has volunteered to highlight the scientific articles that caught his attention in the monthly reference compilations. The opinions expressed are solely his and he can be reached at .
This month there are two papers by Gress and other authors that address diamond formation underneath Botswana. Both papers have lots of detailed information on how isotopic studies are used to date diamonds and the broader tectonic conclusions that can be drawn from the data. In this study, 36 e-type garnet and clinopyroxene inclusions from 16 diamonds from the Jwanang mine were studied using SM-Nd isotope systematics. Isochrons suggest at least two ages of diamond formation, around 1.8 Ga (Paleoproterozoic) and .85 Ga (Neoproterozoic). The Paleoproterozoic diamonds are thought to have formed by large-scale (>100 km) volatile-rich metasomatism related to formation and reworking of the Proto-Kalahari craton. The Neoproterozoic diamonds are thought to have formed on a smaller scale (<10 km) during the breakup of the Rodinia supercontinent.
A journal pre-proof from Lithos. Re-Os systematics are used to study diamonds from Jwaneng and Orapa. Their work supports previous Sm-Nd and Re-Os ages suggesting that tectono-magmatic events formed at least three discrete diamond populations, 2.0-1.7 Ga, 1.2-1.0 Ga and 0.9-0.75 Ga. They conclude that "The inclusion isochron ages emphasise that diamond formation is a multi-stage and episodic process that can occur contemporaneously in disparate substrates and produce multiple diamond populations in the sub-continental lithospheric mantle." Fluid-rich, fibrous, pollycrystalline diamonds younger than 300 Ma are also described and the authors state that they are more common than previously recognized.
This is essential reading for those interested in the study of craton roots using seismic methods. The authors report a unique fabric in olivine underneath cratonic continental lithospheric roots where at depths of approx. at 150 km the fast crystallographic axis is preferentially aligned vertically. This is in contrast to most of the earth where the olivine axes are horizontally aligned. They believe the vertical fabric at 150 km under cratons is evidence of a shortening event that created cratonic roots.
The authors propose that subducting slabs might cause lithospheric removal by directing mantle flow along craton margins, shaping the cratons and impacting the stability of the lithosphere.
Peregrine Diamonds provided rock samples to students at the U of British Columbia and the U of Alberta from the Chidliak diamond district on south Baffin Island and a number of good studies were completed by graduate students. In this study, Dr. Kopylova focused on rare 3-20 micron clinopyroxene coronas on some orthopyroxene grains in peridotite xenoliths. She describes fluxes from carbonate-rich metasomatism that helps shape the lithospheric mantle and its melts.
