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.
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 .
Geological Assoc. of Canada Special Paper 51 is a collection of papers devoted to the geology of the Archean Slave craton in Nunavut and the Northwest Territories. There are 17 chapters and about 200 pages. The geology at surface today, the geologic/tectonic evolution over time, the upper mantle and five kimberlite fields are covered. The kimberlite discoveries and development of five diamond mines since 1998 has dramatically increased the understanding of the craton. Mantle and upper crustal xenoliths brought up by kimberlites tell us about the subsurface. Tertiary/Cretaceous petrified wood and mudstone found in kimberlites has provided information on the extent of the Cretaceous sea and post-Tertiary erosion.
The authors investigate the factors that promote stability of Archean cratons. A key point from the paper follows: "The survival of Archean cratons depends both upon their nature-the initial conditions of formation-and nurture-the subsequent tectonic processes that may modify and destabilize cratonic lithosphere." They emphasize that metasomatism can have a particularly negative impact on craton stability.
This is a pre-proof that is a detailed study of mineral concentrates from a Brazilian kimberlite named after veteran prospector Osvaldo Franca who made the discovery and whom I have the pleasure of knowing. The kimberlite is 90 million years old and located in the Alta Paranaiba Igneous Province near the edge of the Archean Sao Francisco craton. The igneous province hosts carbonatites, kamafugites, kimberlite and ultramafic lamprophyres, all in close proximity to placer diamond deposits and the region has seen extensive diamond exploration activity.
A very thorough study that should be essential reading for anyone considering a new venture in South Africa. The small diamond mining sector has seen dramatic decline since 2004. The report states that there is an urgent need to revise South African mineral and mining policy and regulations to stimulate the small and junior mining sector in the country.
The core compositions of many kimberlite olivines are similar to the compositions of olivines in mantle peridotites, implying a xenocrystic origin. A group of olivine macrocrysts in kimberlites are interpreted by the authors to be associated with Cr-poor and Cr-rich megacryst suites and it is suggested that a majority of kimberlitic olivine has a cognate (formed in the magma) origin.
A good discussion of cratons and lithosphere and the conditions under which stable mantle roots, critical for lithospheric diamond formation and preservation, are formed and preserved. The effects of depletion by magma extraction from the upper mantle is discussed. Dr. Pearson has suggested, notably in a talk in the 2021 PDAC diamond session, that the most critical thing for diamond formation and preservation is a stable craton with a demonstrated deep root. He believes that it may not be necessary for the root to have been stable since the Archean. The longest lived cratons, and those prospected most intensely for diamonds, assembled during the Archean and Early Proterozoic. It is suggested that the definition of craton should be extended to include extensive regions of long-stable Mesoproterozoic (1600-1000 Ma) crust underlain by thick lithospheric roots.
Very good study of the setting and geology of the Kasai placer diamond field in the southern DRC which is part of a field where over 200 million carats have been produced, mostly from Quaternary deposits. In the study area, diamond concentration improves but diamond size diminishes with decreasing deposit age, with modern river sediments contain the most, but smallest diamonds. The authors state that Southern African fluvial deposits have an opposite grade and diamond size trend.