Petrology and geochemistry of Canadian diamonds: An up-to-date review

Canada is one of the most important diamonds producers in the world despite the first diamond mine opening relatively recently in 1998 in the Slave craton. Given the increasing economic and scientific interest towards Canadian diamonds, an investigation of their geochemical and petrological properties was needed to better understand their genesis. A detailed review is given of all available petrological and geochemical data from >3000 Canadian diamonds and their silicate, oxide and sulfide inclusions from published literature and un-published datasets, compared with data from worldwide datasets. Based on the available published data, different abundances of peridotites and eclogites in the lithosphere of the Canadian cratons are indicated by mineral inclusions, with the Slave craton exhibiting a high amount of eclogitic diamonds, and the Superior craton exhibiting a strong prevalence of peridotitic diamonds. Diamond formation from extremely C-13-depleted subducted organic matter is necessary to explain the extremely low delta C-13 observed in some samples from the Canadian lithosphere, which, as of today, are the lowest values ever recorded in mantle diamonds. Core-to-rim delta C-13 analyses revealed progressive rimward enrichment in 13C for some of the samples, a behavior which is associated to the crystallization of diamonds from oxidized C species (e.g., CO2).Using the available data geothermobarometric calculations were performed on both single inclusions and inclusion pairs and provide a formation window for Canadian lithospheric diamonds from similar to 140 to similar to 210 km, with temperatures ranging from 900 to 1400 degree celsius, which are generally higher than mantle residence temperature given by N aggregation geothermometry. Sub-lithospheric diamonds are sampled from similar to 240 km to >660 km based on geobarometry on majoritic garnets and observations of inclusion assemblages. The age range of Canadian diamonds suggest numerous diamond-forming events that took place from the Paleo-Archean to the Neoproterozoic.

Automated summary

Canada is one of the most important diamond producers in the world. Understanding the geochemical and petrological properties of Canadian diamonds is crucial for understanding their origin. Petrological and geochemical data from thousands of Canadian diamonds were analyzed and compared with worldwide datasets. Different abundances of peridotites and eclogites were found in the lithosphere of Canadian cratons. The extremely low delta C-13 values observed in some Canadian diamonds suggest diamond formation from C-13-depleted subducted organic matter. Geothermobarometric calculations revealed the formation window and sampling range of Canadian lithospheric and sub-lithospheric diamonds, as well as multiple diamond-forming events throughout Canadian history.