John-Paul Zonneveld1, Bruce A. Kjarsgaard2, and Shawn
1 Geological Survey of Canada, Calgary, AB
2 Geological Survey of Canada, Ottawa, ON
3 Saskatchewan Industry and Resources, Regina, SK
Diamond-bearing kimberlites in the Fort à la Corne region, east-central Saskatchewan, consist primarily of extra-crater pyroclastic deposits which are interstratified with Lower Cretaceous (Albian and Cenomanian) strata. Kimberlites occur interstratified continental, marginal marine and shallow marine strata of the Mannville Group (Cantuar and Pense formations and shallow to deep marine deposits of the Colorado Group (Joli Fou, Viking and Westgate Formations). The oldest kimberlites at Fort à la Corne occur in the Cantuar Formation. Kimberlites within the Cantuar Formation include terrestrial airfall deposits as well as kimberlitic sandstone and conglomerate deposited in fluvial and estuarine successions. Successive eruptive events occurred contemporaneous with deposition of the marginal marine upper Mannville Group (Pense Formation). Kimberlites within the Pense Formation consist primarily of subaerial and marine fall deposits . Fine- to medium-grained cross-stratified kimberlitic (olivine dominated) sandstone in this interval reflects reworking of these airfall deposits during a regional marine transgression. The youngest kimberlite in the study area occurs within the predominantly marine Lower Colorado Group (Joli Fou, Viking and Westgate Formations). Kimberlite beds, which occur at several horizons within these units, consist of subaerial and marine fall deposits, the latter commonly exhibiting evidence of wave-reworking. Black shale-encased resedimented kimberlite beds, likely deposited as subaqueous debris flows and turbidites, are particularly common in the Lower Colorado Group. Primary and reworked pyroclastic kimberlite in these deposits can be differentiated by a number of means including facies relationships, assessment of sedimentologic characteristics (grading, sorting, bedforms, etc...), petrographic characterization and geophysical techniques.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005