When kimberlite outshines diamond! Mapping Alberta one window of opportunity at a time.

2008

Robert A. Creaser, Larry M. Heaman, Antonio Simonetti, Stefanie S. Simonetti, Richard Cox, Arthur R. Sweet,

The consensus reached on kimberlites is that they are formed deep within the mantle (at a depth between 150 and 450 km) from enriched exotic mantle compositions. In their, rapid ascent to the Earth’s surface, kimberlitic melts capture and transport xenoliths (fragments) or xenocrysts (minerals) from the mantle, Archean and Proterozoic lower crust, and Phanerozoic carbonate and clastic rock formations. This kimberlite sample tract provides a unique opportunity to view the nature of inaccessible geologic environments. In addition, the preservation of intra- and extra-crater facies kimberlite in northern Alberta allows us to study the uppermost portion of kimberlite bodies that are sheared off or eroded away in many other parts of the world. We intend to provide examples of some of these windows of opportunity that will shed new light on the geology of Alberta and western Laurentia. The lower crust-mantle window: A suite of xenoliths from the Kendu ultramafic body in northeastern Alberta and a comprehensive set of garnet xenocrysts from the three separate ultramafic rock fields in northern Alberta have been selected for mineralogical, geochemical and isotopic studies. These data and subsequent interpretations represent critical information on the ‘deep’ geological history of northern Alberta and evolution of western Laurentia. Knowledge of inter- and intra-field mantle variations can also serve as a proxy for future evaluation of garnet compositions in Alberta. The kimberlite—Upper Cretaceous host rock window: Radiogenic and palynological studies used to understand kimberlite-host rock relationships of the Buffalo Head Hills kimberlite field, indicate two distinctive events: Turonian to Campanian (~88-81 Ma) volcanism-sedimentation and a younger Paleocene-aged (~64-61 Ma) eruptive event. Within these events, three different emplacement settings are recognized that collectively define a kimberlite field characterized by stacked, often tabular, kimberlite layers of several ages. The surficial window: Since the initial discovery of kimberlitic pipes in northern Alberta in 1989-1990, government and exploration companies have collected many bedrock, till and stream-sediment heavy-mineral concentrate samples throughout Alberta. One area of interest includes numerous lakes in east-central Alberta that contain local concentrations of beach sand with up to 75 modal % garnet. A reconnaissance-scale investigation of these purple sands was completed to quantify the proportions of all the ordinary garnet species (almandine, andradite, grossular, spessartine) to fingerprint the source regions for the beach sands, and to check the content of kimberlite and other indicator minerals.

Mots Clés: Mountain Lake, Kimberlite, radiogenic isotopes, emplacement, Birch Mountains, geochemical, Palynological, Northern Alberta, Kimberlite-indicator minerals, Buffalo Head Hills