The Fort a La Corne Kimberlites, Saskatchewan, Canada: Geology, Emplacement and Economics

The Cretaceous Fort a la Come kimberhte province includes at least seventy well preserved bodies ranging up to 200 hectares in size Kimberhte volcanism spanned at least 20 Ma The main bodies formed by a two stage process (i) excavation of shallow craters into Cretaceous sediments, and (ii) crater infilling by subaerial magmatic pyroclastic processes, both during regressions of the Western Interior Seaway Each of the twenty five bodies investigated is different but dominated by a few volumetrically significant phases of kimberlities Subsequent eruptions formed nested craters withm earlier indurated kimberlites Eruption styles varied from Hawaiian and Strombolian to a probable kimberlite specific type of eruption which formed unique mega-graded beds Separation of olivine grains from the low viscosity melts was a widespread process that resulted in discrete olivine grains forming approximately half of the pyroclasts across the province Ash-sized clasts are not common indicating removal by a large scale sorting process No diatremes, ischolar_main zones, dykes, hypabyssal or tuffisitic kimberlite or significant amounts of resedimented material were found The contrast in geology of the Fort a la Come bodies supports, rather than negates, the 'classic' kimberlite pipe model The Fort ala Come mode of emplacement comprises a second style of emption or model which is applicable to kimberhtes The new models have been an important foundation of the ongoing economic evaluation of the Fort a la Come bodies Applying predictive geology based on knowledge obtained from other kimberhte bodies would have been misleading.