EMPLACEMENT AND REWORKING OF CRETACEOUS, DIAMOND-BEARING, CRATER FACIES KIMBERLITE OF CENTRAL SASKATCHEWAN, CANADA

In central Saskatchewan, Canada, kimberlites were emplaced into Cretac eous marine and nonmarine elastic sediments, Core recovered from one d rill hole that intersects kimberlite (Smeaton FAC/UK core 169/8) was s elected for an integrated study involving sedimentology, volcanology, mineralogy, geochemistry, palynology, micropaleontology, organic petro logy, and radiometric age determination, Only crater facies kimberlite has been observed; there is no indication of the locations of feeder dikes, Four varieties of kimberlite occur, all originating from subaer ial volcanism: (1) fluvial-reworked kimberlite; (2) diamondiferous kim berlite lapillistone air-fall deposits; (3) kimberlite olivine crystal -tuff air-fall deposits; and (4) diamondiferous marine wave-reworked k imberlite. Within the multiple primary eruptive phases of the kimberli te air-fall deposits, the volcanic style changed upward with time, fro m violent Strombolian to more explosive volcanism, The bulk of the vol canism formed conformable, air-fall deposits on terrestrial sediments of the Cantuar Formation, resulting in the development of positive-rel ief tephra cones, Subsequent marine transgression associated with the Westgate Formation partially beveled the top of the cone, The kimberli te air-fall deposits contain microdiamonds, 5 to 25 mu m in diameter, The maximum temperature and vitrinite reflectance values of coaly matt er in the kimberlites indicate that these deposits, although originall y derived from magma at high temperatures, did not thermally affect en trained surficially derived clasts or the country rock during emplacem ent, The chemical content of intrakimberlite shale clasts is markedly different from the marine and nonmarine shales and indicates significa nt synem-placement and postemplacement fluid movement through the volc anic pile, At least two episodes of kimberlite volcanism occurred in t he middle and late Albian (paleontologically assigned), A U-Pb perovsk ite radiometric age of 101.1 +/- 2.2 Ma from a kimberlite lapillistone from the younger episode of volcanism is internally consistent with b iostratigraphic studies that constrain the kimberlite volcanism as pos t-middle Albian and pre-late AlAlbian to late Albian.