Diamondiferous Kimberlites of Central Saskatchewan Project: Update

Transcription

1 Diamondiferous Kimberlites of Central Saskatchewan Project: Update S.E. Harvey, J.-P. Zonneveld 1, and B.A. Kjarsgaard 2 Harvey, S.E., Zonneveld, J.-P., and Kjarsgaard, B.A. (2003): Diamondiferous Kimberlites of Central Saskatchewan Project: Update; in Summary of Investigations 2003, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep , CD-ROM, Paper C-1, 5p. Abstract Additional research has been completed on the partnered multi-disciplinary federal-provincial-industry-university Diamondiferous Kimberlites of Central Saskatchewan project. Several more cores have been logged from the Fort à la Corne Joint Venture s 140/141 kimberlite and Shore Gold s Star kimberlite. Results from micropaleontology studies, U-Pb perovskite dating, 2-D and 3-D seismic studies and downhole logging have been integrated with volcanological and sedimentological data derived from the detailed core logging. New 2-D and 3-D models of the architecture of the two kimberlites are being developed. These are revealing that both kimberlites had a complex emplacement history characterized by multiple eruptive events each with a spectrum of distinct facies. Keywords: kimberlite, diamonds, TGI, Fort à la Corne, seismic, geophysics, biostratigraphy, geochronology, volcanology, Cretaceous. 1. Introduction The Diamondiferous Kimberlites of Central Saskatchewan project is a multi-disciplinary federalprovincial-industry-university project designed to facilitate and promote diamond exploration in Saskatchewan (Harvey et al., 2001). The second year of the project concentrated on examining core drilled between 2000 and 2002 from the Fort à la Corne 140/141 kimberlite body (joint venture of De Beers, Kensington, and Cameco) and Shore Gold s Star body (Figure 1). Results from micropaleontology studies, U- Pb perovskite dating, and downhole geophysical logging have been integrated with volcanological and sedimentological studies based on this detailed core logging. 2D and 3D seismic surveys have been completed on the 140/141 and Star bodies (Kjarsgaard et al., 2002). This paper summarizes the goals, strategies, and initial results for the various subprojects that are part of the investigation. 2. Sub-project 1: Geographic Information System (GIS) Data Storage ArcView Platform B. Slimmon, L. Kelley, and S.E. Harvey (Saskatchewan Industry and Resources) Goals: Design a GIS database for the acquisition and utilization of digital data is order to make all data easily accessible, integrated, and analyzed. An ArcView GIS database is the principal platform for project data. Figure 1 - Central Saskatchewan kimberlite location map showing the distribution of kimberlite bodies including those that are the focus of this investigation (modified from Jellicoe et al., 1998). 1 Geological Survey of Canada, Natural Resources Canada, rd Street NW, Calgary, AB T2L 2A7. 2 Geological Survey of Canada, Natural Resources Canada, 601 Booth Street, Ottawa, ON K1A 0E8. Saskatchewan Geological Survey 1 Summary of Investigations 2003, Volume 2

2 Work Plan: Compile and process digital data generated by the various sub-projects and incorporate existing data found in Saskatchewan Industry and Resources assessment files. An ArcView GIS database has been constructed and data entry and analysis are underway. Preliminary entries from the sub-projects include data locations, drill logs, images, and indicator mineral data. 3. Sub-project 2: High-resolution 3-D and 2-D Seismic Surveys D. White, B.A. Kjarsgaard, and G. Buffet (Geological Survey of Canada) Goals: To develop high-resolution 3-D and 2-D depictions of the geometry and internal structure of the kimberlite bodies. Work Plan: To complete a high-resolution 2-D seismic survey on the Fort à la Corne Joint Venture s 141/140 kimberlite and high-resolution 2-D and 3-D surveys on Shore Gold s Star kimberlite. Seismic data were acquired in the fall and winter of Combined 3-D and 2-D surveys were completed on the Star kimberlite, and a 2-D survey was completed over the Fort à la Corne Joint Venture s 140/141 kimberlite. 2-D survey images are nearing completion. Preliminary images depict internal structure, contacts, and gross architecture of the kimberlite bodies. Data processing and interpretation on the 3-D survey is in progress. 4. Sub-project 3: Multiparameter Borehole Geophysics C.J. Mwenifumbo (Geological Survey of Canada) Goals: To utilize multiparameter borehole geophysics to define the internal architecture of selected kimberlite bodies and to develop exploration applications of this technology. Work Plan: Multiparameter borehole geophysical logging, including full waveform sonic, gamma-ray spectrometry (TC, K, U, and Th), density, magnetic susceptibility, and temperature measurements is to be undertaken on selected kimberlite bodies. Multi-sensor geophysical combinations were measured on seven boreholes from the Star and Fort à la Corne 140/141 kimberlites. Attributes of several of the geophysical parameters recorded directly correlate with lithology, allowing clearer unit identification. Physical rock property data have been utilized to assist in the interpretation of the seismic data. 5. Sub-project 4: Micropaleontology, Biostratigraphy, and Palynology D.H. McNeil (Geological Survey of Canada) Goals: To enhance the understanding of paleoenvironmental conditions and timing of sedimentation in relation to kimberlite emplacement. Work Plan: Micropaleontologic, biostratigraphic, and palynologic analyses of selected sedimentary rocks in order to refine bio- and chronostratigraphic correlations in the eastern part of the Western Canada Sedimentary Basin (WCSB) during the Cretaceous. The main focus is examination of foraminifera in the Cretaceous sedimentary rocks that host the kimberlite. Several 100 gram samples from both targeted kimberlite bodies and some regional drill cores have been collected and processed to recover foraminifera. Initial results provide age and depositional constraints which outline periods of kimberlite emplacement. Biostratigraphic evidence supports the hypothesis that multiple-phase kimberlite eruptions occurred. Saskatchewan Geological Survey 2 Summary of Investigations 2003, Volume 2

3 6. Sub-project 5: Cretaceous Sedimentology and Stratigraphy J.-P. Zonneveld (Geological Survey of Canada) Goals: Establishment of a regionally consistent stratigraphic and architectural framework for the kimberlite deposits in the Mannville and Lower Colorado groups of central Saskatchewan (Zonneveld et al., 2002). At the local scale, the purpose is to improve the understanding of sedimentology and stratigraphy and the role of sedimentological processes in kimberlite emplacement, reworking, and influence on diamond grade. Some sedimentary processes have the potential to concentrate diamonds in specific beds or layers. Work Plan: Detailed logging of about 90 cores will improve understanding of facies relationships, stratigraphy, and sedimentology, and their direct and indirect relationships with the kimberlite bodies. Sixty-five drill holes have been logged in detail from the 140/141 and Star kimberlites as well as some regional holes. Core logging has provided the foundation for constructing a regionally consistent stratigraphic framework for the Fort à la Corne area. Kimberlites are interstratified with Lower Cretaceous (Albian and Cenomanian) marine, marginal marine, and continental sediments (Figure 2). The oldest kimberlites are Cantuar-equivalent in age (lower Mannville Group), but Penseequivalent (upper Mannville Group) kimberlite is also observed. Younger eruptive events are predominantly equivalent to the lower Colorado Group (Joli Fou, Viking, and Westgate). Work has distinguished secondary kimberlite deposits, including fluvial channel deposits, shoreface olivine sandstone beds, and offshore (marine and lacustrine) tempestites, mass flows, and turbidites. Grain flow and rock fall/talus slope deposits have also been recognized. 7. Sub-project 6: Kimberlite Petrology and Volcanology B.A. Kjarsgaard (Geological Survey of Canada) and S.E. Harvey (Saskatchewan Industry and Resources) Goals: Characterization of kimberlite phases and volcanological processes involved in kimberlite emplacement, deposition, and reworking. Work Plan: Detailed core logging and petrology of 90 drill holes, which provide the basis and context for all the work outlined in the project. Sixty-five drill holes have been logged in detail on the targeted bodies, with further logging planned for Logging has elucidated several kimberlite phases, each with distinctive mineralogy, grain-size variation, and chemical signature. Distinct eruptive episodes have been defined in both kimberlite complexes. Figure 2 - Stratigraphic position of central Saskatchewan Cretaceous kimberlites. Vertical hatched pattern represents time intervals with no rock record (modified from Kjarsgaard, 1995). Saskatchewan Geological Survey 3 Summary of Investigations 2003, Volume 2

4 Individual kimberlite magnetic anomalies consist of multiple (three or more) stacked kimberlite phases of differing stratigraphic assignment and age (plus their reworked equivalents) as well as coalescent eruptive centers, which resulted in individual kimberlite bodies with extremely complex internal geometry. Several deposit types have been recognized, including subaerial and marine fall deposits, pyroclastic flow deposits, debris flows, and possible base-surge deposits. Distinct feeder vents have been correlated with particular eruptive phases within the kimberlite complexes. There is evidence for both intra- and extra-crater kimberlite deposits. Interstratification of extra-crater kimberlite with lower Cretaceous (Albian) marine, marginal marine, and continental sediment reveals a prolonged and complex history of repeated volcanism with hiatuses separating individual eruptive events. 8. Sub-project 7: Synthesis Volume B. Jellicoe (Kensington Resources); P. Robertshaw (Robertshaw Geophysics); B.A. Kjarsgaard, J.-P. Zonneveld (Geological Survey of Canada); S.E. Harvey, L. Kelley, G. Delaney, C.D. Card, and J.E. Campbell (Saskatchewan Industry and Resources) Goals: To produce a synthesis report and database as stimulants for future diamond exploration in Saskatchewan. Work Plan: The synthesis will include the following aspects: i) regional Precambrian and Phanerozoic geology and relevant structural information; ii) exploration techniques relevant to Saskatchewan; iii) summaries of known kimberlite bodies, including detailed information regarding basement and host geology, geochemical indicator mineral analysis, Quaternary studies, geophysical studies, kimberlite geology, and diamond grades; iv) diamond prospectivity in Saskatchewan based on regional indicator mineral geochemistry surveys, regional geophysical data sets and the understanding of cratonic, lithospheric, and crustal structures; and v) a discussion of the petrology and emplacement of Saskatchewan kimberlites. Precambrian basement overview with regard to Saskatchewan kimberlites is complete. Review of general kimberlite geology and diamond exploration in Canada is complete. Overviews of known kimberlites in Saskatchewan are underway and partially complete. 9. Sub-project 8: Geochronology L.M. Heaman (University of Alberta) and B.A. Kjarsgaard (Geological Survey of Canada) Goals: To determine absolute age constraints on phases of kimberlite emplacement, Cretaceous sedimentation, and reworking. Work Plan: Five to 10 U-Pb perovskite age determinations on kimberlite samples. Initial dating has defined specific ages for kimberlite eruption within the Star kimberlite. This data supports and augments detailed logging and biostratigraphic work. Additional age dating is in progress on both the Star and Fort à la Corne 140/141 kimberlites. Evidence supports multiple kimberlite eruptive phases. 10. References Harvey, S.E., Zonneveld, J.-P., Kjarsgaard, B.A., Delaney, G.D., and Kelley, L.I. (2001) Targeted geoscience initiative (TGI) project diamondiferous kimberlites of central Saskatchewan Overview; in Summary of Investigations 2001, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep CD-ROM, p144. Jellicoe, B.C., Robertshaw, P., Williamson, P., and Murphy, J. (1998): Summary of exploration activities and results for the Fort à la Corne diamond project, Saskatchewan; in Summary of Investigations 1998, Saskatchewan Geological Survey, Sask. Energy Mines, Misc. Rep. 98-4, p Kjarsgaard, B.A. (1995) Research on kimberlites and applications of diamond exploration techniques in Saskatchewan; in Richardson, D.G. (ed.), Investigations completed by the Saskatchewan Geological Survey Saskatchewan Geological Survey 4 Summary of Investigations 2003, Volume 2

5 and the Geological Survey of Canada under the Geoscience Program of the Canada-Saskatchewan Partnership Agreement on Mineral Development ( ), Geol. Surv. Can., Open File 3119, p Kjarsgaard, B.A., Zonneveld, J.-P., Harvey, S.E., Heaman, L., McNeil, D., Mwenifumbo, J., and White, D. (2002) New multidisciplinary geological studies in the Fort à la Corne kimberlite field; in Summary of Investigations 2002, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep CD-ROM, Paper C-3, 1p. Zonneveld, J.-P., Kjarsgaard, B.A., Harvey, S.E., and Marcia, K.Y. (2002) Sedimentary constraints on kimberlite emplacement in the Fort à la Corne kimberlite field; in Summary of Investigations 2002, Volume 2, Saskatchewan Geological Survey, Sask. Industry Resources, Misc. Rep , CD-ROM, Paper C-4, 1p. Saskatchewan Geological Survey 5 Summary of Investigations 2003, Volume 2