Progress in the Search for a Major Meteorite Impact Structure in the Palaeoproterozoic Kisseynew Domain and Flanking Volcanic Belts, Manitoba, Canada

English Abstract:

Central Manitoba is underlain by the Kisseynew Domain, a basinal structure flanked by the Palaeoproterozoic Flin Flon- and Snow Lake volcanic belts to the south and the Lynn Lake and Leaf Rapids volcanic belts to the north. The volcanic belts are important present and past metal producers from VMS type copper-zinc-gold deposits. Lithogeochemical data of host rock to VMS ores were examined. It was found that the Flin Flon and Lynn Lake deposits have a strong magmatic component. Tholeiitic volcanics and gabbros pre-concentrate copper and produce copper-rich hydrous fluids. The open question is the source of the thermal energy to create large volumes of iron-rich magma. Meteorite impacts would deliver sufficient energy to generate the required temperatures and melt volumes. Some indirect pointers to a major crater were observed: In the Palaeoproterozoic Kisseynew basin at several locations outliers of Ordovician limestone are noted, suggesting local depression. Several VMS deposits along the boundary between underlying Amisk volcanic and overlying Missi clastic sediments show large scale signs of fluidization. This is expressed in major pegmatoidal bulges of pegmatized and dispersed ore along the otherwise sheet like ore horizons. Many graphitized fault zones can be traced for tens of kilometers and suggest possible remnants of a transient crater. The VMS deposits derive their copper from mafic volcanic and gabbroic rocks. A large impact would have created the necessary volume of high temperature melt. The various signs observed lend support to the hypothesis for a major impact as the energy source. Future work will benefit by using the impact hypothesis to refine our understanding of the process. This will lead to defining targets of higher potential for future ore searches.