Abstract
Vertical pipes comprised of loose silica and lined by chert nodules have been observed in the abandoned Mafeking Quarry in central Manitoba, Canada. Discovery of microfossils within these features of the same age as the carbonate host rock indicates that they are a dissolution/replacement structure rather than infill of karst features by younger sediments. These features occur on the low thermal maturity edge of the intercratonic Williston Basin, are not associated with any known tectonic or hydrothermal activity, and show no sign of localized discharge of high-temperature fluids. Modern low-temperature brine springs with silica-filled discharge channels occur nearby, which suggests the silica chimneys are relic spring channels. Geochemical models have shown that dissolution/replacement reactions would be expected due to mixing of brine spring water with shallow groundwater in the region. Results indicate that silica pipe features in the rock record cannot be assumed to be indicative of hydrothermal activity. At the same time, results increase the astrobiological significance of low-temperature siliceous deposits. Key Words: Geochemistry—Hydrothermal systems—Silica. Astrobiology 9, 931–941.
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