GEOSCAN Search Results: Fastlink


TitleOn elevated fluoride and boron concentrations in groundwaters associated with the Lake Saint-Martin impact structure, Manitoba
AuthorDesbarats, A J
SourceApplied Geochemistry vol. 24, no. 5, 2009 p. 915-927,
Alt SeriesGeological Survey of Canada, Contribution Series 20080230
Mediapaper; on-line; digital
File formathtml; pdf (Adobe® Reader®)
NTS62O/09SW; 62O/09NW; 62O/10; 62O/15SE; 62O/15SW; 62O/16SW
AreaLake Saint-Martin; Lake Pineimuta; Gypsumville; Little Saskatchewan First Nation; Lake St-Martin First Nation; Pinaymootang First Nation; Lake Winnipeg
Lat/Long WENS-98.8833 -98.3000 51.8333 51.5500
Subjectshydrogeology; geochemistry; regional geology; structural geology; meteorite craters; groundwater resources; groundwater geochemistry; fluorides; boron; concentration; wells; water wells; well samples; water quality; geochemical analyses; sodium; chlorine; isotope geochemistry; stable isotope studies; oxygen isotopes; morphology; source rocks; source areas; bedrock geology; sedimentary rocks; shales; phosphates; aquifers; structural analyses; crustal uplift; hydrostratigraphic units; groundwater regimes; groundwater flow; groundwater movement; geochemical facies; modelling; ion exchange; fluorite; calcite; solubilities; Lake Saint-Martin impact structure; Winnipeg Formation; impact structures; drinking water; anions; groundwater recharge; geochemical signatures; pH; Phanerozoic; Cretaceous; Jurassic; Triassic; Paleozoic; Devonian; Silurian; Ordovician; Precambrian
Illustrationssketch maps; schematic cross-sections; profiles; cross-plots; ternary diagrams; tables
ProgramGroundwater Mapping Program
AbstractHydrogeological investigations conducted by the Geological Survey of Canada in the Lake Saint-Martin region of Manitoba have confirmed earlier reports of naturally elevated F- and B concentrations in local groundwaters. Fluoride and B concentrations are highly correlated (r-squared = 0.905) and reach 15.1 mg/L and 8.5 mg/L, respectively. Virtually all groundwaters with F- concentrations greater than the drinking water limit of 1.5 mg/L are from wells within the Lake Saint-Martin impact structure, a 208 Ma complex crater 23 km in diameter underlying a large part of the study area. The high-F- groundwaters can be classified into two groups according to their anionic and isotopic compositions. Group I samples consist of Na-mixed anion groundwaters, with Cl greater than 100 mg/L and highly depleted 18O compositions indicative of recharge under much cooler climatic conditions than at present. Samples belonging to this group exhibit a striking relationship to crater morphology, and are found in an arcuate belt within the southern rim of the impact structure. Group II high-F- samples consist of Na-HCO3-SO4 groundwaters, with little Cl, and less depleted 18O compositions. Samples belonging to this group are associated with groundwaters recharged locally, on a low ridge within the impact structure. This paper traces the probable source of high-F- groundwaters to phosphatic pellets in shales of the Winnipeg Formation, a regional basal clastic unit which sub-crops at shallow depth beneath the crater rim as a result of more than 200 m of structural uplift associated with the impact event. This extensive aquifer is known elsewhere in southern Manitoba for its naturally-softened groundwaters and locally elevated F- concentrations. Group I groundwaters are interpreted as discharge from the Winnipeg Formation where it abuts against crater-fill deposits. Group II high-F- groundwaters are interpreted as modern recharge from within the impact structure, displacing Group I groundwaters. Thus, elevated F- and B concentrations observed in groundwaters of the Lake Saint-Martin area represent the geochemical signature of upwelling from a deep regional aquifer. The previously unsuspected discharge zone occurs within an isolated sub-crop of the aquifer formed as a result of structural uplift caused by the impact event.