|Résumé||(disponible en anglais seulement)|
The extent to which glaciated landscapes have been modified by channelized and/or regional subglacial meltwater processes is controversial. The significance of
such processes, however, where documented, may have important implications for mineral exploration programs and thus requires further enquiry and evaluation. Esker sampling, for example, played a key role in the discovery of Canada¿s first diamond
mining camp at Lac de Gras. Recent work completed on a number of mineral exploration properties suggests that there has been inadequate testing of hypotheses of glacial landform and sediment origin. Hence, process based models to interpret indicator
mineral trends have been poorly developed and applied. This could be the case, for example, in areas affected by cryogenic processes that may confound recognition of glaciofluvial sedimentation.
Recent exploration and sampling in Slave Province,
NWT has recognized and identified well defined corridors and broader fields or belts affected by subglacial meltwater processes, in addition to classic esker forms. These features appear to be nested or ordered in the landscape, whereby broad fields
or belts are older than corridors, with eskers forming the youngest inset features. Eskers are glaciofluvial landforms that form extensive tree-shaped networks of sorted sediment readily observed across the barren lands of the Canadian north.
Distinct, narrow (less than 0.5 km wide) to wide (more than 2 km wide) corridors, defined by scoured bedrock and till, lags, gravel deposits and landforms, occur adjacent to and sub-parallel with esker ridge networks. Scoured glaciofluvial corridors
also contain a variety of s-forms, potholes, plunge pools, sculpted scarps (e.g. defining till plateaus), and in places, rock and sediment drumlins. Less obvious, broad fields and belts (greater than 2 km wide) occur beyond distinct corridors and are
marked by glaciofluvial landforms, and gravel lags, blankets, transverse ridges and bars. A viable sequence of events for identified features includes: i) widespread deposition of till; ii) local and regional meltwater erosion/ deposition, and iii)
esker deposition in response to intermittent meltwater floods from surface or subsurface reservoirs associated with active and/or stagnating ice.
Glaciofluvial processes will erode and concentrate indicator minerals in a variety of terrain
settings. Widespread erosion may exhume older or deeper till units, thus confounding simple spatial comparison of near surface sample results. In addition, winnowing of fines may concentrate heavy minerals on erosional surfaces. Glaciofluvial
deposits and landforms possess distinct dispersal patterns of indicator minerals and metals. Eskers are widely recognized and sampled glaciofluvial medium. Little is known, however about indicator mineral sourcing, dispersal and partitioning within
esker sediment. Additional exploration targets include gravel bars, transverse ridges and glaciofluvial lags. Elongated bars may merge with crag and tail features, and thus form landforms with gravelly tails. Gravel bars may form depositional traps
for heavy minerals. For example, kimberlite indicator minerals have been found concentrated in heads of gravel bars in glaciofluvial settings. Subglacial meltwater processes may also provide a viable mechanism for the formation of dispersal trains
that are narrow, continuous, elongate and traceable in a down flow direction from their source, such as identified at several exploration properties (e.g. Snap Lake). There is a need to recognize and study glaciofluvial landscapes in more detail and
to assess patterns of indicator mineral dispersal with evolving glaciofluvial and glacial process models.